387156 Economic Viability of Consolidated Bioprocessing As Compared to Separate Hydrolysis and Fermentation for the Production of Biochemically Derived Ethanol from Biomass

Monday, November 17, 2014
Galleria Exhibit Hall (Hilton Atlanta)
Jonathan P. Raftery and M. Nazmul Karim, Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX

As oil prices continue to increase worldwide, the current research has targeted various alternative energy sources. One such energy source is ethanol, an interesting renewable liquid fuel option, which can be produced via biochemical means from many different types of biomass. This biochemical pathway involves two steps, the first of which involves the conversion of the sugar polymers found in plant cells to simple sugars via a chemical pretreatment and enzyme hydrolysis. The second step involves the mixed fermentation of these sugars using a recombinant organism. The resulting ethanol must them be separated from a very dilute water mixture into a pure product.

Our previous research in biochemically derived ethanol production using separate hydrolysis and fermentation (SHF) processes has shown that this technology is economically feasible for large scale process development. The mixing of multiple feedstock options with corresponding pretreatment methods were considered, and an optimization of the resulting mixed-integer nonlinear program (MINLP) showed that a viable process design producing approximately 62 million gallons of ethanol per year calls for the use of sugarcane bagasse and sodium hydroxide pretreatment with a minimum ethanol selling price (MESP) of $2.42 per gallon of ethanol. However, this research also showed that a major cost factor was the purchase of enzymes. The removal of enzymes in the production process, thereby eliminating the hydrolysis step, can be a means to further reduce the MESP.

The development of an enzyme-free bioethanol production process has already been considered by many researchers (1-4). Mascoma Corporation, based out of New Hampshire, USA, has developed a consolidated bioprocessing (CBP) design that uses microorganisms capable of performing the hydrolysis and fermentation in a single step. In this research we look to analyze the consolidated bioprocessing method to determine if the use of costly enzymes is a necessary evil for the biological method bioethanol production. The optimization of a consolidated bioprocessing plant will be done, allowing for various biomass feedstocks and pretreatment methods as in previous studies, using an MINLP model to find the MESP associated with this conversion method. The results will then be compared with the previously studied SHF design to determine the most cost effective large scale method of bioethanol production.

  1. Lynd, L. R., Weimer, P. J., van Zyl, W. H. & Pretorius, I. S. Microbial Cellulose Utilization: Fundamentals and Biotechnology. Microbiol Mol Biol Rev 66, 506–577 (2002).
  2. Lynd, L. R., Zyl, W. H. van, McBride, J. E. & Laser, M. Consolidated bioprocessing of cellulosic biomass: an update. Current Opinion in Biotechnology 16, 577–583 (2005).
  3. Mascoma Corporation. http://www.mascoma.com/index.php
  4. Ryu, S. & Karim, M. N. A whole cell biocatalyst for cellulosic ethanol production from dilute acid-pretreated corn stover hydrolyzates. Appl Microbiol Biotechnol 91, 529–542 (2011).

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