Catalyst plant scale catalytic reactor

Table I lists the categories of laboratory reactors used for catalyst testing and catalytic process studies, viz., in the order of decreasing size pilot-plant, bench-scale and microflow reactors. Table II compares the feed requirements of some representative examples of these three classes for a typical case of oil hydroprocessing. The large effect of scale is evident whereas the pilot plant consumes monthly amounts of liquid and gas that require supply on a periodic basis by tank car and tube trailers, the microflow needs can be covered by a small drum or can and a few gas bottles. The size of the test reactor does not only have consequences for the logistics of supply, storage and disposal of feeds and products, but can also dictate the scale of preparation of special feedstocks and catalysts.

The catalytic hydrogenation of methyl linoleate was carried out in a laboratory-scale slurry reactor in which hydrogen gas was bubbled up through the liquid and catalyst. Unfortunately, the pilot-plant reactor did not live up to the laboratory reactor expectations. The catalyst particle size normally used was between 10 and 100 pm. In an effort to deduce the problem, the experiments listed in Table E12-5.1 were carried out on the pilot plant slurry reactor at 121°C. 

There were basically two approaches, which were used in the past for HDT process development studies using catalyst in the commercially applied size and shape. The first one, which was followed 30-40 yr ago in various industrial research and development centers, was to test the commercial catalyst in large pilot plants. The second approach was to use a smaller pilot plant and simulate the data generated in these units, applying a suitable hydrodynamic model to predict the performance of a commercial unit. These are generally known as small-scale TBRs. Because of the presence of a liquid phase, the problems in these small TBRs are more complex as compared to those present in other small-scale fixed-bed catalytic reactors handling only vapor phases. 

The MTO process employs a turbulent fluid-bed reactor system and typical conversions exceed 99.9%. The coked catalyst is continuously withdrawn from the reactor and burned in a regenerator. Coke yield and catalyst circulation are an order of magnitude lower than in fluid catalytic cracking (FCC). The MTO process was first scaled up in a 0.64 m /d (4 bbl/d) pilot plant and a successfiil 15.9 m /d (100 bbl/d) demonstration plant was operated in Germany with U.S. and German government support. 

Typical performance is a selectivity higher than 90% at a conversion in the 50-90% range, mainly depending on the type of substrate. Substituted pyridines yield better selectivities at high conversion than the equivalent alkylaromatics. The nature and position of the substituents in substituted alkylaromatics also play an important role in determining selectivity and activity. The commercial application of this technology is mainly hindered by the relatively small plant necessary for these products as compared to full-scale processes. The further implementation of the process of alkylaromatic catalytic ammoxidation would thus require the development of multi-purpose small-size continuous plants using small fluidized bed-reactors (to better control temperature and allow easier substitution of the catalyst). 

It seems that fluid-bed cracking reactor (thermal or catalytic) is the best solution for industrial scale. However, regeneration and circulation of so-called equilibrium cracking catalyst is possible for relatively pure feeds, for instance crude oil derived from vacuum gas oils. Municipal waste plastics contain different mineral impurities, trace of products and additives that can quickly deactivate the catalyst. In many cases regeneration of catalyst can be impossible. Therefore in waste plastics cracking cheap, disposable catalysts should be preferably applied. Expensive and sophisticated zeolite and other molecular sieves or noble-metal-based catalysts will find presumably limited application in this kind of process. The other solution is thermal process, with inert fluidization agent and a coke removal section or multi-tube reactor with internal mixers for smaller plants. 

Example 12-3 A pilot plant for a liquid-solid catalytic reaction consists of a cylindrical bed 5 cm in radius and packed to a depth of 30 cm with 0.5-cm catalyst pellets. When the liquid feed rate is 0.2 liter/sec the conversion of reactant to desirable product is 80%. To reduce pressure drop, a radial-flow reactor (Fig. 12-5) is proposed for the commercial-scale unit. The feed will be at a rate of 5 ft /sec and will have the same composition as that used in the pilot plant. The inside radius of the annular bed is i to be 2 ft, and its length is also 2 ft. What must the outer radius of the bed be to achieve a conversion of 80% ... 

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