Converting forage sorghum and sunn hemp into biofuels through dilute acid pretreatment

Abstract

Forage sorghum [Sorghum bicolor (L.) Moench], Brown Mid-Rib (SBMR) and non-BMR (SNBMR) types, and sunn hemp (Crotalaria juncea L.) are primarily used as forage and fiber crops, respectively. In this study, these crops were evaluated as feedstocks for biofuels and value added chemicals. This was achieved using dilute acid pretreatment and enzymatic hydrolysis using commercial cellulase enzymes. The highest xylose yield was observed was for SNBMR 95wt%, followed by SBMR with 91wt% at combined severity factor (CSF) 1.56 and 1.44. However, for sunn hemp the maximum xylose yield was observed at 72wt% at CSF 1.48. At harsher pretreatment conditions the xylose yield decreased in all the biomasses due to degradation. In similar fashion, the overall glucan saccharification yield after enzymatic hydrolysis for SNBMR was found to be 90wt% followed by SBMR 84wt% at CSF 1.47, and 1.24. For sunn hemp it was observed to be 68wt% at CSF 2.06. This was mainly due to the high crystallinity index of sunn hemp as compared with that of sorghum. In addition the FTIR and 1H NMR, 13C NMR analysis did not prove any major variation in the individual functional groups or chemical structures in these raw and pretreated biomasses. Overall, from the results it can be concluded that SBMR and SNBMR have better potential for biofuel production as compared with sunn hemp biomass.