Vinyl chloride from ethane

Figure 6-1. The Transcat process for producing vinyl chloride from ethane. ...

A small portion of vinyl chloride is produced from ethane via the Transcat process. In this process a combination of chlorination, oxychlo-rination, and dehydrochlorination reactions occur in a molten salt reactor. The reaction occurs over a copper oxychloride catalyst at a wide temperature range of 310-640°C. During the reaction, the copper oxychloride is converted to copper(I) and copper(II) chlorides, which are air oxidized to regenerate the catalyst. Figure 6-1 is a flow diagram of the Transcat process for producing vinyl chloride from ethane. ... 

Transcat An oxychlorination process for making vinyl chloride from ethane and chlorine ... 

The results obtained substantiate that the utilization of copper—cement catalysts offers promise for the synthesis of vinyl chloride from ethane at law temperatures in a single step. The proposed efficient and stable copper-cement catalyst will assist in the development of a new technology for the production of vinyl chloride Ifom ethane. This technology is low-waste and balanced in raw materials with meeting modem requirements of ecological safety. 

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. 

Most industrial interest, however, has been attached to the use of melts containing CuCil2 for the production of vinyl chloride and related compounds from ethane and ethylene. British Petroleim (9)(10) claims the formation of vinyl chloride from ethylene directly in KCil/CuCil2/CuCil melts. 

The formation of 1,2-dichloroethane from ethane and ethylene is described in patents issued to National Distillers (11) and I.C.I. (12), respectively. Englin et at. (13) report the formation of vinyl chloride from chloroalkanes using catalysts containing melts of cuprous and cupric chloride. The details of the mechanism and kinetics of many of these reactions are still unresolved. It appears, though, that copper chloride can function effectively as a catalyst for chlorination and dehydrochlorination as well as being able to participate in os chlorination reactions. 

Ethane has been investigated as a feedstock for production of vinyl chloride, at scales up to a large pilot plant, but nearly all vinyl chloride is stiH produced from ethylene. 

The small molecules used as the basic building blocks for these large molecules are known as monomers. For example the commercially important material poly(vinyl chloride) is made from the monomer vinyl chloride. The repeat unit in the polymer usually corresponds to the monomer from which the polymer was made. There are exceptions to this, though. Poly(vinyl alcohol) is formally considered to be made up of vinyl alcohol (CH2CHOH) repeat units but there is, in fact, no such monomer as vinyl alcohol. The appropriate molecular unit exists in the alternative tautomeric form, ethanal CH3CHO. To make this polymer, it is necessary first to prepare poly(vinyl ethanoate) from the monomer vinyl ethanoate, and then to hydrolyse the product to yield the polymeric alcohol. 

Particularly the chlorinated compounds have enjoyed range of applications vinyl chloride (chloro-ethene) as monomer for the production of PVC, tetra- and trichloroethenes as solvents for degreasing, and the insecticides l,l,l-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and isomers of hexachlorocyclohexane (HCH) (benzene hexachloride). The biodegradation of fluorinated aliphatic compounds is generally different from the outlines that have emerged from investigations on their chlorinated, brominated, and even iodinated analogues. They are therefore treated separately in Part 4 of this chapter. 

One of the most important challenges in the modern chemical industry is represented by the development of new processes aimed at the exploitation of alternative raw materials, in replacement of technologies that make use of building blocks derived from oil (olefins and aromatics). This has led to a scientific activity devoted to the valorization of natural gas components, through catalytic, environmentally benign processes of transformation (1). Examples include the direct exoenthalpic transformation of methane to methanol, DME or formaldehyde, the oxidation of ethane to acetic acid or its oxychlorination to vinyl chloride, the oxidation of propane to acrylic acid or its ammoxidation to acrylonitrile, the oxidation of isobutane to... 

Not observed were chloroethane (CH3-CH2C1) and vinyl chloride (CH2=CHC1). An interesting finding was that 1,1-DCA reacted much too slowly to represent an intermediate in the formation of ethane. The authors postulated a scheme involving successive one- or two-electron reduction steps to form radicals and carbenes to explain the absence of other observable intermediates, as well as the formation of products originating from radical or possibly from carbene coupling. Try to constmct such a hypothesized reaction scheme yourself. 

Ethene and ethane account for 80% of the mass of the hydrocarbons identified as products. Trace amounts of methane and acetylene are also produced (Orth and Gillham, 1996). The reduction of PCE forms cis-1,2-dichloroethylene (DCE), frans-l,2-DCE, 1,1-DCE, vinyl chloride, ethylene, dichloroacetylene, acetylene, ethene, ethane, chloroacetylene, methane, and several alkenes ranging from C3 to C6. The trace amounts of dichloro-ethylene and vinyl chloride formed during the reduction of PCE and TCE are further reduced (Burris et al., 1995). Reaction rates vary with substrate, chemical, and microbiological conditions. Selected f1/2 values are provided in Table 13.3. 

Chemical intermediates are listed first in Table 1.1. These are the chemicals that are used to synthesize other chemicals, and are generally not sold to the public. For example, ethlyene is an intermediate produced from hydrocarbons by cracking natural gas derived ethane or petroleum derived gas oil, either thermally using steam or catalytically. Ethlyene is then used to produce polyethylene (45%), a polymer and ethlyene oxide (10%), vinyl chloride (15%), styrene (10%), and... 

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. 

The most common method for industrial preparation of 1,1,1-trichloroethane is the reaction of hydrochloric acid with vinyl chloride (obtained from 1,2-dichloroethane) to obtain 1,1-dichloroethane, followed by either thermal or photochemical chlorination. Other methods include the catalyzed addition of hydrogen chloride to 1.1-dichloroethylene, and the direct chlorination of ethane itself, followed by separation from the other products produced (Archer 1979). Commercial grades of... 

Formation of the mixed cement-containing systems within the range of low copper concentrations with addition of alkali metal dopants as well as catalytical properties of these systems in the ethane oxidative chlorination process have been investigated. Based on the obtained data the efficient and stable copper-cement catalyst has been worked out. This catalyst will assist in the development of a new technology of the vinyl chloride production from ethane. The basic peirameters of the ethane oxychlorination process have been determined at 623-673K, time-on-stream 3-5s and reactant ratio of C2H6 HCI 02 = 1 2 1 the conversion of ethane is more than 90% and the total selectivity to ethylene and vinyl chloride is 85-90%. 

It was found during the investigations that when the temperature was raised from 623 to 773 K, the conversion of ethane somewhat increased, and sample I exhibited better activity in comparison with that of sample 2. At the moderate temperatures (623—673K), an extended specific surface of sample 1 was favorable for increasing the yield of target unsaturated compounds ethylene and vinyl chloride. The further temperature increase led to a decrease in the process selectivity because of a noticeable increase in the yield of deep oxidation products, COx- The effect is more pronounced for sample 1 (see Fig. 3). 

As in steam cracking, a large number of by-products is produced. Some of them result from the consecutive reactions of the chlorination of vinyl chloride and of its derivatives obtained by dehydrochlorination (tri-, tetra-, pentachloroethane, perchloro-ethane, di-, trichloroethylene. perchloroethyleneX and the others from the hydrochlorination of vinyl chloride il.l-dichloroethane), while others result from decomposition reactions (acetylene, cokei or conversion of impurities initially present (hydrocarbons such as ethylene, butadiene and benzene, chlorinated derivatives such as chloroprene, methyl and ethyl Chlorides, chloroform, carbon tetrachloride, eta, and hydrogen) ... 

High purity vinyl chloride is produced in an overall yield of 80 mol% based on ethane. The feed can contain ethane, ethylene, mixed ethylene-chlorination products, and HCl in various mixtures, and can thereby allow recovery of values from such materials. The flow sheet for the simultaneous chlorination, oxidation, and dehydrochlorination for producing vinyl chloride by the Transcat process is shown in Figure 3. 

This process flourished, particularly in the United States, where an abundant supply of low cost ethylene from ethane and liquified petroleum gas (LPG) rapidly developed throughout the 1960s and 1970s. Today more than 96 0 of vinyl chloride in the United States is based on the balanced process. In Europe, ethylene based on cracking more expensive naphtha and gas oil favored the acetylene technology for vinyl chloride for a time, but, today, most European plants are also based on the balanced process. Of course, today, acetylene is almost nonexistent as a petrochemical feedstock and vinyl chloride plants worldwide are the balanced ethylene-based process. 

In an attempt to simulate the anaerobic conditions for biodegradation in landfills, experiments were performed under anoxic conditions using inocula from anaerobic digester units of wastewater treatment facilities that were not acclimated to industrial solvents. After 1 week of incubation with 10 jg/L of 1,1,2-trichloroethane, 0.44 pg/g of vinyl chloride was formed, the highest level observed from any of the chlorinated ethanes or ethenes studied (Hallen et al. 1986). In further experiments when the concentration of inoculum was increased, 4.3 and 5.8 pg/g of vinyl chloride was formed after 1 and 2 weeks, respectively. The degradation reactions observed not only include reductive dehalogenation but the transformation of chlorinated ethanes into ethenes. It is interesting to note... 

Ethylene from cracking of the alkane gas mixtures or the naphtha fraction can be directly polymerized or converted into useful monomers. (Alternatively, the ethane fraction in natural gas can also be converted to ethylene for that purpose). These include ethylene oxide (which in turn can be used to make ethylene glycol), vinyl acetate, and vinyl chloride. The same is true of the propylene fi action, which can be converted into vinyl chloride and to ethyl benzene (used to make styrene). The catalytic reformate has a high aromatic fi action, usually referred to as BTX because it is rich in benzene, toluene, and xylene, that provides key raw materials for the synthesis of aromatic polymers. These include p-xylene for polyesters, o-xylene for phthalic anhydride, and benzene for the manufacture of styrene and polystyrene. When coal is used as the feedstock, it can be converted into water gas (carbon monoxide and hydrogen), which can in turn be used as a raw material in monomer synthesis. Alternatively, acetylene derived from the coal via the carbide route can also be used to synthesize the monomers. Commonly used feedstock and a simplified diagram of the possible conversion routes to the common plastics are shown in Figure 2.1. 

---