Correlation of Liquid Viscosity at the Normal Boiling Point

The importance of liquid viscosity in chemical process design makes it one of the most measured transport properties. Nevertheless, of the 1893 compounds in the DIPPR 801 pure-component database, liquid viscosity and its temperature dependence (at 1 atm, or 0.1 MPa) have been predicted for nearly 50% of the compounds because no experimental data are available. Unfortunately, prediction methods for liquid viscosity often fail significantly, particularly near the normal boiling point. Moreover, experimental data measured at lower temperatures are often extrapolated to higher temperatures with erroneous results. To improve liquid viscosity prediction and extrapolation of experimental data to higher temperatures, we propose an empirical rule for estimating the viscosity of organic compounds at their normal boiling point, ηLb. The proposed rule, developed and validated with the available experimental data in the DIPPR 801 database, was applied as a quality control check on the 1893 compounds in the database and was found to improve the available temperature dependent viscosity correlation in the database for 250 compounds. Of particular significance is a smooth trend within chemical families for the value of the viscosity at the normal boiling point.