Experimental Study on the Morphology and Memory Effect of Methane

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Experimental Study on the Morphology and Memory Effect of Methane Hydrate Reformation Chuanxiao Cheng, Yongjia Tian, Fan Wang, Xuehong Wu, Jili Zheng, Jun Zhang, Longwei Li, and Penglin Yang Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b02934 • Publication Date (Web): 15 Mar 2019 Downloaded from http://pubs.acs.org on March 17, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

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The visual experimental system for simulating the formation and dissociation of natural gas hydrate. 143x55mm (300 x 300 DPI)

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The visual reactor of hydrate formation and dissociation.


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The armor effect of methane hydrate.


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Sequential images of the first formation of hydrate.


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Schematic concept of hydrate formation above the porous media. 51x33mm (300 x 300 DPI)


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The unstable flocculated hydrates in the process of hydrate reformation.


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The morphology of the first hydrate formation. 60x60mm (300 x 300 DPI)


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The morphology of hydrate reformation.


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Appearance of gaps. 60x60mm (300 x 300 DPI)


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The turbid solution during hydrate dissociation.


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Hydrate clumps. 60x60mm (300 x 300 DPI)


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The release of bubbles from the solution. 60x60mm (300 x 300 DPI)


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Memory effect stability in the closed and heating dissociation pattern. 68x79mm (600 x 600 DPI)


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The correlation between the induction time of hydrate formation and the cooling rate. 80x58mm (600 x 600 DPI)


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The effect of the dissociation temperature on the memory effect. Td is the hydrate dissociation temperature (°C) and ti is the induction time (min). 73x60mm (600 x 600 DPI)


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Comparison of the hydrate reformation before and after dissociation via depressurization. 79x60mm (600 x 600 DPI)


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Experimental Study on the Morphology and Memory Effect of Methane Hydrate Reformation Chuan-Xiao Cheng, Yong-Jia Tian, Fan Wang, Xue-Hong Wu, Ji-Li Zheng, Jun Zhang,* Long-Wei Li, Peng-Lin Yang School of Energy and Power Engineering, Zhengzhou University of Light Industry, Zhengzhou 450002, China KEYWORDS: Methane hydrate

Memory effect

Visualization

Morphology Reformation

Depressurization ABSTRACT: The memory effect of hydrate reformation has an important influence on the hydrate growth mechanism and technological application. This paper focuses on the relation between the morphologies and memory effects of hydrate reformation and the stability of the memory effect using a visual research method. The results indicated that the hydrate morphology differed between the first formation and the reformation. A specific flocculated hydrate was observed only in the process of hydrate reformation. Moreover, the flocculated hydrate was unstable, and it was observed to first grow and then shrink. In this study, the free water was observed to also become turbid during hydrate dissociation. In addition, many gaps were generated during hydrate dissociation, which affected the hydrate dissociation efficiency and the geological safety of hydrate exploitation. The effects of the dissociation temperature and


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pressure difference on the stability of the memory effects were investigated. The results showed that the memory effect tended to be stable in the closed and heating dissociation patterns. Furthermore, depressurization significantly inhibited the memory effect of hydrate reformation. After depressurization, the induction time of first hydrate formation was increased 4-fold compared with the induction time before depressurization. The experimental results are well explained by the mechanism of dissolved gas remaining in solution after hydrate dissociation. 1. INTRODUCTION Natural gas hydrates are nonstoichiometric inclusion compounds composed of guest molecules (methane, ethane, propane, and carbon dioxide) and water molecules, which are formed at certain temperatures and pressures.1 Natural gas hydrates are potential alternative sources of future energy given their enormous energy reserves, high purity levels and environmentally friendly characteristics.2,3 It was estimated that the global natural gas hydrates contain a carbon content that is approximately two-fold larger than that of fossil fuels, with a value of at least 10000 Gt.4 In the Nankai Trough (Japan) and Mallik (Canada), exploitation tests of natural gas hydrates were conducted using thermal stimulation and depressurization.5 In the Shenhu area (China), an exploitation test of natural gas hydrates within silt and silty clay sediments was successfully carried out for the first time.6-9 The rate of gas produced was 5000 m3/day, and a historic breakthrough was obtained with regards to a stable gas production time.9 These tests provided important data for gas hydrate exploitation. The commercial application of natural gas hydrate is promising. In addition, as a phase change material, gas hydrate has an important specific characteristic, in which its formation and dissociation are simultaneously controlled by its temperature, pressure and intrinsic kinetics. Considering that a gas hydrate has the characteristics of a satisfactory cold


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storage density (240-390 kJ kg-1), suitable phase change temperature (5-12 °C), high heat transfer performance and few additives, gas hydrate technology will be widely used in industrial production, such as cold storage,10,11 gas separation,12,13 desalination of seawater,14,15 gas storage and transportation,16-19 and carbon dioxide capture.20-24 However, certain problems associated with the mechanisms of hydrate formation and dissociation are still not clearly explained, such as the memory effect,25-32 a specific phenomenon in which the induction time of hydrate reformation is shorter than that of the first formation. With regards to the mechanism of the memory effect, scholars have proposed two hypotheses: the residual cage structure hypothesis33,34 and the hypothesis of dissolved gas remaining in solution after hydrate dissociation35. The first hypothesis indicates that the residual cage structure after hydrate dissociation provides a driving force for hydrate reformation, thereby causing the memory effect.36 The location of hydrate dissociation becomes the potential area of hydrate reformation.37 However, some results were negative. Rodger38 observed no distinct residual cage structure after hydrate dissociation using molecular dynamics simulations. Buchanan et al.39 concluded that the structures of water before and after methane hydrate dissociation were not notably different. The second hypothesis has attracted more attention in recent years due to the occurrence of MNBs (bubbles between 100 and 10000 nm in diameter) in the hydrate-dissociated water. In the hydrate dissociation process, the discharge rate of gas is higher than its diffusion rate, so the dissociation solution is oversaturated with gas.40 The oversaturated solution is favorable for gas aggregation to form MNBs.35,40-42 The occurrence of MNBs is a remarkable phenomenon in the hydrate dissociation process because MNBs exhibit a long lifespan.43,44 MNBs in solution could provide a larger gas-liquid interface and a more heterogeneous nucleation position for hydrate reformation. Thus, MNBs play a key role in memory effects. If there are still large amounts of


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MNBs in the solution used for hydrate formation, the second hypothesis would become important. Uchida et al.45 reported that MNBs were substantially retained in the solution for longer than 1 day, and the lifespan of MNBs depended on the discharge rate of dissolved gas. In addition, MNBs in the hydrate dissociation solution would enhance the role of memory effects for hydrate reformation.45 Pressure difference46-51 helps the MNBs to escape from the solution, thereby affecting the memory effect of hydrate reformation. However, the characteristics of the memory effects before and after hydrate dissociation via depressurization remain unclear. When studying the morphologies or memory effects of gas hydrates, visualization can be an effective method.52 Ohmura et al.53 observed that the morphology of methane hydrate was skeletal, columnar or dendritic and that these forms were affected by the pressure. Babu et al.54 studied the growth morphologies of methane hydrates in different porous media. Uchida et al.35 studied the memory effects using transmission electron microscopy and reported that there were MNBs in the hydrate dissociation solution. Overall, the studies on the relationship between the memory effect and hydrate morphology were not comprehensive. Memory effects also affect the stochastic nature of hydrate formation. Duchateau et al.55 reported that memory effects inhibited the stochastic nature and enhanced the repeatability of hydrate formation experiments. Other methods are available to inhibit the stochastic nature. Sun et al.56 studied the growth kinetics of THF (tetrahydrofuran) hydrates using statistical methods and demonstrated that sands had a larger effect on reducing the stochastic nature than did ions. Veluswamy et al.57 reported a lower stochastic nature of the hydrate formation process via the combination of batch mixing and amino acids. The reduction in stochastic nature can make hydrate reformation more stable, and the formation mechanism of hydrates can then be studied more accurately.


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Although studies on the memory effect of hydrate reformation have been extensively carried out, the mechanism of the memory effect remains controversial. In this paper, the relationship between the memory effect and hydrate morphology is analyzed through a visual experiment system. The stability of the memory effect is assessed by performing repeated hydrate experiments considering the effects of pressure and temperature. Especially, hydrate reformation experiments after dissociation via depressurization are conducted to explore the influence of depressurization on the memory effect. 2. EXPERIMENTAL SECTION A schematic diagram of the visual experimental system is presented in Figure 1a and 1b. The high-pressure cylindrical reactor (with a volume of 1.16 L) with two sapphire windows (with diameters of 70 mm) was made of 316 stainless steel and may sustain pressures of up to 10 MPa. A thermostat (XT5718RC-E800L, Xutemp, Co., Ltd., China) with an accuracy of ±0.1 K and a temperature range from -15 to 50 °C was used to regulate the temperature of the reactor. The reactor temperature was measured by two Pt-1000 units (JM608I, Hefei Zhongding Electromechanical Equipment Co., Ltd., China) with an accuracy of ±0.2 %. The pressure was measured using a Unik 5000 pressure transducer (PTX5072-TB-A1-CA-H0-PA, GE Sensing and Inspection Co., Ltd., China) with a pressure range from 0 to 25 MPa and a precision of 0.25 % FS (full scale). A gas mass flow controller (AST10 series, Asert Instruments, Beijing, Co., Ltd., China) was used to record the gas transport rate. A digital camera (EOS 6D, Canon Company, lens model EF24-105 mm f/4L IS USM, Japan) was used to collect methane hydrate morphological data. A constant flux pump with a maximum working pressure of 20 MPa and a repeat precision of ±1 % was obtained from Beijing Xingda Science and Technology Development Co., Ltd.


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Figure 1a. The visual experimental system for simulating the formation and dissociation of natural gas hydrate.

Figure 1b. The visual reactor of hydrate formation and dissociation. Methane (99.9 %, Henan Yuanzheng Technology Development Co., Ltd., China) was used to form hydrates. The porous media were composed of glass beads (BZ-02, with a porosity of 37.2 % from As-One Co., Ltd., Japan). Deionized water (with a resistivity of approximately 17 to 18 MΩ·cm) was used in all experiments. In the experiments, the visual reactor was cleaned with deionized water 3 times. Then, 300 g of deionized water and 300 g of porous media were loaded into the reactor. The reactor was placed in a tank in which the cooled glycol aqueous solution was controlled by a thermostat to maintain the reactor temperature. After the air inside the reactor was flushed by methane 3 times, methane


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was injected into the reactor. To calculate the amount of gas injected, the flow rate of methane was controlled by a pressure-reducing valve and a flow transmitter. Methane injection was stopped when the pressure reached the target value. The morphological changes in the methane hydrates were recorded by the camera. The pressure and temperature were recorded continuously every 30 s by the data acquisition system in all experiments. When the pressure reduction was lower than 0.1 MPa in the subsequent 10 hours, the hydrate formation was judged to have been completed. In this paper, the amount of methane in the reactor was calculated using the BWRS (Benedict-Webb-Rubins) equation.58,59 The amount of methane injected into the reactor was 2.66 mol, and the amount of methane consumed by hydrate formation was approximately 1.44-1.47 mol. The detailed calculation methods and formulas are provided in the supporting information. To study the effect of the dissociation temperature and pressure difference on the memory effects of hydrate reformation, hydrate dissociation experiments were performed based on two patterns: the closed and heating dissociation pattern and the dissociation via depressurization pattern. The closed and heating dissociation pattern implied that the reactor was closed, and the hydrate dissociation exclusively depended on the increase in temperature. During the dissociation process, no gas or water flowed out of the reactor. This hydrate dissociation method differed from the study methods of Uchida and Sefidroodi et al.,45,60 in which the dissociated methane was discharged to the environment. The effect of different dissociation temperatures on the memory effects was also studied by maintaining a constant hydrate formation temperature in the closed and heating dissociation pattern and setting the hydrate dissociation temperature at 11 °C, 15 °C, 20 °C and 25 °C. The stability of the memory effects was studied by repeating the hydrate experiments at a formation temperature of 2 °C and a dissociation temperature of 15 °C. The stability was verified


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by comparing the induction time of three runs of hydrate reformation. The induction time was defined as the time interval from the phase equilibrium point (10.05 °C at 7.4 MPa)61 to the moment when the temperature increased due to hydrate formation.26 The phase equilibrium point was obtained as shown in Figure S.1 in the supporting information. The effect of dissociation via depressurization on the memory effect stability was studied by combining two dissociation patterns. First, the memory effects of hydrate reformation before depressurization were obtained by repeating the hydrate experiments in the closed and heating dissociation pattern. Next, the hydrate dissociation via depressurization was conducted at atmospheric pressure, and hydrate reformation was carried out to obtain the induction time of the hydrate reformation after depressurization. Moreover, to explore the recovery of the memory effects after depressurization, the hydrate formation and dissociation experiments were repeated in the closed and heating dissociation pattern, and the induction time of hydrate formation was analyzed. 3. EXPERIMENTAL RESULTS AND DISCUSSION 3.1. Relation between the memory effect and morphology of hydrate reformation. Because methane has a high degree of hydrophobicity (the solubility of methane is only 3.3 mL/100 mL water at 20 °C35,40) and the concentration of methane in solution is the highest at the gas-liquid interface, hydrates are usually preferentially formed there. However, the hydrates at the gas-liquid interface hinder the transport of gas and water; thus, the hydrate formation rate is low. This phenomenon is known as the armor effect.62 In this paper, the formation experiment of methane hydrates with fresh water was carried out at an initial pressure of 7.5 MPa at 15 °C. Then, 150 hours after the start of the hydrate experiment, only a thin hydrate layer was formed at the gas-liquid interface and visual windows, as shown in Figure 2.


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Figure 2. The armor effect of methane hydrate. In this paper, porous media were used to overcome the armor effect, which were composed of glass beads (BZ-02).63-69 Figure 3 shows that the porous media promoted hydrate formation. Hydrates started to form at 570 min. Hydrate formation was deemed finished at 1208 min, after the pressure reduction remained at lower than 0.1 MPa for 10 hours. Note that the hydrates were not preferentially formed in the porous media or uniformly distributed in the space in the oversaturated water system. The hydrates first formed at the gas-liquid interface and gradually expanded upward via capillary forces. This phenomenon was consistent with the research results of Babu and Linga et al.70,71 The hydrate growth model in this study is shown in Figure 4. In the model, water was pumped into the reactor to fill the interior spaces of the porous media. The reactor was cooled to a suitable temperature for hydrate formation. When the temperature and pressure were favorable for hydrate formation, water would be withdrawn from the porous media to form hydrates above the porous media. The hydrate growth behavior is beneficial to the application of hydrate technology, such as gas separation, desalination of seawater, and so on.70 In addition, many cracks were observed in the hydrate layer. The cracks increased the porosity


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and permeability of the hydrate sediments, which influenced the heat and mass transfer for hydrate dissociation.

Figure 3. Sequential images of the first formation of hydrate.

Figure 4. Schematic concept of hydrate formation above the porous media. During hydrate reformation, a specific unstable flocculated hydrate was first observed, as shown in Figure 5. The flocculated hydrate exhibited a loose morphology. Based on the


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progression of hydrate formation, the flocculation first grew in size and then shrank. At 144 min, the amount of flocculated hydrates reached a maximum value. Because hydrate formation is an exothermic process, increases in the temperature and pressure do occur in local areas. When the temperature and pressure were higher than those at phase equilibrium, parts of the flocculated hydrates could dissociate. Interestingly, the flocculation was exclusively observed during the hydrate reformation, but was not observed in the process of the first hydrate formation. The flocculated hydrates observed in the liquid phase were important pieces of evidence to demonstrate the different growth morphologies of hydrates. Because of the occurrence of MNBs in the hydrate-dissociated water, hydrate reformation was enhanced, causing different growth morphologies of the hydrates. The emergence of flocculated hydrates was verified by repeating the experiments, as is shown in Figure S.2 in the supporting information.

Figure 5. The unstable flocculated hydrates in the process of hydrate reformation.


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The difference in hydrate growth morphologies between the first formation and reformation is reported in this paper. The morphology of the first hydrate formation exhibited a compact form, as shown in Figure 6a. The morphology of the hydrate reformation had a column-like form, and notable spaces occurred between the hydrates, as shown in Figure 6b. Because gas hydrates have a driving force for expansive growth, the column-like morphology can provide a larger hydrategas interface and heat transfer area, thereby promoting the formation of hydrates. In addition, the column-like morphology only appeared in the process of hydrate reformation. Thus, the memory effect affected the growth and morphology of methane hydrates.

Figure 6. Different morphologies of methane hydrates. (a) The morphology of the first hydrate formation; (b) The morphology of hydrate reformation. 3.2. Morphology of hydrate dissociation. The dissociation morphologies of methane hydrates with different dissociation patterns were also studied. In the closed and heating dissociation pattern, the hydrates exhibited a white loosened morphology, and many gaps were observed in the hydrates, as shown in Figure 7a. These gaps would affect the geological safety of natural gas hydrate exploitation because the strength of hydrates is reduced. In the late stage of hydrate dissociation, a phenomenon in which the free water became turbid was observed, as shown in Figure 7b. The turbid solution was


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caused by the presence of many bubbles/MNBs produced by hydrate dissociation.72 As these bubbles increased the gas-liquid interface, the induction time of hydrate reformation was reduced.

Figure 7. Hydrate dissociation in the closed and heating dissociation pattern. (a) Appearance of gaps; (b) The turbid solution during hydrate dissociation. During the dissociation via depressurization, the transparent hydrates rapidly became white and collapsed into clumps, as shown in Figure 8a. Because the gas was rapidly produced by depressurization and could not be discharged in time during the hydrate dissociation, many pores were formed in the hydrates. These pores affected the light reflection; thus, the hydrates appeared white. As depressurization progressed, the pores gradually became larger and disrupted the hydrate morphology, causing hydrates to collapse into clumps. During the late stage of hydrate dissociation, many bubbles emerged from the solution, as shown in Figure 8b. These bubbles indicated that the dissociated methane could be stored in the solution as bubbles/MNBs, which provided a larger gas-liquid interface for hydrate reformation. According to the ideal gas equation of state (𝑃𝑃𝑃𝑃 = 𝑛𝑛𝑛𝑛𝑛𝑛), the bubble volume increased 75-fold when the pressure was reduced from 7.5 MPa to atmospheric pressure. When the hydrates were dissociated at


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atmospheric pressure, the bubbles/MNBs stored in the solution would be released in large quantities given the volume expansion.

Figure 8. Hydrate dissociation via depressurization. (a) Hydrate clumps; (b) The release of bubbles from the solution. 3.3. Hydrate reformation memory effect stability. The hydrate reformation experiments were repeated with the closed and heating dissociation pattern. Figure 9 not only shows that the first formation and reformation of hydrates exhibited differences in the induction time but also demonstrated that the induction times of the three repeated experiments tended to remain stable (22 min). Certain fluctuations in the induction time of the repeated hydrate formations were noted, but these fluctuations were slight and mainly caused by changes in the cooling rates, as shown in Figure 10. These results were verified by repeating the experiments shown in Figure S.3 in the supporting information. Based on the repeated hydrate experiments, this paper proved that the memory effects were stable in the closed and heating dissociation pattern.


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Figure 9. Memory effect stability in the closed and heating dissociation pattern.

Figure 10. The correlation between the induction time of hydrate formation and the cooling rate. The stable memory effect could be reasonably explained by the behavior of MNBs. In the process of hydrate dissociation, large amounts of MNBs were produced. These MNBs could exist in the solution for a long time due to their small diameters. Because MNBs increased the gas-liquid interface, hydrate reformation was promoted. When there were significant amounts of MNBs in the hydrate dissociation solution, the rate of hydrate reformation would be greatly increased, and the influence of the stochastic nature on the induction time of hydrate formation


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could be neglected. When the amounts of MNBs in the solution reached a stable value, the memory effects also tended to remain stable. Therefore, a stable memory effect was obtained. Notably, the application and development of gas hydrate technology would be significantly promoted by changing the amounts of MNBs in the solution to control the memory effect. Adjusting the amounts of MNBs mainly relied on controlling the formation of MNBs and increasing the lifespan of MNBs. The formation of MNBs was related to the rate of hydrate dissociation. However, in the application of hydrate technology, the key to controlling the amounts of MNBs was to adjust their lifespan. The lifespan of MNBs was mainly affected by their rise speed. The rise speed of bubbles is calculated by Stokes’ law as 𝑉𝑉 = (𝜌𝜌 − 𝜌𝜌0 )𝑔𝑔𝑑𝑑2 /18𝜇𝜇,

in which μ is the viscosity of water, ρ and ρ0 are the density of water and methane, respectively, g is the gravitational acceleration, and d is the diameter of the bubbles.35 In this study, the lifespan of the MNBs was estimated to be 1.28 days and the detailed calculations were provided in the supporting information. Moreover, in the processes of hydrate formation and dissociation, the effects of the density and viscosity on the rise speed of bubbles are almost neglected. Therefore, reducing the diameter of the bubbles by adjusting the temperature and pressure difference is the main means to decrease the rise speed of MNBs. A low rise speed would extend the lifespan of MNBs. In this paper, the memory effect was studied by adjusting the dissociation temperature and pressure difference at the same holding time. The dissociation temperature of hydrates is one of the key factors influencing the memory effect. Figure 11 shows that the induction time of hydrate reformation gradually increased with increasing dissociation temperature. In addition, when the dissociation temperature was higher than 25 °C, the memory effect disappeared. The experimental phenomenon was consistent with the conclusion of Takeya et al.73-75 A higher dissociation temperature would increase the


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diameter of bubbles, which caused MNBs to disappear due to the MNBs floating up to the gasliquid interface. Therefore, the memory effect would vanish.

Figure 11. The effect of the dissociation temperature on the memory effect. Td is the hydrate dissociation temperature (°C) and ti is the induction time (min). 3.4. The effect of dissociation via depressurization on the memory effect. To study the effect of the pressure difference on the memory effects, hydrate formation and dissociation experiments were carried out with two different dissociation patterns in this study. Figure 12 shows that the induction time of hydrate formation was gradually shortened and approached a stable value (at 69 min) before dissociation via depressurization occurred. After dissociation via depressurization, the induction time of the first hydrate formation was 265 min, which represented an approximately 4-fold increase compared with the stable induction time. Therefore, the memory effect was weakened by depressurization. Then, the hydrate reformation experiment was carried out in the closed and heating dissociation pattern. The induction time of hydrate reformation was gradually reduced (from 265 to 94 min); thus, the memory effect had been restored.


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Figure 12. Comparison of the hydrate reformation before and after dissociation via depressurization. The key factor of a stable memory effect was the amount of bubbles/MNBs in the solution. However, after hydrate dissociation via depressurization, the bubbles expanded due to the pressure difference, which caused large amounts of bubbles/MNBs to escape from the solution. The decrease in bubbles/MNBs in the solution led to an increase in the induction time of hydrate reformation. In the closed and heating dissociation pattern after depressurization, the amount of bubbles/MNBs in the solution would increase gradually and tended to remain stable with repeated experiments; thus, the memory effect was restored. The results of this paper were in accordance with the behavior of MNBs. For example, the free water became turbid, which was caused by the presence of large amounts of MNBs. The formation of unstable flocculated hydrates was inferred to be caused by MNBs in the hydrate dissociation solution. The stability of the memory effect was attributed to the fact that the amounts of MNBs in the dissociation solution were basically the same because the dissociation temperature, pressure difference and holding time were controlled. The memory effect decreased with increasing dissociation temperature because the higher temperature increased the rise speed of the bubbles, which caused large amounts of MNBs to escape. The attenuation of the memory


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Energy & Fuels

effect after hydrate dissociation via depressurization was caused by the decrease in the amount of MNBs. These results provided support for our further study on the relationship between MNBs and memory effects. 4. CONCLUSION The morphologies of hydrate formation and dissociation were studied using a visualization system. The results indicated that hydrates were preferentially formed at the gas-liquid interface and gradually expanded upward via capillary forces. The first hydrate formation morphologically exhibited a compact form, and the hydrate reformation morphology had a column-like form. In addition, unstable flocculated hydrates were observed in the liquid phase, and they were exclusively present in the process of hydrate reformation. In the process of hydrate dissociation, many gaps were observed in the hydrates. These gaps affect the geological safety of natural gas hydrate exploitation. During heating dissociation, turbid hydrate-dissociated water was observed. The experimental results showed that a high dissociation temperature and pressure difference inhibited the stability of the memory effect. Before the dissociation via depressurization, the induction time of hydrate formation decreased with repeated experiments and tended to remain stable. After the dissociation via depressurization, the induction time of the first hydrate formation was increased 4-fold because of the escape of bubbles/MNBs. These results were explained by the behavior of MNBs. 

AUTHOR INFORMATION

Corresponding Author *

Tel.: +860371-63624373; E-mail: [email protected] (Jun Zhang).

Notes The authors declare no competing financial interest.


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

Page 36 of 47

ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (51606173,

51606172, and 51622603), the Key Laboratory of Gas Hydrate, Guangzhou Institute of Energy Conversion (Y807kg1001) and the Graduate’s Scientific Research Foundation of Zhengzhou University of Light Industry. 

ABBREVIATIONS MNB, micro-nano bubble; THF, tetrahydrofuran.



REFERENCES (1) Sloan Jr, E. D.; Koh, C. Clathrate hydrates of natural gases. CRC press: 2007. (2) Zhao, J. F.; Song, Y. C.; Lim, X. L.; Lam, W. H. Opportunities and challenges of gas

hydrate policies with consideration of environmental impacts. Renewable Sustainable Energy Rev. 2017, 70, 875-885. (3) Yang, J. H.; Tohidi, B. Characterization of inhibition mechanisms of kinetic hydrate inhibitors using ultrasonic test technique. Chem. Eng. Sci. 2011, 66 (3), 278-283.

(4) Klauda, J. B.; Sandler, S. I. Global distribution of methane hydrate in ocean sediment. Energy Fuels 2005, 19 (2), 459-470. (5) Jin, Y.; Konno, Y.; Yoneda, J.; Kida, M.; Nagao, J. In situ methane hydrate morphology investigation: natural gas hydrate-bearing sediment recovered from the Eastern Nankai Trough area. Energy Fuels 2016, 30 (7), 5547-5554.


20

Page 37 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(6) Sun, J. X.; Ning, F. L.; Lei, H. W.; Gai, X. R.; Sánchez, M.; Lu, J. G.; Li, Y. L.; Liu, L. L.; Liu, C. L.; Wu, N. Y.; He, Y.; Wu, M. Wellbore stability analysis during drilling through marine gas hydrate-bearing sediments in Shenhu area: A case study. J. Pet. Sci. Eng. 2018, 170, 345367. (7) Yu, T.; Guan, G.; Abudula, A.; Yoshida, A.; Wang, D.; Song, Y. Gas recovery enhancement from methane hydrate reservoir in the Nankai Trough using vertical wells. Energy 2019, 166, 834-844. (8) Wang, F. T.; Zhao, B.; Li, G. Prevention of potential hazards associated with marine gas hydrate exploitation: A review. Energies 2018, 11 (9), 2384.

(9) Too, J. L.; Cheng, A.; Linga, P. In Fracturing methane hydrate in sand: A review of the current status, Proceedings of the Offshore Technology Conference Asia, Kuala Lumpur, Malaysia, 2018; Offshore Technology Conference: Kuala Lumpur, Malaysia, 2018. (10) Wang, X. L.; Dennis, M. Thermal energy harvest in the discharge of CO2 semi-clathrate hydrate in an emulated cold storage system. Appl. Therm. Eng. 2017, 124, 725-733.

(11) Wang, X. L.; Dennis, M.; Hou, L. Z. Clathrate hydrate technology for cold storage in air conditioning systems. Renewable Sustainable Energy Rev. 2014, 36, 34-51.

(12) Kim, E.; Ko, G.; Seo, Y. Greenhouse gas (CHF3) separation by gas hydrate formation. ACS Sustainable Chem. Eng. 2017, 5 (6), 5485-5492.


21

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 47

(13) Hashimoto, H.; Yamaguchi, T.; Kinoshita, T.; Muromachi, S. Gas separation of flue gas by tetra-n-butylammonium bromide hydrates under moderate pressure conditions. Energy 2017, 129, 292-298. (14) Lv, Y. N.; Wang, S. S.; Sun, C. Y.; Gong, J.; Chen, G. J. Desalination by forming hydrate from brine in cyclopentane dispersion system. Desalination 2017, 413, 217-222.

(15) Yang, M. J.; Song, Y. C.; Jiang, L. L.; Liu, W. G.; Dou, B. L.; Wen, J. Effects of operating mode and pressure on hydrate-based desalination and CO2 capture in porous media. Appl. Energy 2014, 135, 504-511. (16) Erfani, A.; Fallah-Jokandan, E.; Varaminian, F. Effects of non-ionic surfactants on formation kinetics of structure H hydrate regarding transportation and storage of natural gas. J. Nat. Gas Sci. Eng. 2017, 37, 397-408. (17) Prah, B.; Yun, R. CO2 hydrate slurry transportation in carbon capture and storage. Appl. Therm. Eng. 2018, 128, 653-661. (18) Kezirian, M. T.; Phoenix, S. L. Natural gas hydrate as a storage mechanism for safe, sustainable and economical production from offshore petroleum reserves. Energies 2017, 10 (6), 1-8. (19) Charin, R. M.; Sum, A. K. Steady-state and transient studies of gas hydrates formation in non-emulsifying oil systems. Energy Fuels 2017, 31 (3), 2548-2556.


22

Page 39 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(20) Wang, Y. H.; Lang, X. M.; Fan, S. S. Hydrate capture CO2 from shifted synthesis gas, flue gas and sour natural gas or biogas. J. Energy Chem. 2013, 22 (1), 39-47.

(21) Yang, J. H.; Okwananke, A.; Tohidi, B.; Chuvilin, E.; Maerle, K.; Istomin, V.; Bukhanov, B.; Cheremisin, A. Flue gas injection into gas hydrate reservoirs for methane recovery and carbon dioxide sequestration. Energy Convers. Manage. 2017, 136, 431-438.

(22) Zhang, L. X.; Yang, L.; Wang, J. Q.; Zhao, J. f.; Dong, H. S.; Yang, M. J.; Liu, Y.; Song, Y. C. Enhanced CH4 recovery and CO2 storage via thermal stimulation in the CH4/CO2 replacement of methane hydrate. Chem. Eng. J. 2017, 308, 40-49.

(23) Zheng, J. J.; Zhang, P.; Linga, P. Semiclathrate hydrate process for pre-combustion capture of CO2 at near ambient temperatures. Appl. Energy 2017, 194, 267-278.

(24) Kuang, Y. M.; Lei, X.; Yang, L.; Zhao, Y. C.; Zhao, J. F. Observation of in situ growth and decomposition of carbon dioxide hydrate at gas–water interfaces using magnetic resonance imaging. Energy Fuels 2018, 32 (6), 6964-6969.

(25) Ripmeester, J. A.; Alavi, S. Some current challenges in clathrate hydrate science: Nucleation, decomposition and the memory effect. Curr. Opin. Solid State Mater. Sci. 2016, 20 (6), 344-351.


23

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 40 of 47

(26) Zhao, J. F.; Wang, C. J.; Yang, M. J.; Liu, W. G.; Xu, K.; Liu, Y.; Song, Y. C. Existence of a memory effect between hydrates with different structures (I, II, and H). J. Nat. Gas Sci. Eng. 2015, 26, 330-335. (27) Chen, J.; Yan, K. L.; Jia, M. L.; Sun, C. Y.; Zhang, Y. Q.; Si, S.; Ma, Q. L.; Yang, L. Y.; Wang, X. Q.; Chen, G. J. Memory effect test of methane hydrate in water + diesel oil + sorbitan monolaurate dispersed systems. Energy Fuels 2013, 27 (12), 7259-7266.

(28) Martinez de Baños, M. L.; Carrier, O.; Bouriat, P.; Broseta, D. Droplet-based millifluidics as a new tool to investigate hydrate crystallization: Insights into the memory effect. Chem. Eng. Sci. 2015, 123, 564-572. (29) Khurana, M.; Yin, Z. Y.; Linga, P. A review of clathrate hydrate nucleation. ACS Sustainable Chem. Eng. 2017, 5 (12), 11176-11203. (30) Parent, J. S.; Bishnoi, P. R. Investigations into the nucleation behaviour of methane gas hydrates. Chem. Eng. Commun. 1996, 144 (1), 51-64.

(31) Hwang, M. J.; Wright, D. A.; Kapur, A.; Holder, G. D. An experimental study of crystallization and crystal growth of methane hydrates from melting ice. J. Inclusion Phenom. Mol. Recognit. Chem. 1990, 8 (1), 103-116. (32) Lee, J. D.; Susilo, R.; Englezos, P. Kinetics of structure H gas hydrate. Energy Fuels 2005, 19 (3), 1008-1015.


24

Page 41 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(33) Sloan, E. D.; Subramanian, S.; Matthews, P. N.; Lederhos, J. P.; Khokhar, A. A. Quantifying hydrate formation and kinetic inhibition. Ind. Eng. Chem. Res. 1998, 37 (8), 31243132. (34) Oshima, M.; Shimada, W.; Hashimoto, S.; Tani, A.; Ohgaki, K. Memory effect on semiclathrate hydrate formation: A case study of tetragonal tetra-n-butyl ammonium bromide hydrate. Chem. Eng. Sci. 2010, 65 (20), 5442-5446. (35) Uchida, T.; Yamazaki, K.; Gohara, K. Generation of micro- and nano-bubbles in water by dissociation of gas hydrates. Korean J. Chem. Eng. 2016, 33 (5), 1749-1755.

(36) Wu, Q.; Zhang, B. Y. Memory effect on the pressure-temperature condition and induction time of gas hydrate nucleation. J. Nat. Gas Chem. 2010, 19 (4), 446-451.

(37) Sowa, B.; Maeda, N. Statistical study of the memory effect in model natural gas hydrate systems. J. Phys. Chem. A 2015, 119 (44), 10784-10790.

(38) Rodger, P. M. Methane hydrate: melting and memory. Ann. N. Y. Acad. Sci. 2006, 912 (1), 474-482. (39) Buchanan, P.; Soper, A. K.; Thompson, H.; Westacott, R. E.; Creek, J. L.; Hobson, G.; Koh, C. A. Search for memory effects in methane hydrate: Structure of water before hydrate formation and after hydrate decomposition. J. Chem. Phys. 2005, 123 (16), 164507-164513.


25

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 42 of 47

(40) Bagherzadeh, S. A.; Alavi, S.; Ripmeester, J.; Englezos, P. Formation of methane nanobubbles during hydrate decomposition and their effect on hydrate growth. J. Chem. Phys. 2015, 142 (21), 1-8. (41) Yagasaki, T.; Matsumoto, M.; Andoh, Y.; Okazaki, S.; Tanaka, H. Effect of bubble formation on the dissociation of methane hydrate in water: A molecular dynamics study. J. Phys. Chem. B 2014, 118 (7), 1900-1906. (42) Yang, L.; Falenty, A.; Chaouachi, M.; Haberthür, D.; Kuhs, W. F. Synchrotron X-ray computed microtomography study on gas hydrate decomposition in a sedimentary matrix. Geochem., Geophys., Geosyst. 2016, 17 (9), 3717-3732. (43) Liu, G. M.; Craig, V. S. J. Improved cleaning of hydrophilic protein-coated surfaces using the combination of nanobubbles and SDS. ACS Appl. Mater. Interfaces 2009, 1 (2), 481-487.

(44) James, R. T. S.; Detlef, L. Nanobubbles and micropancakes: gaseous domains on immersed substrates. J. Phys.: Condens. Matter 2011, 23 (13), 133001.

(45) Uchida, T.; Yamazaki, K.; Gohara, K. Gas nanobubbles as nucleation acceleration in the gas-hydrate memory effect. J. Phys. Chem. C 2016, 120 (47), 26620-26629.

(46) Zhao, J. F.; Yu, T.; Song, Y. C.; Liu, D.; Liu, W. G.; Liu, Y.; Yang, M. J.; Ruan, X. K.; Li, Y. H. Numerical simulation of gas production from hydrate deposits using a single vertical


26

Page 43 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

well by depressurization in the Qilian Mountain permafrost, Qinghai-Tibet Plateau, China. Energy 2013, 52, 308-319. (47) Zhao, J. F.; Liu, D.; Yang, M. J.; Song, Y. C. Analysis of heat transfer effects on gas production from methane hydrate by depressurization. Int. J. Heat Mass Transfer 2014, 77, 529541. (48) Zhao, J. F.; Zhu, Z. H.; Song, Y. C.; Liu, W. G.; Zhang, Y.; Wang, D. Y. Analyzing the process of gas production for natural gas hydrate using depressurization. Appl. Energy 2015, 142, 125-134. (49) Song, Y. C.; Cheng, C. X.; Zhao, J. F.; Zhu, Z. H.; Liu, W. G.; Yang, M. J.; Xue, K. H. Evaluation of gas production from methane hydrates using depressurization, thermal stimulation and combined methods. Appl. Energy 2015, 145, 265-277.

(50) Wang, B.; Fan, Z.; Wang, P. F.; Liu, Y.; Zhao, J. F.; Song, Y. C. Analysis of depressurization mode on gas recovery from methane hydrate deposits and the concomitant ice generation. Appl. Energy 2018, 227, 624-633.

(51) Wang, B.; Dong, H. S.; Liu, Y. Z.; Lv, X.; Liu, Y.; Zhao, J. F.; Song, Y. C. Evaluation of thermal stimulation on gas production from depressurized methane hydrate deposits☆. Appl. Energy 2018, 227, 710-718.


27

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 44 of 47

(52) Zhao, J. F.; Wang, B.; Sum, A. K. Dynamics of hydrate formation and deposition under pseudo multiphase flow. AIChE J. 2017, 63 (9), 4136-4146.

(53) Ohmura, R.; Matsuda, S.; Uchida, T.; Ebinuma, T.; Narita, H. Clathrate hydrate crystal growth in liquid water saturated with a guest substance: Observations in a methane + water system. Cryst. Growth Des. 2005, 5 (3), 953-957.

(54) Babu, P.; Yee, D.; Linga, P.; Palmer, A.; Khoo, B. C.; Tan, T. S.; Rangsunvigit, P. Morphology of methane hydrate formation in porous media. Energy Fuels 2013, 27 (6), 33643372. (55) Duchateau, C.; Peytavy, J. L.; Glénat, P.; Pou, T. E.; Hidalgo, M.; Dicharry, C. Laboratory evaluation of kinetic hydrate inhibitors: A procedure for enhancing the repeatability of test results. Energy Fuels 2009, 23 (2), 962-966.

(56) Sun, S. C.; Peng, X.; Zhang, Y.; Zhao, J.; Kong, Y. Y. Stochastic nature of nucleation and growth kinetics of THF hydrate. J. Chem. Thermodyn. 2017, 107, 141-152.

(57) Veluswamy, H. P.; Kumar, A.; Kumar, R.; Linga, P. An innovative approach to enhance methane hydrate formation kinetics with leucine for energy storage application. Appl. Energy 2017, 188, 190-199. (58) Starling, K. E.; Han, M. S. Thermo data refined for LPG. Part 15: Industrial applications. Hydrocarbon Process. 1972, 51:6 (6).


28

Page 45 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(59) Cheng, C. X.; Zhao, J. F.; Yang, M. J.; Liu, W. G.; Wang, B.; Song, Y. C. Evaluation of gas production from methane hydrate sediments with heat transfer from over-underburden layers. Energy Fuels 2015, 29 (2), 1028-1039. (60) Sefidroodi, H.; Abrahamsen, E.; Kelland, M. A. Investigation into the strength and source of the memory effect for cyclopentane hydrate. Chem. Eng. Sci. 2013, 87, 133-140.

(61) Loh, M.; Falser, S.; Babu, P.; Linga, P.; Palmer, A.; Tan, T. S. Dissociation of fresh- and seawater hydrates along the phase boundaries between 2.3 and 17 MPa. Energy Fuels 2012, 26 (10), 6240-6246. (62) Lapham, L. L.; Chanton, J. P.; Chapman, R.; Martens, C. S. Methane under-saturated fluids in deep-sea sediments: Implications for gas hydrate stability and rates of dissolution. Earth Planet. Sci. Lett. 2010, 298 (3), 275-285. (63) Linga, P.; Daraboina, N.; Ripmeester, J. A.; Englezos, P. Enhanced rate of gas hydrate formation in a fixed bed column filled with sand compared to a stirred vessel. Chem. Eng. Sci. 2012, 68 (1), 617-623. (64) Li, G.; Li, X. S.; Li, B.; Wang, Y. Methane hydrate dissociation using inverted five-spot water flooding method in cubic hydrate simulator. Energy 2014, 64, 298-306.


29

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 46 of 47

(65) Li, G.; Wu, D. M.; Li, X. S.; Lv, Q. N.; Li, C.; Zhang, Y. Experimental measurement and mathematical model of permeability with methane hydrate in quartz sands. Appl. Energy 2017, 202, 282-292. (66) Wang, B.; Fan, Z.; Lv, P. F.; Zhao, J. F.; Song, Y. C. Measurement of effective thermal conductivity of hydrate-bearing sediments and evaluation of existing prediction models. Int. J. Heat Mass Transfer 2017, 110, 142-150. (67) Song, Y. C.; Kuang, Y. M.; Fan, Z.; Zhao, Y. C.; Zhao, J. F. Influence of core scale permeability on gas production from methane hydrate by thermal stimulation. Int. J. Heat Mass Transfer 2018, 121, 207-214. (68) Wang, J. Q.; Zhang, L. X.; Zhao, J. F.; Ai, L.; Yang, L. Variations in permeability along with interfacial tension in hydrate-bearing porous media. J. Nat. Gas Sci. Eng. 2018, 51, 141146. (69) Yang, L.; Zhou, W. H.; Xue, K. H.; Wei, R. P.; Ling, Z. A pressure core ultrasonic test system for on-board analysis of gas hydrate-bearing sediments under in situ pressures. Rev. Sci. Instrum. 2018, 89 (5), 054904. (70) Babu, P.; Kumar, R.; Linga, P. Unusual behavior of propane as a co-guest during hydrate formation in silica sand: Potential application to seawater desalination and carbon dioxide capture. Chem. Eng. Sci. 2014, 117, 342-351.


30

Page 47 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(71) Linga, P.; Clarke, M. A. A review of reactor designs and materials employed for increasing the rate of gas hydrate formation. Energy Fuels 2017, 31 (1), 1-13.

(72) Li, H. Z.; Hu, L. M.; Xia, Z. R. Impact of groundwater salinity on bioremediation enhanced by micro-nano bubbles. Mater. 2013, 6 (9), 3676-3687.

(73) Fandiño, O.; Ruffine, L. Methane hydrate nucleation and growth from the bulk phase: Further insights into their mechanisms. Fuel 2014, 117, 442-449.

(74) Takeya, S.; Hori, A.; Hondoh, T.; Uchida, T. Freezing-memory effect of water on nucleation of CO2 hydrate crystals. J. Phys. Chem. B 2000, 104 (17), 4164-4168.

(75) Vysniauskas, A.; Bishnoi, P. R. A kinetic study of methane hydrate formation. Chem. Eng. Sci. 1983, 38 (7), 1061-1072.


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Experimental Study on the Morphology and Memory Effect of Methane

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