Design of a Packed-Bed, Continuous-Flow Fermentation Process Tailored for Cellulosic Ethanol Production

Texas Tech University, Lubbock TX

Investigators

Abstract

PI: Hedden, Ronald Institution: Texas Tech University Proposal Number: 1066616 Title: Design of a packed-Bed Continuous-Flow Fermentation Process Tailored for Cellulosic Ethanol Production Intellectual Merit Ethanol (EtOH) derived from lignocellulosic biomass is among the most promising alternative fuels for future automotive energy needs. However, reductions in the cost of producing cellulosic EtOH must be realized in order to make it competitive with gasoline or EtOH derived from crops such as corn and sugarcane. Process economics can be improved both by increasing the EtOH yield per unit of raw materials and by lowering capital equipment and operating costs for industrial-scale fermentations. Capital equipment and operating costs can be lowered tremendously by replacing batch fermentors with continuous-flow, immobilized cell reactors (ICR), which can be significantly smaller due to higher feedstock conversion efficiency and higher volumetric productivity. This project addresses the design of ICR processes tailored for production of cellulosic EtOH by recombinant ethanologens, using novel synthetic porous polymer scaffolds (SPPS) to partially immobilize the cells. Preliminary results show that a continuous-flow column reactor packed with an SPPS material can achieve volumetric productivity at least 14 times higher than that of a comparable batch fermentation, while the porous structure of the SPPS bed mediates problems with CO2 holdup that limit conventional gel-immobilized systems. The performance of two packed bed ICR designs will be compared: a short vertical column reactor and a stirred tank reactor with packed bed section. The PIs will also optimize characteristics of the SPPS materials (pore size, pore volume fraction, and particle size) for fermentation of cellulose-derived feedstocks. This study will systematically optimize porous polymer materials for any ICR fermentations. The investigation will initially be focused on E. coli strain LY01, due to its high specific growth rate, though this ICR designs should be equally applicable to ethanologenic strains of Saccharomyces cerevisiae or Zymomonas mobilis. This study will examine ICR systems specifically for conversion of cellulose-derived feedstocks to EtOH, using genetically modified organisms that can metabolize both hexoses and pentoses. The effects of organic inhibitors on volumetric productivity will be systematically examined with simple sugar mixtures before testing reactor performance with "real" cellulose-derived feedstocks. An analytical model of reactor performance will be developed to achieve an integrated understanding of the effects of parametric variations. Cell density will be studied using E. coli LY01 engineered to express green fluorescent protein (GFP). This study address the design of continuous-flow fermentors that are optimized to handle issues specific to cellulosic EtOH: inhibitors and particulate matter in the feed, and CO2 ventilation. Broader Impact This research offers a benefit to society due to its potential to provide transformative new process technology for production of fuels from renewable non-food resources. The research will generate new knowledge that can potentially benefit the developing cellulosic EtOH industry economically. The project is vital to the PI's efforts to establish educational and outreach programs in Chemical Engineering at Texas Tech, and to support integration of materials and renewable energy research with Chemical Engineering education. The PI's and co-PI's groups have historically supported outreach activities involving high school and undergraduate students, including women and members of underrepresented groups. Through the Undergraduate Research Fellowship program in the Honors College and the ConocoPhilips Bridge program at Texas Tech, undergraduate students will work with graduate students to design biotechnology experiments for the Unit Operations teaching laboratory. Two graduate students involved will complete training in Engineering Ethics through the Murdough Center for Engineering Professionalism at Texas Tech University. Students will acquire training in methods of neutron scattering and radiation safety by studying porous polymers used in fermentors. Results will be disseminated through presentations at national and international meetings and through an educational webpage regarding cellulosic EtOH, which will feature these research efforts.