Co-pyrolysis of lentil husk wastes and Chlorella vulgaris: Bio-oil and biochar yields optimization

Abstract

The ever-increasing demand for fossil fuels has led to environmental issues and depletion of energy resources, as a consequence, a growing interest in biomass as a promising renewable and sustainable feedstock for biofuels production is developing. In this work, lentil husks (agricultural wastes) and Chlorella vulgaris (microalgae) were selected to investigate their interaction during co-pyrolysis process. Using a response surface methodology (RSM), a series of experiments were designed and carried out in a fixed bed reactor varying the temperature of 400–600 °C, heating rate of 5–25 °C/min and algae to husk blend ratios of 0, 25, 50, 75, 100 wt% at constant flow rate of argon carrier gas, 0.4 L min−1. The yield of Bio-oil and biochar as co-pyrolysis products were studied both quantitatively and qualitatively. The results unraveled a significant improvement on bio-oil yield by addition of C. vulgaris to lentil husk. Bio-oil yield increased from 13.8% to 20.8% by increasing algae content from 0% to 100% (T = 500 °C, HR = 15 °C min−1). While at T = 600 °C, the gas yield increased to 40.15%. and lower temperature (400 °C), favored biochar formation (39.5%), finally optimization results could lead to bio-oil yield of 18% (T = 479 °C, HR = of 16 °C min−1, R = 54%). The quality of the product at optimized level was featured by a rise in the carbon and a decrease in the oxygen content of bio-oil, and a bio-oil with improved higher heating value was obtained. The results of volatile products analyzed by Gas chromatography–mass spectrometry (GC-MS) showing that, the co-pyrolytic oil was rich in alkanes and aromatics compounds. Synergistical interactions between C. vulgaris and lentil husk, showed that alcohols, ketones and esters went through a remarkable reduction and phenols formation as valuable chemical compounds was improved.