A method for treating oil production wastewater based on solvent extraction

Abstract

The present application discloses a method for treating oil production wastewater based on solvent extraction, and belongs to the technical field of oil production wastewater treatment. Step one, add adsorption material in an adsorption device to carry out adsorption treatment on oil production wastewater, and obtain pretreated oil production wastewater; Step two, add acid regulator to the pretreated oil production wastewater obtained in step one, adjust pH, and obtain oil production wastewater with a pH of 0 6; Step three, form an extractant after mixing a phosphorus-oxygen neutral extractant, an amide compound, and an alcohol; Step four, mix the oil production wastewater with a pH of 0 6 obtained in step two with the extractant obtained in step three, and extract through 6 levels of countercurrent, so that the oil organic matter in the oil production wastewater is combined with the extractant to form an extractant, and then separated from the aqueous phase; Step five, react with the extractant using a stripping agent to recycle the organic matter in the oil production wastewater. Tertiary oil production wastewater is treated by solvent extraction, and its COD is reduced to discharge below the relevant national standards.

Description

Technical Field

[0001] The present application relates to the technical field of oil production wastewater treatment, and in particular to a method for treating oil production wastewater based on solvent extraction. Background Art

[0002] With the continued development of domestic oil fields, the gradual improvement of oil extraction technology and the increasing degree of development, the recoverable oil and gas reserves of oil fields have gradually decreased. Most domestic oil fields have entered the tertiary oil recovery (TER) stage, mainly relying on polymer flooding and ASP flooding. While the large-scale application of TER has increased oil production, it has also brought many new technical problems: high water content in the middle and late stages of oil field production, the production process generates a large amount of oil production wastewater, which is difficult to treat.

[0003] At present, tertiary oil recovery is mainly based on chemical flooding such as ASP flooding, foam flooding, and polymer flooding, which increases the oil field recovery rate by improving the sweep coefficient. After the application of chemical flooding, the tertiary oil recovery wastewater will contain polymers, alkaline compounds, various inorganic salts, crude oil, surfactants, ammonia nitrogen and other substances. The composition is particularly complex, which increases the difficulty of treating tertiary oil recovery wastewater. Compared with conventional water flooding wastewater, tertiary oil recovery wastewater has the following characteristics: (1) High viscosity. The presence of residual high molecular polymers makes the oil recovery wastewater difficult to degrade; (2) High emulsification degree. The residual polymers will form a highly elastic film with the surfactants in the water at the oil-water interface. The emulsified oil droplets in the tertiary oil recovery wastewater are particularly stable, and conventional demulsifiers are difficult to destroy them and aggregate them together; (3) The particle size of the oil droplets in the wastewater is small, most of which are below 10μm, with a high degree of dispersion. The oil-water separation technology is difficult to treat and the treatment efficiency is extremely low.

[0004] In the current tertiary oil recovery wastewater treatment process, a combination of inorganic salt colloid adsorption and polyacrylamide adsorption is usually used for wastewater treatment. However, such an operation still has many disadvantages. Specifically, a large amount of inorganic coagulants are used in the wastewater treatment process, which results in a large amount of reagents and high costs. At the same time, the added inorganic coagulants will all be converted into chemical sludge, thereby increasing the sludge treatment cost and seriously affecting the effect of wastewater treatment. The polyacrylamide in the tertiary oil recovery wastewater contains oil residues, and the wastewater viscosity is much greater than that of general wastewater. If high molecular weight components such as polyacrylamide are not specially treated, the suspended particles or flocs will settle slowly, the treatment efficiency will be low, and it will not meet production needs.

[0005] Providing a method for treating tertiary oil recovery wastewater that can efficiently treat tertiary oil recovery wastewater, use less chemicals, and has excellent treatment effects has become a difficult problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0006] The purpose of this application is to provide a method for treating oil production wastewater based on solvent extraction, which treats tertiary oil production wastewater by solvent extraction and reduces the COD content to below the relevant national standards for discharge.

[0007] Based on the above objectives, the present application provides a method for treating oil production wastewater based on solvent extraction, comprising the following steps:

[0008] Step 1: Add adsorption material to the adsorption device to perform adsorption treatment on the oil production wastewater, remove the floating oil and dispersed oil in the oil production wastewater, and obtain pretreated oil production wastewater;

[0009] Step 2: Add an acid regulator to the pretreated oil production wastewater obtained in step 1 to adjust the pH to obtain oil production wastewater with a pH of 0-6;

[0010] Step 3: Mixing a phosphorus-oxygen neutral extractant, an amide compound, and an alcohol in proportion to form an extractant;

[0011] Step 4: The oil production wastewater with a pH of 0-6 obtained in step 2 is mixed with the extractant obtained in step 3 and subjected to 6-stage countercurrent extraction to combine the oil organic matter in the oil production wastewater with the extractant to form an extractant, which is then separated from the water phase;

[0012] Step 5: using a stripping agent to react with the extractant to recover and reuse the organic matter in the oil production wastewater encapsulated in the extractant;

[0013] Step 6: Recycle the extractant after stripping.

[0014] Preferably, in step 1, the adsorption material comprises, by weight, 10-15 parts of quartz sand, 25-45 parts of activated carbon, 15-30 parts of perlite, and 5-20 parts of fly ash as a gelling agent; and the mixture is mixed by particle grading.

[0015] Preferably, in step 2, the acid regulator is hydrochloric acid or sulfuric acid with a concentration of 0.1 mol / L-1 mol / L.

[0016] Preferably, in step three, the phosphorus-oxygen neutral extractant is mainly composed of one or two of phosphate esters, monoalkyl phosphate diesters, dialkyl phosphate monoesters, trialkyl phosphate oxides, etc.; the amide is one or two of N,N-di(dodecyl)propionamide, N,N-di(hexadecyl)acetamide, N,N-di(octadecyl)formamide, N,N-dodecyl(tetradecyl)acetamide, N,N-hexadecyl(octadecyl)formamide, etc.; the number of carbon atoms of the alcohol is 3-12, and it contains straight or branched chains; the volume ratio of the phosphorus-oxygen neutral extractant, amide, and alcohol is 15-35:20-30:25-45.

[0017] Preferably, in step 4, when using the extractant to extract organic matter from oil production wastewater, the pH value is 0-6; the temperature is 30-80° C.; the phase ratio is 1:10-10:1; and the extraction time is 5 minutes.

[0018] Preferably, the stripping agent in step five is an alkaline solution, the stripping temperature is 20-50° C.; the stripping volume ratio is 2-10:1, and the stripping time is 3-10 min.

[0019] Preferably, before extraction, the COD content in the oil production wastewater is 100-2000 mg / L, and after treatment, the COD content is below 75 mg / L.

[0020] Therefore, the present application provides a method for treating oil production wastewater based on solvent extraction, which has the following beneficial effects:

[0021] 1. The oil production wastewater treatment method of the present invention uses a small amount of reagents, has a low wastewater treatment cost, does not generate sludge, and ensures the wastewater treatment effect; the present invention can effectively reduce the COD of the wastewater, shorten the wastewater treatment time, and improve the overall treatment efficiency.

[0022] 2. In the present application, the phosphorus-oxygen neutral extractant and the amide extractant work synergistically to form an extractant with the organic matter in the oil production wastewater and transfer it to the organic phase. Then, a suitable stripping agent is selected to destroy the structure of the extractant and the organic matter in the oil production wastewater under certain conditions, thereby achieving effective separation of the extractant from the organic matter in the tertiary oil production wastewater. The alcohol diluent plays the role of diluting the extractant and adsorbing the emulsified oil in the oil production wastewater. After adsorption pretreatment and extraction, the COD of the tertiary oil production wastewater can be reduced to below 100 mg / L, meeting the national emission standards. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is further illustrated by the following examples.

[0024] Example 1

[0025] Taking 500 ml of tertiary oil recovery wastewater from the isolated island of Shengli Oilfield as the sample to be treated, the treatment method of oil recovery wastewater based on solvent extraction includes the following steps:

[0026] Step 1: First, 200g of 140-mesh quartz sand, 80-mesh perlite, 100-mesh activated carbon, and 600-mesh fly ash as a gelling agent are graded according to the weight ratio of 15 parts, 35 parts, 30 parts, and 20 parts, mix them evenly, fill them into the adsorption device, and compact them.

[0027] Step 2: Pass the water sample to be treated through an adsorption device to remove floating oil and dispersed oil in the oil production wastewater, and then adjust the pH value of the treated oil production wastewater to 2.0 with 60 ml of 0.1 mol / L hydrochloric acid;

[0028] Step 3: An extraction solvent consisting of tributyl phosphate, N,N-dihexadecyl acetamide, and octanol in a volume ratio of 30 parts, 25 parts, and 45 parts, was prepared at a ratio of 1:2. Single-stage extraction was performed at 60°C for 5 minutes. After phase separation, the COD in the residual water was determined. The extracted water was then subjected to six-stage countercurrent extraction. The COD of the oil production wastewater after the extraction residue was determined. The results of the oil production wastewater after single-stage extraction and six-stage extraction were as follows: the COD of the untreated tertiary oil production wastewater was 2000 mg / L. After single-stage extraction, the COD in the residual water was 750 mg / L. After six-stage countercurrent extraction, the COD was 75 mg / L, which was lower than the national emission standard.

[0029] Step 4: Use 0.02 mol / L sodium hydroxide solution as a stripping agent to destroy the structure of the extractant formed by the organic matter and the extractant in the oil production wastewater, and recover the dissolved oil and emulsified oil in the oil production wastewater. The stripping agent is 250 ml; the stripping ratio is 2:1, the stripping temperature is 50°C, the single-stage stripping rate is 60%, and after 6 stages of countercurrent stripping, the stripping rate can reach more than 98%, and the extractant can be returned to the extraction section for normal use.

[0030] Example 2

[0031] Taking 500 ml of tertiary oil recovery wastewater from the isolated island of Shengli Oilfield as the sample to be treated, the treatment method of oil recovery wastewater based on solvent extraction includes the following steps:

[0032] Step 1: First, 200g of 140-mesh quartz sand, 80-mesh perlite, 100-mesh activated carbon, and 600-mesh fly ash as a gelling agent are graded according to the weight ratio of 15 parts, 40 parts, 25 parts, and 20 parts, mixed evenly, filled into the adsorption device, and compacted.

[0033] Step 2: Pass the water sample to be treated through an adsorption device to remove floating oil and dispersed oil in the oil production wastewater, and then adjust the pH value of the treated oil production wastewater to 3.0 with 30 ml of 0.2 mol / L hydrochloric acid;

[0034] Step 3. An extractant prepared from trialkylphosphine oxide: N,N-di(hexadecyl)acetamide: n-decanol in a volume ratio of 15 parts, 45 parts, and 40 parts is taken. 500 ml of the extractant is mixed with the pretreated oil production wastewater in a ratio of 1:1. Single-stage extraction is performed at 80°C for 5 minutes. After phase separation, the COD in the residual water is determined. After 6-stage countercurrent extraction, the COD of the oil production wastewater after extraction is measured. The results of the single-stage extraction and the oil production wastewater after 6-stage extraction are as follows: the COD of the untreated tertiary oil production wastewater is 2000 mg / L. After single-stage extraction, the COD in the residual water is 1000 mg / L. After 6-stage countercurrent extraction, the COD is 80 mg / L, which is lower than the national emission standard.

[0035] Step 4: Use 0.015 mol / L sodium hydroxide solution as a stripping agent to destroy the structure of the extractant formed by the organic matter and the extractant in the oil production wastewater, and recover the dissolved oil and emulsified oil in the oil production wastewater. The stripping agent is 250 ml; the stripping phase ratio is 2:1, the stripping temperature is 45°C, the single-stage stripping rate is 65%, and after 6 stages of countercurrent stripping, the stripping rate can reach more than 99%, and the extractant can be returned to the extraction section for normal use.

[0036] Example 3

[0037] Taking 500 ml of tertiary oil recovery wastewater from the isolated island of Shengli Oilfield as the sample to be treated, the treatment method of oil recovery wastewater based on solvent extraction includes the following steps:

[0038] Step 1: First, 200g of 140-mesh quartz sand, 80-mesh perlite, 100-mesh activated carbon, and 600-mesh fly ash as a gelling agent are graded according to the weight ratio of 10 parts, 45 parts, 30 parts, and 15 parts, mixed evenly, filled into the adsorption device, and compacted.

[0039] Step 2: Pass the water sample to be treated through an adsorption device to remove floating oil and dispersed oil in the oil production wastewater, and then adjust the pH value of the treated oil production wastewater to 1.5 with 65 ml of 0.1 mol / L hydrochloric acid;

[0040] Step 3: An extraction solvent consisting of triisobutyl phosphate, N,N-di(dodecyl)acetamide, and isoamyl alcohol in a volume ratio of 40 parts, 15 parts, and 45 parts, was used. The extraction was carried out at a ratio of 1:2 at 60°C for 5 minutes in a single-stage extraction. After phase separation, the COD in the residual water was determined. The extracted water was then subjected to a six-stage countercurrent extraction. The COD of the residual water was measured. The results of the single-stage extraction and six-stage extraction of the wastewater were as follows: the COD of the untreated tertiary oil recovery wastewater was 2000 mg / L. After the single-stage extraction, the COD in the residual water was 1000 mg / L. After the six-stage countercurrent extraction, the COD was 80 mg / L, which is lower than the national emission standard.

[0041] Step 4: Use 0.01 mol / L sodium hydroxide solution as a stripping agent to destroy the structure of the extractant formed by the organic matter and the extractant in the oil production wastewater, and recover the dissolved oil and emulsified oil in the oil production wastewater. The stripping agent is 250 ml; the stripping phase ratio is 2:1, the stripping temperature is 40°C, the single-stage stripping rate is 66%, and after 6 stages of countercurrent stripping, the stripping rate can reach more than 99%, and the extractant can be returned to the extraction section for normal use.

[0042] Comparative Example 1:

[0043] Taking 500 ml of tertiary oil recovery wastewater from the isolated island of Shengli Oilfield as the sample to be treated, the treatment method of oil recovery wastewater based on solvent extraction includes the following steps:

[0044] Step 1: First, 200g of 140-mesh quartz sand, 80-mesh perlite, 100-mesh activated carbon, and 600-mesh fly ash as a gelling agent are graded according to the weight ratio of 15 parts, 35 parts, 30 parts, and 20 parts, mix them evenly, fill them into the adsorption device, and compact them.

[0045] Step 2: Pass the water sample to be treated through an adsorption device to remove floating oil and dispersed oil in the oil production wastewater, and then adjust the pH value of the treated oil production wastewater to 2.0 with 60 ml of 0.1 mol / L hydrochloric acid;

[0046] Step 3: Use extractants composed of tributyl phosphate, N,N-dihexadecyl acetamide, and decanol in different volume ratios, with a ratio of 1:2 between the extractant and the oil production wastewater, and perform single-stage extraction at 60°C for 5 minutes. After phase separation, determine the COD in the raffinate after extraction. The test results are shown in Table 1.

[0047] Table 1. Comparison of extraction effects of different extractant compositions

[0048]

[0049] Untreated tertiary oil recovery wastewater with a COD of 2000 mg / L was extracted using a phosphorus-oxygen neutral extractant (tributyl phosphate), an amide extractant (55% N,N-dihexadecyl acetamide), and a diluent (n-decanol) alone. The single-stage extraction efficiency was low, making it unsuitable for industrial application. The combined use of a phosphorus-oxygen neutral extractant and an amide extractant produced a synergistic extraction effect, significantly improving extraction efficiency.

[0050] Comparative Example 2:

[0051] Taking 500 ml of tertiary oil recovery wastewater from the isolated island of Shengli Oilfield as the sample to be treated, the treatment method of oil recovery wastewater based on solvent extraction includes the following steps:

[0052] Step 1: First, 200g of 140-mesh quartz sand, 80-mesh perlite, 100-mesh activated carbon, and 600-mesh fly ash as a gelling agent are graded according to the weight ratio of 15 parts, 40 parts, 25 parts, and 20 parts, mixed evenly, filled into the adsorption device, and compacted.

[0053] Step 2: Pass the water sample to be treated through an adsorption device to remove floating oil and dispersed oil in the oil production wastewater, and then adjust the pH value of the treated oil production wastewater to 3.0 with 30 ml of 0.2 mol / L hydrochloric acid;

[0054] Step 3: An extractant prepared from trialkylphosphine oxide, N,N-di(hexadecyl)acetamide, and n-decanol in different volume ratios was taken. 500 ml of the extractant was mixed with the pretreated oil production wastewater at a ratio of 1:1. Single-stage extraction was performed at 80°C for 5 minutes. After phase separation, the COD in the residual water was measured to evaluate the single-stage extraction effect.

[0055] Table 2. Comparison of extraction effects of different extractant compositions

[0056]

[0057] Through comparative cases, it can be seen that the extraction effect of organic matter in oil production wastewater using phosphorus-oxygen neutral extractant and amide mixed extractant alone is not obvious. By using phosphorus-oxygen neutral extractant and amide mixed extractant in coordination, the COD in tertiary oil production wastewater is significantly reduced after single-stage extraction. Through theoretical calculation, it can be seen that after 6 countercurrent extractions, the COD index of oil production wastewater can meet national requirements.

[0058] Therefore, the present application provides a method for treating oil production wastewater based on solvent extraction, which treats tertiary oil production wastewater by solvent extraction and reduces the COD content therein to below the relevant national standards for discharge.

[0059] In this specification, references to terms such as "an experimental example," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that experimental example or example are included in at least one experimental example or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same experimental example or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more experimental examples or examples.

[0060] Finally, it should be noted that the above experimental examples are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred experimental examples, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for treating oil production wastewater based on solvent extraction, characterized in that: The following steps are involved: Step 1: Adding adsorption material into the adsorption device to perform adsorption treatment on the oil production wastewater, removing floating oil and dispersed oil in the oil production wastewater, and obtaining pretreated oil production wastewater; Step 2: Add an acid regulator to the pretreated oil production wastewater obtained in step 1 to adjust the pH to obtain oil production wastewater with a pH of 0-6; Step 3: Mixing a phosphorus-oxygen neutral extractant, an amide compound, and an alcohol to form an extractant; Step 4: Mixing the oil production wastewater with a pH of 0-6 obtained in step 2 with the extractant obtained in step 3 and subjecting it to multi-stage countercurrent extraction to combine the organic matter in the oil production wastewater with the extractant to form an extractant, which is then separated from the aqueous phase; Step 5: using a stripping agent to react with the extractant to recycle the organic matter in the oil production wastewater; Step 6: Recycling the extractant after stripping; In step 3, the phosphorus-oxygen neutral extractant is mainly composed of one or two of phosphate ester, monoalkyl phosphate diester, dialkyl phosphate monoester, and trialkyl phosphate oxide; the alcohol has 3-12 carbon atoms and is linear or branched; when preparing the extractant, the volume ratio of the phosphorus-oxygen neutral extractant, amide, and alcohol is 15-35:20-30:25-45.

2. The method for treating oil production wastewater based on solvent extraction according to claim 1, characterized in that: In step 1, the adsorption material includes, by weight, 10-15 parts of quartz sand, 25-45 parts of activated carbon, 15-30 parts of perlite, and 5-20 parts of fly ash as a gelling agent; and the mixture is prepared by particle grading.

3. The method for treating oil production wastewater based on solvent extraction according to claim 1, characterized in that: In step 2, the acid regulator is hydrochloric acid or sulfuric acid with a concentration of 0.1 mol / L-1 mol / L.

4. The method for treating oil production wastewater based on solvent extraction according to claim 1, characterized in that: In step 4, when using an extractant to extract organic matter from oil production wastewater, the pH value is 0-6; the temperature is 30-80° C.; the phase ratio is 1:10-10:1; and the extraction time is 5 minutes.

5. The method for treating oil production wastewater based on solvent extraction according to claim 1, characterized in that: The stripping agent in step five is an alkaline solution, the stripping temperature is 20-50° C., the volume ratio is 2-10:1, and the stripping time is 3-10 min.

6. The method for treating oil production wastewater based on solvent extraction according to claim 1, characterized in that: Before extraction, the COD content in the oil production wastewater was 100-2000 mg / L, and after treatment, the COD content was below 75 mg / L.

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