Reaction rates and mass transfer

Jannasch, H. W., Honeyman, B. D. and Murray, J. W. (1996). Marine scavenging the relative importance of mass transfer and reaction rates, Limnol. Oceanogr. 41, 82-88. 

The reaction rate expressed in terms of surface concentrations provides the relationship between Cs and CL. From the definition of the effectiveness factor, we may express the required equality of mass transfer and reaction rates as... 

The resistance to mass transfer of reactants within catalyst particles results in lower apparent reaction rates, due to a slower supply of reactants to the catalytic reaction sites. Ihe long diffusional paths inside large catalyst particles, often through tortuous pores, result in a high resistance to mass transfer of the reactants and products. The overall effects of these factors involving mass transfer and reaction rates are expressed by the so-called (internal) effectiveness factor f, which is defined by the following equation, excluding the mass transfer resistance of the liquid film on the particle surface [1, 2] ... 

Since we know the mass of ozone transferred has to have reacted or left the system, it is relatively easy to determine the reaction rate for slow reactions, which are controlled by chemical kinetics with this method. For kinetic regimes with mass transfer enhancement, the two rates, mass transfer and reaction rate are interdependent. Whether kLa or kD can be determined in such a system and how depends on the regime. Possible methods are similar to those described below in Section B 3.3.3 (see Levenspiel and Godfrey, 1974). 

In this respect, much depends on the relation between the mass transfer and reaction rates in a particular RSP. The definition of the Hatta number representing the reaction rate in reference to that of the mass transfer helps to discriminate between very fast, fast, average, and slow chemical reactions (68,77). 

Exploitation of liquid-liquid microreactor in organic synthesis offers attractive advantages, including the reduction of diffusion path lengths to maximize the rate of mass transfer and reaction rates. Despite the advantages, interest in liquid-liquid micro reactors did not take off until recently, perhaps because of the complication of flow pattern manipulation combined with the limited numbers of liquid-liquid reactions. Initial interest focused on the control of parameters responsible for variation in flow patterns to engineer microemulsions or droplets. However, it was soon realized that liquid-liquid microdevices are more than just a tool for controlling flow patterns and further interest developed. 

Also chain growth to oligomerization is not uncommon, coating and blocking reactors by precipitation. Furthermore, the insolubility of fluorine in most solvents challenges reactant dosing because the gas-liquid interface, typically not well defined, is now the means to determine and control mass transfer and reaction rate and selectivity. 

Mass Transfer and Reaction Rate in the Nano-Region of Microdroplet/Solution Interfaces... 

MICRODROPLET SIZE EFFECT ON MASS TRANSFER AND REACTION RATE... 

Symbols for Chemical Mass Transfer and Reaction Rates f tortuosity tensor... 

Diameter at which mass transfer and reaction rate resistances are equal is D ... 

Based upon the electrodics, the exchange current density is related to the activation energy (16. pp.ll52). For an Arrhenius relation for the effect of temperature upon corrosion rate, AG and AG j are analogous to activation energy and equal 6.44 kcal/mol and 4.30 kcal/mol, respectively. The literature indicates activation energies for mass transfer limited processes range between 1 and 3 kcal/mol and for reaction limited between 10 and 20 kcal/mol (12). Based upon this criteria, corrosion of the 304 S.S. in pure water in the experimental system may lie between the mass transfer and reaction rate limited cases. 

The rate of reaction is first order in NOx and the overall apparent rate constant (combination of mass transfer and reaction rate) is 43,000 1/hr at 700°F. 

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