Sunday, May 3, 2009
6-29
Fermentation of syngas produced from gasification of switchgrass by P11
Karthikeyan D. Ramachandriya, Krushna Patil, and Mark R. Wilkins. Biosystems and Agricultural Engineering, Oklahoma State University, 111 Agricultural Hall, Stillwater, OK 74078
Syngas fermentation is a thermo-chemical conversion of biomass into liquid biofuels and is carried out in two steps: 1) gasification of feedstocks to produce a mixture of gases which are primarily CO, CO2 and H2 called syngas and 2) fermentation of the syngas by microbial catalysts like Clostridium ljundahlii, Clostridium carboxidivorans and Clostridium P11T. Gas cleaning is an important step in this technology as the contaminants of syngas such as methane, acetylene, ethylene, nitric oxide etc could have deleterious effect on the microbes. The study of the effect of contaminants will help in improving the gas cleaning system thus improving the overall efficiency of the process. In our study, switchgrass syngas was gasified in a fluidized bed reactor to produce syngas with 6.33% H2, 14.22% CO2, 15.87% CO, 2.32% CH4, 0.53 % ethylene, 0.28% ethane, 44.5 ppm NO and the rest N2. This gas was used as a substrate for growth of bacteria and was compared with a bottled gas mix of 20% CO, 15% CO2, 5 % H2 and 60% N2. There was no growth inhibition due to the presence of contaminants and maximum ethanol concentrations using switchgrass syngas were 2.35 times greater than those using bottled gas. Also, isopropanol was produced at concentrations as high as 3.9 g/l when switchgrass syngas was used. Maximum acetic acid concentrations were found to be 2.75 g/l and 1.69 g/l using control and switchgrass syngas, respectively.