Effect of the Isopropanol Impurity in the Feed on Catalytic Dehydration of Bioethanol to Ethylene

Isopropanol is one of the main organic impurities present in bioethanol. Effect of the isopropanol impurity in the feed on catalytic dehydration of 92% ethanol to ethylene over an aluminum oxide catalyst was studied in a gradientless reactor under the conditions of kinetic control at 350–400°С. The maximum permissible concentration of isopropanol in ethanol was found to be 0.7 g L –1 , which is equivalent to 0.05 mol % in the gaseous feed. Such isopropanol concentration in the feed does not decrease the catalyst activity and selectivity to ethylene but suppresses formation of acetaldehyde, hydrogen, and butylene, improving the quality of the ethylene product. A bioethanol sample with ~0.15 g L –1 isopropanol content, produced from miscanthus using nitric acid treatment of the biomass, was tested. The process characteristics and ethylene quality obtained by the bioethanol dehydration are slightly higher because of decreased formation of by-products, compared with the dehydration of commercially available pure ethanol.