Vinyl chloride from ethylene

Until about 1980, mercuric chloride was used extensively as a catalyst for the preparation of vinyl chloride from acetjiene (7). Since the early 1980s, vinyl chloride and vinyl acetate have been prepared from ethylene instead of acetjiene, and the use of mercuric chloride as a catalyst has practically disappeared. 

In a typical balanced plant producing vinyl chloride from EDC, all the HCl produced in EDC pyrolysis is used as the feed for oxychlorination. On this basis, EDC production is about evenly spHt between direct chlorination and oxychlorination, and there is no net production or consumption of HCl. The three principal operating steps used in the balanced process for ethylene-based vinyl chloride production are shown in the block flow diagram in Eigure 1, and a schematic of the overall process for a conventional plant is shown in Eigure 2 (76). A typical material balance for this process is given in Table 2. 

Halogenation and dehalogenation are catalyzed by substances that exist in more than one valence state and are able to donate and accept halogens freely. Silver and copper hahdes are used for gas-phase reactions, and ferric chloride commonly for hquid phase. Hydrochlorination (the absoration of HCl) is promoted by BiCb or SbCl3 and hydrofluorination by sodium fluoride or chromia catalysts that form fluorides under reaction conditions. Mercuric chloride promotes addition of HCl to acetylene to make vinyl chloride. Oxychlori-nation in the Stauffer process for vinyl chloride from ethylene is catalyzed by CuCL with some KCl to retard its vaporization. 

The monomer is produced from trichloroethane by dehydrochlorination Figure 17.2). This may be effected by pyrolysis at 400°C, by heating with lime or treatment with caustic soda. The trichlorethane itself may be obtained from ethylene, vinyl chloride or acetylene. 

Write out and balance the overall equation for the manufacture of vinyl chloride from ethylene, chlorine and oxygen. 

The block diagram shows the main steps in the balanced process for the production of vinyl chloride from ethylene. Each block represents a reactor and several other processing units. The main reactions are ... 

DOC [direct oxychlorination] A one-stage process for making vinyl chloride from ethylene and chlorine. Piloted by Hoechst in Germany in 1989. 

The vast majority of commercial polymers based on the vinyl group (H2C=CHX) or the vinylidene group (H2C=CX2) as the repeat unit are known by their source-based names. Thus, polyethylene is the name of the polymer synthesized from the monomer ethylene poly(vinyl chloride) from the monomer vinyl chloride, and poly(methyl methacrylate) from methyl methacrylate. 

A competing process produces vinyl chloride from acetylene, which also can be derived from petroleum feed stocks but is usually made from calcium carbide. It has been estimated (17) that 45% of current production of vinyl chloride is from ethylene, the remainder from acetylene. 

Demonstration of the technical feasibility of producing mixtures of acetylene and ethylene by pyrolysis of hydrocarbons (Wulff process or Kureha process) has led to the manufacture of vinyl chloride from such mixtures. The acetylene component reacts selectively with hydrogen chloride to form vinyl chloride, the residual ethylene is converted to dichloroethane, and the latter is cracked to vinyl chloride, with the resulting hydrogen chloride being recycled. However, this type of process has not achieved the industrial importance of the all-ethylene type of process. 

The ethylene dichloride was then cracked to vinyl chloride and hydrochloric acid with the hydrochloric acid recycled to produce vinyl chloride from ethylene as shown above. 

Figure 10.11 shows an integrated plant for producing EDC and vinyl chloride from ethylene, chlorine, and air. In this process, vinyl chloride (VCM) is produced by the thermal cracking of EDC. The feed EDC may be supplied from two sources. In the first source, ethylene and chlorine are reacted in essentially stoichiometric proportions to produce EDC by direct addition. In the second source, ethylene is reacted with air and HC1 by the oxychlorination process. Ideally, both processes are carried out in balance, and the oxychlorination process is used to consume the HC1 produced in the cracking and direct chlorination steps. The chemical reactions are... 

The tetraalkylammonium cation is not reduced. The solvent is decomposed on the cathode, yielding H2, ethylene, vinyl chloride, and car-banions. Similar processes also occur in the cathode space with the electrolyte R4N + C104. HC104 is formed around the anode and the monomer is polymerized in the anode space so far it is not known whether this is only by the effect of HC104 or whether cations from the supporting electrolyte are also involved. 

In producing vinyl chloride from ethylene, a two-step process is used (6) in which ethylene is first chlorinated to 1,2-dichloroethane (DCE). 

Analytical pyrolysis consists of heating a sample, preferably suddenly, in a vacuum, and analyzing the vapors produced. It is very much an art, but identification of the vapors - olefins such as ethylene, vinyl chloride, MCN, aldehydes, etc. - provides obvious clues to the composition of the material from which they are broken down. Analysis of the vapors is usually by gas chromatography (GC) or infrared (IR) spectrophotometry. 

The HCl can be recovered and converted to CI2 for further production of 1,2-dichloroethane from ethylene. Vinyl chloride has a much lower boiling point than 1,2-dichloroethane (-13°C compared with 84°C), so the two are easily separated by fractional distillation. Vinyl chloride is used in the production of polyvinyl chloride plastic (see Section 23.1). 

Hydrogen chloride may be used as a chlorinating agent. It is sometimes employed in such a manner that it adds to the double bond as in the preparation of ethyl chloride from ethylene 75 or in the synthesis of vinyl chloride from acetylene 16. Kainer 48 has surveyed the patents dealing with the preparation of vinyl chloride. A review 21 of the patent literature and the apphcation of the Deacon reaction, which uses hydrogen chloride and air, has also been published. Some of the material on this reaction has been mentioned before 26, 82, 61. ... 

Desulfurization of petroleum feedstock (FBR), catalytic cracking (MBR or FI BR), hydrodewaxing (FBR), steam reforming of methane or naphtha (FBR), water-gas shift (CO conversion) reaction (FBR-A), ammonia synthesis (FBR-A), methanol from synthesis gas (FBR), oxidation of sulfur dioxide (FBR-A), isomerization of xylenes (FBR-A), catalytic reforming of naphtha (FBR-A), reduction of nitrobenzene to aniline (FBR), butadiene from n-butanes (FBR-A), ethylbenzene by alkylation of benzene (FBR), dehydrogenation of ethylbenzene to styrene (FBR), methyl ethyl ketone from sec-butyl alcohol (by dehydrogenation) (FBR), formaldehyde from methanol (FBR), disproportionation of toluene (FBR-A), dehydration of ethanol (FBR-A), dimethylaniline from aniline and methanol (FBR), vinyl chloride from acetone (FBR), vinyl acetate from acetylene and acetic acid (FBR), phosgene from carbon monoxide (FBR), dichloroethane by oxichlorination of ethylene (FBR), oxidation of ethylene to ethylene oxide (FBR), oxidation of benzene to maleic anhydride (FBR), oxidation of toluene to benzaldehyde (FBR), phthalic anhydride from o-xylene (FBR), furane from butadiene (FBR), acrylonitrile by ammoxidation of propylene (FI BR)... 

Magnetic tapes are usually coated with coatings from solvents, such as methyl ethyl ketone, methyl isobutyl ketone, and toluene. Aqueous replacements can eliminate all or nearly all of the solvents.352 One system used iron oxide in a blend of a polyurethane and ethylene-vinyl chloride copolymer emulsions thickened with hydroxyethyl cellulose, which was cross-linked with a melamine-formaldehyde resin. Coating was done at line speeds of 100 m/min. The whole system proved to be 15% cheaper than coating from solvent. In another system, traces of methanol are evolved on drying and would have to be captured. This replaces a line where 600 kg/h of solvent would have to be recovered and recycled. 

Processes for manufacturing vinyl chloride from acetylene, which, for many years, were the only ones employed, offer the advantage of simplicity. Hence they benefit from lower capital expenditures, but, on the other hand, require the use of a much more expensive hydrocarbon raw material. This explains why they have been supplanted by technologies employing ethylene, and why they enjoyed a revival as the price of crude oil increased, although ethylene produced from gas-field ethane is ultimately the most advantageous economic alternative. 

Joint production of vinyl chloride from acetylene and ethylene in so-called balanced schemes or processes... 

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