Study On Adsorption Of Low Concentration Gasoline Vapor Upon Activated Carbon And Its Regeneration Process By The Integration Of Microwave-Vacuum

Activated carbon adsorption process is one of the most common processes in oil vapor recovery technology,which can remove most of the volatile organic compounds（VOCs）from oil vapor.At present,activated carbon adsorption technology is often combined with other treatment techniques in oil vapor recovery process to strengthen the treatment of low concentration oil vapor.When the activated carbon is saturated by the vapor adsorption,it should be regenerated by vacuum desorption and hot air purging in the later stage.However,the regeneration effect of the current process is poor for the activated carbons saturated by oil vapor,accompanying with the problems including low desorption rate of gasoline vapor,incomplete regeneration of activated carbons and high treatment cost.Microwave regeneration is a new,efficient and environmental regeneration technology based on thermal regeneration,with the advantages such as rapid heating,low energy consumption,simple operation,etc.Relevant researches have showed that microwave regeneration could bring less loss to the adsorbent,and better restore its adsorption performance.Therefore,the microwave regeneration method was introduced in this article,to explore the appropriate regeneration process for the activated carbon saturated with gasoline vapor at low concentration.In this thesis,three types of solvent-recycled activated carbon（RAC-1,RAC-2 and RAC-3）were selected as the adsorbents for gasoline vapor,and oil vapor of 92#gasoline was used as the target adsorbent.With the BET method,the dynamic adsorption performances for gasoline vapor upon activated carbons at 25℃and the influences of activated carbons characteristics on the adsorption for gasoline vapor were investigated.The results were as follows:（1）The specific surface area of RAC-1 and RAC-2 were similar,both larger than RAC-3.While RAC-1 had higher micropore content and wider pore size distribution in the range of0.8～2 nm.（2）In the dynamic adsorption experiment of gasoline vapor concentration at 50 mg/L,the breakthrough adsorption capacity of RAC-1 was 38.5%higher than RAC-2,and nearly twice the capacity of RAC-3.In the adsorption equilibrium experiments of gasoline vapor concentration at 25-350mg/L,the equilibrium adsorption capacities of RAC-1 were higher than those of RAC-2 and RAC-3 at all concentrations.All of above indicated that RAC-1 should have better adsorption performance for gasoline vapor at low concentration.The fitting results of Logistic model towards adsorption experiment data were excellent（R²≥0.995）,while Yoon-Nelson model could be better used to describe the adsorption process of gasoline vapor before C/C₀ reached 0.6.Based on the experimental results in Chapter 2,RAC-1 was optimized to study the effects of various operation modes of microwave-vacuum coupling regeneration process on the desorption and regeneration for the vapor loaded activated carbon under the conditions of microwave power of 120 W and activated carbon dosage of 8 g.The operation modes were as follows:the desorption by continuous microwave-vacuum（mode I）;the desorption by intermittent microwave-vacuum at the constant temperature（mode II（1））;and the desorption by intermittent microwave-vacuum at the constant temperature,assisted by intermittent flushing with nitrogen（mode II（2））.The results showed that the optimal operation mode and process condition was from mode II（2）:cyclic 4.5 min of vacuum pumping-0.5min of vacuum breaking,which was called mode II（2）-c for shot.Under this condition,the bed temperature of activated carbon was at 115～130℃.After the desorption process within 60 min,the final desorption efficiency was 93.33%,which was higher than that of mode II（1）（85.42%）.According to the characterization results of the activated by BET,SEM and FTIR,it was showed that the specific surface area and micropore content of the regenerated activated carbons were slightly lower than that of the original carbon,while their skelitons were clear and orderly,the pore structures were still relatively abundant.Besides,the acid oxygen-containing functional groups from the surface of activated carbon were reduced,which was more conducive to the adsorption for gasoline vapor.At the same time,the difference of characterization parameters between mode II（2）-c and the original carbon was smaller,which indicated that the regeneration effect of mode II（2）-c was better.In this paper,the microwave-vacuum coupling regeneration process was compared with the conventional vacuum regeneration process to verify and evaluate the superiority of the microwave-vacuum regeneration process.The results were as follows:（1）At the same vacuum of-0.088 MPa),the desorption efficiency of vacuum desorption at room temperature was only2.5%,and that of vacuum desorption at 120℃by conventional heating was 62.92%,which were far lower than that of microwave-vacuum process.The single vacuum regeneration method was difficult to meet the regeneration demands of gasoline vapor loaded activated carbon.Increasing the desorption temperature could effectively improve the desorption efficiency,while microwave heating could improve the desorption rate of gasoline vapor by selectively heating the adsorbate.（2）Mode II（2）-c had higher desorption concentration and moderate activated carbon bed temperature,which was conducive to gasoline vapor recovery,activated carbon regeneration,and effectively avoided the loss of activated carbon at high temperature.In the process of desorption,nitrogen was intermittently introduced for vacuum breaking treatment,which also effectively improved the regeneration efficiency.（3）In the einmal desorption process,the unit vapor recovery cost of mode II（2）-c was 0.173 yuan/g,which was about 50.4%lower than that of conventional heating vacuum regeneration process and 6.0%lower than that of mode II（1）.Based on the above,considering gasoline vapor recovery,activated carbon regeneration performance and energy saving,the best regeneration method for oil vapor loaded activated carbon was intermittent microwave-vacuum at the constant temperature with the condition of cyclic vacuum pumping for 4.5 min-vacuum breaking by nitrogen for 0.5 min.