G. A. Dibrov

Elaboration of composite hollow fiber membranes with selective layer from poly[1-(trimethylsylil)1-propyne] for regeneration of aqueous alkanolamine solutions

The results of research on elaboration of the hollow fiber composite membranes for regeneration of aqueous solutions of alkanolamines in membrane gas-liquid contactor are presented in this work. Asymmetric polysulfone (PSF) hollow fiber UF membranes were used as a porous support, poly[1-(trimethylsylil)-1-propyne] (PTMSP) was employed as a diffusion layer. The influence of PSF hollow fiber casting conditions on hydraulic permeability was studied. Samples of composite membranes were obtained with a defectfree layer of PTMSP and carbon dioxide permeance of 0.26 m3 (STP) (m2 h bar)−1. It was revealed by SEM that the thickness of the PTMSP separation layer is 2.5 microns, where in X-ray spectrometry analysis data and calculations according to resistance-in-series model discovered that the selective layer penetration depth to the pores of the support was 1.4 microns. Calculation by resistance-in-series model showed that 98.6% of resistance to the gas transport is attributed to PTMSP, partially intruded in the pores of the support. Chemical stability of materials which comprise composite membrane makes promising their using for regeneration of aqueous solutions of alkanolamines (pH > 11) from carbon dioxide at a temperature of 100°C and a pressure drop of 10 bar in the membrane gas-liquid contactors.

Percolation of composite poly(vinyltrimethylsilane) membranes with carbon nanotubes

Recent years have seen a flurry of activity in research on the use of nanoparticles to improve the properties of polymeric membranes. It is known that the change in the macroscopic properties of these hybrid materials is associated with the parameters of the cluster of incorporated nanoparticles. The percolation threshold is higher than 15 vol % for the spherical particles and decreases with the increasing aspect ratio of the embedded nanoparticles of another shape. The paper presents the results of study on the permeability of gases (N2, O2, CH4 and C3H8) and a test liquid (ethanol) through hybrid membranes based on the glassy polymer poly(vinyltrimethylsilane) (PVTMS) with embedded multiwall carbon nanotubes (MWCNT) with a concentration of 0.3–3 wt %. It has been found that the permeability of gases and liquids alters at MWCNT concentrations above 0.4 wt %, which corresponds to the percolation threshold for the given particles as proved by calculations. In addition, the gas permeability coefficients measured indicate a change in the transport mechanism and selectivity of the membrane.

Gas permeability of homogeneous and composite membranes based on poly(trimethylsilylpropyne)/poly(vinyltrimethylsilane) blends

Gas transport properties of membranes based on a blend of two silicon-hydrocarbon polymers, poly(trimethylsilylpropyne) (PTMSP) and poly(vinyltrimethylsilane) (PVTMS), have been investigated. The N2 and CO2 permeability of the membranes decreases by two orders of magnitude, and CO2/N2 selectivity increases about threefold with increasing PVTMS content in the blend from 0 to 100%. The effect of the volume contraction of the membranes has been found. The results of the experiments and calculations showed that the membrane properties throughout all the range of concentrations are in good agreement with the single-phase blend permeability model. The results of the research open the possibility of preparing PTMSP/PVTMS membranes with stable gas separation properties combining a high permeability of PTMSP and a rather high selectivity of PVTMS.

Effect of absorbent vapor on stability of characteristics of a composite PTMSP membrane on nonwoven polyester support during regeneration of diethanolamine solution in membrane contactor

The regeneration of a carbon dioxide-loaded aqueous solution of diethanolamine (DEA) in a membrane contactor-stripper at a temperature of 100°C, an absorbent pressure of 10 atm, and a varying absorbent feed flow rate has been studied. The membranes used were laboratory samples of composite membranes prepared by deposition of thin separation layers of poly[1-(trimethylsilyl)-1-propyne] (PTMSP) on a porous support. The support was MFFK-1 microfiltration membrane (Vladipor) with the filtering porous layer of fluoroplastic F-42 (tetrafluoroethylene-vinylidene fluoride copolymer) deposited on a nonwoven polyethylene terephthalate (PET) support. After the first 10 days of testing, the CO2 flux at the membrane contactor outlet was reduced by a factor of 3 and then stabilized at 2 m3/(m2 h) within the next 80 days. It has been found that along with CO2 transport through the membrane, the vapor of the absorbent solution components is transferred. The concentration of DEA in the condensate was 0.5 wt %, that corresponds to the composition of equilibrium vapor over a 30 wt % DEA aqueous solution at 100°C. Since PTMSP is chemically resistant to the DEA solution at the regeneration temperature, the deterioration of the transport properties of the PTMSP/MFFK(PET) composite membrane with time during the absorbent regeneration is associated with the chemical degradation of the nonwoven PET support by the action of penetrating DEA vapor at a temperature of 100°C. It has been concluded that more chemically and thermally resistant porous supports such as ceramic microfiltration membranes should be used.

Investigation of gas transport properties of poly(2-methyl-5-vinyltetrazole) membranes

In recent years, progressively increasing attention of researchers has been given to vinyltetrazoles and their polymeric derivatives. However, despite the variety of properties revealed, a limited number of studies focus on the possibility of their practical application and there is no published data on the gas permeability of these polymers. This paper presents the results of study of the gas transport properties of polymeric membranes based on poly(2-methyl-5-vinyltetrazole) for helium, oxygen, nitrogen, and methane. It has been found that these properties depend on the membrane thickness. The permeability and diffusion coefficients increase with the decreasing kinetic diameter of penetrant molecules or the increasing temperature. Poly(2-methyl-5-vinyltetrazole) exhibits behavior typical of most of the known polymers.

Cold rolling for controllable narrowing of pore size and pore size distribution of commercial fluoroplastic microfiltration membrane

A cold-rolling method for modifying MFFK commercial microfiltration membranes based on the fluoroplastic F-42L has been developed and investigated. The method is based on the cold flow property of fluoropolymers and make it possible to alter the physical properties of a membrane without affecting its chemical structure. Scanning electron microscopy and capillary flow porometry studies have shown that this method also makes it possible to controllably narrow the through-pore diameter distribution, reduce the maximum pore size, and vary permeability depending on the applied force. In addition, rolling is a simple fluoroplastic-membrane modification process that is appropriate in engineering design and is easy to integrate into the membrane manufacturing cycle. According to available published data, this is a pioneering attempt to use the method for controllable reducing the pore diameter and narrowing the pore size distribution of fluoroplastic microfiltration membranes.