Reactors for catalytic processes

Here is the porosity of die bed, which is equal to die difference between the bed volume and the volume of particles, divided by the bed volume. It can 

It follows that the position of thermodynamic equilibrium will change along the reactor for those reactions in which a change of tire number of gaseous molecules occurs, and therefore that the degree of completion and heat production or absorption of the reaction will also vaty. This is why the external control of the independent container temperature and the particle size of the catalyst are important factors in reactor design. 

The gas velocity requhed to suspend these small particles is (0.1)2 X 981 X 3 

It can be seen from the above equations that the viscosity of the gas only becomes important at these low gas velocities for typical particle sizes which are used in fluidized beds. 

As an example of the chemical signihcance of the process technology, the products of die Fischer-Tropsch synthesis, in which a signihcant amount of gas phase polymerization occurs vary markedly from hxed bed operation to the fluidized bed. The hxed bed product contains a higher proportion of straight chain hydrocarbons, and the huidized bed produces a larger proportion of branched chain compounds. 

The gas velocity required to suspend these small particles is 

---

Example 43 Scale-up of reactors for catalytic processes in the petrochemical industry... 

Neiiv methodologies and reactors for catalytic process development... 

Fuel industry is of increasing importance because of the rapidly growing energy needs worldwide. Many processes in fuel industry, e.g. fluidized catalytic cracking (FCC) [1], pyrolysis and hydrogenation of heavy oils [2], Fischer-Tropsch (FT) synthesis [3,4], methanol and dimethyl ether (DME) synthesis [5,6], are all carried out in multiphase reactors. The reactors for these processes are very large in scale. Unfortunately, they are complicated in design and their scale-up is very difflcult. Therefore, more and more attention has been paid to this field. The above mentioned chemical reactors, in which we are especially involved like deep catalytic pyrolysis and one-step synthesis of dimethyl ether, are focused on in this paper. 

The use of computers has made it possible to characterise models with large numbers of individual steps. Andersson and Lamb [25] used an analogue computer to estimate parameters in a model with 15 reactions which described naphthalene production by hydrodealkylation. Also, they were able to predict temperature distributions and effluent concentrations for a commercial reactor. Kurtz [26] took 200 simultaneous reactions into account in an experimental study of the gas-phase chlorination of methyl chloride. Model discrimination and parameter estimation for catalytic processes are discussed in a comprehensive review by Froment [27]. 

The basic idea is to examine operating parameters to find the optimum combination of them for optimum performance. A short list of the most important might include the following Fj, Cjo, Cj, v, V, T, Tq, u, P, and, of course. For catalytic processes additional variables include D, d, Sg, e, shape, and catalyst chemical properties such as chemical composition, activity, and selectivity. Most catalytic reactors operate with significant mass transfer limitations because one usually wants to raise the temperature until mass transfer becomes noticeable in order to attain the highest rate possible. In all cases one determines the effects of these variables on reactor performance. 

Acrylonitrile 100 000 tonnes Fixed-bed catalytic reactor for ammoxidation process for propylene and ammonia reaction. 

For chemical processes requiring heterogeneous catalysts a high density of surface exposed active sites in a given reactor volume is desirable. This can be achieved by using porous materials, either as catalysts or as supports for small clusters of a catalytic material. For catalytic processes with large molecules, the pore dimensions are of interest in particular, for liquid phase catalysis multidimensional pore with diameters exceeding 2.0nm may be required. 

Non-Steady-State Reactors for Testing Fixed-Bed Catalysts In non-steady-state reactors, reaction conditions such as temperature or reactant concentrations are changed temporarily [103-105]. Temperatnre-programmed snrface reaction (TPSR) experiments, temperatnre-programmed desorption (TPD), and temperature-programmed reduction and oxidation (TPR, TPO) [106,107] are established methods dealing with non-steady-state reactor operation. Among these methods, TPSR is a technique that can be applied directly under reaction conditions relevant for catalytic processes. 

Kinetic models can be used to link the reactor design with its performance. The reaction rate may be expressed by power law functions, by more complex expressions, as Langmuit-Hinselwood-Hougen-Watson (LHHW) correlations for catalytic processes, or by considering user kinetics. There are two ideal models, continuous stirred tank reactor (CSTR) or plug flow (PFR), available in rating mode (reaction volume fixed) or design mode (conversion specified). 

A major advantage of the riser reactor for catalytic cracking is that the gas and solid move in nearly plug flow, which gives more uniform catalytic activity and better selectivity than with a bubbling or turbulent fluidized bed. A riser reactor can be used for other rapid catalytic reactions, such as the production of acrolein from propylene [3] or the partial oxidation of n-butane to make maleic anhydride. In DuPont s butane oxidation process... 

Abba, I. A., Grace, J. R., Bi, H. T. (2002). Variable-gas-density fluidized bed reactor model for catalytic processes. Chemical Engineering Science, 57, 4797—4807. Scopus Exact. 

Two-bed membrane reactor for integrated process involving aqueous-phase glycerol reforming to synthesis gas coupled with DME synthesis process combines two physically separated enclosures (Figure 5.13). The first unit is a tube-in-tube fixed-bed water perm-selective membrane reactor for DME synthesis process. The reaction-side compartment (outer tube) is packed with bifunctional catalytic particles for DME synthesis, whereas the permeate-side compartment (inner tube) is an empty... 

Kolodziej A, Lojewska J. Short-channel structured reactor for catalytic combustion Design and evaluation. Chemical Engineering and Processing Process Intensification 2007 46 637-648. 

---