(315b) Highly Active and Recyclable Hydroformylation Catalysis Using Soluble Polymer Supports In CO2-Expanded Liquids (CXLs)

A process concept that
exploits CXLs to intensify hydroformylation reactions was recently
demonstrated.[1]  When dense CO₂ is used to
partially replace the excess substrate (1-octene) to create a CO₂-expanded
liquid (CXL) phase, the 1-octene hydroformylation turnover frequency (~300 h^-1)
and the selectivity towards the linear aldehyde (~90%) are significantly
enhanced relative to the reaction in neat media. Further, these enhancements
occur at mild pressures (~40 bar) and temperatures (60°C). Preliminary
economic analysis indicates that near-quantitative (>99.8%) recovery of the
Rh-based catalysts is essential for commercial viability.[2]
Toward this end, soluble polymer supported bidentate phosphite ligands for
hydroformylation of higher (> C₄) alkenes have been developed and
evaluated.  The efficient
separation and recycle of homogeneous rhodium catalyst complexes from reaction
mixtures is attempted by using membrane filtration technology in a
high-pressure filtration cell equipped with cross-linked asymmetric polyimide nano-
and ultra- filtration membranes. Experiments with the catalyst complex
dissolved in pure toluene revealed a Rh loss in the permeate of less than 1%
while no P was detectable in the permeate. Similar measurements at actual
hydroformylation conditions are ongoing. The effects of dissolved CO₂
(in the CXL media) on the solution viscosity and the permeate flux will be
discussed. In addition, results on the recyclability and durability of
polymer supported rhodium catalyzed 1-octene hydroformylation in CXLs will be
presented.