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Enrichment of Components at Interfaces and Mass Transfer in Fluid Separation Technologies

Periodic Reporting for period 3 - ENRICO (Enrichment of Components at Interfaces and Mass Transfer in Fluid Separation Technologies)

Reporting period: 2019-10-01 to 2021-03-31

Techniques for separating fluid mixtures are important in many industries like the chemical and pharmaceutical industry. The most relevant of these separation techniques, distillation and absorption, are based on mass transfer through fluid interfaces. Results from molecular thermodynamics show that for many industrially important mixtures a strong enrichment of components occurs of the fluid interface. There is a striking congruence between shortcomings of the present design methods for fluid separations and the occurrence of that enrichment. It is the central hypothesis of the research in the ENRICO project that the enrichment leads to a mass transfer resistance of the fluid interface, which has to be accounted for in fluid separation process design. The fact that it is presently neglected causes unnecessary empiricism and inconsistencies in the design. ENRICO advances the knowledge on the enrichment of components at fluid interfaces using a novel combination of two independent theoretical methods, namely molecular simulations with force fields on one side and density gradient theory coupled with equations of state on the other. This enables reliable predictions of the occurrence of the enrichment and its magnitude. These results are used to establish a model for the mass transfer resistance of the interface due to the enrichment. On that basis, a new approach for designing fluid separation processes is developed in ENRICO, which will enable more efficient and robust designs in industry. The theoretical results are validated by experiments from laboratory to pilot plant scale, and the benefits of the new approach will be demonstrated. ENRICO will thus establish a link between molecular physics and engineering practice. The results from ENRICO will have a major impact on chemical engineering worldwide and change the way fluid separation processes are designed.
In the reporting period, the conditions under which the interfacial enrichment occurs were clarified. The hypothesis was confirmed that they are highly correlated with those, for which separation process design with traditional methods is difficult. Methods for predicting the enrichment were developed and successfully tested. The predictions from molecular simulations and density gradient theory agree very well, both for model systems that were studied systematically and real systems. Furthermore, a proof for a transport resistance due to the enrichment at vapor-liquid interfaces has been given by non-equilibrium molecular dynamics simulations. The scientific results were disseminated in more than 35 presentations at conferences and papers, and awareness has been created in the chemical industry for the importance of the enrichment at vapor-liquid interfaces for separation processes.
The research that has been carried out in ENRICO so far covers the following work areas: A1 (molecular simulations), A2 (density gradient theory and equations of state), A3 (improved understanding of the fluid interface), B1 (mass transfer theory), B2 (mass transfer experiments), C1 (process modeling and simulation) and is essentially in line with the description of the action. The focus was on work areas A1, A2, A3 and B1.
The ENRICO project aims at developing a new theory of mass transfer through vapor-liquid interfaces that unifies the existing, inconsistent approaches and alleviates their empiricism. The results that we have achieved in the reporting period make us confident of reaching this goal.
The project has already yielded methods for the quantitative prediction of the interfacial enrichment. The central element in the new approach is the introduction of a mass transfer resistance of the vapor-liquid interface. This resistance depends on the interfacial enrichment and vanishes if there is no enrichment. The new approach for designing fluid separation processes will lead to more efficient and more robust designs of industrial processes and have a major impact on chemical engineering worldwide.
Three objectives were defined in the description of the action:
Objective A (Molecular Thermodynamics): Establishing methods which enable the reliable prediction of the enrichment of components at interfaces in equilibrium and in non-equilibrium processes, identifying the conditions in which an enrichment of components at the interfaces has to be expected, and structuring that knowledge so that it can be used in fluid separation process design.
This objective has already been reached.
Objective B (The Link): Establishing a model for the mass transfer resistance due to that effect, integrating that model in an overall model for the mass transfer, and validating the mass transfer resistance of the interface caused by the enrichment by laboratory experiments.
Substantial progress has been achieved regarding this goal.
Objective C (Process Engineering): Applying the knowledge created above for studying fluid separation processes and demonstrating the benefits of the new approach for the design.
Work on this objective has begun and yielded promising results.
New mass transfer model
Enrichment of components at vapor-liquid interfaces
Experimental studies of mass transfer with a laminar jet apparatus