Energy-dense liquid fuel intermediates by pyrolysis of guayule (Parthenium argentatum) shrub and bagasse Akwasi A. Boateng a, * , Charles A. Mullen a , Neil M. Goldberg a , Kevin B. Hicks a , Colleen M. McMahan b , Maureen C. Whalen b , Katrina Cornish c a Eastern Regional Research Center, Agricultural Research Service, US Department of Agriculture, 600 E. Mermaid Lane, Wyndmoor, PA 19038, United States b Western Regional Research Center, Agricultural Research Service, US Department of Agriculture, 800 Buchanan Street Albany, CA 94710, United States c Yulex Corporation, 37860 W. Smith-Enke Road, Maricopa, AZ 85238, United States article info Article history: Received 4 September 2008 Received in revised form 1 May 2009 Accepted 26 May 2009 Available online 12 June 2009 Keywords: Pyrolysis Bio-oil Guayule Biofuels and bioenergy abstract Guayule is a perennial shrub grown in the southwestern United States that is used to produce high qual- ity, natural rubber latex. However, only about 10% of the plant material is used for latex production; the remaining biomass, called bagasse, can be used for renewable fuel production. Fast pyrolysis of guayule, both whole shrub and bagasse was performed. From both feedstocks a very viscous, high energy content (30 MJ/kg) pyrolysis liquid (bio-oil) was produced in yields averaging over 60% without any catalyst. The properties and compositions of the bio-oils were found to be similar in the two feedstocks. Co-prod- ucts, charcoal (20–30 wt%) and non-condensable gas (5–15%), were also dense and had a high energy content. Of the two feedstocks, the whole shrub yielded higher quantities of charcoal that also had a higher energy content than the charcoal produced from bagasse. As a result, the energy recovery, esti- mated as the percentage of the energy products, to energy input into the reactor was lower (60%) for gua- yule bagasse than for the whole shrub (73%). This notwithstanding, the bagasse is a more attractive feedstock for thermochemical conversion, not only because it is a residue from a primary process (latex extraction) that is on-site, but also because it has a high energy content. Moreover, it produces high qual- ity pyrolysis products. Co-production of latex rubber from the whole shrub and renewable fuels from the residual bagasse by pyrolysis should improve the already positive economics of the guayule latex rubber industry. Published by Elsevier Ltd. 1. Introduction Guayule (Parthenium argentatum), is a hardwood desert shrub native to the Chihuahuan desert of Texas and North Central Mexico that biosynthesizes high quality natural rubber. Recent commer- cial success in producing guayule latex has resulted in guayule’s re-introduction as a new crop in the United States. Prior efforts (pre 1990s) to commercialize guayule had been abandoned be- cause production of solid/bulk rubber from guayule was not eco- nomically competitive with imported Hevea latex [1]. Latex use is widespread in medical and personal hygiene products; however, products containing Hevea latex can cause life-threatening allergic reactions. The relativity recent discovery that guayule latex is safe for people with Type I latex allergy [2–4] sparked new interest in guayule production and research and added value. Because only about 10% of the guayule biomass is used for latex, sustainable commercialization of guayule would be further improved with in- come derived from co-products [1]. With the recent interest in renewable sources of energy, fuel produced from conversion of the residual biomass after latex extraction could be an important co-product. Latex is extracted from guayule shrubs by an alkaline aqueous extraction process, throughout which the extracted rubber is maintained as a stable emulsion [3,4]. In this process, extraction of rubber from guayule shrubs (usually harvested just above the ground) leaves a finely-divided, solid biomass residue (guayule ba- gasse), made up mostly of cellulose, hemicellulose, lignin, and re- sin. Resin, a complex mixture including terpenes, sesquiterpenes, and fatty acid compounds, can be extracted from the bagasse or the whole plant [5], and may be used as a plastic binder, adhesive, or wood treatment for insect control [1]. The bagasse, with or with- out resin, can be used in plastic composite materials [6] and for soil amendment. It has also been proposed as a source of bioenergy. Because of the drive to reduce the use of fossil fuels, the bioen- ergy proposition has sparked great interest. Previously, guayule has been used as an energy source in the form of fireplace logs [7] and pelletized fuel by blending with cotton gin trash [1]. How- ever, few reports on conversion of guayule to liquid fuels exist with 0016-2361/$ - see front matter Published by Elsevier Ltd. doi:10.1016/j.fuel.2009.05.023 * Corresponding author. Tel.: +1 215 233 6493; fax: +1 215 233 6406. E-mail address: akwasi.boateng@ars.usda.gov (A.A. Boateng). Fuel 88 (2009) 2207–2215 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel