Study Of Adsorption And Desorption CO₂on Pore Structure Of Activated Carbon

The production and exportation of activated carbons in China is the most in the world, butthe advanced technique of preparation activated carbons is fall behind Amercia, Japan. Forinstance the activated carbons which are used PSA refine H2are relied on import, domesticsimilar samples have disadvantage of little adsorption capacity and short using period. In thisthesis, coal-based and coconut activated carbons using PSA refine H2in the market are appliedto characterize, the effect of pore structure and surface chemistry performance of activatedcarbon on CO₂adsorption and desorption are studied, then the influence activation reaction bydifferent activation medium and condition of preparation are also studied, they werechemically modified by HNO3, H2O2and （NH4）2S2O8, circulate adsorption and desorption CO₂were used to characterize performance of activated carbons. Main contents and results aresummarized as follows:1、Adsorption and desorption CO₂The adsorption and desorption properties of CO₂oncoal-based and coconut activated carbons were investigated in an atmospheric dynamicadsorption reactor. The adsorbents were characterized by CO₂and N2adsorption isotherms,FT-IR analysis and Boehm titration. The results show that micropore volume of activatedcarbons is an important factor to characterize the adsorption performance of CO₂, the pore sizedistribution in the range of0.5～1.0nm or2.0～4.5nm trend to enhance the adsorption of CO₂.The carboxyl and hydroxy groups on activated carbons could enhance CO₂adsorption capacity.However, the carbonyl groups would reduce CO₂.The high desorption rate and wide pore sizedistribution made adsorption capacity reduced more slowly in cyclic adsorption.2、Preparation of activated carbon by steam and CO₂Developed microporous activatedcarbons were prepared from carbonized coal by using steam activation and CO₂activation. TheN2adsorption-desorption isotherms, iodine value, methylene blue value, CO₂adsorptioncapacity and desorption value, SEM were applied to characterize activated carbons. The resultsshow that the main pore of activated carbons distribute in the range of0.5～1.0nm both using steam activation and CO₂activation, the pore in the range of0.5～1.0nm of C_900,3are more10%than H900,3, while the mesopore of H900,3and C_900,3respectively distribute in the range of2.0～3.0nm and2.0～2.5nm. The methylene blue value, iodine value and CO₂desorption value ofH900,3are higher than C_900,3, but the CO₂adsorption capacity of C_900,3are higher than H900,3,and the adsorption capacity of C_900,3decrease more less in process of cyclic adsorption.3、Technology of activation Coal-based and coconut activated carbons are preparationby CO₂activation, they were chemically modified by HNO3, H2O2and （NH4）2S2O8, circulateadsorption and desorption CO₂were used to characterize performance of activated carbons.Results showed that CO₂adsorption capacity of coal-based and coconut activated carbons are52.23and68.25mL/g in preparation condition of900℃,3h, and3L/min of gas flow, thenBET surface area, total volume, micropore volume,0.5～1.0nm volume and microporosity ofcoconut activated carbons are higher than coal-based activated carbons, while the pore size ofcoal-based and coconut activated carbons respectively distribute in the range of2.0～3.0nmand2.0～2.5nm. The HNO3could reduce CO₂adsorption capacity, while H2O2and（NH4）2S2O8could enhance CO₂adsorption capacity, but the cycle adsorption capacity arereduced remarkably by the chemically modified.4、Adsorption kinetics The diffusion behavior and adsorption kinetics of CO₂at differenttemperature on activated carbons were studied. Results showed that the diffusion coefficientincreases with an increase of temperature, the value of diffusion coefficient is between surfacediffusion and Kundsen diffusion. The kinetics of CO₂adsorption are satisfied with Banghamequation, and the value of CO₂adsorption capacity obtained through Bangham equation is veryclose to experimental date.