Auburn UniversityRobert Kline

1/19/12

Why? How?

• Data Regression• Analogous Systems• Estimation

Pure component data exists for most commercially interesting chemicals• Can be estimated for new chemicals

Mixture data is available for a small fraction of all binary pairs• Interaction parameters (activity and

fugacity coefficients) are critical model chemical processes

Sources of data• Journals• Compilations (DECHEMA, Horsley)• Internal Reports• Measurements

Data quality• Not all data is created equally• GC Technology (1970s +) greatly increased

liquid composition accuracy

When should you have it measured?• If it is a critical split between important

chemicals Products with close boiling components Key splits in columns If the presence of an azeotrope will render a

separation infeasible

How to regress?• Use ASPEN• Set mode to Data Regression under Setup• Create a new Data Set under Properties• Create a new Regression Set under

Properties• Run the Regression• Set mode back to Flowsheet Simulation

under Setup

Sometimes an unknown system is like a known system (butyl acetate + water vs isobutyl acetate + water)

Two options• Use the same parameters (if the boiling

points are similar)• Use the same infinite dilution activity

coefficients and regress new parameters

UNIFAQ• Group contribution method

• Breaks down the molecule into chunks called groups• Calculates activity coefficients based on group

concentrations instead of molecule concentrations • Estimates data and regresses your parameters• Can be reasonably accurate, but you should always

review the results to make sure it makes sense

H3C CH2 CH2

OHH3C O C CH3

OGroup # in A # in B 50/50

Mix75/20Mix

Alkane 2 3 2.5 2.25

Ester 1 0 0.5 0.75

Alcohol

0 1 0.5 0.25