- Email: [email protected]
The investigation of phase equilibria and kinetics of CH4 hydrate in the presence of bio-additives
Fluid Phase Equilibria 452 (2017) 143e147
Contents lists available at ScienceDirect
Fluid Phase Equilibria j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / fl u i d
The investigation of phase equilibria and kinetics of CH4 hydrate in the presence of bio-additives Qiang Sun a, Bo Chen a, Xingxun Li a, Xuqiang Guo a, b, *, Lanying Yang a a b
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, 102249, China Department of Engineering, China University of Petroleum-Beijing, Karamay, 834000, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 1 June 2017 Received in revised form 1 September 2017 Accepted 2 September 2017 Available online 4 September 2017
The conventional hydrate promoters and inhibitors, such as tetrahydrofuran (THF), sodium dodecyl sulfate (SDS) and methanol, have the common disadvantages of chemical substances, i.e., pungent flavor, corrosivity, toxicity and anti-degradability. It severely pollutes the environment and limits the application of hydrate-based technologies. Consequently, it is necessary to develop new and green substances as the hydrate promoters or inhibitors. In this work, L-arginine and isooctyl glucoside were used as bioadditives for CH4 hydrate to form bio-hydrate. The effects of L-arginine and isooctyl glucoside on the formation thermodynamics and kinetics of CH4 hydrate were investigated first. Then, the equilibrium separation of CH4/N2 via hydrates formation was conducted in isooctyl glucoside solution. The results show that formation pressure of CH4 hydrate in L-arginine solution is higher than that in pure water at the same temperature. Isooctyl glycosidase can greatly accelerate the hydration rate and increase the gas storage capacity of hydrate. In the separation of CH4/N2, the recovery of CH4 and gas storage capacity of hydrate are significantly increased after adding isooctyl glucoside in water. In conclusion, L-arginine can be used as hydrate inhibitor to replace conventional alcohols in the inhibition of hydrates formation. Isooctyl glycosidase is an effective kinetic promoter of hydrate, which is suitable for CH4 storage in hydrate, and separation of CH4-containing gas mixture via hydrates formation. This work provides two environment friendly bio-additives for hydrate, which will definitely promote the development and application of hydrate research. © 2017 Published by Elsevier B.V.
Keywords: Bio-additives Hydrate Thermodynamics Kinetics Separation
1. Introduction Hydrate (or clathrate hydrate) is a kind of icelike nonstoichiometric compound formed by gas and water at certain temperature and pressure [1,2]. More than 100 substances have been found to form hydrates so far, and the thermodynamics theory of hydrates has been well-established [3]. In addition, hydrate additives, including promoters and inhibitors, have been widely applied to change the phase equilibria conditions and formation kinetics of hydrates. The common thermodynamic promoters of hydrates are tetrahydrofuran (THF), tetrahydropyrane (TPF), tetra-butyl ammonium bromide (TBAB), cyclopentane (CP) [4e11]. The frequently-used kinetic promoters are sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate
* Corresponding author. Department of Engineering, China University of Petroleum-Beijing, Karamay, 834000, China. E-mail address: [email protected] (X. Guo). http://dx.doi.org/10.1016/j.fluid.2017.09.002 0378-3812/© 2017 Published by Elsevier B.V.
(SDBS), alkyl polyglucoside (APG), linear alkyl sodium sulfonate (LABSA) [12e16]. The common inhibitors of hydrate includes methanol, ethanol, polyvinylpyrrolidone (PVP) and so on [17e20]. The presence of above additives in the formation of hydrates makes the application of hydrate-based technologies more feasible and convenient in the industrial. However, as the chemical substances, they also have obvious drawbacks, i.e., pungent flavor, corrosivity, toxicity and anti-degradability. It severely pollutes the environment and limits the application of hydrate-based technologies. Consequently, it is necessary to develop new and green substances as the hydrate promoters or inhibitors. Wang et al. found that certain fungi and plant extracts could be used as the surfactants for CH4 hydrate to increase hydration rate and gas storage capacity [21]. The hydrates formed by these biomass are accordingly called as bioclathrates. Fakharian et al. put forward through experiments that potato starch is also able to increase gas storage capacity of hydrate [22]. Rogers et al. demonstrated that natural gas hydrate (NGH) in subsea sediments is
144
Q. Sun et al. / Fluid Phase Equilibria 452 (2017) 143e147
accelerated by the surfactants generated from microbes in seafloor [23]. Consequently, the proposing of biosurfactants for hydrate offers a novel idea for the development of hydrate additives, especially for the kinetic promoters of hydrates. Biosurfactants and bio-based surfactants are collectively called as eco-friendly surfactants [24]. The former are amphipathic compounds, for instance, glycolipid, polysaccharide, peptide lipid, and neutral lipid derivatives, generated by the various organisms with the characteristics of surfactants, such as germs, yeast, fungus, and so on. The latter are synthetic compounds based on the natural structures of renewable biosurfactants, such as amino acid, saccharides and vegetable oil. Eco-friendly surfactants have the advantages of high safety, mild nature, low skin irritation and toxicity, good biodegradation and environmental performance. Therefore, we choose L-arginine and isooctyl glucoside in this work as bio-additives for CH4 hydrate. As a reagent chemical, isooctyl glucoside is one kind of APGs. L-arginine is one kind of amino acid. The effects of L-arginine and isooctyl glucoside on the phase equilibria and kinetics of CH4 hydrate were investigated, respectively. 2. Experimental 2.1. Materials and apparatus The experimental materials and apparatus are shown in Table 1 and Fig. 1, respectively. Industrial-grade isooctyl glucoside was used in this work because it is cheaper and more convenient for industrial application. The composition of CH4/N2 gas mixture is determined by gas chromatograph (Agilent 7890). A precision electric balance with an accuracy of 0.0001 g is used to weigh additives and water for the solution preparation. The apparatus is mainly composed of air bath, hand pump, hydrate crystallizer, and temperature and pressure measurement system. The air bath keeps a constant temperature for the crystallizer. The hand pump adjusts and controls a constant pressure for the reaction system through acting on a piston in the crystallizer. The temperature and pressure are measured by a platinum resistance thermometer with the accuracy of 0.1 K and a pressure sensor with the accuracy of 0.01 MPa, respectively. In addition, a magnetic stick is placed in the crystallizer to constantly stir the gasliquid mixture. 2.2. Methods The formation thermodynamics and kinetics of CH4 hydrate in the presence of L-arginine and isooctyl glucoside were measured using “pressure searching” and “constant temperature and pressure” method, respectively. Then, the influence of isooctyl glucoside on the separation of CH4/N2 gas mixture is investigated. The separation of CH4/N2 via hydrate formation was also conducted using “constant temperature and pressure” method. The specific procedure of the methods above were described in our previous work [25e27], which show good reliability of the apparatus and methods.
3. Results and discussion 3.1. Formation conditions of CH4 hydrate in the presence of Larginine and isooctyl glucoside The formation conditions of CH4 hydrate in the presence of Larginine and isooctyl glucoside are shown in Fig. 2 and Fig. 3, respcetively. The concentrations of the bio-additives are relatively low in this work, because too much use will definitely increase the operation cost, which goes against the potential industrial application. The results show that the measured formation conditions of CH4 hydrate in pure water are in good agreement with the reference data [28,29]. L-arginine plays an inhibiting role in the formation of CH4 hydrate, and the inhibiting effect increases with the concentration of L-arginine. Therefore, it could be used as an novel thermodynamic inhibitor to replace the conventional alcohols for gas hydrates. The specific application of L-arginine to hydrate inhibition in different systems will be further studied in our future work. Also, the effects of other amino acids on the formation of gas hydrates will be further studied, in order to check if all amino acids are hydrate inhibitors. In Fig. 3, the presence of isooctyl glucoside slightly decreases the formation pressure of CH4 hydrate at the same temperature, and the formation pressure of CH4 hydrate decreases with the concentration of isooctyl glucoside. However, the overall drop of pressure is tiny, and the phase equilibria curves of different systems in Fig. 3 are very close. 3.2. Formation kinetics of CH4 hydrate in the presence of L-arginine and isooctyl glucoside Fig. 4 presents the formation kinetics of CH4 hydrate in different solutions at 275.15 K and 8.0 MPa. The results show that isooctyl glucoside could significantly increase the formation rate and gas storage capacity of CH4 hydrate. Meanwhile, the reaction time to reach equilibrium state is greatly shortened after adding isooctyl glucoside in water. The formation rate and gas storage capacity of CH4 hydrate increase with the concentration of isooctyl glucoside. It indicates that isooctyl glucoside is an effective kinetic promoter for hydrates. By contrast, L-arginine decelerates the formation rate of CH4 hydrate. This occurs because L-arginine is a thermodynamic inhibitor for CH4 hydrate. Consequently, the presence of L-arginine reduces the driving force of hydrate nucleation, and results in slow rate of hydration reaction. The inhibition effect of L-arginine on hydrate formation becomes particularly evident after half an hour of hydration. As a result, the equilibration time is prolonged about 2 h. Fig. 5 illustrates the formation kinetics of CH4 hydrate at different temperatures. In 0.20 wt% isooctyl glucoside solution, the formation rate of CH4 hydrate decreases with the temperature, because low temperature helps CH4 hydrate form. The formation rate of CH4 hydrate in isooctyl glucoside solution at 277.15 K is still faster than that in water at 275.15 K, which reveals the promotion effect of isooctyl glucoside to hydrate. At constant 279.15 K, the kinetic results also demonstrate that isooctyl glucoside accelerates
Table 1 Specifications of experimental materials. Materials
Brand
Purity
Suppliers
CH4 CH4/N2 L-arginine Isooctyl glucoside Deionized water
/ / Apollo Greensense /
99.90 mol% 34.65/65.35 mol% 99% 61% 15 106 U cm
Beijing Bei Temperature gas factory Beijing Bei Temperature gas factory Beijing Wohai Global Technology Co. Ltd. Beijing Wohai Global Technology Co. Ltd. SZ-93 water distillation unit
Q. Sun et al. / Fluid Phase Equilibria 452 (2017) 143e147
145
Fig. 1. Schematic sketch of the experimental apparatus.
the formation of CH4 hydrate, and L-arginine performs as an inhibitor for CH4 hydrate. 3.3. Separation of CH4/N2 via hydrates formation in the presence of isooctyl glucoside Taking advantage of the promotion function of isooctyl
Fig. 2. Formation conditions of CH4 hydrate in the presence of arginine.
glucoside to CH4 hydrate, we investigated its effect on the equilibrium separation of CH4/N2 gas mixture via hydrates formation. The separation experiments were conducted at constant 274.15 K and 9.0 MPa. Table 2 and Fig. 6 present the experimental results. The separation factor (SF), recovery (R) of CH4 in the hydrate and the gas storage capacity (GSC) of hydrate are calculated as follows [30e32]:
Fig. 3. Formation conditions of CH4 hydrate in the presence of isooctyl glucoside.
146
Q. Sun et al. / Fluid Phase Equilibria 452 (2017) 143e147
Fig. 6. The separation results of CH4/N2 via hydrates formation in isooctyl glucoside solutions.
Fig. 4. Formation kinetics of CH4 hydrate at 275.15 K and 8.0 MPa.
G hydrate phase, respectively. yG CH4 and yN2 stand for the concentraF tions of CH4 and N2 in equilibrium gas, respectively. nH CH4 and nCH4
are the numbers of moles of CH4 in hydrate and feed gas, respec-
Fig. 5. Formation kinetics of CH4 hydrate at 8.0 MPa and different temperature.
SF ¼
G yH CH4 yN2 , H 100% G yCH4 yN2
nH CH4
(1)
100%
(2)
GSC ¼
VH;0 VH;0 G ¼ G VH VL
(3)
where
yH CH4
R¼
nFCH4
and
yH N2
stand for the concentrations of CH4 and N2 in
Table 2 Separation of CH4/N2a via hydrates formation in the presence of isooctyl glucoside.b Gas
yG CH4 , mol%
yH CH4 , mol%
SF
R, 100%
GSC
H2O 0.1 wt% isooctyl glucoside 0.2 wt% isooctyl glucoside
28.32 23.38 22.94
61.34 56.12 55.65
4.02 4.19 4.22
33.94 52.01 52.20
70.89 118.28 119.18
a b
The concentration of CH4 is 34.65 mol%. u(T) ¼ 0.01 K, u(p) ¼ 0.01 MPa.
is the volume of dissociated gas from hydrate at the tively. VH;0 G standard conditions. VH is the volume of hydrate at the equilibrium state, which could be regarded as the volume of liquid (VL ) added in the crystallizer if the volume change during the hydration is ignored. Compared with pure water, the presence of isooctyl glucoside greatly increases the recovery of CH4 and gas storage capacity of hydrate. This should be attributed to the surfactant action of isooctyl glucoside, which reduces the gas-liquid interfacial tension and accordingly increases the solubility of gas, both CH4 and N2, in liquid. As a result, more CH4 and N2 form hydrate, and the concentration of CH4 in hydrate decreases slightly. The reason is that the concentration of N2 in feed gas is higher than that of CH4, resulting in relatively more N2 than CH4 enter the hydrate phase. In general, the separation factor is increased after adding isooctyl glucoside in water. Besides, the recovery of CH4 and gas storage capacity of hydrate are slightly increased with the concentration of isooctyl glucoside. It demonstrates isooctyl glucoside improves the separation efficiency of CH4/N2 via hydrates formation. Consequently, isooctyl glucoside could be used as an effective ecofriendly kinetic promoter of hydrate. This conclusion is in good agreement with the work of Sun [33] and Zhang [34]. Although the material gases and the promoters are different between our work and the reference data, the promotion effects of APGs on the formation of gas hydrates are verified as well. 4. Conclusions Two different bio-additives, L-arginine and isooctyl glucoside, were investigated the effects on the formation and separation equilibria of CH4 hydrate in this work. The results indicate that Larginine is a thermodynamic inhibitor of hydrates, which could be used in the inhibition of hydrates formation to replace the conventional alcohols. The presence of isooctyl glycosidase greatly increases the hydration rate and gas storage capacity of hydrate. It also improves the separation efficiency of CH4/N2 via hydrate formation. Consequently, isooctyl glycosidase is an effective kinetic promoter of gas hydrates, which could be applied in the study of CH4 storage in hydrate, and separation of CH4-containing gas mixture by hydrate method. The green and eco-friendly
Q. Sun et al. / Fluid Phase Equilibria 452 (2017) 143e147
characteristics of L-arginine and isooctyl glucoside are beneficial to environmental protection, which will definitely promote the development and industrial application of hydrate-based technologies. Acknowledgments This work is supported by Science Foundation of China University of Petroleum, Beijing (2462017BJB05), National Natural Science Foundation of China (21306226) and Science Foundation of CUPBK (RCYJ2017A-02-001, RCYJ2017A-03-001), which are greatly acknowledged. References [1] E.D. Sloan, Clathrate Hydrates of Natural Gases, second ed., Marcel Dekker Inc., New York, 1998. [2] P. Englezos, Ind. Eng. Chem. Res. 32 (1993) 1252e1253. [3] G. Chen, C. Sun, Q. Ma, Gas hydrate Science and Technology, Chem. Ind. Press, Beijing, 2008. [4] A.H. Mohammadi, L.J.F. Martinez, D. Richon, Chem. Eng. Sci. 65 (2010) 6059e6063. [5] L.J. Florusse, C.J. Peters, J. Schoonman, K.C. Hester, C.A. Koh, S.F. Dec, K.N. Marsh, E.D. Sloan, Science 306 (2004) 469e471. [6] R.M. Deugd, M.D. Jager, J.S. Arons, AIChE J. 47 (2001) 693e704. [7] M.M. Heuvel, C.J. Peters, J.S. Arons, Fluid Phase Equilib. 172 (2000) 73e91. [8] M. Yang, W. Jing, J. Zhao, Z. Ling, Y. Song, Energy 106 (2016) 546e553. [9] C. Xu, S. Zhang, J. Cai, Z. Chen, X. Li, Energy 59 (2013) 719e725. [10] H.P. Veluswamy, W.I. Chin, P. Linga, Int. J. Hydrogen Energy 39 (2014) 16234e16243. [11] F. Tzirakis, P. Stringari, N. v. Solms, C. Coquelet, G. Kontogeorgis, Fluid Phase
147
Equilib. 408 (2016) 240e247. [12] D. Posteraro, J. Pasieka, M. Maric, P. Servio, J. Nat. Gas. Sci. Eng. 35 (2016) 1579e1586. [13] J. Yoslim, P. Linga, P. Englezos, J. Cryst. Growth 313 (2010) 68e80. [14] Z. Sun, R. Wang, R. Ma, Energy Convers. Manage 44 (2003) 2733e2742. [15] B. ZareNezhad, F. Varaminian, Energy Convers. Manage 73 (2013) 144e149. [16] U. Karaaslan, U. Evrim, J. Pet. Sci. Eng. 35 (2002) 49e57. [17] H. Najibi, Z. Kamali, A.H. Mohammadi, Fluid Phase Equilib. 342 (2013) 71e74. [18] P.F. Ferrari, A.Z. Guembaroski, M.A.M. Neto, R.E.M. Morales, A.K. Sum, Fluid Phase Equilib. 413 (2016) 176e183. [19] J. Long, J. Lederhos, A. Sum, Kinetic inhibitors of natural gas hydrates, in: Proceedings of the 73rd Annual GPA Convention, 1994. New Orleans, LA. [20] C. Moon, P.C. Taylor, P.M. Rodger, Can. J. Phys. 81 (2003) 451e457. [21] W. Wang, C. Ma, P. Lin, L. Sun, A.I. Cooper, Energy Environ. Sci. 6 (2013) 105e107. [22] H. Fakharian, H. Ganji, A.N. Far, M. Kameli, Fuel 94 (2012) 356e360. [23] R.E. Rogers, C. Kothapalli, M.S. Lee, Can. J. Chem. Eng. 81 (2003) 973e980. [24] L. Chen, M. Zhou, Fine Spec. Chem. 12 (2004) 7e11. [25] Q. Sun, X. Guo, A. Liu, B. Liu, Y. Huo, G. Chen, Ind. Eng. Chem. Res. 50 (2011) 2284e2288. [26] Q. Sun, X. Guo, A. Liu, J. Dong, B. Liu, J. Zhang, G. Chen, Energy fuels. 26 (2012) 4507e4513. [27] Q. Sun, J. Liu, A. Liu, X. Guo, L. Yang, J. Zhang, Int. J. Hydrogen Energy 40 (2015) 6358e6364. [28] S. Adisasmito, R.J. Frank, E.D. Sloan, J. Chem. Eng. Data 36 (1991) 68e71. [29] W.M. Deaton, E.M. Frost, Gas hydrates and Their Relationship to the Operation of Natural Gas Pipeline, vol. 8, US Bureau of Mines Monograph, New-York, 1946, p. 101. [30] P. Linga, A. Adeyemo, P. Englezos, Environ. Sci. Technol. 42 (2007) 315e320. [31] P. Linga, R. Kumar, P. Englezos, J. Hazard. Mater 149 (2007) 625e629. [32] Y. Luo, A. Liu, X. Guo, Q. Sun, L. Yang, Int. J. Hydrogen Energy 40 (2015) 16248e16255. [33] Z. Sun, R. Wang, R. Ma, K. Guo, S. Fan, Energy Convers. Manage 44 (2003) 2733e2742. [34] C. Zhang, S. Fan, D. Liang, K. Guo, Fuel 83 (2004) 2115e2121.
Contents lists available at ScienceDirect
Fluid Phase Equilibria j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / fl u i d
The investigation of phase equilibria and kinetics of CH4 hydrate in the presence of bio-additives Qiang Sun a, Bo Chen a, Xingxun Li a, Xuqiang Guo a, b, *, Lanying Yang a a b
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, 102249, China Department of Engineering, China University of Petroleum-Beijing, Karamay, 834000, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 1 June 2017 Received in revised form 1 September 2017 Accepted 2 September 2017 Available online 4 September 2017
The conventional hydrate promoters and inhibitors, such as tetrahydrofuran (THF), sodium dodecyl sulfate (SDS) and methanol, have the common disadvantages of chemical substances, i.e., pungent flavor, corrosivity, toxicity and anti-degradability. It severely pollutes the environment and limits the application of hydrate-based technologies. Consequently, it is necessary to develop new and green substances as the hydrate promoters or inhibitors. In this work, L-arginine and isooctyl glucoside were used as bioadditives for CH4 hydrate to form bio-hydrate. The effects of L-arginine and isooctyl glucoside on the formation thermodynamics and kinetics of CH4 hydrate were investigated first. Then, the equilibrium separation of CH4/N2 via hydrates formation was conducted in isooctyl glucoside solution. The results show that formation pressure of CH4 hydrate in L-arginine solution is higher than that in pure water at the same temperature. Isooctyl glycosidase can greatly accelerate the hydration rate and increase the gas storage capacity of hydrate. In the separation of CH4/N2, the recovery of CH4 and gas storage capacity of hydrate are significantly increased after adding isooctyl glucoside in water. In conclusion, L-arginine can be used as hydrate inhibitor to replace conventional alcohols in the inhibition of hydrates formation. Isooctyl glycosidase is an effective kinetic promoter of hydrate, which is suitable for CH4 storage in hydrate, and separation of CH4-containing gas mixture via hydrates formation. This work provides two environment friendly bio-additives for hydrate, which will definitely promote the development and application of hydrate research. © 2017 Published by Elsevier B.V.
Keywords: Bio-additives Hydrate Thermodynamics Kinetics Separation
1. Introduction Hydrate (or clathrate hydrate) is a kind of icelike nonstoichiometric compound formed by gas and water at certain temperature and pressure [1,2]. More than 100 substances have been found to form hydrates so far, and the thermodynamics theory of hydrates has been well-established [3]. In addition, hydrate additives, including promoters and inhibitors, have been widely applied to change the phase equilibria conditions and formation kinetics of hydrates. The common thermodynamic promoters of hydrates are tetrahydrofuran (THF), tetrahydropyrane (TPF), tetra-butyl ammonium bromide (TBAB), cyclopentane (CP) [4e11]. The frequently-used kinetic promoters are sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate
* Corresponding author. Department of Engineering, China University of Petroleum-Beijing, Karamay, 834000, China. E-mail address: [email protected] (X. Guo). http://dx.doi.org/10.1016/j.fluid.2017.09.002 0378-3812/© 2017 Published by Elsevier B.V.
(SDBS), alkyl polyglucoside (APG), linear alkyl sodium sulfonate (LABSA) [12e16]. The common inhibitors of hydrate includes methanol, ethanol, polyvinylpyrrolidone (PVP) and so on [17e20]. The presence of above additives in the formation of hydrates makes the application of hydrate-based technologies more feasible and convenient in the industrial. However, as the chemical substances, they also have obvious drawbacks, i.e., pungent flavor, corrosivity, toxicity and anti-degradability. It severely pollutes the environment and limits the application of hydrate-based technologies. Consequently, it is necessary to develop new and green substances as the hydrate promoters or inhibitors. Wang et al. found that certain fungi and plant extracts could be used as the surfactants for CH4 hydrate to increase hydration rate and gas storage capacity [21]. The hydrates formed by these biomass are accordingly called as bioclathrates. Fakharian et al. put forward through experiments that potato starch is also able to increase gas storage capacity of hydrate [22]. Rogers et al. demonstrated that natural gas hydrate (NGH) in subsea sediments is
144
Q. Sun et al. / Fluid Phase Equilibria 452 (2017) 143e147
accelerated by the surfactants generated from microbes in seafloor [23]. Consequently, the proposing of biosurfactants for hydrate offers a novel idea for the development of hydrate additives, especially for the kinetic promoters of hydrates. Biosurfactants and bio-based surfactants are collectively called as eco-friendly surfactants [24]. The former are amphipathic compounds, for instance, glycolipid, polysaccharide, peptide lipid, and neutral lipid derivatives, generated by the various organisms with the characteristics of surfactants, such as germs, yeast, fungus, and so on. The latter are synthetic compounds based on the natural structures of renewable biosurfactants, such as amino acid, saccharides and vegetable oil. Eco-friendly surfactants have the advantages of high safety, mild nature, low skin irritation and toxicity, good biodegradation and environmental performance. Therefore, we choose L-arginine and isooctyl glucoside in this work as bio-additives for CH4 hydrate. As a reagent chemical, isooctyl glucoside is one kind of APGs. L-arginine is one kind of amino acid. The effects of L-arginine and isooctyl glucoside on the phase equilibria and kinetics of CH4 hydrate were investigated, respectively. 2. Experimental 2.1. Materials and apparatus The experimental materials and apparatus are shown in Table 1 and Fig. 1, respectively. Industrial-grade isooctyl glucoside was used in this work because it is cheaper and more convenient for industrial application. The composition of CH4/N2 gas mixture is determined by gas chromatograph (Agilent 7890). A precision electric balance with an accuracy of 0.0001 g is used to weigh additives and water for the solution preparation. The apparatus is mainly composed of air bath, hand pump, hydrate crystallizer, and temperature and pressure measurement system. The air bath keeps a constant temperature for the crystallizer. The hand pump adjusts and controls a constant pressure for the reaction system through acting on a piston in the crystallizer. The temperature and pressure are measured by a platinum resistance thermometer with the accuracy of 0.1 K and a pressure sensor with the accuracy of 0.01 MPa, respectively. In addition, a magnetic stick is placed in the crystallizer to constantly stir the gasliquid mixture. 2.2. Methods The formation thermodynamics and kinetics of CH4 hydrate in the presence of L-arginine and isooctyl glucoside were measured using “pressure searching” and “constant temperature and pressure” method, respectively. Then, the influence of isooctyl glucoside on the separation of CH4/N2 gas mixture is investigated. The separation of CH4/N2 via hydrate formation was also conducted using “constant temperature and pressure” method. The specific procedure of the methods above were described in our previous work [25e27], which show good reliability of the apparatus and methods.
3. Results and discussion 3.1. Formation conditions of CH4 hydrate in the presence of Larginine and isooctyl glucoside The formation conditions of CH4 hydrate in the presence of Larginine and isooctyl glucoside are shown in Fig. 2 and Fig. 3, respcetively. The concentrations of the bio-additives are relatively low in this work, because too much use will definitely increase the operation cost, which goes against the potential industrial application. The results show that the measured formation conditions of CH4 hydrate in pure water are in good agreement with the reference data [28,29]. L-arginine plays an inhibiting role in the formation of CH4 hydrate, and the inhibiting effect increases with the concentration of L-arginine. Therefore, it could be used as an novel thermodynamic inhibitor to replace the conventional alcohols for gas hydrates. The specific application of L-arginine to hydrate inhibition in different systems will be further studied in our future work. Also, the effects of other amino acids on the formation of gas hydrates will be further studied, in order to check if all amino acids are hydrate inhibitors. In Fig. 3, the presence of isooctyl glucoside slightly decreases the formation pressure of CH4 hydrate at the same temperature, and the formation pressure of CH4 hydrate decreases with the concentration of isooctyl glucoside. However, the overall drop of pressure is tiny, and the phase equilibria curves of different systems in Fig. 3 are very close. 3.2. Formation kinetics of CH4 hydrate in the presence of L-arginine and isooctyl glucoside Fig. 4 presents the formation kinetics of CH4 hydrate in different solutions at 275.15 K and 8.0 MPa. The results show that isooctyl glucoside could significantly increase the formation rate and gas storage capacity of CH4 hydrate. Meanwhile, the reaction time to reach equilibrium state is greatly shortened after adding isooctyl glucoside in water. The formation rate and gas storage capacity of CH4 hydrate increase with the concentration of isooctyl glucoside. It indicates that isooctyl glucoside is an effective kinetic promoter for hydrates. By contrast, L-arginine decelerates the formation rate of CH4 hydrate. This occurs because L-arginine is a thermodynamic inhibitor for CH4 hydrate. Consequently, the presence of L-arginine reduces the driving force of hydrate nucleation, and results in slow rate of hydration reaction. The inhibition effect of L-arginine on hydrate formation becomes particularly evident after half an hour of hydration. As a result, the equilibration time is prolonged about 2 h. Fig. 5 illustrates the formation kinetics of CH4 hydrate at different temperatures. In 0.20 wt% isooctyl glucoside solution, the formation rate of CH4 hydrate decreases with the temperature, because low temperature helps CH4 hydrate form. The formation rate of CH4 hydrate in isooctyl glucoside solution at 277.15 K is still faster than that in water at 275.15 K, which reveals the promotion effect of isooctyl glucoside to hydrate. At constant 279.15 K, the kinetic results also demonstrate that isooctyl glucoside accelerates
Table 1 Specifications of experimental materials. Materials
Brand
Purity
Suppliers
CH4 CH4/N2 L-arginine Isooctyl glucoside Deionized water
/ / Apollo Greensense /
99.90 mol% 34.65/65.35 mol% 99% 61% 15 106 U cm
Beijing Bei Temperature gas factory Beijing Bei Temperature gas factory Beijing Wohai Global Technology Co. Ltd. Beijing Wohai Global Technology Co. Ltd. SZ-93 water distillation unit
Q. Sun et al. / Fluid Phase Equilibria 452 (2017) 143e147
145
Fig. 1. Schematic sketch of the experimental apparatus.
the formation of CH4 hydrate, and L-arginine performs as an inhibitor for CH4 hydrate. 3.3. Separation of CH4/N2 via hydrates formation in the presence of isooctyl glucoside Taking advantage of the promotion function of isooctyl
Fig. 2. Formation conditions of CH4 hydrate in the presence of arginine.
glucoside to CH4 hydrate, we investigated its effect on the equilibrium separation of CH4/N2 gas mixture via hydrates formation. The separation experiments were conducted at constant 274.15 K and 9.0 MPa. Table 2 and Fig. 6 present the experimental results. The separation factor (SF), recovery (R) of CH4 in the hydrate and the gas storage capacity (GSC) of hydrate are calculated as follows [30e32]:
Fig. 3. Formation conditions of CH4 hydrate in the presence of isooctyl glucoside.
146
Q. Sun et al. / Fluid Phase Equilibria 452 (2017) 143e147
Fig. 6. The separation results of CH4/N2 via hydrates formation in isooctyl glucoside solutions.
Fig. 4. Formation kinetics of CH4 hydrate at 275.15 K and 8.0 MPa.
G hydrate phase, respectively. yG CH4 and yN2 stand for the concentraF tions of CH4 and N2 in equilibrium gas, respectively. nH CH4 and nCH4
are the numbers of moles of CH4 in hydrate and feed gas, respec-
Fig. 5. Formation kinetics of CH4 hydrate at 8.0 MPa and different temperature.
SF ¼
G yH CH4 yN2 , H 100% G yCH4 yN2
nH CH4
(1)
100%
(2)
GSC ¼
VH;0 VH;0 G ¼ G VH VL
(3)
where
yH CH4
R¼
nFCH4
and
yH N2
stand for the concentrations of CH4 and N2 in
Table 2 Separation of CH4/N2a via hydrates formation in the presence of isooctyl glucoside.b Gas
yG CH4 , mol%
yH CH4 , mol%
SF
R, 100%
GSC
H2O 0.1 wt% isooctyl glucoside 0.2 wt% isooctyl glucoside
28.32 23.38 22.94
61.34 56.12 55.65
4.02 4.19 4.22
33.94 52.01 52.20
70.89 118.28 119.18
a b
The concentration of CH4 is 34.65 mol%. u(T) ¼ 0.01 K, u(p) ¼ 0.01 MPa.
is the volume of dissociated gas from hydrate at the tively. VH;0 G standard conditions. VH is the volume of hydrate at the equilibrium state, which could be regarded as the volume of liquid (VL ) added in the crystallizer if the volume change during the hydration is ignored. Compared with pure water, the presence of isooctyl glucoside greatly increases the recovery of CH4 and gas storage capacity of hydrate. This should be attributed to the surfactant action of isooctyl glucoside, which reduces the gas-liquid interfacial tension and accordingly increases the solubility of gas, both CH4 and N2, in liquid. As a result, more CH4 and N2 form hydrate, and the concentration of CH4 in hydrate decreases slightly. The reason is that the concentration of N2 in feed gas is higher than that of CH4, resulting in relatively more N2 than CH4 enter the hydrate phase. In general, the separation factor is increased after adding isooctyl glucoside in water. Besides, the recovery of CH4 and gas storage capacity of hydrate are slightly increased with the concentration of isooctyl glucoside. It demonstrates isooctyl glucoside improves the separation efficiency of CH4/N2 via hydrates formation. Consequently, isooctyl glucoside could be used as an effective ecofriendly kinetic promoter of hydrate. This conclusion is in good agreement with the work of Sun [33] and Zhang [34]. Although the material gases and the promoters are different between our work and the reference data, the promotion effects of APGs on the formation of gas hydrates are verified as well. 4. Conclusions Two different bio-additives, L-arginine and isooctyl glucoside, were investigated the effects on the formation and separation equilibria of CH4 hydrate in this work. The results indicate that Larginine is a thermodynamic inhibitor of hydrates, which could be used in the inhibition of hydrates formation to replace the conventional alcohols. The presence of isooctyl glycosidase greatly increases the hydration rate and gas storage capacity of hydrate. It also improves the separation efficiency of CH4/N2 via hydrate formation. Consequently, isooctyl glycosidase is an effective kinetic promoter of gas hydrates, which could be applied in the study of CH4 storage in hydrate, and separation of CH4-containing gas mixture by hydrate method. The green and eco-friendly
Q. Sun et al. / Fluid Phase Equilibria 452 (2017) 143e147
characteristics of L-arginine and isooctyl glucoside are beneficial to environmental protection, which will definitely promote the development and industrial application of hydrate-based technologies. Acknowledgments This work is supported by Science Foundation of China University of Petroleum, Beijing (2462017BJB05), National Natural Science Foundation of China (21306226) and Science Foundation of CUPBK (RCYJ2017A-02-001, RCYJ2017A-03-001), which are greatly acknowledged. References [1] E.D. Sloan, Clathrate Hydrates of Natural Gases, second ed., Marcel Dekker Inc., New York, 1998. [2] P. Englezos, Ind. Eng. Chem. Res. 32 (1993) 1252e1253. [3] G. Chen, C. Sun, Q. Ma, Gas hydrate Science and Technology, Chem. Ind. Press, Beijing, 2008. [4] A.H. Mohammadi, L.J.F. Martinez, D. Richon, Chem. Eng. Sci. 65 (2010) 6059e6063. [5] L.J. Florusse, C.J. Peters, J. Schoonman, K.C. Hester, C.A. Koh, S.F. Dec, K.N. Marsh, E.D. Sloan, Science 306 (2004) 469e471. [6] R.M. Deugd, M.D. Jager, J.S. Arons, AIChE J. 47 (2001) 693e704. [7] M.M. Heuvel, C.J. Peters, J.S. Arons, Fluid Phase Equilib. 172 (2000) 73e91. [8] M. Yang, W. Jing, J. Zhao, Z. Ling, Y. Song, Energy 106 (2016) 546e553. [9] C. Xu, S. Zhang, J. Cai, Z. Chen, X. Li, Energy 59 (2013) 719e725. [10] H.P. Veluswamy, W.I. Chin, P. Linga, Int. J. Hydrogen Energy 39 (2014) 16234e16243. [11] F. Tzirakis, P. Stringari, N. v. Solms, C. Coquelet, G. Kontogeorgis, Fluid Phase
147
Equilib. 408 (2016) 240e247. [12] D. Posteraro, J. Pasieka, M. Maric, P. Servio, J. Nat. Gas. Sci. Eng. 35 (2016) 1579e1586. [13] J. Yoslim, P. Linga, P. Englezos, J. Cryst. Growth 313 (2010) 68e80. [14] Z. Sun, R. Wang, R. Ma, Energy Convers. Manage 44 (2003) 2733e2742. [15] B. ZareNezhad, F. Varaminian, Energy Convers. Manage 73 (2013) 144e149. [16] U. Karaaslan, U. Evrim, J. Pet. Sci. Eng. 35 (2002) 49e57. [17] H. Najibi, Z. Kamali, A.H. Mohammadi, Fluid Phase Equilib. 342 (2013) 71e74. [18] P.F. Ferrari, A.Z. Guembaroski, M.A.M. Neto, R.E.M. Morales, A.K. Sum, Fluid Phase Equilib. 413 (2016) 176e183. [19] J. Long, J. Lederhos, A. Sum, Kinetic inhibitors of natural gas hydrates, in: Proceedings of the 73rd Annual GPA Convention, 1994. New Orleans, LA. [20] C. Moon, P.C. Taylor, P.M. Rodger, Can. J. Phys. 81 (2003) 451e457. [21] W. Wang, C. Ma, P. Lin, L. Sun, A.I. Cooper, Energy Environ. Sci. 6 (2013) 105e107. [22] H. Fakharian, H. Ganji, A.N. Far, M. Kameli, Fuel 94 (2012) 356e360. [23] R.E. Rogers, C. Kothapalli, M.S. Lee, Can. J. Chem. Eng. 81 (2003) 973e980. [24] L. Chen, M. Zhou, Fine Spec. Chem. 12 (2004) 7e11. [25] Q. Sun, X. Guo, A. Liu, B. Liu, Y. Huo, G. Chen, Ind. Eng. Chem. Res. 50 (2011) 2284e2288. [26] Q. Sun, X. Guo, A. Liu, J. Dong, B. Liu, J. Zhang, G. Chen, Energy fuels. 26 (2012) 4507e4513. [27] Q. Sun, J. Liu, A. Liu, X. Guo, L. Yang, J. Zhang, Int. J. Hydrogen Energy 40 (2015) 6358e6364. [28] S. Adisasmito, R.J. Frank, E.D. Sloan, J. Chem. Eng. Data 36 (1991) 68e71. [29] W.M. Deaton, E.M. Frost, Gas hydrates and Their Relationship to the Operation of Natural Gas Pipeline, vol. 8, US Bureau of Mines Monograph, New-York, 1946, p. 101. [30] P. Linga, A. Adeyemo, P. Englezos, Environ. Sci. Technol. 42 (2007) 315e320. [31] P. Linga, R. Kumar, P. Englezos, J. Hazard. Mater 149 (2007) 625e629. [32] Y. Luo, A. Liu, X. Guo, Q. Sun, L. Yang, Int. J. Hydrogen Energy 40 (2015) 16248e16255. [33] Z. Sun, R. Wang, R. Ma, K. Guo, S. Fan, Energy Convers. Manage 44 (2003) 2733e2742. [34] C. Zhang, S. Fan, D. Liang, K. Guo, Fuel 83 (2004) 2115e2121.