Frequently Asked Questions

We don't get many questions so we made up some to put on this page. Please help us add to this page and ask us questions, lots of questions.

What is ChemSep?

ChemSep is a software system for modeling distillation, absorption, and extraction operations.

Does the world really need yet another distillation simulation program?

ChemSep was created specifically for use in courses on thermodynamics and/or separation processes for those many situations where using a flowsheet simulation program such as may not be the most appropriate solution. may not be the most appropriate solution. ChemSep integrates flash, the classic equilibrium stage column model and a nonequilibrium or rate-based column model in one easy to use program. It doesn't take up much disk space and it doesn't take long to learn how to use; most students can do so in about 15 minutes.

What makes ChemSep unique?

ChemSep was one of the first packages to make available a nonequilibrium (also referred to as rate-based) column model. Now, most major flowsheet simulation programs can boast a nonequilibrium model so that isn't something unique to ChemSep anymore. However, what we can say with complete truthfulness is that our nonequilibrium model was the one that inspired all of the others. The model in ChemSep boasts many features that are not available in any other model.

ChemSep is truly unique for having a design-mode which allows the user to use this model without specifying the actual column layouts. Only the types of internals for each column section need to be specified (and the height of packing or number of trays).

Another unique aspect to ChemSep is the Liquid-Liquid nonequilibrium column model for simulating extraction columns.

Along with many other programs ChemSep has the ability to estimate physical properties of the mixtures you are dealing with. However, to the best of our knowledge ChemSep is the only program that can let you visualize multicomponent diffusivities. These are used in the nonequilibrium model to compute mass transfer rates in the column.

Can I take ChemSep for "test drive" to see if I like it?

You may indeed. We suggest that you download ChemSep-LITE. It is completely free to use.

Something for nothing! Are you serious?

But of course! We do not charge a fee for ChemSep-LITE, not now, not ever.

So what is lite about ChemSep-LITE?

ChemSep-LITE is a version of ChemSep with somewhat limited functionality that we make available free from the downloads page. ChemSep-LITE is limited to solving problems with no more than 4 components and no more than 50 stages. Also, ChemSep-LITE does not include the nonequilibrium column model?

There you go again, that's the third of fourth time that this page mentions a nonequilibrium model. What is this model anyway?

We are delighted that you asked, and we hope that you plenty of time to read, because there is no short and simple answer. Nonequilibrium - often named rate-based - models consider distillation and related operations as the mass transfer rated-based processes that really they are. This model differs from the traditional model of distillation operations that chemical engineers have been using for over 100 years that is based on the assumption that the streams leaving any given stage are in equilibrium with each other. They aren't and, what's more, chemical engineers have known this for almost as long as they have been using the equilibrium stage model!

How have engineers dealt with this problem?

• Overall
• Murphree
• Hausen
• Vaporization

Efficiencies (usually of the Murphree variety) and HETPs often are estimated simply from past experience with similar processes, and a new one might be expected to have approximately the same efficiency (or HETP). However, for new processes that have not been built this approach is of no use whatsoever (and sometimes fails even for old ones).

There are many other pitfalls connected with the use of efficiencies but we don't have the space to go into details here. We suggest that you consult our extensive reading list.

OK, so what?

Well, the nonequilibrium model dispenses completely with efficiencies of all kinds and goes back to first principles and combines the equations that model mass transport between two phases with the material and energy balances. We solve all of these equations all at once. In this way we avoid having to introduce efficiencies at all (despite the fact that the same mass transfer equations can be used to develop efficiency models). There is a great deal more that we could say about these models but that really goes beyond the scope of this FAQ. For a basic technical introduction to nonequilibrium modeling as well as material with all of the gory details we again suggest that you consult our extensive reading list.

So where do I find these references to nonequilibrium distillation modeling?

Right here!.

What other documentation exists for ChemSep?

There is a great deal of material available online as well as in the program help (although the lite version omits some of the more detailed technical help). Then there is the The ChemSep Book for the most words about ChemSep ever written!

I'm convinced. How may I obtain ChemSep?

As we said above, you can download the LITE version free of charge. But you won't be able to try the nonequilibrium model with that version.

An academic site licenses for the full unrestricted version of ChemSep may be obtained from the CACHE Corporation.

For corporate use of ChemSep your company needs to join rhe ChemSep Consortium.

OK, so I get ChemSep. How do I install it?

Simple, just run the "install" program. ChemSep is a rather compact program and requires very little disk space. So far, most of the problems with the installation that have been reported to us occur following the installation of ChemSep on a network where the directory settings are incorrect. This is most often due to the fact that the directories on your file server might be different than those employed by the program user. Enter the right paths on the Paths panel and save them under Options/Save into the default configuration file (chemsep.cnf).

What do I do if I cannot find the answer to my problem in the help or online?

Write to us! We especially appreciate it if you take the time to document and reproduce your problem so we can fix it. It is very difficult for us to find and fix problems that we cannot reproduce.