(483d) Process Synthesis of Biorefineries: Optimization of Biomass Conversion to Fuels and Chemicals

The depletion of easily recoverable petroleum resources and the increasing emissions of carbon dioxide have compelled society to search for alternative means of producing the industrially important fuels and chemicals that are increasingly relied upon for our standard of living. Biorefineries which are facilities that are capable of producing these fuels and chemicals from biomass are envisioned as part of the solution.

Several technologies are being investigated to convert different biomass feedstocks to fuels and chemicals. The development and commercialization of the biorefinery concept will depend critically on the choice of those feedstocks, technologies and products that will lead to favorable economics. This is best addressed through a process synthesis approach.

Previous studies of process synthesis of biorefineries have focused on either single product or single technology facilities. This has been complemented with work on product portfolio and supply chain optimization. Our study builds on the previous studies by combining and expanding the previous insights into a multi-feed, multi-product superstructure which seeks to maximize economic potential of a biorefinery system that produces a portfolio of products. We focus our study on the NREL description of biorefineries as facilities that combine the production of low-volume, high-value chemicals with low-value, high-volume fuel products.

Initially, we create a superstructure of biorefinery configurations which encompasses the production of fuels and chemicals and includes four feedstock types (corn stover, wheat straw, barley straw and switch grass) and a variety of process technologies (fast pyrolysis, gasification, fermentation and aqueous thermo-chemical). With this we formulate a mixed integer non-linear program which we solve for the biorefinery configuration that maximizes net present value.

In order to account for the many uncertainties present in economic parameters used we perform extensive sensitivity analyses. We investigate the effect of changing material values, fuel prices and finally Fischer-Tropsch product prices. We also implement a Monte Carlo type sampling of the product price parameter space. This allows for the assessment of which chemicals and technologies are most robust to uncertainty.

Our work highlights the importance of combining the production of fuels and chemicals in one facility. We show that the multi-product biorefinery is robust to changing economic conditions. Finally, we show that bio-based chemicals play a pivotal role on the profitability of biorefinery systems.