Oil palm shell

The shell produced from cracking the palm seeds is known as oil palm shell. It is a hard endocarp which surrounds the palm seeds or kernels. It is obtained when the residual nuts from the screw press are crushed mechanically to extract the kernels or seeds. The oil palm shell is a lignocellulosic biomass. Lignocellulose materials have a massive potential as a feedstock to produce electrical power, heat and fuels (Hoekman et al., 2011; Liu et al., 2013). Because of the rapid increase in the oil palm production, the world’s annual generation of oil palm shell also has increased up to 11.1 million tons. Previously its amount was 2.52 and 4.3 million tons in 2004 and 2006 respectively (Lee and Ofori-Boateng, 2013).
Oil palm shell is characterized by proximate analysis and ultimate analysis (Unz, et al., 2010). Meanwhile, these properties may vary with changing the environment and time (Christian, et al., 2006; Lewandowski and Heinz, 2003; Pordesimo, et al., 2005).
The ultimate analysis, proximate analysis, chemical composition, inorganic composition and HHV of oil palm shell (Abnisa et al., 2013; Abnisa et al., 2011; Abubakar and Ani, 2013; Arami-Niya et al., 2010; Asadieraghi and Wan Daud, 2014; Asadullah et al., 2013; Aziz et al., 2012; Aziz et al., 2011; Basiron and Weng, 2004; Chaiyaomporn and Chavalparit, 2010; Hasegawa, et al., 2004; Hussain et al., 2006; Jamaluddin et al., 2013; Kean et al., 2013; Kongab et al., 2013; Lee and Ofori-Boateng, 2013; Mohammed et al., 2012; Mohammed et al., 2011; Özçimen; Salema et al., 2013; Singh, 1999; Uemura et al., 2010; Uemura et al., 2011; Yang et al., 2004; Yusoff, 2006) are listed and compared to those of EFB (Asadieraghi and Wan Daud, 2014; Butler et al., 2011; Chew and Bhatia, 2008; Jamari and Howse, 2012; Lim et al., 2014; Minowa et al., 1998; Nhuchhen and Abdul Salam, 2012; Tye, et al., 2011; Yang, et al., 2004), oil palm trunk (Kelly-Yong, et al., 2007; Varman and Saka, 2011; Yuliansyah et al., 2010), oil palm fronds (Wan Rosli et al., 2004; Yuliansyah, et al., 2010) and oil palm fibers (Asadieraghi and Wan Daud, 2014; Goh, et al., 2010; Luangkiattikhun et al., 2008; Mazaheri et al., 2010; Tye, et al., 2011; Werther et al., 2000; Yang, et al., 2004) in Table 2.2.
Proximate analysis incorporates the quantifiable determination of FC, VM, ash and moisture content (Khan, et al., 2009). The main purpose of proximate analysis is to determine the energy content of biomass or fuel by finding the ratio of combustible substances (FC and VM) to noncombustible constituents (ash and moisture content). On the other hand, an ultimate analysis defines the elemental composition in terms of hydrogen, carbon, nitrogen, oxygen and sulphur contents (Khan, et al., 2009). The ultimate analysis aims to determine the composition and quantity of the gas emitted during combustion, as well as the amount of oxygen needed for burning of biomass or fuels (Chang, 2014).
As shown in Table 2.2, the oil palm shell contains a higher amount of VM, about 66-78 %, which reveals its ease of ignition (Omar et al., 2011). Although, it is less than that of oil palm fronds and trunks. The presence of FC in a large quantity, 13-23 %, points out that a significant amount of heat generation from burning the oil palm shell can be obtained compared to other wastes of the oil palm industry. It also can be noticed the amount of ash present in the oil palm shell is in a small quantity. The oil palm shell has a higher FC to VM ratio and a lower moisture to ash content ratio. This heightens the ratio of combustible to the noncombustible substances resulting a higher HHV of oil palm shell (15.9-22.14 MJ/kg). The HHV of the oil palm shell is comparable to that of hardwood (17.63-20.81 MJ/kg) and softwood (19.66-20.63MJ/kg) (Garcia-Perez et al., 2007; Telmo and Lousada, 2011).

Oil palm

Oil palm (Elaeis guineensis) is a leading perennial oleaginous food crop for edible cooking oil production (Chang, 2014). 

Source

The production and demand of the oil palm are further increasing rapidly. The amount of palm oil produced in Malaysia in 1985 was 4 million tons, which raised to 18.8 million tons in 2012 (Chang, 2014). The oil yield (about 4.87 t/ha/year) from oil palm is 6.5, 8 and 13 times greater than that of rapeseed, sunflower and soya bean respectively (Chang, 2014; Tye et al., 2011). Oil palm grows extensively in tropical regions like Malaysia, Thailand, Indonesia and tropical African countries (Akhtar et al., 2010; Basiron, 2007) with high rainfall; 1200 mm/year and daylight of 5-7 h/day (Schmidt, 2007).

Fuels Produced from Biomass

Fuels Produced from Biomass

A range of fuels can be produced from biomass sources including gaseous fuels (hydrogen and methane), liquid fuels such as biodiesel, Fischer-Tropsch diesel, vegetable oil, bio-alcohols, biosynthetic oil (Demirbas, 2008) and biochar or hydrochar. Biofuels are more advantageous than fossil fuels such as availability of sources in large amount, environmental friendly, energy security, foreign exchange saving, rural development and sustainability and biodegradability (Demirbas, 2007; Guney, 2013; Puppan, 2002). The main difference between biofuels and petroleum fuels is the oxygen content present, which makes their properties different from each other.

Biomass as a source of energy

Before the dawn of fossil fuel based economy in the 19th century, biomass was a major contributor to energy. However, the energy ability in transforming biomass was less. So, fossil fuel energy grew as a more cost-effective and customary alternate for biomass. Recently, the demand for energy has increased because of an increase in population and industrialization worldwide. It has reached a point where fossil fuel energy will not be able to satisfy the supplies of persistent growth of the world economy in the forthcoming ages. The environmental problems by releases of greenhouse gases (GHG), mainly CO2 (Yu et al., 2007), unbalanced market prices and limited availability (Boldor et al., 2004; Fischer and Schrattenholzer, 2001; Huber et al., 2006; Krewitt et al., 2007; Okkerse and Van Bekkum, 1999) are other drawbacks of the fossil fuels based energy. As a result, a shift back to the biomass-based economy is compulsory because only biomass from existing renewable energy resources can be converted into suitable solid, liquid and gaseous fuels (Demirbaş, 2001a, 2001b).

Biomass is a rich source of the energy coming from agriculture, forests and energy crops (Saxena et al., 2009). Annual growth of dry biomass on a contingent basis is 118x109 tons (Bobleter, 1994). The international energy agency (IEA) states that entire oil use of the world in 2007 was 3.53x109 tons, equal to 148.26x1018 J of energy. This amount is less than 10 % of yearly worldwide production of biomass in the energy content (Guo et al., 2012). One investigation by the United Nations Conference on the environment and development (UNCED) evaluates that biomass might possibly supply about 50 % of the existing principal energy need through 2050 globally (Ramage and Scurlock, 1996).
Biomass is a biological matter including all living materials on the earth. Biomass mainly consists of cellulose (C6H10O5)x, hemicelluloses (C5H8O4)m, lignin [C9H10O3(COH3)0.9-1.7]n, small extractives (Duku et al., 2011; Fatih Demirbas et al.,2011), fats, proteins (Verma et al., 2012), sugars, arrowroots, water and ash. The largest fraction of biomass is cellulose (35-50 % of biomass weight). Hemicellulose represents 20-35 % of biomass weight and lignin shares 15-20 % of biomass weight, while remaining 15-20 % includes proteins, fats, extractives and ash content (Haghighi Mood et al., 2013). Biomass is characterized by physical properties, proximate analysis, and ultimate analysis (Unz et al., 2010). These properties may change in every substance (Christian et al., 2006) with growing environment (Xiong et al., 2010), and time or age (Lewandowski and Heinz, 2003; Pordesimo et al., 2005).

Hydrochar and its Applications

A solid fuel with high carbon content, low fibrous structure and high-energy density produced from organic materials such as agricultural waste, dung and firewood using the HydroThermal Carbonization (HTC) is known as hydrochar. 

The applications of hydrochar include; as a carbon material, an amendment of soil, a solid fuel, which is comparable to brown coal for production of energy, a substitute for activated carbon or carbon black, a carbon catalyst used for production of fine chemicals, a material to increase the efficiency of fuel cells and as an absorbent to increase fertility and productivity of soil (Berge et al., 2013; Du et al., 2012; Funke and Ziegler, 2010; Kang, et al., 2012; Kleinert and Wittmann, 2009; Libra et al., 2011; Parshetti et al., 2013; Rillig et al., 2010).

Hydrothermal carbonization

Hydrothermal carbonization alson wtitten as HTC is an environmentally friendly method which converts raw biomass into a high yield percentage and higher quality hydrochar. Pyrolysis and hydrothermal liquefaction are mostly used to increase bio-oil yield. Hydrothermal gasification is preferred for maximum gaseous product. Slow pyrolysis can produce solid fuel, but the yield percentage will be lower than that of the HTC. The temperature of HTC is also lower than that of gasification, pyrolysis and flash carbonization. Besides, water acts as a solvent in HTC thus, pre-drying of biomass is not required as it is needed for pyrolysis (Kang et al., 2012). HTC can handle both wet and dry biomass types, therefore saving the energy, cost, and time that are needed for dry biomass. It is an environmentally friendly process than pyrolysis because of the fewer emission of volatile matter (Cakan, 2008; Titirici et al., 2008; Titirici, Thomas, & Antonietti, 2007; Titirici, Thomas, Yu, et al., 2007). 

Why Thermochemical processes are preferred over biochemical methods

Thermochemical processes are preferred over biochemical methods because of the advantages such as no pretreatment is required for the biomass in the hydrothermal carbonization process. Biochemical processes need pretreatment of biomass material by different pretreatment methods such as chemical, physical, biological and physiochemical to improve the accessibility of enzymes (Kumar, 2010). On the other hand, pretreatment is not needed for thermo-chemical methods.

Biochemical process

Biochemical processes use enzymes as a catalyst to convert biomass into biofuels.

Biochemical processes include fermentation, anaerobic digestion, transesterification and composting (Lee and Ofori-Boateng, 2013).

Thermo-Chemical Processing of Biomass

Since the last few decades, the research interest in renewable energy has been increasing throughout the world. Utilization of biomass resources for biofuels production is at the top of all forms of renewable energy. There are two technologies available to produce biofuels from biomass, thermo-chemical and biochemical methods.

Thermochemical processing of biomass includes paralysis, combustion, gasification and hydrothermal processes (Pramanik, 2003). Thermochemical processes are distinguished from each other by process conditions such as use of oxygen or the amount of heat used.

PRODUCTION AND CHARACTERIZATION OF HYDROCHAR FROM HYDROTHERMAL CARBONIZATION OF OIL PALM SHELL

Abstract

Hydro-char is a most exciting contender of biomass energy. The interest in hydrochar production has increased because of its unique properties, benefits and a wide range of applications. Hydrothermal Carbonization (HTC) supported synthesis of biomass leads to the higher hydrochar yield percentage with higher carbon and energy density. The present work aims to find out the optimized hydrochar production using HTC. To optimize the parameters for higher hydrochar yield, Design Expert® Version 6.0.8 was used. Hydrochar production depends on different parameters such as reaction temperature, reaction time, and biomass to water ratio. The effect of these factors was studied with the help of Central Composite Design (CCD). The range of parameters selected was temperatures from 180-260 C, reaction times from 30-120 minute and biomass to water ratio of 1.10-1.60 by wt. %. The chemical, dielectric, and structural characteristics of the hydrochar product and the oil palm shell were studied. The study found the optimized condition for hydrochar yield percentage is at 180 C, within 30 minutes reaction times and 1.60 biomass to water ratio by wt. %. The elemental analysis suggests the carbon content increased, whereas the hydrogen and oxygen contents decreased with an increase in temperature. FESEM analysis in the study shows the HTC has altered the structure of oil palm shell significantly, in which few pairs were present on the rough surface of the oil palm shell. After the HTC, the surface porosity of hydrochar increased. The BET surface area, average pore diameter, and total pore volume of hydrochar also increased.