Gernot Nell, Parr Instrument Deutschland GmbH
Katrin Böhm, CAT Catalytic Center
The utilisation of CO2 as a feedstock for chemical syntheses has been envisioned by chemists for a long time. However, its chemical inertness and the high activation energy prohibited many straightforward routes to generate value-added products from CO2 so far. Recent developments in high-performance catalysts have finally allowed the fine-tuning of process conditions under which CO2 forms technically relevant co-polymers with epoxides. Monitoring the process allows to optimise the recipe in terms of feeding intervals, temperature profile etc. Due to the demanding process conditions - elevated pressure, gas-liquid regime - only an in situ technique can gather true information on the composition and behaviour of the reacting mixture.
How to force CO2 into chemical reactions
From a thermodynamic and kinetic perspective, CO2 is a rather challenging reactant due to its high inertness. Activating CO2 for chemical reactions requires sophisticated catalysts that sufficiently weaken one of the C=O bonds. Thus, CO2 and epoxides form copolymers with polyether and carbonate units in the presence of double metal cyanide (DMC) catalysts.
An appropriate selection of the catalyst can steer the copolymerisation into the desired direction.