Study On The Preparation Of Enriched Mesoporous EU-1 Zeolite

EU-1 zeolite,as a type of EUO zeolite with micropore structure,contains twelve element ring side pocket?0.68*0.58nm?which is vertically communicated with the twelve element ring side bag?0.58*0.41nm?.Due to the unique pore structure,the EU-1 zeolite has a good catalytic performance in xylene isomerization.Therefore,the EU-1 zeolite has attracted wide interest of domestic and foreign experts and scholars.EU-1 zeolite is one dimensional microporous zeolite and the diffusion is restricted in the micropores.The existence of mesoporosity on the surface of zeolites facilitates better access to active sites inside the pores.As a result,the zeolite activity will be increased.At present,the important task of our research group is to develop new catalytic materials and guide the industrial production technology,our research group which studies the industrial application of EU-1zeolite in xylene isomerization has found that the amorphous silicon aluminum species remaining in the grain gap can not be removed completely and plug the pore channel,cause the low reaction activity of EU-1 zeolite products because of the limit of separation and washing process in the industrial synthesis of EU-1zeolite.It is a way to introduce the mesoporous on the surface of zeolite by using alkali treatment,acid treatment.It is an effective means that improve the performance of catalytic reaction by using alkali treatment,acid treatment to wash out the EU-1 zeolite and improve the diffusion performance of zeolite.The alkali treatment mainly uses the alkali solution to corrode part of zeolite skeleton to produce the mesoporous structure,strengthens the channels of the molecular diffusion by the new intergranular and intragranular pore and then affects the catalytic performance of zeolite in the premise of maintaining that the porous skeleton structure does not collapse;the essence of acid treatment is to remove the aluminum in the framework of zeolite,increase the Si/Al ratios,enhance the strength of the acid and hydrothermal stability,form a number of intergranular mesoporous.In this paper,industrial products were used as the post treatment and reference sample.Firstly,the EU-1 zeolite was treated by alkali and alkali-acid using different concentrations of sodium hydroxide solution,sodium carbonate solution and hydrochloric acid,the structure of the original EU-1 zeolite framework and acidic features could be preserved,and the catalytic activity could be improved and the side reaction of xylene isomerization could be restricted at the same time.The study found that the structure of EU-1 zeolite was seriously destroyed by the strong alkaline of sodium hydroxide solution.The crystallinity of the product is changed from 88%to 106.5%,and the lattice structure is more stable after treatment with mild sodium carbonate solution.With the increase of alkali concentration,the Si/Al ratios decreased,the total specific surface area of BET decreased,the external specific surface area and volume of the mesoporous volume increased first and then decreased.Under the optimized process conditions,the samples were treated with0.05mol/L sodium carbonate solution,and the surface area of the sample was76.3 m²/g and the mesoporous volume was 0.155 cm³/g,the surface area and mesoporous volume was respectively increased 9.8%and 6.9%compared to the untreated sample;the samples that were treated by sodium carbonate 0.05mol/L and hydrochloric acid 0.1mol/L sequentially,exhibited good selectivity and activity in xylene isomerization reaction,the activity increased from 23.03%to23.61%and the selectivity increased from 85.09%to 87.14%.The study found that a relatively mild,low concentration of sodium carbonate and hydrochloric acid post-treatment eroded the amorphous silicon aluminum species in the gap of the zeolite crystallites,increased the mesoporous volume and external specific surface area,but zeolite skeleton structure and acid strength changed little.In order to obtain the optimum technological conditions,the optimization of temperature,solid-liquid ratio,time and other conditions in the post-treatment process of alkali and alkali-acid was further developed on this basis,so the experimental basic data for industrial production and preliminary exploration results was provided.The result showed that the industrial product EU-1 zeolite that was alkali-treated at the temperature 80 degrees,solid-liquid ratio 7,sodium carbonate concentration 0.05mol/L,treatment time 24 hours,could get the post treated samples with large pore volume and high specific surface area.The best technology of sodium carbonate alkali treatment is that the temperature is 80degrees,the ratio of solid-liquid is 7,the concentration of sodium carbonate is0.05mol/L,the time is 24 hours.In the process of acid treatment,it was found that the concentration of hydrochloric acid 0.1mol/L and room temperature were the better technological condition.The method that was synthesized mesoporous EU-1 zeolite by adding surfactant was explored in the last part of this paper.Sodium dodecyl benzene sulfonate was used to synthesis EU-1 zeolite and the effects of different surfactant addition time and additives were also investigated in the synthesis of EU-1 zeolite.The EU-1 zeolite was characterized by XRD,SEM,NH₃-TPD,N₂adsorption-desorption and other characterization methods.The catalytic performance of xylene isomerization of the samples was evaluated.The results showed that the structure of the sample that was synthesized by adding sodium dodecyl benzene sulfonate was still EUO structure.Compared to the original sample,the total specific surface area,total pore volume,surface area,and the volume of mesoporous materials were significantly increased.The mesoporous volume can be increased by up to 18.2%,which greatly reduced the reaction diffusion limitation,and the isomerization activity of toluene increased from23.31%to 23.62%.It indicated that the reaction activity of EU-1 zeolite was improved effectively by the addition of surfactants.