(18e) Applications of Magnetically Responsive Micro/Mesoporous Carbon Adsorbents in Biorefining

Inhibitory compounds commonly arise at multiple points in the biorefining pipeline, including with respect to both toxic byproducts in the feedstock as well as the final target product itself. In both cases, if not effectively removed, their presence can have deleterious effects on the microbial biocatalyst and, in turn, its overall performance. Here we demonstrate how a series of novel, magnetically responsive micro/mesoporous carbon powder (MMCP) adsorbents can be employed for the facile and efficient removal of inhibitory bioproducts and byproducts alike. In addition to large surface areas (>1400 m²/g) promoting high adsorption capacities, said MMCPs also uniquely include magnetic Ni nanoparticles that enable the direct and facile magnetic retrieval of spent adsorbents from the culture broth, bypassing the need for column configurations (e.g., packed or expanded bed). As a preliminary demonstration of concept, the use of MMCPs for in situ removal of n-butanol has been studied under model conditions. Although it represents a promising biofuel, n-butanol production by conventional batch fermentation is limited as a result of its cytotoxic effects. Butanol loading capacities of a family of MMCPs (with 4-10%wt. Ni content) were found to not be significantly impacted by Ni content and, furthermore, performed comparably to other, previously-studied commercial resins and activated carbons. Magnetic retrieval of the mesoporous powder is dependent on the Ni content, with up to 89% retrieval achieved in 6 min with 10%wt. Ni. Desorption studies using retrieved adsorbents demonstrated an average of 93% recovery of the total adsorbed butanol. Kinetic studies, meanwhile, indicate that neither the effective adsorption or desorption rates should constitute a bottleneck with respect to the future development of semi-continuous butanol fermentation processes using MMCPs. Finally, the further utility of MMCPs for the upstream removal of toxic byproducts derived from the pretreatment of lignocellulose has been investigated. Furfural, for example, can be readily removed using MMCPs that are subsequently retrieved from the culture. Said pretreatment steps improve the fermentability of biomass-derived sugar mixtures, supporting improved production of ethanol and lactate by engineered Escherichia coli.