Reactors tubular catalytic

Figure 13.5 shows a flowsheet for the manufacture of phthalic anhydride by the oxidation of o-xylene. Air and o-xylene are heated and mixed in a Venturi, where the o-xylene vaporizes. The reaction mixture enters a tubular catalytic reactor. The heat of reaction is removed from the reactor by recirculation of molten salt. The temperature control in the reactor would be diflficult to maintain by methods other than molten salt. 

There are circumstances when a complex process may involve two competing (i.e., opposing) dynamic effects that have different time constants. One example is the increase in inlet temperature to a tubular catalytic reactor with exothermic kinetics. The initial effect is that the exit temperature will momentarily decrease as increased conversion near the entrance region depletes reactants at the distal, exit end. Given time, however, higher reaction rates lead to a higher exit temperature. 

The differential equations governing heat and mass transfer in tubular catalytic reactor are... 

Experimental Observations of Multiple Steady States in Tubular Catalytic Adiabatic Reactors... 

Alexeeva OK, Alexeev S.Yu., Shapir B.L., Tulskii M.N. Modified tubular catalytic membrane reactor for hydrogen production from hydrocarbons. Eds. M.D. Hampton et al. Hydrogen Materials Science and Chemistry of Metal Hydrides, 2002 Kluwer Academic Publishers, NATO Science Series 11/71, 339-347. 

In this form, the two-mode model is identical to the classical steady-state two-phase model of a tubular catalytic reactor with negligible axial dispersion. There is also a striking structural similarity between the two-mode models for homogeneous reactions and two-phase models for catalytic reactions in the practical limit of Per 1. This could be seen more clearly when Eqs. (137) and (138) are rewritten as... 

Watercatox Not an established process, but a project of the Fifth Framework Program of the European Union. The purpose was to develop catalytic processes for destroying organic residues in water by wet air oxidation ( WAO).The chosen system used a tubular catalytic membrane reactor for contacting the aqueous solution with air. Several companies and research institutes participated in this project from 2000, and the process was piloted with several real industrial liquid effluents. 

Description In the direct oxidation process, ethylene and oxygen are mixed with recycle gas and passed through a multi-tubular catalytic reactor (1) to selectively produce EO. A special silver catalyst (high-selectivity catalyst) is used it has been improved significantly over the years. Methane is used as ballast gas. Heat generated by... 

Other recent work in the field of optimization of catalytic reactors experiencing catalyst decay includes the work of Romero e/ n/. (1981 a) who carried out an analysis of the temperature-time sequence for deactivating isothermal catalyst bed. Sandana (1982) investigated the optimum temperature policy for a deactivating catalytic packed bed reactor which is operated isothermally. Promanik and Kunzru (1984) obtained the optimal policy for a consecutive reaction in a CSTR with concentration dependent catalyst deactivation. Ferraris ei al. (1984) suggested an approximate method to obtain the optimal control policy for tubular catalytic reactors with catalyst decay. 

Figure 20.9 Auctioneering control system for a tubular catalytic reactor.

Construct an inferential control system that uses temperature measurements along the length of a tubular catalytic reactor in order to control the exit concentration. The reaction is exothermic and is cooled by a coolant (see Figure PII.9). 

The analysis in this section focuses on the appropriate dimensionless numbers that are required to analyze convection, axial dispersion and first-order irreversible chemical reaction in a packed catalytic tubular reactor. The catalytic pellets are spherical. Hence, an analytical solution for the effectiveness factor is employed, based on first-order irreversible chemical kinetics in catalysts with spherical symmetry. It is assumed that the catalytic pores are larger than 1 p.m (i.e., > 10 A) and that the operating pressure is at least 1 atm. Under these conditions, ordinary molecular diffusion provides the dominant resistance to mass transfer within the pores because the Knudsen diffusivity,... 

Akyurtlu etal. (1988) carried out a theoretical investigation on multi-phase porous tubular catalytic membrane with the liquid phase on the external side and the gas phase in the membrane tube lumen. They showed the importance of the Tliiele modulus on the reactor performance and that thin-walled catalyst tubes have larger effectiveness factors. 

Pancharatnam S. Homsy GM. An asymptotic solution for tubular flow reactor with catalytic wall at high Peclet numbers. Chemical Engineering Science 1972 27 1337-1340. 

Tubular reactors with catalytically- Cheap and simple Could foul. Pressure drop may be high ... 

Thus, radial concentration profiles, for example, provoked by radial temperature profiles in cooled (or heated) reactors, are not completely smoothed, if Eqs. (4.10.141) and (4.10.142) are not fulfilled. In experimental reactors a typical value of the ratio I/(1r is 10 and Da is mostly smaller than unity (corresponding to a conversion of less than 60% in a PER). Thus unrealistically small dR-to-dp ratios of less than unity are needed to exclude radial concentration gradients. Nevertheless, numerical simulations - for example, by Carberry and White (1969) on the oxidation of naphthalene in a cooled tubular catalytic fixed bed reactor - showed that even for a value of Da of 5, I/dR = 20, and dR/dp= 10 the radial dispersion has no influence on the reactor performance, although the criterion of Eq. (4.10.141) is far from fulfilled. In other words, an insufficient radial mass transport may lead to a certain extent to an uneven radial concentration distribution, but the conversion and the yields are virtually the same as for a PER. 

Figure 6.13.1 Axial profiles of temperature (tube axis) (a), o-xylene conversion (b), and selectivity to PA (c) in the multi-tubular reactor for catalytic o-xylene oxidation with different inlet temperatures [fin = Tool, two-dimensional model, Eqs. (6.13.3), (6.13.15)-(6.13.22) parameters seeTable 6.13.1].

Figure 6.13.4 Influence of internal diameter on the maximum allowable gas inlet (= wall) temperature with regard to a runaway in a multi-tubular reactor of catalytic o-xylene oxidation [determined by Eqs. (6.13.41)-(6.13.43), parameters as given by Table 6.13.1].

The latter is normally the preferred method employed in industry since it is the mass of catalyst present in the reactor that significantly impacts the reactor design. Since the rate expression is often more complex for a catalytic reaction than for a non-catalytic (homogeneous) reactor, the design equation may be difficult to solve analytically. Numerical solution of the reactor design equation is usually required when designing tubular flow reactors for catalytic reactions. 

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