Bioethanol from Lignocellulosic Biomass - Biotechnology in China: Biofuels and Bioenergy - page 26

Contents

1 Introduction.......................................................................................................................... 26

2 Understanding Lignocellulosic Biomass ............................................................................ 27

2.1 Cellulose...................................................................................................................... 28

2.2 Hemicelluloses ............................................................................................................ 28

2.3 Lignin .......................................................................................................................... 29

2.4 Other Components ...................................................................................................... 30

3 Pretreatment ......................................................................................................................... 32

3.1 Physical Pretreatment ................................................................................................. 32

3.2 Chemical Pretreatment ............................................................................................... 34

3.3 Solvent Pretreatment................................................................................................... 36

3.4 Biological Pretreatment .............................................................................................. 37

4 Enzymatic Hydrolysis of Cellulose and Co-Fermentation of C5 and C6 Sugars ............ 37

4.1 Strategies for Hydrolysis and Fermentation .............................................................. 38

4.2 Strain Development .................................................................................................... 42

4.3 Process Integration and Optimization ........................................................................ 45

5 Conclusions.......................................................................................................................... 48

References.................................................................................................................................. 48

1 Introduction

Although the historical production of fermented beverages and alcohol in China
dates back to 2000 years ago in the Han Dynasty, fuel ethanol production is a
recent event in China that was initiated 10 years ago by the government to offset
the rapidly enlarging gap between the country's crude oil consumption, driven up
by its rapid economic growth, and dwindling domestic reserves and production.
The first fuel ethanol plant was put into operation in August 2003 in Jilin Province,
in the northeast of China, with corn as the feedstock. Currently, there are five fuel
ethanol producers across the country, producing 1.52 million tons of fuel ethanol
annually from starch-based feedstocks including corn, wheat and cassava. Taking
into account the country's large population and dwindling arable land due to rapid
urbanization, it is apparent that current fuel ethanol production is not sustainable.
On the other hand, as one of the major grains producers in the world, agri-
cultural residues are abundantly available in China, with an estimated 600-700
million tons produced annually [ 1 ]. Since no economically viable technologies are
available for their conversion, most is burned by farmers in the field, not only
polluting the environment, but also causing other problems such as the disruption
of air transportation by smoke clouds in the sky [ 2 ]. It has been acknowledged
worldwide that agricultural residues are one of the best choices to replace grains
for fuel ethanol production, without endangering food security, although many
challenges still exist for their commercial conversions, due to their recalcitrance
to degradation [ 3 ] as well as their unique chemical composition. In particular,
pentose sugars contained in hemicelluloses cannot be fermented into ethanol and
CO 2 as efficiently as hexose sugars by conventional ethanologenic species like