Preparation method of degradable bactericide for oil field

Abstract

The invention relates to the technical field of sewage treatment, in particular to a preparation method of a degradable bactericide for an oil field. According to the invention, a hydroxypropyl guanidine gum-polycaprolactone-ethylenediamine fragment copolymer is taken as a carrier, a methylisothiazolinone quaternary ammonium salt (Q-MIT) bactericide is loaded, and the degradable bactericide for the oil field is obtained by cooperating with a dodecyl ethyl sulfide (TC-SE) bactericide and combining with sodium polyaspartate. A carrier forms a hydrogen bond with a polar group on the surface of a biological membrane through a hydroxypropyl guanidine gum main chain to realize targeted anchoring, a polycaprolactone branched chain encapsulates Q-MIT through a hydrophobic effect, primary amino groups of ethylenediamine are introduced to form a pH sensitive Schiff base bond with Q-MIT, and the primary amino groups and adipic dihydrazide form a thermal response hydrazide bond to construct a dual dynamic covalent bond, so that controlled release of Q-MIT is realized, and the biomembrane is prepared. And moreover, the components of the whole system are connected through degradable chemical bonds, so that the environmental protection property and sustainability of oil field operation are guaranteed.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sewage treatment, and in particular to a preparation method of a degradable bactericide for oil fields. BACKGROUND

[0002] In the process of oil field development, oil field sewage is rich in nutrients required for microbial growth, and is prone to breed microorganisms such as sulfate-reducing bacteria (SRB), saprophytic bacteria (TGB) and iron bacteria (FB); hydrogen sulfide produced in the metabolic process of these microorganisms will cause equipment corrosion, form a biological membrane to block the pore channel of the formation and reduce the permeability, and also produce organic acid to change the pH value of the formation water, further aggravate the dissolution of the formation rock and the corrosion of the equipment, and ultimately affect the quality of crude oil and the recovery rate, so it is necessary to regulate microbial activity by using bactericides to ensure the long-term stability of the mining operation.

[0003] At present, the bactericides widely used in oil fields mainly include single-component bactericides such as quaternary ammonium salt, isothiazolinone and aldehyde, for example, the Chinese invention patent with the publication number CN111296447A discloses an oil field high-efficiency bactericide and a preparation method thereof, the bactericide is generated by the olefination reaction of 4-hydroxy-1-benzothiophene-6-methyl formate and methyl acrylamide, and under a certain concentration, the bactericide shows high bactericidal performance on microorganisms such as sulfate-reducing bacteria, saprophytic bacteria, iron bacteria, sulfur bacteria and mold. However, the bactericides with single action mechanism are prone to induce the drug resistance of microorganisms after long-term use, and the increase of the amount of the bactericides will lead to the rise of the cost and the increase of the environmental load. In recent years, although there are some improvement schemes such as microcapsule coating and slow-release technology and phosphonate compounding, the microcapsule materials are mostly synthetic polymers which are not degradable, and there is an environmental accumulation risk; and the conventional compounding preparations lack the synergistic mechanism among the components, and cannot realize the multiplication effect of the bactericidal efficiency, and cannot meet the comprehensive needs of the long-acting property, the environmental friendliness and the action efficiency of the bactericides in the oil field mining. SUMMARY

[0004] In view of the deficiencies of the prior art, the purpose of the present application is to provide a preparation method of a degradable bactericide for oil fields, so as to use a hydroxypropyl guar gum-poly (caprolactone)-ethylene diamine (HPG-PCL-EDA) segment copolymer modified by dynamic covalent bonds as a carrier, load a quaternary ammonium salt (Q-MIT) bactericide, a dodecyl ethyl sulfide (TC-SE) bactericide, and a polyaspartic acid (PASP) sodium salt biofilm lysing agent, and prepare a composite system, so that the prepared bactericide realizes targeted anchoring of microbial biofilms, pH response and thermal response ordered release of bactericidal components, effective breaking of biofilm barriers, and multi-path attack of microorganisms, thereby guaranteeing long-term stable bactericidal effect, significantly improving bactericidal efficiency, effectively inhibiting the generation of microbial drug resistance, avoiding environmental accumulation pollution risk through gradual rupture of degradable chemical bonds in the whole system, and adapting to the complex working condition requirements of oil field sewage treatment.

[0005] In order to achieve the above purpose, the present application provides a preparation method of a degradable bactericide for oil field sewage treatment, comprising the following steps:

[0006] S1, mixing hydroxypropyl guar gum (HPG), epichlorohydrin and deionized water, adjusting the viscosity through a first reaction, and obtaining pretreated hydroxypropyl guar gum; mixing poly (caprolactone) (PCL), hexamethylene diisocyanate, dibutyltin dilaurate and N,N-dimethylformamide (DMF), and obtaining a poly (caprolactone)-isocyanate prepolymer through a second reaction;

[0007] S2, mixing the pretreated hydroxypropyl guar gum with N,N-dimethylformamide, removing water, adding the poly (caprolactone)-isocyanate prepolymer dropwise, obtaining a poly (caprolactone) grafted hydroxypropyl guar gum solution through a first reaction, adding ethylenediamine, adding hydrochloric acid to adjust the pH value to 8-9, adding adipic acid dihydrazide through a second reaction, and obtaining a hydroxypropyl guar gum-poly (caprolactone)-ethylene diamine segment copolymer through a third reaction, centrifugation and vacuum drying;

[0008] S3, mixing N,N-dimethylformamide with phosphorus oxychloride to obtain a Vilsmeier reagent; mixing methylisothiazolinone with 1,2-dichloroethane, adding the Vilsmeier reagent dropwise, and obtaining 2-formylmethyl-4-isothiazolin-3-one through reaction, drying of the organic phase, and reduced pressure distillation;

[0009] S4, mixing 2-formylmethyl-4-isothiazolin-3-one, dodecanol, p-toluenesulfonic acid and N,N-dimethylformamide, reacting, adding glacial acetic acid, N,N-dimethylethanolamine and iodomethane in turn under stirring, drying the organic phase, distilling under reduced pressure, adding petroleum ether, crystallizing, suction filtering to obtain a crude crystal; dissolving the crude crystal in a propylene glycol-water solution, adding polyethylene glycol-400 (PEG-400), spray drying to obtain a methylisothiazolinone quaternary ammonium salt;

[0010] S5, mixing dodecanethiol, sodium hydroxide and ethanol to obtain a dodecanethiol sodium solution, adding bromoethane dropwise, reacting, drying the organic phase, distilling under reduced pressure to obtain a dodecyl ethyl sulfide;

[0011] S6, mixing the methylisothiazolinone quaternary ammonium salt, the hydroxypropyl guanidium gum-poly (ε-caprolactone)-ethylene diamine segment copolymer and the propylene glycol-water mixed solution, stirring, adding the dodecyl ethyl sulfide and the polyaspartic acid sodium salt, spray drying to obtain a degradable bactericide for oilfield wastewater treatment.

[0012] In a feasible implementation scenario, in the S1, the mass-volume ratio of the HPG, the epichlorohydrin and the deionized water is (10-15) g:(0.2-0.4) g:(100-150) mL; the temperature of the first reaction is 55-65℃, the stirring rate of the first reaction is 350-450 r / min, and the time of the first reaction is 0.8-1.2 h; the viscosity is adjusted to 3000-3500 mPa·s; the mass-volume ratio of the PCL, the hexamethylene diisocyanate, the dibutyltin dilaurate and the anhydrous DMF is (4-6) g:(2.0-2.4) g:(0.07-0.09) mL:(40-60) mL; the temperature of the second reaction is 55-60℃, the stirring rate of the second reaction is 350-450 r / min, and the time of the second reaction is 1.8-2.2 h.

[0013] The HPG molecular chain is rich in hydroxyl groups, which are both hydrophilic sources and active sites for subsequent chemical reactions. However, the linear structure of the original HPG has low viscosity, and the distribution of hydroxyl groups is dispersed, which can easily lead to chain segment aggregation or uneven grafting when directly grafted with PCL. By modifying with epichlorohydrin, the hydroxyl groups of HPG will undergo nucleophilic ring-opening reaction with the epoxy groups of epichlorohydrin. The hydroxyl groups of HPG act as nucleophilic reagents to attack the electron-deficient carbon atoms on the epoxy ring, causing the three-membered ring to break and form ether bonds and new secondary hydroxyl groups. At the same time, the chlorine atom at the other end of epichlorohydrin can further react with the hydroxyl groups of the HPG molecular chain to form intermolecular cross-linking, converting the HPG from a linear structure to a lightly networked structure, significantly enhancing the intermolecular forces, and thus regulating the viscosity to 3000-3500 mPa·s. This viscosity range can ensure the flowability of the system during subsequent grafting with PCL, while avoiding excessive cross-linking that can lead to decreased solubility.

[0014] The PCL molecular chain contains carboxyl groups at its ends, and the isocyanate groups (-NCO) at both ends of hexamethylene diisocyanate (HDI) have extremely high reactivity. The difference in electronegativity between the nitrogen and oxygen atoms in -NCO makes the carbonyl carbon strongly electron-deficient, making it prone to nucleophilic addition reaction with the oxygen atoms (nucleophilic sites) in the PCL carboxyl groups. First, one -NCO group of HDI forms an unstable carbamate intermediate with the -COOH of PCL, which then rapidly dehydrates to form a stable amide bond, releasing carbon dioxide. At this time, the end of the PCL chain is modified to a structure containing active -NCO groups, i.e., PCL-isocyanate prepolymer. As an organotin catalyst, dibutyltin dilaurate can further enhance the electron deficiency of the carbonyl carbon by coordinating with the oxygen atoms of the -NCO groups, reducing the activation energy and accelerating the formation of the prepolymer.

[0015] In one possible implementation, in the S2, the mass-to-volume ratio of the pretreated HPG and anhydrous DMF is (10-15) g:(100-150) mL; the step of removing water is to add 5 g of 4Å molecular sieves activated at 120°C for 4 h, stir at 45-55°C at 250-350 r / min for 1 h, and filter to remove the molecular sieves; the mass ratio of the pretreated HPG and the polycaprolactone-isocyanate prepolymer is (10-15):(6-8.4); the dropwise addition rate of the polycaprolactone-isocyanate prepolymer is 0.08-0.12 mL / s; the temperature of the first reaction is 50°C, the stirring rate of the first reaction is 450-550 r / min, and the time of the first reaction is 4.5-5.5 h.

[0016] The pre-processed HPG retains a large number of hydroxyl groups, but trace amounts of water in the solution will react with -NCO, so 4A molecular sieves are needed to deeply remove water. The pore size of 4A molecular sieves only allows water molecules to enter its cavity, and trace amounts of water in the HPG solution are removed by physical adsorption. After filtering out the molecular sieves, the reaction of water with -NCO in the PCL-isocyanate prepolymer to form urea bonds can be avoided, preventing uneven carrier structures. During the reaction of the prepolymer with the pre-processed HPG, the prepolymer is slowly added to ensure uniform dispersion of the prepolymer in the HPG solution, avoiding excessive cross-linking of the HPG molecular chain due to high local -NCO concentration. At the same time, the temperature is controlled at 50°C to maintain the reactivity of -NCO. Stirring promotes the contact between the hydroxyl groups of HPG and the -NCO of the prepolymer, and a nucleophilic addition reaction occurs: the hydroxyl oxygen atom of HPG attacks the carbonyl carbon of -NCO, forming an amide bond, allowing the PCL hydrophobic segment to be precisely grafted to the HPG hydrophilic main chain through the amide bond, and finally forming a block structure of HPG hydrophilic main chain-PCL hydrophobic side chain. The key role of this structure is that the hydrophobic segment of PCL can be combined with the hydrophobic long-chain alkyl group in Q-MIT through hydrophobic interaction to effectively encapsulate Q-MIT, while the hydrophilic main chain of HPG retains the ability to form hydrogen bonds with the polar groups on the surface of the microbial biofilm, laying the foundation for the carrier to target and anchor the contaminated area.

[0017] In a feasible implementation scenario, in S2, the mass ratio of ethylenediamine and polycaprolactone-isocyanate prepolymer is 2: (6-8.4); the temperature of the second reaction is 65-75°C, the stirring rate of the second reaction is 350-450 r / min, and the stirring time of the second reaction is 2.8-3.2 h; the mass ratio of adipic acid dihydrazide and ethylenediamine is 0.5:2; the temperature of the third reaction is 55-65°C, the stirring rate of the third reaction is 300-400 r / min, and the time of the third reaction is 1.8-2.2 h; the temperature of the vacuum drying is 55-65°C, the time of the vacuum drying is 3.5-4.5 h, and the concentration of hydrochloric acid is 1-5 mol / L.

[0018] The network of double dynamic covalent bonds is constructed by introducing ethylenediamine and adipic acid dihydrazide (ADH) to provide the mechanism for the pH / temperature dual-responsive release of the bactericide. There are unreacted carboxyl groups at the end of the PCL segment due to the steric hindrance or local concentration difference caused by the reaction of HDI with PCL. The two primary amino groups in the ethylenediamine molecule can be acylated with these unreacted carboxyl groups on one hand: the nitrogen atom of the primary amino group attacks the carbonyl carbon of the carboxyl group, and after forming a transition state, water is removed to form an amide bond, so that the ethylenediamine fragment (-NH-CH2-CH2-NH-) is grafted to the end of PCL; on the other hand, the primary amino group in the ethylenediamine molecule remains in the free form in the carrier molecule. The acylation reaction rate is optimized by adjusting the alkaline environment of pH = 8-9. Under alkaline conditions, the carboxyl group at the end of PCL will dissociate into a carboxylate, and the negative charge of the carboxylate will further enhance the nucleophilicity of the oxygen atom, accelerating the acylation reaction with the primary amino group, while avoiding the protonation of the primary amino group under acidic conditions and losing nucleophilic activity.

[0019] After the successful introduction of free primary amino groups, ADH is added to construct a thermally responsive dynamic bond. The ADH molecule contains two hydrazine groups (-NH-NH2), and the carbonyl carbon can undergo condensation reaction with the nitrogen atom of the free primary amino group: the lone pair of electrons of the free primary amino group attacks the carbonyl carbon of the hydrazine group, and after forming a transition state, one molecule of water is removed to form a stable hydrazone bond (-NH-CO-NH-NH-). At this point, two kinds of dynamic covalent bonds are formed in the carrier: one is the Schiff base bond (-C=N-) formed by the primary amino group introduced by ethylenediamine and the subsequent Q-MIT aldehyde group, and the other is the hydrazone bond (-NH-CO-NH-NH-) formed by the primary amino group and ADH. The difference in dynamic characteristics of these two bonds is the core of realizing controlled release: the Schiff base bond is easily hydrolyzed in the weak alkaline environment of oilfield wastewater treatment, breaking into -NH2 and -CHO, destroying the hydrophobic aggregation force between PCL segments, and promoting the initial rapid release of Q-MIT; while the hydrazone bond will hydrolyze at high temperatures of 120-180℃, but its hydrolysis stability is much higher than that of the Schiff base bond, and it can slowly break down, while the high temperature accelerates the thermal motion of the PCL segment, further weakening the hydrophobic interaction, realizing the sustained release of the bactericide, and thus ensuring the long-term bactericidal effect.

[0020] In one possible implementation, in the S3, the molar volume ratio of the phosphorus oxychloride to DMF is (100-120) mmol:(10-20) mL; the molar volume ratio of the methyl isothiazolinone to 1,2-dichloroethane is 100 mmol:100 mL; the dropwise addition rate of the Vilsmeier reagent is 0.3-0.7 mL / min; the temperature of the reaction is 60°C, the stirring rate of the reaction is 250-350 r / min, and the reaction time is 3 h; the step of drying the organic phase is: the reaction liquid is adjusted to pH 6-7 with 5% sodium carbonate, 50 mL of dichloroethane is added for extraction, the organic phase is collected, 10 g of anhydrous magnesium sulfate is added to the organic phase and stirred for 1 h; the temperature of the reduced pressure distillation is 40°C, and the vacuum degree is 0.08-0.1 MPa.

[0021] The functional aldehyde group is introduced by formylation reaction. In the reaction of phosphorus oxychloride (POCl3) and anhydrous N,N-dimethylformamide (DMF), the oxygen atom with a lone pair of electrons in the DMF molecule first attacks the phosphorus atom of POCl3 to form an unstable adduct, and then rearrangement occurs to generate a Vilsmeier reagent ([Me2N + =CHCl]Cl - , that is, a dimethyl imine chloride methyl chloride salt). The methyl group adjacent to the heterocycle in the methyl isothiazolinone (MIT) molecule is affected by the electron-withdrawing conjugation effect of the isothiazolinone heterocycle, and the electron cloud density of the alpha-H of the methyl group is reduced, the acidity is enhanced, and the alpha-H is easily taken away by an electrophilic reagent. When the Vilsmeier reagent reacts with MIT, the imine salt cation first combines with the alpha-H of the methyl group of MIT to form a carbonium ion intermediate, and then the intermediate undergoes deprotonation and rearrangement, the Cl - of the Vilsmeier reagent is removed, and finally the methyl group of MIT is replaced by an aldehyde group (-CHO) to generate 2-aldehyde methyl-4-isothiazolin-3-one. The aldehyde group introduced in this step is not only a key site for subsequent functional group transformation, but its strong reactivity also lays a foundation for the Schiff base bond combination of Q-MIT and the carrier HPG-PCL-EDA segment copolymer, ensuring the controlled release of the bactericide.

[0022] In one possible implementation, the molar volume ratio of 2-formylmethyl-4-isothiazolin-3-one, dodecanol, p-toluenesulfonic acid and DMF in S4 is 100 mmol:(110-130) mmol:(0.4-0.6) mmol:(40-60) mL; the reaction temperature is 115-125°C, the stirring rate of the reaction is 350 r / min, and the reaction time is 3.5-4.5 h; the molar volume ratio of glacial acetic acid, N,N-dimethylethanolamine and iodomethane is 1 mL:(140-160) mmol:(100-120) mmol; the stirring rate is 350 r / min, and the stirring time is 1-2 h.

[0023] The aldehyde group activity is precisely controlled through acetalization and hydrolysis reaction. The generated 2-formylmethyl-4-isothiazolin-3-one and dodecanol undergo acetalization reaction under the action of p-toluenesulfonic acid: the carbonyl group (C=O) of the aldehyde group is first protonated to enhance electrophilicity, and then undergoes nucleophilic addition with the hydroxyl group of dodecanol to form a hemiacetal, and then dehydrates to form a stable acetal (structure is -C(OR)2-, R is dodecyl). The core role of this step is to protect the aldehyde group. The acetal structure has high stability under neutral or basic conditions, which can avoid the premature Schiff base reaction of the aldehyde group with amine reagents in the subsequent quaternary ammonium reaction, and ensure the directionality of functional group transformation. Subsequently, glacial acetic acid is added, and the acetal undergoes hydrolysis reaction under proton catalysis to regenerate free aldehyde group. At this time, the aldehyde group activity is moderate, which can selectively react with N,N-dimethylethanolamine, and will not cause side reactions due to excessive activity. The N,N-dimethylethanolamine molecule contains both a tertiary amine group (-N(CH3)2) and a hydroxyl group. The hydroxyl group first undergoes nucleophilic addition with the free aldehyde group to form a hemiacetal structure (-CH(OH)-O-CH2CH2N(CH3)2). This structure not only retains the reactivity of the tertiary amine group, but also avoids the interference of the amine group with the isothiazolinone heterocycle through the combination of the hydroxyl group and the aldehyde group. Subsequently, iodomethane (CH3I) is added dropwise. As a strong alkylating agent, iodomethane is easily combined with the tertiary amine group through a bimolecular nucleophilic substitution reaction because the iodine ion is an excellent leaving group: the lone pair of electrons of the nitrogen atom of the tertiary amine group attacks the methyl carbon of iodomethane to form a positively charged quaternary ammonium salt cation (-N + (CH3)3I - ). The key role of quaternization is to introduce a cation unit, which can produce strong electrostatic attraction with the negative groups on the surface of the microbial cell membrane, disrupt the charge balance of the cell membrane, cause the membrane structure to loosen and increase the permeability, and create conditions for the isothiazolinone group to enter the cell.

[0024] In a possible implementation, in the step S4, the organic phase is dried by adding 90-110 mL of ethyl acetate and stirring at 300 r / min for 5-15 min, then the filtrate is washed with 4-6% sodium bicarbonate solution until neutral, and then washed with 40-60 mL of saturated brine, and then 4-6 g of anhydrous magnesium sulfate is added to the organic phase and stirred for 0.5-1.5 h; the temperature of the distillation under reduced pressure is 45-55°C, and the vacuum degree is 0.08-0.1 MPa; the operation of crystallization is that 25-35 mL of petroleum ether is added to the solution after distillation, and the solution is stirred at 300 r / min for 3-7 min at room temperature, and then the solution is left to stand for 0.5-1.5 h to allow the crystals to be naturally precipitated; and the step of suction filtration is that the crystals are washed twice with 10 mL of petroleum ether.

[0025] The essence of the crystallization process is to construct a supersaturated system by using the difference in solvent polarity, so as to realize the selective precipitation and preliminary purification of Q-MIT. In the solution after distillation, 30 mL of low-polarity solvent petroleum ether is added. Since the Q-MIT molecule contains a strong-polarity quaternary ammonium salt cation and a weakly hydrophobic isothiazolinone heterocycle, the solubility of the Q-MIT molecule is higher in a reaction system with higher polarity, i.e., an ethyl acetate-propylene glycol mixed phase. However, the introduction of petroleum ether significantly reduces the polarity of the mixed system, destroys the solubility balance of the Q-MIT, and makes the affinity between the quaternary ammonium salt and the low-polarity solvent poor, so that the interaction between Q-MIT molecules, such as electrostatic attraction and hydrophobic interaction, is stronger than the interaction with the solvent, thereby quickly reaching a supersaturated state. Stirring at room temperature can promote uniform mixing of the solvent, avoid local over-saturation of the crystals, and provide sufficient time for crystal growth, so that the solute molecules form regular crystals in an orderly arrangement. Small-molecule impurities in the reaction, such as unreacted iodomethane and excess N,N-dimethylethanolamine, have higher solubility in the low-polarity system due to the difference in polarity or structure, and most of them remain in the mother liquor, thereby realizing the preliminary separation of Q-MIT from impurities. The crystals are washed with petroleum ether, and the similar-similar-dissolves principle is used: petroleum ether has strong affinity with the residual mother liquor (containing ethyl acetate and unremoved impurities), can dissolve and carry away the impurities adsorbed on the surface of the crystals through diffusion, and will not dissolve the Q-MIT crystals due to its low polarity, so as to reduce the impurity content without damaging the crystal structure.

[0026] In a possible implementation, in the step S4, the volume ratio of propylene glycol to water in the propylene glycol-water solution is 1:3; the addition amount of polyethylene glycol-400 is 0.3%-0.5% of the mass of the propylene glycol-water mixed solution; and the spray drying is centrifugal spray drying, and the parameters of the spray drying are as follows: the inlet air temperature is 55-65°C, the outlet air temperature is 40°C, the feeding rate is 7-9 mL / min, and the atomization rotation speed is 18000-20000 r / min.

[0027] The crude crystals were dissolved in a 1:3 propylene glycol-water mixture, and 0.4% PEG-400 was added to form a steric hindrance stabilizing layer by wrapping the Q-MIT particles with hydrophilic segments, preventing particle agglomeration before drying. The selection of low-temperature parameters is based on the heat sensitivity of Q-MIT: the C=N bond of the isothiazolinone heterocycle is easily broken at high temperatures, and the cationic structure of the quaternary ammonium salt may also cause charge distribution imbalance due to thermal vibration, while a low-temperature environment can minimize these structural damages and preserve their active sites for interaction with microorganisms. At the same time, centrifugal spray drying disperses the solution into micron-sized droplets through high-speed atomization, increasing the evaporation area and allowing the solvent to be quickly removed in a short time, avoiding the fusion and caking between droplets.

[0028] In a feasible implementation scenario, in the S5, the mass-volume ratio of the dodecanethiol, sodium hydroxide and ethanol is (9-11) mmol:(11-13) mmol:(25-35) mL; the molar ratio of the bromoethane and dodecanethiol is (10-12):(9-11); the dropwise addition rate of the bromoethane is 0.02-0.04 mL / min; the reaction is refluxed at 60-70°C for 4.5-5.5 h; the step of drying the organic phase: the reaction solution is added to 100 mL of an ethyl acetate aqueous solution, the volume ratio of ethyl acetate and water in the ethyl acetate aqueous solution is 1:1, after separation, the organic phase is collected, the organic phase is washed with 30 mL of saturated brine, 5 g of anhydrous sodium sulfate is added and stirred for 1.8-2.2 h; the temperature of the reduced pressure distillation is 45-55°C, and the vacuum degree is 0.08-0.1 MPa.

[0029] The synthesis of TC-SE is based on the nucleophilic activation and directional substitution of thiols. The S-H bond of dodecanethiol has weak acidity, and the OH - of sodium hydroxide can abstract the proton of the S-H bond of dodecanethiol to form sodium dodecanethiolate, so that the sulfur atom is converted from electrically neutral to negatively charged S - , significantly improving the nucleophilicity of the sulfur atom, ensuring that the subsequent nucleophilic substitution reaction with bromoethane can generate a thioether bond directionally to obtain the TC-SE bactericide. The molecular structure of TC-SE containing a thioether bond and a dodecyl group determines its unique bactericidal path. The energy metabolism of microorganisms relies on the transfer of electrons by the iron porphyrin coenzyme in cytochrome oxidase. The sulfur atom of the thioether bond in TC-SE contains a lone pair of electrons, which can form a coordinate bond with the Fe 3+Forming stable coordination bond, directly blocking electron transport chain, leading to interrupt of microbial ATP synthesis, energy metabolism failure; and the dodecyl in its molecule can enhance its hydrophobic penetration ability to microbial cell membrane through hydrophobic interaction with the hydrophobic double molecular layer of cell membrane phospholipid, and can form synergy with the dodecyl of Q-MIT to further destroy the membrane structure integrity, creating conditions for the two bactericides to enter the cell interior. This energy metabolism interference target and the target of the membrane destruction + intracellular metabolism blocking of Q-MIT form complementation, so that the microorganism is difficult to avoid the two bactericidal mechanisms through single gene mutation, greatly reducing the probability of drug resistance, so as to realize long-acting sterilization.

[0030] In a feasible implementation case, in the S6, the mass-volume ratio of the methylisothiazolinone quaternary ammonium salt, the hydroxypropyl guanidine gum-polycaprolactone-ethylene diamine fragment copolymer and the propylene glycol-water mixed solution is (4.5-5.5) g:(9-11) g:(45-55) mL; in the propylene glycol-water mixed solution, the volume ratio of propylene glycol and water is 1:3; the stirring temperature is 45-55 DEG C, the stirring rate is 350-450 r / min, and the stirring time is 2 h; the mass ratio of the dodecyl ethyl sulfide, the polyaspartic acid sodium salt and the methylisothiazolinone quaternary ammonium salt is (2.8-3.2):(1.8-2.2):(4.5-5.5); the parameters of the spray drying are as follows: the inlet air temperature is 80-90 DEG C, the outlet air temperature is 48 DEG C, the feeding rate is 9-11 mL / min, and the atomization pressure is 0.18-0.22 MPa; and the degradable bactericide particle size is 30-60 mu m.

[0031] The hydrophobic long-chain alkyl on the Q-MIT molecule can be closely combined with the hydrophobic region of the PCL segment in the carrier through hydrophobic interaction, not only strengthening the encapsulation effect of Q-MIT, but also the large amount of hydroxyl groups reserved in the HPG backbone of the carrier can form hydrogen bonds with the polar groups on the surface of the microbial biofilm, so as to realize the targeted anchoring of the bactericide in the microbial pollution area; in addition, the carboxyl groups of the polyaspartic acid sodium salt can specifically chelate Ca 2+ , destroy the ionic crosslinking network formed by polysaccharides such as alginate, and lead to the collapse of the physical structure of the biofilm, creating a channel for Q-MIT and TC-SE to penetrate the biofilm barrier and directly contact the membrane microorganisms. At the same time, all components in the system are combined through degradable chemical bonds such as ester bonds (PCL and HPG are connected), amide bonds (ethylene diamine and PCL are connected), and peptide bonds (PASP structure), which can be gradually hydrolyzed into small molecular organic matter in the formation environment, avoiding the environmental accumulation problem of traditional bactericides.

[0032] Compared with the prior art, the beneficial effects of the present application are as follows:

[0033] 1) This scheme uses a hydroxypropyl guanidyl gum-poly (caprolactone)-ethylene diamine segment (HPG-PCL-EDA) segment copolymer modified by dynamic covalent bonds as a carrier to load methyl isothiazolinone quaternary ammonium salt (Q-MIT) bactericide, synergistic dodecyl ethyl sulfide (TC-SE) bactericide and polyaspartic acid (PASP) sodium salt biofilm lysing agent to prepare a degradable bactericide for oil fields, which significantly improves the bactericidal efficiency and effectively inhibits the development of microbial drug resistance, and avoids the risk of environmental accumulation pollution through the gradual breaking of the degradable chemical bonds in the whole system, and adapts to the complex working condition requirements of oil field wastewater treatment. Among them, the hydroxypropyl guanidyl gum (HPG) in the HPG-PCL-EDA segment copolymer serves as the backbone, forms hydrogen bonds with the polar groups on the surface of the biofilm through the hydroxyl groups, realizes the targeted enrichment of the bacterial pollution area, and ensures that the bactericidal components act on the microbial aggregation area in the wastewater; through the bridging action of the isocyanate groups at both ends of hexamethylene diisocyanate, one end forms an urethane bond with the hydroxyl group of HPG, and the other end forms an amide bond with the carboxyl group of poly (caprolactone) (PCL), thereby grafting the PCL segment to the HPG backbone to form a block structure of hydrophilic HPG main chain-hydrophobic PCL side chain, and PCL effectively encapsulates Q-MIT by forming hydrophobic interaction with the hydrophobic structure in Q-MIT. On this basis, primary amino groups are introduced by amidation reaction of ethylenediamine with the carboxyl groups at the ends of PCL, which on one hand forms a pH-sensitive Schiff base bond with the free aldehyde group released by the hemiacetal hydrolysis of Q-MIT molecules, and on the other hand forms a thermally responsive hydrazine bond with ethanedioic acid dihydrazide, constructing a double dynamic covalent bond network. In the weak alkaline environment of oil field wastewater, the Schiff base bond will preferentially hydrolyze and break, destroying the hydrophobic aggregation force between PCL segments, realizing the initial rapid release of Q-MIT, and thus preliminarily killing the free bacteria in the oil field wastewater; while in the oil field wastewater treatment temperature of 20-60℃, the hydrazine bond maintains slow breaking with lower hydrolysis rate, while the thermal motion of PCL segments intensifies, the hydrophobic interaction continues to decay, promoting the sustained release of bactericides, and ensuring the long-acting of bactericidal effect.

[0034] 2) PASP sodium salt chelates Ca 2+, break the ionic crosslinking structure of alginate network, leading to the physical collapse of biofilm, providing a channel for the penetration of fungicides. On this basis, Q-MIT molecules integrate isothiazolinone fungicide groups and quaternary ammonium salt cation units, through the strong electrostatic interaction between quaternary ammonium salt cations and the negative groups on the surface of microbial cell membranes, causing cell membrane potential imbalance and structural loosening, and then leading to increased membrane permeability, while the isothiazolinone heterocycle rapidly penetrates into the cell after the increase in membrane permeability, irreversibly binds to the sulfhydryl in the metabolic enzyme, and blocks the cell metabolic pathway; while TC-SE fungicides coordinate with the metal cofactor in cytochrome through sulfide bonds, interfere with the energy metabolism process of microorganisms, while the dodecyl chain further enhances the hydrophobic penetration ability, forms target point complementarity with Q-MIT, and further enhances the bactericidal efficiency, and the multi-target attack and irreversible action mode of the two can effectively delay the development of microbial drug resistance. The components of the whole system are connected by degradable chemical bonds such as ester bonds, amide bonds and peptide bonds, and can be gradually degraded into harmless small molecules in the environment, solving the problems of easy drug resistance of current traditional single fungicides, leading to weakening of long-term bactericidal effect and environmental accumulation. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 Preparation process schematic diagram of the degradable fungicide for oil field. DETAILED DESCRIPTION

[0036] In order to make the technical problems, technical solutions and beneficial effects of the present application clearer, the present application will be further described in detail below in conjunction with the embodiments. However, this should not be understood as limiting the scope of the present application to the following examples. Without departing from the method idea of the present application, all other embodiments obtained by those of ordinary skill in the art without making creative labor belong to the scope of protection of the present application.

[0037] The singular forms "is", "are", "one", "any" and "the" used in the present application are intended to include the plural forms, unless the context clearly indicates otherwise. In addition, if the terms "first", "second" appear, they are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance.

[0038] Example 1

[0039] As Figure 1 shown, a preparation method of a degradable fungicide for oil field includes the following steps:

[0040] 1) 12 g HPG was dissolved in 120 mL deionized water, stirred at 300 r / min at 50 °C until completely dissolved, 0.3 g epichlorohydrin was added, and stirred at 400 r / min at 60 °C for 1 h. The viscosity was adjusted to 3000-3500 mPa·s, and then cooled to room temperature to obtain the pretreated HPG. 5 g PCL was dissolved in 50 mL anhydrous DMF, stirred at 300 r / min until completely dissolved, and then 2.2 g hexamethylene diisocyanate and 0.08 mL dibutyltin dilaurate were added under the protection of nitrogen at a flow rate of 50 mL / min. The mixture was stirred at 400 r / min at 58 °C for 2 h to obtain a PCL-isocyanate prepolymer.

[0041] 2) 12 g of the pretreated HPG was dissolved in 120 mL anhydrous DMF, 5 g of 4 Å molecular sieves activated at 120 °C for 4 h was added, and stirred at 300 r / min at 50 °C for 1 h to remove water. The molecular sieves were removed by filtration, and the PCL-isocyanate prepolymer was added dropwise into the solution at a rate of 0.10 mL / s, while the stirring rate was controlled at 500 r / min and the temperature was controlled at 50 °C. The reaction was carried out for 5 h to obtain a PCL grafted HPG solution. 2 g of ethylenediamine was added to the PCL grafted HPG solution, and 1 mol / L hydrochloric acid was added to control the pH to 8.5. The mixture was stirred at 400 r / min at 70 °C for 3 h, and then 0.5 g of ADH was added. The mixture was stirred at 350 r / min at 60 °C for 2 h, and then the pH was adjusted to 7.0 with 1 mol / L hydrochloric acid. 500 mL of ethanol was added for precipitation, and the solid was collected by centrifugation at 8000 r / min for 20 min. The solid was dried under vacuum at 60 °C for 4 h to obtain a HPG-PCL-EDA segment copolymer.

[0042] 3) 15 mL anhydrous DMF was mixed with 110 mmol phosphorus oxychloride, and stirred at 300 r / min at 0 °C for 30 min to obtain a Vilsmeier reagent. 100 mmol 2-methyl-4-isothiazolin-3-one was added to 100 mL anhydrous 1,2-dichloroethane, and stirred at 300 r / min until dissolved. The Vilsmeier reagent was added dropwise at a rate of 0.5 mL / min, and the temperature was raised to 60 °C. The reaction was carried out for 3 h while stirring at 300 r / min. After the reaction was completed, the temperature was cooled to 25 °C at a rate of 10 °C / h. The pH was adjusted to 6 with 5% sodium carbonate, and 50 mL dichloroethane was added for extraction. The organic phase was dried with 10 g anhydrous magnesium sulfate for 1 h. The drying agent was removed by filtration, and the filtrate was distilled under reduced pressure at 40 °C and 0.09 MPa to obtain 2-aldehyde methyl-4-isothiazolin-3-one.

[0043] 4) 100 mmol 2-formylmethyl-4-isothiazolin-3-one, 120 mmol dodecanol, 0.5 mmol p-toluenesulfonic acid and 50 mL of anhydrous DMF were mixed, and the reaction was kept at 120°C under stirring at 350 r / min for 4 h. The reaction solution was cooled to 60°C at a rate of 15°C / h, 1 mL of glacial acetic acid was added, and stirring was kept at 300 r / min for 30 min to hydrolyze the acetal into free aldehyde group. Then 150 mmol of N,N-dimethylethanolamine was added, and the reaction was kept at 60°C under stirring at 350 r / min for 1 h to form hemiacetal. 110 mmol of iodomethane was added dropwise, and the reaction was continued under stirring at 350 r / min for 1.5 h. After cooling to 25°C, 100 mL of ethyl acetate was added, and stirring was kept at 300 r / min for 10 min. The solution was filtered, and the filtrate was washed with 5% NaHCO3 solution until neutral, and then washed once with 50 mL of saturated brine. The organic phase was dried with 5 g of anhydrous magnesium sulfate for 1 h, and the drying agent was removed by filtration. The filtrate was distilled under reduced pressure at 50°C and 0.09 MPa, and concentrated to 30 mL of solution. 30 mL of petroleum ether was added, and stirring was kept at room temperature and 300 r / min for 5 min. The solution was left to stand for 1 h to allow natural crystallization. The crystals were collected by suction filtration, and washed twice with 10 mL of petroleum ether. The crystals were dried under vacuum at 30°C for 2 h to obtain the crude crystals. The crude crystals were dissolved in 50 mL of 1:3 propylene glycol-water mixture, and 0.4% PEG-400 was added to the mixture. The solution was stirred at 50°C and 600 r / min for 20 min, and then spray-dried by centrifugation. The inlet temperature was 60°C, the outlet temperature was 40°C, the feeding rate was 8 mL / min, and the atomization rate was 19000 r / min to obtain Q-MIT.

[0044] 5) 10 mmol of dodecanethiol and 30 mL of ethanol were mixed and stirred at 300 r / min until completely dissolved. 12 mmol of sodium hydroxide was added, and stirring was kept at 300 r / min for 15 min to obtain sodium dodecanethiolate. 11 mmol of bromoethane was added dropwise at a rate of 0.03 mL / min, and the reaction was kept at reflux at 65°C for 5 h. The reaction solution was cooled to room temperature, and then distilled under reduced pressure at a temperature of 40°C and a vacuum degree of 0.08 MPa. 100 mL of ethyl acetate aqueous solution with a volume ratio of 1:1 was added, and the solution was shaken for 10 min and then separated. The upper organic phase was collected, and the organic phase was washed once with 30 mL of saturated brine. 5 g of anhydrous sodium sulfate was added, and the solution was stirred at 300 r / min for 2 h to dry. The solution was filtered, and the filtrate was distilled under reduced pressure at a temperature of 50°C and a vacuum degree of 0.09 MPa to remove ethyl acetate. TC-SE was obtained.

[0045] 6) Mix 5 g of Q-MIT and 10 g of HPG-PCL-EDA segment copolymer, dissolve in 50 mL of propylene glycol-water mixed solution with a volume ratio of 1:3, stir at 400 r / min at 50°C for 2 h, add 3 g of TC-SE and 2 g of polyaspartic acid sodium salt, use intermittent ultrasonic mode, ultrasonic at 350 W power, work for 30 s and stop for 30 s, total ultrasonic time is 30 min, spray dry the dispersion, inlet temperature is 85°C, outlet temperature is 48°C, feeding rate is 10 mL / min, atomization pressure is 0.2 MPa, collect the powder with a particle size of 30-60 μm, and obtain a degradable bactericide.

[0046] Example 2

[0047] As shown in Figure 1 , a preparation method of a degradable bactericide for oil fields comprises the following steps:

[0048] 1) Dissolve 10 g of HPG in 100 mL of deionized water, stir at 300 r / min at 50°C until completely dissolved, add 0.2 g of epichlorohydrin, react at 350 r / min at 55°C for 0.8 h, adjust the viscosity to 3000-3500 mPa·s, cool to room temperature, and obtain a pretreated HPG; dissolve 4 g of PCL in 40 mL of anhydrous DMF, stir at 300 r / min until completely dissolved, add 2 g of hexamethylene diisocyanate and 0.07 mL of dibutyltin dilaurate under the protection of nitrogen gas with a flow rate of 50 mL / min, and stir at 350 r / min at 55°C for 1.8 h to obtain a PCL-isocyanate prepolymer.

[0049] 2) Dissolve 10 g of the pretreated HPG in 100 mL of anhydrous DMF, add 5 g of 4Å molecular sieves activated at 120°C for 4 h, stir at 250 r / min at 45°C for 1 h to remove water, filter to remove the molecular sieves, and add the PCL-isocyanate prepolymer to the solution at a drop rate of 0.08 mL / s, control the stirring rate to be 450 r / min and the temperature to be 50°C, and react for 4.5 h to obtain a PCL-grafted HPG solution; add 2 g of ethylenediamine to the above reaction solution, add 2 mol / L hydrochloric acid to control the pH to be 9, stir at 350 r / min at 65°C for 2.8 h, then add 0.5 g of adipic acid dihydrazide (ADH), stir at 300 r / min at 55°C for 1.8 h, adjust the pH to 7.0 with 1 mol / L hydrochloric acid, add 500 mL of ethanol for precipitation, centrifuge at 7500 r / min for 20 min to collect the solid, and vacuum dry at 55°C for 3.5 h to obtain an HPG-PCL-EDA segment copolymer.

[0050] 3) 10 mL of anhydrous DMF was mixed with 100 mmol of phosphorus oxychloride, stirred at 300 r / min for 30 min at 0°C to obtain Vilsmeier reagent, 100 mmol of 2-methyl-4-isothiazolin-3-one was added to 100 mL of anhydrous 1,2-dichloroethane, and after stirring at 300 r / min, the Vilsmeier reagent was added at a rate of 0.3 mL / min, and the temperature was raised to 60°C, and the reaction was stirred at 250 r / min for 3 h. After the reaction was completed, it was cooled to 25°C at a rate of 8°C / h, the pH was adjusted to 7 with 5% sodium carbonate, 50 mL of dichloroethane was added for extraction, the organic phase was dried with 10 g of anhydrous magnesium sulfate for 1 h, the drying agent was removed by filtration, and the filtrate was distilled under reduced pressure at 40°C and 0.08 MPa to obtain 2-methyl-4-isothiazolin-3-one aldehyde.

[0051] 4) 100 mmol of 2-methyl-4-isothiazolin-3-one aldehyde, 110 mmol of dodecanol, 0.4 mmol of p-toluenesulfonic acid, and 40 mL of anhydrous DMF were mixed, and the reaction was stirred at 115°C and 350 r / min for 3.5 h. The reaction solution was cooled to 60°C at a rate of 15°C / h, 1 mL of glacial acetic acid was added, and stirring was continued at 300 r / min for 30 min to hydrolyze the acetal to a free aldehyde group. Then, 140 mmol of N,N-dimethylethanolamine was added, and the reaction was stirred at 60°C and 350 r / min for 1 h to form a hemiacetal. Then, 100 mmol of iodomethane was added dropwise, and the reaction was continued at 350 r / min for 2 h. After cooling to 25°C, 90 mL of ethyl acetate was added, and stirring was continued at 300 r / min for 5 min. The mixture was filtered, washed with a 4% NaHCO3 solution until neutral, and then washed once with 40 mL of saturated brine. The organic phase was dried with 4 g of anhydrous magnesium sulfate for 0.5 h, the drying agent was removed by filtration, and the filtrate was distilled under reduced pressure at 45°C and 0.08 MPa. The residue was concentrated to 30 mL, 25 mL of petroleum ether was added, and stirring was continued at room temperature and 300 r / min for 3 min. The mixture was allowed to stand for 0.5 h to allow the crystals to separate. The crystals were filtered, washed twice with 10 mL of petroleum ether, and dried under vacuum at 30°C for 2 h to obtain the crude crystals. The crude crystals were dissolved in 50 mL of a 1:3 propylene glycol-water mixture, 0.3% PEG-400 was added to the propylene glycol-water mixture, and stirring was continued at 50°C and 600 r / min for 20 min. The mixture was dried by centrifugal spray drying at an inlet temperature of 55°C, an outlet temperature of 40°C, a feed rate of 7 mL / min, and an atomization rate of 18000 r / min to obtain Q-MIT.

[0052] 5) 9 mmol of dodecanethiol and 25 mL of ethanol were mixed and stirred at 300 r / min until completely dissolved, 11 mmol of sodium hydroxide was added, and stirred at 300 r / min for 15 min to obtain sodium dodecanethiol; 10 mmol of bromoethane was added dropwise at a rate of 0.02 mL / min, and the reaction was carried out at 60°C under reflux for 4.5 h; after the reaction solution was cooled to room temperature, it was distilled under reduced pressure at a temperature of 40°C and a vacuum degree of 0.08 MPa; 100 mL of an ethyl acetate-water solution with a volume ratio of 1:1 was added, and after oscillation for 10 min, the upper organic phase was collected; the organic phase was washed with 30 mL of saturated brine once, 5 g of anhydrous sodium sulfate was added, and stirred at 300 r / min for 1.8 h; after filtration, the ethyl acetate was removed by distillation under reduced pressure at a temperature of 45°C and a vacuum degree of 0.08 MPa to obtain TC-SE.

[0053] 6) 4.5 g of Q-MIT and 9 g of HPG-PCL-EDA segment copolymer were mixed and dissolved in 45 mL of a propylene glycol-water mixed solution with a volume ratio of 1:3, and stirred at 45°C at 350 r / min for 2 h; 2.8 g of TC-SE and 1.8 g of polyaspartic acid sodium salt were added, and ultrasonic treatment was carried out in an intermittent ultrasonic mode at a power of 350 W, with a working time of 30 s and a rest time of 30 s, and the total ultrasonic time was 30 min; the dispersion was subjected to spray drying, with an inlet temperature of 80°C, an outlet temperature of 48°C, a feeding rate of 9 mL / min, and an atomization pressure of 0.2 MPa; powders with a particle size of 30-60 μm were collected to obtain a degradable bactericide.

[0054] Example 3

[0055] As shown in Figure 1 , a preparation method of a degradable bactericide for oil fields comprises the following steps:

[0056] 1) 15 g of HPG was dissolved in 150 mL of deionized water, and stirred at 300 r / min at 50°C until completely dissolved; 0.4 g of epichlorohydrin was added, and reacted at 450 r / min at 65°C for 1.2 h; the viscosity was adjusted to 3500 mPa·s, and cooled to room temperature to obtain pretreated HPG; 6 g of PCL was dissolved in 60 mL of anhydrous DMF, and stirred at 300 r / min until completely dissolved; 2.4 g of hexamethylene diisocyanate and 0.09 mL of dibutyltin dilaurate were added under the protection of nitrogen at a flow rate of 50 mL / min, and reacted at 450 r / min at 60°C for 2.2 h to obtain a PCL-isocyanate prepolymer.

[0057] 2) 15 g of pretreated HPG was dissolved in 150 mL of anhydrous DMF, 5 g of 4A molecular sieve activated at 120°C for 4 h was added, and the solution was stirred at 55°C at 350 r / min for 1 h to remove water, the molecular sieve was removed by filtration, and the PCL-isocyanate prepolymer was added to the solution at a drop rate of 0.12 mL / s, the stirring rate was controlled at 550 r / min, and the temperature was controlled at 50°C, and the reaction was performed for 5.5 h to obtain a PCL-grafted HPG solution; 2 g of ethylenediamine was added to the above reaction solution, 1 mol / L hydrochloric acid was added to control the pH to 8, and the reaction was performed at 75°C at 450 r / min for 3.2 h, then 0.5 g of adipic acid dihydrazide (ADH) was added, the reaction was performed at 65°C at 400 r / min for 2.2 h, 1 mol / L hydrochloric acid was used to adjust the pH to 7.0, 500 mL of ethanol was added for precipitation, the solid was collected by centrifugation at 8500 r / min for 20 min, and vacuum drying was performed at 65°C for 4.5 h to obtain a HPG-PCL-EDA segment copolymer.

[0058] 3) 20 mL of anhydrous DMF was mixed with 120 mmol of phosphorus oxychloride, and the mixture was stirred at 0°C at 300 r / min for 30 min to obtain a Vilsmeier reagent, 100 mmol of 2-methyl-4-isothiazolin-3-one was added to 100 mL of anhydrous 1,2-dichloroethane, and the mixture was stirred at 300 r / min until dissolved, then the Vilsmeier reagent was added at a rate of 0.7 mL / min, the temperature was increased to 60°C, and the reaction was performed at 350 r / min for 3 h, then the reaction was cooled to 25°C at a rate of 5°C / h, 5% sodium carbonate was used to adjust the pH to 7, 50 mL of dichloroethane was added for extraction, the organic phase was dried with 10 g of anhydrous magnesium sulfate for 1 h, the drying agent was removed by filtration, and the filtrate was distilled under reduced pressure at 40°C and 0.1 MPa to obtain 2-methyl-4-isothiazolin-3-one.

[0059] 4) 100 mmol 2-formylmethyl-4-isothiazolin-3-one, 130 mmol dodecanol, 0.6 mmol p-toluenesulfonic acid and 60 mL anhydrous DMF were mixed, and the reaction was kept at 125 °C under stirring at 350 r / min for 4.5 h. The reaction solution was cooled to 60 °C at a rate of 15 °C / h, 1 mL glacial acetic acid was added, and stirring was kept at 300 r / min for 30 min to hydrolyze the acetal into free aldehyde group. Then 160 mmol N,N-dimethylethanolamine was added, and the reaction was kept at 60 °C under stirring at 350 r / min for 1 h to form hemiacetal. 120 mmol iodomethane was added dropwise, and the reaction was continued under stirring at 350 r / min for 2 h. After cooling to 25 °C, 110 mL ethyl acetate was added, and stirring was kept at 300 r / min for 15 min. The solution was filtered, and the filtrate was washed with 6% NaHCO3 solution until neutral, and then washed with 60 mL saturated brine once. The organic phase was dried with 6 g anhydrous magnesium sulfate for 1.5 h, and the drying agent was removed by filtration. The filtrate was distilled under reduced pressure at 55 °C and 0.1 MPa, and concentrated to 30 mL solution. 35 mL petroleum ether was added, and stirring was kept at room temperature and 300 r / min for 7 min. The solution was left to stand for 1.5 h to naturally crystallize. The crystals were filtered, and then washed with 10 mL petroleum ether twice. The crystals were dried at 30 °C under vacuum for 2 h to obtain the crude crystals. The crude crystals were dissolved in 50 mL 1:3 propylene glycol-water mixture, and 0.5% PEG-400 was added. The solution was stirred at 50 °C and 600 r / min for 20 min, and then spray-dried by centrifugation. The inlet temperature was 65 °C, the outlet temperature was 40 °C, the feeding rate was 9 mL / min, and the atomization rate was 20,000 r / min to obtain Q-MIT.

[0060] 5) 11 mmol dodecanethiol and 35 mL ethanol were mixed and stirred at 300 r / min until completely dissolved. 13 mmol sodium hydroxide was added, and stirring was kept at 300 r / min for 15 min to obtain sodium dodecanethiolate. 12 mmol bromoethane was added dropwise at a rate of 0.04 mL / min, and the reaction was kept at 70 °C under reflux for 5.5 h. The reaction solution was cooled to room temperature, and then distilled under reduced pressure at a temperature of 40 °C and a vacuum degree of 0.08 MPa. 100 mL ethyl acetate aqueous solution with a volume ratio of 1:1 was added, and the solution was shaken for 10 min and then separated. The upper organic phase was collected, and the organic phase was washed with 30 mL saturated brine once. 5 g anhydrous sodium sulfate was added, and stirring was kept at 300 r / min for 2.2 h to dry the solution. The solution was filtered, and then distilled under reduced pressure at a temperature of 55 °C and a vacuum degree of 0.1 MPa to remove the ethyl acetate to obtain TC-SE.

[0061] 6) 5.5 g of Q-MIT and 11 g of HPG-PCL-EDA segment copolymer were mixed and dissolved in 55 mL of a propylene glycol-water mixed solution with a volume ratio of 1:3, stirred at 55°C at 450 r / min for 2 h, 3.2 g of TC-SE and 2.2 g of polyaspartic acid sodium salt were added, ultrasonic was performed in an intermittent ultrasonic mode, 350 W power, 30 s working and 30 s stopping, the total ultrasonic time was 30 min, the dispersion was spray dried, the inlet temperature was 90°C, the outlet temperature was 48°C, the feeding rate was 11 mL / min, the atomization pressure was 0.2 MPa, the powder with a particle size of 30-60 μm was collected, and a degradable bactericide was obtained.

[0062] Comparative Example 1

[0063] A preparation method of a degradable bactericide for oil fields, the implementation steps and parameters of which are different from those of Example 1 in that a commercially available industrial-grade hydroxypropyl methyl cellulose (HPMC) is used instead of the HPG-PCL-EDA segment copolymer carrier, and the remaining steps and parameters are the same.

[0064] Comparative Example 2

[0065] A preparation method of a degradable bactericide for oil fields, the implementation steps and parameters of which are different from those of Example 1 in that TC-SE is not prepared, and the remaining steps and parameters are the same.

[0066] Comparative Example 3

[0067] A preparation method of a degradable bactericide for oil fields, the implementation steps and parameters of which are different from those of Example 1 in that polyaspartic acid sodium salt is not added, and the remaining steps and parameters are the same.

[0068] Comparative Example 4

[0069] A preparation method of a degradable bactericide for oil fields, the implementation steps and parameters of which are different from those of Example 1 in that ethylenediamine and adipic acid dihydrazide (ADH) are not added, and only HPG-PCL copolymer is prepared, and the remaining steps and parameters are the same.

[0070] Performance test:

[0071] Bactericidal performance test: First, bactericides with a concentration of 500 mg / L were prepared for Example 1-Example 3 and Comparative Example 1-Comparative Example 4, respectively, 1.5 wt.% sodium chloride and 0.5 wt.% potassium chloride were added, and the pH was adjusted to 8.0 to simulate an oil field wastewater system. Sulfate-reducing bacteria (SRB, concentration 1×10 6 CFU / mL), saprophytic bacteria (TGB, concentration 1×10 6 CFU / mL), and iron bacteria (FB, concentration 1×10 6CFU / mL) as test strains, 10 mL of simulated oilfield wastewater containing bactericides and 1 mL of bacterial solution were mixed respectively and placed in a 60°C constant temperature water bath for incubation for 24 h. A blank control group was also set up, i.e. the simulated oilfield wastewater without bactericides was mixed with the bacterial solution, and each group was tested in triplicate. After incubation, the mixed solution was diluted to an appropriate concentration by 10-fold serial dilution, 0.1 mL of the diluted solution was spread on the corresponding medium (Postgate B medium for SRB, nutrient agar medium for TGB, and iron bacteria medium for FB), SRB was incubated in an anaerobic incubator at 37°C for 7 d, TGB and FB were incubated in an aerobic incubator at 37°C for 48 h, the viable bacterial colony counts on the plates were counted, and the calculation formula was: bactericidal rate = (1 - average viable bacterial count of the treatment group / average viable bacterial count of the control group) x 100%.

[0072] Sustained release performance test: 0.5 g of the bactericide of Example 1-Example 3 and Comparative Example 1-Comparative Example 4 was weighed respectively and added to 50 mL of simulated oilfield wastewater (same as the bactericidal performance test formula), which was placed in a 25°C constant temperature water bath with magnetic stirring at a speed of 150 r / min, 5 mL of sample was taken at 0.5 h, 1 h and 2 h respectively, filtered through a 0.22 μm organic phase filter membrane, and the Q-MIT concentration in the filtrate was determined by HPLC. After each sampling, 5 mL of simulated oilfield wastewater was added, and the initial release rate formula was calculated as follows: 0-2 h release rate = (cumulative release of Q-MIT mass in 2 h / total Q-MIT mass in the sample) x 100%; then it was transferred to a 150°C oil bath, and the magnetic stirring speed was kept at 150 r / min, and the sample was taken every 12 h and the simulated oilfield wastewater was added, and the Q-MIT concentration was determined by HPLC, and the time required for the cumulative release rate to reach 80% was recorded, which was the long-acting release time. Each group was tested in triplicate, and the average value was taken.

[0073] Biofilm inhibition test: First, the common pathogenic strains of oilfields, sulfate-reducing bacteria (SRB) and saprophytic bacteria (TGB), were inoculated into special culture medium and incubated at 30°C and 150 r / min to reach the logarithmic growth phase (OD 600 =0.6-0.8), and diluted with sterile physiological saline to 1 x 10 6CFU / mL as the test bacteria liquid; then the bactericide powders of Examples 1-3 and Comparative Examples 1-4 were prepared into 200 mg / L test liquid with sterile oilfield sewage simulation liquid (0.5% KCl + 1.5% NaCl, pH = 8.0), and a blank group was set as only the oilfield sewage simulation liquid, and a sterilized stainless steel sheet (1 cm x 1 cm x 0.2 cm) was prepared as a biofilm attachment carrier (which simulates the inner wall of the oilfield sewage treatment equipment and is more prone to biofilm enrichment). 1 mL of bacteria liquid, 1 piece of carrier and 1 mL of test liquid were added to a 24-well plate, and after static culture at 30°C for 72 h, the carrier was washed with sterile normal saline to remove planktonic bacteria, stained with 0.1% crystal violet for 30 min, eluted with 33% glacial acetic acid, and then the OD 570 was measured by an enzyme-labeled instrument. 空白 The biofilm inhibition rate was calculated. The calculation formula is: biofilm inhibition rate (%) = (OD 实验 -OD 空白 ) / OD + x 100%.

[0074] Degradation performance test: first, prepare simulated formation water with the following composition: Na 2+ : 1500 mg / L, Ca 2+ : 200 mg / L, Mg - : 100 mg / L, Cl - : 2000 mg / L, HCO3 100 : 300 mg / L, adjust pH to 7.5, and respectively weigh 1.0 g of the bactericides of Examples 1-3 and Comparative Examples 1-4 into 100 mL of simulated formation water, and place them in a 60°C constant temperature incubator for culture for 30 d, while setting a blank control group with only 100 mL of simulated formation water, and each group is tested in triplicate. During the culture period, 5 mL of headspace gas is extracted every 5 d, and the CO2 concentration is measured by gas chromatography to calculate the cumulative CO2 release amount within 30 d; after the culture is completed, the liquid is centrifuged at 8000 r / min for 20 min, the bottom solid is collected, washed with deionized water for 3 times, and then placed in a 60°C vacuum drying oven for drying to constant weight, and the residual solid rate is calculated, and the calculation formula is: degradation rate = (actual cumulative CO2 release amount / theoretical CO2 release amount of complete degradation of the sample) x 100%.

[0075] The prepared degradable bactericide is degraded by releasing CO2, and the calculation of the theoretical CO2 release amount requires determining the chemical formula and mass fraction of each component of the bactericide, and the calculation is as follows: the HPG-PCL-EDA segment copolymer is calculated as (C3H7NO2) 10 - (C6H 20 O2) 10 - (C2H8N2)5, Q-MIT is calculated as CH 19 N2O3SI, and TC-SE is calculated as C14 H 30 S, sodium polyaspartate (C4H5NO3Na) 50 The carbon mass fraction of each component was calculated accordingly. Based on the formulation of the bactericide compound consisting of 10g HPG-PCL-EDA fragment copolymer, 5g Q-MIT, 3g TC-SE, and 2g sodium polyaspartate, the total carbon mass was calculated to be 8.98g. Based on the principle of carbon conservation, after the degradable chemical bonds such as ester bonds, amide bonds, and peptide bonds in each component are hydrolyzed in the simulated formation water environment, all carbon elements are converted into CO2. The calculation formula is: theoretical CO2 release = (total carbon mass / 12g / mol) × 44g / mol. Finally, the theoretical CO2 release of 1g of degradable bactericide sample is 1.648g.

[0076] Antimicrobial resistance testing: Antimicrobial resistance was assessed using sulfate-reducing bacteria (SRB) as the target strain. First, Postgate B medium containing 300 mg / L of fungicide was prepared (composition: sodium lactate 10 g / L, yeast extract 1 g / L, ferrous sulfate 0.5 g / L, sodium chloride 5 g / L, calcium chloride 0.1 g / L, magnesium sulfate 0.2 g / L, pH=7.2). A blank medium without fungicide was also prepared. SRB were inoculated into the blank medium and anaerobically cultured at 37°C until the logarithmic growth phase. OD... 600 =0.6-0.8, transferred to drug-containing medium at a 1% inoculum rate as the first generation culture system, anaerobically cultured at 37℃ to the logarithmic phase, and then transferred to fresh drug-containing medium at the same 1% inoculum rate. This process was repeated until the 10th generation. Bacterial suspensions from the first and 10th generation drug-containing media were collected, and the viable count was determined using the erasure dilution method. The 24-hour bactericidal rate was calculated, with each group tested in triplicate. Resistance was evaluated using the difference between the bactericidal rate of the 10th generation and that of the first generation. A difference ≤5% was considered weak resistance, 5% < difference ≤15% was considered moderate resistance, and a difference >15% was considered strong resistance. This method was used to assess the delaying effect of the bactericide on microbial resistance.

[0077] Table 1. Test results of the bactericidal performance of the bactericides prepared in Examples 1-3 and Comparative Examples 1-4.

[0078]

[0079] Table 2 Performance test results of the biodegradable bactericides for oilfield use prepared in Examples 1-3 and Comparative Examples 1-4

[0080]

[0081] From Table 1 and Table 2, it can be seen that the bactericidal rate, degradation rate and biofilm inhibition rate of the bactericide obtained in Example 1-Example 3 are higher than those of Comparative Example 1-Comparative Example 4, and the initial release rate and drug resistance of the bactericide are significantly lower than those of Comparative Example 1-Comparative Example 4, which indicates that the bactericidal performance, sustained-release and drug resistance delaying ability of the bactericide prepared in Example 1-Example 3 are all better than those of Comparative Example 1-Comparative Example 4.

[0082] Comparative Example 1 lacks the key structure and function of HPG-PCL-EDA segment copolymer as a carrier because HPMC is used to replace HPG-PCL-EDA segment copolymer. On the one hand, HPMC does not have the block structure of hydrophilic HPG main chain-hydrophobic PCL branch, and cannot stably encapsulate Q-MIT through hydrophobic interaction. Moreover, HPMC does not have the double dynamic covalent bonds of Schiff base bond and hydrazine bond formed by the primary amino group introduced by ethylenediamine and ADH, and loses the controllable release ability of pH and heat response, resulting in a significant increase in the initial release rate of 0-2 h, a greatly shortened time required for 80% release, a rapid loss of bactericide, an insufficient bactericide concentration in the later stage, a difficulty in maintaining an effective concentration in the key period (24-72 h) of biofilm formation, a failure to continuously inhibit the reproduction of bacteria in the biofilm, and a difficulty in achieving targeted enrichment of the bactericide in the bacterial pollution area. On the other hand, HPMC does not have the hydroxyl group of HPG, and cannot form hydrogen bonds with the polar groups of the biofilm, making it difficult to achieve targeted enrichment of the bactericide in the bacterial pollution area. Moreover, HPMC itself has poor degradability, and lacks the regulation of dynamic covalent bonds on the release rate, so microorganisms are prone to adapt to the fluctuation of the bactericide concentration, resulting in a significant decrease in the 24 h bactericidal rate.

[0083] Comparative Example 2 lacks TC-SE bactericide because only Q-MIT single bactericide is used. The core defect is the loss of double-target bactericidal synergistic effect. Q-MIT can destroy the membrane structure through the electrostatic action of quaternary ammonium salt and irreversibly bind to the thiol group of metabolic enzymes through the heterocyclic ring of isothiazolinone, but single action cannot efficiently penetrate the extracellular polymer network of the biofilm, resulting in a low biofilm inhibition rate. Moreover, only a single target point of the metabolic pathway of microorganisms is targeted, and microorganisms only need to cope with a single action target point, which is easy to produce drug resistance through gene mutation, resulting in an increase in drug resistance. Although the dynamic covalent bond of the HPG-PCL-EDA segment copolymer carrier still guarantees a certain sustained-release property, the bactericidal rate is still lower than that of the example because of the loss of double-target complementation, which highlights the key role of double bactericides in improving bactericidal efficiency and delaying drug resistance.

[0084] Comparative Example 3 lacks the biofilm physical disintegration ability because polyaspartic acid sodium salt is not added, resulting in a significant decrease in the biofilm inhibition rate. Harmful bacteria in oilfields exist in the form of biofilm, and SRB secretes alginate to form an extracellular polymer network. Polyaspartic acid sodium salt as a biofilm lytic agent can chelate Ca 2+, destroy the ion cross-linking structure of biofilm, make the biofilm physically collapse, and provide a channel for Q-MIT and TC-SE to penetrate the biofilm and contact the bacteria. After the deletion of the polyaspartic acid sodium salt, the biofilm structure is complete, the bactericide is difficult to break through the extracellular polymeric substance barrier, and can only act on a small amount of free bacteria on the surface of the biofilm, resulting in a significant decrease in the 24h bactericidal rate. At the same time, the bactericide does not fully contact the bacteria, and the selective pressure formed easily induces the bacteria to develop drug resistance.

[0085] In Comparative Example 4, no Schiff base bond and hydrazine bond are formed due to the absence of ethylenediamine and ADH, and the carrier is only HPG-PCL. The core defect is the loss of the slow-release performance regulated by the double dynamic covalent bonds, which further affects the bactericidal long-acting property and drug resistance: the slow-release property of the HPG-PCL-EDA segment copolymer depends on the double dynamic covalent bonds. In an alkaline environment, the Schiff base bond is preferentially hydrolyzed to destroy the hydrophobic aggregation of PCL, and the initial controllable release is promoted. In the 20-60℃ oilfield sewage treatment environment, the hydrazine bond slowly breaks and the thermal motion of PCL intensifies, ensuring sustained release. However, after the loss of the dynamic network, HPG-PCL only relies on the PCL hydrophobic effect to encapsulate Q-MIT, and the stability is poor. In the simulated oilfield sewage, it is easy to quickly depolymerize, resulting in a significant increase in the initial release rate in 0-2h. Although it can inhibit the initial biofilm formation, the bactericide concentration of the system drops sharply after 72h, which cannot prevent the biofilm from regrowing, resulting in a significant decrease in the bactericidal rate. Although the carrier still contains degradable ester bonds and amide bonds, the degradation rate is close to that of the example in 30d. However, the loss of the slow-release function makes it unable to meet the long-term bactericidal needs of the oilfield, which confirms the decisive role of the double dynamic covalent bonds in the slow-release performance of the carrier.

[0086] In Comparative Examples 1-4, the targeting anchoring structure and the double dynamic covalent bond regulation mechanism of the HPG-PCL-EDA segment copolymer as the carrier, the dual-target bactericidal synergistic effect of Q-MIT and TC-SE, and the biofilm cracking function of the PASP sodium salt are lost, which directly leads to the loss of control of the slow-release performance, the decrease in the bactericidal efficiency, and the significant increase in the microbial drug resistance. The bactericidal performance, slow-release long-acting property, and drug resistance delaying ability are significantly deteriorated.

[0087] The above results show and describe the basic principles and main features of the present application and the advantages of the present application.

[0088] The embodiments of the present application are described above in combination with the drawings, but the present application is not limited to the above specific embodiments, which are only illustrative and not limiting. Those skilled in the art can make many forms under the inspiration of the present application without departing from the purpose of the present application and the scope protected by the claims, which are all within the protection of the present application.

Claims

1. A method for preparing a biodegradable bactericide for oilfield use, characterized in that, Includes the following steps: S1. Hydroxypropyl guar gum, epichlorohydrin and deionized water are mixed and reacted in the first reaction to obtain pretreated hydroxypropyl guar gum; polycaprolactone, hexamethylene diisocyanate, dibutyltin dilaurate and N,N-dimethylformamide are mixed and reacted in the second reaction to obtain polycaprolactone-isocyanate prepolymer. S2. Pretreated hydroxypropyl guar gum is mixed with N,N-dimethylformamide, and polycaprolactone-isocyanate prepolymer is added dropwise. After the first reaction, a polycaprolactone-grafted hydroxypropyl guar gum solution is obtained. Ethylenediamine is added, and hydrochloric acid is added to adjust the pH to 8-9. After the second reaction, adipate dihydrazide is added. After the third reaction, the mixture is centrifuged and vacuum dried to obtain a hydroxypropyl guar gum-polycaprolactone-ethylenediamine fragment copolymer. S3. N,N-dimethylformamide was mixed with phosphorus oxychloride to obtain Vilsmeier reagent; methylisothiazolinone was mixed with 1,2-dichloroethane, Vilsmeier reagent was added dropwise, the reaction was carried out, the organic phase was dried and distilled under reduced pressure to obtain 2-aldehydemethyl-4-isothiazolin-3-one. S4. 2-Aldehydemethyl-4-isothiazolin-3-one, dodecanol, p-toluenesulfonic acid, and N,N-dimethylformamide are mixed and reacted. Glacial acetic acid, N,N-dimethylethanolamine, and iodomethane are added sequentially under stirring. The organic phase is dried, distilled under reduced pressure, and petroleum ether is added. Crystals are precipitated and filtered to obtain crude crystals. The crude crystals are dissolved in propylene glycol-water solution, polyethylene glycol-400 is added, and the mixture is spray-dried to obtain methylisothiazolinone quaternary ammonium salt. S5. Mix dodecyl mercaptan, sodium hydroxide and ethanol to obtain sodium dodecyl mercaptan solution, add bromoethane dropwise, react, dry the organic phase and distill under reduced pressure to obtain dodecyl ethyl sulfide; S6. Mix methylisothiazolinone quaternary ammonium salt, hydroxypropyl guar gum-polycaprolactone-ethylenediamine fragment copolymer and propylene glycol-water mixture, stir, add dodecyl ethyl sulfide and sodium polyaspartate, spray dry to obtain a biodegradable bactericide for oil fields.

2. The method for preparing a biodegradable bactericide for oilfield use according to claim 1, characterized in that, In step S1, the mass-to-volume ratio of hydroxypropyl guar gum, epichlorohydrin, and deionized water is (10-15) g : (0.2-0.4) g : (100-150) mL; the temperature of the first reaction is 55-65℃, the stirring rate of the first reaction is 350-450 r / min, and the reaction time is 0.8-1.2 h; the mass-to-volume ratio of polycaprolactone, hexamethylene diisocyanate, dibutyltin dilaurate, and anhydrous N,N-dimethylformamide is (4-6) g : (2.0-2.4) g : (0.07-0.09) mL : (40-60) mL; the temperature of the second reaction is 55-60℃, the stirring rate of the second reaction is 350-450 r / min, and the reaction time is 1.8-2.2 h.

3. The method for preparing a biodegradable bactericide for oilfield use according to claim 1, characterized in that, In step S2, the mass-to-volume ratio of the pretreated hydroxypropyl guar gum to N,N-dimethylformamide is (10-15) g:(100-150) mL; the mass ratio of the pretreated hydroxypropyl guar gum to polycaprolactone-isocyanate prepolymer is (10-15):(6-8.4); the dropping rate of the polycaprolactone-isocyanate prepolymer is 0.08-0.12 mL / s; the temperature of the first reaction is 50℃, the stirring rate of the first reaction is 450-550 r / min, the reaction time is 4.5-5.5 h, and the concentration of the hydrochloric acid is 1-5 mol / L.

4. The method for preparing a biodegradable bactericide for oilfield use according to claim 1, characterized in that, In step S2, the mass ratio of ethylenediamine to polycaprolactone-isocyanate prepolymer is 2:(6-8.4); the temperature of the second reaction is 65-75℃, the stirring rate of the second reaction is 350-450 r / min, and the stirring time of the second reaction is 2.8-3.2 h; the mass ratio of adipic acid dihydrazide to ethylenediamine is 0.5:2; the temperature of the third reaction is 55-65℃, the stirring rate of the third reaction is 300-400 r / min, and the stirring time of the third reaction is 1.8-2.2 h; the temperature of the vacuum drying is 55-65℃, and the vacuum drying time is 3.5-4.5 h.

5. The method for preparing a biodegradable bactericide for oilfield use according to claim 1, characterized in that, In step S3, the molar volume ratio of phosphorus oxychloride to N,N-dimethylformamide is (100-120) mmol:(10-20) mL; the molar volume ratio of methylisothiazolinone to 1,2-dichloroethane is 100 mmol:100 mL; the dropping rate of the Vilsmeier reagent is 0.3-0.7 mL / min; the reaction temperature is 60℃, the stirring rate is 250-350 r / min, and the reaction time is 3 h; the organic phase drying step is as follows: the pH of the reaction solution is adjusted to 6-7 with 5% sodium carbonate, 50 mL of dichloroethane is added for extraction, the organic phase is collected, and 10 g of anhydrous magnesium sulfate is added to the organic phase and stirred for 1 h; the vacuum distillation temperature is 40℃ and the vacuum degree is 0.08-0.1 MPa.

6. The method for preparing a biodegradable bactericide for oilfield use according to claim 1, characterized in that, In step S4, the molar volume ratio of 2-aldehyde methyl-4-isothiazolin-3-one, dodecanol, p-toluenesulfonic acid, and N,N-dimethylformamide is 100 mmol : (110-130) mmol : (0.4-0.6) mmol : (40-60) mL; the reaction temperature is 115-125℃, the stirring rate is 350 r / min, and the reaction time is 3.5-4.5 h; the molar volume ratio of glacial acetic acid, N,N-dimethylethanolamine, and iodomethane is 1 mL : (140-160) mmol : (100-120) mmol; the stirring rate is 350 r / min, and the stirring time is 1-2 h.

7. The method for preparing a biodegradable bactericide for oilfield use according to claim 1, characterized in that, In step S4, the organic phase drying step is as follows: 90-110 mL of ethyl acetate is added to the reaction solution, and the mixture is stirred at 300 r / min for 5-15 min. After filtration, the filtrate is washed with 4-6% sodium bicarbonate solution until neutral, and then washed with 40-60 mL of saturated saline solution. 4-6 g of anhydrous magnesium sulfate is added to the organic phase and stirred for 0.5-1.5 h. The vacuum distillation temperature is 45-55℃, and the vacuum degree is 0.08-0.1 MPa. The crystallization operation is as follows: 25-35 mL of petroleum ether is added to the distilled solution, and the mixture is stirred at 300 r / min for 3-7 min at room temperature. The solution is allowed to stand for 0.5-1.5 h to allow crystals to precipitate naturally.

8. The method for preparing a biodegradable bactericide for oilfield use according to claim 1, characterized in that, In step S4, the volume ratio of propylene glycol to water in the propylene glycol-water solution is 1:3; the amount of polyethylene glycol-400 added is 0.3%-0.5% of the mass of the propylene glycol-water mixture; the spray drying is centrifugal spray drying, and the parameters of the spray drying are: inlet air temperature 55-65℃, outlet air temperature 40℃, feed rate 7-9mL / min, and atomization speed 18000-20000r / min.

9. The method for preparing a biodegradable bactericide for oilfield use according to claim 1, characterized in that, In step S5, the mass-to-volume ratio of dodecyl mercaptan, sodium hydroxide, and ethanol is (9-11) mmol:(11-13) mmol:(25-35) mL; the molar ratio of bromoethane to dodecyl mercaptan is (10-12):(9-11); the dropping rate of bromoethane is 0.02-0.04 mL / min; the reaction is carried out under reflux at 60-70℃ for 4.5-5.5 h; the organic phase drying step involves adding the reaction solution to 100 mL of ethyl acetate aqueous solution, wherein the volume ratio of ethyl acetate to water in the ethyl acetate aqueous solution is 1:1, separating the liquid, collecting the organic phase, washing the organic phase with 30 mL of saturated saline solution, adding 5 g of anhydrous sodium sulfate, and stirring for 1.8-2.2 h; the vacuum distillation temperature is 45-55℃, and the vacuum degree is 0.08-0.1 MPa.

10. The method for preparing a biodegradable bactericide for oilfield use according to claim 1, characterized in that, In step S6, the mass-to-volume ratio of the methylisothiazolinone quaternary ammonium salt, hydroxypropyl guar gum-polycaprolactone-ethylenediamine fragment copolymer, and propylene glycol-water mixture is (4.5-5.5) g : (9-11) g : (45-55) mL; the volume ratio of propylene glycol to water in the propylene glycol-water mixture is 1:3; the stirring temperature is 45-55℃, the stirring speed is 350-450 r / min, and the stirring... The drying time is 2 hours; the mass ratio of the dodecyl ethyl sulfide, sodium polyaspartate, and methylisothiazolinone quaternary ammonium salt is (2.8-3.2):(1.8-2.2):(4.5-5.5); the spray drying parameters are: inlet air temperature 80-90℃, outlet air temperature 48℃, feed rate 9-11mL / min, and atomization pressure 0.18-0.22MPa; the particle size of the biodegradable bactericide is 30-60μm.

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