Cationic flocculants for oilfield produced water and their preparation methods

Abstract

This invention discloses a cationic flocculant for oilfield produced water and its preparation method, relating to the field of oilfield wastewater treatment technology. The preparation method of the flocculant includes the following steps: first, a quaternized monomer is prepared using allyl polyethylene glycol, epichlorohydrin, a tertiary amine, and a quaternizing agent; subsequently, the flocculant is obtained by polymerization using cross-linked starch, acrylamide, unsaturated polyol, and the quaternized monomer. The cationic flocculant for oilfield produced water provided by this invention can effectively remove oil, CODcr, turbidity, and suspended solids from produced wastewater.

Description

Technical Field

[0001] This invention relates to the field of oilfield wastewater treatment technology, specifically to a cationic flocculant for oilfield produced water and its preparation method. Background Technology

[0002] Cationic flocculants are a common type of flocculant. They mainly utilize the adsorption properties of cationic charges to neutralize the charge of suspended particles and colloids in wastewater. Through bridging adsorption and netting sweeping action, they cause the suspended particles and colloids to settle, thereby completing flocculation.

[0003] With the increasing severity of environmental pollution, the control and treatment of water pollution has gradually gained attention and progress has been made in many aspects. Oilfield produced water contains high levels of suspended solids, organic matter, and oil content, making its composition complex and increasingly difficult to treat.

[0004] Oilfields have relatively high requirements for the quality of reinjected water. If the treatment effect is not up to standard, the produced water from the oilfield will be unable to meet the reinjection needs. Summary of the Invention

[0005] To address at least one of the aforementioned problems, this invention proposes a cationic flocculant for oilfield produced water, which can effectively treat oilfield produced water through flocculation.

[0006] The technical solution of this invention is: a method for preparing a cationic flocculant for oilfield produced water, comprising the following steps: Allyl polyethylene glycol and epichlorohydrin were subjected to an epoxy ring-opening reaction under the action of a catalyst to obtain an intermediate after the reaction was completed; a tertiary amine and a quaternizing agent were subjected to monoquaternization to obtain a monoquaternary ammonium monomer; the intermediate and excess monoquaternary ammonium monomer were subjected to a quaternization reaction to obtain a bisquaternized monomer. Starch and epichlorohydrin were reacted to obtain cross-linked starch after the reaction was completed. Cross-linked starch, acrylamide, unsaturated polyol and bisquaternized monomer in a mass ratio of 100:10~20:1~5:10~30 are subjected to free radical polymerization under initiator conditions, and then separated and purified to obtain the final product.

[0007] The aforementioned bisquaternized monomer contains two quaternary ammonium groups at its end, which greatly increases the cationic density of the monomer. At the same time, the monomer also contains a polyoxyethylene ether chain and an alcohol hydroxyl group, which not only enhances the hydrophilicity of the final polymer, making it dissolve faster, but also makes the polymer have better bridging adsorption and net-catching sweeping effects, thereby enhancing the flocculation effect of the flocculant.

[0008] Cross-linked starch is renewable, non-toxic, and biodegradable, and possesses a three-dimensional network structure and abundant active sites, making it a common modifier matrix for flocculants. In this invention, cross-linked starch is prepared using starch and epichlorohydrin.

[0009] Unsaturated polyols can further enhance the adsorption of flocculants, thereby improving their flocculation effect.

[0010] In one embodiment of the present invention, during the preparation of the intermediate, the molar ratio of allyl polyethylene glycol (APEG) to epichlorohydrin is 1:1.2~1.5, the catalyst is BF3·Et2O, the catalyst addition is 0.1~0.4% of the mass of allyl polyethylene glycol, and the reaction conditions are 0~40℃. In this process, the ring-opening reaction of epichlorohydrin mainly occurs; considering the forward reaction, excess epichlorohydrin is added. Simultaneously, no solvent is needed to directly carry out the reaction. To promote the reaction, in actual operation, the catalyst and allyl polyethylene glycol are first mixed and stirred evenly, and then epichlorohydrin is added dropwise for the reaction, with the overall reaction time controlled at 2~4 hours.

[0011] One embodiment of the present invention includes the following separation and purification steps in the preparation of the intermediate: after the reaction is completed, under ice bath conditions, 0.5 to 1 times the mass of the catalyst (triethylamine or pyridine) is added, and the mixture is stirred until homogeneous. After 10 minutes, the solid phase of the system is removed; the liquid phase is taken, and low-boiling substances are removed by vacuum distillation to obtain the intermediate. The addition of triethylamine or pyridine is mainly to remove the catalyst; vacuum distillation is mainly to remove excess epichlorohydrin.

[0012] In one embodiment of the present invention, the tertiary amine is one of bis(dimethylaminoethyl) ether, tetramethylethylenediamine, and tetramethylpropylenediamine; and the quaternizing agent is one of chloroacetic acid, chloroethane, iodomethane, and bromoethane. Preferably, when the tertiary amine is bis(dimethylaminoethyl) ether and the quaternizing agent is chloroacetic acid, the final product exhibits better performance.

[0013] In one embodiment of the present invention, during the preparation of the monoquaternary ammonium monomer, the molar ratio of the bis-tertiary amine to the quaternizing reagent is 1:0.8~1, the solvent is isopropanol, the reaction time is 5~10 h, and the reaction temperature is 0~40℃. After the monoquaternary ammonium monomer is prepared, low-boiling substances are removed by vacuum distillation. During the reaction, to avoid the formation of bis-quaternary ammonium salts, the bis-tertiary amine and the quaternizing reagent are first dissolved separately in a solvent, and then the quaternizing reagent solution is added dropwise to the bis-tertiary amine solution to carry out the reaction.

[0014] In this process, to prevent the formation of bis-quaternary ammonium salts, the amount of quaternizing reagent added must be strictly limited: the molar amount of the quaternizing reagent cannot exceed the molar amount of the bis-tertiary amine. Extensive experiments have shown that a relatively pure mono-quaternary ammonium monomer is obtained when the molar ratio of the bis-tertiary amine to the quaternizing reagent is 1:0.8~1.0. Preferably, a mono-quaternary ammonium monomer with better purity and fewer impurities is obtained when the molar ratio of the bis-tertiary amine to the quaternizing reagent is 1:0.8~0.9. Furthermore, the temperature cannot be too high, as excessively high temperatures will lead to an increase in impurities in the mono-quaternary ammonium monomer.

[0015] One embodiment of the present invention involves preparing a bis-quaternized monomer in which the molar ratio of the intermediate to the mono-quaternized monomer is 1:1.2-1.5, the solvent is isopropanol, the reaction temperature is 10-60°C, and the reaction time is 6-15 hours. After the bis-quaternized monomer is prepared, low-boiling-point substances are first removed by vacuum distillation, followed by recrystallization with isopropanol. In this step, the recrystallization with isopropanol is mainly performed as follows: isopropanol at 60-80°C is added to the solid product after removing low-boiling-point substances, and the mixture is stirred until the solid product is just dissolved. Then, recrystallization is carried out under ice bath conditions, followed by filtration and drying of the solid phase. "Just dissolved" here refers to obtaining a saturated solution of the solid product. In actual operation, this can be tested by adding 10% (by mass) of isopropanol from the solid product every 30 seconds until the solid product is completely dissolved in isopropanol.

[0016] In one embodiment of the present invention, during the preparation of the cross-linked starch, the amount of epichlorohydrin added is 0.5-1.2% of the starch mass. The specific cross-linking method is conventional; for example, 0.7-3.5g of sodium hydroxide, 1.5-5g of sodium chloride, and 150mL of water are added to every 100g of starch, mixed thoroughly, and then the aforementioned amount of epichlorohydrin is added dropwise. The mixture is reacted at room temperature for 18 hours, followed by the addition of hydrochloric acid to adjust the pH to neutral. The cross-linked starch is then obtained through filtration, washing, and drying.

[0017] One embodiment of the present invention is that the unsaturated polyol is α One of allyl glycerol ether and trimethylolpropane monoallyl ether.

[0018] One embodiment of the present invention involves using cerium ammonium nitrate as the initiator, or a water-soluble redox initiator. The initiation temperature and the amount of initiator added depend on the specific type of initiator. Specifically, the amount of cerium ammonium nitrate added is 0.1-0.4% of the mass of the cross-linked starch, the initiation temperature is 30-45°C, and the reaction time is 1-3 hours. For the water-soluble redox initiator, a potassium persulfate / sodium bisulfite mixture with a mass ratio of 1:1 can be selected, with an addition amount of 0.2-0.8% of the mass of the cross-linked starch, an initiation temperature of 35-55°C, and a reaction time of 1-6 hours.

[0019] Another object of the present invention is to provide a cationic flocculant for oilfield produced water, which is prepared by any of the methods described above.

[0020] The beneficial effects of this invention are as follows: The cationic flocculant for oilfield produced water provided by this invention can effectively remove oil, CODcr, turbidity and suspended solids from produced wastewater. The highest removal rate of oil content reaches 95.7%, the highest removal rate of CODcr reaches 86.7%, the highest removal rate of turbidity reaches 92.7%, and the highest removal rate of suspended solids reaches 97.9%. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] In the following embodiments, unless otherwise specified, all raw materials can be purchased through conventional channels; Unless otherwise specified, the operations described in the following embodiments are all conventional operations in the art.

[0023] In the following examples, the temperature of vacuum distillation is 70°C and the pressure is 10 mmHg.

[0024] Example 1: A method for preparing a cationic flocculant for oilfield produced water, comprising the following steps: Add 0.24 g of BF3·Et2O to 80 g of APEG-400 and stir for 10 min at room temperature. Then, add 24 g of epichlorohydrin dropwise to the solution over a period of 30 min. After the addition is complete, continue the reaction for 2.5 h. After the reaction is complete, cool the product to a stable temperature in an ice bath, add 0.20 g of triethylamine, stir for 10 min, filter to remove the solid phase, take the liquid phase, and remove low-boiling substances by vacuum distillation to obtain the intermediate.

[0025] 32.0 g of dimethylaminoethyl ether and 16.2 g of chloroacetic acid were dissolved in isopropanol. Under normal temperature conditions, the chloroacetic acid solution was added dropwise to the dimethylaminoethyl ether solution and the reaction was continued for 8 hours. After the reaction was completed, the low-boiling substances were removed by vacuum distillation to obtain the monoquaternary ammonium monomer.

[0026] 49.2 g of the intermediate and 34.1 g of the monoquaternary ammonium monomer were dissolved in isopropanol, with the concentration of the intermediate being 10 wt%. The monoquaternary ammonium monomer solution was added dropwise to the intermediate solution at 40 °C, and the reaction was continued for 10 h. After the reaction was completed, the low-boiling substances were removed by vacuum distillation to obtain a solid product. Then, the solid product was added to isopropanol at 70 °C until it just dissolved. The solution was then cooled and recrystallized under ice bath conditions. The crystalline solid phase was collected and dried to obtain the bisquaternized ammonium monomer.

[0027] Take 100g of corn starch, 2.5g of sodium hydroxide and 4.2g of sodium chloride and disperse / dissolve them in 150mL of water. Under normal temperature conditions, add 0.8g of epichlorohydrin dropwise. After the addition is complete, react for 18h. Then add hydrochloric acid to adjust the pH of the system to neutral. Then, obtain cross-linked starch by filtration, washing and drying.

[0028] Take 50g of cross-linked starch, 8g of acrylamide, and 1.5g of... α - Allyl glycerol ether and 12g of bisquaternized monomer are dispersed or dissolved in water. Under a nitrogen atmosphere and at 40°C, an aqueous solution prepared from 0.12g of cerium ammonium nitrate is added dropwise. After the addition is complete, the reaction continues for 2 hours. After the reaction is complete, 5 times the volume of ethanol of the reaction system is added and allowed to stand. The precipitate is obtained and dried to obtain the final product.

[0029] Example 2 differs from Example 1 in that 80g of APEG-400 is replaced with 100g of APEG-500, the amount of intermediate added is 59.2g, the amount of acrylamide added is 6g, and the amount of bisquaternized monomer added is 14g, while the rest are the same.

[0030] Example 3 differs from Example 1 in that 32.0g of dimethylaminoethyl ether is replaced with 26.0g of tetramethylpropylenediamine, 16.2g of chloroacetic acid is replaced with 19.2g of bromoethane, and the amount of quaternary ammonium monomer added is 33.9g. All other aspects are the same.

[0031] Example 4 differs from Example 1 in that 80g of APEG-400 is replaced with 160g of APEG-800, and the amount of intermediate added is 89.2g. All other aspects are the same.

[0032] Example 5 differs from Example 1 in that corn starch is replaced with tapioca starch, and the amount of acrylamide added is changed to 9.5g and 1.5g respectively.α - Allyl glycerol ether is replaced with 2g of trimethylolpropane monoallyl ether, and the amount of bisquaternized monomer is replaced with 13g, with the rest remaining the same.

[0033] Comparative Example 1 differs from Example 1 in that 80g of APEG-400 was replaced with 23.2g of hydroxyethyl acrylate, and the amount of intermediate added was 20.8g; all other aspects remained the same.

[0034] Comparative Example 2, compared to Example 1, differs in that no additives were used. α -Allylglycerol ether, the rest are the same.

[0035] Comparative Example 3 differs from Example 1 in that the amount of acrylamide added is 15g, while all other aspects are the same.

[0036] To further illustrate the advantages of the flocculant prepared according to the embodiments of the present invention, it is tested below.

[0037] Produced wastewater from a well site in a Southwest oil and gas field was collected. After removing large particulate impurities, it was added to a test tube. Flocculants from Examples 1-5 and Comparative Examples 1-3 were added at a dosage of 5 g / L. The tube was inverted and shaken 10 times, then allowed to stand for 20 minutes. The oil content, CODcr, turbidity, and suspended solids of the supernatant were measured. Oil content was measured using the method in SL93.2-1994; CODcr using the method in HJ 828-2017; turbidity using the method in GB13200-91; and suspended solids using the method in QSH 1020 1356-2016 "General Technical Conditions for Flocculants for Conventional Produced Water Treatment in Oilfields". Three sets of samples were set up for each test, and the final test results were averaged. The final results are shown in Table 1.

[0038] Table 1. Results of Flocculation Tests on Produced Wastewater ; As shown in Table 1, the flocculant prepared in the embodiments of the present invention can effectively remove oil, CODcr, turbidity, and suspended solids from produced wastewater. Specifically, the highest removal rate for oil content reaches 95.7%, the highest removal rate for CODcr reaches 86.7%, the highest removal rate for turbidity reaches 92.7%, and the highest removal rate for suspended solids reaches 97.9%. This indicates that the flocculant prepared in the embodiments of the present invention has excellent flocculation effect and fully meets the actual operational needs of oilfields.

[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a cationic flocculant for oilfield produced water, characterized in that, Includes the following steps: Allyl polyethylene glycol and epichlorohydrin were subjected to an epoxy ring-opening reaction under the action of a catalyst to obtain an intermediate after the reaction was completed; a tertiary amine and a quaternizing agent were subjected to monoquaternization to obtain a monoquaternary ammonium monomer; the intermediate and excess monoquaternary ammonium monomer were subjected to a quaternization reaction to obtain a bisquaternized monomer. Starch and epichlorohydrin were reacted to obtain cross-linked starch after the reaction was completed. Cross-linked starch, acrylamide, unsaturated polyol and bisquaternized monomer in a mass ratio of 100:10~20:1~5:10~30 are subjected to free radical polymerization under initiator conditions, and then separated and purified to obtain the final product.

2. The method for preparing the cationic flocculant for oilfield produced water according to claim 1, characterized in that, In the preparation of the intermediate, the molar ratio of allyl polyethylene glycol to epichlorohydrin is 1:1.2~1.5, the catalyst is BF3·Et2O, the catalyst addition is 0.1~0.4% of the mass of allyl polyethylene glycol, the reaction conditions are 0~40℃, and the molecular weight of the allyl polyethylene glycol is not greater than 500.

3. The method for preparing the cationic flocculant for oilfield produced water according to claim 1, characterized in that, The preparation of the intermediate also includes the following separation and purification steps: after the reaction is completed, under ice bath conditions, add 0.5 to 1 times the mass of the catalyst, add triethylamine or pyridine, stir to mix evenly, and after 10 minutes, remove the solid phase of the system; take the liquid phase and remove low-boiling substances by vacuum distillation to obtain the intermediate.

4. The method for preparing the cationic flocculant for oilfield produced water according to claim 1, characterized in that, The tertiary amine is one of dimethylaminoethyl ether, tetramethylethylenediamine, and tetramethylpropylenediamine; the quaternizing agent is one of chloroacetic acid, chloroethane, iodomethane, and bromoethane.

5. The method for preparing the cationic flocculant for oilfield produced water according to claim 1, characterized in that, In the preparation of the monoquaternary ammonium monomer, the molar ratio of the bistertiary amine to the quaternizing reagent is 1:0.8~1, the solvent is isopropanol, the reaction time is 5~10h, and the reaction temperature is 0~40℃; after the monoquaternary ammonium monomer is prepared, low-boiling substances are removed by vacuum distillation.

6. The method for preparing the cationic flocculant for oilfield produced water according to claim 1, characterized in that, In the preparation of the bisquaternized monomer, the molar ratio of the intermediate to the monoquaternized monomer is 1:1.2~1.5, the solvent is isopropanol, the reaction temperature is 10~60℃, and the reaction time is 6~15h. After the bisquaternized monomer is prepared, low-boiling substances are first removed by vacuum distillation, and then isopropanol is added for recrystallization.

7. The method for preparing the cationic flocculant for oilfield produced water according to claim 1, characterized in that, In the preparation of the cross-linked starch, the amount of epichlorohydrin added is 0.5 to 1.2% of the starch mass.

8. The method for preparing the cationic flocculant for oilfield produced water according to claim 1, characterized in that, The unsaturated polyol is α One of allyl glycerol ether and trimethylolpropane monoallyl ether.

9. The method for preparing the cationic flocculant for oilfield produced water according to claim 1, characterized in that, The initiator is one of cerium ammonium nitrate or a water-soluble redox initiator.

10. A cationic flocculant for oilfield produced water, prepared by the method described in any one of claims 1 to 9.