Characterisation of Bio-Oil and Bio-Char from Slow-Pyrolysed Nigerian Yellow and White Corn Cobs

Abstract

Cobs from yellow and white corn were slow pyrolysed at 450°C in a laboratory-scaled fixed bed reactor. Product distribution obtained was: 42.6% and 44.8% condensate, 33.3% and 33.5% bio-char, and 24.1% and 21.7% non-condensable gas for white and yellow corn cobs respectively. 13.6% bio-oil was recovered from white cob condensate and 10.12% for yellow cob. The resulting bio-oil with pH of around 5 and density of ~1.1 g/cm3 was found to be stable on storage over a period of 10 months. Ash level and viscosity at 50°C were (0.12% and 0.10%) and (41.2 cSt and 20.8 cSt) in bio-oils from the cobs of yellow and white corn respectively. Characterisation with gas chromatography revealed that the bio-oil contained cellulose and lignin-derived compounds. Bio-chars from these residues have higher heating value of ~30.00 MJ/kg, pH of ~8, bulk density of ~0.220 g/cm3 and ash level of ~1.7%. Scanning Electron Microscopy (SEM) coupled with Energy Dispersive X-ray Spectrometry (EDS) was used to examine the morphology and elemental composition of these bio-chars. The bio-char produced is capable of contributing 83.6 billion MJ to energy demand in Nigeria and preventing about 6.8 million tonnes of CO2 emission into the environment.