Development of CO2-assisted separation techniques for the biomass conversion sector

Abstract

Using current technologies, obtaining chemicals from biomass is typically less environmentally friendly than from petroleum. In many cases, the most significant part of the environmental impact of biomass conversion is caused by the energetic requirements for separating intermediates or products from water. Water removal, via distillation and other drying processes, can account for up to 80% of the total energy consumption of certain biomass conversions. Unless the environmental and energetic costs of separating water from organic products can be lowered, bio-derived products will struggle to be greener and cheaper than fossil-derived products. Carbon dioxide-assisted separations might be an alternative to promote more energetically efficient separations, especially in recovering low-volatility hydrophilic organic molecules from water. The techniques developed take advantage of previously described separations triggered by CO2. Two new methods are proposed: high pressure switchable water (HPSW) and solvent-assisted high pressure switchable water (SA-HPSW). These methods operate from the synergy between switchable water, CO2 expansion of liquids and liquid-liquid extraction while overcoming some drawbacks observed when those three techniques are performed separately. The ionogens used in HPSW and SA-HPSW were also recovered via reverse osmosis. In addition, the ionogens used in HPSW were also applied as a catalyst in a Baylis-Hillman type reaction. After conversion, the addition of CO2 aided the recovery of the desired product, highlighting the dual effect HPSW might have in organic reactions in water. Considerations were also made regarding the energy consumption of the processes, and comparisons were drawn with distillation. This work was focused on biomass products considered in commercial applications. HPSW promoted the separation of acetone (one of the components of the acetone-butanol-ethanol process), isopropanol, and ethyl lactate. SA-HPSW was evaluated for ethanol recovery (which can be obtained via fermentation of sugars). Unfortunately, high energy consumption was calculated for the distillation required to purify the ethanol even after SA-HPSW had already been performed. SA-HPSW was also explored in the recovery of 1,4-butanediol, ethylene glycol, propylene glycol and 1,5-pentanediol, which are being explored as replacements for petroleum-derived chemicals. Finally, considerations were made regarding optimizations necessary to decrease the energy requirements for both HPSW and SA-HPSW.