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CONTINUOUS MICROWAVE REACTORS FOR ORGANIC SYNTHESIS: HYDRODECHLORINATION AND HYDROLYSIS
Citation:
Siridra, *. S., E SahleDemessie*, AND R S. Varma*. CONTINUOUS MICROWAVE REACTORS FOR ORGANIC SYNTHESIS: HYDRODECHLORINATION AND HYDROLYSIS. Presented at AIChE, Austin, TX, November 07 - 12, 2004.
Impact/Purpose:
To inform the public
Description:
Microwave heating has been sought as a convenient way of enhancing chemical processes. The advantages of microwave heating, such as selective direct heating of materials of a catalytic site, minimized fouling on hot surfaces, process simplicity, rapid startup, as well as the possibility of solventless (or "dry") reactions and enhanced chemistry, demonstrate that many processes could be applied in the chemical and pharmaceutical industry. The feasibility of conducting continuous-flow reactors was determined to better understand scale-up possibilities. Problems connected with temperature control, energy consumption and optimizing the conditions for microwave assisted synthesis were studied.
Hydrodechlorination of chloroflorocarbons and chlorobenzenes is observed over 0.5 % Pd/Al2O3 catalyst by conducting the reaction under microwave irradiation conditions. The reaction is expedited under microwave conditions for polar feed materials. Vapour phase catalytic hydrodechlorination/ hydrolysis were also conducted using a continuous microwave reactor to produce C2 fluoro carbon compounds containing -CF3 and one active functional group such as CF3-COCl, CF3-COOH, CF3CH2Cl. When hydrodechlorination/hydrolysis involves more than one halogen atom (C2ClxFy where x+y=6) the product selectivity is more crucial in selective removal of chlorine atom causing consecutive/parallel reactions to catalyze dehydrofluorination assisted by thermal catalytic conditions and yields undesirable fluoro olefins.
Even though the loss of active metal surface area is significant and identical in both microwave and conventional heating reactions, the higher rate and sustainability of microwave reaction may be due to the selective and rapid absorption of microwaves by the polar chlorinated substrates that facilitates their relatively easy removal from the catalyst surface. The rate of desorption of the products (especially the poisonous HCl) is more critical in sustaining the catalyst activity. The experiments also reveal a significant reduction in power consumption under the microwave reaction than the reaction conducted using conventional heating. Better understanding of s to use the underlying principles behind MW assisted chemical synthesis with a view towards developing a larger system that can impact in preventing pollution and waste generation.