CN1117060C - Process for purifying acrylic acid - Google Patents

Abstract

The present invention provides a method for purifying acrylic acid obtained by vapor-phase oxidation, the method comprising: distilling a mixture containing acrylic acid, hydrazine compound and copper dithioformate compound at a temperature not higher than 100°C. According to the present invention, acrylic acid produced by vapor phase oxidation can be efficiently purified while suppressing polymerization during distillation.

Description

Method for purifying acrylic acid

The present invention relates to a method for purifying acrylic acid. In particular, the invention relates to a process for the purification of acrylic acid obtained by vapor phase oxidation.

Although vapor phase oxidation to acrylic acid is a well-known process in the industry, it is known that by-products such as aldehydes (such as furfural and benzaldehyde) and ketones (such as acetone) and the like are formed in the process.

Recently, acrylic has been in increasing demand as a material for water-absorbent resins that are used, for example, in paper towels. In this use, acrylic acid is required to be of high purity. Therefore, acrylic acid is purified by distillation on an industrial scale.

However, it is difficult to remove the above-mentioned by-product (ie, furfural) present in acrylic acid produced by the vapor phase oxidation method by ordinary distillation treatment. Furthermore, when the produced acrylic acid is used as a material for producing acrylic acid polymers without removing such impurities, various problems arise, such as delay in polymerization, decrease in degree of polymerization, and coloration of the resulting polymer.

In order to solve these problems, it has been proposed to add a hydrazine compound during distillation. Although the added hydrazine compound has the effect of removing impurities, this creates another problem of polymerization of acrylic acid during distillation. This polymerized material adheres to heat transfer surfaces in the reboiler of the distillation column during distillation, thereby reducing its heat transfer performance.

Therefore, a distillation method which suppresses such polymerization has been desired.

The object of the present invention is to provide an effective method for purifying acrylic acid produced by vapor phase oxidation while inhibiting its polymerization.

This purpose and others will be given below.

The present inventors studied a method of purifying acrylic acid produced by vapor phase oxidation and found that the above object can be achieved by adding a hydrazine compound and a copper dithiocarbamate compound to acrylic acid produced by vapor phase oxidation and distilling the mixture. The above and further studies constitute the entire content of the present invention.

The present invention relates to a method for purifying acrylic acid obtained by vapor phase oxidation, comprising distilling a mixture containing acrylic acid, hydrazine compound and copper dithiocarbamate compound at a temperature not higher than 100°C.

The present invention is described in detail below.

The acrylic acid used in the present invention is acrylic acid obtained by vapor-phase oxidation of propylene and/or acrolein, so-called vapor-phase acrylic acid. The acrylic acid generally contains aldehydes such as furfural and benzaldehyde and ketones such as acetone concomitantly produced during the production process.

Examples of the hydrazine compound used include free hydrazine, hydrazine hydrate or hydrazine salt, and arylhydrazine such as phenylhydrazine, alkylhydrazine such as methylhydrazine. Hydrazine hydrate, phenylhydrazine, hydrazine sulfate and hydrazine hydrochloride are preferred. More preferably, it is hydrazine hydrate.

The amount of the hydrazine compound added to the acrylic acid is usually about 50PPm-5000PPm by weight, and preferably about 200PPm-3000PPm by weight. By adding a hydrazine compound, impurities contained in acrylic acid and which have an unfavorable effect when the acrylic acid is used as a polymer material can be removed by distillation. In particular, it can remove furfural which is difficult to separate from acrylic acid by ordinary distillation

Copper dithiocarbamate compounds, for example, can be represented by the general formula:

Cu [R ¹ (R ² ) NCS ₂ ] ₂ wherein R ¹ and R ² may be the same or different, and each represents an alkyl group preferably having 1-6 carbon atoms, or R ¹ and R ² collectively represent an optimal is an alkylene group of 2-6 carbon atoms attached to a nitrogen atom, one of which can be optionally replaced by an oxydiethyl group such as -(CH ₂ ) ₂ -O-(CH ₂ ) ₂ - Oxygen group substitution.

Copper dithiocarbamate compounds used include copper dialkyldithiocarbamate such as copper dimethyldithiocarbamate, copper diethyldithiocarbamate, copper dipropyldithiocarbamate and copper dibutyl dithiocarbamate; copper cycloalkylene dithiocarbamate, such as copper ethylene dithiocarbamate, copper tetramethylene dithiocarbamate, pentamethylene dithiocarbamate Copper carbamate and copper hexamethylene dithiocarbamate; and copper epoxydialkylene dithiocarbamate, such as copper oxydiethyldithiocarbamate.

The amount of the copper dithiocarbamate compound added to the acrylic acid is usually about 1PPm-100PPm (weight), preferably about 5PPm-80PPm (weight), and more preferably about 10PPm-50PPm (weight). When the amount added is too small, the effect of inhibiting polymerization is insufficient, especially at the initial stage of distillation. Excessive addition of copper dithiocarbamate will not cause some problems in inhibiting polymerization, but it is not advisable, because too high concentration of copper dithiocarbamate in the solution in the distillation vessel will lead to corrosion of the distillation apparatus.

The method of adding the hydrazine compound and the copper dithiocarbamate compound is not limited. For example, each of them may be directly added to acrylic acid, or they may be dissolved in the same solvent or respective organic solvents and then added to acrylic acid.

The addition temperature can be appropriately determined.

The hydrazine compound and the copper dithiocarbamate compound can be added immediately after the preparation of the acrylic acid, but are preferably added just before distillation. In the industrial field, it is usually added to the acrylic acid which will be fed to the distillation apparatus, or in some cases to the solution which is refluxed into the distillation vessel during distillation.

In addition, when a phenolic compound is added to acrylic acid in addition to the hydrazine compound and the copper dithiocarbamate compound, the effect of the present invention is further improved.

Examples of the phenolic compound include phenol, hydroquinone, methoxyphenol (p-methoxyphenol), catechol and cresol.

The amount of the phenolic compound added to the acrylic acid is usually about 10PPm-500PPm by weight, and preferably about 50PPm-300PPm by weight.

In addition, other polymerization inhibitors such as phenothiazines and manganese salts may also be added. The phenolic compound and the polymerization inhibitor can be added in the same manner as the hydrazine compound and the copper dithiocarbamate compound.

The thus obtained acrylic acid mixture containing the hydrazine compound and the copper dithiocarbamate compound was subjected to distillation to remove impurities in the acrylic acid.

The distillation method is not limited, and various methods such as simple distillation and rectification can be used. Specifically, the method used in the examples disclosed in Japanese Patent Application Laid-Open No. 49-30312 can be employed. Distillation can be performed continuously or batchwise. Continuous mode is preferred industrially.

Parts in the distillation apparatus that come into contact with the liquid or vapor of the mixture of acrylic acid and the like can be made of, for example, stainless steel.

The distillation temperature is not higher than 100°C, preferably not higher than 80°C, more preferably not higher than 70°C.

The residence time of acrylic acid depends on the distillation temperature. When the temperature is in the range of 80-100°C, the residence time is usually not more than 5 hours, preferably not more than 3 hours, more preferably not more than 1 hour. When the temperature is in the range of 70-80°C, the residence time is usually not more than 20 hours, preferably not more than 10 hours, more preferably not more than 5 hours. When the temperature is not higher than 70°C, the residence time is usually not more than 30 hours, preferably not more than 20 hours, more preferably not more than 10 hours.

The concentration ratio of the solution in the distillation vessel depends on the type of distillation, distillation temperature and time, the type and content of impurities and so on.

In order to prevent corrosion of distillation equipment, the concentration of copper dithiocarbamate is preferably kept below 1 wt%.

According to the present invention, polymerization in distillation can be suppressed while efficiently purifying acrylic acid remaining in vapor phase oxidation. As a result, impurities inherent in acrylic acid and which have an adverse effect when acrylic acid is used as a raw material for an acrylic polymer can be removed. Therefore, the present invention has industrial value

The present invention will be described in more detail below by way of examples. Of course, the present invention is not limited to these Examples.

Example 1:

Add copper dibutyldithiocarbamate and water hydrazine in 1Kg thick acrylic acid containing 200PPm (weight) furfural impurity, make in crude acrylic acid containing 20PPm (weight) copper dibutyldithiocarbamate and 0.1% (wt) mixture of hydrazine hydrate. The obtained mixture was subjected to vacuum distillation at a pressure of 50 Torr and a temperature of 69° C. using an evaporator, and 99.5% of the mixture was distilled for 1 hour (the concentration ratio of the mixture was 200). During and after the distillation, essentially no polymer was found in the residue. The furfural content in the obtained distillate is lower than 1PPm.

Example 2-5

These examples were carried out in the same manner as Example 1, except that, as listed in Table 1, the amount of copper dibutyldithiocarbamate was varied or other additives were added. The results are also shown in Table 1.

Table 1 Example serial number CBD ^*1 content other additives Polymer formation in the residue Content of FFP ^*2 in the distillate type content 2 50ppm none 0ppm Essentially no polymer <1ppm 3 80ppm none 0ppm Essentially no polymer <1ppm 4 50ppm MTQ ^*3 100ppm polymer free <1ppm 5 50ppm MTQ ^*3 PTZ ^*4 100ppm200ppm polymer free <1ppm ^* 1: CBD refers to copper dibutyldithiocarbamate. ^* 2: FF refers to furfural. ^* 3: MTQ nail quinone. ^* 4: PTZ means phenothiazine. Comparative example 1-5

These comparative examples were also carried out in the same manner as in Example 1, except that other additives as listed in Table 2 were added instead of copper dibutyldithiocarbamate. The results are also shown in Table 2.

Table 2 Comparative serial number other additives polymer from the residue type content 1 MTQ ^*3 200ppm Turbidity/10min. ^*8 There are many polymers on the wall of the device/at the end ^*10 2 HQ ^*5 200ppm Rust/10min. ^*9 There are many polymers on the wall/At the end ^*10 3 MTQ ^*3 PTZ ^*4 100ppm200ppm Turbidity/10min. ^*8 Rust/30min. ^*9 There are many polymers on the wall/At the end ^*10 4 HQ ^*5 MA ^*5 200ppm50ppm Rust/10min. ^*9 There are many polymers on the wall/At the end ^*10 5 MTQ ^*3 MBD ^*7 PTZ ^*4 100ppm50ppm200ppm Turbidity/10min. ^*8 Rust/30min. ^*9 There are many polymers on the wall/At the end ^{*10 *} 3 and ^* 4: The meanings of MIQ and PTZ are the same as in Table 1. ^* 5: HQ refers to hydroquinone. ^* 6: MA refers to manganese acetate. ^* 7: MBD refers to manganese dibutyldithiocarbamate. ^* 8: Compounding was found due to generation of polymer at about the given time (minutes) from the start of distillation.

The compound is cloudy. ^* 9: Discharge in the distillation volume due to polymer generation at the given time (minutes) since the start of distillation

Corrosion was found on the inner wall of the container. ^* 10: After distillation, a large amount of polymer was found to adhere to the wall of the still.

Having thus described the invention, it is obvious that this equivalent subject matter may be varied in various ways. Such changes are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications are intended to be included within the scope of the following claims as would be obvious to one of ordinary skill in the art.

Claims (6)

1. acrylic acid that purification is obtained by vapor-phase oxidation method, the step that this method comprises is: contain vinylformic acid not being higher than under 100 ℃ of temperature distillation, the mixture of hydrazine compound and dithiocarbamic acid copper compound, described dithiocarbamic acid copper is selected from cupric dimethyldithiocarbamate, copper diethyl dithiocarbamate, dipropyl dithiocarbamic acid copper, copper dibutyldithiocarbamate, ethylene thiocarbamate copper, tetramethylene dithiocarbamic acid copper, pentylidene dithiocarbamic acid copper, the amino first copper of hexylidene dithio, oxydiethylene dithiocarbamic acid copper.

2. method as claimed in claim 1, wherein said mixture also contains phenolic compound.

3. method as claimed in claim 2, wherein said phenolic compound are selected from phenol, quinhydrones, first quinone, catechol and cresols.

4. method as claimed in claim 1, wherein said hydrazine compound is selected from hydrazine hydrate, phenylhydrazine, hydrazonium sulfate and hydrazine hydrochloride.

5. method as claimed in claim 1, wherein the temperature in the distilation steps is not higher than 80 ℃.

6. method as claimed in claim 1, wherein the temperature in the distilation steps is not higher than 70 ℃.