BASIL™—BASF’s Processes Based on Ionic Liquids

By: Dr. Matthias Maase, Dr. Klemens Massonne, Dr. Uwe Vagt, Chemfiles Volume 5 Article 6

BASF Aktiengesellschaft, 67056 Ludwigshafen, Germany,

Currently, the most important application of Ionic Liquids described is their use as reaction media for chemical processes. A major breakthrough was reached with BASF’s introduction of the first application on a commercial scale: the BASIL™-process, which received the “Innovation for Growth Award 2004” of ECN.

Many chemical processes produce acids as by-products—most commonly hydrochloric acid (HCl). In those cases where the reaction product has to be protected from decomposition or other side reactions, the acid needs to be scavenged. Usually, tertiary amines such as triethylamine are added to the reaction mixture, generating an ammonium salt. In many cases, this ammonium salt can be removed via an aqueous extraction phase. In the case of reaction mixtures that are sensitive to water, the situation is more complicated. The generation of ammonium salts leads to the formation of a slurry during the reaction. The slurry formation results in a number of disadvantages: highly viscous solutions, limited heat transfer, and the ammonium salt has to be separated by filtration.

This was exactly the situation BASF faced in the production of diethoxyphenylphosphine, a photoinitiator intermediate prepared by reaction of dichlorophenylphosphine with ethanol. HCl had to be removed from the reaction mixture or the product would have undergone an unwanted side reaction. An aqueous extraction phase would have led to hydrolysis of the desired product and therefore the reaction had to be carried out in a non-aqueous medium in the presence of equimolar quantities of triethylamine. The resulting mixture was a thick, nearly non-stirrable slurry. While attempting to improve this unfavorable process, the idea came up: “If an acid has to be scavenged with a base, the formation of a salt cannot be avoided; but why not form a liquid salt, an Ionic Liquid?”

Instead of triethylamine, 1-methylimidazole was used as an acid scavenger and immediately led to excellent results. The Ionic Liquid formed in the reaction was methylimidazolium chloride. Methylimidazolium chloride has a melting point of 75 °C and, therefore, is a liquid at the reaction temperature of approx. 80 °C.

After the reaction, there are two clear liquid phases that can easily be worked up by a simple phase separation. The upper phase is the pure product and no reaction solvent is needed. The lower phase is the pure Ionic Liquid and can be deprotonated with sodium hydroxide, regenerating the methylimidazole.

1-Methylimidazole was doing a wonderful job in scavenging the acid, but in the very first lab trials another exciting observation was made. The Ionic Liquid functioned as a nucleophilic catalyst. The combined effect is a tremendous increase in the yield per unit volume time from 8 to 690,000 kg m-3h-1. This enabled BASF to carry out the reaction, which previously needed a 20 m3 batch vessel, in a little jet reactor the size of a thumb. This little reactor is part of a continuously operated plant with a capacity of more than 1000 t/a. The plant went on stream in Q3/2004 at BASF’s Ludwigshafen site.

This BASIL™-technology for scavenging acids has been applied for esterifications, acylations, silylations, phosphorylations, sulfurylations, eliminations, deprotonations, and acid removals in general in lab trials. BASF, having gained experience with this process from lab to commercial scale up today, is in a position to offer this process for licensing to others with a full package of services.

An additional process already developed in pilot plant scale at BASF is the chlorination of alcohols with HCl in the presence of methylimidazolium chloride. The chlorination reaction is normally carried out with the use of phosgene or thionyl chloride as chlorinating agents. In the presence of the Ionic Liquid, the Cl- is apparently a much stronger nucleophile and, therefore, makes it possible to carry out the chlorinations in an easier and more cost-efficient method.

Ionic Liquids also show advantages in separation processes, such as azeotropic or extractive distillations. In separation processes, they are used as entrainers or as solvent for the extraction of phenols.

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