Study On The Modification And Application Of Activated Carbon Used For Volatile Organic Compounds

Volatile organic compounds?VOCs?are an important part of atmospheric pollutants,and also a major source of haze particulate matter?PM2.5,PM10?.They have many types with complex compositions,not only can destroy the ecological environment,but also endanger human health.Activated carbon as an environmentally friendly adsorption material,are widely used in the recovery of VOCs industry.By recycling high concentration and high value VOCs,can protect the atmospheric environment and create huge economic benefits for the enterprise.But activated carbon for VOCs recovery get in the market show poor adsorption capacity and regeneration performance,low strength and ignition point,which restricting the application and life of activated carbon.Therefore,the research on the modification of activated carbon has great significance and value for the environmental protection and the industry of activated carbon.In this paper,the strength,ignition point and pore structure of activated carbon used in VOCs recovery are modified by three methods:high temperature reforming,secondary activation by CO₂ and surface coating.We studied adsorption kinetics of butanone on modified activated carbon at last.The main contents and results are summarized as follows:1.Study on the performance of wooden molding activated carbon by high-temperature reformingThe effect of high-temperature reforming method on the performance of commercial wooden molding activated carbon materials prepared by phosphoric acid activation was studied.The effects of different heating and cooling modes,reforming temperature and reforming time on the strength of activated carbon materials were investigated.We found that when the activated carbon were heated to 800 ? by rapid heating-up and reformed for 30-75 min before rapid cooling,the strength of activated carbon increased by 5.75%-6.39% and the yield of activated carbon maintained more than 83.54%.The pore structure and adsorption capacity of activated carbon after reforming at 800 ? for 30 and 60 min were also studied.The results showed that the specific surface area and total pore volume of activated carbon decreased by about 400 m2/g and 0.2 m3/g respectively,the proportion of pores with pore size distribution smaller than 1.2 nm increased;The adsorption capacity of methylene blue showed a small decline,the adsorption capacity of iodine slightly increased,and butane working capacity decreased less than 15%.After high-temperature reforming,ignition point of activated carbon significantly increased:when activated carbon was reformed for one hour at 800 ?,its ignition temperature was improved 100 ? or more.This was mainly related to the reduction of the amount of oxygen functional groups on the surface of activated carbon after high-temperature reforming.The increase of the strength of activated carbon after high-temperature reforming were related to the volume shrinkage and the improvement of the graphitization degree.2.Study on the performance of activated carbon after high-temperature reforming by secondary activationIn order to solve the adsorption performance degradation caused by high-temperature reforming,based on the experimental results of activated carbon after high-temperature reforming,we studied the effect of the secondary activation by CO₂ on the properties of activated carbon adsorption.The results showed that the strength of activated carbon decreased less than 0.5% after secondary activation by carbon dioxide for 30 min,and the butane working capacity return to the level before high-temperature reforming.The adsorption capacity of methylene blue was slightly decreased,and the adsorption capacity of iodine was obviously increased.Experiments showed that the use of CO₂ for the secondary activation made activated carbon generate more developed micropore structure,which can effectively improve the adsorption performance of activated carbon after high-temperature reforming.After reactivation by CO₂,the number of oxygen functional groups on the surface of activated carbon increased,leading to ignition temperature declined.Considering the strength,ignition temperature and yield of activated carbon were going to worse.,the reactivating time should be less than 30 min.3.Study on preparation and properties of the formed activated carbon coated with ethyl celluloseEC was a kind of cellulose alkyl ethers,with thermoplastic and low flammability.The film made by EC has strong permeability,high mechanical strength and flexibility,widely used in solid preparation of film coating and gas separation membrane.In this paper,we used EC as coating material and ethanol as the solvent,dissolve them into coated liquid at 50 ?.In order to prepare activated carbon products coated EC,the coated liquid was uniformly sprayed on the surface of formed activated carbon before heat treatment.The influence of the concentration of coated liquid,spray volume and heat treatment temperature on the strength and adsorption properties of activated carbon after coated were studied.It was found that when the membrane concentration was 2.50%-4.50%,the ratio of spray volume and activated carbon mass was 0.67 m L/g,heat treatment temperature was 110-140 ?,coating can significantly improved the strength of formed activated carbon.Under this conditions,the strength of coated activated carbon increased more than 7% and the butane working capacity decreased within 10%,on the surface of the activated carbon generated a thin film with thickness 3-4 ?m.The pore structure of coated activated carbon remained unchanged,and the surface hydrophobic property was significantly enhanced with the water contact angle close to 90°,which was favorable for the use in the environment with high water content.4.Dynamic analysis of adsorption behavior of butanone on modified activated carbonActivated carbon modified by high-temperature reforming and secondary activation was used to study dynamic analysis of adsorption behavior of butanone.when the water bath temperature at 20?30?40 and 50 ? respectively,carrier gas?N2?flow of 400 mL/min,butanone steam concentration under the condition of 0.314 g/L,we studied the relationship between the adsorption quantity and time,found that the modified activated carbon adsorption butanone was exothermic reaction and the saturated adsorption amount of butanone decreased with the increasing of temperature.The experimental datas of activated carbon adsorption butanone were fit by first order kinetics model,pseudo-second order kinetics model,Elovich kinetics model and Bangham kinetics model.It was found that the adsorption process of butanone followed Bangham kinetics model.The value of experimental data was very close to the value of qe obtained through Bangham kinetics model and correlation coefficient R² reached 0.99 or more.