Jin-Sheng Yang

Novel methods in separation of olefin/paraffin mixtures by functional polymeric membranes

Abstract C 3 and C 4 olefin/paraffin mixtures were separated by means of a linear low density polyethylene (LLDPE) modified reversible complexing membrane, poly(ethylene-graft-acrylic acid) (PE-g-AA) incorporated with silver ions (PE-g-AA-Ag + ). Owing to the formation of a (Ag-olefin) + complex, olefin can be transported across the membrane by facilitated transport. The SEM-EDX spectrum of the complex membrane showed a homogeneous silver ion distribution across the cross-section of the dense membrane at a grafting higher than about 60%. The permeation properties of an olefin/paraffin gas mixture as measured by gas chromatography with a gas permeability analyzer implied a facilitating effect for olefin. The permeability coefficients, separation factors and permeation activation energies of C 3 and C 4 mixtures at various AA% grafts and temperatures were studied. The separation factor decreased upon exposure of the complex membrane to air, thereby showing decreased silver ion facilitated transport. A membrane regeneration method and the gas permeation properties of the regenerated complex membrane are also discussed.

C4 olefin/paraffin separation by poly[(1-trimethylsilyl)-1-propyne]-graft-poly(acrylic acid)-Ag+ complex membranes

Abstract A complex membrane of polyl[(1-trimethylsilyl)-1-propyne]-graft-poly(acrylic acid)-Ag+ (PTMSP-g-AA-Ag+) was synthesized and characterized for C4 olefin/paraffin gases separation. The 121.6% grafted PTMSP-g-AA-Ag+ complex membrane showed a homogeneous silver distribution across the membrane. Olefin could be transported across the complex membrane both by physical dissolution-diffusion phenomenon and by silver ion facilitated transport for subsequently forming the reversible (Ag-olefin)+ complex. The permeation properties of C4 gases, as measured by gas chromatography equipped with a gas permeability analyzer, indicated a facilitating effect for olefin. Typical selectivities of the 121.6% grafted complex membrane at 55°C for the isobutene/isobutane and trans- 2-butene n- butane were 7.7 and 7.3, respectively. The effects of AA% grafting, measuring temperature and permanence stability on the permeability coefficients and separation factors were studied. The solubilities and diffusivities of C4 gases as well as their selectivites were also examined.

Swollen polymeric complex membranes for olefin/paraffin separation

Abstract Swollen complex membrane of linear low density polyethylene-graft-poly(acrylic acid)-Ag + (LLDPE-g-AA-Ag + ) were studied and compared with the corresponding membranes based on silicone rubber (SR) and poly[1-(trimethylsilyl)-1-propyne] (PTMSP), such as SR-g-AA-Ag + and PTMSP-g-AA-Ag + . The polymeric matrix was first grafted with acrylic acid (AA) and then incorporated with silver ions (Ag + ) in glycerol solution for forming the swollen complex membrane. Various metal ions and swollen agents in membranes for isobutene/isobutane separation were presented. The swelling of the complex membrane containing Ag + with glycerol shows a higher olefin/paraffin selectivity than those membranes containing Cu + or Cu 2+ ions and/or other swelling agents. The gas permeability coefficients and the isobutene/isobutane selectivity of LLDPE-g-AA-Ag + membrane were compared with those of SR-g-AA-Ag + and PTMSP-g-AA-Ag + membranes. The PTMSP-g-AA-Ag + complex membrane was found to reach high gas permeability and high olefin/paraffin selectivity. The effects of solubility and diffusivity in membranes are compared with the corresponding non-Ag membranes. The sorption properties in these complex membranes were also included.

Synthesis of acrylic acid grafted silicone rubber via preirradiation graft copolymerization and its physical and dielectric properties

The hydrophilic monomer, acrylic acid (AA), has been grafted onto hydrophobic silicone rubber (SR) film via the γ-ray preirradiation graft technique. The AA percent graft in SR-g-AA film increases with increasing irradiation dose rate. The iron powder in monomer solution serves as one source of ferrous ion that is generated by the oxidation reaction with water. The swelling effect shows that the amount of chloroform taken up by an SR-g-AA membrane decreases with the increasing AA grafting, and the amount of water, alcohol, and glycerol taken up by an SR-g-AA film increases with increasing AA percent grafting. The contact angle, ultimate stress, and elongation at break of SR and SR-g-AA copolymers decrease with increasing AA percent grafting. The oxygen/nitrogen selectivity in these films can be enhanced by the graft modification. The thermal behaviors of SR-g-AA co-polymers show the characteristics of SR and polyacrylic acid. Finally, the dielectric properties show that the SR-g-AA film has a superior dielectric property than the original SR and poly(AA) matrix.

Selective olefin permeation through Ag(I) contained silicone rubber-graft-poly(acrylic acid) membranes

Abstract The silicone rubber (SR) based graft copolymer, SR-graft-poly(acrylic acid) (SR-g-AA), was modified by incorporating silver ion (SR-g-AA-Ag+) for C4 olefin/paraffin gases separation. Olefin could be transported across the complex membrane by the silver ion facilitated transport. The permeation properties, as measured by gas chromatography equipped with a gas permeability analyzer, implied a facilitating effect for olefin. Typical trans-2-butene/n-butane selectivity in the 95.6% grafted complex membrane at 25°C is 4.0. Also, the influences of AA% grafting, measuring temperature and pressure to the permeation properties of C4 gases were studied. In addition, the sorption behaviors of C4 gases in SR based membranes are presented and discussed by the Flory-Huggins equation. Finally, the selectivity of solubility and diffusivity in these SR based membranes are also discussed.

Novel dry poly[(1-trimethylsilyl)-1-propyne]-AgClO4 complex membranes for olefin/paraffin separations

A novel dry complex membrane, poly[(-trimethylsilyl)-1-propyne]-AgClO4 (PTMSP-AgClO4), was prepared for C4 olefin/paraffin separation. Infrared spectra indicates that Ag(I) ions are complexed onto the unsaturated PTMSP main-chains. The olefin/paraffin separation factor could be enhanced by forming the reversible (Ag-olefin)+ complex. For isobutene/isobutane separation, a typical ideal separation factor of 5.6 was obtained for a 32.7 wt% PTMSP-AgClO4 complex membrane. Gas transport in PTMSP and PTMSP-AgClO4 membranes show negative Ep values due to their large negative value of ΔHs. The isobutenes solubility coefficient is greatly increased in the PTMSP-AgClO4 membrane. The gas permeation properties of isobutene/isobutane gases in PTMSP and PTMSP-AgClO4 membranes were studied. Dual-mode behaviors of the sorption of gases in PTMSP and PTMSP-AgClO4 membranes are also discussed.

Stress relaxation in poly(styrene-butadiene-styrene) and poly(styreneisoprene-styrene) triblock copolymers and their derivatives

Abstract The stress relaxation properties of poly(styrene-b-butadiene-b-styrene) (SBS), epoxidized SBS (ESBS), poly(styrene-b-isoprene-b-styrene) (SIS) and 1-vinylimidazole grafted SIS (SIS-g-VIm) copolymers in air were investigated. The stress relaxation of SBS copolymer occurs as a result of the physical flow, the physical entanglements and the domains. The stress relaxations for SBS, ESBS, SIS and SIS-g-VIm copolymers are temperature dependent, with a higher relaxation rate at higher temperatures. The stress relaxation activation energies of SBS, ESBS, SIS and SIS-g-VIm were 83.7, 46.0, 113.0 and 52.2 kj mol −1 , respectively, indicating that ESBS and SIS-g-VIm had higher stress-relaxation rates than SBS and SIS at constant temperature. The procedure X method, previously proposed by Tobolsky and Murakami, was utilized for separation and identification of the three processes causing stress relaxation. A general representative equation, f(t) f(0) = A exp (−k A t)+B exp (−k B t) + C exp (−k c t) , was obtained for the stress relaxation of the physical flow, the physical entanglements and the domain region, respectively. The relationship k A > k B > k C that was found demonstrates that the relaxation rates decrease in the order physical flow > physical entanglements > the domain.

Ag+ contained complex membrane for the separation of C4 olefin/paraffin mixture

The C4 olefin/paraffin mixture was separated by means of the PE modified reversible complexing membrane, polyethylene-g-acrylic acid-Ag+(PE-g-AA-Ag+). The olefin could be transported to the other side of the membrane by silver facilitating phenomenon owing to the formation of (Ag-olefin)+ complex. The SEM-EDX spectrum showed a homogeneous silver ion distribution across the dense complex membranes cross-section at higher than about 60% grafting. The gas permeation properties measured by a gas chromatographic method implied a silver ions facilitating effect towards olefin. At 30°C and 111.7% grafting, the complex membrane exhibited a trans-2-butene/isobutane selectivity of 12.5 and a cis-2-butene/isobutane selectivity of 9.2. The permeation activation energy of the C4 olefins became lower than that of C4 paraffin as a result of the silver ions facilitated effect. The cis-2-butene has a significant higher complex equilibrium constant than that of the trans-2-butene in complexing with the complex membrane.

Kinetics of Ag+ contained polymeric complex membranes for facilitated olefin transport

The reactions of silver ion complexes with polyethylene-graft-poly(acrylic acid)(PE-g-AA) and the olefin reversible coordinates with the PE-g-AA-Ag + complex membranes were studied. Infrared and nuclear magnetic resonance spectra confirmed the complex formation between the carboxylic acid of the PE-g-AA and the Ag + ion. Also, the Ag + ion in PE-g-AA-Ag + membrane was assumed to be a fixed carrier that adsorbs and transports olefin, thereby causing a selective olefin/paraffin separation. A theoretical model of the PE-g-AA-Ag + ( olefin ) complex was proposed. The coordination number of Ag + ion binding to the carboxylic acid of PE-g-AA is about 1.6 in glycerol solution. The coordination number of olefin binding to the Ag + in the PE-g-AA-Ag + complex membrane is 1. Moreover, the kinetics of olefin binding to the PE-g-AA-Ag + complex membranes were studied. The equilibrium, association, and dissociation constants were also presented.