Optimization of primary sewage sludge and coal lignite by microwave-assisted pyrolysis for the production of bio-oil

Abstract

ABSTRACT In the present study, the raw materials and produced bio-oil were characterized in terms of physical and chemical properties. Response surface methodology (RSM) based on central composite was used to investigate the process parameter significance on bio-oil yield. The statistical significance is indicated by P-value of less than 0.05 at 95% confidence level. For raw material, coal lignite spectrum showed potential existence of phenols, alcohol and water linked to mineral water associated with the hydroxyl group found in stretching vibrations that are between 3200 and 3400 cm−1. The oxygen-containing groups such as C = O, C–O and aromatic skeletal lignin from lignocellulosic materials were observed on the coal lignite spectrum. Sewage sludge spectrum showed the presence of amide I, amide II, aliphatic methylene, lipids and fats. Si-O of clay minerals and silicates impurities were attributed by peaks 872 and 1031 cm−1 on the primary sewage sludge spectrum, respectively. The produced bio-oil results from Gas chromatography-Mass spectrometry (GC-MS) were in agreement with Nuclear magnetic resonance (NMR) and Fourier-transform infrared (FTIR) spectroscopy results. Maximum bio-oil of 42 wt% was obtained under the following conditions : temperature, 550°C, heating rate, 180.3°C/min and particle size 425 µm.