A two-step process was investigated for pretreatment and fractionation of rice straw. The two-step fractionation process involves first, soaking rice straw in aqueous ammonia (SAA) in a batch reactor to recover lignin-rich hydrolysate. This is followed by a second-step treatment in a fixed-bed flow-through column reactor to recover xylooligomer-rich hydrolysate. The remaining glucan-rich solid cake is then subjected to an enzymatic process. In the first variant, SAA treatment in the first step dissolves lignin at moderate temperature (60 and 80 oC), while in the second step, hot-water treatment is used for xylan removal at higher temperatures (150~210 oC). Under optimal conditions (190 oC reaction temperature, 30 min reaction time, 5.0 ml/min flow rate, and 2.3 MPa reaction pressure), the SAA-hot-water fractionation removed 79.2% of the lignin and 63.4% of the xylan. In the second variant, SAA was followed by treatment with dilute sulfuric acid. With this process, optimal treatment conditions for effective fractionation of xylo-oligomer were found to be 80 oC, 12 h reaction time, solid-to-liquid ratio of 1:12 in the first step; and 5.0 ml H2SO4/min, 170 oC, and 2.3 MPa in the second step. After this two-step fractionation process, 85.4% lignin removal and 78.9% xylan removal (26.8% xylan recovery) were achieved. Use of the optimized second variant of the two-step fractionation process (SAA and H2SO4) resulted in enhanced enzymatic digestibility of the treated solid (99% glucan digestibility) with 15 FPU (filter paper unit) of CTec2 (cellulase)/g-glucan of enzyme loading, which was higher than 92% in the twostep fractionation process (SAA and hot-water).

Soaking in Aqueous Ammonia (SAA) Lignocellulosic Material Fractionation Ammonia Lignin Xylan

Wyman CE, Dale BE, Elander RT, Holtzapple M, Ladisch MR, Lee YY, Bioresour. Technol., 96(18), 1959 (2005)
Limayem A, Ricke SC, Prog. Energy Combust. Sci., 38(4), 449 (2012)
Ko JK, Bak JS, Jung MW, Lee HJ, Choi IG, Kim TH, Kim KH, Bioresour. Technol., 100(19), 4374 (2009)
Kim TH, Chapter 6: Pretreatment of Lignocellulosic material. Bioprocessing technologies in Biorefinery for Sustainable Production of fuels, chemicals and polymers. 1st ed., John Wiley & Sons, Inc., Hoboken, NJ, USA(2003).
Kim S, Dale BE, Biomass Bioenerg., 26(4), 361 (2004)
Kim SB, Lee SJ, Lee JH, Jung YR, Thapa LP, Kim JS, Um Y, Park C, Kim SW, Biotechnol. Biofuels, 6, 109 (2013)
Binod P, Sindhu R, Singhania RR, Vikram S, Devi L, Nagalakshmi S, Kurien N, Sukumaran RK, Pandey A, Bioresour. Technol., 101(13), 4767 (2010)
Zheng Y, Pan Z, Zhang R, Int. J. Agric. Biol. Eng., 2, 51 (2009)
Won KY, Um BH, Kim SW, Oh KK, Korean J. Chem. Eng., 29(5), 614 (2012)
Kim TH, Korean J. Chem. Eng., 28(11), 2156 (2011)
Koukios EG, Valkanas GN, Ind. Eng. Chem. Prod. Res. Dev., 21, 309 (1982)
Kim TH, Lee YY, Sunwoo C, Kim JS, Appl. Biochem. Biotechnol., 133(1), 41 (2006)
Zhao XQ, Zi LH, Bai FW, Lin HL, Hao XM, Yue GJ, Ho NWY, Adv. Biochem. Engin/Biotechnol., 128, 25 (2012)
Joshi B, Bhatt M, Sharma D, Joshi J, Malla R, Sreerama L, Biotechnol. Molec. Biology Rev., 6(8), 172 (2011)
Harmsen PFH, Huijigen WJJ, Lopez LMB, Bakker RRC, “Literature Review of Physical and Chemical Pretreatment Processes for Lignocellulosic Material,” Energy research Centre of the Netherlands, ECN-E-10-013(2010).
Chen F, Dixon RA, Nat. Biotechnol., 25(7), 759 (2007)
Kim TH, Korean J. Chem. Eng., 29(1), 82 (2012)
Kim TH, Lee YY, Appl. Biochem. Biotechnol.,, 124, 1119 (2003)
Kim TH, Lee YY, Appl. Biochem. Biotechnol., 136-140, 81 (2007)
NREL, “Determination of Structural Carbohydrates and Lignin in Biomass,” NREL/TP-510-42618, 2008. National Renewable Energy Laboratory, Golden, CO, USA(2008).
NREL, “Measurement of Cellulase Activities,” NREL/TP-510-42628, 2008. National Renewable Energy Laboratory, Golden, CO, USA (2008).
NREL, “Enzymatic Saccharification of Lignocellulosic Material,” NREL/TP-510-42629, 2008. National Renewable Energy Laboratory, Golden, CO, USA(2008).
Kabel MA, Bos G, Zeevalking J, Voragen AGJ, Schols HA, Bioresour. Technol., 98(10), 2034 (2007)
Kim TH, Lee YY, Bioresour. Technol., 97, 224 (2003)
Yoo CG, Lee CW, Kim TH, Appl. Biochem. Biotechnol., 164(6), 729 (2011)
Shrestha R, Hur O, Kim TH, Korean Chem. Eng. Res., 51(3), 335 (2013)