Introduction

Vinyl chloride (vinyl chloride, chloroethene, monochlorethylene) CH2=CH-CI - colorless gas with an ethereal odor; m.p. 114.6 K, bp. 259.2 K, highly soluble in common organic solvents.

Vinyl chloride is the main product of organochlorine synthesis; up to 20-35% of chlorine is consumed in its production in various countries.

The main consumer of vinyl chloride is the production of polyvinyl chloride, which ranks second in terms of production volume after polyethylene. In the early 1990s, the annual growth rate of its production in the world was 5%. The total volume of its world production in 2000 reached 25 million tons.

Polyvinyl chloride is used in various industries, including construction, electrical and electronics, pulp and paper, elastomers and fiber-forming polymers, flooring, clothing, and footwear. The largest consumer of polyvinyl chloride is the production of pipes for gas and water supply systems, which consumes up to 20-55% of the polymer. The use of polyvinyl chloride as a wood substitute is rapidly increasing. The total volume of polyvinyl chloride production in Russia is -550 thousand tons/year, or 2% of global industrial production.

Industrial methods for producing vinyl chloride

The starting hydrocarbon raw materials for the production of vinyl chloride are ethane, ethylene or acetylene.

There are four industrial methods for producing vinyl chloride:

1. Balanced two-stage method, including the stages of direct chlorination of ethylene:

or its oxidative chlorination:

to 1,2-dichloroethane followed by pyrolysis to vinyl chloride and hydrogen chloride:

The resulting hydrogen chloride is sent to the oxidative chlorination of ethylene.

2. A combined method based on ethylene and acetylene, consisting of the stages of direct chlorination of ethylene to dichloroethane followed by its pyrolysis to vinyl chloride and hydrogen chloride:

The resulting hydrogen chloride is used for the hydrochlorination of acetylene to vinyl chloride:

or in total:

3. A combined method based on light gasoline, including the stages of pyrolysis of gasoline to produce a mixture of ethylene and acetylene in approximately stoichiometric ratios, followed by hydrochlorination of the mixture to vinyl chloride and chlorination of the remaining ethylene to dichloroethane.

Dichloroethane is then pyrolyzed to vinyl chloride, recycling the resulting hydrogen chloride.

4. Hydrochlorination of acetylene:

Of all the listed methods, the most widely used in industry is the method of synthesizing vinyl chloride based on ethylene. For example, in the USA, since 1989, almost all vinyl chloride has been produced using this method.

A balanced method for the synthesis of vinyl chloridane based on ethylene. The balanced method is based on three chemical reactions:

Direct chlorination of ethylene to dichloroethane;

Oxidative chlorination of ethylene to dichloroethane;

Pyrolysis of dichloroethane to vinyl chloride.

Direct chlorination of ethylene. The most important role in the balanced process of obtaining vinyl chloride is played by the stage of direct chlorination of ethylene. It is at this stage that an additional amount of dichloroethane is formed, which is necessary for supply to the pyrolysis stage. The ratio of the amounts of direct and oxidative chlorination products is usually close to 1:1.

The direct chlorination reaction of ethylene, catalyzed by Lewis acids, proceeds through the mechanism of electrophilic addition according to the equation:

The interaction of chlorine and ethylene occurs in an environment of boiling dichloroethane at 363-383 K. Substitutive chlorination of ethylene with the formation of tri- and polyethane chlorides can be avoided by carrying out the reaction at 323-343 K. The use of inhibitors (oxygen, ferric chloride) allows the reaction temperature to be reduced to 313 -333 K with almost 100% selectivity for dichloroethane.

Oxidative chlorination of ethylene* The main stage in the production of vinyl chloride using a balanced method is the oxidative chlorination of ethylene. All industrial processes of ethylene oxychlorination can be divided according to two main characteristics: carrying out the process on a fixed bed or in a “fluidized bed” of a catalyst and using pure oxygen or air as an oxidizing agent.

Figure 1 - Schematic diagram of direct chlorination of ethylene and rectification of dichloroethane

Currently, most of the world's major vinyl chloride producers use the fluidized bed process.

Oxychlorination of ethylene is carried out in the gas phase at 600-615 K and 150 kPa on a stationary or “fluidized bed” catalyst. Chlorides of copper, potassium, sodium and other metals on carriers are used as a catalyst, but the industrial catalyst is copper chloride (supported on spherical aluminum oxide. The copper content in the catalyst is 4-6%. Air or oxygen is used as an oxidizing agent. Use of oxygen makes it possible to reduce the volume of exhaust gases by tens of times and makes it possible to carry out the process at a lower temperature. In addition, the service life of the catalyst is extended and the productivity of the installation is increased. Despite the high cost of pure oxygen, there is a trend in industry to convert existing plants from air to oxygen.

Figure 2 - Schematic diagram of the production of 1,2 dichloroethane by oxychlorination of ethylene

Figure 3 - Dependence of the degree of conversion of dichloroethane on temperature

Ethylene, hydrogen chloride and air are supplied to the tubular reactor 1; at 483-533 K the reaction occurs in the presence of a copper chloride catalyst supported on aluminum oxide or aluminosilicate. A small excess of ethylene is used. In the quenching column 2, HC1 is separated, from which the acid is obtained. Inert gases leave the upper part of the collection 8, the upper layer from which enters column 2; The chlorine-containing product is neutralized and washed in column 4, and then separated into a light fraction and dichloroethane in columns 5 and b (distillation section). The still remains are removed. In column 5, wet dichloroethane is also dried by azeotropic distillation.

Pyrolysis of dichloroethane. The target product of the balanced process - vinyl chloride - is formed at the stage of dehydrochlorination (pyrolysis) of dichloroethane.

Table 1 - Initiating activity of some compounds at a temperature of 648 K in a flow reactor

Table 2 - Inhibitory activity of some compounds at a temperature of 773 K in a differential reactor

Pyrolysis of dichloroethane is carried out at 723-793 K and 2 MPa:

The degree of conversion of dichloroethane in one pass is 50-60% with a selectivity for vinyl chloride of 96-99%.

Pyrolysis of dichloroethane proceeds by a radical chain mechanism. The reaction begins with the cleavage of the C-C1 bond in the dichloroethane molecule and the formation of free radicals, which further contribute to the development

chains - abstraction of the H atom by the SG radical from the dichloroethane molecule and molecular decomposition of the 1,2-dichloroethyl radical. The chain termination reaction occurs during the recombination of radicals:

Temperature has the main influence on the rate of dichloroethane pyrolysis. Figure 3 shows the dependence of the degree of dichloroethane conversion on temperature.

Additives with initiating and inhibitory effects can have a significant impact on the speed of the process and the composition of products. Dichloroethane containing at least 99.2% of the main substance is usually supplied to the pyrolysis stage. As a rule, impurities contain chloroethanes, chloroethenes and benzene. Tables 1 and 2 provide examples of the initiating and inhibitory effects of some substances.

A balanced method for producing vinyl chloride based on ethylene was developed by Yu.A. Treger et al. (Research Institute "Sintez", Moscow). This method has been implemented on an industrial scale at a number of enterprises in Russia and abroad.

One-step process for the synthesis of vinyl chloride from ethylene (Stuffer process). The Staffer company carried out a one-stage process of thermochlorination of ethylene to vinyl chloride at 625-775 K and a pressure of 0.35-1.4 MPa. Iron, alkali and alkaline earth metals and their oxides, copper chloride mixed with asbestos, molten copper chlorides and other compositions were used as catalysts for this process. Combining the stages of chlorination and pyrolysis (thermochlorination) presents some difficulties, since the parameters of these processes differ significantly. The reactor designed for thermochlorination consists of three sections, in one of which the pyrolysis of dichloroethane coming from the oxychlorination reactor occurs, in the second - the thermochlorination of ethylene dovinyl chloride and dichloroethane, and in the third - the pyrolysis of dichloroethane converted in the first two sections is completed.

Two-stage process for the synthesis of vinyl chloride from ethylene. One of the disadvantages of the technological scheme for producing vinyl chloride described above is its multi-stage nature. Significant difficulties are associated with the process of thermal dehydrochlorination of dichloroethane due to costs large quantity heat and the formation of by-products: acetylene, butadiene, chloroprene, as well as intensive resin and coke formation. A natural way to reduce the activation energy and, accordingly, the process temperature is the use of catalysts. In addition, the most balanced process hides the possibility of using the heat of the exothermic reaction of oxychlorination of ethylene (238.8 kJ/mol) to carry out the endothermic reaction of dehydrochlorination of dichloroethane (71.2 kJ/mol). Obviously, it is possible to combine these processes in one reaction zone or balance them by heat transfer.

The combined process of producing vinyl chloride takes place in a shell-and-tube reactor on a stationary bed of catalyst. Ethylene, hydrogen chloride and air heated to 423 K are fed into a reactor filled with a catalyst under a pressure of 0.4 MPa. The reaction proceeds at 623 K. The main indicators of the process are given below:

Selectivity for vikyl chloride, %54

Selectivity for CO and COj. % 5

Conversion rate, %:

ethylene 76

hydrogen chloride 66

oxygen 91

The process of producing vinyl chloride consists of two main stages: direct chlorination of ethylene and a combined process of oxidative chlorination of ethylene and pyrolysis of dichloroethane.

During the reaction in the reactor /, heat is released, to remove which a coolant is supplied to the inter-tube space. Coolant regeneration is carried out in a waste heat boiler. The reaction gases leaving the reactor, containing organic products (vinyl chloride, 1,2-dichloroethane, ethyl chloride, dichlorethylenes, etc.), carbon oxides, water vapor, nitrogen and unreacted ethylene, hydrogen chloride, oxygen, enter the quenching column cube at 623 K 5. The temperature of the gases in the column is reduced to 383-393 K. Cooled and neutralized gases from the upper part of the quenching column enter the condenser in which partial condensation of moisture and dichloroethane occurs. The condensate is supplied to the phase separation apparatus, from which dichloroethane is sent to the raw dichloroethane collection, and water is sent to the mixer for preparing an alkali solution. A gas stream containing vinyl chloride, ethylene, non-condensed organic products, moisture, inert gases enters the refrigerator, in which it is cooled to 278 K. It passes through a separator and scrubber, where it is dried to a moisture content of 10-20 parts per 1 million and beyond. sent to the absorption column.

With a total conversion of ethylene to vinyl chloride of 89%, the process becomes competitive with the traditional balanced process.

Synthesis of vinyl chloride from ethane. Modern production vinyl chloride from both ethylene and acetylene are characterized by high yields and relatively low capital investments. Therefore, further improvement of the process should follow the path of choosing cheap and accessible hydrocarbon raw materials. Such a raw material is ethane.

At the Sintez Research Institute under the leadership of Yu.A. Treger developed a process for producing vinyl chloride from ethane, which includes the following stages:

Oxychlorination of ethane to vinyl chloride and ethylene;

Chlorination of ethylene to dichloroethane;

Pyrolysis of dichloroethane;

Processing of organochlorine products to produce trichlorethylene.

All stages of the process, excluding the oxychlorination of ethane, are similar to the corresponding stages of the balanced process for producing vinyl chloride from ethylene.

Oxidative chlorination of ethane is a heterogeneous catalytic process, including a series of series-parallel reactions.

Depending on the reaction conditions, various chlorinated derivatives of ethane and ethylene can be formed. The synthesis of vinyl chloride occurs in the temperature range 723-823 K. At lower temperatures (573-623 K), the main reaction products are ethyl chloride and dichloroethane, the yield of vinyl chloride is low.

The process of oxidative chlorination of ethane is accompanied by the formation of ethylene and chloroethylenes as a result of the coupling of substitutive and additive chlorination reactions with the reactions of dehydrogenation and de-hydrochlorination of chloroalkanes. Various ways of formation of vinyl chloride and its further transformations:

Figure 4

Vinyl chloride is formed only as a result of dehydrochlorination of dichloroethane. During the oxychlorination of ethane, a significant formation of carbon oxides occurs due to the oxidation of hydrocarbons and hydrochlorocarbons.

Oxychlorination of ethane is carried out in a “fluidized bed” of a catalyst at 820 K and 0.2 MPa. Silica gel impregnated with copper and potassium chlorides is used as a catalyst.

Figure 5 - Block diagram for the production of vinyl chloride (VC) from ethane

Hydrochlorination of acetylene. The method for producing vinyl chloride by hydrochlorination of acetylene is based on a catalytic reaction that occurs with a large release of heat:

This method is distinguished by the simplicity of the technological design of the process, low capital investment, and high selectivity for vinyl chloride, but the method has not found wide industrial application due to the high cost of acetylene. Acetylene carbide can compete with ethylene as a raw material for the production of vinyl chloride if its cost does not exceed the cost of ethylene by more than 40%.

Hydrochlorination of acetylene is usually carried out in the presence of mercuric chloride applied in an amount of 10-15% to Activated carbon, in a stationary catalyst bed at 425-535 K and 0.2-1.5 MPa. The acetylene conversion rate is 98.5% with a vinyl chloride selectivity of 98%.

Figure 6 - Schematic diagram of vinyl chloride by acetylene hydrochlorination

Although many catalytic systems exhibit high activity, currently only HgCls-based catalyst (sublimate) is used in industry, despite its high toxicity. To increase the holding capacity of activated carbon with respect to mercury chloride, amine additives are introduced.

Acetylene, after compression, drying and purification, passes through a filter and, under a pressure of up to 70 kPa, is mixed with hydrogen chloride. The resulting mixture of gases with a temperature of up to 308 K enters the hydrochlorination reactor. The reactor tubes are filled with a catalyst - sublimate on a carrier. The heat of reaction is removed by water or diethylene glycol circulating in the annulus, followed by cooling in a heat exchanger. The gas leaving the reactor is supplied to the adsorber for purification from mercury compounds and, after cooling in a heat exchanger by a compressor, is supplied to rectification columns. Vinyl chloride then enters the alkaline drying and neutralization column.

The Sintez Research Institute has developed an industrial process for the hydrochlorination of acetylene in a “fluidized bed” of a catalyst. The technological scheme consists of the following stages:

Hydrochlorination of acetylene;

Purification and drying of reaction gas;

Absorption of vinyl chloride from the reaction gas;

Hydrochlorination of acetylene gas;

Rectification of vinyl chloride.

At first, vinyl chloride was obtained by alkaline dehydrochlorination of 1,2-dichloroethane in methyl or ethyl alcohol:

СlCH 2 -CH 2 Cl+ NaOH>CH 2 =CHCl+NaCl+H 2 O

The high consumption of alkali and chlorine during this synthesis accelerated the development and introduction into industry of acetylene hydrochlorination in the 40-50s:

CH?CH+HCl>CH 2 -CHCl

Which is associated with the use of toxic mercury salts as catalysts and relatively expensive acetylene.

The thermal dehydrochlorination of dichloroethane made it possible to avoid the consumption of alkali and use the resulting hydrogen chloride for the hydrochlorination of acetylene. This is how combined methods for the synthesis of vinyl chloride from acetylene and ethylene, balanced in chlorine, appeared.

As of 2010, there are four main methods for producing vinyl chloride, implemented on an industrial scale. Vinyl chloride can be obtained in various ways:

1. Hydrochlorination of acetylene in gas or liquid phases in the presence of a catalyst:

2. Dehydrochlorination of 1,2-dichloroethane (in liquid phase) with sodium hydroxide in an aqueous or alcoholic medium:

CH 2 C1 - CH 2 C1 + NaOH?> CH 2 = CHCl + NaCl + H 2 0

3. Thermal dehydrochlorination of 1,2 - dichloroethane in the vapor phase in the presence of catalysts, initiators or without them:

CH 2 C1 = CH 2 C1 > CH 2 = CHCl + HCl

4. Chlorination of ethylene in the gas phase in bulk, or in the presence of a catalyst, for example aluminum oxide:

CH 2 =CH 2 +Cl 2 >CH 2 =CHCl+HCl

In this course work we will consider in more detail the following methods for producing vinyl chloride: hydrochlorination of acetylene in gas and liquid phases in the presence of a catalyst; and a combined method for the synthesis of vinyl chloride from acetylene and ethylene.

Gas-phase hydrochlorination of acetylene

The process is carried out in the gas phase in the presence of a catalyst. To achieve high conversion of the initial reagents (98-99%) and selectivity (? 99%), mercury dichloride supported on activated carbon is used as a catalyst.

The chemistry of the process is as follows:

Acetylene production:

Hydrochlorination of acetylene:

Activated carbon in this catalytic system is not an inert carrier, but an active component and therefore its chemical nature and structure have a significant effect on the properties of the catalyst. For an industrial catalyst, the most important are economic indicators - the stability of the catalyst, its productivity and selectivity. These indicators are determined mainly by the deactivation of the catalyst associated with the entrainment and reduction of mercury dichloride to metallic mercury, which to a certain extent depends on the nature and structure of the carrier.

The structure of the carrier is determined by its porosity, i.e. the presence of macro-, micro- and transition pores. The linear sizes of the molecules involved in the hydrochlorination reaction are calculated to be: r C H Cl = 0.816 nm, r C H = 0.581 nm and r H Cl = 0.472 nm, and the intermediate β-complex formed in the reaction has a linear size of at least 1.0-1, 2 nm. Therefore, micropores with a diameter less than 1.0 nm cannot participate in the hydrochlorination process. The predominant role in this process belongs to transition pores: the more transition pores, the more actively mercury dichloride is adsorbed and the more active and stable the catalyst. Chemical nature The carrier is determined by the presence of surface functional groups: carboxyl, carbonyl and hydroxyl (phenolic and alcohol type), etc. An increase in the content of carbonyl groups reduces the stability and activity of the catalyst, apparently due to the ability to reduce mercury dichloride up to metallic mercury, and phenolic groups can contribute increasing stability due to their oxidation to quinones.

To increase the stability of the mercury catalyst for acetylene hydrochlorination, organic amines and their salts are applied to specially prepared activated carbon along with mercury chloride. Due to the high activity of the mercury catalyst, using its kinetic capabilities is very difficult. This is due to the fact that, on the one hand, the acetylene hydrochlorination reaction is very exothermic, and, on the other hand, due to the high volatility of mercury dichlorine, the maximum temperature of the process is limited to 150-180 °C.

Is vinyl chloride.

Vinyl chloride (vinyl chloride) Under normal conditions, it is a colorless gas with a boiling point of -13.9 °C. He dissolves well in chloroform, dichloroethane, ethanol, ether, acetone, petroleum hydrocarbons and very little in water. The presence of a double bond determines its ability to undergo polymerization reactions.

Vinyl chloride formula: CH 2 =CHCl

Preparation of vinyl chloride

Vinyl chloride can be produced by various methods.

Figure 1: Reactions to produce vinyl chloride

Hydrochlorination of acetylene (Figure 1 A):

The process can be carried out in gas And liquid phases in a tubular type contact apparatus. Gas phase method is the most common. The process is carried out in a tubular type contact apparatus at 120-220 °C under overpressure 49 kPa above activated carbon, soaked mercuric chloride in an amount of 10% by weight of coal.

For gas-phase hydrochlorination it is used dry 97-99% acetylene And highly concentrated hydrogen chloride V molar ratio 1:1.1. Hydrogen chloride must not contain free chlorine, which with acetylene reacts explosively.

The reaction products are a gaseous mixture that contains 93% vinyl chloride and other impurities. This mixture is separated and purified.

Preparation of vinyl chloride from ethylene and chlorine

Methods for the synthesis of vinyl chloride from and chlorine, since ethylene obtained from petroleum hydrocarbons is cheaper than acetylene obtained from calcium carbide or from natural methane and other hydrocarbons by thermal oxidative pyrolysis or electrocracking.

The production of vinyl chloride from ethylene and chlorine through dichloroethane is carried out in two stages (Figure 1 B):

1. liquid-phase chlorination of ethylene in the presence of copper, iron or antimony chlorides;
2. pyrolysis of dichloroethane formed in the first stage.

Liquid-phase chlorination of ethylene is carried out in a conventional reactor at 45-60 °C in the presence of a catalyst - ferric chloride in the environment dichloroethane. Received dichloroethane subjected pyrolysis at 480-500 °C and pressure 0.15-0.20 MPa. Used as a catalyst granular activated carbon or aluminum oxide, silica gel and iron.

The degree of conversion reaches 70% per cycle. Dichloroethane after its separation it is sent back to the process.

Dehydrochlorination of dichloroethane can be carried out over catalysts used in the pyrolysis of dichloroethane at 480-490 °C, under pressure 24 MPa in a stainless steel tubular reactor.

Designed by one-step method for producing vinyl chloride by high-temperature chlorination of ethylene (Figure 1 B):

Conversion rate of ethylene to vinyl chloride increases with increasing temperature of the chlorination reaction from 350 to 600,°C. At low temperatures, along with substitution, addition reaction.

High temperature chlorination of ethylene can also be carried out in the presence of vinyl chloride as a diluent. This makes it possible to increase the monomer concentration in the reaction products [up to 55% by volume], while the costs of isolating vinyl chloride are noticeably reduced.

Combined methods for producing vinyl chloride

The main disadvantage methods for producing vinyl chloride from ethylene and chlorine is release of hydrogen chloride as a by-product (550-650 kg per 1000 kg of vinyl chloride). Therefore, vinyl chloride is now often obtained combined method(dichloroethane dehydrochlorination units or ethylene chlorination units are combined with acetylene hydrochlorination units).

The problem of using hydrogen chloride released during the dehydrochlorination of dichloroethane is also solved by combining installations for the production and pyrolysis of dichloroethane With hydrogen chloride oxidation plants, formed during the pyrolysis of dichloroethane. The process is described by the equations:

Formed chlorine used for chlorination of ethylene. Instead of the separate oxidation of hydrogen chloride and chlorinated ethylene to dichloroethane, a one-step process of oxidative chlorination of ethylene can be used:

The reaction takes place over a catalyst at 470-500 °C. Used as a catalyst copper chloride And potassium chloride on kieselguhr and others.

Vinyl chloride yield reaches 96% in terms of ethylene and 90% in terms of hydrogen chloride.

Currently developed technological schemes, allowing the use of vinyl chloride in the production ethylene And acetylene without their prior separation from dilute gases. At the first stage there is acetylene hydrochlorination contained in the original mixture. The resulting vinyl chloride extracted with dichloroethane, and the ethylene remaining in the mixture is subjected to chlorination to dichloroethane. The reaction takes place in dichloroethane environment in the presence ferric chloride under pressure 0.39-0.69. MPa.

The separated dichloroethane is processed into vinyl chloride in the usual way, and the resulting hydrogen chloride is used for the hydrochlorination of acetylene.

Purification and storage of vinyl chloride

Vinyl chloride obtained by various methods must be subjected to thorough cleaning from acetylene, hydrogen chloride and other impurities.

Vinyl chloride to obtain polyvinyl chloride must contain not less than 99.9% And minimal amount impurities. Pure vinyl chloride can be long time store in steel tanks at temperatures from -50 to - 30 °C under nitrogen in the absence of inhibitors.

Vinyl Chloride Production

Vinyl chloride CH2=CHN1 Mainly used to produce polyvinyl chloride.

Vinyl chloride can be obtained in various ways:

hydrochlorination of acetylene in gas or liquid phases in the presence of a catalyst:

dehydrochlorination of 1,2-dichloroethane (in liquid phase) with sodium hydroxide in an aqueous or alcoholic medium:

thermal dehydrochlorination of 1,2-dichloroethane in the vapor phase with or without catalysts, initiators:

chlorination of ethylene in the gas phase in bulk, or in the presence of a catalyst, for example aluminum oxide:

Let's look at several of the most common industrial methods for producing vinyl chloride from acetylene and ethylene.

Preparation of vinyl chloride from acetylene

Theoretical foundations of the process

A common method for producing vinyl chloride is the hydrochlorination of acetylene. The reaction of hydrogen chloride adding to acetylene is typical for a compound with a triple bond:

In terms of its exothermicity, it is almost twice as high as the reaction of olefin hydrochlorination.

The acetylene hydrochlorination reaction is somewhat reversible. At the same time, at moderate temperatures the equilibrium is almost completely shifted to the right, since the equilibrium constants are 8-104 at 200°C and 7-102 at 300°C. Moreover, the accession NS1 to acetylene proceeds sequentially - vinyl chloride is formed first, and then 1,1-dichloroethane:

Therefore, to obtain vinyl chloride, it is necessary to use selective catalysts that accelerate only the first reaction. Salts turned out to be the most suitable for this purpose. Hg(II) And Si(1). When using sublimate Hg C12 the hydration reaction of acetylene to produce acetaldehyde (Kucherov reaction) is also greatly accelerated. In this regard, the process is carried out in the gas phase at temperatures of 150--200 ° C, using pre-dried reagents. This produces a small amount of acetaldehyde and 1,1-dichloroethane (=1%). At the same time, the possibility of jointly producing acetaldehyde and vinyl chloride can be considered. In this case, it is necessary to carry out the process in the liquid phase.

Cu(1) salt is more suitable for liquid-phase hydrochlorination, since it is weakly deactivated and poorly accelerates the interaction of acetylene with water. (Consequently, this catalyst is unsuitable for the co-production of vinyl chloride and acetaldehyde.)

The catalytic system is a solution Si2S12 and aluminum chloride in hydrochloric acid. However, dimerization of acetylene also occurs on this catalyst to form vinyl acetylene:

To suppress this reaction it is necessary to use concentrated BUT. In this regard, during the process, HCl is continuously supplied to the catalyst solution to compensate for its consumption for hydrochlorination.

The catalytic effect of these catalysts is explained by the formation of coordination complexes in which acetylene is activated and interacts with chlorine anions. In this case, transition states with metal-carbon bonds or organometallic compounds occur, which are quickly decomposed by acid.

Preparation of vinyl chloride from ethylene and chlorine.

The one-step synthesis of vinyl chloride by chlorination of ethylene can be described by the equation:

CH2=CH2 + Cl2 CH2=CHCl + HCl

This method has not yet found application in industry due to its low selectivity. The process proceeds with the predominant formation of vinyl chloride only when carried out in a large excess of ethylene or

inert gas. However, this makes the subsequent isolation of vinyl chloride difficult. A one-step replacement of the hydrogen atom in ethylene by a chlorine atom, carried out in the presence of excess vinyl chloride or water, has recently been described. This allows us to consider the method in question suitable for use in industry. The reaction occurs with the greatest selectivity at 420-450 0C, the yield of vinyl chloride is about 90%. The disadvantage of this method is the formation, along with vinyl chloride, of an equivalent amount of hydrogen chloride.

Combined, or “balanced” method (from ethylene, acetylene and chlorine).

The problem of using hydrogen chloride formed during the dehydrochlorination of dichloroethane is very often solved by combining the processes of adding chlorine to ethylene, dehydrochlorination of dichloroethane and hydrochlorination of acetylene. Hydrogen chloride, obtained from the dehydrochlorination of dichloroethane, is used as a starting product for the hydrochlorination of acetylene in the same production. The process can be described by the summary equation:

CH2=CH2 + CH=CH + Cl2 2CH2=CHCl

This method is used in the presence of readily available feedstocks - acetylene and ethylene. When producing vinyl chloride by a combined method, acetylene and ethylene can be obtained separately (for example, acetylene from carbide or natural gas, and ethylene from oil), as well as in one process. IN the latter case By pyrolysis or cracking of petroleum fractions, a gas mixture containing acetylene and ethylene is obtained, from which acetylene is separated by selective absorption, and then ethylene is separated in the usual way.

The combined method has become widespread in industry. At the end of 1962, US vinyl chloride synthesis capacity was distributed as follows:

only from acetylene - 41%;

only from ethylene -28%;

from acetylene and ethylene - 31%.

In Japan, from dichloroethane and a combined method, 15% was synthesized in 1964, 25% in 1965, and about 46% vinyl chloride in 1968.

Obviously, after mastering the method of direct chlorination of ethylene (bypassing the stage of dichloroethane formation), under certain conditions it may also be advisable to combine this process with acetylene hydrochlorination.

Preparation of vinyl chloride from dilute gases containing acetylene and ethylene, and chlorine.

The separation of concentrated pure acetylene and ethylene from dilute cracking gases of light gasoline is expensive. In this regard, technological schemes have been developed that make it possible to use ethylene and acetylene in the production of vinyl chloride without their preliminary separation from dilute gases.

At the first stage, acetylene contained in the initial mixture is hydrochlorinated. The resulting vinyl chloride is extracted with dichloroethane, and the ethylene remaining in the gas is chlorinated to dichloroethane. The reaction takes place in the liquid phase (in dichloroethane) in the presence of ferric chloride as a catalyst. The dichloroethane isolated by condensation is then processed into vinyl chloride in the usual way, and the resulting hydrogen chloride is used for the hydrochlorination of acetylene.

The process is also convenient because the exhaust gases containing methane, hydrogen, carbon monoxide and carbon dioxide can be used as fuel for cracking the original gasoline and dichloroethane. Chlorination and dehydrochlorination are carried out under low pressure (4-7 at).

The yield of vinyl chloride based on the starting acetylene and ethylene is close to theoretical, and the cost of the monomer is lower than when it is produced by other methods.

The production of vinyl chloride using the described method was carried out for the first time on an industrial scale in Japan.

Production of vinyl chloride from ethylene and chlorine with regeneration of hydrogen chloride.

When producing vinyl chloride using a combined method, hydrogen chloride formed during the thermal decomposition of dichloroethane is used for the hydrochlorination of acetylene.

However, the use of this method is beneficial only in the presence of inexpensive and accessible acetylene. Otherwise, there is a need to dispose of hydrogen chloride.

In this regard, two methods have been developed for producing elemental chlorine from hydrogen chloride. One of the methods is based on the electrolysis of concentrated hydrochloric acid. In this case, an equivalent amount of hydrogen is formed simultaneously with chlorine. During electrolysis, only part of the hydrogen chloride is converted into chlorine and hydrogen. The resulting dilute hydrochloric acid concentrated by passing gaseous hydrogen chloride, a product of the pyrolysis of dichloroethane, through it.

According to the second method, hydrogen chloride is oxidized with atmospheric oxygen in the presence of a catalyst (Deacon reaction):

2HCl + 1/2O2 Cl2 + H2O

The reaction takes place in the gas phase; Hydrogen chloride and air are passed through silica gel coated with copper chloride. The latter can be activated by the addition of other chlorides.

Depending on the specific conditions, both electrolytic and oxidative methods may be more advantageous. Both methods, in combination with chlorination of ethylene and dehydrochlorination of dichloroethane, can provide the opportunity to slightly reduce the cost of vinyl chloride compared to the cost of the monomer obtained by the combined method. However, this involves quite large capital investments.

Regeneration of chlorine from hydrogen chloride can also be combined with direct chlorination of ethylene to vinyl chloride. The process is described by the following reactions:

electrolytic method

2CH2=CH2 + Cl2 2CH2=CHCl + H2

oxidative method

2CH2=CP2 + Cl2 + 1/2O2 2CH2=CHCl + H2O

Preparation of vinyl chloride from ethylene and hydrogen chloride by oxychlorination.

Instead of separately oxidizing hydrogen chloride and chlorinating ethylene to dichloroethane, a one-step process for ethylene oxychlorination can be used:

CH2=CH2 + 2HCl + 1/2O2 ClCH2-CH2Cl + H2O

Copper salts on supports are used as catalysts. Synthesis is carried out at 250 0C and above. To obtain dichloroethane from ethylene, hydrogen chloride and oxygen in industrial conditions, larger capital investments are required than for the synthesis of dichloroethane from ethylene and chlorine. Despite the fact that during the oxychlorination of ethylene, the yield of dichloroethane based on both initial products exceeds 95%, it is still somewhat lower than when adding elemental chlorine to ethylene. It is advisable to use the oxychlorination method in areas where there is cheap ethylene and hydrogen chloride, which is released as a by-product in various processes, or in areas where the removal of hydrogen chloride from wastewater impossible.