Optimization of palm oil mill sludge biochar preparation for sulfur dioxide removal

In this study, palm oil mill sludge was used as a precursor to prepare biochar using conventional pyrolysis. Palm oil mill sludge biochar (POSB) was prepared at different preparation variables, i.e., heating temperature (300-800 °C), heating rate (10-20 °C/min) and holding time (60-120 min). The prepared biochars were tested for sulfur dioxide (SO₂) adsorption in a fixed bed reactor using 300 ppm of SO₂ gas at 300 ml/min (with N₂ gas as balance). Response surface central composite experimental design was used to optimize the production of biochar versus SO₂ removal. A quadratic model was developed in order to correlate the effect of variable parameters on the optimum adsorption capacity of SO₂ gas. The experimental values and the predicted results of the model were found to show satisfactory agreement. The optimum conditions for biochar preparation to yield the best SO₂ removal was found to be at 405 °C of heating temperature, 20 °C/min of heating rate and 88 min of holding time. At these conditions, the average yield of biochar and adsorption capacity for SO₂ gas was reported as 54.25 g and 9.75 mg/g, respectively. The structure of biochar and their roles in SO₂ adsorption were investigated by surface area, morphology images, infrared spectra, and proximate analysis, respectively. The characterization findings suggested that POSB adsorbs SO₂ mainly by the functional groups.