Preparation Of MFI And FAU Zeolite Membranes And Their Performance For Separation Of Organic Solvent/Water By Pervaporation

In the chemical industry,efficient organic solvent separation is a key objective.It is crucial to create low-energy and environmentally friendly membrane separation technology given the development trend of"two-carbon"with carbon peak and carbon neutrality.For instance,using pervaporation membranes to separate ethanol-water combinations uses only one-tenth as much energy as distillation.The hydrophilic/hydrophobic characteristics of molecular sieve membranes play a major role in the separation of organic/water mixtures by pervaporation for macroporous zeolite membranes.The hydrophilic zeolite membrane is frequently used for the separation of large concentrations of organic solvent/water systems,whereas the hydrophobic zeolite membrane can be employed for low concentrations of organic solvent/water systems.The efficiency of membrane separation can be greatly increased by using various membrane materials to separate low concentration components.In this work,hydrophobic MFI(pore size 0.55 nm)zeolite membranes and hydrophilic FAU(pore size 0.74 nm)zeolite membranes were successfully prepared by using pervaporation to separate different concentrations of organic alcohols mixed with solvent and water to obtain high concentrations of organic alcohols.The systematic study investigated the effect of temperature and concentration of organic solution on the pervaporation separation performance of MFI type zeolite membrane and FAU type zeolite membrane,and explored the separation mechanism of the membrane.The main research content is as follows:(1)MFI type zeolite membrane preparation and pervaporation performance analysis.Tetrapropylammonium hydroxide was used as a template,and an ethyl silicate silicon source was used to create MFI type zeolite membranes.A scanning electron microscope(SEM)and an X-ray diffractometer were used to characterize the MFI type zeolite seeds.The results showed that the crystal sizes were uniform and ranged from 260 nm for the MFI type zeolite to pure phase molecular sieves.The MFI type zeolite membrane displayed high h0h orientation,was flat and smooth without globular defects,and had a 6μm thickness.For the first time,pervaporation organic alcohol solvent-water mixed system separation using h0h-oriented MFI type zeolite membranes.It was thoroughly investigated how the permeation temperature and ethanol concentration affected the membrane’s ability to accomplish separation.The experimental findings demonstrated that the h0h-oriented MFI type zeolite membrane had good ethanol/water separation performance as manufactured.For instance,the membrane demonstrated a separation factor of 26 and flux of 2.88 kg/(m~2h)for a10%wt ethanol/water system at 70°C;and after a lengthy operation time of 90 h,the MFI type zeolite membrane still maintained high separation performance,demonstrating the membrane’s good hydrothermal stability.(2)Preparation of FAU type zeolite membrane and Its Pervaporation Performance Study.Pure phase FAU type zeolite seeds with a size of 30 nm were successfully prepared by using HS-30 as silicon source and aluminum isopropoxide as aluminum source.FAU type zeolite membranes with continuous dense membrane layer and thickness of 4.1μm were prepared by hydrothermal synthesis on tubular alumina support with secondary growth method at 90℃for 8 h.The effect of permeation temperature and water/isopropanol concentration on the separation performance of FAU type zeolite membrane was investigated.The experimental results showed that the separation performance of the membrane was much higher than that of the gas-liquid equilibrium line for the rectification separation,which showed a good separation performance.For example,at 70℃,the membrane exhibited a separation factor of 818 for 10 wt%water/isopropanol and a permeation flux of 1.83 kg/(m~2`h).(3)MFI type zeolite membranes are used to explore the permeation mechanisms of various organic alcohol/water systems.The MFI type zeolite membranes were used in the systematic investigation to investigate the impact of temperature and concentration on the pervaporation performance of water/organic solvents(methanol,ethanol,acetone,and n-propanol).Although the penetration rates of water and solvent molecules began to decrease,the selectivity of the membrane varied little with increasing solvent molecular size.This is because as the solvent’s molecular size increases,its permeation resistance inside the MFI pore channels also increases,resulting in a decrease in the solvent’s penetration rate;The preferred permeability of large-sized organic molecules across MFI membranes prevents the penetration of small-sized water molecules,whereas the hydrophobic MFI type sieves have a preferential adsorption effect on organic solvents.Additionally,the molecular dependence of the permeation rate during pervaporation follows a similar pattern to that of the single gas permeation rate of the membrane,suggesting that the single gas permeation performance of the membrane can be used to anticipate the pervaporation performance of MFI type zeolite membrane.