Zhenjie He

Nanostructured poly(4-methyl-2-pentyne)/silica hybrid membranes for gas separation☆

The separation of hydrocarbons from permanent gases is of considerable importance in the chemical industry. Poly(1-trimethylsilyl-1-propyne) [PTMSP] is extremely permeable to hydrocarbons and has high hydrocarbon/ permanent gas selectivity. However, the poor chemical resistance of this material limits its use as a membrane for industrial applications. To overcome this problem, we studied an alternative acetylene-based polymer, poly(4-methyl-2-pentyne) [PMP], which exhibits much better chemical resistance than PTMSP. Several types of non-porous, nano-sized, fumed silica fillers were incorporated in PMP to manipulate the molecular polymer chain packing. The pure-and mixed-gas permeation properties of the PMP/silica hybrid membranes were studied. The gas permeability and the hydrocarbon/permanent-gas selectivity increased simultaneously with increasing filler content. The n-butane/ methane selectivity was 13 for pure PMP, but increased to 26 for 45 wt% silica-filled PMP. In addition, the n-butane permeability also increased 3–4 fold. Therefore, the silica-filled hybrid PMP membrane showed completely opposite gas permeation behavior to that of conventional polymers filled with non-porous inorganic nanoparticles.

Transport properties of PA12-PTMO/AgBF4 solid polymer electrolyte membranes for olefin/paraffin separation

Abstract A rubbery nylon-12/tetramethylene oxide block copolymer (PA12-PTMO) was used as a polymeric matrix material for silver tetrafluoroborate (AgBF 4 ) based solid polymer electrolyte membranes. Ethane sorption uptake of PA12-PTMO/AgBF 4 increased linearly with increasing feed pressure. Moreover, the ethane sorption capacity decreased by increasing the AgBF 4 concentration in the polymer electrolyte. Ethylene sorption of pure PA12-PTMO also followed Henrys law. On the other hand, the ethylene sorption isotherms of PA12-PTMO/AgBF 4 showed a completely different behavior. As the silver concentration increased in the polymer electrolyte membranes, the sorption isotherms showed a dual-mode sorption behavior. The initial sorption enhancement provides clear evidence of complex formation between ethylene and silver ions. Mixed-gas permeation studies performed with dry ethylene/ethane mixture demonstrated that PA12-PTMO/AgBF 4 composite membranes exhibited good stability. In a 14-day test period, the ethylene/ethane selectivity of this membrane decreased from 25–20. This performance is far better than that of any polymeric membrane for ethylene/ethane separation. The decline in membrane performance occurred only during the first 3 days of operation; thereafter, the membrane showed excellent long-term stability.

Gas permeation of fullerene‐dispersed poly(1‐trimethylsilyl‐1‐propyne) membranes

Homogeneously fullerene-dispersed membranes were prepared under the conditions in which a 10 wt % poly(1-trimethylsilyl-1-propyne) solution containing 0.5 wt % fullerene was dried under a reduced pressure of 50 cmHg at 100 °C. UV-vis spectra and microscopic observations of the fullerene membranes indicated that the fullerene was homogeneously dispersed in the membranes. The permeability coefficients of 1-butene were found to be higher than those of n-butane in the fullerene membranes, although the permeability coefficients of olefin gases were nearly equal to those of paraffin gases having the same number of carbon in poly(1-trimethylsilyl-1-propyne) membranes containing no fullerene. Pressure dependence of permeability coefficients was clearly observed for the permeation of carbon dioxide, ethylene, ethane, 1-butene, and n-butane through the fullerene membranes, while no significant dependence was found for poly(1-trimethylsilyl-1-propyne) membranes except for the permeation of 1-butene and n-butane. The pressure dependence of the permeability was explained by the dual-mode sorption model.

High-performance perfluorodioxolane copolymer membranes for gas separation with tailored selectivity enhancement

Separations using polymer membranes is a rapidly growing field due to membrane advantages such as energy efficiency, environmental friendliness, and compact size. Among the materials considered for membrane use are perfluoropolymers, which offer unprecedented stability for operation in challenging conditions such as those required in industrial gas separations. Despite this favorable attribute, the relative lack of material choices has hindered perfluoropolymer adoption as membranes. Here, we report gas transport properties in a new family of amorphous perfluorodioxolane copolymers that show permselectivities above the polymer upper bound for important gas pairs (e.g., He/CH4, H2/CH4, N2/CH4). For example, the most selective of these membranes has a He/CH4 selectivity more than 5 times higher than any previously reported for a perfluoropolymer. The new copolymer membranes exhibit tunable transport properties through variation in the amount of monomers that function as “selective enhancers”. Such monomers, which show a tendency to crystalize as homopolymers, improve chain packing in the copolymer, enhancing the membrane ability to sieve molecules by size. In this manner, these materials open a new route to achieving tailored performance with inherently stable membranes. Moreover, these copolymers are soluble in fluorinated solvents, and thus are solution processable making their scale-up and conversion to membrane devices straightforward using existing industry methods.

Olefin Recovery from Chemical Industry Waste Streams

The objective of this project was to develop a membrane process to separate olefins from paraffins in waste gas streams as an alternative to flaring or distillation. Flaring these streams wastes their chemical feedstock value; distillation is energy and capital cost intensive, particularly for small waste streams.