Study On Performance Of Modified Activated Carbon Adsorption Of Toluene Waste Gas Containing Water Vapor

VOCs （Volatile Organic Compounds） is one of the worst pollutants for theatmospheric environment in China. In May,2010, the General Office of the StateCouncil put forward a requirement for strengthening prevention and control of VOCs,which put VOCs and SO₂, NO_x, particulate matters together to be the optimal controlconditions for improving atmospheric environment. Adsorption method is one of themost effective to control emissions of VOCs from industrial fixed sources, and it costless than other processes. However the fixes industrial emission of VOCs has a largerelative humidity, amonnts vapor mixed in waste gas have a significant impact on theperformance and regeneration of the activated carbon.After reading a large number of relevant literatures, the author chose cheapcommercial activated carbon using coal materials, modified them with lowconcentration acid/alkali solution, change the surface properties of active carbon byloading acid/alkaline functional groups on it. Evaluate performance by dynamicadsorption that utilize modified activeed carbon as adsorbent and toluene as adsorbate.Through the series of experimental and analysis the data to find a modified condition toactive carbon that has the top performance for removing toluene in mixed gases withamount of vapor.The experimental results show that the specific surface area of the modifiedactivated carbon samples are becoming larger first and then smaller as the solutionconcentration rises. Especially, the specific surface area of the sample modified by1%NaHCO₃is1035.67m²/g, increased by18.01%than the original sample. When solutionconcentration is very low, attachments on commercial activated carbon are dissolved byacid or alkali solution that enriched the microporous structure and enlarged the specific surface area of the modified samples, but afer increasing the solution concentration to abalance point, overmuch acid/alkali solution will destroy the por structure of activatedcarbon samples that reduce the microporous structure and enhance the macroporous andmesoporous, and then diminish the specific surface area of the modified samples. Inaddition to this, undissolved sodium bicarbonate attached to the surface of modifiedactivated carbon samples which becoming impurities. Because of the modifying, thegross of chemical functional groups attached to activated carbon and the proportion ofacid and alkali are both changed: the proportion of acidic functional groups on the acidmodified samples is increased, the maximum is83.02%, then the samples performancecharacteristics of acid; the proportion of acidic functional groups on the alkali modifiedsamples is descreased, the minimum is23.87%, the the samples performancecharacteristics of alkali. Take iodine adsorption number as preliminary assessment forthe adsorption capacity of the activated carbon samples, experimental data indicate thatthe adsorption capacity is impacted by both specific surface area and chemicalfunctional groups: the increasing of specific surface area enhance physical absorptionwhile the changing of chemical functional groups results in the occurrence of chemicaladsorption. The dynamic adsorption experiment declear that the saturated adsorption ofcommercial activated carbon to toluene is243.87mg/g when relative humidity is10%,and this quantitative value can be even bigger by low concertration alkali solutionmodifying, the maximum is338.28mg/g, than the original sample increaseed38.17%.The saturated adsorption reduce24.93%, to143.87mg/g when relative humidityincreased to60%, all the modified samples’ saturated adsorption have significantreductions, alkali modifying is beneficial to toluene’s adsorption, the saturatedadsorption of1%NaHCO3modified sample is95.9%to the original value, however toomuch acid or alkali lead a decreasing of modified samples that weaken physicaladsorption, reduce the adsorption quantity.