AN INDUSTRIAL VIEW ON THE DYNAMIC OPERATION OF CHEMICAL CONVERTERS

The present status and prospects for further implementation of dynamic reactor operation are critically discussed from the industrial viewpo int. In addition to a 'state-of-the-art' review, several promising ide as 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 l iterature for many different reactions. Significant effects on the rea ction rates or chemical pathways were sometimes found experimentally o r predicted for specific systems by model simulations. Commonly, feed concentrations and flow rates, flow direction and temperature were sub ject to (periodic) induced changes in those studies. For industrial ap plication, the savings in raw materials, energy or equipment must outw eigh the drawbacks associated with the replacement of a stationary pro duction line by a non-stationary (e.g., periodic) one. Industrial exam ples of intentional dynamic reactor operation are still very scarce. T he reverse flow operation proposed by Matros has been introduced and d emonstrated technically in Russian industry several years ago. Other t han some solvable technical and safety uncertainties; it is mainly the overall process economics that hamper the introduction of. this elega nt technology in commodity production under the circumstances of a fre e-market economy. On the other hand, in various heterogeneous reactors even under 'overall' stationary operation conditions the catalyst par ticles experience periodic changes in conditions. Examples of such sit uations are some industrial fluid-bed gas-phase oxidations and also hy drogenations conducted in circulated slurry bubble columns. There is p otential for further improvement of such industrial converters. In our laboratories, experimental and modelling studies have been carried ou t to explore the improvement potential for existing plants through for ced periodic reactor operation. Reversed-flow technology has been cons idered extensively. Also, a study focusing on improving the selective hydrogenation of phenylacetylene to styrene in a co-current upflow pac ked bubble column has been conducted. With a periodic hydrogen feed, a t a high selectivity virtually complete conversion could be achieved i n 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 occ ur there is still no reliable basis for scale-up. Recently, the VVO (= variable volume operation) of a single-phase synthesis with complex k inetics has been simulated. It appears that the conventional stationar y process operated in a series of continuous ideally stirred tank reac tors (CISTRs) can be improved.