Study in the Changes on the Functional Groups Present in Biomass during Pyrolysis Process

In this study, investigate the changes occurs on the functional groups of biochar materials. The biomass materials subjected to the pyrolysis, which is a thermochemical conversion process to obtain biochar material. It was produced by slow-pyrolysis method by subjected in different pyrolysis temperatures (400, 600, 800 and 1000°C). Effect of the treatment procedures was determined by the modifications in the functional groups of the obtained bio-char during the pyrolysis treatment was determined with the Fourier transform infrared spectroscopy (FT-IR). FTIR methods deliver fast, low-cost and non-destructive analysis and have shown qualitative and quantitative outcomes. The analysis was applied to some agricultural biomass materials such as saw dust, rice hull, wheat hull, tea wastes, and eucalyptus shell. Results are associated with literature, and species potentially computable by Fourier Transform Infrared Spectroscopy are reviewed. The result showed that the aliphatic, hydroxyl and aromatic groups gradually diminishes by increasing the temperature from 400 to 1000°C.


Introduction
Recently, energy needed in the world has increased dramatically. Therefore, it is likely that fossil fuels cannot meet the energy demand in the next some decade. Besides, the fossil fuels and its derivatives have caused significant environmental risks due to the formation of harmful oxides likes nitrogen, carbon, and sulphur. These reasons have moved our attention towards alternative energy source that is renewable and environmentally friendly. Solid bio-waste is one of the demandable source of energy for future energy demand due to its sustainable nature. Biomass is the leading energy source in the world which comes after fossil fuels and it providing about 14% of the world's energy demand. Biomass is providing 35% of their energy in developing nations [1]. Biomass has likely to provide energy with almost zero-emissions [2]. Biomass and its application provides an effort to utilize the energy stored in it as an alternate fuel in order to conserve the other energy sources like coal, oil etc. Pyrolysis is one of the thermo-chemical processes that are conducted at high temperatures (400-1100°C) in the oxygen-less condition. During the pyrolysis process, biomass is converted into solid, liquid and gaseous products based on heating rates and time of pyrolysis [3]. Hence we can say that energy generated from biomass has a high capacity to bridge the global energy shortage gap caused by the depletion of fossil fuel resources while keeping environmental sustainability. This study includes the influence of temperature on different biomass feedstocks and their physicochemical properties. The different agricultural biomass were characterized by proximate & ultimate analysis, higher heating value (HHV) and field-emission Fourier transform infrared (FTIR) spectroscopy.

Biomass materials
The conditions in which pyrolysis process is accomplished can dramatically change the final properties and composition (solid, liquid and gaseous) of the products obtained from the process. The parameters like feedstock type and heating profile (i.e. pyrolysis temperature) have been frequently recognised as important variables for determining the composition and characteristics of produced biochar [4][5][6][7]. Besides, the significance of pyrolysis time during biochar production is less conclusive due to a limited number of studies varying these conditions. Therefore detailed investigations would aid in reaching a definitive conclusion on the importance and preferred value for these variables. Biomass samples used were mainly woody waste, crop residues and shells, this includes Saw Dust (SD), Rice Hull (RH), Wheat Hull (WH), Tea Wastes (TW), and Eucalyptus Shell (ES). The pyrolysis temperature range studied throughout the experimental work covered a range from 400°C to 1000°C with 600°C and 800°C values serving as intermediate values. This temperature choice covered the main regions of biomass degradation as well as the respective upper and lower limits of temperatures associated with slow pyrolysis at slow heating rate (15-25ºC/min). A low heating rate was selected to provide longer heating time in an attempt to provide tolerable time for sufficient heat transfer and heat penetration into the biomass particles. Based on realistic times seen in industrial sized units to generate fast conversion of feedstock to biochar, the residence times chosen were therefore 60 minutes.

Preparation of Biochar
Biochar is a solid and carbonaceous by-product of biomass. To obtain biochar, selected biomass subjected to reactor at different pyrolysis temperature at a low heating rate for characterization [8]. After pyrolysis, products were determined for biochar and yields of product were calculated as a proportion of feedstock weight on a dry weight basis.

Methodology 2.3.1. Proximate and ultimate analyses and higher heating value (HHV)
-Proximate analysis‖ was employed on selected and prepared materials for the estimation of physiochemical properties with ensuing standards -(ASTM E871-82, E1755-01, and E872-82)‖ [9]. And the proximate analysis for obtained biochar from studied samples was evaluated according to -ASTM D1762-84‖ standard method [10].
-ASTM E777, E778 and E775‖ standard method was ensued for -ultimate analysis‖ [11] to calculate the elemental components of the selected samples and their corresponding biochar using -CHNS analyser‖ (Vario EL III). In the ultimate analysis we determine the Carbon, Hydrogen, Nitrogen and Sulphur in weight percentage. Higher Heating Value (HHV) of all samples were estimated by -bomb calorimeter‖ (Model: AC-350 LECO) according to -ASTM D4809‖ standard [12].

Fourier-transform infrared (FT-IR) spectroscopy
FT-IR spectroscopy has been used as an influential methodical tool for the swift description of different types of biomass. FTIR spectroscopy tracks the existence of ‗molecular vibrations' that are representative of a chemical compound. This technique has broadly been used for the qualitative and quantitative interpretation of modifications in biomass structure during the process [13]. For FT-IR IOP Publishing doi:10.1088/1757-899X/1146/1/012023 4 study, FT-IR spectrometer (Perkin Elmer Spectra 2, USA) was exploited by the ‗pellet method' by blend with dried bio-char and pulverized KBr in the ratio proportion of 1:200 (Potassium Bromide).

Proximate, ultimate analyses and heating values of studied biomass samples
The physicochemical characteristics of the selected biomass samples are tabulated in Table 1 [14]. Their ash depends on the sample types and their geographic region. The HHV of selected biomass vary in the range of 14.77-19.61 MJ/Kg. These values are also within the range of literature value [15] and that is comparable with primary and other renewable energy source. Heating value directly affected by ash, its high or less weight percentage depends on the calorific value which shows their heating energy. From above evident, it can be concluded that high ash containing samples makes it less desirable as a ‗fuel' [16][17]. Agricultural biomass contains much more ash-forming components than some woody biomass [18]. In particular, the straw, grasses, and fast growing crops mostly have higher content of both the ash and high mobile elements (like Cl, K, Mg, S, Na, and Si) than wood biomass; and reverse is true for C content [18][19]. The higher HHV of Saw Dust and Coconut Shell is because of lower content of ash i.e. an incombustible component and higher amount of combustible components such as volatile matter, fixed carbon, carbon and hydrogen than in other biomass materials. Figure 1 Other peaks seemed at 1720 cm -1 i.e., C=O stretching and at 605cm -1 i.e., OH bending modes in WC [20][21]. In Addition the peak at 440, 805 and 1045-1108 cm -1 seemed in Wheat Hull and Rice Hull, i.e., for SiO 2 [22].

Proximate, ultimate analyses and higher heating value of obtained biochars
The ‗proximate', ‗ultimate analyses' and ‗HHV' of the carbonized products of studied biomass samples at different temperature are shown in Figure 2 (a)-(f). Biochar is mainly formed from the thermal breakdown of biomass. During pyrolysis the volatile matter is distorted into the gas and residue left as ashes [23]. From the Figure 2 (a)-(e), it can be seen that volatile matter gradually decreases with rise in temperature from 400 to 1000 o C during the pyrolysis process. Biochar derived at low temperature contains high VM because the existence of lignin in the biomass sample. Lignin cannot decompose at low temperature i.e. 400°C [24]. When the temperature increases upto 800 o C, a rapid loss seen in volatile matter content [25][26] because volatile organic compounds are breakdown at high temperature in organic cyclic and aromatic molecules. The observations of higher content of ash in WHC, RHC, and ESC than SDC, and TWC are similar to the observations of others [27][28].
Enriched content of silica, K 2 O, and other ash forming elements presents the in straw and husk materials, may be this reason of higher content of ash than in woody materials [25,27]. The content of inorganic salts influences the property of volatiles and reduction in the yield of the formation of biochar [28].
Pyrolysis process comprises an increase in aromatic structures in the obtained biochars structure. Figure 3 (a)-(e) demonstrate the FTIR spectra of biochar derived from different agricultural biomass samples at different temperatures. From Figures, it was seen that with increasing temperature from 400 to 1000ºC, the aliphatic losses occurs at 2944-2845 cm -1 band i.e. aliphatic C-H stretch [31]. The peaks appeared at (753-908 and 3040-3005 cm -1 ), (1375-1445 cm -1 ) and (1581-1708 cm -1 ) for aromatic carbon include C-H stretching, C=C & C-C and C-O Carbonyl stretch respectively [32][33]. This is obviously because during the carbonization process modification takes place in the functional group and with this aliphatic C-H band decreases but aromatic C-H band increases [34]. But, at 800-1000ºC, the strength of the hydroxyl groups and aromatic groups [31,35], gradually diminishes, i.e. band occurs at (3204-3411 cm -1 ) and (1570-1610 and 3045-3005 cm -1 ) respectively. At lower temperature (300 and 500ºC) the presence of number of bands representing functional groups in biochars but it disappeared in the temperature 800-1000ºC derived bio-chars. The shoulder around 1610 cm -1 in the WHC and RHC bio-chars, allocated to the ‗aromatic compounds', is still present at 800ºC temperature during the pyrolysis. At 400°C, there was greater transmittance at band of 1700 to 1000 cm -1 , stretching of the carboxyl group of C=O and the molecular bonds of C=C of the aromatic compounds compared to the biochar produced at higher temperatures.
In general, the presence of organic components with chemical responses and distinct structures is observed in the biochar samples, which affects on the reactivity of these materials. The biochars of

Conclusion
This study demonstrated the pyrolysis temperature effect on the physical and chemical characteristics of prepared biochars. The influence of the thermal modification on the Saw Dust, Rice Hull, Wheat Hull, Tea Wastes, and Eucalyptus Shell was investigated. With increasing in pyrolysis temperature, the yield%, VM and hydroxyl and aromatic functional groups of biochar significantly decreases. The degree of carbonization for biochars was enhanced with increasing temperature from 400 o C to 1000 o C. The aromaticity was considerably improved in biochar at high temperatures because a phase transition occurred in studied biomass samples. FT-IR analyses have shown to high potential to get a deeper understanding of structural relationship with their functional groups.