Production of bio-oil from coir pith via pyrolysis: kinetics, thermodynamics, and optimization using response surface methodology

This study evaluates the potentiality of coir pith, an agro-industry by-product, as a low-cost feed-stock for the production of bio-fuels and other value-added chemicals. Thermogravimetric analysis was done to evaluate kinetics, thermodynamic, and mechanistic models of coir pith pyrolysis process. Optimal pyrolysis condition was fixed by using response surface methodology (RSM) in combination with central composite design (CCD). Pyrolysis experiments were carried out by using a miniature fixed-bed reactor at the temperature range of 200–400 °C with the heating rates and nitrogen flow rate ranges of 20–40 °C/min and 70–200 ml/min, respectively. As suggested by the Design expert software, maximum yield of bio-oil (29.31%) can be obtained at temperature of 349.14 °C, heating rate of 21.58 °C/min, and nitrogen flow rate of 196.61 ml/min, which was very much similar to the experimental yield (29.02 ± 0.05%). The bio-oil obtained at this condition was characterized by elemental analysis and different spectroscopic and chromatographic techniques including 1H-NMR, FTIR, and GC-MS. The calorific value of bio-oil was found to be 28.38 MJ/kg. Characterization of bio-oil obtained at the optimum process condition indicates that produced bio-oil is a combination of aliphatic as well as aromatic hydrocarbons which can be represented by the empirical formula of CH1.80 N0.04 O0.35. This investigation also revealed that the kinetic and thermodynamic analyses can correctly predict the possible pyrolysis temperature range for coir pith pyrolysis. The results obtained from the present investigation therefore suggest the suitability of coir pith as a potential feedstock for the conversion of energy and value added chemicals.