Process for separating an aqueous (meth)acrylic acid solution

Abstract

The application relates to the chemical industry field and discloses a separation method of (methyl) acrylic acid aqueous solution. The method comprises the following steps: mixing an extractant and (methyl) acrylic acid aqueous solution, carrying out extraction, and obtaining water phase and organic phase containing (methyl) acrylic acid after phase separation, wherein the extractant is at least one of hydrophobic higher fatty alcohol and (methyl) acrylic acid higher fatty alcohol ester. The method has the advantages of simple operation, high extraction rate, environmental friendliness, and the like. The obtained organic phase containing (methyl) acrylic acid and the extractant can be directly used for preparing (methyl) acrylic acid higher fatty alcohol ester, and further separation is not needed, so that obvious cost advantage is achieved.

Description

Technical Field

[0001] This invention relates to the field of chemical engineering, and specifically to a method for separating an aqueous solution of (meth)acrylic acid. Background Technology

[0002] (Meth)acrylic acid is an unsaturated fatty acid containing active double bonds and carboxyl functional groups. It is suitable for preparing highly absorbent materials, dispersants, flocculants, thickeners, etc., and is widely used in chemical fibers, textiles, coatings, water treatment, daily necessities, and many other fields, making it an important organic chemical raw material. In existing (meth)acrylic acid production processes, the obtained (meth)acrylic acid gas needs to be absorbed with water to obtain an aqueous (meth)acrylic acid solution, which is then further separated and purified for use in various industries. The esterification process of (meth)acrylic acid also yields an aqueous solution containing (meth)acrylic acid.

[0003] There are two main process flows for separating aqueous solutions of (meth)acrylic acid: azeotropic distillation and solvent extractive distillation. In azeotropic distillation, a low-boiling-point solvent that forms an azeotrope with water is added. The azeotropic agent and water continuously form an azeotrope and are removed from the top of the column, achieving the separation of (meth)acrylic acid. (Meth)acrylic acid is chemically very reactive, and its vinyl groups readily self-polymerize. Therefore, preventing the self-polymerization of (meth)acrylic acid is a primary consideration in the design of the distillation process. CN101456807B discloses a novel distillation column design for separating aqueous solutions of (meth)acrylic acid. The rectification section of the distillation column uses structured packing and / or co-current jet packing trays, while the stripping section uses guided floater trays and / or vertical sieve trays. This distillation column effectively reduces the overall pressure drop and operating temperature. Simultaneously, polymerization inhibitors hydroquinone and phenothiazine are added from the top of the column to prevent the polymerization tendency of (meth)acrylic acid at higher temperatures. Toluene is used as the azeotropic solvent for reduced-pressure azeotropic distillation, reducing the acrylic acid content in the aqueous phase at the top of the column to below 0.3%. CN1321968C discloses a method for purifying acrylic acid using tetrachloroethylene as a single azeotropic agent or a combination of tetrachloroethylene and aromatic hydrocarbons as a azeotropic agent via azeotropic distillation. Azeotropic distillation requires the removal of large amounts of water and the azeotropic agent, consuming significant energy. Furthermore, the separation of (meth)acrylic acid requires strict temperature control, placing high demands on equipment design and process control. Additionally, it necessitates the addition of large amounts of polymerization inhibitors, resulting in high economic costs and a high risk of self-polymerization.

[0004] Solvent extraction distillation is a process that combines extraction and distillation to purify (meth)acrylic acid. It uses a low-boiling-point hydrophobic solvent to extract (meth)acrylic acid from water, and then recovers the low-boiling-point solvent through distillation, thus achieving the separation of (meth)acrylic acid. CN1241892C discloses a method that uses extractants such as toluene, ethyl acetate, butyl acetate, isobutyl acetate, ethyl propionate, and (meth)phenyl ether to separate acrylic acid from an aqueous solution, and then removes the extractant through distillation to achieve the separation and purification of (meth)acrylic acid. The main process equipment includes an extraction tower, a solvent separation tower, a solvent removal tower, and an acrylic acid refining tower. The process flow is relatively long, and a polymerization inhibitor needs to be added during the operation of each tower to prevent the polymerization of acrylic acid; the amount of polymerization inhibitor added is relatively large.

[0005] Azeotropic distillation and solvent extraction distillation each have their advantages. The addition of low-boiling-point azeotropic agents and extractants lowers the separation temperature, further reducing the risk of self-polymerization of (meth)acrylic acid. However, the distillation process requires the addition of a large amount of polymerization inhibitors, increasing process costs. Both azeotropic agents and extractants are third solvents, which not only affect the downstream applications of (meth)acrylic acid, necessitating further distillation separation, but also raise significant environmental concerns due to the use of environmentally harmful extractants and the discharge of substantial wastewater. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned problems existing in the prior art and provide a method for separating (meth)acrylic acid aqueous solution. This method is simple to operate, has a high extraction rate, and is environmentally friendly.

[0007] To achieve the above objectives, the present invention provides a method for separating an aqueous solution of (meth)acrylic acid, the method comprising: mixing an extractant and an aqueous solution of (meth)acrylic acid, extracting, and separating the phases to obtain an aqueous phase and an organic phase containing (meth)acrylic acid, wherein the extractant is at least one of a hydrophobic higher fatty alcohol and a higher fatty alcohol ester of (meth)acrylic acid.

[0008] Through the above technical solution, the present invention can achieve the following beneficial effects:

[0009] 1. The technical solution of the present invention is simple to operate, has a high extraction rate, and does not require additional polymerization inhibitors, making it environmentally friendly.

[0010] 2. The technical solution of the present invention provides an organic phase containing (meth)acrylic acid that can be directly used to prepare higher fatty alcohol esters of (meth)acrylic acid, which is more convenient and cost-effective. Detailed Implementation

[0011] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0012] In this invention, "(meth)acrylic acid" refers to acrylic acid and / or methacrylic acid; "(meth)acrylic acid higher fatty alcohol ester" refers to higher fatty alcohol esters of acrylic acid and / or higher fatty alcohol esters of methacrylic acid. "Higher fatty alcohol ester" refers to a fatty alcohol used to form the ester having 9 or more carbon atoms.

[0013] In a first aspect, the present invention provides a method for separating an aqueous solution of (meth)acrylic acid, the method comprising: mixing an extractant and an aqueous solution of (meth)acrylic acid, extracting, and separating the phases to obtain an aqueous phase and an organic phase containing (meth)acrylic acid, wherein the extractant is at least one of a hydrophobic higher fatty alcohol and a higher fatty alcohol ester of (meth)acrylic acid.

[0014] The phrase "the extractant is at least one of a hydrophobic higher fatty alcohol and a (meth)acrylate higher fatty alcohol ester" means that the extractant can be a hydrophobic higher fatty alcohol, a (meth)acrylate higher fatty alcohol ester, or a mixture of a hydrophobic higher fatty alcohol and a (meth)acrylate higher fatty alcohol ester. The hydrophobic higher fatty alcohol and the (meth)acrylate higher fatty alcohol ester can be mixed in any proportion.

[0015] The inventors of this invention discovered in their research that when the method described above is adopted, the operation is simple, the extraction rate of (meth)acrylic acid is high, and no additional polymerization inhibitor is required, which is environmentally friendly.

[0016] According to the present invention, preferably, the hydrophobic higher fatty alcohol is at least one of monohydric fatty alcohols having 9-26 carbon atoms, and more preferably at least one of monohydric fatty alcohols having 9-16 carbon atoms.

[0017] According to the present invention, the hydrophobic higher fatty alcohol is at least one of (n)decyl alcohol, (n)undecyl alcohol, (n)dodecanol, (n)tridecyl alcohol and (n)tetradecyl alcohol.

[0018] According to the present invention, preferably, the higher fatty alcohol residues in the (meth)acrylate higher fatty alcohol ester have 9-26 carbon atoms. The higher fatty alcohol residues refer to the residual hydroxyl groups of the higher fatty alcohol that react during the dehydration of the alcohol and acid to form an ester.

[0019] According to the present invention, preferably, the mass fraction of (meth)acrylic acid in the aqueous solution of (meth)acrylic acid is 0.2-90 wt%; more preferably, it is 0.2-60 wt%.

[0020] When the range described above is met, a higher extraction rate can be obtained.

[0021] According to the present invention, the amount of extractant is not particularly limited, but preferably, the mass ratio of extractant to (meth)acrylic acid aqueous solution is 0.3-5:1.

[0022] According to the present invention, preferably, the mass ratio of the extractant to the aqueous (meth)acrylic acid solution is 0.8-3:1.

[0023] According to the present invention, preferably, the extraction temperature is 0-90°C, more preferably 20-60°C.

[0024] According to the present invention, preferably, the (meth)acrylate higher fatty alcohol ester is synthesized from one or more higher fatty alcohols having 9-26 carbon atoms through esterification or transesterification.

[0025] According to the present invention, preferably, the raw material alcohol and the hydrophobic higher fatty alcohol used for extraction are the same. When the above-described range is met, the resulting organic phase containing (meth)acrylic acid can be directly used in the preparation of (meth)acrylic acid higher fatty alcohol esters without further purification and separation.

[0026] According to the present invention, the method may further include the step of obtaining an aqueous solution of (meth)acrylic acid; and optionally may further include the step of recycling the organic phase containing (meth)acrylic acid obtained from the extraction to obtain an aqueous solution of (meth)acrylic acid.

[0027] According to the present invention, the step of obtaining an aqueous solution of (meth)acrylic acid includes the following steps, which not only obtain an aqueous solution of (meth)acrylic acid but also effectively promote the esterification reaction to proceed in the forward direction, thereby increasing the conversion rate:

[0028] Higher fatty alcohols are contacted with excess (meth)acrylic acid to carry out an esterification reaction. Water generated during the esterification reaction is extracted from the esterification reaction system along with the excess (meth)acrylic acid.

[0029] It is understandable that during the esterification process, when the water generated is drawn out along with excess (meth)acrylic acid, an aqueous solution of (meth)acrylic acid is obtained.

[0030] It is understandable that in esterification reactions, the carboxylic acid group and the hydroxyl group generally react in a molar ratio of 1. When the amount of acid used makes the molar ratio of the carboxylic acid group and the hydroxyl group exceed 1, the acid is considered to be in excess.

[0031] The inventors of this invention discovered in their research that, compared to traditional production methods, the method of this invention uses excess (meth)acrylic acid to continuously remove the byproduct water through azeotropic reaction, which can effectively promote the esterification reaction to proceed in the forward direction, improve the conversion rate, and reduce the difficulty of purification without introducing other azeotropic agents.

[0032] According to the present invention, in order to further ensure sufficient removal of water to further promote the esterification reaction and improve the conversion rate, preferably, the initial molar ratio of (meth)acrylic acid to higher fatty alcohols calculated as hydroxyl groups is greater than 1, preferably 1.01 to 3 (for example, it can be any two of the following numerical ranges: 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.3, 1.5, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, and above).

[0033] According to a particularly preferred embodiment of the present invention, methacrylic acid, dodecanol, a 70% by weight aqueous solution of methanesulfonic acid, and hydroquinone are added to a reaction flask, such that the initial molar ratio of methacrylic acid to higher fatty alcohols (calculated as hydroxyl groups) is 1.01-1.5 (for example, it can be any two of the following values: 1.01, 1.03, 1.05, 1.07, 1.1, 1.2, 1.3, 1.4, 1.5, or a range thereof). The amount of methanesulfonic acid is 0.36-2% by weight of the total weight of methacrylic acid and higher fatty alcohols, and the amount of hydroquinone is 0.037-1% by weight of the total weight of methacrylic acid and higher fatty alcohols. N2 is introduced into the reaction solution and the temperature is raised. Distillation is performed at atmospheric pressure. The esterification reaction is started when the temperature of the reaction solution reaches 100°C. The reaction temperature is controlled between 100°C and 130°C. Water generated during the esterification reaction is continuously distilled off along with the methacrylic acid using a water separator. After the reaction proceeds for 7.5-8.5 hours, the unreacted methacrylic acid is distilled off under reduced pressure. It is then washed with a 1-20 wt% sodium hydroxide solution at 30-40°C, treated with deionized water until neutral, and distilled under reduced pressure at 10-20 kPa. Finally, it is decolorized with bleaching clay to obtain lauryl methacrylate.

[0034] According to a particularly preferred embodiment of the present invention, an aqueous solution of methacrylic acid is separated according to the following method:

[0035] Take an aqueous solution of methacrylic acid, wherein the methacrylic acid content is 20-35%. Add dodecanol to the aqueous solution of methacrylic acid (the volume ratio of dodecanol to aqueous solution of methacrylic acid is 2.8-3.2:1). At 25-35℃, mix the mixed solution thoroughly in a separatory funnel, allow it to stand and separate the phases. After separation, a heavy aqueous phase and a light organic phase are obtained.

[0036] The present invention will be described in detail below through examples. In the following examples, the extraction recovery rate is calculated as follows: the amount of extracted methacrylic acid is obtained based on the residual methacrylic acid content in the aqueous phase after extraction, and the ratio of this amount to the amount of methacrylic acid in the initial aqueous methacrylic acid solution is the extraction rate.

[0037] Example 1

[0038] A 49.54 g aqueous solution of methacrylic acid, containing 1.76% by mass, was taken. 123.98 g of dodecanol was added to the methacrylic acid aqueous solution. The mixture was thoroughly mixed in a separatory funnel at 30°C, and allowed to stand for phase separation. After separation, a heavy aqueous phase and a light organic phase were obtained. The aqueous phase contained 0.05% by mass of methacrylic acid, and the water phase weighed 43.88 g. The extraction recovery rate was 97.58%.

[0039] Example 2

[0040] A 24.05 g aqueous solution of methacrylic acid, containing 6.57% methacrylic acid by mass, was added. 61.59 g of dodecanol was added to the methacrylic acid aqueous solution. The mixture was thoroughly mixed in a separatory funnel at 30°C, allowed to stand, and allowed to separate into two phases. The separated phases yielded a heavy aqueous phase and a light organic phase. The aqueous phase contained 0.19% methacrylic acid and weighed 19.33 g. The extraction recovery rate was 97.68%.

[0041] Example 3

[0042] The aqueous solution of methacrylic acid weighed 49.49 g, of which the methacrylic acid content was 14.75% by mass. 124.11 g of dodecanol was added to the aqueous solution of methacrylic acid. The mixture was thoroughly mixed in a separatory funnel at 30°C, allowed to stand, and allowed to separate into two phases. The separated phases yielded a heavy aqueous phase and a light organic phase. The aqueous phase contained 0.5% methacrylic acid and weighed 32.75 g, with an extraction recovery rate of 97.8%.

[0043] Example 4

[0044] The aqueous solution of methacrylic acid weighed 23.74 g, of which the methacrylic acid content was 29.65% by mass. 61.82 g of dodecanol was added to the aqueous solution of methacrylic acid. The mixture was thoroughly mixed in a separatory funnel at 30°C, and allowed to stand for phase separation. After separation, a heavy aqueous phase and a light organic phase were obtained. The aqueous phase contained 1.07% by mass of methacrylic acid, and the water phase weighed 4.21 g. The extraction recovery rate was 99.37%.

[0045] Example 5

[0046] A methacrylic acid aqueous solution weighing 23.74 g was obtained, containing 59.94% methacrylic acid by mass. 61.66 g of dodecanol was added to the methacrylic acid aqueous solution. The mixture was thoroughly mixed in a separatory funnel at 30°C, allowed to stand, and allowed to separate into two phases. The separated phases yielded a heavy aqueous phase and a light organic phase. The aqueous phase contained 2.19% methacrylic acid by mass, and the total mass of the aqueous phase was 4.84 g. The extraction recovery rate was 99.26%.

[0047] Example 6

[0048] A 48.83 g aqueous solution of methacrylic acid was prepared, containing 14.09% methacrylic acid by mass. 40.98 g of dodecanol was added to the methacrylic acid aqueous solution. The mixture was thoroughly mixed in a separatory funnel at 30°C, allowed to stand, and allowed to separate into two phases. The separated phases yielded a heavy aqueous phase and a light organic phase. The aqueous phase contained 1.47% methacrylic acid by mass and weighed 40.5 g. The extraction recovery rate was 91.35%.

[0049] Example 7

[0050] A 25.03 g aqueous solution of methacrylic acid, containing 2.08% by mass, was added. 75.01 g of dodecanol was added to the methacrylic acid aqueous solution. The mixture was thoroughly mixed in a separatory funnel at 60°C, allowed to stand, and allowed to separate into two phases. The separated phases yielded a heavy aqueous phase and a light organic phase; the aqueous phase contained 0.10% by mass of methacrylic acid, and the aqueous phase itself weighed 20 g. The extraction recovery rate was 96.16%.

[0051] Example 8

[0052] 40 g of aqueous methacrylic acid solution, containing 16.15% methacrylic acid by mass, was used. 60 g of dodecanol and 60 g of dodecyl methacrylate were added to the aqueous methacrylic acid solution. The mixture was thoroughly mixed in a separatory funnel at 18°C, allowed to stand, and allowed to separate into two phases. The separated phases yielded a heavy aqueous phase and a light organic phase. The aqueous phase contained 1.88% methacrylic acid by mass and weighed 28.76 g. The extraction recovery rate was 91.63%.

[0053] Example 9

[0054] 40 g of aqueous methacrylic acid solution, containing 16.15% methacrylic acid by mass, was added to the aqueous methacrylic acid solution. The mixture was thoroughly mixed in a separatory funnel at 18°C, allowed to stand, and allowed to separate into two phases. The separated phases yielded a heavy aqueous phase and a light organic phase. The aqueous phase contained 1.11% methacrylic acid by mass and weighed 17.32 g. The extraction recovery rate was 97.02%.

[0055] The results above show that the embodiments of the technical solution of the present invention can achieve a high recovery rate.

[0056] The following examples illustrate the steps for obtaining an aqueous solution of (meth)acrylic acid provided by the present invention. The conversion rate of dodecyl alcohol is calculated as follows: the amount of dodecyl alcohol converted is obtained by gas chromatography detection of the residual dodecyl alcohol content in the reaction solution, and the ratio of this amount to the initial amount of dodecyl alcohol is the conversion rate.

[0057] Example 10

[0058] 18.32 g of methacrylic acid, 19.44 g of dodecanol, 20 g of a mixed solution containing dodecanol, methacrylic acid, and water (containing 0.44 g of methacrylic acid, 18.5 g of dodecanol, and 1.06 g of water), 0.31 g of 70% methanesulfonic acid aqueous solution, and 0.022 g of hydroquinone were added to the reaction flask. N2 was introduced into the reaction solution and the temperature was raised. Distillation was carried out at atmospheric pressure. The esterification reaction was started at 100°C, and the reaction temperature was controlled between 100°C and 130°C. Water generated during the esterification reaction was continuously distilled off along with the methacrylic acid using a water separator. After 8 hours of reaction, unreacted methacrylic acid was distilled off under reduced pressure. The solution was then washed with a 5 wt% sodium hydroxide solution at 30°C, treated with demineralized water until neutral, and distilled under reduced pressure at 10 kPa. Finally, the solution was decolorized with bleaching clay to obtain lauryl methacrylate. Gas chromatography analysis of the reaction solution showed that the conversion rate of dodecanol was 90.74%.

[0059] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for separating an aqueous solution of (meth)acrylic acid, characterized in that, The method includes: using a mass ratio of The extractant was mixed with an aqueous solution of (meth)acrylic acid at a ratio of -3:1 and extracted at 20-30°C. After standing and phase separation, an aqueous phase and an organic phase containing (meth)acrylic acid were obtained. The extractant was dodecanol. The method further includes the step of recycling the organic phase containing (meth)acrylic acid obtained from the extraction to obtain an aqueous solution of (meth)acrylic acid. The recycling method includes: contacting dodecanol with excess (meth)acrylic acid to carry out an esterification reaction, wherein the water generated during the esterification reaction is extracted from the esterification reaction system along with the excess (meth)acrylic acid.

2. The method according to claim 1, wherein, The mass fraction of (meth)acrylic acid in the aqueous solution is 0.2-90 wt%.

3. The method according to claim 2, wherein, The mass fraction of (meth)acrylic acid in the aqueous solution is 0.2-60 wt%.