Multitube reactors

The catalytic vapor-phase oxidation of propylene is generally carried out in a fixed-bed multitube reactor at near atmospheric pressures and elevated temperatures (ca 350°C) molten salt is used for temperature control. Air is commonly used as the oxygen source and steam is added to suppress the formation of flammable gas mixtures. Operation can be single pass or a recycle stream may be employed. Recent interest has focused on improving process efficiency and minimizing process wastes by defining process improvements that use recycle of process gas streams and/or use of new reaction diluents (20-24). 

In the Godrej-Lurgi process, olefins are produced by dehydration of fatty alcohols on alumina in a continuous vapor-phase process. The reaction is carried out in a specially designed isothermal multitube reactor at a temperature of approximately 300°C and a pressure of 5—10 kPa (0.05—0.10 atm). As the reaction is endothermic, temperature is maintained by circulating externally heated molten salt solution around the reactor tubes. The reaction is sensitive to temperature fluctuations and gradients, hence the need to maintain an isothermal reaction regime. 

The reactions are highly exothermic and very rapid. Consequently conventional practice in the design of fixed bed reactors for phthalic anhydride production has been based on the use of multitube reactors to ensure good heat transfer and good temperature control. These are required to ensure good selectivity. Often a thousand or more small diameter tubes may be... 

Most commercial multitube reactors provide the necessary cooling capacity through the use... 

Yoshida et al. developed similar numbered-up capillary pilot reactors for free radical polymerization (Iwasaki et al. 2006). The capillaries were either arranged in parallel fashion similar to conventional multitube reactors or consecutively branched by multiport valves. 

An additional challenge is that in many cases the catalysts will deactivate rapidly. Provisions have to be taken to start the single reactors of a multitube reactor sequentially to be able to compare time-on-stream behavior. If regeneration procedures are advisable or necessary, it is even recommended to have independent regeneration of the single reactors. 

How can you check the temperature and gas distribution over a multitube reactor ... 

Butane is dehydrogenated isotheimally in multitube reactors, with tubes 3 J m long and a diameter of 5 cm. The operating conditions are as follows ... 

Reactions that are strongly exothermic, such as selective oxidations, or those that are strongly endothermic, such as oxychlorinations, are usually carried out in multitube reactors. The catalyst is dumped into tubes of limited diameter—typically to 1 in. (25 mm)— such as to permit adequate radial heat transfer to/from the liquid bath surrounding them as a result of their limited cross section, the overall number of such tubes is very large (typically on the order of 25,000). Minimization of pressure drop and maximization of... 

With honeycombs (monoliths), pressure drop could be reduced by a factor of 100 or more, with corresponding reductions in equipment and operating costs. The total absence of radial flow in such structures, however, precludes their use in multitube reactors the bulk heat generated by the reaction would not be transported to the tube walls, the selectivity of the process would decrease dramatically, and prevention of reaction runaway would prove difficult. Furthermore, the lack of radial vectors means that inhomogeneities in radial velocity profiles would be maintained these inequalities in residence time would reduce selectivity and result in poor utilization of the catalyst in many of the channels. 

A gas-phase exothermic reaction is carried out in a multitube reactor with the catalyst in 1-in. tubes and boiling water in the jacket. The feed temperature and the jacket temperature are 240°C. The average reactor temperature rises to 250°C a short distance from the inlet and then gradually decreases to 241°C at the reactor exit. The resistance to heat transfer is about equally divided between the bed and the film at the wall. If the tube diameter were increased to 1.5 in. with the same catalyst, what should the jacket temperature be to keep the peak reactor temperature at 250°C Sketch the temperature profiles for the two cases. What pressure steam would be generated for the two cases ... 

The TAME content of the etherified solution is about 28 per cent by weight The main license holders are Gulf Canada, IFP, Mobil, Standard Oil and Texaco. Differences are mainly of a technological nature, particularly in the use of the catalyst multitube reactor with downflow stream or catalyst bed expanded by an upflow stream, presence or absence of a finishing reactor, indispensable if the feed contains basic compounds. 

The first industrial plant for the dehydrogenation of butane to butenes was built by COP I Universal Oil Products) on the iCl (Imperial Chemical Industries) complex at Billingham (United Kingdom) in 1939/1940. The UOP process featured a multitube reactor operating with a chromium oxide/aloinma catalyst, at 570°C and 0.8.10 Pa absolute at the inlet, with a pressure drop of 0l5.10 Pa absolute in the tubes (5 m long, 7.5 cm diameter). Once-through conversion was 215 per cent with a molar selectivity of 80 to 90 per cent... 

The Sasol I version of the fixed bed multitube reactor of ARGE contains about 40 m of catalyst and pro-... 

In Section 6.11, Fischer-Tropsch synthesis in a multitube reactor was used as an example to illustrate the differences between the one- and two-dimensional approaches for the simulation of cooled fixed bed reactors. For o-xylene oxidation to phthalic anhydride, only the two-dimensional reactor model is considered. 

A multitube reactor is used to carry out an exotbermic gas reaction. Catalyst is packed in 0.025-m-diameter tubes and boiling water is used in the reactor jacket. Feed and jacket temperatures are 116°C. During operation the average reactor temperature rises to 121°C a short distance into the reactor and slowly goes down to 116.2°C at the end of the reaetor. Heat transfer resistance is about the same for the bed and the wall. If the tube diameter is increased to 0.038 m (same catalyst), what jacket temperature should be used to keep the peak of 121°C Sketch both cases temperature profiles. Estimate steam pressures. 

The calculated and experimental temperature distribution is shown in Fig. 18. The fit of the axial concentration profile was even better. A perfect fit cannot be expected because of the simplified reactor model and reaction model and the use of constant average parameter values throughout the whole reactor. On the other hand, the agreement between simulation and experiment seems to be sufficient for a study of the behavior of industrial multitube reactors with larger tube diameters. It turned out that for a maximum allowable entrance temperature of 640 K and a conversion larger than 95 %, as demanded by economic considerations, the tube diameter has to be limited to 10 cm, a result that is in excellent agreement with reports on technical units. 

In order to check the accuracy of the measured data and collect information for scale-up, additional experiments were carried out in a pilot plant and the results were compared with these previously obtained in the laboratory reactors. The pilot plant reactor consisted of a tube of 25 mm inner diameter and 4 m length taken from an industrial multitube reactor. 

The flow diagram is shown in Fig. 2-2. In the process,a mixture of benzene and preheated air passes through a multitube reactor cooled by a circulating salt bath. A fixed bed of granular catalyst is used. The conversion of benzene is not complete. 

It would be more convenient to nse a mixing time that is not geometry specific. A number of such times and Damkoehler numbers were compared by Brodkey and Kresta (1999) nsing varions local turbulence scales in the Toor reactor. All of these times nse local tnrbnlence parameters or characteristic times. The position at which these are evalnated for the two multitube reactors is at the point of coalescence of the feed jets. It tnms out that this is very close to Mao and Toor s (1971) characteristic half mixing length. 

In laboratory applications, the scale-up of membrane devices used multitube modules. At ENEA Frascati laboratories, a bundle of 19 Pd-Ag tubes in finger-like configuration was realized for separating up to 6 NL min of ultrapure hydrogen. Scheme and picture of the multitube reactor are shown in Figure 13.44 [12],... 

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