Karel Friess

Triptycene Induced Enhancement of Membrane Gas Selectivity for Microporous Tröger's Base Polymers

A highly gas permeable polymer with exceptional size selectivity is prepared by fusing triptycene units together via a poly-merization reaction involving Trögers base formation. The extreme rigidity of this polymer of intrinsic microporosity (PIM-Trip-TB) facilitates gas permeability data that lie well above the benchmark 2008 Robeson upper bounds for the important O2 /N2 and H2 /N2 gas pairs.

A highly permeable polyimide with enhanced selectivity for membrane gas separations

A highly gas permeable polyimide with improved molecular sieving properties is produced by using a bisanhydride monomer based on the rigid ethanoanthracene unit. The polymer (PIM-PI-EA) demonstrates enhanced selectivity for gas separations so that its gas permeability data lie above the 2008 Robeson upper bounds for the important O2–N2, H2–N2, CO2–CH4 and CO2–N2 gas pairs.

Enhancement of CO2 Affinity in a Polymer of Intrinsic Microporosity by Amine Modification.

Nitrile groups in the polymer of intrinsic microporosity PIM-1 were reduced to primary amines using borane complexes. In adsorption experiments, the novel amine–PIM-1 showed higher CO2 uptake and higher CO2/N2 sorption selectivity than the parent polymer, with very evident dual-mode sorption behavior. In gas permeation with six light gases, the individual contributions of solubility and diffusion to the overall permeability was determined via time-lag analysis. The high CO2 affinity drastically restricts diffusion at low pressures and lowers CO2 permeability compared to the parent PIM-1. Furthermore, the size-sieving properties of the polymer are increased, which can be attributed to a higher stiffness of the system arising from hydrogen bonding of the amine groups. Thus, for the H2/CO2 gas pair, whereas PIM-1 favors CO2, amine–PIM-1 shows permselectivity toward H2, breaking the Robeson 2008 upper bound.

Carbon nanotube- and carbon fiber-reinforcement of ethylene-octene copolymer membranes for gas and vapor separation.

Gas and vapor transport properties were studied in mixed matrix membranes containing elastomeric ethylene-octene copolymer (EOC or poly(ethylene-co-octene)) with three types of carbon fillers: virgin or oxidized multi-walled carbon nanotubes (CNTs) and carbon fibers (CFs). Helium, hydrogen, nitrogen, oxygen, methane, and carbon dioxide were used for gas permeation rate measurements. Vapor transport properties were studied for the aliphatic hydrocarbon (hexane), aromatic compound (toluene), alcohol (ethanol), as well as water for the representative samples. The mechanical properties and homogeneity of samples was checked by stress-strain tests. The addition of virgin CNTs and CFs improve mechanical properties. Gas permeability of EOC lies between that of the more permeable PDMS and the less permeable semi-crystalline polyethylene and polypropylene. Organic vapors are more permeable than permanent gases in the composite membranes, with toluene and hexane permeabilities being about two orders of magnitude higher than permanent gas permeability. The results of the carbon-filled membranes offer perspectives for application in gas/vapor separation with improved mechanical resistance.

Vapour permeation and sorption in fluoropolymer gel membrane based on ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide

The emissions of hydrocarbons from fossil fuels into atmosphere entail both an economic loss and an environmental pollution. Membrane separations can be used for vapour recovery and/or vapour removal from the permanent gas stream, given that the appropriate membrane is identified. A neat poly(vinylidene fluoride-co-hexafluoropropylene) membrane is impermeable to both the representatives of aliphatic hydrocarbons and branched hydrocarbons, namely hexane and isooctane, whereas the permeation flux is enhanced by the presence of 80 mass % of the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide in the membrane, as detailed in this work. The permeabilities of hydrocarbon vapours were determined from the binary mixture containing hydrocarbon and nitrogen to simulate the real input of an air stream containing a condensable hydrocarbon. The diffusion coefficient determined from sorption measurements was higher for hexane, as would be expected for a smaller molecule, whereas both the sorption isotherms and permeabilities of the hydrocarbons studied were found to be almost identical. It is possible that the sorption effect predominates in the transport mechanism for VOCs/N2 separations.

Hyperbranched Polyimide-Silica Hybrid Materials: Synthesis, Structure, Dynamics, and Gas Transport Properties

A series of organic–inorganic hybrid materials were prepared from a hyperbranched polyimide precursor (hyperbranched polyamic acid), tetramethoxysilane, and/or 3-glycidyloxypropyl-trimethoxysilane via a sol-gel process. The hyperbranched polyimide-silica hybrids, whose polyimide moieties were based on commercially available monomers 4,4′,4″-triaminotriphenylmethane and 4,4′-oxydiphthalic anhydride taken in molar ratio 1:1, contained from 10 to 30 wt% silica. Their morphology and dynamics were characterized by using scanning electron microscopy, differential scanning calorimetry, dynamic mechanical analysis, laser-interferometric creep rate spectroscopy, and wide-angle X-ray diffraction. Attention was also focused on the relation between morphology/dynamics and gas transport properties of these materials.

Thin high flux self-standing graphene oxide membranes for efficient hydrogen separation from gas mixtures

The preparation and gas-separation performance of self-standing, high-flux, graphene oxide (GO) membranes is reported. Defect-free, 15-20 μm thick, mechanically stable, unsupported GO membranes exhibited outstanding gas-separation performance towards H2 /CO2 that far exceeded the corresponding 2008 Robeson upper bound. Remarkable separation efficiency of GO membranes for H2 and bulky C3 or C4 hydrocarbons was achieved with high flux and good selectivity at the same time. On the contrary, N2 and CH4 molecules, with larger kinetic diameter and simultaneously lower molecular weight, relative to that of CO2 , remained far from the corresponding H2 /N2 or H2 /CH4 upper bounds. Pore size distribution analysis revealed that the most abundant pores in GO material were those with an effective pore diameter of 4 nm; therefore, gas transport is not exclusively governed by size sieving and/or Knudsen diffusion, but in the case of CO2 was supplemented by specific interactions through 1) hydrogen bonding with carboxyl or hydroxyl functional groups and 2) the quadrupole moment. The self-standing GO membranes presented herein demonstrate a promising route towards the large-scale fabrication of high-flux, hydrogen-selective gas membranes intended for the separation of H2 /CO2 or H2 /alkanes.

Derivation of the permeation equation for diffusion of gases and vapors in flat membrane by using Laplace transform

Abstract Generally, the model of forced diffusion of a penetrant through nonporous polymer membranes can be quantitatively described by a partial differential equation of parabolic type, which is known as Fick’s second law. In this article, the detailed explanation of application of the integral transform method (especially Laplace transform) for the solution of Fick’s second law at given initial and boundary conditions is presented. Obtained final expression for the concentration profile inside a flat membrane and the diffusion flux through a membrane were verified on permeability data of carbon dioxide and cyclohexane through low-density polyethylene membrane. While CO2 permeation data can be successfully fitted by obtained model, in the case of cyclohexane vapors, when the diffusion coefficient cannot be supposed to be constant due to strong polymer–penetrant interactions (swelling), the agreement between model and experimental data is lower.

Evaluation of Two Methods for Measuring Vapor Sorption in Polymers

In this paper, two methods for measuring the equilibrium vapor sorption in polymers are critically compared and data on sorption of toluene, p-xylene, hexane, cyclohexane, and heptane in low density polyethylene are reported. The vapor phase calibration method (VPC) was used to measure vapor sorption at low vapor activities in air (below 0.01), and the gravimetric method was used to measure sorption over wide range of activities of pure vapors (0.1–0.9). The Flory-Huggins interaction parameter (in amorphous phase) varied between 1.00 for cyclohexane and 1.19 for toluene. The resulting confidence intervals are conjunctive, indicating that both methods provide consistent results.

Poly(imide-siloxane)s based on hyperbranched polyimides

Abstract Poly(imide-siloxane)s differing in their composition were prepared and characterized. The starting polymer (control) was the hyperbranched polyimide based on 4,4′-oxydiphthalic anhydride and 4,4′,4″-triaminotriphenylmethane. In the poly(imide-siloxane)s, 10 or 40–50 mol% of the 4,4′,4″-triaminotriphenylmethane was theoretically substituted for by amine-terminated siloxane dimer or oligomers. 1,3-Bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, bis(3-aminopropyl)-terminated poly(dimethylsiloxane) with a theoretical number-average molar mass of 1000 g·mol−1 and bis(3-aminopropyl)-terminated poly(dimethylsiloxane) with a theoretical number-average molar mass of 2500 g·mol−1 were used for this purpose. The thermo-mechanical properties and gas separation characteristics for hydrogen, carbon dioxide and methane of these polymeric products were shown to be dependent on their composition.