Catalysis and extraction using supercritical solutions

The further optimization and development concerning stability and selectivity of the organometallic catalyst in these kinds of media and the application of isolation methodologies similar to CESS (catalysis and extraction using supercritical solutions [43]) together with the physical and chemical advantages of supercritical fluids can lead to high potential catalyst matrices that fulfil the requirements of industrial processes both for bulk and fine chemicals. 

CESS Catalysis and extraction using supercritical solutions... 

Catalysis and Extraction Using Supercritical Solutions (CESS)... 

Leitner reported that lower densities of SCCO2 can be used to extract product from a reaction mixture without coextraction of a homogeneous catalyst. This process, which he called CESS (catalysis and extraction using supercritical solution), was demonstrated with styrene hydroformylation [Eq. (23), ligand L ] and imine hydrogenation [Eq. (22)]. The catalyst was used for three cycles before drops in the conversion and selectivity was observed (101,111,133). Sellin and Cole-Hamilton used catalysts specifically chosen for their insolubility in SCCO2 to facilitate the catalyst/product separation in a CESS process (134). 

SCCO2 has been established recently for the first time these processes have been referred to as catalysis and extraction using supercritical solutions (CESS) [4]. 

Carbon dioxide is a ubiquitous and environmentally benign compound. Several attempts have been made to use it as medium or as support for individual steps of the hydroformylation. The acidic properties of CO2 in solution have been advantageously employed to remove homogeneous catalysts with basic properties from the neutral organic reaction products (see Section A Posteriori Separation of Products and Catalysts ). BASF claimed supercritical carbon dioxide (SCCO2) for the extraction of the so-called heavy ends from low-boiling hydroformylation products and rhodium catalyst [55]. In recent years, also implementations of reactions in compressed carbon dioxide in supercritical or near-critical conditions have attracted particular attention [56]. A first review on the application of supercritical fluids (SFCs) in homogeneous catalysis was authored by Jessop, Ikariya, and Noyori in 1999 [57]. Later on, Leitner and Abraham [58,59] provided updates with special focus on the use of compressed carbon dioxide. 

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