Ionic Liquids for Propene‐Propane Separation

This paper presents an extensive study on the feasibility of ionic liquids (IL) for the extractive distillation of propene‐propane mixtures. A new experimental method for express screening of non‐volatile entrainers was elaborated. A series of ILs and their mixtures were screened at ambient temperature and low pressures. The screening results show that every tested IL turns a low boiler propene into a high boiler and the alkene‐to‐alkane separation factor can be as low as 0.28. The solubility and separation efficiency can be tuned by adjusting the chemical structures of the ions forming the IL. It was found that shortening of the alkyl substituents of the imidazolium ions leads to a decrease in capacity and to an increase in the separation factor. Interestingly, ILs containing nitrile functionalities in either the cation or the anion showed, in our experiments, enhanced separation ability combined with still good capacities. From our thermodynamic measurements, [EMIM][[B(CN)₄] was proved to be the most promising candidate. Binary mixtures of ILs were also tested and resulted in separation factors and capacities between the values for the individual ILs. For the most promising candidates, also autoclave measurements at elevated temperatures and pressures were carried out. These experiments indicate that the separation ability decreases with growing temperature and loading. In general, our study definitely proves the high potential of ILs to act as entrainers in the extractive distillation of propene‐propane mixtures or for the separation of any other low‐boiling alkene‐alkane mixture.     

Ionic Liquids as Modifying Agents for Protein Separation in Centrifugal Partition Chromatography

Aqueous two‐phase systems (ATPSs) can be applied in centrifugal partition chromatography (CPC) to separate biomolecules. Two ionic liquids (ILs) served as modifying agents to tune partition coefficients in the separation of two model proteins, myoglobin and lysozyme. Myoglobin was not affected by the ILs, while the partition coefficient of lysozyme was lowered with addition of IL. High stationary phase retention was achieved with ATPSs in a CPC column with cell size and geometry specially designed for unstable biphasic systems. When ILs were used as modifying agents, no notable decrease in stationary phase retention was observed. The injection volume was increased to 20 % of the total column volume and process simulations indicate that a further increase in the injection volume is possible.     

Ionic liquids for absorption and separation of gases: An extensive database and a systematic screening method

Ionic liquids (ILs) have attracted considerable attention in both the academic and industrial communities for absorbing and separating gases. However, a data‐rich and well‐structured systematic database has not yet been established, and screening for highly efficient ILs meeting various requirements remains a challenging task. In this study, an extensive database of estimated Henry's law constants of twelve gases in more than ten thousand ILs at 313.15 K is established using the COSMO‐RS method. Based on the database, a new systematic and efficient screening method for IL selection for the absorption and separation of gases subject to important target properties is proposed. Application of the database and the screening method is highlighted through case studies involving two important gases separation problems (CO₂ from CH₄ and C₂H₂ from C₂H₄). The results demonstrate the effectiveness of using the screening method together with the database to explore and screen novel ILs meeting specific requirements for the absorption and separation of gases. © 2017 American Institute of Chemical Engineers AIChE J, 63: 1353–1367, 2017     

Long‐Term Stability,Regeneration and Recycling of Imidazolium‐based Ionic Liquids

Ionic liquids (ILs) are discussed in many current research papers extensively in terms of their potential use in the chemical industry, as process aids and novel materials. The long‐term stability of the IL is for industrial applications as important as to know which species arise during the degradation due to thermal, mechanical, chemical or electrochemical stress. The investigation of the long‐term stability of two selected ILs over several months under process‐like conditions is presented with a subsequent analysis by LC‐MS to identify the resulting decomposition products. Knowledge about the occurring species and their analytical quantification are basis for the selection of appropriate processes for the separation of the decomposition products and the development of recycling processes for ILs. Particularly melt crystallization processes are suitable for separating structurally similar decomposition products that typically occur in the IL degradation.     

Use of Ionic Liquids as Solvents for Epoxidation Reactions Catalysed by a Chiral Katsuki-Type Salen Complex: Enhanced Reactivity and Recovery of Catalyst

The Katsuki-type catalyst 2 has been recycled several times following its use in a model epoxidation reaction of 1,2-dihydronaphthalene in an ionic liquid, 3a or 3b. The enantioselectivity was comparable to that in dichloromethane, but recovery of the catalyst was easier, activity was higher, and activity and enantioselectivity were retained in recovered ionic liquid fractions to a much greater extent than those for the Jacobsen-type catalyst 1.     

Tailored Media for Homogeneous Cellulose Chemistry: Ionic Liquid/Co‐Solvent Mixtures

Co‐solvents can minimize two of the major problems associated with the use of ionic liquids (ILs) as solvents for homogeneous derivatization of cellulose: high viscosity and limited miscibility with non‐polar reagents or reaction products. Thus, the effects of 18 solvents and 3 binary solvent mixtures on cellulose solutions in three ILs were systematically studied with respect to the solution phase behavior. The applicable limits of these mixtures were evaluated and general guidelines for the use of co‐solvents in cellulose chemistry could be advanced: Appropriate co‐solvents should have $E_{{\rm T}}^{{\rm N}} $ values (normalized empirical polarity) > 0.3, very low “acidity” (α < 0.5), and relatively high “basicity” (β ≥ 0.4). Moreover, novel promising co‐solvents and binary co‐solvent mixtures were identified.

     

Cu(acac)2 Immobilized in Ionic Liquids: A Recoverable and Reusable Catalytic System for Aza‐Michael Reactions

Copper(II) acetylacetonate immobilized in ionic liquids efficiently catalyzes the aza‐Michael reaction of amines with α,β‐unsaturated carbonyl compounds to produce the corresponding β‐amino carbonyl compounds with great alacrity in excellent yields. The reactions are far more facile than those reported earlier. The recovered ionic liquid phase containing the copper catalyst can be reused for several cycles with consistent activity.     

High Throughput Screening for the Design and Optimization of Chromatographic Processes: Automated Optimization of Chromatographic Phase Systems

Chromatographic processes can be optimized in various ways. However, the two most prominent approaches are either based on statistical data analysis or on experimentally validated simulation models. Both approaches heavily rely on experimental data, the generation of which usually imposes a significant bottleneck on rational process design. Hence, here a closed‐loop optimization strategy is proposed in that an automated high throughput liquid handling platform is combined with a genetic algorithm. This setup enables process optimization on the mini‐scale and thus saves time as well as material costs. The practicability and robustness of the proposed high throughput method is demonstrated with two exemplary optimization tasks: first, optimization of the buffer composition in the capture step for a binary protein mixture (lysozyme and cytochrome), and second, optimization of multilinear gradient elution for the separation of a ternary mixture (ribonuclease and cytochrome, and lysozyme).     

Cover Picture: Screening for Cytochrome P450 Reactivity by Harnessing Catalase as Reporter Enzyme (ChemBioChem 4/2009)

The cover picture shows a bacterial cytochrome P450 enzyme (CYP152A1, blue protein) screening for new substrates, such as nifidepine (highlighted green). The identification of novel reactivities of P450 enzymes is of major importance for applications in biocatalysis, biosensing and metabolic engineering. In their contribution on p. 751 ff, Niemeyer et al. report a novel assay for the rapid and facile screening of substrate libraries for organic hydroperoxide‐mediated P450 reactivity. Peroxide depletion is monitored in a fluorescence microplate assay, by harnessing a previously undescribed reactivity of the enzyme catalase (orange protein structure). The assay thus connects the occurrence of P450 reactivity with a universal read‐out, thereby circumventing the need for substrate‐specific detection schemes.