Aspen property estimation
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Dear experts, since the Aspen estimation options state that it is possible to estimate all missing parameters, including binary interaction parameters, is it still necessary to check the UNIFAC checkbox on the NRTL binary interaction parameters interface? I calculated it, and the results differ depending on whether a check is made or not. Why is that? Weren’t we told in the estimation that all missing binary parameters would be estimated? Moreover, a binary analysis can also be carried out without checking the box to obtain a gas-liquid equilibrium diagram, and this result differs from that obtained after checking the box. Shouldn’t both be based on UNIFAC estimations? How can they be different?
It seems to be two approaches; the estimation is done using UNIFAC, while the other method you mentioned appears to involve using the UNIFAC approach to replace some aspects of the NRTL method
Why isn’t there any expert coming to provide training?
Perform data regression; the data and regression tools can be obtained from NIST
Those of us who have studied chemical engineering thermodynamics know that UNIFAC is a method for estimating activity coefficients based on the group contribution approach, and the principle of this approach is to consider the physical properties of pure substances and mixtures as the sum of the contributions made by the groups that constitute them. In other words, for slightly more complex systems, we only need to break down the compounds in the system into their constituent groups, and by using the properties of these groups, we can calculate the physical properties of each component in the system. Here is an example. For example, in the methanol (CH3OH)–ethanol (CH3CH2OH) system, macroscopically it consists of two compounds, but using the group contribution method, it can be broken down into methyl (-CH3), methylene (-CH2-), and hydroxyl (-OH) groups. According to the UNIFAC model, each group has two group parameters: a volume parameter and a surface area parameter. There are also interaction parameters between groups, and the physical properties of the system can be estimated based on these group parameters and interaction parameters. In fact, the compounds we encounter are extremely diverse, but the number of distinct functional groups into which they can be classified is quite limited. The advantage of the UNIFAC method lies in its ability to use data on a small number of functional groups to readily estimate the properties of a large number of compounds as well as the properties between them.
Although the verification is not yet clear at present, based on your description, it can be understood that the interaction parameters for the binary interactions in different fire toxicity coefficient models are different. Not selecting the NRTL option means using a default estimation method, while estimation is carried out using the NRTL model. It’s just that all the estimation methods are based on the group contribution method.