(738g) Ex-Situ Catalytic Fast Pyrolysis of Beetle Killed Lodgepole Pine in Novel Ablative Reactor

We proposed the use of beetle killed lodgepole pine as feedstock for a mobile ablative fast pyrolysis unit. Fast pyrolysis is the rapid heating of wood in the absence of oxygen and results in a high yield of condensable volatiles with minimal char and non-condensable gases. The condensable volatiles are a valuable fraction as the product is similar in make and use as crude oil. There are a number of challenges that create economic concerns in this process, including biomass particle size requirements, transportation of low energy density biomass, and use of energy to reduce moisture content. Fast pyrolysis requires a rapid heating which often results in a decrease of particle size to achieve a fast heat ramp throughout the particle, and this size adjustment can be costly. The transportation of biomass also increases the cost of the overall process, however if the conversion were to happen at the location of harvesting, transportation of the condensed liquid product would be more efficient and economical. Efficiency in the process can also be improved with the use of beetle killed lodgepole pine that often has a moisture content below the fiber saturation point, making drying unnecessary and allowing for more energy to be used in the decomposition of the biomass.

In a previous work, with these solutions in mind, our group designed an ablative reactor that has no biomass size restrictions, a simplistic design that could be mobilized, and made use of beetle killed lodgepole pine eliminating the need for excess drying. We used the principle of ablative pyrolysis, the rapid heating of biomass through contact of biomass with a hot surface, by using a heated plate attached to a piston to be pressed against a rotating platform of biomass. The motion from the rotating platform combined with the pressure and heat from the piston allows us to pyrolyze complete wood rods (3.5 x 20 cm) eliminating the particle size restriction. The biomass we chose for pyrolysis is beetle killed lodgepole pine, a continually increasing population of very dry structurally precarious material that is prone to falling and feeding forest fires. The use of this biomass in our mobile ablative fast pyrolysis unit would decrease the cost of drying, grinding, and increase efficiency of transportation by transporting a higher energy density oil. Using the BKLP and novel ablative reactor we conducted screening experiments of different parameters (temperature, flow, biomass size, etc.) to determine the effects on bio-oil yield and quality. While high bio-oil yields of up to 60% were attained, the oil created from the ablative unit resulted in heavily oxygenated compounds that are unstable, acidic and corrosive in nature. These qualities are undesirable for fuels and require a catalytic upgrade to remove oxygen containing functional groups to improve the quality of the bio-oil.

In the present work, we have combined the ablative reactor with a packed bed upgrading reactor to create an ex-situ catalytic fast pyrolysis system. We conducted ablative pyrolysis at parameters determined from the previous reactor screening experiments and added dry ice methanol bubblers to collect deoxygenated products, such as benzene, xylene and toluene. We used HZSM-5 as the first catalyst in the ex-situ upgrade reactor, and conducted a temperature screening study at 300, 400, and 550 C. It was found that overall aromatic yield peaked at 400C and produced the most deoxygenated compounds primarily consisting of monoaromatics hydrocarbons. As temperatures increased we saw a decrease in monoaromatic hydrocarbons (xylene and toluene) and an increase in benzene. We accredit the decrease in overall yield to an increase in secondary cracking reactions that occurred within the upgrade reactor because of the high temperature exposure. While deoxygenation was promoted hydrocarbons were undergoing cracking removing the methyl group promoting the production of benzene. Along with testing HZSM-5, we have been looking into the development of a new catalyst using graphene nanoplatelets. Graphene nanoplatetlets are a high quality carbon nanomaterial comprised of short stacks of graphene sheets. The graphene nanoplatetlets provide an inert structure with a high surface area ideal for use as a catalytic support. We used a new solvent-less grinding impregnation method to deposit nickel nanoparticles, as an active site, on the surface of the support in high concentrations producing a uniform size distribution and loading. The solventless grinding method allowed preparation of large batches of catalyst making it viable for lab scale testing in our ex-situ catalytic ablative fast pyrolysis system. Nickel impregnated graphene nanoplatelets (5wt%) were combined with the beaded HZSM-5 catalyst at different ratios to see if the nickel carbon based catalyst increased production of hydrocarbons.