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Although zeolitic imidazolate frameworks (ZIFs) have bright prospects in wide fields like gas storage/separation, catalysis and medicine, etc., their large-scale applications are bottlenecked by the absence of their low-cost commercial production technique. Here, we report an unconventional method suitable for environmentally friendly and low-cost mass-production of ZIFs. In this method, taking the synthesis of ZIF-8 as an example, ZnO was used instead of Zn(NO3)2 in traditional solvent synthesis methods and CO2 was introduced to dissolve ZnO in aqueous solution of 2-methylimidazole (HMeim) and form water soluble salt ([ZnMeim]+[MeimCOO]-) at room temperature. Then, by removing CO2 through heating or vacuuming, Meim-ions are produced and instantaneously assemble with [ZnMeim]+s to generate ZIF-8 without any by-product. Due to the absence of strong acid anions (such as NO3− and Cl− et al.) in solution, the washing of filter cake required in the conventional approaches could be omitted and the filtrate containing only water and HMeim could be reused completely. This method is really green as no waste gas or liquid generates because CO2 and water could be recycled perfectly. It overcomes almost all bottlenecks occurred in commercial production of ZIF-8 when using traditional methods. A pilot plant was established for mass-production of ZIF-8 and hundreds kilograms of ZIF-8 was produced, which indicates that the new method is not only environmentally friendly but also low cost and commercial accessibility. It is expected that the new method would open an avenue for commercial applications of ZIFs.

The development of environmental friendly low dose hydrate inhibitors like kinetic hydrate inhibitors (KHIs) is of great significance for the flow assurance in oil & gas production and transportation. In this work, a combined molecular dynamic simulation and experimental verification approach was adopted to increase the efficiency of KHIs development. The inhibition effect of a series of copolymers (N-vinylpyrrolidone and N-acrylate) on hydrate growth was studied by using both molecular dynamics simulation and experimental approaches. The simulation results demonstrate that introduction of hydrophobic ester and butyl group in PVP is beneficial for the inhibition. The length of the alkyl chain of ester group plays an important role in improving inhibition performance. PVP-A, the one being introduced butyl ester group into PVP gets the best inhibition effect. In addition, inhibitors can restrict methane bubbles to re-dissolve into the liquid phase, thereby inhibiting the growth of methane hydrate. Increasing the interaction between KHIs and methane can also improve the inhibitory effect of KHIs. The experimental results confirm the reliability of the molecular dynamics simulation.

Effective recovery of hydrogen from refinery off-gas and coke oven gas, in which hydrogen and methane are key components, is increasingly important for the development of hydrogen energy. In this paper, we introduced a new energy efficient process for hydrogen purification from CH4/H2 mixture. Firstly, we conducted a phase equilibrium experimental study for CH4/H2 in zeolitic imidazolate framework-8 (ZIF-8)/glycol–water slurry. The simple absorption and desorption configuration is adopted for the continuous separation of CH4/H2 using ZIF-8/glycol–water slurry. The multi-stage pseudo-absorption modeling approach was introduced for the modeling and simulation of the absorption–adsorption and desorption columns via using multiple flash modules in Aspen Plus. The binary interaction parameters in the thermodynamic model were fitted by experimental data within an acceptable error (4.93%). The operating conditions (i.e., the number of theoretical stages, feed stage, flash pressure, and desorption pressure) were determined to increase H2 concentration in product and H2 recovery ratio. The energy performance of the process was also evaluated. Given the feed gas contains 50 mol% H2, the gas–slurry volume ratio of 43.27 is required to produce 95 mol% H2 with a high recovery of 97.94%. The total energy consumption per unit volume of product is 0.06254 kW·h/Nm3. Results indicate that the hybrid absorption-adsorption process is a promising energy efficient technique to separate CH4/H2 in the future.

Graphdiyne (GDY) membrane with intrinsic pore has potential for gas separation. Here we report a multistage gas separation of H2/CO2/N2/CH4 gas mixture through graphdiyne by applying tensile strain...

The increasing concentration of CO2 in atmosphere is deemed the main reason of global warming. Therefore, efficiently capturing CO2 from various sources with energy conservation is of great significance. Herein, a series of experiments were carried out to successfully test the slurry-based ab-adsorption method for continuously capturing CO2 in the large-scale cycled separation unit with cost-effect taking into account the scale-up criteria. A bubble column (with height 4900 mm and inner diameter 376 mm) and a desorption tank (with volume 310 L) are the essential components of the separation unit. The novel slurry used in this study was formed with zeolitic imidazolate framework-8 and 2-methylimidazole-water solution. The influence of operation conditions was investigated systematically. The results show that increasing sorption pressure and slurry height level, decreasing gas volume flow and sorption temperature are beneficial for separation processes. The volume fraction of CO2 in the feed gas was also studied. Although the scale-up effect had been observed and it was found that it exerted a negative effect on CO2 capture, depending on experimental conditions, CO2 removal efficiency could still reach 85%-95% and the maximum CO2 loading in the recycled slurry could be up to 0.007 mol⋅L−1⋅kPa−1. Furthermore, the slurry-based method could be operated well even under very moderate regeneration conditions (333 K and 0.05 MPa), which means that the novel approach shows greater energy conservation than traditional amine absorption methods.

Research on gas hydrates is relevant to many industrial issues including flow assurance in oil and gas production and transportation, exploitation of new energy deposits in the form of natural gas ...

Morphology observation is an important approach to studying the mechanism of one method of improving hydrate formation. In this study, morphology change in methane hydrate formation and dissociatio...

Coal bed methane has been considered as an important energy resource. One major difficulty of purifying coal bed methane comes from the similar physical properties of CH4 and N2. The ZIF-8/water-glycol slurry was used as a medium to separate coal bed methane by fluidifying the solid adsorbent material. The sorption equilibrium experiment of binary mixture (CH4/N2) and slurry was conducted. The selectivity of CH4 to N2 is within the range of 2–6, which proved the feasibility of the slurry separation method. The modified Langmuir equation was used to describe the gas-slurry phase equilibrium behavior, and the calculated results were in good agreement with the experimental data. A continuous absorption–adsorption and desorption process on the separation of CH4/N2 in slurry is proposed and its mathematical model is also developed. Sensitivity analysis is conducted to determine the operation conditions and the energy performance of the proposed process was also evaluated. Feed gas contains 30 mol% of methane and the methane concentration in product gas is 95.46 mol% with the methane recovery ratio of 90.74%. The total energy consumption for per unit volume of product gas is determined as 1.846 kWh Nm−3. Experimental results and process simulation provide basic data for the design and operation of pilot and industrial plant.

Tensile strain of porous membrane materials can broaden their capacity in gas separation. In this work, using van der Waals corrected density functional theory (DFT) and molecular dynamics (MD) simulations, the performance and mechanism of CO2/CH4 separation through strain-oriented graphdiyne (GDY) monolayer were studied by applying lateral strain. It is demonstrated that the CO2 permeance peaks at 1.29 × 106 gas permeation units (GPU) accompanied with CO2/CH4 selectivity of 5.27 × 103 under ultimate strain, both of which are far beyond the Robeson's limit. Furthermore, the GDY membrane exhibited a decreasing gas diffusion energy barrier and increasing permeance with the increase of applied tensile strain. CO2 molecule tends to reoriented itself vertically to permeate the membrane. Finally, the CO2 permeability decreases with the increase of the temperature from 300 K to 500 K due to conserving of rotational freedom, suggesting an abnormal permeance of CO2 in relation to temperature. Our theoretical results suggest that the stretchable GDY monolayer holds great promise to be an excellent candidate for CO2/CH4 separation, owing to its extremely high selectivity and permeability of CO2.

In this work, the mixed porous liquid–solid made of zeolitic imidazolate framework-8 (ZIF-8), 2-methylimidazole (mIm), glycol, and water was first used in a pilot-scale packed system for CO2 captur...

As the source of fossil fuels moves toward gas, pipeline flow assurance has attracted considerable efforts in developing gas hydrate inhibitors, especially kinetic inhibitors (KIs), for prevention ...

Both n-butane and iso-butane are important petrochemical raw materials, and their separation is of great significance and full of challenge because of their close boiling characteristic. The ZIF-8 slurry formed with a novel mixed solvent M-water solution as sorption media was adopted to separate the mixture with high efficiency. The iso-/n-butane selectivity of ZIF-8/M-water slurries is as high as 890 with high kinetic performance, even transcending the upper limit of the new materials or membranes. More encouragingly, continuous pilot separation device was established and test results show that the purity and recovery ratio of iso-butane product achieved 99.46 mol% and 87% respectively, which are remarkably superior to the corresponding performance (98.56 mol% and 54%) of the industrial distillation tower. To our best knowledge, this is the first industrial pilot test using MOFs for gas separation, and also an important step forward to the commercial application of MOFs in gas separation.

Vinyl lactam-based polymers have been shown to be excellent kinetic hydrate inhibitors (KHIs), inhibiting the formation and growth of methane hydrate under low subcooling conditions. However, under moderate/high subcooling conditions, they lose their inhibitory effect and can even be converted into hydrate promoters. In this work, molecular dynamics simulations were employed to explore the invalidation mechanism of two vinyl lactam-based KHIs, namely, PVP-A and PVP, under high subcooling conditions. By analyzing the nucleation and growth trajectories of methane hydrate in the absence/presence of KHIs, we found that the addition of KHIs could shorten the nucleation time of methane hydrate by reducing the mass transfer resistance of methane and water molecules and accelerating the formation of the hydrate precursor. Additionally, KHIs can facilitate the formation and survival of sII hydrate by improving the kinetic superiority of the methane-water homogeneous solution.

A large amount of oily sludge is being produced in the petroleum industry each year and becoming a serious environment issue. An efficient method for separating oil from oily sludge is of great significance for disposing this hazard. In this study, a novel method—water-enhanced CO2 extraction, was proposed to recover oil from the oily sludge. The oily sludge is mixed with water and CO2 thus allowing the oil to be swollen by CO2 under a certain temperature and pressure, leave the solid particles and float upwards to the top interface of the water phase owing to gravitational forces. A series of experiments were conducted to verify the method, optimize the operation conditions and compare it with the traditional approaches like the ultrasonic treatment, the solvent extraction and the supercritical extraction. The results show that up to 80 wt% of the oil in the oily sludge could be recovered using this new method, which is much higher than that using the traditional methods. The most suitable operation temperature, pressure, sludge/water ratio and stirring time were found to be 313–323 K, 3–4 MPa, 1:7 and 90 min, respectively. The proposed water-enhanced CO2 extraction method is efficient in increasing the oil recovery of oily sludge and decreasing its operation conditions compared with traditional oily sludge treatment methods.

Study on the gas hydrates in porous medium has great significance to the formation, accumulation and exploitation of natural gas hydrate (NGH). Consequently, we investigated the formation/dissociation of ethane hydrate in a sub-millimeter sized capillary in this work, and observed the appearance and kinetic rate during the hydrate formation/dissociation process. The dissociation equilibria of ethane hydrate in capillary was measured first, then the influences of hydrate memory effect (dissociation temperature and time) and degree of subcooling on ethane hydrate formation were obtained, respectively. The results demonstrate that hydrate forms more difficultly in capillary than in conventional macro-reactor because of the fluid resistance effect and poor mass transfer of gas-liquid. The appearance and formation kinetics of ethane hydrate are greatly influenced by the memory effect and subcooling degree. The morphology of ethane hydrate formation on the bubble surface in water bulk phase shows that “bridge effect” occurs during the hydrate formation and growth in capillary.

Natural gas hydrate (NGH) is a highly efficient and clean energy, with huge reserves and widespread distribution in permafrost and marine areas. Researches all over the world are committed to developing an effective exploring technology for NGH reservoirs. In this paper, four conventional in-situ hydrate production methods, such as depressurization, thermal stimulation, inhibitor injection and CO2 replacement, are briefly introduced. Due to the limitations of each method, there has been no significantly breakthrough in hydrate exploring technology. Inspired by the development of unconventional oil and gas fields, researchers have put forward some new hydrate production methods. We summarize the enhanced hydrate exploiting methods, such as CO2/N2–CH4 replacement, CO2/H2–CH4 replacement, hydraulic fracturing treatment, and solid exploration; and potential hydrate mining techniques, such as self-generating heat fluid injection, geothermal stimulation, the well pattern optimization of hydrate exploring. The importance of reservoir stimulation technology for hydrate exploitation is emphasized, and it is believed that hydrate reservoir modification technology is a key to open hydrate resources exploitation, and the major challenges in the process of hydrate exploitation are pointed out. The combination of multiple hydrate exploring technologies and their complementary advantages will be the development trend in the future so as to promote the process of hydrate industrialization.

Insights into the mechanism of hydrate nucleation are of great significance for the development of hydrate-based technologies, hydrate relevant flow assurance, and the exploration of in situ natural gas hydrates. Compared with the thermodynamics of hydrate formation, understanding the nucleation mechanism is challenging and has drawn substantial attention in recent decades. In this paper, we attempt to give a comprehensive review of the recent progress of studies of clathrate hydrate nucleation. First, the existing hypotheses on the hydrate nucleation mechanism are introduced and discussed. Then, we summarize recent experimental studies on induction time, a key parameter evaluating the velocity of the nucleation process. Subsequently, the memory effect is particularly discussed, followed by the suggestion of several promising research perspectives.

The structural transition of methane-ethane gas hydrates is generally observed during the forming process; however, it has seldom been reported during the dissociation process. Study on the dissociation behavior of methane-ethane hydrate below ice point has important implications on gas storage and transportation. It was also be helpful for the natural gas hydrate production by depressurization in permafrost zones. The dissociation of a series of methane-ethane hydrate samples at atmospheric pressure and temperatures below ice point (272.15–269.15 K) was performed, and the influence of gas composition and temperature on the structural transition was examined using in situ Raman spectroscopy. The hydrate structures were found to transition from structure I to structure II over a methane composition range of 50–68 mol%. The hydrates remained as sI or sII type compounds, and no structural transition occurred during the dissociation when the methane content in methane-ethane gas mixture was decreased to a certain amount (

Efficient capture of CO2 is of great significance for the reduction of greenhouse gas emissions and the control of global warming. We herein report a pilot experiment demonstrating successful carbon capture under normal pressure using flowable slurry formed with Zeolitic imidazolate framework-8 and 2-methylimidazole-glycol-water solution in continuously cycled setup composed of a sorption bubble column (with height 3.7 m and inner diameter 60 mm) and a desorption tank. A series of factors that affect the carbon capture efficiency were investigated systematically. The experimental results show that the use of finer aperture and installing baffles, lower superficial gas velocity, lower sorption temperature, higher regeneration temperature, and low regeneration pressure are favorable for carbon capture. CO2 concentration in the emission gas could be reduced from 24.9 mol% to 0.5–2.5 mol%, indicating that more than 92% of CO2 could be removed. The working loading of CO2 in the recycled slurry reached 1.53 mol/(L·bar). The slurry could be regenerated under very moderate conditions (333 K and 0.05 MPa), which are far from boiling conditions for the solvent. It was also shown that the performance of the slurry remained stable over more than 100 h of cycling. This work demonstrates that the approach based on the use of the slurry is readily applicable, and could lead to energy savings compared to the traditional amine absorption approach.

Increasing water content in fixed beds is a prospective way to improve the gas storage density by means of hydrate formation. However, the high water content strongly hinders the hydrate formation. In this study, diesel oil was mixed into highly water-saturated activated carbon beds to establish gas channels so that to improve methane hydrate formation. Hydrate formation experiments in four activated carbons with different particle sizes were conducted at 274.15 K and 6.0 MPa. For wet carbon beds without diesel oil, both of the storage capacity of hydrate (Sw) and the storage density of bed (Sb) increased with an decrease in particle size. When the mass ratio of water to activated carbon was set to 2.0, the highest Sw of 67.98 V/Vw and corresponding Sb of 51.92 V/Vbed among the beds were obtained in the bed with particle size of 100–400 mesh. Sodium dodecyl sulfate (SDS) was found to suppress hydrate formation in fine-particle beds. By adding diesel oil, both the formation kinetics and Sw in highly water-saturated beds especially in small-particle ones were significantly improved. The Sw and Sb in the bed with particle size of 100–400 mesh were increased to 180.41 V/Vw and 111.75 V/Vbed, respectively. Furthermore, by adjusting the proportions of water, oil and activated carbon in the bed, the Sw was further improved. The successive gas storage tests suggested that the oil-contained bed can be simply renewed by manual stirring. Gas recovery experiments showed that the hydrate dissociated faster in the oil-contained bed than that in SDS solution, suggesting more efforts should be made to control the hydrate dissociation to drive this method into practical application.

The high efficiency separation of ethane from natural gas becomes significant due to the occurrence of revolution in shale gas. Herein a new approach of continuous sorption separation was developed...

A three-scale in situ observation technique combining the optical microscope, confocal microscope, and Raman spectroscopy was proposed to gain insights into the thickening growth kinetic of hydrate film formed on a gas bubble suspended in water. The evolution of the morphology and mass transfer channels of the hydrate films formed from pure CH4 or the mixture of CH4 and C2H6 during thickening growth was investigated. Results demonstrated that the morphological evolution of hydrate films during thickening growth depended on the initial morphology of the hydrate film formed in the lateral growth. The sI CH4 and sI CH4–C2H6 hydrates had the same ultimate morphology (e.g., a large number of well-defined polyhedral granular hydrates), while the sII CH4–C2H6 hydrates appeared massive. It was clearly observed that the gas pores on the hydrate film gradually vanished with the growth of hydrate film, which suggested that the predominant mass transfer channels on the film changed from the gas pores to the lattices....

To enhance the exploitation efficiency of natural gas hydrate by decreasing the yield of water, a novel “reservoir reformation” concept is proposed that involves the reformation of a natural gas hydrate reservoir by constructing an artificial impermeable overlying CO2 hydrate cap. The feasibility of this concept has been demonstrated in this laboratory-scale experiment. After reformation by injecting CO2 emulsion into the permeable overburden, a confined environment with an impermeable CO2 hydrate cap is successfully constructed for depressurization operation. The cap can maintain mechanical stability until the end of production process. With the protection provided by the artificial CO2 hydrate cap, the production efficiency was greatly improved to 83.3% and the water yield is remarkably decreased. Moreover, the optimal CO2/H2O volume ratio of the emulsion for forming the desired CO2 hydrate cap was confirmed to be 1:1. The formation of CO2 hydrate cap can also protect the geological stability of depleted methane hydrate zones and seal a large amount of CO2, which is of both energetic and environmental significance; however, intensive and extensive research should be conducted in the future.

Although a series of advanced technologies and materials, like ionic liquids and metal organic frameworks, is being developed for carbon capture, traditional techniques, like propylene carbonate (PC) washing, are still widely applied in industry because of their low material costs and ease of operation. Considering the low CO2 solubility and selectivity in PC, we have tried to improve the PC washing process by adding 2-methylimidazole (mIm) to PC in the presence of ethylene glycol (EG) as cosolvent. A series of EG-mIm-PC complex solvents was prepared and their viscosities measured at different temperatures. The absorption isotherms of CO2 in these complex absorbents, as well as in pure PC, were measured at 293.15, 303.15, and 313.15 K at 0.1–0.8 MPa. The heats of CO2 absorption in these solvent mixtures were calculated using the Clausius-Clapeyron equation. For evaluating the effect of mIm on the selectivity of CO2 over other gas species, the absorption isotherms of CH4, N2, and H2 in pure PC and in 24%-mIm complex solvent with highest CO2 solubility were also measured. The results showed that the viscosities of these complex absorbents, as well as the solubility and heats of absorption of CO2 in all of them, moderately or slowly increased with an increase in mIm mass fraction, when the mIm content was lower than 20 wt%, and rapidly increased when it surpassed 20 wt%. The CO2 solubility could be more than doubled when the mIm content reached 24 wt% while viscosity and absorption heat still remains at low levels, that is, lower than 14 mPa·s and 26 kJ/mol, respectively. More importantly, the solubilities of CH4, N2, and H2 drastically decreased in the presence of mIm; using the 24 wt%-mIm complex absorbent instead of pure PC, the selectivity of CO2 over those other gas species increased by: 0.7–2.8 times for CH4, 3.9–6.3 times for N2, and 3.5–7.7 times for H2, with more significant improvements at lower pressure ranges. This work presents a very promising approach to PC washing technology upgrading.

There are huge reserves of natural gas hydrates, a type of low-carbon energy resource, and it is considered important to study the stability conditions of hydrates in situ, to facilitate reserve evaluation and exploitation. The decomposition conditions of methane hydrate were determined in a quartz sand-brine mixing system, using an isothermal, stepwise, depressurising method. Influencing factors, such as sand particle size and pore water salt concentration, and the combined effect of these factors on the hydrate phase equilibrium, were investigated. The results showed that the decomposition pressure was distributed over a small range, and at specific temperatures. This may be partly related to the uneven distribution of pore size, but was shown to be mainly owing to the change of salt concentration during hydrate dissociation, as verified by differential scanning calorimetry. In addition, the hydrate dissociation pressure increased slightly with decreased particle size, and the maximum relative deviation of the dissociation pressure was 1.68%, when the sand particle size was within 100 mesh, which was mathematically negligible. For predicting the decomposition condition of hydrate in the quartz sand-brine mixing system, commercially-available CSMgem and PVTsim software showed high accuracy across a large temperature interval. An in-house, Chen-Guo hydrate model was valid when the temperature was below 277 K, while the Multiflash programme exhibited too large an error to be applied to this system.