How Chain Transfer Leads to a Uniform Polymer Particle Morphology and Prevents Reactor Fouling

The effect of adding diethyl zinc as a chain transfer agent during the polymerization of propylene in heptane performed at 80 degrees C was studied. Although it was expected that the chain transfer would stop after precipitation of the polymer, the polymer molecular weight continued to increase throughout the whole of the polymerization. The presence of diethyl zinc had an additional effect that the polymerizations were devoid of reactor fouling. To unravel this phenomenon, the polymer particle morphology was studied. Under the conditions applied, surprisingly, uniform platelet-shaped polymer particles were formed. At high polymer content, these particles aggregate into microfibrillar structures consisting of nematic columnar strands of the same uniform platelets. The polymer particle morphology, as a result of controlled crystallization, is believed to play a crucial role in preventing reactor fouling

Scale-up of microtechnology for fuel processing applications: comparison between fixed-bed and microchannel reactor systems

Microreactor (microchannel) technology and conventional (fixed-bed) reactor technology for the case of methanol fuel processing were studied. The microreactors were designed using dedicated microreactor models including heat conduction in the microstructured plates and mass transfer limitations in the coated catalyst layer on the microchannel walls. These microreactor designs outperformed the conventional fixed-bed designs, leading to significantly lower reactor volumes and weights. The scaling factors of reactor volume and reactor weight were larger for the microreactor systems as for the conventional fixed-bed systems, indicating that at larger scales the fixed-bed reactors will ultimately outperform the microreactor designs. Microreactor technology may be a viable alternative for conventional reactors for the design of relatively small-scale reactors in which heat exchange is important. Furthermore, the use of a fuel processor and fuel cell system showed a clear weight benefit over other fuel cell systems in applications where a large energy storage capacity is required. This is an abstract of a paper presented at the 2006 AIChE Spring Annual Meeting (Orlando, FL 4/23-27/2006)

Selective oxidation of carbon monoxide in a hydrogen-rich fuel cell feed using a catalyst coated microstructured reactor

Carbon monoxide is known to be poisonous to the proton exchange membrane fuel cell catalyst. Selective oxidation of carbon monoxide in a hydrogen-rich reformate stream is considered to be a practical method with the most potential for reducing concentrations down to tolerant levels. In the present work, nine different noble metal catalysts were investigated using a microstructured reactor in the presence of excess hydrogen and carbon dioxide at a GHSV of 15 500 h-1 and at temperatures up to 160 °C. The most active were Pt–Ru/¿-Al2O3, Rh/¿-Al2O3 and Pt–Rh/¿-Al2O3 yet the most stable was Pt–Rh/¿-Al2O3. Its activity was also investigated using a wet feed and also at a GHSV of 31 000 h-1. Water was found to promote the catalyst activity while at higher GHSV higher temperatures were required to achieve full carbon monoxide conversion. The catalyst exhibited steady performance in the microstructured reactor for 50 h while reducing 1.12% carbon monoxide to 10 ppm with inlet oxygen to carbon monoxide ratio of 4

The Effect of Reactor Conditions on High-Impact Polypropylene Properties and Gas Phase Polymerization Kinetics

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