**3.3 Biological pretreatment**

Biological pretreatment of biomass is mostly linked to the action of enzymeproducing fungi that are able to degrade, depolymerize and cleave the cellulose, hemicellulose and the lignin contents of biomass. This pretreatment method has several advantages over other pretreatment methods including its limited or no generation of toxic substances, high yield of needed products, low energy requirements and specificity of substrate and process reaction [34, 35]. However, its major disadvantages include the fact that the process is too slow and needs careful control of conditions of fungi growth as well as the large space required to carry out the process [36]. According to Agbor et al., 2011 [37], the residence time required for biological pretreatment processes is in the range 10 and 14 days. In addition, the organic components of biomass are consumed by the microorganisms' hence biological pretreatment processes faces techno-economic challenges and are considered commercially less attractive when compared to other pretreatment methods [38–40]. The types of fungi commonly used in biological pretreatment of biomass include *brown-*, *white-* and *soft-rot fungi*, *actinomycetes* and *bacteria*. These fungi are particularly known for their removal of hemicellulose and lignin as well as for their mild effect on cellulose. Nevertheless, *white-* and *brown-rot fungi* have a variety of ways to access and degrade LCB materials such as wood, and their very strong metabolism has been applied in industrial operations. For instance, *white-* and

*brown-rot fungi* are known to have a brightening effect on kraft pulp obtained from hardwoods, with cost reductions in bleaching chemicals and potentially decreasing

**Advantages Disadvantages Reference**

• Power consumption quite high • Require additional pretreatment steps

• High cost of chemicals • Corrosion related issues with equipment • Liable to form inhibitory

• Requires long residence time (time consuming)

• Slightly degrades lignin • Very slow rate of hydrolysis • The process requires a large space • Require long residence

substances

times

[8, 25, 43, 44]

[45–47]

[36, 37, 48]

In spite of the fact that many pretreatment methods have been investigated, while others are still in their developmental stages, it is quite onerous to assess and compare pretreatment technologies. This is because most pretreatment technologies involve upstream and downstream costs associated with processing, capital investment as well as complicated chemical recycling and waste treatment systems [42]. **Table 2** presents a summary of the advantages and disadvantages of the

Heterogeneity remains an inherent characteristic of biomass. The feasibility and viability of products recovery from biomass depends upon its properties. The two main conversion pathways earlier mentioned are basically used to recover products of value from biomass. The choice of the conversion route also depends on the features of biomass hence characterization is essential to better understand quintessential physicochemical properties of biomass that will determine how suitable the material is for conversion; these properties are keys to the efficient utilization of biomass in bioconversion processes [1, 7]. However, the characteristics of biomass are largely swayed by its primary organic components (cellulose, hemicellulose and lignin), which vary depending on biomass source, species, climatic conditions, etc. Depending on the end use of biomass, characterization of biomass is commonly determined and reported in terms of proximate and ultimate analysis using a variety of analytical tools some of which are described in subsequent sections of this review. This provides vital information for evaluating various application potential of biomass, particularly its energy production potential, which also takes into

the environmental impact on paper mill operations [41].

*A summary of the advantages and disadvantages of the classes of pretreatment.*

• Simple and easy operation

handled

*Biomass Pretreatment and Characterization: A Review DOI: http://dx.doi.org/10.5772/intechopen.93607*

sugar fractions

• Simple equipment

moisture contents • Low energy requirements

hemicellulose

• Very large volumes of biomass can be

• Increases surface area and pore size • Increases bulk and energy densities • Reduces cellulose crystallinity • Does not involve the use of chemicals

• Increases accessibility to cellulose • Alters the structure of lignin • Hydrolyzes hemicellulose into various

• Efficiently degrades both cellulose and

• Suitable for both high and low biomass

different classes of biomass pretreatment.

**4. Biomass characterization**

**Pretreatment methods**

Physical pretreatment

Chemical pretreatment

Biological pretreatment

**Table 2.**

**25**

**Figure 3.**

*A schematic representation of the impact of pretreatment on the surface and internal structure of lignocellulosic biomass. Adapted from [31].*

*Biomass Pretreatment and Characterization: A Review DOI: http://dx.doi.org/10.5772/intechopen.93607*


#### **Table 2.**

nature of biomass including the structural complexity and heterogeneity of biomass, the crystalline nature of its cellulose content, and the extent of lignification [7, 28]. Throughout the chemical pretreatment process, the structural recalcitrance of LCB is disrupted, resulting in the reduction of cellulose crystallinity and depolymerization as well as the degradation of cellulose and the breakdown of lignin [29, 30]. For biochemical conversion of biomass, particularly LCB, chemical pretreatment is commonly undertaken in order to isolate the respective biopolymeric constituents of the material. **Figure 3** shows the effect of chemical

Examples of compounds that have been used for the chemical pretreatment of biomass and which had significant effect on its structure include acids, alkali,

Biological pretreatment of biomass is mostly linked to the action of enzymeproducing fungi that are able to degrade, depolymerize and cleave the cellulose, hemicellulose and the lignin contents of biomass. This pretreatment method has several advantages over other pretreatment methods including its limited or no generation of toxic substances, high yield of needed products, low energy requirements and specificity of substrate and process reaction [34, 35]. However, its major disadvantages include the fact that the process is too slow and needs careful control of conditions of fungi growth as well as the large space required to carry out the process [36]. According to Agbor et al., 2011 [37], the residence time required for biological pretreatment processes is in the range 10 and 14 days. In addition, the organic components of biomass are consumed by the microorganisms' hence biological pretreatment processes faces techno-economic challenges and are considered commercially less attractive when compared to other pretreatment methods [38–40]. The types of fungi commonly used in biological pretreatment of biomass include *brown-*, *white-* and *soft-rot fungi*, *actinomycetes* and *bacteria*. These fungi are particularly known for their removal of hemicellulose and lignin as well as for their mild effect on cellulose. Nevertheless, *white-* and *brown-rot fungi* have a variety of ways to access and degrade LCB materials such as wood, and their very strong metabolism has been applied in industrial operations. For instance, *white-* and

*A schematic representation of the impact of pretreatment on the surface and internal structure of lignocellulosic*

pretreatment on LCB.

**Figure 3.**

**24**

*biomass. Adapted from [31].*

**3.3 Biological pretreatment**

organic solvents, and ionic liquids [32, 33].

*Biotechnological Applications of Biomass*

*A summary of the advantages and disadvantages of the classes of pretreatment.*

*brown-rot fungi* are known to have a brightening effect on kraft pulp obtained from hardwoods, with cost reductions in bleaching chemicals and potentially decreasing the environmental impact on paper mill operations [41].

In spite of the fact that many pretreatment methods have been investigated, while others are still in their developmental stages, it is quite onerous to assess and compare pretreatment technologies. This is because most pretreatment technologies involve upstream and downstream costs associated with processing, capital investment as well as complicated chemical recycling and waste treatment systems [42].

**Table 2** presents a summary of the advantages and disadvantages of the different classes of biomass pretreatment.

#### **4. Biomass characterization**

Heterogeneity remains an inherent characteristic of biomass. The feasibility and viability of products recovery from biomass depends upon its properties. The two main conversion pathways earlier mentioned are basically used to recover products of value from biomass. The choice of the conversion route also depends on the features of biomass hence characterization is essential to better understand quintessential physicochemical properties of biomass that will determine how suitable the material is for conversion; these properties are keys to the efficient utilization of biomass in bioconversion processes [1, 7]. However, the characteristics of biomass are largely swayed by its primary organic components (cellulose, hemicellulose and lignin), which vary depending on biomass source, species, climatic conditions, etc. Depending on the end use of biomass, characterization of biomass is commonly determined and reported in terms of proximate and ultimate analysis using a variety of analytical tools some of which are described in subsequent sections of this review. This provides vital information for evaluating various application potential of biomass, particularly its energy production potential, which also takes into


materials and how these components affect the thermochemical conversion process

The FTIR technique relies on the fact that most organic materials absorb light within the IR region of the electromagnetic spectrum. The frequency of absorption of light is measured in wave numbers that is typically in the range 4000–600 cm�<sup>1</sup>

To the best of the author's knowledge, the X-ray diffraction (XRD) is the only analytical instrument able to reveal comprehensive structural information of materials. Structural information that can be obtained includes *chemical composition*, *deformation*, *crystal structure*, *crystal size* and *orientation* as well as *layer thickness*. This

nanomaterials. The XRD is equally a valuable analytical tool for studies involving biomass characterization for various applications. In XRD analysis, the extent of

*I*<sup>002</sup> � *Iam*

where CrI is the crystallinity index, while I002 represents the overall peak inten-

XRD is especially useful for the determination of the efficiency of hydrolysis for chemically pretreated biomass materials intended for the production of various chemical compounds such as sugar molecules and oligosaccharides, which are

For the analysis of biomass materials considered for the purpose of biofuels, biochar or chemicals production, the solid state nuclear magnetic resonance spectroscopy (SSNMR) is the ideal technique. This technique allows detailed structural elucidation of major constituents of biomass, particularly lignocellulosic biomass such as wood. It complements the XRD technique since the degree of cellulose crystallinity can also be determined. Nonetheless, the XRD is based on the proposition that X-ray scattering can be divided into two structural components that are amorphous and crystalline [54], while SSNMR is characterized by orientationdependent interactions that are observed in a very broad spectrum that provides detailed information on material chemistry, structure and dynamics in the solid state. The production of biofuels and chemicals from lignocellulosic biomass require an unfettered access to cellulose and hemicellulose, thus SSNMR can be used to comprehend bioconversion of biomass as a function of process conditions [55]. The chemical barriers resulting from lignin renders the hydrolysis process of biomass into fermentable sugars quite complicated. Therefore, advances in spectroscopic techniques, especially spectroscopic methods, have enabled researchers to elucidate the structural characteristics of biomass in relation to specific applications.

When there is a need to investigate the combustion behavior of biomass materials, the thermo-gravimetric analysis (TGA) is particularly useful and valuable for determining thermal parameters relevant to the thermochemical conversion of biomass. Proximate analysis data can be obtained from TGA. In this technique, the

*<sup>I</sup>*<sup>002</sup> � 100% (1)

instrument can be used to analyze a wide range of materials including

crystallinity is calculated based on an equation: (Eq. (1)) [52, 53]:

products of a fermentation process for the production of bioethanol.

*4.1.3 Solid state nuclear magnetic resonance spectroscopy*

*4.1.4 Thermo-gravimetric analysis analyzer*

**27**

*CrI* ð Þ¼ %

.

of biomass.

*4.1.2 X-ray diffraction analyzer*

*Biomass Pretreatment and Characterization: A Review DOI: http://dx.doi.org/10.5772/intechopen.93607*

sity and Iam the baseline intensity.

#### **Table 3.**

*The properties of various lignocellulosic and non-lignocellulosic biomass materials [49].*

account heating value when the biomass is used as feedstock in thermochemical conversion processes such as gasification [25]. **Table 3** presents the most important characteristics of various lignocellulosic and non-lignocellulosic biomass materials.

The proximate analysis estimates the physical properties of biomass with direct influence on the combustion performance of biomass, while ultimate analysis provides a qualitative and quantitative estimation of chemical properties in terms of the weight fractions of elemental components (such as C, H and O) and determines the heating value of biomass, a vital property of biomass materials intended as feedstock for thermochemical conversion processes; the amounts of other elements such as N, S and Si can help determine the environmental impact of using biomass as a fuel [25, 50, 51]. The proximate and ultimate analyses are discussed further in the following section.

#### **4.1 Analytical techniques for biomass characterization**

As earlier alluded, the determination of biomass characteristics often requires the use of a wide variety of state-of-the-art analytical techniques able to provide not just compositional information, but also pretreatment process validation. However, the type of analytical technique to be used is defined by the application choice of the biomass so that analyses results are interpreted in relation to the specific application. A few of the analytical techniques commonly used in characterization studies involving biomass materials are discussed in the following subsections.

#### *4.1.1 Fourier transform infra-red spectroscopic analyzer*

The Fourier transform infra-red spectroscopic (FTIR) is a sensitive technique for the qualitative and quantitative analysis of organic materials such as biomass. It identifies chemical bonds by generating a range of infrared (IR) retention in the form of spectra that represents sample profile. This analytical tool is particularly useful for tracing and tracking changes in biomass molecular structure caused by pretreatment and can distinguish between functional groups [51]. It is a useful technique for the characterization of biomass materials intended for a whole range of applications including biochemical and thermochemical conversion applications. For example, the FTIR can be used to investigate the possibilities of the removal of hemicellulose and lignin from a chemically pretreated biomass in a pulping process. It can also be used to understand the most reactive components of biomass

#### *Biomass Pretreatment and Characterization: A Review DOI: http://dx.doi.org/10.5772/intechopen.93607*

materials and how these components affect the thermochemical conversion process of biomass.

The FTIR technique relies on the fact that most organic materials absorb light within the IR region of the electromagnetic spectrum. The frequency of absorption of light is measured in wave numbers that is typically in the range 4000–600 cm�<sup>1</sup> .

#### *4.1.2 X-ray diffraction analyzer*

account heating value when the biomass is used as feedstock in thermochemical conversion processes such as gasification [25]. **Table 3** presents the most important characteristics of various lignocellulosic and non-lignocellulosic biomass materials. The proximate analysis estimates the physical properties of biomass with direct influence on the combustion performance of biomass, while ultimate analysis provides a qualitative and quantitative estimation of chemical properties in terms of the weight fractions of elemental components (such as C, H and O) and determines the heating value of biomass, a vital property of biomass materials intended as feedstock for thermochemical conversion processes; the amounts of other elements such as N, S and Si can help determine the environmental impact of using biomass as a fuel [25, 50, 51]. The proximate and ultimate analyses are discussed further in the

*The properties of various lignocellulosic and non-lignocellulosic biomass materials [49].*

**(wt.%)**

**LCB** MC VM FC A C H O S N Wood & woody biomass 5–63 30–80 6–26 1–8 49–57 5–10 32–45 <1–1 <1–1 Herbaceous biomass 4–48 41–77 9–35 1–19 42–58 3–9 34–49 <1–1 <1–3

Animal & human waste biomass 3–9 43–62 12–13 23–34 57–61 7–8 21–25 1–2 6–12 Aquatic biomass 8–14 42–53 22–33 11–38 27–43 4–6 34–46 1–3 1–3 *Abbreviations: Moisture content (MC), Volatile matter (VM), Fixed carbon (FC), Ash (A), Carbon (C),*

**Ultimate analysis (wt.%)**

As earlier alluded, the determination of biomass characteristics often requires the use of a wide variety of state-of-the-art analytical techniques able to provide not just compositional information, but also pretreatment process validation. However, the type of analytical technique to be used is defined by the application choice of the biomass so that analyses results are interpreted in relation to the specific application. A few of the analytical techniques commonly used in characterization studies

The Fourier transform infra-red spectroscopic (FTIR) is a sensitive technique for the qualitative and quantitative analysis of organic materials such as biomass. It identifies chemical bonds by generating a range of infrared (IR) retention in the form of spectra that represents sample profile. This analytical tool is particularly useful for tracing and tracking changes in biomass molecular structure caused by pretreatment and can distinguish between functional groups [51]. It is a useful technique for the characterization of biomass materials intended for a whole range of applications including biochemical and thermochemical conversion applications. For example, the FTIR can be used to investigate the possibilities of the removal of hemicellulose and lignin from a chemically pretreated biomass in a pulping process.

involving biomass materials are discussed in the following subsections.

It can also be used to understand the most reactive components of biomass

**4.1 Analytical techniques for biomass characterization**

**Type of biomass Proximate analysis**

*Biotechnological Applications of Biomass*

*Hydrogen (H), Oxygen (O), Sulfur (S), Nitrogen (N).*

*4.1.1 Fourier transform infra-red spectroscopic analyzer*

following section.

**26**

**NLCB**

**Table 3.**

To the best of the author's knowledge, the X-ray diffraction (XRD) is the only analytical instrument able to reveal comprehensive structural information of materials. Structural information that can be obtained includes *chemical composition*, *deformation*, *crystal structure*, *crystal size* and *orientation* as well as *layer thickness*. This instrument can be used to analyze a wide range of materials including nanomaterials. The XRD is equally a valuable analytical tool for studies involving biomass characterization for various applications. In XRD analysis, the extent of crystallinity is calculated based on an equation: (Eq. (1)) [52, 53]:

$$\text{CrI} \left( \text{\%} \right) = \left( \frac{I\_{002} - I\_{am}}{I\_{002}} \right) \times \mathbf{100\%} \tag{1}$$

where CrI is the crystallinity index, while I002 represents the overall peak intensity and Iam the baseline intensity.

XRD is especially useful for the determination of the efficiency of hydrolysis for chemically pretreated biomass materials intended for the production of various chemical compounds such as sugar molecules and oligosaccharides, which are products of a fermentation process for the production of bioethanol.

#### *4.1.3 Solid state nuclear magnetic resonance spectroscopy*

For the analysis of biomass materials considered for the purpose of biofuels, biochar or chemicals production, the solid state nuclear magnetic resonance spectroscopy (SSNMR) is the ideal technique. This technique allows detailed structural elucidation of major constituents of biomass, particularly lignocellulosic biomass such as wood. It complements the XRD technique since the degree of cellulose crystallinity can also be determined. Nonetheless, the XRD is based on the proposition that X-ray scattering can be divided into two structural components that are amorphous and crystalline [54], while SSNMR is characterized by orientationdependent interactions that are observed in a very broad spectrum that provides detailed information on material chemistry, structure and dynamics in the solid state. The production of biofuels and chemicals from lignocellulosic biomass require an unfettered access to cellulose and hemicellulose, thus SSNMR can be used to comprehend bioconversion of biomass as a function of process conditions [55].

The chemical barriers resulting from lignin renders the hydrolysis process of biomass into fermentable sugars quite complicated. Therefore, advances in spectroscopic techniques, especially spectroscopic methods, have enabled researchers to elucidate the structural characteristics of biomass in relation to specific applications.

#### *4.1.4 Thermo-gravimetric analysis analyzer*

When there is a need to investigate the combustion behavior of biomass materials, the thermo-gravimetric analysis (TGA) is particularly useful and valuable for determining thermal parameters relevant to the thermochemical conversion of biomass. Proximate analysis data can be obtained from TGA. In this technique, the sample is combusted at desired heating rates in a chemically inactive atmosphere of nitrogen or argon such that the mass of the sample is monitored as temperature increases. The change in mass of the sample is usually plotted as a function of time or temperature. The TGA is a high temperature analytical instrument that adequately mimics the conditions existing in a typical thermal energy production system [56]. For studies involving the need to determine the kinetics of thermal decomposition of biomass, TGA is equally very helpful as it provides qualitative information that can be used to understand process conditions and design parameters of thermochemical conversion systems [57]. This requires that TGA be conducted at different heating rates and its derivative (DTG) used to simplify the reading of the characteristic peaks obtained from the thermogram of change in mass versus temperature.

*CV MJ* ð Þ¼� *=kg* 1*:*3675 þ 0*:*3137*C* þ 0*:*7009*H* þ 0*:*0318*O* (3)

Calorific value is an important property of biomass for design calculations or numerical simulation of thermochemical conversion systems using biomass as

The Py-GC/MS is a technique used to identify non-volatile compounds. It involves high temperature heating of a sample to decomposition into smaller molecules that are separated by gas chromatography and identified by mass spectrometry. This technique is particularly suited for the analysis of biomass materials intended as feedstock in pyrolysis or hydrothermal liquefaction (HTL) processes for the production of charcoals and bio-oils as the mechanisms involved in these two thermochemical processes (pyrolysis and hydrothermal liquefaction) can be conveniently investigated. For example, pyrolysis of biomass is a relatively complex process that involves both simultaneous and successive chemical reactions which occurs when the biomass is heated in an unreactive environment. Due to the compositional and structural variability of biomass, major constituents degrade under non-identical mechanisms at different temperature ranges and at different rates. Therefore, to explore the complexity of this process, cutting-edge analytical

The scanning electron microscope (SEM) is a type of electron microscope that

The large-scale substitution of fossil fuel with biomass resources is a topical issue not just for the production of energy but also for the production of chemicals, bio products and materials. Moreover, due to the large availability of biomass throughout the world, the production of the high value-added products from biomass can be achieved under any geographical conditions and the feasibility and viability of

produces the image of a sample by scanning the surface of the sample with a focused beam of electrons that interact with the sample to produce a variety of signals used to obtain information about surface composition and topography. The macroscopic nature of biomass requires that some form of pretreatment, such as size reduction, be performed in order to reveal properties of interest for any microscopic and nanoscopic analyses. Thus, by employing imaging techniques such as the SEM, it is possible to study the physical and chemical underpinnings of the prodigy of biomass recalcitrance to breakdown. The SEM can be used to investigate the morphological properties of biomass relevant to the specific application of the biomass. The information obtained can then be used to hone biomass pretreatment methods that will enhance biomass susceptibility to biochemical or thermochemical conversion. It is however worthy to mention that the moisture content of biomass can be very problematic to some microscopic techniques (such as the SEM) since analyses using these techniques are usually performed on dry samples. As such, samples with reduced moisture content are often required before analysis to avoid the introduction of structural artifacts that may interfere with the SEM images of

where CV is the calorific value of biomass.

*Biomass Pretreatment and Characterization: A Review DOI: http://dx.doi.org/10.5772/intechopen.93607*

tools such as the Py-GC/MS are required.

*4.1.8 Scanning electron microscope*

the sample.

**29**

**5. Future prospects**

*4.1.7 Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS)*

feedstock [25, 60].

#### *4.1.5 Differential scanning calorimetry*

The differential scanning calorimetry (DSC) is a thermoanalytical tool used to directly assess the heat energy uptake that occurs in a sample within a controlled increase or decrease in temperature. The instrument monitors phase transitions that lead to heat flow between crucibles since the process involves the heating of two crucibles (one which contains the sample to be analyzed, and the other serving as a reference without a sample). In this analysis, heat flow is measured as a function of temperature so that combustion profiles that will help determine the series of stages that characterizes the thermal performance of a material can be evaluated. In some instances, the DSC can be used as a complementary analytical tool to the TGA, particularly when monitoring softening or glass transition temperature range [8]. The DSC is very valuable for the analysis of biomass materials intended as feedstock for thermochemical conversion processes and the data from DSC can help improve the understanding of the effect of activation energy on the rate of biomass conversion in the aforementioned thermal energy systems [58]. The reactivity of biomass materials can also be determined using DSC and the volatiles from the analysis can be identified using gas analyzers.

#### *4.1.6 CHNS analyzer*

The CHNS analyzer is the carbon (C), hydrogen (H), nitrogen (N) and sulfur (S) analyzer used to measure the weight percentages of these elements in a given material. In CHNS analysis, the weight fraction of oxygen is usually determined by difference with respect to a generally accepted equation (Eq. (2)).

$$O = 100 - (C + H + N + S) \tag{2}$$

The CHNS analyzer is an elemental analyzer whose principle of operation is based on combustion that allows the quantitative determination of the above elements without the need for time consuming sample preparation steps or the use of toxic chemicals. Elemental composition is one of the most important features for biomass utilization [25, 59]. In addition to facilitating the determination of the environmental compatibility of using biomass as a fuel in thermal energy systems, CHNS analysis can be used to obtain information about calorific value and establish the combustion performance of biomass, if the weight proportions of primary elemental components such as C, H and O are known. One of the simplest ways to calculate the calorific value of biomass without the need for analytical tools is from an equation developed by Sheng and Azevedo, 2005 [60]:

*Biomass Pretreatment and Characterization: A Review DOI: http://dx.doi.org/10.5772/intechopen.93607*

sample is combusted at desired heating rates in a chemically inactive atmosphere of nitrogen or argon such that the mass of the sample is monitored as temperature increases. The change in mass of the sample is usually plotted as a function of time or temperature. The TGA is a high temperature analytical instrument that adequately mimics the conditions existing in a typical thermal energy production system [56]. For studies involving the need to determine the kinetics of thermal decomposition of biomass, TGA is equally very helpful as it provides qualitative information that can be used to understand process conditions and design parame-

ters of thermochemical conversion systems [57]. This requires that TGA be conducted at different heating rates and its derivative (DTG) used to simplify the reading of the characteristic peaks obtained from the thermogram of change in mass

The differential scanning calorimetry (DSC) is a thermoanalytical tool used to directly assess the heat energy uptake that occurs in a sample within a controlled increase or decrease in temperature. The instrument monitors phase transitions that lead to heat flow between crucibles since the process involves the heating of two crucibles (one which contains the sample to be analyzed, and the other serving as a reference without a sample). In this analysis, heat flow is measured as a function of temperature so that combustion profiles that will help determine the series of stages that characterizes the thermal performance of a material can be evaluated. In some instances, the DSC can be used as a complementary analytical tool to the TGA, particularly when monitoring softening or glass transition temperature range [8]. The DSC is very valuable for the analysis of biomass materials intended as feedstock for thermochemical conversion processes and the data from DSC can help improve the understanding of the effect of activation energy on the rate of biomass conversion in the aforementioned thermal energy systems [58]. The reactivity of biomass materials can also be determined using DSC and the volatiles from the analysis can

The CHNS analyzer is the carbon (C), hydrogen (H), nitrogen (N) and sulfur (S) analyzer used to measure the weight percentages of these elements in a given material. In CHNS analysis, the weight fraction of oxygen is usually determined by

The CHNS analyzer is an elemental analyzer whose principle of operation is based on combustion that allows the quantitative determination of the above elements without the need for time consuming sample preparation steps or the use of toxic chemicals. Elemental composition is one of the most important features for biomass utilization [25, 59]. In addition to facilitating the determination of the environmental compatibility of using biomass as a fuel in thermal energy systems, CHNS analysis can be used to obtain information about calorific value and establish the combustion performance of biomass, if the weight proportions of primary elemental components such as C, H and O are known. One of the simplest ways to calculate the calorific value of biomass without the need for analytical tools is from

*O* ¼ 100 � ð Þ *C* þ *H* þ *N* þ *S* (2)

difference with respect to a generally accepted equation (Eq. (2)).

an equation developed by Sheng and Azevedo, 2005 [60]:

versus temperature.

*4.1.5 Differential scanning calorimetry*

*Biotechnological Applications of Biomass*

be identified using gas analyzers.

*4.1.6 CHNS analyzer*

**28**

$$\text{CV(M)}/\text{kg} = -1.3675 + 0.3137C + 0.7009H + 0.0318O \tag{3}$$

where CV is the calorific value of biomass.

Calorific value is an important property of biomass for design calculations or numerical simulation of thermochemical conversion systems using biomass as feedstock [25, 60].

#### *4.1.7 Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS)*

The Py-GC/MS is a technique used to identify non-volatile compounds. It involves high temperature heating of a sample to decomposition into smaller molecules that are separated by gas chromatography and identified by mass spectrometry. This technique is particularly suited for the analysis of biomass materials intended as feedstock in pyrolysis or hydrothermal liquefaction (HTL) processes for the production of charcoals and bio-oils as the mechanisms involved in these two thermochemical processes (pyrolysis and hydrothermal liquefaction) can be conveniently investigated. For example, pyrolysis of biomass is a relatively complex process that involves both simultaneous and successive chemical reactions which occurs when the biomass is heated in an unreactive environment. Due to the compositional and structural variability of biomass, major constituents degrade under non-identical mechanisms at different temperature ranges and at different rates. Therefore, to explore the complexity of this process, cutting-edge analytical tools such as the Py-GC/MS are required.

#### *4.1.8 Scanning electron microscope*

The scanning electron microscope (SEM) is a type of electron microscope that produces the image of a sample by scanning the surface of the sample with a focused beam of electrons that interact with the sample to produce a variety of signals used to obtain information about surface composition and topography. The macroscopic nature of biomass requires that some form of pretreatment, such as size reduction, be performed in order to reveal properties of interest for any microscopic and nanoscopic analyses. Thus, by employing imaging techniques such as the SEM, it is possible to study the physical and chemical underpinnings of the prodigy of biomass recalcitrance to breakdown. The SEM can be used to investigate the morphological properties of biomass relevant to the specific application of the biomass. The information obtained can then be used to hone biomass pretreatment methods that will enhance biomass susceptibility to biochemical or thermochemical conversion. It is however worthy to mention that the moisture content of biomass can be very problematic to some microscopic techniques (such as the SEM) since analyses using these techniques are usually performed on dry samples. As such, samples with reduced moisture content are often required before analysis to avoid the introduction of structural artifacts that may interfere with the SEM images of the sample.

#### **5. Future prospects**

The large-scale substitution of fossil fuel with biomass resources is a topical issue not just for the production of energy but also for the production of chemicals, bio products and materials. Moreover, due to the large availability of biomass throughout the world, the production of the high value-added products from biomass can be achieved under any geographical conditions and the feasibility and viability of

the production of the value-added products depends on biomass characteristics and the pretreatment method employed. However, biomass complexity and the high capital and operation costs associated with biomass pretreatment as well as the mechanisms involved in the conversion process of biomass are some of the challenges associated with the use of biomass for the production of energy, chemicals and fuels. Therefore, efforts should be geared toward the design of more easy-touse and cost effective technologies at all levels so as to encourage the widespread application of biomass and attract investment in this field. In addition, not much is known about the optimal biomass pretreatment conditions because they are seldom reported. Consequently, for the efficient and feasible utilization of biomass in bioconversion processes, information about the optimum conditions of pretreatment is vital and efforts made to report such information. It has been reported [61] that researchers and policy makers are in need of useful information that may lead to the much needed improvements in this field of research. So, efforts made to report optimal pretreatment conditions for biomass will create further awareness on the advantages of the exploitation of biomass resources for the production of renewable energy and other bio products.

**Notes/Thanks/Other declarations**

*Biomass Pretreatment and Characterization: A Review DOI: http://dx.doi.org/10.5772/intechopen.93607*

NLCB Non lignocellulosic biomass

TGA thermo-gravimetric analysis DTG derivative thermogravimetry DSC differential scanning calorimetry SEM scanning electron microscope

**Abbreviations**

LCB biomass

IR infrared

**Author details**

**31**

Anthony Anukam\* and Jonas Berghel

provided the original work is properly cited.

Sciences, Karlstad University, Karlstad, Sweden

\*Address all correspondence to: anthonyanukam16@gmail.com

Environmental and Energy Systems, Department of Engineering and Chemical

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

XRD X-ray diffraction

home environment in the midst of numerous challenges.

FTIR Fourier transform infra-red spectroscopic

SSNMR solid state nuclear magnetic resonance spectroscopy

The first author deems it a great pleasure to place on record his sincere gratitude to his dear wife, Tuliwe-Ndudula Anukam, who stood by him and kept a peaceful

On the other hand, characterization of biomass also faces significant challenges ranging from the nature of the biomass and the multiphase bioconversion processes using the biomass as feedstock as well as the lack of experimental validation of the cutting-edge analytical techniques used for biomass characterization. Efforts made to address these barriers through continued research will equally lead to optimization of bioconversion and bio refinery processes. Needless to say that, since a single analytical technique cannot provide all of the needed information simultaneously with optimal resolution and high sensitivity, complementary techniques are often required to achieve full understanding of the physical and chemical underpinnings of the prodigy of biomass recalcitrance as it undergoes bioconversion processing. This may ease the challenges associated with experimental validation. Nevertheless, it is vital to mention that each type of characterization technique has its own merits and demerits under a particular set of circumstances and that the shortcomings of one technique may be compensated for by the merits of the other.

#### **6. Conclusions**

Pretreatment and characterization of biomass are key steps for the efficient utilization of biomass materials in bioconversion processes. A determination of the best pretreatment method and parameters requires an evaluation of its effects on biomass using cutting-edge analytical tools able to provide information that will facilitate better understanding of the origins of biomass recalcitrance and the mechanism and impact of pretreatment relevant to the optimization of different bioconversion pathways.

#### **Acknowledgements**

The author would like to thank the Department of Engineering and Chemical Sciences of Karlstad University for providing a conducive environment and an opportunity to conduct this synopsis.

#### **Conflict of interest**

The authors declare no conflict of interest.
