Method for preparing high-purity acrylate by removing trace impurity aldehyde

Abstract

The invention provides a method for preparing high-purity acrylate by removing trace impurity aldehyde, which comprises the following steps: mixing crude acrylate with a polymerization inhibitor to form an organic phase; adding an aqueous solution of a dealdehyding agent into the organic phase to form an oil-water two-phase system; the oil-water two-phase system is forcibly stirred for 0.1-2.0 hours at the temperature of 20-40 DEG C, so that the impurity aldehyde and the dealdehyding agent are subjected to nucleophilic addition reaction, and a generated aldehyde-dealdehyding agent addition product is dissolved in a water phase; standing and layering the reacted material, separating and removing a water phase to obtain an organic phase without impurities; carrying out reduced pressure rectification on the organic phase after impurity removal to obtain a high-purity acrylate product with the total aldehyde content lower than 50ppm; wherein the aldehyde removing agent is sodium hydrogen sulfite, potassium hydrogen sulfite, calcium hydrogen sulfite, ammonium hydrogen sulfite or a mixture of any two or more of the sodium hydrogen sulfite, the potassium hydrogen sulfite, the calcium hydrogen sulfite and the ammonium hydrogen sulfite. The method is efficient, economical, free of solid deposition and easy for industrial continuous operation.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing high-purity acrylate, in particular to a method for removing trace impurity aldehyde to prepare high-purity acrylate, and belongs to the technical field of chemical refining. BACKGROUND

[0002] Acrylate is widely used in adhesives, coatings, superabsorbent resins, textiles, building materials and many other fields. At present, the mainstream synthesis process of acrylate is the two-step oxidation method of propylene. After the crude acrylate prepared by this method is esterified with alcohol, trace amounts of aldehyde impurities such as furfural, benzaldehyde and propylene aldehyde are inevitably brought into or generated in the crude acrylate product. The presence of these trace amounts of aldehyde impurities seriously affects the quality of acrylate products in terms of color, storage stability and subsequent polymerization performance. For high-end applications with strict requirements, products containing these impurities often cannot meet user requirements.

[0003] Due to the similar physical properties of impurity aldehyde and target product acrylate, separation by conventional rectification method not only has limited effect, but also has high economic cost. Existing chemical de-aldehyde technologies include primary amine method, phenylhydrazine method and alkyl mercaptan method. The primary amine method uses primary amine to react with aldehyde, which can remove aldehyde, but the generated condensate is solid, which will form deposits at the bottom of the reactor and the rectification tower, seriously affecting the continuous and stable operation of the equipment, and subsequent complex neutralization treatment with organic acid is required. The phenylhydrazine method also has the problems of incomplete de-aldehyde and easy generation of bottom deposits. The alkyl mercaptan method uses alkyl mercaptan and acidic cation exchange resin for catalytic reaction. This method has no deposits, but alkyl mercaptan and resin catalyst are expensive, and the resin needs to be replaced regularly, resulting in high processing cost and complicated operation. SUMMARY

[0004] Based on the above background, the purpose of the present application is to provide a method for removing trace impurity aldehyde to prepare high-purity acrylate, which is efficient, economical, has no solid deposits and is easy to operate continuously in industry.

[0005] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical solutions:

[0006] A method for removing trace impurity aldehyde to prepare high-purity acrylate, the method comprising the following steps:

[0007] The crude acrylate containing impurity aldehyde obtained by reacting acrylate prepared by the two-step oxidation method of propylene with alcohol is used as raw material, and the impurity aldehyde is furfural, benzaldehyde and propylene aldehyde;

[0008] Mixing the crude acrylate with a polymerization inhibitor to form an organic phase;

[0009] adding an aqueous solution of a de-aldehyde agent into the organic phase to form an oil-water two-phase system;

[0010] stirring the oil-water two-phase system at a temperature of 20-40°C for 0.1-2.0 hours to make the impurity aldehyde react with the de-aldehyde agent by nucleophilic addition, and the generated aldehyde-de-aldehyde agent addition product dissolves in the water phase;

[0011] separating and removing the water phase after the reaction to obtain the impurity-removed organic phase;

[0012] subjecting the impurity-removed organic phase to vacuum rectification to obtain a high-purity acrylic ester product with a total aldehyde content of less than 50 ppm;

[0013] The de-aldehyde agent is sodium bisulfite, potassium bisulfite, calcium bisulfite, ammonium bisulfite, or a mixture of any two or more thereof.

[0014] For unsaturated aldehydes, they are prone to nucleophilic addition reaction with bisulfite in the presence of an acidic medium to generate stable addition products. The driving force of the reaction lies in the strong nucleophilicity of bisulfite ion, and the sulfur atom attacks the carbonyl carbon of the aldehyde group to form a sulfide bond, thereby generating water-soluble organic salts. At the same time, by directly adding an aqueous solution of a de-aldehyde agent to the crude ester, the addition product generated by the reaction is immediately captured by the water phase and separated from the organic phase. According to the principle of chemical equilibrium shift, this can continuously push the reaction to the forward direction, thereby achieving extremely high aldehyde conversion rate under mild conditions. Since the product is a water-soluble salt, the problem of solid deposition at the bottom of the kettle in the prior art is fundamentally eliminated.

[0015] As a preferred embodiment, the de-aldehyde agent is a mixture of sodium bisulfite and ammonium bisulfite, and the mass ratio of sodium bisulfite to ammonium bisulfite is 1:1. When sodium bisulfite and ammonium bisulfite are used in a specific ratio, they exhibit a non-obvious synergistic effect, and the de-aldehyde effect is significantly better than that of a single component or other combinations, which can reduce the total aldehyde content to a lower level in a shorter time.

[0016] As a preferred embodiment, the total amount of the de-aldehyde agent added is 3.0-6.0% of the mass of the crude acrylic ester. This addition amount range is the key to achieving a balance between efficiency and economy. If it is less than 3.0%, the de-aldehyde reaction is incomplete, and the product quality is difficult to guarantee. If it is more than 6.0%, although the effect is slightly improved, the cost of the reagent and the subsequent washing load will increase disproportionately.

[0017] As preferred, the time for forced stirring of the oil-water two-phase system is 0.25-1.0 hour. The reaction time range is the optimization of industrial production efficiency under the premise of ensuring the full reaction, shorter than 0.25 hour, the reaction may not be complete, longer than 1 hour, which will reduce the processing capacity of the equipment and increase the production cycle.

[0018] As preferred, the polymerization inhibitor comprises high-efficiency polymerization inhibitor ZJ701 and phenothiazine; the addition amount of the high-efficiency polymerization inhibitor ZJ701 is 100-1000 ppm, and the addition amount of the phenothiazine is 20-200 ppm, relative to the mass of the crude acrylate. The composite polymerization inhibitor system composed of high-efficiency polymerization inhibitor ZJ701 and phenothiazine can effectively inhibit the spontaneous polymerization of acrylate during the reaction and rectification process.

[0019] As preferred, the absolute pressure of the vacuum rectification is 1.0-20 KPa, and the temperature is 80-100℃. The rectification in this vacuum degree and temperature range can significantly reduce the boiling point of acrylate, thereby avoiding the decomposition, polymerization and other side reactions that may occur at high temperature.

[0020] As preferred, after obtaining the impurity-removed organic phase, and before the impurity-removed organic phase is subjected to vacuum rectification, the impurity-removed organic phase is washed one or more times with extraction water to remove unreacted bisulfite and reaction product organic salt.

[0021] As preferred, before the oil-water two-phase system is subjected to forced stirring, a phase transfer catalyst is also added to the oil-water two-phase system, the phase transfer catalyst is a quaternary ammonium salt, and the addition amount of the phase transfer catalyst is 0.05-1.0%, relative to the mass of the crude acrylate. Since the core reaction occurs at the oil-water two-phase interface, its rate is limited by interfacial mass transfer. By introducing a phase transfer catalyst, the reactant ions in the aqueous phase are carried into the main body of the organic phase, so that the reaction that can only occur at the interface is extended to the entire organic phase, thereby making the reaction not only reach a higher conversion rate, but also require a shorter time and lower temperature to reach the conversion rate.

[0022] Compared with the prior art, the present application has the following advantages:

[0023] The method for removing trace impurity aldehyde to prepare high-purity acrylate ester of the present application can effectively reduce the total aldehyde content in the crude ester from hundreds of ppm to below 50 ppm through the integrated reaction and extraction of the synergistic de-aldehyde agent formula, and the purity of the acrylate ester product can reach above 99.70%; the reaction product of the method is a water-soluble salt, which can be completely removed through simple water washing, thereby completely solving the problem of solid deposition at the bottom of the existing kettle and tower, and ensuring the long-term stable operation of the industrial device; the reaction of the method is carried out at normal temperature and pressure, thereby effectively avoiding the side reaction of acrylate ester; and the de-aldehyde agent used in the method is an inexpensive and readily available inorganic salt, which greatly reduces the production cost. DETAILED DESCRIPTION

[0024] The technical solutions of the present application will be further described below through specific examples. It should be understood that the implementation of the present application is not limited to the following examples, and any form of modification and / or change made to the present application will fall within the scope of protection of the present application.

[0025] In the present application, unless otherwise specified, all parts, percentages are by weight, and the equipment and raw materials used can be purchased from the market or are commonly used in the art. The methods in the following examples are conventional methods in the art, unless otherwise specified. The components or equipment in the following examples are general standard components or components known to those skilled in the art, and their structure and principles can be known to those skilled in the art through technical manuals or through conventional experimental methods.

[0026] The examples of the present application are described in detail below. In the following detailed description, many specific details are set forth in order to provide a thorough understanding of the examples of the present application. However, one or more embodiments can be practiced without these specific details.

[0027] The present application discloses a method for removing trace impurity aldehyde to prepare high-purity acrylate ester, which comprises the following steps:

[0028] The crude acrylate ester containing impurity aldehyde obtained by reacting acrylate prepared by the two-step oxidation method of propylene with alcohol is used as the raw material, and the impurity aldehyde is furfural, benzaldehyde and acrolein;

[0029] The crude acrylate ester is mixed with the polymerization inhibitor to form an organic phase;

[0030] The aqueous solution of the de-aldehyde agent is added to the organic phase to form an oil-water two-phase system;

[0031] The oil-water two-phase system is subjected to forced stirring at a temperature of 20-40℃ for 0.1-2.0 hours, so that the impurity aldehyde and the de-aldehyde agent undergo nucleophilic addition reaction to generate aldehyde-de-aldehyde agent adducts which are dissolved in the water phase;

[0032] The post-reaction material is allowed to stand for layer separation, the aqueous phase is separated and removed, and an impurity-removed organic phase is obtained;

[0033] The impurity-removed organic phase is subjected to vacuum rectification, and a high-purity acrylic ester product with a total aldehyde content of less than 50 ppm is obtained;

[0034] The de-aldehyde agent is sodium bisulfite, potassium bisulfite, calcium bisulfite, ammonium bisulfite, or a mixture of any two or more thereof.

[0035] The method disclosed in the present application is further described in detail below in combination with experiments of multiple examples and comparative examples.

[0036] Examples 1-4

[0037] In a 500-ml conical flask, 200 g of crude butyl acrylate containing 250 ppm of furfural, 50 ppm of acrolein, and 250 ppm of benzaldehyde (total aldehyde content of 550 ppm) was added, followed by the addition of 0.2 g of high-efficiency polymerization inhibitor ZJ701 (1000 ppm) and 0.04 g of phenothiazine (200 ppm). Subsequently, 200 ml of desalted water and 5.0% of the mass of the crude ester of a de-aldehyde agent (the specific type is shown in Table 1) were added. In a constant-temperature water bath at 30°C, a magnetic stirrer was used for forced stirring for 30 minutes. After the reaction was completed, the mixture was poured into a separatory funnel for layer separation, and the lower aqueous solution was separated and removed. The upper organic phase was collected and subjected to vacuum rectification in a 500-ml three-necked flask connected to a column with 15 theoretical plates of packing at an absolute pressure of 5.0 KPa. The main fraction was collected, and the total aldehyde content and purity were analyzed. The experimental results are shown in Table 1.

[0038] Table 1 Experimental results of Examples 1-4

[0039] Example No. De-aldehyde agent name Total aldehyde content (ppm) Butyl acrylate purity (wt%) Kettle bottom phenomenon 1 Sodium bisulfite 15 99.73 No precipitate 2 Potassium bisulfite 40 99.72 No precipitate 3 Calcium bisulfite 35 99.72 No precipitate 4 Ammonium bisulfite 50 99.70 No precipitate

[0040] Example 5

[0041] Except that the de-aldehyde agent was replaced by a 1:1 (mass ratio) mixture of sodium bisulfite and ammonium bisulfite, the remaining raw materials, proportions, reaction and rectification conditions were the same as in Example 1. The experimental results are shown in Table 2.

[0042] Table 2 Experimental results of Example 5

[0043] Example No. De-aldehyde agent name Total aldehyde content (ppm) Butyl acrylate purity (wt%) Kettle bottom phenomenon 5 Sodium bisulfite + Ammonium bisulfite (1 : 1) 27 99.72 No precipitate

[0044] Comparative Example 1, Example 4 and Example 5, it can be seen that sodium bisulfite alone has the best effect, ammonium bisulfite alone has the worst effect, however, after mixing ammonium bisulfite with sodium bisulfite, the effect (total aldehyde content 27 ppm) is significantly better than its own (total aldehyde content 50 ppm), which proves that there is a certain synergistic effect between the two.

[0045] Examples 6-9 and Comparative Examples 1-2

[0046] In a 500 ml conical flask, 200 grams of the same crude butyl acrylate as in Example 1 and a polymerization inhibitor were added. Then, 200 ml of desalted water and different mass percentages of sodium bisulfite were added as a de-aldehyde agent. The rest of the reaction and rectification conditions were the same as in Example 1. The experimental results are shown in Table 3.

[0047] Table 3 Experimental results of the effect of the amount of de-aldehyde agent added

[0048] Experiment No. Medicament addition amount (wt%) Total aldehyde content (ppm) Butyl acrylate purity (wt%) Kettle bottom phenomenon Comparative Example 1 1 190 99.70 No precipitate Comparative Example 2 2 100 99.71 No precipitate Example 6 3 40 99.72 No precipitate Example 7 4 30 99.72 No precipitate Example 8 5 17 99.72 No precipitate Example 9 6 11 99.72 No precipitate

[0049] As can be seen from Table 3, when the amount of de-aldehyde agent added is less than the preferred range of 3.0% of the present application (Comparative Examples 1-2), the de-aldehyde effect is obviously poor, and the total aldehyde content is still as high as 100-190 ppm. When the amount added enters the preferred range of 3.0-6.0% (Examples 6-9), the de-aldehyde effect jumps, the total aldehyde content rapidly decreases to below 40 ppm, and continues to decrease with the increase of the amount added. This proves that the amount of 3.0-6.0% defined in the present application is necessary to achieve efficient de-aldehyde.

[0050] Example 10

[0051] The experimental steps of Example 5 were repeated, but at the same time as 200 ml of desalted water and 5.0% of the mass of the crude ester of the de-aldehyde agent were added, 0.2 grams (0.1%) of tetrabutylammonium bromide (TBAB) was additionally added as a phase transfer catalyst. To verify the effect of the phase transfer catalyst on the reaction rate, the forced stirring time was shortened from 30 minutes to 15 minutes. The rest of the conditions were unchanged.

[0052] Experimental results: after 15 minutes of reaction, the total aldehyde content in the final butyl acrylate product obtained was 8 ppm, the purity was 99.74%, and there was no precipitate at the bottom of the kettle.

[0053] Comparative Example 1 (reaction time 30 minutes, total aldehyde 15 ppm), after the addition of the phase transfer catalyst in this example, only about half of the reaction time (15 minutes) was used to obtain a lower residual total aldehyde content (8 ppm). This proves that the introduction of the phase transfer catalyst greatly accelerates the reaction rate kinetically.

[0054] The principles and implementations of the present application are described in the specific examples in this article, and the above examples are only used to help understand the method of the present application and its core idea. It should be pointed out that for ordinary skilled in the art, without departing from the principles of the present application, the present application can be improved and modified, and these improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A method for preparing high-purity acrylate by removing trace impurity aldehydes, characterized in that: The method comprises the following steps: Using crude acrylic acid ester containing impurity aldehydes obtained by reacting acrylic acid prepared by a two-step propylene oxidation process with alcohols as a raw material, the impurity aldehydes being furfural, benzaldehyde and / or acrolein; mixing the crude acrylate with a polymerization inhibitor to form an organic phase; adding a dealdehyde agent to the organic phase to form an oil-water two-phase system; Forcefully stirring the oil-water two-phase system at a temperature of 20-40° C. for 0.1-2.0 hours to allow the impurity aldehyde to undergo a nucleophilic addition reaction with the formaldehyde-deformylating agent, and the generated aldehyde-deformylating agent adduct is dissolved in the aqueous phase; The reacted material is allowed to stand for stratification, and the aqueous phase is separated and removed to obtain an organic phase after impurities are removed; The organic phase after impurities are removed is subjected to vacuum distillation to obtain a high-purity acrylate product with a total aldehyde content of less than 50 ppm; Wherein, the dealdehyde agent is sodium bisulfite, potassium bisulfite, calcium bisulfite, ammonium bisulfite or a mixture of any two or more thereof.

2. The method for preparing high-purity acrylate by removing trace impurity aldehydes according to claim 1, wherein: The dealdehyde agent is a mixture of sodium bisulfite and ammonium bisulfite, and the mass ratio of sodium bisulfite to ammonium bisulfite is 1:

1.

3. The method for preparing high-purity acrylate by removing trace impurity aldehydes according to claim 1, wherein: The total amount of the formaldehyde remover added is 3.0-6.0% of the mass of the crude acrylate.

4. The method for preparing high-purity acrylate by removing trace impurity aldehydes according to claim 1, characterized in that: The time for forced stirring of the oil-water two-phase system is 0.25-1.0 hour.

5. The method for preparing high-purity acrylate by removing trace impurity aldehydes according to claim 1, characterized in that: The polymerization inhibitor includes a high-efficiency polymerization inhibitor ZJ701 and phenothiazine; relative to the mass of the crude acrylate, the addition amount of the high-efficiency polymerization inhibitor ZJ701 is 100-1000 ppm, and the addition amount of the phenothiazine is 20-200 ppm.

6. The method for preparing high-purity acrylate by removing trace impurity aldehydes according to claim 1, characterized in that: The absolute pressure of the vacuum distillation is 1.0-20 KPa, and the temperature is 80-100°C.

7. The method for preparing high-purity acrylate by removing trace impurity aldehydes according to claim 1, characterized in that: After obtaining the organic phase after decontamination, and before subjecting the organic phase after decontamination to vacuum distillation, the organic phase after decontamination is washed once or multiple times with extraction water to remove unreacted bisulfite and reaction product organic salt.

8. The method for preparing high-purity acrylate by removing trace impurity aldehydes according to claim 1, characterized in that: Before the oil-water two-phase system is forcibly stirred, a phase transfer catalyst is added to the oil-water two-phase system. The phase transfer catalyst is a quaternary ammonium salt. The amount of the phase transfer catalyst added is 0.05-1.0% relative to the mass of the crude acrylate.