Steam pretreatment for enzymatic hydrolysis of poplar wood: comparison of optimal conditions with and without SO₂ impregnation

Abstract

Steam refi ning of non-debarked poplar wood with SO 2 impregnation prior to steaming was investigated as pretreatment for enzymatic hydrolysis. Pretreatment conditions were varied in the range of 170 ° C -220 ° C, 3 -30 min and 0.7 -2.5 % SO 2 according to a factorial design. Predicted steaming conditions for highest carbohydrate yields after enzymatic hydrolysis were at 200 ° C, 15 min, and 2.5 % SO 2 . The yield of glucose and xylose from control tests under these conditions was 43 % representing an increase of 9 % compared to results of former experiments without SO 2 impregnation. Investigations on lignin extracted from the fi bers revealed no distinct differences between pretreatment with and without SO 2 . No sulfonation occurred by the impregnation with SO 2 . Topochemical analyses of the fi bers by cellular UV microspectrophotometry (UMSP) showed an inhomogeneous lignin distribution within the S2 of fi bers after pretreatment without SO 2 and local depositions of high UV-absorbing substances in the lumina of fi bers and parenchyma cells. The lignin distribution of fi ber cell walls after pretreatment with SO 2 was more homogeneous with a preserved fi ber network and only little amounts of deposited phenolic compounds in the lumina. Therefore, it might be concluded that the expulsion of lignin hinders the enzymes in accessing the cellulose.

Post-treatment mechanical refining as a method to improve overall sugar recovery of steam pretreated hybrid poplar

“…The overall monomeric glucose and xylose recovery was enhanced from 330 to 544 kg/tonne as a result of increasing pretreatment CS from 0.6 to 2.1. Consistent with previous studies (Schütt et al, 2013(Schütt et al, , 2011, addition of SO 2 improved the overall sugar recovery.…”

“…It can be seen that the glucan and xylan content of steam pretreated WIF ranged from 61.3% to 65.6% and from 0.2% to 2.6%, respectively. Consistent with previous work on steam pretreatment of hardwood, less WIF dry mass was recovered as pretreatment severity increased (De Bari et al, 2007;Schütt et al, 2013) as a result of more carbohydrate and lignin dissolution and/or degradation into the WSF. After steam pretreatment, no statistically significant differences in glucan and xylan content were found among S1, S2 and S3 or among S4, S5 and S6.…”

“…In the case of uncatalyzed pretreatment, acetic acid cleaved from acetyl groups in hemicellulose functions as an acid catalyst to hydrolyze hemicellulose the so called autohydrolysis mechanism (Ramos, 2003). Autohydrolysis has a reduced acidification because of limited acetic acid formation and relative weakness of the acid, resulting in a pretreatment that is mild and slow compared with acid catalyzed pretreatment (Schütt et al, 2013). As shown in Table 3, the lower pH of SO 2 catalyzed pretreatment explains the lower xylan content of SO 2 -pretreated WIF compared to those pretreated without SO 2 .…”

Selection and optimization of a suitable pretreatment method for miscanthus and poplar raw material

“…The tool of choice to gain knowledge about where there is a correlation between the parameters and degree of delignification or glucose yield after saccharification is response surface methodology (RSM) based on design of experiment. According to our knowledge, only two studies were conducted with poplar in order to identify the optimum steam explosion conditions via the design of experiments for the subsequent cellulose hydrolysis (Schütt, Puls, & Sake, ; Schütt et al, ). One study concerns the identification of optimum conditions for the organosolv pretreatment of miscanthus (Goh, Tan, Lee, & Brosse, ).…”

Determination of uronic acids and neutral carbohydrates in pulp and biomass by hydrolysis, reductive amination and HPAEC-UV

“…Delignified or steam treated biomass as well as the application of co-solvent systems enable the hydrolysis by mild enzymatic procedures, which minimize the structural modification (Dahlman et al 2000;Schütt et al 2013;Han et al 2017). According to Dahlman et al (2000), the total determined carbohydrate amounts are between 4.4% and 12.1% higher in case of enzymatic hydrolysis (EH) compared to acid hydrolysis (AH) of pulps.…”