Good physical property and safety data are a prerequisite for a reliable risk evaluation and assessment. Modelling and simulation of chemical processes and scenarios require numerous and, most importantly, consistent data. When only limited experimental information is available, estimation of not available property data or extrapolations are required.
Physical and chemical properties of processed and handled chemicals are vital basic information. Several classes of data can be distinguished:
Many times properties need to be extrapolated well beyond the ranges where data have been originally measured. Figure 1 shows an example where vapour pressure data obtained at higher temperatures were extrapolated to ambient temperature. This kind of extrapolation is often necessary for transport classification (in accordance with GHS/CLP) as well as for the creation of material safety data sheets (MSDS).
The extrapolation with an inappropriate approach or the wrong correlation equation can lead to discrepancies of several orders of magnitude as shown on Figure 1 for the vapour pressure extrapolation of dicyclohexyl methylphosphonate.
Figure 1: Extrapolations can be tricky
The propagation of errors is another problem. E.g. when sizing a safety valve, an error in the vapour pressure would result in a wrong estimated temperature at relief. This would either lead to an oversized or undersized valve with subsequent issues, e.g. valve shattering, undersized downstream treatments or even failure of the mechanical integrity of the protected vessel.
Powerful tools and concepts are available so that data can be safely extrapolated to regions not accessible by experiment.
Various possibilities exist to estimate physical property data:
Empirical correlations and rules
Group contribution methods
Corresponding states approaches
Thermodynamic consistency tests
Interpolation and extrapolation from similar compounds
Homologues series analysis
Chemical family plots and trends
Analogous series methods
Multi property correlations
Patterns of property behaviour
Combinations of above methods
The well-known and comprehensive TÜV SÜD physical property data base software PPDS can be used for retrieving pure component and mixture data. Critically evaluated data and relations for temperature-dependent properties as well as regression programs creating new correlations are also available.
In addition, experimental as well as extrapolated or estimated data must always be rigorously checked and validated for correctness, plausibility, accuracy and precision before use.
The following services can be provided:
Selection of property methods
Choice of correlation equations
Regressions and statistical analysis
Error propagation and visualisation
Interpretation of results
Our laboratories and experts can help you to measure, estimate or predict safety information. We evaluate and assess physical property data to improve the safety of your processes.