Location: Bioproducts ResearchTitle: Valorization of guayule as a feedstock for lignocellulosic biorefineries using ammonia fiber expansion (AFEX) pretreatment) Author
Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2011
Publication Date: 8/19/2011
Citation: Chundawat, S.P.S., Chang, L., Gunawan, C., Balan, V., Mcmahan, C., Dale, B.E. 2012.Guayule as a feedstock for lignocellulosic biorefineries using ammonia fiber expansion (AFEX) pretreatment. Industrial Crops and Products. 37: 486-492. Interpretive Summary: Guayule (Parthenium argentatum), a woody desert shrub indigenous to the southwestern USA, produces high molecular weight natural and has entered the commercial arena as an alternative material for the manufacture of a range of rubber products. Latex extraction leaves ~90% of the crop biomass as a finely-divided, free flowing feedstock suitable for conversion to biofuels. Advantages of guayule bagasse include that the agricultural and harvest costs are borne by the primary product (natural rubber) production, it is relatively high in density, high in energy content (21,000 kJ/kg), can be used for both biochemical and thermochemical processes, and is harvested 12 months/year. Our collaborative research is exploring several avenues to bio-energy, including biochemical and thermochemical conversion. In this study, the use of a specialized biomass pre-treatment, Ammonia Fiber Expansion (AFEX) was studied. Pre-treatment of ground guayule shrub or residues with high pressure, temperature, and pH results in improved efficiency for conversion of the biomass to simple sugars. Use of guayule crop residues to produce bio-energy could have a major impact on sustainability of this new industrial crop.
Technical Abstract: Natural rubber latex extraction from guayule leaves behind greater than 80% (by weight) of agricultural residue as a feedstock suitable for conversion to biofuels via a thermochemical or biochemical route. Untreated guayule shrub and bagasse (after latex extraction) has shown to be very recalcitrant to enzymatic hydrolysis, necessitating application of a chemical pretreatment to enhance cellulase accessibility. Ammonia fiber expansion (AFEX) pretreatment was found to substantially improve overall enzymatic digestibility by 4-20 fold for both untreated guayule shrub and latex-extracted bagasse. Maximum glucan and xylan conversion achieved for the latex-extracted bagasse was 40 and 50%, respectively. Saccharomyces cerevisiae (424A strain) was readily able to ferment both glucose and xylose to ethanol from the guayule bagasse hydrolyzate with or without external nutrient supplementation. Our results highlight the possible valorization for guayule derived biomass as a feedstock for lignocellulosic refineries co-producing natural rubber latex and biofuels. However, further process improvements (e.g., lignin extraction and cellulose decrystallization during AFEX) are necessary to increase the effectiveness of ammonia-based pretreatments for further enhancing enzymatic digestibility of guayule-derived hardwood biomass.