为提高天然气水合物开采耦合重整制氢系统能效，对系统进行了工艺设计及建模，并建立了能效评估和经济性分析模型。围绕重整过程中燃料供热或电重整的选择，电重整中是否集成海上风电，H2分离过程中膜分离或醇胺法的选择，对比了不同技术方案下系统的?效比和年度总费用。结果表明，系统C重整单元采用电重整，未集成海上风电，分离单元采用膜分离，其?效比最高(2.25)。系统B重整单元采用燃料供热，分离单元采用膜分离，年度总费用最低(5803.91×106 CNY/a)。系统F集成了海上风电，分离单元采用醇胺法，年度总费用最高(5862.09×106 CNY/a)，比经济性最好的系统B仅高约1.0%，但系统能效更高。这说明膜分离和海上风电应用于水合物开采平台，在能效和经济性方面都具有较大潜力。

为提高天然气水合物开采耦合重整制氢系统能效，对系统进行了工艺设计及建模，并建立了能效评估和经济性分析模型。围绕重整过程中燃料供热或电重整的选择，电重整中是否集成海上风电，H2分离过程中膜分离或醇胺法的选择，对比了不同技术方案下系统的?效比和年度总费用。结果表明，系统C重整单元采用电重整，未集成海上风电，分离单元采用膜分离，其?效比最高（2.25）。系统B重整单元采用燃料供热，分离单元采用膜分离，年度总费用最低（5803.91×10～6 CNY/a）。系统F集成了海上风电，分离单元采用醇胺法，年度总费用最高（5862.09×10～6 CNY/a），比经济性最好的系统B仅高约1.0%，但系统能效更高。这说明膜分离和海上风电应用于水合物开采平台，在能效和经济性方面都具有较大潜力。

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 byproduct. 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. (c) 2021 Institute of Process Engineering, Chinese Academy of Sciences. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

For natural gas hydrate exploitation, revealing the interaction between flow and geomechanics is the key to accurate prediction of gas production and formation stability. In this work, based on the site GMGS3-W19 of the South China Sea, a numerical model with multilayer hydrate deposits was established to analyze the evolution of geological parameters during depressurization. The results demonstrated that the reservoir underwent sequential process of expansion and compression, which resulted in the corresponding changes of porosity and permeability. The different initial geological parameters of the three hydrate layers showed respective coupling characteristics between flow and geomechanics. Additionally, we also analyzed the geological stability of reservoir. The calculation results of horizontal and vertical effective stresses were within the elastic region away from the Mohr-Coulomb yield function until 1800 d. In contrast, the layer with high hydrate saturation was more likely to produce shear failure. Finally, the gas-water production was determined after the coupled flow and geomechanical analysis. The result showed that gas productions of the two horizontal wells were on par, while water production of upper well was >7 times that of lower well. The numerical model and analysis could provide useful insight into the marine heterogeneous hydrate exploitation. (C) 2022 Published by Elsevier Ltd.

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. © 2021 Institute of Process Engineering, Chinese Academy of Sciences

Understanding the mechanisms of hydrate formation and dissociation is significant for natural gas hydrate exploration. In this study, a porous micromodel was used to visualize the formation and dissociation of methane hydrate in methane-pure water and methane-brine systems via a microfluidic approach. Various methane hydrates with different growth characteristics were formed, which may result from variations in the sizes and distributions of methane bubbles. The differences in the mode of methane hydrate formation were associated with various phenomena during hydrate dissociation. The size, number and size distribution of the dissociated methane bubbles were quantitatively analyzed to describe hydrate dissociation behavior. Hydrate dissociation in the methane-brine system differed significantly from that in the methane-pure water system. Furthermore, multiple formation-dissociation processes of methane hydrate were investigated. The results indicated that multiple formation dissociation processes can significantly impact the characteristics of the gas-liquid interfaces, which could influence the subsequent hydrate formation and dissociation behaviors. (c) 2021 Elsevier Ltd. All rights reserved.

Natural gas hydrates are widely considered one of the most promising green resources with large reserves. Most natural gas hydrates exist in deep-sea porous sediments. In order to achieve highly efficient exploration of natural gas hydrates, a fundamental understanding of hydrate growth becomes highly significant. Most hydrate film growth studies have been carried out on the surface of fluid droplets in in an open space, but some experimental visual works have been performed in a confined porous space. In this work, the growth behavior of methane hydrate film on pore interior surfaces was directly visualized and studied by using a transparent high-pressure glass microfluidic chip with a porous structure. The lateral growth kinetics of methane hydrate film was directly measured on the glass pore interior surface. The dimensionless parameter (- increment G/(RT)) presented by the Gibbs free energy change was used for the expression of driving force to explain the dependence of methane hydrate film growth kinetics and morphology on the driving force in confined pores. The thickening growth phenomenon of the methane hydrate film in micropores was also visualized. The results confirm that the film thickening growth process is mainly determined by water molecule diffusion in the methane hydrate film in glass-confined pores. The findings obtained in this work could help to develop a solid understanding on the formation and growth mechanisms of methane hydrate film in a confined porous space.

Nowadays, the combination of natural gas hydrates exploitation and CO2 storage is considered of excellent application. In this work, we explored reservoir reformation technology to enhance gas recovery from the unsealed water-saturated hydrate-bearing deposits in a large-scale tridimensional simulator. Firstly, recurrent CO2 injection into the overburden was to gradually form CO2 hydrate and reduce its permeability. Then traditional depressurization operations were conducted to compare the influences of overburden thickness and additional reservoir reformation on the evolution of pressure distribution and the gas/water production. The results showed that reservoir reformation could effectively improve the mining efficiency, reaching similar to 2-4 times of gas production and similar to 3-5 times of gas-water ratio compared with the direct depressurization. After a long-term reformation, CH4 recovery ratio was increased from 24.5% to 84.9%. Additionally, we further demonstrated the complete spatiotemporal evolution mechanism of the initial CH4 hydrate and artificial overlying CO2 hydrate during depressurization. A large amount of CO2 was ultimately stored in the depleted reservoir in the form of CO2 hydrate and the CO2 storage ratio was up to 79.5%. Therefore, this reservoir reformation approach is greatly promising for high-efficient and safe exploitation of marine hydrate and CO2 storage.

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. © 2021 Hydrogen Energy Publications LLC