Article pubs.acs.org/EF
Measurements of Cohesion Hysteresis between Cyclopentane Hydrates in Liquid Cyclopentane Nobuo Maeda,*,† Zachary M. Aman,‡ Karen A. Kozielski,∥ Carolyn A. Koh,§ E. Dendy Sloan,§ and Amadeu K. Sum§ †
CSIRO Materials Science and Engineering, Ian Wark Laboratory, Bayview Avenue, Clayton, Victoria 3168, Australia Centre for Energy, School of Mechanical and Chemical Engineering, The University of Western Australia (M050), Crawley, Western Australia 6009, Australia § Center for Hydrate Research, Chemical and Biological Engineering Department, Colorado School of Mines, Golden, Colorado 80401, United States ∥ CSIRO Earth Science and Resource Engineering, Ian Wark Laboratory, Bayview Avenue, Clayton, Victoria 3168, Australia ‡
ABSTRACT: We measured cohesion hysteresis between cyclopentane hydrate particles in liquid cyclopentane in the temperature range from −8 to 6 °C. Cohesion hysteresis was small within scatter, and no clear temperature dependence was observed in the range studied. Too great of applied loads resulted in damage of the cyclopentane hydrate shells, causing the unconverted water core to leak out of the shell. The leaked out water then converted to irregularly shaped cyclopentane hydrate asperities on the shell after contacting the surrounding liquid cyclopentane. Cohesion hysteresis between the cyclopentane hydrate asperities was also measured and found to be similar to those between particles. The implication of these findings to the friction forces is discussed.
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INTRODUCTION Gas hydrates are crystalline inclusion compounds, where a water-bonded network of water cages trap light hydrocarbon components (e.g., methane).1 Hydrate stability conditions depend upon the chemical components in the system; methane hydrates require substantial pressure (e.g., 40 bar) at temperatures near the ice point. Hydrate plug formation is a critical flow assurance challenge in deepwater oil and gas pipelines, which may cool substantially upon exposure to ambient seawater.2 Turner et al.3 have proposed a four-step conceptual mechanism for hydrate plug formation in deepwater flowlines: (i) water dispersion in the hydrocarbon phase, (ii) hydrate shell growth about the water−oil interface, (iii) hydrate particle agglomeration, and (iv) plug formation by large aggregates. Hydrate particle agglomeration represents a critical step in the risk profile of oil and gas transportation systems. The formation of large aggregates may correspond to a nonlinear response in pressure drop and multiphase flow behavior. Current models assume that the contact force experience between hydrate particles is negligible;4 however, this assumption has not been validated in laboratory studies. An accurate understanding of hydrate contact and agglomeration mechanism(s) elucidates one potential management strategy, because hydrates may be allowed to form5 for systems with low residence times. Work by Turner et al.3 suggested that, for emulsified droplets larger than 100 μm in diameter, the initial hydrate reaction would result in a thin hydrate shell (20−50 μm thick) with an interior water core; later work by Davies et al.6 suggested that further growth across a hydrate interface progressed with water diffusion across the crystal lattice. For this reason, measurement of the cohesive “mechanisms” between hydrate particles inherently involves a three-phase © 2013 American Chemical Society
mechanical equilibrium between the bulk phase oil, hydrate shell, and water core. The micromechanical force (MMF) method was proposed by Yang et al.7 and continued by Taylor et al.,8−10 to capture the cohesive force between two tetrahydrofuran (THF) hydrate particles. Continued MMF measurements by Dieker et al.11,12 employed liquid cyclopentane as a structure II hydrate former (similar to most oil and gas pipelines2), which is stable at ambient pressure up to 7.7 °C. Unlike THF, approximately 33 ppm of water is soluble within cyclopentane at equilibrium,13 leading to the formation of a hydrophilic−hydrophobic interface between the water and hydrate former; this condition closely resembles pipeline operations. While some properties of the hydrate system are expected to translate well for the same crystal structures (e.g., moduli), interfacial properties may depend heavily upon the guest molecule. Aman et al.14 presented a comprehensive analysis of cyclopentane hydrate cohesive mechanisms in a liquid cyclopentane bulk phase, concluding the dominance of capillary (water) bridges at low contact times and sintering/fracture forces at high contact times. In measurements with a cyclopentane-saturated bulk water phase, Aman et al.15 proposed solid−solid cohesion as the primary agglomeration mechanism; the results did not disqualify the potential for sintering/fracture at high contact times, although such behavior was not observed on the order of minutes. The three hydrate-specific cohesive mechanisms discussed above are susceptible to hysteretic behavior. In capillary bridge Received: June 25, 2013 Revised: August 6, 2013 Published: August 21, 2013 5168
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Figure 1. Schematic illustration of the experimental setup. Cohesive force measurement technique for cyclopentane hydrate particles with diameters approximately 1000 μm and an interior water core.
interfacial free energy. To overcome the adhesion force and forcibly separate the bodies, a pull-off force of Fp is required.22,23
and solid−solid cohesive mechanisms, hydrate−bulk interfacial tension plays a significant role in the overall force model. Particle wettability hysteresis,16,17 therefore, may manifest in both solid−solid and capillary bridge models, although the potentially small hydrate−water interfacial tension (∼0.5 mN/ m15) may negate wettability hysteresis effects in waterdominated systems. In sintering/fracture systems, hysteretic behavior may arise from dynamic crystal growth behavior,18−20 where even small changes in fracture area can significantly increase fracture force.14,21 The present investigation sought to quantify hysteretic behavior in systems with a cyclopentane bulk phase, where both capillary bridge and sintering/fracture forces may be present.14 Given the large cantilever spring constants used in the current experiments (approximately 100× larger than those used by Aman et al.14 or Dieker et al.11,12), we anticipate solid− solid cohesive forces to dominate over any residual signal from capillary cohesion or sintering observed by previous authors. As discussed below, no temperature dependence was observed in the present data, providing support for this assumption. We have used the Johnson, Kendall, and Roberts (JKR) framework22,23 to interpret solid−solid cohesion mechanics, because it may be used to describe the contact force between two macroscopic bodies. The JKR framework allows for an estimation of the extent of deformation of an elastic body upon compression22,23 a3 =
3R (F + 6γπR + 4E
12γπRF + (6γπR )2 )
Fp = 3πRγ
(2)
Equation 2 may be adapted to non-spherical bodies but requires an alteration to the geometric terms proceeding solid− liquid interfacial tension (γ). Cohesion hysteresis between gas hydrates has not been measured. Cohesion hysteresis is defined as the interfacial free energy difference during loading (γloading) and unloading (γunloading).23 Δγ ≡ γunloading − γloading
(3)
It is generally expected that γunloading is larger than γloading (consequently, Δγ will be positive), because of the dissipative nature of breaking contacts (entropic penalty); not all of the interfacial free energy that is required to create interfaces can be recovered by bringing the interfaces together. It is pertinent to note at this stage that, because cohesion hysteresis is a measure of dissipation of interfacial energy involved in making and breaking contacts, cohesion hysteresis generally does not correlate with the size of cohesion forces. Rather, it correlates more squarely with friction forces between the contacts.24 Therefore, the measurements of cohesion hysteresis between hydrate particles is expected to provide first-order estimates of the interparticle friction forces. It is difficult to directly measure friction forces between hydrate particles, and perhaps, for this reason, no direct study on friction forces between hydrate particles has been reported to date. The present work evaluates cohesion hysteresis by measuring cyclopentane hydrate cohesive forces, over a wide range of temperatures (−6 ≤ T ≤ 6 °C) and under higher preloading forces (≈2mN) than in previous studies (enforcing the dominance of solid−solid cohesive force).
(1)
where a is the contact radius, R is the mean radius of curvature of the body, E is the elastic modulus of the body, F is the applied load, and γ is the interfacial free energy between the elastic body and the surrounding medium. In the present work, we use the harmonic mean radius (1/R = 1/R1 + 1/R2) of both hydrate particles for the mean radius of curvature (R in eq 1). Thus, the JKR theory predicts the size of the contact diameter under a given load when the interfacial free energy and the elastic modulus of the body are provided. As expected, the smaller the E (i.e., more deformable), the greater the deformation (i.e., a increases more sharply with F). The contact radius remains non-zero at F = 0 upon unloading, because of the adhesion force that arises from the
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MATERIALS AND METHODS
Experimental Setup. A MMF apparatus was used to measure cyclopentane hydrate cohesive forces (Figure 1). The details of the description of the instrument can be found in the literature.14 In brief, two handmade ice particles (∼1000 μm diameter) are mounted on glass fiber cantilevers in a bulk phase of liquid cyclopentane. Cyclopentane was used as a low-pressure analogue to natural gas 5169
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hydrate formers, because of pressure limitations with the MMF apparatus. One cantilever (bottom cantilever, Figure 1) has a precalibrated spring constant8 and is used for the loading and the measurements of cohesion forces. When the unloading/loading trials are visually captured on a distance-calibrated camera, the product of the final particle displacement (Figure 1) and the spring constant yields the “cohesive force” or “preloading force” (respectively) for the trial. The system temperature is maintained by an aluminum cooling jacket connected to an external glycol cooler. The drybox surrounding the microscope and system is filled with cyclopentane-saturated nitrogen (minimizing the evaporation rate of cyclopentane from the cell). The cyclopentane hydrate particles were produced by warming two ice particles at the tip of the cantilevers to above 273 K in cyclopentane; hydrate formation is deterministic using this formation method, because the initial hydrate may template off the residual, hydrogen-bonded ice structure.1 The inverted light microscope is equipped with lenses at 2.5×, 10×, and 20×; higher microscope magnifications were used in this study as opposed to those by Dieker et al.11 and Aman et al.,14 to enhance measurement resolution. It should be noted that hydrate conversion (by warming ice particles) was consistently performed above the ice point, prior to decreasing the system temperature for measurement; although hydrate remains the thermodynamically preferred phase below 273 K, mass transport limitations across the hydrate lattice may well result in ice formation in the core of the hydrate particle. Protocols. Figure 2 shows an example photographic image of two cyclopentane hydrate particles in liquid cyclopentane prior to contact.
Figure 3. Typical cohesion hysteresis curve (loading branch, blue; unloading branch, red) of cyclopentane hydrate particle−particle contact in liquid cyclopentane. This particular hysteresis curve was recorded at the experimental temperature of 4.1 °C.
energy (γloading for the loading branch and γunloading for the unloading branch) as the fitting parameters. Two-parameter fitting was difficult to carry out in practice with confidence, because the program that we used might find one of the local minima and miss the global minimum. As such, we analyzed our data as follows. We first estimated γunloading from the pull-off force Fp at the end of an unloading branch, with the use of eq 2. Then, we applied least-squares regression analysis of eq 1 to the entire unloading branch with E as the sole fitting parameter. Finally, we applied least-squares regression analysis of eq 1 to the entire loading branch with γloading as the sole fitting parameter, with the assumption that E does not change during the loading and subsequent unloading processes. We will show normalized (unitless) cohesion hysteresis; Δγ/γunloading = (γunloading − γloading)/γunloading. It is worth emphasizing that, although the cohesion hysteresis correlates well with the frictional forces between the same surfaces, it is intrinsically less sensitive (less quantitatively accurate) than friction forces, as shown in refs 24, 26, and 27. As such, it should be treated as semi-quantitative information. The physical explanation behind this intrinsically less sensitive nature of the cohesion hysteresis than the direct measurements of friction forces is that a hysteresis is a difference between two quantities, while a friction force is a direct measure. Figure 4 shows the work of cohesion (2γunloading), calculated from Fp, at various temperatures. The work of cohesion of about 0.1 N/m (γunloading of about 50 mN/m) was in the similar range as measured previously.25 We note that the measurements of cohesion hysteresis inevitably resulted in longer contact times (typically several minutes and depended upon the number of data points measured on the loading and unloading branches) than in the previous studies. Because we did not observe a clear trend with the temperature in Figure 5, we also calculated the overall average of the whole hydrate particle cohesion hysteresis data at all temperatures. We found the normalized cohesion hysteresis to be 0.17 ± 0.26. Given that cohesion hysteresis is theoretically expected to be positive, the scatter that extends to negative values is a non-physical result and suggests that the cohesion hysteresis for cyclopentane interparticle contact is below the force resolution of the apparatus. When a hydrate particle was pressed too hard against another, the hydrate shell broke and water “thread” could be pulled out of the particle upon unloading (pulling out) of the particle. An example photo of such a water thread is shown in
Figure 2. Example photo of cyclopentane hydrate particle−particle contact setup in liquid cyclopentane. The mean radii of curvature of each particle, R1 and R2, the contact diameter, 2a, and the applied force, F, can be directly measured. We changed F in steps for both the loading and unloading processes and waited for 5−10 s after each change in F. The contact diameter, 2a, was measured after this waiting time, following the change in the applied force, F. The pull-off force, Fp, was also measured at the end of each unloading process. The mean radii of curvature of each particle, R1 and R2, were measured for each contact position when the two particles are separated. The applied force, F, was calculated from the measured deflection on the image, using the precalibrated spring constant and Hooke’s law. We changed F in steps for both the loading and unloading processes and waited for 5−10 s after each change in F. The contact diameter, 2a, was measured from the image after the waiting time following the change in F. The pull-off force, Fp, was also measured at the end of each unloading process from the last image prior to the jump apart of the particles.
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RESULTS Figure 3 shows typical cohesion hysteresis curves between two cyclopentane hydrate particles. The loading and unloading branches of the applied load−contact diameter curve typically overlap, suggesting small hysteresis. We measured a large number (>150) of such loading and unloading curves at various temperatures. The results were analyzed by fitting the JKR theory (eq 1) to each of the loading and unloading branches, with the effective elastic modulus (E) and the interfacial free 5170
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Figure 4. Work of cohesion measured from the pull-off force, Fp, at the end of each unloading branch and then calculated using eq 2. The work of cohesion was about 0.1 N/m, which translates to γunloading of about 50 mN/m. The measurements of cohesion hysteresis inevitably resulted in contact times of several minutes prior to the pull-offs. Error bounds represent one standard deviation of 10−30 pull-off measurements at each subcooling temperature.
Figure 6. Example photo of cyclopentane hydrate shell damage after the two particles were compressed too hard. Upon subsequent separation of the surfaces, water “thread” was pulled out of the liquid water core of the cyclopentane hydrate particle. The water “thread” could be broken off when stretched, resulting in the formation of “asperities” on each hydrate particle surface. The asperities subsequently formed a cyclopentane hydrate shell around them because they were in contact with the surrounding liquid cyclopentane. These asperities could be brought back to contact for cohesion hysteresis measurements between the asperities. The hydrate shell could be broken when the asperities were compressed too hard, resulting in the formation of water “thread” upon subsequent separation. These observations suggest that the hydrate shell is highly porous. The “effective bulk modulus” of the cyclopentane hydrate shell is thus expected to be lower than that of bulk cyclopentane hydrates.
Figure 5. Normalized cohesion force hysteresis between two cyclopentane hydrate particles in liquid cyclopentane as a function of the experimental temperature. Theoretically, the hysteresis is expected to be positive. No clear temperature dependence was observed in the range studied. Error bounds represent one standard deviation of 10−30 pull-off measurements at each subcooling temperature.
Figure 6. We realized that the shell thickness was not uniform because some parts of the hydrate shell were clearly weaker than other parts. However, we did not attempt to quantify the shell thickness that could have contributed to the large scatter in our data in this study. Because the water thread is surrounded by liquid cyclopentane, cyclopentane hydrate newly formed around the water thread (i.e., at the interface between the water and the cyclopentane). The “thread” could then be broken off by applying appropriate mechanical force. When the thread was manually aligned with the direction of applied force, the broken hydrate thread could result in hydrate asperities on either particle surface that are oriented suitably for force measurements (Figure 7). We could then measure cohesion hysteresis between such cyclopentane hydrate asperities after annealing in liquid cyclopentane. We note that the time scales for the formation of cyclopentane hydrate “walls” around the water thread that was being pulled out were instant. In a few instances, when the motion was reversed during a pull-off, i.e., when the water thread was pushed instead of being continually pulled out, the thread buckled. The inference was that the
Figure 7. Example photo of cyclopentane hydrate asperity−asperity contact setup in liquid cyclopentane. The asperities were formed by inducing surface damage to hydrate shells and then annealed in cyclopentane.
thread already possessed some mechanical strength. We note that the speed of the pull-off rate was typically 10−15 μm/s. Figure 8 shows typical cohesion hysteresis curves between two such cyclopentane hydrate asperities. As was the case between two cyclopentane hydrate particles, the loading and unloading branches of the applied load−contact diameter curve typically overlap, suggesting hysteresis effects below the resolution of the instrument. We measured a large number (>60) of such loading and unloading curves between two 5171
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Figure 8. Typical cohesion hysteresis curve (loading branch, blue; unloading branch, red) of cyclopentane hydrate asperity−asperity contact in liquid cyclopentane. This particular hysteresis curve was recorded at the experimental temperature of 4.6 °C.
Figure 10. Effective bulk modulus of the cyclopentane hydrate shell as a function of the experimental temperature, obtained from fitting of the JKR theory to the data. As expected, the “effective bulk modulus” was much smaller than that of the bulk cyclopentane hydrates (5−9 GPa, depending upon the source). No clear temperature dependence was observed within the range studied.
cyclopentane hydrate asperities at various temperatures and applied the JKR analyses. The results are summarized in Figure 9. Similar to between hydrate particles, cohesion hysteresis
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DISCUSSION Effective Elastic Modulus of Cyclopentane Hydrate Particles. Our results show that the effective elastic modulus of cyclopentane hydrate particles and asperities, obtained from the fitting of the JKR theory to the measured data, varied over many orders of magnitude and was consistently lower than the value expected from bulk hydrate solids. This wildly variable and consistently lower effective elastic modulus of cyclopentane hydrate particles and asperities can arise from at least two sources. First, even though the surface of the particles/asperities was coated with cyclopentane hydrates, the inner core remained liquid water. Taylor et al. measured such cyclopentane hydrate shell thickness and found that the initial values were in the range of 25−50 μm.8 The effective elastic modulus of the particles/asperities is thus expected to be lower than that of the bulk solid hydrates and increases with the thickness of the hydrate shells. Second, we observed pulling-off of water “thread” after contact with large compressive forces. The magnitude of the force required to achieve this depended upon the specific location on the shell, suggesting that (1) the structure and/or the thickness of the hydrate shell was not uniform and (2) the hydrate shell itself (on some locations, at least) may have been highly porous. Such a porous structure of the hydrate shell is expected to result in a lower effective elastic modulus than that of the bulk solid hydrate. Implications to Friction Forces between Gas Hydrate Particles. Our findings have some important implications to the friction forces between cyclopentane hydrate particles. Figure 11 illustrates the general relationship between the adhesion hysteresis and the sliding friction forces,24 where we consider two paths for the move of an object from point A to
Figure 9. Normalized cohesion force hysteresis between two cyclopentane hydrate asperities in liquid cyclopentane as a function of the experimental temperature. Theoretically, the hysteresis is expected to be positive. No clear temperature dependence was observed, except at the highest temperature studied.
between cyclopentane hydrate asperities was small at all temperatures studied. Similar to what we did for the particle−particle data above, we calculated the average of the whole hydrate asperity cohesion hysteresis data at all temperatures and found the normalized cohesion hysteresis to be 0.07 ± 0.45. For the reasons noted above, the scatter that extends to negative values is a non-physical result and suggests that the cohesion hysteresis for cyclopentane interasperity contact is also below the force resolution of the apparatus. We note that, when a hydrate asperity was pressed too hard against another, the hydrate shell broke and another water thread could once again be pulled out of the asperity upon unloading. Because we used eq 1 to fit our data, we can also plot the effective modulus of the cyclopentane hydrate particles as a function of the temperature (Figure 10). The results show a slight tendency for the effective modulus to increase at the lowest temperature studied. This trend may be the result of ice formation in the core of the hydrate particles for some samples at these temperatures; this hypothesis could not be confirmed through warming past the ice point, because this would lead to additional hydrate formation.
Figure 11. Schematic illustration of the relationship between cohesion hysteresis and friction forces. Sliding friction can be regarded as a very large number of breaking/reforming of contacts between two surfaces, whereas cohesion hysteresis is just a single such event. 5172
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Energy & Fuels point B. The adhesion hysteresis path corresponds to the path that detaches the surface upward, moves along the surface in air, and then deposits on the surface at point B. The frictional path corresponds to the path that drags the object along the surface from point A to point B. This second path could be interpreted as an accumulation of a very large number of detaching/landing events because the “adhesive bonds” between the object and the surface are continually broken and reformed as the object slides (i.e., integration of a very large number of adhesion hysteresis events). Because of this accumulative nature of friction forces, an increase in adhesion hysteresis as a result of a change in the surface properties will be magnified when friction forces between the same surfaces are measured (i.e., friction forces are more sensitive to a change than adhesion hysteresis). This general relationship holds for non-elastic (viscoelastic) bodies.26,27 We did not observe any clear temperature dependence in the limited experimental accessible temperature range. These data support our hypothesis that the large cantilever spring constants used in these experiments (relative to previous reports) render solid−solid cohesion as the dominant contact force. Our results of near zero cohesion hysteresis, within the resolution of our method, thus suggests that the friction forces between cyclopentane hydrates in liquid cyclopentane are likely to be small. We note that it remains to be seen if the same result will hold for friction forces between cyclopentane hydrates in other media (e.g., an aqueous bulk phases) or friction forces between different types of gas hydrates in a medium. Direct visual experiments of hydrate particle drag would offer more quantitative assessment of the actual frictional forces experienced in flow. This result is of particular use to systems in which hydrate particles are transported within a liquid hydrocarbon stream (e.g., oil and gas transport systems). As a first approximation, these results on minimal friction force suggest that hydrate may not experience significant drag in flow, which is a critical parameter to determine whether hydrate particles may accumulate in transport pipeline sections. On the other hand, ubiquitous forces that are already present in a flow line, such as capillary forces, may cause the same effects (e.g., the formation and the break-off of hydrate “threads” as the hydrate particles collide at high speeds) as the external force that we had applied in this study.
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CONCLUSION
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AUTHOR INFORMATION
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ACKNOWLEDGMENTS
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REFERENCES
Article
This work was performed at the Center for Hydrate Research (CHR) at the Colorado School of Mines (CSM) during Nobuo Maeda’s visit. The CHR is mainly funded by the CSM Hydrate Consortium that is sponsored by (current and past): BP, ConocoPhillips, Chevron, Eni, ExxonMobil, Halliburton, Multichem, Nalco, Petrobras, SPT Group, Schlumberger, Shell, and Total. Carolyn A. Koh acknowledges partial support by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences (BES), Division of Materials Sciences and Engineering (DOE− BES award DE-FG02-05ER46242). Nobuo Maeda acknowledges the funding support of the Australian Research Council Future Fellowship (FT0991892) and CSIRO’s Petroleum and Geothermal Research Portfolio for the visit.
(1) Sloan, E. D.; Koh, C. A. Clathrate Hydrates of Natural Gases, 3rd ed.; CRC Press (Taylor and Francis Group): Boca Raton, FL, 2008. (2) Sloan, E. D.; Koh, C. A.; Sum, A. K. Natural Gas Hydrates in Flow Assurance; Gulf Professional Publishing (Elsevier, Inc.): Houston, TX, 2011. (3) Turner, D.; Miller, K.; Sloan, E. Methane hydrate formation and an inward growing shell model in water-in-oil dispersions. Chem. Eng. Sci. 2009, 64, 3996−4004. (4) Sinquin, A.; Palermo, T.; Peysson, Y. Rheological and flow properties of gas hydrate suspensions. Oil Gas Sci. Technol. 2004, 59 (1), 41−57. (5) Turner, D.; Talley, L. Hydrate inhibition via cold flowNo chemicals or insulation. Proceedings of the 6th International Conference on Gas Hydrates (ICGH 2008); Vancouver, British Columbia, Canada, 2008; pp 1−12. (6) Davies, S. R.; Sloan, E. D.; Sum, A. K.; Koh, C. A. In situ studies of the mass transfer mechanism across a methane hydrate film using high-resolution confocal Raman spectroscopy. J. Phys. Chem. C 2010, 114 (2), 1173−1180. (7) Yang, S.-o.; Kleehammer, D.; Huo, Z.; Sloan, J.; Dendy, E.; Miller, K. Temperature dependence of particle−particle adherence forces in ice and clathrate hydrates. J. Colloid Interface Sci. 2004, 277, 335−341. (8) Taylor, C.; Dieker, L.; Miller, K.; Koh, C.; Sloan, J.; Dendy, E. Micromechanical adhesion force measurements between tetrahydrofuran hydrate particles. J. Colloid Interface Sci. 2007, 306, 255−261. (9) Taylor, C. J.; Dieker, L. E.; Miller, K. T.; Koh, C. A.; Sloan, E. D., Hydrate particles adhesion force measurements: Effects of temperature, low dosage inhibitors, and interfacial energy. Proceedings of the 6th International Conference on Gas Hydrates (ICGH 2008); Vancouver, British Columbia, Canada, 2008. (10) Taylor, C. J.; Miller, K. T.; Koh, C. A.; Sloan, E. D., Jr. Macroscopic investigation of hydrate film growth at the hydrocarbon/ water interface. Chem. Eng. Sci. 2007, 62 (23), 6524−6533. (11) Dieker, L. E.; Aman, Z. M.; George, N. C.; Sum, A. K.; Sloan, E. D.; Koh, C. A. Micromechanical adhesion force measurements between hydrate particles in hydrocarbon oils and their modifications. Energy Fuels 2009, 23, 5966−5971. (12) Dieker, L. E.; Taylor, C. J.; Koh, C. A.; Sloan, E. D. Micromechanical adhesion force measurements between cyclopentane hydrate particles. Proceedings of the 6th International Conference on Gas Hydrates (ICGH 2008); Vancouver, British Columbia, Canada, 2008. (13) Infochem. Multiflash for Windows 4.1; Infochem Computer Services, Ltd.: London, U.K., 2012. (14) Aman, Z. M.; Brown, E. P.; Sloan, E. D.; Sum, A. K.; Koh, C. A. Interfacial mechanisms governing cyclopentane clathrate hydrate adhesion/cohesion. Phys. Chem. Chem. Phys. 2011, No. 13, 19796− 19806. (15) Aman, Z. M.; Joshi, S. E.; Sloan, E. D.; Sum, A. K.; Koh, C. A. Micromechanical cohesion force measurements to determine cyclo-
We measured cohesion hysteresis between cyclopentane hydrate particles and between cyclopentane hydrate asperities in liquid cyclopentane in the temperature range from −8 to 6 °C. In both cases, cohesion hysteresis is found to be small within the scatter of the data and no clear temperature dependence was observed in the range studied. These results suggest that the friction force between cyclopentane hydrates is likely to be small.
Corresponding Author
*
[email protected]. Notes
The authors declare no competing financial interest. 5173
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pentane hydrate interfacial properties. J. Colloid Interface Sci. 2012, 376 (1), 283−288. (16) Willett, C. D.; Adams, M. J.; Johnson, S. A.; Seville, J. P. K. Capillary bridges between two spherical bodies. Langmuir 2000, 16 (24), 9396−9405. (17) Asserson, R.; Hoffmann, A.; Hoiland, S.; Asvik, K. Interfacial tension measurement of freon hydrates by droplet deposition and contact angle measurements. J. Pet. Sci. Eng. 2009, 68, 209−217. (18) Uchida, T.; Shiga, T.; Nagayama, M.; Gohara, K. Sintering of clathrate hydrates. Energies 2010, 3, 1960−1971. (19) Saito, K.; Kishimoto, M.; Tanaka, R.; Ohmura, R. Crystal growth of clathrate hydrate at the interface between hydrocarbon gas mixture and liquid water. Cryst. Growth Des. 2011, 11 (1), 295−301. (20) Kishimoto, M.; Iijima, S.; Ohmura, R. Crystal growth of clathrate hydrate at the interface between seawater and hydrophobicguest liquid: Effect of elevated salt concentration. Ind. Eng. Chem. Res. 2012, 51 (14), 5224−5229. (21) Ohmura, R.; Mori, Y. H. Pull-out test of clathrate-hydrate films formed at water/hydrochlorofluorocarbon interfaces. J. Mater. Sci. Lett. 1998, 17, 1397−1399. (22) Johnson, K. L.; Kendall, K.; Roberts, A. D. Surface energy and contact of elastic solids. Proc. R. Soc. London, Ser. A 1971, 324 (1558), 301. (23) Israelachvili, J. Intermolecular and Surface Forces, 2nd ed.; Academic Press: Waltham, MA, 1991. (24) Yoshizawa, H.; Chen, Y. L.; Israelachvili, J. Fundamental mechanisms of interfacial friction. 1. Relation between adhesion and friction. J. Phys. Chem. 1993, 97 (16), 4128−4140. (25) Aman, Z. M.; Olcott, K.; Pfeiffer, K.; Sloan, E. D.; Sum, A. K.; Koh, C. A. Surfactant adsorption and interfacial tension investigations on cyclopentane hydrate. Langmuir 2013, 29 (8), 2676−2682. (26) Chen, N.; Maeda, N.; Tirrell, M.; Israelachvili, J. Adhesion and friction of polymer surfaces: The effect of chain ends. Macromolecules 2005, 38 (8), 3491−3503. (27) Maeda, N.; Chen, N.; Tirrell, M.; Israelachvili, J. Adhesion and friction mechanisms of polymer-on-polymer surfaces. Science 2002, 297 (5580), 379−382.
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