Natural Gas Upgrading Research Articles

Large-Scale Screening and Design of Metal-Organic Frameworks for CH4 /N2 Separation.

CH4 /N2 separation is one of the great challenges in gas separation, which is of scientific and practical importance, such as in the upgrading of unconventional natural gas. Unfortunately, the separation performance is still quite low so far mainly due to their very close physical properties. In this work, a high-throughput computational screening method was performed to develop metal-organic frameworks (MOFs) for efficient CH4 /N2 separation. General designing rules as well as the correlation between selectivity and our proposed adsorbility (AD) parameter were obtained by carrying out systematic GCMC simulations of the existing 5109 CoRE MOFs. With the aid of this information, five virtual MOFs were screened out from the large database with 303 991 generated MOFs constructed in our previous work, exhibiting much higher selectivities than all the reported values. Among them, the selectivity of Zn-PYZ-BPY-1 can reach over 29.0, about 2.4 times of the highest value reported in the literature. These results may not only suggest promising candidates for CH4 /N2 separation but also provide useful information for large screening of MOFs for other specific separation mixtures.

Fabricating Mechanically Robust Binder-Free Structured Zeolites by 3D Printing Coupled with Zeolite Soldering: A Superior Configuration for CO2 Capture.

3D‐printing technology is a promising approach for rapidly and precisely manufacturing zeolite adsorbents with desirable configurations. However, the trade‐off among mechanical stability, adsorption capacity, and diffusion kinetics remains an elusive challenge for the practical application of 3D‐printed zeolites. Herein, a facile “3D printing and zeolite soldering” strategy is developed to construct mechanically robust binder‐free zeolite monoliths (ZM‐BF) with hierarchical structures, which can act as a superior configuration for CO2 capture. Halloysite nanotubes are employed as printing ink additives, which serve as both reinforcing materials and precursor materials for integrating ZM‐BF by ultrastrong interfacial “zeolite‐bonds” subjected to hydrothermal treatment. ZM‐BF exhibits outstanding mechanical properties with robust compressive strength up to 5.24 MPa, higher than most of the reported structured zeolites with binders. The equilibrium CO2 uptake of ZM‐BF reaches up to 5.58 mmol g−1 (298 K, 1 bar), which is the highest among all reported 3D‐printed CO2 adsorbents. Strikingly, the dynamic adsorption breakthrough tests demonstrate the superiority of ZM‐BF over commercial benchmark zeolites for flue gas purification and natural gas and biogas upgrading. This work introduces a facile strategy for designing and fabricating high‐performance hierarchically structured zeolite adsorbents and even catalysts for practical applications.

A water-stable fcu-MOF material with exposed amino groups for the multi-functional separation of small molecules

The energy-efficient purification of methane from C2-hydrocarbons is of great significance for the upgrading of natural gas. So does the capture of carbon dioxide for remission of greenhouse effect. It is well established that some functional sites, such as open metals sites, Lewis basic nitrogen sites and fluorine groups, have shown significantly enhanced affinity toward more polarizable molecules. Thus, a water-stable Eu3+-based fcu-metal-organic framework (MOF) (compound 1 ) with amino functional groups has been successfully constructed through a reticular chemistry approach. As a result, the activated compound 1 exhibits moderately high uptakes of C2-hydrocarbons, but a less obvious adsorption of CH4 at the same conditions. Among them, the adsorption capacity of C2H2 is up to 143.6 cm3 cm−3 and a relatively high selectivity of C2H2/CH4 (107.7) is obtained at near room temperature. Moreover, compound 1 is also validated as an exceptional adsorbent for CO2 capture, with the fairly high capacity of CO2 (92.6 cm3 cm−3) and CO2/N2 selectivity (151.7) at ambient conditions. The excellent performance of compound 1 is mainly driven by the exposed amino functional groups within the contracted pores. Such effect thus leads to the achievement of dual-functional platform for methane purification and carbon dioxide capture. Furthermore, compound 1 features a satisfactory water stability, which is confirmed by the powder X-ray diffraction (PXRD) analysis and the retest of porosity after being soaked in water.

Molecular Design of Microporous Polymer Membranes for the Upgrading of Natural Gas

Microporous polymer membranes (MPMs) are attractive for gas separation due to their high porosity and tuneable functionalization. In this study, two new MPMs (namely PILP-1 and PILP-3) are designed...

Thermodynamic and molecular insights into the absorption of H2S, CO2, and CH4 in choline chloride plus urea mixtures

AbstractDeep eutectic solvents (DESs) are a class of promising media for gas separation. In order to examine the potential application of DESs for natural gas upgrading, the solubilities of H2S, CO2, and CH4 in choline chloride (ChCl) plus urea mixtures were measured in this work. The solubility data were correlated with Henry's law equation to calculate the thermodynamic properties of gas absorption processes, such as Henry's constants and enthalpy changes. Grand‐canonical Monte Carlo simulations and quantum chemistry calculations were also performed to examine the mechanism of gas absorption processes. It is found that the absorption of H2S in ChCl + urea mixtures is governed by the hydrogen‐bond interaction between Cl of ChCl and H of H2S, whereas the absorption of CO2 and CH4 in ChCl+urea mixtures is governed by the free volume of solvents. Based on the different behavior of gas absorption, high H2S/CO2, H2S/CH4, and CO2/CH4 selectivities can be achieved by adjusting the ratio of ChCl/urea in mixtures.

Author Correction: Natural gas upgrading using a fluorinated MOF with tuned H2S and CO2 adsorption selectivity

In the version of this Article originally published, the name of author Gongping Liu was mistakenly written with the names in reverse order. This has now been corrected.

Screening and Design of Covalent Organic Framework Membranes for CO2/CH4 Separation

Membrane based CO2/CH4 separation is an effective and energy saving way for highly demanded natural gas upgrading. Herein, high-throughput computational screening of covalent organic frameworks (CO...

Theoretical Study of Moisture-Pretreated Lithium as Potential Material for Natural Gas Upgrading

For efficient natural gas upgrading at near ambient temperatures, moisture-pretreated lithium is proposed as a reactive adsorbent, and its separation performance was examined for selected gas mixtures (involving combination of CH4, CO2, O2, N2, and/or H2) by theoretical studies. For evaluating the proposed adsorbent, we used density functional theory calculations as well as temperature-programmed kinetic Monte Carlo calculations. Contributions of different mechanisms for the gas capture were examined, including diffusion, adsorption, and reaction. Among these mechanisms, reaction was found to be the dominant factor during the gas-capture process. In contrast to the conventional reactive adsorbents where gases directly react with adsorbents and thus are captured, the gas-capture mechanism herein follows the reaction between gases and species generated upon pre-exposure of lithium to moisture. The proposed separation process is thermodynamically favorable and would progress spontaneously. It is shown that f...

Natural gas upgrading using a fluorinated MOF with tuned H2S and CO2 adsorption selectivity

The process used to upgrade natural gas, biogas and refinery-off-gas directly influences the cost of producing the fuel and often requires complex separation strategies and operational systems to remove contaminants such as hydrogen sulfide (H2S) and carbon dioxide (CO2). Here we report a fluorinated metal–organic framework (MOF), AlFFIVE-1-Ni, that allows simultaneous and equally selective removal of CO2 and H2S from CH4-rich streams in a single adsorption step. The simultaneous removal is possible for a wide range of H2S and CO2 compositions and concentrations of the gas feed. Pure component and mixed gas adsorption, single-crystal X-ray diffraction and molecular simulation studies were carried out to elucidate the mechanism governing the simultaneous adsorption of H2S and CO2. The results suggest that concurrent removal of CO2 and H2S is achieved via the integrated favourable sites for H2S and CO2 adsorption in a confined pore system. This approach offers the prospect of simplifying the complex schemes for removal of acid gases. Contaminants such as CO2 and H2S present in natural gas and biogas streams must be removed before use; existing strategies to do so can be rather complex. Here, the authors use a fluorinated porous metal–organic framework to remove CO2 and H2S from CH4-rich feeds in a single step, potentially simplifying the process.

Trianglamine-Based Supramolecular Organic Framework with Permanent Intrinsic Porosity and Tunable Selectivity.

Here we introduce for the first time a metal-free trianglamine-based supramolecular organic framework, T-SOF-1, with permanent intrinsic porosity and high affinity to CO2. The capability of tuning the pore aperture dimensions is also demonstrated by molecular guest encapsulation to afford excellent CO2/CH4 separation for natural gas upgrading.

Photocatalytic upgrading of natural gas.

Cerium salts catalyze formation of value-added molecules from methane and small alkanes

An amine functionalized carbazolic porous organic framework for selective adsorption of CO2 and C2H2 over CH4

Abstract A new microporous organic polymer (PCB NH2) has been synthesized based on amine functionalized carbazole derivative by oxidative coupling polymerization with anhydrous FeCl3. Polymer PCB-NH2 exhibits microporous nature with a BET surface area of 542.4 m2 g−1, and shows moderately high CO2 and C2H2 adsorption capacities, 51.6 cm3 g−1 (10.3 wt%), 58.4 cm3 g−1 (7.5 wt%) at 278 K, 1 atm, respectively. Remarkably, at 278 K, the predicted IAST selectivities of PCB-NH2 are 16.7–5.8 for a CO2/CH4 (5:95 v/v) gas mixture and 34.3–21.0 for a C2H2/CH4 (50:50 v/v) gas mixture at pressures varying from 0 to 1 atm, respectively. More interesting, PCB-NH2 displays higher CO2/CH4 selectivity than its matrix polymer PCB. The isosteric heats of CO2 adsorption (Qst) for PCB-NH2 and PCB further indicate that the amine group may facilitate the interaction between the polarizable CO2 molecules and the polymer by local dipole−quadrupole interactions, subsequently favors selective gas separation for these gas molecules. The high selectivity of CO2/CH4 and C2H2/CH4 makes PCB-NH2 possible candidate for future natural gas upgrading and acetylene purification.

Enhanced CO2/CH4 Separation Performance of a Mixed Matrix Membrane Based on Tailored MOF-Polymer Formulations.

Membrane‐based separations offer great potential for more sustainable and economical natural gas upgrading. Systematic studies of CO2/CH4 separation over a wide range of temperatures from 65 °C (338 K) to as low as −40 °C (233 K) reveals a favorable separation mechanism toward CO2 by incorporating Y‐fum‐fcu‐MOF as a filler in a 6FDA‐DAM polyimide membrane. Notably, the decrease of the temperature from 308 K down to 233 K affords an extremely high CO2/CH4 selectivity (≈130) for the hybrid Y‐fum‐fcu‐MOF/6FDA‐DAM membrane, about four‐fold enhancement, with an associated CO2 permeability above 1000 barrers. At subambient temperatures, the pronounced CO2/CH4 diffusion selectivity dominates the high permeation selectivity, and the enhanced CO2 solubility promotes high CO2 permeability. The differences in adsorption enthalpy and activation enthalpy for diffusion between CO2 and CH4 produce the observed favorable CO2 permeation versus CH4. Insights into opportunities for using mixed‐matrix membrane‐based natural gas separations at extreme conditions are provided.

Highly efficient separation of methane from nitrogen on a squarate‐based metal‐organic framework

Highly selective capture of methane from nitrogen is considered to be a feasible approach to improve the heating value of methane and mitigate the effects of global warming. In this work, an ultramicroporous squarate‐based metal‐organic framework (MOF), [Co3(C4O4)2(OH)2] (C4O42− = squarate), with enhanced negative oxygen binding sites was synthesized for the first time and used as adsorbent for efficient separation of methane and nitrogen. Adsorption performance of this material was evaluated by single‐component adsorption isotherms and breakthrough experiments. Furthermore, density functional theory calculation was performed to gain the deep insight into the adsorption binding sites. Compared with the other state‐of‐the‐art materials, this material exhibited the highest adsorption selectivity (8.5–12.5) of methane over nitrogen as well as the moderate volumetric uptake of methane (19.81 cm3/cm3) under ambient condition. The unprecedented selectivity and chemical stability guaranteed this MOF as a candidate adsorbent to capture CH4 from N2, especially for the unconventional natural gas upgrading. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3681–3689, 2018

Assessing the Potential of Biochars Prepared by Steam-Assisted Slow Pyrolysis for CO2 Adsorption and Separation.

The potentialities in the use of biochars prepared by steam-assisted slow pyrolysis as adsorbents of gases of strategic interest (N2, CO2, and CH4) and their mixtures were explored. The biochars prepared from Populus nigra wood and cellulose fibers exhibited a narrow microporosity, with average pore sizes ranging between 0.55 and 0.6 nm. The micropore volume increased with the pyrolysis temperature, allowing CO2 and CH4 uptakes at room temperature between 1.5 and 2.5 mmol/g and between 0.1 and 0.5 mmol/g, respectively. These values are in line with those from the literature on biomass-derived carbon-based materials, exhibiting much higher porous features than those reported herein. As for the separation of CO2/N2 and CO2/CH4 gas mixtures, data showed that the prepared biochars exhibited good selectivities for CO2 over both N2 and CH4: between ca. 34 and 119 for a CO2/N2 mixture in typical post-combustion conditions (15:85, v/v) and between 14 and 34 for a CO2/CH4 mixture typical of natural gas upgrading (30:70, v/v).

Natural gas upgrading by selective separation on zeotype adsorbents

In this study, three kinds of zeotype adsorbents (synthesized NaA and SAPO-34 in comparison with natural Clinoptilolite) were compared to find out their abilities of separating CO2 and N2 from CH4. The adsorbents were characterized by SEM (scanning electron microscope) for morphological property, powder X-ray diffraction for the phase structure, and BET (Brunauer, Emmett and Teller) for the pore textural properties. The adsorption experiments of CO2, N2, and CH4 by the adsorbents were carried out at three temperatures (278, 298, and 323 K) and for pressures up to 1000 kPa. The experimental adsorption equilibrium isotherms were well described by the Sips equation. Breakthrough curves were measured for the fixed bed. The adsorption heats for the gases on the adsorbents were calculated using the van't Hoff equation. The heats of adsorption at zero coverage of CO2, N2, and CH4 on SAPO-34 were found to be 36.74, 23.05, and 23.12 kJ mol−1, respectively, while the values for the other adsorbents were approximately lower than these. The ideal selectivity of carbon dioxide over methane for NaA, Clinoptilolite, and SAPO-34 were 22.7, 16.4, and 22.8, respectively, at atmospheric pressure and 278 K Henry's law regime. The ideal selectivity of the adsorbents for carbon dioxide over methane was 22.7, 16.4 and 22.8 for NaA, Clinoptilolite and SAPO-34, respectively, at atmospheric pressure and 278 K Henry's law regime. Under the same conditions, the selectivity of nitrogen over methane for NaA, Clinoptilolite, and SAPO-34 were 14.6, 7.9, and 8.8, respectively. The selectivity increased with increasing the pressure in all cases studied, especially in the SAPO-34. The effect of the moisture content in the adsorbents on the separation performance was investigated by dynamic experiments. The dynamic adsorption experiments of CO2/N2/CH4 gas mixture confirmed that for large amount of moisture in natural gas, the SAPO-34 is the best candidate among the studied adsorbents, and it has more promising performance for the separating N2 and CO2 from methane, while in the case of large amount of nitrogen in natural gas, the NaA is the best one.

Cover Feature: An Activated TiC–SiC Composite for Natural Gas Upgrading via Catalytic Oxyhalogenation (ChemCatChem 6/2018)

Cover Feature: An Activated TiC–SiC Composite for Natural Gas Upgrading via Catalytic Oxyhalogenation (ChemCatChem 6/2018)

Mixed Matrix Membranes for Natural Gas Upgrading: Current Status and Opportunities

In the past few decades, natural gas has attracted worldwide attention as one of the most desired energy sources owing to its more efficient and cleaner combustion process compared to that of coal and crude oil. Due to the presence of impurities, raw natural gas needs to be upgraded to meet the pipeline specifications. Membrane-based separation is a promising alternative to conventional processes such as cryogenic distillation and pressure swing adsorption. Among the existing membranes for natural gas upgrading, polymeric membranes and inorganic membranes have been extensively explored, but each type has its own pros and cons. The development of mixed matrix membranes (MMMs) by incorporating organic/inorganic fillers into the polymer matrix provides a good strategy to combine the merits of each material and fabricate novel membranes with superior gas separation performance. In this review, we first discuss the recent advances in MMMs showing potentials in natural gas upgrading. Special attention is paid to a detailed evaluation on the polymer and filler choices for acidic gas removal. After that, we analyze factors that influence the membrane separation performance and summarize effective strategies reported in the open literature for the fabrication of high-performance MMMs. Finally, a perspective on future research directions in this field is presented.

Ultra-thin MFI membranes for removal of C3+ hydrocarbons from methane

The removal of propane and heavier hydrocarbons (C3+) from natural gas is an important part of natural gas upgrading. In the present work, ultra-thin MFI zeolite membranes with a thickness of 400 nm and an estimated Si/Al ratio of 152 were evaluated for separation of C3H8 and n-C4H10 from binary and ternary mixtures with CH4. The membranes were selective towards the heavier hydrocarbons and showed high permeance at all investigated temperatures. At room temperature, the n-C4H10/CH4 separation selectivity was 25, coupled with an n-C4H10 permeance of 31 × 10−7 mol m−2 s−1 Pa−1 for a 10/90 n-C4H10/CH4 binary feed mixture. As the temperature was decreased to 281 K, the separation selectivity increased to as high as 55 with an n-C4H10 permeance of 25 × 10−7 mol m−2 s−1 Pa−1. The separation selectivities for a 10/90 C3H8/CH4 binary mixture were 9.5 and 19, with C3H8 permeances as high as 54 and 37 × 10−7 mol m−2 s−1 Pa−1 at 297 and 271 K, respectively. The higher selectivities observed for n-C4H10 containing mixtures was ascribed to stronger adsorption of n-C4H10 than C3H8 in MFI, thus resulting in higher adsorption selectivities of the n-C4H10 containing mixtures over CH4. For a 10/10/80 n-C4H10/C3H8/CH4 ternary mixture, the highest sum selectivity of (n-C4H10 + C3H8)/CH4 was 48 and the corresponding sum permance of (n-C4H10 + C3H8) was 26 × 10−7 mol m−2 s−1 Pa−1 at 283 K, which were similar to the separation results of n-C4H10/CH4 binary mixture at the same conditions. The n-C4H10/CH4 and C3H8/CH4 separation selectivities from the ternary mixture were of course lower, but still as high as 32 and 16 at 283 K, with n-C4H10 and C3H8 permeances of 17 and 8 × 10−7 mol m−2 s−1 Pa−1, respectively. The results show that ultra-thin MFI zeolite membranes are promising candidates for separation of C3+ hydrocarbons from natural gas.

An Activated TiC–SiC Composite for Natural Gas Upgrading via Catalytic Oxyhalogenation

AbstractAlkane oxyhalogenation has emerged as an attractive catalytic route for selective natural gas functionalization to important commodity chemicals, such as methyl halides or olefins. However, few systems have been shown to be active and selective in these reactions. Here, we identify a novel and highly efficient TiC–SiC composite for methane and ethane oxyhalogenation. Detailed characterization elucidates the kinetics and mechanism of the selective activation under reaction conditions to yield TiO2–TiC–SiC. This catalyst outperforms bulk TiO2, one of the best reported catalysts, reaching up to 85 % selectivity and up to 3 times higher titanium‐specific space‐time‐yield of methyl halides or ethylene. This is attributed to the fact that the active TiO2 phase generated in situ is embedded in the thermally conductive SiC matrix, facilitating heat dissipation thus improving selectivity control.