An industrial view on the dynamic operation of chemical converters

Abstract The present status and prospects for further implementation of dynamic reactor operation are critically discussed from the industrial viewpoint. In addition to a ‘state-of-the-art’ review, several promising ideas for the improvement of commercial-scale reactors are presented. The influence of forced non-stationary conditions on both homogeneous and heterogeneous reaction systems has been reported extensively in the literature for many different reactions. Significant effects on the reaction rates or chemical pathways were sometimes found experimentally or predicted for specific systems by model simulations. Commonly, feed concentrations and flow rates, flow direction and temperature were subject to (periodic) induced changes in those studies. For industrial application, the savings in raw materials, energy or equipment must outweigh the drawbacks associated with the replacement of a stationary production line by a non-stationary (e.g., periodic) one. Industrial examples of intentional dynamic reactor operation are still very scarce. The reverse flow operation proposed by Matros has been introduced and demonstrated technically in Russian industry several years ago. Other than some solvable technical and safety uncertainties, it is mainly the overall process economics that hamper the introduction of this elegant technology in commodity production under the circumstances of a free-market economy. On the other hand, in various heterogeneous reactors even under ‘overall’ stationary operation conditions the catalyst particles experience periodic changes in conditions. Examples of such situations are some industrial fluid-bed gas-phase oxidations and also hydrogenations conducted in circulated slurry bubble columns. There is potential for further improvement of such industrial converters. In our laboratories, experimental and modelling studies have been carried out to explore the improvement potential for existing plants through forced periodic reactor operation. Reversed-flow technology has been considered extensively. Also, a study focusing on improving the selective hydrogenation of phenylacetylene to styrene in a co-current upflow packed bubble column has been conducted. With a periodic hydrogen feed, at a high selectivity virtually complete conversion could be achieved in a laboratory-scale reactor. The performance of such periodic reactor was clearly better than that of its stationarily operated equivalent, but due to the lack of a basic understanding of the effects which occur there is still no reliable basis for scale-up. Recently, the VVO ( = variable volume operation) of a single-phase synthesis with complex kinetics has been simulated. It appears that the conventional stationary process operated in a series of continuous ideally stirred tank reactors (CISTRs) can be improved.

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