AUTOHYDROLYSIS AND ACID HYDROLYSIS OF OLIVE-TREE PRUNING DEBRIS. FERMENTATION BY DEBARYOMYCES HANSENII TO OBTAIN ETHANOL AND XYLITOL

摘要

Debris from olive-tree pruning represents a great volume of residual biomass in Spain, where annualrnproduction reaches 4.0 million tonnes, from which chemical, fuel and biological products can be developed. Therneconomic feasibility of the process involves making use of the entire debris in its three main fractions: hemicellulose,rncellulose and lignin. In this study we have studied the main factors that affect to the autohydrolysis processrn(temperature, time and acid concentration) as well as the influence of the hydrolytic agent concentration in the acidrnhydrolysis of the olive-tree pruning debris. Subsequently the obtained hydrolizates were fermented by Debaryomycesrnhansenii (NRRL Y-7426) to produce ethanol and xylitol. The autohydrolysis experiments were performed on a batchrnstainless reactor and the acid hydrolysis experiments were performed using hydrochloric acid in concentrationsrnranging from 0.1 to 1.0 kmol/m~3, a temperature of 90 ℃, and a time of 180 min. The fermentation experiments werernconducted on a laboratory scale in a batch-culture bioreactor at pH 4.5 and 30 ℃. We have verified that the betterrnconditions for time, temperature and acid concentration during the autohydrolysis process were 0 min, 200℃ andrn0.025 kmol/m~3 of sulphuric acid respectively (severity factor, log Ro = 3.4). On the other hand, we have assayed thernhydrolysis of all the autohydrolysis matter and just the solid residue, concluding that it is more interesting to carry out all the starting material because of the greater monosaccharides yields.