## March 17, 2009

### Calculate Diffusion Coefficient in Liquids

The order of magnitude of diffusion coefficients in liquids is 10^-9 m2/s with the bulk of data in the range between 0.5 x 10^-9 m2/s and 5 x 10^-9 m2/s. Note that these data also hold for gases dissolved in liquids.

Equation of Chen and Othmer for gases is used for

• Its Simplicity
• Sufficiently Accurate
• Availability of Input Data

Correlation for liquids is that of Wilke and Chang (AIChE J. 1 (1955), 264):

The equation is very simple to use & is given below.

D(1,2) = 7.4 x 10 ^ -12 x (T / mu) x (C x M2)^0.5 x (V1)^-0.6

Where

D(1,2) = is the diffusion coeff of solute 1 in Solvent 2 (M2/s)
T = Temperature in K
mu = dynamic viscosity of solvent 2 (mPa s)
M2 = Mol Wt of solvent 2
V1 = Molar volume of solute 1 at NBP (Cm3/mol)
C = association factor of solvent 2 as below

C = 2.6 for water
C = 1.9 for methanol
C = 1.5 for Ethanol
C = 1.0 for non polar solvents.

I hope it is useful for many of you.

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#### 4 comments:

Luis A. said...

Good formula. Thanks. We are interested in the diffusion of pyrene in n-hexane to check some work by FĂ¶rster and Kasper.

Yongmei said...

Thanks a lot. Very helpful. Do you have any references on the opening statement that the bulk of diffusion coefficient data in liquids is in the range between 0.5x 10^-9 and 5 x 10^-9 m2/s? I really appreciate if you can point me to this information.

Deep said...

what is 7.4*10-12 in calcualting diffusivity

Luis said...

Hola Deep: No units are given with that number. I guess that number could be the value of the diffusion coefficient for a particular specie in a given solvent at a specified temperature.

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