(3ch) Passivating Alkali Metals During Pyrolysis of Biomass to Obtain Higher Yield of Sugars

Authors: 
Kuzhiyil, N., Iowa State University


Sugars are excellent feedstocks for producing fuels and chemicals using fermentation and chemical technologies. My research is focused on producing sugars from biomass and cellulosic wastes. By depolymerizing cellulose and hemicellulose of biomass using fast pyrolysis, which is rapid heating in the absence of oxygen, anhydrosugars such as levoglucosan (LG) can be produced. However, inherently contained alkali in biomass catalyzes the glucose ring fragmentation reaction instead of the depolymerization reaction during pyrolysis resulting in very low yield of anhydrosugars. By passivating alkali, the reaction mechanism can be driven through the depolymerization pathway to increase the yield of anhydrosugars. The present study invented a method to passivate alkali using phosphoric and sulfuric acid infusion thereby increasing the yield of anhydrosugars significantly. A correlation between the amount of alkali contained in biomass feedstocks and the amount of acid to be infused to obtain maximum yield of levoglucosan was developed that can be used for commercial production of sugars from biomass. The recovery of these sugars from the pyrolysis reactor was found to be difficult because of the polymerization and charring of LG at the operating temperature of 500°C. Analytical pyrolysis of acid infused biomass feedstocks at various temperatures indicated that a temperature range of 350-400°C can be the best for recovering the LG formed in the reactor. Methods are under development to maximize the recovery of pyrolytic sugars from a fluid bed and auger reactors using low temperature pyrolysis and increased sweep gas flow.