EFFECT OF PRETREATMENT CONDITIONS ON STRUCTURAL CHARACTERISTICS OF WHEAT STRAW

Abstract

Structural characteristics of lignocellulosic biomass such as surface area, pore volume, crystallinity, hemicellulose, and lignin content significantly affect the yield of fermentable sugars for bioethanol production. In the present work, the effect of dilute acid pretreatment was studied on structural characteristics of wheat straw, using different combinations of process variables (temperature, time, and acid concentration). Pretreated wheat straw (PWS) exhibited higher available surface area and pore volume along with low hemicellulose and lignin content. Crystallinity index (CrI) of biomass at different pretreatment conditions showed an increased trend followed by sharp decrease at high temperature (190°C) conditions. Maximum increase in surface area (7.1 m²/g compared to 4.0 m²/g for untreated wheat straw) was obtained at pretreatment conditions of 180°C temperature, 0.5% (v/v) acid, and 7 min time. SEM imaging of biomass revealed that pore breaking, compression of pores, and partial pore blocking in the case of high temperature (190°C) pretreatment conditions may be the reason behind decreased surface area of biomass. FT-IR analysis showed almost complete hemicellulose removal and acid-soluble lignin removal after dilute acid pretreatment but insufficient removal of acid insoluble lignin.

[Supplementary material is available for this article. Go to the publisher's online edition of Chemical Engineering Communications for the following free supplemental resource: figure showing XRD pattern of biomass with respect to different pretreatment conditions.]

Keywords:

• Crystallinity
• Pretreatment
• Structural characteristics
• Surface area
• Wheat straw

Acknowledgments

The authors acknowledge Natural Sciences and Engineering Research Council of Canada (NSERC), Agricultural Biorefinery Innovation Network (ABIN), and Canada Research Chair (CRC) for their financial support for the study. The authors also acknowledge Heli Eunike, Richard Blondin, and Siddharth Mohanty for their help in the analysis part.

Notes

^a BET surface area was measured using nitrogen adsorption isotherm at −196°C.

^b Single-point pore volume of pores less than 1135 Å diameter at P/P _O  = 0.9826.

^c CrI is a measure of crystalline material in biomass.

*Values taken from Dhabhai et al. (2012).