Evaluation of support matrices for an immobilized cell gas lift reactor for fermentation of coal derived synthesis gas

The fermentation of synthesis gas by Butyribacterium methylotrophicum is limited by the poor solubility of the substrate in water. Gas lift reactors allow for increased gas liquid mixing and may be employed in synthesis gas fermentations to enhance gas mass transfer rates. Studies were conducted to evaluate different matrices for the immobilization of B. methylotrophicum in a gas lift reactor. The performance of celite, molecular sieves, alumina, activated carbon, wood, and ion exchange was analyzed on the basis of cell growth, cell attachment, product formation, and minimum fluidization velocity. Maximum cell growth was evidenced with molecular sieves, whereas celite proved best for cell attachment. The total electron content of the products was higher in the molecular sieves system than in the ion exchange or celite systems. However, the total available electron normalized to protein content varied between 25-33 meq/l/mg for celite, ion exchange and molecular sieves. The minimum fluidization velocity of molecular sieves > celite > ion-exchange. Based on the results, both celite and molecular sieves were found to be effective for cell immobilization.