Moving catalyst bed

Moving catalyst beds are used in catalytic reactors continuously to remove and replace spent... 

Description This process features moving bed reactors and a continuous catalyst regeneration system coupled with a hard, smoothflowing catalyst. Feed enters the reactor (1), passes radially through the moving catalyst bed, exits at the reactor bottom and proceeds in the same manner through the 2-3 remaining reactors (2). The robust... 

Figure L2 Common reactor types with moving catalyst beds (a) fluid-bed reactor (b) bubble column with suspended catalyst (c) sparged stirred tank with suspended catalyst.

Internal recycle reactors with moving catalyst bed... 

Distributed inflow to a moving catalyst bed of continuously deactivated catalyst accompanied by continuous regeneration... 

Table 12.2 lists the characteristics of the aromatization of C3—C4 paraffins developed at the Institute of Catalysis (IC) SB RAS and similar process developed abroad, such as Cyclar (UOP and BP) and Z-Forming (Mitsubishi Oil). In addition to providing higher yields of the target products (70—72% vs. 60—63%), the IC process has a simpler technological scheme. It is carried out in tubular reactors with a fixed catalyst bed, while the other processes are conducted in reactors with a moving catalyst bed. In 2006, the pilot plant with a production capacity of lOOOton/year [340] was launched into operation. 

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. 

The catalyst is employed in bead, pellet, or microspherical form and can be used as a fixed bed, moving bed, or fluid bed. The fixed-bed process was the first process used commercially and employs a static bed of catalyst in several reactors, which allows a continuous flow of feedstock to be maintained. The cycle of operations consists of (/) the flow of feedstock through the catalyst bed (2) the discontinuance of feedstock flow and removal of coke from the catalyst by burning and (J) the insertion of the reactor back on-stream. The moving-bed process uses a reaction vessel, in which cracking takes place, and a kiln, in which the spent catalyst is regenerated and catalyst movement between the vessels is provided by various means. 

FIG. 23-24 Reactors with moving catalysts, a) Transport fluidized type for the Sasol Fischer-Tropsch process, nonregenerating, (h) Esso type of stable fluidized bed reactor/regeuerator for cracldug petroleum oils, (c) UOP reformer with moving bed of platinum catalyst and continuous regeneration of a controlled quantity of catalyst, (d) Flow distribution in a fluidized bed the catalyst rains through the bubbles. 

Several processes based on non-precious metal also exist. Because of high catalyst deactivation rates with these catalyst systems, they all require some form of continuous regeneration. The Fluid Hydroforming process uses fluid solids techniques to move catalyst between reactor and regenerator TCR and Hyperforming use some form of a moving bed system. 

It is reported [1] that the fluidization quality was drastically decreased when the hydrogenation of CO2 was carried out in a fluidized catalyst bed (FCB). Recently, the phenomena occurring in the bed were directly observed [2] and it was found that the upper part of the emulsion phase was defluidized and this packed particles was lifted up through the column like a moving piston. 

The rate model contains four adjustable parameters, as the rate constant k and a term in the denominator, Xad, are written using the Arrhenius expression and so require a preexponential term and an activation energy. The equilibrium constant can be calculated from thermodynamic data. The constants depend on the catalyst employed, but some, such as the activation energy, are about the same for many commercial catalysts. Equation (57) is a steady-state model the low velocity of temperature fronts moving through catalyst beds often justifies its use for periodic flow reversal. 

Catalytic cracking is a process that is currently performed exclusively over fluidized catalyst beds. The fluid catalytic cracking (FCC) process was introduced in 1942 and at that time replaced the conventional moving bed processes. These early processes were based on acid-treated clays as acidic catalysts. The replacement of the amorphous aluminosilicate catalysts by Faujasite-type zeolites in the early-1960s is regarded as a major improvement in FCC performance. The new acidic catalysts had a remarkable activity and produced substantially higher yields than the old ones. 

The upper instrument is placed at the exit of the catalyst bed. The middle instruments moves along the catalyst bed with the same linear velocity as the gas flowing in the catalyst bed. When the yellow instrument reaches the end of the reactor, the green and the yellow instruments show the same concentrations illustrating the equivalence of position and contact time. 

In FBRs, particles are significantly larger than in slurry (1 to 10 mm) and packed in a fixed bed. A slowly moving L wholly wets the catalyst bed, giving excellent temperature stability and a close to perfect piston flow, whereas small gas bubbles ascend through the bed. The low gas flow makes FBRs not quite adapted for hydrogenation... 

Reactor design is a key element in each process listed in Table XX. The method of feed introduction, the arrangement of the catalyst bed, and the mode of operation have an impact on the ability to process residua. For this reason, classification by reactor type provides a convenient and appropriate distinction for discussing hydroprocessing technology. The most common reactor designs include fixed beds, ebullated or expanded beds and slurry beds, and moving-bed reactors. These classifications are discussed in more detail next. 

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