Natural Gas Purification Research Articles

Theoretical investigation of graphene kirigami membrane for natural gas processing

Membrane separation technology plays a vital role in natural gas processing due to its cost-effectiveness, excellent efficiency and low energy consumption. In this study, we demonstrate the superior permeability and selection capability of the graphene kirigami (GK) membrane for natural gas purification via molecular dynamics insights. The results indicate that the separation rate of the GK membrane can reach up to 4.1 × 106 GPU (gas permeance unit) with nearly 100% selectivity of the permeating gases mixture (H2S, CO2 and N2) over the non-permeating gas (CH4). Furthermore, the Monte Carlo simulation reveals that the unique geometry of the GK structure introduces a funnel-shaped adsorption channel to guide specific molecules’ separation and enhance the efficiency of the membrane. Compared with the nano-porous graphene (NPG) membrane, the gas separation rate of the GK membrane can be increased by more than four times. Moreover, the GK membrane does not require the modification of functional groups in natural gas purification, which provides great convenience for future applications in practical projects. The considerable potential of the GK membrane underpinned by the findings of this study will attract broad interest in the field of separation and purification.

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

Determination of mass transfer coefficient of CO2 removal in water-in-oil emulsion

The removal of carbon dioxide is an important process in natural gas purification since its lower down the calorific value of the natural gas. In addition, carbon dioxide also capable of forming corrosion in the pipeline, thus its removal is crucial. Water-in-oil emulsion was proposed in this research since the absorption of carbon dioxide in emulsion would be an effective method to prevent corrosion. However, the absorption capability of the emulsion and the mass transfer coefficient of carbon dioxide during absorption process needs further investigation. The aim of this study is to determine the diffusivity and mass transfer coefficient of carbon dioxide in the emulsion and observed the correlation between mass transfer coefficient and the carbon dioxide absorption values obtained from experiment. In this study, water-in-oil emulsion was prepared by mixing the aqueous phase and organic phase solutions under two different formulation conditions. Firstly, the methyldiethanolamine (MDEA) and 2 amino-2-methyl-1-propanol (AMP) blending was mixed in different alkaline solution; sodium hydroxide (NaOH) solution, potassium hydroxide (KOH) solution and distilled water (H2O) to form aqueous phase solution. Secondly, MDEA was combined with different alkanolamines; dimethylethanolamine (DMEA), diethanolamine (DEA) and triethanolamine (TEA) in KOH solution to form another aqueous phase solution. The synthesized aqueous phase is then mixed with the organic phase consists of kerosene and Span-80 mixtures. Furthermore, viscosity and particle sizes of the emulsions at different emulsion formulations were measured and the diffusivity and mass transfer coefficients of carbon dioxide were calculated. This study showed that, by using suitable emulsion formulation containing MDEA/AMP in KOH solution, the estimated value of diffusivity and mass transfer coefficient of carbon dioxide was 1.0876 × 1010 m2/s and 1.15 × 103 m/s respectively, with viscosity of 261.03 mPa s and particle size of 189.71 nm was achieved. It was found the diffusion coefficient and mass transfer coefficient of carbon dioxide is highly influenced by the characteristics of emulsion such as viscosity and particles sizes.

Study on the Performance of Cellulose Triacetate Hollow Fiber Mixed Matrix Membrane Incorporated with Amine-Functionalized NH2-MIL-125(Ti) for CO2 and CH4 Separation

The increase in the global population has caused an increment in energy demand, and therefore, energy production has to be maximized through various means including the burning of natural gas. However, the purification of natural gas has caused CO2 levels to increase. Hollow fiber membranes offer advantages over other carbon capture technologies mainly due to their large surface-to-volume ratio, smaller footprint, and higher energy efficiency. In this work, hollow fiber mixed matrix membranes (HFMMMs) were fabricated by utilizing cellulose triacetate (CTA) as the polymer and amine-functionalized metal-organic framework (NH2-MIL-125(Ti)) as the filler for CO2 and CH4 gas permeation. CTA and NH2-MIL-125(Ti) are known for exhibiting a high affinity towards CO2. In addition, the utilization of these components as membrane materials for CO2 and CH4 gas permeation is hardly found in the literature. In this work, NH2-MIL-125(Ti)/CTA HFMMMs were spun by varying the air gap ranging from 1 cm to 7 cm. The filler dispersion, crystallinity, and functional groups of the fabricated HFMMMs were examined using EDX mapping, SEM, XRD, and FTIR. From the gas permeation testing, it was found that the NH2-MIL-125(Ti)/CTA HFMMM spun at an air gap of 1 cm demonstrated a CO2/CH4 ideal gas selectivity of 6.87 and a CO2 permeability of 26.46 GPU.

Investigation of the adsorption properties of the sorbent obtained in the process of modification of clinoptilothite in the purification of natural gas from sulfur compounds

The study of the possibility of using modified clinoptilolite as an adsorbent and the adsorption properties of zeolite in the purification of natural gas supplied to gas processing plants from sulfur compounds contained in it is an urgent task. In the experimental study, the adsorbent fraction was chosen as 0.5÷1.0 mm, density - 0.8 g/cm3, adsorbent layer height - 600 mm. Optimal conditions are selected in such a way that the pressure in the experimental process is 0.2-5.0 MPa, the amount of mercaptans in the purified natural gas is 50÷400 mg/nm3, the temperature is 20÷25°C, the gas flow rate is 0.2÷250°C. 0.25 m/s. Experiments IR spectroscopic studies were carried out on a NikoletIS-10 IR spectrometer in the frequency range 400-5000cm-1. The phase composition was studied using a 2DPHASER Bruker X-ray analyzer (CuKa - radiation, 2nd, 20-80 degrees). Electron microscopic images were taken under a Hitachi TM-3000 microscope. Elemental analysis was performed at Oxford Science. The intensity and accuracy of desorption of sulfur compounds adsorbed on clinoptilolite at 250°C, the same results were obtained on NaX zeolite at 320°C. The catalytic activity of regeneration of clinoptilolite at lower temperatures than that of NaX zeolite, although small, made it possible to minimize the decomposition of mercaptans. The purpose of this work is to study the adsorption properties of the sorbent obtained in the process of modifying clinoptilotite during the purification of natural gas from sulfur compounds.

Thermodynamics of Carbon (IV)-Oxide adsorption on NaA Zeolite obtained by modification of angren kaolin

Purification of natural gas from carbon dioxide is extremely important for the gas processing industry of Uzbekistan. Type A zeolites are the most suitable for this purpose. The patterns of water adsorption in the NaA zeolite have been considered. It was found that an appreciable amount of water is adsorbed in β-cavities. The carbon dioxide molecule is somewhat larger than the water molecule and, therefore, at room temperature it is unable to penetrate into the β-cavities through the six-membered oxygen windows of 2.6 Å diameter and form there ion-molecule clusters with sodium cations. However, the cations themselves can migrate from the β-cavities to the α-cavities under the influence of adsorbing molecules.

A linker conformation induced metal-organic framework with high stability and efficient upgrading of natural gas.

Natural gas plays an important role in daily life and the petrochemical industry, but there are often large amounts of impurities which prevent the full use of methane in natural gas. Developing excellent adsorbents to purify CH4 from multi-component mixtures is crucial, but also faces great challenges. Here, by utilizing a ligand conformation preorganization strategy, we employ a flexible nonplanar hexacarboxylate ligand with C2 symmetry to successfully construct a robust microporous metal-organic framework {[Cu3(bmipia)(H2O)3]·(DMF)(CH3CN)2}n (GNU-1, bmipia = 5-[N,N-bis(5-methylisophthalic acid)amion] isophthalate) with an unprecedented topology. More importantly, the obtained GNU-1 not only exhibits good stability in acid-base and water environments, but also shows potential utility as an adsorbent for efficient separation and purification of natural gas under ambient conditions. The adsorption isotherms of GNU-1a (activated GNU-1) exhibit strong binding affinities for C2H6 and C3H8, a remarkable uptakes of C3H8 (6.64 mmol g-1) and C2H6 (4.6 mmol g-1) and an excellent selectivity of 330.1 and 17.5 for C3H8/CH4 and C2H6/CH4 mixtures, respectively, at 298 K and 1 bar. The breakthrough experiments demonstrate that the ternary CH4/C2H6/C3H8 mixtures are completely separated using a fixed-bed separator packed with GNU-1a at ambient temperature and also show great potential for recovering the C2H6 and C3H8 contents from natural gas. Finally, Grand Canonical Monte Carlo simulations are adopted to ascertain potential gas adsorption mechanisms. This work proves the feasibility of optimizing the structure and pore size of MOF materials by regulating the conformation of ligands for application in the field of light hydrocarbon adsorption/separation.

Determination of adsorption capacities of N2 and CO2 on commercial activated carbon and adsorption isotherm models

In today’s technologies of gas purification systems, adsorption processes offer more advantages than traditional processes (amine absorption and cryogenic distillation). Thanks to advantages such as high efficiency, low energy consumption and ease of operation, the adsorption process plays an important role in today’s natural gas purification and carbon capturing processes. In order to bring natural gas to the usage standards and to ensure carbon capture in the emission sources (coal mines, landfills, agricultural activities, etc.) that emit CO2-CH4 as a result of human activities, it is extremely important to purify impurities such as CO2 and N2, which are highly present in the gas mixture. In the study, the adsorption of N2 and CO2 gases on activated carbon and the effect of pressure and temperature on adsorption were examined. The operating conditions pressure range was 1-6 bar and temperatures below room temperature. Experimental studies were carried out in laboratory scale adsorption cell system. As a result of the studies, it was determined that the adsorption capacity of activated carbon N2 and CO2 increased with pressure. N2 adsorption capacities were determined between 0.4-7.8 mmol/g and CO2 adsorption capacities were determined in the range of 2.7-7.4 mmol/g. In addition, Langmuir and Freundlich isotherm models were created, model parameters were examined and the adsorption behaviour of activated carbon for CO2 and N2 gases was obtained.

Preparation of Mixed Matrix Membranes Containing COF Materials for CO<sub>2 </sub>Removal from Natural Gas/Review

Gas separation membranes are one of the most important processes in purifying natural gas. CO2 reduction of natural gas is essential for purifying the gas and increasing its calorific value. A covalent organic framework (COF) has been developed as a filler in mixed-matrix membranes (MMM) to separate gases. COF materials were chosen because of their economical rate, good thermal and chemical stability, and flexible microporous structure. Mixed matrix membranes (MMMs) have received significant interest for their improved permeability and selectivity in natural gas purification. The results of using COF combined with other chemicals added to MMM. It has been observed that CO2 permeability increases as the COF content in the MMM increases, which enhances the gas-separation performance of the MMM. This review evaluated and analyzed the current scientific and the technical breakthroughs in developing MMMs, especially the unique type of organic fillers, which has been the basis of numerous new research for CO2 separation.

Fabrication and evaluation of novel sulfur/epoxy resin composites

In recent years, and with the progress of oil and natural gas purification processes, it has been noticed that huge quantities of sulfur are produced with millions of tons as byproducts, which is considered a dangerous substance that may threaten the safety and health of the environment. So, this study aims to maximize elemental sulfur benefits in construction applications, especially in the coating sector. In this study, sulfur has been modified to be used with epoxy as a high-performance coating material. Firstly, sulfur was modified with linseed oil at 160 °C. The modified sulfur was chemically characterized by using FTIR and XRD. After that, epoxy was then partially replaced by polymeric sulfur with different weight percentages starting from 10 to 40%. Then, the hardener was added to form cured sulfur/epoxy composites. Different techniques were used to examine the morphology of the prepared composites such as AFM, polarizing microscope, and SEM. The thermal study was also conducted by TGA. In addition, the mechanical properties were comprehensively studied including Young’s modulus, toughness, tensile strength, hardness, and adhesion. The results approved that Young’s modulus, toughness, tensile strength, hardness, and adhesion of the PC4 composite have been improved by 54%, 87%, 15%, 40%, and 33%, respectively. Moreover, the prepared composites give high thermal stability than virgin epoxy. The overall results approved that the epoxy can be partially replaced by modified sulfur with high weight ratios reached to 40%.

Ligand-Functional Groups Induced Tuning MOFs' 2D into 1D Pore Channels for Pipeline Natural Gas Purification.

The solvothermal reactions of CoCl2 ⋅ 6H2 O, 3,5-pyridinedicarboxylic acid (H2 L) and isonicotinic acid (HL1 )/3-amino isonicotinic acid (HL2 )/3-chloro isonicotinic acid (HL3 ) successfully led to three tfz-d topological pillar-layer [Co4 (μ-F)2 (COO)6 (NC5 H4 )4 ] cluster-based MOFs, namely, [Co4 (μ-F)2 (L)2 (L1 )2 ⋅ 2DMA] ⋅ DMA ⋅ 2H2 O (SNNU-Bai76, SNNU-Bai=Shaanxi Normal University Bai's group), [Co4 (μ-F)2 (L)2 (L2 )2 ⋅ 2H2 O] ⋅ 2DMA ⋅ 2H2 O (SNNU-Bai77) and [Co4 (μ-F)2 (L)2 (L3 )2 ⋅ 2H2 O] ⋅ 2DMF ⋅ 2H2 O (SNNU-Bai78). With the 2D pore channels in SNNU-Bai76 and SNNU-Bai77 being tuned to the 1D pore channel in SNNU-Bai78, C3 H8 and C2 H6 adsorption uptakes are apparently improved and the IAST selectivities of C3 H8 /CH4 and C2 H6 /CH4 almost remain, which indicate that SNNU-Bai78 may be one potential separation material for the pipeline natural gas purification. These were further confirmed by the breakthrough experiments for the simulated pipeline natural gas (C3 H8 /C2 H6 /CH4 : 5/10/85 gas mixture) of three isostructural MOFs. Furthermore, GCMC simulations revealed that due to one of the pore channels blocked by Cl atoms in a couple of 3-chloro isonicotinic acid with the changed conformation as the pillar, the pore wall of the formed 1D pore channel in SNNU-Bai78 may interact with the adsorbed C3 H8 or C2 H6 molecule more strongly, for which more atoms of framework at the new adsorption site will interact with the adsorbed gas molecule by more intermolecular interactions. This was also evidenced by the increased binding energies, being consistent with the tuning of adsorption enthalpies for C3 H8 and C2 H6 gas molecules, and the reduced C3 H8 and C2 H6 gas diffusion coefficients in SNNU-Bai78. Very interestingly, this work is the first example of finely tuning the pore connectivity of MOFs toward strengthened host-guest interactions for the gas adsorption and separation.

Constructing multiple sites of metal-organic frameworks for efficient adsorption and selective separation of CO2

Efficient capture and selective separation of CO2 is of great significance for alleviating the greenhouse effect. However, it is still a challenge to achieve efficient, reversible and selective capture of CO2. Here, stable Al-based MOFs with multiple adsorption sites were constructed for capture and selective separation CO2. It was found that MOF-303(Al) with multiple active sites (μ-OH, N-H, N-N and H-C) demonstrated a high CO2 capacity of 5.1 mmol/g, and can be recycled for more than 50 times. Moreover, MOF-303(Al) shows excellent selective separation performance of CO2 from CO2/CH4 and CO2/N2 mixtures, which could be used as a potential material for natural gas purification. Mechanism results revealed that the excellent CO2 adsorption and selective separation performance is arose from the multiple adsorption sites (μ-OH, N-H, N-N and C-H) of MOF-303(Al), where the contribution of μ-OH and N-H adsorption sites are higher than that of N-N and H-C sites.

Comparative Analysis of Natural Gas Purification Efficiency for Low Degree of Expansion Using a Throttle and a High-Flow Three-Flow Vortex Tube

Comparative Analysis of Natural Gas Purification Efficiency for Low Degree of Expansion Using a Throttle and a High-Flow Three-Flow Vortex Tube

(Invited) 20 Years of CO2 Capture By Ionic Liquids, Molecular Liquids, and Liquids in-between

In 2002 we reported the first synthesis and use of a functionalized ("task-specific") ionic liquid for the reactive but reversible capture of CO2. Our original application target was the use of these salts in natural gas purification. However, in succeeding years considerable fervor grew up around us focused on accomplishing large-scale CO2 capture due to concerns about its contribution to global climate change, and that has since supplanted the former application as a major driver of our research. Recognizing that our early materials were likely prohibitively expensive for large scale use, we then spent five years devising new ones which could be made inexpensively from bulk commodity chemicals. In the time since, work with that class of salts, including the edible-in-principle salt choline taurate, has continued apace. These efforts have now resulted in systems which are being actively assessed by the Navy and NASA for closed-system removal of CO2 from breathing air, and which are being tested at pilot plant scale, in collaboration with Norton Engineering, for industrial emissions gas CO2 capture, as well as CO2 capture from ambient air. A brief discussion of the timeline of these developments will be presented, as will details about the ionic liquids currently being used in these tests and our results to date. In addition, we will briefly discuss the potential for using in-situ electrochemical reduction of CO2 in the 'loaded' ILs as a means to convert them into value-added products. Finally, we will also briefly comment on terminology as it relates to ionic liquids, molecular liquids, and liquids "in-between." Figure 1

Influence of shock wave/boundary layer interaction on condensation flow and energy recovery in supersonic nozzle

Shock train phenomenon occurs when the Mach number increases during the process of energy recovery in the nozzle. However, the reduction of wet natural gas purification efficiency and the increase in energy loss can be caused by shock wave in the supersonic separator. This study focused on the condensation characteristics and pressure energy recovery efficiency under the shock train in the Laval nozzle. A mathematical model was developed for the process of methane-water vapour supersonic condensation and verified by condensation experiments. The results demonstrate that the length of the boundary layer separation interval can be reduced by 0.142 m with a decrease of 0.909 upstream Mach number from 2.367 to 1.458. Multiple nucleation of vapour occurs under the effect of shock train. The droplet growth interval increases from 0 to 0.0859 m and the liquid mass fraction enhances from 0 to 0.12% as the pressure energy recovery efficiency decreasing from 80% to 30%. This indicates that the suitable pressure energy recovery efficiency from 40% to 60% can effectively control the location of the shock train and organize its structure in the nozzle to reduce the separation length of boundary layer and improve the nozzle liquefaction efficiency.

Numerical Simulation of Acid Gas Distribution and Corrosion Characteristics in Connecting Pipe of Lean/Rich Amine Heat Exchanger

In the high sulfur natural gas purification unit, the connecting pipe of a lean/rich amine heat exchanger is extremely susceptible to corrosion due to the acid gas and amine liquid condition. This work numerically investigated the gas–liquid flow and corrosion of the real-scale connecting pipeline with two horizontal sections, one vertical section and four elbow sections. The effect of acid gas holdup on the gas–liquid flow pattern, distribution of velocity and pressure, and corrosion rate was investigated using an experimental validated model. With an increase in the acid gas fraction from 0.03 to 0.12, the flow pattern of the horizontal section changes from bubbly flow to a stratified flow in the horizontal section, while the flow pattern of the vertical section and elbow section keeps bubbling, and the proportion of gas bubbles increases in the vertical section and all elbow sections. The maximum pressure gradient was observed on the top of the horizontal section. The most serious corrosion section was found out on the outlet of the first elbow section where the gas liquid flow starts to stratify, which is consistent with the measured minimum wall thickness. A solution measure for anti-corrosion acid gas in the pipeline was proposed by adding a bifurcated pipe to separate the acid gas in the first horizontal section. The accumulated acid gas was effectively thrown out from the outlet of the bifurcated pipe. This method provides a promising way to eliminate the acid gas in the pipe and avoid forming stratified flow, which is helpful for prolonging the service life of the pipe.

Development and Simulation of Natural Gas Refining Mechanism Based on Exergy Study

Abstract: This study will examine a domestic gas field in Bayelsa, Nigeria, to improve the natural gas purification process. This study's main goals are to reduce energy use and improve purification levels. A complete technical and economic assessment was carried out utilizing Aspen Plus TM software. The absorption parameters reflux ratio and stage number were estimated using single-factor sensitivity analysis. The energy system's energy-saving technique was used to examine the heat transfer mechanism and recommend a change. The optimization results show that the suggested system has better purifying performance, lower total energy consumption, and 9 percent improved energy efficiency.

Development and coalescence mechanism of an improved filter cartridge for oil mist separators

Oil mist coalescence and filtering are extensively used in the fields of natural gas purification and chemical production. However, it remains technically challenging to capture high-concentration, small-sized, oil mist droplets under complex industrial field conditions. To solve this problem, three novel high-efficiency coalescence filter cartridges are proposed, which have improved filter material arrangements. The filtering performance of the cartridges was evaluated in the laboratory and at a natural gas pipeline pressure station under different working conditions to understand the mechanism by which high-concentration small-sized droplets are captured. According to the laboratory results, the filtration efficiency for droplets> 0.2 µm can reach 99.99% if the first layer in the cartridge has a small pore size (1.5 µm). The use of a filtering material with a large pore size can reduce the pressure drop. An arrangement of layers with increasing pore sizes can significantly improve the quality factor of the cartridges and decrease secondary entrainment. In the field test, the size distributions of the oil mist under compressor “hot standby” and operating conditions were gained for the first time. The median size of oil mist droplets was 1.2 µm during hot standby and 0.5 µm during operation. Under both compressor modes, the downstream oil mist concentrations of the proposed cartridges were> 95% lower than that of an existing commercial cartridge once filtering reached a steady state. In a long-cycle test under field conditions, the proposed cartridges showed more stable filtering performance than the existing product, with the filtration efficiency being about 40% higher after 15 days. Moreover, the oil mist coalescence mechanism was determined by microscopic characterization of liquid channels.

Exergy, advance exergy, and exergo-environmental based assessment of alkanol amine- and piperazine-based solvents for natural gas purification

Purification of Natural gas is vital for utilizing it as a source of energy harvesting for the world. Amine-based chemical absorption technique is the most utilized in the gas field for the purification of gas that ensures the purity of the sweet gas stream with the elimination of carbon dioxide. However, it is considered an energy-intensive process to deal with considerable energy loss and environmental damage to the ecosystem. Five cases have been developed in this study based on various blends comprising mono and tertiary amines in combination with piperazine with a focus on the use of Aqueous Monodiethanolamine (Aq. MDEA), Aqueous Monoethanolamine (Aq. MEA) and piperazine (Pz) for the CO2 sequestration from the sour natural gas extracted from the remote location located in the province of Baluchistan in Pakistan. The use of exergy, advanced exergy, and exergo environment for optimizing and selecting a suitable solvent combination that may result in an effective separation process has been proposed. Five cases have been developed based on various blends such as mono and tertiary amines combined with piperazine. From the results of all the studied scenarios, Case IV, based on the combination of Aqueous monoethanolamine and piperazine, provides reduced exergy destruction of 2551.7 KW. It was observed that the maximum removal of CO2 around 99.87 wt% is achieved in case IV. In addition, advance exergy analysis also highlights that case-IV has a venue of 25% exergy destruction avoidable, which would further enhance its performance. Nevertheless, still, case-IV has 75% exergy destruction unavoidable. The environmental factors show that Case-IV has a reduced exergy destruction factor of 0.96, a highly environmentally benign choice as a solvent with a high value of 1.03, and case-IV has the higher operational stability and higher exergy efficiency with an exergy stability value of 0.40. Therefore, monoethanolamine combined with piperazine to be an effective and efficient solvent blend that could be an energy-effective approach for sweetening the natural gas.

Activated carbon from polyurethane residues as molecular sieves for kinetic adsorption/separation of CO2/CH4

Activated carbon-based molecular sieves were synthetized, characterized and their kinetics of adsorption were evaluated to be used in separation processes of CO2/CH4 mixtures. Polyurethane (PU) foams were used as carbon precursors and the PU-derived carbons were physical activated with CO2. All the samples present a preferential adsorption of CO2 over methane in kinetic adsorption experiments. Samples activated at 800 ºC during 6 h exhibited the highest selectivity due to the absence of methane adsorption at lower resident times, which makes those samples very interesting for industrial processes of natural gas purification. Kinetic studies were performed to explain the kinetic profiles obtained, confirming that in the samples with smallest pore size, intraparticle diffusion was the limiting step, evidencing that certain oxygen groups favour CO2 adsorption, whereas adsorption was the limiting step in the samples with wider pores.