Low-temperature composite pour point depressant for crude oil and preparation method thereof

Abstract

The application discloses a low-temperature composite pour point depressant for crude oil and a preparation method thereof. The pour point depressant comprises a comb-shaped copolymer which is copolymerized by monomers in the following molar percentages: C16-C30 alkyl methacrylate 50-70 mol%, polyethylene glycol monomethyl ether methacrylate 8-18 mol%, 4-hydroxycyclohexyl methacrylate 10-20 mol% and 2-(2-pyridyl dithio)ethyl methacrylate 0-5 mol%. The pour point depressant maintains excellent low-temperature compatibility in the temperature range of pipeline transportation in cold regions through specific monomer combination and molecular structure design. The steric hindrance provided by 4-hydroxycyclohexyl effectively hinders the formation of three-dimensional network structure of wax crystals, the hydroxyl group forms a hydrogen bond anchor with the surface of the wax crystal, and the disulfide bond realizes a self-repairing function. The pour point depressant has a pour point reduction range of 14-18 DEG C and is suitable for pipeline transportation of crude oil in cold regions.

Description

Technical Field

[0001] This invention relates to the field of petrochemical technology, specifically to a low-temperature composite crude oil pour point depressant and its preparation method. Background Technology

[0002] In recent decades, waxy crude oil has been produced in large quantities worldwide (such as in India, Egypt, Russia, and the North Sea), and accounts for a significant proportion of my country's crude oil production. High-pour-point crude oil is a typical paraffin-based crude oil with a high wax content, typically ranging from 10% to 50%; low asphaltenes and gum content, usually not exceeding 15%; a high pour point, generally between 30 and 50°C; and low high-temperature viscosity, generally below 100 mPa·s at 50°C. The paraffin in this type of crude oil can usually dissolve completely in the crude oil at a certain temperature. When the temperature drops to a certain point, the dissolved paraffin begins to precipitate as crystals; this temperature is called wax precipitation. During crude oil production, as the temperature decreases, the number of paraffin microcrystals precipitated in the crude oil gradually increases. Some of these microcrystals adsorb onto oil production equipment and transportation pipelines, aggregating and growing to form wax deposits, a major factor causing pipeline blockage. Others form a three-dimensional network structure within the crude oil, encapsulating it and causing it to lose its low-temperature fluidity and solidify. When the temperature falls below the solidification temperature, the viscosity of the crude oil increases sharply, increasing the load on oil wells and transportation pipelines. The aforementioned phenomena pose serious safety hazards to the production, transportation, and storage of crude oil. Currently, both domestically and internationally, physical and chemical methods are mainly used in crude oil pipeline transportation to address these issues. Physical methods primarily employ heating to lower the pour point, which involves huge investments, wastes a large amount of energy, and also presents challenges such as difficulty in restarting operations after a shutdown. Chemical methods mainly utilize pour point depressants, which are widely used due to their advantages such as lower equipment investment, simple operation, significant improvement in the low-temperature fluidity of crude oil, and the elimination of the need for post-treatment.

[0003] Currently, the most commonly used high-pour-point crude oil depressants are mainly high-molecular polymers with good oil solubility, which generally consist of two parts: polar groups and non-polar groups. The non-polar groups are usually long-chain alkyl groups, which can interact with wax crystal molecules through adsorption, nucleation, or co-crystallization; the polar groups, such as vinyl acetate (VA), maleic anhydride (MAH), and long-chain esters, inhibit the formation of a three-dimensional network structure of wax crystals by hindering wax crystal growth and changing the morphology and structure of wax crystals.

[0004] However, the effectiveness of pour point depressants is influenced by several factors. First, the composition of crude oil significantly affects the pour point depressing effect. Crude oil from different oil fields and regions exhibits varying compositions, leading to different pour point depressants having varying effects on different crude oils. Second, the structural characteristics of the polymer itself also affect its pour point depressing effect. For example, the length and branching degree of the polymer molecular chain affect its interaction with sediments and colloidal substances in crude oil. Furthermore, existing pour point depressants have the following technical limitations in low-temperature environments: (1) Insufficient low-temperature compatibility: Traditional pour point depressants are prone to phase separation or crystallization at pipeline transportation temperatures (-20℃ to -30℃) in cold regions, resulting in loss of pour point depressant activity; (2) Poor shear stability: Under high shear conditions such as pumping, polymer molecular chains are prone to irreversible breakage, resulting in permanent attenuation of the decondensation effect; (3) Poor interfacial compatibility with gum / asphalt in crude oil affects the uniformity of pour point depressant dispersion in crude oil.

[0005] Therefore, in practical applications, it is necessary to develop a new type of pour point depressant that is suitable for low-temperature environments, has good shear stability and interfacial compatibility, in order to improve the pour point depressing effect. Summary of the Invention

[0006] The purpose of this invention is to provide a low-temperature composite crude oil pour point depressant and its preparation method, so as to solve the technical problems of insufficient compatibility, poor shear stability and poor compatibility with crude oil interface of the existing pour point depressants in low-temperature environment.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a low-temperature composite crude oil pour point depressant, comprising a comb-type copolymer, wherein the comb-type copolymer has the following general formula: In this context, R1 represents either hydrogen or methyl, R2 is a long carbon chain with 16 to 30 carbon atoms, x:y:z:k = (50 to 70): (8 to 18): (10 to 20): (0 to 5), and n is a natural number between 4 and 10.

[0008] Specifically, the comb copolymer is copolymerized from the following monomers in molar percentages: 50-70 mol% C16-C30 alkyl methacrylate, 8-18 mol% polyethylene glycol monomethyl ether methacrylate, 10-20 mol% 4-hydroxycyclohexyl methacrylate, and 0-5 mol% 2-(2-pyridyl dithio)ethyl methacrylate.

[0009] In some preferred embodiments of the invention, the comb copolymer is copolymerized from monomers in the following molar percentages: C16-C30 alkyl methacrylates: 50~70 mol% Polyethylene glycol monomethyl ether methacrylate: 8~18 mol% 4-Hydroxycyclohexyl methacrylate: 10~20 mol% 2-(2-pyridyldithio)ethyl methacrylate: 0.5~5 mol%.

[0010] In some preferred embodiments of the present invention, the average molecular weight of the polyethylene glycol monomethyl ether methacrylate is 300-550 g / mol. When the average molecular weight is less than 300 g / mol, the temperature sensitivity of the polyether segments is lost, and an effective conformational transition of "low-temperature shrinkage-high-temperature stretching" cannot be formed in crude oil. When the average molecular weight is greater than 550 g / mol, the polyether segments are too long, and the solubility in dehydrated crude oil decreases with the molecular weight index. Phase separation easily occurs below -20°C, and the pour point depressant itself precipitates to form a PEG-rich phase. At the same time, when the side chains are too long, at low temperatures (-30°C) in cold regions, the PEG segments may crystallize themselves to form "pseudo-wax crystals," or easily co-crystallize with wax crystals and lose dispersibility.

[0011] In some preferred embodiments of the present invention, the number-average molecular weight of the comb copolymer is 5000-50000 g / mol, preferably 10000-30000 g / mol. This molecular weight range ensures that the pour point depressant has suitable solubility and dispersibility in crude oil.

[0012] Specifically, the disulfide bonds in 2-(2-pyridyldithio)ethyl methacrylate can be broken under shearing, and after standing, they can slowly recombine through molecular thermal motion, thus achieving the viscosity self-repair function after low temperature and high shear.

[0013] In some preferred embodiments of the present invention, the preparation method of the 4-hydroxycyclohexyl methacrylate includes the following steps: dissolving cyclohexane-1,4-diol in an anhydrous organic solvent, adding an acid-binding agent, and cooling to 0-10°C; under nitrogen protection, adding methacryloyl chloride dropwise, controlling the dropping rate to maintain the reaction temperature at 0-15°C, wherein the molar ratio of cyclohexane-1,4-diol to methacryloyl chloride is 1.2:1-1.5:1; after the dropwise addition is complete, reacting at room temperature for 2-5 hours, followed by filtration, washing, drying, and purification to obtain 4-hydroxycyclohexyl methacrylate. Preferably, the organic solvent is dichloromethane or toluene; the acid-binding agent is triethylamine or pyridine; the temperature is controlled at 0-5°C during the dropwise addition; and the purification is performed by silica gel column chromatography, with the eluent being a mixed solvent of petroleum ether and ethyl acetate.

[0014] In some preferred embodiments of the present invention, the C16-C30 alkyl methacrylate is selected from at least one of hexadecyl methacrylate, octadecyl methacrylate, eicosinate methacrylate, and dodecyl methacrylate.

[0015] In some preferred embodiments of the present invention, the low-temperature composite crude oil pour point depressant further includes synergists, solvents, and additives.

[0016] In some preferred embodiments of the present invention, the low-temperature composite crude oil pour point depressant comprises, by weight: 30-50 parts of comb-type copolymer, 8-10 parts of synergist, 60-100 parts of solvent, and 0-3 parts of additives.

[0017] In some preferred embodiments of the present invention, the synergist is ethylene-vinyl acetate copolymer (EVA), wherein the vinyl acetate (VA) content is 20-30% and the molecular weight is 2000-3000.

[0018] In some preferred embodiments of the present invention, the solvent is heavy aromatic naphtha or diesel oil; the additives include 1-2 parts of dispersant, 0.2-0.5 parts of antioxidant and 0.1-0.3 parts of wax inhibitor.

[0019] Secondly, the present invention provides a method for preparing the above-mentioned low-temperature composite crude oil pour point depressant, comprising the following steps: C16-C30 alkyl methacrylate monomers were dissolved in an organic solvent and subjected to a first-stage polymerization reaction under the action of an initiator at a reaction temperature of 70-80°C for 50-70 min, forming primary segments of hydrophobic long-chain alkyl esters. Polyethylene glycol monomethyl ether methacrylate, 4-hydroxycyclohexyl methacrylate, and 2-(2-pyridyl dithio)ethyl methacrylate were mixed and dissolved with the remaining initiator to prepare a mixed dropping solution. The temperature was raised to 80-90°C, and the mixed dropping solution was added dropwise to the aforementioned reaction system at a rate of 1.5-2.5 L / h. After the addition was completed, the reaction was continued for 3-5 h. After the reaction was completed, the solution was cooled to 35-45°C, a stabilizer was added, and the reaction solution was poured into cold methanol to precipitate. After filtration, washing, and drying, the comb-shaped copolymer was obtained.

[0020] In some preferred embodiments of the present invention, the organic solvent is anhydrous toluene; the initiator is benzoyl peroxide (BPO), and the amount used is 0.5 to 1.5% of the total weight of the monomer; the first polymerization reaction uses 60 to 80% of the total amount of initiator.

[0021] In some preferred embodiments of the present invention, the stabilizer is hydroquinone monomethyl ether (MEHQ), and the amount used is 0.03~0.08 wt% of the weight of the reaction solution.

[0022] Thirdly, the present invention provides a method for preparing the above-mentioned low-temperature composite crude oil pour point depressant, comprising the following steps: (1) Add the comb-type copolymer to part of the solvent and heat to 40~50℃ and stir to dissolve; (2) Heat to 60~70℃, add synergist, and stir until completely dissolved; (3) Cool down to below 30℃, add the additives, and stir to disperse evenly; (4) Add the remaining solvent and adjust to the target viscosity.

[0023] In some preferred embodiments of the present invention, the target viscosity is 500~1500 mPa·s at 25°C, preferably 800 mPa·s.

[0024] Beneficial effects

[0025] Compared with the prior art, the present invention has the following beneficial effects: (1) Excellent low-temperature compatibility and molecular chain mobility: The molecular weight of polyethylene glycol monomethyl ether methacrylate used in this invention is controlled at 300~550 g / mol. Its polyether side chain still maintains micro Brownian motion capability at a cold temperature of -30℃ (glass transition temperature Tg≈-60℃), avoiding low-temperature freezing failure. At the same time, this molecular weight range ensures the solubility boundary in dehydrated crude oil, preventing phase separation or self-crystallization tendency caused by excessively long chain segments, so that the pour point depressant remains in a homogeneous solution state under pipeline transportation conditions of -20℃~-30℃.

[0026] (2) Synergistic effect of steric hindrance and anchoring dual functions: The rigid cyclohexyl structure of 4-hydroxycyclohexyl methacrylate provides an effective physical barrier, blocking the growth of the three-dimensional network structure of wax crystals; its hydroxyl functional groups form hydrogen bonds with the polar defects and colloidal components on the surface of wax crystals in crude oil, enhancing interfacial compatibility. This monomer achieves the functions that traditional formulations require separate steric hindrance monomers and polar monomers with a single component, significantly reducing raw material costs and process complexity.

[0027] (3) Shear stability and performance retention: When using functional unsaturated monomers containing disulfide bonds (such as 2-(2-pyridyl dithio)ethyl methacrylate), the disulfide bonds can selectively break under high shear conditions such as pumping, reducing instantaneous viscosity; under low shear or static conditions, slow recombination is achieved through molecular thermal motion, partially restoring the network structure, thereby alleviating the permanent loss of pour point depreciation efficiency caused by shear thinning, and ensuring that the pour point depreciation activity retention rate after long-distance pipeline transportation is >90%.

[0028] (4) Controllable molecular structure and broad-spectrum adaptability: The present invention adopts a segmented polymerization process, first polymerizing hydrophobic long-chain alkyl esters to form the main chain skeleton, and then adding polar monomers to form side chains, ensuring the reasonable distribution of each functional group on the molecular chain; by adjusting the carbon number ratio of C16-C30 alkyl methacrylates, precise matching can be achieved for the wax carbon number distribution of different crude oils, and the pour point reduction can reach 14-18℃. The pour point depressant of the present invention reduces the pour point of Daqing crude oil by 14-18℃, with a low-temperature (-25℃) viscosity recovery rate >90% and a yield stress <10 Pa; proving the synergistic effect of the low-temperature composite crude oil pour point depressant of the present invention. Attached Figure Description

[0029] Figure 1 This is the general structural formula of the comb-type copolymer of the present invention; Figure 2 The infrared spectrum of the comb copolymer prepared in Example 1 of this invention is shown. Detailed Implementation

[0030] The technical solutions 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.

[0031] The raw materials used in the examples and comparative examples are described below: Octadecyl methacrylate: 99% purity, Zhongshan Yuanda New Materials Co., Ltd.; 2,2-dimethyl methacrylate: 85% purity, Guangdong Wengjiang Chemical Reagent Co., Ltd.; Polyethylene glycol monomethyl ether methacrylate 1: average molecular weight 475, P109711, Shanghai Aladdin Biochemical Technology Co., Ltd. Polyethylene glycol monomethyl ether methacrylate 2: average molecular weight 300, P816112, Shanghai Maclean Biochemical Technology Co., Ltd. Polyethylene glycol monomethyl ether methacrylate 3: average molecular weight 950, P816114, Shanghai Maclean Biochemical Technology Co., Ltd. Polyethylene glycol monomethyl ether methacrylate 4: Triethylene glycol methyl ether methacrylate, molecular weight 232,729,841, Sigma-Aldrich; 2-(2-pyridyldithio)ethyl methacrylate: Henan Alpha Chemical Co., Ltd.; 4-Hydroxycyclohexyl methacrylate: Prepared in-house, the preparation method is as follows: Under a dry nitrogen atmosphere, cyclohexane-1,4-diol (1.3 mol) and MEHQ (0.1 g) were dissolved in 500 mL of anhydrous DCM and transferred to a three-necked flask (equipped with a mechanical stirrer, a constant-pressure dropping funnel, a cryostat, and a nitrogen delivery tube). The mixture was cooled to 0–5 °C (ice-salt bath), and triethylamine (1.05 mol) was added in one go. Methacrylamide chloride (1.0 mol) was dissolved in 100 mL of anhydrous DCM and transferred to a constant-pressure dropping funnel. The solution was slowly added dropwise to the reaction system, controlling the dropping rate to keep the reaction temperature below 10 °C (the addition was completed in approximately 2–3 hours). An excess of the diol ensured that MAC preferentially reacted with one hydroxyl group, reducing diester byproducts. After the addition was complete, the mixture was stirred at 0–5 °C for 1 hour, then the temperature was raised to room temperature (20–25 °C) and the reaction continued for 3–4 hours. Complete MAC consumption was confirmed by TLC monitoring (developing solvent: petroleum ether / ethyl acetate = 2:1, Rf values: diester 0.8, monoester 0.4, diol 0.1). Triethylamine hydrochloride (white precipitate, byproduct) was removed by vacuum filtration, and the filter cake was washed with DCM (2 × 50 mL). The filtrates were combined and washed twice with 5% NaHCO3 solution (300 mL) (to remove residual HCl and MAC), and then with saturated NaCl solution (300 mL) until neutral (pH≈7). The organic phase was dried over anhydrous MgSO4 for 4 hours. DCM was removed by vacuum distillation (40℃ / -0.09 MPa) to obtain a pale yellow oily crude product. Silica gel column chromatography (petroleum ether / ethyl acetate gradient elution, 3:1→1:1) was performed, and the monoester fraction (Rf≈0.4) was collected to give a colorless, transparent, viscous liquid in 77.5% yield. The structure of the product was confirmed by ¹H NMR (CDCl3, 400MHz): δ5.73 (s, 1H, =CH2), δ5.60 (s, 1H, =CH2), δ4.74 (tt, 1H, -O-CH<cyclohexyl H-1), δ3.77 (m, 1H, HO-CH<cyclohexyl H-4), δ3.33 (br s, 1H, -OH), δ1.95 (s, 3H, =C-CH3), δ1.65-1.79 (ddd, 8H, cyclohexyl H-2, H-3, H-5, H-6).

[0032] Dispersants: Jeffamine M-600 (polyetheramine); Huntsman; Antioxidant: BHT, commercially available; Wax inhibitor: Dodecyl phosphate, commercially available.

[0033] Unless otherwise specified, all components and raw materials used in the embodiments and comparative examples of this invention are commercially available, and the components and raw materials used in each parallel experiment or comparative experiment are the same, and the experimental methods used are all carried out under the same conditions.

[0034] Example 1

[0035] A low-temperature composite crude oil pour point depressant, by weight, comprises a comb-type copolymer, having the following properties: Figure 1 The structural formula shown is specifically derived from the copolymerization of the following monomers in the following molar percentages: 67 mol of C16-C30 alkyl methacrylate; 13 mol of polyethylene glycol monomethyl ether methacrylate; 15 mol of 4-hydroxycyclohexyl methacrylate; and 5 mol of ethyl methacrylate-2-(2-pyridyl dithio)methacrylate.

[0036] C16-C30 alkyl methacrylates are octadecyl methacrylate and dodecyl methacrylate in a molar ratio of 45:22; Polyethylene glycol monomethyl ether methacrylate is polyethylene glycol monomethyl ether methacrylate 1; The method for preparing the comb-type copolymer is as follows: Before use, all monomers were subjected to a neutral alumina column to remove polymerization inhibitors. 30 L of anhydrous toluene was added to the reactor, and stirring (80 rpm) and nitrogen purging (5 L / min for 30 min) were initiated. Octadecyl methacrylate and dodecyl methacrylate were added and stirred until dissolved. The temperature was raised to 75°C, and benzoyl peroxide (BPO) was added as an initiator (70% of the total initiator, approximately 0.20 kg), and timing was started. The reaction was maintained at 75°C for 60 min (conversion rate approximately 25-30%), forming the primary segments of hydrophobic long-chain alkyl esters. In this stage, the hydrophobic monomers preferentially polymerized, establishing the main chain backbone. Polyethylene glycol monomethyl ether methacrylate, 4-hydroxycyclohexyl methacrylate, 2-(2-pyridyl dithio)ethyl methacrylate, and the remaining BPO (30%, 0.09 kg) were mixed and dissolved in 15 L of anhydrous toluene to prepare a mixed dropping solution. The mixture was heated to 85 °C and slowly added dropwise at a rate of 2 L / h (to be completed in approximately 7.5 h). After the addition was complete, the reaction was maintained at 85 °C for another 4 h. The monomer conversion was monitored by FT-IR. When the double bond peak (1635 cm⁻¹) was reached... -1 The reaction endpoint was considered reached when the strength decreased by >95%. The reaction solution was cooled to 40°C, and MEHQ (hydroquinone monomethyl ether, 0.05 wt%) was added as a stabilizer. The reaction solution was slowly poured into 10 times its volume of cold methanol (-20°C), and the mixture was stirred continuously until the copolymer precipitated as a white flocculent precipitate. The white solid filter cake was collected using a plate and frame filter press (400 mesh filter cloth). The filter cake was washed twice with cold methanol (-10°C) (10 L each time) to remove residual initiator, unreacted monomers, and solvent. The mixture was transferred to a vacuum drying oven (40°C / -0.095 MPa, 48 h) until constant weight was achieved. Yield: 88.2%, GPC number-average molecular weight: 21700.

[0037] When using, heat 30 parts of the comb copolymer to 40~50℃, stir and dissolve it in 70 parts of -20# diesel solvent to prepare a homogeneous mother liquor for later use.

[0038] Example 2

[0039] A low-temperature composite crude oil pour point depressant, compared with Example 1, differs in that the polyethylene glycol monomethyl ether methacrylate is polyethylene glycol monomethyl ether methacrylate 2, and the GPC-detected number-average molecular weight is 18900.

[0040] Example 3

[0041] A low-temperature composite crude oil pour point depressant, compared with Example 1, differs in that the comb-type copolymer is copolymerized from the following molar percentages of monomers: 70 mol of C16-C30 alkyl methacrylate; 15 mol of polyethylene glycol monomethyl ether methacrylate; 10 mol of 4-hydroxycyclohexyl methacrylate; 5 mol of ethyl methacrylate-2-(2-pyridyl dithio)methacrylate, with a GPC-detected number-average molecular weight of 22,500.

[0042] C16-C30 alkyl methacrylates are octadecyl methacrylate and dodecyl methacrylate in a molar ratio of 45:25.

[0043] Example 4

[0044] A low-temperature composite crude oil pour point depressant, compared with Example 1, differs in that the comb-type copolymer is copolymerized from the following molar percentages of monomers: 65 mol of C16-C30 alkyl methacrylate; 15 mol of polyethylene glycol monomethyl ether methacrylate; 20 mol of 4-hydroxycyclohexyl methacrylate; 0 mol of 2-(2-pyridyl dithio)ethyl methacrylate, with a GPC-detected number-average molecular weight of 21000.

[0045] C16-C30 alkyl methacrylates are octadecyl methacrylate and dodecyl methacrylate in a molar ratio of 45:20.

[0046] Example 5

[0047] A low-temperature composite crude oil pour point depressant, compared with Example 1, differs in that the low-temperature composite crude oil pour point depressant, by weight, comprises 30 parts of comb-type copolymer, 8 parts of synergist, 60 parts of solvent, and 2 parts of additive.

[0048] The synergist is ethylene-vinyl acetate copolymer (EVA) with a VA content of 25% and a molecular weight of 2500; The solvent is heavy aromatic naphtha; The additives are 1.5 parts dispersant, 0.3 parts antioxidant, and 0.2 parts wax inhibitor.

[0049] The comb-type copolymer was added to heavy aromatic naphtha, heated to 45°C, and stirred (200 rpm) for 2 hours until completely dissolved; the temperature was raised to 65°C, EVA was added, and stirring was continued for 1 hour until a homogeneous solution was formed; the temperature was lowered to 25°C, and 1.5 parts of dispersant, 0.3 parts of antioxidant, and 0.2 parts of wax inhibitor were added in sequence, and stirred for 30 minutes; 20 parts of heavy aromatic naphtha were added to adjust the viscosity to 800 mPa·s (25°C) to obtain a pour point depressant concentrate that can be directly pumped.

[0050] The finished product remained homogeneous without precipitation at -30℃ and showed no stratification after 7 days of storage.

[0051] Comparative Example 1 A crude oil pour point depressant, differing from Example 1 in that it is copolymerized from the following molar percentage of monomers: 100 mol% C16-C30 alkyl methacrylates. C16-C30 alkyl methacrylates are octadecyl methacrylate and dodecyl methacrylate in a molar ratio of 60:40.

[0052] Comparative Example 2 A crude oil pour point depressant, which differs from Example 1 in that it comprises a comb copolymer copolymerized from the following molar percentages of monomers: 80 mol of C16-C30 alkyl methacrylate; 15 mol of 4-hydroxycyclohexyl methacrylate; and 5 mol of ethyl methacrylate-2-(2-pyridyl dithio)methacrylate.

[0053] C16-C30 alkyl methacrylates are octadecyl methacrylate and dodecyl methacrylate in a molar ratio of 50:30; Comparative Example 3 A crude oil pour point depressant, which differs from Example 1 in that the polyethylene glycol monomethyl ether methacrylate is polyethylene glycol monomethyl ether methacrylate 3.

[0054] Comparative Example 4 A crude oil pour point depressant, which differs from Example 1 in that the polyethylene glycol monomethyl ether methacrylate is polyethylene glycol monomethyl ether methacrylate 4.

[0055] Comparative Example 5 Commercially available pour point depressant: Evonik Viscoplex® 10-330.

[0056] Performance testing The target crude oil for the pour point depressants prepared in the examples and comparative examples was Daqing crude oil. The component content of the oil sample is shown in Table 1. The test oil was a blend of No. 1 and No. 2 in a mass ratio of 1:1.

[0057] Table 1. Composition content of Daqing crude oil samples

[0058] 1. FT-IR Analysis: The structure of the pour point depressant was analyzed using a TENSOR27 infrared spectrometer (Bruker, Germany). Test conditions: spectral range: 4000-500 cm⁻¹ -1 Number of scans: 32. This experiment used the smear method to prepare infrared samples: First, KBr was dried in an oven to remove moisture. Then, KBr was ground into a fine powder, and blank KBr sheets were prepared using the compression method and placed in the oven for later use. A small amount of the solid polymerization product was dissolved in dichloromethane, and then the solution was dropped onto the prepared KBr sheet. After the dichloromethane evaporated, a KBr sheet with the sample film attached was obtained.

[0059] 2. Pour Point: Referring to the petrochemical industry standard - Determination of Pour Point of Petroleum Products (GB / T510-2018), the pour point of crude oil samples with added pour point depressants was tested using the SYD-510F1 multi-functional low-temperature tester from Shanghai Changji Geological Instrument Co., Ltd.

[0060] 3. Low-temperature solubility: Using a low-temperature constant-temperature water bath (temperature control accuracy ±0.5℃, minimum -40℃) and stoppered colorimetric tubes (100 mL, graduation accuracy 1 mL), the pour point depressant mother liquor (30 wt% diesel solution) was placed in a constant temperature environment of -30℃±1℃ and left to stand for 7 days. Visual observation was conducted to check for flocculation, stratification, crystallization, or sudden viscosity changes to verify the phase stability of the pour point depressant under extremely cold conditions. The performance evaluation level was: Excellent – ​​The solution is clear and transparent, without turbidity, layering, or sedimentation, and flows evenly after slight shaking; Good – Slightly cloudy but with no visible sediment; no layering at the bottom after standing; disperses evenly after shaking. General – visibly turbid or slightly flocculated, with a small amount of sediment (<1% by volume) after standing, which partially disperses after shaking; Poor – obvious stratification (clear upper layer / turbid lower layer) or flocculation and sedimentation (1-5% by volume), which cannot be completely dispersed after shaking; Poor – Completely separated or solidified into a gel-like consistency, with no flow when shaken.

[0061] 4. Maintenance of Low-Temperature Pour Point Depressant Activity: A SYD-510F1 multi-functional low-temperature tester (or an equivalent low-temperature test chamber, temperature control range -40℃ to +50℃) was used in conjunction with a pour point tester. The pour point depressant mother liquor was stored at -20℃±1℃ under sealed and light-proof conditions for 30 days. Samples were taken periodically (on the 7th, 15th, and 30th days), and the pour point depressant efficiency against Daqing crude oil (pour point reference value 27℃) was tested according to GB / T 510-2018 to verify the chemical stability of the MPEG-MA side chain and disulfide bonds during long-term low-temperature storage.

[0062] 5. Low-temperature shear stability: A rotational rheometer (Anton Paar MCR 302, equipped with a low-temperature circulating liquid nitrogen / alcohol bath system) was used. Under constant temperature conditions of -25℃±0.1℃, a high shear rate of 1000 s⁻¹ was first applied to the crude oil sample with additives. -1 It lasted for 60 s, then dropped to a low shear rate of 0.1 s. -1 The viscosity recovery rate was measured.

[0063] 6. Crude oil low-temperature fluidity test: A Brookfield PVS low-temperature rheometer was used. Yield stress test (stress scan mode 0.01-50 Pa) was conducted under constant temperature conditions of -25℃±0.1℃ to verify the macroscopic fluidity of crude oil under pipeline transportation conditions in cold regions.

[0064] The test results are shown in Table 2.

[0065] Table 2. Performance test results of pour point depressants in the examples and comparative examples.

[0066] like Figure 2 As shown, the results indicate that the comb-type copolymer at 3408 cm⁻¹ -1 A broad absorption peak at 2923 cm⁻¹ appears, attributed to the OH stretching vibration of the secondary hydroxyl group associated with hydrogen bonding in the 4-hydroxycyclohexyl methacrylate unit. -1 and 2852 cm -1 The position shows strong double peaks at 1722 cm⁻¹, representing both asymmetric and symmetric stretching vibrations of the long-chain methylene groups of octadecyl methacrylate and dodecyl methacrylate. -1 The strongest absorption peak of the C=O stretching vibration of the ester carbonyl group, common to all methacrylate units, was detected at 1637 cm⁻¹. -1 The C=C stretching vibration of the pyridine ring in ethyl methacrylate-2-(2-pyridyl dithio)methacrylate is visible at 1462 cm⁻¹. -1 With 1380 cm -1 These correspond to the scissor bending vibration of the long-chain methylene group and the symmetric bending vibration of the α-methyl group of methacrylate, respectively; 1322 cm -1 and 1294 cm -1The in-plane bending vibration of the CH group of the cyclohexyl unit of 4-hydroxycyclohexyl methacrylate and the torsional vibration of the long-chain alkyl methylene group were detected at 1109 cm⁻¹. -1 A strong characteristic absorption peak of COC ether bond in the side chain of methoxy polyethylene glycol methacrylate appears at 949 cm⁻¹. -1 847 cm -1 The position represents the out-of-plane bending vibration of CH in cyclohexyl and long-chain alkyl groups; 718 cm -1 A characteristic in-plane rocking vibration peak of a long-chain alkyl methylene unit was detected at 646 cm⁻¹. -1 The vibrations are attributed to stretching vibrations of the CS bond in the disulfide monomer or bending vibrations of the pyridine ring skeleton. These spectroscopic features confirm that the copolymer simultaneously contains long-chain alkyl side chains, polyethylene glycol methyl ether side chains, a 4-hydroxycyclohexyl structure, and a methacrylate backbone, consistent with the designed comb-type copolymer chemical structure.

[0067] The test results in Table 2 show that: (1) The pour point depressants in Examples 1-5 all exhibited excellent pour point depressing effects, with a pour point reduction of 14-18℃, which was significantly better than that in Comparative Examples 1-5. This indicates that the comb copolymer composition design of the present invention (a combination of C16-C30 alkyl methacrylate, polyethylene glycol monomethyl ether methacrylate, 4-hydroxycyclohexyl methacrylate and functional unsaturated monomers) has a synergistic effect.

[0068] (2) Comparative Example 1 (without polyethylene glycol monomethyl ether methacrylate and 4-hydroxycyclohexyl methacrylate) had the worst pour point depressing effect, with a pour point reduction of only 6°C and poor low-temperature solubility. This indicates that polyethylene glycol monomethyl ether methacrylate and 4-hydroxycyclohexyl methacrylate are crucial for improving the low-temperature compatibility and pour point depressing effect of the depressant.

[0069] (3) Although Comparative Example 2 (without polyethylene glycol monomethyl ether methacrylate) contains 4-hydroxycyclohexyl methacrylate, its low-temperature solubility is still poor, and its pour point depressant effect is significantly lower than that of the Example. This further demonstrates the key role of polyethylene glycol monomethyl ether methacrylate in improving low-temperature compatibility. Meanwhile, although Comparative Example 2 contains disulfide monomers, it lacks the thermosensitive polyether side chains of MPEG-MA. After high shear cessation, although the disulfide bonds can slowly repair the broken polymer backbone, the lack of the conformational shrinkage-stretching dynamic response of MPEG-MA at low temperatures prevents the redispersibility of the aggregated wax crystals. The three-dimensional wax crystal network is rapidly rebuilt after shear cessation, at a rate much faster than the chemical repair rate of the disulfide bonds, resulting in the inability to effectively restore the macroscopic viscosity.

[0070] (4) Although both Comparative Example 3 and Comparative Example 4 had poor pour point reduction effects, their failure mechanisms were different: Comparative Example 3 had excessively long polyether segments, which co-crystallized with high carbon wax (C26+) in crude oil at low temperatures, and its solubility decreased at -30℃, leading to phase separation and loss of dispersion activity; its redispersibility also decreased accordingly; Comparative Example 4 had excessively short polyether segments, which lost its thermo-responsiveness and could not form effective conformational shrinkage anchoring and steric hindrance at low temperatures, and the short chain polar anchoring points were insufficient, making it difficult to resist the competitive adsorption of colloidal substances. At the same time, it lacked thermo-responsiveness and could not form an effective steric hindrance brush layer at low temperatures. After shearing stopped, the wax crystal network was quickly rebuilt.

[0071] (6) Compared with Example 4, Example 1 containing disulfide bonds has better shear stability. Although the shear stability of Example 4 decreased, the drop in pour point was comparable to that of Example 1 containing disulfide bonds, proving that disulfide bonds mainly affect dynamic shear recovery and have no significant negative impact on static pour point reduction.

[0072] (7) Example 5 (containing synergist formulation) has the best pour point reduction effect, with a pour point reduction of up to 18°C, indicating that there is a synergistic effect between the comb copolymer and the EVA synergist.

[0073] In summary, the low-temperature composite crude oil pour point depressant of the present invention achieves excellent low-temperature compatibility, pour point depressing effect and shear stability through specific monomer composition and molecular structure design, and is suitable for crude oil pipeline transportation in cold regions.

[0074] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A low-temperature composite crude oil pour point depressant, comprising a comb-type copolymer, characterized in that, The comb-type copolymer has the following general formula: In this context, R1 represents either hydrogen or methyl, R2 is a long carbon chain with 16 to 30 carbon atoms, x:y:z:k = (50 to 70): (8 to 18): (10 to 20): (0 to 5), and n is a natural number between 4 and 10.

2. The low-temperature composite crude oil pour point depressant as described in claim 1, characterized in that, The comb copolymer is copolymerized from the following monomers in the following molar percentages: 50-70 mol of C16-C30 alkyl methacrylate; 8-18 mol of polyethylene glycol monomethyl ether methacrylate; 10-20 mol of 4-hydroxycyclohexyl methacrylate; and 0.5-5 mol of ethyl methacrylate-2-(2-pyridyl dithio)methacrylate.

3. The low-temperature composite crude oil pour point depressant according to claim 1, characterized in that, The average molecular weight of the polyethylene glycol monomethyl ether methacrylate is 300~550 g / mol, and the number average molecular weight of the comb copolymer is 5000~50000 g / mol.

4. The low-temperature composite crude oil pour point depressant according to claim 1, characterized in that, The preparation method of the 4-hydroxycyclohexyl methacrylate includes the following steps: Cyclohexane-1,4-diol was dissolved in an anhydrous organic solvent, an acid-binding agent was added, and the temperature was lowered to 0-10°C. Under nitrogen protection, methacryloyl chloride was added dropwise, and the dropping rate was controlled to maintain the reaction temperature at 0-15°C. The molar ratio of cyclohexane-1,4-diol to methacryloyl chloride was 1.2:1 to 1.5:

1. After the addition was complete, the reaction was allowed to proceed at room temperature for 2-5 hours. After filtration, washing, drying, and purification, 4-hydroxycyclohexyl methacrylate was obtained.

5. The low-temperature composite crude oil pour point depressant according to claim 1, characterized in that, The C16-C30 alkyl methacrylate is selected from at least one of hexadecyl methacrylate, octadecyl methacrylate, ecicoacrylate, and dodecyl methacrylate.

6. The low-temperature composite crude oil pour point depressant according to claim 1, characterized in that, It also includes synergists, solvents, and additives.

7. The low-temperature composite crude oil pour point depressant according to claim 6, characterized in that, By weight, it includes: 30-50 parts of comb copolymer, 8-10 parts of synergist, 60-100 parts of solvent, and 0-3 parts of additives.

8. The low-temperature composite crude oil pour point depressant according to claim 6, characterized in that, The synergist is an ethylene-vinyl acetate copolymer, the solvent is heavy aromatic naphtha or diesel oil, and the additives include 1-2 parts of dispersant, 0.2-0.5 parts of antioxidant and 0.1-0.3 parts of wax inhibitor.

9. The preparation method of the low-temperature composite crude oil pour point depressant according to any one of claims 1 to 8, characterized in that, The process includes the following steps: C16-C30 alkyl methacrylate monomers are dissolved in an organic solvent and subjected to a first-stage polymerization reaction under the action of an initiator at a reaction temperature of 70-80°C for 50-70 min to form primary segments of hydrophobic long-chain alkyl esters; polyethylene glycol monomethyl ether methacrylate, 4-hydroxycyclohexyl methacrylate, and 2-(2-pyridyl dithio)ethyl methacrylate are mixed and dissolved with the remaining initiator to prepare a mixed dropwise solution; the temperature is raised to 80-90°C, and the mixed dropwise solution is added dropwise to the aforementioned reaction system, and the reaction continues for 3-5 h after the addition is complete; after the reaction is completed, the temperature is cooled to 35-45°C, a stabilizer is added, the reaction solution is poured into cold methanol to precipitate, and after filtration, washing, and drying, the comb-shaped copolymer is obtained.

10. A method for preparing a low-temperature composite crude oil pour point depressant according to any one of claims 6 to 8, characterized in that, Includes the following steps: (1) Add the comb-type copolymer to part of the solvent and heat to 40~50℃ and stir to dissolve; (2) Heat to 60~70℃, add synergist, and stir until completely dissolved; (3) Cool down to below 30℃, add the additives, and stir to disperse evenly; (4) Add the remaining solvent and adjust to the target viscosity.

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