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Hybrid Vapor Stripping-Vapor Permeation Process for Recovery and Dehydration of 1-Butanol and Acetone/Butanol/Ethanol from Dilute Aqueous Solutions. Part 1. Process Simulations
Vane, L. M. AND F. R. Alvarez. Hybrid Vapor Stripping-Vapor Permeation Process for Recovery and Dehydration of 1-Butanol and Acetone/Butanol/Ethanol from Dilute Aqueous Solutions. Part 1. Process Simulations. Journal of Chemical Technology and Biotechnology. John Wiley and Sons, LTD, , Uk, 88(8):1436-1447, (2013).
Each step of an alcohol biofuel supply chain involves the expenditure of energy; whether to grow, harvest, and transport biomass, to convert the biomass to biofuel components, or to recover/concentrate those components. The “upstream” greenhouse gas (GHG) emissions and environmental impacts associated with this energy use directly impacts the sustainability and even marketability/financial incentives related to the biofuel. The focus of this paper will be on the separation of 1-butanol/water and ABE/water mixtures using a process that combines unit operations of vapor stripping, vapor compression, and vapor permeation membrane separation in an energy efficient manner – termed the Membrane Assisted Vapor Stripping (MAVS) process.
BACKGROUND: Fermentative production of butanol is limited to low concentrations, typically less than 2 wt% solvent, due to product inhibition. The result is high separation energy demand by conventional distillation approaches, despite favorable vapor-liquid equilibrium and partial miscibility with water. In previous work, a process integrating steam stripping, vapor compression, and vapor permeation separation was proposed for separating ethanol from water. Such a Membrane Assisted Vapor Stripping (MAVS) process is considered in this work for 1-butanol/water and acetone/butanol/ethanol/water (ABE/water) separation. RESULTS: Using process simulations, the earlier MAVS design was estimated to require 6.2 MJ-fuel/kg-butanol to produce 99.5 wt% 1-butanol from a 1 wt% 1-butanol feed, representing an energy savings of 63% relative to a benchmark distillation/decanter system. Adding a fractional condensation step to the original MAVS design is predicted to reduce energy demand to only 4.8 MJ-fuel/kg-butanol and reduce membrane area by 65%. CONCLUSION: In the hybrid distillation/membrane MAVS systems, the stripping column provides high butanol recovery and low effluent concentration while the vapor compression and membrane steps enable the efficient recovery of latent and sensible heat from both the retentate and permeate streams from the membrane system. Addition of the dephlegmator condenser reduces both compressor size and membrane area.