Research On Vacuum Thermal Regeneration Characteristics Of Activated Carbon Adsorbed Of VOCs

Regeneration and recycling of activated carbon are of great significance to reduce the cost of VOCs-containing waste gas treatment by adsorption and to reduce the amount of hazardous waste generated.Thermal regeneration has the characteristics of simple process and wide application range,but there are limitations such as incomplete adsorption mass desorption and short lifetime of activated carbon.In order to improve the regeneration efficiency of activated carbon,the vacuum thermal regeneration method was adopted to study the vacuum thermal regeneration characteristics of activated carbon for adsorption of VOCs and to provide a reference for the application of vacuum thermal regeneration.The research contents are as follows:(1)The physicochemical properties of coal honeycomb activated carbonⅠ,coal honeycomb activated carbonⅡ,coal columnar activated carbon and coconut shell activated carbon were analyzed.The results showed that the specific surface area sizes of the four activated carbons were 147,442,763 and 736 m~2/g,respectively,of which coal honeycomb activated carbonⅠwas mainly mesoporous,while coal honeycomb activated carbonⅡ,coal columnar activated carbon and Coconut shell activated carbon is mainly microporous;three functional groups,hydroxyl(-OH),carboxyl(-COOH)and lactone(C-O-C),exist on the surfaces of the four activated carbons;the results of TG-FTIR experiments show that the four activated carbons have good stability at temperatures less than 500℃,and this stage is mainly for the desorption of water,CO2 and volatile components adsorbed by the activated carbons and the pyrolysis of the chemical functional groups on the surfaces.The loss rate of activated carbon is small.(2)To investigate the effects of regeneration temperature and holding time on the regeneration effect under vacuum,four types of activated carbons adsorbed with ethyl acetate were regenerated under vacuum with different regeneration temperatures and holding times,and the results showed that the higher the regeneration temperature and the longer the holding time,the greater the desorption rate.The adsorption capacity of the regenerated activated carbons for ethyl acetate was restored to 92.4%,97.9%,98.7%and98.8%,respectively;the specific surface area and pore size distribution showed that the pore size distribution of the regenerated activated carbons was similar to that of the new activated carbons under the regeneration condition of 200℃,i.e.,the pore structure of the activated carbons was not affected at this temperature,which was beneficial to the restoration of their adsorption performance.The pore size distribution of activated carbon after regeneration at 200℃was similar to that of the new activated carbon.To investigate the influence of the pore structure of activated carbon on the regeneration effect,the pore volumes of different pore size ranges in different activated carbons were fitted linearly with the desorption rate of ethyl acetate respectively,and the results showed that the volume of micropores with pore size less than 1.34 nm was negatively correlated with the desorption rate,while the volume of pores with pore size greater than 4 nm was positively correlated with the desorption rate.In order to study the effect of the nature of VOCs on the regeneration effect,vacuum thermal regeneration experiments were conducted on coal column activated carbon adsorbed with different VOCs,and the results showed that the order of the desorption rate of different VOCs was isopropyl alcohol>ethyl acetate>toluene,which was related to the adsorption energy,polarity and saturation vapor pressure of VOCs.The thermal regeneration experiments of coal columnar activated carbon adsorbed with ethyl acetate were conducted under vacuum,air atmosphere and nitrogen atmosphere,and the desorption rates of thermal regeneration under vacuum at 100℃for40 min increased by 46.2%and 43.4%,respectively,compared with the other two regeneration methods,and at 200℃for 40 min increased by 17.3%and 15.7%,respectively,indicating that the regeneration under vacuum conditions The regeneration effect was better under vacuum conditions.(3)The results of cyclic regeneration of four activated carbons for ethyl acetate adsorption showed that the desorption rate of ethyl acetate decreased gradually with the increase of regeneration times,while the desorption rate was greater than 100%when the regeneration temperature was increased.The main reason was that the adsorption rate decreased due to the stronger adsorption force between ethyl acetate and activated carbon surface during the cyclic regeneration process,and the specific surface area of the regenerated activated carbon decreased,resulting in the decrease of the adsorption performance of the activated carbon.Furthermore,the feasibility of pyrolysis disposal of waste activated carbon was studied through vacuum pyrolysis experiments.The results showed that the volatile matter in the activated carbon could be completely removed at1000℃,resulting in a carbon material with a fixed carbon content of 85.98%.