Computer-aided design methodology for separation processes with ionic liquids

Yuqiu Chen*

*Corresponding author for this work

Research output: Book/ReportPh.D. thesis

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In the process industries, separation represents a fundamental step to reach the products quality and purity required by the market. Its efficiency could promote the development of industry to reap great energy and environmental benefits. Therefore, any new separation technologies or intensified process designs allowing energy efficient and sustainable operations are highly desirable, especially for energy intensive and difficult separation processes. Separations of close-boiling and azeotropic mixtures as well as many gas separations are representatives of high energy consuming processes, while the downstream separation in bioprocesses is usually difficult and expensive because of recovery of targeted products from dilute aqueous solutions. In response to increasing energy and environmental challenges, several new innovative separation technologies and intensified process designs have been widely studied. Among them, separation        technologies using ILs as solvents are being paid more attention due to its attractive properties such as non-volatility, inflammability exhibiting good solubility and selectivity for a wide range of organic and inorganic chemicals. Nonetheless, some challenges need to be addressed before taking their place in industrial applications, such as how to lower the price of ILs and reduce their viscosities, and particularly how to design/screen suitable ILs for different separation systems.

The main objective of this work is to develop a systematic computer-aided design method that is able to rapidly and reliably screen suitable ILs with desired properties as well as meet specific objectives. Since the performance of this non-experimental based design method largely depend on the predictive property models; group contribution (GC)-based property models covering various ILs are developed. Alongside, a comprehensive UNIFAC-IL-Gas model that combines IL-gas and other IL-solute systems is also proposed to predict the thermodynamic behaviors of the studied IL containing systems. In all cases, property models are validated by using 20-30% of data points as test datasets. These models can be easily integrated in the computer-aided design method of ILs, and they can also be used to predict properties of ILs that have not yet been synthesized. This is essential to find new high-performance ILs for different industry applications. Unlike experimental-based or other trial-and-error solvent screening methods that are usually time consuming and expensive, the design method of ILs proposed in this work is both cost- and time-efficient due to the fact that this methodology is completely based on the  predictive property models.

On the other hand, ILs are introduced to the intensified process designs including hybrid process schemes, integrated solvent and process design, and in situ product removal (ISPR). Furthermore, different design methodologies are proposed accordingly for each of the intensified process design involving ILs. These IL-based intensified process designs along with associated algorithms, knowledge bases and tools are, respectively, tested with different case studies. (1) Hybrid process schemes with ILs: separation of aqueous solutions and production of aldehydes by bio-oxidation of alcohols. (2) Integrated IL and process design: separation of ethanol-water, separation of acetone-methanol, and CO2 capture process. (3) IL-based ISPR design: biobutanol production from acetone-butanol-ethanol (ABE) fermentation. For all intensified process designs, the computer-aided design method of ILs as well as the physical and thermodynamic property models are included. In each of the case study, new IL(s) and optimized process operations are achieved using proposed design methodologies.

Besides all the case studies described above, the proposed computer-aided design method of ILs is also used to design optimal ILs for some other applications: for removing acid gas (e.g. CO2, H2S) from shale/natural gas, for recovering bio-isoprene from fermentation off-gas, and as electrolyte additives in lithium titanate (LTO) batteries. In all studied cases, the designed ILs provide better process performance when compared to their corresponding benchmark solvents or additives.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages219
Publication statusPublished - 2020


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