Synthesis Of Hierarchical Zeolites And Their Performances Of Toluene Adsorption And Desorption

Adsorption enrichment-combustion technology was one of the most popular processes for VOCs?volatile organic compounds?abatement from industrial source characterized as low concentration and large flow rate.The key point of adsorptive enrichment process was the development of high-performance adsorbent.Compared to active carbon,zeolite possess the advantages of non-flammable as well as high thermal stability.However,high diffusion resistance of traditional microporous zeolite and the adsorptive capacity of mesoporous zeolite were not satisfactory.Hierarchical zeolite with both micropores and mesopores,not only has lower diffusion resistance,but also maintains well adsorptive performance,which showed great potential for practical application.In this paper,different hierarchical zeolites have been synthsised via template and template-free approaches in order to reduce diffusion resistance of microporous zeolite.The main content of this work focused on adsorption/desorption performances of the as-prepared adsorbents and its physical properties such as pore and phase structure and so on.Firstly,the preparation conditions of spherical SBA-15 have optimized.The experimental results showed that the adsorption capacity of toluene for spherical SBA-15 could reach 110.9 mg/g under the preparing conditions as:P123/CTAB molar ratio was 0.36,P123/TEOS molar ratio was 1/100,hydrochloric acid concentration was 2 mol/L and hydrothermal temperature was 70 ?.At the same time,the spherical SBA-15 synthesized under this condition had a relatively small pore size?smaller than 4 nm?still required further modification to reduce its diffusion resistance.Secondly,the swelling agent 1,3,5-trymethylbenzene?TMB?was used to expand the pore size of spherical SBA-15.The influences on the structure and the adsorption/desorption performance of the adsorbents with different amount of swelling agent was added and aging temperature have been investigated.The experimental results indicated that the pore size of spherical SBA-15 can be expanded effectively by adding TMB and the pore size increased with the rising of TMB addition.Meanwhile,the adsorptive capacity was found to be decreased to a certain content accordingly.When the mass ratio of P123 to TMB was 1/1,althrough its adsorption capacity was 83.6 mg/g,which decreased by 27.6%compared with unmodified sample,the modified sample had the best thermal desorption performance at 100?.The modified spherical SBA-15 possessed larger pore size and more stablility after aging at 120 ? exhibiting excellent desorption and regeneration performance.Finally,hierarchical USY zeolite were prepared via alkaline treatment.The effects of alkaline species,alkaline concentration and treatment temperature on the structure and the adsorption/desorption properties of the hierarchical USY zeolite were investigated.It was found that the hierarchical USY zeolite treated with 0.02 mol/L NH₄OH solution at 35 ? could not only obtain the best adsorption capacity but also excellent thermal desorption property.Moreover,the NH₄OH solution can protect the microporous structure effectively and matain high crystallinity,showing a high yield ratio of more than 97%.