Process

The flow diagram of the process is given in Fig 3. The liquid mixture from the reactor is first depressurized. The separation of acetic acid from catalyst components is done by distillation. In the first distillation column, the light ends are removed. In the second distillation column, the acetic acid product is removed at the top and the heavy end at the bottom, containing Rh catalysts, is recycled back to the reactor. Catalyst deactivation is associated with high solution acidity caused by increasing free HI leading to formation of an inactive complex [Rh(CO)₂I₄]⁻.

In this process the following side reactions occur reducing the selectivity of the process.

1. Water is essential for the reaction to occur but at high concentration it can reacts with CO resulting in loss of one of the reactant.

   

2. The other side reaction involves HI which oxidize Rh(I) to Rh(III) iodide which may precipitate from the reaction. It has to be converted back to Rh (I) complex.

Text Reference

• Piet W.N.M. van Leeuwen, Homogeneous catalysis: Understanding the Art, Springer, 2004
• Piet W.N.M. van Leeuwen, and John C. Chadwick, Homogeneous catalysis: Activity-stability –deactivation, Wiley, VCH, 2011
• B. Cornils and W.A. Hermann (Ed.) Applied homogeneous catalysis with organometallic compounds, Wiley-VCH,2000
• H. Bartholomew and R. J. Farrauto, Fundamentals of Industrial catalytic Processes, Wiley, VCH, 2006