Interaction Between the Cyclopentane Hydrate Particle and Water Droplet in Hydrocarbon Oil

Abstract

The presence of immiscible water drops in bulk hydrocarbon is likely to bridge hydrate particles to cause hydrate agglomeration, leading to potential pipeline blockage. This can become a major challenge for flow assurance in offshore petroleum transportation. To avoid hydrate aggregation, the attachment between hydrate and water drops should be avoided. In this study, we used our home-designed integrated thin film drainage apparatus to investigate the interactions between a hydrate particle and a water drop inside model oil (i.e., mixture of cyclopentane and toluene with a volumetric ratio of 1:1). Our experiments showed that asphaltenes, a natural component in crude oil, were an effective inhibitor for the attachment between water drops and hydrate particles. Without asphaltenes in the system, the water drop adhered to the hydrate particle immediately after the two surfaces contacted. By adding 0.03 g/L asphaltenes into the oil phase, the attachment was delayed by 0.7 s when the applied preload force was set to around 0.05 mN. By increasing the asphaltenes addition to 0.05 g/L, the attachment between the hydrate and water drop was prevented even when the contact time lasted up to 25 s. This phenomenon could be explained by the adsorption of an asphaltenes layer along the interface between the aqueous drop and hydrocarbon. Measurements of the dynamic interfacial tension and crumping ratio confirmed the presence of the adsorption layer. The addition of 0.6 mol/L NaCl or 0.3 mol/L CaCl2 in the aqueous drop could further enhance the strength of the adsorption layer. Results of this research provide understanding of the benefits of asphaltenes and salt in preventing hydrate agglomeration.

Surface morphology effects on clathrate hydrate wettability

“…7, blue), which is in excellent agreement with our simulation results (88.6 mN/m). To test applicability and reliability of the method, we constructed additional simulation systems composed of the droplet on C5 hydrates immersed in (50 %C5 + 50 %C7) mixtures at 275 K. We obtained a Young contact angle of $ 30°and an interfacial tension of $ 42.7 ± 2.1 mN/m (close to the experimental value of $ 42.2 mN/m obtained for this interface) [94], leading to a work of adhesion of $ 79.7 mN/m, which agrees well with experimental data reported by Chen et al [93] (78.8 mN/m). This suggests that the direct simulation of water contact angle on an atomically smooth, chemically homogeneous hydrate surface immersed in a liquid, combined with the surface free energy estimated for water-surrounding liquid interfaces could be used to predict, rather accurately, experimental adhesion force measurements.…”

“…This interpretation allows us to reconcile the discrepancy between experimental contact angle values reported as low as 20°, and as high as 80-90°in the literature [16,25,28,88]. We found that our estimates for the work of adhesion are consistent with experimental measurements [93], suggesting that simulations such as those presented here could be useful for the estimation of adhesion force interactions between hydrate particles and water droplets. To our knowledge, this is the first determination of the hydrate-water adhesive forces achieved by employing molecular simulations under realistic conditions, as most previous experimental studies were performed using hydrates stable at atmospheric pressure, such as cyclopentane [93,[95][96][97].…”

“…We found that our estimates for the work of adhesion are consistent with experimental measurements [93], suggesting that simulations such as those presented here could be useful for the estimation of adhesion force interactions between hydrate particles and water droplets. To our knowledge, this is the first determination of the hydrate-water adhesive forces achieved by employing molecular simulations under realistic conditions, as most previous experimental studies were performed using hydrates stable at atmospheric pressure, such as cyclopentane [93,[95][96][97]. Our work contributes to closing the gap between experimental and realistic models of clathrate hydrates.…”

“…7, we compare the work of adhesion calculated from our simulations (yellow columns) to experimental results. For example, Chen et al [93] recently reported that the equilibrium attractive forces measured experimentally between a water droplet (D d = 2.00 ± 0.05 mm) and a C5 hydrate particle (D h = 4.00 ± 0.22 mm) immersed in C5 are of 0.23 ± 0.01 mN at 275 ± 0.5 K, yielding a work of adhesion of $ 86.3 mN/m (see Fig. 7, blue), which is in excellent agreement with our simulation results (88.6 mN/m).…”

Conceptual Design of a Sustainable Hybrid Desalination Process Using Liquefied Natural Gas Cold Energy

“…Number of publications on different hydrate formers from 2019 to 2020 − based on search results from Google Scholar using keywords “refrigerant” + “hydrate” on 23 February 2021.…”