A Critical Review on the Various Pretreatment Technologies of Lignocellulosic Materials

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 925-935

J. Environ. Treat. Tech.

ISSN: 2309-1185

Journal weblink: http://www.jett.dormaj.com

A Critical Review on the Various Pretreatment

Technologies of Lignocellulosic Materials

Amirreza Talaiekhozani , Shahabaldin Rezania

Department of Civil Engineering, Jami Institute of Technology, Isfahan, Iran

Department of Environment and Energy, Sejong University, Seoul 05006, South Korea

Received: 12/01/2020

Accepted: 11/06/2020

Published: 20/09/2020

Abstract

Nowadays, finding new sources of renewable energy is an absolutely essential need for human. Production of biofuel is a

suitable way to find such a renewable energy source. Pretreatment is considered as an important step for biofuel production.

The aim of this study was to collect recent achievements in pretreatment techniques to have a comprehensive and precious

source about this topic. In this study many pretreatment techniques: microwaves, biological, alkaline, ionic liquid, organic

solvent, acidic, mechanical, pyrolysis, steam, wet oxidation, ammonia fiber explosion and liquid hot techniques have been

introduced. Although several new techniques have been developed to pretreatment of lignocellulosic biomasses, many

obstacles are still needed to be overcome to use these techniques for industrial application.

Keywords: Lignocellulosic biomass, Pretreatment, Biofuel production, Energy production

Table of Contents

Introduction ........................................................................................................................................................................925

Effecting parameters...........................................................................................................................................................926

.1 Delignification ............................................................................................................................................................926

.2 Enzymatic hydrolysis...................................................................................................................................................928

Types of pretreatments........................................................................................................................................................928

.1 Microwave assisted technique.....................................................................................................................................928

.2 Alkaline technique.......................................................................................................................................................929

.3 Ionic liquid technique..................................................................................................................................................929

.4 Organic solvent technique...........................................................................................................................................930

.5 Acid technique.............................................................................................................................................................930

.7 Biological technique ...................................................................................................................................................930

.8 Mechanical techniques................................................................................................................................................931

.9 Pyrolysis .....................................................................................................................................................................931

.10 Steam pretreatment ...................................................................................................................................................931

.11 Liquid hot water...................................................................................................................................................932

.12 Wet oxidation .......................................................................................................................................................932

.14 Ammonia fiber explosion......................................................................................................................................932

Conclusion and future recommendation .............................................................................................................................932

References..............................................................................................................................................................................932

Introduction

Energy demand is increased every day by developing

biofuels production such as biohydrogen, biogas, and

bioalcohols is necessary. Lignocellulosic biomasses are

inexpensive and abundance; therefore, these types of

biomasses are attractive to be used as row materials for

biofuel production (6). Raw lignocellulosic biomass

cannot easily used for biofuel production due to

existence of some recalcitrant compounds and very

complex structure (7). Consequently, pretreatment is so

important to have a fast and efficient conversion of

lignocellulosic biomasses to final products. Several

futures have been introduced for an ideal pretreatment

technique such as feasible and effective with high solids

loadings, lower energy demand and moderate cost,

preserving solubilized carbohydrates, avoiding formation

of inhibitors to the subsequent fermentation step,

industries (1). Nowadays, fossil fuels are considered as

main source of energy worldwide (2). Since fossil fuels

are not renewable, many studies have been carried out to

find alternative energy sources (3). Therefore,

lignocellulosic biomass conversion to biological fuels

has attracted a huge amount of scientist’s attention (4).

Pretreatment process is the first stage for biomass

conversion to biofuel. Many studies reported the

importance of pretreatment step on biofuel production

processes (5). The well-known technique for biomass

pretreatment is thermochemical technique. This

techniques is faced whit several economic,

environmental, and technical difficulties. That is why

finding more appropriate pretreatment techniques for

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 925-935

producing highly digestible feedstock, and little or no

biomass size reduction (8). Although many pretreatment

techniques have been developed by scientists, there is no

technique that to have all the above mentioned futures.

Various developed techniques for pretreatment of

lignocellulosic biomass have been categorized in Figure

cultivation of this plant is faced with several difficulties

(24). Based on the above mentioned explanations, it is

necessary to find an alternative way to produce biofuels.

Lignocellulosic biomasses including cereal straws which

are widely cultivated worldwide may consider as a

suitable feedstock for biofuel production. Cereal straws

are usually burned by farmers which produces a large

amount of air pollutants (25). Several inexpensive

lignocellulosics agricultural waste are accessible such as

wheat straw, rice straw, softwood, switch grass, salix,

willow, timber species, rice hull, and sugarcane baggase

as a feedstock for biofuel production. In some countries

that have a wide agricultural activities the agricultural

wastes have a good potential to produce biofuels.

Different biofuel production yields can be obtained using

various crops. The cost of biofuel production depends on

the cost of agricultural wastes, transportation method of

agricultural wastes from farms to factories, and

processing technology. Also, government policies about

biofuel production can be considered as an influential

factor on biofuel cost. The cost of biofuel production and

market price are other factors which are effective on final

biofuel cost. Seasonal availability of agricultural wastes

depend on the type of it; for example cotton stalk is

available between January and March whereas maize

stalk is available from August and December.

Information about seasonal availability of agricultural

wastes is very important to guarantee the feedstock

availability all over the year for the biofuel factory. The

most important part of plant cell wall is composed of

lignocellulos. Lignocellulos is a natural and complex

composite including lignin, hemicellulose, and

biopolymers— cellulose (26, 27). Some other materials

such as ash can be found herewith lignocellulosic

biomass. Lignocellulosic biomass is a heterogeneous

composite of lignin and carbohydrate polymers which

contains up to 75% of carbohydrates (based on dry

weight) (24). Lignocellulosic biomass contains complex

sugars; therefore, it is not readily converted to biofuel.

Also, it is contains several polysaccharides including

hemi-cellulose and cellulose which require to be

converted to the monosaccharide. Lignin, hemicellulose,

and Cellulose are strictly associated with each other so

this association can almost stop the access to the

hydrolytic agents. The lignin should be eliminated or

modified to access the hydrolytic agents using different

chemical or biological techniques (28). Cellulose