Natural Gas Separation Research Articles

Nitrogen rejection from natural gas by dual reflux-pressure swing adsorption using activated carbon and ionic liquidic zeolite

The separation of a natural gas mixture containing 85 mol% CH4 and 15 mol% N2 by dual reflux pressure swing adsorption (DR PSA) was investigated using dynamic non-isothermal numerical simulations previously benchmarked against experiments. Two different adsorbents were employed: a commercially available activated carbon (AC1) and the recently developed ionic liquidic zeolite (ILZ), which has about twice the selectivity for methane over nitrogen than the activated carbon. Four DR PSA cycle configurations (PL-A, PH-A, PL-B and PH-B) were studied and iteratively optimized in terms of separation performance and energy consumption. The dynamic non-isothermal simulations, implemented in the software platform Aspen Adsorption, included a polytropic compressor model with temperature dependent heat capacities for more realistic predictions of the compressor duty. The heavy product to feed ratio, the feed step time and the light reflux ratio were selected as key optimization parameters for all four cycles at fixed bed pressure ratio, feed location and feed flow rate. The simulations showed that A-cycles were superior to B-cycles in terms of their separation performance for both adsorbent materials. Overall, the separation performance achieved by AC1 was lower than that by ILZ. At optimized conditions for AC1, PL-A and PH-A cycles achieved approximately 92 mol% CH4 in the heavy product and 4.5 mol% CH4 in the light product with corresponding energy requirement at 9.9 kJ mol−1 (feed) and 8.7 kJ mol−1 (feed), while using the ILZ adsorbent, both PL-A and PH-A cycles were able to deliver 0.9 mol% CH4 in the light product and 93.5 mol% CH4 in the heavy product. The cycle work of the PL-A and PH-A configuration using ILZ was 8.8 and 7.7 kJ mol−1 (feed), respectively. These simulation results show that DR PSA processes using ionic liquidic zeolites can meet strict natural gas separation requirements and that such processes can efficiently upgrade sub-quality natural gas.

High-pressure CO2/CH4 separation of Zr-MOFs based mixed matrix membranes

The gas separation properties of 6FDA-DAM mixed matrix membranes (MMMs) with three types of zirconium-based metal organic framework nanoparticles (MOF NPs, ca. 40 nm) have been investigated up to 20 bar. Both NPs preparation and MMMs development were presented in an earlier publication that reported outstanding CO2/CH4 separation performances (50:50 vol% CO2/CH4 feed at 2 bar pressure difference, 35 °C) and this subsequent study is to demonstrate its usefulness to the natural gas separation application. In the current work, CO2/CH4 separation has been investigated at high pressure (2–20 bar feed pressure) with different CO2 content in the feed (10–50 vol%) in the temperature range 35–55 °C. Moreover, the plasticization, competitive sorption effects, and separation of the acid gas hydrogen sulfide (H2S) have been investigated in a ternary feed mixture of CO2:H2S:CH4 (vol% ratio of 30:5:65) at 20 bar and 35 °C. The incorporation of the Zr-MOFs in 6FDA-DAM enhances both CO2 permeability and CO2/CH4 selectivity of this polymer. These MMMs exhibit high stability under separation conditions relevant to an actual natural gas sweetening process. The presence of H2S does not induce plasticization but increases the total acid gas permeability, acid gas/CH4 selectivity and only causes reversible competitive sorption. The overall study suggests a large potential for 6FDA-DAM Zr-MOF MMMs to be applied in natural gas sweetening, with good performance and stability under the relevant process conditions.

A Computational Fluid Dynamics Approach for the Modeling of Gas Separation in Membrane Modules

Natural gas demand has increased rapidly across the globe in the last decade, and it is set to play an important role in meeting future energy requirements. Natural gas is mainly produced from fossil fuel and is a side product of crude oil produced beneath the earth’s crust. Materials hazardous to the environment, like CO2, H2S, and C2H4, are present in raw natural gas. Therefore, purification of the gaseous mixture is required for use in different industrial applications. A comprehensive computational fluid dynamics (CFD) model was proposed to perform the separation of natural gas from other gases using membrane modules. The CFD technique was utilized to estimate gas flow variations in membrane modules for gas separation. CFD was applied to different membrane modules to study gas transport through the membrane and flux, and to separate the binary gas mixtures. The different parameters of membrane modules, like feed and permeate pressure, module length, and membrane thickness, have been investigated successfully. CFD allows changing the specifications of membrane modules to better configure the simulation results. It was concluded that in a membrane module with increasing feed pressure, the pressure gradient also increased, which resulted in higher flux, higher permeation, and maximum purity of the permeate. Due to the high purity of the gaseous product in the permeate, the concentration polarization effect was determined to be negligible. The results obtained from the proposed CFD approach were verified by comparing with the values available in the literature.

Modeling and simulation of adsorption of methane, ethane, hydrogen sulfide and water from natural gas in (FP)YEu Metal–Organic Framework

Metal Organic Frameworks (MOFs) are novel type of hybrid porous materials that have been proposed for natural gas separation and purification due to the possibility of tailoring their capabilities by changing the organic linkers, tuning the length of the organic linker and changing or mixing the metal ion. Molecular simulation helps to understand experimental results by providing a detailed picture on the molecular scale that is not easily accessible from experimental and can be used to study the applicability of classical force fields.In this work, FPYEu MOF [1] [2] was carefully chosen as an example of a model MOF for studying applicability of force fields, cutoff radius besides the effect of different distributions of metal ions in FPYEu MOF on adsorption of CH4, C2H6, H2S as well as H2O.Grand Canonical Monte Carlo (GCMC) simulations were used to perform gases adsorption on FPYEu MOF cells containing different distributions of Yttrium and Europium. All simulations in this work have been carried out using Towhee code [3].The applicability of different force fields available in the literature was tested and some of them were applicable like H2S, where good agreement was found with experimental results, while others were not applicable, like CH4, C2H6 and H2O, where the calculated isotherms “over or under” estimated the experimental ones. In addition, eight different configurations having Eu atoms arbitrarily located in the system were explored to evaluate the sensitivity of distribution of metal ions.

Mapping the Material-Property Space for Feasible Process Operation: Application to Combined Natural-Gas Separation and Storage

A multiscale-optimization-based feasibility-mapping approach is introduced to identify the target properties of materials that would guarantee the desired process performance. The approach is successfully applied to screen a database of 178 known and 139 500 hypothetical zeolites to find materials that are most suited for the combined separation and storage (CSS) of natural gas. Maps of material properties that include the equilibrium adsorption loading and the Henry coefficients are obtained for feasible process operation subject to the constraints imposed. On the basis of these maps, materials with high methane-storage capacities but moderate Henry coefficients, such as SBN and h8124791, are found to be most suitable for CSS applications. The constraints imposed on the purity of stored methane and methane loss during the process operation influence the desired material properties. Beyond identifying feasibility, maps of constraint violations are constructed that can be useful in analyzing the effects of...

Role of oxygen, nitrogen and sulfur functionalities on the surface of nanoporous carbons in CO2 adsorption: A critical review

Abstract In todays’ perspective, separation of CO2 from different gas streams is extremely important. Besides the key separation need of CO2 that lies with its isolation from N2 in flue gas, different other separation needs of CO2 includes natural gas separation, biogas upgrading, direct CO2 capture from air and purification other gas streams from the mixtures of CO2. The technical challenges of CO2 separation varies with the type of gas mixtures and CO2 concentration. Within different CO2 separation techniques, adsorptive separation of CO2 has gained attention owing to its low cost, regenerability and zero hazard. Among different types of adsorbents, nanoporous carbons are highly attractive because of their lowest cost, versatile synthesis protocol and efficient separation. In past several years, both computation and experimental results established that few selected heteroatoms, including oxygen, nitrogen and sulfur on the surface of porous carbon influences CO2 adsorption to a great extent compared to pristine carbons. This critical review summed up the synthesis procedure, characterization protocol and surface characteristics of oxygen, nitrogen and sulfur functionalized porous carbons, specific type of functionalities in each type of heteroatom that particularly influences CO2 adsorption and computational results as well as experimental findings that corroborated the positive role of heteroatoms in CO2 separation. At the end, few sets of critical comments and recommendations have been provided on the need of accurate analysis, exact interpretation of the role of heteroatoms in CO2 separation and future direction of research that might benefit the CO2 separation by heteroatom doped carbons in real-world.

Selective Adsorption-Based Separation of Flue Gas and Natural Gas in Zirconium Metal-Organic Frameworks Nanocrystals.

Carbon capture from flue gas and natural gas offers a green path to construct a net-zero emissions economic system. Selective adsorption-based gas separation by employing metal-organic frameworks (MOFs) is regarded as a promising technology due to the advantages of simple processing, easy regeneration and high efficiency. We synthesized two Zirconium MOFs (UiO-66 and UiO-66-NH2) nanocrystals for selective capture and further removal of CO2 from flue gas and natural gas. In particular, UiO-66-NH2 nanocrystals have a smaller grain size, a large amount of defects, and pending –NH2 groups inside their pores which display effective CO2 selective adsorption abilities over CH4 and N2 with the theoretical separation factors of 20 and 7. This breakthrough experiment further verified the selective adsorption-based separation process of natural gas and flue gas. In one further step, we used the Monte Carlo simulation to investigate the optimized adsorption sites and energy of CO2, N2 and CH4 molecules in the gas mixture. The significantly large adsorption energy of CO2 (0.32 eV) over N2 (0.19 eV) and N2 (0.2 eV) may help us to reveal the selective adsorption mechanism.

Ultra-selective carbon molecular sieve membranes for natural gas separations based on a carbon-rich intrinsically microporous polyimide precursor

A highly contorted, carbon-rich intrinsically microporous polyimide (PIM-PI) made from spirobifluorene dianhydride and 3,3-dimethylnaphthidine (SBFDA-DMN) was employed as a precursor for the formation of carbon molecular sieve (CMS) membranes at pyrolysis temperatures from 550 to 1000 °C. The high carbon content of SBFDA-DMN (∼84%) resulted in only 28% total weight loss during pyrolysis under a nitrogen atmosphere at 1000 °C. The development of the various microstructural textures was characterized by gas sorption analysis, Brunauer-Emmett-Teller (BET) surface area, X-ray diffraction, Raman spectroscopy, electrical conductivity, and gas transport properties. Heat treatment of a pristine SBFDA-DMN membrane at 550 °C resulted in reduced permeability for all gases (e.g.: PCO2 dropped from 4700 to 1500 barrer) as well as lower BET surface area from 621 to 545 m2 g−1. At 600 °C, new pores induced by pyrolysis increased the BET surface area to nearly that of the precursor and significantly improved gas separation performance. Above 600 °C, a progressive collapse of the micropores became evident with CMS membranes showing higher gas-pair selectivity but lower permeability. At 1000 °C, ultra-micropores comparable in size with the kinetic diameter of CH4 emerged and induced a prominent molecular sieving effect resulting in very high CH4 rejection. This strong size exclusion effect, further supported by gravimetric gas sorption measurements, resulted in unusually high N2/CH4 and CO2/CH4 selectivities of 35 and 1475, respectively.

Preparation of Indigenous Coppor Oxide Nanoparticles for Desulfurization of Natural Gas

Nanotechnology has attained significant concern in the field of Environmental Protection, Health Risk Energy, Material Science, Biotechnology, Information Technology, Pharmaceuticals, Tissue Engineering, Cosmetics, Food and Agriculture, and others. In this research the preparation of indigenous copper oxide Nanoparticles (Cu 2 O NPs) were prepared by the bottom up approach in the presence of Sodium do Decyl Sulfate (SDS). Material properties of Copper oxide NPs such as Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Fourier Transforms Infrared (FTIR) spectroscopy were also studied. The SEM demonstrated the surface of indigenous Copper Oxide NPs was non-agglomerated powders with irregular ball resembling particles. The X-ray Diffraction (XRD) analysis explained that the Cu 2 O NPs were highly crystalline in nature with average size was found to be 3.5 nm ranging from 2 to 5 nm were recorded by the help of scherrer formula. The Fourier transforms infrared (FTIR) spectroscopy described the carbonyl group are responsible for formation of stable indigenous Cu 2 O NPs. These stable Indigenous cuprous oxide nanoparticles would be applied for the desulfurization of natural Gas separation purpose. Keywords: Indigenous, Copper oxide nanoparticles (Cu 2 O NPs), chemical reduction, SDS, morphology, desulfurization and natural gas. DOI : 10.7176/CPER/61-04 Publication date : April 30 th 2019

Natural gas separation at CO2CRC's Otway National Research Facility

CO2CRC, in collaboration with the University of Melbourne and the University of New South Wales, is testing two novel CO2 capture technologies designed for both on-shore and off-shore natural gas applications in a state-of-the-art experimental capture rig at CO2CRC’s Otway National Research Facility. The goal is to develop robust and compact technology for high pressure natural gas separation over a range of adjusted high CO2 concentrations mimicking various gas field conditions. These technologies would facilitate developing new gas fields to recover methane in a cost-effective manner which is currently uneconomical with conventional technologies. In the first stage of testing, commercially available materials (adsorbents and membranes) were used for benchmarking. Results from both adsorbent and membrane technologies are encouraging with respect to recovery and purity of CO2 and methane with the prospect of commercial application.

A ligand conformation preorganization approach to construct a copper–hexacarboxylate framework with a novel topology for selective gas adsorption

A ligand conformation preorganization strategy was employed to design a hexacarboxylate ligand, and its corresponding copper-based MOF was constructed, exhibiting a novel topological structure and the potential for the separation and purification of acetylene and natural gas.

Production and functionalization of carbon nanotubes for application in membrane synthesis for natural gas separation

Abstract In this study, carbon nanotubes (CNTs) were produced using catalyst-assisted chemical vapour deposition method. Ferrocene was used as the catalyst. Effects of carbon sources (acetylene and methane) and production conditions (temperature and type of carrier gas) on the quality of as-produced CNTs were investigated using field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), electronic precision balance (EPB) and raman spectroscopy. The best of as-produced CNTs was purified and functionalized using carboxylation protocol. The surface chemistry, thermal stability, textural property and crystallinity of functionalized CNTs (FCNTs) were obtained using Fourier transform infrared spectroscopy (FTIR), Thermo-gravimetric analysis (TGA), N2 physisorption at 77 K and X-ray diffraction (XRD), respectively. CNT produced from methane and argon at 900 °C has the best quality with ID/IG ratio of 0.17 while the CNT produced from acetylene and mixture of argon and hydrogen at 1000 °C has the highest yield of 1.78 mg/s. FTIR confirms successful functionalization of CNTs. The degree of functionalization obtained from TGA is consistent with that of EPB. N2 physisorption at 77 bK indicates increase in pore volume and average pore size of the FCNTs indicating more adsorption sites for the adsorbate. Thereby suggesting that FCNT could be a good filler in membrane synthesis for gas separation.

Semi-clathratic impact of tetrabutylammonium hydroxide on the carbon dioxide hydrates

In the present experimental study, the phase behaviour of Tetrabutylammonium hydroxide (TBAOH) on Carbon dioxide (CO2) hydrates is evaluated via the T-cycle method. All the experiments performed in high-pressure hydrate reactor for various concentrations of TBAOH (1, 5 and 10 wt%) at moderate pressure and temperature ranges of 2.0-4.50 MPa and 276.0-285.0 K, respectively. The hydrate dissociation enthalpy (ΔHdiss) is also calculated for all the studied systems via Clausius Clapeyron equation. Results revealed that the TBAOH able to shift the hydrate liquid vapour equilibrium (HLwVE) curve towards higher temperature and lower pressure regions hence provide the promotional impact on all the studied concentrations. 10 wt% TBAOH able to heighten hydrate promotional impact (ΔŦ) up to 1.15 K. Additionally, enthalpy (ΔHdiss) data revealed that the promotional impact of TBAOH attributed due to the semi-clathratic nature of TBAOH. Thus, it can be concluded that the studied TBAOH in the present work has the immense potential for the industrial applications like natural gas separation and gas storage.

Copolymers of 1-(3,3,3-Trifluoropropyldimethylsilyl)-1-Propyne with 1-Trimethylsilyl-1-Propyne as Membrane Materials for Separation of Gas Mixtures Containing Hydrocarbons

Fluorinated copolymers with different compositions and geometric structures have been prepared from 1-trimethylsilyl-1-propyne and its fluorinated containing analogue 1-(3,3,3-trifluoropropyldimethylsilyl)-1-propyne and then studied. The copolymers combine resistance to different hydrocarbons with high permeability coefficients and high selectivity of n-butane separation from its mixture with the noncondensable hydrocarbon methane. High microporosity of the copolymers is confirmed by the results of the determination of the pore volume and pore surface area using low-temperature sorption of nitrogen and the investigation of the film surface by atomic force microscopy (AFM). It has been found that microporosity, which determines the transport properties of the copolymers, depends on both their comonomer composition and the microstructure formed at the stage of polymer synthesis catalyzed by a certain catalyst system. In particular, the copolymers produced in the presence of a TaCl5–Ph3Bi catalyst have a greater pore size and a larger pore surface area relative to copolymers with a similar composition formed in the presence of the NbCl5–Ph3SiH system. The high values of gas transport parameters of the obtained copolymers and their selectivity for recovery of condensable hydrocarbons from vapor–gas mixtures together with resistance to higher hydrocarbons make these copolymers promising membrane materials, e.g., for use in natural gas conditioning processes or separation of C3+ hydrocarbons from associated petroleum gas.

Effect of The natural Green Materials on Methane Hydrate Formation Kinetics

The kinetic effect of resin (terpene) and ajinomoto (monosodium glutamate) for methane hydrate formation was reported. The induction time of 0.2wt% natural green materials was measured in a sapphire hydrate reactor at 12°C at 9.5MPa. The induction time of all materials were found to be less than pure water. In the presence of resin induction time decreased 20% more than pure water and the initial rate of hydrate formation was enhanced. Resin enhanced the rate of methane hydrate formation 17% more than pure water. However, compared to SDS the rate of hydrate formation by both natural materials was less. Moreover, natural materials consumed more methane during hydrate formation than pure water. In addition, resin promote methane hydrate formation and could act as suitable kinetic promoter for the natural gas separation, transportation and storage.

Combined Natural Gas Separation and Storage Based on in Silico Material Screening and Process Optimization

We propose an intensified process for combined separation and storage (CSS) of natural gas from various unconventional sources using a single multifunctional unit. The CSS process involves selectively storing methane in a column filled with an existing nanoporous zeolite material, while venting out the impurities. A multiscale model is used to optimize the methane storage and screen for the top zeolites under minimum purity requirements and loss constraints. Adsorption properties for different zeolites are obtained via Monte Carlo simulations. Zeolite SBN with a high storage capacity for pure methane is found to be most suitable for combined separation and storage over a range of feed compositions. A rank ordered list of top zeolites is also obtained along with the optimal process conditions. It is, however, observed that the effectiveness of the intensification of natural gas separation and storage is limited by the constraint on the loss of methane exiting the column.

Incorporating Heavy Alkanes in Metal-Organic Frameworks for Optimizing Adsorbed Natural Gas Capacity.

Metal-organic frameworks (MOFs) as methane adsorbents are highly promising materials for applications such as methane-powered vehicles, flare gas capture, and field natural gas separation. Pre- and post-synthetic modification of MOFs have been known to help improve both the overall methane uptake as well as the working capacity. Here, a post-synthetic modification strategy to non-covalently modify MOF adsorbents for the enhancement of the natural gas uptake for the MOF material is introduced. In this study, PCN-250 adsorbents were doped with C10 alkane and C14 fatty acid and their impact on the methane uptake capabilities was investigated. It was found that even trace amounts of heavy hydrocarbons could considerably enhance the raw methane uptake of the MOF while still being regenerable. The doped hydrocarbons are presumably located at the mesoporous defects of PCN-250, thus optimizing the framework-methane interactions. These findings reveal a general approach that can be used to modify the MOF absorbents, improving their ability to be sustainable and renewable natural gas adsorption platforms.

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.

Investigations on the formation kinetics of semiclathrate hydrate of methane in an aqueous solution of tetra-n-butyl ammonium bromide and sodium dodecyl sulfate in porous media

ABSTRACTNatural gas hydrate is considered to be an attractive sustainable energy resource for the world. Hydrate as a technology can be of immense importance for various industrial processes, such as multicomponent natural gas separation, gas storage and transportation, and carbon dioxide capture from flue gases and sequestration. A variety of hydrate additives, which includes promoters (thermodynamics and kinetics) and porous media, are being researched to improve the hydrate formation kinetics. However, studies involving the combinations of these are rare in the open literature. In this work, the formation kinetics of methane hydrate/semiclathrate hydrate using tetra-n-butyl ammonium bromide (TBAB) and sodium dodecyl sulfate (SDS) aqueous solutions at various concentrations in a porous medium containing silica sand at initial hydrate formation pressures (7.5 and 5.5 MPa) and temperatures (273.65 and 276.15 K) have been investigated. All the experiments were conducted using 75% water saturation. Various kinetics parameters, such as gas uptake, gas-to-hydrate conversion, and induction time, have been reported. It was found that the combination of TBAB+ SDS showed favorable hydrate formation kinetics in porous media than the TBAB system. This work provides information for further studies involving semiclathrate hydrate applications for various industrial processes.

The inhibition effect of water on the purification of natural gas with nanoporous graphene membranes.

Molecular dynamics simulations are used to investigate the inhibiting effect of water on the natural gas separation with nanoporous graphene. The membrane separation process involves CH4 + N2 mixtures with and without the addition of water. The results show that water is able to form hydrogen bonds with nitrogen atoms located in a nanopore rim. This effect causes a decrease of separation selectivity as well as a reduction of gas permeation. In the extreme case, when the nanopore rim contains only nitrogen atoms, water agglomerates at the center of the nanopore and effectively closes down the permeation path. The conclusions are confirmed by the analysis of stability and kinetics of hydrogen bonds.