| The rapid development of industry all over the world has greatly pushed forward the vigorous growth of global economy,however,the economic growth has also brought about severe atmospheric pollution and resources waste.The various atmospheric pollutants,volatile organic compounds are particularly serious and threatening to the life and health of all living beings,including humans.Many scholars and scientists have presented a variety of methods to volatile organic compounds(VOCs)treatment.Among these treatments,adsorption method draws considerable attentions from the scholars,due to its simple technique and convenience to operate.Especially,it has obvious its superiority,to deal with benzene and the related aromatic ring compounds in industrial exhaust emissions for their toxicity and recycling difficulty.But it is a must to select the appropriate adsorbent for the recycling of benzene by adsorption method.Currently,activated carbon is commonly used as benzene adsorbents,which,however,has many drawbacks.When VOCs gas temperature reaches too high,it is liable to be oxidized and combust and brings high risk to the industrial production risk.In addition,the fatal problem is that,due to the increasing the times of activated carbon adsorption of benzene,activated carbon adsorbent comes with difficult regeneration,resulting in industrial production interruption.Therefore,to solve this problem,it is necessary to study the zeolite adsorbent to replace the activated carbon adsorbent,which is characterized by non-flammability,strong heat resistance,high hydrothermal stability,easy to regenerate.In this thesis,vesicle system used as template,mesoporous silica is prepared before the ordered treatment of pore walls.Then the treated mesoporous silica works as an adsorbent to recycle benzene emissions from maleic anhydride plant(benzene oxidation),by applying pressure swing adsorption(PSA)process treatment.The procedures are as follows:1.AE3S anionic surfactant and a cationic surfactant CTAB solution were mixed by different the volume ratio till the mixture turned blue,visually with spontaneous formation of vesicles;With certain total concentration of CTAB in AE3S,the vesicle particle size along with the change of the amount of CTAB is examined,and it is found that the vesicle particle size increased before it decreased with increase of the amount of CTAB;At a relatively high concentration of AE3S and CTAB complex system,vesicles appeared tubular,and with the passage of time,the tubular vesicles showed a growing trend;The relationship between the total concentration of CTAB was studied,and the results show that with the total concentration AE3S and CTAB increased,the particle size of vesicles showed an increasing trend;The effects of temperature on this vesicle system were studied,the results show that AE3S vesicle system and CTAB good thermal stability,temperature changes have little effect on the structure of vesicles.Under extremely high or low temperatures vesicles bursts,while under normal temperature,the vesicles system will spontaneously reform;PH value on the vesicle formation was investigated to find that pH value within the range from 7.1 to 12 there was the presence of vesicles,when the pH value got greater than 12,there was no presence of vesicles.The vesicles in the arrangement of ions was studied by AE3S and CTAB by calculating vesicle complex thickness,calculated that AE3S and CTAB molecules appeared the head-to-head connection pattern or side-by-side arrangement.2.The formed vesicles system of anionic AE3S and cationic surfactant CTAB used as a template,with the pH range of 7.6 to 12 tetraethylorthosilicate(TEOS)hydrolysis can be effectively synthesized to mesoporous silicon oxide material with stable structure.It is tested by experiments that mesoporous silica calcined samples had surface area different from pore through different calcination procedure;calcined samples had maximum surface area and the largest pore volume through the thermal gravimetric analyzer(TAG)the calcination procedure;different calcination procedures have little effect on the pore size of the sample.The effects of solution pH value on the mesoporous silica surface area and pore volume was studied,it is found that with the raise of the pH value,mesoporous silica mesoporous materials SBET specific surface increased first and then decreased.The specific surface area and pore volume reaches the maximum when pH value is 9.2,then as the pH value increases,the specific surface area and pore volume decreases.With TPAOH as a template,the synthesis of mesoporous silica was hole wall orderly processed,and the results indicate that the mesoporous silica can make rearrangement of the hole wall.Ordered mesoporous silica disordered amorphous crystalline was transited towards the pore wall and display part of ZSM-5 zeolite crystal characteristics,so that the material has the dual advantages of mesopores and micropores.With the crystallization temperature of 150?,a hole wall ordered mesoporous silica material(MESCD)is obtained to have specific surface area of 600.03m2·g-1,pore volume of 0.20m3·g-1.3.The pore wall ordered mesoporous silica MESCD used as adsorbent to examine effects of different inlet concentration,airflow than the speed,relative humidity on the solid component of benzene and toluene in a fixed bed adsorption performance.The results show that the initial inlet concentration or airflow speed ratio of one component benzene and toluene raised,then penetration times of MESCD adsorbent fixed bed and adsorption equilibrium time decreased,while the mass transfer zone(MTZ)increased in length,MESCD adsorbent fixed bed utilization efficiency decreased,and at the same time,adsorption capacity did not change with airflow speed change.Air relative humidity increased,benzene penetration time of MESCD adsorbent fixed bed went down,and penetration adsorption reduced,the mass transfer zone(MTZ)in length increased.However,penetration time,the adsorption volume and mass changes are little changed.It indicates that the increase of airflow relative humidity had little effects on MESCD adsorbent penetration,that is,competitive adsorption of water molecules did not have a significant impact on the adsorption.Semi-empirical Yoon-Nelson adsorption equation is applied to do penetration curve fitting of inlet different concentration,airflow speed,relative humidity,the study found penetration curve obtained experiment and penetration curve simulated by adsorption theory model equations had good compliance.Yoon-Nelson can effectively predict benzene and toluene adsorption layer penetration in MESCD adsorbent fixed bed.In the two-component Benzene and toluene mixing system,adsorption penetration curves of the two-component system and that of one-component systems were similar.In relatively large concentrations of VOCs,when adsorption spots on the surface of the adsorbent MESCD were limited,the different components showed differences in the strength of adsorption,which produced competitive adsorption.This is relevant to the component adsorption performance on surface and the pores of the adsorbent.Toluene molecule has stronger adsorbent capacity than benzene molecule,toluene molecule substituted pre-occupied benzene during the adsorption of adsorption,causing benzene earlier than toluene molecules in penetration.Benzene adsorption of MES,MESCD and granular activated carbon were compared,the experimental results show that the penetration curve of adsorption of benzene in a fixed bed is sharp,with good S-shaped penetration curve.It indicates that the internal diffusion mass transfer resistance plays a dominant role in the whole adsorption process and the controlling steps the adsorption process.As MESCD adsorbent pore size distribution in addition to part of the mesoporous pore structure similar things,there is a certain amount of ZSM-5 zeolite microporous structure.In this micro-mesoporous composite MESCD adsorbent,the MESCD pore diameter may be similar the benzene dynamic diameter,it can be a good benzene adsorption,while large mesopore volume can effectively accommodate more benzene molecules,resulting MESCD adsorbent showed better adsorption performance than MES,MES breakthrough time compared to long,the adsorbent bed utilization is relatively high.4.The producing maleic anhydride(benzene oxidation)factory emissions taken as the research object,MESCD used as adsorbent,PSA process is applied to recycle benzene in exhaust gas.The effects of the adsorption pressure,gas flow,pressure equalization time,adsorption time and the various parameters on the exhaust gas concentration and desorption concentration were studied,meanwhile the adsorbent properties stability was tested.Experimental results show that at the same desorption and adsorption time,the benzene concentration of exhaust gas and desorption of benzene concentrations increased as absorption time went up.In the given process parameters,the adsorption time had an optimum point.With given pressure,exhaust gas flow and adsorption time,the concentration of benzene in desorption gas increased as pressure time went on,the concentration increased before it increased,there is an extreme point.At a pressure of 0.1 MPa,exhaust flow 110L/min,adsorption time of 40s,the pressure time 4s,the benzene concentration is 1.05%concentration.At a pressure of 0.15MPa,exhaust flow 120L/min,adsorption time 40s,the pressure time or 4s,the benzene concentration can be raised to 1.05%.The experimental setup functioned smoothly in the factory for 1286h continuously,and MESCD adsorbent can still maintain good adsorption properties.It shows that the adsorbent has good mechanical strength and wear resistance,operating stability with need of frequent replacement of adsorbent.These researches above play a positive role in vesicle mesoporous silica material in the synthesis and the pore walls orderly process,as well as in the application and developments of mesoporous silica adsorbents of the pore wall ordered process in the PSA to process and recycle VOCs. |
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