Composition and Method for Removing and Recovering Hydrocarbons from a Solid Phase

Abstract

A method for removing hydrocarbons from a solid phase and recovery thereof comprising the steps of

washing the solid phase contaminated with hydrocarbons by means of a composition comprising at least a surfactant so as to obtain a clean solid surface and a hydrocarbon-rich aqueous solution,
separating the hydrocarbon-rich aqueous solution from the clean solid phase, and
treating the hydrocarbon-rich aqueous solution by means of electrocoagulation/electroflotation to recover the hydrocarbons.

Claims

1. A method for removing hydrocarbons from a solid phase and recovery thereof comprising the steps of: a) washing the solid phase contaminated with hydrocarbons by means of a composition comprising at least a surfactant so as to obtain a clean solid phase and a hydrocarbon-rich aqueous solution; b) separating the hydrocarbon-rich aqueous solution from the clean solid phase; and c) treating the hydrocarbon-rich aqueous solution by means of electrocoagulation/electroflotation to recover the hydrocarbons.

2. The method according to claim 1, characterized in that it comprises, after step b), a step c1) of allowing solid matter remaining in the hydrocarbon-rich aqueous solution to further sediment and separating the hydrocarbon-rich aqueous solution from the sediment.

3. The method according to claim 1, characterized in that said solid phase is a soil contaminated by hydrocarbons.

4. The method according to claim 1, characterized in that said surfactant is selected from the group of anionic surfactants and non-ionic surfactants.

5. The method according to claim 1, characterized in that said composition comprises: 10 to 20% by weight, based on the total weight of the composition, of an alkylpolyglucoside with an alkyl chain having average length between 6 and 14 carbon atoms; 2 to 10% by weight, based on the total weight of the composition, of a non-ionic surfactant comprising a triglyceride alkoxylated with ethylene oxide and/or propylene oxide and esterified at least partially with a fatty acid with an alkyl chain having 6 to 22 carbon atoms; and 0.5 to 6% by weight, based on the total weight of the composition, of an alkylbenzenesulfonate; and water.

6. The method according to claim 1, characterized in that said composition comprises: 20 to 35% by weight, based on the total weight of the composition, of an anionic surfactant selected from the group consisting of alkoxylated fatty acid sulfates and alkoxylated fatty acid ether sulfates; 0.5 to 8% by weight, based on the total weight of the composition, of an alkoxylated alcohol; 0.5 to 8% by weight, based on the total weight of the composition, of a propoxylated ethoxylated alcohol; and water.

7. The method according to claim 6, characterized in that said composition further comprises up to 1% by weight, based on the total weight of the composition, of a chelating agent.

8. The method according to claim 6, characterized in that said composition further comprises up to 5% by weight, based on the total weight of the composition, of an organic solvent.

9. The method according to claim 8, characterized in that said organic solvent is selected from the group consisting of isopropanol and ethanol.

10. The method according to claim 6, characterized in that said composition further comprises up to 3% by weight, based on the total weight of the composition, of a suspending agent.

11. The method according to claim 5, characterized in that said composition further comprises up to 1% by weight, based on the total weight of the composition, of a chelating agent.

12. The method according to claim 5, characterized in that said composition further comprises up to 5% by weight, based on the total weight of the composition, of an organic solvent.

13. The method according to claim 12, characterized in that said organic solvent is selected from the group consisting of isopropanol and ethanol.

14. The method according to claim 5, characterized in that said composition further comprises up to 3% by weight, based on the total weight of the composition, of a suspending agent.

15. The method of claim 1 wherein said solid phase is a soil contaminated by hydrocarbons and further including the step of selecting said surfactant from the group of anionic surfactants and non-ionic surfactants.

16. The method for removing hydrocarbons from soil and recovering the hydrocarbons comprising the steps of: a) washing the soil with a composition comprising— an anionic or non-ionic surfactant; a chelating agent; a suspending agent; and a solvent; so as to obtain a clean solid phase and a hydrocarbon-rich aqueous solution; b) separating the hydrocarbon-rich aqueous solution from the clean solid phase; c) treating the hydrocarbon-rich aqueous solution by means of electrocoagulation/electroflotation to recover the hydrocarbons.

17. The method of claim 16 wherein the chelating agent is glutamic acid tetrasodium salt, N,N diacetic acid.

18. The method of claim 16 wherein the suspending agent is sodium metasilicate.

19. The method of claim 16 wherein the solvent is either isopropanol or ethanol.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0033] The method for removal of the hydrocarbons from a solid phase and the recovery thereof according to the present invention will now be described in detail with reference to the figures of the attached drawings, which show purely illustrative and non-limiting embodiment examples, in which FIG. 1 illustrates a schematic representation of an embodiment of the method of the present invention.

[0034] Advantageously, the method of the invention allows the recovery of hydrocarbons with alkyl chains containing mainly 5 to 40 carbon atoms, but also hydrocarbons with longer chain from soil contaminated also by bentonites and polymers.

BEST MODE FOR CARRYING OUT THE INVENTION

[0035] The method shown in FIG. 1 refers to the process for removing hydrocarbons from contaminated soil, for example sand, taken near plants for the extraction and refinement of hydrocarbons or along hydrocarbon distribution and transport lines.

[0036] Before being processed to remove the hydrocarbons, the soil taken from the extraction site can be mechanically mixed, if necessary, so as to obtain a uniform product (step 1).

[0037] The sample can be further analysed to obtain a characterization thereof so as to optimize the process parameters for removal of the hydrocarbons (step 2).

[0038] Optionally, the sample is screened (step 3). The fragments with larger dimensions than those of the screen meshes are furthermore crushed so as to increase the surface area of the soil sample to be treated (step 4). The crushed sample is re-sent to the screening step.

[0039] At this point, the pre-treated soil sample undergoes the process for removal of the hydrocarbons according to the invention.

[0040] In particular, the contaminated soil is mixed in a tank with water and a solution comprising: [0041] 10 to 20% by weight, based on the total weight of the composition, of an alkylpolyglucoside with an alkyl chain having average length between 6 and 14 carbon atoms; [0042] 2 to 10% by weight, based on the total weight of the composition, of a surfactant comprising a triglyceride alkoxylated with ethylene oxide and/or propylene oxide and esterified at least partially with a fatty acid with alkyl chain having 6 to 22 carbon atoms; [0043] 0.5 to 6% by weight, based on the total weight of the composition, of an alkylbenzenesulfonate; and water.

[0044] For example, the composition consists of the following:

TABLE-US-00001 TABLE 1 Quantity (% by weight, based on the total weight of the composition) Trade name/Category Function 0.50 Sodium metasilicate Suspending (silicate) agent 0.01 Dissolvine FL38 Chelating (Glutamic acid, agent diacetic acid, tetrasodium salt) 18 Glucopon GD70 Non-ionic (alkylpolyglucoside) surfactant 6 Marlowet LVS Non-ionic (Polyethoxylated castor surfactant oil esters) 2 Marlon A350 (Sodium dodecylbenzenesulfonate) 3 Isopropanol Solvent 70.49 Water Solvent

[0045] For every cubic metre of soil treated, approximately 1.4 cubic metres of water and 7 to 13 litres of the composition of table 1 are added.

[0046] The mixture thus obtained is mechanically agitated to facilitate washing (step 5) of the soil and passage of the hydrocarbons to the aqueous phase to form a suspension. Preferably, said process is carried out using water at a temperature ranging from 30 to 60° C., more preferably at a temperature of 45° C.

[0047] The solid phase consisting of the clean soil is then left to sediment and the supernatant, consisting of a hydrocarbon-rich aqueous suspension, is collected.

[0048] The results obtained with the composition of table 1 subjecting a soil sample to the washing step only (step 5) are reported in table 2.

TABLE-US-00002 TABLE 2 Hydrocarbon Removal Sample concentration percentage Sample 1 before 5516 ppm washing Sample 1 after 1500 ppm 72.8% washing Sample 2 before 9000 ppm washing Sample 2 after 3500 ppm 62.4% washing Sample 3 before 3600 ppm washing Sample 3 after  802 ppm 77.7% washing

[0049] The clean soil can therefore be washed with water (step 9) and dried (step 10) before reintroduction into the environment (step 11).

[0050] The supernatant of step 5 composed of the hydrocarbon-rich aqueous suspension is then treated to separate and recover the hydrocarbons and the water for possible re-use thereof.

[0051] In particular, the supernatant of step 5 is treated by means of electrocoagulation/electroflotation (step 7) so as to eliminate the solids still present in suspension and to separate the water and the hydrocarbons. Before said step 7, the supernatant of step 5 can be optionally pre-treated by allowing the solid phase contained in it, consisting of clean soil, to further sediment; said soil is then recovered and reintroduced into the environment.

[0052] Electrocoagulation/electroflotation is a technique that allows the separation of a hydrocarbon suspended in an aqueous solution by the application of an electric current. The application of an electric current by means of electrodes immersed in the suspension generates, by electrolytic oxidation of the anode, ions which act as a coagulant.

[0053] In particular, in the case of an anode made of aluminium, the following reactions occur when the electric current is applied:

Al(0)->Al.sup.3++3e.sup.−

H.sub.2O+2e.sup.−->2OH.sup.−+H.sub.2(gas)

Al.sup.3++3OH.sup.−->Al(OH).sub.3(solid)

[0054] In this case, the gaseous hydrogen that develops facilitates flotation of the hydrocarbons towards the surface of the suspension. The aluminium hydroxide, on the other hand, precipitates and, if necessary, with the aid of a flocculating polymer such as polyacrylamide or polydiallyldimethylammonium chloride (PDADMAC), facilitates precipitation of the suspended solids.

[0055] Preferably, step 7 of electrocoagulation/electroflotation is conducted at a slightly basic pH, for example 7.5, obtained by the addition of a base, for example sodium or calcium hydroxide.

[0056] The end of step 7 results in re-usable hydrocarbons, a sediment and water that can be re-used, by means of recirculation, both in the process of the invention, for example in step 5 of washing the contaminated soil or in step 9 of washing the clean soil, and, for example, for agricultural use.

[0057] Optionally, it is possible to treat the water, prior to re-introduction into the environment, with an acid (step 8), for example hydrochloric acid or sulphuric acid, to neutralize the pH after addition of the base in the electrocoagulation step 7.

[0058] In terms of yield, for each cubic metre of contaminated soil treated, with an initial water consumption of 1.4 m.sup.3, the method of the invention allows 0.9 m.sup.3 of clean soil and 0.8 m.sup.3 of re-usable water to be recovered. 60 to 80% of hydrocarbons present in the contaminated soil are also recovered.

[0059] In one alternative embodiment, after screening, the contaminated soil is mixed in a tank with water and a solution comprising: [0060] 20 to 35% by weight, based on the total weight of the composition, of an anionic surfactant selected from the group consisting of alkoxylated fatty acid sulfates and alkoxylated fatty acid ether sulfates; [0061] 0.5 to 8% by weight, based on the total weight of the composition, of an alkoxylated alcohol; [0062] 0.5 to 8% by weight, based on the total weight of the composition, of a propoxylated ethoxylated alcohol; and water.

[0063] For example, the composition consists of the following (table 3):

TABLE-US-00003 TABLE 3 Quantity (% by weight, based on the total weight of the composition) Trade name/Category Function 25 Lauryl ethersulfate Anionic surfactant 3 C9-11 ethoxylated Surfactant alcohol (4 moles ethylene oxide) 2 C10-16 propoxylated Surfactant ethoxylated alcohol 70 Water

[0064] For each cubic metre of soil treated, approximately 1.4 cubic metres of water and 5 to 13 litres of the composition of table 3 are added.

[0065] The mixture thus obtained is treated as described above.

[0066] The results obtained by subjecting a soil sample to the washing step only (step 5) are shown in table 4.

TABLE-US-00004 TABLE 4 Hydrocarbon Removal Sample concentration percentage Sample 1 before 15520 ppm  washing Sample 1 after 1023 ppm 93.4% washing Sample 2 before 9000 ppm washing Sample 2 after  750 ppm 91.7% washing Sample 3before 13600 ppm  washing Sample 3 after  880 ppm 93.5% washing

[0067] The clean soil can therefore be washed with water (step 9) and dried (step 10) before being reintroduced into the environment (step 11).

[0068] The supernatant of step 5 consisting of the hydrocarbon-rich aqueous suspension can then be treated to separate and recover the hydrocarbons and the water for possible re-use by means of electrocoagulation/electroflotation (step 7) as described above.

[0069] The yields are as follows: for each cubic metre of contaminated soil treated, with an initial water consumption of 1.4 m.sup.3, the method of the invention allows the recovery of approximately 0.95 m.sup.3 of clean soil and 1.25 m.sup.3 of re-usable water. 80 to 90% of hydrocarbons present in the contaminated soil are also recovered.

[0070] Advantageously, therefore, the method for removing and recycling hydrocarbons and process water according to the invention allows rapid remediation of the soil directly in situ, entails low water consumption (85 to 95% of the water initially used for the process is recovered) and a high productivity, and does not involve the production of toxic gases.