Observation of In Situ Growth and Decomposition of Carbon Dioxide

Subscriber access provided by Kaohsiung Medical University

Environmental and Carbon Dioxide Issues

Observation of in-situ growth and decomposition of Carbon dioxide hydrate at gas-water interfaces using MRI Yangmin Kuang, Xu Lei, Lei Yang, Yuechao Zhao, and Jiafei Zhao Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 16 May 2018 Downloaded from http://pubs.acs.org on May 16, 2018

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.

Page 1 of 17 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

Observation of in-situ growth and decomposition of Carbon dioxide hydrate at gas-water interfaces using MRI Yangmin Kuang1, Xu Lei1, Lei Yang1*, Yuechao Zhao1, Jiafei Zhao1* 1

Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of

Education, Dalian University of Technology, Dalian 116024, China

Abstract: The kinetics of gas hydrate formation and decomposition at gas-water interface are of crucial importance to the application of hydrate-based technique and the gas recovery process from marine sediments. Herein, the behaviors of in-situ CO2-hydrate growth and dissociation at the interface of liquid CO2 and water were observed using Magnetic Resonance Imaging (MRI). The results indicated that the growth of hydrate film was primarily controlled by the mass transfer of CO2 into the water phase. Notably, the stepwise depressurization beyond the equilibrium pressure was found to facilitate the thickening of hydrate films due to the enhanced evolution of dissolved gas out of water for hydrate formation. The addition of surfactants (SDS) could contribute to a shorter induction time and a thinner hydrate film. The dissolution of gas molecule and bubbles in the water phase was suggested the crucial factor impacting the thickening of CO2 hydrate films. Keywords: Carbon dioxide hydrate; Hydrate film; Gas-water interfaces; Surfactants; Magnetic resonance imaging

1 Introduction The amount of CO2 in the atmosphere has increased prominently over the past century due to the heavy consumption of fossil fuels, thus enhancing the ‘greenhouse effect’. Therefore, how to deal with CO2 has become a hot issue of international concern [1]. It is known that Carbon Capture Use and storage (CCUS) technologies are expected to be an effective solution for mitigating global warming. One of particular CCUS technology is to store liquid CO2 on the deep seafloor. However, 1

ACS Paragon Plus Environment

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

under such conditions of a pressure higher than 4.45 MPa and a temperature lower than 283.4 K, CO2 hydrate crystals will generate between water and liquid CO2 [2]. Since the water in the deep ocean conforms to this specified condition, CO2 hydrate crystals will form as a layer of film at the interface between the seawater and the stored liquid CO2, and then reduce the dissolution rate of CO2 into the water. In short, formation, growth and morphology of hydrates at interfaces between water and gas under quiescent conditions are the focus of increasing interest, motivated by both fundamental reasons and practical applications [2, 3]. Now the question is that when the process of confining CO2 into the deep oceans occurred, the formation of CO2 hydrate was expected to engender strong resistance to the diffusion of CO2 into bulk water. Therefore, the formation rate will be significantly controlled by the diffusion rate through the hydrate film, which effectively isolates the gas from the water. The respective roles of heat and mass transfer [4] and of surfactant molecules added in small amounts to the water or guest phase [5] are not yet fully understood. Sun et al. [4] recently pointed out that the important works in future mainly focus on investigating morphology of film, measuring or estimating the lateral growth rate of film, the film thickness as well as its growth rate of film, developing the mechanism of film growth, and measuring the tensile strength of hydrate film. Uchida et al. [6] carried out the observations of CO2-hydrate growing on the surface of water droplet suspended in CO2, and they concluded that the propagation rate is primarily dependent on an increasing function of subcooling ∆T=Teq-Texp, where Texp stands for the temperature of the experiment and Teq is the hydrate phase equilibrium temperature at the pressure of the experiment. The numerical models calculated the variation of lateral growth rates with subcooling, which found that heat transfer processes at the edge of the advancing hydrate front was the controlling factor [4], but mass transfer limitations seemed to act as an important role as well [7]. In addition, most of the research conducted with surfactant additives (such as SDS) in order to promote hydrate formation processes, which was mostly and loosely regarded as ‘capillary-driven’. Meanwhile, it is also one of the most challenging fundamental issues in gas hydrate research. Interestingly, 2


Page 2 of 17

Page 3 of 17 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

Daniel-David et al. [8] reported that anionic surfactants such as SDS or AOT can promote CH4 hydrates growth, but it is not for CO2 hydrates. In addition, some research has also measured the surface tension of hydrate. Aman et al. [9] has reported the relationship between cohesive force of cyclopentane hydrate and temperature based upon their measured experimental result of surface tension. To investigate the hydrate film thickness based on temperature, Uchida et al. [10] estimated the hydrate film thickness by measuring the surface tension and strength. In addition, Peng et al. [11] found that the mixed gas hydrate films had a relatively thin thicknesses compared with those of pure gas hydrate. Taylor et al. [12] investigated that mostly the hydrate film grew into the water phase. Their results indicated that hydrate former was supplied by the aqueous phase during the initial hydrate growth, while the free gas supplied the hydrate former for film thickening. The results of Liang et al. [13] pointed out that interstitial diffusion served as an important mechanism for the mass transport of H2O molecules through gas hydrates. Make a general survey of different points of view; the mechanism of hydrate films thickening is still undefined. Now, the reported technologies for measuring hydrate film thickening rate include micrometry, microscopy [6, 14-15], laser interferometry [16], the magnetic resonance imaging (MRI)[17] and NMR methods [18]. Even though the laser interferometry or MRI method cannot be good at determining the absolute initial thickness of the hydrate film compared with microscopy technique, the MRI methods can detect the inner structure of the hydrates film as well as the film growth rate while other methods could not. Moreover, microscopic camera can only observe the surface of the film, which may results some errors. Abe et al. [16] developed the CO2 hydrate film formation and growth models for different temperature and flow velocity conditions combined with the laser interferometry. To obtain the volumetric hydrate growth rate, it is of vital importance to measure the key parameters of the initial thickness and lateral growth rate of the hydrate film, even though it is often very difficult to measure. Therefore, it is worthy and essential to investigate the characteristics of hydrate films growth rate. In the present study, we observed the behavior of water surface in liquid CO2 to 3


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

reveal the formation process of CO2-hydrate film at the interface between liquid CO2 and water using MRI. To define the rate-determination process and discuss the formation and dissociation mechanism, we have measured the formation rates for CO2-hydrate film under various surfactant additives concentration and pressures

2 Materials and Methods Figure 1 has shown the schematic of our experimental apparatus. In this study, we use an NMR system (400MHZ and 9.4T, Varian, Inc., U.S.) to observe the formation and dissociation of CO2 hydrate film. A fast spin echo multi slice (FSEMS) pulse sequence was used; the time of repetition (TR) and time of echo (TE) are 6000 ms and 9.26 ms, respectively. The thickness of the slices in our imaging software was set to 2 mm. And the image matrix was 256 × 128. The field of view (FOV) was 13 mm × 13 mm and the acquisition time of the FSEMS was 1 min 48 s. The spatial resolution was 0.051 × 0.102 × 2 mm3. The thermostatic bath system was a circulator (F25-ME, Julabo Inc., Germany), which can control the temperature ranging from −28 °C to 200 °C and has a precision of ± 0.01 °C. The coolant is fluorinert FC-40 (produced by 3 M, MN, US), since this kind of fluid does not contain imaginable hydrogen and has low dielectric properties to minimize RF losses. A thermocouple (SAKAGUCHI E.H VOC CORP, Japan) was placed in the coolant jacket to monitor temperature. In addition, all the pipes were wrapped with thermal insulation coverings to reduce the heat loss and maintain a steady temperature. Noticed that the temperature difference between the coolant jacket and the circulator is about 0.5 °C. In addition, a high-precision syringe pump (260D，Teledyne ISCO Inc., US) was used to inject water or carbon dioxide with constant flow rate and control the experimental pressure. A vacuum pump（SHB-111 A, SJSK Exp. Co., Ltd, China）was used for discharging the gas out of the pressure tube. The estimated errors of temperature and pressure measurements are ± 0.1 K and ± 0.01 MPa, respectively. In the whole experiments, CO2 of 99.9% purity (provided by Dalian Special Gas Co., Ltd., China) and deionized water were used. The additives of Sodium dodecyl sulfate (SDS) were confected into different concentration solution with the deionized water using a 4


Page 4 of 17

Page 5 of 17 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

high-precision balance with a minimum precision of 0.0001 g (Shanghai Minqiao Precise Science Instrument Co., Ltd., China). After injecting water into the pressure tube, we used the vacuum pump to discharge the air inside, and then injected the CO2 gas into the tube with the design flow rate until the pressure achieved the design value. At last, the pressure tube was sealed with pressure valve. The whole pressure chamber was maintained at a steady temperature of 1 °C in our experiment. At the same time, MRI was acquiring images continuously. In fact, in our experimental apparatus of NMR system, since the magnetic field intensity is up to 9.4 T, the relaxation time of the hydrogen protons is very short in gas or solid like hydrate and ice, which could not be detected by this apparatus. We could only get the signal intensity of the hydrogen content in liquid water. Therefore, when hydrate forms in the pressure chamber, the intensity of the MRI signal will change owing to water content reduction. In our experiment, hydrate formation in all cases was directly observed for more than 18 hours. The experimental conditions are listed in Table 1.

Figure 1. Schematic diagram of gas hydrate experimental apparatus. Table 1. The initial conditions of CO2 hydrate film formation and dissociation in this study. Formation Case 1 2 3 4

SDS concentration （ppm）） 288a 288b 288c 250

Initial Pressure （MPa））

gas state

Temperature （K））

3.818 3.804 3.081 3.905

Liquefied Liquefied Gas Liquefied

274.15 274.15 274.15 274.15

5


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

5 6 7

Dissociation Case A B C

280 300 342

SDS concentration （ppm）） 288 288 300

Page 6 of 17

3.809 3.820 3.815

Liquefied Liquefied Liquefied

274.15 274.15 274.15

Initial Pressure （MPa））

gas state

Temperature （K））

3.570 3.260 3.570

Liquefied Gas Liquefied

274.15 274.15 274.15

Note：a: CO2 hydrate dissociation water with SDS was used in case 1. b: CO2 hydrate dissociation water at room temperature with SDS was used in case 2. c: CO2 hydrate dissociation water at room temperature with SDS was used in case 3.

3 Results and Discussion The CO2 hydrate films were formed and dissociated in a pure water medium in the presence of additive solutions (SDS). Our experiments were carried out at 274.15 K and 3.0~3.9 MPa. In this work we mainly focus on the hydrate films formation at the interface between water and liquid CO2 except case 4. Five SDS concentrations (250, 280ppm, 288, 300, and 342 ppm) were studied.

3.1 Measurement results of CO2 hydrate films growth and dissociation Figure 2 shows the morphologies of gas hydrate films formation and dissociation. In this study, we have selected 3 points location of the film interface to calculate the average growth rate of the hydrate films. The cambered liquid level was formed due to the hydrophilicity of the tube wall and the surface tension of water. And the initial diameter of the liquid film is 1 cm. As shown in Figure 2, the hydrate films was the fastest growing at the lowest liquid level. It can also be found that there existed thin water layer along the tube wall in the progress of hydrate films slow growth. However, in the decomposition progress, the hydrate film firstly dissociated at the water phase interface. Since there was no dissociation water found on the upside of the hydrate film. Hydrate decomposition is an endothermic progress, the absorbed latent heat for hydrate film dissociation from the water is much more than from the gas phase. 6


Page 7 of 17 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

Therefore, the decomposition direction was more likely from down to up. The results also indicated that hydrate regeneration occurred frequently in the depressurization progress. It can be explained by the fact that a large amount of dissolved gas escaped from the solution when the pressure decreased, the mixing of formed gas bubbles and liquid created more gas-water contact areas. Then the hydrate grew rapidly in this condition. Therefore, it provides a useful method to promote the CO2 hydrate formation by creating the pressure oscillation condition.

Figure 2. Characteristic of gas hydrate films formation and decomposition. (1) Formation for case 1. (2) Dissociation for case 1. (3) Regeneration for case 7.

3.2 Effects of SDS and initial gas injection rate on hydrate films growth Figure 3 shows the initial gas injection rate of case 1-7. The initial gas injection rate was 50 mL/min for case 1, 40 mL/min for case 2-6 and 30 mL/min for case 7, respectively. The initial pressure was defined as the highest injected pressure, which was listed in Table 1. Then all of the cases reached the liquefied pressure of 3.57 MPa except case 3. And the hydrate film growth proceed at gaseous phase in case 3. As shown in Figure 4, it can be found that CO2 hydrate films thickness in case 1 7


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

increased to 200 min and the rate of increase was low thereafter. This characteristic increase was thought to be related to the diffusion of CO2 molecules through the CO2 hydrate layer. These results were good agreement with those of Hirai et al. [17]. The hydrate films thickening was the fastest for case 1. And the main reason is that the CO2 hydrate dissociation water was used in case 1. The gas was immediately injected into the hydrate dissociation water after the depressurization process completed. However, comparing case 2 with case 1, the hydrate films growth was slow in case 2 even though the dissociation water was both used in the two cases. The significant

Figure 3. The initial gas injection rate of case 1-7 in this study.

8


Page 8 of 17

Page 9 of 17 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

Figure 4. The total gas hydrate film growth rate for case 1-7.

difference appeared because of that the dissociation water of case 2 was placed in the pressure vessel for three hours at atmospheric pressure. The CO2 hydrate dissociation water have large amount of dissolved gas and bubbles compared with other low solubility gas like methane. The results of Uchida et al. [19, 20] also confirmed that the hydrate dissociation water contained lots of micro-and nanobubbles which acted as a role of nucleation acceleration in the gas hydrate memory effect. In addition, more remarkable, the freezing-memory effect mentioned in the Takeya et al. [21] study suggested that a particular substance or structure existed in water or on the wall after melting from ice. Their conclusions confirmed that the nucleation rates decreased by degassing, and increased with the O2 concentration in water, this particular substance or structure was probably composed of gaseous molecules such as O2. Thus, the results indicated that this dissolved gas and bubbles played a significant role correlated with ‘memory effects’ in hydrate film growth especially in the initial hydrate formation period. Compared with case 1 and 2, the hydrate films growth in case 3 was very slowly which could be found in Figure 5. The results shows that hydrate films thickening was more difficult in a gaseous phase condition at initial 9


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

stage. Lehmku¨hler et al. [22] also concluded that the adsorption of gas molecules on the water surface leaded to a high supply of CO2 at the water surface but does not trigger the gas hydrate formation process. The presence of a macroscopic amount of liquid CO2 induced the local formation of mobile CO2 hydrate crystallites which could be explained by the so-called local structuring hypothesis [22, 23]. The mass transfer was limited in this case. However, compared case 3 with case 2, the final thickness had little difference between the gas and liquefied gas state. In addition, we also investigated the surfactant (SDS) effects on gas hydrate films growth in case 4 to 7. The results manifested that the SDS concentration of 280 ppm had the best effect to promote the hydrate films thickening. While the cases of 250 ppm and 300 ppm had the same final thickness which was lower than 280 ppm. Moreover, when the SDS concentration exceeds 280 ppm, the effects of promotion for hydrate films growth would gradually decrease. Meanwhile, the SDS concentration effects on hydrate ‘induction time’ of formation were also discussed as shown in Figure 6. Herein, the ‘induction time’ was defined as the time between the point which gas injection pressure reached the phase equilibrium pressure and the points of beginning formation time. The results indicated that the SDS effects on the induction time were opposite to the final hydrate films thickness. The best SDS concentration of 280 ppm lead to relatively longer induction time. And generally, the shorter induction time corresponded to a lower hydrate films thickness. In short, the faster hydrate films growth in the early stage would restricted the later films thickening more obviously. It also demonstrated that the dissolved gas in water phase was the crucial factor controlling the CO2 hydrate films thickening. Zhong et al. [24] found that the formation rates of gas hydrates can be increased multiple orders of magnitude if the host water is a micellar solution containing SDS or related surfactant. The critical micellar concentration at ethane and natural gas hydrate forming conditions of a SDS solution was found to be 242 ppm which had a significant change in hydrate induction time.

10


Page 10 of 17

Page 11 of 17 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

Figure 5. The initial gas hydrate film growth rate of case 1-7 in this study.

Figure 6. The induction time and total thickness of gas hydrate films formation for case 1-7.

3.3 Behaviours of hydrate films growth at depressurization condition 11


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

Figure 7 shows the hydrate films growth rate in the depressurization progress. The stepwise depressurization was carried out in case A, the growth rate results at 50 min in case A showed that the faster depressurization rate was, the slower hydrate films growth rate was. While comparing case A with case B, it could be found that the hydrate films growth rate in case B was obviously slower than the growth rate of case A. This results also implied that the stepwise depressurization could be conductive to the hydrate films thickening due to the enhanced diffusion of dissolved gas molecules controlled by the depressurization approach. In addition, it also confirmed the truth that the mass transfer plays a significant role in hydrate films growth. Meanwhile, the results of case B and C showed that the SDS concentration of 300 ppm had a better effect on hydrate films growth than that of 288 ppm at the initial depressurization stage. All the results indicated that the tendency of the hydrate films growth was likely to continue until the pressure declined to the phase equilibrium pressure. However, the limitation of mass transfer still existed in the later growth stage. Figure 8 depicted the characteristics of gas hydrate regeneration in the later depressurization progress. Herein the starting point in Fig. 8 was recorded at the time when the pressure declined to the phase equilibrium point. As shown in Fig. 8, the first picture shows the CO2-hydrate film dissociated around the phase equilibrium point. While the second and third pictures depicted that the hydrate dissociated at 20 kpa/min and 100 kPa/min, respectively. The heat absorbed by thin hydrate films dissociation may couldn’t result in a low temperature area at the container bottom for ice generation (red circle shown in Fig. 8) when the hydrate films dissociated very slowly. It is noteworthy that there existed a very thin hydrate layer (the yellow curve shown in Figure 8) isolated the SDS diffusion from the bottom up when the hydrate films dissociated near the phase equilibrium point. It can be found that the brighter white area was the dissociation water without SDS concentration because of no surfactant contained in the hydrate films. These results also indicated that the rapid decompression rate is more likely to induce the CO2 hydrate regeneration since this process caused temperature reduction and enhanced the gas-liquid disturbance. 12


Page 12 of 17

Page 13 of 17 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

Figure 7. The gas hydrate film growth rate in the depressurization progress. (The data points represent the hydrate film thickness at different time. The lines represent the dissociation pressure at different time.)

13


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

Figure 8 The characteristics of gas hydrate regeneration in the depressurization progress. (1) First group: hydrate dissociated at phase equilibrium point. (2) Second group: depressurization rate at 20 kPa/min. (3) Third group: depressurization rate at 100 kPa/min.

4 Conclusions This study has shown the formation and dissociation process of CO2-hydrate film at the interface between liquid CO2 and water using MRI. The results has shown that the CO2-hydrate films thickening was very fast in the dissociation water conditions which was mainly controlled by the dissolved gas in water. The SDS concentration of 280 ppm had the best effects to promote the hydrate films thickening. The results also indicated that the SDS effects on the ‘induction time’ were opposite to the final hydrate films thickness. The best SDS concentration of 280 ppm lead to relatively longer induction time. A shorter induction time corresponded to a lower hydrate films thickness. The stepwise depressurization could be conductive to the hydrate films thickening due to the enhanced diffusion of dissolved gas molecules controlled by the depressurization approach. The dissolved gas in water phase was the crucial factor impacting the CO2 hydrate films thickening. And the hydrate film firstly dissociated at the water phase interface in the decomposition progress. A very thin hydrate layer isolated the SDS diffusion from the bottom up when the hydrate films dissociated near the phase equilibrium point.

Author Information Corresponding author: *E-mail address: [email protected] ; *E-mail address: [email protected] ; Notes The authors declare no competing financial interest.

Acknowledgements The authors are grateful for the support provided by the Major Program of 14


Page 14 of 17

Page 15 of 17 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

National Natural Science Foundation of China (Grant No. 51436003) and the National Natural Science Foundation of China (Grant No.51622603) and the National Key R&D Program of China (Grant No. 2017YFC0307300, 2016YFC0304001) and the National Science Foundation of China (Grant No.51676205).

Reference (1) Bachu, S. Aquifer disposal of CO2: hydrodynamic and mineral trapping. Energy Convers. Manage, 2000, 41, 953-970. (2) Sloan, E.D.; Koh, C.A. Clathrate Hydrates of Natural Gases, 3rd ed. Boca Raton: CRC Press, 2007. (3) Chatti, I.; Delahaye, A.; Fournaison, L.; Petitet, J.P. Benefits and drawbacks of clathrate hydrates: a review of their areas of interest. Energy Convers. Manag. 2005, 46, 1333–1343. (4) Sun, C.Y.; Peng, B.Z.; Dandekar, A.; Ma, Q.L.; Chen, G.J. Studies on hydrate film growth. Annu. Rep. Prog. Chem. Sect. C: Phys. Chem. 2010, 106, 77–100. (5) Sun, C.H.; Chen, G.J.; Ma, C.F.; Huang, Q.; Luo, H.; Li, Q.P.; The growth kinetics of hydrate film on the surface of gas bubble suspended in water or aqueous surfactant solution. J. Cryst. Growth, 2007, 306, 491–499. (6) Uchida, T.; Ebinuma, T.; Kawabata, J.; Narita, H. Microscopic observations of formation processes of clathrate-hydrate films at an interface between water and carbon dioxide. J. Cryst. Growth, 1999, 204, 348–356. (7) Saito, K.; Sum, A.K.; Ohmura, R. Correlation of hydrate-film growth rate at the guest/liquid–water interface to mass transfer resistance. Ind. Eng. Chem. Res. 2010, 49, 7102–7103. (8) Daniel-David, D.; Guerton, F.; Dicharry, C.; Torré J-P.; Broseta, D. Hydrate growth at the interface between water and pure or mixed CO2/CH4 gases: Influence of pressure, temperature, gas composition and water-soluble surfactants. Chem. Eng. Sci. 2015,132, 118-127. (9) Aman, Z.M.; Brown, E.P.; Sloan, E.D.; Sum, A.K.; Koh, C.A. Interfacial 15


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 16 of 17

mechanisms governing cyclopentane clathrate hydrate adhesion/cohesion. Phy. Chem. Chem. Phys. Pccp. 2011, 13, 19796–19806. (10)

Uchida, T.; Kawabata, J. Measurements of mechanical properties of the

liquid CO2–water–CO2–hydrate system. Energy. 1997, 22(2–3), 357–361. (11)

Peng, B.Z.; Dandekar, A.; Sun, C.Y.; Luo, H.; Ma, Q.L.; Pang, W.X. Hydrate

Film Growth on the Surface of a Gas Bubble Suspended in Water. J Phys Chem. B. 2007, 111, 12485-12493. (12)

Taylor, C.J.; Miller, K.T.; Koh, C.A.; Sloan, E.D. Macroscopic investigation

of hydrate film growth at the hydrocarbon/water interface. Chem. Eng. Science. 2007, 62, 6524-6533. (13)

Liang, S.; Kusalik, P.G. The mobility of water molecules through gas

hydrates. Journal of the American Chem. Society. 2011, 133, 1870-1876. (14)

Servio, P.; Englezos, P. Morphology of methane and carbon dioxide hydrates

formed from water droplets. AIChE Journal. 2003, 49, 269-276. (15)

Kobayashi,

I.;

Ito, Y.; Mori,

Y.H.

Microscopic

observations

of

clathrate-hydrate films formed at liquid/liquid interfaces. I. Morphology of hydrate films. Chem. Eng. Sci. 2001, 56, 4331–4338. (16)

Abe, Y.; Ma, X.; Yanai, T.; Yamane, K. Development of formation and

growth models of CO2hydrate film. AIChE Journal. 2016, 62, 4078-4089. (17)

Hirai, S.; Tabe, Y.; Kuwano, K.; Ogawa, K.; Okazaki, K. MRI measurement

of hydrate growth and an application to advanced CO2 sequestration technology. Ann NY Acad Sci, 2000, 912, 246–253. (18)

Haber, A.; Akhfash, M.; Loh, C.K.; Aman, Z.M.; Fridjonsson, E.O.; May,

E.F.; Johns, M.L. Hydrate Shell Growth Measured Using NMR. Langmuir : the ACS journal of surfaces and colloids. 2015, 31, 8786-8794. (19)

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, 1749-1755. (20)

Uchida, T.; Yamazaki, K.; Gohara, K. Gas Nanobubbles as Nucleation

Acceleration in the Gas-Hydrate Memory Effect. J. Phy. Chem. C. 2016, 120, 16


Page 17 of 17 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

26620-26629. (21)

Takeya, S.; Hori, A.; Hondoh, T.; Uchida, T. Freezing-Memory Effect of

Water on Nucleation of CO2 Hydrate Crystals. J. Chem. Phys. B. 2000, 104, 4164-4168. (22)

Lehmkuhler, F.; Paulus, M.; Sternemann, C.; Lietz, D.; Venturini, F.; Gutt,

C.; Tolan, M. The Carbon Dioxide-Water Interface at Conditions of Gas Hydrate Formation. J. Am. Chem. Soc. 2009, 131, 585-589. (23)

Radhakrishnan, R., Trout, B.L. A new approach for studying nucleation

phenomena using molecular simulations: Application to CO2 hydrate clathrates. J. Chem. Phys. 2002, 117, 1786-1796. (24)

Zhong, Y.; Rogers. R.E. Surfactant effects on gas hydrate formation. Chem.

Eng. Sci. 2000, 55, 4175-4187.

17


Observation of In Situ Growth and Decomposition of Carbon Dioxide

Recommend Documents