Crystal Growth of Clathrate Hydrate at the Interface between Seawater

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Crystal Growth of Clathrate Hydrate at the Interface between Seawater and Hydrophobic-Guest Liquid: Effect of Elevated Salt Concentration Masatoshi Kishimoto, Satoshi Iijima, and Ryo Ohmura* Department of Mechanical Engineering, Keio University, Yokohama 223-8522, Japan ABSTRACT: This paper reports the visual observations of the clathrate hydrate crystal growth and morphology at the interface of aqueous NaCl solutions and a guest-substance liquid. The hydrate crystal growth was visually characterized in the systems of a wide range of NaCl concentrations from 0.035 to 0.264 in mass fraction. The mass fraction 0.035 was corresponding to that of ordinary seawater, and the salt concentration tested was extended up to the saturation level, i.e., 0.264. Cyclopentane was used as the guest substance. Formation and growth of hydrate crystals at the cyclopentane-NaCl solution interface were observed. We visually analyzed the individual hydrate crystals and classified the morphology of the crystals according to ΔTsub at atmospheric pressure. It was found that the size of the individual hydrate crystals decreased with increasing ΔTsub. The results showed that the morphology of the individual hydrate crystals in any NaCl concentration is roughly similar at a given ΔTsub. We also measured the lateral growth rates of the hydrate-film propagation. The hydrate film growth rate decreased with decreasing ΔTsub in any of the systems and decreased with increasing concentration of NaCl at a given ΔTsub.

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INTRODUCTION Clathrate hydrates are crystalline solid compounds consisting of hydrogen-bonding water molecules forming cages that enclose other small molecules. Water molecules are called “host molecules”, while the encaged molecules are the “guest molecules”. Depending on the size and shape of the guest substances, water molecules form several different cage structures that interconnect to yield hydrates of different crystallographic structures, such as structure I, II, and H.1 Hydrocarbons and noble gases are the typical guest substances that form clathrate hydrates. Hydrates are typically stable at low-temperature and high-pressure conditions. Clathrate hydrates have several unique properties, such as a large heat of formation/decomposition, guest-substance selectivity, and a high gas storage capacity. Recently, research and development of novel energy-environment-related technologies, exploiting these properties and characteristics of hydrates, are being performed. Some of these novel technologies are transportation and storage of natural gases2 and hydrogen,3 ground/ocean sequestration of carbon dioxide,4−6 development of heat pump/refrigeration systems,7 removal of hydrogen sulfide from biogas,8 isolation of greenhouse gas,9 etc. With reference to the development of the novel hydrate-based technology, we need to predict the morphology of the hydrate crystals and understand what controls the morphology. “Crystal morphology” means the geometric configuration of crystals such as their sizes or shapes. The crystal morphology is important because it can critically impact the efficiency of handling hydrate crystals, specifically, dewatering and storage of hydrates and pumping of hydrate slurries.10,11 Consequently, it is important to understand the systematic behavior of the morphology of hydrate crystals formed at the guest-water interface. The importance of understanding crystal morphology has been highlighted in the literature, such as a recent review12 on crystal shape engineering and the previous studies on hydrate crystal morphologies.13−18 © 2012 American Chemical Society

In recent years, substantive progress is seen in the studies on the morphology of the hydrate crystals formed at the guestwater interfaces, which is briefly reviewed here. Freer et al.13 observed methane hydrate crystals formed at the interface of liquid water and gaseous methane. They reported that the crystal morphology was different under the different pressure conditions at a given temperature, and the growth rate of the hydrate crystal was proportional to the driving force. Servio and Englezos14 reported in their study on the morphology of CO2 hydrate and CH4 hydrate crystals formed on water droplets exposed to gaseous CO2 and CH4 that the size of the droplet had no noticeable effect on the induction time or crystal morphology. On the other hand, the driving force significantly affected the crystal morphology. Peng et al.15 observed hydratefilm growth on the gas bubble surfaces exposed to liquid water at different temperatures. They concluded that the hydrate-film growth rate of the mixed-gas CH4 + C2H4 hydrate films was slower than that of the pure gases for the same driving force, and the rate of the CH4 + C3H8 mixed-gas hydrate-film growth was the slowest. They also qualitatively demonstrated that the thickness of the hydrate film was inversely proportional to the driving force, and the thicknesses of mixed-gas hydrate films were thicker than those of the pure gases. Tanaka et al.16 reported detailed observations of the morphology of individual hydrate crystals on the surface of a water droplet exposed to guest gases, that is, methane, ethane, or propane. Their results indicated that the hydrate crystal morphology has a significant dependence on the system subcooling ΔTsub, and the size of the individual hydrate crystals decreased with the increasing ΔTsub irrespective of the guest substances. They concluded that the Received: Revised: Accepted: Published: 5224

November 29, 2011 February 29, 2012 March 6, 2012 March 6, 2012 dx.doi.org/10.1021/ie202785z | Ind. Eng. Chem. Res. 2012, 51, 5224−5229

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saturated mass fraction at the ice-solid NaCl eutectic point 252.0 K, 0.264 is the saturated mass fraction at T = 288.1 K.29 Cyclopentane is used as the guest substance because cyclopentane is easier to handle at atmospheric pressure conditions. Cyclopentane hydrate could be the model substance of natural gas hydrates because the crystallographic structure of these hydrates is structure II.30 Cyclopentane may be used for the hydrate-based desalination.21 Figure 1 illustrates a schematic of

crystal morphology of the hydrate formed at the interface between the methane, ethane, or propane gas and liquid water are classified with ΔTsub as the common criterion. Saito et al.17 and Watanabe et al.18 reported the visual observations of the formation and growth of hydrate crystals in the systems with a methane + ethane + propane gas mixture. They revealed the variations in the hydrate crystal morphology depending on ΔTsub and gas composition. For many of the hydrate-based technologies, knowledge is needed on the hydrate formation from seawater. For example, when we consider the transportation of natural gas from an offshore gas field to the market, seawater is readily available for natural gas hydrate formation at the gas field. In the sequestration of carbon dioxide in the ocean and below the ocean floor,19 seawater is the medium for hydrate formation. Yet, in another example, the utilization of hydrates in the desalination of seawater is obviously done in seawater.20−23 Hence, it is essential to understand the effect of salts, such as NaCl, in seawater on the hydrate formation, so that the development of hydrate-based technologies can be effectively done. Our knowledge on the hydrate crystal growth in seawater is still quite limited despite the recent progress in the hydrate morphology studies as reviewed above. This is simply because the pure water has been used in most of the previous studies on the hydrate morphology. It is known that the hydrate phase equilibrium shifts to lower temperature in the seawater system1,24 and the hydrate crystal growth rate decreases with increasing salt concentration.25 There are also a few reports on visual observations in the hydrate-forming systems with seawater.26−28 Recently, Sakemoto et al.28 reported the visual observations on the cyclopentane hydrate crystal growth in the seawater system. They concluded that the morphology of the hydrate crystals in water and seawater are generally similar at a given subcooling, ΔTsub. However, they performed the experiments exclusively with the seawater of the ordinary concentration, i.e, ∼0.035 mass fraction of the salts and hence the effect of elevated salt concentration is not known. When hydrate crystals are continuously formed from the seawater, the salt concentration in seawater continuously elevates. Therefore, it is important to identify the morphology of the hydrates corresponding to the various mass fractions of NaCl for the process design of the continuous formation of hydrates in the seawater systems. In this study, we performed the experiments with the mass fraction of NaCl in the aqueous solution from 0.050 to 0.264 mass fraction of NaCl in aqueous solution to investigate the effect of elevated salt concentration on the crystal growth. The salt concentration tested ranged from that of ordinary seawater and up to the saturation level, i.e., 0.264. Corresponding to the NaCl concentration, the experiments were performed at the temperatures from 250 to 278 K. The rate data of the hydratelayer propagation along the liquid cyclopentane-NaCl aqueous solution interface are also reported.

Figure 1. Schematic diagram of the major portion of the apparatus.

the apparatus used in the observations of the hydrate crystals growth formed at the interface of NaCl aqueous solution and liquid cyclopentane. Aqueous NaCl solutions (1.5 cm3) is first injected into the glass test tube (external diameter 10 mm, bore diameter 8 mm, height 90 mm), followed by 3.0 cm3 liquid cyclopentane. Hydrate crystals formed at the liquid−liquid interface between NaCl aqueous solution and cyclopentane were observed with a microscope (EdmundOptics, model VZM450). A digital camera (Fortissimo, model CMOS300-USB2) was attached to the microscope to acquire the digital images of the hydrate crystals. The system temperature was controlled by a chiller (Tokyo Rikakikai Co., CTP-300). The temperature was measured with a thermistor temperature sensor with the uncertainty of ±0.1 K. A seed of cyclopentane hydrates crystals (about 5 mg), formed separately and in advance, was then placed at the liquid−liquid interface (cyclopentane hydrate density is in between that of cyclopentane and NaCl aqueous solution). It should be noted that the densities of the hydrates formed with the gas mixture used in the present experiments are estimated to be about 970 kg/m3. In this estimation, the cage occupancies were unity and the lattice constant of the structure II hydrate unit cell was assumed to be 1.73 nm. This procedure artificially induced nucleation and growth of hydrate in the test tube. The instance the seed crystal was placed in the test cell was set as the starting time for crystal growth (t = 0 min). As the experiments were performed with the batch procedure, the salt concentration should increase after the hydrate growth in the system. If we assume the thickness of the hydrate film grown at the watercyclopentane interface to be 0.1 mm, the amount of water converted to the hydrate is estimated to be 6% of the water in the test tube and thus the increase in the salt concentration due to the hydrate growth is also estimated to be 6%. Separate experiments were performed to determine the equilibrium temperature of cyclopentane hydrate in all the systems. For this, the system temperature was first set to a

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EXPERIMENTAL APPARATUS AND PROCEDURE The fluid samples used in the experiments were deionized and distilled liquid water and liquid cyclopentane with a certified purity of 99% from Aldrich Chemical Co. NaCl aqueous solution was prepared with reagent grade NaCl (99.5% certified purity from Aldrich Chemical Co.). The NaCl aqueous concentration of the solution was set at 0.050, 0.070, 0.100, 0.233, or 0.264 in mass fraction. Mass fraction 0.233 is the 5225

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Table 1. Experimental Temperature for Hydrate Crystal Growth in NaCl Aqueous Solutiona NaCl (mass fraction 0.05)

a

NaCl (mass fraction 0.07)

NaCl (mass fraction 0.10)

NaCl (mass fraction 0.233)

NaCl (mass fraction 0.264)

Teq/K

Tex/K

ΔTsub/K

Teq/K

Tex/K

ΔTsub/K

Teq/K

Tex/K

ΔTsub/K

Teq/K

Tex/K

ΔTsub/K

Teq/K

Tex/K

ΔTsub/K

277.6

275.8 275.0 274.5 273.2 272.4 271.8

1.8 2.6 3.1 4.4 5.2 5.8

276.8

275.0 274.2 273.7 272.4 271.6 271.0

1.8 2.6 3.1 4.4 5.2 5.8

274.4

272.6 271.3 268.6

1.8 3.1 5.8

259.9

258.1 256.8 254.1

1.8 3.1 5.8

256.3

254.5 253.1 250.5

1.8 3.2 5.8

Uncertainty of the temperature measurements: ±0.1 K.

prescribed temperature in the range from T = 250.0 to 273.1 K, depending on the NaCl concentration. A sufficient amount of hydrate crystals was formed in the test tube, and then the system temperature was increased stepwise in increments of 0.1 K. At each temperature step, the temperature was kept steady for at least 1 h. If no noticeable hydrate dissociation was visually observed within 1 h, the system temperature was increased. By repeating this procedure of visual observation and temperature increase, the equilibrium temperature of cyclopentane hydrate was determined. The equilibrium temperature measurements were performed by using the same apparatus as used for the crystal growth observations. We defined the system subcooling ΔTsub, the deficiency of the system temperature from the hydrate equilibrium temperature (ΔTsub = Teq − Tex) as the index of the driving force for the crystal growth, where Teq is the equilibrium temperature of the hydrate and Tex is the system temperature. The lateral growth rates of the hydrate crystals formed at the interface between liquid cyclopentane and NaCl aqueous solution were determined from the observational records. Table 1 lists the specific values of Teq, Tex, and ΔTsub set in the experiments. The equilibrium temperature of hydrates was lowered because the chemical potential decreased with increasing NaCl concentration.

completed in 53.5 h in this experiment. After the complete coverage, no noticeable further hydrate crystal growth was observed. This crystal growth behavior, coverage of the interface with a polycrystalline hydrate layer, is similarly observed in all the systems (NaCl aqueous solutions of the mass fraction 0.070, 0.100, 0.233, and 0.264) tested. Figures 3 and 4 show the sequential images similar to those in Figure 2 at a lower Tex (higher ΔTsub): Tex = 274.5 K (ΔTsub

Figure 3. Sequential images of cyclopentane hydrate crystal growth at the mass fraction 0.050 NaCl aqueous solution and cyclopentane interface at atmospheric pressure and Tex = 274.5 K (ΔTsub = 3.1 K). Images in the lower part are the close-up views corresponding to these in the upper part.

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RESULTS AND DISCUSSION Figure 2 shows the sequential images of cyclopentane-hydrate crystal growth at the interface of the mass fraction 0.050 NaCl aqueous solution and liquid cyclopentane at Tex = 275.8 K (ΔTsub = 1.8 K) under atmospheric pressure. As seen in the images, hydrate crystals preferentially grow to form a polycrystalline layer covering the entire interface, which was

Figure 4. Sequential images of cyclopentane hydrate crystal growth at the mass fraction 0.050 NaCl aqueous solution and cyclopentane interface at atmospheric pressure and Tex = 271.8 K (ΔTsub = 5.8 K). Images in the lower part are the close-up views corresponding to these in the upper part.

= 3.1 K) for Figure 3 and Tex = 271.8 K (ΔTsub = 5.8 K) for Figure 4. As recognized in a comparison of Figures 2, 3, and 4, the time required for complete coverage of the interface with hydrate crystals depends on the subcooling. As shown in Figure 3, at ΔTsub = 3.1 K, 8.5 h elapsed for complete coverage of the interface with hydrate crystals, while only 32 min was needed at

Figure 2. Sequential images of cyclopentane hydrate crystal growth at the mass fraction 0.050 NaCl aqueous solution and cyclopentane interface at atmospheric pressure and Tex = 275.8 K (ΔTsub = 1.8 K). Images in the lower part are the close-up views corresponding to these in the upper part. 5226

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Figure 5. Sequential images of the hydrate crystal growth in the mass fraction 0.070, 0.100, 0.233, and 0.264 NaCl aqueous solution systems, respectively, at the same subcooling, ΔTsub = 5.8 K (Tex = 271.0, 268.6, 254.1, 250.5 K).

Figure 6. Arrangement of hydrate crystal observations along the axis of the subcooling ΔTsub.

ΔTsub = 5.8 K (Figure 4). It is also evident from these figures that the morphology of the hydrate crystals covering the interface significantly varies depending on the subcooling. The hydrate crystal growth behavior in the systems with different salt concentrations was similar to that observed in the system with the mass fraction 0.050 NaCl aqueous solution, as

exemplified in Figure 5 showing sequential images of the hydrate crystal growth in the NaCl aqueous solution systems of mass fraction 0.070, 0.100, 0.233, and 0.264, respectively, at Tex = 271.0, 268.6, 254.1, 250.5 K (ΔTsub = 5.8 K). In all cases, hydrate crystals grew along the interface between NaCl aqueous solution and liquid cyclopentane and formed a 5227

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required for the growth. This definition is illustrated in Figure 8. The lateral growth rate represents the rate of two-

polycrystalline layer covering the entire interface. Precipitation of salts was not observed visually in all the systems. The comparison of the morphology of the hydrate crystals formed in all the system is discussed in detail below. A comparison of the crystal morphology observed in the systems with different NaCl mass fraction (0.050, 0.070, 0.100, 0.233, and 0.264) and with pure water and mass fraction 0.035 by Sakemoto et al.28 are arranged along the horizontal axis of ΔTsub in Figure 6. In this figure, the grain boundaries of typical hydrate crystals are outlined in red. As it can be seen, the size of the hydrate crystals decreases with increasing subcooling in all the systems. The geometric shape of the hydrate crystals also changes from irregular hexagons or pentagons at ΔTsub < 3.5 K to slender polygons, triangular or sword-like at ΔTsub > 3.5 K. These trends in the variation in the size and shape of the hydrate crystals are similarly observed in all the systems (pure water, NaCl aqueous solutions of the mass fraction 0.070, 0.100, 0.233, and 0.264). The details of the crystal morphologies in each system are summarized as follows. In the mass fraction 0.050 NaCl aqueous solution system, when the subcooling is ΔTsub < 2.4 K, the shape of hydrate crystals was polygonal with a length of about 0.8−1.0 mm, and the crystal shape changed to triangular with a size of 0.3−0.8 mm at ΔTsub = 2.4−3.5 K. At ΔTsub > 3.5 K, the shape of the crystals is sword-like of 0.05−0.3 mm in dimension. Similarly, in the mass fraction 0.070 and 0.100 NaCl aqueous solution systems, for ΔTsub < 2.4 K, the shape of cyclopentane hydrate crystals is predominantly hexagonal or pentagonal, with the length of the side typically in the 0.7−1.4 mm range. At ΔTsub = 2.4−3.5 K, both slender polygons and triangular crystals of 0.2−0.5 mm in dimension are observed, and at ΔTsub > 3.5 K, the crystal shape was sword-like with a size less than 0.5 mm. For the systems with NaCl aqueous solutions of mass fraction 0.233 and 0.264, at ΔTsub = 3.1 K, the shapes of the hydrate crystal were polygonal with a length of about 0.2−0.5 mm, and the crystal shape changed to an elongated polygonal or triangle with a length of about 0.05−0.3 mm at ΔTsub = 5.8 K. Overall, the morphology of the cyclopentane hydrate crystals formed with NaCl aqueous solution is roughly similar at a given subcooling. Figure 7 shows the relation between the ΔTsub and the lateral hydrate growth rates that were deduced from the sequential observations in the present study. In deducing these growth rate data, the lateral growth rate v is defined as v ≡ l/Δt, where l is the length of the lateral growth of a crystal and Δt is the time

Figure 8. Illustration of the definition of the lateral growth rate of the hydrate v. v is defined as v ≡ l/Δt, where l is the length of the lateral growth of a crystal and Δt is the time required for the growth.

dimensional hydrate crystal growth, sometimes referred to as the “rate of hydrate-film/layer propagation”. We have performed three independent measurements at a given thermodynamic condition to determine the crystal growth rate. The standard deviations of the measured data were always less than 5%. Consistent with the previous studies,13,15,31,32 the hydrate film growth rate decreased with decreasing ΔTsub in all the systems. In addition, the hydrate film growth rate decreased with increasing concentration of NaCl. The data in Figure 7 clearly indicate that the crystal growth rate decreased with increasing concentration of the NaCl aqueous solution at a given ΔTsub, while there was no change in the crystal morphology at a given ΔTsub as shown in Figure 6. It is then inferred that the nucleation rate is decreased with increasing NaCl concentration. Crystal morphology, specifically the size and shape of the crystals, should be determined by the balance between the rate of nucleation of the hydrate crystals and the crystal growth rate. For example, at a large ΔTsub, the rate of hydrate crystal growth is greater than that at a small ΔTsub, whereas the rate of hydrate nucleation is also greater at a large ΔTsub. Thus, smaller crystals were observed at a large ΔTsub as seen in Figure 6.

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CONCLUSIONS We performed a set of observations of hydrate formation and growth at the interface of the NaCl aqueous solution and liquid cyclopentane to clarify the effect of elevated salt concentration on the crystal growth. The concentration of the NaCl solution was set at 0.050, 0.070, 0.100, 0.233, or 0.264 in mass fraction. Hydrate crystals grew along the interface of liquid cyclopentane and the NaCl solution covering the interface. The crystal morphology has a significant dependence on the system subcooling ΔTsub. It was found that the size of the individual cyclopentane hydrate crystals decreased with the increasing ΔTsub. The results showed that the morphology of the individual cyclopentane hydrate crystals in any levels of NaCl concentration is roughly similar at a given ΔTsub. As a general trend, when the subcooling is ΔTsub < 3.5 K, the shape of hydrate crystals is typically polygons with one side of the polygon 0.3−1.0 mm in length; when the subcooling is ΔTsub > 3.5 K, that changes to triangular or sword-like. The rate of the hydrate-film/layer propagation also depends on ΔTsub. The hydrate film growth rate decreased with decreasing ΔTsub in any of the systems and decreased with an increasing concentration of NaCl.

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Figure 7. Growth rate of hydrate crystals at the interface of the liquid cyclopentane and NaCl aqueous solution. The standard deviations for the data are smaller than the size of the symbols.

AUTHOR INFORMATION

Corresponding Author

*Phone: +81-45-566-1813. E-mail: [email protected]. 5228

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Notes

(18) Watanabe, S.; Saito, K.; Ohmura, R. Crystal growth of clathrate hydrate in liquid water saturated with a simulated natural gas. Cryst. Growth Des. 2011, 11, 3235−3242. (19) Tohidi, B.; Yang, J.; Salehabadi, M.; Anderson, R.; Chapoy, A. CO2 Hydrates could provide secondary safety factor in subsurface sequestration of CO2. Environ. Sci. Technol. 2010, 44, 1509−1514. (20) Barduhn, A. J.; Towlson, H. E.; Hu, Y.-C. The properties of gas hydrate and their use in demineralizing sea water. Office of Saline Water, Research and Development, Progress Report No. 44, U.S. Dept. of the Interior: Washington, DC, 1960. (21) Corak, D.; Barth, T.; Høiland, S.; Skodvin, T.; Larsen, R.; Skjetne, T. Effect of subcooling and amount of hydrate former on formation of cyclopentane hydrates in brine. Desalination 2011, 278, 268−274. (22) Park, K. N.; Hong, S. Y.; Lee, J. W.; Kang, K. C.; Lee, Y. C.; Ha, M. G.; Lee, J. D. A new apparatus for seawater desalination by gas hydrate process and removal characteristics of dissolved minerals (Na(+), Mg(2+), Ca(2+), K(+), B(3+)). Desalination 2011, 274, 91− 96. (23) Sarshar, M.; Sharafi, A. H. Simultaneous water desalination and CO(2) capturing by hydrate formation. Des. Water Treatment 2011, 28, 59−64. (24) Ohgaki, K.; Makihara, Y.; Takano, K. Formation of CO2 hydrate in pure and sea waters. J. Chem. Eng. Jpn. 1993, 26, 558−564. (25) Uchida, T.; Ikeda, I. Y.; Takeya, S.; Ebinuma, T. CO2 hydrate film formation at the boundary between CO2 and water: effects of temperature, pressure and additives on the formation rate. J. Cryst. Growth 2002, 237−239, 383−387. (26) Makogon, T. Y. Phase equilibrium for methane hydrate from 190 to 262 K. An Experimental and Computer Study of Gas. Hydrate Formation and Inhibition. M.Sc. Thesis, Colorado School of Mines, Golden, CO, 1994. (27) Makogon, Y. F.; Makogon T. Y.; Holditch, S. A. Gas hydrate formation and dissociation with thermodynamic and kinetic inhibitors. In Proceedings of the SPE Annual Technical Conference and Exhibition, Houston, TX, October 3−6, 1999; paper no. 56568. (28) Sakemoto, R.; Sakamoto, H.; Shiraiwa, K.; Ohmura, R.; Uchida, T. Clathrate hydrate crystal growth at the seawater/hydrophobicguest-liquid interface. Cryst. Growth Des. 2010, 10, 1296−1300. (29) Martínez, I. Termodinámica básica y aplicada; Dossat S.A.: Madrid, Spain, 1992. (30) Aman, Z. M.; Dieker, L. E.; Aspenes, G.; Sum, A. K.; Sloan, E. D. J.; Koh, C. A. Influence of model oil with surfactants and amphiphilic polymers on cyclopentane hydrate adhesion forces. Energy Fuels 2010, 24, 5441−5445. (31) Saito, K.; Sum, A. K.; Ohmura, R. Correlation of hydrate-film growth rate at the guest/liquid-water interface to mass rransfer resistance. Ind. Eng. Chem. Res. 2010, 49, 7102−7103. (32) Taylor, C. J.; Miller, K. T.; Koh, C. A.; Sloan, E. D. J. Macroscopic investigation of hydrate film growth at the hydrocarbon/ water interface. Chem. Eng. Sci. 2007, 62, 6524−6533.

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This study was supported by a Grant-in-Aid for Science Research from the Japan Society for the Promotion of Science (Grant 22760157) and by a Grant-in-Aid for the Global Center of Excellent Program for “Center for Education and Research of Symbiotic, Safe and Secure System Design” from the Ministry of Education, Culture, Sport, and Technology in Japan.

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