Production of bermudagrass for bio-fuels: effect of two genotypes on pyrolysis product yield

Authors: Boateng, Akwasi; Anderson, William - Bill; Phillips, John

Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2006
Publication Date: 12/29/2006
Citation: Boateng, A.A., Anderson, W.F., Phillips, J.G. 2007. Production of bermudagrass for bio-fuels: effect of two genotypes on pyrolysis product yield. Energy and Fuels 21, p.1183-1187.

Interpretive Summary: There are two approaches to convert biomass materials including grasses to energy carriers such as liquid transportation fuels like ethanol and intermediate combustible gases (syngas) which can themselves be burned or, in turn, be converted to liquids. The former involves processes that include fermentation and the latter is by thermally heating the biomass in an absence of oxygen or air (pyrolysis). It is thought that the type of biomass and its maturity can have an affect on the yields of the conversion platforms. Bermudagrass is considered a potential feedstock for biofuel production so we investigated the effect of two major genotypes, Coastal and Tifton-85, and plant part, leaf or stem harvested at the same time on pyrolysis products. No significant effect of these characteristics on pyrolysis yields was found although others have reported Tifton-85 to yield 12% more ethanol than Coastal with fermentation. Rather, there was significant effect of temperature on pyrolysis yields. The study shows that when bermudagrass is harvested at the same maturity, the genotype and plant part may not have any significant effect on the produced gas yield, its heat content, and char yield. The results may be beneficial to farmers who intend to grow bermudagrass for use as biomass for biofuel.

Technical Abstract: Bermudagrass is the perennial grass used as forage for livestock and harvested as hay on 10 to 15 million acres in Southern United States. It has potential as an energy crop for the production of biofuels through the lignocellulosic conversion program. Coastal was released in 1943 and was the primary forage genotype until the development of Tifton-85 which has greater yield and quality for ruminants. Pyrolysis of these two genotypes harvested at the same maturity and separated into leaf and stem was carried out to establish their effect on the yield of pyrolysis products. The pyrolysis was carried out in an analytical pyrolysis-gas chromatography system at the 500, 700, and 900 deg C temperatures. The non-condensable gas yielded, comprising CO, CO2, H2 and low molecular weight hydrocarbons, was estimated between 10 and 12.5 wt%. The char yielded ranged between 5.5 and 16 wt% with remainder, comprising condensable aerosols that constitute to bio-oils when condensed, was 73-82 wt% estimated by difference. Statistical analysis of variance showed no significant difference between pyrolysis products due to genotype or whether the sample was leaf or stem. However, there was a strong significant difference between yields due to pyrolysis temperature with the maximum gas yield and minimum char yield occurring at 900 deg C. The calorific value of the gas reached 2300-2500 kcal/kg for both genotypes, about 20-25% of the heating value of natural gas. The study helps to ascertain that when harvested at the same maturity, the effect of bermudagrass genotype and plant part on pyrolysis gas and char yields may not be significant during thermochemical conversion. However, the condensable liquids were not analyzed.