RU2612254C1 - Method of utilizing methyl methacrylate production distillation residues - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: utilization is carried out by distillation in two stages, wherein the first stage is carried out in a distillation column with efficiency of 3-4 theoretical plates in a vacuum of 0.8-0.85 atm at a column bottom temperature of 60-106°C, a column top temperature of 58-74°C and a reflux ratio of 0.5-1.0, the second stage is carried out in a distillation column with efficiency of 4-5 theoretical plates, fraction obtained in the first stage is loaded into the colomn bottom and rectified in a vacuum of 0.8-0.85 atm at a column bottom temperature of 60-86°C, a column top temperature of 58-59°C and a reflux ratio of 1 at the beginning of the distillation with a gradual increase to 3 at the end of distillation. At both stages 2.3% inhibitor solution in methyl methacrylate is slowly fed into the upper part of the distillation column at the rate of 50-70 kg of solution per 1000-1100 kg of distilled methyl methacrylate or per 1100-1200 kg of initial methyl methacrylate contained in the bottom of the column. At the first stafe of distillation, hydrooquinone, or para-methoxyphenol, or copper dibutyldithiocarbamate, or thiodiphenylamine, or a mixture of two or three of mentioned compounds is used as an inhibitor which is fed into the upper part of the distillation column. At the second stage of distillation, para-methoxyphenol, or diphenylolpropane, or topanol is used as an inhibitor which is fed into the upper part of the distillation column. At the second stage, radical polymerization inhibitor is added to the bottom of the distillation column in an amount of 0.01-0.4 wt % of the distilled fraction. Hydroquinone, or para-methoxyphenol, or copper dibutyldithiocarbamate, or thiodiphenylamine, or para-phenylenediamine, or a mixture of two or three of mentioned compound is added to the bottom of the distillation column as the radical polymerization inhibitor. Before the start of distillation at the first stage, it is possible to add a strong acid (para-toluenesulfonic acid, or concentrated sulfuric acid, or polyphosphoric acid) to the initial distillation residues in an amount of 2 to 10 wt % of the initial distillation residues.

EFFECT: improved method.

8 cl, 9 ex

Description

The invention relates to the disposal of bottoms of methyl methacrylate production, during which the target product is additionally recovered.

A known method of disposal of bottoms of methyl methacrylate produced by the acetone cyanohydrin method [A.S. USSR №1397429, IPC С07С 69/54. С07С 67/48, з. 06/27/86., Op. 05.23.88]. Disposal of residues containing methyl methacrylate (MMA), methacrylic acid (MAA), methyl α-hydroxyisobutyrate (MOIB), methyl α-methoxy propionate is carried out by dehydration of high-boiling residues with concentrated sulfuric acid at 90-100 ° C in the presence of 0.02-0 , 04 wt. % thiodiphenylamine. The degree of extraction increases to 60-70% against ~ 50.7% in the known prototype method.

The above method is adopted as a prototype.

The objective of the invention is to increase the degree of extraction of the target product.

This problem is solved by the method of disposal of bottoms of methyl methacrylate production containing methyl methacrylate (MMA), methacrylic acid (MAA), methyl-α-hydroxyisobutyrate (MOIB), in which according to the invention the utilization is carried out by distillation in two stages, the first stage being carried out in a distillation column with an efficiency of 3-4 theoretical plates, in a vacuum of 0.8-0.85 atm at a cube temperature of the column of 60-106 ° C, the top of the column of 58-74 ° C and reflux ratio of 0.5-1.0, and the second stage is carried out in distillation 4-5 t column theoretical plates, into the cube of which the fraction obtained in the first stage of distillation is loaded at a temperature of the cube of the column of 60-86 ° C, the top of the column of 58-59 ° C and reflux number 1 at the beginning of the distillation with its gradual increase to 3 at the end of the distillation. In this case, it is advisable at the first stage to supply a 2-3% solution of the inhibitor in methyl methacrylate to the top of the distillation column at the rate of 50-70 kg of solution per 1000-1100 kg of distilled methyl methacrylate or, for 1100-1200 kg of the initial methyl methacrylate contained in the cube of the column .

Hydroquinone, or para-methoxyphenol, or copper dibutyldithiocarbamate, or thiodiphenylamine, or a mixture of two or three of these substances are suitable as an inhibitor. At the second stage of distillation, before the start of the process, it is necessary to add a radical polymerization inhibitor to the cube of the distillation column in an amount of 0.01-0.4% by weight of the loaded fraction (radical polymerization inhibitors are not loaded into the cube of the first column, since the bottoms from the distillation of MMA always contains a large number of inhibitors (3-5% hydroquinone, etc.); a high content of inhibitors (mainly hydroquinone), due to the technology of MMA production itself). As an inhibitor of radical polymerization, in this case, hydroquinone, para-methoxyphenol, copper dibutyldithiocarbamate, thiodiphenylamine, para-phenylenediamine or a mixture of two or three of these substances can serve. These substances do not constitute an exhaustive series. Other radical polymerization inhibitors can be used, as well as mixtures of 2-3 different inhibitors recommended to prevent premature polymerization of (meth) acrylates.

At the second stage of rectification, it is also advisable to supply a 2-3% solution of the inhibitor in methyl methacrylate to the upper part of the column at the rate of 50-70 kg of solution per 1000-1100 kg of distilled methyl methacrylate or 1100-1200 kg of the initial methyl methacrylate contained in the cube of the column. At this stage, only those inhibitors that are allowed in commercial MMA can be used, namely: para-methoxyphenol, diphenylol propane, topanol.

It is possible to add strong acid in an amount of from 2 to 10% of the weight of the bottom residue before starting distillation residues before starting the rectification in the first stage. The process is characterized by the fact that not only the methyl methacrylate that is part of the starting bottoms is recovered, but also the one that is formed as a result of the transesterification of methyl-α-hydroxyisobutyrate (MOIB) with methacrylic acid (MAA). This reaction requires acid catalysis; therefore, it proceeds in the presence of sufficiently strong acids. Of a sufficiently large variety of strong acids, three acids can be of practical importance: para-toluenesulfonic acid, concentrated sulfuric acid and polyphosphoric acid. One of these acids is added to the processed bottoms in an amount of from 2 to 10% of their weight before rectification in the first stage of MMA extraction. Other acids are unacceptable either because of their volatility (hydrohalic acids), or strong oxidizing properties (nitric, perchloric), or high cost (fluorosulfonic, etc.). Under these conditions, as a result of the interaction of MAA and MOIB, a high-boiling α-hydroxyisobutyric acid (OIMK) is formed, which remains in the cube, and MMA. The latter is driven away from the reaction sphere, due to which the equilibrium of transesterification is shifted towards the formation of the target product. Or schematically:

As a result of acid catalysis, more MMA can be isolated from the bottoms of the indicated composition than it was contained in the initial bottoms, i.e. over 100% based on the initial MMA. The amount of additional MMA depends not only on the conditions of extraction, but also on the molar ratio of MAA to MOIB in the bottom residue: the larger the relative excess of MOIA, the more MAA will go into MMA. The average composition of bottoms from the distillation (production) of MMA is, wt. %:

MMA 34.5 MOIB 35,2 POPPY 18.6 Other impurities (hydroquinone, poly-MMA, etc.) 11.7

In the above average composition of bottoms, the molar ratio of MOIB and MAK is 1: 1.45. At the same time, with a molar excess of MOIB greater than 1.1, the amount of MMA formed as a result of transesterification almost directly depends on the total amount of MAC in the initial bottoms.

In the described combined process (transesterification + rectification), more MMA can be extracted from bottoms than was contained in the starting bottoms, despite the inevitable losses. Therefore, if we take for 100% the amount of MMA, which theoretically could be distinguished without losses only as a result of distillation (rectification), then due to the formation of additional MMA as a result of transesterification, the total yield will exceed 100% even taking into account losses.

The claimed invention is illustrated by the following examples, while the scope of the invention is not limited to these examples.

Example 1

Two-stage extraction of MMA from bottoms from industrial production of MMA is carried out in a laboratory unit consisting of two rectification systems. Both systems consist of a cube, a packed column filled with Fenske glass rings (or another nozzle, for example, from nichrome spirals), a complete condensation distribution head and two receiving tanks. The efficiency of the column of the first system is 3 t (3 theoretical plates), the second system - 5 t.t. The receivers of both systems are connected to a vacuum pump.

At the first stage, 600 g of bottoms of MMA production of an average composition (see above) are loaded into a cube of the first column (3 tp). Deviations in the composition of the components usually do not exceed 2-3%.

The distillation is carried out at a cube column vacuum of 0.8-0.85 atm (i.e., at a residual pressure of 0.15-0.2 atm), at a cube column temperature of 60-106 ° C, a column top of 58-74 ° C and reflux ratio 0.5-1.0. Collect 213 g of the fraction (minus the MMA supplied together with the inhibitor to the top of the column) containing 93% MMA and 7% impurities (6.4% MOIB, 0.3% MAA, 0.1% others). 399 g of “bottoms 2” consisting of impurities containing 0.8% MMA are drained from the bottom of the column. When reproducing the process on an industrial scale, “bottoms 2”, consisting of organic substances, is sent to the incinerator.

In the second stage, the obtained fraction (213 g) is loaded into the cube of the second column with an efficiency of 5 tons, 0.42 g of hydroquinone are added and a similar distillation is carried out at the temperature of the cube column of 60-86 ° C, the top of the column is 58-59 ° C and reflux number from 1, at the beginning of the acceleration, gradually increasing it to 3, at the end of the acceleration. Obtain 188 g of 99.9% MMA (hereinafter, the yield of MMA minus the inhibitory solution of MMA supplied to the top of the column). The yield of pure MMA isolated from 600 g of the starting bottoms of the above composition is 90.7%.

Example 2

According to example 1, characterized in that both stages are carried out sequentially on the installation with a single column efficiency of 4 t After the first stage is carried out and the “bottom residue 2” is drained into the same column cube, the obtained fraction is loaded and the second stage of rectification is carried out under the conditions described in Example 1, with the difference that the column “runs on yourself ”, i.e. all MMA condensate is sent to irrigate the column. From 600 g of starting bottoms, 186 g of 99.5% MMA, (89.4%, based on those contained in the starting bottoms) are obtained. In the "VAT residue 2" remains 1.5% of MMA.

Example 3

According to example 1, characterized in that the distillation is carried out on a semi-industrial installation, consisting of two rectification systems. The first system is equipped with a distillation column 3 m high, 0.32 m in diameter. Nozzle - Rashig rings. On the second system, a similar column is 5 m high. The efficiency of the first column is about 3 tons, the second is about 5 tons. In the cube of the first system, with a volume of 4 m ³ , 2800 kg of bottoms of MMA production are loaded. After the first stage, 978 kg of a fraction containing 95.7% MMA are obtained.

In the second stage receive 903 kg of MMA containing 99.86% of the basic substance. The output of MMA from 2800 kg of cubic meters leaves 93.4%. The main losses are with gases. "VAT residue 2" in the amount of 1763 kg is sent for combustion.

Example 4 (for comparison)

According to example 1, characterized in that the process of extracting MMA from vat was carried out in one stage on a laboratory distillation column with an efficiency of 8-9 tons As a result, 132 g of 97.5% MMA were recovered from 600 g of bottoms. The yield is 62.2%. The content of MMA in the "bottom residue 2" - 9.6%. The amount of “bottom residue 2” is 417 g. The viscosity of the “bottom residue 2” is about 2-3 times higher than in the previous examples of extraction in a two-stage way.

Example 5

According to example 1, characterized in that to 600 g of the original bottoms are added 24 g (4% by weight of the bottoms) of para-toluenesulfonic acid. After the first stage of rectification, combined simultaneously with transesterification, 328 g of a fraction of 90.6% MMA are obtained. The degree of conversion of MAA into MMA is 75%. The amount of "bottoms 2" - 288

After the second stage of rectification, from 328 g of 90.6% MMA, 287.4 g of 99.7% MMA are obtained. The yield of MMA is 138.4%, calculated on the MMA contained in the original bottoms.

Example 6

According to example 5, characterized in that to 600 g of VAT residue add 60 g (10% by weight of VAT) of polyphosphoric acid. In the first stage, 326.5 g of 93.3% MMA are obtained. The degree of conversion of MAA into MMA is 76.4%. After the second stage, 289.8 g of 99.5% MMA are obtained. The output of MMA is 139.3%, calculated on the MMA contained in the original bottoms.

Example 7

According to example 5, characterized in that to 2800 kg of vat add 84 kg (3% by weight of vat) of concentrated (92%) sulfuric acid. The process is conducted on a semi-industrial installation described in example 3. After the first stage, 1501 kg of a fraction consisting of 90.6% MMA are obtained. The degree of conversion of MAA into MMA is 71.7%. After rectification on the second column, 1321 kg of 99.85% MMA are obtained. The output of MMA is 136.7%, based on the content in the original bottoms.

The amount of "VAT residue 2" remaining after the 1st stage is 1348 kg. These bottoms containing 6.22% sulfuric acid are sent for combustion.

Example 8

According to example 5, characterized in that the composition close to that indicated in the prototype (in ed. St. 1397429, 1988), namely, wt. %:

MMA 33.7 MOIB 20.1 POPPY 34.6 other impurities 11.6

To 600 g of which 12 g (2% by weight of the initial bottoms residue) of concentrated sulfuric acid was added. In the first stage, 295.7 g of 90.6% MMA are obtained. The degree of conversion of MAA into MMA is 38.5%. After the second stage of rectification, 260.8 g of 99.7% MMA are obtained. The yield of MMA is 128.6% per MMA contained in the initial bottoms. The amount of “bottom residue 2” after the first stage is 326.5 g. The sulfuric acid content in the “bottom residue 2” leaves 3.7%.

Example 9 (for comparison)

According to example 5, characterized in that to 600 g of bottoms, 90 g (15% by weight of bottoms) of concentrated sulfuric acid were added. In the first stage, 311.3 g of 90.6% MMA are obtained. The degree of conversion of MAA into MMA is 60.5%. After the second stage of rectification, 270.5 g of 99.7% MMA are obtained. The yield of MMA is 119.8% per MMA contained in the initial bottoms. Thus, with an increase in the amount of sulfuric acid over the declared yield of the target product decreases.

Examples 1-3 and 5-8 characterize the claimed method in a wide range of implementation options. Moreover, in each case, a significant increase in the yield of the target product was recorded. The yield of MMA increases by 2-3%, which, when implementing this method of utilizing bottoms under conditions of production with a capacity of 30-40 thousand tons of MMA per year, makes it possible to obtain an additional about 1 thousand tons per year of a commodity target product with minimal costs.

Claims (8)

1. The method of disposal of bottoms of methyl methacrylate production containing methyl methacrylate, methacrylic acid, methyl-α-hydroxyisobutyrate, characterized in that the utilization is carried out by distillation in two stages, while the first stage is carried out in a distillation column with an efficiency of 3-4 theoretical plates, in vacuum 0.8-0.85 atm at a column cube temperature of 60-106 ° C, a column top of 58-74 ° C and a reflux ratio of 0.5-1.0, and the second stage is carried out in a distillation column with an efficiency of 4-5 theoretical plates, into which load fractions s, obtained in the first stage, and rectified in a vacuum of 0.8-0.85 atm at a cube temperature of the column of 60-86 ° C, the top of the column of 58-59 ° C and reflux number 1 at the beginning of the distillation with a gradual increase to 3 in end of the acceleration. 2. A method for utilizing bottoms of methyl methacrylate production according to claim 1, characterized in that at both stages a 2-3% solution of the inhibitor in methyl methacrylate is slowly fed to the top of the distillation column at the rate of 50-70 kg of solution per 1000-1100 kg of distilled methyl methacrylate or 1100-1200 kg of the original methyl methacrylate contained in the bottom of the column. 3. The method for the disposal of bottoms from the production of methyl methacrylate according to claim 2, characterized in that in the first stage of rectification, hydroquinone, or para-methoxyphenol, or copper dibutyl dithiocarbamate, or thiodiphenylamine, or a mixture of two, are used as an inhibitor fed to the top of the distillation column or three of these substances. 4. A method for utilizing bottoms of methyl methacrylate production according to claim 2, characterized in that in the second stage of rectification, para-methoxyphenol, or diphenylol propane, or topanol is used as an inhibitor fed to the top of the distillation column. 5. The method of disposal of bottoms of methyl methacrylate production according to claim 1, or 2, or 3, or 4, characterized in that in the second stage a radical polymerization inhibitor is added to the cube of the distillation column in an amount of 0.01-0.4% by weight of the distilled fractions. 6. A method for utilizing bottoms of methyl methacrylate production according to claim 5, characterized in that hydroquinone, or para-methoxyphenol, or copper dibutyl dithiocarbamate, or thiodiphenylamine, or para-phenylenediamine, or a mixture of two or these three substances. 7. A method for utilizing bottoms of methyl methacrylate production according to claim 1, or 2, or 3, or 4, or 6, characterized in that strong acid is added to the initial bottoms before rectification in the first stage in an amount of from 2 to 10 % of the mass of the initial bottoms. 8. The method for utilizing bottoms of methyl methacrylate production according to claim 7, characterized in that one of the following acids is added: para-toluenesulfonic acid, concentrated sulfuric acid, polyphosphoric acid.