Author details

Luís Adriano Santos do Nascimento\*, Deborah Terra de Oliveira, Alex Nazaré de Oliveira, Luiza Helena de Oliveira Pires, Carlos Emmerson Ferreira da Costa and Geraldo Narciso da Rocha Filho

\*Address all correspondence to: adrlui1@yahoo.com.br

Federal University of Pará, Belém, Brazil

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Valorization of Wastes for Biodiesel Production: The Brazilian Case

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**Chapter 3**

**Provisional chapter**

**Properties of Torrefied Palm Kernel Shell via**

**Properties of Torrefied Palm Kernel Shell via** 

DOI: 10.5772/intechopen.81374

This study describes the characteristic and thermal properties of torrefied palm kernel shell (PKS) by microwave irradiation pretreatment. The microwave power level (200, 300, 450, and 600 W) and processing time (4, 8, and 12 min) were used in this study. The pretreated samples were analyzed for mass and energy yield, calorific value, proximate and elemental composition, and thermal decomposition. Results showed that the characteristic of pretreated PKS was enhanced by increasing the microwave power level and processing the time. The oxygen content and O/C ratio of torrefied PKS were reduced by increasing the microwave power level. The carbon content of pretreated PKS, which was closed to the untreated MB coal properties with comparable calorific value, was obtained. The microwave power level of 450 W and processing time of 8 min were suitable to upgrade the PKS to a respectable quality feedstock. Thus, it can be concluded that the alteration in physical, chemical, and thermal properties of torrefied PKS discovered the potential of this feedstock to be applied in subsequent thermochemical conversion

**Keywords:** pretreatment, torrefaction, microwave irradiation, palm kernel shell,

, SOx

lization of the world energy [1]. In the midst of limited availability of fossil fuels and high level of air pollution, energy efficient technologies are gaining importance, and gasification, being

> © 2016 The Author(s). Licensee InTech. 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, provided the original work is properly cited.

© 2018 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, provided the original work is properly cited.

, and NOx

has become a concern on the uti-

**Microwave Irradiation**

**Microwave Irradiation**

Razi Ahmad, Mohd Azlan Mohd Ishak, Nur Nasulhah Kasim and Khudzir Ismail

Razi Ahmad, Mohd Azlan Mohd Ishak, Nur Nasulhah Kasim and Khudzir Ismail

http://dx.doi.org/10.5772/intechopen.81374

such as pyrolysis and gasification.

In recent years, the increasing emission of CO<sup>2</sup>

**Abstract**

gasification

**1. Introduction**

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter


#### **Properties of Torrefied Palm Kernel Shell via Microwave Irradiation Properties of Torrefied Palm Kernel Shell via Microwave Irradiation**

DOI: 10.5772/intechopen.81374

Razi Ahmad, Mohd Azlan Mohd Ishak, Nur Nasulhah Kasim and Khudzir Ismail Razi Ahmad, Mohd Azlan Mohd Ishak, Nur Nasulhah Kasim and Khudzir Ismail

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.81374

#### **Abstract**

[54] Martins GI, Secco D, Tokura LK, Bariccatti RA, Dolci BD, Santos RF. Potential of tilapia oil and waste in biodiesel production. Renewable and Sustainable Energy Reviews. 2015;42:

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[62] Souza AF, Rodriguez DM, Ribeaux DR, Luna MAC, Lima e Silva TA, Silva Andrade RF, et al. Waste soybean oil and corn steep liquor as economic substrates for bioemulsifier and biodiesel production by Candida lipolytica UCP 0998. International Journal of Molecular

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[64] Gomes MG, Pasquini D. Utilization of eggshell waste as an adsorbent for the dry purification of biodiesel. Environmental Progress & Sustainable Energy. 2018:1-7. DOI: 10.1002/

mental. 2014;160–161:122-128. DOI: 10.1016/j.apcatb.2014.04.039

Sciences. 2016;17:1-18. DOI: 10.3390/ijms17101608

234-239. DOI: 10.1016/j.rser.2014.10.020

Journal. 2013;81:15-23. DOI: 10.1016/j.bej.2013.09.017

acids. Renewable Energy. 2017;114:725-732

2017.03.013

28 Biofuels - Challenges and opportunities

2010.03.035

10.1002/jctb.5002

ep.12870

This study describes the characteristic and thermal properties of torrefied palm kernel shell (PKS) by microwave irradiation pretreatment. The microwave power level (200, 300, 450, and 600 W) and processing time (4, 8, and 12 min) were used in this study. The pretreated samples were analyzed for mass and energy yield, calorific value, proximate and elemental composition, and thermal decomposition. Results showed that the characteristic of pretreated PKS was enhanced by increasing the microwave power level and processing the time. The oxygen content and O/C ratio of torrefied PKS were reduced by increasing the microwave power level. The carbon content of pretreated PKS, which was closed to the untreated MB coal properties with comparable calorific value, was obtained. The microwave power level of 450 W and processing time of 8 min were suitable to upgrade the PKS to a respectable quality feedstock. Thus, it can be concluded that the alteration in physical, chemical, and thermal properties of torrefied PKS discovered the potential of this feedstock to be applied in subsequent thermochemical conversion such as pyrolysis and gasification.

**Keywords:** pretreatment, torrefaction, microwave irradiation, palm kernel shell, gasification

#### **1. Introduction**

In recent years, the increasing emission of CO<sup>2</sup> , SOx , and NOx has become a concern on the utilization of the world energy [1]. In the midst of limited availability of fossil fuels and high level of air pollution, energy efficient technologies are gaining importance, and gasification, being

> © 2016 The Author(s). Licensee InTech. 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, provided the original work is properly cited. © 2018 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, provided the original work is properly cited.

a highly efficient technology, has received significant attention [2]. Currently, coal is the main feedstock in gasification and is expected to be applied as the energy resource for many decades ahead. However, this direction is difficult to achieve due to the increase in energy demand that had caused the shortage supply and reduction of coal [3]. Consequently, one of the approaches is to utilize the biomass in thermochemical conversion such as pyrolysis, liquefaction, and gasification. The traditional use of biomass has been restricted to cooking and heating purposes, which has affected adverse impacts such as land degradation and desertification. However, the current use of biomass with a high-quality energy carrier transformed from raw biomass for electricity and heat production can substantially reduce emissions from the conventional power plants. This ability to convert raw biomass into convenient energy carriers increases the interest on biomass use for energy purpose, especially the lignocellulosic biomass [4].

conversion such as in gasification. As a result, prior to gasification, it might be attractive to

Properties of Torrefied Palm Kernel Shell via Microwave Irradiation

http://dx.doi.org/10.5772/intechopen.81374

31

A pretreatment method prior to thermal conversion is required in direction to reduce some of the aforementioned problems. Thus, torrefaction pretreatment appears to be an effective route. The thermal pretreatment or torrefaction at low temperature between 200 and 300°C, which operated in the nonappearance of oxygen, upgraded the untreated feedstock to more value feedstock. Nitrogen is generally used as carrier gas to provide a nonoxidizing atmosphere in most laboratory tests. Since torrefaction is conducted at conditions similar to those of pyrolysis that usually takes place between 350 and 650°C, torrefaction has also been known as mild pyrolysis [16]. The pretreated biomass has high calorific value and carbon fraction with low moisture content and O/C ratio compared to the untreated or original material. The energy value of pre-

treated material will increase with increasing carbon fraction and calorific value [17].

moisture removal and hemicellulose breakdown, which produce H<sup>2</sup>

The previous studies have also shown other advantages of this torrefaction pretreatment, such as it improves feedstock hydrophobicity, homogeneity, and grindability [4, 18]. Satpathy et al. [19] found that the torrefied wheat and barley straw are more hydrophobic and the moisture uptake is reduced by 61–68% under suitable torrefaction condition. Torrefaction of marula seeds and blue gum improves the higher heating value and energy content of the biomass. The weight loss also increases when the torrefaction temperature increases due to

Torrefaction temperature is one of the important parameters in torrefaction pretreatment [4]. Ibrahim et al. [21] found that the lower temperature and shorter residence time were the best treatment to achieve good physical properties with a relatively high energy yield. When treated at these conditions, the softwood mixture had the highest energy (95%), followed by the hardwood mixture (80%), then willow (79%), and finally eucalyptus (75%). Increasing the severity of the torrefaction conditions greatly improved the physical characteristics of the torrefied biomass, in terms of grindability properties and hydrophobicity. The optimum temperatures were reliant on raw material, and consequently, the effects specify that careful optimization is necessary for all feedstock types to increase the advantages of torrefaction at the same time preserving an adequate energy yield. As pretreatment conditions became more severe between temperature of 250 and 300°C, this led to a more qualified and energydense solid fuel with higher fixed carbon content, increased calorific values, and reduced hydrogen and oxygen contents [22]. By increasing the torrefaction temperature, the weight loss increased and bulk density decreased. The torrefied wood samples improved solid fuel property with high fuel ratio, which are close to lignite coal [23]. Mamvura et al. [20] found that the nonoxidative conditions with low heating rates and shorter residence time resulted in the best torrefied biomass. The increase in HHV together with increase in energy density for torrefied marula seeds during investigation intended that it is potential to coconversion with coal making it a promising biomass source. Therefore, the pretreated or torrefied biomass, which has been improved in energy density, hydrophobicity, and grindability, overcomes the weakness of untreated biomass and is then driven to be applied in

O, CO, CO<sup>2</sup>

, and other

transform the biomass characteristics.

hydrocarbons [20].

thermochemical conversion [4, 16].

Biomass is one of the capable renewable energy sources and is applied as solid, liquid, and gas fuels [5]. The biomass is an appealing concern worldwide, because of its nonedible characteristic, carbon neutrality, and relative abundance. Moreover, the rising worries about the effects of CO<sup>2</sup> emissions from fossil fuels call for sustainable energy sources, such as biomass [6]. In Malaysia, oil palm residues are considered to be the most plentiful biomass and the greatest prospects for fuel generation. Malaysia produces about 47% of the world's palm oil source and can be reflected as one of the world's largest producers of palm oil. Therefore, Malaysia creates huge quantity of oil palm biomass including palm kernel shell (PKS), oil palm trunks, oil palm fronds, empty fruit bunches, and fibers as residues from harvesting and processing activities [7]. The PKS as one of the residues from oil palm industry generated about 4.19 MnT in 2016 [8]. Therefore, PKSs appear to have prominent capacities to become an alternative source of energy for the country.

However, the utilization of biomass, which is a renewable and environmental friendly resource during thermal conversion, imposed several problems. The untreated biomass has the drawbacks as follows:


Likewise, it is reasonably challenging for straight application of untreated PKS as raw material for fuel production such as gasification or pyrolysis. Typically, the palm plantations and their processing plants are located in rural areas. Thus, the untreated PKS is opened to fungal attack and biodegradation through storage and transportation. The high moisture content also can interrupt the thermal conversion process for energy production [9]. The low energy density of PKS, normally 18 MJ/kg, with high moisture content typically around 10 wt.% as a result of its hygroscopic character, is a weakness of biomass [10–12]. As shown by the previous researcher [13–15], highly oxygenated biomass with high O/C ratio will lower the gasification efficiency in contrast with low O/C feedstock such as coal. Consequently, these properties of the untreated PKS were associated with several problems in biomass thermal conversion such as in gasification. As a result, prior to gasification, it might be attractive to transform the biomass characteristics.

a highly efficient technology, has received significant attention [2]. Currently, coal is the main feedstock in gasification and is expected to be applied as the energy resource for many decades ahead. However, this direction is difficult to achieve due to the increase in energy demand that had caused the shortage supply and reduction of coal [3]. Consequently, one of the approaches is to utilize the biomass in thermochemical conversion such as pyrolysis, liquefaction, and gasification. The traditional use of biomass has been restricted to cooking and heating purposes, which has affected adverse impacts such as land degradation and desertification. However, the current use of biomass with a high-quality energy carrier transformed from raw biomass for electricity and heat production can substantially reduce emissions from the conventional power plants. This ability to convert raw biomass into convenient energy carriers increases the

interest on biomass use for energy purpose, especially the lignocellulosic biomass [4].

effects of CO<sup>2</sup>

30 Biofuels - Challenges and opportunities

an alternative source of energy for the country.

**ii.** High moisture and oxygenated compound

the drawbacks as follows: **i.** Low energy content

**iii.** Hygroscopic behavior

**iv.** Poor grindability

Biomass is one of the capable renewable energy sources and is applied as solid, liquid, and gas fuels [5]. The biomass is an appealing concern worldwide, because of its nonedible characteristic, carbon neutrality, and relative abundance. Moreover, the rising worries about the

[6]. In Malaysia, oil palm residues are considered to be the most plentiful biomass and the greatest prospects for fuel generation. Malaysia produces about 47% of the world's palm oil source and can be reflected as one of the world's largest producers of palm oil. Therefore, Malaysia creates huge quantity of oil palm biomass including palm kernel shell (PKS), oil palm trunks, oil palm fronds, empty fruit bunches, and fibers as residues from harvesting and processing activities [7]. The PKS as one of the residues from oil palm industry generated about 4.19 MnT in 2016 [8]. Therefore, PKSs appear to have prominent capacities to become

However, the utilization of biomass, which is a renewable and environmental friendly resource during thermal conversion, imposed several problems. The untreated biomass has

Likewise, it is reasonably challenging for straight application of untreated PKS as raw material for fuel production such as gasification or pyrolysis. Typically, the palm plantations and their processing plants are located in rural areas. Thus, the untreated PKS is opened to fungal attack and biodegradation through storage and transportation. The high moisture content also can interrupt the thermal conversion process for energy production [9]. The low energy density of PKS, normally 18 MJ/kg, with high moisture content typically around 10 wt.% as a result of its hygroscopic character, is a weakness of biomass [10–12]. As shown by the previous researcher [13–15], highly oxygenated biomass with high O/C ratio will lower the gasification efficiency in contrast with low O/C feedstock such as coal. Consequently, these properties of the untreated PKS were associated with several problems in biomass thermal

emissions from fossil fuels call for sustainable energy sources, such as biomass

A pretreatment method prior to thermal conversion is required in direction to reduce some of the aforementioned problems. Thus, torrefaction pretreatment appears to be an effective route. The thermal pretreatment or torrefaction at low temperature between 200 and 300°C, which operated in the nonappearance of oxygen, upgraded the untreated feedstock to more value feedstock. Nitrogen is generally used as carrier gas to provide a nonoxidizing atmosphere in most laboratory tests. Since torrefaction is conducted at conditions similar to those of pyrolysis that usually takes place between 350 and 650°C, torrefaction has also been known as mild pyrolysis [16]. The pretreated biomass has high calorific value and carbon fraction with low moisture content and O/C ratio compared to the untreated or original material. The energy value of pretreated material will increase with increasing carbon fraction and calorific value [17].

The previous studies have also shown other advantages of this torrefaction pretreatment, such as it improves feedstock hydrophobicity, homogeneity, and grindability [4, 18]. Satpathy et al. [19] found that the torrefied wheat and barley straw are more hydrophobic and the moisture uptake is reduced by 61–68% under suitable torrefaction condition. Torrefaction of marula seeds and blue gum improves the higher heating value and energy content of the biomass. The weight loss also increases when the torrefaction temperature increases due to moisture removal and hemicellulose breakdown, which produce H<sup>2</sup> O, CO, CO<sup>2</sup> , and other hydrocarbons [20].

Torrefaction temperature is one of the important parameters in torrefaction pretreatment [4]. Ibrahim et al. [21] found that the lower temperature and shorter residence time were the best treatment to achieve good physical properties with a relatively high energy yield. When treated at these conditions, the softwood mixture had the highest energy (95%), followed by the hardwood mixture (80%), then willow (79%), and finally eucalyptus (75%). Increasing the severity of the torrefaction conditions greatly improved the physical characteristics of the torrefied biomass, in terms of grindability properties and hydrophobicity. The optimum temperatures were reliant on raw material, and consequently, the effects specify that careful optimization is necessary for all feedstock types to increase the advantages of torrefaction at the same time preserving an adequate energy yield. As pretreatment conditions became more severe between temperature of 250 and 300°C, this led to a more qualified and energydense solid fuel with higher fixed carbon content, increased calorific values, and reduced hydrogen and oxygen contents [22]. By increasing the torrefaction temperature, the weight loss increased and bulk density decreased. The torrefied wood samples improved solid fuel property with high fuel ratio, which are close to lignite coal [23]. Mamvura et al. [20] found that the nonoxidative conditions with low heating rates and shorter residence time resulted in the best torrefied biomass. The increase in HHV together with increase in energy density for torrefied marula seeds during investigation intended that it is potential to coconversion with coal making it a promising biomass source. Therefore, the pretreated or torrefied biomass, which has been improved in energy density, hydrophobicity, and grindability, overcomes the weakness of untreated biomass and is then driven to be applied in thermochemical conversion [4, 16].

Most of the biomass torrefactions applied the conventional electric heater, while there is an alternative technology designated microwave irradiation. Microwave technology has expanded remarkable importance in the thermochemical pretreatment of waste materials, including biomass, waste cooking oil, scrap tires, and others. Innovative fields are being exposed in which microwave can be applied as an alternative source of heating. The application of microwave in waste treatment originated about two decades ago. Therefore, it can be considered at an early stage of enlargement [24]. Microwave irradiation is an electromagnetic irradiation in the range of wavelengths from 0.01 to 1 m and the equivalent frequency range of 0.3–300 GHz. Normally, the microwave reactors for chemical synthesis and all domestic microwave ovens operate at 2.45 GHz frequency, which corresponds to a wavelength of 12.25 cm. Microwave irradiation has attracted much attention in recent years due to the advantages associated with dielectric heating effects. Microwave dielectrics are known as a material, which absorbs microwave irradiation; thus, microwave heating is called dielectric heating [25]. The pretreatment using microwave irradiation is an effective method for upgrading the biomass [26]. Unlike conventional heating technique in which heat gradually enters into samples over normal heat transfer mechanisms (convection, conduction, and radiation) [27], microwave irradiation employs electromagnetic energy to produce heat, which can enter deep into samples, permitting heating to initiate volumetrically [28]. Microwave irradiation has many advantages such as:

Consequently, more research is required to entirely understand the characteristic of torrefied biomass using microwave irradiation prior to further thermochemical conversion. It is also necessary to understand the thermal decomposition of torrefied biomass during pyrolysis in thermogravimetric analyzer (TGA) since, in the thermal conversion studies, the beginning stage involves the feedstock devolatilization. Therefore, in this study, the PKS was initially torrefied in microwave, and the properties of torrefied PKS were explored. Subsequently, the thermal decomposition and behavior of torrefied PKS during pyrolysis process using TGA

Properties of Torrefied Palm Kernel Shell via Microwave Irradiation

http://dx.doi.org/10.5772/intechopen.81374

33

PKS as a biomass sample was obtained from United Oil Palm Mill Sdn. Bhd., Nibong Tebal, Penang, Malaysia. The PKS is produced from the shell/kernel separator. The PKS sample was crushed and sieved through progressively finer screen to obtain particle sizes in the range of 200–400 μm. The untreated PKS sample was dried in an oven at 105°C for 24 h for rendering moisture-free and finally stored in an air-tight container until the experiments and analyses were carried out. The pre-drying is needed to avoid further biodegradation of the sample through storage since the moisture mass fraction of the raw PKS is relatively high [33]. Moreover, the pre-drying is used to simulate the industrial practice of sun-drying the

The torrefaction experiment was carried out in a domestic microwave oven (Samsung) with technical specifications of ~240 V and 50 Hz and a maximum power of 800 W. The microwave output power levels of 200, 300, 450, and 600 W were used in this study. The untreated PKS of 5 g was put in the sample crucible placed at the center of the microwave oven. Then, the nitrogen gas at a flow rate of 50 mL/min was purged in the reaction compartment to retain the inert atmosphere condition. After 10 min purging, the microwave system was turned on, and the microwave output power level was selected with respective processing time of 4, 8, and 12 min. The inert atmosphere condition was continued during the microwave irradiation. The power supply was turned off, and the nitrogen gas flow was stopped after the set processing time was achieved. The final temperature of the pretreated PKS was measured using infrared thermometer immediately after the pretreatment process. The final weight of pretreated PKS was measured once it reached the room temperature. The experiment under all of the studied parameters was repeated to confirm the measurement quality and repeatability of the achieved results.

), mass yield (*Ym*), and energy yield (*Ye*

) of the pretreated samples

**2.3. Calculation of solid conversion, mass yield, and energy yield**

were calculated according to Eqs. (1)–(3), respectively:

were examined.

**2. Method**

**2.1. Materials**

materials before storage [6].

**2.2. Torrefaction experiment**

The solid conversion (*Xs*


Wang et al. [30] utilized microwave irradiation to upgrade the properties of rice husk and sugarcane residues by varying different parameters, including microwave power level and processing time. They found that the suitable microwave power levels are proposed to be set between 250 and 300 W for the torrefaction of these two agricultural wastes. Also, with appropriate processing time, the caloric value is able to increase 26% for rice husk and 57% for sugarcane residue. Huang et al. [31] found that higher microwave power levels contributed to higher heating rate and reaction temperature and therefore produced the torrefied biomass with higher heating value and lower H/C and O/C ratios. The torrefied biomass or biochar probably substitutes coal due to high heating value and fuel ratio as well as low atomic H/C and O/C ratios. The microwave torrefaction of *Leucaena* produced thermally stable biochar compared with sewage sludge at lower microwave power levels, which means that the microwave heating performance of *Leucaena* is better. Compared with conventional torrefaction, mass and energy yields of microwave torrefaction were lower, which might be attributable to the further severe reaction accomplished by microwave irradiation [32].

Consequently, more research is required to entirely understand the characteristic of torrefied biomass using microwave irradiation prior to further thermochemical conversion. It is also necessary to understand the thermal decomposition of torrefied biomass during pyrolysis in thermogravimetric analyzer (TGA) since, in the thermal conversion studies, the beginning stage involves the feedstock devolatilization. Therefore, in this study, the PKS was initially torrefied in microwave, and the properties of torrefied PKS were explored. Subsequently, the thermal decomposition and behavior of torrefied PKS during pyrolysis process using TGA were examined.
