Vinyl chloride production costs

Vinyl chloride has gained worldwide importance because of its industrial use as the precursor to PVC. It is also used in a wide variety of copolymers. The inherent flame-retardant properties, wide range of plastici2ed compounds, and low cost of polymers from vinyl chloride have made it a major industrial chemical. About 95% of current vinyl chloride production worldwide ends up in polymer or copolymer appHcations (83). Vinyl chloride also serves as a starting material for the synthesis of a variety of industrial compounds, as suggested by the number of reactions in which it can participate, although none of these appHcations will likely ever come anywhere near PVC in terms of volume. The primary nonpolymeric uses of vinyl chloride are in the manufacture of vinyHdene chloride and tri- and tetrachloroethylene [127-18-4] (83). 

If desired, the hydrochloric acid can be obtained via cracking of ethylene dichloride. The oxychlorination process freed vinyl chloride production from the economics of a more costly raw material, acetylene. Deliberate acetylene manufacture is energy intensive and relatively expensive. By-product acetylene from gas cracking is less expensive, but it has not been available in sufficient supply for the large, approximately billion-pound-per-year plus, vinyl chloride production units. 

DCE Manufacturing Cost = From cracking DCE in associated vinyl chloride production. 

Raw Materials. PVC is inherently a hard and brittle material and very sensitive to heat it thus must be modified with a variety of plasticizers, stabilizers, and other processing aids to form heat-stable flexible or semiflexible products or with lesser amounts of these processing aids for the manufacture of rigid products (see Vinyl polymers, vinyl chloride polymers). Plasticizer levels used to produce the desired softness and flexibihty in a finished product vary between 25 parts per hundred (pph) parts of PVC for flooring products to about 80—100 pph for apparel products (245). Numerous plasticizers (qv) are commercially available for PVC, although dioctyl phthalate (DOP) is by far the most widely used in industrial appHcations due to its excellent properties and low cost. For example, phosphates provide improved flame resistance, adipate esters enhance low temperature flexibihty, polymeric plasticizers such as glycol adipates and azelates improve the migration resistance, and phthalate esters provide compatibiUty and flexibihty (245). 

Membrane Sep r tion. The separation of components ofhquid milk products can be accompHshed with semipermeable membranes by either ultrafiltration (qv) or hyperfiltration, also called reverse osmosis (qv) (30). With ultrafiltration (UF) the membrane selectively prevents the passage of large molecules such as protein. In reverse osmosis (RO) different small, low molecular weight molecules are separated. Both procedures require that pressure be maintained and that the energy needed is a cost item. The materials from which the membranes are made are similar for both processes and include cellulose acetate, poly(vinyl chloride), poly(vinyHdene diduoride), nylon, and polyamide (see AFembrane technology). Membranes are commonly used for the concentration of whey and milk for cheesemaking (31). For example, membranes with 100 and 200 p.m are used to obtain a 4 1 reduction of skimmed milk. 

Internal Plasticizers. There has been much dedicated work on the possibiUty of internally plasticized PVC. However, in achieving this by copolymerization significant problems exist (/) the affinity of the growing polymer chain for vinyl chloride rather than a comonomer implies that the incorporation of a comonomer into the chain requites significant pressure (2) since the use of recovered monomer in PVC production is standard practice, contamination of vinyl chloride with comonomer in this respect creates additional problems and (J) the increasing complexity of the reaction can lead to longer reaction times and hence increased costs. Thus, since standard external plasticizers are relatively cheap they are normally preferred. 

Chlorinated by-products of ethylene oxychlorination typically include 1,1,2-trichloroethane chloral [75-87-6] (trichloroacetaldehyde) trichloroethylene [7901-6]-, 1,1-dichloroethane cis- and /n j -l,2-dichloroethylenes [156-59-2 and 156-60-5]-, 1,1-dichloroethylene [75-35-4] (vinyhdene chloride) 2-chloroethanol [107-07-3]-, ethyl chloride vinyl chloride mono-, di-, tri-, and tetrachloromethanes (methyl chloride [74-87-3], methylene chloride [75-09-2], chloroform, and carbon tetrachloride [56-23-5])-, and higher boiling compounds. The production of these compounds should be minimized to lower raw material costs, lessen the task of EDC purification, prevent fouling in the pyrolysis reactor, and minimize by-product handling and disposal. Of particular concern is chloral, because it polymerizes in the presence of strong acids. Chloral must be removed to prevent the formation of soflds which can foul and clog operating lines and controls (78). 

Alternatives to oxychlorination have also been proposed as part of a balanced VCM plant. In the past, many vinyl chloride manufacturers used a balanced ethylene—acetylene process for a brief period prior to the commercialization of oxychlorination technology. Addition of HCl to acetylene was used instead of ethylene oxychlorination to consume the HCl made in EDC pyrolysis. Since the 1950s, the relative costs of ethylene and acetylene have made this route economically unattractive. Another alternative is HCl oxidation to chlorine, which can subsequently be used in dkect chlorination (131). The SheU-Deacon (132), Kel-Chlor (133), and MT-Chlor (134) processes, as well as a process recently developed at the University of Southern California (135) are among the available commercial HCl oxidation technologies. Each has had very limited industrial appHcation, perhaps because the equiHbrium reaction is incomplete and the mixture of HCl, O2, CI2, and water presents very challenging separation, purification, and handling requkements. HCl oxidation does not compare favorably with oxychlorination because it also requkes twice the dkect chlorination capacity for a balanced vinyl chloride plant. Consequently, it is doubtful that it will ever displace oxychlorination in the production of vinyl chloride by the balanced ethylene process. 

If the production of vinyl chloride could be reduced to a single step, such as dkect chlorine substitution for hydrogen in ethylene or oxychlorination/cracking of ethylene to vinyl chloride, a major improvement over the traditional balanced process would be realized. The Hterature is filled with a variety of catalysts and processes for single-step manufacture of vinyl chloride (136—138). None has been commercialized because of the high temperatures, corrosive environments, and insufficient reaction selectivities so far encountered. Substitution of lower cost ethane or methane for ethylene in the manufacture of vinyl chloride has also been investigated. The Lummus-Transcat process (139), for instance, proposes a molten oxychlorination catalyst at 450—500°C to react ethane with chlorine to make vinyl chloride dkecfly. However, ethane conversion and selectivity to vinyl chloride are too low (30% and less than 40%, respectively) to make this process competitive. Numerous other catalysts and processes have been patented as weU, but none has been commercialized owing to problems with temperature, corrosion, and/or product selectivity (140—144). Because of the potential payback, however, this is a very active area of research. 

Tile is based mainly on vinyl chloride and vinyl acetate copolymers. Some polypropylene tile systems have recendy been iatroduced. A petroleum resia is usually employed as an extender and processiag aid conventional vinyl plasticizers and stabilizers also are iacorporated. Reinforcing fibers and limestone constitute the remainder of the tile composition the fibers contribute hot strength for processiag and dimensional stabiHty ia the finished tile, limestone suppHes bulk at an economical cost. Stable pigments are also iacorporated. Siace tile is iastalled oa and below grade level, it is important that the finished product be resistant to the effects of moisture and alkaH. 

Plastics and Synthetic Products. To prevent degradation of plastics at elevated processing temperatures, it is necessary to use suitable heat stabilizers. Eor example, flexible poly(vinyl chloride) (PVC) manifests uncontroUed color development in the absence of stabilizers. Accordingly, cadmium salts of organic acids are typically used in a synergistic combination with corresponding barium salts, in about a 1 3 cadmium barium ratio, to provide a cost-competitive heat stabilizer for flexible PVC. 

Another major chlorinated hydrocarbon is vinyl chloride. For many years acetylene was the sole raw material for the production of vinyl chloride by a catalytic fixed bed vapor-phase process. This process is characterized by high yields and modest capital investment. Nevertheless, the high relative cost of acetylene provided an incentive to replace it in whole or in part by ethylene. The first step in this direction was the concurrent use of both raw materials. Ethylene was chlorinated to di-chloroethane, and the hydrogen chloride derived from the subsequent dehydrochlorination reacted with acetylene to form additional vinyl chloride. 

Although acetylene still is used in a number of organic syntheses on an industrial scale, its use on a high-tonnage basis has diminished because of the lower cost of other starting materials, such as ethylene and propylene. Acetylene has been widely used in the production of halogen derivatives, acrylonitrile, acetaldehyde, and vinyl chloride. Within recent years, producers of acrylonitrile switched to propylene as a starting material. 

A major trend in industrial chemistry has been an emphasis on improved processes for the production of major chemicals such as ethylene, propylene, vinyl chloride, styrene, alkylene oxides, methanol, terephthalates, and so on. The necessity for higher efficiency, lower cost processes has been accentuated by the relatively slow growth rates of major industrial chemicals over the past two decades or so. The fertilizer portion of the agricultural chemicals market as described in Table 2.6 is an example of the slow growth. 

Conventional poly(vinyl chloride) (PVC) batch preparation in which the dry materials are blended in a heated mixer and then cooled in a cooler mixer, was compared with the double batching preparation process. In this process, twice the required additives are added to the PVC, blended in the hot mixer, and the balance of the PVC then added to the mixed materials in the cooler mixer. This reduces the overall energy requirements. Rigid PVC for pipe manufacture was processed by both methods, and assessed by studying the rheological and physical properties and extrudability. Material of acceptable quality and pipe to the required standards were produced by the double batching process, with enhanced productivity and cost savings on power and labour. 4 refs. INDIA... 

ABB Lummus Global/Sohray SA Polyvinyl chloride (suspension) Vinyl chloride monomer On-site initiator synthesis and high reactor productivity minimize operating costs wide range of high quality products NA NA... 

Oxy Vinyls LP Polyvinyl chloride (suspension) Vinyl chloride monomer Efficient, low-cost, high productive technology includes environment, health and safety controls, High level DCS, low RVCM condensers 16 1998... 

The moisture resistance, low cost, and low-density closed-cell structure of many cellular polymers resulted in their acceptance for buoyancy in boats, floating docks, and buoys. Because each cell is a separate flotation unit, these materials cannot be destroyed by a single puncture. Foamed-in-place polyurethane between thin skins of high tensile strength is used in pleasure craft [98]. Other cellular polymers that have been used where buoyancy is needed are produced from polystyrene, polyethylene, poly(vinyl chloride), and certain types of rubber. Foams made from styrene-acrylonitrile copolymers are resistant to petroleum products [99,100]. 

To illustrate this point consider the production of lacquers for PVC films and sheeting. Such lacquers contain a PVC homopolymer or low-acetate vinyl chloride-vinyl acetate copolymer, poly(methyl methacrylate), a plasticizer and perhaps some stabilizers, dulling agents (such as silica), pigments, and so on. Methyl ethyl ketone (MEK) is the solvent of choice because it gives the best balance of low toxicity, volatility, and low cost. Any other solvent is effectively... 

The high pressure polymerization of ethylene can be slightly modified for the copolymerization of ethylene with vinyl- and acrylic-type monomers such as vinyl acetate, vinyl chloride, acrylonitrile, or acrylic esters. Some of these copolymers of ethylene and vinyl acetate or maleic anhydride are already available and have found various applications in plastics, coatings, and adhesives. Copolymers of ethylene and vinyl chloride and of ethylene and acrylonitrile appear particularly interesting because of the low cost of monomers and the properties of the copolymers. Although their synthesis has been disclosed in a number of patents their larger scale production is still in a state of development. 

Some producers achieve a balanced operation by a combination of processes in which the by-product HCl reacts with acetylene to yield additional vinyl chloride. This is not generally the most attractive alternative because of the relatively high cost of acetylene compared with ethylene. Acetylene and ethylene can be produced in balanced yield ratios (i, 2), but these processes involve separation problems. Consequently, a very considerable amount of research effort has gone into other techniques to use HCl directly for chlorination purposes. 

Thermoplastics may be further subdivided into two broad categories on the basis of their cost and suitable end uses. Commodity plastics are typified by high volume production, good properties, and low resin cost. The four major commodity plastics are polyethylene, polypropylene, poly(vinyl chloride), and polystyrene. Their adequate properties and low cost have led to the extensive use of these plastics in packaging applications where they are very competitive with paper, steel, and glass. They are also used for some less demanding applications as components of durable goods (Table 22.1). 

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