Regeneration ionic liquid

The regenerated ionic liquid phase was investigated dectrochemically to determine its quality. Cyclic voltammetry was performed using a rotating platinum disk electrode (500 rpm), a platinum counter electrode and a platinum wire as (quasi ) reference electrode placed closed to the rotating disk. 

In the fresh electrolyte a first anodic step starts at 1500 mV. This could be a hint for chloride impurity. Since this signal almost vanished for the regenerated ionic liquid, it can be assumed that the procedure presented is suitable also for purifying fresh ionic liquids. 

Fig. 11.21 Cyclic voltammograms of original and regenerated ionic liquid [BMP]Tf2N)). The potential was determined vs. Pt as quasireference electrode. Scan rate 5 mVs 1.

This may be attributed due to the ability of [MOEMIM][TFA] to hydrogen bond with aromatic/heterocyclic/l,2-phenylenediamine. Smdies for recyclability of the regenerated ionic liquids cleared that the yield of the products decreases in various cycles, yet ionic liquid can be reused with significant success. The absence of catalyst and recyclability of ionic liquid make this procedure cleaner and promising for scale-up. 

Raston has reported an acid-catalyzed Friedel-Crafts reaction [89] in which compounds such as 3,4-dimethoxyphenylmethanol were cyclized to cyclotriveratrylene (Scheme 5.1-57). The reactions were carried out in tributylhexylammonium bis(tri-fluoromethanesulfonyl)amide [NBu3(QHi3)][(CF3S02)2N] with phosphoric or p-toluenesulfonic acid catalysts. The product was isolated by dissolving the ionic liq-uid/catalyst in methanol and filtering off the cyclotriveratrylene product as white crystals. Evaporation of the methanol allowed the ionic liquid and catalyst to be regenerated. 

Scheme 4.3 Regeneration of Ni-H active species in ionic liquid...

In contrast, we intend to demonstrate the principle aspects of catalyst recycling and regeneration using the ionic liquid methodology. These aspects will be explored in more detail for the example of Rh-catalysed hydroformylation (see Section 7.2). First, however, we will briefly introduce important general facts concerning transition metal catalysis in ionic liquids (see Section 7.1.2). This will be followed by a consideration of liquid-liquid biphasic reactions in these media from an engineering point of view (see Section 7.1.3). 

On the base of a Rh-price of about 20,000 /kg and a ligand price of about 1000 /kg it becomes quite obvious that the loss of the ionic liquid would only be a minor part of the overall cost arising from the case of complete SILP-catalyst deactivation. It should be noted that a deactivated SILP catalyst may still offer some options for regeneration (e.g. extraction with scC02 to remove heavies). However, these options are not yet developed and their efficiency is unclear at this point. 

Phillips, D.M., Drummy, L.F., Naik, R.R., Trulove, P.C., De Long, H.C., and Mantz, R.A. "Silk regeneration with ionic liquids". Abstracts of Papers of the American Chemical Society... 

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. 

Towards Regeneration and Reuse of Ionic Liquids in Electroplating 319... 

However, it can be assumed for most electrochemical applications of ionic liquids, especially for electroplating, that suitable regeneration procedures can be found. This is first, because transfer of several regeneration options that have been established for aqueous solutions should be possible, allowing regeneration and reuse of ionic liquid based electrolytes. Secondly, for purification of fiesh ionic liquids on the laboratory scale a number of methods, such as distillation, recrystallization, extraction, membrane filtration, batch adsorption and semi-continuous adsorption in a chromatography column, have already been tested. The recovery of ionic liquids from rinse or washing water, e.g. by nanofiltration, can also be an important issue. 

Possibility of regeneration, recycling and reuse of the ionic liquid... 

In general, recyclability is crucial for the design of sustainable chemical processes [83]. The aspect that should be elaborated here is the possibility of regeneration and reuse of the ionic liquid, depending on the type of impurity and the sensitivity of the specific application towards contamination. 

Despite the huge number of publications dealing with the application of ionic liquids, there are only a couple that include reuse aspects. To the best of our knowledge, there is none that deals with regeneration of spent ionic liquid based electrolytes. The intention of this contribution is to bridge this gap and suggest potential concepts for ionic liquid regeneration. 

In this chapter, an introduction to the principles of regeneration as they have been developed in the field of water-based electroplating is given. With this background, a discussion of the purification options for ionic liquids is presented, followed by a first case study. 

Other unit operations that have been established for aqueous solutions could be considered, to allow regeneration and reuse of ionic liquid based electrolytes. 

Actually, as can be seen in the following section, several of the separation methods mentioned above have already been tested in the purification of at least fresh ionic liquids. However, there is still some development necessary to come up with sustainable regeneration emits. 

Every single regeneration problem has to be analysed individually, however, the following case study demonstrates how a selection of separation techniques, extraction and phase separation, can successfully be applied to regenerate a spent ionic liquid based electrolyte satisfactorily. As a case study the electrolyte 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide ([BMP]Tf2N) was chosen, which is used for electrodeposition of aluminum as described in the literature [137, 138],... 

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