DE3007634C2 - Process for the production of vinyl chloride - Google Patents

Description

The production of vinyl chloride, the monomer of the mass-produced plastic polyvinyl chloride, has in the has seen a tremendous upswing in the last few decades. Be in the Federal Republic of Germany currently produces more than one million tons of vinyl chloride annually.

After the Second World War, vinyl chloride was used almost exclusively through the addition of hydrogen chloride to acetylene in the presence of catalysts won.

Due to the development of petrochemicals and the associated availability of inexpensive Ethylene, vinyl chloride (VC) production was mainly based on ethylene and chlorine in the 1960s Raw material base changed.

In practice, a two-stage process is predominantly carried out. In the first stage will Ethylene reacted with chlorine to form 1,2-dichloroethane, which is dehydrohalogenated to vinyl chloride in the second stage will.

The production of vinyl chloride is described in detail in the literature, e.g. B. in »Ullmann's Encyclopedia der technical chemistry "4th edition, volume 9, Verlag Chemie, Weinheim / Bergstr., 1975, p. 442 ff and in "Hydrocarbon Processing", March 1979, p. 75 ff.

In the processes currently used on a large scale, monomeric vinyl chloride is mainly through thermal cleavage of 1,2-dichloroethane produced. The endothermic reaction is usually at Temperatures around 500 ° C and at pressures of around 25 bar in cracking furnaces. sales According to the literature, it is about 50-60%. After leaving the furnace, the gas mixture is quenched, to prevent unwanted side reactions.

The reaction gases are then condensed and separated by distillation. The one in the split Occurring hydrogen chloride is highly corrosive at the required high temperatures, so that the cans must be made of highly resistant, very expensive materials, which in the process occurring thermal and chemical loads as well as the occurring pressure loads resist. After a certain period of operation, soot and soot appear in the tubes of the cracking furnace Tar deposits that require cleaning. This can be done by "burning out" the pipes or mechanical removal of the residues.

Here, but in any case a significant environmental impact i triffi on.

Despite significant process improvements in recent years, the amount of residue is still always about 2.5% by weight of vinyl chloride production (see article »Measures for environmentally friendly production of vinyl chloride «by Dr. H. Weber, D. W. Dimmling and Ing.K. H. Möller in DECHEMA monograph 80, Part I, Verlag Chemie Weinheim, p. 57 ff).

ίο In another process variant, the catalytic Cleavage of 1,2-dichloroethane is the formation of Although by-products are largely restricted, the cost of the catalyst and the Production stoppages during the catalyst change have been a breakthrough in this process so far prevented. The inadequacies of the thermal processes for the dehydrochlorination of 1,2-dichloroethane such as high investment costs for the plant, limited sales, complex separation of the fission products, The inevitable accumulation of by-products and waste products, high energy consumption, favored the development of processes in the dehydrochlorination of 1,2-dichloroethane in the liquid phase. In this procedure will be usually aqueous bases are used as acceptors for the hydrogen chloride to be split off. One off However, the rate of elimination of hydrogen chloride in alkaline, liquid media can be sufficient only reach at higher temperatures. In the “Ulimann” already quoted, for example, on p. 447 indicated that 1,2-dichloroethane with 6% sodium hydroxide solution in a molar ratio of 2: 1 at approx. 145 ° C and 11 bar in 2 Reacts to 3 minutes with a yield of about 90% of theory, with by-products through Competitive reactions z. B., ethylene, ethylene glycol, acetylene or acetaldehyde arise. The kind and the Amount of byproducts incurred are available to the application of this process for reasons of economy and environmental protection.

The solution to the problem according to the invention is based on the following findings:

At room temperature to about 50 ° C is 1,2-dichloroethane dehydrohalogenated only at a barely noticeable rate in an aqueous alkaline medium. By Addition of a surface-active substance, especially suitable ones that do not tend to foam Quaternary ammonium salts, which act as phase transfer catalysts, can prevent the formation of Strongly accelerate vinyl chloride.

The reaction conditions can be determined by simple experiments optimize. The speed of reaction depends primarily on the type and amount of the catalyst used, on the alkalinity of the solution and the reaction temperature.

The invention relates to a process for the preparation of vinyl chloride by dehydrochlorination of 1,2-dichloroethane with an aqueous solution of an alkyl hydroxide in the presence of phase transfer catalysts, characterized in that to an aqueous solution of an alkali hydroxide which the Contains catalyst in concentrations of 0.1 to 30% by weight, added 1,2-dichloroethane and the cleavage is carried out at temperatures between 15 and 80 ° C, the molar ratio of 1,2-dichloroethane to alkali metal hydroxide is 1: 1.1 to 1:20.

The compounds used as phase transfer catalysts are known and are described, for example, in the journal "Angewandte Chemie", 86 (1974), pp. 187 ff.

Of the sulfonium, phosphonium and ammonium compounds in question, the latter are preferred. Peralkylated ones are particularly suitable Ammonium hydroxides or halides with one or more long-chain alkyl or alkylaryl substituents, such as B. Bis- (2-hydroxypropyl) -benzyl-hexadecyl-ammonium bromide, Tribulylhexdecyl ammonium bromide and bis (2-hydroxypropyl) dodecyl benzyl ammonium chloride.

As a rule, the catalyst is aqueous alkaline Solution given. The alkali hydroxide solution contains 0.1 to 30% by weight, preferably 1 to 20 % By weight of the catalyst.

The catalyst concentration in the aqueous-alkaline solution influences among other parameters greatly the rate of dehydrohalogenation. Accelerate catalysts of different structures the reaction varies in strength. For every catalyst the most favorable reaction conditions must therefore be determined by simple experiments.

In addition to the catalyst concentration, a rise in temperature and an increase in the alkali hydroxide concentration are beneficial the rate of dehydrohalogenation.

For reasons of energy saving efforts will be made at temperatures a little above the Room temperature to work. Temperatures between 25 and 50 ° C. have proven to be the preferred range proven to be above the boiling point of vinyl chloride (-14 ° C) and below the boiling point of 1,2-dichloroethane ( + 84 ° C).

A high reaction rate can be achieved, for example, with a given analyzer concentration and achieve a specified temperature in that a high alkali metal hydroxide concentration, preferably before the start 10-20 wt .-%, is presented in the solution, and 1,2-dichloroethane always with the equivalent Alkali amount is replenished in the solution. The sodium chloride formed can be effortlessly over a Remove part of the stream from which the NaCl is separated off by crystallization (possibly by salination). the Mother liquor with the catalyst returns to the process. Only more adherent to the crystallized NaCl Catalyst must be used to maintain steady-state concentration ratios in the aqueous alkaline Solution to be replaced.

The dehydrochlorination can be carried out either batchwise or continuously.

General manufacturing instructions for the phase transfer catalysts used

1 mole of amine is with 1.5 moles of alkylating agent in Acetonitrile at 90 ° C for two days with exclusion of moisture touched. The reaction mixture is stored overnight at -10 ° C and the crystal slurry or the The flakes are filtered off, washed twice with a little petroleum ether and dried in vacuo.

Examples
Experiment description

The aqueous-alkaline solution is placed in a three-necked sulphonation flask (volume 250 ml) with intensive stirring in the concentration predetermined for the respective experiment with the predetermined amount of catalyst submitted. The weighed out amount of 0.05 mol of 1,2-dichloroethane is poured into a dropping funnel with pressure compensation given. A short hose connection is made from the sulphonation flask to a calibrated gas collecting vessel, which is filled with saturated saline solution. After it was determined that the The apparatus is tight, 1,2-dichloroethane is added and the evolution of gas in the collecting vessel ceases The sulphonation flask is placed in a thermostated vessel for experiments with given reaction temperatures placed and assumed that the disturbance of the reaction temperature by the added dropwise 1,2-dichloroethane very is small and therefore negligible.

example 1

a) DCE: 0.05 mol

NaOH: 0.10 mol (20% by weight) catalyst: without temperature: 20 ° C VC development:

gas evolution barely noticeable after 5 ^h

b) as a), but with the following change: Catalyst *):

10% by weight of tributyl-hexaclccyi-ammonium bromide VC development: after 5 ^h 150 ml of gas

Example 2

a) DEC: 0.05 mol

NaOH: 0.10 muI (30% by weight) catalyst: without temperature: 25 ° C VC development:

no noticeable evolution of gas after 2 ^h

b) wiea), but with the following change: Catalyst:

4% by weight bis (2-hydroxyporpyl) dodecylammonium broinide VC development:

after 2 ^b about 1, ¹ OI gas (1.12 I Gas r = 100% d.Th.)

*) All information on catalysts is based on the Total amount of DCE related.

Example 3

a) DCE: 0.05 mol NaOH: 0.075 mol catalyst:

Bis- (2-hydroxypropyl) -dodecylammonium bromide Temperature: 25 C VC development: after 2 ^h approx. 1.05 l gas (1.12 l gas = 100% of theory)

Example 4

a) DCE: 0.05 mol NaOH: 0.075 mol catalyst: without temperature: 50 ^° C. VC development:

in l ^h approx. 0.080 1 gas b) wiea) but with the following change:

Catalyst:

1% by weight bis (2-hydroxypropyl) dodecylbenzylammonium chloride VC development: ^{approx. 1.10 l of gas in 1 h} c) as b) instead of 1% by weight catalyst:

0.5 wt%

VC development:

in I ^h about 0.651 gas

in 2 ¹ 'approx. 0.801 gas in 3 ^h approx. 0.931 gas in 4 ^h approx. 1.021 gas in 5 ^h approx. 1.081 gas

In the examples, DEC = 1,2-dichloroethane and VC = vinyl chloride.

Claims (2)

Patent claims: 1. Process for the production of vinyl chloride by dehydrochlorination of 1,2-Diehloräthan with an aqueous alkaline solution in the presence of phase transfer catalysts, characterized in that that for the aqueous solution of an alkali metal hydroxide which contains the catalyst in concentrations of 0.1 to 30% by weight, 1.2 Dichloroethane is added, the molar ratio of 1.2 dichloroethane to alkali metal hydroxide being 1: 1.1 to 1:20 and the reaction is carried out at temperatures between 15 and 80 ° C. 2. The method according to claim 1, characterized in that the concentration of the alkali hydroxide in the aqueous phase is from 1 to 50% by weight.