A Multidisciplinary Approach to Characterize Coalescence in Petroemulsions

Mayonnaise, vinaigrettes, milk, and petroleum are all emulsions: a liquid-liquid mixture composed by two, or more, immiscible components. When mayonnaise splits or become curdled, quite some efforts are required to re-establish the original emulsion state. Similarly, petro-emulsion generates significant problems in the extraction and transport when the mixture is 'broken'. While the problem is simple to visualize, the process is actually extremely complex to describe, control and predict for the large variates of petroleum types and treatment conditions. In this project, we combined the expertise of three prominent researchers working in three different, but adjacent, fields (chemical engineering, biotechnology and theoretical chemistry). Specifically, we studied the region in between two liquid drops immersed in the second liquid (e.g. two oil drops in water) in the presence of soaps (surfactants) and other components. Thereafter, we described the drop-drop merging, commonly defined as coalescence, via experiments, computer simulations, and theoretical models. This project not only produced publications on the subject, also the open-source codes PyVISA and PyRETIS were developed for visualisation, analysis of COALES simulations, and running long-timescale dynamics (rare event algorithms). These codes were instrumental for the combined molecular simulation/experimental papers, which revealed the structure of the thin film just before breakage. In addition to this, the same code was used for two papers on membrane permeation, which were published with the Ghent University. This collaboration is presently still continued and the newly developed Monte Carlo techniques will be applied to even further unravel the remaining unknown aspects of the coals phenomenon. Obtaining the experimental results, that led to the publications mentioned above, was very challenging. However, PhD student Ola Aarøen managed to overcome these which lead to a successful thesis delivery and defense on the on 29th of October. The continuous modeling group was also quite successful. They established a very useful model that produced results that were in agreement with other experimental studies (film thinning experiments) like the critical velocity value, at which there is no coalescence but the rebound regime starts. Ozan defended his thesis successfully on September 17. Ozan is presently researcher at Sintef with an affiliation with the NTNU.

The project has delivered two PhD's and also the postdoc in the project made a next career move in the field of Machine Learning at the university of Oslo. Besides a set of papers, we also established novel simulation methods that were implemented in the open source computer code PyRETIS that is developed and maintained by the van Erp group. Despite that the project itself is now finished, some of the research lines are still continued such as rare event simulations applied to thin film breakage, on which Dr. Enricco Riccardi and Prof. Titus van Erp are still working together. The methods developed in the Coales project are presently also used in other fields such as membrane permeation and DNA protein assembly that is continued with the University of Ghent, Belgium, and the University of Amsterdam, the Netherlands.

Coalescence is a critical phenomenon in separation and transport processes involving petroleum emulsions. Extensive experimental campaigns inferred that the primary factor controlling the dynamics of coalescence is the interactions between inter-phase layers enveloping individual droplets which are composed of surface active resins and asphaltene molecules. This project proposes a methodology based on a multiscale and multidisciplinary combination of advanced experimental and simulation techniques in order to close the gap between the mechanisms considered in state of the art models for film drainage during coalescence and the mechanisms responsible for the stability behaviour of petroemulsions. Specifically, the proposed methodology combines (a) novel equilibration procedures and rare event methods for molecular simulations providing a description of the inter-phase layers and of the thin film formed between two droplets at a molecular resolution to study the effects of long range intermolecular forces on inter-phase stability and film rupture, (b) the experimental technique of ultra-sensitive Optical Tweezers to control the separation distance between two emulsion droplets and to measure their interaction forces (and vice versa) as well as facilitate the determination of the eventual dimension of the thin film present in between two interacting drops, and (c) numerical film drainage modeling that will employ the simulated and measured interfacial force functionalities and critical film rupture thicknesses. The new methodology will first be applied to systems employing simple surfactants and work towards model asphaltene and resin surfactants. The proposed methodology to improve coalescence models would add value to the development of next-generation process concepts and equipment for energy efficient production of petroleum. The fundamental perspective of the project is applicable to a broad set of fields, such as food, pharmaceutical, separation, etc.