Isothemal Adsorption Of Sulfur Dioxide On Activated Carbon

Four different commercial activated carbons (ACs) were selected as adsorbent for desulfurization. The pore structure of activated carbon was characterized by surface area analyzer, and the surface functional groups on activated carbon were characterized by Fourier transformed infrared spectroscopy (FTIR) and Boehm titration. Then, using the simulated flue gas containing SO2, N2, O2and H2O as adsorbates, the isothermal adsorption experiments were carried in a fixed-bed under different conditions. The adsorption characteristics of SO2in a fixed-bed under different process parameters were conducted. The correlation between the properties of ACs and their adsorption capacities were discussed. The adsorption kinetics and equilibrium of SO2on different ACs were analyzed. Besides, a mass transfer model of fixed-bed system was derived. The primary conlutions are listed as follows:(1) The SO2adsorption performance in different kinds of activated carbon under different adsorption conditions, such as temperature, particle size of adsorbents, inlet concentration and the height of fixed-bed, were studied. The results showed that the breakthrough time and SO2adsorption capacity increased with the relative humidity increase and the particle size of adsorbents decrease, with the inlet concentration increasing, the breakthrough time decreased, and SO2adsorption capacity increased obviously at the low concentration region. As the adsorption temperature increased, both the breakthrough time and SO2adsorption capacity decreased obviously. Besides, when the height of fixed-bed increased, the breakthrough time increased obviously, while SO2adsorption capacity increased slowly. Moreover, the breakthrough time decreased while SO2adsorption capacity increased with the superficial velocity increased.(2) Correlation between the properties of activated carbon and SO2adsorption capacity were discussed. It was illustrated that the SO2absorption capacity has a good linear relation with supermicropore volume, micropore volume and micropore specific surface area, respectively. Supermicropore of activated carbon had a negative effect on SO2adsorption. The effect of activated carbon properties on SO2adsorption capacity can be ranked in order as supermicropore volume, micropore volume, micropore specific surface area, total specific surface area, total volume and ultramicropore volume. SO2adsorption capacity decreased with the acidic functional group increase, and increased with basic functional group increase. The basic functional groups on activated carbon exhibited a benefit effect on SO2adsorption.(3) The adsorption kinetics and equilibrium models were used to predict the SO2adsorption performance. The results showed that the nonlinear fitting models of adsorption kinetics for SO2adsorption in activated carbon were ranked in order as Bangham model, Lagergren model, Ho model and Elovich model. The linear fitting of adsorption isotherm were ranked in order as the Redlich-Peterson, Freundlich, Langmuir-1, Langmuir-2, Langmuir-3, and Langmuir-4. The nonlinear fitting of adsorption isotherm were ranked in order as the Redlich-Peterson, Freundlich, and Langmuir. The nonlinear fitting of Redlich-Peterson isotherm and Freundlich isotherm were better than the linear fitting.(4) A mass transfer model of fixed-bed system was derived. The effects of mass transfer coefficient, temperature, inlet concentration and superficial velocity on concentration distribution were studied. The results showed that simulation values by model were agreement with experiment. With the mass transfer coefficient decreasing, the mass transfer zone widened, and concentration curve slowed. When the adsorption temperature and inlet concentration increased, the mass transfer zone moved faster. As the superficial velocity increased, the length of mass transfer zone was change from short to long, and the breakthrough time decreased. With the adsorption temperature and superficial velocity increasing, the mass transfer coefficient increased. However, there was a little increase of the mass transfer coefficient, when the inlet concentration increased to an extent.