CS238715B1 - Process for producing chlorobenzyl ethylbenzene - Google Patents

Abstract

A method for producing ethylbenzene with reduced chlorine content by alkylating benzene with ethylene in the presence of a catalyst, which is a liquid complex of aluminum chloride, in which the reaction product is separated by distillation into circulating unreacted benzene, ethylbenzene produced, diethylbenzene fraction and heavy residues. To reduce the chlorine content in the ethylbenzene obtained, fresh benzene is added to the inlet of the distillation separation of the alkylation product in an amount such that the benzene concentration in the feed is in the range of 55 to 75% by weight.

Description

The present invention relates to a process for the production of ethylbenzene by alkylation of benzene with ethylene in the presence of an aluminum chloride catalyst complex, whereby a suitable arrangement of the distillation separation of the alkylation product results in a reduction in the chlorine content of the pure ethylbenzene produced.

Ethylbenzene is one of the most important aromatic hydrocarbons in industry. A significant portion of benzene, whether produced from liquid coal heat treatment products or in recent years in an ever-increasing volume as a by-product of olefin production by pyrolysis of hydrocarbons, is subjected to alkylation with ethylene to form ethylbenzene. Ethylbenzene is a raw material for the production of styrene, which is one of the basic monomers of many plastics technologies.

The alkylation of benzene with ethylene can be carried out in the gas phase on a fixed catalyst, the active ingredient of which is, for example, phosphoric acid or boron trifluoride. However, the bulk of ethylbenzene production is still produced worldwide by liquid-phase alkylation of benzene on Friedel-Crafts catalysts. The catalyst in this alkylation of benzene with ethylene is a viscous liquid having a density higher than that of aromatic hydrocarbons. It is a complex compound formed by the interaction of aluminum chloride, aromatic hydrocarbons and some catalysts, which may be ethylene chloride, hydrogen chloride, water, and the like.

The alkylation of benzene with ethylene in the liquid phase is usually carried out in a column bubbled reactor in which three phases are present:

- a gaseous phase consisting of ethylene, inert gases and hydrocarbon vapors

- lighter liquid phase, i. mixture of aromatic hydrocarbons

- heavier liquid phase, i. catalytic complex.

In addition to the basic addition of ethylene to benzene with the formation of ethylbenzene, a number of side and subsequent reactions take place in the reactor, in particular to produce the above-alkylated benzene derivatives, i. diethylbenzenes and triethylbenzenes. In order to suppress the formation of the above alkylated derivatives, the reaction is usually conducted in excess of benzene, which also makes it possible to work with virtually complete ethylene conversion.

A typical alkylaoe product then has the following composition:

benzene 44.4 wt.

toluene 0.9% wt.

Ethylbenzene 39.8 wt.

cumene 0.1 wt.

% diethylbenzenes 13.0 wt.

% triethylbenzenes and above 1.8 wt.

In addition to these side and subsequent reactions, the formation of chlorinated hydrocarbons takes place to a small extent in the alkylation reactors. From the point of view of the quality of the final product, the formation of chlorobenzene having a boiling point close to ethylbenzene is very harmful:

substance normal boiling point, ° C ethylbenzene monochlorobenzene

136.3 131.7

The alkylation product in the distillation column system is divided into the following fractions:

- unreacted benzene circulated back into the reactors

- pure ethylbenzene (product of production)

- diethylbenzene fraction returned to the reactors for the conversion to ethylbenzene by reaction with benzene

- heavy shares.

The distillation step of the separation of unreacted benzene must be carried out in such a way that chlorobenzene also enters the distilled benzene. Upon re-passage through the alkylation reactor, it is alkylated, for example, to ethyl chlorobenzene with a high normal boiling point. This distillation compartment, which is very difficult due to the low relative volatility of chlorobenzene versus ethylbenzene, is aided by the low lack of realism in the behavior of said binary system.

The requirements for the separation of chlorobenzene from ethylbenzene are very strict, in the produced ethylbenzene the chlorine content is limited to 5 ppm by weight, which corresponds to approximately 5 ppm by weight. chlorobenzene. The stringent requirement for chlorine content is steadily increasing, some styrene production technologies have a chlorine content of 3bp in the ethylbenzene input.

Fresh benzene, in an amount corresponding to the consumption of the alkylation reaction, is fed to the system according to the prior art by mixing it with re-circulated unreacted benzene (separated on the distillation column from the alkylation product) at the entrance to the alkylation reactors.

It has now been found that it is possible to reduce the chlorine (ie chlorobenzene) content of ethylbenzene produced by alkylation of benzene with ethylene in the presence of a catalyst which forms a liquid aluminum chloride complex and subsequently distilling the alkylation reaction product to circulating unreacted benzene, ethylbenzene produced. 2. The method of claim 1 wherein the fresh benzene is introduced into the system to enter the distillation separation of the alkylation product in an amount such that the benzene concentration in the feed is in the range of 55 to 75 wt.

The two - component benzene - chlorobenzene mixture shows a significant deviation from ideal behavior and the activity coefficient of chlorobenzene in the region of its small concentrations, which are interesting from the point of view of distillation refining of ethylbenzene, reaches y = 1.33. The high benzene content of the three-component benzene-chlorobenzene-ethylbenzene mixture then increases the activity coefficient of chlorobenzene, its relative volatility to ethylbenzene, thereby allowing the separation of chlorobenzene from ethylbenzene.

The mixture fed as a feed to the distillation column of the benzene separation has, for example, the following composition in the process according to the invention (in comparison with the previously mentioned composition of the alkylation product:

benzene toluene ethylbenzene cumene diethylbenzenes trlethylbenzenes and higher

61.5 $ wt. 0.6 * wt. k7.6 »wt. 0.1 wt. 9.0% wt. 1.2 »wt.

Calculations of temperature and concentration profiles in a benzene separation column on a computer have shown that distillation with increased benzene concentration in the feed of this column aligns such profiles to substantially separate chlorobenzene from ethylbenzene.

On a column of 35 theoretical degrees the composition of the composition (moles fractions) is distilled.

Example 1

benzene 0.6964 toluene 0.5984. 10 ² chlorobenzene 0.1617. 10 ^-4 ethylbenzene 0.2296 kumen 0.5096. 10 ³ n-propylenebenzene 0.5096. 10 “ ² m-Diethylbenzene 0.5935. 10 ' ¹ 1,3,5-triethylbenzene 0.3022. 10 “ ²

At a reflux ratio of R = 0.3, a distillate is taken in which the molar fraction of ethylbenzene is 0.0135. The chlorobenzene concentration in the distillation residue is 4.5 ppm.

Example 2

In a laboratory distillation of a 54-glass bell tray column, the alkylation product was continuously distilled under otherwise identical conditions, in the first case a reaction product containing 48.1 wt. benzene, in the latter case benzene was added to the column distillation feed to a concentration of 62 wt. The proportion of the chlorobenzene present in the feed was compared and transferred to the column distillate to remove it from ethylbenzene:

A B benzene concentration in feed,% wt. 48, t 62.0% chlorobenzene removed,% 29.5 61.5

Claims (1)

A process for the production of ethylbenzene with a reduced chlorine content by alkylation of benzene with ethylene in the presence of a catalyst which forms a liquid aluminum chloride complex, wherein the reaction of the alkylation product is separated by distillation into circulating unreacted benzene, ethylbenzene produced, diethylbenzene fraction and heavy residues. adds to the system to enter the distillation separation of the alkylation product in an amount such that the benzene concentration in the feed is in the range of 55 to 75 wt.