JPS5980650A - Method for purifying methacrylonitrile - Google Patents

Abstract

PURPOSE:To save the equipment and cost and purify the titled compound at a low cost, by removing prussic acid from a crude ammoxidation reaction product containing methacrylonitrile in a column for removing the prussic acid, and taking out a vapor or a liquid containing low-boiling substances, e.g. methacrolein, simultaneously from the system. CONSTITUTION:An ammoxidation reaction product, consisting of methacrylonitrile essentially, and further containing methacrolein, acrylonitrile and prussic acid, etc. is distilled to give methacrylonitrile. In the process, the reaction product is distilled in a column (4a) for removing the prussic acid to remove the prussic acid from the top thereof. A vapor or liquid containing concentrated methacrolein and acrylonitrile is partially taken out of a conduit 10 at a level between a feed tray 9 and the top, and the resultant process liquid distilled in the column 4 for removing the prussic acid and water is feed directly to a product column 7 without passing through a separation column for removing low- boiling substances. The aimed product methacrylonitrile is obtained from a conduit 8 at the topmost tray in the product column 7.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying methacrylonitrile C (hereinafter abbreviated as MAN).The purpose of the present invention is to simplify the purification process, reduce equipment costs and expenses, and reduce manufacturing costs. be.

MAN is produced by a gas phase contact reaction between inbutylene, tertiary-butyl alcohol, etc., ammonia 2 and hydrocyanic acid, that is, an ammoxidation reaction. This reaction product was mainly composed of MAN) and contained methacrolein, hydrocyanic acid, acetonitrile, acrylonitrile, isobutyronitrile, etc., and was purified by distillation or extractive distillation using water as a solvent to obtain the product MAN.

An example of a conventional MAN purification process will be explained with reference to FIG. The ammoxidation reaction product mainly composed of MAN absorbed in the absorption water is subjected to extractive distillation with water in the recovery column 1, and the top vapor is condensed in the condenser 2, and decanter 3.
At one point, the aqueous layer is separated, the aqueous layer is ashed in recovery tower 1, and MA
You T idiot methacrolein, prussic acid, acrylonitrile,
Reactants such as isobutyronitrile are recovered as an oil layer containing water at a saturation level of nLtt. This recovered liquid is fed to the middle stage of the upper membrane acid tower 4a of the deback acid/dehydration tower 4, and hydrocyanic acid is separated from the top of the tower. :l! : The bottom extracted liquid is separated into an oil layer and an aqueous layer by a decanter 5, and the oil layer is sent to a dehydration tower 4 at the bottom.
Feed to the upper row of b.

The bottom liquid is extracted and fed to the middle stage of the low boiling point separation column 6.

In the low-boiling fraction I'J column 6, methachloro 1/in from the top of the column,
After removing low-boiling substances such as acrylonitrile, the JI′f bottom liquid is extracted and fed to the product column 7, and a trace amount of remaining low-boiling substances 2 and high-boiling substances such as isobutyronitrile are removed from the top 2 and bottom of the column, respectively. force) and obtain product 1・ζAN from lead a8.

An example of the conventional MAN 1'# manufacturing method is as above,
The liquid from which the ammoxidation reaction product was collected is decomposed.
'i: Sequentially distilled in the 2nd column, dehydration column, low-boiling separation column, and product column to remove hydrocyanic acid, water, 3, and low-boiling substances such as methacrolein and acrylonitrile, and high-boiling substances such as inftironite + fur. , MAR was obtained for 44 items. For this reason, there was a drawback that the number of columns (four distillation columns) was large, resulting in high equipment costs and expenses.

This invention was made focusing on the above problems,
The gist is that the product MAN is obtained by distillation from an ammoxidation reaction product containing MAN as a main component, methachlorene, acrylonitrile, and hydrocyanic acid. Methacrolein and acrylonitrile-concentrated vapor or part of the liquid is extracted from the system from a height position between the feed stage and the top of the column during removal.
This is a method for refining in.

In the distillation in step 13 of the hydrocyanic acid removal tower, hydrocyanic acid, which has the lowest boiling point, is concentrated and removed at the top of the tower, but other low-boiling substances such as methacrolein and acrylonitrile are removed from the feed stage and the top of the tower. It is concentrated between. Therefore, by extracting a part of the distilled vapor or liquid from this concentrated part to the outside of the system, the low boiling point in the process liquid can be significantly reduced, and the negative 8i of the subsequent 11U 7' process can be reduced. I can do it.

FIG. 2 is an example of an embodiment of a purification process applying this purification method. When distilling the recovered liquid fed from the recovery column to the hydrocyanic acid removing column 4a and removing hydrocyanic acid from the top of the column, from the height position between the feed stage 9 of the recovered liquid and the top of the column,
A portion of the vapor or liquid enriched with methacrolein and acrylonitrile is removed from the system through conduit 10. The process liquid distilled in the prussic acid removal towers 4a and 2 and the dehydration tower 4b is directly fed to the product grade 7 for distillation without passing through the low boiling point separation tower, and the remaining low boiling matter 3 and High boilers are removed from the top 2 and bottom of the column, and the product MAN is obtained from the upper column conduit.

This invention has the above-described configuration, and in the prussic acid removal tower, it is possible to remove low-boiling substances at the same time as removing 1-sulfuric acid, and to significantly reduce the concentration of low-boiling substances in the process liquid, thereby facilitating the subsequent n-manufacturing process. For example, it is possible to omit a low boiling point separation column. Therefore, equipment cost 2 and expenses can be reduced, and production costs can be reduced.

2. This purification method is not limited to the case where a recovered liquid recovered by extractive distillation using water is distilled in a prussic acid removal column. Without extractive distillation, e.g.
It can be applied even when a recovered liquid obtained by cooling and condensing an ammoxidation reaction gas is distilled in a prussic acid removal tower.

This will be explained below with reference to examples.

〔Example〕

Extractive distillation is carried out in the recovery tower at the 34th stage from the bottom of the prussic acid removal tower, which has 55 stages. ( ) Recovered liquid f 1
, feed and distill at a ratio of I T/T-MAN ,
Hydrocyanic acid was removed from the top of the tower, and at the same time, steam was discharged from the 45th stage from the bottom to the side cathode at a rate of 0.15 T//T-MAN to the outside of the system.

In this case, the concentrations of acrylonitrile, methacrolein, and water in the feed liquid, side-cut steam, and tower bottom liquid were as shown in the table below. [Comparative Example] All were the same as the examples except that the steam from the hydrocyanic acid removal tower was not side-cut. It was operated under the same conditions. In this case, the quality of acrylonitrile and methacrolein in the bottom liquid was 66o, respectively.
oppm, soooppm) (compared to the bottom liquid of the example) (AN purity/!'(0)

[Brief explanation of the drawing]

Figure 1 shows an example of the conventional MAN Japanese manufacturing process.
-Sheet, Figure 2 is a flow route showing an example of a process to which this glass manufacturing method is applied. 1. Collection, 2. Wall x1h, 6. Decanter 1.
4... Hydrocyanic acid removal/dehydration tower, 4e... Oxidation removal tower, 4b... Dehydration tower, 5... Decanter 16... Low boiling point separation tower, 7... Product column, 8... Conduit, 9... Feed stage, 10...N tubes. Figure 1 Figure 2

Claims (1)

[Claims] (1) In the purification method 2, the product methacrylonitrile is obtained by distillation from an ammoxidation reaction product containing methacrolein, acrylonitrile, hydrocyanic acid, etc. as a main component, and distillation is performed in a de-mono-acid tower. When removing hydrocyanic acid from the top of the column, a part of the vapor or liquid enriched with methacrolein and acrylonitrile is extracted from the system from a height between the feed stage and the top of the column. Method 6 for purifying methacrylonitrile