Experimental Studies on Intermediate Pyrolysis of Lignocellulosic Biomass Coconut Shells

Abstract

In the present scenario, the energy sectors and individual entrepreneurs can opt for a new way of producing energy using the most abundant renewable energy sources available in the form of lignocellulosic agricultural waste. Among the lignocellulosic biomass, agricultural residues, coconut shells are carbon-rich and sustainable resources. In 2016-17, global coconut production has potentially exceeded upto 22 billion nuts. India is the world's third largest producer of coconuts after Indonesia and the Philippines. The total amount of coconut shell residue in India is as high as 2887 (kt/year). If used properly, coconut shells can generate 157 MW of potential power. The literature review showed that limited research studies have been conducted on the yield of the product from coconut pyrolysis. The novelty of current work is to envisage the methodology by intermediate pyrolysis to obtain a high quality of exhaustive end products which could be used as fuel or as raw material for value added chemicals. Pyrolysis is a thermal decomposition technology which decomposes carbonaceous bio wastes into liquids, gases, and char (solid residue) in the absence of oxygen. The thermochemical conversion of agricultural waste residues coconut shell is considered in the overall study through intermediate pyrolysis process. It is a fixed bed pilot scale reactor heated externally with the help of electric heaters. In this work experiments were conducted at elevated temperature 550-575 °C, three major end products are solid (Bio-char), liquid (Bio-oil/Tar) and pyro gases. The bio-oil resulted from intermediate pyrolysis was analysed for chemical composition using, Fourier transform infrared (FT-IR) spectra and gas chromatography mass spectroscopy (GC-MS). Additionally, bio-tar was separated into saturate, aromatic resin and asphaltene (SARA) fractions by using the column chromatography with the combination of n-pentane, toluene and ethanol solvents. The SARA fractions were further characterized by FT-IR spectra, elemental analysis and nuclear magnetic resonance (NMR) analysis. Challenges in using bio-oil as drop-in fuel or as a fuel additive include high moisture content, lower heating value, and low thermal stability. Besides, the bio-oils have limited miscibility with conventional petroleum fuels due to the presence of polar compounds like alcohols and carbonyl compounds. The storage stability of bio-oils is typically low due to the presence of compounds with reactive functional groups. Therefore, the bio-oil was upgraded for better physicochemical and elemental properties prior use. Hydrodeoxygenation (HDO) has attracted considerable attention as an efficient way of removing oxygen atoms from bio-oil rich in oxygenated compounds. Although several works have reported HDO chemistry on various bio-oils, HDO chemistry has never been applied to coconut shell derived pyrolytic oil. The bio-oil was upgraded with mild thermal and catalytic hydrodeoxygenation (HDO) and compares the elemental properties of the upgraded bio-oil samples. The higher heating value (HHV) of cr-CSPO was found to be 16.46 MJ/kg. The thermal and catalytic upgrading was performed at 250 °C, 30 bar of hydrogen pressure, a reaction time of 3 h, and a stirring speed of 350 rpm. In the case of catalytic upgrading, 10% of catalysts Ru-C and Pd-C (10 wt.% of cr-CSPO) were used as the catalyst. Also, the developed activated charcoal is implemented as counter electrode in demonstrating Dye Sensitised Solar Cell (DSSC) using naturally available sensitizer. In addition, Dye Sensitised Solar Cell based current and temperature sensors were developed for highly remote optoelectronics applications. Anthocyanin dye extracted from pomegranate juice generated maximum current of 10 mA/cm2. The characteristics of the cell were performed with different optic filters wavelength ranging 400-650 nm and the maximum efficiency was developed for wavelength of 443nm.