PNNL

Abstract

Here we demonstrate the proof-of-concept for microchannel reactive distillation for alcohol-to-jet application: combining ethanol/ water separation and ethanol dehydration in one unit operation. Ethanol is first distilled into the vapor phase, converted to ethylene and water, and then the water co-product is condensed to shift the reaction equilibrium. Process intensification is achieved through rapid mass transfer—ethanol stripping from thin wicks using novel microchannel architectures—leading to lower residence time and improved separation efficiency. Energy savings are realized with integration of unit operations. For example, heat of condensing water can offset vaporizing ethanol. Furthermore, the dehydration reaction equilibrium shifts towards completion by immediate removal of the water byproduct upon formation while maintaining aqueous feedstock in the condensed phase. Conversion of 40% ethanol in water to ethylene was demonstrated with 91% ethylene selectivity and 71% ethanol conversion at 220°C, 600 psig, and 0.28 hr-1 weight hour space velocity. Almost three stages of separation (2.7) were also demonstrated, under these conditions, using a device length of 9.1 cm. This provides a height equivalent of a theoretical plate (HETP), a measure of separation efficiency, of ~3.4 cm. By comparison, conventional distillation packing provides an HETP of ~30 cm. Thus, 8? reduction in HETP was demonstrated over conventional technology, providing a means for significant energy savings and an example of process intensification. Finally, preliminary process economic analysis indicated that by using microchannel reactive distillation technology, the operating and capital costs could be reduced by at least 35% and 55%, respectively, relative to conventional ethanol distillation and dehydration technology, provided future improvements to microchannel reactive distillation design and operability are made.