Homogeneous Catalysis and the Role of Multiphase Operations

Catalysis is thus a driver for sustainability and societal challenges [51] and for a sustainable energy [52, 53[. New demand for applications (e.g., the area of biorefineries [54, 55[) and new advances in both the ability to control catalyst characteristics through nanotechnologies [56, 57[ and to understand catalytic reactions [58-62] have greatly renewed the interest in catalysis and changed the research topics and approaches with respect to few years ago. We could thus conclude that catalysis is not only a key element for the sustainability of chemical processes but also that the recent advances in this area have further enhanced its critical role. 

Several large-scale industrial processes use homogeneous catalysts [e.g., hydrofor-mylation, hydrocyanation (DuPont), ethene-oligomerization (SHOP), acetic add (Eastman Kodak), acetic acid anhydride (Tennessee-Eastman), acetaldehyde (Wacker) and terephthalic acid (Amoco)] as well as smaller scale applications [e.g., metolachlor (Novartis), citronellal (Takasago), indenoxide (Merck) and glycidol (ARCO, SIPSY)]. 

However, homogenous catalysts are stUl far less used on an industrial scale than heterogeneous catalysts, despite the great advantages in terms of selectivity and possibility of fine tuning of performance (e.g., by changing the ligands), for two main reasons (i) cost of catalyst recovery and (ii) low turnover per reactor volume, for example, productivity. The latter aspect is often not considered. 

Homogeneous catalysts, in addition, often pose problems of safety of preparation, which also increase the costs. 

As discussed later regarding the role of multiphase operations for homogeneous catalysis, research has been focused mainly on the issue of recyclability of homogeneous catalysts. Relevant progress has been made in this aspect, but the other problem, which could be indicated as intensification of homogeneous catalysis processes, is the issue that should be solved, at least for medium-large scale industrial productions. 

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