This method is also known as the Dortmund modified UNIFAC. Similar to UNIFAC TDEP-1, the binary group energy interaction parameter was given temperature dependence by development of a three parameter form. The combinatorial term was also modified from the original UNIFAC expression.
In 1993 and 1998, many interactions were updated and new ones added for the UNFT2 method. Several structural groups from the original formulation were changed.
The following changes first appeared in PRO/II version 5.6
The
original group 18 (SIMSCI group number 144) was changed from the entire
molecule, C5H5N, to just a fragment,
AC2H2N. This new form replaces
the older one as SIMSCI group 144. To use the new interaction, the definition
of the structure of components must be changed to eliminate the older
form and to incorporate this newer one.
New
groups were also introduced for naphthenic
or cyclic hydrocarbons. To take advantage of this new data, the
structural groups used to define these molecules must be changed from
SIMSCI groups 1000 - 1002 and be replaced with SIMSCI groups 1010 - 1012.
New
groups also were introduced for the cyclic
ethers. Usage of these groups is different than for any other UNIFAC
group in that half of a methylene group is employed. The following table
illustrates the new structure of three components effected by these changes.
Component |
Description of New Structure |
tetrahydrofuran |
The new structure now is defined by using one 611 group and two 1010 groups. |
1,3-Dioxane |
The new structural definition uses a single 1010 group and two 612 groups that share the methylene group between the oxygens. |
1,3,5-trioxane |
uses three 613 groups in which all the methylene groups are shared. |
Once again, to take advantage of these new UNFT2 groups, the existing library structures must be changed.
Additional
new groups were added to UNFT2 for pyrrolidones
and thiophenes. N-methylpyrrolidone can be described using one
2511 group and three 1010 groups. The previous NMP group 2500 was based
upon the entire molecule. In contrast, new thiophene group 1541 is similar,
but is used with two 1200 groups to describe the thoiphene molecule. Previously,
thiophene structures needed to use a sulfide group, but that did not yield
very good results.
The stated purpose of all these modifications was to improve the accuracy of the UNIFAC method by accounting for temperature effects.
See "Modifications to UNIFAC" in the PRO/II Reference Manual, Volume I, Chapter 2, for additional information on this method.