Improved microreactor for polymer production
There is a growing demand for polymer production (for example, polyethene) and it is therefore important to optimise their quality and production. Optical microscopy was used for direct measurement of the growth of the polymer in gas-phase ethylene and ethylene-1-hexene. Ziegler-Natta and supported metallocene were the catalysts used. Measuring polymerisation rate profiles helps to overcome averaging over the lifetime of a catalyst but the individual behaviour of single particles can vary significantly from these averages. This can lead to dramatic consequences in an industrial setting. In a worst case scenario, particle melt can occur due to high catalyst activity and limited heat transfer through the particle surface, which can ultimately cause fluid bed collapse. Also possible, due to fines (particles) generation is the destruction of the catalyst. Using micro-reaction technology, different experiments were performed on a particle level. This was done to achieve a better understanding of the processes involved in particle growth, fragmentation and change in the morphology of the particle surface during growth. The experiments were performed under industrial conditions and the results showed good reproducibility. High activity and shape replication were observed for the two catalysts used. Furthermore, it was demonstrated that catalyst particles of the same size and under identical conditions could demonstrate different activities. Also important was the fact that catalyst/polymer particle fragmentation led to the formation of sub-grains that stayed attached to the big particle. Using micro-reaction technology provides vital information and helps to explain many phenomena and to decrease the complexity of the whole process. Improvements at this level mean much less waste and emissions with the possibility of waste disposal by incineration or recycling.
