Field

The present invention relates to an apparatus for, and a method of, mutually separating a first phase and a second phase entrained in the first phase.

Background to the invention

Separation of two-phase or multi-phase flows is vital for many industrial processes. Desirable is the ability to facilitate separation with maximum efficiency while minimising process cost, energy, volume and complexity. The separation of fine gas bubbles in water can be particularly challenging when operating within these constraints. The separation of the liquid and gas phases of foams is a well-studied and reported area of research, particularly because gas may become entrained or mixed into the liquid phase by some intentional, or otherwise, mechanical process. Foams occur in industrial processes when gas becomes dissolved in a processing liquid. Normally the dissolved gas would behave as part of the processing liquid, however, the gas can come out of solution as small bubbles, for example, when there is a release of pressure. These bubbles rise to the surface of the liquid and collect as a foam. The presence of foams (also known as liquid entrained gases) in processing liquids can lead to a number of efficiency and performance problems in industrial processes and other applications. For example, foams result in reduced efficiency of equipment such as pumps, reduced capacity of pumps and storage tanks, reduced effectiveness of the fluid and drainage problems to name but a few. There is often a need to remove foams from industrial processes to avoid the problems described above. This usually involves separating the gas phase from the liquid phase of the foam and, ideally, this needs to be done rapidly, efficiently and with minimum power consumption. One method is to use mechanical separation devices such as hydro-cyclones and centrifuges. These techniques consume significant amounts of power which can be a problem in certain industries or applications, for example, portable or automotive applications. Another possibility is to use a helical separator technology, which like the aforementioned two devices, utilises enhanced centrifugal force to effect mechanical separation but at lower power. However, there is an ever present requirement to improve separation efficiency at reduced power and in a smaller physical volume. To achieve this, it is not possible to rely solely on mechanical separation.

Conventional methods of separation include gravity and kinetic separation, such as settling chambers and cyclone-based technologies, respectively. For a given volume of gas, fine bubble dispersions present a greater collective interfacial area and therefore, require more effort and/or time to collapse (i.e. larger and/or more powerful separation equipment). Under the influence of a motive force (for example, gravity or centrifugal), fine bubbles reach slower terminal velocities and hence, require greater separation time and/or force to affect separation, as apparent from Equation 1 : where: v is the terminal velocity of the bubble (ms ¹ ); g is gravitational acceleration (ms ² );

R is the radius of the spherical bubble (m); p _b is the mass density of the bubbles (kgnr ³ ); p _f is the mass density of the liquid (kgnr ³ ); and p is the dynamic viscosity of the liquid (kgm ¹ s- ¹ ).

In the case of gravity settling equipment, where the motive force is fixed, chamber volumes must be appropriately scaled in order to allow sufficient residence time for separation. As such, chamber size can become impractically large, taking up much needed space and demanding a high capital cost. By contrast, kinetic separators can maintain a more compact footprint but at much increased energy cost.

An energy efficient alternative to mechanical separation is to use antifoam. The action of antifoam in the disruption of liquid films and bubbles is well known and exploited. The mechanisms of antifoam in the disruption of a foam interface, i.e. the interface between the gas and liquid phases, are varied, depending on the formulation and form of the antifoam. However, it can generally be described by the interaction of a low surface energy or hydrophobic surface with the liquid film. Generally antifoam agents take the form of particles having a low surface energy or hydrophobic surface. Such low surface energy surfaces can be created by forming the particles from or coating the particles with a low surface energy or hydrophobic material. Examples of such materials from which the particles may be formed or coated include polytetrafluoroethylene (PTFE), halogenated organic polymers, silicone polymers and hydrocarbon polymers such as polythene and polypropylene. PTFE, having a surface energy of approximately 20 mJ/m ² , is a very effective hydrophobic material, although any suitable hydrophobic material may be used. Antifoaming agents are by nature an additive and therefore, may be unacceptable for product quality and/or environmental purposes (e.g. oil or micro plastic contamination). It is generally not possible to use antifoam as described above in industrial processes where foams are desirable or a necessary product of a particular process, for example, in aeration or oxidation processes. Foams are useful in such processes because they create a large surface area of liquid in contact with a gas which aids the absorption or solution of the gas in the liquid. The presence of an antifoam agent in such processes would be undesirable because it would prevent the formation of the foam. However, once the particular process involving the foam has completed, it may still be desirable to remove the foam prior to the next processing step. Therefore, an alternative method of removal is required.

Within the context of a closely packed foam or entrained bubble mass (i.e. high gas-liquid ratio), bubble collapse is dependent on the rate at which liquid drains from the boundaries between bubbles. Again, the finer the bubbles the greater the time and/or energy required to bring about final collapse and separation.

A known static coalescer induces and accelerates coalescence of fine bubble flows in static (i.e. immobile, non-moving) devices mounted within a pipeline or vessel. The static coalescers achieve coalescence by crossflowing bubbles over low surface free energy materials, for example PTFE mesh. The hydrophobic nature of the material repels the aqueous phase in favour of the gas and, in so doing, causes a breakdown in the liquid boundaries between bubbles, thus achieving coalescence. The process is driven by: i) the motive energy within the flow stream and ii) the released elastic energy of the bubble interface. The static coalescers are described as being simple, compact, energy efficient (i.e. low pressure drop) and inexpensive. The principle by which such static coalescers brings about bubble collapse is depicted schematically in Figure 1 . As shown in Figure 1 , upon contacting a low surface free energy material such as PTFE, high contact angles and weak surface attachment allows surface tension to tear the liquid boundaries between bubbles away from the active surface, thereby coalescing the bubbles.

Figures 2A to 2C show a known static coalescer 20. The static coalescer 20 is designed to sit directly within a pipeline conveying the two-phase flow and consists of a support framework 201 fitted with multiple PTFE mesh panels 202 in parallel (referred to as streamers). Similar to static mixers, this static coalescer 20 has no moving parts and remains immobile within the flow stream. Intimate contact and interaction occur as the fine bubbles flow past, between and across the hydrophobic streamers, thus, promoting coalescence. The result is a much coarser two- phase outflow (i.e. larger bubbles). Gas-liquid separation is still required in order to facilitate complete phase stream segregation. However, this stage is made easier by the increased bubble size and hence, can be accomplished by smaller and/or less energetic separation apparatus. As such, this static coalescer may be used as a pre-treatment to conventional gasliquid separation (i.e. installed within an upstream pipeline). The static coalescer 20 consists of a rack 201 comprising an array of vertical mesh screens 1602 alongside one another, each screen 202 folded and held proximal to the respective folds 210, within the rack 201 . Opposed ends 213 of the screens 202 are free such that portions 212 of the screens 202 between the folds 210 and free ends 213 may also move freely. The rack 201 is open at its input (upper, as shown) and output (lower, as shown). Figures 3A and 3B show examples of a settling chamber 2 operating without and with the static coalesce 20, respectively. The rapid elimination of gasliquid interface is also important in the context of controlling the rate of mass transfer between phases. Some processes, for example ammonia stripping from water, require that the interface is created and rapidly destroyed in order to optimise mass transfer yields. However, these static coalescers 20 have been implemented in only carefully controlled conditions, such as removal of spent oxidation gas from an electrolyte salt solution for fuel cells. Attempts to apply these static coalescers 20 to brackish borehole water, for example, have been unsuccessful, resulting in failure to induce coalescence and prevent fine bubble breakthrough to the outlet after relatively short use. Failure is understood to arise from surface contamination during use. Although the identity of the contaminant(s) is not known, this failure indicates the lack of durability and robustness of the technology for such applications. Figures 4A and 4B compare surface wetting behaviour of as-received PTFE mesh and used PTFE mesh of the static coalesce 20. In contrast to Figure 4A, the surface of the PTFE mesh of Figure 4B is wetted such that relatively little coalescence occurs. Figures 5A and 5B compare the performance of as-received PTFE mesh and used PTFE mesh in static coalescers 20. It is clear to see that relatively little coalescence is achieved by the static coalescer 20 including the used PTFE mesh and significant fine bubble breakthrough is the consequence.

Hence, there is a need to improve separation of two-phase and/or multi-phase flows.

Summary of the Invention

It is one aim of the present invention, amongst others, to provide an apparatus for separation of two-phase and/or multi-phase flows, for example accelerated coalescence of bubbles, which at least partially obviates or mitigates at least some of the disadvantages of the prior art, whether identified herein or elsewhere. For instance, it is an aim of embodiments of the invention to provide an apparatus that improves separation of two-phase and/or multi-phase flows, compared with conventional apparatus. For instance, it is an aim of embodiments of the invention to provide an apparatus that having improved durability and/or robustness, compared with conventional apparatus.

A first aspect provides an apparatus for mutually separating a first phase and a second phase entrained in the first phase, the apparatus comprising: a vessel, defining a volume therein, for receiving a flow of the first phase and the second phase therethough, wherein the vessel comprises a set of inlets, including a first inlet, and a set of outlets, including a first outlet and a second outlet, defining a flow path therebetween; and a set of separators, including a first separator, having a surface for causing coalescence of at least some of the entrained second phase, arranged within the vessel; wherein the surface comprises micro protrusions and/or nano protrusions.

A second aspect provides a method of manufacturing a first separator according to the first aspect, comprising: providing a precursor for the first separator; and creating micro protrusions and/or nano protrusions in and/or on the precursor, thereby forming the surface; optionally, wherein creating the micro protrusions and/or nano protrusions in and/or on the precursor comprises heating the precursor, for example with a laser beam.

A third aspect provides a method of mutually separating a first phase and a second phase entrained in the first phase, optionally wherein the first phase comprises and/or is a first liquid and wherein the second phase comprises and/or is bubbles of a first gas, the method comprising: flowing the first phase and the second phase over a surface of a set of separators, including a first separator, wherein the surface comprises micro protrusions and/or nano protrusions; and causing, by the surface, coalescing of at least some of the entrained second phase. A fourth aspect provides use of a laser-processed (also referred to as laser-treated) polymeric composition, comprising a first polymer, mesh to separate a foam comprising gas bubbles entrained in a liquid.

A fifth aspect provides a separator according to the first aspect.

A sixth aspect provides a substrate according to the first aspect.

Detailed Description of the Invention

According to the present invention there is provided an apparatus, as set forth in the appended claims. Also provided is a method of manufacturing, a method of separating and a use. Other features of the invention will be apparent from the dependent claims, and the description that follows.

Apparatus

The first aspect provides an apparatus for mutually separating a first phase and a second phase entrained in the first phase, the apparatus comprising: a vessel, defining a volume therein, for receiving a flow of the first phase and the second phase therethough, wherein the vessel comprises a set of inlets, including a first inlet, and a set of outlets, including a first outlet and a second outlet, defining a flow path therebetween; and a set of separators, including a first separator, having a surface for causing coalescence of at least some of the entrained second phase, arranged within the vessel; wherein the surface comprises micro protrusions and/or nano protrusions.

In this way, separation of two-phase and/or multi-phase flows, for example, is improved compared with conventional apparatus, since the micro and/or nano protrusions of the surface increases hydrophobicity thereof, thereby promoting fine bubble coalescence, for example. For example, in this way, coalescence of bubbles, such as in foams or liquid entrained gases, is accelerated. For example, a fine two-phase flow (i.e. small bubbles) maybe transformed into a course two-phase flow (i.e. large bubbles or partially separated). A subsequent separation stage may be still required in order to facilitate complete separation in a practical sense (e.g. settling tank). However, the duty on such stage will be greatly reduced due to the prior coalescence achieved. Since the separation is improved, the apparatus may be smaller and/or more energy efficient while maintaining performance, compared with conventional apparatus. Furthermore, the micro and/or nano protrusions of the surface improves durability and/or robustness, compared with conventional apparatus, as discussed below. Further advantages may include: compactness (i.e. small volume), low energy, low mist generation, improved resistance to effects of surface contamination and/or potential to use less costly materials for the surface.

Although this disclosure is focused on aqueous liquid-gas coalescence, the separators described herein with respect to the first aspect may be similarly used to cause liquid-liquid or multi-fluid phase coalescence. The key requirements are: i) at least one but not all of the phases must ‘wet’ the active surface (i.e. present a low contact angle) and ii) at least one but not all of the phase must be repelled by the active surface (i.e. present a high contact angle) and iii) the phases must possess a high surface tension. It should be understood that references to hydrophobicity may refer additionally and/or alternatively to oleophobicity and vice versa, mutatis mutandis.

It is known that surface roughness at the micro and nano scale (often referred to as a hierarchical surface) can have a significant influence on hydrophobicity. Roughing a surface, in order to create tiny protuberance and cavities, can markedly increase its overall hydrophobic properties. Surface features at this scale exploit existing liquid contact angles to fend off and diminish liquidsurface contact. The result is a decrease in surface wettability - i.e. increased hydrophobicity. As such, overall surface hydrophobicity becomes a product of both the material physicalchemistry and surface topography. As such, materials already in possession of low surface free energy can be made super hydrophobic (i.e. water contact angle >150°) by surface modification. The phenomenon is described by the Cassie-Baxter model, which differs from Wenzel wetting in that the droplet sits on an inhomogeneous surface instead of penetrating into surface texture, and when combined with low or no adhesion is commonly referred to as the Lotus Flower Effect, as shown in Figure 6.

Without wishing to be bound by any theory, as overall hydrophobicity is the product of both surface physical-chemistry and micro/nano scale surface topography, then a roughened surface may be capable of maintaining sufficient hydrophobicity even if the physical-chemical contribution is diminished through contamination. As such, control of surface topography may improve both the durability and robustness of static coalescers. Furthermore, control of surface topography may provide more intensive bubble breakdown (i.e. increase bubble destruction rate per unit area of active surface), thus, enabling smaller and/or more efficient designs (i.e. less material, cost, obstruction to flow, pressure drop and therefore, less energy).

Control of surface topography, particularly the micro/nano scale surface features, may also improve the interception and coalescence of similarly sized bubbles, thus, targeting improved efficiency at the finer bubble size range.

Control of surface topography by surface modification may also reduce material costs by improving the hydrophobic properties of less expensive materials to the point of process viability. Although PTFE possesses a naturally low surface free energy, it is a relatively expensive polymeric material. Lower cost materials, such as polyethylene, polypropylene or nylon, could potentially be used.

Apparatus

The apparatus is for mutually separating the first phase and the second phase entrained in the first phase, for example for separating the liquid and gas phases of a foam. It should be understood that the first phase and second phase are fluids, for example liquids and/or gases. It should be understood that at least one of the first phase and the second phase is a liquid. It should be readily understood that the term 'foam' encompasses froth and liquid entrained gases and can be fine (having small gas bubbles) or coarse (having larger gas bubbles) or a combination of foam having different-sized gas bubbles. In one example, the first phase is a liquid and the second phase is a gas, i.e. a foam. In one example, the first phase is a first liquid and the second phase is a second liquid, for example immiscible in the first liquid, i.e. an emulsion.

In one example, the apparatus is a static apparatus (i.e. unpowered, not having actuators or pumps, for example). That is, separation arises from the flow of the first phase and the second phase entrained therein over the surface, for example without external mechanical action. Vessel

The apparatus comprises the vessel, defining a volume therein, for receiving the flow of the first phase and the second phase therethough. For example, the vessel may be a container or chamber, such as an open vessel or a closed vessel. Generally, the apparatus will be provided as part of or in cooperative relationship with an industrial unit generating a foam comprising at least one useful and reusable phase, there being provided means for supplying foam from the industrial unit to the separator, and means for recovering the at least one useful and reusable component and supplying the same to the or an alternative industrial unit.

The vessel comprises the set of inlets, including the first inlet, and the set of outlets, including the first outlet and the second outlet, defining the flow path therebetween. It should be understood that the first phase and the second phase entrained in the first phase flow into the vessel via the set of inlets, in use, and that the at least partially separated first phase and second phase flow out of the vessel via a set of outlets. In this way, the first phase may be recovered or discharged via the first outlet, for example, while the second phase may be recovered or discharged via the second outlet. It should be understood that the first phase flowing out of the vessel via the first outlet may include at least some of the second phase, for example a residual amount and entrained therein. Similarly, it should be understood that the second phase flowing out of the vessel via the second outlet may include at least some of the first phase. That is, an efficiency of the separation may be less than 100%.

Separators

The apparatus comprises the set of separators, including the first separator, arranged within the vessel. It should be understood that the set of separators is in the flow path. In one example, the set of separators includes N separators including the first separator, wherein N is a natural number greater than or equal to 1 , for example 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10 or more. In one example, the respective separators of the set thereof are replaceable, for example during maintenance. In one example, the set of separators is scalable, whereby the number of separators may be increased or reduced, according to a required throughput, for example. Each separator of the set there of maybe as described with respect to the first separator.

The set of separators, for example the first separator, has the surface for causing coalescence of at least some of the entrained second phase. That is, the surface of the first separator comprises and/or is a coalescence enhancing surface. It should be understood that separation plus includes coalescence, being the removal of liquid boundaries between bubbles, which comprises and/or is separation. Hence, it should be understood that there is a distinction between true separation of phases and the coalescence of a first phase whilst it still remains within a second phase, the latter which is described herein. In this way, the first phase and the second phase are mutually separated. It should be understood that the surface is in the flow path and hence the flow of the first phase and the second phase is over the surface. That is, the surface is exposed, in use, to the flow of the first phase and the second phase. It should be understood that generally, flow of the first phase and the second phase over the surface is required to cause separation by coalescence of at least some of the entrained second phase. In one example, the flow path is overthe first separator. In one example, the flow path is the through the first separator.

In one example, the first separator comprises set of perforations, including a first perforation, for example a mesh, a perforated sheet or an array of tubes. It should be understood that the flow is through the set of perforations. In this way, a specific surface area (i.e. a surface area to volume ratio) of the first separator and hence of the surface may be increased. Particularly, it is desirable to increase the specific surface area of the first separator while maintaining a sufficiently high fluidic conductance. For example, as the specific surface area of the first separator increases, the surface area exposed to the first phase and the second phase entrained therein increases, thereby enhancing coalescence of at least some of the entrained second phase, though increasing also the fluidic resistance of the first separator. As discussed below, the first separator may be designed so as to optimise this balance.

In one example, the surface is provided by a substrate i.e. the surface is the surface of the substrate. In one example, the substrate comprises and/or is a substantially linear substrate such as a filament, a fibre, a rod or a tube; a substantially planar substrate for example a plate, a sheet or a ribbon; and/or a substantially volumetric substrate; or an array thereof, optionally wherein the substrate comprises and/or is a porous substrate, having open pores.

In one example, the substrate is formed of low surface energy or hydrophobic polymer filaments or the mesh may be formed of filaments of another material and coated with the low surface energy or hydrophobic material. The mesh or perforated plate hole size can vary in diameter from 0.1 mm to 10mm, with the polymer filaments when present ranging from 50pir) to 1 mm in thickness. The disruptive interface phenomenon is enhanced when surface material has a low surface energy and a microfilament or rough finish at the length scale of the foam liquid film thickness. For example, when a foam is passed over the low surface energy surface or through the low surface energy mesh, the gas liquid interfaces of the foam are ruptured and the gas and liquid separate into a dense liquid phase and a gaseous phase.

In one example, the first separator, for example a substrate thereof, extends, at least in part, along the flow path. In this way, the first phase and the second phase flow over the first separator, for example along a length thereof. In this way, coalescence of the entrained second phase is caused by the surface of the first separator during a relatively longer duration, thereby increasing an efficiency of separation. In one example, the substrate has a pleated pan fold configuration extending, at least in part, along the flow path. In one example, the substrate has an annular fan fold configuration with combined flow flowing inside and/or outside the annular space.

In one example, the first separator, for example a substrate thereof, comprises one or more layers, for example including one or more of a mesh, a perforated sheet and an array of tubes having the surface. One or more layers may be provided transverse to, parallel to or at an angle to the flow. Alternatively, a randomly packed configuration may be provided. In one example, a portion of the substrate is convex or pointed so that it is projecting away from other portions of the surface. In one example, the portion is formed by elongate strands of a mesh. In one example, the portion is oriented at least partly parallel to the flow path.

In one example, the first separator, for example a substrate thereof, comprises a flexible material having the surface. In this way, the first separator, for example the substrate, may flex due to flow of the first phase and the second phase, for example oscillate or vibrate in the flow. In this way, an efficiency of separation may be increased since the oscillation or vibration may promote coalescence of the entrained second phase. In one example, a first end of the substrate, relatively more proximal the set of inlets, is a fixed end, for example fixedly attached such as coupled directly or indirectly to the first separator, and a second end of the first substrate, opposed to the first end and relatively more proximal the set of outlets, is a free end. In this way, transverse movement of the substrate and hence the surface is inhibited at the first end but permitted increasingly towards the second end, thereby enhancing oscillation or vibration thereof. In one example, the first end is resiliently attached such as coupled indirectly to the first separator via a resilient member such as spring or last elastomeric coupling. In this way, at least some transverse movement of the substrate at the first end is permitted while the first end is biased towards a predetermined position. In this way, an efficiency of separation may be increased. In one example, the set of separators is configured to enhance oscillation or vibration of the respective separators, for example by mutual interaction such as due to flow therebetween and/or mutual contact. For example, coalescence of the second phase may urge the surface transverse to the flow, thereby resulting in lateral movement of the substrate and in turn, lateral movement of a substrate.

In one example, the first separator, for example a substrate thereof, has a plurality of surfaces, for example provided by a plurality of substrates. In one example, adjacent surfaces are mutually held spaced apart transverse to the flow path at respective first ends (i.e. a fixed end) and respective second ends are free ends, as described above. For example, the plurality of surfaces may extend unidirectionally (e.g. a brush head). In one example, adjacent surfaces are mutually held spaced apart axially to the flow path at respective first ends (i.e. a fixed end) and respective second ends are free ends, as described above. For example, the plurality of surfaces may radiate from a hub, for example upstream or downstream (e.g. mop head).

In one example, the first separator comprises a frame and a substrate is attached thereto, for example fixedly attached such as mechanically attached. In one example, the first separator is arranged to expose the surface to the flow, for example to expose a substantially all of the surface to the flow, for example at least 60%, preferably at least 70%, more preferably at least 80%, most preferably at least 90% of the surface to the flow. In this way, the rate of coalescence may be increased by increasing the contact experience between the surface and the flowing fluid phases. In one example, is arranged to expose the surface to the flow by comprising one or more streamers for example sheets of a flexible material as described above, having the surface, having a fold and supported by a frame proximal or at the fold, for example supported by a ridged beam spanning a cross-section of the first separator, wherein the streamer includes an aperture, such as one or more of a V notch and/or other hole, proximal or at the fold. In this way, fluid contact with the inner surface of the folded streamer is improved. Being oriented in the direction of the flow (i.e. ‘windward’ to the flow), the aperture presents an easy route for bubbles to gain access to the hitherto sheltered inner streamer surface.

In one example, the first separator comprises a substrate such as a flexible sheet and/or ribbon or plurality thereof, having a free end relatively more proximal the set of outlets. For example, the streamers are at least partially divided, for example having lengthwise cuts, so as to create ribbons, tapes or tassel-like formations of the leeward edge. In this way, contact of the entrained second flow with the surface is increased and thereby, coalescence.

In one example, the first separator, for example a substrate thereof, projects, at least in part, transverse to the flow path. For example, the streamers may include multiple lateral zig-zag folds, or riffles (i.e. perpendicularto the direction of flow). In this way, impingement and therefore, greater interaction between the bulk two-phase throughflow and the surface is increased (e.g. discourages bubbles from being able to slip between and not encounter, a streamer surface). In this way, a volume efficiency of the in-stream device is improved and therefore, an intensification of coalescence process.

In one preferred example, the first separator comprises a frame and a flexible substrate, having the surface, attached thereto, wherein the first separator is arranged to expose the surface to the flow by comprising one or more streamers for example sheets of the substrate as described above, having a fold and supported by the frame proximal or at the fold, wherein the streamer includes an aperture proximal or at the fold, wherein the streamers are at least partially divided, optionally, wherein the streamers include multiple lateral zig-zag folds and wherein the substrate comprises and/or is a mesh formed from a polymeric composition comprising a first polymer, for example as described below.

Surface

The surface comprises micro protrusions and/or nano protrusions. In one example, the micro protrusions and/or nano protrusions are formed as described with respect to the second aspect. In one example, the first separator comprises a substrate providing the surface.

In one example, the micro protrusions and/or nano protrusions comprise a hierarchical distribution thereof (i.e. a hierarchical structure). In this way, hydrophobicity of the surface is improved. The role of the hierarchical surface roughness (i.e. nanoscale details imposed upon microscale details, also known as multiscale) has been discussed in the literature but is not fully understood. For example, the models due to Wenzel and Cassie-Baxter do not require roughness to be hierarchical or multiscale. Furthermore, while the Wenzel and Cassie-Baxter models remain the standard in describing how roughness and/or surface chemistry affects wetting, these simple models, which operate with only two parameters — the so-called Wenzel roughness factor (the ratio of the surface area to the projected area) and the fractional area of the solid-liquid interface-may be insufficient to describe the complexity of wetting scenarios. In one example, the surface comprises concavities, such that the surface is re-entrant. For example, hierarchical roughness may provide a small-scale roughness that constitutes an additional stability factor to the three-phase line at the surface. In this way, interface stability may be increased by having a concave (re-entrant) surface. In one example, the surface comprises and/or is a lamellar surface, comprising a plurality of lamellae having the micro protrusions and/or nano protrusions, and/or a filamentous surface, comprising a plurality of filaments having the micro protrusions and/or nano protrusions.

In one example, the surface has a contact angle of at least 133°, at least 135°, at least 140°, at least 145°, at least 150°, at least 155°, at least 160°, at least 165° or at least 170°, as measured by the static sessile drop method, for example as described below. Other measurement methods are known, including the pendant drop method, the dynamic sessile drop method, the dynamic Wilhelmy method, the single fibre Wilhelmy method and the single fibre meniscus method. That is, the surface may be super hydrophobic or ultra hydrophobic. It should be understood similarly, that the surface may be super oleophobic or ultra oleophobic.

Conventional surface parameters used for feature roughness characterization in tribology may be used to characterise the surface, particularly the amplitude and spatial orientation of the micro protrusions.

In one example, the surface has an arithmetical mean height S _a in a range from 0.53 pm to 100 pm, preferably in a range from 0.75 pm to 50 pm, more preferably in a range from 1 pm to 10 pm, most preferably in a range from 1 .86 pm to 8.99 pm.

The arithmetical mean height S _a is the 3D equivalent of the arithmetical mean height of a line R _a to a surface. The arithmetical mean height S _a expresses, as an absolute value, the difference in height of each point compared to the arithmetical mean of the surface. This parameter is used generally to evaluate surface roughness.

By increasing the arithmetical mean height S _a , the surface roughness of the surface is increased. For an arithmetical mean height S _a less than the lower bound of the ranges, the surface roughness of the surface does not appear to significantly contribute to an improvement in hydrophobicity of the surface. However, increasing the arithmetical mean height S _a greater than the upper bound of the ranges does not appearto significantly further improve hydrophobicity of the surface and/or may be deleterious to robustness, for example. In order to affect the superhydrophobic state of a PTFE surface structure engineered using a CO2 laser, for example, the arithmetical mean height S _a is most preferably in a range from 1 .86 pm to 8.99 pm. Although the arithmetical mean height S _a provides information on the height variations of the surface, the arithmetical mean height S _a provides little information on the spatial distribution or shape of the surface features, and so to further characterise the surface, altitudinal and/or spatial characteristics of the surface may be defined, as set out in Table 1.

Table 1 : Definition of 3D roughness parameters, according to ISO 25178-2 (2012) and EUR 15178N (1993) calculated and analysed in this study

By way of example, parameter values for as received PTFE (sheet): S _a : 0.52 pm; S _sc : 0.004 1/pm; S _dq : 0.052; and Sdr: 0.133

In one example, the surface has a root mean square gradient S _dq in a range from 0.053 to 10, preferably in a range from 0.075 to 5, more preferably in a range from 0.1 to 1 , most preferably in a range from 0.182 to 0.781 .

The root mean square gradient S _dq is calculated as a root mean square of slopes at all points in the definition area. The root mean square gradient S _dq of a completely level surface is 0. The root mean square gradient S _dq is a general measurement of the slopes which comprise the surface and may be used to differentiate surfaces with similar arithmetical mean height S _a . The root mean square gradient S _dq typically finds application for sealing systems, surface cosmetic appearance and may be related to the degree of surface wetting by various fluids. The root mean square gradient S _dq is affected both by texture amplitude and spacing. Thus for a given arithmetical mean height S _a , a wider spaced texture may indicate a lower root mean square gradient S _dq value than a surface with the same arithmetical mean height S _a but finer spaced features.

For a root mean square gradient S _dq less than the lower bound of the ranges, the spacing of features of the surface does not appear to significantly contribute to an improvement in hydrophobicity of the surface. However, increasing the root mean square gradient S _dq greater than the upper bound of the ranges does not appear to significantly further improve hydrophobicity of the surface and/or may be deleterious to robustness, for example.

In one example, the surface has an arithmetic mean summit curvature S _sc in a range from 0.005 pm ¹ to 1 pm ¹ , preferably in a range from 0.0075 pm ¹ to 0.5 pm ¹ , more preferably in a range from 0.01 pm ¹ to 0.1 pm ¹ , most preferably in a range from 0.016 pm ¹ to 0.076 pm ¹ .

The arithmetic mean summit curvature S _sc is the mean summit curvature for surface features, particularly peaks. Peaks are found for summit density, in which is the number of summits per unit area making up the surface. Summits are derived from peaks. A peak is defined as any point, above all 8 nearest neighbours. Summits are constrained to be separated by at least 1 % of the minimum X or Y dimension comprising the 3D measurement area. Additionally, summits are only found above a threshold that is 5% of the maximum height of the surface S _z above the mean plane. The arithmetic mean summit curvature S _sc is typically useful in predicting the degree of elastic and plastic deformation of a surface under different loading conditions and thus may be used in predicting friction, wear and real area of contact.

For an arithmetic mean summit curvature S _sc less than the lower bound of the ranges, the mean summit curvature S _sc ofthe surface does not appearto significantly contribute to an improvement in hydrophobicity of the surface. However, increasing the arithmetic mean summit curvature S _sc greater than the upper bound of the ranges does not appear to significantly further improve hydrophobicity of the surface and/or may be deleterious to robustness, for example.

In one example, the surface has a developed area ratio S _dr in a range from 0.15% to 75%, preferably in a range from 0.25% to 50%, more preferably in a range from 0.75% to 25%, most preferably in a range from 1 .56% to 23.17%.

The developed area ratio S _dr is expressed as the percentage of additional surface area contributed by the texture as compared to an ideal plane the size of the measurement region. The developed area ratio S _dr of a completely planar surface is 0. The developed area ratio S _dr may further differentiate surfaces of similar amplitudes and average roughness. Typically, the developed area ratio S _dr will increase with the spatial intricacy of the texture whether or not the arithmetical mean height S _d changes. The developed area ratio S _dr is useful in applications involving surface coatings and adhesion. The developed area ratio S _dr may find relevance when considering surfaces used with lubricants and other fluids. The developed area ratio S _dr is affected both by texture amplitude and spacing. Thus, a higher arithmetical mean height S _a , wider spaced texture may have actually a lower developed area ratio S _dr value than a lower arithmetical mean height S _d but finer spaced texture.

Polymer

In one example, the first separator comprises a polymeric composition comprising a first polymer. It should be understood that the surface is provided, at least in part, by the polymeric composition. In one example, the surface is provided by a substrate and the substrate comprises and/or is the polymeric composition. Polymeric compositions may be chemically compatible with the first phase and/or the second phase, may have relatively low surface energies and/or the surface topography thereof may be suitably controlled. In one example, the polymeric composition is provided as a coating on the first separator or a part thereof. In one example, the polymeric composition is provided as a sheet or a mesh, for example.

In one example, the first polymer has a surface energy of at most 40 mJ nr ² , preferably at most 30 mJ nr ² , more preferably at most 25 mJ nr ² . That is, the first polymer has a relatively low surface energy and hence may be described as hydrophobic.

In one example, the first polymer is a polyolefin, a polystyrene, a polyvinyl, a polyvinyl halide, a polyvinylidenehalide, a polyhaloolefin, a poly(meth)acrylate, a polyester, a polyamide, a polycarbonate, a polyol efin oxide, a polyester, a polyaryletherketone (PAEK) or a polyetheretherketone (PEEK).

In one example, the first polymer is linear or branched polyethylene-linear, isotactic polypropylene, polyisobutylene, polystyrene, polymethylstyrene, polyvinyltoluene, polyvinyl fluoride, polyvinylidene fluoride, polytrifluoroethylene, polytetrafluoroethylene, polyvinylchloride, polyvinylidene chloride, polychlorotrifluoroethylene, polyvinylacetate, polymethylacrylate, polyethylacrylate, polymethylmethacrylate, polyethylmethacrylate, polybutylmethacrylate, polyisobutylmethacrylate, poly(t-butylmethacrylate), polyhexylmethacrylate, polyethyleneoxide, polytetramethylene oxide, polytetrahydrofurane, polyethyleneterephthalate, polyamide-6,6, polyamide-12, polydimethylsiloxane, polycarbonate or polyetheretherketone.

In one example, the first polymer is selected from Table 2.

Table 2: Surface free energy (SFE) of selected polymers. The contact angle for water is for as received sheet i.e. without surface modification.

Method of manufacturing

The second aspect provides a method of manufacturing a first separator according to the first aspect, comprising: providing a precursor for the first separator, for example of a substrate thereof; and creating micro protrusions and/or nano protrusions in and/or on the precursor, thereby forming the surface; optionally, wherein creating the micro protrusions and/or nano protrusions in and/or on the precursor comprises heating the precursor, for example with a laser beam.

In this way, the precursor is physically modified to create topographic features at the micro/nano scale, for the improvement hydrophobicity and hence fine bubble collapse.

It should be understood that the surface is thus formed in and/or on the precursor, for example thereby providing the substrate, for example. That is, the precursor may be the substrate before the surface is formed therein and/or thereon. Hence, generally, the precursor may be as described with respect to the substrate according to the first aspect, mutatis mutandis. In one example, providing the precursor comprises applying a coating and/or processing a film of a polymeric composition comprising a first polymer, as described with respect to the first aspect. In one example, the precursor corresponds with the substrate, for example wherein the precursor comprises and/or is a substantially linear precursor such as a filament, a fibre, a rod or a tube; a substantially planar precursor for example a plate, a sheet or a ribbon; and/or a substantially volumetric precursor; or an array thereof, optionally wherein the precursor comprises and/or is a porous precursor, having open pores.

In one example, creating the micro protrusions and/or nano protrusions in and/or on the precursor comprises depositing material thereon, thereby creating the micro protrusions and/or nano protrusions. Suitable deposition techniques include film/coating deposition techniques such as spray deposition and electrospraying. In one example, creating the micro protrusions and/or nano protrusions in and/or on the precursor comprises surface modification. Suitable surface modification techniques including electron irradiation, reactive ion etching, plasma etching, laser processing by different methodologies and/or mechanical abrasion. Using these techniques, hierarchal structures including the micro protrusions and/or nano protrusions maybe created, thereby achieving contact angles generally exceeding 150° (indicating super hydrophobicity) for polymeric compositions comprising polymers such as PTFE, for example.

In one preferred example, creating the micro protrusions and/or nano protrusions in and/or on the precursor comprises heating the precursor, for example with a laser beam.

The laser treatment improves the performance of the active material surfaces within existing gas bubble coalescer devices. This enables the device to more rapidly breakdown fine gas bubbles (i.e. merges small bubbles into big bubbles). As such, gas bubble coalescer devices can be made more effective, more compact and/or more energy efficient. The coalescence of fine bubbles into larger bubbles can assist subsequence gas-liquid separation processes (i.e. settling chambers, cyclones, etc.) and/or rapidly control the rate of reactions which rely on gas-liquid interaction (e.g. hot gas ammonia stripping).

The laser treatment forms micro protrusions and/or nano protrusions on an existing hydrophobic (i.e. water repelling) surface at the micro/nano scale, creating a ‘lotus leaf like surface structure which further increases hydrophobicity - potentially making it super-hydrophobic (i.e. contact angles >150°). The structure works to exploit the innate high angle of contact with which liquid naturally touches the solid surface. Micro/nano surface prominences work to repel the contacting liquid, allowing gas to slip between the two as surface tension compels the liquid to withdraw in on itself and away from the solid surface. As a consequence, the liquid that surrounds and thus, defines each gas bubble is removed, hence, merging the bubbles together and, by definition, bringing about coalescence.

Laser enhancement of hydrophobic surfaces offers a route to more compact, low energy and more efficiency fine bubble gas-liquid separation.

Coalescence by exposure to hydrophobic surfaces also has an additional advantage with respect to mist generation. Both settling chamber and cyclone technologies collapse bubbles by draining the liquid film between bubbles to the point of rupture. However, bubble disintegration in this way leads to the generation and release of fine droplets, or mist. The entrained mist then exits with the separated gas stream thus, undermining separation efficiency. The mechanism of coalescence by exposure to hydrophobic surfaces avoids mist generation and is therefore able to greatly reduce liquid carryover to the gas outflow. Laser enhancement improves this further.

Due to the nature of laser surface enhancement, cheaper materials (i.e. relative to Teflon) can be made sufficient hydrophobic so as to render them a useful substrate for the facilitation of fine bubble coalescence.

Laser modification also provides a resistance to the effects of surface contamination. Hydrophobicity resulting from the physical/chemical properties of material can be effected by the build-up of a surface contaminant layer. However, the architectural component of hydrophobicity, afforded by laser surface modification at the micro/nano scale, is less prone to such interference and thus, makes the surface more robust.

As discussed above, laser enhanced surface coalescence avoids the need for additives (i.e. antifoaming agents).

Use of lasers to modify the micro and nanostructure of surfaces of polymeric compositions is known, typically using laser sources including excimer lasers (UV), frequency doubled/tripled Nd:YAG lasers (visible/UV), and CO2 lasers (mid-long wavelength infra-red). Lasers modification of polymer surfaces works through either melting or ablation mechanisms, depending on the properties of the material being processed and the wavelength of the incident laser beam.

In the case of this work, CO2 lasers have been used to process a PTFE mesh to create a roughened, hierarchical outer surface that contrasts greatly with the unprocessed mesh samples.

The hierarchal surface acts to increase the native hydrophobicity of the PTFE, to create a state of near-perfect non-wetting. The advantages of using a CO2 laser over other systems, is the relatively low cost, high efficiency, diversity and availability of CO2 systems plus the fact that the standard emitting wavelength of 10.6 pm is readily absorbed by most polymers without the need for additives or coatings when compared to more technologically advanced, but industrially impractical systems (e.g. ultrashort pulse systems) that operate at wavelengths most polymers do not readily interact with.

In one example, heating the precursor with a laser beam (i.e. laser processing) comprises linear and/or crosshatch scanning, for example at a line spacing in a range from 0.1 mm to 0.5 mm, at a scanning speed in a range from 50 mm/s to 500 mm/s and/or add a laser power in a range from 5 W to 40 W, using a CO2 laser.

Method of separating

The third aspect provides a method of mutually separating a first phase and a second phase entrained in the first phase, optionally wherein the first phase comprises and/or is a first liquid and wherein the second phase comprises and/or is bubbles of a first gas, the method comprising: flowing the first phase and the second phase over a surface of a set of separators, including a first separator, wherein the surface comprises micro protrusions and/or nano protrusions; and causing, by the surface, coalescing of at least some of the entrained second phase.

In one example, the method of mutually separating the first phase and the second phase and entrained in the first phase comprises and/or is a method of coalescing at least some of the entrained second phase.

The separating, the first phase, the second phase, the first liquid, bubbles, the first gas, flowing, the surface, a set of services, the first separator, the set of separators, the micro protrusions, the nano protrusions, the causing and/or the coalescing maybe as described with respect to the first aspect.

Use

The fourth aspect provides use of a laser-processed polymeric composition, comprising a first polymer, mesh to separate a foam comprising gas bubbles entrained in a liquid.

The laser processing, the polymer composition, the first polymer, the mesh, the foam, the gas bubbles and/or the liquid maybe as described with respect to the first aspect.

Separator

The fifth aspect provides a separator according to the first aspect.

Substrate

A sixth aspect provides a substrate according to the first aspect.

Definitions

Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of other components. The term “consisting essentially of’ or “consists essentially of’ means including the components specified but excluding other components except for materials present as impurities, unavoidable materials present as a result of processes used to provide the components, and components added for a purpose other than achieving the technical effect of the invention, such as colourants, and the like. The term “consisting of’ or “consists of’ means including the components specified but excluding other components. Whenever appropriate, depending upon the context, the use of the term “comprises” or “comprising” may also be taken to include the meaning “consists essentially of’ or “consisting essentially of’, and also may also be taken to include the meaning “consists of’ or “consisting of’. The optional features set out herein may be used either individually or in combination with each other where appropriate and particularly in the combinations as set out in the accompanying claims. The optional features for each aspect or exemplary embodiment of the invention, as set out herein are also applicable to all other aspects or exemplary embodiments of the invention, where appropriate. In other words, the skilled person reading this specification should consider the optional features for each aspect or exemplary embodiment of the invention as interchangeable and combinable between different aspects and exemplary embodiments.

Brief description of the drawings

For a better understanding of the invention, and to show how exemplary embodiments of the same may be brought into effect, reference will be made, by way of example only, to the accompanying diagrammatic Figures, in which:

Figure 1 schematically depicts principle of bubble collapse by exposure to low surface energy materials;

Figure 2A schematically depicts a static coalescer according; Figure 2B is a photograph of a static coalescer according to Figure 2A; and Figure 2C is a photograph of a static coalescer of Figure 2B;

Figure 3A is a photograph of a settling chamber for gas-liquid separation in brackish salt water, without using a conventional separator; and Figure 3B is a photograph of the settling chamber gas-liquid for separation in brackish salt water, using a conventional separator;

Figure 4A is a photograph of uncontaminated (unwetted) PTFE mesh having a 1.2 mm longitudinal pore span; and Figure 4B is a photograph of contaminated (wetted) PTFE mesh having a 1 .2 mm longitudinal pore span;

Figure 5A is a photograph of the settling chamber gas-liquid for separation in brackish salt water of Figure 3B, using a separator according to an example embodiment, after extended use; and Figure 5B is a photograph of the settling chamber gas-liquid for separation in brackish saltwater, using a conventional separator, after extended use;

Figure 6 schematically depicts of Wenzel and Cassie-Baxter models of wetting;

Figure 7 A schematically depicts a part of a separator according to an example embodiment; Figure 7B is a photograph of a separator according to an example embodiment; and Figure 7C is a photograph of the separator of Figure 7B, in more detail;

Figure 8A is a photograph of as-received (untreated) PTFE mesh having a 1 .2 mm longitudinal pore span; and Figure 8B is a photograph of laser-treated PTFE mesh having a 1.2 mm longitudinal pore span;

Figure 9A is a 3D profile image of as-received (untreated) PTFE mesh; and Figure 9B is a 3D profile image of laser-treated PTFE mesh;

Figures 10A and 10B are SEM images of as-received (untreated) PTFE mesh;

Figures 11 A and 11 B are SEM images of laser-treated PTFE mesh, according to an exemplary embodiment;

Figures 12A to 12C are 3D profile images of laser-treated PTFE mesh, according to exemplary embodiments;

Figure 14 schematically depicts a method according to an exemplary embodiment; and Figure 15 schematically depicts a method according to an exemplary embodiment.

Detailed Description of the Drawings Figure 5A is a photograph of the settling chamber gas-liquid for separation in brackish salt water of Figure 3B, using a separator according to an example embodiment, after extended use; and Figure 5B is a photograph of the settling chamber gas-liquid for separation in brackish saltwater, using a conventional separator, after extended use.

In sequential tests, laser-treated and untreated as-received PTFE mesh was cut and fashioned into static coalescers (as shown generally in Figures 2A to 2C). Each mesh was 10 cm in length and 4 cm diameter. Two static coalescers were installed within the exit pipe of a bubble generating apparatus. The static coalescers were mounted with an axial rotation of 90° to each other in order to improve contact. In each test, the static coalescers were subjected a ~300 micron bubble flow at a rate of 20 L/min water and 20 NL/min air. Water was circulated from a 50 L reservoir which was filled prior to each test with borehole extracted tap water (as supplied at Thornton Science Park, Cheshire, UK). The water was also heated to 40 °C and dosed with 15 g/L salt. During the initial minute of operation both laser-treated and untreated materials appeared to perform well. Significant breakdown of bubbles was observed within the first centimetre of the static coalescer. Bubbles were coalesced to coarse ‘glugs’ (see Figure 5A). However, within 20 minutes, fine bubble breakthrough was observed from the untreated material outlet as surface contamination took hold (see Figure 5B). However, after several hours’ operation, the treated material continued to perform well, albeit some advancement of the fine bubbles was observed beyond initial condition. Importantly, a coarse 2-phase discharge was maintained - thus suggesting a significant improvement in performance and durability.

Mesh

PTFE mesh was obtained from Dexmet Inc. (USA), having naming convention is XX MM YY - ZZZ (XX: material thickness before expansion; MM: material; Y: width of strand; ZZZ: length of expanded diamond; HST: stabilised; DB: meshed pulsed after expansion; F: flattened). Polyethylene (PE) and polypropylene (PP) mesh were obtained from Industrial Netting, having 0.1 -inch (about 2.5 mm) square pores. Perfluoroalkoxy alkane (PFA) mesh 5PFA9-100DDBST and polyetheretherketone (PEEK) mesh 10PEEK10 - 077 were obtained from Dexmet.

The mesh was presented for laser processing as single sheets. Both sides of the mesh were processed.

Sandpaper pre-treatment

500, 800 and 1200 grit papers were used to roughen the PTFE mesh applied for 10 seconds in an upwards direction, 10 seconds 90° to the first sanding direction and then 10 seconds in a circular motion.

Hydrophobic particle pre-treatment

PTFE mould release aerosol/spray (Rocol Ltd) was applied onto the mesh by spraying for a period of 10 seconds until the sample became visibly wetted.

Laser processing A 60 W Synrad Firestar series ti60 CO2 laser, fitted with a galvanometric scanning head was used, according to operating conditions defined in Table 1 , at a spot size of about 171 pm FWHM.

Table 1. Laser operating conditions

Surface profilometry apparatus, measurement and processing methods

Surface topography was analysed using a coherence correlation interferometry (CCI) profilometer (Micromesure 2, STIL, France) including a CCS-Prima sensor, according to manufacturer’s instructions. Sample areas of 0.5 mm x 0.5 mm were examined for each of the samples. Samples were ultrasonically cleaned in isopropanol for 3 minutes at room temperature before measurements were taken. Samples were then left to air dry. The results were analysed using Surface Map software (STIL, France).

Contact angle

Sessile drop contact angles of advancing contact angles were analysed via sessile needle in method using a goniometer (OCA20; Dataphysics Instruments, GmbH). Prior to contact angle measurements being taken, samples were ultrasonically cleaned in isopropanol for 3 minutes each at room temperature. Samples were then left to air dry. A droplet of 8 pL of ultra-pure water was deposited on a sample and a high-resolution image acquired, from which the contact angle was measured within 1 ° error.

Roll off

Initially the sessile drop method will be followed before executing the roll off method. The tilt will be set to 90° with a set step tilt of 0.1 °.

Optical microscopy

Optical observations and images were taken between x0.8 and x100 magnification on LEICA DM2700 M microscopes fitted with a digital camera connected to imaging software. Lacunarity (measure of space and voids on the surface of the material), line width and mesh pore encroachment (where the fibrous structure the laser creates begins to fill the pore and join with the opposite side) were measured.

Scanning electron microscopy

SEM was performed using a Hitachi EM3030 SEM set up to detect back scattered electrons at 15 KHz. Each sample was examined generally at magnifications between x60 to x300 and more closely between x500 and x4000.

Figure 7A schematically depicts a part of a separator 70 according to an example embodiment; Figure 7B is a photograph of a separator 70 according to an example embodiment; and Figure 7C is a photograph of the separator 70 of Figure 7B, in more detail. The separator 70 is generally as described with respect to the static coalescer 20 and like references signs denote like integers.

In contrast with the static coalescer 20, in this example, the separator 70 has a surface for causing coalescence of at least some of the entrained second phase, wherein the surface comprises micro protrusions and/or nano protrusions. In this example, the micro protrusions and/or nano protrusions comprise a hierarchical distribution thereof, as described with respect to Figures 8B and 9B. In this example, the surface has an arithmetical mean height S _a in a range from 0.53 pm to 100 pm. In this example, the surface has a root mean square gradient S _dq in a range from 0.053 to 10. In this example, the surface has an arithmetic mean summit curvature S _sc in a range from 0.005 pm ¹ to 1 pm ¹ . In this example, the surface has a developed area ratio S _dr in a range from 0.15% to 75%. In this example, the separator 70 comprises a polymeric composition comprising a first polymer. In this example, the separator 70 comprises set of perforations, including a first perforation, for example a mesh or a perforated sheet. In this example, the separator 70 extends, at least in part, along the flow path. In this example, the separator 70 projects, at least in part, transverse to the flow path. In this example, the separator 70 is arranged to expose the set of surfaces to the flow. In this example, the separator 70 comprises a flexible sheet and/or ribbon or plurality thereof, having a free end relatively more proximal the set of outlets.

In this example, the separator 70 comprises a frame 701 and a flexible substrate 702, having the surface, attached thereto, wherein the separator 70 is arranged to expose the surface to the flow by comprising one or more streamers 702 for example sheets of the substrate as described above with respect to the first aspect, having a fold 710 and supported by the frame 701 proximal or at the fold 710, wherein the streamer 702 includes an aperture 703 proximal or at the fold 702, wherein the streamers 702 are at least partially divided, optionally, wherein the streamers 702 include multiple lateral zig-zag folds and wherein the substrate comprises and/or is a mesh formed from a polymeric composition comprising PTFE.

In this example, the substrate has a plurality of surfaces, provided by a plurality of substrates. In this example, adjacent surfaces are mutually held spaced apart transverse to the flow path at respective first ends 710 (i.e. a fixed end) and respective second ends 713 are free ends, as described above with respect to the first aspect.

Fluid flow enters the array of screens 702 as a downwardly flowing jet from. A useful feature is that each screen 702 is can be supported along, or proximal to, its upper or leading perimeter or edge(s) 710 so as to resist deformation by the downward jetting flow of the fluid which is input to the secondary coalesce.

There are at least three mechanisms for this very effective means of foam destruction. First according to a first mechanism, foam destruction begins during its initial passages into the screen array as it moves or courses across the LEM screen surface beneath the inlet (the flow direction of foam being downward). Secondly, the screens 702 of the coalescer 70 inhibit any surviving froth from advancing laterally with respect to the main fluid flow direction. De-gassed liquid is allowed to drain through apertures of the screens 702. However, bubbles larger than these apertures are prevented from passing through the apertures (typically mesh) and are detained or held up until they are collapsed or burst. Bubbles smaller than the apertures can pass though the apertures with the liquid. However, most of the bubbles are prevented from reaching the screen surface by the detained larger bubbles. This can be considered as advantageous in that, in effect, the screen or mesh acts like a bubble filter with the retention of smaller bubbles (within the regions between adjacent screens) being assisted by a 'filter cake' of larger bubbles in a region between the region containing the smaller bubbles and the surface of the screen facing that region (not illustrated).A third mechanism may arise due to a flow field existing beneath the fluid-plunging inlet of the secondary coalesce device.

In more detail, static coalescer or separator 70 comprises multiple (typically mesh) surfaces mounted at least partially parallel to the flow stream. This arrangement has the following advantages: i) it minimises impedance of the flow stream (i.e. it provides lower pressure drop and lower energy consumption) due to the parallel mounting of the surfaces, and ii) it takes advantage of crossflow shear action, in which the fluid courses, or is directed, across the low-energy surface, in a direction at least partially parallel to the surface of the LEM, in order to sweep or drag larger coalesced bubbles from the active surface of the LEM.

Coursing, or directing, the fluid flow across the surface, as described above, enables exposure or contact of the incoming finer bubbles with the surface of the LEM. Without a shear action as described above, which acts to tear or drag the bubbles away from the surface, the only mechanism for bubble removal is buoyancy of the bubbles relative to the liquid, due to their lower density compared to that of the liquid. If buoyancy is the only mechanism, the active surface becomes isolated from a significant portion of the bubbles by an established gas layer resulting from many coalesced bubbles forming a single volume of gas. As a result, the process of gas-liquid separation or segregation is less effective. In addition, crossflow shear action has also been observed to encourage bubbles to grow by coalescing, or merging, with one another in a 'snowball-like' fashion as they are swept downstream across the surface, which typically comprises a mesh structure.

Figure 8A is a photograph of as-received (untreated) PTFE mesh having a 1 .2 mm longitudinal pore span; and Figure 8B is a photograph of laser-treated PTFE mesh having a 1.2 mm longitudinal pore span. The laser-treated PTFE mesh has lamellar micro and/or nano protrusions, due to the laser-treating, having a spacing of about 0.1 mm.

Figure 9A is a 3D profile image of as-received (untreated) PTFE mesh; and Figure 9B is a 3D profile image of laser-treated PTFE mesh, showing micro and/or nano protrusions.

Figures 10A and 10B are SEM images of as-received (untreated) PTFE mesh.

Figures 11 A and 11 B are SEM images of laser-treated PTFE mesh, according to an exemplary embodiment. Figures 12A to 12C are 3D profile images of laser-treated PTFE mesh, according to exemplary embodiments. Table 4 summarises surface roughness parameters of the laser-treated PTFE.

Table 4: Surface roughness parameters of the laser-treated PTFE.

Tests Table 5 summarise test parameters for the samples of Tables 6.001 to 6.200.

Table 5: Test parameters.

Samples

Tables 6.001 to 6.200 summarise results for the tests of Table 5. Tables are numbered corresponding to tests, for convenience.

Table 6.001 : Samples for Test 001 .

Table 6.002: Samples for Test 002.

Table 6.003: Samples for Test 003.

Table 6.004: Samples for Test 004.

Table 6.005: Samples for Test 005.

Table 6.006: Samples for Test 006.

Table 6.007: Samples for Test 007.

Table 6.008: Samples for Test 008.

Table 6.009: Samples for Test 009.

Table 6.010: Samples for Test 010.

Table 6.011 : Samples for Test 011 .

Table 6.012: Samples for Test 012.

Table 6.015: Samples for Test 015.

Table 6.016: Samples for Test 016. Table 6.017: Samples for Test 017.

Table 6.018: Samples for Test 018.

Table 6.019: Samples for Test 019.

Table 6.020: Samples for Test 020.

Table 6.021 : Samples for Test 021 .

Table 6.023: Samples for Test 023.

Table 6.100: Samples for Test 100. Table 6.101 : Samples for Test 101 .

Table 6.200: Samples for Test 200.

Discussion

Test 001

Laser parameters (frequency, power, scan path, beam focus) suitable for melting PTFE were selected. Scan spacing was varied between 350 pm and 100 pm. Generally, contact angle increases as scan spacing is reduced. At a scan spacing of 350 pm, the contact angle of 138.7° is somewhat greater than the contact angle for the untreated mesh of 132°. At a scan spacing of 150 pm, the surface of the mesh is rastered multiple times, due to beam overlap, resulting in a spongey like texture and PTFE fibres are seen being to encroach into the pores. At a scan spacing of 100 pm, the PTFE mesh is degraded, appearing melted.

As the scan spacing is reduced, expansion of strands of the mesh is observed, from around 200 pm for a scan spacing of 350 pm to about 600 pm for a scan spacing of 150 pm. This could indicate that as the PTFE is heated it expands and breaks down in to polymer fibres where entropy begins to reign. It could be described where the energy from the laser contacts the molecular bonds in the PTFE the second law of thermodynamics causes disorder in the formed, orientated molecular strands.

Tests 002 & 003

Generally, for test 002, contact angle increases as scan spacing is reduced, as observed for test 001. At a scan spacing of 100 pm and a power of 10%, the treated mesh appeared similar to that for test 001 result 1 .3 but provides a larger contact angle of 157.9°. Without wishing to be bound by any theory, this may be due to overlapping of raster lines, creating greater surface roughness and lacunarity, with no untreated PTFE.

For test 003, samples were treated at the focal point of the laser beam. Comparing samples of 2.1 , 2.2 & 3.1 , 3.2 show that there is less 'splatter' of PTFE material encroaching between pores in 003 at 0 mm beam focus. Raster scan lines are more apparent for test 003 than for test 002, while vertical expansion of strands of the mesh, rather than horizontal expansion, appears to dominate - while for result 2.1 , a strand width of nearly 700 pm was observed, for result 3.1 , a strand with of 300 pm was observed, the lack of focus in the apparent depth of field ofthe images further supports a vertical expansion. Increasing scan speed to 450 mm/s at 20% power samples in regions of untreated mesh.

Test 004, 005 & 006.

Test 005 fails again below 200 pm c.f. test 002. Comparing tests 004 and 002 at +/-10 mm beam focus, the visual make up is less precise in test 002 than test 004 where strand encroachment over pores is random compared with the individual strands that fully encroach and many join the other side of the pore area. Contact angle is consistently higher for test 004 but failed in the closer scan spacing. Without wishing to be bound by any theory, this may be due, at least in part, to particle plume shielding, where particles ablated by the laser interfere with the proceeding scanning. In front of the focus beam, the focal point sits above the sample, which all the energy must travel through to reach the surface, hence, it could be deduced that as the particles are removed, they interfere, deflect and absorb energy at the lasers most focused point, which in turn leads to a more jumbled surface finish. The sample behind the focal point as its particles are removed incoming laser of a wider beam width interacts with it and less energy per area of beam is absorbed or unfocused, leading to the individual joined mesh sections.

For test 005, the strands are not as defined, lacking in encroachment of pores with fine linkages unlike test 004. Contact angle decreases although there was still enough intensity to degrade the mesh sample with samples similar to that of test 001 with the same distance away from focus point of 30mm. Microscope images of 005 show a more 'spongey' characteristic of PTFE after ablation, with holes beginning to round off in samples 5.3 & 5.4. Samples 4.3 and 4.4 share this spongey texture to a degree especially under higher magnification where depth of field focus demonstrates the difference. Sample 4.2. showed the highest contact angle of all tests at 167° well into the superhydrophobic range. SEM images show full ablation of the surface and fibre encroachment filling pores. The profile of ablation could be described like a sheep's woollen coat, which are designed to wick away water and dirt. Mesh strands become undefined with only the pore to denote the starting material was not a solid sheet. Under higher x3000 magnification the surface structure holds true with similar visual texture and absence of unprocessed material unlike the other tested samples. It is worth noting that result 4.3 survived the laser treating, however upon handling to measure contact angle it was realised no structural integrity was present. For this reason, the sample had to be discounted due to the industrial robust end use intended.

Test 006 was a reaffirmation of samples to investigate whether varying power leads to less degradation. This was demonstrated as being true where result 6.4. was tuned down to 15% no degradation occurred in the material as had in result 4.4 on an identical run.

Test 007 further concluded this as a re run of result 1.5 which degraded at 20% power 12W. Sample 7.5 at 12% power 7.2W the sample visually looked similar to 1.2 with no degradation. However, result 1 .2 has a contact angle at 147° and 7.5 as 129° seemingly making the sample worse than untreated PTFE. Without wishing to be bound by any theory, an interpretation behind this could be that the PTFE needs a certain amount of pulse energy to split into fibres. If the requirement is not reached it smooths out loosing hydrophobic properties seen in result 7.5. The overlap of processing in result 7.5 is 3 passes of the beam over each part of the surface and result 1 .2 it is a single pass no overlapping. Furthering the hypothesis that a longer, less intense pulse degraded PTFE at an architectural/chemical level? It cannot be said as far as chemical bond breakage due to the contact angle still being in the upper bounds of referenced PTFE values.

Tests 008 & 009

Tests 008 and 009 investigated two different meshes to compare with 15PTFE16 - 077HST. Test 008 mesh has undergone a flattening process to smooth the finish but started thicker than the other meshes before expansion and flattening. Test 009 mesh is a finer thinner PTFE than all meshes used but like 15PTFE has undergone stability processing. All PTFE meshes are supplied by DexMet. Test 008 was treated under the same conditions as Test 001 with a 12% power adjustment at result 8.5 due to the previous experience with degradation. Initial reckoning was that the mesh being more compact would hold up better against the laser conditions however, it appears the flattening process is a rolling process which spreads the PTFE more thinly. Generally, the resulting mesh was structurally degraded by the laser processing, precluding use thereof. That is, the pre-treatment applied to the mesh may be an important factor regarding robustness after laser processing.

The aim of test 009 was to conclude whether sample dimensions affected robustness or that only a certain laser condition causes a particular surface ablation. Briefly, the mesh of test 009 was 3 times thinner than 15PTFE with the resultant being the laser conditions were too harsh for the sample. Due to this, no measurement was possible and a conclusion that material dimensions play an important part of ideal parameters for optimal laser enhancements.

Test 011 Following on from test 009, a thicker sample of PTFE is tested in test 011 , in which the sample was stabilised and had relatively larger pore dimensions and thickness. While significant ablation was observed for a 200 pm scan spacing, relatively larger scan spacings did not appear to result in significant ablation. This further adds to the findings that material dimension is a function of ablation/enhancement alongside laser parameters. Contact angle measurement on the other hand was problematic, since droplets fell through the pores. When a droplet with sufficient size of around 25pL sat on the surface the architecture of the mesh was too undulating to obtain any clear measurement using the equipment in the experiment. It is therefore inconclusive that a denser mesh would provide better coalescence as contact angle cannot accurately be measure. Evidence is presented which suggest laser enhancement occurred however.

Tests 012 to 014

Tests 012 to 014 were carried out under test 001 laser conditions to establish whether power could improve the surface and prevent it from degrading. These new parameters prevented degradation but there are no significant samples in terms of contact or structural quality to report on that previous parameters have not covered.

Test 015

To further improve and explore surface enhancement techniques other parameters and techniques were investigated. Sample 4.2 resulted in a contact angle of 167° and the parameters were further refined in an attempt to improve further the contact angle. Sample 15.2 used a raster scan at 10% power vertically and 10% horizontally, perpendicular, with the thought that a combined power of 20% would occur. On inspection this was not the case and there were no significant markings of the scanned area of PTFE. Leading to a conclusion that it is a single pulse energy that is required to ablate the PTFE surface and connect be done so by combined intensity. However, a combination of lower power at right angles does suggest it is the single pulse intensity that cause ablation.

Test 016

A 15% power was used again at perpendicular scan paths, which at 15% power raster scan known ablation occurs. Combined power of 30% which had not been trailed was thought to be subjected to the surface. On analysis the surface was measured and produced values consistent with being untreated at around 120° contact angle. This was unusual due to visible and microscopic observations suggesting otherwise. On reflection, there could be scope to argue that 15% power is not enough to degrade the surface but the first treatment is degraded by the second scan. Entrainment was investigated using brine and electrolyte experiments. Table salt (NaCI) was dissolved to just below saturation point in warm house hold tap water, to observe the effects of contamination by the salt and tap water impurities. High optical magnification revealed a shiny flocculation in the mesh, where the back light is causing it to reflect like a crystal. SEM revealed foreign objects caught in the mesh. This could be the salt crystals due their uniform size or water impurities from the tap. On removal from the salt solution, the sample was cleaned which suggests binding to the treat sites or the salt is not subject to the same hydrophobic properties as water, therefore, can enter the ablated matrices. However, due to the repelling nature of the surface water cannot get back into the pore to retrieve and rinse away the salt. Cleaning with a solution which salt is soluble in but with less surface tension than water may be a conclusion to maintaining performance. These findings add a new depth to hydrophobic surface research and ability to become contaminated as a pose to broken down by the process they are exposed to.

Tests 017 to 019

A different scan path is examined here with a circle array. Optical microscopy of sample 17.1 shows images of the tight circle array and shows single strands of PTFE being displaced across the material. In the background there does not appear to be any ablation. The contact angle of each sample is valid that enhancement is present, but values do not reach the level of test 016. The reason for the ceased investigation into circular scanning was the more general context of industrial scale up. On average, each sample took around 8 seconds of laser processing to complete. The circular scan took a minimum of 8 minutes to complete on the wideset array of test 019. For industrial purposes or even further development for insertion into device prototypes the amount of treated material needed would take far too long to machine. It is there for an efficiency trade off of if the benefit is so substantial processing times can be this high.

Tests 020 to 023

In these tests, micro surface roughness was provided on the PTFE before laser treatment. In test 020, samples were sanded and then laser treated with parameters of test 016. Optical microscopy of sanded samples shows visible marking while high magnification shows fibre pull out from the surface, similarly observed in laser processing. The contact angle remains high but not significantly higher although the comparison between microscope images against test 016 shows how the sanded PTFE shows great porosity and is very fibrous. A general point is that when sanding the PTFE surface layers are removed and on one sample a hole developed.

In test 021 , PTFE spray was applied to the samples which was found to cover the surface of the PTFE and stick to it. Interestingly this brought the contact angle down to 150° towards standard PTFE, apparently resulting from the laser has stripping the PTFE (spray) from the mesh, which has protected the mesh from any ablation. The channels of scan path can be observed and there is no expansion like seen previously of the mesh strands. Concluding that PTFE spray only adds another surface to the mesh and because on bound through adhesion is removed upon laser application. Not what was originally hypothesised that the PTFE would add an extra layer and become fibrous in nature on top of the PTFE fibres.

Test 023 combines both sanding and PTFE spray. Sample 23.0 again exhibited the signs of PTFE protecting the mesh and being removed by the laser. On contact angle measurement this surprisingly remained at 170° although looking visibly the same under optical magnification. Once the laser processes the area it not only removes some spray PTFE by ablated the mesh beneath which in turn ablates the spray coating it. This adds an extra layer of architecture along with 5.23. B where the fibres can be observed protruding out through the encasing layer. Each treatment and combined does not produce a contact angle any higherthan standard mesh. The findings still give a superhydrophobic surface through micro and nano structure. A contradiction is found where the manual addition of the said extra structure does not provide sufficient difference or increase in contact angle. Concluding that there could be limit to superhydrophobicity and manual manufacture of around 171 °. Furtherwork could be conducted to investigate the possibility of how close 180° contact angle is obtainable with surface robustness maintained.

Tests 100 to 200

Results using PE, PPEK and PFA were generally unsuccessful at the laser parameters used, though test 200 may be further refined for PEEK.

Summary of results

Reflecting on the data collected and analysed it is clear that laser treatment can enhance PTFE surfaces to improve contact angles causing them to be super hydrophobic. This is shown to be dependent on a variety of parameters including laser set-up, treating technique, pre-treatment surface preparation and material type and properties of the surface to be treated. A number of the surfaces created and tested exhibited super hydrophobic interaction with water. Some surfaces increased from the base contact angle of PTFE and some degraded to the point of failure. Of the combinations tested, sample 4.2 is most promising. The material is 15PTFE16- 077HST expended mesh manufactured by DexMet. It showed little sign of structural weakness after being laser processed (60W laser operating at 20% power, scan speed of 200mm/s 250pm scan spacing, and sample placed -10mm behind the beam focus) and returned a high contact angle of 171 °. A clear statement when analysing the graphical representations of tests 001 to 005 is that focal point of the laser beam is a function of scan spacing at a set laser power and speed. Particle plume shielding effected samples in front of the beam focus, deduced by the less aggressive and precise surface ablation by visual inspection. Moreover, the higher contact angles were produced by samples positioned behind the beam. When exploring scan paths by the laser the discovery of multiple passes of lower power does not equate to the accumulation of that power. There is an argument that for PTFE requires an optimum energy packet delivered to the incident surface creating ablation. The effect of the smooth surface 'popping' like elastic bands into a skeletal like state is demonstrated in sample 015.2. The combined double scan of 10% power should equal a 20% power scan path the same as sample 015.1 . However, this was not the case and no ablation were noticeable on inspection. This provides enough evidence to suggest such conclusion.

In the case of sample 016.2 secondary treatment ruined the surface reducing the contact angle by over 20°. Further strengthening that an optimum single incident packet of energy needs to be delivered for maximum effect of causing PTFE to display superhydrophobic character. In the case of test 016 with salt emersion it can be summarised that salt is either filtered and trapped in the fibre matrix and that it is not affected by the superhydrophobic properties of the PTFE. Evidence is there to suggest that water cannot enter the PTFE to dissolve the salt to clear it from the matrix.

Although a preferred embodiment has been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims and as described above. Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All of the features disclosed in this specification (including any accompanying claims and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at most some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.