Tubular mixing apparatus and method

Technical Field

The present invention relates to a tubular mixing apparatus and method. In particular, the present invention relates to an improved apparatus and method for phase separation of two liquids, and phase separation of gases from liquids, in continuously operated baffled reactors.

Background Art

Traditionally, large scale chemical reactions are carried out in batch processes, and many of these reactions involve liquid and gas phases. For example, a reaction may involve the addition of gas to a mainly liquid phase. Some examples of industrial processes that use this method are the manufacture of food flavouring chemicals via oxidation, the manufacture of dyes and pigments using hydroge nation, and the synthesis of pharmaceuticals using carbonylation. Alternatively, gas may be generated as a product of a reaction, the reactants being mainly liquid- phase. For example, saponification reactions, and hydrolysis reactions both produce gases as products.

In batch stirred tank reactors (STR) there is usually free head space to allow generated gas to escape. However, large STR vessels have the inherent problem of inefficient mixing, resulting in poor dispersion of gas in liquid and large mass transfer gradient. This leads to inconsistent product quality, an increase in non-specification product and an increase in byproducts.

The use of continuous reactors, such as continuous oscillatory baffled reactors (cf. WO 2006136850), overcomes many of the problems associated with using STRs. For example, continuous oscillatory baffled reactors ensure uniform mixing conditions throughout the reactor, and deliver consistent product quality with a significant reduction in non- specification products and by-products. Continuous oscillatory baffled reactors produce this mixing effect by use of oscillations which promote efficient gas-liquid, liquid-liquid, and solid-liquid dispersion.

However, the use of continuous oscillatory baffled reactors for processes that involve the use or generation of gas is problematic. More specifically, as gas is compressible, the oscillations produced are dampened when gas is present. This dampening effect reduces the degree of mixing, hence the degree of plug flow achievable, along the flow path of continuous oscillatory baffled reactors. As continuous oscillatory baffled reactors produce extremely efficient dispersion of gases in liquids, it is very difficult to periodically or continuously remove these gases. In addition, the removal of gas is essential to maintain the reaction stoichiometry for some reversible reactions. Therefore, performing reactions that involve the use or generation of gas is a major obstacle in continuous oscillatory baffled reactor operations.

Other large scale chemical reactions carried out in batch processes involve the use of two liquid phases. For example, the manufacture of domestic detergents typically involves an organic phase and an aqueous phase, and often produces two intermediate liquids with contrasting densities. The less dense liquid must be separated from the more dense liquid so that it can participate in a further reaction to produce the final detergent. In addition, the removal of the more dense liquid is favourable for the forward reaction in this exothermic, reversible reaction.

In traditional batch STR operations, the two liquids are charged into the vessel until a sufficient amount has been collected, and the two liquids are separated by decanting. As such, the reaction mixture must be taken "off- line" to perform the separation, employing a "stop and start" protocol. Alternatively, a second STR can be employed for accumulation and subsequent separation, but this increases the plant inventory and cost, as well as process time. Furthermore, the inherent problems associated with poor mixing, and poor mass and heat transfer remain present in STR operations.

Again, the use of continuous plug flow reactors, such as continuous oscillatory baffled reactors, overcomes many of the problems associated with using STRs. For example, continuous oscillatory baffled reactors ensure uniform mixing conditions throughout the reactor and deliver consistent product quality with a significant reduction in non-specification products and by-products.

However, because continuous oscillatory baffled reactors produce extremely efficient dispersion of liquids in liquids, it is very difficult to periodically or continuously separate liquids of different densities. In addition, as outlined above, the removal of one liquid is essential to maintain or shift the reaction stoichiometry for some reversible reactions.

Therefore it is an object of the present invention to obviate or at least mitigate at least some of the problems and disadvantages associated with the prior art.

A further object of the present invention is to provide an apparatus and method for selectively removing fluids from a vessel containing an efficiently dispersed mixture.

Disclosure of Invention

According to a first aspect of the present invention, there is provided a tubular mixing apparatus for applying oscillatory motion to a mixture, the apparatus comprising: a vessel defining a flow path; a plurality of orificed plates extending inwards from the side of the vessel; a member operable to apply motion to the mixture; and at least one fluid isolator fluidly connected to the vessel wherein the at least one fluid isolator is configured to isolate fluid from the flow path during operation of the apparatus.

The apparatus of the present invention allows the isolation, separation and removal of fluids from a mixture flow path whilst the flow path remains online.

The mixture contains at least two partially immiscible fluids. These fluids may be two liquids, or a liquid and a gas. Suitable mixtures may be a reaction mixture of a chemical reaction; a dispersion, suspension, emulsion or micro-emulsion; or any other suitable material with at least some fluid properties.

The orificed plates may be annular baffles, which are joined together by rails in a substantially equidistant manner, and arranged substantially in parallel, such that they extend radially inwards from the side of the vessel.

In the context of this description orificed plates are understood to be substantially flat plates that control or direct the flow of fluids including liquids and gases. The orificed plates are configured to perform the function of stationary baffles or a reciprocating agitator.

Preferably the vessel is configured to receive and discharge fluids, and has a series of tubular members, arranged and operatively connected in a flow system to form at least one continuous fluid flow path having an inlet and an outlet, the orificed plates being provided within the flow path.

Preferably the vessel is configured to follow a succession of return paths in one plane thereby forming a substantially repeating S-pattem or serpentine flow path. For example, the plurality of tubular members may be operatively connected and configured to follow a serpentine flow path to confine the apparatus to a relatively compact volume (small footprint).

The tubular members may be aligned in parallel in one plane, and connected by U-connectors to form a plurality of return paths close enough together to reduce the area or "footprint" required but spaced apart to form a grid pattern assembly.

The tubular members may be alternatively positioned and assembled using C-connectors to provide a substantially S-shaped configuration wherein the tubular members are more compactly assembled, alternately diverging and converging rather than lying in parallel.

The vessel may be of modular, or alternatively one-piece, construction. The U-connectors and C-connectors form bends in the vessel to provide a serpentine flow path.

Optionally the fluid isolator is a gas isolator and the fluid is a gas.

Preferably the gas isolator comprises a compartment fluidly connected to the vessel, said compartment located laterally with respect to the flow path.

The compartment may take the form of a trap suitable for collecting and storing gas.

The compartment may have a tapered channel comprising an orifice at either extremity, the orifices being relatively narrow and relatively wide in diameter, so-forming a channel that reduces in diameter as the compartment extends away from the vessel. The compartment may have a further relatively narrow channel fluidly connected to the relatively narrow orifice of the tapered channel, and extending outwardly therefrom. The relatively wide orifice of the tapered channel may be fluidly connected to the flow path of the vessel.

The tapered channel enables gas to gather at any point along the vessel and thus enables placement of the gas isolator at any location along the vessel, including along a vertical column. The narrow channel acts to direct gas towards an escape valve which can be located at the end of the narrow channel furthest from the tapered channel. The reduction in diameter of the narrow channel in comparison to the tapered channel causes an acceleration of gas bubbles within the narrow channel, thus inhibiting gas from re-entering the vessel.

Preferably the apparatus further comprises a membrane, said membrane being configured to prevent flow of liquid between the compartment and the vessel.

Preferably the membrane is located between the compartment and the vessel and substantially covers the fluid path therebetween. The membrane permits the flow of gas, but prevents the flow of liquid.

Optionally the membrane is a hydrophobic gas-permeable membrane. Alternatively the membrane is a hydrophilic gas-permeable membrane. The membrane may be a gas-permeable polytetrafluoroethylene membrane.

Optionally the gas isolator is juxtaposed to an external apex of a bend.

In use, the apparatus can be positioned such that the longest axis of the individual tubular members that form the serpentine flow path is vertical. In this position, the vessel has upper and lower U-connectors or bends.

Optionally the gas isolator is juxtaposed to an external apex of an upper bend when the apparatus is in use.

The apparatus of the present invention enables the online and controlled removal of a gas from the flow path of a mixture in a plug flow continuous reactor.

Preferably the gas isolator further comprises a controllable gas outlet. The controllable gas outlet allows venting of gas in a controllable manner.

The controllable gas outlet may be a tap.

Alternatively, the controllable gas outlet may be a valve. The valve may be a pressure operated valve. The valve may be operated electronically or may be an electronic valve. In particular, the movement of the valve may be automated such that it opens to release gas depending on the conditions (for example, pressure or temperature) within the vessel and/or within the gas isolator.

The controllable gas outlet may further comprise a pump operable to remove gas from the gas isolator. The pump may be a vacuum pump.

Optionally the fluid isolator is a liquid isolator and the fluid is a liquid.

Preferably the liquid isolator comprises a substantially unobstructed flow path configured to provide non-turbulent flow.

Preferably the liquid isolator comprises a U-connector and forms a bend in the vessel.

Preferably the liquid isolator comprises a U-shaped section of the vessel, said U-shaped section of the vessel comprising a substantially unobstructed flow path configured to provide non-turbulent flow therein.

The liquid isolator may extend beyond the footprint of the vessel.

Preferably the liquid isolator comprises two substantially parallel tubular members fluidly connected by way of a U-shaped section of the vessel, the substantially parallel tubular members being fluidly connected by a tubular bridging member configured to permit fluid to bypass the U-shaped section of the liquid isolator via an alternative flow path. The substantially

parallel tubular members may be spaced equidistantly with respect to the tubular bridging member located therebetween. The tubular bridging member may be located substantially equidistantly in relation to the longest dimension of the two substantially parallel tubular members that form part of the liquid isolator. The tubular bridging member may be positioned substantially perpendicular to the two substantially parallel tubular members.

Optionally, the liquid isolator comprises two converging tubular members fluidly connected to form a V-shaped section of the vessel. Optionally the converging tubular members are fluidly connected by a tubular bridging member configured to permit fluid to bypass the V-shaped section of the liquid isolator via an alternative flow path.

Optionally the tubular bridging member is positioned at any angle suitable to permit flow between the two substantially parallel tubular members.

Preferably the tubular bridging member of the liquid isolator comprises a substantially unobstructed flow path configured to provide non-turbulent flow.

Optionally the tubular bridging member of the liquid isolator comprises orificed plates or annular baffles, configured to provide mixing, along the flow path.

The V-shaped section of the liquid isolator may comprise a substantially unobstructed flow path configured to provide non-turbulent flow therein.

The absence of baffles or any inserts promotes separation of the two phases, thus allowing the controlled and selective removal of one of the liquid phases.

Optionally the fluid isolator comprises a compartment fluidly connected to the vessel, said compartment located laterally with respect to the flow path.

The compartment may take the form of a trap suitable for collecting and storing liquid.

Preferably the compartment is juxtaposed to an external apex of a bend.

In use, the apparatus can be positioned such that the longest axis of the individual tubular members that form the serpentine flow path is vertical. In this position, the vessel has upper and lower U-connectors or bends. Likewise, the apparatus has upper and lower fluid isolators that form upper and lower bends.

Liquid isolators that form lower bends are used to remove the more dense of two liquids, and liquid isolators that form upper bends are used to remove the less dense of two liquids.

The liquid isolator may form a lower bend when the apparatus is in use.

Preferably the liquid isolator further comprises a controllable liquid outlet. The controllable liquid outlet allows removal of liquid in a controllable manner.

The controllable liquid outlet may be a tap.

Alternatively, the controllable liquid outlet may be a valve. The valve may be a pressure operated valve, or may operate when a certain volume of liquid has been reached. The valve may be operated electronically or may be an electronic valve. In particular, the movement of the valve may be automated such that it opens to release liquid depending on the conditions (for example, pressure or temperature, or liquid level) within the vessel and/or within the liquid isolator.

The controllable liquid outlet may further comprise a pump operable to remove liquid from the liquid isolator. The pump may be a vacuum pump.

According to a second aspect of the present invention there is provided a tubular mixing process for applying oscillatory motion to a mixture, the process comprising the steps of: supplying at least one fluid to a vessel; imparting motion to the fluid to transport the fluid along a flow path defined by the vessel; forming a mixture by initiating and maintaining substantially uniform mixing and efficient dispersion of the at least one fluid using a plurality of orificed plates extending inwards from the side of the vessel; and isolating at least one fluid from the flow path.

Optionally the process comprises the further step of imparting non- turbulent flow to the at least one fluid along at least part of the flow path.

Optionally the non-turbulent flow is imparted in a fluid isolator.

Brief Description of Drawings

The present invention will now be described by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a cut-away view of a continuous oscillatory baffled apparatus equipped with gas isolators of the present invention; and

Figure 2 shows a cut-away view of a continuous oscillatory baffled apparatus equipped with a liquid isolator of the present invention.

Modes for Carrying Out the Invention

Referring to Figure 1 , in this embodiment of the invention there is generally depicted at 101 a continuous oscillatory baffled reactor (COBR), which is a type of plug flow tubular mixing apparatus. The COBR 101 features a vessel 102 which is configured to follow a succession of return paths in one plane thereby forming a substantially repeating S-pattern or serpentine flow path.

Attached to the inside of the vessel 102 is a plurality of orificed plates in the form of annular baffles 103 which are joined together by rails 104 in a substantially equidistant manner, and arranged substantially in parallel, such that they extend radially inwards from the side of the vessel 102. The annular baffles 103 or orificed plates promote efficient mixing.

In the context of this description orificed plates are understood to be substantially flat plates that control or direct the flow of fluids including liquids and gases. The orificed plates are configured to perform the function of stationary baffles or a reciprocating agitator.

The COBR 101 is equipped with a pump 105 that pumps a liquid phase reactant (not shown) into the vessel 102 from a feed tank 106, via a flow meter 107. Oscillation may be applied to the mixing and is achieved via a piston arrangement 108. A second reactant or gas (not shown) can be added in along the vessel 102 via access ports (not shown). As such, the vessel 102 is configured to receive and discharge fluids.

The vessel 102 has a series of tubular members 109, arranged and operatively connected in a flow system to form a continuous fluid flow path having an inlet and an outlet, the annular baffles 103 being provided within the flow path.

The tubular members 109 may be alternatively positioned and assembled using U-connectors and C-connectors which form bends 110 in the apparatus, providing a substantially S-shaped or serpentine configuration.

Note that the vessel, comprising tubular members, and U-connectors and C-connectors which form bends, may be of modular or one-piece construction.

The vessel further comprises a fluid isolator 111 a connected to an external apex of an upper bend 110a. The fluid isolator 111a acts as a gas isolator and comprises a compartment 113 into which gas from the flow path can enter via a gas-permeable hydrophobic polytetrafluoroethylene membrane 114. Any suitable gas-permeable membrane can be used, and the gas- permeable membrane can also be hydrophilic.

In an alternative embodiment, the apparatus does not have a membrane between the flow path and the gas isolator.

As gas is generally lighter than liquid, and will move upwards, gas collects in the gas isolator 111a. Therefore, the gas isolator 111a allows the collection of gas from the flow path, the hydrophobic membrane 114 allowing only gas to escape the flow path and collect in the gas isolator 111a. Gas is removed from the gas isolator using a controllable valve or tap 115. Similar gas isolators are provided at 111e and 111f.

The controllable valve or tap acts as a controllable gas outlet. The controllable gas outlet allows venting of gas in a controllable manner.

Alternatively, gas can be removed using a pressure operated valve. The valve may be operated electronically or may be an electronic valve. In particular, the movement of the valve may be automated such that it opens to release gas depending on the conditions (for example, pressure or temperature) within the vessel and/or within the gas isolator.

The controllable gas outlet may further comprise a pump operable to remove gas from the gas isolator. The pump may be a vacuum pump.

Referring once again to Figure 1 , a gas isolator 111 b is located on a vertical section of the vessel 102, being juxtaposed to the vessel where a tubular member 108 connects with a U-connector 110. This gas isolator 111b does not make use of a membrane.

Still referring to Figure 1 , gas isolators 111c and 111 d are located on a vertical section of the vessel 102, being juxtaposed to the vessel where a tubular member 108 connects with a U-connector 110. Gas isolators 111c and 111 d are located transversely with respect to each other. These gas isolators 111c and 111 d do not make use of a membrane. However, it will be understood that a membrane can also be included in gas isolators

111b, 111c, and 111d. Such a membrane can be hydrophilic or hydrophobic.

Gas isolators 111 b, 111c and 111d have compartments 120b, 120c, 12Od which have tapered channels 121b, 121c, 121 d comprising two orifices that are relatively narrow 122b, 122c, 122d and relatively wide 123b, 123c, 123d in diameter. This forms tapered channels 121 b, 121c, 121 d that reduce in diameter as the compartments extend away from the vessel. The compartments have further relatively narrow channels 124b, 124c, 124d f luidly connected to the relatively narrow orifices 122b, 122c, 122d of the tapered channels 121b, 121c, 121d, and extending outwardly therefrom. The relatively wide orifices 123b, 123c, 123d of the tapered channels 121 b, 121c, 121d are f luidly connected to the flow path of the vessel 102.

The tapered channel enables gas to gather at any point along the vessel and thus enables placement of the gas isolator at any location along the vessel, including along a vertical column. The narrow channel acts to direct gas towards an escape valve which can be located at the end of the narrow channel furthest from the tapered channel. The reduction in diameter of the narrow channel in comparison to the tapered channel causes an acceleration of gas bubbles within the narrow channel, thus inhibiting gas from re-entering the vessel.

It should be noted that it is feasible to have multiple gas isolators in at any section along the vessel, and particularly where the vessel is jointed.

In use, gas is generated along the vessel either via a chemical reaction or the addition of gas. The removal of gas can be done via any of the gas isolators described above.

This type of apparatus provides plug flow under laminar flow conditions, significantly reducing the reactor/plant size, ensuring uniform mixing and consistent product quality. Moreover, the reactor described above facilitates online separation of gas from liquid in continuous processes. In this way, gas is continuously removed allowing reactions to proceed to the full. In addition, the removal of gas is also excellent for the propagation and maintenance of oscillatory motion.

Referring now to Figure 2, there is shown at 201 a continuous oscillatory baffled reactor (COBR), which is a type of plug flow mixing apparatus. The COBR 201 features a vessel 202 which is configured to follow a succession of return paths in one plane thereby forming a substantially repeating S-pattern or serpentine flow path.

Attached to the inside of the vessel 202 is a plurality of orificed plates in the form of annular baffles 203 which are joined together by rails 204 in a substantially equidistant manner, and arranged substantially in parallel, such that they extend radially inwards from the side of the vessel 202. The annular baffles 203 or orificed plates promote efficient mixing.

The COBR 201 is equipped with a pump 205 that pumps a liquid phase reactant (not shown) into the vessel 202 from a feed tank 206, via a flow meter 207. Oscillation may be applied to the mixing and is achieved via a piston arrangement 208. A second reactant (not shown) can be added in along the vessel 202 via access ports (not shown). As such, the vessel 202 is configured to receive and discharge fluids.

The vessel 202 has a series of tubular members 209, arranged and operatively connected in a flow system to form a continuous fluid flow path having an inlet and an outlet, the annular baffles 203 being provided within the flow path.

The tubular members 209 may be alternatively positioned and assembled using U-connectors and C-connectors which form bends 210 in the apparatus, providing a substantially S-shaped configuration.

Note that the vessel, comprising tubular members, and U-connectors and C-connectors which form bends, may be of modular or one-piece construction.

The vessel further comprises a fluid isolator 211. The fluid isolator 211 acts as a liquid isolator and comprises two substantially parallel tubular members 209a and 209b attached by way of a U-connector 210a. The tubular members 209a and 209b are also connected by a tubular bridging member 217, which form a fluid flow path between tubular members 209a and 209b. The tubular members 209a and 209b are spaced equidistantly, and the tubular bridging member 217 is located therebetween. The tubular bridging member 217 is located substantially equidistantly in relation to the longest dimension of the two substantially parallel tubular members 109a and 109b. In this case, the tubular bridging member 217 is positioned substantially perpendicular to the two substantially parallel tubular members 209a and 209b.

The tubular bridging member 217 can also be positioned at any angle with respect to the two substantially parallel tubular members 209a and 209b,

said angle being suitable to permit flow between the two substantially parallel tubular members 209a and 209b.

The tubular bridging member 217, the U-shaped section of the liquid isolator, and the tubular members 209a and 209b, of the liquid isolator 211 , do not contain any annular baffles or any inserts, and therefore have a substantially unobstructed flow path configured to provide non-turbulent flow. As such the liquid isolator does not contain any annular baffles or any inserts, and has a substantially unobstructed flow path configured to provide non-turbulent flow.

In one embodiment, the tubular bridging member contains annular baffles to provide mixing, while the tubular members of the liquid isolator do not contain any annular baffles, and therefore the separated flow is mixed along the flow path as defined by the tubular bridging member.

The tubular bridging member permits fluid to bypass the U-connector, thus allowing mixed fluid to continue along the vessel, whilst fluid that gathers in the U-connector separates into the component liquids that make the mixture. The separation occurs because the liquid isolator has an unobstructed flow path, without annular baffles, which stops the fluid in this part of the vessel from being intimately mixed.

Attached to the external apex of a lower U-connector 210a there is a trap 213, said trap 213 located laterally with respect to the flow path. Attached to the trap 213 there is a tap 215 which allows removal of liquid in a controllable manner.

In one embodiment, the trap is located substantially perpendicular with respect to the flow path. However, it will be appreciated that the trap can

be located at any angle suitable for collecting gas from the flow path. The trap may be any compartment suitable for collecting and storing liquid, and the tap can be replaced by any suitable liquid outlet which allows removal of liquid in a controllable manner.

For example, the controllable liquid outlet may be a valve. The valve may be a pressure operated valve, or may operate when a certain volume of liquid has been reached. The valve may be operated electronically or may be an electronic valve. In particular, the movement of the valve may be automated such that it opens to release liquid depending on the conditions (for example, pressure or temperature or liquid level) within the vessel and/or within the liquid isolator.

The controllable liquid outlet may further comprise a pump operable to remove liquid from the liquid isolator. The pump may be a vacuum pump.

In another embodiment, the liquid isolator comprises two converging tubular members fluidly connected to form a V-shaped section of the vessel. The converging tubular members are fluidly connected by a tubular bridging member configured to permit fluid to bypass the V-shaped section of the liquid isolator via an alternative flow path. The two converging tubular members of the liquid isolator may have a substantially unobstructed flow path from the tubular bridging member to the V-shaped section of the liquid isolator, said substantially unobstructed flow path configured to provide non-turbulent flow.

In use, the apparatus can be positioned such that the longest axis of the individual tubular members that form the serpentine flow path is vertical. In this position, the vessel has upper and lower U-connectors and C-

connectors or bends. Likewise, the apparatus has upper and lower fluid isolators that form upper and lower bends.

Liquid isolators that form lower bends are used to remove the more dense of two liquids, and liquid isolators that form upper bends are used to remove the less dense of two liquids.

This type of reactor provides plug flow under laminar flow conditions, significantly reducing the reactor/plant size, ensuring uniform mixing and consistent product quality. The product can be collected at the end.

When intermediate products involve two liquid phases with contrasting densities, the removal of the lighter from the heavier one can be done via the liquid isolator. The lighter phase will gather around the top part of the liquid isolator, and will continue along the flow path defined by the tubular bridge member. The lighter phase can then participate in further reactions with (for example) the addition of a third reactant.

The tap in the lower U-connector can be opened for the controlled removal of the heavier liquid. This can be achieved continuously, periodically or intermittently. For some reversible reactions, the removal of one of the intermediates is also of benefit to the shifting of the reaction stoichiometry.

It should be noted that it is feasible to locate the liquid separator at any suitable point of the vessel. For example, it can be located towards the end of the apparatus, at which there is the highest concentration of products, to continuously separate lighter liquid products from heavier ones.

When the liquid of the heavier phase is the desired reactant or species, and the liquid of the lighter phase is the phase to be separated, the said

liquid isolators can be connected upside down to the plug flow tubular mixing apparatus. That is they are, or form part of, upper U-connectors.

Therefore, the apparatus of the present invention can be used in a plug flow mixing process for applying oscillatory motion to a mixture.

As described above and in the following examples, such a process comprises the steps of: supplying at least one fluid into a vessel; imparting motion to the fluid to transport the fluid along a flow path defined by the vessel; forming a mixture by initiating and maintaining uniform mixing and efficient dispersion of the at least one fluid using a plurality of orificed plates extending inwards from the side of the vessel; and isolating at least one fluid from the flow path wherein the at least one fluid is isolated from the flow path during operation of the apparatus.

The mixture so-formed in the flow path of the vessel contains at least two partially immiscible fluids. These fluids may be two liquids, or a liquid and a gas. Suitable mixtures may be a reaction mixture of a chemical reaction; a dispersion, suspension, emulsion or micro-emulsion; or any other suitable material with at least some fluid properties.

Use of the apparatus suitable for liquid separation will now be described with reference to biodiesel production. In biodiesel production, a type of oil (e.g. rapeseed, palm, or melted animal tallow) is continuously pumped into the COBR at 50 ⁰ C, and fluid oscillation is applied at a preset amplitude and frequency. A type of alcohol (e.g. methanol), which is premixed with a catalyst, (typically a base catalyst) is fed into the COBR at a position further along the flow path from the oil feed. The temperature of the COBR is raised to the reaction temperature, and the trans- esterification reaction takes place. As the reaction proceeds, biodiesel

(the desired product) and glycerol (a side product) are produced continuously in a ratio of 10:1. As the reaction proceeds along the flow path, the glycerol and biodiesel remain intimately mixed until such point that they reach the liquid separator. At this point, the fluids separate and the glycerol can be removed from the flow path using the tap connected to the liquid separator.

Continuous removal of glycerol during the reaction is important to both the degree of the completion of the reaction and the final conversion of biodiesel. Traditional processes of biodiesel production involve two stirred tanks, one for reaction, and one for separation. As the density of glycerol is generally much higher than that of biodiesel, separation by gravity is the normal practise. This involves leaving the mixture of biodiesel and glycerol in a settling tank for certain periods of time, and then decanting off the biodiesel. If only one STR is used, significant down time is often associated with this process.

In the liquid isolator of the present invention, the mixture of biodiesel and glycerol is separated by gravity continuously, and the oscillatory motion without the presence of baffle plates or any inserts at the limbs of the tubular isolator allows the lighter portion of the liquids (biodiesel) to rise up, while the heavier portion (glycerol) of the liquid sinks downwards. The biodiesel flows through the COBR via the bridge across the two limbs of the COBR, and the glycerol is removed continuously or periodically at the bottom of the liquid isolator. In this way, the removal of the glycerol is carried out simultaneously with the procession of the reaction in the COBR. This affords better controllability, and the reaction can be performed in either a single stage or in multi-stages. Moreover, this ^• process promotes fuller conversion of the reactants to biodiesel, as the

constant removal of glycerol shifts the reaction stoichiometry more towards the production of biodiesel.

Use of the apparatus suitable for gas separation will now be described with reference to the reaction of starch with acid. Water is pumped into the vessel continuously, and fluid oscillation takes place with preset oscillation frequency and amplitude. A slurry of starch and water is fed into the vessel, further along the flow path from the water feed, and at the same time the vessel is heated up to a given reaction temperature. When the reaction temperature has been reached, an acid is added at a point further along the flow path from the slurry feed, and a reaction takes place. Air entrained from the feed tanks is then subsequently released into the vessel during the temperature increase in the reaction. Air will be collected in the gas isolator as the reaction mixture flows past, and this gas can be removed either continuously or periodically once it occurs.

The presence of gas within the vessel dampens the fluid oscillation, and lessens the degree of solid-liquid mixing during the reaction. This leads to the sedimentation of starch, lower product conversion and poor product quality. Therefore, air must be removed continuously or periodically from the vessel.

Traditionally this type of reaction is carried out in batch stirred tank reactors and, although the gas is removed from the free head spaces in the stirred tanks, the stirred tank reactors suffer from the disadvantages outlined previously. In the operation of the COBR, the efficient fluid mixing enables up to 50% of starch concentration without sedimentation compared to about 20% in stirred tanks; and the reduction of reaction time from 50 minutes to 10 seconds (cf. stirred tank reactors). However, removal of gas presents a challenge in continuous operations, as the

presence of gas reduces the efficiency of plug flow reactors. Using the gas isolator of the present invention, the gas in the vessel can be easily and continuously trapped along the flow path of the vessel, and subsequently removed. This allows continuous and full propagation of fluid oscillation along the length of vessel, and allows all the advantages of using a COBR to be retained.

It will be appreciated that the liquid and gas isolators may be incorporated into the same apparatus, for example, they may both be present in the same continuous oscillatory baffled reactor. Also, it will be understood that any particular apparatus may contain fluid isolators that are gas isolators only, or fluid isolators that are liquid isolators only.

Industrial Applicability

The apparatus of the present invention can be used in the chemical, petroleum, process, pharmaceutical, cosmetic, bioscience, bioengineering, and food and associated industries. In particular, the use of present invention can be used to promote and maintain efficient mixing in a controlled environment in the aforementioned industrial or technical fields.

Various modifications and variations to the described embodiments of the invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes of carrying out the invention which are obvious to those skilled in the art are intended to be covered by the present invention.