Vinyl chloride manufacturing methods

Significant quantities of ethyl chloride are also produced as a by-product of the catalytic hydrochlorination over a copper chloride catalyst, of ethylene and hydrogen chloride to produce 1,2-dichloroethane, which is used as feedstock in the manufacture of vinyl choride (see Vinyl polymers). This ethyl chloride can be recovered for sale or it can be concentrated and catalyticaHy cracked back to ethylene and hydrogen chloride (25). As the market for ethyl chloride declines, recovery as an intermediate by-product of vinyl chloride manufacture may become a predominant method of manufacture of ethyl chloride. 

There are three general methods of interest for the preparation of vinyl chloride, one for laboratory synthesis and the other two for commercial production. Vinyl chloride (a gas boiling at -14°C) is most conveniently prepared in the laboratory by the addition of ethylene dichloride (1,2-dichloroethane) in drops on to a warm 10% solution of sodium hydroxide or potassium hydroxide in a 1 1 ethyl alcohol-water mixture Figure 12.1). At one time this method was of commercial interest. It does, however, suffer from the disadvantage that half the chlorine of the ethylene dichloride is consumed in the manufacture of common salt. 

The initiator can be a radical, an acid, or a base. Historically, as we saw in Section 7.10, radical polymerization was the most common method because it can be carried out with practically any vinyl monomer. Acid-catalyzed (cationic) polymerization, by contrast, is effective only with vinyl monomers that contain an electron-donating group (EDG) capable of stabilizing the chain-carrying carbocation intermediate. Thus, isobutylene (2-methyl-propene) polymerizes rapidly under cationic conditions, but ethylene, vinyl chloride, and acrylonitrile do not. Isobutylene polymerization is carried out commercially at -80 °C, using BF3 and a small amount of water to generate BF3OH- H+ catalyst. The product is used in the manufacture of truck and bicycle inner tubes. 

Vinyl chloride has been known for over a hundred years and its polymerization to polyvinyl chloride (PVC) was achieved in 1912. Industrial-scale production of this plastic began in 1927. PVC is still the most versatile plastic. One of the reasons for this is the numerous variations made possible by the method of manufacture of the polymer, namely by copolymerization with other monomers and their processing. Thus, PVC can be thermoformed on all conventional processing machines if the slight thermal damage is taken into consideration. Machining is easy and the material can be bonded, bent, welded, printed and thermoformed. 

Vinyl chloride monomer (VCM) is the main substrate for the manufacture of polymers used as packaging materials for food. Since VCM is considered by lARC to be a human carcinogen, monomer levels in PVC food packaging materials are strictly controlled. To ensure a safe product, the residual content of VCM in the finished material or article is limited to one mg per kg in the final product (Council Directive 78/142/EEC). Furthermore, VCM should not be detectable in foodstuflfs. Commission Directives 80/766/EEC and 81/432/ EEC give the method of analysis for official control of the VCM level in food packaging materials and in foods - gas-phase chromatography using the headspace method, after dissolution or suspension of samples in N,N-dimethylacetamide. Both residual monomer content of the polymer and... 

In contrast to this direct chlorination there is the oxychlorination of ethylene using hydrogen chloride and oxygen, the other major method now used. Since the chlorine supply is sometimes short and it is difficult to balance the caustic soda and chlorine demand (both are made by the electrolysis of brine), hydrogen chloride provides a cheap alternate source for the chlorine atom. Most of the ethylene dichloride manufactured is converted into vinyl chloride by eliminating a mole of HCl, which can then be recycled and used to make more EDC by oxychlorination. EDC and vinyl chloride plants usually are physically linked. Most plants are 50 50 direct chlorinationroxychlorination to balance the output of HCl. 

The first successful static firing of plastisol propellant took place late in 1950 as part of a broad program conducted by Atlantic Research Corp. to investigate and evaluate plastisol propellants and methods for their manufacture (16). Major attention was directed to poly (vinyl chloride), cellulose acetate, and nitrocellulose, although other polymers were tested for their suitability (17). Patent applications were filed for plastisol propellant compositions and manufacturing processes, based on poly(vinyl chloride) (PVC) (19) and on nitrocellulose (18). The commercial availability of dispersion grade PVC enabled work with this resin to advance rapidly. The balance of this paper is devoted to a discussion of PVC plastisol propellants and their manufacture. 

A recent achievement worthy of note is the manufacture of microspheres containing an inert gas, e.g. nitrogen, or a volatile liquid, such as the freons The patent literature contains methods for producing microspheres based on poly(vinyl chloride) and poly(divinyl chloride), containing isobutane or carbon tetrachloride 52>, and based on poly(methyl methacrylate), containing neopentane . Microspheres containing liquid dyes and oils are also used to make syntactic foams 58>. 

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... 

Dichloroethane is produced commercially through the reaction of hydrogen chloride and vinyl chloride at 20°-55°C in the presence of an aluminum, ferric, or zinc chloride catalyst (Grayson 1978). Other production methods include the direct chlorination of ethane, the reaction of PCI s with acetaldehyde as a by-product during the manufacture of chloral (Browning 1965), and as intermediate in the production of vinyl chloride and 1,1,1-trichloroethane by photochlorination (Windholz 1983). 

Vinyl chloride monomer (VCM) manufacture Maximization of VCM production and minimization of environmental burden, environmental impact and operating cost simultaneously. e-constraint method A design methodology consisting of 4 steps was proposed and applied to VCM plant The steps are (1) life cycle analysis of the process, (2) formulation of the design problem, (3) MOO, and (4) multi-criteria decision-making to find best compromise solutions. Khan et al. (2001)... 

Table 11.4 lists economic data on the main methods for produdng ethylene dichloride and vinyl chloride. Table 11.5 gives data on the three main types of process for manufacturing chlorine by the electrolysis of sodium chloride. 

The important manufacturing methods of vinyl chloride monomer currently in practice are the oxychlorination method and the mixed-gas method. 

The pyrolysis of CH2CI-CH2CI is of great industrial importance, as it is a method of manufacturing vinyl chloride monomer CH2=CHC1. The experimental kinetic characteristics of this reaction (sensitivity to the nature of the walls, existence of an induction period...) permit this reaction to be classed as a straight chain radical reaction. 

Especially in the case of macromolecular materials, not only the method of synthesis, but also the manufacturing process has a large influence on size and structure of the molecules, and consequently on the physical properties. For example, poly(vinyl chloride), produced by radical polymerization in suspension, differs in some practical properties from PVC obtained by radical polymerization in bulk. Changes in the... 

Polymers contain various elements, metallic and nonmetallic. Some elements are a constituent part of the monomers, such as nitrogen in acrylonitrile or chlorine in poly(vinyl chloride), while other elements occur as impurities or are part of some additives (e.g., zinc stearate). Their concentrations range from a (tg per kg level to several percent. Analysis of the element content is especially important for manufacturing process control. Elements can be determined after chemical or physical destruction of polymer, or directly by nondestructive methods. 

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