Fixed bed reactor packing

Find the vessel dispersion number in a fixed-bed reactor packed with 0.625-cm catalyst pellets. For this purpose tracer experiments are run in equipment shown in Fig. E13.3. 

The catalytic activities for pyridine hydrogenation (HDN) were evaluated at 4.5MPa in a fixed bed reactor packed with 30ml of catalyst. The catalyst first were sulfided with a H2S/H2 (92/8) mixture gas at flow rate of 60 ml/min at 300°C for 3 hr at 4.5Mpa. After cooling down to 270 °C, the mixture of pyridine and Hexane was introduced into reactor, at constant pressure (4.5MPa). The reaction products were analyzed by gas chromatography. 

Results of the present study could be incorporated into a new process using a fixed bed reactor packed wi th Amber lyst 15 catalyst. Ethylacelate could be the solvent... 

Your task as a design engineer in a chemical company is to model a fixed bed reactor packed with the company proprietary catalyst of spherical shape. The catalyst is specific for the removal of a toxic gas at very low concentration in air, and the iifformation provided from the catalytic division is that the reaction is first order with respect to the toxic gas concentration. The reaction rate has units of moles of toxic gas removed per mass of catalyst per time. 

The pressure drop in the fixed bed reactors packed with edged particles can be estimated using the Ergun equation [44] ... 

Regenerative Oxidation. There is a group of regenerative processes in which HCl reacts with another material A to form an intermediate which then oxidizes back to compound A while releasing chlorine. The oxidation reaction usually requires the use of a catalyst or more severe conditions than the chlorination. The Grosvenor-Miller process is an example. This uses a fixed-bed reactor packed with ferric, rather than cupric, chloride. The course of reaction is... 

Son, S. M., Kimura, H., Kusakabe, K. (2011). Esterification of oleic acid in a three-phase, fixed-bed reactor packed with a cation exchange resin catalyst. Bioresource Technology, 102 2), 2130-2132. 

Consider the unrmolecular, irreversible solid-catalyzed gas-phase reaction, A—yB, carried out in a fixed-bed reactor packed with completely nonporous particles. Assume that the chemical steps of adsorption-reaction-desorption are represented by first-order kinetics and that the bulk temperature, Tin and surface temperature, Ts, are the same around a particle located at any point along the length of the reactor. 

To illustrate the above points in a simple manner, let us consider a nonisothermal adiabatic fixed-bed reactor packed with nonporous catalyst pellets for a simple exothermic reaction... 

Fixed-bed reactors in the form of gas absorption equipment are used commonly for noncatalytic gas-liquid reactions. Here the packed bed serves only to give good contact between the gas and liquid. Both cocurrent and countercurrent operations are used. Countercurrent operation gives the highest reaction rates. Cocurrent operation is preferred if a short liquid residence time is required. 

Vanadium phosphoms oxide-based catalysts ate unstable in that they tend to lose phosphoms over time at reaction temperatures. Hot spots in fixed-bed reactors tend to accelerate this loss of phosphoms. This loss of phosphoms also produces a decrease in selectivity (70,136). Many steps have been taken, however, to aHeviate these problems and create an environment where the catalyst can operate at lower temperatures. For example, volatile organophosphoms compounds are fed to the reactor to mitigate the problem of phosphoms loss by the catalyst (137). The phosphoms feed also has the effect of controlling catalyst activity and thus improving catalyst selectivity in the reactor. The catalyst pack in the reactor may be stratified with an inert material (138,139). Stratification has the effect of reducing the extent of reaction pet unit volume and thus reducing the observed catalyst temperature (hot... 

Figure 4-8 shows a continuous reactor used for bubbling gaseous reactants through a liquid catalyst. This reactor allows for close temperature control. The fixed-bed (packed-bed) reactor is a tubular reactor that is packed with solid catalyst particles. The catalyst of the reactor may be placed in one or more fixed beds (i.e., layers across the reactor) or may be distributed in a series of parallel long tubes. The latter type of fixed-bed reactor is widely used in industry (e.g., ammonia synthesis) and offers several advantages over other forms of fixed beds. 

A packed-bed nonpermselective membrane reactor (PBNMR) is presented by Diakov et al. [31], who increased the operational stability in the partial oxidation of methanol by feeding oxygen directly and methanol through a macroporous stainless steel membrane to the PB. Al-Juaied et al. [32] used an inert membrane to distribute either oxygen or ethylene in the selective ethylene oxidation. By accounting for the proper kinetics of the reaction, the selectivity and yield of ethylene oxide could be enhanced over the fixed-bed reactor operation. 

Laboratory reactor for studying three-phase processes can be divided in reactors with mobile and immobile catalyst particles. Bubble (suspension) column reactors, mechanically stirred tank reactors, ebullated-bed reactors and gas-lift reactors belong the class of reactors with mobile catalyst particles. Fixed-bed reactors with cocurrent (trickle-bed reactor and bubble columns, see Figs. 5.4-7 and 5.4-8 in Section 5.4.1) or countercurrent (packed column, see Fig. 5.4-8) flow of phases are reactors with immobile catalyst particles. A mobile catalyst is usually of the form of finely powdered particles, while coarser catalysts are studied when placing them in a fixed place (possibly moving as in mechanically agitated basket-type reactors). 

Two fixed-bed reactors can be used in parallel, one reacting and the other regenerating. However, there are many disadvantages in carrying out this type of reaction in a packed bed. The operation is not under steady state conditions, and this can present control problems. Eventually, the bed must be taken off line to replace the solid. Fluidized beds (to be discussed later) are usually preferred for gas-solid noncatalytic reactions. 

Fixed Bed Reactors. In its most basic form, a fixed bed reactor consists of a cylindrical tube filled with catalyst pellets. Reactants flow through the catalyst bed and are converted into products. Fixed bed reactors are often referred to as packed bed reactors. They may be regarded as the workhorse of the chemical industry with respect to the number of reactors employed and the economic value of the materials produced. Ammonia synthesis, sulfuric acid production (by oxidation of S02 to S03), and nitric acid production (by ammonia oxidation) are only a few of the extremely high tonnage processes that make extensive use of various forms of packed bed reactors. 

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