Scaling-up of Ionic Liquid Synthesis

For commercial ionic liquid synthesis, quality is a key factor. However, since availability and price are other important criteria for the acceptance of this new solvent concept, the scaling-up of ionic liquid production is a major research interest too. 

Many historical ways to make ionic liquids proved to be impractical on larger scales. Sometimes expensive starting materials are used (anion-exchange with silver salts, for example [2]), or very long reaction times are necessary for the alkylation steps, or filtration procedures are included in the synthesis, or hygroscopic solids have to be handled. All these have to be avoided for a good synthesis on larger scales. 

Other important aspects to consider during the scaling-up of ionic liquid synthesis are heat management (alkylation reactions are exothermic ) and proper mass transport. For both of these the proper choice of reactor set-up is of cmcial importance. 

Innovation s production plants at the Institut fur Technische Chemie und Makromolekulare Chemie, University of Technology Aachen, Germany. 

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Recently, Deetlefs and Seddon83 reported the solvent-free synthesis and scale-up of ionic liquids under microwave irradiation. Using a commercial microwave reactor they prepared ionic liquids based upon the 1-alkylpyridinium, l-alkyl-3-methylimida-zolium, l-alkyl-2-methylpyrazolium and 3-alkyl-4-methylthiazolium cations, on scales from 50 mmol to 2 mol (Scheme 9.2). Under microwave irradiation, because of efficient... 

The German public funded project NEMESIS focuses on the design and development of microreactors for the synthesis of ionic liquids at pilot scale [52], Scientific objectives are to increase the yield of the corresponding ionic liquid as well as to decrease reaction time from hours up to days currently. Ionic liquids, a new innovative class of materials, are synthesized using microreaction technology. Possible application fields are their use as electrolytes for the elaborate deposition of metals. A concept for regeneration of the electrolyte is also considered. 

Efforts have been made to accelerate the reaction. Ionic liquids can be obtained in < 1 min using microwave-assisted preparation, and ultrasound-assisted synthesis leads to the rapid isolation of ionic liquids with high chemical purity. If a microwave reactor with reaction condition control mechanisms is used, ionic liquids can be conveniently prepared even on a large scale (up to 2 moles), both in high yields and with short reaction times. ... 

On the contrary, in ionic liquids, the isolation and purification after the graft polymerization was easily achieved, because untreated monomer can be removed under high vacuum as well as solvent-free dry-system Therefore, it is expected that we can achieve scale-up and environmentally friendly synthesis of polymer-grafted nanoparticles by use of ionic liquid. 

Therefore, the reduction of waste solvent and environmentally friendly scale-up synthesis of polymer-grafted nanoparticles can be achieved by use of ionic liquid as a reaction solvent. 

The reduction of waste solvent was achieved by use of ionic liquid as reaction solvent, because unreacted monomer could be removed under high vacuum after the reaction and the reuse of ionic liquid was easily achieved. Therefore, the graft polymerization onto nanoparticle surface in ionic liquid enables environmentally friendly scale-up synthesis of polymer-grafted nanoparticles. 

Based on the practical experience of the working group in Jena in recent years, this chapter is mainly devoted to a selection of our own results. Figure 2.21 illustrates step-by-step scale-up for synthesis of the innovative compound family ionic liquids [88, 89]. 

At 100 °C no product was ever observed. At 150 °C the imidazolium-based ionic liquids could be prepared. For ionic liquids bearing pyridinium cations a reaction temperature of 200 °C was required. The reactions could be scaled up to 50 g and no large excess of alkyl halide was needed. Deetlefs and Seddon studied the synthesis of pyrazolium, thiazolium, imidazolium, and pyridine-based ionic liquids [21]. Selected results are summarized in Table 7.1. The authors reported that the reactions are up to 72 times faster than when using conventional heating. They also found that if the microwave irradiation is prolonged, decomposition of the ionic liquid occurs. Imidazolium halide based ionic liquids could be prepared in 150,... 

S. Safaei, I. Mohammadpoor-Baltork, A.R. Khosropour, M. Moghadam, S. Tangestaninejad, V. Mirkhani, R. BCi, Application of a multi-SOsH Bronsted acidic ionic liquid in water a highly efficient and reusable catalyst for the regioselective and scaled-up synthesis of pyrazoles under mild conditions, RSC Adv. 2 (2012) 5610-5616. 

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