Master Assignments

Novel NaDES Affinity Process for Aliphatic-Aromatic Separations

Tutor:                 Thomas Brouwer

Supervisor:        Boelo Schuur

Chair:                 Sascha Kersten


Novel NaDES Affinity Process for Aliphatic-Aromatic Separations

Sometimes, distillation is impractical to separate mixtures due to high energy consumption, or even it might be impossible due to azeotropes. Alternatively, affinity separation processes such as extractive distillation (ED) and Liquid-Liquid Extraction (LLX) can be applied. The separation of aromatic from aliphatic compounds is one example where ordinary distillation can be impractical. The addition of an affinity agent, or solvent, can bring a solution by increasing the relative volatility or even breaking azeotropes.

This MSc-project is part of a larger project where we try to understand molecular interactions between solvents and mixtures that we want to separate. In order to do so, we study both common solvents such as sulfolane that have been industrially used for decennia already and innovative new solvents, such as Natural Deep Eutectic Solvents (NaDESs). A key aspect in this larger project is to bridge the understanding of the molecular interactions to process evaluation.

Figure 1: The Vapor-Liquid Equilibrium diagram of C5 to C10 alkanes over benzene. *estimation from COSMO-RS

In our specific case of studying the separation of aromatic compounds from aliphatic compounds, a complex mixture, often referred as the naphtha cut, is considered. Initially, we simplify this naphtha cut to solely aromatic compounds, e.g. benzene, toluene, and alkanes, e.g. n-heptane. As can be seen in Figure 1, some alkanes are more volatile than benzene, while others are less volatile. An appropriate solvent most therefore be able to separate all aliphatic compounds from the aromatic compound. This can be done by selectively increasing the relative volatility of the aliphatic compounds, thereby changing the natural order of boiling. Sulfolane is the benchmark solvent, which will be used to compare our results.

Currently, 3 processes are being performed to separate all the aliphatic compounds from the aromatic compounds. Liquid-Liquid Extraction (LLX), Extractive Distillation (ED) and Azeotropic Distillation (AD).  Weissermel et al. state without much clarification that LLX is economically most viable if the aromatic content of the feed is between 20 and 65 wt.%, ED between 65 and 90 wt.% and AD only at even higher aromatic contents.

This MSc. Assignment will continue on previous work done by a Master Student. She simulated the LLX and ED process in AspenPlus and in the end could make a cost assessment for one specific case; the separating toluene from methylcyclohexane as can be seen in Figure 2.

Figure 2: The Total Annual Cost (TAC) analysis for Extractive Distillation and Liquid-Liquid Extraction process for the separation of toluene and methylcyclohexane

This MSc. Assignment will be on finding and evaluating a Natural Deep Eutectic Solvent (NaDES) and perform LLX and ED process simulations and compare the NaDES performance with those of sulfolane.

Natural Deep Eutectic Solvents (NaDESs) are a relatively new concept [1, 2], they consist of two solids that upon mixing become a liquid, because the melting point of the mixture is significantly lower than the melting points of the two constituents. These NaDESs are designer solvents, same as ionic liquids, but lack the expensive fabrication costs, raw material costs and are environmentally friendly.


Figure: DES of malic acid and choline chloride [2]

 This assignment consists out of two clear parts; experimental and simulation.

  1. Experimental: After a thorough literature review concerning NaDES, you will need to test several NaDESs to evaluate critical properties such as melting point and the distribution and partitioning coefficient for the mixture toluene/methylcyclohexane. In addition, Vapor-Liquid Equilibria will be made to evaluate the recovery of the toluene from the NaDES
  2. Simulation: You will simulate the LLX and ED process (existing Aspen Plus files of the previous master student are of course the starting point). For the chosen NaDES you will correlate binary interaction parameters from experimental data and use this correlation to simulate the NaDES process. 

Note: “This is an initial idea of the assignment. The assignment can of course be altered to the wished and interest of the master student.”


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