Effects of pyrolysis temperature on production and physicochemical characterization of biochar derived from coconut fiber biomass through slow pyrolysis process

The purposes of this research were to investigate the competence of coconut fiber to produce biochar by slow pyrolysis process and analyze the effects of different pyrolysis temperatures on the yield and physicochemical properties of biochars. Coconut fiber biomass was subjected to slow pyrolysis process using a laboratory scale fixed bed reactor at six different temperatures ranging from 350 to 600 °C (at an interval of 50 °C). The slow pyrolysis process was carried out in an inert environment for 1 (one) hour at a constant heating rate of 10 °C/min. The physicochemical properties of biomass and obtained biochars were characterized by proximate analysis (VM, FC, ash), ultimate analysis (CHNSO), higher heating value (HHV), bulk density, BET surface area, pH, and electrical conductivity (EC). Functional groups and particle sizes of biomass and biochars were identified by FTIR and particle size distribution respectively. Surface morphology and pore distribution of the biochars were observed by SEM images. The pyrolysis temperature had a negative effect on biochar yield and reduced from 48.13 to 29.34% as the pyrolysis temperature increased from 350 to 600 °C. Fixed carbon, ash content, pH, organic carbon, specific surface area, EC, degree of aromaticity, and porosity of the biochars enhanced as the pyrolysis temperature rose from 350 to 600 °C. However, the volatile matter, VM/FC ratio, H/C ratio, HHV, bulk density, and particle sizes of biochars were negatively correlated with the pyrolysis temperatures. Higher pyrolysis temperatures increased aromatic C groups and recalcitrant characteristics, yielded smaller particles, and formed elongated and porous structures. The physicochemical properties of high-temperature biochars (500–600 °C) showed the potential to be used as soil amendments and an efficient tool for C sequestration and retention of nutrients, and water. The porous structures of high-temperature biochars can accommodate suitable soil-microorganism activities, increase water sorption, and increase soil density. Moreover, the high alkalinity of the biochars can assist to neutralize acidic soil and increases soil fertility and plant growth. On the contrary, low-temperature biochars (350–450 °C) are promising tools for solid fuels.