Packings heterogeneous systems

For practical purposes it is often beneficial to use a heterogeneous system with the enzyme as a solid preparation which easily can be separated from the product in the liquid phase. Solid enzyme preparatiorrs can conveniently be used in packed bed and stirred tank reactors. As in other cases with heterogeneous catalysis, mass trarrsfer limitations can reduce the overall reaction rate, but usually this is no major problem. 

In heterogeneous systems, however, the question of pressure drop may be more serious. If the reaction system is a two-phase mixture of liquid and gas, or if the gas flows through a deep bed of small particles, the pressure drop should be checked at an early stage in the design so that its influence can be assessed. The methods of calculating such pressure drops are much the same as those for flow without reaction (e.g. for packed beds, see Volume 2, Chapter 4). 

A distillation process involves a heterogeneous system formed of at least two phases, gas and liquid. Distillation is impossible unless at least two phases are present. Packed bed distillation columns are formed of three phases that also take the solid packing phase into consideration. Most distillation processes are not only heterogeneous, but also multistage. 

On-line detection can be classified as either homogeneous or heterogeneous. In the homogeneous system, the effluent is mixed with a liquid scintillation cocktail before passing through a flow cell that is positioned in a scintillation counter. In the heterogeneous system, the effluent passes through a flow cell packed with a solid scintillator. 

The various aspects that are to be considered to achieve a proper and efficient catalyst testing approach are presented. This applies to heterogeneous systems in which the catalyst is the solid phase and the reactants are in the gaseous and/or the liquid phase. The presence of a solid phase introduces complicating phenomena on which this chapter focuses. In this respect, homogeneous catalysis is a limiting case and does not need separate treatment. The solid catalyst can be present as either a packed bed of particles, a wash-coated monolith, a fluid bed, an entrained bed, or in a liquid-phase slurry. 

Effect of Diffusional Restrictions on Enzyme Reactor Design and Performance in Heterogeneous Systems. Determination of Effectiveness Factors. Batch Reactor Continuous Stirred Tank Reactor Under Complete Mixing Continuous Packed-Bed Reactor Under Plug Flow Regime... 

Chemiluminescence continues to be a very selective and sensitive detection tool in FIA immunoassays. The main component in the most commonly used heterogeneous systems is an immunoreactor column, consisting of PTFE tubing packed with immobilized antibodies or haptens. The immunoreac-tion and the chemiluminescence reaction takes place within the immunoreactor, and the emitted light is collected directly from the cell. 

Calcium is miscible with Sr in the liquid and in all the solid bcc, hep and fee allotropic forms (Fig. 1). Barium exhibits no hep or fee forms, however, so that solid solubility between the close-packed structures of Ca and Sr, and the bcc structure of Ba is restricted in the Ca-Ba and also in the Sr-Ba systems. A continuous series of solid solutions is only achieved in Ca-Ba and Sr-Ba for the high-T bcc modifications. In Ca-Ba, the solid solutions are separated by a narrow heterogeneous field between 32 and 36 mol% Ba in Sr-Ba this occurs between 24 and 30 mol% Ba (Fig. 1). 

Chapter 10 begins a more detailed treatment of heterogeneous reactors. This chapter continues the use of pseudohomogeneous models for steady-state, packed-bed reactors, but derives expressions for the reaction rate that reflect the underlying kinetics of surface-catalyzed reactions. The kinetic models are site-competition models that apply to a variety of catalytic systems, including the enzymatic reactions treated in Chapter 12. Here in Chapter 10, the example system is a solid-catalyzed gas reaction that is typical of the traditional chemical industry. A few important examples are listed here ... 

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