Formation of high-performance 6FDA-2,6-DAT asymmetric composite hollow fiber membranes for CO2/CH4 separation

We report that 6FDA-2,6-DAT polyimide can be used to fabricate hollow fiber membranes with excellent performances for CO₂/CH₄ separation. In order to simplify the hollow fiber fabrication process and verify the feasibility of 6FDA-2,6-DAT hollow fiber membranes for CO₂/CH₄ separation, a new one-polymer and one-solvent spinning system (6FDA-2,6-DAT/N-methyl-pyrrolidone (NMP)) with much simpler processing conditions has been developed and the separation performance of newly developed 6FDA-2,6-DAT hollow fiber membranes has been further studied under the pure and mixed gas systems.Experimental results reveal that 6FDA-2,6-DAT asymmetric composite hollow fiber membranes have a strong tendency to be plasticized by CO₂ and suffer severely physical aging with an initial CO₂ permeance of 300 GPU drifting to 76 GPU at the steady state. However, the 6FDA-2,6-DAT asymmetric composite hollow fibers still present impressive ultimate stabilized performance with a CO₂/CH₄ selectivity of 40 and a CO₂ permeance of 59 GPU under mixed gas tests. These results manifest that 6FDA-2,6-DAT polyimide is one of promising membrane material candidates for CO₂/CH₄ separation application.     

Natural gas permeation in polyimide membranes

Polyimide membranes derived from 6FDA-DAM:DABA and 6FDA-6FpDA:DABA copolymers have been used to separate 50/50 CO₂/CH₄ mixtures and multicomponent synthetic natural gas mixtures at 35 °C and feed pressures up to 55 atm. For 6FDA-DAM:DABA 2:1 membranes the effects of thermal annealing and covalent crosslinking are decoupled with respect to effects on permeabilities and selectivity. Crosslinking at 295 °C with 1,4-butylene glycol and 1,4-cyclohexanedimethanol increases CO₂ permeabilities by factors of 4.1 and 2.4, respectively, at 20 atm feed pressure, without a loss in selectivity, relative to crosslinking at 220 °C. Thermal annealing and crosslinking also reduce CO₂ plasticization effects. Crosslinking of DABA-containing copolymers, therefore, can produce membranes with tunable transport properties that offer significantly higher performance with better plasticization-resistance than that reported in the literature for the commercial polymers Matrimid^® and cellulose acetate for CO₂ removal from natural gas mixtures. Separation of complex mixtures containing CO₂, CH₄, C₂H₆, C₃H₈, and C₄H₁₀ or toluene results in a significant decrease of the CO₂ permeability, but only a moderate decrease in the CO₂/CH₄ selectivity.     

Preparation of composite hollow fiber membranes of poly(ethylene oxide)-containing polyimide and their CO2/N2 separation properties

Composite hollow fiber membranes were prepared by a dry-jet wet spinning process using a double layer spinneret. These membranes were composed of a thin and dense outer-layer of poly(ethylene oxide)-containing polyimide and a sponge-like inner layer of other polyimide. The outer layer was responsible for the separation and fabricated as thin as 1 μm. The permeation flux of CO₂, R_CO2, and the CO₂/N₂ selectivity decreased 40% and 10–20%, respectively, in a month after the membrane preparation. The steady performance was still high; for example, R_CO2=69×10⁻⁶cm³ (STP)/(cm² s cm Hg) and the selectivity of 33 at 323 K.     

Pressure and temperature dependence of the gas‐transport properties of dense poly[2,6‐toluene‐2,2‐bis(3,4‐dicarboxylphenyl)hexafluoropropane diimide] membranes

The gas‐transport properties of poly[2,6‐toluene‐2,2‐bis(3,4‐dicarboxylphenyl)hexafluoropropane diimide] (6FDA‐2,6‐DAT) have been investigated. The sorption behavior of dense 6FDA‐2,6‐DAT membranes is well described by the dual‐mode sorption model and has certain relationships with the critical temperatures of the penetrants. The solubility coefficient decreases with an increase in either the pressure or temperature. The temperature dependence of the diffusivity coefficient increases with an increase in the penetrant size, as the order of the activation energy for the diffusion jump is CH₄ > N₂ > O₂ > CO₂. Also, the average diffusion coefficient increases with increasing pressure for all the gases tested. As a combined contribution from sorption and diffusion, permeability decreases with increases in the pressure and the kinetic diameter of the penetrant molecules. Even up to 32.7 atm, no plasticization phenomenon can be observed on flat dense 6FDA‐2,6‐DAT membranes from their permeability–pressure curves. However, just as for other gases, the absolute value of the heat of sorption of CO₂ decreases with increasing pressure at a low‐pressure range, but the trend changes when the feed pressure is greater than 10 atm. This implies that CO₂‐induced plasticization may occur and reduce the positive enthalpy required to create a site into which a penetrant can be sorbed. Therefore, a better diagnosis of the inherent threshold pressure for the plasticization of a glassy polymer membrane may involve examining the absolute value of the heat of sorption as a function of pressure and identifying the turning point at which the gradient of the absolute value of the heat of sorption against pressure turns from a negative value to a positive one. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 354–364, 2004     

Immobilized glycerol-based liquid membranes in hollow fibers for selective CO2 separation from CO2–N2 mixtures

Glycerol-based liquid membranes immobilized in the pores of hydrophilic microporous hollow fibers have been studied for selective separation of CO₂ from a mixed gas (CO₂, N₂) feed having low concentrations of CO₂ characteristic of gases encountered in space walk and space cabin atmosphere. The immobilized liquid membranes (ILMs) investigated consist of sodium carbonate–glycerol or glycine-Na–glycerol solution. Based on the performances of such liquid membranes in flat hydrophilic porous substrates [Chen et al., Ind. Eng. Chem. Res. 38 (1999) 3489; Chen et al., Ind. Eng. Chem. Res. 39 (2000) 2447], hollow fiber-based ILMs were studied at selected CO₂ partial pressure differentials (Δp_CO2 range 0.36–0.50 cmHg), relative humidities (RH range 45–100%), as well as carrier concentrations. The sodium carbonate concentration was primarily 1.0 mol/dm³; the glycine-Na concentration was 3.0 mol/dm³. The sweep gas was always dry helium and it flowed on the shell side. Very high CO₂/N₂ selectivities were observed with porous polysulfone microfiltration membranes as substrate. As in the case of flat film-based ILMs (see references above), feed side RH is an important factor determining the ILM performances. Generally, lower permeances and greater CO₂/N₂ selectivity values were observed at lower feed stream RHs. When the feed side average RH=60%, p_CO2,f=0.005 atm and glycine-Na concentration was 3.0 M, the CO₂/N₂ separation factor observed was over 5000. Prolonged runs lasting for 300 h showed that the hollow fiber-based ILM permeation performances were stable.     

CO2-induced plasticization phenomena in glassy polymers

A typical effect of plasticization of glassy polymers in gas permeation is a minimum in the relationship between the permeability and the feed pressure. The pressure corresponding to the minimum is called the plasticization pressure. Plasticization phenomena significantly effect the membrane performance in, for example, CO₂/CH₄ separation processes. The polymer swells upon sorption of CO₂ accelerating the permeation of CH₄. As a consequence, the polymer membrane loses its selectivity. Fundamental understanding of the phenomenon is necessary to develop new concepts to prevent it.In this paper, CO₂-induced plasticization phenomena in 11 different glassy polymers are investigated by single gas permeation and sorption experiments. The main objective was to search for relationships between the plasticization pressure and the chemical structure or the physical properties of the polymer. No relationships were found with respect to the glass-transition temperature or fractional free volume. Furthermore, it was thought that polar groups of the polymer increase the tendency of a polymer to be plasticized because they may have dipolar interactions with the polarizable carbon dioxide molecules. But, no dependence of the plasticization pressure on the carbonyl or sulfone density of the polymers considered was observed. Instead, it was found that the polymers studied plasticized at the same critical CO₂ concentration of 36±7 cm³ (STP)/cm³ polymer. Depending on the polymer, different pressures (the plasticization pressures) are required to reach the critical concentration.     

Fabrication of multi-layer composite hollow fiber membranes for gas separation

Using multilayer composite hollow fiber membranes consisting of a sealing layer (silicone rubber), a selective layer (poly(4-vinylpyridine)), and a support substrate (polysulfone), we have determined the key parameters for fabricating high-performance multilayer hollow fiber composite membranes for gas separation. Surface roughness and surface porosity of the support substrate play two crucial roles in successful membrane fabrication. Substrates with smooth surfaces tend to reduce defects in the selective layer to yield composite membranes of better separation performance. Substrates with a high surface porosity can enhance the permeance of composite membranes. However, SEM micrographs show that, when preparing an asymmetric microporous membrane substrate using a phase-inversion process, the higher the surface porosity, the greater the surface roughness. How to optimize and compromise the effect of both factors with respect to permselectivity is a critical issue for the selection of support substrates to fabricate high-performance multilayer composite membranes. For a highly permeable support substrate, pre-wetting shows no significant improvement in membrane performance. Composite hollow fiber membranes made from a composition of silicone rubber/0.1–0.5 wt% poly(4-vinylpyridine)/25 wt% polysulfone show impressive separation performance. Gas permeances of around 100 GPU for H₂, 40 GPU for CO₂, and 8 GPU for O₂ with selectivities of around 100 for H₂/N₂, 50 for CO₂/CH₄, and 7 for O₂/N₂ were obtained.     

Synthesis of a PEBAX-1074/ZnO nanocomposite membrane with improved CO_2 separation performance

In this investigation, polymeric nanocomposite membranes(PNMs) were prepared via incorporating zinc oxide(ZnO) into poly(ether-block-amide)(PEBAX-1074) polymer matrix with different loadings. The neat membrane and nanocomposite membranes were prepared via solution casting and solution blending methods, respectively. The fabricated membranes were characterized by field emission scanning electron microscopy(FESEM) to survey cross-sectional morphologies and thermal gravimetric analysis(TGA)to study thermal stability. Fourier transform infrared(FT-IR) and X-ray diffraction(XRD) analyses were also employed to identify variations of the chemical bonds and crystal structure of the membranes, respectively. Permeation of pure gases, CO_2, CH_4 and N_2 through the prepared neat and nanocomposite membranes was studied at pressures of 3–18 bar and temperature of 25 °C. The obtained results showed that the fabricated nanocomposite membranes exhibit better separation performance compared to the neat PEBAX membrane in terms of both permeability and selectivity. As an example, at temperature of 25 °C and pressure of 3 bar, CO_2 permeability, ideal CO_2/CH_4 and CO_2/N_2 selectivity values for the neat PEBAX membrane are 110.67 Barrer, 11.09 and 50.08, respectively, while those values are 152.27 Barrer,13.52 and 62.15 for PEBAX/ZnO nanocomposite membrane containing 8 wt% ZnO.     

Dimeric and monomeric palladium(II) parent-amido (NH2) complexes: Synthesis,characterization, and reactivity

The treatment of [PdL₃(NH₃)]OTf (L₃ = (PEt₃)₂(Ph) (1), (2,6-(Cy₂PCH₂)₂C₆H₃) (3)) with NaNH₂ in THF afforded dimeric and monomeric parent-amido palladium(II) complexes with bridging and terminal NH₂, respectively, anti-[Pd(PEt₃)(Ph)(μ-NH₂)]₂ (2) and Pd(2,6-(Cy₂PCH₂)₂C₆H₃)(NH₂) (4). The dimeric complex 2 crystallizes in the space group P2₁/n with a = 13.228(2) Å, b = 18.132(2) Å, c = 24.745(2) Å, β = 101.41(1)°, and Z = 4. It has been found that there are two crystallographically independent molecules with Pd(1)–Pd(2) and Pd(3)–Pd(4) distances of 2.9594 (10) and 2.9401(9) Å, respectively. The monomeric amido complex 4 protonates from trace amounts of water to give the cationic ammine species [Pd(2,6-(Cy₂PCH₂)₂C₆H₃)(NH₃)]⁺. Complex 4 reacts with diphenyliodonium triflate ([Ph₂I]OTf) to give aniline complex [Pd(2,6-(Cy₂PCH₂)₂C₆H₃)(NH₂Ph)]OTf (5). Reaction of 4 with dialkyl acetylenedicarboxylate (DMAD, DEAD) yields diastereospecific palladium(II) vinyl derivative (Z)–(Pd(Cy₂PCH₂)₂C₆H₃)(CR = CR(NH₂)) (R = CO₂Me (6a), CO₂Et (6b)). Reacting complexes 6a and 6b with p-nitrophenol produces (Pd(Cy₂PCH₂)₂C₆H₃)(OC₆H₄–p-NO₂) (8) and cis-CHR = CR(NH₂), exclusively.     

ZIF-8 based polysulfone hollow fiber membranes for natural gas purification

Mixed matrix membranes (MMMs) have received worldwide attention for natural gas purification due to their superior performance in terms of permeability and selectivity. The zeolitic imidazole framework-8 (ZIF-8) blended polysulfone (PSf) membranes have been fabricated for natural gas purification. ZIF-8 was selected due to its low cost, remarkable thermal and chemical stabilities, and tunable microporous structure. The neat PSf hollow fiber membrane and mixed matrix hollow fiber membranes incorporated with the various ZIF-8 loadings up to 1.25% were fabricated. The prepared membranes were evaluated using field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), and gas separation performance. The low loading of ZIF-8 nanoparticles to the MMM improved thermal stability and glass transition temperature and yielded low surface roughness. MMMs were tested using pure gases with a significant improvement of 36% in CO₂ permeability and 28% in CO₂/CH₄ selectivity compared to the neat membrane. However, the high ZIF-8 loading reduced the separation performances. Moreover, CO₂/CH₄ selectivity decreased at elevated pressure (8 and 10 bar) due to CO₂-induced plasticization. Previously, the incorporation of ZIF-8 particles has primarily been subjected to the fabrication of flat sheet membranes, whereas this work focused on hollow fiber membranes which are rarely investigated. Hence, the promising results obtained at low feed pressure in this study demonstrated the potential of ZIF-8 based hollow fiber membrane for natural gas purification.     

(Vapour + liquid) equilibria (VLE) of CO2 in aqueous solutions of 2-amino-2-methyl-1-propanol: New data and modelling using eNRTL-equation

This work presents new experimental results for carbon dioxide (CO₂) solubility in aqueous 2-amino-2-methyl-1-propanol (AMP) over the temperature range of (298 to 328) K and CO₂ partial pressure of about (0.4 to 1500) kPa. The concentrations of the aqueous AMP lie within the range of (2.2 to 4.9) mol · dm^?3. A thermodynamic model based on electrolyte non-random two-liquid (eNRTL) theory has been developed to correlate and predict the (vapour + liquid) equilibrium (VLE) of CO₂ in aqueous AMP. The model predictions have been in good agreement with the experimental data of CO₂ solubility in aqueous blends of this work as well as those reported in the literature. The current model can also predict speciation, heat of absorption, enthalpy of CO₂ loaded aqueous AMP, pH of the loaded solution, and AMP volatility.     

Visualization of the effect of die shear rate on the outer surface morphology of ultrafiltration membranes by AFM

We have demonstrated the effect of shear rate on the outer surface morphology of polyethersulfone (PES) hollow fiber ultrafiltration (UF) membranes by an atomic force microscope (AFM). A digital instrument (DI) AFM was used to reveal the surface morphology of hollow fiber membranes prepared with varying shear rates from 1305 to 11,066 s⁻¹. A tapping mode was operated for studying the polymeric membranes when AFM was applied to image the surface of a fiber in air. AFM images of the outer surface have revealed that the nodules in the outer skin appeared to be randomly arranged at low shear rates but formed bands that were aligned in the direction of dope extrusion when the shear rate increased. Both nodule sizes in the fiber spinning and transversal directions decreased with increasing shear rate possibly because of chain disentanglement and thermodynamically favored. This result has not been reported so far. The analysis of AFM images showed that the roughness of the outer surface of hollow fiber UF membranes in terms of R_ms, R_a and R_z decreased with an increase in shear rate. The pure water flux of the membranes was nearly proportional to the mean roughness and higher mean roughness resulted in lower separation of membranes. AFM data also imply that there was a certain critical value of shear rate around 3585 s⁻¹, the roughness decreased significantly with an increase in shear rate below 3585 s⁻¹ and almost leveled off or in a much slower pace above this shear rate.     

Polyimide hollow fiber gas separation membranes: preparation and the suppression of plasticization in propane/propylene environments

Asymmetric hollow fiber membranes were prepared using the polyimide Matrimid^® 5218. The fibers had an effective top layer thickness of 0.3–0.4 μm. The fibers were used in propane and propylene permeation experiments. Whereas the propane permeance remained more or less constant, the propylene permeance increased with feed pressure greater than 1 bar. This indicated that propylene plasticized the membrane material.The fibers were given different heat-treatments in order to investigate the possibilities to suppress the propylene plasticization. This treatment also reduced the permeance considerably, the effect being more pronounced the more intense the heat-treatment was. This was in agreement with scanning electron microscopy studies, which revealed that densification of the fibers occurred due to the heat-treatments. Most important, relatively mild heat-treatments already appeared to be effective in suppressing the propylene plasticization. Since these heat-treated fibers still readily dissolved it is concluded that the plasticization suppression was not due to crosslinking, but to an annealing effect. Due to thermal curing (annealing) at temperatures below the T_g aromatic polyimides tend to form charge transfer complexes, which restrict the polymer chain mobility. Presence of these complexes seems to be responsible for suppression of propylene plasticization.     

Effects of temperature and anion species on CO2 permeability and CO2/N2 separation coefficient through ionic liquid membranes

The permeability of carbon dioxide (CO₂) through imidazolium-based ionic liquid membranes was measured by a sweep gas method. Six species of ionic liquids were studied in this work as follows: [emim][BF₄], [bmim][BF₄], [bmim][PF₆], [bmim][Tf₂N], [bmim][OTf], and [bmim][dca]. The ionic liquids were supported with a polyvinylidene fluoride porous membrane. The measurements were performed at T = (303.15 to 343.15) K. The partial pressure difference between feed and permeate sides was 0.121 MPa. The permeability of the CO₂ increases with temperature for the all ionic liquid species. Base on solution diffusion theory, it can be explained that the diffusion coefficient of CO₂ in an ionic liquid affects the temperature dependence more strongly than the solubility coefficient. The greatest permeability was obtained with the [bmim][Tf₂N] membrane. The membrane of [bmim][PF₆] presents the lowest permeability.The separation coefficient between CO₂ and N₂ through the ionic liquid membranes was also investigated at the volume fraction of CO₂ at feed side 0.10. The separation coefficient decreases with the increase of temperature for the all ionic liquid species. The membrane of [emim][BF₄] and [bmim][BF₄] gives the highest separation coefficient at constant temperature. The lowest separation coefficient was obtained from [bmim][Tf₂N] membrane which presents the highest permeability of CO₂.     

Suppression of CO2-plasticization by semiinterpenetrating polymer network formation

CO₂-induced plasticization may significantly spoil the membrane performance in high-pressure CO₂/CH₄ separations. The polymer matrix swells upon sorption of CO₂, which accelerates the permeation of CH₄. The polymer membrane looses its selectivity. To make membranes attractive for, for example, natural gas upgrading, plasticization should be minimized. In this article we study a polymer membrane stabilization by a semiinterpenetrating polymer network (s-ipn) formation. For this purpose, the polyimide Matrimid 5218 is blended with the oligomer Thermid FA-700 and subsequently heat treated at 265°C. Homogeneous films are prepared with different Matrimid/Thermid ratios and different curing times. The stability of the modified membrane is tested with permeation experiments with pure CO₂ as well as CO₂/CH₄ gas mixtures. The original membrane shows a minimum in its permeability vs. pressure curves, but the modified membranes do not indicating suppressed plasticization. Membrane performances for CO₂/CH₄ gas mixtures showed that the plasticizing effect indeed accelerates the permeation of methane. The modified membrane clearly shows suppression of the undesired methane acceleration. It was also found that just blending Matrimid and Thermid was not sufficient to suppress plasticization. The subsequent heat treatment that results in the s-ipn was necessary to obtain a stabilized permeability. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1547–1556, 1998     

Improvement of CO2/CH4 separation characteristics of polyimides by chemical crosslinking

Uncrosslinked and crosslinked polyimides and copolyimides have been synthesized in order to increase selectivity without an unacceptable loss in permeability. The goal was to reduce undesirable effects caused by CO₂ induced swelling in CO₂/CH₄ separation processes by stabilizing the polyimide structure with crosslinks. In the polymerization reaction 6FDA (4,4′-(hexafluoroisopropylidene)diphthalic anhydride) was used as dianhydride monomer and mPD (m-phenylene diamine) and DABA (diamino benzoic acid) were used as diamine monomers. With copolyimides containing strong polar carboxylic acid groups (i.e. 6 FDA–mPD/DABA 9:1) reduced plasticization was seen up to a pure CO₂ feed pressure of 14 atm, presumably due to hydrogen bonding between the carboxylic acid groups. By chemical crosslinking of the free carboxylic acid groups of the 6FDA–mPD/DABA 9:1 with ethylene glycol, the swelling effects due to CO₂ can be reduced at least up to a pure CO₂ feed pressure of 35 atm. With increasing degree of crosslinking, increasing CO₂/CH₄ selectivity was found because of reduced swelling and polymer chain mobility. By using ethylene glycol as a crosslinking agent, CO₂ permeability was not significantly lowered because the reduced chain mobility was compensated by the additional free volume caused by the crosslinks.     

Synthesis,X-ray structure and reactivity of μ-(CF3COO)2-[Mo(N-2,6-i-Pr2-C6H3)(CHCMe2Ph)(OOCCF3)(Et2O)]2, the first Bis(trifluoroacetate) derivative of a Schrock catalyst

Reaction of Mo(N-2,6-i-Pr₂-C₆H₃)(CHCMe₂C₆H₅)(OSO₂CF₃)(DME) (DME = 1,2-dimethoxyethane) with 2 equiv. of CF₃COOK yields μ-(CF₃COO)₂-[Mo(N-2,6-i-Pr₂-C₆H₃)(CHCMe₂Ph)(OOCCF₃)(Et₂O)]₂ (1). Compound 1 crystallizes in the orthorhombic space group Pna2₁ with a = 17.2485(3), b = 17.0336(3), c = 25.4031(5) Å, α = β = γ = 90°, V = 7463.5(2) Å³, Z = 4. In contrast to alkoxide based Schrock type initiators, 1 is virtually inactive in numerous metathesis reactions including ring-closing metathesis (RCM) and homo metathesis reactions, the cyclopolymerization of 1,6-heptadiynes, and even ring-opening metathesis polymerization (ROMP) of norborn-2-ene. However, addition of quinuclidine results in the in situ formation of 1a (Mo(N-2,6-i-Pr₂-C₆H₃)(CHCMe₂C₆H₅)(OOCCF₃)₂(quinuclidine) which displays moderate activity in ROMP, cyclopolymerization of 1,6-heptadiynes and RCM. Theoretical investigations carried out on the B3LYP/LACVP¹ level provide substantial explanation for these findings.     

Separation of carbon dioxide from nitrogen using ion-exchanged faujasite-type zeolite membranes formed on porous support tubes

Faujasite-type zeolite membranes were reproducibly synthesized by hydrothermal reaction on the outer surface of a porous α-alumina support tube of 30 or 200 mm in length. The membrane properties were evaluated by CO₂ separation from an equimolar mixture of CO₂ and N₂ at a permeation temperature of 40°C. CO₂ permeance and CO₂/N₂ selectivity of the NaY-type membranes were in the ranges of 0.4×10⁻⁶–2.5×10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ and 20–50, respectively. The NaY-type membranes were ion-exchanged with alkali and alkaline earth cations. The LiY-type membrane showed the highest N₂ permeance and the lowest CO₂/N₂ selectivity. The KY-type membrane gave the highest CO₂/N₂ selectivity. The NaY-type membrane was stable against exposure to air at 400°C. NaX-type zeolite membranes, formed by decreasing the ratio of SiO₂/Al₂O₃ in the starting solution, exhibited lower CO₂ permeances and higher CO₂/N₂ selectivities than those of the NaY-type zeolite membranes.     

Gas solubility of CO2 in aqueous solutions of N-methyldiethanolamine and diethanolamine with 2-amino-2-methyl-1-propanol

Gas solubility of carbon dioxide in an aqueous solution of 32.5 wt.% N-methyldiethanolamine and 12.5 wt.% diethanolamine with 4, 6, and 10 wt.% 2-amino-2-methyl-1-propanol has been measured, at 313.15, 343.15, and 393.15 K, over a range of pressure from 3 to 2000 kPa, using a chromatographic method for analysis of the liquid phase. The results of the gas solubility are given as the partial pressure of CO₂ against its mole ratio α (mol CO₂/mol alkanolamine) and its mole fraction at each temperature studied. The solubility of CO₂ in all the systems studied decreases with an increase in temperature and increases with an increase in the partial pressure of CO₂ at a given temperature and it is a function of the concentration of the mixture of alkanolamines in solution. The enthalpy of solution of CO₂ has been calculated from the experimental solubility data.     

Phase equilibria for H2 + CO2 + H2O system containing gas hydrates

Isothermal phase equilibrium (pressure–composition in the gas phase) for the ternary system of H₂ + CO₂ + H₂O has been investigated in the presence of gas hydrate phase. Three-phase equilibrium pressure increases with the H₂ composition of gas phase. The Raman spectra suggest that H₂ is not enclathrated in the hydrate-cages and behaves only like the diluent gas toward the formation of CO₂ hydrate. This fact is also supported by the thermodynamic analysis using Soave–Redlich–Kwong equation of state.