Pervaporative Enrichment of 1,3-Propanediol from Model Fermentation Broths By Hydrophobic Specialty Polymers

While 1,3 PD can be easily separated from the other by products of bacterial metabolism, the real challenge lies in enriching it from dilute concentrations in aqueous mixtures which amounts to almost 50 – 70% of the total production cost in fermentative 1,3-PD production.  The hydrophilic character of 1,3 PD compounds the difficulty of purification. Conventional and reported separation techniques have had their limitations in due cost and energy consumption and hence applicability. Membrane separation processes offer a cheap and energy efficient method of upgrading the value of specific components typically produced in dilute mixtures.  Although pervaporation is an energetically advantageous process. 1,3-PD cannot be enriched by materials conventionally used for pervaporation. The development of novel materials with a good cost performance balance is essential for the establishment of industrial separation procedures for 1,3-PD enrichment from dilute broths. The present work describes a study on the pervaporation enrichment of 1,3-propanediol from model fermentation broths using three hydrophobic polymer families – functionalized siloxanes, cyclohexylamine base methacrylates and imidazolium ionic liquid based methacrylates with progressively increasing separation efficiency. While the highest 1,3-PD permeabilities were seen with the siloxane polymers, the imidazolium IL based methacrylates exhibited the best separation factors both with respect to water and glycerol. The effect of glycerol on transport coupling was evaluated. The permeability and separation factors from the pervaporation experiments with these polymers were siloxanes were collated to arrive at a Robeson’s upper bound of pervaporation of 1,3-propanediol from aqueous solution by polymeric membranes. The development of novel materials with a good cost/performance balance is central to the establishment of industrial separation procedures for 1,3-PD enrichment from fermentation broths. The removal of this process bottleneck may increase the feasibility of using waste industrial glycerol as a sustainable resource for producing 1,3-PD as a biorenewable alternative to a petroleum platform.