(532a) Comparisons of SPORL and Dilute Acid Pretreatments for Sugar and Ethanol Productions From Aspen

Authors: 
Zhu, J. Y., USDA Forest Service, Forest Products Laboratory
Tian, S., Capital Normal University
Zhu, W., South China University of Technology
Gleisner, R., University of Wisconisn, Madison
Pan, X., University of Wisconsin-Madison


This study reports comparative evaluations of sugar and ethanol production between sulfite (SPORL) and dilute acid (DA) pretreatments from a native aspen. All aqueous pretreatments were carried out in a laboratory wood pulping digester using wood chips at 170oC with a liquid to oven dry (od) wood ratio (L/W) of 3 at two levels of acid charge on wood of 0.56 and 1.11%. Pretreatment duration ranged from 0 to 30 min with an increment of 10 min. The only difference between corresponding SPORL and DA pretreatment was sodium bisulfite charge with 0 for DA and 1.5 or 3.0% on od wood for SPORL. Both SPORL and DA pretreatments were effective in removing hemicelluloses. SPORL removed about the double amount of lignin (20-40%) than DA did (10-20%). All substrates produced by both pretreatments (except DA with pretreatment duration of 0) had good enzymatic digestibility of over 80%. However, SPORL pretreatment produced higher enzymatic digestibility than its corresponding DA pretreatment for all the experiments conducted. As a result, SPORL produced higher glucose yield from enzymatic hydrolysis, EHGY, total sugar yield, and ethanol yield from simultaneous saccharification and fermentation (SSF) of cellulosic substrate, than its corresponding DA pretreatment did. The enzyme loading in SSF were 10 FPU cellulase/cellullose and 15 CBU beta-glucosidase/g cellulose for SSF runs. The maximum EHGY, total sugar, and ethanol yields were 442 kg/ton, 590 kg/ton, and 238 L/ton, respectively, for SPORL, vs 408 kg/ton, 543 kg/ton, and 214 L/ton, respectively, for the corresponding DA pretreatment. Both SPORL and DA pretreatment significantly reduced energy consumption for wood chip size-reduction, however SPORL was more effective than its corresponding DA pretreatment. SPORL, with the lower energy input and higher sugar and ethanol yield, produced higher sugar and ethanol production energy efficiencies than its corresponding DA pretreatment. The maximal sugar and ethanol production energy efficiency was 395 kg/GJ and 273%, respectively, for SPORL, vs 339 kg/GJ and 213% for DA. Although SPORL produced more acetic acid than the corresponding DA pretreatment, the effectiveness of SPORL pretreatment affords to use a mild pretreatment condition (such as short pretreatment duration) than DA to achieve similar sugar yield. This can help to reduce the production of other fermentation inhibitors, such as furfural and HMF, favorable to the fermentation of the pretreatment hydrolysate that mainly consists of hemicelluloses sugars.