A novel process for continuous hydroformylation in CO2-expanded liquids (CXLs) is demonstrated using bulky phosphite ligands that are effectively retained in the stirred reactor by a nanofiltration membrane. The reactor is operated at 50 degrees C with a syngas pressure of 0.6 MPa to avoid CO inhibition of reaction rate and selectivity. The nanofiltration pressure is provided by approximate to 3.2 MPa CO2 that expands the hydroformylation mixture and increases the H-2/CO ratio in the CXL phase resulting in enhanced turnover frequency (approximate to 340 h(-1)), aldehydes selectivity (>90%) and high regioselectivity (n/i approximate to 8) at nearly steady operation. The use of pressurized CO2 also reduces the viscosity in the CXL phase, thereby improving the mass-transfer properties. Constant permeate flux is maintained during the 50 h run with Rh leakage being less than 0.5 ppm. This technology concept has potential applications in homogeneous catalytic processes to improve resource utilization and catalyst containment for practical viability. (c) 2013 American Institute of Chemical Engineers AIChE J, 59: 4287-4296, 2013