Ethylene (CAS 74-85-1) forms the cornerstone starting material for the industrial synthesis of vinyl chloride monomer (VCM), a process critical for the large-scale manufacture of polyvinyl chloride (PVC). The route typically leverages ethylene in conjunction with chlorine (CAS 7782-50-5) and oxygen (CAS 7782-44-7) as core feedstocks. Iron(III) chloride and cupric chloride species function as catalysts in the oxychlorination stage, promoting high selectivity over a range of reaction regimes, as documented in standard industrial practice and patents such as US3025268; relevant data are corroborated by peer-reviewed studies, including DOI:10.1021/ie50488a006.
The established synthesis proceeds via a two-step route, commencing with direct chlorination of ethylene to produce 1,2-dichloroethane (EDC, CAS 107-06-2). This step employs ethylene and chlorine in a solvent-free, vapor-phase reaction within tubular reactors, managed at temperatures typically between 45 °C and 70 °C. Patents and primary literature, for example, US3025268 and the review by Sittig (Industrial Organic Chemicals, Third Edition), detail this conversion. Published yield percentages for this step are not universally standardized; yield data not available in public literature.
Following EDC synthesis, thermal cracking of the intermediate generates the target vinyl chloride monomer (CAS 75-01-4) along with hydrogen chloride as a by-product. The dehydrochlorination reaction unfolds at elevated temperatures, routinely around 500 °C, within a cracking furnace. This step is conducted without solvent, relying on precise thermal management and high-purity feed streams to suppress side reactions and minimize coke formation, as specified in industrial process descriptions and the aforementioned references. The hydrogen chloride released is typically recycled into the oxychlorination subsystem, maximizing overall atom economy.
Oxychlorination constitutes a parallel route using ethylene, hydrogen chloride, and oxygen, mediated by copper(II) chloride supported on alumina or silica. Reaction temperatures for this process generally span 200 °C to 250 °C. The literature indicates flexibility with respect to pressure management; slight positive pressures support throughput but are not universally mandatory. In all cases, severe moisture sensitivity is not characteristic of these steps, though stringent feed purification protocols are implemented to prevent catalyst deactivation.
Throughout the process, purification of EDC and vinyl chloride is primarily achieved through carefully controlled distillation sequences, aligning with ICH Q3C guidelines for residual solvents and ensuring separation of both chlorinated by-products and solvent residues, when present. Chromatographic techniques are not required due to the scale and boiling-point separation of components. Specifications for VCM and PVC feedstocks are maintained to USP/EP benchmarks, typically referencing color, purity (GC >99.5%), and absence of stabilizer additives.
Safety management forms an integral part of process design given the hazardous profiles of the intermediates. Ethylene is classified under GHS as a flammable gas (Flam. Gas 1, H220), while vinyl chloride monomer holds GHS designations for flammability (Flam. Gas 1, H220), carcinogenicity (Carc. 1A, H350), and acute toxicity (Acute Tox. 3, H331). EDC is identified as a flammable liquid (Flam. Liq. 3, H226) and as acutely toxic by inhalation (Acute Tox. 3, H331). Thermal hazard review is pivotal, especially during the cracking stage, where rapid exotherms and pressure excursions mandate robust controls and remote monitoring. Personnel should utilize flame-retardant lab coats, chemical splash goggles, and respiratory protection approved for organic chlorides and dusts, as outlined in industry standards and chemical safety data sheets.
In summary, the synthesis of vinyl chloride monomer via ethylene chlorination and oxychlorination is robust and well-optimized, provided that critical process parameters and rigorous safety measures are maintained. For detailed synthetic procedures, the reader is directed to patent US3025268 and journal literature such as DOI:10.1021/ie50488a006, which collectively provide both historical context and kinetic data essential for successful scale-up. If additional routes or novel catalyst systems are ever reported in future publications, specific procedural and safety updates should be adopted in accordance with the latest regulatory and process analytical technologies.
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