Roles of Non-thermal Plasma in Gas-phase Glycerol Dehydration Catalyzed by Supported Silicotungstic Acid
Date of Award
Doctor of Philosophy
Douglas G. Hayes, Joseph J. Bozell, Igor Alexeff
Acrolein is an indispensable chemical intermediate with a rising demand in recent years. The concern of the increase of propylene prices due to the shrinking supply of nonrenewable crude oil makes the acid-catalyzed gas-phase glycerol dehydration to acrolein a prime candidate for research. Our analysis showed that the sustainable acrolein production from glycerol was both technically and economically viable. Alumina2700® (Al) and Silica1252® (Si) loaded with silicotungstic acid (HSiW) possessed distinct features while provided equally good acrolein yield (73.86mol% and 74.05mol%, respectively) optimally.
Due to the unique non-equilibrium characteristics, non-thermal plasma (NTP) could promote a variety of chemical reactions; however, its application in a dehydration process remained blank. This study used the reaction of glycerol dehydration to acrolein to probe whether NTP could 1) improve acrolein yield during dehydration, 2) suppress the coke formation and regenerate the catalyst, and 3) modify the properties of the catalyst.
The dielectric barrier discharge configuration was used to generate NTP; various NTP field strengths and also their interaction with temperature and the catalyst were investigated. The results showed that NTP improved the glycerol conversion and that NTP with a proper field strength increased acrolein selectivity. The optimal acrolein yields of 83.6 mol% and 83.1 mol% were achieved with 3.78 kV/cm NTP and 4.58 kV/cm NTP at 275°C for HSiW-Al and HSiW-Si, respectively.
The application of NTP-O2 (5% oxygen in argon, 4.58 kV/cm) during glycerol dehydration significantly suppressed coke formation on HSiW-Si. NTP-O2 could regenerate the deactivated HSiW-Si at low temperatures by removing both soft and hard coke at various rates. NTP-O2 with higher field strength, at medium operation temperature (150ºC) and in argon atmosphere was more effective for coke removal/catalyst regeneration.
Applying NTP to the catalyst fabrication showed some capabilities in modifying catalyst properties, including enlarging surface area, preserving mesopores, increasing acid strength and Brønsted acidity. NTP with argon as the discharge gas performed better in these modifications than NTP with air as the discharge gas.
Liu, Lu, "Roles of Non-thermal Plasma in Gas-phase Glycerol Dehydration Catalyzed by Supported Silicotungstic Acid. " PhD diss., University of Tennessee, 2011.