(613g) Process Intensification of Bio-Ethanol Dehydration Under Compressed Liquid Phase Conditions

Global ethylene demand is consistently growing as its uses as a precursor for plastics, detergents and lubricants expand. Although the majority of ethylene is produced from petrochemical sources, an existing green alternative is dehydration of ethanol derived from biorenewable feeds to produce ethylene. High feed costs and process inefficiencies limit bio-based ethanol as an economic alternative to crude oil for ethylene production. Specifically, the highly endothermic bioethanol dehydration reaction and poor heat transfer to the vapor phase necessitate operation through a series of adiabatic reactors and boilers to maintain high ethylene selectivity. In addition, agriculture and fermentation are highly localized, which necessitates costly ethanol transportation through trucking, waterways, and pipelines. Operation of ethanol dehydration in the compressed liquid phase has potential to intensify the dehydration process by improving heat transfer, product recovery, and energy efficiency. A process intensified reactor operating under liquid phase conditions has potential to reduce capital costs sufficiently to justify distributed ethylene production.

Catalytic activity in the liquid phase is a major knowledge gap that hampers development of process intensified, liquid phase ethanol dehydration reactors. To assess the effects of conditions on activity, we performed both liquid and vapor phase ethanol dehydration studies, studying both space velocity and the effect of the water content of the fed. Ethanol dehydration reactions were performed in a continuous phase packed bed reactor catalyzed using ZSM-5 zeolite. Ethylene activity was compared when operated under both liquid and vapor phase (0.1 or 24 MPa) and varying weight hourly space velocities (30 - 1200 hr^‑1) and water loadings (0 - 33 wt%). ZSM-5 is more active for ethanol dehydration reactions under vapor phase conditions compared to liquid phase conditions, however, differences in ethylene yield are negligible when operated at low space velocities and high water loadings. Characterization of ZSM-5 catalyst after reaction reveals only a minor loss in framework after both the vapor and liquid phase reaction. Ethanol dehydration throughput and heat transfer improvements using a compressed, liquid phase packed bed reactor compared to vapor phase reactors suggest a potential alternative to current industrial processes.