The present invention relates to a process for the removal of hydrocarbons from a water body by means of selective permeation, and the relative apparatus.

The increasingly frequent pollution episodes, in particular pollution of water systems, deriving from the release of hydrocarbons into the environment, in particular of crude oil during extraction, transportation and storage operations thereof, have made the necessity of controlling these operations more effectively and developing technologies for the recovery of spilled crude oil, extremely urgent.

The most commonly used mechanical-type methods adopt containment systems of crude oil in restricted areas (for example, so-called booms) and suction systems possibly coupled with absorption systems (for example, so-called skimmers) . Crude oil/water separation systems based on gravity (see for example patent US 3,784,010), associated with pumping devices, are also used.

Systems of the physico-chemical type have also been created, which are based on the use of solidifying agents, gelling agents, demulsifying agents, dispersing agents, absorbing agents, filtering systems, etc. The solidifying/gelling agents generally consist of substances which react with the crude oil to form a solid mass which floats on water. In order to obtain a good recovery, it is necessary, however, to use huge amounts of solidifying/gelling agent. The demulsifying agents are generally surfactants of the hydrophilic type which tend to break the emulsion so as to separate the two crude oil-water phases. The dispersing agents approximately have the same solubility in the two phases and therefore allow the crude oil to be dispersed in water in the form of droplets. The cleaning agents are capable of removing the oily substances from solid surfaces thanks to their detergent properties.

As far as the use of absorbing materials is concerned, these facilitate the passage of crude oil from the liquid phase to the solid phase by means of absorption, allowing an easier recovery of the polluting product. Different materials with absorbing properties have been developed, characterized by a high porosity and hydrophobicity, such as hydrophobized S1O ₂ aerogels, zeolites made hydrophobic by dealumination processes or by using silylation agents, organo-clays , expanded perlite, graphite, polypropylene, polyurethane (see for example, the article of M.O. Adebajo et al . , J. of Porous Materials, 1_0 (2003) 159-170) .

Patent US 5,725,805 describes an absorbing material consisting of an organo-clay (clay modified with organic compounds having a binding group of the quaternary ammonium type) capable of solidifying crude oil at very low temperatures, unlike traditional organo-clays which act at temperatures higher than 20°C. This feature allows the use of the flocculating agent in cold environments, for example in arctic climates. A surface treatment of clay with suitable compounds insoluble in water also allows its floating properties to be improved.

Patent GB 1,096,420 describes the synthesis of an absorbing material consisting of granules of expanded perlite coated with a thin silicone film. With respect to untreated perlite, this treated material shows a selective absorption of crude oil and does not show release into the aqueous environment, also for long periods of time.

Patent application WO 2008/045433 describes a synthesis method of an absorbing material consisting of a superhydrophobic porous membrane composed of "nanowires" of the inorganic type, such as manganese oxide, modified on the surface with a thin film of hydrophobic compound, such as polydimethylsiloxane. The film allows the surface of the material to be transformed from hydrophilic to superhydrophobic, with a contact angle up to 170°. The film may be removed by a thermal treatment of the membrane which re-acquires hydrophilicity . The material may be used, among other things, for the purification of a fluid contaminated by organic products, which are removed by absorption on the material itself.

A waste water filtration system is proposed in patent application FR 2,552,133, which comprises a floating barrier capable of filtering water contaminated by hydrocarbons: a filter cartridge allows the passage of water and retains the organic phase by absorption .

Fuel filtration systems, in particular diesel, are also well known in literature, for the removal of water residues from the mixture directed towards the injector. The separation of the two phases takes place by permeation of the diesel through a hydrorepellent filter (see for example patents GB 2,138,693, US 2008/0105629, EP 0 821 989) .

In order to separate an aqueous phase from a hydrocarbon phase, coalescent filters are also used, for both the removal of water residues from fuels (see for example, patent EP 0 257 265) and for the decontamination of water bodies (see for example, patent GB 2,418,374) . Coalescent filters are particularly effective when the separation must be carried out on emulsions. These filters are composed of fine fibres/corrugated surfaces which capture the emulsified phase (water or diesel) and force it to agglomerate in drops whose dimensions increase as they pass through the filter. Due to the different density with respect to the predominant liquid, the two phases may be separated by gravity. In the case of the purification of fuel, the water is separated in a collection tank at the outlet of the filter. In the presence of water contaminated by organic substances, such as hydrocarbons, the organic phase is brought to the form of drops which do not pass through the filter, but return in countercurrent onto the surface of the water body.

Patent application CA 2 227 520 Al describes a composite material consisting of particles of polyethylene (PE) and polypropylene (PP) sintered with polytetrafluoroethylene (PTFE) , which exerts the function of interfacial tension modifier. This material may be used for the production of filters to be used for the removal of hydrocarbons from water. These filters, in fact, would be able of allowing the hydrocarbons to selectively permeate, thus enabling them to be separated from the aqueous phase. The use of powders of sintered polymeric materials, however, gives these filters a poor resistance to mechanical stress and physico-chemical attack by the components present in the crude oil.

The Applicant has observed that, for the removal of hydrocarbons from a water body, following, for example, an oil spill in seas, rivers, lakes and the like, the mechanical methods so far studied are substantially ineffective and costly, in particular under extreme conditions, for example bad weather conditions, turbulences, etc. These methods, moreover, in any case require a subsequent treatment/purification phase in order to decontaminate the water and recover the spilled oil. Furthermore, crude oil/water separation systems based on gravity, i.e. on the different density of the two phases, have the disadvantage of requiring large volumes and/or lengthy separation times.

New generation skimmers (developed for example by Elastec/American Marine) couple suction with the use of hydrophobic materials (discs/drums) having a high roughness, capable of selectively absorbing the organic phase, obtaining recovery rates of up to 10 ⁶ 1/h and recovery efficiencies higher than 90%. These systems, however, are generally used in easily accessible areas, require frequent maintenance and continuous monitoring by the operator, they consume energy for the continuous rotation of the absorbing discs and have a reduced efficiency with low viscosity hydrocarbons (V. Broje et al, Environ. Sci. Technol . 40(24) (2006), 7914-7918) .

Physico-chemical methods, on the other hand, require the use of high quantities of chemicals and do not allow the oil to be recovered as such. Furthermore, rather than a cleaning of the aqueous phase, these methods cause a dispersion of the hydrocarbon phase in water .

With respect to the use of materials which absorb the hydrocarbon phase, the separation process of spilled crude oil evidently cannot be carried out continuously, and the absorbing materials used must then be suitably treated in order to recover the crude oil. Furthermore, the application of these absorbing materials is intrinsically limited in its efficacy as the material has a limited absorption capacity.

The use of selective filtration systems, on the contrary, allows the process to be carried out continuously, in which the separation of the phases takes place in association with the direct collection of the permeate. The application of coalescent filters in the decontamination of water bodies is mainly useful when the two phases form an emulsion and the volume to be treated is limited (as, for example, in the case of the treatment of waste water) , whereas it is not very suitable for the removal and recovery of petroleum products spilled in large quantities over huge volumes of water. These methods, in fact, are practically only used in the automotive field in the case of mixtures in which the aqueous phase is mainly a minority with respect to the hydrocarbon phase. Similarly, fuel filtration systems based on the use of hydrophobic porous supports are used for the removal of water residues from the mixture.

The Applicant has now found a process for the removal of hydrocarbons from a water body in which the hydrocarbons are separated from the aqueous phase by means of selective permeation through a sintered porous filter pre-immersed in a liquid hydrocarbon, said filter having an average porosity ranging from 0.5 to 200 μπι, preferably from 50 to 100 μπι, so as to collect the hydrocarbons and remove them from the water without using additional chemicals or products capable of absorbing hydrocarbons. This allows the water body to be remediated, and at the same time recovering the spilled hydrocarbons in a clean and substantially continuous way. Said pre-immersed filter is obtained by immersing said filter in a hydrocarbon, advantageously in the same hydrocarbon to be removed.

According to a first aspect, the present invention therefore relates to a process for removing hydrocarbons from a water body comprising:

immersing in said water body at least one filter made of sintered porous material pre-immersed in a liquid hydrocarbon, said filter having an average porosity ranging from 0.5 to 200 μπι, preferably from 50 to 100 μπι;

keeping the hydrocarbons in contact with an outer surface of said at least one filter in order to allow the selective permeation of the hydrocarbons through said at least one filter from said outer surface to an inner surface of the filter;

removing the hydrocarbon phase permeated through said at least one filter.

In a second aspect, the present invention relates to an apparatus for removing hydrocarbons from a water body, which comprises:

at least one filter made of sintered porous material pre-immersed in a liquid hydrocarbon, said filter having an average porosity ranging from 0.5 to 200 μπι, preferably from 50 to 100 μπι;

at least one suction device in order to remove the hydrocarbon phase permeated through said at least one filter .

As far as the filter is concerned, this preferably consists of a sintered inorganic material, such as, for example, a metallic material, a vitreous material, a ceramic material. More preferably, the filter consists of a sintered metal alloy, in particular steel, stainless steel or nickel alloys known with the trademark of Hastelloy™. Sintered filters made of metal alloy are well known in the art and are used in various industrial fields thanks to their features of high mechanical resistance, resistance to corrosion, pressure and high temperatures, and also to brusque variations thereof. They are generally produced by filling a mould with the metal in the form of particles having predetermined dimensions, followed by sintering at a high temperature (generally slightly lower than the melting point of the metal) in a controlled atmosphere, so as to obtain a porous structure having high mechanical properties. The controlled atmosphere generally consists of endothermic gases, for example those deriving from a partial combustion process, mainly consisting of hydrogen, nitrogen and CO. The presence of hydrogen and/or CO preserves the end- product from oxidation during the sintering phase. It is important to note that the selection of sintered filter pre-immersed in a liquid hydrocarbon, having an average porosity within the above indicated ranges allows to avoid the surface treatments of the same filters with hydrophobic products, commonly selected, for example, from: high molecular weight solid hydrocarbons, preferably substituted with functional groups which are able to interact with the material which constitutes the filter (for example, fatty acids or tiols having at least 12 carbon atoms), polyolefins, polystyrenes, polialkylacrylates , polyalkylmethacrylates ; silanes having at least one alkyl or fluoroalkyl group, polysiloxanes (for example, polydimethylsiloxane ) . In fact, the hydrophobizing treatment is often required in order to improve the selectivity so as to allow the use of filters having high porosity, which allow a more rapid separation of hydrocarbons from the aqueous phase. Accordingly, the possibility to avoid such hydrophobizing treatment has clear advantages, not only in terms of costs, but also in terms of filter-life, as in order to maintain the selectivity of the filter itself, it is not required the repetition of the hydrophobizing treatment after a certain usage time.

According to a preferred embodiment of the present invention, said liquid hydrocarbon wherein the filter is pre-immersed may be one hydrocarbon or a mixture of hydrocarbons, preferably hydrocarbons of different length. Particularly preferred hydrocarbons are oil and/or diesel. According to a further aspect of the present invention, the filter pre-immersion in the liquid hydrocarbon occurs at room temperature.

Preferably, between the outer surface of the filter, in contact with the hydrocarbons to be removed, and the inner surface of the filter, a pressure difference (Δρ) lower than 100 mbar is applied, more preferably lower than 20 mbar. In a preferred embodiment, said pressure difference applied is substantially null. The Applicant has in fact found that the application of a pressure difference between said surfaces through which the selective permeation of hydrocarbons takes place, in order to increase the flow of the same through the filter and consequently the efficiency of the process, may cause a consistent reduction in the selectivity, and therefore the process does not allow to obtain an effective separation of the hydrocarbons from the water, which tends to permeate together with the same hydrocarbons. The maximum Δρ values indicated above are indicative and mainly depend on the type of filter used and the average pore diameter of the same, the type and viscosity of the hydrocarbon product to be removed, the temperature at which the process is carried out.

According to a preferred embodiment, the filter made of sintered material has a hollow structure, for example a hollow cylindrical structure closed at one end, which defines an internal space in which the hydrocarbons permeated through the filter are collected, and from which the same are removed.

According to another preferred embodiment, the filter made of sintered material is inserted as a filtering window in a hollow structure which allows the hydrocarbons permeated inside said structure to be collected .

The removal of the hydrocarbons may be preferably carried out by means of a suction device, for example a pump, discontinuously or, preferably, continuously.

The Applicant has found that the specific flow through the filter according to the present invention, may undergo a certain decrease over time, probably due to a progressive blockage of the pores present in the filtering material. This effect is particularly significant when the hydrocarbon phase must be separated from seawater. In order to rapidly re ^¬ establish the initial flow, preferably the process according to the present invention additionally comprises a cleaning step of the filter after a pre- established period of use. For example, this step may be carried out through compressed air. Preferably, the compressed air jet (for example, of 6 bar) is addressed within the filter and forced to flow from the inside to the outside of the same filter. Alternatively, said cleaning step may be carried out by washing with solvent, preferably by back-washing with an organic solvent for dissolving hydrocarbons.

For example, the solvent may be introduced into the filter and forced to flow through it from the inside to the outside of the same filter. A counter-pressure higher than 1 bar, more preferably higher than 1.5 bar, may be generally applied to facilitate this step. The back-washing may be carried out using also a rate of the same hydrocarbon phase, recovered through the process .

The present invention is now further illustrated with particular reference to the following figures, in which :

Figures 1A and IB are SEM microphotographs of the surface of two filters having an average pore size equal to 60 and 90 um, respectively;

Figure 2 is a schematic representation of a device used for effecting many of the examples provided hereunder, in which the flow rate of the crude oil removed is measured and the latter is then re ^¬ introduced into the tank in which the water body is present ;

Figure 3 is a schematic representation of an apparatus for the removal of hydrocarbons from a water body according to the present invention; Figure 4 shows the permeation rate of the filter with respect to the start of the test and during the test respectively, highlighting the effect of the cleaning by compressed air.

With reference to Figure 2, the device comprises a tank (1) in which there is a volume of water (2) and crude oil (3) . The latter, having a lower density than the water, tends to stratify above the volume of water (2) . A filter (4) made of sintered steel, having the form of a hollow cylinder closed below, is immersed in the tank (1) . A first pipe (5) connected to a pump (6) is inserted inside said filter (4), which allows to suck the crude oil which permeates through the walls of the filter (4) . The pump (6) is in turn connected by means of a second pipe (7) to the tank (1), in order to allow the re-entry of the crude oil into the tank (1) . A flow-rate meter (8) is present along the pipe (5), which allows to measure the volume of crude oil removed by means of the permeation process through the filter (4) . The first pipe (5) is equipped with a valve (9) for regulating the inflow of the crude oil recovered.

With reference to Figure 3, this schematically represents a possible embodiment of the apparatus for removing hydrocarbons according to the present invention. This apparatus (20) comprises a plurality of filtering devices (21), each having a filtering element (22) inserted in a hollow structure (23) suitable for receiving the hydrocarbon phase which permeates through the filtering element (22) . Each hollow structure (23) may be possibly equipped with floating devices (not represented in Figure 3) which allow said structure to float on the water body (24) with a floating line in correspondence with the filtering element (22), to allow the permeation of the hydrocarbons (25) present on the surface of the water body (24) . Each hollow structure (23) is connected by means of suitable ducts to a pump (26), which discharges the permeate collected into a collection tank (27), from which the hydrocarbons may be recovered.

The following examples are provided for purely illustrative purposes of the present invention and should not be considered as limiting the protection scope defined by the enclosed claims.

EXAMPLE 1

Commercial filters purchased by the company

Swagelok, (sintered filter, Part Number SS-4F-K4-60, having an outer diameter = 1.25 cm, height = 2 cm, made of AISI 316 steel), having an average pore diameter = 60 μπι, were installed in a device according to Figure 2 (filters not surface-treated with hydrophobic products) .

The filters were used as obtained from the supplier, without further cleaning treatment in addition to that one carried out by the producer according to the Swagelok Standard Cleaning and Packaging SC-10 protocol.

Demineralized water (conductivity = 1 μΞ/αη at 20°C) and diesel (density = 0.84 g/ml at 20°C, viscosity = 4.4 cP at 20°C) were introduced into the tank of the device according to Figure 2. The filters were pre-immersed into diesel for 10 seconds and then inserted in the tank. The outer surface of the filter is immersed in contact with diesel and water in a 60:40 ratio. The specific flow of diesel sucked by the pump (6) was measured over time, by means of the flow-rate meter (8) . The water content (Karl Fischer method) was determined on samples of the diesel removed, collected at different times. The results are indicated in Table 1. TABLE 1

(pore diameter 60 μπι)

EXAMPLE 2

Example 1 was repeated with filters having an average pore diameter of 90 μπι (filters not surface- treated with hydrophobic products) . The filters used were purchased by the company Swagelok (sintered filter, Part Number SS-4F-K4-90, having an outer diameter = 1,25 cm, height = 2 cm, made of AISI 316 steel) . The results are indicated in Table 2.

TABLE 2

(pore diameter 90 μπι)

EXAMPLE 3 (comparison)

In order to assess the behavior of not pre-immersed filters, a comparative test using a sintered filter GKN Sinter Metals, Article Code 9461, having an outer diameter = 2.54 cm, height = 5.6 cm, made of AISI 316 steel, with an average pore diameter equal to 100 μπι, was carried out. Said filter was immersed in demineralized water (conductivity = 1 μΞ/αη at 20°C) and then diesel was added (density = 0.84 g/ml at 20°C, viscosity = 4.4 cP at 20°C) . The filter started the permeation, immediately after its immersion in water. After the diesel addition, the filter permeated even diesel showing an absence of selectivity. The starting mixture has a water amount of 90%, the permeated has a water amount of 83 %.

EXAMPLE 4

On the same device according to figure 2 a sintered filter Swagelok, Part Number SS-4F-K4-60, having an outer diameter = 1.25 cm, height = 2 cm, made of AISI 316 steel, with an average pore diameter equal to 90 μπι, was installed. In the tank of the device, seawater was added (conductivity = 50.5 mS/cm at 20°C) and diesel (density = 0.84 g/ml at 20°C, viscosity = 4.4 cP at 20°C) . The filter was pre-immersed in diesel for 10 seconds and then inserted into the tank. The outer surface of the immersed filter was exposed to diesel and water in a ratio 50:50. The specific diesel flow aspired by the pump (6) was measured over time by the flow-rate meter (8) . The water content of removed diesel samples, collected at different times, was determined (Karl Fischer method) . The results are reported in Figure 4 (rhombus symbol) . A water content lower than 5% by weight was determined in all the samples. After this first test, the filter was subjected to back-washing with compressed air at 6 bar for a time of about 2 minutes. That allowed the permeation rate observed at the beginning of the test to be re-established, as illustrated by the data indicated in Figure 4 (square symbol) . From this test it may be seen that, in the case of a reduction in the permeation flow of diesel over time, a washing by compressed air, preferably a back-washing, allows the initial performances to be re-established.