离子液体与动力学抑制剂作用下混合气体水合物生成特性研究

利用等温恒容法实验考察了一种高性能离子液体N-丁基-N-甲基吡咯烷四氟硼酸盐([BMP][BF₄])、两种动力学抑制剂(KHIs)[聚乙烯基吡咯烷酮(PVP)和聚乙烯己内酰胺(PVCap)]及[BMP][BF₄]与KHI的二元混合物对甲烷/乙烷/丙烷三元混合气体水合物生成动力学过程的影响规律。通过分析压力和气相组分变化规律，发现混合气体水合物呈现两步骤生长模式。在高过冷度(>10℃)和高搅拌速率(1000 r/min)条件下，单一添加剂基本失效，而[BMP][BF₄]可较好协助增强PVCap的抑制性能。粉末X射线衍射和激光拉曼光谱测试结果均显示，所有体系中形成的水合物样品结构同时存在sⅠ型和sⅡ型，抑制剂的添加主要影响两种晶体结构的相对含量和各客体分子的笼子占有率。最后探讨了协同抑制机理。     

甲烷水合物生成分解的实验研究

海底存在着大量可燃冰,1 m3可燃冰能够储存160 m3的天然气。因此,可燃冰的开采与利用可燃冰储存与运输天然气具有重要意义。在改变搅拌、过冷度及低浓度动力学抑制剂的条件下,对甲烷水合物生成量与生成速率进行了实验研究。将甲烷水合物进行升温分解,分析水合物分解时的压力变化情况。结果表明:搅拌对甲烷水合物生成的促进效果最好,其次是过冷度,最后是超低浓度动力学抑制剂;水合物生成的传质过程最终被阻碍,采取将水与天然气的上下位置交换的方法,可以生成更多水合物。水合物升温可以得到相平衡曲线;改变初始时刻压力,可以得到不同温度区间的相平衡曲线;降低水合物分解时的升温速度,可以得到更长温度区间的相平衡曲线。     

含砂搅拌体系甲烷水合物生成与分解实验研究

利用高压反应釜装置,在不同初始压力、砂粒粒径等条件下进行甲烷水合物的生成与分解实验,研究细质砂粒固相颗粒对甲烷水合物成核诱导时间、生成和分解等的影响规律。结果表明:砂粒能够促进甲烷水合物生长,体系初始压力越高,水合物生成速率越高;体系初始压力为7.2 MPa、砂粒粒径为2 000目(6.5μm)时,水合物生成过程最稳定,且水合物生成量最多;在分解过程中,纯水体系和含砂体系的分解速率相当,只存在气体释放量的差异。进而得出结论:砂粒固体颗粒的存在会促进水合物生成,所以在水合物开采过程中,若工况满足水合物生成条件,水合物二次生成会更易发生,使得矿藏砂粒、水合物、天然气、海水在管道内的多相混输堵塞风险增加;含砂条件对水合物分解的影响作用不大,矿砂在水合物分解过程中对流动安全的影响有待深入研究。该研究成果为解决深水浅层水合物开采过程中的流动安全保障问题,提供了重要的理论基础和技术支撑。     

离子液体与PVP K90复合抑制剂对甲烷水合物的生成影响

注入抑制剂是油气行业解决管道输送过程因水合物生成而引发的堵塞问题最常用的方法。但现有大多数动力学抑制剂（KHIs）存在抑制性能不足、高过冷度条件下会失效等问题，可应用场合大大受限。离子液体作为绿色溶剂对甲烷水合物具有良好的热力学抑制作用。为改进KHIs的性能，提出将离子液体与KHIs复合。本文实验考察8.0 K过冷度、两种浓度下[1.0%(质量)、2.0%(质量)]离子液体N-丁基-N-甲基吡咯烷四氟硼酸盐([BMP][BF₄])、聚乙烯基吡咯烷酮（PVP K90）以及二者复配构成的复合型抑制剂对甲烷水合物抑制规律，得到了最佳组分配比。利用粉末X射线衍射（PXRD）和低温激光拉曼光谱测量了不同抑制剂体系中形成的甲烷水合物晶体微观结构和晶穴占有率，发现添加抑制剂不会改变sI型甲烷水合物晶体结构，但会影响水合物晶体的大、小笼占有率和水合数。结合宏观动力学实验和微观结构测试结果，揭示离子液体与PVP K90复合抑制剂的抑制机理。     

复配型抑制剂对高二氧化碳天然气水合物抑制效果评价

高含二氧化碳气田在开采、输送过程中生成天然气水合物易生成天然气水合物,严重影响气田的顺利开发。添加水合物抑制剂是高效的防治手段,但目前单独使用动力学抑制、热力学抑制都存在一定弊端。本文通过对比使用不同用量的动力学抑制剂、热力学抑制剂以及复配型抑制剂的抑制效果和经济指标,说明动力学抑制剂与热力学抑制剂复配后抑制效果更优,不仅降低了水合物生成温度,减少热力学抑制使用量,缩减抑制剂成本,提高了经济效益,同时减小对地层伤害。     

天然气水合物生成与相平衡曲线的试验分析

通过改变动力学抑制剂、过冷度、搅拌,借助生成实验装置,分析天然气水合物的生成效果,比较以上三个条件下的天然气水合物的生成速度和生成量,进而得出以上三个变量的对天然气水合物生成效果的贡献。结果表明:增加搅拌在天然气水合物生成过程中起主要作用,其次是过冷度以及动力学抑制剂。通过对水合物生成以及分解过程中压力-温度曲线的拟合,放缓反应釜内温度的升幅,可以得到更长更精确的拟合曲线。     

水合物动力学抑制剂的作用机理研究进展

水合物动力学抑制剂作为低液量抑制剂,其可应用于深水流动保障风险控制水合物冻堵问题,受到国内外研究者的广泛关注。本文重点阐述了动力学抑制剂的可承受最大过冷度和对诱导时间的延长这两个评价指标,同时梳理了动力学抑制剂对水合物生成及分解过程影响的研究成果。总体而言,可承受最大过冷度越大、延长诱导时间程度越强的动力学抑制剂,抑制水合物生成并保障流动安全的可靠性越高;动力学抑制剂对水合物生成与分解过程存在复杂的影响规律。本文将其对气体消耗速率、气体消耗量和形态,分解温度、时间和分解速率,“记忆效应”等影响进行了分析。结合上述研究成果,总结了动力学抑制剂对水合物的影响机理,特别是提出了化学型动力学抑制剂对水合物吸附抑制机理的概念示意图。最后,给出了未来深入开展动力学抑制剂研究的建议。     

一种可生物降解水合物动力学抑制剂的研究

目前用于天然气水合物防治的工业动力学抑制剂主要是水溶性聚合物，如聚乙烯基吡咯烷酮（PVP）、聚乙烯基己内酰胺（PVCap）、Gaffix VC-713等，然而生物降解性低限制了其工业应用。因此，开发环保型的抑制剂具有重要意义。实验采用易生物降解的海藻酸钠与PVCap的单体接枝共聚，合成一类新型水合物动力学抑制剂NaAlg-g-PVCap，结合最大过冷度及耗气量评价了新型抑制剂在水合物生成过程中的抑制性能，并通过BOD₅/COD值评价了新型抑制剂的生物降解性。结果表明低剂量[0.25%（质量）]下NaAlg-g-PVCap的最大耐受过冷度优于PVP K90，但低于PVCap，且随着添加剂量增大而微弱降低；在其最大耐受过冷度以下（ΔT_sub=5℃），NaAlg-g-PVCap表现出较好的水合物成核和生长抑制作用，其体系水合物初始生长速率值约只为纯水体系的 1/10，也远高于PVP体系，且总耗气量相比纯水及PVP体系减少了60%以上，与PVCap体系接近，但随着过冷度增大，NaAlg-g-PVCap成核抑制作用下降明显，这可能是共聚物中两部分共同作用的结果；同时，NaAlg-g-PVCap相比PVCap其生物降解性提高了26%， 倾向于易降解。说明PVCap与NaAlg共聚后优化了整体的性能，表现出较好的水合物抑制性能和生物降解性。     

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。     

含盐蒙脱石中甲烷水合物的生成/分解特性及离子分布研究

目前,天然气水合物成藏和开采是新能源开发应用的热点,但海域沉积物中天然气水合物的形成/分解特性,及盐离子对水合物稳定性的影响等关键问题亟待解决。利用天然气水合物原位取样技术对甲烷水合物在含盐多孔介质中生成和分解过程进行原位扫描电镜(Scanning Electron Microscopy, SEM)测试和能谱分析(Energy Dispersive Spectrometry, EDS),系统研究了含0.5 mol/L NaCl溶液的蒙脱石中甲烷水合物生成、分解过程中形貌的变化及离子分布特征。研究发现水合物生成和分解过程元素分布发生明显改变,水合物生成的排盐效应使得NaCl在水合物颗粒与颗粒交结处以水合盐离子的形成存在,并且Na+和Cl-在蒙脱石表面分层排布。水合物生成后蒙脱石表面呈独立颗粒状,水合物分解后蒙脱石表面凹陷并形成微小的气体通道,并且水合物分解后蒙脱石的骨架堆积结构发生改变。研究得出水合物成核、生长、分解过程均在特定基元颗粒间是独立进行的,并且生长与分解过程与水合物晶胞结构有关。     

Effect of complex inhibitors containing ionic liquids and PVP K90 on formation of methane hydrate

Injecting inhibitors is the most commonly used method in the oil and gas industry to solve the problem of blockage caused by hydrate formation during pipeline transportation. However, most of the kinetic hydrate inhibitors (KHIs) are strictly limited by weak inhibition performance and low subcooling. Ionic liquids, a kind of green solvent, have been recognized to act as excellent thermodynamic inhibitors on methane hydrate formation. So, it is proposed to add the ionic liquids into KHIs to improve their overall performance. In this paper, the kinetic effects of an ionic liquid N-butyl-N-methylpyrrolidine tetrafluoroborate ([BMP][BF₄]), a commercial kinetic inhibitor polyvinyl pyrrolidone (PVP K90) and their mixtures with different mass ratios on the methane hydrate formation were experimentally studied at 8.0 K subcooling and two concentrations [1.0%(mass) and 2.0%(mass)]. The best mass ratio of the compound inhibitor was determined. Moreover, the crystal structures and cage occupancy characteristics of methane hydrates formed without and with inhibitors at different mass concentrations and composition ratios were measured by using powder X-ray diffraction (PXRD) and low-temperature Laser Raman spectrometers. It was found that the addition of inhibitors did not change the crystal structure of methane hydrate, but affected the cage occupancies and hydration numbers. Based on the results from macroscopic kinetics and microscopic structure tests, the inhibition mechanism of compound inhibitors was proposed.     

Kinetic Modeling of Methane Hydrate Formation in the Presence of Low‐Dosage Water‐Soluble Ionic Liquids

The kinetic and thermodynamic effects of three typical low‐dosage imidazolium‐based ionic liquids (ILs) on methane hydrate formation and dissociation were investigated, considering the anion nature and subcooling and/or overpressure driving forces. Isochoric hydrate formation and dissociation data were obtained by the modified slow step‐heating method. ILs proved to have a dual effect on both formation and dissociation of methane hydrate including thermodynamic and kinetic inhibition. Kinetic modeling of methane hydrate inhibition by low‐dosage ILs was performed. Kinetic analysis showed that IL inhibitors mainly cause a delay in the nucleation or hydrate growth step. The related inhibition mechanism was resolved regarding the ionic nature and electrostatic interactions of ILs with water molecules. Two binomial exponential kinetic relations were derived and used for simple methane hydrate formation in the presence of ILs as kinetic hydrate inhibitors. The proposed relations can serve for a quick estimation of the nature, extent, strength, and effectiveness of ILs on various gas hydrates.     

Evidence for pore-filling gas hydrates in the sediments through morphology observation

To provide an evidence of natural gas hydrate occurrence state, a series of experiments on multiple growth and dissociation of 90.0% methane/10.0% propane hydrates at 1.3 MPa and 270.15 K were carried out in two sediments for morphology observation via a visible jacketed-reactor. The gas hydrate crystals were observed to form and grow on the surface of sediments at the initial growth. During the thermal decomposition, gas and liquid products had an unceasingly impact on the sediments, then gas/liquid–solid migration occurred, and a large number of cavitation appeared. In the later growth and dissociation experiments, the gas hydrate particles were in suspension or supporting states in the interstitial pore space between the sediment particles, indicating that the gas hydrate displayed a pore-filling characteristics. Through analyzing the distribution of gas hydrates and bubbles, it was found that the amount of gas hydrates distributed in the sediments was improved with multiple growth-dissociation cycle proceedings. Gas migration enhanced the sediment movement, which led to the appearance of the increasing quantity of gas bubbles in the sediments during cycles. Salts affected the growth of the gas hydrates and the migration of sediment grains, which also restricted the accumulation of gas bubbles in the sediments. According to the Raman analysis, the results showed that sII hydrates were formed for CH₄ and C₃H₈ gas mixtures in different sediments and solutions with hydration number of 5.84–6.53. The Salt restricted the access of gas into the hydrate cages.     

天然气水合物生成焓的实验研究

This paper reports the measurements of enthalpies of natural gas hydrates in typical natural gas mixture containing methane, ethane, propane and iso-butane at pressure in the vicinity of 2000 kPa (300 psi) and 6900 kPa(1000psi). The measurements were made in a multi-cell differential scanning calorimeter using modified high pressure cells. The enthalpy of water and the enthalpy of dissociation of the gas hydrate were determined from the calorimeter response during slow temperature scanning at constant pressure. The amount of gas released from the dissociation of hydrate was determined from the pumped volume of the high pressure pump. The occupation ratio (mole ratio) of the water to gas and the enthalpy of hydrate formation are subject to uncertainty of 1.5%.The results show that the enthalpy of hydrate formation and the occupation ratio are essentially independent of pressure.     

Experimental and Theoretical Investigation of Double Gas Hydrate Formation in the Presence or Absence of Kinetic Inhibitors in a Flow Mini‐Loop Apparatus

Double gas hydrate formation in the presence or absence of kinetic inhibitors in a flow mini‐loop apparatus was investigated. For the prediction of the gas consumption rate during hydrate formation in this system, the rate equation based on the Kashchiev and Firoozabadi model for simple gas hydrate formation in a batch system was developed for double gas hydrate formation in a flow mini‐loop apparatus. To complete the theoretical evaluation of gas hydrate formation through the mini‐loop apparatus in the presence or absence of kinetic hydrate inhibitors (KHI), a laboratory flow mini‐loop apparatus was set up to measure the induction time for hydrate formation and the uptake rate when a gaseous mixture (such as 75 % C1/25 % C3, 25 % C1/75 % C3, 75 % C1/25 % i‐C4, and 25 % C1/75 % i‐C4) is contacted with water containing or not containing dissolved inhibitor under suitable temperature and pressure conditions. In each experiment, a water blend saturated with gas mixture was circulated up to the required pressure. The pressure was maintained at a constant value during the experimental runs by means of a required gas mixture make‐up. The effect of pressure on gas consumption during hydrate formation was investigated in the presence or absence of polyvinylpyrrolidone (PVP) and L ‐tyrosine as kinetic inhibitors at various concentrations. A good agreement was found between the predicted and experimental data in the presence or absence of KHI. The total average absolute deviation percents between the experimental and predicted values of gas consumption were found to be 16.4 and 17.5 % for the double gas hydrate formation in the presence or absence of the kinetic inhibitors, respectively.     

0℃以下含SDS的甲烷水合物生成方式及过程对其分解速率的影响

The dissociation rates of methane hydrates formed with and without the presence of sodium dodecyl sulfate(methane-SDS hydrates),were measured under atmospheric pressure and temperatures below ice point to investigate the influence of the hydrate production conditions and manners upon its dissociation kinetic behavior.The experimental results demonstrated that the dissociation rate of methane hydrate below ice point is strongly dependent on the manners of hydrate formation and processing.The dissociation rate of hydrate formed quiescently was lower than that of hydrate formed with stirring;the dissociation rate of hydrate formed at lower pressure was higher than that of hydrate formed at higher pressure;the compaction of hydrate after its formation lowered its stability,i.e.,increased its dissociation rate.The stability of hydrate could be increased by prolonging the time period for which hydrate was held at formation temperature and pressure before it was cooled down,or by prolonging the time period for which hydrate was held at dissociation temperature and formation pressure before it was depressurized to atmospheric pressure.It was found that the dissociation rate of methane hydrate varied with the temperature(ranging from 245.2 to 272.2 K) anomalously as reported on the dissociation of methane hydrate without the presence of surfactant as kinetic promoter.The dissociation rate at 268 K was found to be the lowest when the manners and conditions at which hydrates were formed and processed were fixed.     

Stability and growth of gas hydrates below the ice–hydrate–gas equilibrium line on the P–T phase diagram

Using a previously developed experimental technique, the behavior of small methane and propane hydrate samples formed from water droplets between 0.25 and 2.5 mm in size has been studied in the pressure–temperature area between the ice–hydrate–gas equilibrium line and the supercooled water–hydrate–gas metastable equilibrium line, where ice is a stable phase. The unusual persistence of the hydrates within the area bounded by these lines and the isotherms at T=253 K for methane hydrate or at T=263 K for propane hydrates was observed. This behavior has not previously been reported. For example, in the experiment carried out at 1.9 MPa and 268 K, the methane hydrates existed in a metastable state (the equilibrium pressure at 268 K is 2.17 MPa) for 2 weeks, then immediately dissociated into liquid supercooled water and gas after the pressure was isothermally decreased slightly below the supercooled water–hydrate–gas metastable equilibrium pressure. It was found that dissociation of metastable hydrate into supercooled water and gas was reversible. The lateral hydrate film growth rates of metastable methane and propane hydrates on the surface of supercooled water at a pressure below the ice–hydrate–gas equilibrium pressure were measured. The temperature range within which supercooled water formed during hydrate dissociation can exist and a role of supercooled water in hydrate self-preservation is discussed.     

Experimental investigation of double gas hydrate formation in the presence of modified starch as a kinetic inhibitor in a flow mini‐loop apparatus

The main objective of the present work is experimental investigation of double gas hydrate formation with or without presence of modified starch as kinetic inhibitors in a flow mini‐loop apparatus. To this object, a laboratory flow mini‐loop apparatus was set up to measure the induction time for hydrate formation and the rate uptake when a gaseous mixture (such as 75% C1–25% C3, 25% C1–75% C3, 75% C1–25% i‐C4 and 25% C1–75% i‐C4) is contacted with water containing or not containing dissolved inhibitor under suitable temperature and pressure conditions. In each experiment, water blend saturated with gas mixture is circulated up to a required pressure. Pressure is maintained at a constant value during experimental runs by means of required gas mixture make‐up. The effect of pressure on gas consumption during hydrate formation is investigated with or without presence of polyvinylpyrrolidone and modified starch as kinetic inhibitors at various concentrations. Our results were shown that the modified starch can be applied as inhibitors in prevention of double gas hydrate formation in mini‐loop apparatus. © 2011 Canadian Society for Chemical Engineering     

甲烷水合物分解实验

在体积10 L的静态反应器中研究了水合物分解动力学,考察了储存温度和水合物量等因素对水合物分解的影响。实验结果表明,水合物在273.15 K以下时存在一种异常的自我保护效应,其在268.05 K时分解速度最慢;而水合物的储运压力与储罐中的水合物量有关,当储罐容积一定时,分解压力随着储罐中水合物量的增加而增加,但水合物的分解百分比随着水合物量的增加而减少;最后提出了在一定压力下储运水合物的方法。以期为水合物法固态储存气体技术的工业化应用提供实验数据和理论依据。