Techno-economic analysis for recovery of fermentation inhibitors: comparison of conventional bioseparation methods

During the process of lignocellulosic biomass conversion to bioethanol, in the pretreatment step, many chemical compounds are produced that are inhibitory to the fermentation process.  These inhibitors are categorized in three groups: weak acids (like acetic and formic acid) which are mostly produced during the breakage of hemicellulose structure, furans (like furfural and hydroxymethyl furfural), and phenols which are byproducts of lignin aromatic units.

The amount of each of these inhibitors and the intensity of their inhibition effect on the fermentation performance highly depends on the biomass type and also on the pretreatment method that was applied on the biomass.  Many of these inhibitory compounds can be recovered as chemical commodities and as a byproduct stream add to the profit of the biorefinery.  In this work separation and purification of acetic acid, levullinic acid, formic acid, furfural, and phenol were studied.  The different conventional biopseparation technology including liquid-liquid extraction, adsorption, and membrane separation were investigated for their thermodynamic potential and economic viability to take away these compounds from pre-fermentation broth.

In each of these separation method different factors was governing the practicality of the method within the biorefinery system.  These factors are solvent recycling yield for liquid-liquid extraction, column regeneration energy intake for adsorption, and the membrane durability for membrane separation.  In general, based on the biomass feedstock and infrastructure of the facilities, addition of a separation unit to an existing biorefinery is an economical alternative.