Ethylene vinyl chloride monomer process

Over the past years considerable attention has been paid to the dispersing system since this controls the porosity of the particle. This is important both to ensure quick removal of vinyl chloride monomer after polymerisation and also to achieve easy processing and dry blendable polymers. Amongst materials quoted as protective colloids are vinyl acetate-maleic anhydride copolymers, fatty acid esters of glycerol, ethylene glycol and pentaerythritol, and, more recently, mixed cellulose ethers and partially hydrolysed polyfvinyl acetate). Much recent emphasis has been on mixed systems. 

Telescope the Process by Combining Stages. This has been done successfully in the conversion of propylene to acrylonitrile by direct ammoxidation rather than oxidation to acrolein followed by reaction with ammonia in a separate stage, as was described in the earlier patent literature. The oxychlorination of ethylene and HC1 directly to vinyl chloride monomer is another good example of the telescoping of stages to yield an economic process. 

On November 8, 2000, U.S. EPA listed as hazardous two wastes generated by the chlorinated aliphatics industry.18 The two wastes are wastewater treatment sludges from the production of ethylene dichloride or vinyl chloride monomer (EDC/VCM), and wastewater treatment sludges from the production of vinyl chloride monomer using mercuric chloride catalyst in an acetylene-based process. 

Originally, vinyl chloride polymers were based on acetylene. The switch to ethylene,chemistry came after the development of the oxychlorination process for vinyl chloride described in Chapter 9. Today very little acetylene-, based vinyl chloride monomer (VCM) processing remains. 

World-wide consumption of PVC [poly(vinyl chloride)] has increased dramatically in the past few years. It has now exceeded 8 billion lbs annually. The production of VCM (vinyl chloride monomer) has also been expanded to meet the PVC demand. Future trends for VCM and PVC pro-ductions for the next five years can be forecast on the basis of the raw materials sources, the different process techniques in manufacturing VCM and PVC, and their relative economics, technical merits, and limitations. VCM will be produced principally through the ethylene route by fluid-bed oxyhydrochlorination of ethylene and thermal cracking of ethylene dichloride. PVC will be produced by various processes resulting in more specialized PVC varieties tailored for specific end markets and new processing technologies. 

Technological advances in the production of the vinyl chloride monomer (VCM) have contributed to the declining price of the polymer. Figure 4 illustrates this statement the price of the vinyl chloride monomer (1) over a period of 20 years is plotted against two curves that represent the annual production of monomer made from two different bases, acetylene and ethylene. The classic acetylene route was the first to be exploited commercially, but its popularity has declined as more processes were developed that could utilize ethylene, a cheaper base. 

This process is shown schematically in Figure 7. The ethylene part of the feed reacts with chlorine in the liquid phase to produce 1,2-di-chloroethane (EDC) by a simple addition reaction, in the presence of a ferric chloride catalyst (9). Thermal dehydrochlorination, or cracking, of the intermediate EDC then produces the vinyl chloride monomer and by-product HC1 (1). Acetylene is still needed as the other part of the over-all feed, to react with this by-product HC1 and produce VCM as in the all-acetylene route. 

The current trend for vinyl chloride monomers is toward ethylene as the hydrocarbon raw material, replacing electrochemical acetylene, and it promises to continue. Electrochemical acetylene will be phased out almost completely, except in special cases. The high activation energy level required for forming the acetylene triple bond precludes design of a low cost process for its formation. In addition, the difficulties encountered in handling such a highly reactive material will deter its use. 

Oxychlorination Process to produce vinyl chloride monomer from ethylene, hydrogen chloride, and oxygen over a copper chloride on alumina catalyst. 

Application A process to produce vinyl chloride monomer (VCM) and ethylene dichloride (EDC) from ethylene, chlorine and oxygen using a high efficiency fixed-bed oxychlorination process. 

Mitsui Chemicals, Inc. Vinyl chloride monomer Chlorine, ethylene, oxygen Oxygen-based balanced oxychlorination process, high temp, direct chlorination process 23 1998... 

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. 

Another type of branching occurs in some free-radical polymerizations of monomers like ethylene, vinyl chloride, and vinyl acetate in which the macroradicals are very reactive. So-called self-branching can occur in such polymerizations because of atom transfer reactions between such radicals and polymer molecules. These reactions, which are inherent in the particular polymerization process, are described in Chapter 6. 

Presence of impurities in excipients can have a dramatic influence on the safety, efficacy or stability of the drug product. Monomers or metal catalysts used during a polymerization process are toxic and can also destabilize the drug product if present in trace amounts. Due to safety concerns, the limit of vinyl chloride (monomer) in polyvinyl pyrrolidone is nmt 10 ppm, and for hydrazine (a side product of polymerization reaction) nmt 1 ppm. Monomeric ethylene oxide is highly toxic and can be present in ethoxylated excipients such as PEGs, ethoxylated fatty acids, etc. 

Ethylene dichloride (EDC) is used to manufacture vinyl chloride monomer (VCM), which is one of the largest commodity chemicals produced in the world. EDC may be produced by the direct chlorination of ethylene or oxychlorination of ethylene in the presence of oxygen and hydrogen chloride. Pyrolysis of EDC produces VCM and an equal amount of hydrogen chloride as a co-product. This hydrogen chloride produced in the pyrolysis reactor is utilized by the oxychlorination process as one of the reactants. Therefore, the component processes of direct chlorination, EDC pyrolysis and oxychlorination are combined to develop a balanced process for the production of VCM with no net consumption or production of hydrogen chloride ... 

Vinyl chloride monomer, the basic building block of polyvinylchloride (PVC), is commercially manufactured by dehydrochlorination of 1,2-dichloroethane. The modern process for producing 1,2-dichloroethane involves oxychlorination of ethylene in a fluidized bed catalytic reactor ... 

Thermal cracking of ethane, propane, butane, naphthas, gas oils, and/or vacuum gas oils is the main process employed for the production of ethylene and propylene butadiene and benzene, toluene, and xylenes (BTX) are also produced. Thermal cracking of these hydrocarbons is also called pyrolysis of hydrocarbons. Ethylene is the organic chemical produced worldwide in the largest amoimts and has been called keystone to the petrochemical industry. This technology is well documented in the literature. Somewhat similar thermal cracking processes are used to produce vinyl chloride monomer (VCM) from ethylene dichloride (EDQ, styrene from ethylbenzene, and allyl chloride from propylene dichloride (PDC). Production of charcoal and coke from wood and coal is actually a pyrolysis process, but it is not discussed here. 

In its original version, this process operates on naphtha, which is cracked by injection into a hot medium, achieved by the combustion of the same naphtha with oxygen in the presence of steam. The latest technological developments, achieved jointly with Union Carbide and Chivoda. are designed to convert crude ofl in a reactor whose operation can be directed towards the preferential production of ethylene (see Section 21.3.4), or towards that of an acetylene/ethylene mixture in a molar ratio close to 1 (see Section 3.4.2). This possibility is exploited to produce vinyl chloride monomer in a process (Fig. 11.6) whose main stages are discussed below ... 

The flow sheet for a balanced chlorination-oxychlorination of ethylene to vinyl chloride monomer is shown in Figure 2. Currently this process, with its variations involving fixed and fluid beds and different methods of heating and separation, dominates the commercial production of vinyl chloride with 93% of VCM being made by this route. 

Selection of pertinent process units A process unit is defined as any major item of process equipment. The following units could be identified, for example, in a fumace/quench section in a vinyl chloride monomer/ethylene dichloride plant ethylene dichloride pre-heater, ethylene dichloride evaporator, furnace, quench column, ethylene dichloride absorber and tar pot. Important factors for selecting pertinent process units include ... 

Finally, two case studies were presented briefly to give a better feel for what research and development activities are all about. Vinyl chloride monomer production showed how the availability of cheap raw materials (e.g. ethylene) stimulated the development of processes to utilize these, and how continuing research and development led to new, even better processes. It also emphasized the importance of reading the chemical literature. Development and production of CFC replacements demonstrated what an enormous R D effort can achieve in such a short time. Great emphasis on research and development is a key characteristic of high technology industries like the chemical industry. 

By far the greatest part of PVC production across the world is now made by the suspension process. Vinyl chloride monomer (derived from a reaction between ethylene (derived from oil) and chlorine (derived from common salt) is dispersed in deionised water with the help of small quantities of chemical dispersants and polymerisation initiators (typically peroxide compounds). At moderately raised temperature (50 C) and pressure (0.7 MPa) polymerisation proceeds and the polymer can be removed from the resulting slurry by de-watering and steam stripping the unconverted vinyl chloride monomer. 

In 1964, Goodrich, Dow, and Monsanto commercialized oxychlorination processes to make vinyl chloride monomer. The earlier processes either added chlorine to acetylene or ethylene. In the latter, the cracking of the initial product. 

Most vinyl chloride monomer today is made via a three-step process using ethylene oxyhydro-chlorination. A small amount is made by the reaction of acetylene and hydrogen chloride, either as liquids or gases, with a copper chloride catalyst in the liquid process and a mercury catalyst in the gas process. Vinyl chloride is also made by the heating of ethylene chloride with alcoholic alkali. 

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