泡沫铜强化甲烷水合物生成动力学实验研究

提高水合物生成速率和储气密度对天然气水合物技术应用非常重要。将三种孔密度的泡沫铜（CF）分别浸入十二烷基硫酸钠（SDS）溶液中构建水合储气强化体系,在高压静态反应釜中研究泡沫金属对甲烷水合物生成动力学特性。实验结果表明,泡沫铜骨架能为水合物生成提供充足的结晶点,同时可作为水合物生长过程水合热迁移的“高速公路”。甲烷水合物在SDS/CF体系中可快速生成,最大水合储气速率分布在19.24~21.04 mmol·mol^-1·min^-1之间,其中添加15 PPI泡沫铜的SDS溶液储气量最高（139 mmol·mol^-1）,且达到最大储气量90%所用时间最短（10.1 min）。在6.0~8.0 MPa压力下,相比SDS溶液,添加15 PPI泡沫铜的SDS溶液储气量提高了8.8%~35.6%,储气速率提高了4.7%~40.4%;特别在压力为5.0 MPa时,该孔密度SDS/CF体系储气量甚至比SDS溶液增加13倍,储气速率增加16倍。     

Enhance hydrates formation with stainless steel fiber for high capacity methane storage

In order to realize efficient gas storage of hydrate, stainless steel fiber (SSF) was added to 0.03% (mass) sodium dodecyl sulfate (SDS) solution for gas storage experiment. SSF can not only improve the problem that hydration heat cannot be removed effectively in the hydration process, but also improve gas storage speed and gas storage by increasing hydrate nucleation sites. Under the experimental conditions (273.2 K, 5-9 MPa), the peaks of temperature rise in SDS + SSF systems were found to become much smaller than those in SDS systems. The maximum gas storage rate and the maximum methane uptake of SSF + SDS system reached 9.89-24.90 cm³·g^-1·min^-1 and 178.65-200.89 cm³·(g H₂O)^-1, respectively. Compared with the surfactant SDS solution without SSF, they increased by 10.47%-33.22% and 9.16%-25.36%, respectively. The effect of SSF length on gas storage performance was studied. Due to the continuous thermal conduction network, longer SSF showed a higher gas storage capacity and methane uptake rate compared with shorter SSF. At the same time, compared with other metal fillers, SSF + SDS not only had excellent gas storage performance, but also the amount of SSF (0.1 g·ml^-1) was only 7.6% of foamed aluminum, and the volume gas storage density was increased by 145.4%. The use of stainless steel fiber made the best use of the thermal conductivity of metal, reduced the amount of metal used, and improved the volume density and mass density of gas storage.     

表面活性剂吸附对促进甲烷水合物生成效果的影响

基于表面活性剂固-液界面吸附理论,在无搅拌条件下研究了十二烷基硫酸钠（SDS（、脂肪醇聚乙烯醚硫酸钠（AES（、脂肪醇聚乙烯醚（AEO（3种表面活性剂在不锈钢反应釜中对甲烷水合物生成的促进效果。结果表明：水合物的生成形态与表面活性剂吸附金属表面形态有良好的对应关系;SDS与AES在金属表面的吸附作用可使水合物成核速率提高,成核位置增多。由于AEO不能在金属壁面发生吸附,导致对水合物生成促进效果降低,在浓度为300 mg·L^-1的SDS、AES和AEO溶液中,水合物储气密度及平均储气速率分别为131.4、128.3、12.3（体积比（和5.8、7.6、0.07 mmol·min^-1;逐步提高SDS溶液浓度（80~1200 mg·L^-1（和AES溶液浓度（60~1350 mg·L^-1（,水合物储气密度首先增大然后减小,储气速率线性增大。因此,合理选择表面活性剂种类及浓度,可显著促进水合物生成。     

A型分子筛对甲烷水合物生成的影响

The porous medium has an important effect on hydrate formation. In this paper, the formation process and the gas storage capacity of the methane hydrate were investigated with A-type zeolite and Sodium Dodecyl Sulfate (SDS) existing in the system. The results show that A-type zeolite can influence methane hydrate formation. At the temperature of 273.5 K and pressure of 8.3 MPa, the distilled water with A-type zeolite can form methane hydrate with gaseous methane in 12 hours. The formation process of the system with A-type zeolite was quite steady and the amount of A-type zeolite can influence the gas storage capacity significantly. The adding of A-type zeolite with 0.067 g•(g water)－1 into 2×10－3 g•g－1 SDS-water solution can increase the gas storage capacity, and the maxi-mum increase rate was 31%. Simultaneously the promotion effect on hydrate formation of 3A-type zeolite is much more obvious than that of 5A-type zeolite when the water adding amounts are 0.033 g•g－1 and 0.067 g•g－1 at the experimental conditions.     

Induction time,storage capacity,and rate of methane hydrate formation in the presence of SDS and silver nanoparticles

In this communication, the kinetic parameters of methane hydrate formation (induction time, quantity and rate of gas uptake, storage capacity (SC), and apparent rate constant) in the presence of sodium dodecyl sulfate (SDS), synthetized silver nanoparticles (SNPs), and mixture of SDS?+?SNPs have been studied. Experimental measurements were performed at temperature of 273.65?K and initial pressure of 7?MPa in a 460?cm³ stirred batch reactor. Our results show that adding SDS, SNPs and their mixture increases the quantity of gas uptake, water to hydrate conversion, and SC of methane hydrate formation, noticeably. Using 300?ppm SDS increases the SC and the quantity of methane uptake 615, and 770%, respectively, compared with pure water. Investigating the hydrate growth rate at the start of hydrate formation process shows that, using SNPs, SDS, and their mixture increases the initial apparent rate constant of hydrate rate, considerably. Our results show that the system of methane?+?water?+?SDS 500?ppm?+?SNPs 45?µM represents the maximum value of initial apparent rate constant, compared with other tested systems.     

SDS对甲烷水合物生成动力学和微观结构的影响

表面活性剂是促进水合物生成的有效手段之一。在高压反应釜中研究了十二烷基硫酸钠（SDS）对水合物生成过程的动力学影响,利用XRD和拉曼光谱探究了SDS存在条件下水合物的微观结构。宏观结果表明SDS缩短了诱导时间,加快了水合物生长速率。微观结果表明SDS没有影响sI型水合物的晶型结构,晶面间距与理想sI型水合物及纯水甲烷对比误差在千分之几。水合物中甲烷在大笼小笼中的拉曼位移分别为2904和2915 cm^-1,SDS没有改变大笼小笼结构。大笼绝对占有率（q_L）接近饱和时,SDS可以进一步提高小笼绝对占有率（q_S）,从微观角度证明了SDS可以减少水合数,提高储气率。     

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.     

Effect of synthesized silver nanoparticles in promoting methane hydrate formation at 4.7 MPa and 5.7 MPa

Using gas hydrates as materials for storage and transportation of natural gas have attracted much attention in recent years. However, there are two barriers in industrializing this new method. Firstly, methane hydrate induction time is relatively high. On the other hand the amount of gas trapped in methane hydrate crystals is too low. In this survey, silver nanoparticles were synthesized using a chemical reduction method and introduced to the hydrate reactor. Experiments were conducted at initial reactor pressures of 4.7 MPa and 5.7 MPa. At each pressure three independent experiments were performed. According to the results, in the presence of silver nanoparticles, methane hydrate induction time decreased by 85% and 73.9%, and the amount of methane trapped in hydrate crystals increased by 33.7% and 7.4% at the pressures of 4.7 MPa and 5.7 MPa respectively.     

凹凸棒石体系下CO2水合物生成动力学实验

油气生产、储运及CO₂管道输送的过程中易生成CO₂水合物,添加抑制剂是预防CO₂水合物生成的有效手段。为解决CO₂水合物堵塞问题,本文采用超声波处理后的凹凸棒石作为抑制剂,利用可视化高压反应釜实验装置,在初始条件3 MPa和2℃下,研究了添加浓度为0、0.05mg/mL、0.30mg/mL、0.50mg/mL、0.75mg/mL、1.00mg/mL和1.50 mg/mL的凹凸棒石对CO₂水合物生成动力学的影响。用压力变化法测定了水合物生成诱导时间,用动力学模型计算了水合物生成量,并分析了凹凸棒石影响CO₂水合物生成的微观机理。实验结果表明凹凸棒石能延长CO₂水合物生成诱导时间,浓度为0.75mg/mL时作用效果最佳,较纯水体系CO₂水合物生成诱导时间延长了200%;凹凸棒石能减少CO₂水合物的生成量,浓度为1.5mg/mL时作用效果最佳,与纯水体系相比减少了12.8%。凹凸棒石抑制水合物生成的微观机理主要是由于其独特的选择吸附性以及对传质传热的阻碍。研究表明以凹凸棒石作为CO₂水合物抑制剂效果良好,能有效延长其诱导时间,兼具经济性和环境友好的特点。     

丁二酸二异辛酯磺酸钠对甲烷水合物生长动力学特性的影响

通过改变添加量（600mg/L、900mg/L、1200mg/L）、过冷度（3.5℃、5.5℃、7.5℃）以及压力（4.90MPa、6.0MPa、7.31MPa）的方式,考察了在静态体系下绿色促进剂丁二酸二异辛酯磺酸钠（AOT）对甲烷水合物生长动力学特性的影响。实验结果表明,3种浓度下AOT均能够有效缩短诱导时间,并且浓度越大,诱导时间越小（1200mg/L时为0.21h）,但储气量随着添加量的增加,先增大后减小,最终确定最佳添加量为900mg/L,水合物储气量为55.76m³/m³;另外,过冷度越大,实验压力越高,水合物成核速度越快,诱导时间越短,耗气速率越高。当过冷度为7.5℃时,诱导时间最小为0.31h,耗气速率最大为0.275mol/h,储气量最大为63.95m³/m³;但压力过大,釜内气液界面会快速生成水合物层,阻碍水合物继续生成,导致水合物储气量减少为46.84m³/m³。所以,在静态体系下,合理选择促进剂的浓度和驱动力的大小,可显著促进水合物生成。     

Experimental determination of methane hydrate dissociation curve up to 55 MPa by using a small amount of surfactant as hydrate promoter

Methane hydrate equilibrium has been studied upon continuous heating of the water-hydrate-gas system within the temperature range of 275-300 K. This temperature range corresponds to equilibrium pressures of 3.15-55 MPa. The hydrate formation/dissociation experiments were carried out in a high-pressure reactor under isochoric conditions and with no agitation. A small amount of surfactant (0.02 wt% sodium dodecyl sulfate, SDS) was added to water to promote hydrate formation. It was demonstrated that SDS did not have any influence on the gas hydrate equilibrium, but increased drastically both the hydrate formation rate and the amount of water converted into hydrate, when compared with the experiments without surfactant. To understand and clarify the influence of SDS on hydrate formation, macroscopic observations of hydrate growth were carried out using gas propane as hydrate former in a fully transparent reactor. We observed that 10^-3 wt% SDS (230 times less than the Critical Micellar Concentration of SDS) were sufficient to prevent hydrate particles from agglomerating and forming a rigid hydrate film at the liquid-gas interface. In the presence of SDS, hydrates grew mainly on the reactor walls as a porous structure, which sucked the solution due to capillary forces. Hydrates grew with a high rate until about 97 wt% of the water present in the reactor was transformed into hydrate.Our data on methane hydrate equilibrium both confirm already published literature data and complement them within the pressure range of 20-55 MPa.     

低温常压条件下水合物法储存甲烷的实验研究

利用水合物法实现对天然气的工业储运,需要提高水合物的储气量并解决水合物的分解速度问题。为此,文章研究了在十二烷基硫酸钠（SDS）体系中,甲烷水合物的储气量和在冰点以下的常压分解规律。研究发现,SDS浓度为650 mg/L时甲烷水合物储气量达到最高值,约为170 V/V。分解温度为268.2~272.2 K区域内,甲烷水合物的分解速率随温度的降低而降低;在268.2 K时,甲烷水合物分解速率最低。     

EXPERIMENTAL INVESTIGATION ON GAS HYDRATE FORMATION IN PRESENCE OF ADDITIVE COMPONENTS

Additives were used to increase gas hydrate formation rate and storage capacity. Experimental tests of methane hydrate formation were carried out in surfactant water solutions in a high-pressure cell. Sodium dodecyl sulfate (SDS) and alkyl polysaccharide glycoside (APG) were used to increase hydrate formation. The effect of SDS on hydrate formation is more pronounced compared APG. Cyclopentane (CP) also improves hydrate formation rates while it cannot increase methane gas storage capacity.     

干水固化甲烷过程及反应特性研究

利用天然气水合物合成实验系统,采用5%纳米SiO2与纯净水配制的干水和纯甲烷为原料,获得了水合物生成过程中温度、压力、反应速率以及最终的储气密度之间的关系。通过以温度和压力值作为变量进行实验结果表明：在高压条件下,反应温度接近0℃,反应的速率较快,生成的水合物中甲烷含量也较高。在低温条件下,压力接近8 MPa时,干水固化甲烷效果较好。     

Static Formation and Dissociation of Methane+Methylcyclohexane Hydrate for Gas Hydrate Production and Regasification

The formation and decomposition of methane+methylcyclohexane (MCH) hydrate in a static batch reactor, which was also designed as a high‐pressure microwave reactor, were investigated. The addition of 300 ppm sodium dodecyl sulfate (SDS) provides continuous formation of CH₄+MCH hydrate under static conditions. Increasing the initial pressure within the narrow range of 2.7 to 4.6 MPa at 274 K enhances the formation rate by even several times. The gas storage capacity can be largely improved with partial coexisting of sI CH₄ hydrate. Unlike a stirred formation, an increase of nonaqueous MCH inhibits the static formation of sH hydrate. The following regasification by 2.45 GHz microwave heating indicates that the dissociation is rate‐controlled by the parallel connection of efficient internal heating and conventional external heating. The multiphase convection characterized by osmotic dehydration and driven by intensified regasification is considered as the dominant mechanism affecting the quiescent dissociation.     

水合物法分离低浓度煤层气中的甲烷

向模拟煤层气(13.11vol% CH4+86.89vol% N2)中添加5.8mol%四氢呋喃(THF)?0.03mol%十二烷基硫酸钠(SDS)促进剂溶液分离提纯煤层气,考察了压力、温度、反应时间对气体消耗量、反应速率、分解气中甲烷浓度、甲烷回收率和甲烷分离因子的影响,采用色谱分析法分别测定了CH4在剩余气相和分解气相中的浓度。结果表明,压力增加,CH4回收率增大,CH4分离因子增大,CH4分离效果越好;温度是影响甲烷分离因子的关键因素,温度降低,氮气和甲烷竞争进入水合物晶体中,导致水合物相中甲烷浓度降低;温度升高有利于提高水合物对甲烷的选择性。甲烷回收效率最高可达98.65%,分离因子最大为14.83。随反应时间增加,分解气中CH4浓度升高。     

Measurements of methane hydrate heat of dissociation using high pressure differential scanning calorimetry

The methane hydrate heat of decomposition was directly measured up to 20 MPa and 292 K using a high pressure differential scanning calorimeter (DSC). The methane hydrate sample was formed ex-situ using granular ice particles and subsequently transferred into the DSC cell under liquid nitrogen. The ice and water impurities in the hydrate sample were reduced by converting any dissociated hydrate into methane hydrate inside the DSC cell before performing the thermal properties measurements. The methane hydrate sample was dissociated by raising the temperature (0.5-1.0 K/min) above the hydrate equilibrium temperature at a constant pressure. The measured methane hydrate heat of dissociation (H→W+G), ΔH_d, remained constant at 54.44±1.45 kJ/mol gas (504.07±13.48 J/gm water or 438.54± 13.78 J/gm hydrate) for pressures up to 20 MPa. The measured ΔH_d is in agreement with the Clapeyron equation predictions at high pressures; however, the Clausius-Clapeyron equation predictions do not agree with the heat of dissociation data at high pressures. In conclusion, it is recommended that the Clapeyron equation should be used for hydrate heat of dissociation estimations at high pressures.     

高含水油包水乳液的水合物储气性能研究

油包水乳液是近年来新兴的一种水合强化材料,具有良好的水合储气潜力,但是为了保证乳液的稳定性,通常所用的油包水乳液含水量不超过50%。然而水合物的储气量与水含量密切相关,因此高含水的油包水乳液更具有应用前景。对含水量超过50%的油包水乳液进行了水合物的储甲烷研究,考察了乳化剂用量、初始压力及搅拌速率对储气性能的影响,最后考察了乳液的循环储气能力。结果表明：含水量超过55%后,含水量的增加会造成乳液液滴的增大,储气量的降低。乳液含水量为55%,复合乳化剂Span80 / Tween80（m_Tween80∶m_Span80=0.783∶1）用量5%（质量）（以水量为基准）的乳液最适合水合储气;初始压力的增加有利于水合储气性能的提高,但压力过高会造成水合物壳的快速形成,从而降低整体储气能力;适宜的搅拌速率有利于水合物的生成,过快或过慢都会引起水合速率的下降。本实验中最佳的乳液水合储气条件为：温度274.15 K、反应釜中气水体积比10∶1、甲烷初始压力6 MPa、搅拌速率700 r/min,在此条件下,储气量可达141.42 L 气/L 水。在此条件下进行循环储气实验证明该乳液具有良好的循环利用性,四次循环中储气量均在130 L 气/L 水以上。研究结果可为天然气储运以及含烃混合气分离提供技术参考。     

促进剂体系中二氧化碳水合物常压分解

目前,水合物法捕获二氧化碳时,都会添加不同的形成促进剂。而这些促进剂对后期二氧化碳水合物运输条件、封存条件的影响还未可知,因此本文对比研究了纯冰粉体系、单一促进剂体系和复配体系中CO₂水合物的稳定性,促进剂分别选用0.24g/L十二烷基酸钠（SDS）、0.288g/L四丁基溴化铵（TBAB）、5g/L纳米石墨（GN）及0.33g/L NaCl 4种促进剂。在常压、274.65K条件下利用定压分解方法研究不同体系中CO₂水合物的分解动力学特性。结果表明：单一促进剂体系中CO₂水合物的稳定性由强到弱的顺序为SDS>TBAB>GN≈纯冰粉>NaCl,并且SDS能够延长CO₂水合物分解时间,其平均分解速率相对于纯冰粉体系分别减少了29.6%、15.8%及18.5% 。在复配促进剂体系中TBAB+NaCl中水合物稳定性最强,TBAB占主导作用,NaCl＋GN中水合物稳定性最弱,NaCl占主导作用。此外文章还分析了促进剂体系中CO₂水合物稳定性提高的作用机理,主要与促进剂本身的性质有关。     

全可视化反应釜内二氧化碳水合物的生成分解特征

二氧化碳水合物封存技术已成为目前碳封存研究的热点。该技术中对于二氧化碳水合物的生成分解特征及其影响因素的研究是当前的重点和难点。本文设计了高压全透明双反应釜实验平台,以高纯度二氧化碳和去离子水作为研究对象,在17℃、7MPa的初始温压条件下,进行了二氧化碳水合物的初次和二次生成分解实验,并设置对照组对搅拌的影响进行了研究,而后与甲烷在相同条件下的实验进行对比。实验结果表明,搅拌会促进二氧化碳水合物的生成,在400r/min的转速条件下,缩短诱导时间可达40%,增大压降速率可达15%,形成更多且更致密厚实的水合物,并延缓了分解;多次生成可以减少水合物的诱导时间,但对于水合物生成的总量几乎没有影响。与甲烷水合物相比,二氧化碳水合物生成的量大且更难以分解,实验结果有利于二氧化碳的海洋水合物封存技术的开发应用。