Direct Synthesis of Ethylene Glycol by Use of Rh4(C0)12-N-methy1-2pyrrolidone Catalyst System under High Pres s ure of CO and H2

Abstract

The direct synthesis of ethylene glycol (EG) from carbon monoxide and hydrogen with Rh4(C0)12-N-methyl-2-pyrrolidone (NMP) catalyst system is described. The reactions w ere carried out at temperatures of 190-270°C and pressures of 400-4800 kgicrii2. 'Oxygenated compounds such as methanol (MeOH), 1, 2-propanediol (PD), glycerol (GL), methyl formate (MF), ethylene glycol monoformate (EGMOF), ethanol (EtOH), and propyl alcohol were formed as the by-product.
The yield of EG and Me0H increased as the reaction pressure increased and showed a maximum at about 1200 kg/cm^' of CO and H². On the contrary, the yield of PD and GL increased with increasing the pressure. Increasing reaction temperature increased the ratio of EGMOF selectivity to EG selectivity and increased also the selectivity to MF and EtOH. Increasing catalyst concentration diminished the selectivity to EG and increased that to Me0H.
The influence of addition of NMP on Rh, (C0)12-toluene and Rh4(CO)¹²-tetraglyme catalyst systems which give MF and Me0F1 as the major product was investigated. The addition of NMP suppressed the formation of Me0H and MF and gave a remarkable effect on the activity and selectivity for EG formation. It was suggested that NMP served to improve the stability of the catalyst and to accelerate the formation of mononuclear Rh species from the catalyst precursor Rh4(C0)12. It was also suggested that NMP contributed advantageously to the formation of a Rh-CH2OH intermediate compared with that of a Rh-OCH³ intermediate and promoted insertion of CO into the Rh-C bond of the Rh-CH2OH intermediate.
A possible reaction path of the products is discussed.