Yupo J. Lin

The Separative Bioreactor: A Continuous Separation Process for the Simultaneous Production and Direct Capture of Organic Acids

Abstract The replacement of petrochemicals with biobased chemicals requires efficient bioprocesses, biocatalysis, and product recovery. Biocatalysis (e.g., enzyme conversion and fermentation) offers an attractive alternative to chemical processing because biocatalysts utilize renewable feedstocks under benign reaction conditions. One class of chemical products that could be produced in large volumes by biocatalysis is organic acids. However, biocatalytic reactions to produce organic acids typically result in only dilute concentrations of the product because of product inhibition and acidification that drives the reaction pH outside of the optimal range for the biocatalyst. Buffering or neutralization results in formation of the acid salt rather than the acid, which requires further processing to recover the free acid product. To address these barriers to biocatalytic organic acid production, we developed the “separative bioreactor” based on resin wafer electrodeionization, which is an electrodeionization platform that uses resin wafers fabricated from ion exchange resins. The separative bioreactor simultaneously separates the organic acid from the biocatalyst as it is produced, thus it avoids product inhibition enhancing reaction rates. In addition, the separative bioreactor recovers the product in its acid form to avoid neutralization. The instantaneous separation of acid upon formation in the separative bioreactor is one of the first truly one‐step systems for producing organic acids. The separative bioreactor was demonstrated with two systems. In the first demonstration, the enzyme glucose fructose oxidoreductase (GFOR) was immobilized in the reactor and later regenerated in situ. GFOR produced gluconic acid (in its acid form) continuously for 7 days with production rates up to 1000 mg/L/hr at >99% product recovery and GFOR reactivity >30 mg gluconic acid/mg GFOR/hour. In the second demonstration, the E. coli strain CSM1 produced lactic acid for up to 24 hours with a productivity of >200 mg/L/hr and almost 100% product recovery.

An attempt towards simultaneous biobased solvent based extraction of proteins and enzymatic saccharification of cellulosic materials from distiller's grains and solubles

Distillers grains and solubles (DGS) is the major co-product of corn dry mill ethanol production, and is composed of 30% protein and 30-40% polysaccharides. We report a strategy for simultaneous extraction of protein with food-grade biobased solvents (ethyl lactate, d-limonene, and distilled methyl esters) and enzymatic saccharification of glucan in DGS. This approach would produce a high-value animal feed while simultaneously producing additional sugars for ethanol production. Preliminary experiments on protein extraction resulted in recovery of 15-45% of the protein, with hydrophobic biobased solvents obtaining the best results. The integrated hydrolysis and extraction experiments showed that biobased solvent addition did not inhibit hydrolysis of the cellulose. However, only 25-33% of the total protein was extracted from DGS, and the extracted protein largely resided in the aqueous phase, not the solvent phase. We hypothesize that the hydrophobic solvent could not access the proteins surrounded by the aqueous phase inside the fibrous structure of DGS due to poor mass transfer. Further process improvements are needed to overcome this obstacle.

Electrokinetic desalination of brackish water and associated challenges in the water and energy nexus

This review explores the current state-of-the-art in the removal of ions from water to treat brackish water using electrokinetic technologies, while identifying emerging technologies and potential advances in materials science, process engineering, and system integration. We first provide a definition of the class of electrokinetic desalination methods, and propose measurement and reporting standards to improve technology comparisons. The review focuses on two major types of electrochemical processes: electrodialysis (and electrodeionization) and capacitive deionization. We include hybrid systems that combine battery-based desalination, and capacitive neutralization deionization. Finally, we consider the interconnectivity between desalination and energy, and discuss the balance between energy efficiency, water throughput in the context of large-scale deployment of a desalination plant, and environmental impacts.