Differential Scanning Calorimetry Studies of Clathrate Hydrate Formation

Abstract

Differential scanning calorimetry was applied to investigate the formation of tetrahydrofuran (THF) and cyclopentane (CP) clathrate hydrates. An emulsion technique was developed to determine the hydration number and the enthalpy of CP hydrate dissociation to liquid water and liquid cyclopentane, which were found to be 16.8 ( 0.7 and 82.3 kJ/mol CP, respectively. The hydration number corresponds to the theoretical number of 17 if all of the large cavities in the structure II hydrate are occupied. Experiments with water-in-CP emulsions did not identify homogeneous nucleation for the hydrate since ice and hydrate always formed together on supercooling. With water-in-heptane emulsions, for which no hydrate forms, the homogeneous ice supercooling limit was -37.8 °C. With the CP emulsion, ice and hydrate formed close to this temperature. For bulk THF/ H 2 O solutions, even at the hydrate stoichiometric molar ratio of 1:17, ice and hydrate were found to form in the same crystallization event upon cooling, which impeded the identification of the homogeneous nucleation temperature of the hydrate. To overcome this, a method based on emulsification of stoichiometric THF/water solutions in an immiscible fluorocarbon fluid enabled determination of the homogeneous nucleation of THF hydrate without the formation of ice. The homogeneous THF hydrate nucleation temperature was -32 °C. We believe this is the first measurement of homogeneous nucleation of a clathrate hydrate. Our experimental results suggest that ice is a good nucleating agent for heterogeneous formation of clathrate hydrates, whereas the hydrates are not efficient nucleators for ice.

Hydrophobic Particle Effects on Hydrate Crystal Growth at the Water–Oil Interface

“…The Span 80 system (no silica nanoparticles) was used as a reference sample, and the heat of hydrate dissociation from the reference sample shows 260 J g À1 of water, which is in good agreement with a previous result (269 J g À1 of water) reported by Zhang et al [17] As shown in Figure 4A, the second endothermic signal from the CP hydrate dissociation greatly decreases and exhibits an upward shift, thereby implying a reduction of the hydrate amount in the Span 80/particles system. Figure 4B clearly represents the significant inhibition of hydrate formation with the particle-injected samples as the amount of SiNPs increases in the micro-DSC experiments.…”

Investigation into the Formation and Adhesion of Cyclopentane Hydrates on Mechanically Robust Vapor-Deposited Polymeric Coatings

“…When the temperature is raised just above the ice melting point, the high contact area between the continuous phase liquid water and the dispersed oil drops promotes nucleation and growth of the cyclopentane hydrate. Zhang et al 41 and Karanjkar et al 31 also observed the formation of hydrate without continuous agitation in their DSC studies of hydrate formation. In our work, the interfacial area between the water and the CyC5 is higher than previous literature reports due to the small size of the CyC5 droplets (~ 5-10 µm in diameter).…”

Hydrogen Production by Reforming Clathrate Hydrates Using the in-Liquid Plasma Method

“…In addition, H 2 , C and light hydrocarbon as byproduct were resulted from direct decomposition of methane. Similarly, dissociation enthalpy of cyclopentane hydrate is 82.3 kJ/mol [19] and the reaction of plasma decomposition of cyclopentane hydrate is also shown in Table 30. The direct decomposition of cyclopentane also produced the light hydrocarbon as a byproduct.…”