Development of clean technology for the production of triols

Abstract

An alternative clean production technology was developed for the synthesis of two triols, trimethylolpropane (2,2-di(hydroxymethyl)butan-1-ol) and trimethylolethane (2,2-di(hydroxymethyl)propan-1-ol) starting from formaldehyde, propionaldehyde and butyraldehyde; the technology is based on the use of solid heterogeneous catalysts in the key process steps, aldolization and aldol hydrogenation. Catalyst screening and kinetic experiments with propionaldehyde and butyraldehyde showed that the desired aldols can be obtained with a high yield and selectivity when anion exchangers with amine groups are used as heterogeneous catalysts and the reaction is carried out in aqueous environment. Suitable reaction temperatures are 50–80 °C with formaldehyde∶propion or butyraldehyde ranging from 3∶1 to 4∶1. In the second process step, the excess of formaldehyde was separated from the reaction mixture with atmospheric distillation in the presence of excess of water. Catalyst screening and kinetic experiments showed that nickel–chromium and copper–chromium are the most suitable catalysts for the aldol hydrogenation. The experiments carried out at 50–80 °C and 40–80 bar hydrogen gave 100% yields of trimethylolpropane and trimethylolethane. A process scheme for the continuous production of trimethylolpropane and trimethylolethane was proposed.