For the most part PREDICT has more methods and more properties than ASPEN Plus. ASPEN Plus has a few simple properties, Zc and UNIQUAC R & Q (pure component properties) that PREDICT doesn't. PREDICT has liquid heat capacity (ASPEN Plus calculates this using their "route" involving ideal gas and ideal gas heat capacity) and vapor thermal conductivity that ASPEN Plus does not.
Both products have help facilities that point out to the user on-line what each method is. ASPEN Plus does not include the original references on-line or in the manual, PREDICT does. ASPEN Plus gives some general references in the manual, but not all of the exact, specific references. Why is this? I don't know. I wonder if ASPEN Plus wants people to think that they have something that's not easily available in the literature. In PREDICT we want people to know where they can find these methods in the literature and know that PREDICT offers many advantages (such as ease of use and assurance of correct calculations) over the original article.
One difference between PREDICT and ASPEN Plus is that PREDICT requires that the user enter various different sets of groups if different methods are chosen for the same compound. ASPEN Plus requires that the user describe the molecule once. Their method of describing the molecule (e.g., atom 1, a C, is connected to atom 2, an O, by a double bond, etc.) is not user friendly and does not help users understand the various methods. In PREDICT we display screens of groups available for each different method. By doing this, you can readily see if a method will work with your compound. As an example, it is easy to examine the critical temperature methods and discover that only two methods accommodate silicon containing compounds. With ASPEN Plus you need to put the structure in and run the program before you find out that your properties of your compound cannot be estimated. ASPEN Plus has the groups in their documentation. You can enter the groups, similar to PREDICT, but in a very cryptic method of using group numbers from the manual and not from a user friendly screen like PREDICT. So in summary on the entry of the groups, ASPEN Plus may be easier because you enter the structure only once, but their system is ackward and you don’t know what you are getting. PREDICT on the other hand requires you to select the groups that describe your compound, but you are allowed to do it with a user friendly group selection screen.
ASPEN Plus allows you to specify various methods for the same property to be calculated in one run. This is interesting, but brings up several problems. First, ASPEN Plus is not as interactive or as quick as PREDICT, so it is more important that ASPEN Plus put more in a run than PREDICT. Second, and most importantly, most properties require other supporting properties, such as Pitzer vapor pressure in PREDICT requires the critical constants (see pp. 10-2, 3 in the ASPEN Plus manual for other examples of supporting property requirements). If you specify that the critical temperature, critical pressure and acentric factor be calculated by several methods and then request that the vapor pressure also be calculated, it is not clear in ASPEN Plus which of the estimated Tc, Pc, and w values are used for the vapor pressure calculation, it can make a big difference! In PREDICT we are very clear about which support properties are being used and allow the user to specify or select other methods if they desire, but it always very clear to the user what was used. This also applies when the ASPEN Plus PCES system is used with an ASPEN Plus simulation. If you request that a property be estimated by two methods, which is used for the simulation calculation? You don’t seem to be able to tell. This is disconcerting, to say the least.
PREDICT integrates tables, graphs and access to regression. ASPEN Plus PCES must be combined with TGS (Table Generation System) or DRS (Data Regression) systems and the user must have more knowledge to do these functions. ASPEN Plus does provide regressed parameters to the common ASPEN Plus function (e.g., parameters for the ideal gas heat capacity equation, CPIG from heat capacity estimations) as does PREDICT. However, PREDICT shows the user the regression statistics, i.e. goodness of fit, and immediate plots of the regression results.
Not only does PREDICT have more properties and methods, PREDICT is more up to date. As an example there has been a new study of estimation properties for organometallic compounds (including silicon containing). In that study there were new, much better parameters available for silicon and other groups for the Lyderson, Ambrose and Benson methods. These are in PREDICT, and not in ASPEN Plus.
Finally, the PREDICT manual is much better than the ASPEN Plus. The PREDICT manual not only tells you how to operate the program, but includes all references, equations and data used in the program! PREDICT also includes expected errors and recommendations for which method to use. ASPEN Plus only tells you how to run the program and a little about each method (some expected errors and suggestions for use).
All in all, PREDICT is a great value!! In many ways it is better than the PCES system in ASPEN Plus and is only a fraction of the cost of ASPEN Plus.