The production of sugars from forest and agricultural wastes is a critical step for making bio-fuels and bio-chemicals to replace petroleum. One way to do this is by using an ancient technique called "pyrolysis", which simply involves heating up this biomass. When cellulose (one of the main components in plant cell tissues) is heated very fast between 300 and 600 oC (fast pyrolysis) under vacuum it is possible to convert almost 95 % of it into sugars that can be easily upgraded into bio-fuels and bio-chemicals. The quantity of sugars obtained with this process is comparable to other well-developed, more expensive methods like enzymatic hydrolysis. Unfortunately, when the biomass is heated very fast at atmospheric pressure in commercial fast pyrolysis reactors, the production of sugars is much lower than when using vacuum. In fact, we typically see less than 20 % of the original cellulose. The decreased sugar yield at atmospheric pressure is due to very poorly understood secondary reactions that happen during fast pyrolysis on plant cell walls. In this proposal we will combine laboratory experiments and computer modeling tools to understand the reasons for the low quantities of sugars obtained at atmospheric pressure. New practical strategies are proposed to dramatically increase the production of sugars during fast pyrolysis and in this way reduce the price of bio-fuels derived from our renewable biomass resources.
The main practical goal of this proposal is to better understand the role of intermediate pyrolysis liquid phase oligomeric sugars (cellobiosan, cellotriosan,...) that typically are lost through undesirable dehydration, cross-linking, and polycondensation secondary reactions. We will combine innovative experimental and kinetic modeling tools to better understand these secondary reactions and the mechanisms by which acids, for example, mitigate some of the undesirable interactions with the lignocellulosic matrix (or their products). Micro-explosion enhancers (blowing agents) will be evaluated to promote anhydrosugar aerosolization to decrease residence time in the pyrolytic liquid intermediate as well as the probability for undesirable secondary reactions to occur inside the pyrolysis reactor. We will broaden our impact by working with Walla-Walla Community College (WWCC) in the development and evaluation of courses for associate degrees in Bioenergy Operations and in Renewable Resource Recovery Operations. We will organize an annual workshop between our graduate students, postdoctoral researchers and WWCC students to exchange ideas and encourage WWCC students to continue their professional development. This project will also serve as a platform for undergraduate electrical engineering students to conduct their Senior Design Project constructing and improving new wire mesh fast pyrolysis reactors capable of vacuum operation. Results from this project will be incorporated into lectures in graduate-level courses on kinetics and reaction engineering at Northwestern University and on biomass thermochemical conversion at Washington State University. Prof. Broadbelt will participate in a program to interest girls in science and engineering. Joint collaboration between WSU and Northwestern University will yield cross-institutional synergy in the future.
