Multi Fixed Bed Reactor System

In addition, a secondary screening HT method is well suited to test the catalytic properties of materials using a parallel flow-through reactor system (i.e. the Multi Fixed Bed Reactor System—MFBR) fitted with parallel detection and quantification techniques by MS and GC [32-35],... 

The Multi Fixed Bed Reactors system (MFBR) is the heart of the secondary screening unit used in this work [49]. Figure 15.3 shows a single reactor, which allows the introduction of gas or vapor reactants by the top, following either the capillary exhaust or passing through the catalyst bed. The latter is... 

FIGURE 15.10 HT and Combinatorial evaluation of catalytic properties by means of the Multi Fixed Bed Reactor System (MFBR). 

Alvarez A, Ancheyta J. Modeling residue hydroprocessing in a multi-fixed-bed reactor system. Appl. Catal. A Gen. 2008 351 148-158. 

Catalytic partial oxidation of o-xylene and naphthalene is performed mostly in intensively cooled multi-tubular fixed bed reactors, but systems with a fluidized bed were also developed. Typically, V20s/Ti02 catalysts with K2SO4 or A1 phosphates as promoter are used. In fixed bed reactors, the conversion of both feedstocks per pass is around 90%, and the selectivity is in the range 0.86-0.91 mol PA per mol naphthalene and 0.78 mol per mol o-xylene. (Note that the selectivity would be 100%, if only the reactions according to Eqs. (6.13.1) and (6.13.2), respectively, would take place.) The active compounds are distributed on spheres of porcelain, quartz, or silicium carbide (shell catalyst). The thickness of the shell is only around 0.2 mm, and the diffusion paths for the reactants are short. By this means, the influence of pore diffusion is small, and the unwanted oxidation of phthalic acid anhydride to CO2 is suppressed compared to a catalyst with an even distribution of active compounds where the influence of pore diffusion would be much stronger (see Section 4.5.6.3 Influence of Pore Diffusion on the Selectivity of Reactions in Series ). Thus the intrinsic reaction rates are utilized for the modeling of a technical reactor (next Section 6.13.2). 

The effect of physical processes on reactor performance is more complex than for two-phase systems because both gas-liquid and liquid-solid interphase transport effects may be coupled with the intrinsic rate. The most common types of three-phase reactors are the slurry and trickle-bed reactors. These have found wide applications in the petroleum industry. A slurry reactor is a multi-phase flow reactor in which the reactant gas is bubbled through a solution containing solid catalyst particles. The reactor may operate continuously as a steady flow system with respect to both gas and liquid phases. Alternatively, a fixed charge of liquid is initially added to the stirred vessel, and the gas is continuously added such that the reactor is batch with respect to the liquid phase. This method is used in some hydrogenation reactions such as hydrogenation of oils in a slurry of nickel catalyst particles. Figure 4-15 shows a slurry-type reactor used for polymerization of ethylene in a sluiTy of solid catalyst particles in a solvent of cyclohexane. 

Still another multi-reactor approach is to divide the MTG reaction into two steps as shown in Figure 7. In the first step, methanol is partially dehydrated to form an equilibrium mixture of methanol, dimethyl ether and water over a dehydration catalyst. About 15% of the reaction heat is released in this first step. In the second step, this equilibrium mixture is converted to hydrocarbons and water over ZSM-5 catalyst with the concomitant release of about 85% of the reaction heat. Though this two step approach does not have any of the inherent complications of the previously mentioned multibed reaction systems, it leaves one with a substantial amount of the reaction heat (85%) still to be taken over one catalyst bed. This requires a fairly high recycle stream to moderate the temperature rise over the second reactor. Such a high recycle design would require careful engineering in order to transfer heat efficiently from the reactor effluent to the recycle gas and reactor feed. However, this two stage reactor system is the simplest of the fixed-bed systems to develop. 

The above reactions, which arc highly Exothermic, take place in the presence of a catalyst This catalyst may be in a fixed bed in multi-tube reactors with 5,000 to 20,000 tubes. Heat is removed by means of a coolant fluid consisting either of a bath of molten salts (nitrate/nitrite), or the sodium potassium eutectic opmating between 360 and 420 C. The catalyst may also be used in a fluidized bed traversed by cooling systems (coils, etc.). The heat generated is used to produce high-pressure steam. 

It is the model library for fixed-bed catalytic reaction, fluidised-bed and various polymer reactors and so on. Different tools are available in gPROMS software for simulation and modelling of various systems. Some of the following are (i) multi-scale modelling of complex processes and phenomena, (ii) State-of-the-art model validation tools allow estimation of multiple model parameters from steady-state and dynamic experimental data, and provide rigorous model-based data analysis, (iii) The maximum amount of parameter information from the minimum number of experiments, (iv) The gPROMS-CFD Hybrid Multitubular interface provides ultimate accuracy in the modelling of... 

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