METHOD AND SYSTEM FOR PRODUCING (ALKYL)ACRYLATES

Abstract

The present invention relates to a method for preparing an (alkyl) acrylate, characterized in that the method comprises the following steps: (1) mixing an (alkyl) acrylic acid, an alcohol and optionally a polymerization inhibitor, to carry out a first stage esterification reaction; (2) separating an aqueous phase in the product of the first stage esterification reaction, and adding the (alkyl) acrylic acid, and optionally the alcohol and / or the polymerization inhibitor, to the remaining organic phase, to cause the organic phase to undergo a second stage esterification reaction; and optionally (3) separating and removing an aqueous phase in the product of the previous stage esterification reaction, obtaining and discharging the remaining organic phase containing an esterification product, or adding the (alkyl) acrylic acid, and optionally the alcohol and / or the polymerization inhibitor, to the remaining organic phase to carry out an N-th stage esterification reaction of the organic phase, where N≥3, and repeating this cycle multiple times, to obtain and discharge the remaining organic phase containing the esterification product. The present invention also relates to a reaction system used to implement the method according to the present invention.

Description

Method and system for preparing (alk)acrylates Technical Field

[0001] The present invention relates to the field of organic synthesis, in particular to a method for preparing (alkyl) acrylate and a system for preparing (alkyl) acrylate. Background Art

[0002] (Meth)acrylates have active double bonds and are an important type of fine chemical product and polymer monomer. Their homopolymers or copolymers are water-resistant, flexible, hard, and impact-resistant. They are often used as oil additives, adsorption resins, adhesives, and internal plasticizers. They are widely used in coatings, oil additives, plastics, papermaking, leather, and cosmetics.

[0003] (Meth)acrylates are typically prepared using an ester exchange method or a direct esterification method of (meth)acrylate. Compared to the ester exchange method, the direct esterification of (meth)acrylate with fatty alcohols is more efficient, i.e., the esterification reaction of (meth)acrylate with higher fatty alcohols. To promote the reaction, water needs to be continuously removed. Typically, a low-boiling-point solvent that can form an azeotrope with water is added to the reaction system. The azeotropy of the low-boiling-point solvent and water increases the water removal rate. CN1733687A discloses a method for preparing (meth)acrylates, wherein benzene, toluene, cyclohexane, carbon tetrachloride, chloroform, n-pentane, and n-hexane are added to the reaction system as water entrainers to enhance water removal, achieving a product yield of up to 97.8%. The drawback of this method is that it adds a new substance to the reaction mixture as an azeotropic solvent, which increases the difficulty of distillation and purification of the reaction system. Furthermore, the azeotropic solvent must be purified before being recycled upstream for reuse. While the solvent azeotropic method can efficiently and quickly increase the conversion rate of the esterification reaction, it is subject to significant issues such as secondary solvent distillation and process losses. The overall energy consumption and time are long, and the product color is poor. Existing continuous methacrylate production methods, such as CN113416133A, incorporate a solid acid catalyst into a distillation column and improve reaction efficiency through real-time, in-situ removal of water. This method is energy-intensive and, while it can promote the forward progress of the esterification reaction to a certain extent, the risk of methacrylate self-polymerization remains high, even with the use of a large amount of polymerization inhibitor, affecting the methacrylate yield.

[0004] In addition, the acrylic acid ester preparation process produces a large amount of acidic aqueous solution. This acidic aqueous solution mainly includes acrylic acid and has characteristics such as high acid concentration, complex composition, and high toxicity. This poses serious environmental problems, so it is necessary to post-process the acidic aqueous solution. However, post-processing methods bring additional costs and energy consumption. Moreover, the prepared product also contains impurities such as polymerization inhibitors. In the prior art, alkali washing methods are generally used to remove polymerization inhibitors. However, alkali washing methods will produce a large amount of alkaline waste solution, which also has adverse effects on the environment and increases the burden of post-processing.

[0005] Summary of the Invention

[0006] The purpose of the present invention is to overcome the problems of high energy consumption and high risk of self-polymerization in the process of preparing (alkyl) acrylates in the prior art, as well as the problem of generating a large amount of acidic aqueous solution and alkaline waste solution that require post-treatment during the preparation of acrylates.

[0007] In order to achieve the above object, according to a first aspect of the present invention, the present invention provides a method for preparing (alkyl) acrylate, the method comprising:

[0008] (1) mixing (alkyl) acrylic acid, alcohol and an optional polymerization inhibitor to carry out a first-stage esterification reaction;

[0009] (2) separating the aqueous phase from the product of the first stage esterification reaction, and adding (alkyl) acrylic acid, optional alcohol and / or polymerization inhibitor to the remaining organic phase to subject the organic phase to a second stage esterification reaction; and optionally

[0010] (3) separating the aqueous phase from the product of the previous esterification reaction and discharging the remaining organic phase containing the esterification product, or continuing to add (alkyl) acrylic acid, optional alcohol and / or polymerization inhibitor to the remaining organic phase to carry out the Nth stage esterification reaction of the organic phase, N ≥ 3, and repeating this cycle multiple times, and discharging the remaining organic phase containing the esterification product, and optionally,

[0011] (4) The remaining organic phase containing the esterification product obtained in step (3) is post-treated to obtain purified (alkyl)acrylate.

[0012] According to the second aspect of the present invention, the present invention provides a system for preparing (alkyl) acrylic acid esters, in particular a system for implementing the method according to the first aspect above, which comprises: a plurality of esterification reactors connected in series, and one or more phase separators or distiller for separating an organic phase and an aqueous phase respectively connected to each reactor; wherein each esterification reactor comprises a separate inlet for feeding fresh reaction raw materials or an inlet between the esterification reactor and the phase separator or distiller for introducing fresh reaction raw materials into the remaining organic phase from the previous reaction and from which the aqueous phase has been separated.

[0013] The inventors have proposed the present invention based on the following discovery: when a method for preparing (alkyl)acrylate is carried out by a staged reaction to control the conversion rate of each reaction stage within a certain range, and the aqueous phase is removed after each reaction stage and an appropriate amount of (alkyl)acrylate is added to the remaining organic phase, the amount of (alkyl)acrylate used in the method can be significantly reduced (thereby reducing the amount of acid-containing aqueous solution that requires post-treatment) while also improving the conversion rate of the alcohol. In addition, the staged reaction can significantly shorten the reaction time.

[0014] Through the above-mentioned technical scheme of the present invention, the present invention can realize the continuous preparation of (alkyl) acrylates, and the reaction cycle of the method of the present invention is short, and the process energy consumption, three waste emissions and (alkyl) acrylic acid self-polymerization risk are significantly low, which has significant economic benefits and environmental advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings are used to illustrate the technical solutions of the present invention and constitute part of the specification, but do not limit the present invention.

[0016] FIG1 shows a simple schematic flow chart of the technical solution according to the present invention. DETAILED DESCRIPTION

[0017] The following specific embodiments describe the technical solutions of the present invention in detail. It should be understood that the specific embodiments described herein are only used to illustrate preferred embodiments of the present invention and are not intended to limit the scope of the present invention.

[0018] Any specific numerical value disclosed in the present specification (including the endpoints of a numerical range) is not limited to the exact value of the numerical value, but should be understood to also include values ​​close to the exact value, such as all possible values ​​within ±5% of the exact value. Moreover, for a disclosed numerical range, the values ​​between the endpoints of the range, between the endpoints and the specific points in the range, and between the specific points can be arbitrarily combined to form one or more new numerical ranges, and these new numerical ranges should also be considered to be specifically disclosed herein.

[0019] Unless otherwise specified, the terms used in the specification of the present invention have the same meanings as commonly understood by those skilled in the art. If a term is defined herein and its definition is different from the commonly understood meaning in the art, the definition in this article shall prevail.

[0020] In the description of the present invention, except for the contents explicitly described, any matters or issues not mentioned are directly applicable to those known in the art without any changes. Moreover, any embodiment described herein can be freely combined with one or more other embodiments described herein, and the technical solutions or technical ideas formed thereby are considered part of the original disclosure or original description of the present invention, and should not be regarded as new content not disclosed or anticipated herein, unless a person skilled in the art considers that the combination is obviously unreasonable.

[0021] All patent and non-patent literature, including but not limited to textbooks and journal articles, mentioned in the specification of the present invention are incorporated herein by reference in their entirety.

[0022] In the present specification, the term "comprising" is synonymous with "including" and "containing" and is inclusive or open-ended, without excluding other unspecified elements. It should be understood that the term "comprising" includes the exclusive and closed term "consisting of." In the present specification, the term "support" and "substrate support" have the same meaning and are used equivalently in the present invention.

[0023] Unless otherwise specified, the performance parameters disclosed in the present invention are measured by the most common methods in the art. In the present invention, unless otherwise specified, the term "(alk)acrylic acid" refers to acrylic acid and / or (alk)acrylic acid; and "(alk)acrylate" refers to acrylate and / or (alk)acrylate.

[0024] According to a first aspect of the present invention, the present invention provides a method for preparing (alkyl) acrylate, characterized in that the method comprises:

[0025] (1) mixing (alkyl) acrylic acid, alcohol and optional polymerization inhibitor to carry out a first-stage esterification reaction (also referred to as "primary esterification reaction");

[0026] (2) separating the aqueous phase from the product of the first stage esterification reaction, and adding (alkyl) acrylic acid, optional alcohol and / or polymerization inhibitor to the remaining organic phase to subject the organic phase to a second stage esterification reaction (also referred to as "secondary esterification reaction"); and optionally

[0027] (3) separating the aqueous phase from the product of the previous esterification reaction, obtaining and discharging the remaining organic phase containing the esterification product, or adding (alkyl) acrylic acid, optional alcohol and / or polymerization inhibitor to the remaining organic phase, and allowing the organic phase to continue the Nth stage esterification reaction (also known as "N-stage esterification reaction"), N ≥ 3, and repeating this cycle multiple times, and discharging the remaining organic phase containing the esterification product, and optionally,

[0028] (4) The remaining organic phase containing the esterification product obtained in step (3) is post-treated to obtain purified (alkyl)acrylate.

[0029] According to a preferred embodiment of the first aspect of the present invention, as shown in FIG1 , (alkyl) acrylic acid, alcohol and optional polymerization inhibitor are mixed and fed as reaction materials into a first esterification reactor to carry out a first stage esterification reaction (also referred to as “primary esterification reaction”). After the conversion rate of the alcohol reaches a certain value, the reaction is terminated, and the reaction materials are cooled to room temperature and then enter a dehydration device to separate the aqueous phase and the organic phase. The organic phase, the added (alkyl) acrylic acid and the optional polymerization inhibitor are fed into a second esterification reactor to carry out a second stage esterification reaction (also referred to as “secondary esterification reaction”), wherein the added (alkyl) acrylic acid and the optional polymerization inhibitor are fed into the second esterification reactor separately or together with the organic phase. reactor; after the alcohol conversion rate reaches a certain value, the reaction is terminated, and the reaction mass is cooled to room temperature and then enters a dehydration device to separate the aqueous phase and the organic phase. Optionally, the remaining organic phase, additional (alkyl) acrylic acid, and optional polymerization inhibitor are passed to an Nth esterification reactor to carry out an Nth stage esterification reaction (also known as "Nth-stage esterification reaction"), wherein the additional (alkyl) acrylic acid and optional polymerization inhibitor are fed to the Nth esterification reactor separately or together with the organic phase; after the secondary esterification reaction or the Nth-stage esterification reaction, the organic phase product obtained by removing the aqueous phase through the dehydration device is subjected to post-treatment, including removal of the polymerization inhibitor and dehydration, to obtain a purified (alkyl) acrylic acid ester product. The dehydration device used to treat the products obtained in the different stage esterification reactions can be the same dehydration device or different dehydration devices, for example, selected from a distillation column or a centrifugal separator.

[0030] According to the method of the present invention, controlling the conversion rate of each esterification reaction within a suitable range can more effectively reduce the amount of (alkyl) acrylic acid used, promote the reaction of the alcohol, and reduce the risk of self-polymerization of the reaction materials and products. Preferably, the conversion rate of the first esterification reaction is 40-96% based on the alcoholic hydroxyl group, more preferably 70-94%, for example 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, 92% and 93% or any value or range therebetween. In the present invention, the conversion rate of a particular esterification reaction refers only to the conversion rate calculated based on the alcoholic hydroxyl group in that stage. The inventors have discovered that for the method for preparing (alkyl) acrylic acid esters of the present invention, performing the esterification reaction in multiple stages, controlling the conversion rate of each esterification reaction within a certain range, and adding new (alkyl) acrylic acid esters in a certain proportion can achieve the desired high conversion rate with a shorter esterification reaction time, significantly reduce the amount of (alkyl) acrylic acid used, and reduce the self-polymerization reaction of the unsaturated acid and ester.

[0031] Preferably, the conversion rate of the second stage esterification reaction is 40-100%, more preferably 70-99.5%, calculated based on the alcoholic hydroxyl groups.

[0032] Preferably, the conversion rate of the Nth stage esterification reaction is 40-100%, more preferably 70-99.5%, calculated on the basis of alcoholic hydroxyl groups.

[0033] Preferably, the total conversion rate of each stage of the esterification reaction is ≥99%, more preferably ≥99.5%.

[0034] Controlling the conversion rates of the first, second and Nth esterification reactions according to the conversion rates described above allows further acceleration of the esterification reaction (shortening the reaction cycle), significantly reducing the amount of (alkyl) acrylic acid used and reducing the risk of self-polymerization.

[0035] According to one embodiment of the first aspect, step (3) is an optional step, that is, it can be performed or not performed. According to the method of the present invention, not performing step (3) can also better achieve the purpose of the present invention and make the equipment requirements simpler and the energy consumption lower. If production conditions permit, step (3) can be performed according to actual conditions and the total number of stages (or the value of N) of the esterification reaction can be selected, thereby facilitating full utilization of the equipment and further improving production efficiency. Preferably, N is an integer greater than or equal to 2 and less than or equal to 5.

[0036] According to one embodiment of the first aspect, the aqueous phase in the reaction materials can be separated using methods commonly used in the art. However, preferably, in step (2) and the optional step (3), the method for separating the aqueous phase in the esterification reaction product is distillation and / or liquid-liquid phase separation, for example, at least one selected from distillation, flash evaporation, stripping, sedimentation, decantation, coalescence, and centrifugal separation, more preferably centrifugal separation. In step (2) and the optional step (3), the aqueous phase in the esterification reaction product can be separated in the same separation device or dehydration device, such as a distillation tower or centrifugal separator, or in different separation devices or dehydration devices, such as a distillation tower or centrifugal separator.

[0037] According to a preferred embodiment of the first aspect above, in order to further improve production efficiency and reduce the risk of self-polymerization, each stage of the esterification reaction is carried out under the condition of an inert gas co-flow. More specifically, if the esterification reaction is carried out in a fixed bed reactor, the inert gas is introduced into the reactor together with the liquid reaction raw material and passes through the fixed bed together to contact the catalyst at the same time. During each stage of the esterification reaction, the ratio of the volumetric hourly space velocity of the inert gas to the liquid hourly space velocity of the liquid raw material is independently: 0-1000:1, more preferably 10-250:1. More preferably, during each stage of the esterification reaction, the volumetric hourly space velocity of the inert gas is 3-500h -1, preferably 4-200h -1 , more preferably 8-80h -1 , preferably 9-15h -1 The inert gas can be a common gas in the art that does not react with any of the raw materials in the method of the present invention and is gaseous under the esterification reaction conditions, for example, nitrogen and / or a noble gas. The preferred embodiment in which each stage of the esterification reaction is carried out under the co-flow of the inert gas is particularly suitable for processes in which the esterification reaction pressure is positive. Based on research, the inventors surprisingly discovered that for the esterification reaction of the present invention, contacting the liquid reaction raw materials with the catalyst under the co-flow of the gas during the esterification reaction can significantly increase the reaction rate and significantly reduce the reaction time while achieving the same conversion rate. Without being bound by any particular theory, the inventors believe that the advantages of the co-flow of the inert gas may be related to the contact state and contact time between the catalyst, especially the solid catalyst, and the liquid reaction materials. This is because when the inert gas contacts the catalyst together with the liquid material, the inert gas can disturb and accelerate the flow of the liquid reaction material on the catalyst surface, thereby improving the mass transfer of the liquid reaction material on the catalyst surface and accelerating the removal of heat generated by the reaction and water produced by the esterification reaction, thereby enhancing the esterification reaction kinetics, lowering the reaction temperature, and effectively preventing self-polymerization of the reaction materials and products.

[0038] According to a preferred embodiment of the first aspect, in order to further improve the conversion rate of the alcohol, the method further comprises: in step (2) and / or step (3), adding (alkyl) acrylic acid so that the molar ratio of each additional (alkyl) acrylic acid added in terms of carboxyl groups to the alcohol in the remaining organic phase in terms of hydroxyl groups is 0.1-2, more preferably 0.1-1.5, more preferably 0.2-1.0, such as 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8. In order to more effectively reduce the risk of self-polymerization of the reaction materials and products, the method further comprises: in step (2) and / or step (3), adding a polymerization inhibitor, wherein the amount of the polymerization inhibitor added each time is 0.01-3% by weight of the total weight of the (alkyl) acrylic acid and the alcohol, more preferably 0.01-1% by weight, further preferably below 0.08% by weight, and particularly preferably below 0.07% by weight. In step (2) and / or step (3), alcohol may also be added as appropriate.

[0039] According to one embodiment of the first aspect above, in step (1), the molar ratio of (alkyl) acrylic acid calculated as carboxyl groups to alcohol calculated as hydroxyl groups can be 0.1-2, preferably 0.5-1.5, more preferably 0.8-1.1, for example 0.9 or 1.0.

[0040] According to one embodiment of the first aspect above, the total molar ratio of (alkyl)acrylic acid calculated as carboxyl groups and alcohol calculated as hydroxyl groups during the entire preparation method can be 1-4, preferably 2-3, more preferably 1.05-1.5, for example 1.1, 1.2, 1.3 or 1.4.

[0041] According to one embodiment of the first aspect above, the (alkyl) acrylic acid can be various (alkyl) acrylic acids commonly used in the art that can be used to prepare (alkyl) acrylates. Preferably, the number of carbon atoms of the alkyl group in the (alkyl) acrylic acid is less than or equal to 8, preferably less than or equal to 4. More preferably, the alkyl group in the (alkyl) acrylic acid is methyl, ethyl or propyl. Further preferably, the (alkyl) acrylic acid is (meth) acrylic acid.

[0042] According to one embodiment of the first aspect, the alcohol may be any of various alcohols commonly used in the art for preparing (alkyl)acrylates. Preferably, the alcohol is a fatty alcohol having a normal boiling point greater than 100°C and being insoluble or slightly soluble in water. "Insoluble or slightly soluble in water" refers to an alcohol having a solubility of less than or equal to 1g in 100g of water at 20°C. More preferably, the alcohol is at least one monohydric alcohol having 9 to 22 carbon atoms, further preferably at least one of n-decanol, n-undecanol, n-dodecanol, n-tetradecanol, n-hexadecanol, and n-octadecyl alcohol.

[0043] According to a preferred embodiment of the first aspect, the total amount of the polymerization inhibitor is 0.03-5% by weight, based on the total weight of the (alkyl)acrylic acid and the alcohol, more preferably 0.2% by weight or less, and particularly preferably 0.15% by weight or less. The present invention can prevent the self-polymerization of the (alkyl)acrylate even when the amount of polymerization inhibitor is relatively low, thereby achieving higher (alkyl)acrylate production efficiency.

[0044] According to one embodiment of the first aspect, the polymerization inhibitor may be selected from polymerization inhibitors commonly used in the art, but preferably, the polymerization inhibitor is at least one of a phenolic polymerization inhibitor, a quinone polymerization inhibitor, an aromatic amine polymerization inhibitor, and an inorganic salt polymerization inhibitor. The phenolic polymerization inhibitor may be selected from at least one of hydroquinone, pyrogallol, and p-tert-butylcatechol. The quinone polymerization inhibitor may be selected from at least one of tetrachlorobenzoquinone, 1,4-naphthoquinone, etc. The aromatic amine polymerization inhibitor may be selected from at least one of p-phenylenediamine, benzidine, diphenylamine, and p-(methyl)aniline. The inorganic salt polymerization inhibitor may be selected from at least one of ferric chloride, cuprous oxide, etc.

[0045] According to one embodiment of the first aspect, the conditions for each esterification reaction can independently include: a temperature of 80-140° C., preferably 90-130° C. Preferably, the temperature of the first esterification reaction is 1-10° C. lower than that of the second esterification reaction, particularly preferably 1-5° C. lower.

[0046] According to one embodiment of the first aspect, the conditions for each esterification reaction stage may further independently include a pressure of 0-10 MPaG, preferably 0.002-2 MPaG, and more preferably 0.01-1.5 MPaG. More preferably, the pressure of the first esterification reaction stage is 0.2-1 MPaG lower than the pressure of the second esterification reaction stage, and particularly preferably 0.35-0.85 MPaG lower.

[0047] According to a preferred embodiment of the first aspect, step (1), step (2) and step (3) are respectively carried out in separate reactors and / or separators, so that the preparation process can be carried out continuously. The reactor can be filled with a solid acid catalyst (such as an acidic resin) in the form of a fixed bed, wherein the total liquid hourly space velocity (volume) of the (alkyl) acrylic acid, alcohol and optional inhibitor can be 0.1-3h -1 , preferably 0.18-1h -1 More preferably, the liquid hourly space velocity of the latter esterification reaction (including the liquid hourly space velocity of the added reaction raw materials, such as the added (alkyl) acrylic acid and the optional inhibitor) is 0-0.2h higher than the liquid hourly space velocity of the former esterification reaction. -1 , further preferably 0-0.11h -1 .

[0048] According to one embodiment of the first aspect above, the conditions of each esterification reaction may be the same or different, but controlling the temperature, pressure and liquid hourly space velocity of the previous esterification reaction and the subsequent esterification reaction in the manner described above can further promote the progress of the reaction and reduce the risk of self-polymerization of (alkyl)acrylates.

[0049] According to a kind of embodiment of above-mentioned first aspect, in order to promote the carrying out of reaction, described esterification can be carried out in the presence of the catalyst that is usually used for esterification, described catalyst can be selected from at least one of sulfuric acid, sulfonic acid catalyst, heteropolyacid catalyst and acidic resin, and the consumption of described catalyst is 0.05-10 weight % of the total weight of (alkyl) acrylic acid and alcohol, more preferably 0.3-3 weight %.Described sulfonic acid catalyst can be selected from at least one of p-toluenesulfonic acid and methanesulfonic acid.Heteropolyacid catalyst is a kind of oxygen-containing polyacid that is made up of heteroatoms and multi-coordinate atoms by oxygen atom coordination bridging, and described heteropolyacid catalyst can be selected from at least one of phosphotungstic acid, phosphotungstomolybdic acid and silicotungstic acid etc.Acidic resin can release hydrogen ion, and wherein said acidic resin can be selected from macroporous acidic resin etc.

[0050] Since the organic phase obtained after the reaction and water removal steps contains a polymerization inhibitor and is colored, the reaction product needs to be post-treated to obtain a final product that meets the requirements. The post-treatment of the reaction product includes: removing the polymerization inhibitor and decolorizing the reaction product in sequence. Therefore, according to one embodiment of the first aspect, in order to purify the esterification reaction product, the method of the present invention may further include step (4): after removing the aqueous phase from the second-stage esterification reaction product of step (2) or the Nth-stage esterification reaction product of step (3), post-treating the product to obtain a purified (alkyl)acrylate. Preferably, step (4) includes removing the polymerization inhibitor contained in the product obtained in the previous step. The polymerization inhibitor can be removed by alkali washing or extraction. The alkali washing method can be: alkali washing with an alkali metal hydroxide solution (especially sodium hydroxide solution) having a concentration of 1-20% by weight, followed by treatment with deionized water until neutral. Preferably, the polymerization inhibitor is removed by extraction. More preferably, the extractant used for extraction includes an alcohol-based extractant and / or a water-based extractant, and a water-based extractant is further preferred. Most preferably, the water content in the water-based extractant is 10-100% by weight, preferably 50-95% by weight, more preferably 55-90% by weight, and the balance is a hydrophilic monohydric alcohol and / or a hydrophilic polyhydric alcohol, the hydrophilic monohydric alcohol being, for example, a C1-C6 monohydric alcohol, preferably methanol, ethanol, most preferably methanol, and the hydrophilic polyhydric alcohol being, for example, ethylene glycol. Preferably, the extraction is carried out in a continuous manner or in a multi-stage cross-flow manner. According to one embodiment of the first aspect above, the extraction conditions are: the extraction temperature is 25-70°C; the ratio of the mass of the extractant to the mass of the (alkyl) acrylate solution containing hydroquinone is 0.1-5:1, preferably 0.3-1.2:1; and / or the extraction equipment is a combination of one or more of a packed tower, a plate tower, a rotating disk tower, a centrifugal extractor, a spiral extractor, and a mixing and settling tank.

[0051] According to one embodiment of the first aspect above, in order to purify the esterification reaction product, step (4) may further include decolorizing the product. The decolorization may be performed in a manner commonly used in the art, for example, using bleaching clay for decolorization, which will not be described in detail herein.

[0052] The aqueous phase removed during the above-mentioned interstage water removal process contains a large amount of (alkyl) acrylic acid and needs to be treated to meet environmental protection requirements. A preferred method for removing (alkyl) acrylic acid contained in the aqueous phase is extraction. Therefore, according to one embodiment of the above-mentioned first aspect, the method may further include step (5): further recovering (alkyl) acrylic acid from the aqueous phase obtained in step (2) and / or step (3), preferably using an extractant to extract and recover (alkyl) acrylic acid in the aqueous phase to obtain an extract containing (alkyl) acrylic acid. The extraction and recovery step may specifically include: mixing the extractant and the aqueous phase, performing extraction, and obtaining water and an organic phase containing (alkyl) acrylic acid after phase separation, wherein the extractant is selected from at least one of hydrophobic higher fatty alcohols. When the above-mentioned method is adopted to recover (alkyl) acrylic acid, the operation is relatively simple, the extraction rate of (alkyl) acrylic acid is high, and no additional polymerization inhibitor is required, which is environmentally friendly. Preferably, the hydrophobic higher fatty alcohol is selected from at least one monohydric fatty alcohol having a carbon number of 9-26, preferably at least one monohydric fatty alcohol having a carbon number of 9-16. More preferably, the hydrophobic higher fatty alcohol is at least one of (n-) decanol, (n-) undecanol, (n-) dodecanol, (n-) tridecanol and (n-) tetradecanol. According to a particularly preferred embodiment of the present invention, the extractant is dodecanol, and the volume ratio of dodecanol to the aqueous phase is 2.8-3.2:1. According to a preferred embodiment, the extraction is carried out in a packed tower filled with fillers for continuous countercurrent extraction, preferably, the ratio of the mass flow rate of the (alkyl) acrylic acid-containing aqueous phase to the mass flow rate of the extractant is 0.5-10:1, preferably 0.8-5:1, more preferably 1-3:1, and the extraction temperature is 0-90°C, preferably greater than room temperature (25°C) to less than 60°C, more preferably greater than 35°C and less than 50°C. According to a preferred embodiment, the extractant is at least one or more of a hydrophobic alcohol and a hydrophobic (alkyl) acrylic acid ester that participate in the esterification reaction; the extraction conditions are: the extraction temperature is 0-90°C, preferably 30-60°C; the ratio of the mass of the extractant to the mass of the aqueous phase is 0.1-5:1, preferably 0.3-1.0:1; the extraction equipment is one or more of a packed tower, a plate tower, a rotary disk tower, a centrifugal extractor, a spiral extractor, and a mixing and settling tank, preferably a packed extraction tower, and the packing is preferably a surface hydrophilic packing. According to a preferred embodiment, the (alkyl) acrylic acid-containing extract recovered in step (5) is returned to any one of steps (1) to (3) as a reaction raw material.

[0053] According to the second aspect of the present invention, the present invention provides a reaction system for implementing the method according to the first aspect above, which comprises: a plurality of esterification reactors connected in series, and one or more phase separators or distiller connected to each reactor for separating the organic phase and the aqueous phase; wherein each esterification reactor comprises a separate inlet for feeding fresh reaction raw materials or an inlet between the esterification reactor and the phase separator or distiller for introducing fresh reaction raw materials into the remaining organic phase from the previous reaction and from which the aqueous phase has been separated.

[0054] According to one embodiment of the second aspect, the phase separator or distiller is selected from a centrifugal phase separator or a distillation tower.

[0055] According to one embodiment of the second aspect, the reaction system further comprises an extraction device connected to the last phase separator for separating the polymerization inhibitor. Preferably, the extraction device is selected from one or more of a packed tower, a plate tower, a rotating disk tower, a centrifugal extractor, a spiral extractor, and a mixer-settler.

[0056] The present invention will be described in detail below through examples. In the following examples, the macroporous acidic resin is a commercially available macroporous sulfonic acidic resin; "room temperature" refers to 25°C; the temperature of the mixed raw materials after preheating is about 100°C;

[0057] The conversion rate of alcohol is calculated by measuring the residual alcohol content in the reaction solution by gas chromatography, and then obtaining the amount of converted alcohol. The ratio of the amount of alcohol initially added is the conversion rate.

[0058] In the following examples and comparative examples, the yield of lauryl methacrylate = molar yield of lauryl methacrylate / molar amount of alcohol initially fed × 100%.

[0059] In the following examples and comparative examples, all raw materials are commercially available. Unless otherwise specified, the measurement methods for the parameters involved are conventional measurement methods in the art.

[0060] Example 1

[0061] 571.98 g of methacrylic acid, 1179.03 g of 1-dodecanol and 1.22 g of hydroquinone were thoroughly mixed. After the mixed raw materials were preheated to about 100°C, the mixture was heated at a liquid hourly space velocity of 0.1936 h -1 The liquid was introduced into the first fixed bed reactor filled with macroporous acidic resin. The center temperature of the first fixed bed reactor was 111°C and the reaction pressure was 1.6 MPa. During the reaction, the liquid reaction material was accompanied by nitrogen at a nitrogen space velocity of 9.61 h -1During the reaction, the conversion of dodecanol in the first stage of the reaction was monitored by periodic sampling and gas chromatography. The reaction was terminated when the conversion of dodecanol reached 93.18%. The reaction solution was then discharged from the reactor, cooled to room temperature, and centrifuged (at a speed of 2000 rpm for 20 minutes, the same below) to obtain an organic phase and an aqueous phase. The aqueous phase was removed, and the aqueous phase was post-treated to recover the methacrylic acid contained therein (for details, see Example 14 below). 151.19 g of methacrylic acid and 1.22 g of hydroquinone were added to the organic phase, and after thorough mixing, the mixture was stirred at a liquid hourly space velocity of 0.2581 h / min. -1 The liquid was introduced into the second fixed bed reactor filled with macroporous acidic resin. The center temperature of the second fixed bed reactor was 113°C and the reaction pressure was 1.3 MPa. During the reaction, the liquid reaction material was accompanied by nitrogen at a nitrogen space velocity of 11.24 h -1 The conversion of dodecanol in the second stage of the reaction was monitored by periodic sampling and gas chromatography. The reaction was terminated when the conversion of dodecanol reached 99.69%. The reaction solution was cooled to room temperature after being discharged from the reactor. The organic phase obtained by centrifugation was post-treated to remove the polymerization inhibitor (for details, see Example 10 below) and to decolorize the product, thereby obtaining purified dodecanol methacrylate. Gas chromatography analysis of the final product revealed a yield of 98.70% for dodecanol methacrylate. The total residence time of the reaction solution in the two-stage fixed-bed reactor was 9.04 hours.

[0062] Example 2

[0063] 628.34g of methacrylic acid, 1301.78g of 1-dodecanol and 1.3g of hydroquinone were mixed thoroughly. After the mixed raw materials were preheated to about 100°C, the mixture was heated at a liquid hourly space velocity of 0.2582h -1 The liquid was introduced into the first fixed bed reactor filled with macroporous acidic resin. The center temperature of the first fixed bed reactor was 111°C and the reaction pressure was 0.68 MPa. During the reaction, the liquid reaction material was accompanied by nitrogen at a nitrogen space velocity of 14.98 h -1 During the reaction, the conversion rate of dodecanol in the first stage of the reaction was monitored by periodic sampling and gas chromatography. When the conversion rate of dodecanol reached 87.61%, the reaction was terminated. The reaction solution was discharged from the reactor and cooled to room temperature. The organic phase and the aqueous phase were obtained by centrifugation, and the aqueous phase was removed. 30.57 g of methacrylic acid and 1.3 g of hydroquinone were added to the organic phase, and after thorough mixing, the mixture was stirred at a liquid hourly space velocity of 0.2582 h / s. -1 The liquid was introduced into the second fixed bed reactor filled with macroporous acidic resin. The center temperature of the second fixed bed reactor was 113 ° C, the reaction pressure was 1.04 MPa, and the liquid reaction material was accompanied by nitrogen during the reaction. The nitrogen space velocity was 12.18 h-1 The conversion of dodecanol in the second stage of the reaction was monitored by periodic sampling and gas chromatography. The reaction was terminated when the conversion reached 98.54%. The reaction solution was discharged from the reactor and cooled to room temperature. The organic phase obtained by centrifugation was post-treated to remove the polymerization inhibitor and decolorize the product, thereby obtaining purified dodecanol methacrylate. Gas chromatography analysis of the final product revealed a yield of 98.67% for dodecanol methacrylate. The total residence time of the reaction solution in the two-stage fixed-bed reactor was 8.15 hours.

[0064] Example 3

[0065] 628.34g of methacrylic acid, 1301.78g of 1-dodecanol and 1.3g of hydroquinone were mixed thoroughly. The mixed raw materials were preheated to about 100℃ and heated at a liquid hourly space velocity of 0.2582h -1 The liquid was introduced into the first fixed bed reactor filled with macroporous acidic resin. The center temperature of the first fixed bed reactor was 111°C and the reaction pressure was 0.68 MPa. During the reaction, the liquid reaction material was accompanied by nitrogen at a nitrogen space velocity of 14.98 h -1 During the reaction, the conversion rate of dodecanol in the first stage of the reaction was monitored by timed sampling and gas chromatography. When the conversion rate of dodecanol reached 87.61%, the reaction was terminated. The reaction solution was discharged from the reactor and cooled to room temperature. The organic phase and the aqueous phase were obtained by centrifugation. 80.36 g of methacrylic acid and 1.3 g of hydroquinone were added to the organic phase, and the mixture was thoroughly mixed and heated at a liquid hourly space velocity of 0.2582 h -1 The liquid was introduced into the second fixed bed reactor filled with macroporous acidic resin. The center temperature of the second fixed bed reactor was 113 ° C, the reaction pressure was 1.2 MPa, and the liquid reaction material was accompanied by nitrogen during the reaction. The nitrogen space velocity was 10.75 h -1 The conversion of dodecanol in the second stage of the reaction was monitored by periodic sampling and gas chromatography. The reaction was terminated when the conversion of dodecanol reached 99.04%. The reaction solution was discharged from the reactor and cooled to room temperature. The organic phase obtained by centrifugation was post-treated to remove the polymerization inhibitor and decolorize the product, thereby obtaining purified dodecanol methacrylate. Gas chromatography analysis of the final product revealed a yield of 98.85% for dodecanol. The total residence time of the reaction solution in the two-stage fixed-bed reactor was 7.55 hours.

[0066] Example 4

[0067] 633.34 g of methacrylic acid, 1301.78 g of 1-dodecanol and 1.3 g of hydroquinone were thoroughly mixed. After the mixed raw materials were preheated to about 100°C, the mixture was heated at a liquid hourly space velocity of 0.2151 h-1 The liquid reaction material was introduced into the first fixed bed reactor filled with macroporous acidic resin. The center temperature of the first fixed bed reactor was 111°C and the reaction pressure was 0.68 MPa. During the reaction, the liquid reaction material was accompanied by nitrogen at a nitrogen space velocity of 14.61 h -1 During the reaction, the conversion rate of dodecanol in the first stage of the reaction was monitored by periodic sampling and gas chromatography. When the conversion rate of dodecanol reached 89.77%, the reaction was terminated. The reaction solution was discharged from the reactor, cooled to room temperature, and centrifuged to obtain an organic phase and an aqueous phase, which was then removed. 95.49 g of methacrylic acid and 1.3 g of hydroquinone were added to the organic phase, thoroughly mixed, and heated at a liquid hourly space velocity of 0.2797 h / min. -1 The liquid was introduced into the second fixed bed reactor filled with macroporous acidic resin. The center temperature of the second fixed bed reactor was 113 ° C, the reaction pressure was 1.49 MPa, and the liquid reaction material was accompanied by nitrogen during the reaction. The nitrogen space velocity was 10.47 h -1 The conversion of dodecanol in the second stage of the reaction was monitored by periodic sampling and gas chromatography. The reaction was terminated when the conversion reached 99.33%. The reaction solution was discharged from the reactor and cooled to room temperature. The organic phase obtained by centrifugation was post-treated to remove the polymerization inhibitor and decolorize the product, thereby obtaining purified dodecanol methacrylate. Gas chromatography analysis of the final product revealed a yield of 98.92% for dodecanol methacrylate. The total residence time of the reaction solution in the two-stage fixed-bed reactor was 8.22 hours.

[0068] Example 5

[0069] 633.34 g of methacrylic acid, 1301.78 g of 1-dodecanol and 1.3 g of hydroquinone were thoroughly mixed. After the mixed raw materials were preheated to about 100°C, the mixture was heated at a liquid hourly space velocity of 0.2151 h -1 The liquid reaction material was introduced into the first fixed bed reactor filled with macroporous acidic resin. The center temperature of the first fixed bed reactor was 111°C and the reaction pressure was 0.68 MPa. During the reaction, the liquid reaction material was accompanied by nitrogen at a nitrogen space velocity of 14.61 h -1 During the reaction, the conversion rate of dodecanol in the first stage of the reaction was monitored by periodic sampling and gas chromatography. When the conversion rate of dodecanol reached 89.76%, the reaction was terminated. The reaction solution was discharged from the reactor and cooled to room temperature. The organic phase and the aqueous phase were obtained by centrifugation, and the aqueous phase was removed. 95.49 g of methacrylic acid and 1.3 g of hydroquinone were added to the organic phase, mixed thoroughly, and heated at a liquid hourly space velocity of 0.3227 h / min. -1The liquid was introduced into the second fixed bed reactor filled with macroporous acidic resin. The center temperature of the second fixed bed reactor was 113 ° C, the reaction pressure was 1.2 MPa, and the liquid reaction material was accompanied by nitrogen during the reaction. The nitrogen space velocity was 10.4h -1 The conversion of dodecanol in the second stage of the reaction was monitored by periodic sampling and gas chromatography. The reaction was terminated when the conversion of dodecanol reached 99.25%. The reaction solution was discharged from the reactor and cooled to room temperature. The organic phase obtained by centrifugation was post-treated to remove the polymerization inhibitor and decolorize the product, thereby obtaining purified dodecanol methacrylate. Gas chromatography analysis of the final product revealed a yield of 98.8% for dodecanol methacrylate. The total residence time of the reaction solution in the two-stage fixed-bed reactor was 7.75 hours.

[0070] Example 6

[0071] 485.065 g of methacrylic acid, 1000 g of 1-dodecanol and 1.0 g of hydroquinone were thoroughly mixed. After the mixed raw materials were preheated to about 100°C, the mixture was heated at a liquid hourly space velocity of 0.3240 h -1 The liquid reaction material was introduced into a first-stage fixed-bed reactor filled with a macroporous acidic resin. The center temperature of the first-stage fixed-bed reactor was 111° C., the reaction pressure was 0.10 MPa, and no nitrogen was present in the liquid reaction material during the reaction. The conversion rate of dodecanol in the first-stage reaction was monitored by timed sampling and gas chromatography. After 3.09 hours of reaction, the conversion rate of dodecanol was determined to be 47.83%.

[0072] Example 7

[0073] 607.08 g of methacrylic acid, 976.56 g of 1-dodecanol, 312.39 g of 1-tetradecanol and 1.3 g of hydroquinone were mixed thoroughly. After the mixed raw materials were preheated to about 100°C, the mixture was heated at a liquid hourly space velocity of 0.323 h -1 The liquid reaction material was introduced into the first fixed bed reactor filled with macroporous acidic resin. The center temperature of the first fixed bed reactor was 111°C and the reaction pressure was 0.3 MPa. During the reaction, the liquid reaction material was accompanied by nitrogen at a nitrogen space velocity of 70.41 h -1 During the reaction, the conversion rate of dodecanol in the first stage of the reaction was monitored by periodic sampling and gas chromatography. When the conversion rate of dodecanol reached 92.55%, the reaction was terminated. After the reaction liquid was discharged from the reactor, the organic phase was distilled under reduced pressure to reduce the water content in the organic phase to 870 ppm. At this time, the conversion rate of tetradecanol was 90.17%. 148.54 g of methacrylic acid and 1.3 g of hydroquinone were added to the organic phase, and after thorough mixing, the mixture was heated at a liquid hourly space velocity of 0.387 h / min. -1The liquid was introduced into the second fixed bed reactor filled with macroporous acidic resin. The center temperature of the second fixed bed reactor was 111 ° C, the reaction pressure was 0.3 MPa, and the liquid reaction material was accompanied by nitrogen during the reaction. The nitrogen space velocity was 8.4h -1 The conversion of dodecanol in the second stage of the reaction was monitored by periodic sampling and gas chromatography. The reaction was terminated when the conversion of dodecanol reached 99.45%. The reaction solution was discharged from the reactor and cooled to room temperature. The organic phase obtained by centrifugation was post-treated to remove the polymerization inhibitor and decolorize the product, thereby obtaining a purified mixture of dodecanol and tetradecyl methacrylate. Gas chromatography analysis of the final product revealed a conversion of tetradecyl alcohol of 99.5%, a yield of dodecanol of 98.75%, and a yield of tetradecyl methacrylate of 98.25%. The total residence time of the reaction solution in the two-stage fixed-bed reactor was 5.68 hours.

[0074] Example 8

[0075] 607.08 g of methacrylic acid, 976.56 g of 1-dodecanol, 312.39 g of 1-tetradecanol and 1.3 g of hydroquinone were mixed thoroughly. After the mixed raw materials were preheated to about 100°C, the mixture was heated at a liquid hourly space velocity of 0.323 h -1 The method comprises the following steps: introducing the first fixed-bed reactor filled with a macroporous acidic resin, wherein the center temperature of the first fixed-bed reactor is 111° C., the reaction pressure is 10 kPa, and no nitrogen is co-flowed during the reaction; monitoring the conversion rate of dodecanol by timed sampling and gas chromatography during the reaction; terminating the reaction when the conversion rate of dodecanol reaches 96.25%, discharging the reaction liquid from the reactor, and centrifuging to obtain an organic phase and an aqueous phase; at this time, the conversion rate of tetradecanol is 93.57%; adding 210.36 g of methacrylic acid and 1.3 g of hydroquinone to the organic phase, mixing thoroughly, and centrifuging at a liquid hourly space velocity of 0.43 h / min. -1 The reaction was passed through a second fixed-bed reactor filled with a macroporous acidic resin. The center temperature of the second fixed-bed reactor was 112°C, the reaction pressure was 10 kPa, and there was no nitrogen co-flow during the reaction. The dodecanol conversion was monitored by periodic sampling and gas chromatography. The reaction was terminated when the dodecanol conversion reached 99.41%. The reaction solution was cooled to room temperature after being discharged from the reactor. The organic phase obtained by centrifugation was post-treated to remove the polymerization inhibitor and decolorize the product, yielding a purified mixture of dodecyl methacrylate and tetradecyl methacrylate. Gas chromatography analysis of the final product revealed a tetradecyl alcohol conversion of 98.78%, a dodecyl methacrylate yield of 98.85%, and a tetradecyl methacrylate yield of 98.45%. The total residence time of the reaction solution in the two fixed-bed reactors was 5.42 hours.

[0076] Example 9

[0077] 607.08 g of methacrylic acid, 976.56 g of 1-dodecanol, 312.39 g of 1-tetradecanol and 1.3 g of hydroquinone were mixed thoroughly. After the mixed raw materials were preheated to about 100°C, the mixture was heated at a liquid hourly space velocity of 0.323 h -1 A first-stage fixed-bed reactor filled with a macroporous acidic resin was introduced from the bottom of the reactor. The center temperature of the first-stage fixed-bed reactor was 111° C., the reaction pressure was 0.1 MPa, and no nitrogen was co-flowed during the reaction. During the reaction, the conversion rate of dodecanol was monitored by timed sampling and gas chromatography. After 3.10 hours of reaction, the conversion rate of dodecanol was measured to be 58.86%. The reaction was terminated, and the reaction liquid was discharged from the reactor and centrifuged to obtain an organic phase and an aqueous phase. At this time, the conversion rate of tetradecanol was 54.38%.

[0078] Example 10

[0079] 607.08 g of methacrylic acid, 976.56 g of 1-dodecanol, 312.39 g of 1-tetradecanol and 1.3 g of hydroquinone were mixed thoroughly. After the mixed raw materials were preheated to about 100°C, the mixture was heated at a liquid hourly space velocity of 0.323 h -1 The liquid reaction material was introduced into the first fixed bed reactor filled with macroporous acidic resin. The center temperature of the first fixed bed reactor was 111°C and the reaction pressure was 0.3 MPa. During the reaction, the liquid reaction material was accompanied by nitrogen at a nitrogen space velocity of 70.41 h -1 During the reaction, the conversion rate of dodecanol in the first stage of the reaction was monitored by periodic sampling and gas chromatography. When the conversion rate of dodecanol reached 92.55%, the reaction was terminated. After the reaction liquid was discharged from the reactor, the organic phase was distilled under reduced pressure to reduce the water content in the organic phase to 870 ppm. At this time, the conversion rate of tetradecanol was 90.17%. 148.54 g of methacrylic acid and 1.3 g of hydroquinone were added to the organic phase, and after thorough mixing, the mixture was heated at a liquid hourly space velocity of 0.387 h / min. -1 The liquid was introduced into the second fixed bed reactor filled with macroporous acidic resin. The center temperature of the second fixed bed reactor was 111 ° C, the reaction pressure was 0.3 MPa, and the liquid reaction material was accompanied by nitrogen during the reaction. The nitrogen space velocity was 8.4h -1The conversion of dodecanol in the second stage of the reaction was monitored by periodic sampling and gas chromatography. The reaction was terminated when the conversion of dodecanol reached 99.45%. The reaction solution was discharged from the reactor and cooled to room temperature. The organic phase obtained by centrifugation was post-treated to remove the polymerization inhibitor and decolorize the product, thereby obtaining a purified mixture of dodecanol and tetradecyl methacrylate. Gas chromatography analysis of the final product revealed a conversion of tetradecyl alcohol of 99.5%, a yield of dodecanol of 98.75%, and a yield of tetradecyl methacrylate of 98.25%. The total residence time of the reaction solution in the two-stage fixed-bed reactor was 5.68 hours.

[0080] Comparative Example 1

[0081] Methacrylic acid 905.62g, 1-dodecanol 1305.8g and hydroquinone 1.3g were mixed thoroughly. After the mixed raw materials were preheated to about 100°C, the mixture was heated at a liquid hourly space velocity of 0.172h -1 The liquid was introduced into the first fixed bed reactor filled with macroporous acidic resin. The center temperature of the first fixed bed reactor was 115°C and the reaction pressure was 0.3 MPa. During the reaction, the liquid reaction material was accompanied by nitrogen at a nitrogen space velocity of 10.71 h -1 The reaction liquid was discharged from the reactor and cooled to room temperature, and centrifuged to obtain an organic phase and an aqueous phase. At this time, the conversion rate of dodecanol was 94.92%. 1.3 g of hydroquinone was added to the organic phase, and after thorough mixing, the mixture was heated at a liquid hourly space velocity of 0.172 h -1 The liquid was introduced into the second fixed bed reactor filled with macroporous acidic resin. The center temperature of the second fixed bed reactor was 115°C and the reaction pressure was 0.3 MPa. During the reaction, the liquid reaction material was accompanied by nitrogen at a nitrogen space velocity of 11.13 h -1 After the reaction liquid was discharged from the reactor, it was cooled to room temperature. The resulting organic phase was centrifuged and post-treated to remove the polymerization inhibitor and decolorize the product, yielding purified dodecyl methacrylate. Gas chromatography analysis of the final product revealed a conversion of dodecanol of 97.26% and a yield of dodecyl methacrylate of 93.11%. The total residence time of the reaction liquid in the two-stage fixed-bed reactor was 11.63 hours.

[0082] Comparative Example 2

[0083] Methacrylic acid, dodecanol and hydroquinone were mixed in the following proportions: 766.55 g methacrylic acid, 1102.05 g 1-dodecanol and 2.65 g hydroquinone. After the mixed raw materials were preheated to about 100°C, the mixture was heated at a liquid hourly space velocity of 0.1 h -1The liquid was introduced into a fixed bed reactor filled with macroporous acidic resin. The center temperature of the fixed bed reactor was 111°C and the reaction pressure was 0.95 MPa. During the reaction, the liquid reaction material was accompanied by nitrogen at a nitrogen space velocity of 33.63 h - 1 After the reaction liquid was discharged from the reactor, it was cooled to room temperature and centrifuged to obtain an organic phase and an aqueous phase. The aqueous phase contained 86% of the generated water. The organic phase was post-treated to remove the polymerization inhibitor and decolorize the product, yielding purified dodecyl methacrylate. Gas chromatography analysis of the final product revealed a conversion of dodecanol of 98.99% and a yield of dodecyl methacrylate of 94.75%. The residence time of the reaction liquid in the fixed-bed reactor was 10 hours.

[0084] Comparative Example 3

[0085] To a reaction flask, 77.48g of methacrylic acid, 111.81g of 1-dodecanol, and 0.28g of hydroquinone were added and thoroughly mixed. 5g of a macroporous acidic resin catalyst was added. N2 was introduced into the reaction solution and the temperature was raised. Normal pressure distillation was performed. The esterification reaction was started when the reaction solution was heated to 100°C. The reaction temperature was controlled at 113°C. The water generated in the esterification reaction was continuously distilled off along with the methacrylic acid using a water separator. After 14.0 hours of reaction, the unreacted methacrylic acid was distilled off under reduced pressure. The catalyst was filtered to remove the catalyst. The solution was then alkali-washed with 5% by weight sodium hydroxide solution at 30°C, then treated with deionized water until neutral, and distilled under reduced pressure at a vacuum of 10kPa. The reaction solution was then decolorized using white clay to obtain lauryl methacrylate. The reaction solution was analyzed by gas chromatography, and the conversion rate of lauryl alcohol was 98.01%.

[0086] The implementation schemes and technical effects obtained in the above examples and comparative examples are listed in the following Table 1.

[0087] Table 1.

[0088] According to the above examples and comparative examples, it can be seen that in Comparative Example 1, after the aqueous phase is separated between stages, no methacrylic acid is added to the organic phase; compared with Examples 1-9 according to the present invention, Comparative Example 1 requires a significantly longer reaction time; Comparative Example 2 does not adopt a staged reaction mode, and compared with Examples 1-9 according to the present invention, Comparative Example 2 requires a significantly longer reaction time, and the alcohol conversion rate and product yield are significantly lower; Comparative Example 3 carries out the reaction in a reactor instead of a fixed bed reactor, wherein a water separator is used to continuously distill and separate the water generated in the esterification reaction along with the methacrylic acid. Compared with Examples 1-9 according to the present invention, Comparative Example 3 requires a significantly longer reaction time, and the conversion rate and yield are significantly lower; In Examples 1-5 and 7, the esterification reaction was carried out under nitrogen co-flow conditions, which can achieve results similar to the esterification reaction under negative pressure conditions in Example 8. However, the nitrogen co-flow method can better control the reaction conditions and reduce energy consumption compared to negative pressure conditions. By comparing Examples 5 and 6 and Comparative Examples 7 and 9, it can be seen that co-flowing nitrogen with the reaction liquid during the esterification reaction can further improve the kinetics of the esterification reaction, increase the reaction rate, and thus further reduce the reaction time. In addition, the co-flow of nitrogen with the reaction liquid can also carry away some of the moisture generated by the reaction. According to the above examples and comparative examples, it can also be seen that controlling the liquid hourly space velocity, the esterification reaction temperature difference, and the amount of additional (alkyl) acrylic acid within the preferred range can achieve better reaction results.

[0089] The following examples are used to further illustrate the technical solution for removing polymerization inhibitors according to the present invention and the obtained effect of removing polymerization inhibitors.

[0090] Example 10

[0091] In Example 1, after the reaction terminated, the aqueous phase was removed by centrifugation, and the resulting organic phase solution containing dodecyl methacrylate was analyzed by spectrophotometry to contain 0.14 wt% hydroquinone. This organic phase solution was subjected to a two-stage cross-current extraction at 30°C in a centrifugal extractor using a 60 wt% water-based extraction solvent (a mixture of 60 wt% water and 40 wt% methanol) as an extractant. The amount of the single-stage extractant used was 60 wt% of the mass of the solution containing hydroquinone and dodecyl methacrylate. After extraction, the hydroquinone content in the dodecyl methacrylate solution was 0.0008 wt%, and the hydroquinone removal rate was as high as 99.43%.

[0092] Example 11

[0093] The same organic phase solution containing 0.14 wt % hydroquinone from Example 1 was used as in Example 10 above. However, in this example, a water-based extraction solvent (a mixture of 80 wt % water and 20 wt % methanol) having a water content of 80 wt % was used as the extractant for continuous countercurrent extraction at 30° C. in a packed tower. The flow rate of the organic phase solution containing hydroquinone and dodecyl methacrylate was 265.83 g / h, and the flow rate of the extractant was 159.50 g / h. After extraction, the hydroquinone content in the dodecyl methacrylate solution was 0.0010 wt %, and the hydroquinone removal rate was as high as 99.29%.

[0094] Example 12

[0095] The same organic phase solution containing 0.14 wt % hydroquinone from Example 1 was used as in Example 10 above. However, in this example, a water-based extraction solvent having a water content of 100 wt % was used as the extractant for continuous countercurrent extraction in a packed tower. The flow rate of the organic phase solution containing hydroquinone and dodecyl methacrylate was 265.83 g / h, the flow rate of the extractant was 159.50 g / h, and the extraction temperature was 61.14°C. After continuous countercurrent extraction, the hydroquinone content in the dodecyl methacrylate solution was 0.0015 wt %, and the hydroquinone removal rate was as high as 98.93%.

[0096] Example 13

[0097] The same organic phase solution containing 0.14 wt% hydroquinone from Example 1 was used as in Example 10. However, in this example, water having a water content of 100 wt% was used as the extractant for a two-stage cross-current extraction at 60°C in a centrifugal extractor. The amount of the single-stage extractant used was 100 wt% of the mass of the solution containing hydroquinone and dodecyl methacrylate. After extraction, the hydroquinone content in the dodecyl methacrylate solution was 0.0019 wt%, and the hydroquinone removal rate was as high as 98.64%.

[0098] The technical solutions and technical effects of the above embodiments 10-13 are listed in Table 2 below.

[0099] Table 2.

[0100] As shown in Table 2, the use of a water-based solvent to extract an organic solution containing hydroquinone and lauryl methacrylate almost completely extracts the hydroquinone, yielding high-purity lauryl methacrylate. The extract can then be distilled to recover the alcohol. Furthermore, since the water-based solvent contains no alkali, this method does not generate secondary pollution. Comparisons of Examples 10 and 13, or 11 and 12, show that including a small amount of alcohol in the water-based extractant can significantly improve extraction efficiency.

[0101] The following Examples 14-15 and Comparative Example 4 illustrate the effectiveness of the present invention's technical solution for separating (alkyl)acrylic acid from an aqueous phase and recovering (alkyl)acrylic acid. The packed columns used in Examples 14 and 15 differed only in the type of packing; the packing amount and method were the same.

[0102] Example 14

[0103] After the completion of the first stage reaction in Example 1, the aqueous phase (aqueous solution) obtained by phase separation was analyzed by gas chromatography to contain 18 wt % methacrylic acid. Continuous countercurrent extraction was carried out in a packed tower packed with hydrophilic packing using dodecanol as the extractant. The flow rate of the methacrylic acid aqueous solution was 141.45 g / h, the flow rate of the extractant was 132.96 g / h, and the extraction temperature was 45.87° C. After 1 hour of continuous countercurrent extraction, the methacrylic acid content in the extracted methacrylic acid aqueous solution was 0.0010 wt %, and the mass was 116.0 g. Therefore, the methacrylic acid removal rate was 99.99%.

[0104] Example 15

[0105] This example was carried out according to the method of Example 14, except that: a mixed dodecaethanol / tetradecaethanol was used as the extractant, and continuous countercurrent extraction was carried out in a packed tower packed with hydrophilic packing. The flow rate of the methacrylic acid aqueous solution was 141.45 g / h, the flow rate of the extractant was 152.15 g / h, and the extraction temperature was 47.87°C. After one hour of continuous countercurrent extraction, the methacrylic acid content in the extracted methacrylic acid aqueous solution was 0.0017 wt %, with a mass of 116.0 g, and a methacrylic acid removal rate of 99.98%.

[0106] Comparative Example 4

[0107] This comparative example was carried out according to the operating method of Example 14, except that the extraction was carried out in a packed tower filled with a lipophilic packing, using a continuous countercurrent extraction method. The flow rate of the methacrylic acid aqueous solution was 141.09 g / h, the flow rate of the extractant was 141.10 g / h, and the extraction temperature was 45.96°C. After one hour of continuous countercurrent extraction, the methacrylic acid content in the methacrylic acid aqueous solution was 0.45% by weight, with a mass of 118.9 g, and a methacrylic acid removal rate of 97.94% by weight.

[0108] Comparative Example 5

[0109] This comparative example was carried out using the same aqueous solution containing 18 wt% methacrylic acid and extractant as in Example 15, except that the extraction was carried out in a separatory funnel, the amount of methacrylic acid aqueous solution added was 50 g, the amount of extractant added was 140 g, and the extraction temperature was 40°C. The mixed solution was thoroughly mixed in the separatory funnel and allowed to stand for phase separation, yielding a heavy component aqueous phase and a light component organic phase. The methacrylic acid content in the aqueous phase was 0.6 wt%, the mass of the aqueous phase was 32.75 g, and the methacrylic acid removal rate was 97.82%.

[0110] The extraction schemes and extraction effects of Examples 14-15 and Comparative Example 4 are listed in Table 3 below.

[0111] Table 3.

[0112] The data in Table 3 above demonstrate that the methacrylic acid extraction results obtained in Examples 14-15 using hydrophilic fillers were significantly better than those obtained in Comparative Example 4 using lipophilic fillers. Furthermore, the methacrylic acid extraction results obtained by continuous countercurrent extraction using a packed column were significantly better than those obtained in Comparative Example 5 using a separatory funnel. The aqueous phases treated in Examples 14-15 meet environmental requirements. The extracts obtained in these examples can be returned as raw material to the esterification reaction.

[0113] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for producing (alkyl) acrylates, wherein the method is characterized in that it includes the following stages: (1) mixing (alkyl)acrylic acid, alcohol and an optional polymerization inhibitor to carry out a first-stage esterification reaction; (2) separating the aqueous phase from the first-stage esterification reaction product, and adding (alkyl)acrylic acid, an optional alcohol, and / or a polymerization inhibitor to the remaining organic phase to introduce the organic phase into a second-stage esterification reaction; and optionally (3) separating an aqueous phase from the esterification reaction product of the preceding esterification step to obtain and remove a remaining organic phase containing the esterification product, or adding (alkyl)acrylic acid, an optional alcohol and / or a polymerization inhibitor to the remaining organic phase to introduce the organic phase into the esterification reaction of step N, wherein N is not less than 3, repeatedly reproducing said cycle to obtain and remove a remaining organic phase containing the esterification product.

2. The method according to paragraph 1, wherein the method is distinguished in that it additionally provides for the following stage: (4) directing the remaining organic phase containing the esterification product obtained in step (3) to subsequent processing to obtain purified (alkyl) acrylates, wherein the subsequent processing preferably includes removing the polymerization inhibitor and / or decolorizing the product.

3. The method according to claim 1 or 2, characterized in that the esterification reaction is carried out in the presence of a solid acid catalyst, preferably the esterification reaction is carried out in a fixed bed reactor.

4. The method according to any one of paragraphs 1-3, characterized in that, in terms of alcohol hydroxyl groups, the degree of conversion in the first stage esterification reaction is 40-95%, preferably 70-94%; and / or, in terms of alcoholic hydroxyl groups, the degree of conversion in the second stage esterification reaction is 40-100%, preferably 70-99.5%; and / or, in terms of alcoholic hydroxyl groups, the degree of conversion in the esterification reaction of stage N is 40-100%, preferably 70-99.5%; and / or, in terms of alcoholic hydroxyl groups, the overall conversion in the esterification reaction for all stages is not less than 99%, preferably not less than 99.5%.

5. The method according to any one of claims 1 to 4, characterized in that in step (2) and / or in step (3) the method of separating the aqueous phase from the esterification reaction product is distillation and / or separation of two liquid phases, preferably at least one of the following methods: distillation, flash evaporation, stripping, sedimentation, decantation, coalescence and centrifugation.

6. The method according to any one of paragraphs 1-5, characterized in that each stage of the esterification reaction is carried out in an atmosphere of a flow of inactive gas, preferably the ratio of the space velocity of the inactive gas to the space velocity of the liquid feedstock is 0-1000:1, more preferably 10-250:1; and / or the space velocity of the inactive gas is 3-500 h -1 , preferably 8-80 hours -1 , preferably 8-40 hours -1 .

7. The method according to any one of claims 1 to 6, wherein the method is characterized in that it further provides that in step (2) and / or in step (3) the amount of (alkyl)acrylic acid added is determined in such a way that the molar ratio of (alkyl)acrylic acid at each addition, calculated as carboxyl groups, and the total amount of alcohol, calculated as hydroxyl groups, is 0.05-2:1, preferably 0.05-0.5:1, and the amount of polymerization inhibitor added at each step is 0.01-3 wt.% with respect to the total weight of (alkyl)acrylic acid and alcohol, preferably 0.01-1 wt.%.

8. The method according to any one of claims 1 to 7, characterized in that the molar ratio of (alkyl)acrylic acid in terms of carboxyl groups and alcohol in terms of hydroxyl groups in step (1) is 0.1-2:1, preferably 0.8-1.1:1; and / or the molar ratio of (alkyl)acrylic acid in terms of carboxyl groups and alcohol in terms of hydroxyl groups in the entire production process is 1-4:1, preferably 1.05-1.5:

1.

9. The method according to any one of claims 1 to 8, characterized in that the alkyl group in the (alkyl)acrylic acid contains no more than 8 carbon atoms, preferably no more than 4 carbon atoms, and more preferably the alkyl group in the (alkyl)acrylic acid is methyl, ethyl or propyl; and / or the alcohol is a fatty alcohol whose boiling point at atmospheric pressure is above 100°C and which is insoluble or slightly soluble in water, preferably at least one of the monohydric alcohols containing 9 to 22 carbon atoms, more preferably at least one of the following alcohols: n-decanol, n-undecanol, n-dodecanol, n-tetradecanol, n-hexadecanol and n-octadecanol.

10. The method according to any one of claims 1 to 9, characterized in that the total amount of the polymerization inhibitor used is 0.03 to 5% by weight relative to the total weight of the (alkyl)acrylic acid and alcohol; and / or the polymerization inhibitor is at least one of the following: a phenol-based polymerization inhibitor, a quinone-based polymerization inhibitor, an aromatic amine-based polymerization inhibitor, and an inorganic salt-based polymerization inhibitor.

11. The method according to any one of claims 1 to 10, characterized in that at each stage the esterification reaction is independently carried out under the following conditions: the temperature is 80-140°C, preferably 90-130°C; the absolute pressure is 0-10 MPa, preferably 0.002-2 MPa; and the space velocity of the liquid starting material for the reaction is 0.1-3 h -1 , preferably 0.18-1 h -1; and / or the temperature in the preceding stage of the esterification reaction is less than the temperature in the subsequent stage of the esterification reaction by 1-10°C, preferably by 1-5°C.

12. The method according to claim 2, characterized in that in step (4) the method for removing the polymerization inhibitor is alkaline washing or extraction, preferably extraction, wherein the extraction is carried out under the following conditions: the extraction temperature is 0-90 °C, preferably 25-70 °C; the ratio of the mass of the extracting substance and the mass of the (alkyl) acrylate solution containing the polymerization inhibitor is 0.1-5:1, preferably 0.3-1.2:1; and / or the extraction device is one or more of the following devices in combination: a packed column, a tray column, a rotating disk column, a centrifugal extractor, a spiral extractor and a mixer-precipitator; and / or the extracting substance comprises an alcohol-based extracting substance and / or a water-based extracting substance, preferably a water-based extracting substance; more preferably, the water content in the mixture of water and alcohol is 10-100 wt.%, preferably 60-90 wt.%.

13. The method according to any one of claims 1 to 12, wherein the method is characterized in that it additionally comprises a step (5): further extraction of the aqueous phase obtained in step (2) and / or in step (3) using an extracting agent for isolating (alkyl)acrylic acid and obtaining an extract containing (alkyl)acrylic acid; preferably, the extracting agent is at least one or more hydrophobic alcohols that take part in the esterification reaction and hydrophobic (alkyl)acrylates; the extraction is carried out under the following conditions: the extraction temperature is 0-90°C, preferably 25-60°C; the weight ratio of the extracting agent and the aqueous phase is 0.1-5:1, preferably 0.3-1.0:1;the extraction device is one or more devices selected from the following: a packed column, a plate column, a rotating disk column, a centrifugal extractor, a spiral extractor and a mixer-precipitator, preferably a packed extraction column, and preferably the packing material is a packing material with a hydrophilic surface.

14. The method according to claim 13, characterized in that the extract containing (alkyl)acrylic acid and isolated in step (5) is returned to any of steps (1) to (3) as starting material for the reaction.

15. A reaction system for carrying out the method according to any one of claims 1 to 14, comprising: a plurality of esterification reactors connected in series, and one or more phase separators or distillers that perform separation of the organic phase and the aqueous phase and that are respectively connected to each reactor; wherein each esterification reactor comprises an inlet for introducing fresh starting material for the reaction or, alternatively, an inlet located between the esterification reactor and the phase separator or distiller and for introducing fresh starting material for the reaction into the remaining organic phase from the previous reaction stage.

16. The reaction system according to paragraph 15, characterized in that a centrifugal phase separator or distillation column is selected as the phase separator or distiller.

17. The reaction system according to claim 16, characterized in that it further comprises an extraction device designed to separate the polymerization inhibitor and connected to the last phase separator or distillation column, preferably said extraction device is one or more devices selected from the following: a packed column, a plate column, a rotating disk column, a centrifugal extractor, a spiral extractor and a mixer-precipitator.