Top ten fundamental challenges of biomass pyrolysis for biofuels

Abstract

Pyrolytic biofuels have technical advantages over conventional biological conversion processes since the entire plant can be used as the feedstock (rather than only simple sugars) and the conversion process occurs in only a few seconds (rather than hours or days). Despite decades of study, the fundamental science of biomass pyrolysis is still lacking and detailed models capable of describing the chemistry and transport in real-world reactors is unavailable. Developing these descriptions is a challenge because of the complexity of feedstocks and the multiphase nature of the conversion process. Here, we identify ten fundamental research challenges that, if overcome, would facilitate commercialization of pyrolytic biofuels. In particular, developing fundamental descriptions for condensed-phase pyrolysis chemistry (i.e., elementary reaction mechanisms) are needed since they would allow for accurate process optimization as well as feedstock flexibility, both of which are critical to any modern high-throughput process. Despite the benefits to pyrolysis commercialization, detailed chemical mechanisms are not available today, even for major products such as levoglucosan and hydroxymethylfurfural (HMF). Additionally, accurate estimates for heat and mass transfer parameters (e.g., thermal conductivity, diffusivity) are lacking despite the fact that biomass conversion in commercial pyrolysis reactors is controlled by transport. Finally, we examine methods for improving pyrolysis particle models, which connect fundamental chemical and transport descriptions to real-world pyrolysis reactors. Each of the ten challenges is presented with a brief review of relevant literature followed by future directions which can ultimately lead to technological breakthroughs that would facilitate commercialization of pyrolytic biofuels. Paper bodyAs the world population grows, there is a need for new energy technologies that are domestic and sustainable. Achieving both objectives requires improving existing energy systems as well as utilizing renewable feedstocks, such as biomass. In addition to supporting agricultural economies, biomass is the only renewable source for liquid fuels and chemicals. 1,2 For this reason, the U.S. Department of Energy has made it a goal to replace 30% of all transportation fuels with biofuels. 3 The 2005 'Billion-Ton Study' (BTS) sponsored by the U.S. Department of Energy employed conservative assumptions to determine that more than a billion tons of biomass (unrestricted by price) is available annually for biofuels. This amount of biomass is capable of displacing 30% of U.S. petroleum consumption, as put forth in the government targets. 3 In 2011, an update to the BTS revisited the resource availability and confirmed the findings of the 2005 study. 4 Both government-

A Review of Thermal Co-Conversion of Coal and Biomass/Waste

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“…It is likely that there will be other fuels derived from lignocellulosic biomass beyond 2MF and DMF. 3 (1)…”

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