Reactors with Catalysts

In many of the examples we have considered and wiU consider later in this chapter, a catalyst is present to promote the reaction. If this is a homogeneous catalyst in one of the reactant phases such as an acid, base, or a dissolved organometallic complex, there are no mass transfer resistances to reaction, and the process behaves as a true homogeneous reaction. 

The mass transfer of A from the bubble to the solution and from the solution to the catalyst surface is described by an overall coefficient k,. Any of these steps can be rate limiting, and the overall reaction rate will be a function of each of these coefficients. 

If we simply turn the drawing of the bubble column upside down, we have a spray tower reactor. Now we have dense liquid drops or solid particles in a less dense gas so we spray the liquid from the top and force the gas to rise. The same equations hold, but now the mass transfer resistance is usually within the hquid drop. 

We have the same geometry for reacting solid particles such as the burning of pulverized coal that was discussed in Chapter 10, but now the mass transfer resistance is in the gas phase as the reaction is limited by the diSusion of O2 to the surface. 

If reaction occurs only in the boundary layer around the drop of radius R, then a steady-state energy balance around the drop yields 

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Typically, reactors require some type of catalyst. Reactors with catalyst can be of the fixed-bed style for fiuid-bed types. Fixed-bed reactors are the most common. The feed often enters the reactor at an elevated temperature and pressure. The reaction mixtures are often corrosive to carbon steel and require some type of stainless steel alloy or an alloy liner for protection. If the vessel wall is less than 6 mm, the vessel is constmcted of all alloy if alloy is provided. Thicker reactor walls can be fabricated with a stainless overlay over a carbon steel or other lower alloy base steel at less cost than an all-alloy wall constmction. 

Process flow for a typical batch-mass polystyrene process(1) is shown in Figure 1. Styrene monomer is charged to the low conversion prepolymerization reactor with catalyst and other additives, and the temperature is increased stepwise until the desired conversion is reached. It is then transferred into the press. Polycycles are 6 to 14 hours in the low conversion reactor, and 16 to 24 hours in the press. At completion, the cakes are then cooled with water and removed from the press to be ground and then (usually) extruded into pellets. 

Figure 3.12 Residence time distribution in a micro reactor which is tightened by different means. ( ) Glued reactor without catalyst coating (X) glued reactor with catalyst coating ( ) reactor with graphite joints. Calculated curves for tubular reactors with the Bodenstein number Bo = 33 (solid line) and Bo = 70 (dashed line).

A second order reaction takes place in a flow reactor with catalyst particles in the shape of lamellae. At the inlet the concentration is 2 lbmol/cuft and the Thiele modulus is

[Pg.778]

Simple control policies for reactors with catalyst decay (with A. Chou and W.H. Ray). Trans. Instn Chem. Engrs. 45,153-159 (1967). 

Chou, A., Ray, W. H. and Aris, R. Trans. Inst. Chem. Eng. 45 (1967) T153. Simple control policies for reactors with catalyst decay. 

Ziogas et al. [28] performed catalyst screening with this reactor with catalysts coatings, which were made of various base aluminas such as corundum, boehmite and y-alumina. Testing of Cu/Cr and Cu/Mn catalysts based on the different coatings for methanol steam reforming revealed differences in activity which were ascribed... 

Ideal plug-flow conditions can also be established in so-called nano-flow reactors with catalyst particle sizes from 50 to 200 pm. These reactors were operated in 16-and 64-barrel mode at Avantium for the regression of intrinsic kinetics [4],... 

Two cases are considered an adiabatic reactor with no catalyst and an adiabatic reactor with catalyst. The void volume of the catalyst is 0.5, so the total volume of the reactor with catalyst must be twice as large as the volume of the reactor without catalyst. The reactor length is increased to 20 m in this case. The density of the solid catalyst is 2000 kg/m3, so the total amount of catalyst in the reactor is... 

Figure 6.34 shows the Aspen Plus flowsheet with these two adiabatic reactors installed. The empty reactor is 10 m in length. The catalyst-filled reactor is 20 m in length. The reactor effluents for the two cases are identical. Control valves are installed on the gas feedline and the gas reactor effluent line. Figure 6.35 shows the Catalyst page tab window under Setup for the reactor with catalyst. The catalyst properties are specified. 

Dynamics of Adiabatic Reactors with and without Catalyst We want to show the difference in the dynamic responses between an adiabatic reactor without catalyst and one with catalyst. A plot is set up in the usual way using Tools on the top toolbar and selecting New Forms and Plot. The variables to be plotted are dragged and dropped from the feedstream and from the reactor block. The feed temperature and the reactor exit temperatures are plotted. In addition, the temperatures at several locations down the length of the reactor with catalyst are plotted the temperatures at 5, 10, and 15 m in the 20 m reactor containing the catalyst. The models of the two adiabatic reactors use 20 lumps. 

However, the exit temperature of the reactor with catalyst (rout)cat takes about 2 hours to attain the same steady state. And in fact, it initially actually decreases The inverse response or wrongway effect is caused by the thermal capacitance of the catalyst. 

In order to lighten the calculations, a simplified loop is taken into account, in which dehydration of H2S04 into S03 + H20 is performed in a single isotherm reactor (without catalyst), whereas dissociation of S03 into S02 + V2 02 is performed in another single isotherm reactor (with catalyst), at a higher temperature called Tmax. Only this last temperature is varied in the sensitivity analysis. 

The process is conducted in a vertical steel apparatus filled with the catalyst suspended in liquid ethylchloride. This mixture is treated by hydrogen chloride and ethylene, while the contents of the reactor are intensively agitated. With the formation of ethylchloride, the volume of the liquid in the apparatus grows therefore, the surplus of ethylchloride is constantly withdrawn from the reaction zone. Liquid ethylchloride, leaking from the reactor with catalyst particles, as well as dissolved hydrogen chloride, is vapourised, washed in a scrubber with a 10% alkaline solution, dried with sulfuric acid and condensed. The reaction gases, laden with ethylchloride vapours, are washed with water from hydrogen chloride, dried with concentrated sulfuric acid and sent into an absorber, where ethylchloride is extracted with kerosene. By distillation and subsequent condensation, ethylchloride is extracted from the obtained solution. 

Figure 25. Equivalence of operation with periodical flow re versa and countercurrent heat exchange A) Fixed-bed reactor with periodic flow reversal, B) Temperature profiles with rapid flow reversal, C) Countercurrent reactor with catalyst at the wall D) Schematic concentration and temperature profiles m both reactors [141...

The general redox mechanism of metal-oxide catalyzed oxidation of hydrocarbons involves two major stages in the catalytic process, reduction of the surface layers by hydrocarbons and their reoxidation by interaction with oxygen. While these two stages occur simultaneously in a reactor with the catalyst working under steady-state conditions, they can be carried out in two separate reaction zones in a reactor with catalyst circulation [37]. A hydrocarbon is fed into the first zone where a desirable intermediate product of partial oxidation is formed after interaction with the oxidized catalyst. In the second zone, gas phase oxygen reoxidizes the catalyst. Obviously, the residence time of the catalyst in the first zone should be short enough to prevent formation of an inactive reduced state of the catalyst. If only surface layers participate in the interaction with hydrocarbons, the time of catalyst reduction is approximately several seconds. 

E. Reactors with Catalyst Impregnated on Reactor Walls or Placed in an Annular Basket... 

Fig. 7.9. Schematic of Fluid Catalytic Cracking (FCC) reactor with catalyst regenerator.

Modeling of Tubular Nonisothermal Nonadiabatic Packed-Bed Reactors with Catalyst Poisoning... 

Acid-Amine Technology, Inc. Methyl formate Methanol and carbon monoxide AAT Trimode reactor with catalyst yields 95% to 99.5% pure product 7 1992... 

Figure 7 CPC reflectors for a tubular reactor with catalyst supported in a vertical stripe. Adapted from Chaves and Collares Pereira (2007), with permission from The American society of Mechanical Engineers.

Alkyladon t es place in the vapor phase, in the presence of a gaseous eminent (nitrogen or hydrogen) around 475 C, at adiabatic reactors, with catalyst, around 450 to 500, and in the presence of steam. The blend of methylstyrenes currently commerdaitzed by Dow results from the liquid phase alkylation of toluene with aliuninom diloride. 

Several reactors are presently used for studying gas-solid reactions. These reactors should, in principle, be useful for studying gas-liquid-solid catalytic reactions. The reactors are the ball-mill reactor (Fig. 5-10), a fluidized-bed reactor with an agitator (Fig. 5-11), a stirred reactor with catalyst impregnated on the reactor walls or placed in an annular basket (Fig. 5-12), a reactor with catalyst placed in a stationary cylindrical basket (Fig. 5-13), an internal recirculation reactor (Fig. 5-14), microreactors (Fig. 5-16), a single-pellet pulse reactor (Fig. 5-17), and a chromatographic-column pulse reactor (Fig. 5-18). The key features of these reactors are listed in Tables 5-3 through 5-9. The pertinent references for these reactors are listed at the end of the chapter. 

Figure S-12 Catalytic reactors.1 in) Reactor with catalyst lined or coated onto the reactor walk b reactor wilh catalyst placed in an annular basket...

Table 5-6 Key features of a reactor with catalyst placed in a stationary cylindrical basket...

Figure 9.6 Total conversion for inert membrane reactor with catalyst on the feed side (IMRCF), catalytic membrane reactor (CMR) and conventional fixed-bed reactor (FBR) with uniform and Dirac delta catalyst activity distributions as a function of the dimensionless residence time [Yeung et al., 1994]...

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