Removal Of O-xylene From Streams By Supported Sulfuric Acid/Sulfonic Acid

The ideal atmosphere environment is one of the indispensable factors for the survival of life and the development of human society.With the rapid development of global economy and the improvement of social productivity,air pollution is becoming increasingly serious,causing a serious threat to life,health and the environment.Therefore,the search for economical,efficient and environmental-friendly technology and materials has become a hot topic at the present stage.Adsorption technology has the advantages of high efficiency,low cost,green and pollution-free,and it is one of the most potential methods to treat VOCs.Moreover,the rich diversity of adsorbent materials and the stability of adsorption products make the technology practical application and operability.To date,widely used activated carbon,silica gel and other solid adsorbents only have physical adsorption at low temperature,the research of using chemical adsorption method to treat VOCs is less.Therefore,in this paper,on the basis of a brief analysis of the present situation of VOCs pollution and purification technology,the maily study was the feasibility of remval VOCs by chemical adsorption,the effects of adsorbent structural characteristics and load state on adsorption capacity were investigated by dynamic adsorption experiments,this can provide a new theoretical and experimental basis for the application of adsorption method in the treatment of VOCs.The main research contents are as follows:1.Removal of o-xylene by silica supported sulfuric acidsSilica supported sulfuric acids（SSAs）were prepared with chromatography silica gel（SG）and molecular sieve SBA-15,MCM-41 as the carriers,o-xylene was used as the model pollutant to investigate the effects of carrier properties,sulfuric acid loading state,reaction temperature,bed height,carrier gas flow rate and inlet concentration on the removal performance of the synthetic materials by dynamic adsorption test.The materials and adsorption product were characterized by Thermo gravimetric-differential scanning calorimetry（TG-DSC）,Fourier transform infrared spectrum（FTIR）,cold field emission scanning electron microscopy and energy dispersive X-ray spectroscopy（SEM-EDS）,X-ray photoelectron spectroscopy（XPS）,cryogenic-nitrogen adsorption using Brunauer-Emmett-Teller method（N₂-BET）,NMR hydrogen spectrum（¹H NMR）and NMR carbon spectrum(¹³C NMR).The results showed that the sulfuric acid was successfully supported on the surface of silicas and existed in two ways:physiosorbed（P）-state sulfuric acid and chemically bonded（C）-state sulfuric acid,the proportion of the C-state sulfuric acid decreased in the order SSA/MCM-41>SSA/SBA-15>SSA/SG.The removal rate of o-xylene by SSAs in the reactive region was more than 95%,which was mainly due to the chemical reaction-type（sulfonation reaction）adsorption between SSAs and o-xylene.The fitting curves of Yoon-Nelson model coincided well with the experimental data,and the model predicted values agree well with the experimental values.Among the three adsorbents,SSA/MCM-41showed the highest breakthrough adsorption capacity(Q_B,th,526.71 mg/g),indicating that the adsorption capacity was closely related to the content or proportion of C-state sulfuric acid on the surface of each SSAs.The breakthrough time（t _B）can be prolonged and the breakthrough adsorption capacity（Q_B）can be increased by increasing the bed height and decreasing the flow rate and inlet concentration.The functional group and molecular structure analysis proved that the adsorption product was 3,4-dimethylbenzene sulfonic acid which established the sulfonation reaction-type adsorption mechanism between o-xylene and SSAs.The adsorption product can be recovered effectively and the carriers can be reused.Finally,the effectiveness of the method for removing other benzene series gases was verified.2.Effect of preparation method on removal of o-xylene by silica gel supported sulfuric acidSilica supported sulfuric acids（SSAⅠand SSAⅡ）were prepared with chromatography silica gel（SG）as the carrier by sulfuric acid impregnation method and chlorosulfonic acid direct sulfonation method for the removal of o-xylene and comparing the effects of preparation methods on the reaction adsorption performance of SSAs.The adsorption materials and product were also characterized by the methods described above.The results showed that SSAⅡhad higher C-state sulfuric acid content.FTIR analysis proved that SSAⅡand SSAⅠhad characteristic peaks of P-state sulfuric acid and C-state sulfuric acid while retaining the original characteristic peaks of SG.The surface morphology analysis showed that the surface of SSAⅠand SSAⅡwere rough,the surface had etached traces,the adsorption product crystal existed on the surface;the surface element analysis showed that SSAⅡhad a higher sulfur content than SSAⅠ.BET analysis showed that both SSAⅠand SSAⅡwere mesoporous materials with low porosity,which had almost no adsorption capacity at low temperature.Adsorption performance analysis showed that with the increase of loading,the reaction region of SSAⅠand SSAⅡincreased,t_B,th and Q_B,th also increased correspondingly;most experimental results showed that SSAⅡhad higher breakthrough time and breakthrough adsorption capacity than SSAⅠ.The surface adsorption product analysis proved that the adsorption product（3,4-dimethylbenzene sulfonic acid）and mechanism of SSAⅡand SSAⅠwere the same;SG can be regenerated and reused after the adsorption.3.Removal of o-xylene by activated carbon supported sulfuric acidActivated carbon supported sulfuric acids（CSA/ZnCl₂,CSA/H₃PO₄）were prepared by wet impregnation method using two kinds of activated carbon（ZnCl₂ method activated carbon,ZnCl₂-AC and H₃PO₄ method activated carbon,H₃PO₄-AC）as the carriers,combined with TG-DSC,FTIR,SEM-EDS,XPS and N₂-BET analysis to characterize the adsorbent and investigate the adsorption of o-xylene by CSAs.A series of characterization analysis showed that the content of C-state sulfonic acid（C-SO₃H）was:CSA/H₃PO₄>CSA/ZnCl₂;the surface of the samples became uneven after loading sulfuric acid,the boundary is fuzzy and had deposits;the specific surface area of CSA/ZnCl₂ and CSA/H₃PO₄ were reduced to 1.7‰and1.9‰,respectively;the pore size became 14 times and 7 times,respectively.The results of the adsorption experiments showed that the t _B,th of the same loading of CSA/ZnCl₂ and CSA/H₃PO₄ were 38.56 min and 45.51 min,and the Q_B,th were 265.64 mg/g and 313.84 mg/g,respectively.Increasing the bed height can increase the adsorption capacity of o-xylene,the adsorption capacity was CSA/H₃PO₄>CSA/ZnCl₂.Increasing the carrier gas flow rate and the inlet concentration of o-xylene shortened the breakthrough time,which is more conducive to the equilibrium of the adsorption reaction.