RU2232749C2 - Two-step method for preparing n-methylaniline - Google Patents

Abstract

FIELD: organic chemistry, chemical technology.

SUBSTANCE: invention proposes two-step method for preparing N-methylaniline by paraphase catalytic N-alkylation of aniline with methanol. On the first step aniline and methanol are fed in the mole ratio = 1:2 and process is carried out at temperature 230-260 C and contact loading value 0.7-0.9 h^-1 up to the conversion degree of aniline to N-methylaniline 85-95%. Catalysate is fed to the second step (additional alkylation) and process is carried out at 220-240 C up to the conversion degree of aniline to N-methylaniline above 98%. In both steps copper oxides-base catalysts are used promoted with metal oxides from the group including manganese, iron, chrome, nickel, cobalt. The depleted catalyst from the first step can be used as a catalyst on the second step and its activity is 60-70% of the initial activity. Invention provides preparing catalysate with mass part of N-methylaniline in oily fraction above 98% that provides possibility to isolate the marketing product by simplified schedule of rectification, reducing energy consumption, prolonged time for catalyst exploitation.

EFFECT: improved preparing method.

2 cl, 1 sch, 2 tbl

Description

This invention relates to chemical technology, more specifically to an improved method for producing N-methylaniline (MMA), which is mainly used as an octane-enhancing additive to gasolines, as well as in the manufacture of dyes, polymers, herbicides.

To obtain N-alkylated amines, a number of methods have been developed for liquid-phase and vapor-phase alkylation of amines with alcohols or corresponding esters. On an industrial scale, monomethylaniline is obtained by vapor-phase alkylation of aniline with methanol in column type plants on a stationary catalyst, followed by separation of the desired product from the catalytic fraction by distillation.

Aniline conversion usually does not exceed 87–97% [1-3], and the catalysts contain, in addition to the target product, unreacted aniline, methanol, reaction water, a by-product N, N-dimethylaniline (DMA), trace elements of high boiling products; those. the catalysts consist of water-methanol and oil fractions. The content of MMA in the oil fraction is not more than 90-95%. At the same time, the current specifications [4] for MMA brand "premium" provides for the content of the main substance in it at least 98 wt.%, Aniline not more than 0.5 wt.% and DMA not more than 1.3 wt.%; even more stringent requirements are imposed on the quality of MMA exported: the content of aniline is not more than 0.3 wt.%.

The degree of conversion of aniline to the target product is determined by the technological parameters of the process and, first of all, the used catalyst: a significant amount of unreacted aniline remains on an insufficiently active catalyst, and too active a catalyst contributes to the formation of DMA. All patents on the synthesis of MMA identified by the applicant are devoted to the selection of a catalytic system, however, none of the known methods allows the stage of contacting with aniline conversion of more than 98%, while eliminating the presence of aniline and DMA in the catalyst in amounts significantly higher than permissible. The selection of the target product with the desired properties by rectification of the oil fraction is a complex and energy-intensive stage due to the fact that the relative volatility for the aniline-MMA pair is 1.28-1.33, and for the DMA-MMA pair it is only 1.15-1.18 in depending on the concentration of aniline and DMA in the catalyst [5]. So, with the composition of the mixture fed to the rectification, wt.%:

MMA 84-89

Aniline 6-13

DMA 1-2

Water + methanol Up to 1

steam consumption for the allocation of 1 ton of commodity MMA is 4.0-4.5 Gcal during distillation on traditional plate columns and 1.1-1.2 Gcal when the process is carried out in an apparatus equipped with special heat and mass transfer packages. In addition, a long rectification process leads to the resinification and decomposition of products, i.e. the loss of the initial components of the synthesis, the deterioration of the quality of commodity MMA.

The purpose of the invention is to improve the quality of a commercial product, improve the economic performance of the process.

This goal is achieved by a two-stage method for conducting N-alkylation of aniline with methanol, in which at the first stage a gaseous mixture of aniline and methanol is fed into a reactor (alkylator) with a stationary copper oxide catalyst at a molar ratio of 1: 2 and the process is conducted at a temperature of 230-260 ° C, a contact load of 0.7-0.9 h ^-1 until the degree of conversion of aniline to N-methylaniline is 85-95%, the catalyzate from this stage is sent to a second reactor (doalkylator) and the process is carried out at a temperature of 220-240 ° C to degree of conversion of aniline in N-methylaniline more than 98%

As the N-alkylation catalyst in the first and second stages, one of the catalysts known in the art based on copper oxides promoted by metal oxides from the group consisting of manganese, iron, chromium, zinc, cobalt, for example, the catalyst according to RF patent 1327342, can be used; moreover, in the second stage, spent and regenerated catalyst from the first stage can be used (its activity usually does not exceed 60-70% of the initial one).

From the catalate from the second stage, a marketable product can be obtained by distillation of water and methanol.

Implementation of the proposed method will allow:

- receive catalysis with a mass fraction of MMA in the oil fraction of more than 98%;

- extend the inter-regeneration period and the service life of the catalyst of the first stage (due to the additional alkylation of aniline in the second stage using spent catalyst from the first stage);

- reduce the time it takes to pass the aniline → commodity MMA path by 2.5-3 times;

- to reduce the loss of raw materials as a result of a decrease in gum formation and to improve the quality of the commercial product;

- significantly reduce energy costs (steam, water),

- to increase the removal of marketable product from one distillation operation by reducing the number of aniline and intermediate fractions.

Data on the rectification of catalysts with an MMA content in the oil fraction from 90 to 99%, obtained during operation of an industrial distillation column, are given in table 1.

A method of obtaining a commodity MMA, including two-stage alkylation, is carried out on the installation shown in the drawing, as follows.

A mixture of aniline and methanol in a molar ratio of 1: 2 after evaporator 1 is passed through a contact apparatus 2 (alkylator) with a stationary catalyst at a temperature of 230-260 ° C. The process is conducted to an aniline conversion of 85-95%. After the reactor 2, gaseous catalysis enters the heat exchanger 3, in which its temperature is brought to 220-240 ° C and sent to the contact apparatus 4 (doalkylator), where the concentration of MMA in the oil fraction of the catalysis is brought to 98-99.5% and the catalysis is directed to distillation column 5. Each of the reactors 2 and 4 can operate in stand-alone mode.

The catalysts loaded into reactors 2 and 4 may have the same or different composition. The activity of the catalyst in the doalkylator depends on the degree of conversion of aniline to MMA in the alkylator. The catalyst recovery is carried out in methanol vapors at 240-260 ° C.

The results of using this method are shown in table 2.

The left part of the table reflects the course of the aniline alkylation process in reactor 2 (alkylator), and the right - in reactor 4 (pre-alkylator); The composition of the oil fraction of catalysis is shown depending on the process temperature in each reactor.

The duration of the distillation of the catalyzate discharged from reactor 2 is 61-75 hours, and the productivity of the distillation column is 0.26-0.16 t / h of a commercial product. The duration of the separation by fractions of catalysis, discharged from the reactor 4, is 30 hours, and the performance of the distillation column, respectively, 0.71 t / h of marketable product.

Sources of information

1. US patent 5159115.

2. US patent 5055617.

3. RF patent 1327342.

4. TU 6-14-37-80.

5. RF patent 2163593.

Claims (2)

1. The method of producing N-methylaniline by vapor-phase catalytic alkylation of aniline with methanol in the presence of a copper-containing N-alkylation catalyst promoted with metal oxides from the group consisting of manganese, iron, chromium, zinc, cobalt, characterized in that the process is carried out in two stages: to the first stage aniline and methanol are fed in a molar ratio of 1: 2 and the reaction is carried out at a temperature of 230-260 ° C and a contact load of 0.9 - 0.7 h ^-1 to the degree of conversion of aniline to N-methylaniline 85-95%, the catalate is fed to the second alkylation step and reacted at a temperature of 220-240 ° C until a conversion degree of 98%, followed by distillation resulting catalysate. 2. The method of producing N-methylaniline according to claim 1, wherein the spent catalyst of the first stage, the activity of which is 60-70% of the initial, is used as the second-stage N-alkylation catalyst.

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