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Title: Identification of Reaction Pathways Active in the Production of Refrigerant Feedstocks by Oxychlorination
Author: Sutherland, lain William
ISNI:       0000 0001 3491 6824
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2006
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HFC-134a can be produced on an industrial scale from trichloroethene. The trichloroethene for this process is produced via the oxychlorination of 1,2-dichl~roethane over a supported copper catalyst. Unfortunately, this process currently exhibits relatively poor selectivity towards trichloroethene and results in the formation of toxic, oligomeric by-products. The current process also produces significant. quantities of CO2 through combustion ofits chlorocarbon feedstock. In order to understand the ongms of the selectivity of the oxychlorination of 1,2dichloroethane, this study has examined the chlorination and oxychlorination of higher chlorocarbons via thermodynamic calculations, eql;lilibrium measurements, and a continuous flow micro-reactor in order to understand the delicate balance. between the. surface and gas-phase chemistry within the system. It was found that the presence of the catalyst is not necessary to affect the desired chemistry. However, it was found that the presence of the catalyst favoured the formation of pentachloroethane and tetrachloroethene, as well as supplying chlorine via the Deacon process (conversion ofHCl and oxygen to chlorine). Tetrachloroethene was found to be the thermodynamic minimum of the system, with trichloroethene an intermediate in the formation oftetrachloroethene. At low temperatures « 473 K) and long reaction times (2 h, batch reactor), radical chlorination to form pentachloroethane was the dominant reaction. Increasing the reaction temperature to > 573 K and moving from a batch to continuous system resulted in the loss ofradical chlorination activity for the system, with radical dehydrochlorination to form trichloroethene becoming the dominant reaction. Heterogeneous chlorination was be performed under flow conditions, and was found to provide a route to pentachloroethane and tetrachloroethene from. High conversions were found favour the formation of oligomeric products, and results suggest that trichloroethene and tetrachloroethene may themselves be major sources ofoligomer formation. Oxychlorination reactions using the continuous flow micro-reactor have shown that, for this system, it is possible to explain the observed chemistry by a series of chlorination and dehydrochlorination processes alone, without the need to invoke additional surface processes. Results have shown that the selectivity of the reaction can be manipulated by parameter control, and that, on a laboratory scale at least; the system can be operated with minimal oligimer and CO2 formation. The knowledge gained from tIiis work provides a framework for the improvement ofthe industrial oxychlorination process.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available