Chemical Pretreatments of Corn Stover for Enhancing Enzymatic Digestibility

Abstract

Corn stover, the most abundant agricultural residue in Hungary, is a potential raw material for the production of fuel ethanol as a result of its high content of carbohydrates, but a pretreatment is required for its efficient hydrolysis. In this article, we describe the results using various chemicals such as dilute H2SO4, HCl, and NaOH separately as well as consecutively under relative mild conditions (120 degrees C, 1 h). Pretreatment with 5% H2SO4 or 5% HCl solubilized 85% of the hemicellulose fraction, but the enzymatic conversion of pretreated materials increased only two times compared to the untreated corn stover. Applying acidic pretreatment following a 1-d soaking in base achieved enzymatic conversion that was nearly the theoretical maximum (95.7%). Pretreatment with 10% NaOH decreased the lignin fraction >95%, increased the enzymatic conversion more than four times, and gave a 79.4% enzymatic conversion. However, by increasing the reaction time, the enzymatic degradability could also be increased significantly, using a less concentrated base. When the time of pretreatment was increased three times (0.5% NaOH at 120 degrees C), the amount of total released sugars was 47.9 g from 100 g (dry matter) of untreated corn stover.

Application of Response Surface Methodology to Optimize Alkali Concentration, Corn Stover Particle Size, and Extruder Parameters for Maximum Sugar Recovery

“…Although large corn stover particles was used in the present study, the glucose and xylose recovery obtained in this study was comparable with most of the alkali pretreatments listed in the table. However, the result of present study was higher than the values reported for alkali (Varga et al, 2002), wet oxidation (Varga et al, 2003), aqueous ammonia soaking pretreatment , lime and alkali pretreatment ). Rodgers et al (2009) achieved higher glucose and xylose yield than the current study.…”

“…The sugar recovery obtained in the present study was comparable with that of the 88-93% glucose reported for dilute acid pretreatment at 140°C with 0.98% H 2 SO 4 for 40 min (Lloyd & Wyman, 2005), more than 95% glucose and 77% xylose from the dilute acid percolation process at 180°C with 1% acid (w/w) at a flow rate of 10 mL/min for 3 min, followed by N 2 through quenching (Zhu et al, 2004). Varga et al (2002) obtained 95.7% glucose when corn stover was pretreated with 1% NaOH for a day followed by a 60 min autoclaving with 1% H 2 SO 4 . A similar result was reported from compressed hot water pretreatment of corn stover at 200°C with a flow rate of 10 mL/ min for 24 min (Liu & Wyman, 2005).…”

“…Karunanithy and Muthukumarappan (2011a) achieved 85.7, 87.5, and 86.3% of glucose, xylose, and combined sugar recovery, respectively for the optimized pretreatment condition of 180°C barrel temperature, 155 rpm screw speed, 20% wb moisture content, and corn stover particle size 8 mm. The literatures report a sugar recovery of more than 90% or near quantitative using dilute acid (Lloyd & Wyman, 2005;Yan et al, 2009;Zhu et al, 2004Zhu et al, , 2005, lime (Kim & Holtzapple, 2005 ), compressed hot water (Liu & Wyman, 2005), steam pretreatment (Bura et al, 2009), steam explosion Tucker et al, 2003), a combination of acid and alkali (Varga et al, 2002), ammonia recycle process and AFEX (Chundawat et al, 2007). These results show that there still is room to improve sugar recovery from corn stover when pretreated in extrusion in combination with other pretreatment methods.…”

Process Modeling of Enzymatic Hydrolysis of Wet-Exploded Corn Stover

“…Optimal process conditions for enzymatic hydrolysis to high glucose included both high SC and low enzyme loading. This is a remarkable improvement over previous studies done with pretreated corn stover either at low SC (<10 %) or high enzyme loading (>10 FPU, equivalent to 30 mg EP/g glucan) to achieve higher cellulose conversion [5,6,18,19]. By increasing the SC, the glucose yield improved significantly.…”

The effects of boron derivatives as pretreatment chemicals for biodegradation of sunflower stalks

“…Gaspar et al (2005) and Wang et al (2010) reported 95 % lignin removal for corn fiber (2,5 % conc.,121 °C, 60 min) and 86 % removal for bermuda grass (3 % conc., 121 °C, 90 min), respectively. The higher lignin removal (95 %) for corn stover reported by Varga et al (2002) might be attributed to the higher NaOH concentration (10 %). In the present study, the NaOH concentration was limited to 2 %.…”