DOE Big Hill C5-175 degF PIANO molar-mass qualification
Scope
This qualification freezes public U.S. Department of Energy Strategic Petroleum Reserve data for
the Big Hill Sweet C5-175 degF fraction and exercises
OilAssayCharacterisation.calculatePianoMolarMassKgPerMol(...). The helper converts a mass-basis
PIANO family/carbon-number table into the mixture number-average molar mass required by NeqSim’s
existing explicit-molar-mass pseudo-component path.
This is a composition and mass-bookkeeping qualification. It does not identify individual isomers, infer a missing lower boiling boundary, or validate critical-property, VLE, flash, distillation-yield, or conversion-unit predictions.
Public evidence and provenance
The numerical inputs are taken from the official DOE SPR Big Hill Sweet workbooks:
- comprehensive assay: C5-175 degF yield 5.22 mass%, SG60/60 0.6731, and upper boundary 175 degF;
- PIANO analysis: the hydrocarbon-family/carbon-number mass table used below.
Both workbooks report 24 September 2021. Only cited numerical facts are reproduced in NeqSim; the source workbooks are not redistributed. The calculation uses the conventional atomic weights C = 12.011 and H = 1.008 g/mol, which are within the current standard atomic-weight intervals published by the CIAAW.
Frozen PIANO inputs
| Family | Carbon number | Mass% |
|---|---|---|
| Paraffin | 3 | 0.32 |
| Paraffin | 4 | 3.49 |
| Paraffin | 5 | 21.47 |
| Paraffin | 6 | 15.28 |
| Paraffin | 7 | 0.94 |
| Iso-paraffin | 4 | 0.59 |
| Iso-paraffin | 5 | 10.96 |
| Iso-paraffin | 6 | 17.99 |
| Iso-paraffin | 7 | 4.04 |
| Iso-paraffin | 8 | 0.05 |
| Aromatic | 6 | 3.34 |
| Aromatic | 7 | 0.12 |
| Naphthene | 5 | 3.39 |
| Naphthene | 6 | 14.38 |
| Naphthene | 7 | 3.60 |
| Naphthene | 8 | 0.05 |
The row sum is 100.01 mass% because the source reports two decimals. The implementation therefore accepts a small source-rounding closure error and normalizes by the actual submitted total. Frozen family sums are 41.50% paraffins, 33.63% iso-paraffins, 3.46% aromatics, and 21.42% naphthenes.
Calculation
The family formulas are paraffin and iso-paraffin CnH(2n+2), naphthene CnH(2n), and aromatic
CnH(2n-6). For mass fractions w_i and species-group molar masses M_i, the number-average
mixture molar mass is
M_n = 1 / sum_i(w_i / M_i)
The frozen expected result is 0.0791538366563 kg/mol. The API is intentionally O(n), independent
of input row order, and rejects null families, impossible family/carbon-number combinations,
non-finite or negative weights, and totals outside the documented rounding tolerance.
Application and acceptance criteria
The regression applies the published 5.22 mass% C5-175 degF cut to a 1 kg assay using:
- the PIANO-derived explicit molar mass;
- the measured SG60/60 of 0.6731;
- only the published 175 degF upper boiling boundary.
Acceptance requires:
- PIANO row closure within 0.02 percentage point and the expected molar mass within
1e-14 kg/mol; - identical output after reversing source-row order;
- exact 0.0522 kg pseudo-component mass closure within
1e-10 kg; - retention of the one-sided 175 degF boundary without creating a lower boundary; and
- fail-closed invalid-input behavior before the thermodynamic system is mutated.
No individual species distribution or mean boiling point is claimed. The resulting molar mass is a reproducible family/carbon-number aggregate suitable for the explicit assay-cut bookkeeping path.