Activated Carbon Adsorption Properties And Mechanisms Of Processing Of Benzene And Toluene Gas

Benzene and toluene could be found to exist widely in decoration materials as toxic organic compounds, which are harmful to the environment due to their long cycle, low concentration and slow-release process. Elimination of benzene series pollution is becoming a hot research topic now. In this work, activated carbon, which can absorb the benzene and toluene effectively, has been prepared by use of microwave heating from waste raw materials.In this dissertation, waste coconut shell and the spent catalyst of vinyl acetate synthesis were used as raw materials to prepare high-performance activated carbon. The optimum conditions of the preparation were investigated. The optimized parameters were obtained as follows: the temperature from 850℃to 920℃and the steam flow rate from 3.5mL/min to 4.5mL/min. The characteristics and adsorption capacity for the methylene blue adsorption value and the iodine value of the activated carbon prepared by microwave heating were as follows:the surface area of 900-1000 m2/g, the pore volume of 0.80-0.95 mL/g, the average pore size of 5.10-5.90 nm,90-110 mL/g and 950-1100 mg/g. Energy saving, emission reduction, consumption reduction, environmental prevention could be realized by using microwave heating technology during preparation process. Nitrogen adsorption was used to study the pore structure of the activated carbon. The results indicated that the peaks of pore size in coconut shell activated carbon were centered at around 0.6nm,1.2nm and 1.5nm respectively, microporous accounted for 78.63%, regeneration activated carbon from spent catalyst were located in the peak pore size 0.8nm, 1.2nm and 1.6nm near the 73.03% total pores, which micropore peak with molecular diameter of benzene and toluene rather, which was suitable for adsorption of benzene and toluene. Moreover, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to observe the microstructures. Our results showed that activated carbon were one kind of non-crystalline material with rich pores. The activated carbon contained zinc oxide, which has the adsorption and photochemical catalysis effect. The concentrations of benzene and toluene were determined by photo-ionization detection gas chromatography (PID-GC). And the effects of the chromatographic column temperature, carrier gas pressure (chromatographic column carrier gas current capacity), injection volume and sample amount on gas chromatography column efficiency were studied, resolution and retention time effects, the optimal chromatograph conditions were as follows:the chromatographic column temperature of 50℃, the injection time of 5 seconds, the sampling time of 8 seconds, the nitrogen pressure for 41.2-41.5kPa. The photo-ionization gas chromatography was easier to control than the conventional chromatography, the method of determination can be used to the direct analysis of gas samples, which could reduce the gas concentration, thermal desorption, giving rise to the more accurate results of the experimental adsorption data.The adsorption isotherms, breakthrough curves and kinetic curves of benzene and toluene on microwave coconut-shell activated carbons were measured at different conditions. The adsorption experimental data were processed by Langmuir, Freundlich, Bangham, and the adsorption capacity of benzene were 326.6 mg/g,317.46 mg/g and 309.6 mg/g, toluene were 341.3 mg/g,322.58 mg/g, and 306.75 mg/g on microwave coconut-shell activated carbon at 20℃,30℃and 40℃, and the average heat of adsorption (△H), the adsorption free energy (△G) and adsorption entropy (△S) were calculated, the results indicated that the adsorption process was exothermic and spontaneous physical adsorption process, in practical applications, low temperature and enhancement flow of gas was the more favorable to the adsorption of activated carbon, and predicted the adsorption isotherm of character similar adsorbate on microwave coconut-shell activated carbons at the same conditions with Polanyi theory, the experimental results were closer to the predicted results, the maximum deviation was smaller than 6%.The adsorption isotherms, breakthrough curves and kinetic curves of benzene and toluene on regeneration activated carbons loaded zinc oxide were measured at different conditions. The adsorption experimental data were processed by Langmuir, Freundlich, Bangham, and the adsorption capacity of benzene were 278.55 mg/g,277.78 mg/g and 263.16 mg/g, toluene were 273.23 mg/g,273.22 mg/g and 264.55 mg/g on regeneration activated carbons loaded zinc oxide at 20℃,30℃and 40℃, and the average heat of adsorption (△H), the adsorption free energy (△G) and adsorption entropy (△S) were calculated, the results indicated that the adsorption process was exothermic and spontaneous physical adsorption process, in practical applications, low temperature and enhancement flow of gas was the more favorable to the adsorption of activated carbon, the photocatalytic properties of on regeneration activated carbon loaded zinc oxide were studied in the light conditions, The penetration time of the benzene and the toluene have longer, and predicted the adsorption isotherm of character similar adsorbate on regeneration activated carbons loaded zinc oxide at the same conditions with Polanyi theory, the experimental results were closer to the predicted results, the maximum deviation was smaller than 6%.The results indicated that the adsorption capacity of benzene and toluene onto the coconut-shell activated carbon and the activated carbon loaded zinc oxide was huger than that of other activated carbons. The photo-ionization gas chromatography was more accurate, easier and faster than traditional gas chromatography. The experiments were of great significance to the disposal of waste, environmental protection and the recycling economy.