Industrial use of ionic liquids

What can drive the switch from existing homogeneous processes to novel ionic liquids technology One major point is probably a higher cost-effectiveness. This can result from improved reaction rates and selectivity, associated with more efficient catalyst recovery and better environmental compatibility. 

The cost of ionic liquids can, of course, be a limiting factor in their development. However, this cost has to be weighed against that of current chemicals or catalysts. 

If the ionic liquid can be recycled and if its lifetime is proven to be long enough, then its initial price is probably not the critical point. In Difasol technology, for example, ionic liquid cost, expressed with respect to the octene produced, is lower than that of the catalyst components. 

The manufacture of ionic liquids on an industrial scale is also to be considered. Some ionic liquids have already been commercialized for electrochemical devices (such as capacitors) applications [45]. 

Chloroaluminate laboratory preparations proved to be easily extrapolated to large scale. These chloroaluminate salts are corrosive liquids in the presence of protons. When exposed to moisture, they produce hydrochloric acid, similarly to aluminium chloride. However, this can be avoided by the addition of some proton scavenger such as alkylaluminium derivatives. In Difasol technology, for example, carbon-steel reactors can be used with no corrosion problem. 

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Ionic liquids will never find application in industry , I don t understand this fad for ionic liquids and there is no widespread interest in these systems are just three of quotes from the reports of referees for research proposals that I have received over the years. I wonder what these people think today. There are currently at least nine large-scale industrial uses of ionic liquids, including, we now recognise, the production of e-Caprolactam (a monomer for the production of nylon-6) [1], There has been a steady increase in the interest in ionic liquids for well over a decade and last year the number of papers and patents including ionic liquids was counted in the thousands. This remarkable achievement has been built on the hard work and enthusiasm, first of a small band of devotees, but now of huge numbers of scientists all over the world who do not see themselves as specialists in ionic liquids. 

To be applied industrially, performances must be superior to those of existing catalytic systems (activity, regioselectivity, and recyclability). The use of ionic liquid biphasic technology for nickel-catalyzed olefin dimerization proved to be successful. 

The aspects of medium engineering summarized so far were a hot topic in biocatalysis research during the 1980s and 1990s [5]. Nowadays, all of them constitute a well-established methodology that is successfully employed by chemists in synthetic applications, both in academia and industry. In turn, the main research interests of medium engineering have moved toward the use of ionic liquids as reaction media and the employment of additives. 

However, little has entered the public domain concerning the use of ionic liquids on an industrial scale, and nothing has been claimed, even in general terms, to suggest that room-temperature ionic liquids are being used in a viable chemical process being operated commercially. Recent emphases on ionic liquid research and applications could change this. 

Other groups are working on the use of ionic liquids for chemical and industrial processes. In order to push the development of the industrial application of ionic liquids, a European consortium was formed several years ago (Seddon, 1999). This three-year arrangement between academics and industry has three major goals ... 

The use of ionic liquids in most applications is stiU in development. The chemical industry in Europe is showing increasing interest in them, particularly for olefin dimerizations and Friedel-Crafts reactions. A two-phase loop reactor has been designed for large-scale preparations which allows for continuous reaction, separation of the product, and recycling of the ionic liquid (Chauvin and Helene, 1995). 

Davis, J. H., Jr. Working salts syntheses and uses of ionic liquids containing functionalized ions. In Ionic Liquids Industrial Applications for Green Chemistry, eds. 

The biggest obstacle to the widespread use of ionic liquids is their cost. Normal organic solvents used in industry typically cost a few cents per liter, but ionic liquids can cost hundreds of times that amount. However, the environmentally friendly nature of ionic liquids (they produce no vapors because the ions are not volatile) and the flexibility of these substances as reaction media make them very attractive. As a consequence, efforts are under way to make their use economically feasible. 

Many petrochemical companies hold extensive patent portfolios relating to ionic liquid technologies. However, the first of these to announce an industrial process is PetroChina. The process for alkylation of isobutene uses an alumi-nium(iii) chloride based ionic liquid and is called lonikylation. After success at the pilot plant stage, the technology is currently being retrofitted into an existing sulfuric acid alkylation plant in China with an output of 65 000 tonnes per year. This retrofit will increase yield and capacity at the site and is the largest commercial use of ionic liquids reported to date. ... 

The work from Sheldon s group [10] was the first to present the use of ionic liquids in the enzymatic synthesis of esters. Since then, there have been many reports on biosynthesis of esters in ionic liquids. De los Rios et al. [64,65] synthesised a wide range of aliphatic organic esters, commonly used in the perfumery, flavour and pharmaceutical industries, by transesteriflcation from vinyl esters and alcohols catalysed by free CaLB in different 1,3-dialkylimidazolium-based ILs (Fig. 7.2). They analysed the effects of the alkyl chain lengths of the acyl donor and the alcohol. The optimum (C6 for acyl donor and C4 for alcohol) chain lengths were found because the activity decreased with further increase in alkyl chain length. The authors attributed the enzyme behaviour to a substrate modulation mainly due to the different affinity of the lipase towards the different substrates and steric hindrance and denaturalisation by small alcohol molecules. 

The use of ionic liquids (also called molten or fused salts) as reaction media is a relatively new area, although molten conditions have been well established in industrial processes (e.g. the Downs process. Figure 10.1) for many years. While some molten salts are hot as the term suggests, others operate at ambient temperatures and the term ionic Uquids is more appropriate. This section provides only a brief introduction to an area which has implications for green chemistry (see Box 8.3). 

During the 1990s, two truly novel green approaches to industrial solvents began to mature. One of these involves tbe use of ionic liquids and tbe other supercritical carbon dioxide. The term ionic liquids almost suggests an oxymoron (internal inconsistency). One normally... 

Intellectual property is also a concern in the future development of ionic liquids. Given that one of the main targets of these solvents is use in industrial processes, a relatively large number of patents are already protecting this field. Patents cover mainly (1) the preparation and/or new types of ionic liquids and (2) the use of ionic liquids as materials (solvent, catalyst, extraction medium, etc.). 

Ionic liquids appeared as novel liquid system for the chemical industry. The scope of ionic liquids has been broadly extended into many areas as IL can reduce environmental impacts and that lead to more energy-efficient applications. With this tremendous development of LLs together with various commercially available ionic liquids in different scales, the industrial applicability of ionic liquids has begun. However, the industrialization of IL technology into different applications is rather slow. There are huge amount of patents and publications which have appeared during last decade and often describe numerous applications such as catalysis, separation, and so on. For the industrial use of ILs, some major issues must be addressed which are barriers to IL process commercialization (Table 20.2). 

An effective assessment of the use of ionic liquids as solvents in commercial liquid-liquid extraction and extractive distillation processes requires consideration of numerous factors associated with the thermo-physical and chemical properties of ionic liquids as well as the economical and environmental impact of the use of ionic liquids in the chemical and petrochemical industry. 

Solvents for chromatography, for electrochemistry, or for titrimetric analysis of weak acids or bases all must satisfy appropriate criteria. Enzymatic reactions have special requirements, some of which are surprising to the uninitiated, who may assume that biochemistry is always aqueous chemistry. Freemantle (2000) cites industrial research into the use of ionic liquids as media for enzyme-catalyzed reactions. 

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