Phosgen-freier Zugang zu Isocyanaten : Untersuchung der Spaltung von 2,4-Toluol dimethyl dicarbamat (TDC) zu 2,4-Toluol diisocyanat (TDI) in einem kontinuierlichen Rührkesselreaktor

• Phosgene-free access to isocyanates : Investigations on the cleavage of 2,4-toluene dicarbamate (TDC) to 2,4-toluene diisocyanate (TDI) in a continuous stirred tank reactor

Erdkamp, Eric; Liauw, Marcel (Thesis advisor); Leitner, Walter (Thesis advisor)

Aachen : RWTH Aachen University (2021, 2022)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2021

Abstract

The cleavage of aromatic carbamates with the final application in a continuous reactor was investigated for this thesis. First, potential solvents were tested in experiments with the model substrate N-methyl phenyl carbamate in a mmol-scale set-up. As a result, sulfolane and diphenyl ether (DPE) were chosen for further experiments. In the next step the cleavage of the target substrate toluene dicarbamate (TDC) to the bifunctional 2,4-toluene diisocyanate (TDI) was performed at different reaction temperatures in the mmol-scale set-up. In summary, the TDC cleavage achieves significant yields above 200°C. Furthermore, the selectivity towards isocyanates is decreased above 240 °C, as the isocyanate products are decomposed into carbodiimids. Besides the screening of reaction conditions in the mmol-scale set-up, a kg-scale continuous stirred tank reactor (CSTR) was designed based on previous work. In the first place, batch experiments were performed with the model and the target system. In both cases the results were reproducible. However, the carbamate conversion and the yield of isocyanate were decreased in comparison to the mmol-scale set-up. As a consequence of difficulties with the separation of the product-containing gas phase utilizing the model substrate, only the target system was transferred into continuous operation. To achieve significant conversions in continuous reactions high temperatures, long residence times and high amounts of stripping gas (Ar) were necessary. Best results were achieved at 228 °C reactor temperature, an average residence time of 350 minutes and an elevated stripping gas flow of 120 L/h. Furthermore, the yield of the target product TDI is limited, due to the complexity of the reaction network and the formation of urea side products. The majority of the converted TDC is detected as isocyanate in the product mixture, but mostly mono isocyanate intermediate products are formed. Besides, the reaction is very selective and only urea species occured as side products. In the final section, a model for the TDC conversion at the steady state of a continuous reaction was calculated based on kinetic data from mmol-scale experiments. The results were comparable to the experiments, although the model expected slightly higher conversions than the experiment achieved.