- Email: [email protected]
Hydrate formation of (CH4 + C2H4) and (CH4 + C3H6) gas mixtures
Fluid Phase Equilibria 191 (2001) 41–47
Hydrate formation of (CH4 + C2 H4 ) and (CH4 + C3H6) gas mixtures C.-F. Ma, G.-J. Chen, F. Wang, C.-Y. Sun, T.-M. Guo∗ High Pressure Fluid Phase Behavior and Property Research Laboratory, University of Petroleum, Beijing 102200, PR China Received 4 June 2001; accepted 9 August 2001
Abstract Hydrate formation conditions of (CH4 + C2 H4 ) and (CH4 + C3 H6 ) binary gas mixtures in the presence of pure water were measured in a sapphire cell using the “pressure search” method. The experimental temperature-range was 273.7–287.2 K, and pressure-range was 0.53–6.6 MPa. Ethylene content in the gas mixtures varied from 7.13 to 100 mol%, and the propylene content varied from 0.66 to 71.96 mol%. The Chen–Guo hydrate model has been successfully applied to represent the measured data. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Hydrate formation; Data; Gas mixture; Methane; Alkene
1. Introduction (Methane + alkene) and (methane + hydrogen) mixtures occur widely in the petroleum refining and petrochemical processes. Recently, a promising method for separating hydrogen from methane through hydrate formation/dissociation was developed in our laboratory [1]. For exploring the feasibility of extending this new technology to (methane + alkene) gas mixtures, basic hydrate formation data are required. Some earlier work related to the initial hydrate formation conditions of (methane + ethylene) and (methane + propylene) mixtures are available [2,3], but they are not sufficient for our project. In addition, the experimental data were presented in figures, which are inconvenient for practical applications. In this work, we have systematically measured the hydrate formation data of (methane + ethylene) and (methane + propylene) gas mixtures. Five synthetic (methane + ethylene) and four (methane + propylene) binary gas mixtures have been prepared. The hydrate formation conditions of those gas mixtures and pure ethylene were measured by using the “pressure search” method [4]. The experimental temperature-range was 273.7–287.2 K, and pressure-range was 0.53–6.6 MPa. The ethylene and propylene contents in the mixtures varied from 7.13 ∗
Corresponding author. Tel.: +86-10-6234-0132; fax: +86-10-6234-0132. E-mail address: [email protected] (T.-M. Guo). 0378-3812/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 3 8 1 2 ( 0 1 ) 0 0 6 1 0 - 0
42
C.-F. Ma et al. / Fluid Phase Equilibria 191 (2001) 41–47
to 100 mol%, and 0.66 to 71.96 mol%, respectively. The recently developed Chen–Guo hydrate model [5] was used to represent the measured data. 2. Experimental 2.1. Apparatus The experimental apparatus used in this work had been described in detail in the previous papers published by this laboratory [6–8]. The apparatus consists of a cylindrical transparent sapphire cell (2.54 cm in diameter, effective volume 60 cm3 ) installed in an air–bath and equipped with a magnetic stirrer for accelerating the equilibrium process. The formation/dissociation of the hydrate crystals in the solution can be observed directly through the transparent cell wall. The accuracy of temperature and pressure measurement is ±0.2 K and ±0.025 MPa, respectively. 2.2. Materials and preparation of samples Analytical grade methane (99.99%), ethylene (99.95%) and propylene (99.95%) supplied by Beifen Gas Industry Corporation were used in preparing the synthetic gas mixtures. The compositions of gas mixtures were analyzed by a Hewlett-Packard gas chromatograph (HP 6890). 2.3. Experimental procedure Firstly, the transparent cell was washed by distilled water and then rinsed three times with deionized water. After the cell was thoroughly cleaned, ∼10 cm3 deionized water was added into the cell. The vapor space of the cell was purged with the gas mixture under study. A gas sample was collected and analyzed to ensure the absence of air. The air-bath temperature was then adjusted to the chosen temperature. Once the temperature was stabilized, the following “pressure search” method [4] was applied to determine the hydrate formation conditions. The pressure in the cell was raised to ∼1 MPa higher than the estimated equilibrium pressure (using an in-house software) via the floating piston. When a trace of hydrate crystal was observed, the pressure was reduced gradually to allow the hydrate crystals decompose slowly. When all the hydrate crystals disappeared, the pressure of the system was raised again by a small pressure-step of 0.05 MPa until the hydrate crystal appears again (clinging to the cell wall or floating on the water surface). Maintain the system temperature and pressure for 6 h, if the hydrate crystals disappeared during this period, the pressure of the system was raised slightly until a trace of hydrate crystals appeared again. When the hydrate crystals are kept in the cell after 6 h, the system pressure is taken as the equilibrium hydrate formation pressure at the given temperature. The above procedure was repeated for a series of temperatures. 2.4. Experimental results Following the above procedure, the initial hydrate formation data (in the presence of pure water) of pure ethylene, five (methane + ethylene) and four (methane + propylene) gas mixtures have been measured.
C.-F. Ma et al. / Fluid Phase Equilibria 191 (2001) 41–47
43
Fig. 1. The comparison of the hydrate formation data measured for pure ethylene: (䊉) this work; (䊐) data of Snell et al. [2].
The comparison of the measured hydrate formation data of pure ethylene with those data reported by Snell et al. [2] is depicted in Fig. 1. From Fig. 1, it can be seen that the agreement between the two data sets is excellent. The compositions of the five (methane+ethylene) and four (methane+propylene) gas mixtures studied and the corresponding hydrate formation data measured are presented in Tables 1 and 2. Table 1 Hydrate formation conditions of (methane + ethylene) gas mixtures Composition of gas mixture (mol%)
T (K)
P (MPa)
100% C2 H4
273.7 275.2 277.2 278.2 279.2 281.2 283.2 285.2 286.2 287.2
0.665 0.739 0.920 1.010 1.100 1.439 1.838 2.345 2.830 3.210
5.60% CH4 + 94.40% C2 H4
273.7 278.2 281.2 283.2 286.2
0.712 1.178 1.592 1.956 2.916
34.09% CH4 + 65.91% C2 H4
273.7 278.2 281.2 283.2 286.2
0.784 1.292 1.755 2.220 3.115
44
C.-F. Ma et al. / Fluid Phase Equilibria 191 (2001) 41–47
Table 1 (Continued ) Composition of gas mixture (mol%)
T (K)
P (MPa)
64.28% CH4 + 35.72% C2 H4
273.7 278.2 281.2 283.2
1.146 1.875 2.406 3.120
85.69% CH4 + 14.31% C2 H4
273.7 278.2 281.2 283.2
1.800 2.714 3.758 4.640
92.87% CH4 + 7.13% C2 H4
273.7 278.2 281.2 283.2
2.230 3.448 4.720 6.002
Table 2 Hydrate formation conditions of (methane + propylene) gas mixtures Composition of gas mixture (mol%)
T (K)
P (MPa)
28.04% CH4 + 71.96% C3 H6
273.7 278.2 281.2 283.2
0.529a 1.081a 1.515a 1.963a
92.40% CH4 + 7.60% C3 H6
273.7 278.2 281.2 283.2
1.081 1.765 2.501 3.161
96.60% CH4 + 3.40% C3 H6
273.7 278.2 281.2 283.2
1.421 2.381 3.287 4.121
99.34% CH4 + 0.66% C3 H6
273.7 278.2 281.2 283.2
2.531 3.681 5.179 6.585
a
Four-phase equilibrium (V–Lw –LHC −H).
3. Data processing Chen–Guo hydrate model [5] was used to represent the experimental data measured in this work. The required parameters for (methane + ethylene) system are available in [5]. In our calculation, (methane + ethylene) gas mixtures were presumed to form structure I hydrates in the full composition range. As the anomalous increase of deviation from experimental data was not observed (which might occur for
C.-F. Ma et al. / Fluid Phase Equilibria 191 (2001) 41–47
45
Fig. 2. Hydrate formation conditions of (methane + ethylene) gas mixtures: (䊏) pure ethylene; (䊐) M1; (䊉) M2; (䊊) M3; (䉱) M4; () M5; (+) pure methane [10]. Calculated by Chen–Guo hydrate model [5].
(methane+ethane) system due to the hydrate structure change from I to II at higher methane concentration (>62 mol%) [9]), we believe that the structure transition will not be happened in the hydrate formation for (methane + ethylene) system. Certainly, this presumption should be further confirmed by using more reliable experimental methods such as Raman spectra and NMR technique [9]. The calculation results for (methane + ethylene) system are illustrated in Fig. 2. The overall average absolute deviation (AAD) of the calculated hydrate formation pressures is 2.48%. For the (methane + propylene) system, as the hydrate-vapor–water-rich liquid equilibrium of (propylene + water) system exists over a very narrow temperature range 273.15–274.50 K, the pure propylene hydrate formation data are not sufficient for correlating its parameters (A , B and C ) to be used in the Chen–Guo hydrate model [5]. Thus, propylene’s parameters were determined indirectly from the hydrate formation data of (methane + propylene) system measured in this work. As propylene cannot form structure I hydrate, structure II was assumed in the regression. The regressed A , B , C values for propylene are listed in Table 3 along with the binary cross parameter Aij value for (methane + propylene) system. The calculated results are illustrated in Fig. 3. The overall AAD of the calculated hydrate formation pressures for (methane + propylene) system is 3.36%. The hydrate formation pressure data of Table 3 Parameter values used in the Chen–Guo hydrate model Gas species
A (Pa)
B (K)
C (K)
Aij a
Ethylene b (structure I) Propylene (structure II)
4.8418 × 1016 2.4256 × 1031
−5597.59 −18421
51.80 −42.35
0 506
a b
Binary cross parameter Aij for (methane + ethylene) and (methane + propylene) systems. Parameter values adopted from Chen and Guo [5].
46
C.-F. Ma et al. / Fluid Phase Equilibria 191 (2001) 41–47
Fig. 3. Hydrate formation conditions of (methane + propylene) gas mixtures: (䊉) M1; (䊊) M2; (䉱) M3; () M4; (䊐) pure propylene [3]; (+) pure methane [10]. Calculated by Chen–Guo hydrate model [5].
pure propylene have been predicted also and compared with literature data [3] as shown in Fig. 3. The maximum absolute deviation between predicted values and literature data is less than 3%. 4. Conclusions The hydrate formation data of five synthetic (methane + ethylene), four (methane + propylene) gas mixtures and pure ethylene gas have been measured in the temperature range of 273.7–287.2 K and pressure range of 0.53–6.6 MPa using the “pressure search” method. The uncertainty of temperature and pressure measurement is ±0.2 K and ±0.04 MPa, respectively. The reported data are valuable for testing existing hydrate models/software. Chen–Guo hydrate model was used to represent the experimental data measured in this work and satisfactory calculation results were obtained. Acknowledgements The financial support received from the National Natural Science Foundation of China (No. 29806009) and the China National Petroleum and Natural Gas Corporation is gratefully acknowledged. References [1] C.-F. Ma, Separation of Gas Mixtures using Hydrate Technology, Ph.D. Thesis, University of Petroleum, 2001. [2] L.E. Snell, F.D. Otto, D.B. Robinson, AIChE J. 7 (1961) 482–485. [3] F.D. Otto, D.B. Robinson, AIChE J. 6 (1960) 602–605.
C.-F. Ma et al. / Fluid Phase Equilibria 191 (2001) 41–47 [4] [5] [6] [7] [8] [9] [10]
D.-H. Mei, J. Liao, J.-T. Yang, T.-M. Guo, Ind. Eng. Chem. Res. 35 (1996) 4342–4347. G.-J. Chen, T.-M. Guo, Chem. Eng. J. 71 (1998) 145–151. S.S. Fan, T.M. Guo, J. Chem. Eng. Data 44 (1999) 829–832. D.-H. Mei, J. Liao, J.-T. Yang, T.-M. Guo, J. Chem. Eng. Data 43 (1998) 178–182. S.-X. Zhang, G.-J. Chen, C.-F. Ma, L.-Y. Yang, T.-M. Guo, J. Chem. Eng. Data 45 (2000) 908–911. S. Subramanian, R.A. Kini, S.F. Dec, E.D. Sloan Jr., Chem. Eng. Sci. 55 (2000) 1981–1999. E.D. Sloan, Clathrate Hydrates of Natural Gases, 2nd Edition, Marcel Dekker, New York, 1998.
47
Hydrate formation of (CH4 + C2 H4 ) and (CH4 + C3H6) gas mixtures C.-F. Ma, G.-J. Chen, F. Wang, C.-Y. Sun, T.-M. Guo∗ High Pressure Fluid Phase Behavior and Property Research Laboratory, University of Petroleum, Beijing 102200, PR China Received 4 June 2001; accepted 9 August 2001
Abstract Hydrate formation conditions of (CH4 + C2 H4 ) and (CH4 + C3 H6 ) binary gas mixtures in the presence of pure water were measured in a sapphire cell using the “pressure search” method. The experimental temperature-range was 273.7–287.2 K, and pressure-range was 0.53–6.6 MPa. Ethylene content in the gas mixtures varied from 7.13 to 100 mol%, and the propylene content varied from 0.66 to 71.96 mol%. The Chen–Guo hydrate model has been successfully applied to represent the measured data. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Hydrate formation; Data; Gas mixture; Methane; Alkene
1. Introduction (Methane + alkene) and (methane + hydrogen) mixtures occur widely in the petroleum refining and petrochemical processes. Recently, a promising method for separating hydrogen from methane through hydrate formation/dissociation was developed in our laboratory [1]. For exploring the feasibility of extending this new technology to (methane + alkene) gas mixtures, basic hydrate formation data are required. Some earlier work related to the initial hydrate formation conditions of (methane + ethylene) and (methane + propylene) mixtures are available [2,3], but they are not sufficient for our project. In addition, the experimental data were presented in figures, which are inconvenient for practical applications. In this work, we have systematically measured the hydrate formation data of (methane + ethylene) and (methane + propylene) gas mixtures. Five synthetic (methane + ethylene) and four (methane + propylene) binary gas mixtures have been prepared. The hydrate formation conditions of those gas mixtures and pure ethylene were measured by using the “pressure search” method [4]. The experimental temperature-range was 273.7–287.2 K, and pressure-range was 0.53–6.6 MPa. The ethylene and propylene contents in the mixtures varied from 7.13 ∗
Corresponding author. Tel.: +86-10-6234-0132; fax: +86-10-6234-0132. E-mail address: [email protected] (T.-M. Guo). 0378-3812/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 3 8 1 2 ( 0 1 ) 0 0 6 1 0 - 0
42
C.-F. Ma et al. / Fluid Phase Equilibria 191 (2001) 41–47
to 100 mol%, and 0.66 to 71.96 mol%, respectively. The recently developed Chen–Guo hydrate model [5] was used to represent the measured data. 2. Experimental 2.1. Apparatus The experimental apparatus used in this work had been described in detail in the previous papers published by this laboratory [6–8]. The apparatus consists of a cylindrical transparent sapphire cell (2.54 cm in diameter, effective volume 60 cm3 ) installed in an air–bath and equipped with a magnetic stirrer for accelerating the equilibrium process. The formation/dissociation of the hydrate crystals in the solution can be observed directly through the transparent cell wall. The accuracy of temperature and pressure measurement is ±0.2 K and ±0.025 MPa, respectively. 2.2. Materials and preparation of samples Analytical grade methane (99.99%), ethylene (99.95%) and propylene (99.95%) supplied by Beifen Gas Industry Corporation were used in preparing the synthetic gas mixtures. The compositions of gas mixtures were analyzed by a Hewlett-Packard gas chromatograph (HP 6890). 2.3. Experimental procedure Firstly, the transparent cell was washed by distilled water and then rinsed three times with deionized water. After the cell was thoroughly cleaned, ∼10 cm3 deionized water was added into the cell. The vapor space of the cell was purged with the gas mixture under study. A gas sample was collected and analyzed to ensure the absence of air. The air-bath temperature was then adjusted to the chosen temperature. Once the temperature was stabilized, the following “pressure search” method [4] was applied to determine the hydrate formation conditions. The pressure in the cell was raised to ∼1 MPa higher than the estimated equilibrium pressure (using an in-house software) via the floating piston. When a trace of hydrate crystal was observed, the pressure was reduced gradually to allow the hydrate crystals decompose slowly. When all the hydrate crystals disappeared, the pressure of the system was raised again by a small pressure-step of 0.05 MPa until the hydrate crystal appears again (clinging to the cell wall or floating on the water surface). Maintain the system temperature and pressure for 6 h, if the hydrate crystals disappeared during this period, the pressure of the system was raised slightly until a trace of hydrate crystals appeared again. When the hydrate crystals are kept in the cell after 6 h, the system pressure is taken as the equilibrium hydrate formation pressure at the given temperature. The above procedure was repeated for a series of temperatures. 2.4. Experimental results Following the above procedure, the initial hydrate formation data (in the presence of pure water) of pure ethylene, five (methane + ethylene) and four (methane + propylene) gas mixtures have been measured.
C.-F. Ma et al. / Fluid Phase Equilibria 191 (2001) 41–47
43
Fig. 1. The comparison of the hydrate formation data measured for pure ethylene: (䊉) this work; (䊐) data of Snell et al. [2].
The comparison of the measured hydrate formation data of pure ethylene with those data reported by Snell et al. [2] is depicted in Fig. 1. From Fig. 1, it can be seen that the agreement between the two data sets is excellent. The compositions of the five (methane+ethylene) and four (methane+propylene) gas mixtures studied and the corresponding hydrate formation data measured are presented in Tables 1 and 2. Table 1 Hydrate formation conditions of (methane + ethylene) gas mixtures Composition of gas mixture (mol%)
T (K)
P (MPa)
100% C2 H4
273.7 275.2 277.2 278.2 279.2 281.2 283.2 285.2 286.2 287.2
0.665 0.739 0.920 1.010 1.100 1.439 1.838 2.345 2.830 3.210
5.60% CH4 + 94.40% C2 H4
273.7 278.2 281.2 283.2 286.2
0.712 1.178 1.592 1.956 2.916
34.09% CH4 + 65.91% C2 H4
273.7 278.2 281.2 283.2 286.2
0.784 1.292 1.755 2.220 3.115
44
C.-F. Ma et al. / Fluid Phase Equilibria 191 (2001) 41–47
Table 1 (Continued ) Composition of gas mixture (mol%)
T (K)
P (MPa)
64.28% CH4 + 35.72% C2 H4
273.7 278.2 281.2 283.2
1.146 1.875 2.406 3.120
85.69% CH4 + 14.31% C2 H4
273.7 278.2 281.2 283.2
1.800 2.714 3.758 4.640
92.87% CH4 + 7.13% C2 H4
273.7 278.2 281.2 283.2
2.230 3.448 4.720 6.002
Table 2 Hydrate formation conditions of (methane + propylene) gas mixtures Composition of gas mixture (mol%)
T (K)
P (MPa)
28.04% CH4 + 71.96% C3 H6
273.7 278.2 281.2 283.2
0.529a 1.081a 1.515a 1.963a
92.40% CH4 + 7.60% C3 H6
273.7 278.2 281.2 283.2
1.081 1.765 2.501 3.161
96.60% CH4 + 3.40% C3 H6
273.7 278.2 281.2 283.2
1.421 2.381 3.287 4.121
99.34% CH4 + 0.66% C3 H6
273.7 278.2 281.2 283.2
2.531 3.681 5.179 6.585
a
Four-phase equilibrium (V–Lw –LHC −H).
3. Data processing Chen–Guo hydrate model [5] was used to represent the experimental data measured in this work. The required parameters for (methane + ethylene) system are available in [5]. In our calculation, (methane + ethylene) gas mixtures were presumed to form structure I hydrates in the full composition range. As the anomalous increase of deviation from experimental data was not observed (which might occur for
C.-F. Ma et al. / Fluid Phase Equilibria 191 (2001) 41–47
45
Fig. 2. Hydrate formation conditions of (methane + ethylene) gas mixtures: (䊏) pure ethylene; (䊐) M1; (䊉) M2; (䊊) M3; (䉱) M4; () M5; (+) pure methane [10]. Calculated by Chen–Guo hydrate model [5].
(methane+ethane) system due to the hydrate structure change from I to II at higher methane concentration (>62 mol%) [9]), we believe that the structure transition will not be happened in the hydrate formation for (methane + ethylene) system. Certainly, this presumption should be further confirmed by using more reliable experimental methods such as Raman spectra and NMR technique [9]. The calculation results for (methane + ethylene) system are illustrated in Fig. 2. The overall average absolute deviation (AAD) of the calculated hydrate formation pressures is 2.48%. For the (methane + propylene) system, as the hydrate-vapor–water-rich liquid equilibrium of (propylene + water) system exists over a very narrow temperature range 273.15–274.50 K, the pure propylene hydrate formation data are not sufficient for correlating its parameters (A , B and C ) to be used in the Chen–Guo hydrate model [5]. Thus, propylene’s parameters were determined indirectly from the hydrate formation data of (methane + propylene) system measured in this work. As propylene cannot form structure I hydrate, structure II was assumed in the regression. The regressed A , B , C values for propylene are listed in Table 3 along with the binary cross parameter Aij value for (methane + propylene) system. The calculated results are illustrated in Fig. 3. The overall AAD of the calculated hydrate formation pressures for (methane + propylene) system is 3.36%. The hydrate formation pressure data of Table 3 Parameter values used in the Chen–Guo hydrate model Gas species
A (Pa)
B (K)
C (K)
Aij a
Ethylene b (structure I) Propylene (structure II)
4.8418 × 1016 2.4256 × 1031
−5597.59 −18421
51.80 −42.35
0 506
a b
Binary cross parameter Aij for (methane + ethylene) and (methane + propylene) systems. Parameter values adopted from Chen and Guo [5].
46
C.-F. Ma et al. / Fluid Phase Equilibria 191 (2001) 41–47
Fig. 3. Hydrate formation conditions of (methane + propylene) gas mixtures: (䊉) M1; (䊊) M2; (䉱) M3; () M4; (䊐) pure propylene [3]; (+) pure methane [10]. Calculated by Chen–Guo hydrate model [5].
pure propylene have been predicted also and compared with literature data [3] as shown in Fig. 3. The maximum absolute deviation between predicted values and literature data is less than 3%. 4. Conclusions The hydrate formation data of five synthetic (methane + ethylene), four (methane + propylene) gas mixtures and pure ethylene gas have been measured in the temperature range of 273.7–287.2 K and pressure range of 0.53–6.6 MPa using the “pressure search” method. The uncertainty of temperature and pressure measurement is ±0.2 K and ±0.04 MPa, respectively. The reported data are valuable for testing existing hydrate models/software. Chen–Guo hydrate model was used to represent the experimental data measured in this work and satisfactory calculation results were obtained. Acknowledgements The financial support received from the National Natural Science Foundation of China (No. 29806009) and the China National Petroleum and Natural Gas Corporation is gratefully acknowledged. References [1] C.-F. Ma, Separation of Gas Mixtures using Hydrate Technology, Ph.D. Thesis, University of Petroleum, 2001. [2] L.E. Snell, F.D. Otto, D.B. Robinson, AIChE J. 7 (1961) 482–485. [3] F.D. Otto, D.B. Robinson, AIChE J. 6 (1960) 602–605.
C.-F. Ma et al. / Fluid Phase Equilibria 191 (2001) 41–47 [4] [5] [6] [7] [8] [9] [10]
D.-H. Mei, J. Liao, J.-T. Yang, T.-M. Guo, Ind. Eng. Chem. Res. 35 (1996) 4342–4347. G.-J. Chen, T.-M. Guo, Chem. Eng. J. 71 (1998) 145–151. S.S. Fan, T.M. Guo, J. Chem. Eng. Data 44 (1999) 829–832. D.-H. Mei, J. Liao, J.-T. Yang, T.-M. Guo, J. Chem. Eng. Data 43 (1998) 178–182. S.-X. Zhang, G.-J. Chen, C.-F. Ma, L.-Y. Yang, T.-M. Guo, J. Chem. Eng. Data 45 (2000) 908–911. S. Subramanian, R.A. Kini, S.F. Dec, E.D. Sloan Jr., Chem. Eng. Sci. 55 (2000) 1981–1999. E.D. Sloan, Clathrate Hydrates of Natural Gases, 2nd Edition, Marcel Dekker, New York, 1998.
47