Packed reactive distillation

Sundmacher K, Hoffmann U. Multicomponent mass and energy transport on different length scales in a packed reactive distillation column for heterogeneously catalyzed fuel ether production. Chem Eng Sci 1994 49 4443 4464. 

Eldrige, R.B., A comparison of steady-state equilibrium and rate based models for packed reactive-distillation columns,... 

K. Sundmacher, U. Hoffmann, Multicomponent Mass and Energy Transport on Different Length Scales in a Packed Reactive Distillation Column for Heterogeneously Catalysed Fuel Ether Production, Chem. Eng. Sci., 1994, 49, 3077-3089. 

Peng J., Edgar T. and Eldridge R.B. (2003). Dynamic rate-based and equilibrium models for a packed reactive distillation column. Chemical Engineering Science 58, 2671-2678. 2.9.3... 

Continuous benzene alkylation was conducted in a reactive distillation column of the type illustrated in Figure 1. The process unit comprises the following principal elements a double column of solid catalyst 32, packing columns above and below the catalyst bed, a liquid reboiler 42 fitted with a liquid bottoms product takeoff 44, a condenser 21 fitted with a water collection and takeoff, and a feed inlet... 

The variation of efficiencies is due to interaction phenomena caused by the simultaneous diffusional transport of several components. From a fundamental point of view one should therefore take these interaction phenomena explicitly into account in the description of the elementary processes (i.e. mass and heat transfer with chemical reaction). In literature this approach has been used within the non-equilibrium stage model (Sivasubramanian and Boston, 1990). Sawistowski (1983) and Sawistowski and Pilavakis (1979) have developed a model describing reactive distillation in a packed column. Their model incorporates a simple representation of the prevailing mass and heat transfer processes supplemented with a rate equation for chemical reaction, allowing chemical enhancement of mass transfer. They assumed elementary reaction kinetics, equal binary diffusion coefficients and equal molar latent heat of evaporation for each component. 

Fixed-bed catalytic reactors and reactive distillation columns are widely used in many industrial processes. Recently, structured packing (e.g., monoliths, katapak, mella-pak etc.) has been suggested for various chemical processes [1-4,14].One of the major challenges in the design and operation of reactors with structured packing is the prevention of liquid flow maldistribution, which could cause portions of the bed to be incompletely wetted. Such maldistribution, when it occurs, causes severe under-performance of reactors or catalytic distillation columns. It also can lead to hot spot formation, reactor runaway in exothermic reactions, decreased selectivity to desired products, in addition to the general underutilization of the catalyst bed. 

The design of RD is currently based on expensive and time-consuming sequences of laboratory and pilot-plant experiments, since there is no commercially available software adequately describing all relevant features of reactions (catalyst, kinetics, holdup) and distillation (VLE, thermodynamics, plate and packing behavior) as well as their combination in RD. There is also a need to improve catalysts and column internals for RD applications (1,51). Figures 8 and 9 show some examples of catalytic internals, applied for reactive distillation. 

Hoffmann A, Gorak A. Scale-up of reactive distillation columns with catalytic packing. Chem Eng Process (submitted). 

Noeres C, Benvenuti C, Hoffmann A, Gorak A. Reactive distillation nonideal-flow behavior of the liquid phase in structured catalytic packings. Proceedings of International Symposium on Multifunctional Reactors (ISMR-2), Nuremberg, 2001. 

Moritz P, Hasse H. Fluid dynamics in reactive distillation packing Katapak-S. Chem Eng Sci 1999 54 1367-1374. 

Sulzer katapak-S were developed for use in reactive distillation, though their use for trickle bed operations [18, 19] and as catalyst carrier in bubble flow columns [20] has also been investigated. Like DX, these packings consist of corrugated sheets made from wire gauze. Every second channel between the corrugated sheets is closed to form a tea bag which is filled with catalyst particles (Fig. 8.13). Therefore, voidage (ca. 40 %) and surface area (440 m2 m-3) are approximately half of those for the DX. 

Ind. Eng. Chem. Res., 41, 2735, 2002 Ellenberger, J Krishna, R., Counter-current operation of structured catalytically packed distillation columns, Chem. Eng. Sci., 54,1339-1345, 1999 Krishna, R Hardware selection and design aspects for reactive-distillation columns, Reactive Distillation, eds Sundmacher K. and Kienle, A., Wiley-VCH, Weinheim, Germany, 169-189,... 

Figure 3.6 Homogeneous (a) and heterogeneous (b) reactive distillation (c) structured packing (Katapak-S, from Sulzer) for reactive distillation, consisting of layers of metal wire gauze in which a catalyst is embedded and immobilized in pockets. ...

Related topics are gas absorption (Section 16.11.4.8), distillation (Section 16.11.4.2), and reactive distillation (Section 16.11.6.32). Porosity 0.6 to 0.95, depending on the packing. (Contrast with trickle bed with solid catalyst packing, Section 16.11.6.15.)... 

Use concentration profiles developed from either equilibrium or nonequilibrium reaction-separation to identify the reactive zone. The reflux ratio for reactive distillation is greater than for distillation. Use 1.2 to 1.4 X minimum. For catalytic structured packing, use liquid loadings up to 14 L/s-m and vapor capacities, F factor, of 2.5 m/s (kg/m ) (based on velocity and the root of vapor density). 

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