Study on synthesis and properties of polyacrylate wax inhibitor

Synthesis and properties of polyacrylate ester paraffin inhibitior based on polyacrylate ester start from dodecanol, tetradecanol, hexadecanol, octadecanol respectively were introduced in this paper. Hexadecyl polyacrylic showed the most potent paraffin inhibition, and then the optimum reaction condition of it was ascertained. The percentage inhibition of hexadecyl polyacrylic, synthesized under the optimized conditions, reached to 79.3%. Then crosslinked polyacrylate ester paraffin inhibitiors were synthesized and screened by static wax precipitation experiment, and find the percentage inhibition of crosslinked hexadecyl polyacrylic reached to 88.4%.


Introduction
The wax exists in the dissolved state in the formation reservoir.During the mining process, the waxy crude oil rises along the tubing.With the continuous decrease of pressure and temperature and the continuous escape of light components, the wax in the crude oil begins to crystallize and precipitate, and continues to deposit.When the crude oil temperature is lower than the critical cloud point temperature, the wax crystal molecules will diffuse to the solid surface, and begin to form a solid three-dimensional network structure with this as the center.The wax crystals are thin or needle-like adsorbed on the wall of the tube to form wax deposition.Wax deposition has a great influence on the production, gathering and storage of crude oil, which can lead to the decline of oil well production and even lead to shutdown [1].Wax deposition is mainly divided into three processes: wax crystal formation, wax crystal growth and precipitation, and wax deposition.Controlling wax deposition in any step can prevent wax deposition in oil wells.
At present, there are three types of paraffin inhibitors used in oil fields: polycyclic aromatic hydrocarbon type, surface active agent type and polymer type.The non-polar part of the polymer type paraffin inhibitor crystallizes with wax, while the polar link distorts the crystal form of the wax crystal, which is not conducive to the continuous growth of the wax crystal to form a network structure, so it has excellent anti-wax effect [2][3][4].In this paper, a series of paraffin inhibitors of polyacrylic acid high-carbon alcohol ester were synthesized.Polyhexadecyl acrylate was selected as paraffin inhibitor by static paraffin inhibition method, and the synthesis conditions, dosage and other factors were investigated.

Synthesis of high-carbon acrylate
High-carbon alcohols (dodecanol, tetradecanol, hexadecanol and octadecanol) were added to the threeport flask and completely melted by heating.Then 1.2 times the amount of acrylic acid, 0.6 % inhibitor and 1 % catalyst were added and heated to 110 °C for 6 hours.After the reaction, cool, add ethyl acetate, wash with saturated sodium carbonate solution to weak alkaline, and then wash with saturated sodium chloride solution to neutral, separate the organic layer, add anhydrous calcium chloride to dry, filter, evaporate the solvent to obtain acrylic high carbon alcohol ester.

Determination experiment of wax prevention rate
Accurately weigh 100 g paraffin and 300 g 0# diesel in a 500 ml beaker, put it in an electric thermostatic water bath, control it at 50 °C, and stir it until the paraffin is completely dissolved and sealed for later use.Select multiple iron sheets with similar external surface area, smooth the surface until the surface is rust-free, and then put them in alcohol.After a few hours, it was taken out and dried.Three pieces with similar surface area were selected and numbered, weighed and recorded respectively.Method for determination of wax prevention rate (static wax prevention method) [6]: Accurately weigh the quality of steel sheets (including fixed fine lines), measure 50 ml of wax-containing oil in an iodometric bottle, add a certain amount of wax prevention agent, steel sheets are suspended in oil, sealed with a lid, at a constant temperature of 60 °C for 1 h, naturally cool to 30 °C, remove the steel sheet and accurately weigh the quality of the steel sheet.The wax inhibition rate η is calculated by the following formula.
(1) where η is the wax prevention rate, %; m0 is the mass of steel sheet, m1 is the mass of steel sheet without wax inhibitor, and m2 is the mass of steel sheet with wax inhibitor.

Synthesis and optimisation of polyacrylic acid polycarbol ester anti-waxing agents
The carbon chain length of high-carbon alcohols in monomers is the basic factor affecting the antifouling effect.Firstly, the antifouling agents with different monomer polymerisation were selected, and their dosage was fixed at 150 mg/L to evaluate and compare the antifouling effect.The results are shown in Fig. 1.From the figure, it can be seen that the antifouling effect of poly(cetyl acrylate) was the best, 84.5%.Therefore, the synthesis conditions of poly(hexadecyl acrylate) were optimized.3.1.1.Effect of reaction temperature on the anti wax effect of polyacrylic acid hexadecanol ester.In the free radical polymerization reaction of olefinic monomers, the reaction temperature mainly affects the decomposition rate of the initiator.The lower the reaction temperature, the slower the decomposition rate of the initiator, and the larger the molecular weight of the generated polymer.There is a certain relationship between the molecular weight of the polymer and its anti wax effect.Therefore, the anti wax rate of polyacrylic acid hexadecanol ester synthesized at different reaction temperatures (reaction time 6 hours) was experimentally studied, and the results are shown in Figure 2. As can be seen from the figure, when the reaction temperature is 60 ℃, the wax inhibitor obtained has the highest wax prevention rate.Therefore, in the following synthesis, the reaction temperature is set at 60 ℃.

Effect of reaction time on the anti wax effect of polyacrylic acid hexadecanol ester.
The reaction time affects the degree of polymerization and conversion rate, and the effect of reaction time on the wax prevention rate of polyacrylic acid hexadecanol ester is shown in Figure 3.As shown in the figure, after the reaction time reaches 4 hours, the anti wax rate of the polymer basically does not change and is above 86%.Therefore, the reaction time is selected as 4 h.

The effect of polyacrylic acid hexadecanol ester dosage on the anti wax effect.
The amount of anti wax agent has a significant impact on the anti wax rate, and the anti wax effect of polyacrylic acid hexadecanol ester at different amounts is shown in Fig. 4. As shown in the figure, as the amount of wax inhibitor increases, the wax prevention rate also increases accordingly.When the amount of wax inhibitor is 150 mg/L, the wax prevention rate reaches 89.3%.Continuing to increase the dosage, the wax prevention rate remains basically unchanged, so the optimal dosage is 150 mg/L.The low wax prevention rate at low dosage is due to the insufficient amount of action to effectively disperse wax crystals.Before the eutectic effect is exerted, a large amount of wax crystals have already precipitated, and adsorption can only be used to disperse wax crystals, which inevitably has a limited effect, thus affecting the wax prevention effect [5].

Anti-waxing effect of N,N'-dimethylene acrylamide-crosslinked poly(acrylic acid) polycarbol esters
N,N'-dimethylene acrylamide was applied as a cross-linking agent to synthesize polymers with a reticulated structure, which is conducive to preventing wax deposition by preventing paraffin wax intermolecular connections from forming gels or agglomerating into clumps.Therefore, we investigated the wax prevention effect of N,N'-dimethylene acrylamide crosslinked polyacrylic acid polycarbonate esters.The wax prevention effect of poly(high carbonyl acrylate) synthesized with 1% cross-linking agent is shown in Fig. 5, from which it can be seen that the wax prevention rate increased to different degrees compared with that of poly(high carbonyl acrylate) with no cross-linking agent, and the crosslinking poly(hexadecanol poly(acrylate)) was the most effective, reaching 82.4%.The amount of crosslinking agent determines the mesh size of the network structure, which also affects the deposition effect of wax.Therefore, the amount of crosslinking agent (the percentage of crosslinking agent added to the total mass) was studied, and the results are shown in Figure 6.From the figure, it can be seen that when the amount of crosslinking agent added is 2%, the anti wax effect is the best, reaching 98.4%; Excessive or insufficient dosage can lead to a weakened wax prevention effect, which may be due to the network structure formed when the dosage of crosslinking agent is 2%, which is suitable for the precipitation of paraffin on the network.Its long chain leads to loose and dendritic crystal pile masonry, preventing the deposition of wax.When the dosage is too large, it may lead to dense crystal stacking, making it difficult to prevent the deposition of wax.

Conclusion
(1) We synthesized polyacrylic acid high carbon alcohol ester and characterized the structure of the synthesized monomer and polymer using infrared spectroscopy, which is consistent with the target compound.
(2) The effects of factors such as the carbon chain length of monomer compounds, the synthesis conditions of polymers, and the amount of anti-wax agent on the anti-wax effect were investigated through static wax formation experiments.It was found that the reaction temperature of poly (hexadecyl ester) was 60 ℃, the reaction time was 4 hours, and the optimal anti wax effect was achieved at a dosage of 150 mg/L, reaching 89.3%.
(3) A network polyacrylic acid high carbon alcohol ester was synthesized by adding N, N'dimethylacrylamide as a crosslinking agent.The cross-linked polyacrylic acid hexadecanol ester was selected as an anti-wax agent, and the amount of crosslinking agent was investigated.The best anti wax effect was achieved at a dosage of 2%, reaching 98.4%.

Figure 2 .
Figure 2. The effect of reaction temperature on wax prevention effect.

Figure 3 .
Figure 3.The effect of reaction time on wax prevention effect.

Figure 4 .
Figure 4.The effect of the amount of anti-wax agent on the anti-wax rate.

Figure 5 .
Figure 5.The anti wax effect of different cross-linked polyacrylic acid high carbon alcohol ester.

Figure 6 .
Figure 6.The influence of the dosage of crosslinking agent on the wax prevention effect.