Vinyl from pyrolysis

Ethylene Dichlonde and Vinyl Chloride. In the United States, all ethylene dichloride [107-60-2] (EDC) is produced from ethylene, either by chlorination or oxychlorination (oxyhydrochlorination). The oxychlorination process is particularly attractive to manufacturers having a supply of by-product HCl, such as from pyrolysis of EDC to vinyl chloride [75-01-4] monomer (VCM), because this by-product HCl can be fed back to the oxychlorination reactor. EDC consumption follows demand for VCM which consumed about 87% of EDC production in 1989. VCM is, in turn, used in the manufacture of PVC resins. Essentially all HCl generated during VCM production is recycled to produce precursor EDC (see Chlorocarbons and Cm OROHYDROCARBONS ViNYLPOLYAffiRS). 

Polymers are used frequently in paints and varnishes. These materials are usually filled with opaque materials and are difficult to separate or analyze by other procedures. Pyrolysis can be used to identify the nature of the paint, to measure quantitatively residual monomers, for quality control, and to examine additives [5, 13, 14]. Paints may contain a variety of polymers and copolymers such as vinyl derivatives, polyurethanes, phthalate polyesters, etc. Varnishes may contain various copolymers, siloxanes, etc. and can have a complex composition. This composition can be successfully analyzed using analytical pyrolysis. For example, the composition of a coating material consisting of the terpolymer poly(2-hydroxyethyl methacrylate-co-butyl acrylate-co-ethyl methacrylate) crosslinked with butoxy melamine resin has been analyzed with excellent results based on various monomer ratios resulting from pyrolysis at 590° C [15]. 

Trisection of the experimental data by determination of the label distribution in the enantiomers from pyrolysis of 4 S -4-( jc6>[ C]vinyl)cyclohexene, SV, at 380" C revealed that the formal 3,3-shift pathway accounted for 74% of the product, inversion without rearrangement accounted for 23% of the product with the rest ca. 3%) resulting from inversion with rearrangement (Scheme 9.82). ... 

Poly(ethylene terephthalate) decomposes upon heating through a series of different reactions. These run either concurrently or consecutively. The result is a complex mixture of volatile and nonvolatile products. It was found that when poly(ethylene terephthalate) is maintained in molten condition under an inert atmosphere at 282-323°C, it slowly converts to a mixture of gaseous low molecular weight fragments [581]. The major products from pyrolysis of poly(ethylene terephthalate) are carbon dioxide, acetaldehyde and terephthalic acid. In addition, there can be detected trace amounts of anhydrides, benzoic acid, p-acetylbenzoic acid, acetophenone, vinyl benzoate, water, methane, ethylene, acetylene, and some ketones [505]. The following mechanism of degradation was postulated [505] ... 

Table 4.11 Composition results calculated from pyrolysis peak intensities compared with H-NMR results of five compositions of vinylidene chloride (VDC)/vinyl chloride (VC) copolymer ...

Apart from one citation, all the papers collected here to illustrate the reactions of vinyl sulphoxides deal with addition reactions. " As would be expected from the nature of the sulphoxide functional group, there are several novel features in these addition reactions compared with those of other vinyl compounds. Pyrolysis of alkyl styryl sulphoxides gives benzothiophens. The proposed mechanism, which involves formation and homolysis of a sulphenic acid followed by cyclization, (54) (55), is supported by the formation of benzo-... 

Table 7.24 Composition Results Calculated from Pyrolysis Peak Intensities Compared with the H-NMR Results of Five Different Compositions of Vinylidene Chloride/Vinyl Chloride Copolymer ...

Most of the ethylene dichloride produced is utilized for the manufacture of vinyl chloride, which may be obtained from it by pyrolysis or the action of caustic soda. Large quantities are also used in anti-knock additives for gasoline. As a solvent It has been displaced by trichloroethylene and tetrachloroelhyJene. U.S. production 1978 4-75 megatonnes. 

Pyrolysis. Vinyl chloride is more stable than saturated chloroalkanes to thermal pyrolysis, which is why nearly all vinyl chloride made commercially comes from thermal dehydrochlorination of EDC. When vinyl chloride is heated to 450°C, only small amounts of acetylene form. Litde conversion of vinyl chloride occurs, even at 525—575°C, and the main products are chloroprene [126-99-8] and acetylene. The presence of HCl lowers the amount of chloroprene formed. 

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. 

By-products from EDC pyrolysis typically include acetjiene, ethylene, methyl chloride, ethyl chloride, 1,3-butadiene, vinylacetylene, benzene, chloroprene, vinyUdene chloride, 1,1-dichloroethane, chloroform, carbon tetrachloride, 1,1,1-trichloroethane [71-55-6] and other chlorinated hydrocarbons (78). Most of these impurities remain with the unconverted EDC, and are subsequendy removed in EDC purification as light and heavy ends. The lightest compounds, ethylene and acetylene, are taken off with the HCl and end up in the oxychlorination reactor feed. The acetylene can be selectively hydrogenated to ethylene. The compounds that have boiling points near that of vinyl chloride, ie, methyl chloride and 1,3-butadiene, will codistiU with the vinyl chloride product. Chlorine or carbon tetrachloride addition to the pyrolysis reactor feed has been used to suppress methyl chloride formation, whereas 1,3-butadiene, which interferes with PVC polymerization, can be removed by treatment with chlorine or HCl, or by selective hydrogenation. 

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. 

Figure 12.11 shows the pyrograms of vinyl paints from two monochromes by the Italian artist Piero Manzoni. The two paints are clearly different in composition acetic acid (peak 1) and benzene (peak 2) are present as common markers of the PVAc binder in both cases, but sample (a) contains dibutyl phthalate (peak 6) as external plasticizer. Peak 5 was recognized as bis(2-methylpropyl)-phthalate which is formed from dibutylphthalate isomerization, while butyl acetate (peak 3) and butyl benzoate (peak 4) are secondary products of recombination reactions occurring during the pyrolysis. Sample (b), however,... 

Methylene cyclopropene (5), the simplest triafulvene, is predicted to be of very low stability. From different MO calculations5 it has been estimated to possess only minor resonance stabilization ranging to 1 j3. Its high index of free valency4 at the exocyclic carbon atom causes an extreme tendency to polymerize, a process favored additionally by release of strain. Thus it is not surprising that only one attempt to prepare this elusive C4H4-hydrocarbon can be found in the literature. Photolysis and flash vacuum pyrolysis of cis-l-methylene-cyclopropene-2,3-dicarboxylic anhydride (58), however, did not yield methylene cyclopropene, but only vinyl acetylene as its (formal) product of isomerization in addition to small amounts of acetylene and methyl acetylene65 ... 

Levin, B.C., A summary of the NBS litterature Reviews on the chemical nature and toxicity of the pyrolysis and combustion from seven plastics acrylonitrite-butadien-styrenes (ABS), nylons, polyesters, polyetylenes, polysterenes, poly(vinyl-chlorides) and rigid polyurethane foams, KB SIR 85-3267, 1986... 

The next three procedures provide useful synthetic intermediates. A stereospecific synthesis of ETHYL (Z)-3-BROMO-2-PROPENOATE affords an alternative vinyl bromide partner for the coupling chemistry in the preceding procedure. A very simple but elegant illustration of the flash vacuum pyrolysis technique is used to prepare BENZOCYCLOBUTENONE from o-toluoyl chloride. Another member of the functionalized indole family of synthetic intermediates is presented in a four-step procedure for 5-METHOXYINDOLE-2-ACETIC ACID METHYL ESTER. 

---