Calculate the Density of a solution of Formic acid in Water

Go to the Top

The density of a Formic acid is a difficult problem, due to association.  We can adjust the interaction between molecules (the dread kij factors) to account for this association

Setup

Note:  this is the path to the installed EOS packages

Last Run on:

Formic Acid Solution Density--Finding minimum errors using (an) adjustable Kij value(s)

Formic Acid (HCOOH) represents a very difficult calculation, since it is found mostly in dimers.  Hence, it represents  a 'worst case' scenario for EOS of associating species.  We handle it using interaction coefficients in the most accurate of the models, the Aasberg-Petersen

Functions

Lden is the density of the mixture z at temperature t, atomospheric pressure (.98 bar).

Next,the dtermining the sqr.error.LiquidDensityError takes a range of t's,a range of z's,and a list of real data,which should be of the form:

Data

Formic acid solution density {concentration__List:{__temperature}}, where concentration is mole percent HCOOH, temperature is 0, 15, 20, 30 ºC

Reform  data and sample at every 0.05 change in mole fraction

NOw, Examine graph of density of 4 temperatures

Using Equations of State to make Predictions

No kij adjustments

Plot the predictions along with the experimental

Store the MS error

Adapt the models to include one kij Adjustment

The following is a table of errors as a function of the k11 value

Now, replicate the data using the above 'best' k11 value for the water-formic acid mix

Though more kij adjustments slightly improve the guess, they do not SIGNIFICANTLY improve the guess (as shown below)

Two kij Adjustments

Three kij Adjustments

four kij Adjustments