SILP Catalysis – An Innovative Concept for Benign Continuous, Solvent-free Processes using Ionic liquids
Sustainable process-product development & green chemistry
Green Organic Synthesis Routes (T1-2)
Keywords: supported ionic liquids, homogeneous catalysis, continuous reactions
In recent years, non-volatile room-temperature ionic liquids (mixed organic-inorganic salts) have proven to be very versatile solvents for organic synthesis and for immobilizing of homogeneous catalysts in two-phase organic liquid-liquid reactions, due to their tunable properties by various cation-anion combinations [1]. As a consequence, significant interest to implement catalysts based on ionic liquids into technical applications has arisen from chemical industry [2]. However, for industrial utilization a solid catalyst is usually preferred instead of liquid catalyst systems due to the ease of catalyst separation by filtration and the possibility for applying fixed-bed technology leading to, e.g. continuous-flow operation mode, avoidance of solvent handling and tedious – but required - catalyst recycling.
Inspired by the demand for solid, ionic liquid-based catalyst systems we have in the last years contributed to the development of novel homogeneous catalyst systems comprised of ionic liquids containing transition metal complexes on porous high-area supports, i.e. Supported Ionic Liquid-Phase (SILP) catalysts [3,4]. In SILP catalysts the reaction takes place in the diffusion layer of the highly dispersed ionic liquid catalyst phase, thereby offering significant advantage of relatively short diffusion distances compared to conventional two-phase catalysis and an efficient use of the catalyst components. Moreover, SILP catalysts benefit from unique advantages which are not provided by analogous supported catalyst systems containing traditional solvents (i.e. SLP catalysts) such as, e.g. non-volatility, large thermal-/liquid-phase window and adjustable properties. Consequently, processes applying SILP catalysts can be conducted at flexible reactions conditions using preferred fixed-bed reactor designs in continuous-flow operation mode, thus offering simple and complete product separation under solvent-free conditions.
In this work, catalytic and spectroscopic results obtained from our studies of Rh-complex based SILP catalysts for fixed-bed, gas-phase hydroformylation of C3-C5 alkenes [4,5] and methanol carbonylation [6] will be highlighted. Furthermore, prospective examples of processes with high technical potential implying Rh-SILP catalyst in cascade reactions will be introduced.
[1] P. Wasserscheid and T. Welton (Eds.), Ionic Liquids in Synthesis, Wiley-VCH, 2003.
[2] R.D. Rogers and K.R. Seddon, Science 2003, 302, 792.
[3] C.P. Mehnert, Chem. Eur. J. 2005, 11, 50.
[4] A. Riisager, R. Fehrmann, M. Haumann and P. Wasserscheid, Eur. J. Inorg. Chem. 2006, 695 and cited references.
[5] M. Haumann, K. Dentler, J. Joni, A. Riisager and P. Wasserscheid, Adv. Synth. Catal. 2007, in press.
[6] A. Riisager, B. Jørgensen, P. Wasserscheid and R. Fehrmann, Chem. Commun. 2006, 994.
Presented Tuesday 18, 15:00 to 15:20, in session Green Organic Synthesis Routes (T1-2).
