Operating continuous catalyst regeneration

Dehydrogenation of /i-Butane. Dehydrogenation of / -butane [106-97-8] via the Houdry process is carried out under partial vacuum, 35—75 kPa (5—11 psi), at about 535—650°C with a fixed-bed catalyst. The catalyst consists of aluminum oxide and chromium oxide as the principal components. The reaction is endothermic and the cycle life of the catalyst is about 10 minutes because of coke buildup. Several parallel reactors are needed in the plant to allow for continuous operation with catalyst regeneration. Thermodynamics limits the conversion to about 30—40% and the ultimate yield is 60—65 wt % (233). 

The CCR Meta-4 process features are a hard, highly active and robust catalyst, low catalyst inventory, low operating temperature and pressure, outstanding yields, liquid-phase operation, and continuous operation and catalyst regeneration. 

The fluidized reactor system is similar to that of a refineiy FCC unit and consists of riser reactor, regenerator vessel, air compression, catalyst handling, flue-gas handling and feed and effluent heat recovery. Using this reactor system with continuous catalyst regeneration allows higher operating temperatures than with fixed-bed reactors so that paraffins, as well as olefins, are converted. The conversion of paraffins allows substantial quantities of paraffins in the feedstream and recycle of unconverted feed without need to separate olefins and paraffins. 

This catalyst regeneration operation is performed using published processes, examples of which include the use of a fixed bed switching reactor system in the case of the Z-Forming process(l), and the use of a continuous catalyst regeneration system in the case of the Cyclar process(2). However, catalyst activity gradually decreases due to the repeated reaction and regeneration. Catalyst life, therefore, is considered terminated at the point where its activity falls below the point at which it is able to maintain a pre-set aromatic yield. 

This is a very slow reaction under normal reforming operation. Feed composition, temperature, H2/hydrocarbon ratio, and the pressure strongly influence the rate of coke deposition. Modern catalysts produce less coke and allow operation under more severe conditions, such as those used in the cyclic and in the continuous catalyst regeneration (OCR) reformers. The different reforming technologies are briefly described later. 

Moving-bed reactors are preferred when there is a need for continuous catalyst regeneration. In this operation, fresh catalyst is fed from the top of the reactor, and it moves in the downflow direction by gravitational forces. Spent catalyst leaving the reactor at the bottom is usually replaced in the continuous mode. While the catalyst movement is downward, reactive mixture flow can be cocurrent or countercurrent to that of the catalyst flow. 

Since the first catalytic reformers were used in the 1950s the hydrogen/ hy-drocaibon mole ratio and the reformer operating pressure have both been gradually decreased. These developments resulted from improvements in the alumina support, the use of bimetallic catalysts, and finally the introduction of the low-pressure, continuous catalyst regeneration processes. The trends in operation are shown in Table 6.18. 

I. G. Farben also produced butene by butane dehydrogenation. A moving catalyst bed system was used in a tubular reactor. The total catalyst charge was 1.5 tonnes with a residence time of 4 h in the tubes. Yields of 85% at 20-25% conversion were obtained at a liquid space velocity of 2 h and 620°-650°C operating temperature. This was an impressive result for a new reactor design that has now been developed as the continuous catalyst regeneration process and is widely used in refineries. 

Figure 5.38 shows typical continuous catalyst regeneration (CCR) that we will use the build the model in question. We extensively discussed the features and operating issues associated with this type unit in Section 5.2. In the context of this chapter, we also build models for the remixing and hydrogen recontactor section of this flowsheet Tables 5.25 to 5.29 show some typical operating data for this unit... 

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