Chunbao (Charles) Xu, Liao Baoqiang and Wei Shi

Abstract This chapter presents some recent research results on pretreatment of pine sawdust for bio-ethanol production, using organosolv extraction-based methods, combined with other methods including ultrasonic treatment, and sodium hydroxide treatment, and enzymatic hydrolysis of the pretreated pine sawdust samples. The pre­treatment efficiency (PE) and delignification efficiency (DE) of various pretreatment methods were studied. All the pretreatment methods, in particular the organosolv extraction, resulted in significant removal of lignin and hemicellulose. The results indicated that the combination of three pretreatment methods (organosolv extraction + ultrasound + NaOH) achieved the best PE (61.6 % + 1 %) and DE (86.4 % + 3 %). Enzymatic hydrolysis of pine samples treated with different pretreatment methods was comparatively studied. Glucose yields, total sugar yields, and total weight loss were obtained under various enzyme loadings (0~15.6 FPU cellulase) and reaction times (up to 48 h). The maximum glucose yield and the maximum total sugar yield were 5.8 % and 7.1 %, respectively, for un-pretreated raw pine samples, compared with 19.3 % and 22.40 % for the (organosolv extracted + ultrasound + NaOH) treated samples.

Keywords Softwood ■ Jack pine ■ Pretreatment ■ Organosolv extraction ■ Ultrasound Sodium hydroxide ■ Pretreatment efficiency ■ Delignification efficiency ■ Enzymatic hydrolysis ■ Glucose

19.1 Introduction

Fossil fuels, mainly coal, petroleum and natural gas, account to more than 80 % of the primary energy consumption in the world. The burning of fossil fuels emits around 21.3 billion tonnes of greenhouse gases (GHGs) annually. As such, it is

C. Xu (H)

Department of Chemical and Biochemical Engineering, Western University, London, ON,

N6A 5B9, Canada e-mail: cxu6@uwo. ca

B. Liao ■ W. Shi

Department of Chemical Engineering, Lakehead University, Thunder Bay,

Ontario P7B 5E1, Canada

Z. Fang (ed.), Pretreatment Techniques for Biofuels and Biorefineries, 435

Green Energy and Technology,

DOI 10.1007/978-3-642-32735-3_19, © Springer-Verlag Berlin Heidelberg 2013

strategically pivotal to pursue alternative and renewable energy sources due to the rapidly increasing demand for energy, the depleted fossil resources and the growing concerns over climate changes and energy security. The pursuit of bio-ethanol as an alternative energy source has attracted increasing interest recently.

As a typical bio-fuel, bio-ethanol is considered carbon neutral since the carbon dioxide released from combustion of ethanol produced from renewable lignocellu — losic materials is the CO2 sequestered by the plants during their growth. Bio-ethanol can be used in various ways for energy and chemicals, while more commonly as a blended fuel in gasoline. Nowadays, all gasoline engines can use up to 10 wt% ethanol blended fuel without any need of engine modification [1,2]. However, the main challenges for commercialization of the bio-ethanol technologies (particularly for the cellulosic ethanol) may be the combination of the low cost of conventional energy resources and the high biomass processing cost [1]. Compared with the con­ventional starch-based bio-ethanol manufacture, production of cellulosic ethanol using non-food lignocellulosic feedstock is advantageous as it does not compete with the food industry for feedstocks. Typical feedstock for cellulosic bio-ethanol production includes crop residues, grasses, forest biomass and waste, such as saw­dust and wood chips [1, 3]. Softwoods are the dominant wood species in North America. Softwoods, for example, pine and spruce, contain about 40-45 wt% cel­lulose, 20-25 wt% hemicelluloses, and 25-30 wt% lignin. Because of the structural characteristics of woody biomass (large polymeric molecules and high crystallinity) of the cell wall and the presence of hemicellulose and lignin, enzymatic hydrolysis of cellulose into glucose for bio-ethanol production is challenging due to its low ac­cessibility to enzymes. As a result, pretreatment of lignocellulosic biomass to loosen the cellulose crystalline structures and increase its accessibility is necessary, impor­tant, and the key in the bioconversion process. For instance, Zhu and his team in US Forest Service of Forest Products Laboratory reported a very high enzymatic hy­drolysis efficiency for softwood species (e. g., spruce, red pine) with combined dilute acid and sulfite pretreatment, or hot water, dilute acid or sulfite pretreatment, com­bined with disk-milling pretreatment [4-6]. With sulfite pretreatment using 8-10 % bisulfite and 1.8-3.7 % sulfuric acid on oven dry wood at 180 °C for 30 min, enzy­matic hydrolysis of spruce chips led to more than 90 % cellulose conversion at an enzyme loading of about 14.6 FPU cellulase plus 22.5 CBU в-glucosidase per gram of od substrate after 48-h hydrolysis [4]. Enzymatic hydrolysis of lignocellulosic materials into fermentable sugars can achieve a glucose yield from 10 % to 60 %, depending on the type of lignocellulosic materials [7]. There are a number of differ­ent pretreatment methods that can be generally classified into the following types: physical pretreatment, physical-chemical pretreatment, chemical pretreatment, and biological pretreatment, whose details will be overviewed as follows.