Pretreatment of Wheat Straw by Liquid Hot Water and Organosolv Processes

Wheat straw was subjected to liquid hot water (LHW) and ethanol organosolv (EOS) pretreatment in order to find optimum treatment conditions. The results were then used further to quantify the influence of the utilization of ethanol in the treatment liquor on the sugar and lignin yields. The data was collected in two experimental works (the one LHW, the other EOS) which were carried out independently. Both were constructed as Central Composite experimental designs, which should cover most of the applicable treatment conditions. In the LHW experiments, residence time and temperature were varied, while in the EOS experiments the water-ethanol ratio was also varied. The resulting slurry fractions were analyzed for dry matter content, the liquid fractions were centrifuged and analysed for dry matter content, solubilized sugars and sugar degradation products. The amount of solubilised lignin was then estimated from these measurements under the assumption that the dry matter in the obtained liquor consisted of solubilised sugars, their degradation products, lignin and unspecified other residue. Lignin solubilisation was between 6.2 % and 22.8 % of lignin present in the initial biomass in the LHW process, and between 9.2 % and 31.6 % in the EOS process. The EOS centerpoint combination of temperature and time was used in both experimental plans, (180 degrees C, 60 min), so the influence of ethanol could be investigated. Statistics proved that significantly more lignin was solubilised by the EOS treatment (22.1 % opposed to 6.2 %). On the other Hand, the average amount of sugars solubilised by the EOS treatment was only 0.9 % of the sugars in the biomass, opposed to 5.7 % solubilised by LHW treatment. The results show that using a water-ethanol mixture improves selectivity in the pretreatment process. This could aid in downstream fractionation and production of value-added chemicals. Another observed advantage of the organosolv treatment is that apparently no sugars were degraded to Furfural or HMF, since these could not be detected in the liquors obtained in EOS experiments.