Study of the reaction mechanism for preparing powdered activated coke with SO_(2)adsorption capability via one-step rapid activation method under flue gas atmosphere

In this study,the impact of different reaction times on the preparation of powdered activated carbon(PAC)using a one-step rapid activation method under flue gas atmosphere is investigated,and the underlying reaction mechanism is summarized.Results indicate that the reaction process of this method can be divided into three stages:stage I is the rapid release of volatiles and the rapid consumption of O_(2),primarily occurring within a reaction time range of 0-0.5 s;stage II is mainly the continuous release and diffusion of volatiles,which is the carbonization and activation coupling reaction stage,and the carbonization process is the main in this stage.This stage mainly occurs at the reaction time range of 0.5 -2.0 s when SL-coal is used as material,and that is 0.5-3.0 s when JJ-coal is used as material;stage III is mainly the activation stage,during which activated components diffuse to both the surface and interior of particles.This stage mainly involves the reaction stage of CO_(2)and H2O(g)activation,and it mainly occurs at the reaction time range of 2.0-4.0 s when SL-coal is used as material,and that is 3.0-4.0 s when JJ-coal is used as material.Besides,the main function of the first two stages is to provide more diffusion channels and contact surfaces/activation sites for the diffusion and activation of the activated components in the third stage.Mastering the reaction mechanism would serve as a crucial reference and foundation for designing the structure,size of the reactor,and optimal positioning of the activator nozzle in PAC preparation.

Optimization of process parameters for preparation of powdered activated coke to achieve maximum SO_(2)adsorption using response surface methodology

Powdered activated coke(PAC)is a good adsorbent of SO_(2),but its adsorption capacity is affected by many factors in the preparation process.To prepare the PAC with a high SO_(2)adsorption capacity using JJ-coal under flue gas atmosphere,six parameters(oxygen-coal equivalent ratio,reaction temperature,reaction time,O_(2)concentration,CO_(2)concentration,and H_(2)O concentration)were screened and optimized using the response surface methodology(RSM).The results of factor screening experiment show that reaction temperature,O_(2)concentration,and H_(2)O(g)concentration are the significant factors.Then,a quadratic polynomial regression model between the significant factors and SO_(2)adsorption capacity was established using the central composite design(CCD).The model optimization results indicate that when reaction temperature is 904.74℃,O_(2)concentration is 4.67%,H_(2)O concentration is 27.98%,the PAC(PAC-OP)prepared had a higher SO_(2)adsorption capacity of 68.15 mg/g while its SO_(2)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 m^(2)/g and 0.1475 cm3/g,significantly higher than the 186 m^(2)/g and 0.1041 cm3/g of AC1,and the 132 m^(2)/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 SO_(2)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.