Optimization of process parameters for preparation of powdered activated coke to achieve maximum SO₂ adsorption using response surface methodology

Abstract

Powdered activated coke (PAC) is a good adsorbent of SO₂, but its adsorption capacity is affected by many factors in the preparation process. To prepare the PAC with a high SO₂ adsorption capacity using JJ-coal under flue gas atmosphere, six parameters (oxygen-coal equivalent ratio, reaction temperature, reaction time, O₂ concentration, CO₂ concentration, and H₂O concentration) were screened and optimized using the response surface methodology (RSM). The results of factor screening experiment show that reaction temperature, O₂ concentration, and H₂O (g) concentration are the significant factors. Then, a quadratic polynomial regression model between the significant factors and SO₂ adsorption capacity was established using the central composite design (CCD). The model optimization results indicate that when reaction temperature is 904.74°C, O₂ concentration is 4.67%, H₂O concentration is 27.98%, the PAC (PAC-OP) prepared had a higher SO₂ adsorption capacity of 68.15 mg/g while its SO₂ adsorption capacity from a validation experiment is 68.82 mg/g, and the error with the optimal value is 0.98%. Compared to two typical commercial activated cokes (ACs), PAC-OP has relatively more developed pore structures, and its S_BET and V_tot are 349 m²/g and 0.1475 cm³/g, significantly higher than the 186 m²/g and 0.1041 cm³/g of AC1, and the 132 m²/g and 0.0768 cm³/g of AC2. Besides, it also has abundant oxygen-containing functional groups, its surface O content being 12.09%, higher than the 10.42% of AC1 and 10.49% of AC2. Inevitably, the SO₂ adsorption capacity of PAC-OP is also significantly higher than that of both AC1 and AC2, which is 68.82 mg/g versus 32.53 mg/g and 24.79 mg/g, respectively.

Keywords

powdered activated coke (PAC) / SO₂ adsorption capacity / parameters optimization / response surface methodology

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