V. Vasilevsky

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.

Influence of the composition of concentrate solutions on the efficiency of carbon dioxide removal from monoethanolamine aqueous solution by electrodialysis

The feasibility of optimizing the electromembrane removal of carbon dioxide from an aqueous monoethanolamine (MEA) solution with a CO2/MEA molar ratio of 0.2 after the regeneration stage aimed to reduce the loss of MEA with the concentrate has been explored. The influence of the composition of the concentrate solution on the recovery of carbon dioxide and the specific loss of MEA (g MEA/g CO2 recovered) for a process duration of 1 h has been studied. The solution in the concentration cells was either distilled water or aqueous MEA solutions with a different carbon dioxide loadings. It has been found that the CO2 recovery ranges within 56.6–66.5%; the maximum and minimum specific losses of MEA make 4.80 and 1.49 g MEA/g CO2 recovered; and the specific energy consumption is 6.48–9.72 MJ/kg CO2 recovered.

Electrodialysis of solutions of tartaric acid and its salts

Electrodialysis with ion-exchange membranes is an effective method for the separation and concentration of food acids, and it has considerable capabilities as a step of their manufacture in both microbiological and chemical syntheses. A barrier effect and a facilitated electromigration effect in the electrodialysis of solutions of tartaric acid and its salts has been revealed. The dependence of the flux of hydrotartrate ions on current density is characterized by the occurrence of a plateau in the region of the barrier effect with the subsequent increase in mass transfer in the region of the facilitated electromigration effect. The found regularities of electrical mass transfer should be taken into account in the optimization of the separation, recovery, and concentration of food acids whose anions are organic ampholytes capable of charge exchange upon changing the pH at the membrane/solution interface.

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.

Porous hollow fiber membranes with varying hydrophobic–hydrophilic surface properties for gas–liquid membrane contactors

In relation to the demand for asymmetric porous hollow fiber membranes to be used in gas–liquid membrane contactors designed for operation in organic media, polysulfone membranes of this type have been prepared and subsequently modified to impart oleophobic properties to their surface. The structure and properties of the membranes have been characterized using various techniques, such as optical and scanning electron microscopy, and by measuring contact angles and the permeability of helium, carbon dioxide, and hexane. The surface properties of the membranes have been modified by etching with a mixture of hydrogen peroxide and sulfuric acid or coating with a perfluorinated acrylic copolymer. In the latter case, modified membrane samples have shown a significant reduction in wettability with both water and organic liquids. The hexane permeability data indicate the absence of hexane flow through the membrane modified with perfluorinated acrylic copolymer until a gauge pressure of about 1 atm. The results of the study lead to the conclusion that these membranes can find use in gas–liquid membrane contactors, e.g., for the removal of dissolved gases from liquid hydrocarbons.

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.