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

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 SBET and Vtot 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.