Reactions with VOLUME

Slide 8 A technological expertise name reactions with volume ranges and examples of processes done on industrial scale... 

Communications on the theory of diffusion and reaction-IX Internal pressure and forced flow for reactions with volume change (with J.P.G. Kehoe). Chem. Eng. ScL 28, 2094-2098 (1973). 

In the two preceding examples there was no volume change with reaction consequently, we could use concentration as our dependent variable. We now consider a gas-phase reaction with volume change taibng place in a PFR, Under these conditions, we must use the molar flow rates as our dependent variables. 

This allows the concentration units to be changed to suit the problem, and other measures of concentration, such as mole fraction, partial pressure, or fugacity, might be introduced, g is a good measure to use for gaseous reactions with volume changes and will be mentioned later in connection with tubular reactors otherwise we will phrase our problems in terms of c, recognizing that this implies no limitation on the method. 

A special case of batch reactors is constant-volume or constant-density operation typical of liquid-phase reactions, with volume invariant with time ... 

The corresponding general equation for a reaction with volume change is... 

In addition to diffusion, bulk flow can occur within a reacting pellet (Beveridge and Goldie, 1968 Gower, 1971 Sohn and Sohn, 1980). This effect is considerably magnified for reactions with volume change such as... 

In summary, total pressure differences may arise in catalyst pores due to either (a) reactions with volume change or (b) the pressure drop in a flow reactor. Whenever such pressure differences arise we can expect a forced flow of molecules to occur. This forced flow may be either of Knudsen or Poiseuille type, depending on whether the mean free path in... 

Thus for a typical (and common) gas-phase reaction with volume change... 

R. S. Hay, The Use of Solid-State Reactions with Volume Loss to Engineer Stress and Porosity into the Fiber-Matrix Interface of a Ceramic Composite, Acta Met., 43 [9] 3333-3348 (1995). 

Example 2.6 Design equation for 1/2 order reaction with volume change. 

Reactions with volume change Let ns first consider the volume change resulting from a change in the number of moles, such as in the reaction... 

Reactions without volume change Reactions with volume change Nonisothermal operation... 

From a thermodynamic point of view, high pressure supports reactions with volume contraction (e.g.. Equations (4.10) and (4.8)) whereas volume-increasing reactions are suppressed (e.g., Equations (4.6) and (4.7) or gas release caused by pyrolysis and tar cracking). Consequently, higher quantities of ChU and CO2 are the consequence in the case of increased pressure if the same operating temperature is applied. 

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