Interfacial phenomena of cyclopentane hydrate

Abstract

Clathrate hydrate is an ice-like crystalline compound, where water molecules encage lighter hydrocarbon species. The formation of hydrate crystals can introduce operational and safety hazards in conventional energy transportation. Much work to date has focused on understanding the requisite thermodynamic conditions for hydrate formation, potential kinetic pathways to explain hydrate growth, and the various macroscopic phenomena associated with hydrate plug formation in a pipeline. Most of the experimental measurements presented herein use a micromechanical force (MMF) technique developed at the Colorado School of Mines. Nine key results are presented: 1. Experimental error in hydrate adhesion and cohesion force measurements was reduced by approximately 80 per cent, and the distribution was established as normal. 2. The first indirect evidence was collected to support the existence of a quasi-liquid layer present at the hydrate interface, where the temperature-dependence was consistent with published theory. 3. Novel experimental techniques have resulted in a new understanding of hydrate cohesive forces in multiple phases: gas phase forces are twice that of the liquid phase, which is thrice that of the water phase. 4. Sintering (or growth) between hydrate particles was observed experimentally to begin after approximately 30 seconds of contact time, where interparticle forces increased thereafter by 70 per cent for each order of magnitude in time the particles are held together. 5. Carboxylic acids (simple surfactants) reduce hydrate cohesive force, where the greatest reductions were observed in acids with acyclic aliphatic and aromatic hydrophobic tail groups. 6. The hydrate-liquid hydrocarbon interfacial tension was estimated at 47 plus or minus 5 mN slash m, and the hydrate-water interfacial tension was estimated at 0.5 plus or minus 0.4 mN slash m. 7. The first surfactant adsorption isotherms for the hydrate-hydrocarbon interface were constructed, based on a fundamental model for hydrate cohesive force. 8. A systematic study of adsorption for multiple carboxylic acids suggests that these amphiphilic chemistries may pack up to 2x tighter (by 100x lower concentrations) at the hydrate-hydrocarbon interface than at the water-hydrocarbon interface. 9. A new fundamental model for hydrate particle agglomeration in industrial pipelines is presented, based on simple system properties, improves macroscopic pressure drop predictions by 56 per cent on average for appropriate systems.