Reactive Adsorption Of Loaded Sulfuric Acid On Volatile Benzene Series

Volatile organic compounds（VOCs）are key precursors of atmospheric PM2.5 and O3pollution,and the exploration of materials and methods for their pollution control has been a hot research topic in multidisciplinary fields such as chemistry,materials and environment.For the emission of low concentration VOCs in industry,adsorption is a mature and widely used technology.Silica and molecular sieves are commonly used as VOCs adsorbents due to their large specific surface,rich pore structure and high stability,but most of the current adsorption of VOCs by silica and molecular sieves is physical adsorption with small adsorption capacity.Therefore,it is important to study the adsorption and removal methods based on new mechanisms to improve the level of VOCs pollution control.In this thesis,commercial silica gel,molecular sieve and homemade silica gel were used as carriers,and sulfuric acid was used as a modifier to prepare loaded sulfuric acid adsorbents,and volatile benzene VOCs were selected as model pollutants.The theoretical and experimental basis for the effective purification of benzene VOCs is provided by the influence of the adsorbent source and preparation method on the adsorption.The work carried out in this thesis is as follows.1.Removal performance and mechanism of benzene-based VOCs by MCM-41 loaded sulfuric acid.Loaded sulfuric acid（SSA/MCM-41）with a loading capacity of 9.25 mmol/g was prepared by the sulfuric acid solution impregnation method using MCM-41 as a carrier,and its reactive adsorption and removal performance of four phenyl VOCs gases（benzene,toluene,m-xylene,and p-xylene）at different temperatures was comparatively investigated using an independently constructed reactive adsorption platform,and toluene was used as the treatment target.The effects of adsorbent dosage,gas flow rate and initial inlet concentration on the adsorption and removal performance were investigated in detail;the adsorbent materials and adsorption performance were characterized by fourier transform infrared spectroscopy（FTIR）,cold field emission scanning electron microscopy and energy spectroscopy（SEM-EDS）,low-temperature nitrogen adsorption（N2-BET）,nuclear magnetic resonance hydrogen spectroscopy（¹H NMR）and nuclear magnetic resonance carbon spectroscopy(¹³C NMR).The adsorption materials and products were characterized.The results showed that H2SO4 was loaded on the surface of MCM-41 in both chemically bonded and physisorbed states,and its surface loading led to a significant decrease in the specific surface area and pore volume of SSA/MCM-41;The curves of benzene,toluene,m-xylene and p-xylene on SSA/MCM-41showed"several"characteristics（activation zone,reaction zone and deactivation zone）,and the temperature range of reaction zone was different,but they all covered the range of150-160℃.The adsorption penetration curves of these phenyl VOCs at different temperatures were comparatively measured,and the results showed that the 5%adsorption penetration time（t B）and the 5%penetration adsorption volume（QB）both showed a variation pattern of increasing and then decreasing with the increase of temperature,and the optimum temperatures were 150℃for benzene and p-xylene,and 160℃for toluene and m-xylene,the corresponding QB values were 355.0,328.2,801.3,and 239.8 mg/g,and were ranked by QB size as toluene>benzene>p-xylene>m-xylene.The effects of adsorbent dosage,gas flow rate and initial inlet concentration on the adsorption and removal performance were investigated in detail at 160℃using toluene as a typical VOC.It was found that increasing the adsorbent dosage could prolong the penetration time,and increasing the carrier gas flow rate and inlet concentration would reduce the penetration time.Through the separation,purification and characterization of the adsorption products,the reactive adsorption main product was determined to be p-methylbenzenesulfonic acid,and a small amount of bis（4-methylphenyl）sulfone by-product was detected.Based on the above study,a mechanism for the removal of phenyl VOCs by SSA/MCM-41 adsorption was proposed.2.Effect of process conditions on the adsorption of o-xylene by MCM-41 loaded sulfuric acid and theoretical simulation.In this part,the dynamic adsorption penetration behavior of o-xylene on the SSA/MCM-41（9.25 mmol/g）/o-xylene treatment system was investigated,and the effects of bed height,flow rate and inlet concentration of o-xylene on the adsorption performance were systematically examined.The penetration curves were simulated using Thomas,Yoon-Nelson and dose-response models,and the theoretical penetration time and theoretical penetration adsorption amount were calculated based on the obtained parameter values.The results showed that the flow rate（Vg）,bed height（h）and inlet concentration（Cin）of o-xylene affected the adsorption behavior of o-xylene,and increasing the bed height and appropriately decreasing the flow rate and inlet concentration could improve the adsorption performance of SSA/MCM-41 on o-xylene.The dynamic adsorption behavior of the system was well described by Thomas,Yoon-Nelson and dose-response models,among which the dose-response model was the best,which predicted the maximum penetration adsorption capacity of 545.6 mg/g.The cyclic adsorption/desorption experiments showed that MCM-41had good cyclic stability.3.Effect of preparation method on the performance of silica gel loaded sulfuric acid for o-xylene removal.In order to explore the influence of the preparation method of loaded sulfuric acid on the performance of treating phenyl VOCs,two types of Si O2-loaded sulfuric acid（SSAI and SSAII）were prepared by sol-gel and impregnation methods in this part,and their adsorption and removal performance on o-xylene was studied comparatively and their mechanism of action was analyzed with various analytical characterizations.The results showed that there were two anchoring states of sulfuric acid on the surface of the Si O2 carrier:the physisorbed state（P state）and the chemically bonded state（C state）,and the sulfur content of the C state was higher in SSAI（74.3%）than that of SSAII（72.8%）.The effect of SSAs on the removal of o-xylene with temperature also showed activation,reaction and deactivation zones,and the starting reaction temperature of SSAI（～120℃）was～10℃lower than that of SSAII（～130℃）.The adsorption penetration curves of o-xylene at different temperatures were comparatively measured,and the results showed that the best adsorption temperatures were150℃and 160℃for SSAI and SSAII,respectively,and the penetration adsorption capacity QB was 184.9 mg/g for SSAI and 142.8 mg/g for SSAII,and the QB values SSAI>SSAII were consistent with the C-state sulfuric acid content in the same order.The effects of different process conditions on the adsorption and removal performance of SSAI and SSAII were measured at 150℃and 160℃,respectively,and it was found that increasing the adsorbent mass and decreasing the carrier gas flow rate and inlet concentration could increase the penetration adsorption capacity.both SSAI and SSAII had good cycling stability.4.Effect of loading medium on the performance of silica gel sulfuric acid for o-xylene removal.In order to investigate the effect of loading sulfuric acid preparation conditions on the performance of treating phenyl VOCs,this part of the paper uses chromatographic silica gel（SG）as the carrier,and H2SO4 was dispersed into ethyl acetate and distilled water solvent media at the same concentration to obtain two kinds of Si O2-loaded sulfuric acid（SSA-E and SSA-H）by solvent method,and comparatively study their adsorption and removal performance on o-xylene.The effects of the two Si O2-loaded sulfuric acids（SSA-E and SSA-H）on the adsorption and removal of o-xylene were investigated and their mechanisms were analyzed by various analytical characterizations.The results showed that both SSA-E and SSA-H formed two forms of loaded sulfuric acid:P-state（-HSO4H-）and C-state（Si-O-SO3H）,and the C-state sulfuric acid content of SSA-E（76.2%）was more than that of SSA-H（70.2%）.Characterization analysis showed that the surface of the sample was rough after loading sulfuric acid,and the specific surface areas of SSA-E and SSA-H were also reduced to 2.2%and 6.5%of the original silica gel due to the etching effect of sulfuric acid.The adsorption performance tests showed that the t B,th of SSA-E and SSA-H with the same loading amount were 63.2 min and 50.7 min at 160℃,and the QB,th were 221.0 mg/g and176.5 mg/g,respectively.t B,th and QB,th of SSA-E and SSA-H increased gradually with the increase of sulfuric acid loading,and most of the The adsorption data under the experimental conditions showed that SSA-E had better adsorption performance than SSA-H.After adsorption,SSA-E and SSA-H could be regenerated and reused.