Tubular reactor consecutive reactions

Ortho-xylene (A) is oxidised to phthalic anhydride (B) in an ideal, continuous flow tubular reactor. The reaction proceeds via the complex consecutive parallel reaction sequence, shown below. The aim of the reaction is to produce the maximum yield of phthalic anhydride and the minimum production of waste gaseous products (C), which are CO2 and CO. 

Tubular flow reactors—minimum volume for second-order reversible reactions, maximum yield of consecutive reactions, minimum cost with and without recycle, and maximum profit with recycle... 

Isothermal tubular reactor with two consecutive reactions... 

Write the component continuity equations for a tubular reactor as in Example 2.5 with consecutive reactions occurring ... 

Fig. 1.28. Reactions in series—comparison between batch or tubular plug-flow reactor and a single continuous stirred-tank reactor. Consecutive first-order reactions,...

Beside consecutive-competing reactions, instantaneous (generally acid-base) reactions are also used as an indicator of segregation, especially in multijet tubular reactors. Ottino (102) deduced the relationship t (t) between nwarpedn and real time from the comparison between experimental conversion X(t) along the axis of a tube and the theoretical expression X(tw). ay was then calculated by (7-10) and the efficiency eff(t) by ... 

In dealing with chemical process engineering, conducting chemical reactions in a tubular reactor and in a packed bed reactor (solid-catalyzed reactions) is discussed. In consecutive-competitive reactions between two liquid partners, a maximum possible selectivity is only achievable in a tubular reactor under the condition that back-mixing of educts and products is completely prevented. The scale-up for such a process is presented. Finally, the dimensional-analytical framework is presented for the reaction rate of a fast chemical reaction in the gas/liquid system, which is to a certain degree limited by mass transfer. 

Example 44 Dimensioning of a tubular reactor, equipped with a mixing nozzle, designed for carrying out competitive-consecutive reactions... 

Example 44 Dimensioning of a tubular reactor, equipped with a mixing nozzle, designed for carrying out competitive-consecutive reactions 193 Example 45 Mass transfer limitation of the reaction rate of fast chemical reactions in the heterogeneous material system gas/liquid 197... 

Fio. 19. Influence of micromixing and mass transfer limitations on the yield of competitive-consecutive reactions (of which one reaction is homogeneous and the other is wall-catalyzed) in a tubular reactor. 

The accuracy of low-dimensional models derived using the L S method has been tested for isothermal tubular reactors for specific kinetics by comparing the solution of the full CDR equation [Eq. (117)] with that of the averaged models (Chakraborty and Balakotaiah, 2002a). For example, for the case of a single second order reaction, the two-mode model predicts the exit conversion to three decimal accuracy when for (j>2(— pDa) 1, and the maximum error is below 6% for 4>2 20, where 2(= pDd) is the local Damkohler number of the reaction. Such accuracy tests have also been performed for competitive-consecutive reaction schemes and the truncated two-mode models have been found to be very accurate within their region of convergence (discussed below). 

If the first reaction is slow and the second reaction is fast, it will be extremely difficult to produce species B. If the first reaction (formation of B) is fast and the reaction to form C is slow, a large yield of B can be achieved. However, if the reaction is allowed to proceed for a long time in a batch reactor, or if the tubular flow reactor is too long, the desired product B will be converted to C. In no other type of reaction is exactness in the calculation of the time needed to carry out the reaction more important than in consecutive reactions. 

A pipe reactor (tubular reactor) is much more suitable, when correctly designed (suppression of any back-mixing), for carrying out competitive-consecutive reactions than a stirred tank reactor. 

It is now proposed to design a tubular reactor which will operate at 1 atm pressure and 1400°F. (d) Determine the total conversion of benzene to di- and triphenyl as a function of space velocity, (b) Determine the reactor volume required to process 10,000 Ib/hr of benzene as a function of the total conversion. First carry out the solution with the assumption that only reaction 1 occurs, and then proceed to the solution for the two consecutive reactions. Assume that the reactor will be operated isothermally and that no other reactions are significant. 

Fig. 4-16 Selectivity for consecutive reactions m stirred-tank and tubular-flow reactors...

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. 

Triethanolamine is produced from ethylene oxide and ammonia at 5 atm total pressure via three consecutive elementary chemical reactions in a gas-phase plug-flow tubular reactor (PFR) that is not insulated from the surroundings. Ethylene oxide must react with the products from the first and second reactions before triethanolamine is formed in the third elementary step. The reaction scheme is described below via equations (1-1) to (1-3). All reactions are elementary, irreversible, and occur in the gas phase. In the first reaction, ethylene oxide, which is a cyclic ether, and ammonia combine to form monoethanolamine ... 

Experimental test of this mechanism was conducted by performing a competition study with ethylene/methane mixtures in the tubular reactor. The results, summarized in Table 5, demonstrate that ethylene oxidation competes readily with methane oxidation under the experimental conditions of the electrocatalytic cell. The ratios of 2/ 1 calculated for these experiments are 4.0 and 4.6. This is in reasonable agreement with the ratio derived from the methane coupling experiments. Thus, the consecutive reaction mechanism can be applied successfully to systems of this type. The inescapable conclusion is that methane dimerization is limited by the relative rates of methane and ethylene activation. 

M. R. Newberger and R. H. Kadlec [AIChE J., 17,1381-1387 (1971)] studied the conditions for optimal operation of a tubular reactor in which consecutive second-order reactions are being carried out. Of particular interest was the saponification of diethyl adipate with sodium hydroxide in aqueous solution. The stoichiometry of these reactions can be expressed as... 

To avoid mass and heat transfer resistances in practice, the characteristic transfer time should be roughly 1 order of magnitude smaller compared to the characteristic reaction time. As the mass and heat transfer performance in microstructured reactors (MSR) is up to 2 orders of magnitude higher compared to conventional tubular reactors, the reactor performance can be considerably increased leading to the desired intensification of the process. In addition, consecutive reactions can be efficiently suppressed because of a strict control of residence time and narrow residence time distribution (discussed in Chapter 3). Elimination of transport resistances allows the reaction to achieve its chemical potential in the optimal temperature and concentration window. Therefore, fast reactions carried out in MSR show higher product selectivity and yield. 

In complex reaction systems, axial dispersion will also affect the product yield and selectivity attainable in real tubular reactors. This will be demonstrated for first order consecutive reactions. 

Liden, G. and L. Vamling, Periodic Operation of a Tubular Reactor A Simulation Study of Consecutive Reactions in a Chromatography Reactor, Chem. Eng. J. 40, 31-37 (1989). 

We will illustrate the design problem using the consecutive reactions network problem for CSTR, batch and tubular reactors. We consider the following reaction network ... 

Morbidelli, M. and Varma, A. (1989) A Generalized Criterion for Parametric Sensitivity Application to a Pseudohomogeneous Tubular Reactor with Consecutive or Parallel Reactions , Chem. Engng. Sci. 44, 1675-1696. 

It is instructive to consider the composition within a tubular reactor, or the composition change along the reaction coordinate, for a consecutive reaction. Recall that our consecutive reactions are described as... 

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