CN103058849A - Interval reaction rectification process for synthesizing methacrylic anhydride - Google Patents

Abstract

The invention discloses a batch reaction rectification process for synthesizing methacrylic anhydride. The reaction rectification equipment is a batch reaction rectification tower, and the reaction is mainly carried out in the tower still of the rectification tower. The process uses reactive distillation technology to remove the by-product acetic acid from the reaction system in time, so that the reaction moves in the positive direction and the conversion rate of methacrylic acid increases. The polymerization inhibitor is added from the tower kettle and the reflux port of the tower respectively, effectively preventing the polymerization of methacrylic acid. The batch reaction distillation process for synthesizing methacrylic anhydride has the characteristics of high reaction conversion rate, high purity of tower top acetic acid, stable product quality and the like. The conversion rate of methacrylic acid in this process is over 98%, and the reaction yield of methacrylic anhydride exceeds 80%.

Description

A batch reaction rectification process for synthesizing methacrylic anhydride

technical field

The invention belongs to the field of chemical industry, and in particular relates to a batch reaction rectification process for synthesizing methacrylic anhydride.

Background technique

Methacrylic anhydride is a strong esterification agent, and it is a necessary reagent for the preparation of methacrylic acid thioester, methacrylamide and methacrylic acid ester (especially the ester of tertiary alcohol). The coupling agent is used in the synthesis of materials such as photocurable coatings and cross-linked resins, and can also be used as a raw material for the synthesis of special fine chemicals, which has broad market application prospects.

At present, the synthesis technology of methacrylic anhydride is mainly divided into two categories: the first category is the preparation of methacrylic anhydride with metal methacrylic acid salt and chloroformate as raw materials. The second type is to use methacrylic acid and acetic anhydride as raw materials to prepare methacrylic anhydride in a rectifying tower. The first type of preparation method adopts a batch stirred tank reactor, the production efficiency is low, and the raw materials used are complicated, and not only a phase transfer catalyst but also a polymer carrier is required. The production efficiency of the second method is 35% higher than that of the first method, and reactive distillation has the advantages of high reaction conversion and selectivity. But during the preparation process, there will be white powder deposits. This deposit will scale the walls, bottom, back of the paddles and the stirring shaft of the reactor. In addition, this white powder can also clog the filter upstream of the storage tank.

On the basis of Jean-Michel Paul's methacrylic anhydride production method, Bernard Dupont proposed an improved method for producing methacrylic anhydride: using methacrylic acid and acetic anhydride as raw materials, the inhibitor is dithiocarbamate metal salt and its Mixtures with phenol derivatives or phenothiazines and their derivatives, or N-oxyl compounds in the presence of 2,4-dimethyl-6-tert-butylphenol. The phenol derivatives are preferably 2,6-di-tert-butyl-4-methylphenol (BHT) and 2,4-dimethyl-6-tert-butylphenol (TOPANOLA). These polymerization inhibitors can inhibit the appearance of the white powder scaling deposits described above in the presence of air, and improve the conversion rate and yield of the reaction. However, to further increase the conversion rate of methacrylic acid, the method of reactive distillation can be selected.

Reactive Distillation (referred to as RD) is a special field of distillation technology and one of the important methods of chemical process intensification. Reactive distillation is a unit operation that couples chemical reaction and rectification process. Through rectification, reactants and products are separated in time to destroy the original reaction balance, so that the reaction continues toward the direction of product formation, thereby improving the reaction rate. conversion, selectivity and productivity. Compared with traditional processes, reactive distillation significantly reduces the amount of catalyst used, saves energy to a certain extent, and has the advantages of high conversion rate, good selectivity, low energy consumption, and low investment, so it has been extensively studied in recent years and apply.

This method is based on the predecessors, using methacrylic acid and acetic anhydride as raw materials, adding a suitable polymerization inhibitor, and using the method of reactive distillation to synthesize methacrylic anhydride. Compared with previous studies, the conversion rate of methacrylic acid and the yield of methacrylic anhydride in this method are greatly improved.

Contents of the invention

The object of the present invention is to provide a kind of batch reaction rectification process of synthesizing methacrylic anhydride, this batch reaction rectification process synthetic methacrylic anhydride has characteristics such as high reaction conversion rate, high purity of tower top acetic acid, stable product quality. The conversion rate of methacrylic acid in this process is over 98%, and the reaction yield of methacrylic anhydride exceeds 80%.

To achieve the above object, the present invention adopts the following technical solutions:

A batch reaction rectification process for synthesizing methacrylic anhydride, comprising the following steps:

(1) Add acetic anhydride, methacrylic acid and polymerization inhibitor to the tower kettle after mixing, turn on the heating, and acetic anhydride and methacrylic acid react in the presence of polymerization inhibitor;

(2) The initial pressure at the top of the tower is controlled at 10kPa, and then the operating pressure of the tower is continuously reduced during the reaction process. Taking the steam at the top of the tower as the standard, when there is no more steam at the top of the tower to be condensed, the vacuum degree of the tower is appropriately increased , so that one of the products of the reaction, acetic acid, is continuously steamed out from the rectifying tower;

(3) When reflux occurs at the top of the tower, dissolve part of the polymerization inhibitor with acetic acid and add it continuously and slowly from the reflux port of the tower to prevent the polymerization of methacrylic acid in the tower;

(4) At the beginning of tower top extraction, set the reflux ratio to 1, and then gradually increase the reflux ratio to 3;

(5) The acetic acid produced by the reaction is evaporated from the top of the tower and then condensed, part of the condensate is refluxed to the reactive distillation column, and the other part of the condensate is extracted;

(6) When almost no acetic acid is extracted from the top of the tower, the reaction ends, and the heating of the tower kettle is stopped.

The molar ratio of acetic anhydride and methacrylic acid is 1:1.5~1:4, and the feeding method is one-time feeding.

Described polymerization inhibitor is 2,4-di-tert-butyl-p-cresol, 2,6-di-tert-butyl-6-p-cresol and phosphoric acid triester, and the mass ratio of the three is 1:1:1～ 1:3:5.

The theoretical plate number of the reactive distillation column is 10-20, and the reflux ratio is 1-3.

The amount of the polymerization inhibitor in step (1) is 0.01-1.5% of the total mass of acetic anhydride and methacrylic acid.

The amount of the polymerization inhibitor added from the reflux port of the tower in step (3) accounts for 0.01-2% of the proportion of acetic acid.

By adjusting the top pressure of the batch reaction rectification tower, the temperature of the bottom of the tower does not exceed 110°C.

The reactive distillation tower is a packed tower, and the packing is one or a mixture of structured packing and random packing.

The beneficial effect of the present invention is that: in the process, the main equipment is a reaction device composed of a tower reactor and a rectification tower. In the presence of a polymerization inhibitor, the polymerization of methacrylic acid is effectively prevented. Under reduced pressure conditions, the by-products generated by the reaction of acetic anhydride and methacrylic acid can be removed from the separation system in time, so that the reaction balance moves to the positive direction, and the conversion rate and yield of the reaction are improved. Moreover, under reduced pressure operation, the temperature of the tower reactor is relatively low, which reduces the possibility of polymerization reaction.

Description of drawings

Fig. 1 is a schematic flow sheet of the process for producing methacrylic anhydride by batch reaction distillation of the present invention. The labels in the figure are as follows: 1. Tower top pressure gauge, 2. Rectification tower, 3. Packing, 4. Tower kettle inlet, 5. Thermometer, 6. Tower kettle outlet, 7. Tower kettle, 8. Resistance Polymer feed inlet, 9, tower top extraction, 10, reflux ratio controller, 11, tower top condenser, 12, tower top reflux.

Detailed ways

The present invention will be further described below through specific embodiments, but the present invention is not limited to these examples.

Example 1

Adopt technological process shown in accompanying drawing 1, concrete steps are as follows:

1) After the raw materials acetic anhydride and methacrylic acid are mixed with the polymerization inhibitor, they are fed into the tower kettle through the pipeline 4. The molar ratio of the raw materials acetic anhydride and methacrylic acid is 1:1.5~1:4, and the feeding method is one-time feeding.

2) Turn on the heating and control the initial top pressure at 10kPa. Then in the reaction process, the operating pressure of the tower is continuously reduced (taking the steam at the top of the tower as the standard, and when the steam at the top of the tower is no longer condensed, then the vacuum degree of the tower is appropriately increased), so that one of the products, acetic acid, is constantly distilled from the rectification The tower steams out.

3) When there is reflux at the top of the tower, dissolve part of the polymerization inhibitor with acetic acid and slowly add it through the pipeline 8, merge with the reflux liquid into the pipeline 12, and then enter the rectification tower to prevent the polymerization of methacrylic acid in the tower. The consumption of the polymerization inhibitor that adds accounts for 0.2% of raw material liquid total amount.

4) Set the reflux ratio to 1. After 2 hours of extraction, adjust the reflux ratio to 2. After continuous extraction for 1 hour, adjust the reflux ratio to 3 until the reaction is over.

5) The acetic acid produced by the reaction is evaporated from the top of the tower and then condensed by the condenser, part of the condensate is refluxed to the reactive distillation column, and the other part of the condensate is extracted from the pipeline 9.

6) When there is almost no acetic acid produced at the top of the tower, it can be considered that the reaction is over, and the heating of the tower kettle is stopped.

The batch reaction distillation tower is a packed tower, the packing is a structured packing, and the number of theoretical plates is 20.

The reaction results are as follows: the reaction time is 5.65 hours, the conversion rate of methacrylic acid is 99.2%, the purity of acetic acid at the top of the tower is 99.1%, and the reaction yield of methacrylic anhydride is 88.1%.

Example 2

Similar to the operation method of Example 1, the molar ratio of raw materials acetic anhydride and methacrylic acid is 1:1.5~1:4, and the feeding method is one-time feeding.

The reaction results are as follows: the reaction time is 5.58 hours, the conversion rate of methacrylic acid is 99.11%, the purity of acetic acid at the top of the tower is 99.82%, and the reaction yield of methacrylic anhydride is 85.99%.

Example 3

Similar to the operation method of Example 1, the polymerization inhibitor is 2,4-di-tert-butyl-p-cresol (6BX), 2,6-di-tert-butyl-6-p-cresol (BHT), phosphoric acid triester (TOP ), the mixing ratio of the three is still mass ratio 1:2:3, and the amount of polymerization inhibitor is 0.5% of the raw material liquid quality. When the top of the tower starts to extract, set the reflux ratio to 1. After 2.5 hours of extraction, adjust the reflux ratio to 1.5. After continuous extraction for 1 hour, adjust the reflux ratio to 3 until the end of the reaction. Other operating conditions are the same as Example 1.

The reaction results are: the reaction time is 4.75h, the conversion rate of methacrylic acid is 99.2%, the purity of acetic acid at the top of the tower is 99.1%, and the reaction yield of methacrylic anhydride is 86.10%.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims (8)

1. the batch reactive distillation technique of a synthesize methyl acrylic acid anhydrides is characterized in that: may further comprise the steps:

(1) acetic anhydride, methacrylic acid and stopper are mixed the rear tower reactor that adds, open heating, acetic anhydride and methyl-prop diluted acid react under the condition that stopper exists;

(2) initial tower top pressure is controlled at 10kPa, then in reaction process, constantly reduce the working pressure of tower, take overhead vapours as standard, when no longer including steam and be condensed, then suitably improves cat head the vacuum tightness of tower, and one of the resultant acetic acid of reaction is constantly steamed from rectifying tower;

(3) when cat head occur to reflux, the part stopper is slowly added from the tower refluxing opening after with acetate dissolution continuously, prevent that methacrylic acid from polymerization occuring in tower;

When (4) beginning overhead extraction, reflux ratio is set to 1, then gradually reflux ratio is increased to 3;

(5) acetic acid of reaction generation steams rear condensation from cat head, and a part of phlegma is back to reaction fractionating tower, the extraction of another part phlegma;

(6) when cat head does not have the acetic acid extraction substantially, reaction finishes, the tower reactor stopped heating.

2. the batch reactive distillation technique of synthesize methyl acrylic acid anhydrides according to claim 1, it is characterized in that: the mol ratio of aceticanhydride and methacrylic acid charging is 1:1.5 ~ 1:4, feed way is for once reinforced.

3. the batch reactive distillation technique of synthesize methyl acrylic acid anhydrides according to claim 1, it is characterized in that: described stopper is 2,4-ditertbutylparacresol, 2,6-di-t-butyl-6-p-cresol and phosphotriester, three's mass ratio are 1:1:1～1:3:5.

4. the batch reactive distillation technique of synthesize methyl acrylic acid anhydrides according to claim 1, it is characterized in that: the number of theoretical plate of reaction fractionating tower is 10～20, reflux ratio is 1～3.

5. the batch reactive distillation technique of synthesize methyl acrylic acid anhydrides according to claim 1, it is characterized in that: the consumption of the stopper of step (1) is 0.01 ~ 1.5% of acetic anhydride and methacrylic acid total mass.

6. the batch reactive distillation technique of synthesize methyl acrylic acid anhydrides according to claim 1 is characterized in that: the consumption of the described stopper that adds from the tower refluxing opening of step (3) accounts for 0.01 ~ 2% of acetic acid proportion.

7. the batch reactive distillation technique of synthesize methyl acrylic acid anhydrides according to claim 1 is characterized in that: by adjusting the tower top pressure of batch reactive distillation tower, make the temperature of tower reactor be no more than 110 ℃.

8. the batch reactive distillation technique of synthesize methyl acrylic acid anhydrides according to claim 1, it is characterized in that: described reaction fractionating tower is packing tower, filler is one or both mixture of structured packing, random packing.

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