Study of the changes in the structural and thermochemical behaviour of Nigerian de-oiled physic nut (Jatropha curcas L.) seed kernel

Abstract

Biobriquettes are a type of biofuel made from compressed organic waste materials such as agricultural residues, that are used for cooking, heating, and electricity generation. In this work, raw, hydrolysed (acid and alkali) and torrefied Jatropha curcas L de-oiled seed kernel were subjected to elemental, thermal, higher heating value (HHV), surface functional chemical groups (FTIR) and Scanning electron microscopy (SEM). The pulverized de-oiled J. curcas L. kernel (DJSK) was transformed to torrefied biomass through torrefaction within a temperature range of 200-300 ℃ under nitrogen ambience for 30 min. duration of residence. The atomic O/C and H/C ratios of the raw DJSK, torrefied raw DJSK, torrefied acid-hydrolysed DJSK and torrefied alkali-hydrolysed DJSK biomasses at 300 ℃ were 0.83, 0.12, 0.13, 0.13 and 0.16, 0.10, 0.07 and 0.07 wt % respectively. A decrease in O/C and H/C ratios were observed in the raw and pretreated biomass samples, upon torrefaction, which may be due to torrefaction temperature. Elemental analysis of the raw and pretreated biomass samples shows that at the second weight loss step, volatilization and burning of the volatiles occur between 150 ℃ and 500 ℃, with a cellulose and lignin loses. The second stage pyrolysis is indicated as 332.4774 and 396.0412 wt % for DJSK. Increase in HHV were observed on both raw and hydrolysed samples as temperature rises from 200-300 ℃. For the raw DJSK, the HHV were enhanced by factors of 1.00, 1.17 and 1.46 at 200, 250 and 300 ℃ and the same observation was detected in acid and alkali- hydrolysed samples. The spectra of the raw, acid and alkali- hydrolysed samples were similar. The stretching of the hydroxyl group, H-bonded (OH stretch) extended between 3200 and 3570 cm^-1. The absorption peaks at 2800 to 3000 cm^-1 were allocated to Aliphatic C-H stretching in all DJSK samples and much more. The micrographs (via SEM) of the DJSK failed to exhibit any fiber-like compositions (woody biomass).