Polymeric coatings and membranes with extended stability toward a wide range of organic solvents are practical for application in harsh environments; on the other hand, such stability makes their ...processing quite difficult. In this work, we propose a novel method for the fabrication of films based on non-soluble polymers. The film is made from the solution of block copolymer containing both soluble and insoluble blocks followed by selective decomposition of soluble blocks. To prove this concept, we synthesized copolymer (imide)n-(polyurethane)m, in which the imide blocks were combined with polyurethane blocks based on polycaprolactone. By selective hydrolysis of urethane blocks in the presence of acid, it was possible to obtain the insoluble polyimide film for the first time. It was shown that the combination of thermal and acid treatment allowed almost complete removal of urethane blocks from the initial copolymer chains. IR spectroscopy, TGA, DSC and DMA methods were used to study the evaluation of the structure and properties of polymeric material as a result of thermal oxidation and hydrolysis by acid. It was shown that the polymeric films obtained by controlled decomposition were not soluble in aprotic solvent, such as dimethylformamide, n-methylpyrrolidone and dimethyl sulfoxide, and showed very close similarity to the homopolymer consisting of the same imide monomer, poly-(4,4′oxydiphenylene)pyromellitimide, confirming the feasibility of the proposed concept and its perspectives for fabrication of organic solvent-resistant membranes.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Recently, a strong structural ordering of thermoplastic semi-crystalline polyimides near single-walled carbon nanotubes (SWCNTs) was found that can enhance their mechanical properties. In this study, ...a comparative analysis of the results of microsecond-scale all-atom computer simulations and experimental measurements of thermoplastic semi-crystalline polyimide R-BAPB synthesized on the basis of dianhydride R (1,3-bis-(3′,4-dicarboxyphenoxy) benzene) and diamine BAPB (4,4′-bis-(4″-aminophenoxy) biphenyl) near the SWCNTs on the rheological properties of nanocomposites was performed. We observe the viscosity increase in the SWCNT-filled R-BAPB in the melt state both in computer simulations and experiments. For the first time, it is proven by computer simulation that this viscosity change is related to the structural ordering of the R-BAPB in the vicinity of SWCNT but not to the formation of interchain linkage. Additionally, strong anisotropy of the rheological properties of the R-BAPB near the SWCNT surface was detected due to the polyimide chain orientation. The increase in the viscosity of the polymer in the viscous-flow state and an increase in the values of the mechanical characteristics (Young’s modulus and yield peak) of the SWCNT-R-BAPB nanocomposites in the glassy state are stronger in the directions along the ordering of polymer chains close to the carbon nanofiller surface. Thus, the new experimental data obtained on the R-BAPB-based nanocomposites filled with SWCNT, being extensively compared with simulation results, confirm the idea of the influence of macromolecular ordering near the carbon nanotube on the mechanical characteristics of the composite material.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The hydrogen flux through the foil (thickness 30 μm) with the composition Pd–6.0 wt % In–0.5 wt % Ru in the temperature range from 593 to 823 K is studied. The permeability of Pd–In–Ru foil at 823 K ...is 3 times higher than the foil of the Pd–23 wt % Ag alloy. The H2 flux in the Pd–In–Ru foil is controlled by the diffusion of atomic hydrogen in the membrane bulk. The apparent activation energy of the hydrogen permeance is 18.7 kJ/mol. The influence of impurities (CO, N2, Ar) on the hydrogen flux is studied using both a sweep gas (N2) and transmembrane pressure. An insignificant negative effect of CO is observed in experiments using a sweep gas. When the transmembrane pressure is used, CO exerts a negative effect on the H2 flux, and this influence decreases with increasing temperature. The negative effect of CO decreases with the simultaneous use of transmembrane pressure and sweep gas. Contact of the foil with pure CO results in an insignificant formation of carbon deposits on the membrane surface, which exerts almost no effect on the H2 flux. No carbon deposits are formed on contact of the foil with the mixture H2–22.5% CO due to CO methanation with the formation of CH4 and H2O.
•Permeability of Pd–In–Ru foil at 823 K is 3 times higher than that of Pd–Ag foil.•The flux of H2 in the Pd–In–Ru foil is controlled by atomic hydrogen diffusion.•No negative effect of CO on the flux of H2 is observed using a sweep gas.•For using transmembrane pressure, CO exerts a negative effect on the flux of H2.•No carbon deposits are formed when the foil contacts with a mixture of H2–CO.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
A model of steam reforming of pure ethane in a membrane catalytic reactor is proposed. The working elements of the reactor are cylindrical chambers, between which a hydrogen-selective palladium foil ...is placed. The upper chamber is vacuumized, and the lower one contains a nickel catalyst. In the case of uniform feed of the feedstock (С
2
Н
6
and Н
2
О) along the perimeter of the lower chamber, the problem is reduced to finding the average flows of С
2
Н
6
, СН
4
, Н
2
О, СО, СО
2
, and Н
2
by solving a system of nonlinear ordinary differential equations. The studies are carried out in the temperature range of 700–1000 K at acceptable steam/ethane input flow ratios of more than four. The optimal conditions for the process, at which the hydrogen yield is 100%, are found. It is proved that under these conditions and a fixed temperature, the maximum hydrogen flow through the membrane is observed at the minimum permissible ratio of the steam and ethane input flows, equal to four. Comparison of the calculations with the experimental data confirm the assumption of the existence of two sections in the lower chamber (short initial and main sections).
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The propane conversion in a membrane reactor with NIAP–03-01 commercial Ni catalyst at temperatures of 673, 723, 773, and 823 K, feed space velocities of 1800 and 3600 h
–1
, and steam/propane ratios ...of 5 and 7 was studied. The Н
2
removal through the membrane leads to an increase in the conversion of the feed to Н
2
and СО
2
formed by the water-gas shift reaction. The conversion in this reaction increases when the rate of the Н
2
recovery through the membrane is increased by the permeate evacuation. In the temperature interval 773–823 K, the feed conversion is 100%, and about 90% of high-purity Н
2
is recovered from the reaction mixture. An increase in the feed/catalyst contact time leads to a decrease in the feed conversion to the target products and to an increase in the rate of carbon deposit formation. The regularities of the steam conversion of propane in a membrane reactor are similar to those found previously for
n
-butane with the same catalyst and under the same conditions.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The present work evaluates the transport properties of thermoplastic R-BAPB polyimide based on 1,3-bis(3,3',4,4'-dicarboxyphenoxy)benzene (dianhydride R) and 4,4'-bis(4-aminophenoxy)biphenyl (diamine ...BAPB). Both experimental studies and molecular dynamics simulations were applied to estimate the diffusion coefficients and solubilities of various gases, such as helium (He), oxygen (O
), nitrogen (N
), and methane (CH
). The validity of the results obtained was confirmed by studying the correlation of the experimental solubilities and diffusion coefficients of He, O
, and N
in R-BAPB, with their critical temperatures and the effective sizes of the gas molecules, respectively. The solubilities obtained in the molecular dynamics simulations are in good quantitative agreement with the experimental data. A good qualitative relationship between the simulation results and the experimental data is also observed when comparing the diffusion coefficients of the gases. Analysis of the Robeson plots shows that R-BAPB has high selectivity for He, N
, and CO
separation from CH
, which makes it a promising polymer for developing gas-separation membranes. From this point of view, the simulation models developed and validated in the present work may be put to effective use for further investigations into the transport properties of R-BAPB polyimide and nanocomposites based on it.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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A model is proposed for steam reforming of methane in a catalytic reactor, the working section of which includes two cylindrical chambers separated by a palladium foil membrane of the Pd, Pd–23% ...Ag, Pd–6% Ru, Pd–10% Ru, Pd–6% In–0.5% Ru, and Pd–6% In compositions. The upper chamber is evacuated and the atmospheric pressure is maintained in the lower chamber. Upon uniform feed of raw materials to the lower chamber, the problems are reduced to determination of the CH
4
, H
2
O, CO
2
, CO, and H
2
flows from the solution of a system of first-order nonlinear ordinary differential equations. The 100% conversion of methane is achieved only when the ratio of water steam and methane input flows is more than two. Calculations are performed in the temperature range 700
1000 K at the ratio of steam/methane input flows belonging to this range 2, 10. The optimum values of input flows of raw materials, at which the yield of hydrogen and the conversion of methane reach 100%, are determined. At optimum flows and specified temperature, the maximum hydrogen flow through the membrane is observed at the minimum permissible ratios of steam and methane input flows.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Steam reforming of methane and its mixtures containing 5 and 10% propane has been studied in a membrane reactor with an industrial nickel catalyst NIAP-03-01 and a membrane in the form of 30-μm foil ...made of a Pd–Ru alloy. At
T
= 823 K and a feed space velocity of 1800 h
−1
, the almost complete methane conversion is achieved, the selectivity for CO
2
is more than 50%, and about 80% H
2
is recovered from the reaction mixture. High conversion of CH
4
in the membrane reactor under mild conditions allows the steam reforming of its mixtures with C
2+
alkanes to be conducted in a single process, as shown by the example of model mixtures containing C
3
H
8
. Under selected conditions (
T
= 773 or 823 K, a feed space velocity of 1800 or 3600 h
−1
, a steam/methane ratio of 3 or 5, atmospheric pressure), almost complete C
3
H
8
conversion is observed. The main “undesirable” reaction is methanation, leading to a decrease in the CH
4
conversion. In the system under study, CH
4
is formed with an increase in the feed space velocity. Methanation occurs as a result of C
3
H
8
hydrocracking at a steam/feedstock ratio = 3 or the hydrogenation of CO
2
as this ratio is increased to 5. The optimal conditions for steam reforming of methane mixtures containing up to 10% C
3
H
8
are
T
= 823 K, steam/feedstock ratio = 5, and the feed space velocity of 1800 h
−1
. Under these conditions involving evacuation of the permeate, the feedstock conversion is complete, the selectivity for CO
2
is 50%, and more than 70% H
2
is recovered from the reaction mixture.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Poly-(4,4'-oxydiphenylene) pyromellitimide or Kapton is the most widely available polyimide with high chemical and thermal stability. It has great prospects for use as a membrane material for ...filtering organic media due to its complete insolubility. However, the formation of membranes based on it, at the moment, is an unsolved problem. The study corresponds to the rediscovery of poly(4,4'-oxydiphenylene-pyromellitimide)-based soluble copoly(urethane-imides) as membrane polymers of a new generation. It is shown that the physical structure of PUI films prepared by the solution method becomes porous after the removal of urethane blocks from the polymer, and the pore size varies depending on the conditions of thermolysis and subsequent hydrolysis of the membrane polymer. The film annealed at 170 °C with a low destruction degree of polycaprolactam blocks exhibits the properties of a nanofiltration membrane. It is stable in the aprotic solvent DMF and has a Remasol Brilliant Blue R retention coefficient of 95%. After the hydrolysis of thermally treated films in acidic media, ultrafiltration size 66-82 nm pores appear, which leads to an increase in the permeate flow by more than two orders of magnitude. This circumstance provides opportunities for controlling the membrane polymer structure for further optimization of the performance characteristics of filtration membranes based on it. Thus, we proposed a new preparation method of ultra- and nanofiltration membranes based on poly(4,4'-oxydiphenylene-pyromellitimide) that are stable in aprotic solvents.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
A model of steam propane reforming in a catalytic reactor was developed. The main reactor elements were two cylindrical chambers separated by a thin partition (highly hydrogen-selective palladium ...foil or impermeable steel plate). The upper chamber was evacuated, and the lower chamber was filled with a nickel catalyst and was maintained under constant pressure. The feed (C
3
H
8
and H
2
O) was uniformly introduced through the perimeter of the lower chamber; in this case, the problem reduced to the determination of the average fluxes of C
3
H
8
, CH
4
, H
2
O, CO, CO
2
, and H
2
via the solution of six first-order, nonlinear, ordinary differential equations. The study was carried out in a temperature range of 673 K <
T
< 823 K at a steam : propane inlet flux ratio of 5 and a feed flow rate of 1800–3600 1/h. A comparison between the calculated and experimental data confirmed the assumption that there are two steam reforming ranges (a short initial range and the main range). It was proven that the optimal conditions of steam propane reforming are a feed flow rate of ∼2000 1/h and a temperature of ∼800 K.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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