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Title: Mild pyrolysis of P3HB/Switchgrass blends for the production of bio-oil enriched with crotonic acid

item Mullen, Charles
item Boateng, Akwasi
item SCHWEITZER, DIRK - Metabolix, Inc
item SPARKS, KEVIN - Metabolix, Inc
item SNELL, KRISTI - Metabolix, Inc

Submitted to: Journal of Analytical & Applied Pyrolysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2014
Publication Date: 5/14/2014
Citation: Mullen, C.A., Boateng, A.A., Schweitzer, D., Sparks, K., Snell, K. 2014. Mild pyrolysis of P3HB/Switchgrass blends for the production of bio-oil enriched with crotonic acid. Journal of Analytical & Applied Pyrolysis. 107:40-45.

Interpretive Summary: The petroleum refinery produces a large number of products including fuels, chemicals and chemical building blocks for plastics and other materials. Because of the social and environmental issues associated with petroleum recovery, transportation and usage including energy security and climate change concerns, biobased alternatives for these products are desirable. Pyrolysis, a process where a material is heated in the absence of oxygen so it does not burn, is capable of producing bio-crude oils from non-food or feed used “cellulosic” biomass such as wood or switchgrass. These bio-crude oils can be used as feedstocks to produce bio-fuels that are indistinguishable from petroleum based fuels or used to make bio-based chemicals. Because bio-based plastic alternatives are also of interest, switchgrass that is capable of producing a bio-degradable polyester plastic, P3HB, has been developed. P3HB can also be pyrolyzed and one of the products is crotonic acid, a chemical that can be converted to many other valuable chemicals, which could replace some produced form petroleum. Therefore in an effort to produce bio-crude oil and crotonic acid for use as a bio-based chemical feedstock we studied the pyrolysis of physical mixtures of switchgrass and P3HB as a model system for genetically-modified switchgrass that produces P3HB. We found that we could simultaneously produce bio-crude oil and crotonic acid. Crotonic acid yields were maximized at 45% of the input P3HB. The fractionation of the bio-crude oil and crotonic acid was also studied and the results will be used towards producing a collection system that could collect a more pure form of crotonic acid from pyrolysis of such a mixture. This information is important to those designing pyrolysis based biorefinery processes for the production of both biofuels and biobased chemicals.

Technical Abstract: The mild pyrolysis of switchgrass/poly-3-hydroxybutyrate (P3HB) blends that mimic P3HB-producing switchgrass lines was studied in a pilot scale fluidized bed reactor with the goal of simultaneously producing crotonic acid and switchgrass-based bio-oil. Factors such as pyrolysis temperature, residence time, flow rates and particle size of the P3HB were studied for their effects on the recovery of crotonic acid as a component of the pyrolysis oil produced from the mixture. Crotonic acid yields were maximized at 45 wt% of the input P3HB by using small P3HB particles and pyrolysis temperature of 375 °C. The remaining components of the liquid product were similar to those produce via fast pyrolysis of switchgrass alone. Fractional collection within the condensation system of the pyrolysis process development unit PDU did not significantly fractionate crotonic acid more than the total liquids collected. Concentrations of 6-10 wt% crotonic acid in the liquids were found in all factions and crotonic acid was effectively collected by both condensation and electrostatic precipitation suggesting that pyrolysis of P3HB produces crotonic acid in both gas and aerosol phases.