Natural Gas Purification Research Articles

Molecular Dynamics Simulation Study of the Diffusion of Carbon Dioxide in Heptane: Application in Natural Gas Cleaning

Using solvents to remove carbon dioxide is an effective way to purify natural gas. Diffusion of solute in solvent is key to natural gas purification. In this study, molecular dynamics (MD) simulations of the diffusion of carbon dioxide in heptane at different temperatures and pressures were performed to simulate the conditions of industrial purification process. The diffusion coefficients were measured in two different configurations; pure solvent and binary solute-solvent systems. The diffusion coefficients of the binary system were observed to be in the order of 10-9 m2/s. An increased temperature was observed to increase the diffusion coefficient of the carbon dioxide in heptane while an increase in pressure reduced the value of the diffusion coefficient. The diffusion coefficient was also observed to follow an Arrhenius-type relationship with respect to temperature. The activation energy of the system increased from 9.228 kJ/mol to 11.139 kJ/mol with pressure increase. A linear relationship was detected between the diffusion coefficient and the viscosity of the system and an increased viscosity of the system results in a decreased diffusion coefficient. The results of the research showed that carbon dioxide behavior in heptane offers the theoretical backing for the development of a new natural gas desulphurization solvent.

Synthesis and performance analysis of a polysulfone braid-supported hollow fiber membrane for natural gas purification

Synthesis and performance analysis of a polysulfone braid-supported hollow fiber membrane for natural gas purification

Optimizing the cask effect in multicomponent natural gas purification to provide high methane productivity

AbstractThe efficient separation of CH4 from natural gas containing C2H6 and C3H8 impurities is an important topic. Previous work on the separation of CH4/C2H6/C3H8 mixtures often focuses on the C3H8/CH4 selectivity, inadvertently sidelining the critical importance of C2H6/CH4 selectivity. This oversight results in reduced CH₄ productivity and compromised separation efficiency, a phenomenon often termed as the “cask effect.” Herein, we fine‐tune the interrelationship between thermodynamics and kinetics, targeting enhanced CH4 production. A synergistic thermodynamic–kinetic C3H8/CH4 and C2H6/CH4 selectivity is achieved using dynamic breakthrough experiments, underpinned by the stable metal–organic framework TIFSIX‐Cu‐TPA. The CH4 productivity in TIFSIX‐Cu‐TPA is up to 5 mmol g−1, surpassing most of the popular materials. Detailed density functional theory and molecular dynamics computational insights reveal a counteractive thermodynamic–kinetic relationship, proving pivotal for the simultaneous breakthrough of C2H6 and C3H8 under optimal conditions. Moreover, precise adsorption sites of C2H6 and C3H8 are clearly determined through in situ single‐crystal structures.

Wastewater from natural gas Cansolv desulfurization process: Comprehensive characterization and effective removal of organic compounds

The wastewater generated by the solvent amine desulfurization process in natural gas purification plants is characterized by its recalcitrant organic compounds and high salinity. Without effective treatment, it has the potential to inflict severe environmental harm. The composition of organic matter, however, exerts a profound influence on the outcomes of oxidation processes. To rectify the limitations associated with indiscriminate oxidation that yields suboptimal results, this investigation meticulously performed a molecular-level analysis of organic matter. Based on the organic matter composition in the influent, this study compared the treatment efficacy of three oxidation processes and determined O3/H2O2-Fenton as the optimal joint approach. After O3/H2O2 oxidation, long-chain unsaturated organic compounds (C > 40,DBE > 20) underwent degradation into short-chain aldehydes and low-molecular-weight fatty acids, with priority given to reactions involving CC, CO, and OH over CH reactions. Subsequent Fenton oxidation effectively removed the refractory organics (CHOS, CHONS) and significantly reduced the diversity of organic matter (from 7730 to 4237). The carboxylation, demethylation, and dehydrogenation reactions further facilitated the removal of recalcitrant organic compounds. In light of these findings, this study substantiates that the conversion of extended-chain unsaturated compounds into abbreviated-chain saturated compounds within the system through O3/H2O2 oxidation significantly enhances the subsequent efficacy of Fenton oxidation in organic matter removal. These insights offer valuable perspectives for the efficient remediation of analogous high-salinity organic wastewater scenarios.

Application of Portable CH4 Detector Based on TDLAS Technology in Natural Gas Purification Plant

Methane (CH4) is the main pollutant in oil and gas production. The detection and accounting of CH4 is an important issue in the process of greenhouse gas control and emission reduction in oil and gas industry. In this study, a portable CH4 detector based on tunable diode laser absorption spectroscopy (TDLAS) technology was deployed. The three-dimensional distribution of CH4 in a natural gas purification plant in Sichuan was obtained through vertical unmanned aerial vehicle (UAV) flight observations and ground mobile observations. According to the mass balance method, the emission of CH4 on 30 m above ground level (AGL) and 60 m AGL in this site was about 0.012 kg/s (±42% at 1σ) and 0.034 kg/s (±47% at 1σ), respectively, in one day. The vertical distribution showed that the CH4 concentration reached the maximum (2.75 ± 0.19 ppm) with height of 0 to 100 m AGL. The CH4 concentration from 100 to 300 m AGL showed a downward trend with height. Atmospheric instability at high altitude and high wind speed promoted the diffusion of CH4. The CH4 concentrations of horizontal distribution on 30 m AGL and 60 m AGL were 2.48 ± 0.11 ppm and 2.76 ± 0.34 ppm. In the observation of mobile campaigns, the connecting equipment of natural gas treatment facilities was prone to leakage, such as in valves and flanges. CH4 leakage was also detected at the torch mouth, especially when there was an open flame at the torch mouth. During the mobile movement investigation, the downwind measurement (OTM-33A) was applied to determine the overall CH4 emission rate shortly after patrolling the site. This work plays a vital role in optimizing the operation and maintenance of natural gas production stations pipe network, ensuring human safety and minimizing greenhouse gas emissions.

A High-Performance N2-Selective MXene Membrane with Double Selectivity Mechanism for N2/CH4 Separation.

Membrane-based separation process for unconventional natural gas purification (mainly N2/CH4 separation) has attracted more attention due to its considerable economic benefits. However, the majority of separation membranes at this stage, particularly N2-selective membranes, achieve the desired separation target by mainly relying on the diffusivity-selectivity mechanism. To overcome the limitation of a single mechanism, 2D lamellar MXene membranes with a double selectivity mechanism are prepared to enhance N2 permeance and N2/CH4 selectivity via introducing unsaturated metal sites into MXene, which can form specific interactions with N2 molecules and enhance N2 permeation. The resulting membranes exhibit an inspiring N2/CH4 separation performance with an N2 permeance of 344 GPU and N2/CH4 selectivity of 13.76. The collaboration of the double selectivity mechanism provides a new idea for the development of a novel N2-selective membrane for N2 removal and CH4 purification, which further broadens the application prospects of membrane separation technology in the field of unconventional natural gas purification.

Cu incorporating into OMS-2 lattice creates an efficient Hg0 removal sorbent in natural gas with ambient-temperature H2S/H2O tolerance

Removing mercury in wet natural gas containing acidic components is essential to developing the natural gas purification industry and mitigating corrosion in aluminum heat exchangers. In this work, the Cu-doped manganese oxide octahedral molecular sieve (OMS-2) nanorods were designed for oxidation of Hg0 in wet natural gas. The Hg0 removal efficiency over Cu(0.05)-OMS-2 reached 98.2 % under a high space velocity of 24 × 104 h−1 and a complex atmosphere containing H2O, CO2, and H2S. Surface reactive oxygen species produced by strong electronic interactions owing to Mn-O-Cu hybridization was the main active sites for Hg0 oxidation. The reactive oxygen species on Cu(0.05)-OMS-2 reacted with H2S to form active sulfur species, which could combine with Hg0 to form HgS. Cu(0.05)-OMS-2 exhibited excellent ambient-temperature water resistance, which was attributed to the good redox properties caused by Cu incorporation. This work provided a new strategy for designing efficient sorbents to remove Hg0 from wet natural gas.

Hierarchical nanocomposites derived from UiO-66 framework and zeolite for enhanced CO2 adsorption

In this study, a new nanocomposite composed of zeolite Y incorporated into the UiO-66 framework has been synthesized by solvothermal growth of UiO-66 on the support of zeolite Y, and investigated for CO2 adsorption and separation of CO2/CH4 gas mixtures. The aim of this work was to increase the CO2 uptake and the selectivity of the base framework, as well as to increase its thermal stability. Various weight ratios of UiO-66/zeolite Y were prepared to achieve the optimal composition subject to the highest adsorption capacity. The formation of UiO-66/zeolite Y nanocomposites was verified with different characterization methods. It was observed that UiO-66/zeolite Y with a weight ratio of 90:10 has the same morphology as pristine UiO-66 but with superior porosity. Compared to base UiO-66, its surface area and micropore volume increased by about 80 % and 50 %, respectively. Moreover, the results indicate a substantial improvement of 50 % in the CO2 adsorption capacity of nanocomposite (14.6 mmol/g, 298 K, 30 bar) compared to pristine UiO-66. To our knowledge, the newly synthesized nanocomposites exhibited the record-highest CO2 adsorption capacity among the reported UiO-66 composites. The predicted CO2/CH4 adsorption selectivity of the nanocomposite based on IAST is also higher than that of the pristine MOF. Finally, the cyclic adsorption/desorption test revealed more than 95 % desorption efficiency after ten cycles. Due to the high capacity, selectivity, and reversibility of CO2 adsorption on the UiO-66/zeolite Y, and also the high thermal stability of the nanocomposite, it is suggested as an excellent potential adsorbent for the practical application of biogas and natural gas purification. Furthermore, this contribution also presents an insight into the role of zeolite Y in the nanocomposite framework which could comprehend pore size distribution control by varying its amount.

Simultaneous extraction of C3H8 and C2H6 from ternary C3H8/C2H6/CH4 mixtures in an ultra-microporous metal–organic framework

The efficient purification of methane from other light hydrocarbons is of prime importance in natural gas purification. However, the exploitation of stable adsorbents with both high selectivity and high adsorption capacity remains a challenge. Herein, an ultra-microporous Co-based metal–organic framework (Co-MOF) with abundant selective binding sites decorating the pore wall was applied for the highly efficient separation of ternary C3H8/C2H6/CH4 mixtures. The Co-MOF shows remarkable C3H8 and C2H6 adsorption capacities with uptakes of 59.4 cm3/g and 58.6 cm3/g, respectively, while only adsorbing a low amount of CH4 with an uptake of 16.6 cm3/g at 298 K and 100 kPa. The ideal adsorbed solution theory selectivities for C2H6/CH4 (v/v = 50/50) and C3H8/CH4 (v/v = 50/50) reach 26.0 and 290.0 at 298 K, respectively, surpassing most of the state-of-the-art MOF materials. The molecular simulation reveals that the excellent adsorption and separation performance of Co-MOF derives from its suitable pore size and functional pore surfaces. Furthermore, the breakthrough experiments reveal that the Co-MOF exhibits excellent separation performance of C3H8 and C2H6 from natural gas. Notably, the dynamic separation performance of Co-MOF can be well-maintained after five cycles, demonstrating its excellent cycling stability. The high stability and excellent separation performance make Co-MOF a promising adsorbent for natural gas purification.

Rational Design of Porous Ionic Liquids for Coupling Natural Gas Purification with Waste Gas Conversion

AbstractRemoval of trace impurities for natural gas purification coupled with waste gas conversion is highly desired in industry. We here report a type of porous ionic liquids (PILs) that can realize the continuous flow separation of CH4/CO2/H2S and the conversion of the captured H2S to useful products. The PILs are synthesized through a step‐by‐step surface modification of ionic liquids (ILs) onto UiO‐66‐OH nanocrystals. The introduction of free tertiary amine groups on the nanocrystal surface endows these PILs with an exceptional ability to enrich H2S from CO2 and CH4 with impressive selectivity, while the permanent pores of UiO‐66‐OH act as containers to store an exceptionally higher amount of the selectively captured H2S than the corresponding nonporous ILs. Simultaneously, the tertiary amines as dual functional moieties offer effective catalytic sites for the conversion of the H2S stored in PILs into 3‐mercaptoisobutyric acid, a key intermediate required for the synthesis of Captopril (an antihypertensive drug). Molecular dynamics, density functional theory calculations and Grand Canonical Monte Carlo simulations help understand both the mechanisms of separation and catalysis performance, confirming that the tertiary amines as well as the permanent pores in UiO‐66‐OH play vital roles in the whole procedure.

Rational Design of Porous Ionic Liquids for Coupling Natural Gas Purification with Waste Gas Conversion.

Removal of trace impurities for natural gas purification coupled with waste gas conversion is highly desired in industry. We here report a type of porous ionic liquids (PILs) that can realize the continuous flow separation of CH4 /CO2 /H2 S and the conversion of the captured H2 S to useful products. The PILs are synthesized through a step-by-step surface modification of ionic liquids (ILs) onto UiO-66-OH nanocrystals. The introduction of free tertiary amine groups on the nanocrystal surface endows these PILs with an exceptional ability to enrich H2 S from CO2 and CH4 with impressive selectivity, while the permanent pores of UiO-66-OH act as containers to store an exceptionally higher amount of the selectively captured H2 S than the corresponding nonporous ILs. Simultaneously, the tertiary amines as dual functional moieties offer effective catalytic sites for the conversion of the H2 S stored in PILs into 3-mercaptoisobutyric acid, a key intermediate required for the synthesis of Captopril (an antihypertensive drug). Molecular dynamics, density functional theory calculations and Grand Canonical Monte Carlo simulations help understand both the mechanisms of separation and catalysis performance, confirming that the tertiary amines as well as the permanent pores in UiO-66-OH play vital roles in the whole procedure.

Adaptive Data‐Driven Modeling Strategy Based on Feature Selection for an Industrial Natural Gas Sweetening Process

AbstractAs the core process of natural gas purification plant, natural gas sweetening directly affects the production efficiency and product quality of the purification plant. However, process modeling based on sulfur content prediction presents challenges in adaptability and accuracy. To tackle this, a machine learning‐based modeling approach is proposed that integrates an adaptive immune genetic algorithm with random forest (RF) to intelligently select process features as input variables for RF modeling. The industrial result indicates that the proposed method is able to remove interfering variables and adaptively achieve optimal model precision for different scenarios. It offers a novel research instrument for product quality monitoring in natural gas sweetening plants.

Sub-Tg cross-linked thermally rearranged polybenzoxazole derived from phenolphthalein diamine for natural gas purification

Thermally rearranged (TR) polymers have shown a great potential for gas separation. However, the temperature of TR reaction often goes beyond the glass transition temperature (Tg) of polymer precursor and results in pore collapsing and low gas permeance to asymmetric membranes. To solve this problem, we prepared a series of crosslinked thermally rearranged (XTR) polybenzoxazoles (PBO) at sub-Tg. We synthesized crosslinkable phenolphthalein-based polyimides via chemical imidization (EPPI) and azeotropic distillation (HPPI). The two polyimides were crosslinked at 300–335 °C to increase their Tg so that the subsequent TR reaction were accomplished at sub-Tg. The HPPBO-425 exhibited the best separation performance with a CO2 permeability of 122 barrer and a CO2/CH4 selectivity of 40.4 for pure gases. Moreover, the XTR PBO was not plasticized at a CO2 pressure of 30 atm. After aged for 60 days, the CO2 permeability decreased to 100 barrer and the CO2/CH4 selectivity increased to 44. When separating CO2/CH4 (1:1) mixed gases, the CO2 permeability gradually decreased from 120 to 74 barrer with a decrement in the CO2/CH4 selectivity from 47 to 26 because of the progressively saturated Langmuir sorption sites and the competitive sorption by CH4 decreasing the solubility of CO2. The excellent and stable CO2/CH4 separation property makes the sub-Tg XTR PBO an ideal material for fabricating hollow fiber gas separation membranes.

Pore Space Partitioning MIL-88(Co): Developing Robust Adsorbents for CO2/CH4 Separation Featured with High CO2 Adsorption and Rapid Desorption.

Metal-organic frameworks (MOFs) have attracted significant attention as sorbents for gas separation and purification. Ideally, an industrially potential adsorbent should combine exceptional gas uptake, excellent stability, and a lower regeneration energy; however, it remains a great challenge. Here, by utilizing the pore space partition (PSP) strategy, we develop three isostructural MOF materials (Co-BDC-TPB, Co-DCBDC-TPB, and Co-DOBDC-TPB) based on pristine MIL-88(Co). The three pore-space-partitioned crystalline microporous MOFs have triangular bipyramid cages and segmented one-dimensional channels, and among them, Co-DOBDC-TPB exhibits the highest CO2 uptake capacity (4.35 mmol g-1) and good CO2/N2 (29.7) and CO2/CH4 (6.2) selectivity. The selectivity-capacity synergy endows it with excellent CO2/N2 and CO2/CH4 separation performance. Moreover, Co-DOBDC-TPB can complete desorption within 10 min. The satisfactory CO2 adsorption ability can be attributed to both microporous aperture arising from PSP and modification of the pore surface by the polar hydroxy group, which enhances the interaction between Co-DOBDC-TPB and CO2 molecules significantly. The exceptional regeneration property may be due to its lower CO2 isosteric heat of adsorption (23.6 kJ/mol). The developed pore-space-partitioned MIL-88(Co) material Co-DOBDC-TPB may have potential application to flue gas and natural gas purification.

Reconstruction of mixed matrix membranes by in situ vapor aminolysis for CO2/N2 and CH4/N2 separations

Membrane technology has great potential for gas separation. Incorporation of nanoporous fillers in polymers is attractive for constructing high-performance mixed matrix membranes (MMMs). However, for some mixtures, especially those molecules with similar properties, efficient membrane separation remains extremely challenging. In this study, we report post-synthetic reconstruction of MMMs by in situ aminolysis via chemical vapor deposition for enhancing gas separation performance. By utilization of amine substitution to functional groups of polymers of intrinsic microporosity and chelation to metal centers of metal-organic frameworks (MOFs), the MMMs are modified under mild conditions. Since aminolysis promotes amino grafting, boosts preferential sorption, regulates pathway, and enhances filler-polymer adhesion, the MMMs have substantially improved antiaging property and CO2/N2 separation performance, with permeability of 6986 Barrer and selectivity of 30.7. Importantly, for CH4/N2 mixture separation, that is critical for natural gas purification but difficult to separate, the MMMs also exhibit competitive selectivity and permeability of 5.0 and 897 Barrer, respectively. The performances for CO2/N2 and CH4/N2 separations can be close to and surpass the least trade-off upper bounds, respectively. Moreover, in situ aminolysis by vapor deposition has universal applicability for reconstructing various MMMs. This strategy is an alternative route to fabricate membranes for efficient separations.

Bulk and interfacial properties of methane-heavy hydrocarbon mixtures

Methane-heavy hydrocarbons are typical mixtures in natural gas extraction, purification and production processes. However, the microscopic behavior of methane diffusion, dissolution and adsorption within heavy hydrocarbon liquids has not been solved yet. Therefore, the bulk and interfacial characteristics of methane-heavy hydrocarbon mixtures were systematically analyzed. And the real and rippled interfaces were identified using a new method. The results indicate that density of heavy hydrocarbon-rich phase decreases with decreasing chain length and increasing pressure, while that of the methane-rich phase increases instead. When methane molecules dissolve into bulk liquids, heavy hydrocarbon chains stretch and the intermolecular separation distances increase. Additionally, the interaction energy between the two molecules is the main reason for system swelling. The Gibbs relative adsorption of methane improves until reaching the saturation limit as pressure adds. The intrinsic interface analyses show that the strong adsorption of methane mainly exists in the first surface layer in dilute solutions, which becomes more pronounced with increasing methane fraction. For heavy hydrocarbons with shorter chains, surface layers are narrower and their separation distances are reduced. Furthermore, methane molecules prefer staying at the outer edge of surface layers and are nearer to gas phase than heavy hydrocarbons by approximately 0.2–0.7 Å.

ZIF-8-based dual layer hollow fiber mixed matrix membrane for natural gas purification

To prevent pipe damage and lower operating costs, natural gas must be cleaned of pollutants like carbon dioxide (CO2) and hydrogen sulphide (H2S). High selectivity of the functional material in the mixed matrix membranes (MMMs) allows for a more efficient gas separation compared to traditional polymeric membranes. However, poor dispersion and compatibility between the functional material and the polymer matrix become one of the major problems of MMMs. The use of zeolite imidazole (ZIF-8) in MMMs has been explored for its ability to separate CO2/CH4 due to its versatile gas molecule diameter range and effective CO2 adsorption. In this study, the effects of ZIF-8 at various loadings were examined on the physical and chemical properties of dual layer hollow fiber MMMs and gas separation efficiency. Following the successful production of 86.25 nm ZIF-8 nanoparticles, ZIF-8-based DLHF MMMs were created. The results showed that 0.5 wt% ZIF-8 loading provided the best results, with excellent interaction between the polymer PSf and the inorganic filler ZIF-8, strong heat resistance, and chemical stability. Increased CO2 permeability and CO2/CH4 ideal selectivity by 72.5 % and 1196.2 % respectively, compared to the unmodified membrane. It was inferred through this study that minimal loading of 0.5 wt% ZIF-8 in the DLHF MMMs improved their ability to separate gases, making them a good option for capturing CO2.

Polymeric Membranes for H2S and CO2 Removal from Natural Gas for Hydrogen Production: A Review

Natural gas, an important source of hydrogen, is expected to be crucial in the transition to a hydrogen-based economy. The landscape of the gas processing industry is set to change in the near future with the development of highly acidic sour gas wells. Natural gas purification constitutes a major share of the gas separation membrane market, and the shift to low-quality sour gas wells has been mirrored in the trends of membrane material research. Purification also constitutes the major portion of the cost of natural gas, posing implications for the cost of hydrogen production. This review provides an update on the current state of research regarding polymeric membranes for H2S removal, along with CO2 separation, from natural gas that is used for hydrogen production via steam methane reforming. The challenges of adapting polymeric membranes to ternary H2S/CO2/CH4 separations are discussed in detail. Key polymeric materials are highlighted, and the prospects for their application in H2S removal from natural gas are evaluated. Finally, the growing interest in H2 production from H2S is discussed. Advances in the membrane industry and the emergence of new membrane materials may significantly improve the commercial viability of such processes.

Ionic Liquids Functionalized MOFs for Adsorption.

Metal-organic frameworks (MOFs) and ionic liquids (ILs) represent promising materials for adsorption separation. ILs incorporated into MOF materials (denoted as IL/MOF composites) have been developed, and IL/MOF composites combine the advantages of MOFs and ILs to achieve enhanced performance in the adsorption-based separation of fluid mixtures. The designed different ILs are introduced into the various MOFs to tailor their functional properties, which affect the optimal adsorptive separation performance. In this Perspective, the rational fabrication of IL/MOF composites is presented, and their functional properties are demonstrated. This paper provides a critical overview of an emergent class of materials termed IL/MOF composites as well as the recent advances in the applications of IL/MOF composites as adsorbents or membranes in fluid separation. Furthermore, the applications of IL/MOF in adsorptive gas separations (CO2 capture from flue gas, natural gas purification, separation of acetylene and ethylene, indoor pollutants removal) and liquid separations (separation of bioactive components, organic-contaminant removal, adsorptive desulfurization, radionuclide removal) are discussed. Finally, the existing challenges of IL/MOF are highlighted, and an appropriate design strategy direction for the effective exploration of new IL/MOF adsorptive materials is proposed.

Scalable and Depurative Zirconium Metal-Organic Framework for Deep Flue-Gas Desulfurization and SO2 Recovery.

Deep SO2 removal and recovery as industrial feedstock are of importance in flue-gas desulfurization and natural-gas purification, yet developing low-cost and scalable physisorbents with high efficiency and recyclability remains a challenge. Herein, we develop a viable synthetic protocol to produce DUT-67 with a controllable MOF structure, excellent crystallinity, adjustable shape/size, milli-to-kilogram scale, and consecutive production by recycling the solvent/modulator. Furthermore, simple HCl post-treatment affords depurated DUT-67-HCl featuring ultrahigh purity, excellent chemical stability, fully reversible SO2 uptake, high separation selectivity (SO2/CO2 and SO2/N2), greatly enhanced SO2 capture capacity, and good reusability. The SO2 binding mechanism has been elucidated by in situ X-ray diffraction/infrared spectroscopy and DFT/GCMC calculations. The single-step SO2 separation from a real quaternary N2/CO2/O2/SO2 flue gas containing trace SO2 is implementable under dry and 50% humid conditions, thus recovering 96% purity. This work may pave the way for future SO2 capture-and-recovery technology by pushing MOF syntheses toward economic cost, scale-up production, and improved physiochemical properties.