Improved Methods for Approximating Critical and Thermal Properties of Petroleum Fractions

Abstract

H E published literature and the files of every petroleum laboratory contain many data on the physical p r o p T erties of petroleum fractions, the value of which is limited by the difficulty of correlating them into relationships of general applicability. Such correlations should permit prediction of difficultly measurable properties from the results of standardized inspections such as the Engler distillation and the specific gravity. I n our present state of knowledge it is necessary to resort to many purely empirical relationships which have no apparent theoretical foundation but are valuable in that they correlate existing data with accuracy and permit its extrapolation with some degree of assurance. The relationships presented below are for the most part of the empirical type based on consideration of the best data available at this time. It is recognized that in some cases they are not entirely Iogical and that in all cases the actual numerical values will be subject to revision as more data are collected. AVERAGE BOILING POINT Several different m e t h o d s of e s t a b l i s h i n g a so-called average boiling point of petroleum f r a c t i o n s have been in m o r e o r l e s s g e n e r a l use.By calculating an integrated a v e r a g e o r d i n a t e of the true boiling point curve, an accurate a v e r a g e boiling point may be o b t a i n e d . This average will be weighted on either a volum e t r i c o r a weight basis, depending on the units in which the distillation curve is plotted. An integrated average of the 100-cc. E n g l e r d i s t i l l a t i o n c u r v e s i m i l a r l y gives a fair approximation to the volumetric a v e r a g e boiling point with a tendency toward higher values than are obtained by averag-, ing a volumetric true boiling point curve.As a basis for the correlation of p h y s i c a l p r o p e r t i e s , part i c u l a r l y the so-called molal p r o p e r t i e s , a volumetrically weighted average boiling point offers a l e s s logical basis than what may be termed the "molal average boiling point." The molal average boiling point is less than the volumetric average because of the fact that the ratio of specific gravity to molecular weight is higher for the low-boiling members of a hydrocarbon series. Thus, in determining the average boiling point from a volumetric distillation curve, the lower boiling fractions should be given increased weighting in proportion to the variation with boiling point of this ratio of specific gravity to molecular weight. I n Figure 1 is presented a curve giving a correction to be subtracted from the volumetric average boiling point of a petroleum fraction in order to obtain an approximation to its molal average boiling point. This correction is expressed as a function of the slope of the 100-cc. Engler distillation curve and becomes zero as the slope of the curve approaches zero, denoting a pure compound. The general form of this curve was derived by plotting the ratio of specific gravity Two new concepts are introduced f o r correlatio...

Uncertainty analysis applied to thermodynamic models and process design – 1. Pure components

“…There are dozens of correlations available in the literature developed to estimate critical properties [20][21][22][23][24][25][26][27][28][29][30][31][32]. These properties often depend on some easily measurable physical properties such as molecular weight, normal boiling point, and standard liquid density (or specific gravity).…”

Overview and Computational Approach for Studying the Physicochemical Characterization of High-Boiling-Point Petroleum Fractions (350°C+)

“…It is used as an approximate index of the paraffinicity of a petroleum cut, thus a high value for this index indicates a high percent of saturated pure components and paraffin components (Gharagheizi and Fazeli, 2008;Watson and Nelson, 1933).…”

“…Moreover, the results predicted were entirely consistent with those obtained experimentally in the research laboratories (LDPS/LOPCA), in which conventional Differential Scanning Calorimetrry (DSC) was employed. For ATR-W, the method of Kesler and Lee (1976) gave an overall Average Absolute Deviation (AAD%) of 2.61%, as compared to 8.65% for the Watson and Nelson (1933) method; for ATR-Y the method of Kesler and Lee (1976) gave 9.72 % as compared to 12.19% for the Watson and Nelson (1933) method, and for ATR-Z the method of Kesler and Lee (1976) gave 8.58% AAD as compared to 13.00% for the Watson and Nelson (1933) method (Tab. 16).…”

“…1 200 400 0.50 0.75 1.00 Mehrotra (1995) Aboul-Seoud and Moharam (1999a) Experimental data Mehrotra (1995) Aboul-Seoud and Moharam (1999a) Riazi and Faghri (1985) Aboul-Seoud and Moharam (1999b) Experimental data Thermal conductivity, Watson and Nelson (1933) Kesler and Lee (1976) Experimental data Specific heat capacity, C p (J.kg chart that shows graphs of P vap versus temperature for ATR-W, ATR-Y and ATR-Z (Fig. 13).…”

Characterization of hydrocarbon systems by DBE concept

“…These characterization factors are calculated from the physical properties of the total sample. The most widely known number in the petroleum industry is the Watson Characterization Factor (Watson and Nelson, 1933). Watson and Nelson noted that the Characterization Factor calculated as the ratio of the cube root of the absolute boiling point (in OR) to the specific gravity would be mainly constant for the paraffin hydrocarbons that boil between 38°C and 371°C, if the averages of all the reported isomers are considered.…”