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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 2. Experimental Validation with Simple Mixtures and Actual Fermentation Broth
Vane, L., F. Alvarez, L. Rosenblum, AND S. Govindaswamy. Hybrid Vapor Stripping-Vapor Permeation Process for Recovery and Dehydration of 1-Butanol and Acetone/Butanol/Ethanol from Dilute Aqueous Solutions. Part 2. Experimental Validation with Simple Mixtures and Actual Fermentation Broth. Journal of Chemical Technology and Biotechnology. John Wiley and Sons, LTD, , Uk, 88(8):1448-1458, (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. In Part 1 of this work, chemical process simulations were carried out to estimate the energy usage of a hybrid process combining the unit operations of vapor stripping, vapor compression, and vapor permeation membrane separation in an energy efficient manner – termed the Membrane Assisted Vapor Stripping (MAVS) – to separate 1-butanol/water and acetone-butanol-ethanol/water (ABE/water) mixtures. In this paper, the solvent removal and drying performance of a pilot-scale MAVS system with laboratory-prepared 1-butanol/water and ABE/water mixtures will be reported and compared to performance with an actual bacterial ABE fermentation broth.
BACKGROUND: In Part1 of this work, a process integrating vapor stripping, vapor compression, and a vapor permeation membrane separation step, Membrane Assisted Vapor Stripping (MAVS), was predicted to produce energy savings compared to traditional distillation systems for separating 1-butanol/water and acetone-butanol-ethanol/water (ABE/water) mixtures. Here, the separation performance and energy usage of a MAVS pilot system with such mixtures and an ABE fermentation broth were assessed. RESULTS: The simple stripping process required 10.4 MJ-fuel/kg-butanol to achieve 85% butanol recovery from a 1.3 wt% solution. Addition of the vapor compressor and membrane unit and return of the membrane permeate to the column raised 1-butanol content from 25 wt% in the stripping vapor to 95 wt% while cutting energy usage by 25%. Recovery of secondary fermentation products from the ABE broth were based on their relative vapor-liquid partitioning. All volatilized organic compounds were concentrated to roughly the same degree in the membrane step. Membrane permeance, selectivity, and overall MAVS energy usage were the same with the broth as with the ABE/water solution. CONCLUSION: Energy usage of the MAVS experimental unit corroborated process simulation predictions. Simulations of more advanced MAVS designs predict 74% energy savings compared to a distillation-decanter system.