Understanding Pyrolysis Chemistry to Improve Biomass-to-Chemical Process

The selective production of platform chemicals from thermal conversion of biomass-derived carbohydrates is challenging. Anhydrosugars, such as levoglucosan, are recognized as promising platform chemicals to produce fuel and chemicals (e.g., biologically active compounds, surfactants and polymers). Most of their chemical applications require the use of nearly pure crystalline compounds. However, anhydrosugars are very difficult to synthesize in large quantities and without side products, due to the nonselective nature of carbohydrate dehydration during pyrolysis. This leads to high production costs and currently limits the availability and use of anhydrosugar industrially.

Researchers have studied anhydrosugar production since early 1900, but until now, have not provided any great improvements in this field because no one understands why the selectivity was low for anhydrosugar production on the molecular level.

To address this problem, I developed two new methods to enhance anhydrosugar selectivity: (1) “ex-situ ring-locking” strategy: protecting the carbohydrate compounds before pyrolysis by alkoxy or aryloxy substitution at the anomeric carbon prior to the thermal treatment; or (2) “in-situ ring-locking” strategy: we eliminated the initial ex-situ ring-locking step by pretreating the carbohydrate substrate with an acid catalyst and an alkali salt. Both approaches can effectively suppress the formation of undesirable side products, and therefore significantly enhance the yield of the target product such as levoglucosan.

Furthermore, we received a grant from National Science Foundation Innovation-Corps (NSF I-Corps) to explore the commercialization potential for this patent-pending technology. We discovered a $300M market for our product after conducting 100+ customer interviews across the pharmaceutical, biochemical and the oil field chemical industries.

Since we have demonstrated our chemistry in a micropyrolyzer system, and validated the commercial potential of our product, we moved to next stage to validate the technology feasibility in larger scale. We studied the interplay of reaction and transport within biomass particle during fast pyrolysis. First, we developed a particle level model comprising of kinetics, energy and mass conservation equations. Through characteristic timescale analysis by using the non-dimenisonal numbers like Biot, Pyrolysis, Peclet, Damkohler and Lewis number, we categorize the operating conditions into three different regimes based on the dominant phenomena: chemical regime, mass transfer regime and thermal regime. We compared our experiments results with this map to identify the dominant phenomena for levoglucosan’s yield under different operating conditions.