Preparation And Properties Of Adsorbents For Deep Purification Of Oxygenates From Olefins

Olefins,such as ethylene and propylene,which were mainly derived from naphtha cracking and methanol conversion(MTO,MTP et al.;),always contain trace amounts of oxygenates.In nomal conditions,these oxygenates should be removed by zeolite adsorbents before the olefins involved in the polymerization reaction.Higher requirements for the purity of olefins are put forward in the market as the polymer materials functionalization,high-end,and the catalysts used in polymerization constantly innovating.Na X zeolite membranes and EMT zeolite membranes have great potential applications as new materials to purify the trace amounts of oxygenates from olefins,because of its anvantages,such as high removal efficiency,high removal accuracy,low mass transfer resistance,high zeolite utilization and low thermal effect.However,the preparation of the structural integrity of Na X zeolite membranes and EMT zeolite membranes,as well as the low-cost preparation of pure EMT zeolite with high crystallinity affects its performance and industrialization.In this paper,the XRD,SEM,BET and other characterization methods were used to study the preparation of Na X zeolite membranes,EMT zeolite and EMT zeolite membranes in detail,and its adsoption performance of dimethyl ether,methanol and propanal were evaluated by a dynamic adsorption experiment.Moreover,the sorption mechanism to the impurities was investigated by in-situ FTIR spectroscopy,and the microscopic adsorption simulation was carried out by GCMC method.Structural integrity of Na X zeolite membranes was prepared on porous?-Al₂O₃tube by a combination method of 3-aminopropyltriethoxy silane(APTES)surface modification and vacuum pre-coating sol technique.When the APTES concentration was 46 g/L,a thickness of 5?6?m dense and continuous Na X zeolite membranes without any cracks,pinholes or other defects had been achieved.The trace amounts of oxygenates could be deeply purified to below 1 ppm by the Na X zeolite membranes.Compared with the Na X particle adsorbents,the Na X zeolite membranes exhibited much more excellent purification performance,longer lifetime and better structural stability.Pure EMT zeolites with high crystallinity had been successfully prepared by steam crystalization and microwave-hydrothermal(i.e.two-step)crystallization method in a short time,respectively.The samples of EMT zeolite with relative crystallinity up to 102%were obtained under 80°C microwave crystallization for 45min,then treated under 50°C hydrothermal crystallization for 18 h in the two-step method.The prepared EMT zeolites exhibited better deep purification performance for methanol and propanal.Moreover,the regeneration experiments showed that the EMT zeolie had more stable structure and longer lifetime.Thickness of 5?6?m,dense and continuous EMT zeolite membranes without any cracks were prepared on porous?-Al₂O₃ by a combination method of polyallyl dimethyl ammonium chloride surface modification and vacuum pre-coating sol technique.Compared with the EMT zeolite particles,the prepared EMT zeolite membranes exhibited more excellent methanol and propanal purification performance,longer lifetime and better structural stability.The in-situ FTIR spectra showed that the purification processes of Na X zeolite and EMT zeolite for dimethyl ether,methanol and propanal were mainly via interaction between the oxygenateds O lone-pair electrons and the skeleton cation Na⁺.Moreover,the interaction between the O-H bond of methanol and lattice oxygen was also detected during the removal of methanol.GCMC simulations showed that the adsorption capacity of EMT zeolite for methanol and propanal decreased with the temperature increasing,but increased with the pressure increasing in single-component systems.The adsorption capacity order was propanal>methanol>>ethylene.In two-component system,the adsorption capacity of methanol and propanal by EMT zeolite was much higher than that of ethylene.The selective adsorption coefficients of methanol to ethylene and propanal to ethylene were 318 and 383,respectively.In the methanol-propanal two-component system,the adsorption amount of propanal was higher than that of methanol,and the adsorption energy peaks of propanal and methanol shifted to high adsorption energy and low adsorption energy,respectively.Propanal was removed more easily by EMT zeolite.