Pseudocomponent Molecular Weight Estimation Methods

Assay and Pseudo-component Molecular Weight Estimation Methods

When a molecular weight curve is not provided for an assay stream, the molecular weights for the pseudo-components must be estimated with one of the methods provided. Keywords support these options using the MW entry on the ASSAY statement.

SimSci (TWU)

This method was developed by SimSci [1] and estimates molecular weight for each petroleum component, based on its normal boiling point and gravity. The molecular weights are derived by application of a correction factor to the molecular weight for normal alkanes.

Heavy Oil (HOIL)

This is the SimSci method (see immediately above) modified to better represent components having a normal boiling point above 1000K, Below 1000K, characterization essentially is identical to the SimSci method.

CAV80 (API80)

This method uses an improved nomogram published in the 1980 API Technical Data Book which relates molecular weight, normal boiling point and specific gravity. This method in most cases is preferred to using the older correlations.

EXTAPI Extended 1980 API

This is a version of the CAV80 method (immediately above) with the following enhancement. The molecular weights for normal boiling points lower than 300 degrees F are predicted with a method developed by SimSci based on pure component data. This usually results in a better fit than the unmodified correlation when dealing with well-behaved (PONA) hydrocarbon systems.

Lee Kesler (LK)

Methods developed For Mobil Oil Company by M.G. Kesler and B.I. Lee [5] are used to predict all of the properties above, based on the component normal boiling points, gravities, and molecular weights.

Old (1967) API (CAVETT)

This method uses a nomogram from the 1967 API Technical Data Book which relates molecular weight, normal boiling point and specific gravity. The molecular weight prediction for normal boiling points lower than 300 degrees F are predicted with a method developed by SimSci based on pure component data.

In the SimSci Process Simulation Program and earlier versions of the PRO/II Program this method was designated by the keyword CAVETT.

Additional Information

Assay Processing Reference Help

References

[1] Twu, C.H.,"An Internally Consistent Correlation for Predicting Critical Properties and Molecular Weight of Petroleum and Coal Tar Liquids", Fluid Phase Equilibria, 16, pp 137-150, (1984).

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