Natural Gas Separation Research Articles

Three-dimensional linker-promoted hierarchical porous metal–organic framework for natural gas purification

The purification of methane from natural gas is extremely important for industrial applications. In this study, hierarchical porous material LIFM-Z1 with microporous cages and mesoporous hexagonal one-dimensional channels was successfully synthesized and evaluated. The results show that LIFM-Z1 can effectively separate CH4 from the mixed gas containing CH4, C2H6, C3H8 and n-C4H10. Single-component adsorption experiments revealed the selective adsorption ability of LIFM-Z1 for C2H6, C3H8, and n-C4H10, enabling a clear distinction between these components and CH4. This selectivity was further verified by dynamic breakthrough experiments. Theoretical analysis shows that the interaction between LIFM-Z1 and gas molecules mainly depends on the synergistic effect of C–H⋯O hydrogen bond and C–H⋯C van der Waals force. The results highlight the potential of utilizing 3D linkers to enhance the inner wall interaction with CH4 and its related gases in MOF construction. These characteristics of LIFM-Z1 not only successfully demonstrate the potential of separation and purification of natural gas with high efficiency, but also show its broad application prospects in the actual natural gas processing.

Preparation of novel highly stable fluorinated microporous polyketone networks through direct C–H arylation polycondensation for efficient natural gas separation

Two novel hyper-cross-linked fluorinated microporous polyketone networks (FMPN-1 and FMPN-2) with permanent porosity and narrow pore size distribution were synthesized via a facile “one-step” polycondensation between the trifluoroacetophenone-based monomers and 1,3,5-triphenylbenzene. The result polymers were investigated by FTIR, solid state NMR, EDX, XRD, TGA, SEM, and TEM et al. The geometry configurations difference of building blocks resulted in the polyketone networks exhibiting the BET special surface areas from 622 to 706 m2 g−1 and total volume from 0.58 to 0.66 cm3 g−1. What's more, ideal adsorbed solution theory (IAST) analysis showed that the two polymers possessed good C3H8/CH4, C2H6/CH4 selectivities at 298K/1 bar. Together with the excellent thermal and physicochemical stabilities, the microporous fluorinated polyketone networks obtained in this work showed promising applications in adsorption/separation for C1–C3 hydrocarbons.

The study of solid particles effect on the gas bubble dispersion dynamics of complex gas-liquid mixtures at the intake screen of submersible pump

The study of gas phase dispersion at the intake of submersible pumping equipment is an actual issue, since changes in gas phase dispersion can lead to changes in natural separation. At the same time, the gas separation efficiency can be affected by the presence of solid phase in the well products, which would change the structure of gas-liquid mixture and operation mode of electric submersible pump. The results of the research are novel, which takes into account the influence of the properties of multi-component gas-liquid mixture on the character of operation of ESP well. The new dependences of gas bubble diameter at the submersible equipment intake on gas content for four model gas-liquid mixtures: «water – air», «water – surfactants – air», «water – air – solids» and «water – surfactants – air – solids» with the concentration of suspended particles in the flow of 1.0 g/l have been experimentally obtained in conditions of gauge pressure at the intake 0.04 - 0.05 MPa, gas content of mixture was increased up to 71%, liquid flow rate was changed in the range of values from 13 to 68 m3/day. High-speed video recording with fixing the structure of gas-liquid mixture in the near-intake space of the ESP was carried out during the tests. Visualization allows us to clarify the boundary of the flow regime transition from «bubble» to «slug/churn» compared to the Caetano method. There were developed new correlations of natural gas separation coefficient taking into account the influence of solid phase at different operating modes of ESP well. Keywords: gas-liquid mixture (GLM); gas bubble; natural gas separation; solid particles; surfactants.

Dual‐Wing Ligand Constructed Metal–Organic Framework Membranes with Finely Tuned Apertures for Natural Gas Separation

AbstractMetal–organic framework (MOF) membranes with apparent molecular sieving effects have great potential for gas separation. However, their application in light‐gas separation (e.g., CO2/CH4 and H2/CH4) remains challenging due to their enlarged pore structures under transmembrane pressure. In this work, a series of MOF membranes constructed from dual‐wing (DW) ligands including 2‐chloromethylbenzimidazole, 2‐methylbenzimidazole, 2‐ethylbenzimidazole, and 2‐phenylbenzimidazole are reported, to finely tune apertures and enhance molecule sieving property for small‐size gases. These DW‐ligands provide steric resistance in two directions perpendicular to the coordination bond, leading to a much finer pore structure. The introduction of the DW‐ligands endows the DW/ZIF‐8 membranes with an adjustable bottleneck door for regulating gas diffusion, blocking the transport of large‐sized CH4 while allowing small‐sized H2 and CO2 to permeate. The membranes show significantly improved molecular sieving property with a CO2/CH4 mixed‐gas selectivity of 58.6 in the case of 2‐chloromethylbenzimidazole23/ZIF‐8, which represents the highest value among the reported ZIF membranes. This membrane also exhibits exceptional separation performance for H2/CH4 and H2/C3H8 with separation factors of 430 and 34341, which are the highest values among the reported MOF membranes. This study presents a facile and efficient strategy for regulating MOF aperture and constructing high‐performance membranes for natural gas separation.

Analysis of multi-objective optimization applied to the simulation of a natural gas separation plant

This study concentrated on simulating and optimizing a natural gas separation plant using Unisim Design® software. The optimization procedure aimed to maximize gas production and the higher-molecular-weight hydrocarbons (yC5+) in the produced gas. The maximum water dew point of −45 °C of the produced gas was specified. The Nelder Mead/Weight Sum Method (NM/WSM) algorithm was employed in Python to optimize five decision variables involving the temperature and pressure of the main process streams. Results indicated that the relative deviations below 1%, compared to reference values, were obtained for the main process variables. The multi-objective optimization (MOO) results showed an increase in gas production of up to 5.58% (maximum value of 62,736.10 kg/h) and a rise in the molar fraction of yC5+ by up to 32.2% compared to the reference values. However, it was noted that maximizing gas production indirectly maximizes the yC5+, with only a single decision variable differing in the optimal direction, represented by the intermediate temperature of one compression stage. A Pareto curve was built to display the range of optimal solutions, showing variations of 0.035% in optimal gas production and 0.11% in yC5+. Furthermore, various simulation scenarios were optimized with different thermodynamic conditions at the unit's inlet. In all cases, the optimization resulted in an average gain of 1.57% in gas production regarding the reference (non-optimal case).

Oilfield Brine as a Source of Water and Valuable Raw Materials—Proof of Concept on a Laboratory Scale

Oilfield brine is the largest byproduct stream generated during the extraction of crude oil and natural gas and may be considered a resource for the production of potable water and valuable raw materials. The high salinity of such waters limits the application of typical membrane-based techniques. In most oilfields, waste cold energy from the process of the low-temperature separation of natural gas is available and may be used as a source of cold for the freezing desalination (FD) of brine. As a result of the FD process, two streams are obtained: partially desalinated water and concentrated brine. The partially desalinated water may be suitable for non-potable applications or as a feed for membrane desalination. The concentrated brine from the FD could be used as a feed for the recovery of selected chemicals. This paper focuses on verifying the above-described concept of the freezing desalination of oilfield brine on a laboratory scale. The brine from a Polish oilfield located in the Carpathian Foredeep was used as a feed. Four freezing–thawing stages were applied to obtain low-salinity water, which subsequently was treated by reverse osmosis. The obtained permeate meets the criteria recommended for irrigation and livestock watering. The concentrated brine enriched with iodine (48 mg/L) and lithium (14 mg/L) was subjected to recovery tests. Ion exchange resin Diaion NSA100 allowed us to recover 58% of iodine. Lithium recovery using Mn- and Ti-based sorbents varies from 52 to 93%.

Co-fa nanoplates incorporated 6FDA-DAM mixed-matrix membranes for enhanced CO2/CH4 separation

Plate-like or sheet-like porous materials with nanometer thickness have been considered as the preferred fillers to improve mixed-matrix membranes (MMMs)-based separation. Herein, hexagonal Co-fa (HG-Co-fa) nanoplates were simply synthesized without the addition of any modifier and used as fillers to construct 6FDA-DAM-based MMMs for efficient CO2/CH4 separation. HG-Co-fa nanoplates exhibit high dispersion and interface compatibility in 6FDA-DAM matrix. The results demonstrated that the CO2/CH4 separation performance of 6FDA-DAM was obviously improved after the incorporation of HG-Co-fa nanoplates. The resultant MMMs with nanoplate loading of 10 wt% showed CO2/CH4 selectivity of 27 and CO2 permeability of 1419 Barrer at 25 ℃ and 0.2 MPa, surpassing 2008 Robeson upper bound. Meanwhile, the high lattice integrity and structural stability of HG-Co-fa nanoplates contribute to the excellent thermal and mechanical stability of MMMs, contributing to their anti-plasticization property up to 14 bar and long-term stability up to 240 h, indicating their potential for natural gas separation.

Efficient Ethane and Propane Separation from Natural Gas Using Heterometallic Metal-Organic Frameworks with Interpenetrated Structures.

The development of efficient technology for natural gas separation in industrial processes has become imperative. In this regard, the exploration of novel and effective adsorbents has gained significant attention. One promising approach is the metal regulation of metal-organic frameworks (MOFs), particularly heterometallic MOFs, which offer greater potential for gas separation due to their diverse composition. This study presents the synthesis of a series of iron- and vanadium-based heterometallic MOFs (MIL-126), featuring interpenetrated structures, and investigates their adsorption performance for methane (CH4), ethane (C2H6), and propane (C3H8). Experimental results reveal that the choice of metal combinations within the MOF framework significantly influences the adsorption performance of MIL-126. Notably, heterometallic MIL-126(Fe/Ni) exhibits a stronger binding affinity for C3H8, with an impressive uptake of 177 cm3/g. The C3H8/CH4 ideal adsorbed solution theory selectivity of MIL-126(Fe/Ni) surpasses that of MIL-126(Fe) by a factor of 7, reaching a value of 853, second only to the highest reported value. Furthermore, MIL-126(Fe/Ni) exhibits remarkable potential for the recovery of pure CH4 from the equimolar C3H8/CH4 mixture, with the amount of pure CH4 approaching the maximum reported value for MOFs. Insights from isosteric heat at zero loading and Henry's coefficients indicate that the transformation of metal types leads to a change in the interaction energy between C3H8 and the framework. Furthermore, breakthrough experiments validate the effective separation capability of MIL-126(Fe/Ni) for CH4/C2H6/C3H8 mixtures. These findings underscore the remarkable potential of heterometallic MOFs in constructing a wide range of new MOFs with tailorable properties, thereby enhancing their gas separation performance.

Microporous Fluorinated MOF with Multiple Adsorption Sites for Efficient Recovery of C2H6 and C3H8 from Natural Gas.

Purifying C2H6/C3H8 from a ternary natural gas mixture through adsorption separation is an important but challenging process in the petrochemical industry. To address this challenge, the industry is exploring effective strategies for designing high-performance adsorbents. In this study, we present two metal-organic frameworks (MOFs), DMOF-TF and DMOF-(CF3)2, which have fluorinated pores obtained by substituting linker ligands in the host material. This pore engineering strategy not only provides suitable pore confinement but also enhances the adsorption capacities for C2H6/C3H8 by providing additional binding sites. Theoretical calculations and transient breakthrough experiments show that the introduction of F atoms not only improves the efficiency of natural gas separation but also provides multiple adsorption sites for C2H6/C3H8-framework interactions.

Three-Dimensional Hydrogen-Bonded Porous Metal-Organic Framework for Natural Gas Separation with High Selectivity.

A 3D hydrogen-bonded metal-organic framework, [Cu(apc)2]n (TJU-Dan-5, Hapc = 2-aminopyrimidine-5-carboxylic acid), was synthesized via a solvothermal reaction. The activated TJU-Dan-5 with permanent porosity exhibits a moderate uptake of 1.52 wt% of hydrogen gas at 77 K. The appropriate BET surface areas and decoration of the internal polar pore surfaces with groups that form extensive hydrogen bonds offer a more favorable environment for selective C2H6 adsorption, with a predicted selectivity for C2H6/CH4 of around 101 in C2H6/CH4 (5:95, v/v) mixtures at 273 K under 100 kPa. The molecular model calculation demonstrates a C-H···π interaction and a van der Waals host-guest interaction of C2H6 with the pore walls. This work provides a strategy for the construction of 3D hydrogen-bonded MOFs, which may have great potential in the purification of natural gas.

INSTABILITY OF MECHANICAL EQUILIBRIUM IN NON-IDEAL GAS MIXTURES

To describe phenomena caused by the spatial heterogeneity of density, as well as the processes of natural gas purification, separation and enrichment of gas mixtures with certain components, it is necessary to take into account not only diffusion processes, but also convective currents that arise in the presence of a concentration gradient. Under certain conditions, in multicomponent gas mixtures, a violation of the stability of mechanical equilibrium is possible, i.e. a transition from a stable diffusion process to a convective one is realized in the systems under consideration. The use of linear stability analysis permits to determine on the plane of partial Rayleigh numbers the boundary of the transition of the diffusion process to convective, as well as the values of the thermophysical and geometric characteristics at which this transition is possible. When using this approach to describe experimental data obtained for gas systems containing components with pronounced non-ideal properties, discrepancies are observed. Therefore, the purpose of this work is to develop a method for determining the boundary of loss of stability of mechanical equilibrium in non-ideal gas mixtures. To achieve this goal, the mathematical model describing the change of regimes uses an equation of state in virial form. Based on the developed approach, stability maps were obtained for the C3H8 + CO2 – N2O and C3H8 + N2O – CO2 systems. A comparison of the calculation results with experimental data showed that the proposed technique could be used to determine the conditions for changing mixing modes in three-component gas mixtures containing components with real properties.

Separation of Natural Gas by Gas Hydrate Crystallization Technology: Calculation of Gas Hydrate Distribution Coefficients

Separation of Natural Gas by Gas Hydrate Crystallization Technology: Calculation of Gas Hydrate Distribution Coefficients

Solid–solid thermal synthesis of bimetallic Ni/Zn embedded in N-doped porous carbon for efficient adsorptive separation based on CO2 adsorption at low pressure

High-efficient adsorptive materials for carbon dioxide (CO2) capture and separation of a gas mixture are vital for energy consumption and emission reduction but are still a substantial challenge. A facile synthesis of bimetallic nickel/zinc embedded in N-doped carbon (Ni/Zn@NC) through the solid–solid thermal method (SST) is developed herein. The SST method is a straightforward procedure with the advantage that the materials are obtained in a single step and solvent-free conditions. Thermal analysis and material characterization were used to investigate the synthesis mechanism during the SST process. The results revealed that an intermediate material, initially obtained at a low thermal temperature, was sacrificed to generate Ni/Zn@NC at high temperatures of the SST method. The resulting robust carbon structure, decorated with heteroatoms (Ni, Zn, N), exhibits a potential for efficient CO2 adsorption during the capture and separation of biogas (CO2/CH4), off-gas (CO2/N2), and natural gas (CH4/ N2). The synergetic effect of Ni in the materials enhances the selectivity of SCO2/CH4, SCO2/N2, and SCH4/N2. The improved selectivities by effective sites were confirmed by computational modeling. Significantly, the Ni/Zn@NC material obtained through a mild yet simple synthesis method (SST) exhibits substantially higher CO2 adsorption capacity and selectivity when compared to commercial carbon (activated charcoal).

Performance Study of a Supersonic Swirl Separator

At present, as a new separation technology, supersonic separators have great potential in the separation of natural gases. However, their system performance is still low. In this paper, a supersonic swirl separator design is proposed with an integration approach of the discrete phase model (DPM), bi-coupling, and the random walk model, and it is used to predict the flow process of liquid droplets within the device. Such a numerical method is further employed to study the influence of key parameters on system performance. The results show that with an increase in the inlet port number and the ratio of the gas-liquid area, the separation performance decreases. As a result, the expansion, condensation effect, and economy of the separation system are greatly improved. When the deflection angle exceeds 20°, the separation temperature increases greatly. Consequently, this may ruin the condensing environment. The working pressure ranges are: (1) the boost ratio (the dry outlet pressure/total inlet pressure) is less than 0.76; (2) the wet pressure ratio (the wet outlet pressure/total inlet pressure)is less than 0.46. The increase in droplet diameter can improve the separation performance, and the droplets are completely separated as the diameter reaches 1.75 μm.

Study on the effect of high temperature heat treatment of H2 on the pore structure of activated carbon

As a high-quality adsorbent, activated carbon is widely used in air purification, natural gas storage, sewage treatment, gas enrichment, and separation, etc. The pore microstructure of activated carbon directly affects the adsorption capacity. In this paper, the altered in the microstructure of activated charcoal before and after high-temperature treatment were investigated by high-temperature thermal treatment of activated charcoal at 600°C and 700°C under an H2 atmosphere. The results of low-temperature (77 K) nitrogen adsorption showed that after high-temperature H2 heat treatment, the pores of activated carbon would be ablated and the pore structure would be significantly changed. The specific surface area, micropore specific surface area, total pore volume, and micropore pore volume all increased, and the degree of enhancement was proportional to the temperature of the heat treatment. The pore size distribution of activated charcoal before and after heat treatment was analyzed by density functional theory, and it was concluded that the pore volume of activated carbon mesopores (2-4 nm) increased significantly after high-temperature heat treatment, which could effectively improve the adsorption and separation capacity of activated carbon in larger molecular systems.

Extraction of helium from neon-helium mixture by the adsorption method

Helium is an importantnatural resourceand it hasgreat importance for scientific research. It is currently extracted mainly from natural gas or inlarge air separation units. Heliumandneonareusually separatedfrom an separationcolumntogether. In order to obtain pure neon and helium they are further purified. This article discusses the main methods of extracting helium from the neon-helium mixture.Having compared rectification, freezing, membrane separation and sorption methods, the authors concluded that the adsorption method allows separation at relatively high temperature intervals and is more energy-efficient than the other methods considered. The paper presents existing examples of the application of the adsorption method for the purification of helium from neon, which have been implemented in Chinaand in the CIS. An overview of adsorption separation on new adsorbents, both on metal-organic bases and on single-walled carbon nanotubes, is also presented. In the future, the authors will conduct experiments to fill in the data gaps on adsorption and desorption of neon-heliummixture on different adsorbents.

Investigating two synthetic routes for gas hydrate formation to control the trapping of methane from natural gas

Gas hydrate is considered as an emerging technique for natural gas storage and CH4 separation from natural gas, because assorted nano-sized cages of gas hydrate allow selective trapping of specific gaseous guests such as CH4, C2H6, and C3H8. When a mixture of CH4, C2H6, and C3H8 forms gas hydrates with a liquid promoter at 5.6 mol%, sII large cages (sII-L) can be fully occupied by a promoter, while only CH4 remains in the hydrate phase by occupying sII small cages (sII-S). Based on this, can CH4 be selectively stored or separated from natural gas? Here, we aimed to elucidate the cage-filling behavior of gaseous and liquid guests in CH4 + C2H6 + C3H8 hydrates formed with the addition of tetrahydrofuran (THF), trimethylene oxide (TMO), or 1,3-dioxolane (DIOX). We examined feasible strategies for synthesizing gas hydrate focusing on ice-borne or water-borne route. Our results suggested that ice-borne gas hydrates were a promising option for CH4 separation, because only CH4 was trapped in ice-borne gas hydrates. In contrast, C2H6 and C3H8 shared sII-L with promoters in water-borne gas hydrates. Although partial occupation of sII-L by C2H6 and C3H8 reduced CH4 purity in the hydrate phase, it resulted in enhancing the CH4 uptake in THF hydrate formed via water-borne route, unlike TMO and DIOX. The present findings will broaden the understanding of the cage occupation behavior in ternary gas hydrates formed with liquid promoters, and provide feasible strategies for synthesizing gas hydrates for storing natural gas or CH4 separation from natural gas.

Carbon molecular sieve membranes derived from hydrogen-bonded organic frameworks for CO2/CH4 separation

Carbon molecular sieve (CMS) membranes are ideal candidates for natural gas separation due to their rigid pore structures and stability. The chemical composite and spatial configuration of the used precursors for deriving CMS membranes can greatly influence the final microporous structure and separation performance of the membranes. Most CMS membranes are transformed from amorphous precursors such as polymers nowadays. Here, for the first time, we report a new type of CMS membrane derived from a crystalline porous hydrogen-bonded organic framework membrane (named HCMS). The conversion process has been studied with the characterization of TGA, FTIR, XRD, SEM, and pore size distribution. The effect of pyrolysis temperature on the membrane structure has been investigated to achieve optimized CO2/CH4 separation performance. On the one hand, as the pyrolysis temperature increases from 550 to 650 °C, the pore size distribution of HCMS membrane is narrowed, which is conducive to improving the molecular sieving effect of the membrane. On the other hand, higher ratios of graphitic N and pyrrolic N, which show better affinity for CO2 molecules than pyridinic N, are obtained on the HCMS membranes, leading to more favorable adsorption of CO2. The optimized HCMS membrane pyrolyzed at 600 °C shows a remarkable CO2/CH4 selectivity of 128 and excellent separation stability at varying temperatures and pressures. The HCMS membranes derived from the crystalline HOF precursor can also maintain a stable separation performance against physical aging. The results reported in this work may open the door to constructing CMS membranes with the precursor of crystalline porous membranes.

Rational Construction of Ultrahigh Thermal Stable MOF for Efficient Separation of MTO Products and Natural Gas

Considering the important application foundation of propylene (C3H6) and ethylene (C2H4) production, as well as methane (CH4), in petrochemical industries, this report comprehensively investigated an innovative MOF material (Zn-BPZ-SA) that was synthesized by 3,3′,5,5′-tetramethyl-4,4′-bipyrazole (H2BPZ) and squaric acid (H2SA) for separating methanol-to-olefins (MTO) products (C3H6/C2H4 mixtures) and natural gas (C3H8/C2H6/CH4 mixtures). Zn-BPZ-SA with great resistance toward water and exceptional thermal stability (520 °C), can preferentially adsorb C3H8 and C3H6 rather than C2H6 and C2H4, and in particular, reveals high C3H6 and C3H8 uptakes of 46.6 and 48.0 cm3 g–1 under the crucial low pressure (10 kPa, 298 K). The experimental and simulated transient breakthroughs for C3H6/C2H4 binary mixtures and C3H8/C2H6/CH4 ternary mixtures demonstrated that the MOF can separate these mixtures with long breakthrough time differences, yielding high-purity (>99.95%) products with high productivities: C2H4 (21.9–142.8 L kg–1) and CH4 (34.9–73.0 L kg–1). The excellent separation abilities can be attributed to the rich accessbile O/N and methyl binding sites scattered at the pore surfaces in framework.

Advances in metal-organic frameworks for efficient separation and purification of natural gas

Advances in metal-organic frameworks for efficient separation and purification of natural gas