Bermudagrass for biofuels: Effect of two genotypes on pyrolysis product yield

Bermudagrass is a perennial grass used as forage for livestock and harvested as hay on 10-15 million acres in the 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 500, 700, and 900 degrees C temperatures. The noncondensable gas yielded, comprising CO, CO2, H-2, 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 bio-oils when condensed, was 73-82 wt % estimated as the difference between the biomass and the produced gas and char. 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 effect of pyrolysis temperature on the product yields with the maximum gas yield and minimum char yield occurring at 900 degrees 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.