Synthesis Of 4-Morpholine Carboxylate PEGMA And Its Aromatic/Aliphatic Separation Performance

The"pore-filling"pervaporation composite membrane has unique advantages for the separation of aromatic/aliphatic mixtures that is difficult to separate and energy-intensive.The pervaporation performance of the"pore-filling"composite membrane is mainly determined by the material of the functional layer.It has been found that the"pore-filling"composite membranes made from macromonomer polyethylene glycol methacrylate(PEGMA)with different end groups exhibits significantly different aromatic/aliphatic separation performance.In this work,a new type of polyethylene glycol methacrylate monomer,4-morpholine carboxylate polyethylene glycol methacrylate(MORPEGMA),was designed and synthesized.Using toluene/n-heptane and toluene/methylcyclohexane mixetures as feeds,the pervaporation performance of aromatic/aliphatic separation for MORPEGMA homopolymer was studied.The swelling adsorption-desorption experiments and molecular dynamics simulation were utilized to explore the molecular transport mechanism.The"pore-filling"composite membranes were prepared by the double-plasma grafting strategy.The influence of feed temperature and feed concentration on the pervaporation performance of aromatics/aliphatics was investigated.Firstly,PEG400 and 4-morpholine carbonyl chloride are used as raw materials to synthesize the monomer MORPEG400MA through a two-step esterification method.The synthesized macromonomers were characterized by hydrogen nuclear magnetic resonance spectroscopy(~1H-NMR),matrix-assisted laser desorption ionization-time of flight mass spectrometry(MALDI-TOF MS),etc.,which proved that the MORPEG400MA macromonomer was synthesized successfully.Secondly,the homopolymer of MORPEG400MA was obtained by the free radical polymerization.The homogeneous membrane was prepared by the solvent evaporation method.The swelling adsorption-desorption experiment was used to characterize the adsorption selectivity of toluene/n-heptane and toluene/methylcyclohexane of the MORPEG400MA homopolymer.The results showed that the MORPEG400MA homopolymer has good toluene adsorption selectivity,and the adsorption selectivity of toluene/n-heptane is greater than that of toluene/methylcyclohexane.Thirdly,molecular dynamics(MD)simulations were performed using Materials Studio2017 software.The diffusion coefficients of small molecules in polyethylene glycol methacrylate homopolymers with hydroxyl end group and methyl ether end group at various temperature were determined.The diffusion and solution behaviors of small molecules of toluene,n-heptane,and methylcyclohexane in MORPEGMA homopolymer and the mixing energy of the binary system MORPEGMA macromonomer-polyacrylonitrile(PAN)and MORPEGMA homopolymer-PAN were investigated.It was found that the diffusion coefficients of toluene and n-heptane in the PEGMA homopolymers with hydroxyl end group or methyl ether end group increased with increasing temperature.For the MORPEGMA homopolymer,the toluene/n-heptane diffusion selectivity was less than 1,the solubility selectivity and the selectivity of toluene/n-heptane are 56.06 and 32.51,respectively;the diffusion selectivity of toluene/methylcyclohexane is greater than 1,and the solubility selectivity and the selectivity of toluene/methylcyclohexane are 13.00 and 15.86,respectively.Thus,the separation of aromatic/aliphatic with MORPEGMA homopolymer is dominated by the solubility selectivity.The mixing energy of the system increases with increasing temperature.The MORPEGMA is compatible with PAN,and the compatibility between MORPEGMA homopolymer and PAN is better than MORPEGMA/PAN.The PAN/MORPEG400MA"pore-filling"composite membranes were prepared by the double-plasma grafting strategy.The composite membranes were characterized by attenuated total reflection flourier transformed infrared spectroscopy(ATR-FTIR),scanning electron microscopy(SEM)and X-ray photoelectron spectroscopy(XPS).The separation factor and permeation flux of the toluene/n-heptane mixture(toluene content 20 wt%)at 80 ~oC are 4.20and 2.67 kg/(m~2·h),respectively.For the toluene/methylcyclohexane(toluene content 1 wt%),the separation factor and permeation flux are 4.37 and 1.18 kg/(m~2·h),respectively.With the increase of the toluene content in the feed,the separation factors decreases,and the permeation flux increases.As the feed temperature increases,the separation factors of toluene/n-heptane and toluene/methylcyclohexane increases gradually and then decreases,and the permeation flux increases.