客体分子数对甲烷水合物导热性能影响的分子动力学模拟

本文通过采用EMD方法Green-Kubo理论计算263.15 K 晶穴占有率0-100% sI甲烷水合物导热系数,研究客体分子数对甲烷水合物导热性能的影响。模拟结果显示,甲烷水合物的低导热性能由主体分子构建的笼型结构决定。而在相同温压条件下,随着客体分子甲烷进入晶胞数目增多,晶穴占有率增大后,密度增大,同时客体分子对声子的散射也增强,二者均导致导热性能增强。     

The status of exploitation techniques of natural gas hydrate

Natural gas hydrate (NGH) has been widely considered as an alternative form of energy with huge potential, due to its tremendous reserves, cleanness and high energy density. Several countries involving Japan, Canada, India and China have launched national projects on the exploration and exploitation of gas hydrate resources. At the beginning of this century, an early trial production of hydrate resources was carried out in Mallik permafrost region, Canada. Japan has conducted the first field test from marine hydrates in 2013, followed by another trial in 2017. China also made its first trial production from marine hydrate sediments in 2017. Yet the low production efficiency, ice/hydrate regeneration, and sand problems are still commonly encountered; the worldwide progress is far before commercialization. Up to now, many gas production techniques have been proposed, and a few of them have been adopted in the field production tests. Nevertheless, hardly any method appears really promising; each of them shows limitations at certain conditions. Therefore, further efforts should be made on the economic efficiency as well as sustainability and environmental impacts. In this paper, the investigations on NGH exploitation techniques are comprehensively reviewed, involving depressurization, thermal stimulation, chemical inhibitor injection, CO₂–CH₄ exchange, their combinations, and some novel techniques. The behavior of each method and its further potential in the field test are discussed. The advantages and limitations of laboratory studies are also analyzed. The work could give some guidance in the future formulation of exploitation scheme and evaluation of gas production behavior from hydrate reservoirs.     

Extraction of methane hydrate energy by carbon dioxide injection-key challenges and a paradigm shift

Significant effort including field work has been devoted to develop a natural gas extraction technology from natural gas hydrate reservoirs through the injection of carbon dioxide. Natural gas hydrate is practically methane hydrate. The hypothesis is that carbon dioxide will be stored as hydrate owing to its favorable stability conditions compared to methane hydrate. Although the dynamics of the CO₂/CH₄ exchange process are not entirely understood it is established that the exchange process is feasible. The extent is limited but even if the CH₄ recovery is optimized there is a need for a CH₄/CO₂ separation plant to enable a complete cyclic sequence of CO₂ capture, injection and CH₄ recovery. In this paper we propose an alternative paradigm to the Inject (CO₂)/Exchange with (CH₄)/Recover (CH₄) one namely Recover (CH₄) first and then Inject (CO₂) for Storage.     

季铵盐类化合物水合分离烟道气中CO2的实验研究

利用季铵盐类化合物[四丁基溴化铵（TBAB）、四丁基氟化铵（TBAF）]作为热力学促进剂对CO₂（9.06%,摩尔分数）+N₂（90.94%,摩尔分数）混合气体进行水合分离实验。结果表明：在279.15 K、2.0 MPa下,0.293% TBAF溶液中,CO₂能够在水合物相中富集到37.73%（摩尔分数）,分离因子13.23,回收率28.44%。TBAF对CO₂的富集程度和分离效果要优于TBAB。同时将实验结果与文献中季铵盐类化合物以及同样实验条件下四氢呋喃（THF）水合分离实验结果进行比较,发现本实验的分离效果要低于文献中CO₂-N₂-TBAB体系,分离因子高于同样实验条件下CO₂-N₂-THF体系,但回收率低于CO₂-N₂-THF体系。     

水合物存在条件下CH4和CO2在溶液中溶解度计算

实验测定了在不同温度、压力条件下,水合物存在时CO2和CH4在水溶液中的溶解度。将Chen-Guo水合物模型和拓展的P-T状态方程应用到水合物存在条件下CH4和CO2在溶液中的溶解度计算,对于V-Lw-H三相条件下CH4和CO2在液相中的溶解度取得了较高的计算精度。本文将vander Waals-Platteeuw模型和拓展的P-T状态方程结合,建立了用于计算高于三相平衡压力条件下CH4和CO2在液相中溶解度的模型。考察了系统压力对CH4和CO2在液相中溶解度的影响。结果表明,压力增加会显著影响CH4和CO2在其溶液中的溶解度。模型基于两点假设经过改进后具有较高的计算精度,能够用于水合物存在条件下CH4和CO2在液相中溶解度的计算。     

Experimental and modeling study of the kinetics of methane hydrate formation and dissociation

In this work, several experiments were conducted at isobaric and isothermal condition in a CSTR reactor to study the kinetics of methane hydrate formation and dissociation. Experiments were performed at five temperatures and three pressure levels (corresponding to equilibrium pressure). Methane hydrate formation and dissociation rates were modeled using mass transfer limited kinetic models and mass transfer coefficients for both formation and dissociation were calculated. Comparison of results, shows that mass transfer coefficients for methane hydrate dissociation are one order greater than formation conditions. Mass transfer coefficients were correlated by polynomials as relations of pressure and temperature. The results and the method can be applied for prediction of methane production from naturally occurring methane hydrate deposits.     

Initial thickness measurements and insights into crystal growth of methane hydrate film

The initial thickness of methane hydrate film was directly measured by suspending a single methane bubble in water at 274.0, 276.0, and 278.0 K. The results show that the initial hydrate film thickness decreases from tens of micrometers to about 10 µm with the subcooling increased from 0.5 K to about 3 K. When subcooling is higher than 1.0 K, all initial film thickness data measured under different temperatures vary inversely with the subcooling. Notable three‐dimensional growths of hydrate crystals of different sizes and shapes at film front and emergence of new crystal were clearly observed at lower subcooling that resulting in the rougher surface of hydrate film and uncertainty of initial thickness measurement under lower subcooling. The hydrate film growth was dominated by film growth in thickness, not by lateral growth at low subcooling. The growth in thickness of hydrate shell covering one whole bubble surface was also investigated. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2145–2154, 2013     

CO2置换CH4水合物中CH4的实验和动力学

在自行设计的反应装置中考察了2.8 MPa和3.25 MPa压力下，温度271.2、273.2和276.0 K时CO2气体置换十二烷基硫酸钠（SDS）体系CH4水合物中CH4的置换过程。实验数据表明，在反应的前50 h，CH4水合物的分解速率较快，其后分解速率变慢。冰点以上CH4水合物的分解速率较快。基于动力学数据，建立了SDS体系置换反应过程中CH4水合物的分解动力学模型和CO2水合物的生成动力学模型。计算得到CH4-CO2置换反应过程中CH4水合物的分解活化能为28.81 kJ·mol-1，CO2水合物的生成活化能为68.40 kJ·mol-1。数据表明，CH4水合物的分解可能受置换反应过程中水分子的重排控制，而CO2水合物的生成可能受CO2气体在水合物中的扩散控制。     

Effect of surfactant on the formation and dissociation kinetic behavior of methane hydrate

The effects of anionic surfactant sodium dodecyl sulfate (SDS) on the formation/dissociation kinetic behaviors of methane hydrate have been studied experimentally, with an emphasis put on dissociation kinetic behavior below ice point. The experimental results on hydrate formation show that the formation rates of methane hydrate could be speeded up by adding SDS to water and a critical SDS concentration of 650 ppm corresponding to a maximum storage capacity of 170V/V is determined. The SDS concentrations are fixed at this value in preparing hydrate samples for all dissociation tests. The dissociation experiments have been performed in two ways, at atmospheric pressure where the dissociation rates are determined by measuring the accumulative evolved gas volume, and in a closed system where the dissociation rates are determined by measuring the increasing system pressure profiles. For comparison, the dissociation tests with respect to two different cases, with and without the presence of SDS, are done in parallel. The results from tests in the first way show that the presence of SDS increases the dissociation rate of methane hydrate in whole temperature region below ice point. The results for the second way are somewhat different. The presence of SDS increases the dissociation rate and meta-stable system pressure in temperature region lower than . But when temperature is equal to or higher than , SDS speeds up the dissociation process only in beginning period, it turns to suppress the dissociation of methane hydrate several hours later and leads to a lower meta-stable system pressure compared with the case of without SDS. The experiments in closed system also demonstrate that the dissociating system approaches a meta-stable state with a pressure much lower than equilibrium dissociation pressure.     

甲烷与冰快速形成天然气水合物的影响因素研究

设计了冰-气生成天然气水合物的实验装置,对由冰和甲烷反应生成天然气水合物的影响因素进行实验研究。结果表明,压力越高,温度越低,冰粒越小,越有利于水合物的生成,促进水合物快速形成的搅拌速度和促进剂浓度最佳值分别是800 r/min和800 mg/L。     

CO2置换开采天然气水合物研究进展

介绍了近年来CO2置换开采天然气水合物技术的研究进展;论述了CO2与天然气水合物中CH4置换反应在热力学上的可能性;认为正确理解置换反应机理、探索新的反应技术并提高反应速率是置换开采技术走向产业化的关键。     

降低“固封”对甲烷水合物生成的影响

随着天然气的大量使用,其储存、运输及调峰越来越重要。天然气水合物在常压状态下具有高储存比,适合应用于天然气的储存、运输及调峰过程中。因此,对天然气水合物的生成研究具有重要意义。本文研究了如何大量生成水合物并保证水合物具有较高储气率的方法。在含聚乙烯吡络烷酮[PVP(K90)]的溶液中,改变PVP(K90)的质量分数、搅拌器的转速与搅拌器的类型,研究甲烷水合物生成量与水合物储气率的变化。结果表明,添加一定低质量分数的PVP(K90)和增加搅拌速度,均可以延迟水合物层的"固封"作用,增加水合物的生成量。在PVP(K90)质量分数高于2%时,生成水合物的密封性降低,水合物"固封"作用被破坏,但是水合物储气率较低。采用不同形式的搅拌杆,在旋转过程中形成空心圆柱,破坏水合物层的"固封"作用,搅拌杆附近的甲烷与水合物晶核被输送到溶液底部,增加了水合物的生成量,而且水合物的储气率较高。在水合物生成过程中,存在水合物微粒多次聚结的现象,使甲烷的消耗量迅速增加。     

Advances of experimental study on gas production from synthetic hydrate reservoir in China

China has entered the area of new normal economy which requires the harmonious development of energy consumption, environmental protection and economic development. Natural gas hydrate is a potential clean energy with tremendous reserve in China. The successful field test of marine hydrate exploitation in South China Sea created a new record of the longest continuous gas production from natural gas hydrate. However, the corresponding fundamental research is still urgently needed in order to narrow the gap between field test and commercial production. This paper reviewed the latest advances of experimental study on gas production from hydrate reservoir in China. The experimental apparatus for investigating the performance of hydrate dissociation in China has developed from one dimensional to two dimensional and three dimensional. In addition, well configuration developed from one tube to complicated multi-well networks to satisfy the demand of different production models. Besides, diverse testing methods have been established. The reviewed papers preliminary discussed the mechanical properties and the sediment deformation situation during the process of hydrate dissociation. However, most reported articles only consider the physical factor, the coupled mechanism of physical and chemical factor for the mechanical properties of the sediment and the sand production problem should be studied further.     

非金属氮掺杂活性炭催化剂制备及其催化CH4-CO2重整反应

采用硝酸和尿素联合对活性炭进行改性,制备了富含氮元素的氮掺杂活性炭,考察了孔结构、氮含量和氮种类（吡啶氮、吡咯氮和石墨氮）对CH₄-CO₂重整反应催化性能的影响。采用BET、SEM、EA、FTIR、XPS、CO₂-TPD和TG表征手段对反应前后催化剂的物理化学性质进行了表征,对引入活性炭表面的含氮官能团的种类及其在重整过程中所起的作用进行了分析。相比于未改性的原活性炭,硝酸和尿素同时改性制备的氮掺杂活性炭（AC-U.NA）引入了更多的羟基官能团和含氮官能团。特别是通过两者共同改性后,所制备的氮掺杂活性炭引入的吡啶氮官能团比例明显提高,为CH₄-CO₂重整反应提供了更多的活性位点,初始CH₄和CO₂转化率达到55.94%和66.46%。同时经过两者联合改性后,所制备的AC-U.NA材料表面具有极性,不仅有利于酸性CO₂分子的吸附和活化,而且有利于CO₂消碳反应,减少了积炭的生成,对所制备的非金属重整催化剂的活性和抗积炭性具有重要的意义。     

含环戊烷体系中二氧化碳水合物形成分解热特性

水合物法分离捕集二氧化碳（CO₂）是实现碳减排的重要技术。然而,受制于气体水合物形成分解微观机理的不明确,水合物形成速度慢及气体消耗量低两个关键问题还未得到解决,气体水合物CO₂分离捕集技术还未得到商业应用。为了揭示气体水合物形成微观机理,本研究利用激光Raman光谱仪对不同实验条件下生成的CO₂水合物进行测试,详细分析了生成的气体水合物的Raman峰,利用低温高压差式扫描量热仪（DSC）对含环戊烷（CP）体系中CO₂水合物形成分解进行热表征。研究发现,恒容条件下,初始压力为2.5MPa时,气体消耗量为0.0187 mol/mol,CO₂的Raman峰出现在1276.3 cm^-1和1379.6 cm^-1;初始压力为5.0MPa时,气体消耗量为0.744mol/mol,CO₂的Raman峰出现在1276.1 cm^-1和1379.6 cm^-1。CO₂水合物形成分解热结果表明,一方面,随着操作温度、压力条件的变化,形成水合物的种类与结构发生改变;另一方面,对于相同初始体系,最终形成的水合物不是单一的,而是多种水合物共存。此研究结果为进一步理清气体水合物形成微观机理提供了理论基础和重要的科学依据。     

Integrated solvent and process design using a SAFT-VR thermodynamic description: High-pressure separation of carbon dioxide and methane

The increasing importance of natural gas as an energy source poses separation challenges, due to the high pressures and high carbon dioxide concentrations of many natural gas streams. A methodology for computer-aided molecular and process design (CAMPD) applicable to such extreme conditions is presented, based on the integration of process and cost models with an advanced molecular-based equation of state, the statistical associating fluid theory for potentials of variable range (SAFT-VR). The approach is applied to carbon dioxide capture from methane using physical absorption. The search for an optimal solvent is focused on n-alkane blends. A simple flowsheet is optimised using two objectives: maximum purity and maximum net present value. The best equipment sizes, operating conditions, and average chain length of the solvent (the n-alkane) are identified, indicating n-alkane solvents offer a promising alternative. The proposed methodology can readily be extended to wider classes of solvents and to other challenging processes.     

Separation of binary mixtures of carbon dioxide and methane through sulfonated polycarbonate membranes

Polycarbonate (PC) was sulfonated to varying degrees using acetyl sulfate. FTIR and NMR experiments were carried out to confirm sulfonation. The membranes were characterized by DSC and TGA to assess thermal stability. Ion exchange capacity (IEC) and degree of sulfonation (DS) were determined and their effect on permeation of CO₂ and CH₄ gases was investigated. Free volume fractions (FVF) of the membranes were found to decrease from 0.31 to 0.19 as the DS increased from 0 to 39.4%. Single gas permeation studies revealed that sulfonated PC exhibited higher selectivities than unmodified PC at reduced permeability. For a DS of 14.4%, sulfonated PC exhibited a selectivity of 36.1, which was 1.7 times that of unmodified PC, whereas the permeability dropped from 8.4 to 4.7 Barrers. In case of binary CO₂/CH₄ mixture permeation through PC membrane of the same DS, an increase in CO₂ feed concentration from 5 to 40 mol % produced an increase in permeability from 0.24 to 2.0 Barrers and a rise in selectivity from 11.7 to 27.2 at constant feed pressure (20 bar) and temperature (30°C). A rise in the feed pressure from 5 to 30 bar at a constant feed composition of 5% CO₂ resulted in a reduction in permeability from 0.38 to 0.2 Barrers and selectivity from 15.6 to 10.2. Sulfonated PC was found to be a promising candidate for separation of CO₂ from CH₄. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

CH4与CO2催化重整制合成气研究进展

本文综述了CH4与CO2重整制合成气的研究进展,对重整催化剂、重整反应机理及重整动力学进行了评述。     

Molecular simulation of confined ethaline-based deep eutectic solvents for separations of carbon dioxide from methane

Classical molecular dynamics (MD) simulations were used to study the separation of carbon dioxide from methane by three formulations of the deep eutectic solvent (DES) ethaline (choline chloride: ethylene glycol at 1:2, 1:4, and 1:8 molar ratios), confined inside graphite and titania (rutile) slit pores of two different pore widths, 2 and 5 nm. In addition, equivalent DES systems in the bulk were studied, which can also be viewed as a model supported DES membrane with μm-sized pores. Our results indicate that variations in the ratio of ethylene glycol, which in turn affect the interactions of all DES species with the gas molecules and the different pore walls, plus confinement effects resulting from varying the pore sizes, can affect the gas separation performance of these systems in complex ways. The highest permselectivities (~20), computed as the product of the diffusivity and solubility selectivities, are observed for 1:2 ethaline in a 5 nm graphite pore, followed by the 1:4 DES in a 5 nm graphite pore, 1:2 ethaline in a 2 nm graphite pore, and the 1:8 bulk DES. In bulk systems, all three selectivities reach their highest values for 1:8 ethaline. When the DESs are confined in the nanopores, the solubility selectivity for most systems improves compared to the equivalent bulk systems, with the graphite pores having the largest solubility selectivities for any given ethylene glycol ratio. In contrast, the diffusivity selectivities in confined systems tend to be similar to the values observed in the bulk DESs. Interaction energies and local density profiles were used to rationalize absorption and diffusivity of gases in our systems. Confining ethaline in graphite and rutile nanopores tends to weaken the CO₂-ethylene glycol and CO₂-cation interactions compared to the values observed in equivalent bulk ethaline systems, which also affect the local density profiles. Our results confirm that variations in ethylene glycol ratio, pore size, and pore wall material can lead to significant changes in gas separation performance. Other porous matrices, for example, nanoporous polymer formulations and graphene oxides, should be considered in follow-up studies as they may lead to significant improvements in gas separation performance as compared to the bulk DES.     

超重力旋转填料床中天然气水合物含气量研究

研究了在旋转填料床中制备天然气水合物,主要考察了超重力因子β、液气比等因素对含气量的影响。实验结果表明,当在压力5 MPa、温度277.15 K状态下:含气量随着超重力因子β增大而增大,β大于120后对含气量的影响不明显;天然气水合物含气量随液气比的增大呈现出先增大后减小的趋势,其最佳液气比为10 L/m3。结合晶体化学方法探讨了超重力方式合成天然气水合物的机理。与传统方式相比,加快了溶解、成核及生长过程,最终含气量显著提高。