Gas Separation Studies Research Articles

Study of gas and liquid separation in a closed drilling well with self-propelled drilling rigs

The article deals with the gas release in the process of drilling wells from jack-up drilling rigs. The article attempts to analyze the nature of the change in pressure at the blowout of the preventer after its closure due to gas releases on jack-up drilling rigs. Numerous observations in drilling rigs have shown that the pressure value increases rapidly to a maximum, then gradually decreases and stabilizes at a certain value. There are cases when the value of pressure increases rapidly. Then, without decreasing, it stabilizes. It is proposed that the phenomenon of gas segregation in a well, leading to an increase in pressure, has theoretical and practical significance. In addition, in a real well, a change in bottom hole pressure can occur under various conditions, if the rate of pressure growth due to gas segregation in the riser pipes is greater than the pressure rate due to the work of the formation, while part of the fluid from the well must be squeezed out into the formation. Keywords: well drilling; gas release; complications; open fountain; drilling fluid; preventer; gas segregation; oil and gas.

Numerical simulation of novel gas separation microdevice with oscillating elements

Present paper uses Direct Simulation Monte Carlo method to perform a numerical study of a new MEMS-based gas separation device prototype. The core part of the device is represented by a microchannel with a row of elements-barriers oscillating with high frequency perpendicular to channel axis and periodically blocking the flow. The influence of practical aspects (device geometry, arrangement of phases of barriers oscillation, gas leakage and etc.) on separation performance was investigated. It is demonstrated that separation factor of the device can approach values of free-molecular (Knudsen) diffusion at any rate of gas rarefaction (defined by Knudsen number) and feasible barriers oscillation frequency (below 10 kHz) given that the necessary number of barriers is used in the device. Moreover, it was shown that in case of partial sampling of gas at the outlet, separation factor of the device can increase significantly beyond the Knudsen diffusion limit.

Gas separation simulation based on ab initio and variable soft sphere model in ratchet-shaped microchannels

A technique for the separation of rarefied gas mixtures based on microelectromechanical systems (MEMS) has recently attracted the attention of researchers. The mechanism of gas separation is the thermally induced flow caused by inhomogeneous temperature gradients within the microchannel, which distinguishes the velocity of different gas species. In this paper, the effects of Knudsen number Kn and equilibrium temperature T0 on the flow properties of each gas species within the gas mixture, such as velocity, molar fraction, streamlines, temperature, and pressure, are investigated by the Direct simulation Monte Carlo (DSMC) method. The flow of the gas mixture is numerically simulated using a quantum scattering-based ab initio (AI) potential and compared with the results of numerical simulations based on the variable soft sphere (VSS) model. The results show that the gas velocity accelerates with increasing temperature, but decreases with increasing Knudsen number. The streamlines are very sensitive to the Knudsen number, yet they are only affected by the temperature in the transitional flow. When the conditions are the same, He flows faster than Ne and the streamlines are smoother. The gas separation factor increases with equilibrium temperature at T0<100K and decreases slightly with equilibrium temperature at T0≥100K. The gas separation efficiency is best in the transitional flow. The temperature discrepancy for the different gas species is less affected by the equilibrium temperature and Knudsen number, with the maximum discrepancy rate being only 2.727% for He and Ne. The pressure discrepancy is more affected by the equilibrium temperature and Knudsen number, with the maximum rate of discrepancy reaching 39.228% for He and Ne. At T0=10K and Kn=1, the discrepancy rates of the gas separation factor, temperature, and pressure obtained based on the AI potential and the VSS model reach maximum values of 44.802%, 4.675%, and 52.716%, respectively. Compared to the VSS model, the AI potential based on quantum scattering is applicable to a wider range of temperatures and is more accurate for both low and high temperatures. Furthermore, the AI potential is more accurate than the VSS model in the transitional flow. The results obtained from the AI potential based on quantum scattering will be more desirable when performing gas separation studies based on thermally induced flows in rarefied gases.

Functionalized KIT-6/Polysulfone Mixed Matrix Membranes for Enhanced CO2/CH4 Gas Separation.

The development of mixed matrix membranes (MMMs) for effective gas separation has been gaining popularity in recent years. The current study aimed at the fabrication of MMMs incorporated with various loadings (0–4 wt%) of functionalized KIT-6 (NH2KIT-6) [KIT: Korea Advanced Institute of Science and Technology] for enhanced gas permeation and separation performance. NH2KIT-6 was characterized by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and N2 adsorption–desorption analysis. The fabricated membranes were subjected to FESEM and FTIR analyses. The effect of NH2KIT-6 loading on the CO2 permeability and ideal CO2/CH4 selectivity of the fabricated membranes were investigated in gas permeation and separation studies. The successfulness of (3-Aminopropyl) triethoxysilane (APTES) functionalization on KIT-6 was confirmed by FTIR analysis. As observed from FESEM images, MMMs with no voids in the matrix were successfully fabricated at a low NH2KIT-6 loading of 0 to 2 wt%. The CO2 permeability and ideal CO2/CH4 selectivity increased when NH2KIT-6 loading was increased from 0 to 2 wt%. However, a further increase in NH2KIT-6 loading beyond 2 wt% led to a drop in ideal CO2/CH4 selectivity. In the current study, a significant increase of about 47% in ideal CO2/CH4 selectivity was achieved by incorporating optimum 2 wt% NH2KIT-6 into the MMMs.

Tunable sour gas separations: Simultaneous H2S and CO2 removal from natural gas via crosslinked telechelic poly(ethylene glycol) membranes

Gas separation studies typically investigate polymeric materials in the context of pure gas, and occasionally binary mixed gas properties, yet real world separations involve a myriad of components that can affect separation performance. The purification of sour gas demands efficient separations of both H2S and CO2 from natural gas, making realistic testing critical. In this work, we introduce a novel crosslinking scheme of the commercially ubiquitous polymer, poly(ethylene glycol) (PEG), via a facile route amenable to thin film composite formation. We crosslinked a systematic series of telechelic PEG oligomers with average molecular weights of 200–2050 g mol−1 and investigated the gas transport properties of the corresponding membranes in pure, binary CO2/CH4, and ternary H2S/CO2/CH4 sour gas mixtures. Crosslinking effectively eliminated PEG crystallinity for molecular weights up to 1000 g mol−1 and favorably increased CO2/CH4 selectivity. Though previously unexplored for H2S separations, crosslinked PEG membranes demonstrated exceptionally high H2S/CH4 selectivities ranging from 65-116 in ternary sour gas feeds. We achieved tunable transport performance of CO2/CH4 and H2S/CH4 separations by balancing PEG content with crosslink density to disrupt crystallinity. Crosslinked PEG derived from a 2050 g mol−1 oligomer showed a semi-crystalline microstructure, defining the upper limit of PEG chain length of this system for gas separation applications. Thermal and diffraction studies on the PEG membranes further revealed only amorphous morphologies up to 1000 g mol−1 and that the resulting membranes spanned both glassy and rubbery regimes, which resulted in profound differences on CO2/CH4 and H2S/CH4 transport performance.

Biomass derived carboxylated carbon nanosheets blended polyetherimide membranes for enhanced CO2/CH4 separation

The fillers/nanofillers combinations with ideal interfacial morphologies could adjust the performance of pristine polymeric membranes and enhance the gas separation performances. In this study, biomass-derived 2D carboxyl functionalized nanocarbon (nanosheets) were produced from pyrolysis of the rain/monkey pod tree (Samanea saman) leaves. The X-ray diffraction, Raman spectroscopy, and X-Ray photoelectron spectroscopy (XPS) confirmed the chemical structure and carboxyl functionalization of carbon nanosheets (CCNS). The carboxyl-functionalized nanosheets blended into polyetherimide (PEI) solutions was used to fabricate mixed matrix membranes (MMMs) through modified dry/wet phase inversion method using different wt. % [0.0%, 0.25%, 0.5% and 1.0% of CCNS] of fillers into the pristine PEI NMP solutions. Surface and cross-sectional micrographs discerned the defects and dispersion of CCNS into the polymer matrix. Finally, the transport properties of pure gases (CH4 and CO2) were evaluated using constant pressure/variable volume apparatus. The gas separation studies showed improved permeance and selectivity of MMMs [(PCO2 = 1.84 GPU, (α = CO2/CH4) = 42.73] than pristine PEI membranes [PCO2 = 1.29 GPU, (α = CO2/CH4) = 23.30] under identical conditions of pressure and temperature.

Study of Gas Separation using A Hollow Fiber Membrane with Orifices

Study of Gas Separation using A Hollow Fiber Membrane with Orifices

Preliminary Fractional Factorial Design (FFD) study using incorporation of Graphene Oxide in PVC in mixed matrix membrane to enhance CO2/CH4 separation

Mixed matrix membranes (MMMs) comprising of where polyvinyl chloride (PVC) and graphene oxide (GO) were employed in the membrane fabrication in order to improve the membrane characteristics. In this study of gas separation using mixed matrix membrane, gases such as CO2 and CH4 were used. The objectives of this research were to synthesize and develop MMMs PVC/GO, and also to carry out screening to determine best factors condition for membrane to function at high selectivity. The development of MMMs PVC/GO was based on 5 factors. Based on the screening tests, the run which was made up of factors PVC 20%, GO 4%, 1 bar of pressure during gas permeation, NMP solvent, and immersion time of 300s, shows to have the highest selectivity at 26.09 which was above the upper bound lines in the Robeson’s Upper bound plot. Fractional Factorial Design (FFD) was applied to study the minimalization of influenced factors during MMMs preparation. Based on the FFD run, the R-squared (R2) was

Synthesis and Characterization of Covalent Triazine Framework CTF-1@Polysulfone Mixed Matrix Membranes and Their Gas Separation Studies.

Covalent triazine framework CTF-1 and polysulfone (PSF) are used to form mixed-matrix membranes (MMMs) with 8, 16, and 24 wt% of the porous filler material CTF-1. Studies on permeability and selectivity are carried out concerning the gases O2, N2, CO2, and CH4. CO2 permeability of the synthesized MMMs increases by 5.4 Barrer in comparison to the pure PSF membrane. The selectivity remains unchanged for O2/N2 and CO2/CH4 but was found to be increased for CO2/N2. Further, comparisons to theoretical models for permeability prediction yield a permeability for CTF-1 which is about six times higher than the permeability of PSF. The inverse of the sum of the free fractional volumes (FFV) of the polymer and the filler correlate linearly to the logarithm of the permeabilities of the gases which conversely indicates that the porosity of the filler contributes to the gas transport through the membrane.

Synthesis, characterization and CO2 separation performance of novel PVA/PG/ZIF-8 mixed matrix membrane

This work reports the synthesis of zeolitic imidazolate framework-8 (ZIF-8) having regular pore size (~0.35 nm) embedded to the poly (vinyl alcohol) (PVA)/piperazine glycinate (PG) solution. High performance mixed matrix membranes (MMMs) prepared by solution coating of PVA/PG/ZIF-8 solution onto a polyethersulfone (PES) support were utilized for CO2/N2 gas separation studies. Detailed thermal, structural and microscopic analysis of the synthesized ZIF-8 particles was conducted. The characterization studies and the performance evaluation tests were performed for the prepared MMMs. The excellent compatibility of ZIF-8 filler in the PVA/PG matrix resulted in enhancement of CO2 permeance and CO2/N2 selectivity. The results depicted that PVA/PG membrane loaded with 5 wt% ZIF-8 (PVA/PG/ZIF-8(5)) showed a high CO2 permeance of 82 GPU and CO2/N2 selectivity of 370 which was 82.2% and 76.2% higher when compared to pure PVA/PG membrane. Thus ZIF-8 doped PVA mixed matrix membrane serves as a potential candidate for industrial gas separation studies.

Neutron diffraction study of gas adsorption and separation in metal–organic frameworks

Neutron diffraction study of gas adsorption and separation in metal–organic frameworks

Polyetherimide-montmorillonite mixed matrix hollow fibre membranes: Effect of inorganic/organic montmorillonite on CO2/CH4 separation

Abstract Hollow fibre mixed matrix (HFMM) membranes with nano-filler embedded in polymer matrix offer an attractive route for the fabrication of high performance gas separation membranes. However, the quest to achieve high performance mixed matrix membranes remains a challenge without acquiring even filler distribution in polymer matrix. In this work, HFMM membranes comprising polyetherimide (PEI) with various inorganic and organic montmorillonite (I-MMT and O-MMT) loadings ranging from 1 to 4 wt%, were developed via phase inversion method and coated with PDMS for CO2/CH4 separation. Morphological, filler distribution, dispersion, surface topology and gas separation studies were carried out for developed hollow fibre (HF) membranes. Pure gases (CO2 and CH4) were used at varying pressure of 2–10 bars at ambient conditions. In addition, mixed gas test at CO2/CH4 composition of 50/50 v/v % was carried out for selected membranes. Upon incorporation of I-MMT, the developed mixed matrix membranes (MMMs) showed decrease in CO2/CH4 gas separation performance compared to neat PEI membrane. In contrast, the performance of asymmetric membrane was enhanced by incorporating O-MMT in PEI matrix to form MMMs. Uniform dispersion, void-free morphology and reduced surface roughness were observed for the aforementioned membranes. Furthermore, an increasing trend in ideal selectivity was observed up to 2 wt% O-MMT loading against all feed pressures. Thereafter, opposite trend was observed with increasing filler loading due to filler agglomeration. The maximum ideal selectivity achieved was 18.35 with 2 wt% loading at 4 bar pressure which is 52.2% higher than neat PEI hollow fibre membrane.

On the use of the IAST method for gas separation studies in porous materials with gate-opening behavior

Highly flexible nanoporous materials, exhibiting for instance gate opening or breathing behavior, are often presented as candidates for separation processes due to their supposed high adsorption selectivity. But this view, based on "classical" considerations of rigid materials and the use of the Ideal Adsorbed Solution Theory (IAST), does not necessarily hold in the presence of framework deformations. Here, we revisit some results from the published literature and show how proper inclusion of framework flexibility in the osmotic thermodynamic ensemble drastically changes the conclusions, in contrast to what intuition and standard IAST would yield. In all cases, the IAST method does not reproduce the gate-opening behavior in the adsorption of mixtures, and may overestimates the selectivity by up to two orders of magnitude.

Gas Separation through Bilayer Silica, the Thinnest Possible Silica Membrane.

Membrane-based gas separation processes can address key challenges in energy and environment, but for many applications the permeance and selectivity of bulk membranes is insufficient for economical use. Theory and experiment indicate that permeance and selectivity can be increased by using two-dimensional materials with subnanometer pores as membranes. Motivated by experiments showing selective permeation of H2/CO mixtures through amorphous silica bilayers, here we perform a theoretical study of gas separation through silica bilayers. Using density functional theory calculations, we obtain geometries of crystalline free-standing silica bilayers (comprised of six-membered rings), as well as the seven-, eight-, and nine-membered rings that are observed in glassy silica bilayers, which arise due to Stone-Wales defects and vacancies. We then compute the potential energy barriers for gas passage through these various pore types for He, Ne, Ar, Kr, H2, N2, CO, and CO2 gases, and use the data to assess their capability for selective gas separation. Our calculations indicate that crystalline bilayer silica, which is less than a nanometer thick, can be a high-selectivity and high-permeance membrane material for 3He/4He, He/natural gas, and H2/CO separations.

A hybrid zeolitic imidazolate framework Co-IM-mIM membrane for gas separation

A zeolitic imidazolate hybrid membrane (Co-IM-mIM) containing two imidazolate ligands deposited on a macroporous α-alumina support was prepared by pre-depositing and secondary growth technique. XRD, TGA and SEM characterizations demonstrate that a stable and thin, but dense and pure-phase Co-IM-mIM membrane can be obtained on the macroporous-alumina discs in Teflon-lined autoclave at 120 °C after pre-depositing by dip-coating at room temperature. No visible cracks, pinholes or other defects were observed on the membrane layer. The gas separation studies of Co-IM-mIM membrane were carried out at 25 °C and 1×105 Pa, showing ideal selectivity of 6.95, 5.25, 3.40 for H2/CO2, H2/N2 and H2/CH4, respectively, and a permeance of 17.37× 10−6 mol/(m2·s·Pa) for H2. The influence of temperature and trans-membrane pressure on hydrogen separation and permeation was also carried out. The gas permeation and selectivity demonstrate that this membrane may have potential applications for efficient H2 separation.

Solvothermal Metal Metathesis on a Metal-Organic Framework with Constricted Pores and the Study of Gas Separation.

Metal-organic frameworks (MOFs) with constricted pores can increase the adsorbate density of gas and facilitate effective CO2 separation from flue gas or natural gas due to their enhanced overlapping of potential fields of the pores. Herein, an MOF with constricted pores, which was formed by narrow channels and blocks of functional groups, was fabricated from the assembly of a methyl-functionalized ligand and Zn(II) centers (termed NPC-7-Zn). Structural analysis of the as-synthesized NPC-7-Zn reveals a series of zigzag pores with pore diameters of ∼0.7 nm, which could be favorable for CO2 traps. For reinforcing the framework stability, a solvothermal metal metathesis on the pristine MOF NPC-7-Zn was performed, and a new Cu(II) MOF (termed NPC-7-Cu) with an identical framework was produced. The influence of the reaction temperatures on the metal metathesis process was investigated. The results show that the constricted pores in NPC-7-Zn can induce kinetic issues that largely slow the metal metathesis process at room temperature. However, this kinetic issue can be solved by applying higher reaction temperatures. The modified MOF NPC-7-Cu exhibits significant improvements in framework stability and thus leads to a permanent porosity for this framework. The constricted pore structure enables enhanced potential fields for these pores, rendering this MOF with high adsorbate densities for CO2 and high adsorption selectivity for a CO2/N2 gas mixture. The adsorption kinetic studies reveal that CH4 has a faster diffusion rate constant than CO2, showing a surface diffusion controlled mechanism for CO2 and CH4 adsorption.

Study of gas separation by the means of high-frequency membrane oscillations

The study of a free-molecular flow through the membrane oscillating in its own plane has been conducted. Optimal values of membrane oscillation parameters for most efficient gas separation have been found.

Thermal, mechanical and structural investigation of copolyimide–silica hybrids containing phosphine oxide

Abstract In this study, a novel hybrid copolyimide was synthesized from copolyamic acid solutions (PAAs) obtained by the reaction between bis(3-aminophenoxy-4-phenyl)phenylphosphine oxide ( m -BAPPO), 3,3′-diaminodiphenyl sulfone (DDS) and 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA), followed by thermal imidization. Hybrid materials containing 5% SiO 2 were synthesized by sol–gel technique. The polyimide–silica hybrids were characterized by Fourier Transform Infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Thermogravimetric analysis showed that the weight loss of hybrids is shifted to the higher temperature compared to the neat copolyimide. The contact angle measurements confirmed the hydrophobic surface of hybrids. Moreover, the gas permeability measurements were also done to take a step for forthcoming gas separation studies. The tensile modulus and strength of the copolyimides are good.

Synthesis of ceramic hollow fiber supported zeolitic imidazolate framework-8 (ZIF-8) membranes with high hydrogen permeability

Purification and recovery of hydrogen from hydrocarbons in refinery streams in the petrochemical industry is an emerging research field in the study of membrane gas separation. Hollow fiber membrane modules can be easily implemented into separation processes at the industrial scale. In this report, hollow yttria-stabilized zirconia (YSZ) fiber-supported zeolitic imidazole framework-8 (ZIF-8) membranes were successfully prepared using a mild and environmentally friendly seeded growth method. Our single-component permeation studies demonstrated that the membrane had a very high hydrogen permeance (∼15×10−7mol/m2sPa) and an ideal selectivity of H2/C3H8 of more than 1000 at room temperature. This high membrane permeability and selectivity caused serious concentration polarization in the separation of H2/C3H8 mixtures, which led to almost 50% drop in both the H2 permeance and the separation factor. Enhanced mixing on the feed side could reduce the effect of the concentration polarization. Our experimental data also indicated that the membranes had excellent reproducibility and long-term stability, indicating that the hollow fiber-supported ZIF-8 membranes developed in this study have great potential in industry-scale separation of hydrogen.

Isomerism in Metal-Organic Frameworks: "Framework Isomers".

Metal-organic frameworks (MOFs) are very important in the development of new technologies and study of gas storage and separation. MOFs are based on the complexation of metal clusters with organic ligands. Occasionally, the same building components combine in multiple different ways to produce different structures. These different structures are what we would call "framework isomers." This type of isomerism is unique to the field of MOFs. In this Perspective, we classify the different types of framework isomers and provide examples of each type. Additionally, we provide an analysis of the structure/property relationship. In addition, possible methods for future control over the synthesis of a particular framework isomer and characterization techniques have also been discussed.