Estimation of dissociation rate constant of CO 2 hydrate in water fl ow

1© 2014 Society of Chemical Industry and John Wiley & Sons, Ltd | Greenhouse Gas Sci Technol. 4:1–11 (2014); DOI: 10.1002/ghg

Received May 11, 2014 ; revised August 2, 2014 ; accepted August 19, 2014 Published online at Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/ghg.1469

Modeling and Analysis

Estimation of dissociation rate constant of CO 2 hydrate in water fl ow Ayako Fukumoto , University of Tokyo , Kashiwa , Japan Wu-Yang Sean, Chung Yuan Christian University , Chung-Li , Taiwan Toru Sato, University of Tokyo , Kashiwa , Japan Akihiro Yamasaki, Seikei University , Musashino-shi , Tokyo , Japan Fumio Kiyono, National Institute of Advanced Industrial Science and Technology , Tsukuba , Japan

Abstract: Dissociation processes of CO 2 hydrate under water fl ow conditions were investigated by experimental measurements and numerical calculation. Dissociation experiments were carried out with a CO 2 hydrate ball (diameter 10 mm) mounted in a fl ow cell, and the overall dissociation rate of CO 2 hydrate without bubble formation was measured under various conditions of temperature, pressure, and water fl ow rate. A linear phenomenological rate equation in the form of the product of the disso-ciation rate constant and the molar Gibbs free energy difference, between the hydrate phase and the ambient aqueous phase, was derived by considering the Gibbs free energy difference as the driving force for the dissociation. The molar Gibbs free energy difference was expressed by the logarithm of the ratio of the concentration of CO 2 dissolved in water at the hydrate surface to the solubility of CO 2 in the aqueous solution in equilibrium with the hydrate. The dissociation rate constant was determined from the experimental results of the overall dissociation rate combined with the numerical simulation results of the concentration profi le of CO 2 constructed by the computational fl uid dynamics (CFD) method. The obtained dissociation rate constant at the same pressure was found to be dependent on the temperature with the apparent activation energy of 97.51 k J/mol . A general form with product of the dissociation rate constant times driving force is proposed to calculate the dissociation rate of CO 2 hydrate in the water. © 2014 Society of Chemical Industry and John Wiley & Sons, Ltd

Keywords: CO 2 hydrate ; carbon capture and storage ; hydrate dissociation ; dissociation rate constant ; Gibbs free energy, CFD

Correspondence to: Wu-Yang Sean, Department of Bioenvironmental Engineering, Chung Yuan Christian University, 32023 Chung-Li, Taiwan.

E-mail: [email protected]

Introduction

To lower the CO 2 concentration in the atmosphere, carbon dioxide capture and storage (CCS) is thought to be eff ective. One of CCS schemes is

to store CO 2 in the form of gas hydrate in sub-seabed geological formation, as was proposed by Inui and Sato. 1 In addition, much research about the formation and dissociation of CO 2 hydrate during sequestration in the deep ocean has been discussed. 2–5 To estimate

the effi ciency of storing CO 2 , it is necessary to obtain physical properties of CO 2 hydrate. In this study, the dissociation rate constant of CO 2 hydrate was estimat-ed at a given surface area of the hydrate by combina-tion of experimental observation and a computational fl uid dynamics (CFD) method. Th e methodology to obtain the rate constant is essentially the same as that used for methane hydrate by Sean et al ., 6 who dissoci-ated a hydrate ball in fresh water fl ow under specifi c temperature T and pressure P , which were set in the

Current address: Chemical Engineering Department, ENSTA ParisTech, 828 Boulevard des Maréchaux, 91762 Palaiseau Cedex, France.

A Fukumoto et al. Modeling and Analysis: Estimation of dissociation rate constant of CO2 hydrate in water fl ow

2 © 2014 Society of Chemical Industry and John Wiley & Sons, Ltd | Greenhouse Gas Sci Technol. 4:1–11 (2014); DOI: 10.1002/ghg

regime of so-called hydrate stability zone, and as-sumed that the driving force for the dissociation was expressed as the shift of the Gibbs free energy, GΔ :

dndt

k G k RTxx

k RTCC

ln ln ;bl blH

Ibl

H

I= Δ = ≈

(1)

where dn dt/ is the mole fl ux per unit area F mols m( , )cal

1 2= − − , kbl is the dissociation rate coeffi -cient = > − −mol J J s m( )2 1 1 2 , T is the temperature (K), R is the gas constant J mol( 8.314 K )1 1= − − , xH is the mole fraction of CO 2 equilibrated with hydrate in the ambient aqueous phase, and xI is that at the hydrate surface and should vary depending on the local position on the surface. CH and CI are the volumetric molar concentrations of CO 2 mol m( )3− corresponding to xH and xI , respectively. Major features of this modeling are summarized as follows:

• Th e dissociation rate of CO 2 hydrate is expressed in a simple form based on the dissociation rate constant multiplied by the driving force (e.g. Gibbs free energy). And, the driving force may be in-duced by higher temperature, lower pressure, or lower concentration in the ambient fl ow.

• Heat, mass transfer, and dissociation rate constant have been considered together in this modeling. Particularly, the dissociation rate constant is analyzed in an alternative way of slow fl ow rate with stable surface area in transient state.

• A combination of experimental observation and CFD method provides a precise approach to obtain the intrinsic dissociation rate constant.

Method and materials Outline of the determination process of rate constant Experimentally observable dissociation rate Fobs is the integration of local dissociation rate on the surface of hydrate and local surface concentration CI varies depending on local circumstances. In this study, a CFD technique, which can treat local CI on hydrate surface, was adopted, as was done by Sean et al . 6 Th e present process to determine kbl follows: a series of dissociation experiments are conducted for a CO 2 hydrate ball located in water fl ow and measure Fobs; the dissociation of hydrate, water fl ow, and transfers of heat and dissolved mass are analyzed by the CFD method by which overall dissociation rate Fcal can be

calculated for various values of kbl : calibration curves between kbl and Fcal are drawn, and, fi nally, kbl can be determined by applying measured Fobs to the calibra-tion curves. Th e overall dissociation rate is given by

F QC ;obs x= (2)

Dissociation experiment Preparation of CO 2 hydrate balls Fine CO 2 hydrate powder was prepared from fi ne ice powder by the ice-gas interface method. 7,8 Th e fi ne ice powder was prepared by condensation of atmospheric water vapor onto a plate cooled by liquid nitrogen. Th e ice powder was then converted into hydrate powder in a high-pressure vessel under high pressure with pure CO 2 gas (about 8.5‒10 MPa) at a tempera-ture near the melting point of ice (271–275 K). Th e ice powder was converted almost completely into CO 2 hydrate powder aft er several days of mixing. A given amount of the hydrate powder was then mounted in a pair of half-spherical molds made of stainless steel, the inner diameters of which were 0.01 m. Both molds had a groove on the edge for an iron skewer of diameter 0.1 mm. Th e two half-spherical molds were then joined together with an iron skewer being placed between the modules, and the sphere was pressurized by an oil jack at a pressure of 8.0 MPa. Finally, a spherical ball of CO 2 hydrate 10 mm in diameter, skewered on the iron wire, was obtained. 6

Experimental procedures Hydrate dissociation experiments were conducted for a CO 2 hydrate ball located in water flow with a known flow rate Q m( /s)3 under given conditions of temperature T and pressure P , which were set to be in the regime in which hydrate (H) and liquid water (L w ) coexist. T ranged from 277.65 to 282.15 K at P = 5.0MPa. The dissociation of hydrate was driven by low CO 2 mole fraction in pure water flow, which is schematized as a vector from Point A to Point B shown in Fig. 1. The experimental set-up for the CO 2 hydrate dissociation was almost the same as that used by Sean et al ., 6 except for the apparatus to measure CO 2 concentration Cx , which was ob-tained by analyzing the composition of the aqueous phase by gas chromatography (GC); water was sampled with a syringe at a location about 10 cm downstream from the observation cell; the sampled

Modeling and Analysis: Estimation of dissociation rate constant of CO2 hydrate in water fl ow A Fukumoto et al.


liquid was introduced to the GC to analyze water content, which was conducted by a thermal conduc-tivity detector (TCD) and CO 2 was displaced by methane with a methanizer and the content was detected by a flame ionization detector (FID) as shown in Fig. 2.

Numerical simulation We used an axisymmetric two-dimensional CFD code that was simplifi ed from the original three-dimen-sional method developed by Jung and Sato 9 that adopts collocated fi nite-volume formulation and moving unstructured grids. Th is method has success-fully been used to predict the behavior of a rising and deforming droplet. Th e CO 2 hydrate ball can be regarded as a solid and thus grids around the ball were fi xed in this study. For the infl ow and the outfl ow boundaries, a laminar parabolic velocity profi le and the zero-gradient Neumann condition were imposed, respectively. Figure 3 is the overall computational cell. A no-slip condition was used on the sidewall and the surface of the hydrate ball. In this calculation, the maximum Reynolds number over the hydrate ball is about 200. Th e computational domain is in conformity with the cylindrical observation cell of the experimental facility.

Mass transfer of CO 2 Th e boundary condition for CO 2 concentration on the hydrate surface is given by

k RT

CC

D C DC C

rln ;bl

H

I

I k= ∇ ≈ −Δ

(3)

Figure 1. Schematic drawing of mole fraction-pressure ( x-P ) phase diagram for CO 2 -water-hydrate in equilibrium under constant temperature.

Figure 2. Schematic drawing of experimental apparatus for CO 2 hydrate dissociate study.



T

T

(8.8286 10 )

(5.3886 10 ) 8.314 10 ;L

10 2

7 5

ν = ×

− × + ×

−

− −

(5)

T487.85 ln 2173.8;Lλ ( )= − (6)

Th e following physical properties of CO 2 hydrate were also used: the thermal diff usivity of aqueous phase of ms1.38 10 ( )7 2× − − , the heat capacity of hydrate of J kg2080.0( K )1 1− − , and the heat conductiv-ity of m0.324(WK )1 1− − . 12 Th e density of CO 2 hydrate is given as kgm1116.8( 3− ) by Sloan. 13 Sloan 13 modeled the quadruple equilibrium pressure P Paeq ( ) for CO 2 hydrate as a function of T :

P

Texp 10 ;eq

3α β= +⎛⎝⎜

⎞⎠⎟ ×

(7)

where α = 44.580 and β = −10246.28. Gas solubility xG and xH must cross exactly on the quadruple point, Eqn ( 7) . Based on this principle and the data of Aya et al. , 14 Yang et al., 15 and Servio et al., 16 we provided a model equation for xH under the condi-tion that 275.15K < T < 282.15K:

x a b P Texp( 10 1.321 10 2.292 10 );H

6 4 2= ⋅ ⋅ × + × − ×− − −

(8)

a T0.0016 273.15 ;0.9211( )= − (9)

b T0.0199 log 273.15 0.0942;( )= − − + (10)

Heat transfer Th e heat transfer at the surface of CO 2 hydrate is given by

Q T T ;H H H L L.

λ λ+ ∇ = ∇ (11)

where QH.

( H FL obs= , where HL is the latent heat of hydrate dissociation) is the rate at which the latent heat is transferred to the CO 2 hydrate by dissociation;

Hλ and Lλ are the heat conductivities in the hydrate and water, respectively. Heat of dissociation per mole hydrate HL is interpolated from Anderson 17 as

H T207,917 530.97 ;L I= − × (12)

where TI is the surface temperature. Th en we have

T

h T h T F h hh h F h h

207,917530.97

;IL H L H L H cal L H

L H H L cal L H

λ λλ λ

= + − ⋅+ − ⋅

(13)

where D is the diff usion coeffi cient of CO 2 in the aqueous phase m s( )2 1− , Ck is the calculated CO 2 concentration in a computational grid neighboring to the hydrate surface, Δ r is the distance of the grid centroid from the hydrate surface, and CI was calculated locally on the hydrate surface by using Eqn ( 3) . D is given by the conventional Wilke-Chang equation: 10

DM T

V7.4 10

( );B

L A

121/2

0.6ϕ

η= × −

(4)

where ϕ (= 2.6) is the association parameter for the solvent water, M mol( 18 g )B

1= − is molecular weight of water, V m mol( 3.4 10 )A

5 3 1= × − − is the molar volume of CO 2 , and Lη ( smPa ⋅ ) is the viscosity of water. Empirical functions cited in a handbook 11 were adopted for kinematic viscosity ms( )L

2ν − and heat conductivity m(WK )L

1λ − of water:

Figure 3. Schematic image of overall compu-tational cell of CO 2 hydrate.



Figure 7 is an example of the calibration curve between the assumed kbl and the resultant Fcal . By applying Fobs to this curve, one can obtain kbl . For expressing temperature dependency, an Arrhenius-type equation was adopted:

k k

ERT

exp ;bl 0= − Δ⎛⎝⎜

⎞⎠⎟

(14)

where k0 is the dissociation rate constant, and EΔ is the activation energy. From the plot of kln( )bl vs. 1/ T (Fig. 8), the values of k mol J s m2.91 100

11 2 1 1 2= × − − − and E Jmol97.51 k 1= −Δ were obtained in the tempera-ture ranges between 277.65 ∼282.15 K at P = 5.0 MPa. It should be noted that a small diff erence in Δ E leads to a large change in k0 . Th us, it is important to clarify the temperature range in which the values of k0 and Δ E are valid. Clarke and Bishnoi 18 modeled the dissociation rate of hydrate:

where TL and TH are the temperatures defi ned at the centroids of a cell in the aqueous phase and at a cell in the solid hydrate, respectively; hL and hH are the centroids of a cell in the aqueous phase and at a cell in the solid hydrate, respectively. Th ese cells are attached to the hydrate surface, as shown in Fig. 4.

Results and discussion Figure 5 shows the photographs of a hydrate ball suspended in the observation cell at 0 and 3.0 min aft er the start of water fl ow. Because of the cylindrical shape of the cell, the spherical ball seems stretched in the horizontal direction. It was found that, as the hydrate dissociation is an endothermic process, ice covered the hydrate ball soon aft er the water was fi lled in the observation cell (Fig. 5(a)) and that the ice disappeared about 1.0 min aft er the water fl ow started. Th e surface ice must have suppressed hydrate dissociation and this was evidenced by the fact that Fobs was 0 till the ice disappeared. We used the instantaneous value of Fobs measured 3.0 min aft er the start of the water fl ow to extract the rate constant. In numerical calculation, a hydrate ball was assumed to be ellipsoidal, the size of which was set to be the same as that measured from the photograph taken 3.0min aft er water fl ow started (Fig. 5(b)). Th e contour maps of calculated T and C in a case study are shown in Fig. 6. At this trial, the parameters were set to be k mol J s m5.0 10bl

6 2 1 1 2= × − − − − under the condition that T = 277.65 K, P = 5.0 MPa, and Q m s1.67 10 5 3 1= × − − . Figure 6(a) clearly shows a ring vortex downstream of the hydrate ball and that tempera-ture is the lowest near the separation point. In Fig. 6(b), it is noted that CI is not uniform on the hydrate surface.

Figure 4. Schematic image of computational cell for heat transfer at the surface.

Figure 5. Photographs of CO 2 hydrate ball taken at t = 0 min (a) and 3.0 min (b) after the start of water fl ow under the condition that T = 282.05K, P = 5.0MPa, and Q m s11 6677 1100. 55 33 11== ×× −− −− .



respectively, at temperature and pressure ranging from 274.15 to 281.15 K and from 1.4 to 3.3 MPa. Th e driving force of Clarke and Bishnoi 18 is the diff erence in fugacity and, therefore, the unit of the constant is diff erent from ours. Basically, their model is appli-cable to the dissociation from the H-L w regime to the Vapor(V)-L w shown in Fig. 1, not to that from the H-L w to the L w , in other words, not the dissociation by lowering dissolved gas concentration in water. Nihous and Masutani 19 proposed a model for the dissociation of hydrate in undersaturated water and it can be applied to the dissociation from the H-L w regime to the L w by considering two liquid fi lms separating hydrate surface and bulk water: desorption and diff usive boundary layers. Th ey found that Eqn ( 15) failed to explain some of the fi eld observations and suggested that E Jmol96.49 k 1Δ = − if kD0 is set to be the same as that of Clarke and Bishnoi. 18 Although original kbl was obtained by the dissociation from the H-L w regimes to the L w in this study, Sean et al . 20 proved that it can also be applied to the dissociation from the H-L w regime to the V-L w in the case of methane hydrate. Here, we converted kD to kbl for the comparison by

kk f f

RT x x( )

ln( / );bl

D eq

H G=

−

(16)

where xG is the solubility for gas CO 2 in aqueous water (Kohl and Nielsen 21 ).

Figure 9 shows the comparison in kbl between the model of Clarke and Bishnoi, 18 Nihous and Masu-tani, 19 and the present model converted by Eqn ( 16) in the temperature range between 278.15∼281.15 K at P = 1.0, 1.5, and 2.0 MPa. Although kbl and kD should be independent of P , kD predicted by the present model varies with P . Th is is simply because the mathematical models commonly used to calculate f , xH , and xG do not have consistent pressure infl uences. It is seen that kbl of new model is larger than those of Clarke and Bishnoi 18 model converted from kD by one or two decades, but it is compared well with those of Nihous and Masutani. 19 Th e relative result of fl ux expressed in terms of various fugacity change are shown in Fig. 10. Th is model showed good agreement with the Nihous and Masutani model.

dndt

k RTxxln ;bl

H

G=

(17)

dndt

k f f k ERT

f f( ) exp ( );D eq g D eq g0= − = −⎛⎝⎜⎜⎜

⎞⎠⎟⎟⎟ −

Δ

(15)

where k mol s m( Pa )D01 1 2− − − is the rate constant,

f Pag ( ) is the fugacity of gaseous CO 2 , and feq is the fugacity of the quadruple equilibrium. kD0 and

EΔ for CO 2 hydrate were estimated as mol s m1.83 10 Pa8 1 1 2× − − − and Jmol102.88 k 1− ,

Figure 6. Contour maps of calculated CO 2 concentration (a) and temperature (b) for k mole J s m55 00 1100. bl

77 22 11 11 22== ×× −− −− −− −− under the condition that T = 281.95 K, P = 5.0 MPa, and Q m s11 6677 1100. 55 33 11== ×× −− −− .



the quadruple equilibrium point, above which hydrate is thermodynamically stable. In the model, hydrate dissociation is driven by low mole fraction of CO 2 in fresh water fl ow. Th e methodology used in this study for CO 2 is the same as that of Sean et al . 6 for methane. Experimental temperature ranged from 277.65 to 281.95 K at the pressure of 5.0 MPa. To obtain the dissociation rate constant, measured aqueous

k

Texp

11,72926.398 ;bl = − +⎛

⎝⎜⎞⎠⎟

(18)

Conclusions Th e intrinsic dissociation rate constant of CO 2 hydrate, kbl was obtained under the condition beyond

Figure 7. An example of calibration curve between kbl and Fcal under the condition of T = 279.15K, P = 5.0MPa, and Q m s11 1133 1100. 55 33 11== ×× −− −− .

Figure 8. Resultant dependency of dissociation rate coeffi cient kbl of CO 2 hydrate

on temperature.



obtained result was compared to that based on the driving force of fugacity change and it is in good agreement with one of published fugacity-based

concentration of CO 2 in the wake of a hydrate ball was applied to the calculated calibration curves of CO 2 concentration vs. the dissociation rate. Th e

Figure 9. Comparison of dissociation rate klog bl at Jmole660000 11115500 11μμ ≈≈Δ ∼ −− , and T = 282.15 K.

Figure 10. Comparison of fl ux ⎛⎛⎝⎝⎜⎜

⎞⎞⎠⎠⎟⎟

dn

dt at f 00 33 11 55 . . MPa==Δ ∼ , and T = 282.15 K.



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models. Th e form of proposed modeling of CO 2 dissociation fl ux generally in Vapor(V)-L w regime was summarized as Eqn ( 17) .

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NOMENCLATURE

C volumetric molar concentration of CO 2 in the ambient water mol m[ ]3⋅ −

C H volumetric molar concentration of CO 2 in the aqueous solution equilibrated with the stable hydrate phase mol m[ ]3⋅ −

C K volumetric molar concentration of CO 2 in water at the centroid of a cell attaching to the hydrate surface mol m[ ]3⋅ −

C I volumetric molar concentration of CO 2 in the ambient aqueous solution at the surface of the hydrate ball mol m[ ]3⋅ −

C X average molar volumetric concentration of CO 2 in the ambient water fl ow for a given cross section of water fl ow mol m[ ]3⋅ −

d diameter of the CO 2 hydrate ball [ m ]

D diff usion coeffi cient of CO 2 in water m s[ ]2⋅ − E activation energy Jmol[ ]1− F dissociation rate fl ux mols m[ ]1 2− − feq fugacity of the quadruple equilibrium [Pa] fg fugacity of gaseous CO 2 [Pa] G molar Gibbs free energy Jmol[ ]1− H L latent heat of hydrate dissociation Jmol[ ]1− h L length of the water layer attached on the hydrate

surface [ m ] kD0 intrinsic dissociate rate constant based on

Clarke-Bishnoi model mol s m[ Pa ]1 1 2− − − k bl dissociation rate constant based on new model

mol J s m[ ]2 1 1 2− − − L thickness of computational cell [ m ] MB molecular weight of water mol[g ]1−



P thermodynamic pressure [Pa] Peq quadruple equilibrium pressure for CO 2 hydrate

as a function of T [Pa] Q volumetric fl ow rate of the ambient water

m s[ ]3 1− QH

. the rate at which the latent heat is transferred to

the CO 2 hydrate by dissociation Jm s[ ]2 1− − R gas constant, 8.314 J mol[ K ]1 1− − T absolute temperature [K] T L temperature at the centroids of a cell in the solid

hydrate [K] T H temperature at the centroids of a cell in the

aqueous phase [K] x mole fraction of CO 2 [–] x eq solubility of CO 2 in the aqueous solution in

equilibrium with the stable hydrate phase [–]

x I mole fraction of CO 2 in the aqueous phase at the surface of the hydrate ball [–]

α L thermal diff usivity in the aqueous phase ms[ ]2− α H thermal diff usivity in the hydrate ball ms[ ]2− Δr thickness of the computational cell [ m ] δ thickness of the boundary layer [ m ] Δμ chemical potential diff erence Jmol[ ]1− ρ density of the ambient water kgm[ ]3− ϕ the association parameter for the solvent water Lη is the viscosity of water [ smPa ]⋅ VA is the molar volume of CO 2 m mol[ ]3 1− Lν kinematic viscosity of water ms[ ]2− Lλ heat conductivity of water m[WK ]1 1− − Hλ and Lλ the heat conductivities in the hydrate

and water m[WK ]1 1− −

Wu-Yang Sean

Wu-Yang Sean obtained his PhD in engineering in 2005 at the University of Tokyo (Japan) for research in methane hydrate. From 2006 till he joined CYCU in 2013, he worked in the fi eld of green energy and electric vehicles in non-organization, ITRI in Taiwan. In ITRI, he was a group

head and responsible for the research of industrial technologies. The solid research achievements include 11 patents fi led in Taiwan, China, and US with strong team work. Now, he joined the environmental research department in CYCU in 2013. His interests are focus on meso-scale numerical modelings, new energy and system integration.

Toru Sato

He has been engaged in environmen-tal impact assessment of CO2 sub-seabed geological storage (CCS), development and application of multi-scale ocean model, development of dissociation and formation models of methane and CO2 hydrate, design and feasibility study on CO2 storage in

the form of gas hydrate, and has written number of articles on the topics in internationally infl uential journals. He has also devoted himself as the member of some governmental committees, such as Technical Committees on CO2 Ocean Sequestration of RITE, Sub-Seabed CCS of RITE, Environmental Impact Assessment for Sub-Seabed CCS of MOE, Antarctic Expedition Ship of MEXT, Ocean-Space Collaboration of JAXA, etc. From April 2013, he has been taking a position of Chair of Environmental Studies, Graduate School of Frontier Sciences, University of Tokyo.1980–1984 Department of Naval Architecture, University of Tokyo (BEng).1984–1986 Department of Naval Architecture, University of Tokyo (MEng).1986–1996 Research Engineer at Bridgestone Corporation.1990–1993 Department of Chemical Engineering and Chemical Technology, Imperial College, London (PhD).1996–2004 Associate Professor at Department of Environmental and Ocean Engineering, University of Tokyo.2004–now Professor at Department of Ocean Technology, Policy, and Environment, University of Tokyo.

Ayako Fukumoto

Ayako Fukumoto is currently a post-doctoral researcher in the chemical engineering department at ENSTA-ParisTech. She holds BEng, MS, and PhD degrees in environmental study from the University of Tokyo. Fukumoto’s current focus is on the gas storage and gas separation using semi-clathrate hydrates.



Akihiro Yamsaki

Akihiro Yamsaki obtained his PhD in chemical engineering at the University of Tokyo. He is a Summit fellow at National Research Council, Canada; Senior Research Scientist at National Institute of Advanced Industrial Science and Technology (AIST); and Professor at Department of Materials and Life

Sciences, Seikei University, 3-3-1 Kichijoji-kitamachi, Musashino, Tokyo 1808633, Japan ([email protected]).

Fumio Kiyono

Fumio Kiyono is a leader of the Environmental Fluid Engineering Research Group at the National Institute of Advanced Industrial Science and Technology. He holds BEng, MEng, and PhD degrees in resources engineering from Tohoku University. With 20 years of

professional research experience, Kiyono has authored numerous studies in a variety of fi elds.

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Estimation of dissociation rate constant of CO 2 hydrate in water fl ow