| Atmosphere is one of the indispensable environmental factors for human survival and development.It provides an ideal environment for the multiplication of life and the development of human beings on earth.With the high development of human social productivity,the atmospheric problem is becoming increasingly serious,which seriously affects the survival of all kinds of organisms and seriously damages human health on earth.Therefore,it is urgent to protect the environment and find materials to improve the current situation of atmospheric pollution.Adsorption technology is one of the most potential treatment methods for VOCs,and the rich diversity of adsorbent materials and the stability of adsorption products make the technology has the advantages of high efficiency,low cost,green and pollution-free,with practical application and operability.In this paper,the pollution status and treatment technology of VOCs were briefly analyzed,and adsorption technology was adopted to deal with VOCs.Sulfuric acid was selected as modifier,o-xylene as model compound of benzene series in VOCs,silica gel?SG?and activated carbon?AC?as the adsorbent carrier.The removal mechanism and removal ability of o-xylene from modified silica gel?Modi-SG?and modified activated carbon?Modi-AC?were systematically investigated by dynamic adsorption.This study can provide a new theoretical and experimental basis for the application of adsorption method in the treatment of VOCs.The main research contents and results are as follows:1.Removal and mechanism of o-xylene by silica gel supported sulfuric acidSupported sulfuric acid?SSA?was prepared with chromatography silica gel as the carrier,and o-xylene was used as the model pollutant to systematically investigate the influence of adsorption reaction temperature,supported sulfuric acid mass concentration,sample preparation temperature,sample preparation time,sulfuric acid load and gas purification process conditions on the removal performance of the target material.The removal mechanism of o-xylene by supported sulfuric acid was investigated by means of nitrogen absorption and desorption isotherm?BET?,cold field emission scanning electron microscope?SEM?,X-ray diffractometer?XRD?,Fourier transform infrared spectrum?FTIR?,NMR hydrogen spectrum?1H NMR?and NMR carbon spectrum(13C NMR).The results showed that:?1?compared with the removal rate?about 5%?of o-xylene by original chromatography silica gel,the adsorption reaction temperature of the supported sulfuric acid sample showed three obvious regions:an activation region?<125??,a reactive region?125160??and a deactivated region?>160??.When the reactive region temperature at 130?and 140?,the removal rate of o-xylene can reach 99%,the breakthrough time?tB?and the adsorption capacity?qB?were 117 min,408.49 mg/g and 119 min,414.37 mg/g,respectively.?2?when the mass concentration fraction of sulfuric acid changed from 50%to 98%,the SSA breakthrough time was 87 min,91 min and 76 min,respectively.The removal ability of o-xylene from large to small was?70%??50%??98%.The removal effect of 70%supported sulfuric acid sample was the best.?3?The sample preparation time had little effect on the removal rate of o-xylene,and the maximum time difference was 7 min,accounting for only 7.1%of the adsorption breakthrough time.The removal rate of o-xylene could be improved by increasing the pretreatment temperature of samples and the breakthrough time was prolonged by 11 minutes and 13 minutes respectively,when the temperature rose from 80?to 120?.The removal efficiency of o-xylene at 100?and 120?was similar.?4?The silica gel supported sulfuric acid samples with different sulfuric acid loadings all had certain removal capacity for o-xylene,and the removal capacity from small to large was as follows:SSA-5<SSA-10<SSA-15<SSA-20,20 mmol/g of SSA had the best removal efficiency for o-xylene.?5?The removal performance of o-xylene by target materials was obviously affected by the change of process conditions,and the optimum process conditions were as follows:the inlet cooling pump temperature was set at 0?,the sample mass was 0.1 g,and the carrier gas velocity was 50 mL/min.?6?A series of characterizations were analyzed from the physical properties of the material itself,and further analysis was made on the recognition of functional groups and the level of molecular structure.It was proposed and verified the reaction mechanism of o-xylene on the surface of modified materials to be chemical adsorption,that was,sulfonation reaction mechanism.2.Removal of o-xylene by desiccant silica gel supported sulfuric acidThe desiccant silica gel supported sulfuric acid?Modi-DBSG?Modi-FDSG?were prepared by isovolumetric impregnation with two cheap commercial desiccants silica gel as carriers.The effects of adsorption temperature,sample particle size and process conditions on the removal of o-xylene from sulfuric acid modified silica gel were investigated by dynamic adsorption experiment.The original sample,modified sample and adsorbed sample were characterized by BET,SEM,XRD and FTIR.The results showed that:?1?There were three regions of adsorption temperature,and the removal rate of o-xylene could reach more than 90%when the temperature of reactive region was at160?.?2?The effect of particle size on adsorption efficiency was as follows:the smaller the particle diameter of sample,the greater the contact probability with o-xylene,the higher the removal rate of o-xylene.The breakthrough time of samples with different particle size was:20-40 mesh/78 min,40-60 mesh/114 min,and 60-100 mesh/166 min,respectively.The o-xylene removal efficiency of60-100 mesh sample was the best.?3?The effect of adsorption process on the removal of o-xylene from two modified silica gels was similar to that of SSA,and the optimum experimental conditions were cooling pump temperature at 0?,sample mass at 0.1 g and carrier gas velocity at 50 mL/min.?4?The removal efficiency of o-xylene by flower desiccant silica gel supported sulfuric acid?Modi-FDSG?and desiccant silica gel supported sulfuric acid?Modi-DBSG?was almost the same when the sample mass was the same.When converted to the same sulfuric acid load?20 mmol/g?,the adsorption efficiency was Modi-FDSG(tB,177 min)>Modi-DBSG(tB,166 min).?5?The effect of cooling pump temperature and carrier gas velocity on sulfuric acid load sample breakthrough curve was similar,and the effect on sample o-xylene removal was Modi-DBSG>Modi-FDSG.?6?A series of characterization results further confirmed that the experimental adsorption mechanism was chemical adsorption.3.Removal of o-xylene by activated carbon supported sulfuric acidSupported sulfuric acid was prepared by using two kinds of commercial activated carbon?analytical pure activated carbon,AC and coconut hush activated carbon,CHAC?as carriers.The effects of adsorption temperature and process conditions on the removal of o-xylene were investigated by dynamic adsorption experiment.And combined with BET,SEM,XRD and FTIR,the effects of carrier changes on the adsorption of o-xylene by supported sulfuric acid were investigated.The results showed that:?1?The removal rate?>95%?of o-xylene was higher at 160?when the adsorption temperature is roughly selected.When the adsorption temperature was selected,Modi-AC and Modi-CHAC both showed certain removal efficiency of o-xylene at different temperatures,ranging from large to small:Modi-AC,160?>170?>150?;Modi-CHAC,150?>160?>170?.?2?The removal of o-xylene could be improved by increasing the mass of sample determination and the removal efficiency was Modi-AC>Modi-CHAC.?3?Increasing the carrier gas velocity and the concentration of o-xylene at the inlet shortened the breakthrough time,which is more conducive to the equilibrium of the adsorption reaction.The effect of the two factors on the adsorption breakthrough curve was Modi-CHAC>Modi-AC.?4?A series of characterization experiments proved that the removal capacity of two supported sulfuric acid samples for o-xylene was Modi-AC>Modi-CHAC.Modi-AC was more suitable for the removal of o-xylene in the experiment. |
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