Amine absorption processes designed to remove acid gases from gas streams generally face a major challenge of solvent degradation. This degradation leads to the formation of heat-stable salts (HSS), ...corrosive agents that irreversibly bind free alkanolamine. The present study proposes, for the first time, a method for HSS perstraction using a liquid–liquid membrane contactor that allows HSS to transfer through porous membranes from the solvent into a hydrophobic extractant represented by a methyltrioctylammonium solution in 1-octanol. The perstraction provides selective extraction of HSS anions without direct mixing of liquid phases or the formation of stable emulsions of the solvent and the extractant. For this purpose, a number of industrial and laboratory porous membrane samples fabricated from polyvinylidene fluoride, polypropylene, and polysulfone were investigated. Their chemical and morphological stability, surface properties, and transport properties were tested under prolonged (>600 h) contact with a model solvent (an aqueous monoethanolamine solution) and with the components of the selective extractant. The feasibility of HSS perstraction was demonstrated using the formic acid (as an HSS model) extraction from the model solvent. The most promising results were obtained for a system with a polyvinylidene fluoride membrane: up to 50% of formic acid was extracted over 18 h.
The insoluble polyimides are the most promising group of polymer materials for fabrication of solvent stable filtration membranes suitable for operation at elevated temperatures. In order to ...synthesize asymmetric membranes from insoluble polyimide, it is proposed to fabricate the membranes from a pre-polymer solution (polyamide acid - PAA) by non-solvent induced phase separation method followed by imidization to form non-soluble porous polyimide membrane. The thermoplastic crystallizable polyimide R-BAPB, which is resistant to a number of known organic solvents, was chosen as a membrane material. For the first time, hollow fiber membranes based on imidized PAA (R-BAPB) with a controlled distribution of pores on the inner side of the hollow fiber were formed. It has been established that the use of "hard" non-solvents, such as water or aqueous-organic solutions, is preferable for the formation of a porous structure in the membranes based on PAA (R-BAPB). Synthesized PAA membranes were used to prepare porous membranes based on the thermoplastic polyimide R-BAPB by thermal imidization. Imidization process was confirmed by an increase in the glass transition temperature of the material to 220 °C (corresponds to the glass transition temperature of polyimide (R-BAPB)) and is accompanied by a significant increase in its elastic modulus. The results of the measurements of the transport properties of polyimide membranes for gases and liquids indicate that microfiltration transport pores are present in the membranes.
Dense bilayer PTMSP/PIM-1 membranes and PTMSP/PIM-1 blends were prepared and studied in order to obtain insight into the recently observed synergistic effect of increased CO2/N2 selectivity for ...thin-film composite (TFC) membranes consist of PIM-1 (selective layer) and PTMSP (gutter layer). It was shown that the mixing of these two polymers does not lead to a synergistic effect in gas permeance, since dense films made by blending of PIM-1 and PTMSP showed classical trade-off permeation/selectivity behavior. Analysis of gas-transport property data using a bicomponent resistance-in-series model allowed us to conclude that the increased N2 transport resistance of the layer formed on the border of the two polymers is presumably responsible for the increased ideal selectivity.
In this paper, we analyzed the possibility of using cellulose membranes in gas-liquid contactors to separate CO2 from physical absorbents and stabilize gas condensate. It was shown that a solid ...cellulose film "cellophane" is not impermeable to hexane and tetraethylene glycol dimethyl ether due to the absence of pores. It also has been found that these solvents are not adsorbed in the membrane, and the cellulose does not swell therein. This lack of interaction of the investigated organic solvents with the natural polymer was explained in terms of Hansen's solubility parameters, which in the case of hexane and tetraethylene glycol dimethyl ether are more than twofold less than of Hansen's solubility of cellulose. The impermeability and lack of interaction of the solvents under investigation with cellulose membranes makes them promising as membranes for gas-liquid contactors. But in order to realize the process it is necessary to create a membrane structure whose pore size not going to have hexane and tetraethylene glycol dimethyl ether penetration, but the permeance of CO2 and CH4 will be high.
Composite membranes with a thin selective layer based on poly1-trimethylsilyl-1-propyne (PTMSP) and crosslinked PTMSP containing 10 wt % of nanoparticles of porous aromatic frameworks (PAF-11) have ...been synthesized and studied. Monitoring of changes in the gas transport characteristics of the membranes under ambient conditions for 7500 h has revealed that for all the samples, the transport characteristics abruptly decrease within the first 1000–2000 h; after that, the mass transfer constants gradually change over time. In the case of a composite membrane with the selective layer based on crosslinked PTMSP and PAF-11 nanoparticles, stable permeability values after 7000 h are 2.1, 3.5, and 12.9 m
3
/(m
2
h atm) for N
2
, O
2
, and CO
2
,respectively (at an ideal selectivity of α(O
2
/N
2
) = 1.6 and α(CO
2
/N
2
) = 6.1); to date, this is the best published result for thin-film composite membranes based on highly permeable glassy polymers.
Two methods for monitoring the physical aging of polymer membranes by gas permeability measurements are compared. The traditional method with intermittent permeability monitoring is compared to the ...continuous permeability monitoring when the membrane occurs under excess pressure of the permeating gas throughout the experiment. A composite membrane with a thin (1 μm) selective polytrimethylsilylpropyne layer containing 10 wt % organic nanoparticles (porous aromatic frameworks) was taken as an example. The continuous permeability monitoring allows acceleration of the physical aging of the membrane and considerable (by two orders of magnitude) reduction of the experiment time. Fast physical aging in a carbon dioxide stream can be an efficient way to reach equilibrium gas permeability of membranes based on glassy polymers with high void volume.
The effect of particles of porous aromatic frameworks, synthesized by the Friedel–Crafts reaction (PAF-FC), introduced into matrix of glassy polymer poly(1-trimethylsilyl-1-propine) (PTMSP), on the ...stabilization of the transport characteristics of composite membranes with a thin selective layer (2.0–2.2 Μm) was studied. As a comparison, samples of composite membranes with a selective layer based on PTMSP and PTMSP filled with PAF-11 particles synthesized by the Suzuki reaction are considered. All samples of composite membranes showed a decrease in the absolute values of gas permeability for all gases over time due to relaxation of the nonequilibrium free volume of PTMSP, therewith the greatest decrease is observed during the first thousand hours since membrane creation. The stabilization of the transport characteristics of composite membranes with PTMSP/PAF-FC occurs after 5000 h since membrane creation, further the carbon dioxide performance remains at the level of 8–9 m
3
m
–2
h
–1
atm
–1
for 9200 h. Similar performance values for aged composite membranes based on PTMSP and PTMSP/PAF-11 were about 1.5 m
3
m
–2
h
–1
atm
–1
.
A method is proposed for the synthesis of new membrane materials based on polydimethylsiloxane (PDMS) and polybutadiene (PB). It has been shown that all components of the mixture completely enter ...into the hydrosilylation reaction and form a chemically crosslinked composite material. It has been found that in the region of low PB concentrations, the composite has a less crosslinked and dense structure. The gas transport properties of the synthesized materials have been experimentally investigated. The proposed materials have higher selectivity for organic components than the industrially used membrane polymer PDMS, which is determined by their high sorption selectivity. A membrane containing 17 wt % PB has enhanced fluxes of organic components and an increased separation factor for all alcohols (ethanol,
n
-propanol, and
n
-butanol) examined relative to those of the PDMS membrane in the pervaporative separation of water–alcohol solutions. At the same time, the ethanol–water permselectivity of such a membrane is greater than 1, a value that has been first achieved by modifying PDMS with polymers. Materials of this type have a great potential for the creation of membranes with high permeability and selectivity in the recovery of volatile organic compounds from aqueous media.
Radon is a noble gas that is one of the natural radioactive decay products of radium resulting from the disintegration of uranium. Humans are exposed to sources of natural radiation activity, being ...radon and its progeny breathing air responsible for more than 50% of the annual dose received from natural radiation. The aim of this study was to determine the radon concentration in the air in settlements’ dwellings and social objects and calculate the annual effective dose of population from radon on the territory mining activities in Stepnogorsk area. The study has shown that activity concentrations of indoor radon in the buildings ranged from 8 to 870 Bq · m−3 in Aqsu, 3-540 Bq · m−3 in Kvartsitka located close to former gold mining sites. The Einh corresponding to the activity concentrations ranged from 1-27 mSv · y−1 received by the settlements’ public. The highest value of Einh in Aqsu School reaches up to 68 mSv · y−1 received by the critical group of public was found at the territory of former mining the Stepnogorsk area. The results of this study show significant radiation hazards in Aqsu School which located at the territory of former mining site, and there is evidence of radon health risk to the members of the public.
The main objective of current study is to assess the dose burden and health status of workers at the uranium processing hydrometallurgical plant in order to develop measures aimed at reducing their ...incidence. This article presents the results of radiation monitoring and data on the health status of workers at the hydrometallurgical plant of the Stepnogorsk Mining and Chemical Combine (SMCC). The data of the accumulated effective dose for the entire length of service, as well as data on the incidence rate for the period 2013-2019, obtained from the base of the Industrial Radiation and Epidemiological Register, have been analyzed. Based on the results of measurements of the uranium content in urine, the expected effective dose of internal irradiation of the enterprise personnel was calculated. The assessment of the health status of workers was carried out based on the materials of outpatient and hospital visits, as well as the results of mandatory periodic medical examinations over the past 5 years. Based on the results, an excess of the expected effective dose of internal irradiation was revealed based on the analysis of a urine sample by 3 times. The most typical for the studied contingent of the main group turned out to be diseases of the eye and its adnexa (23%).
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