Lecture 4 – Crude Oil Properties
Some of the most important physical properties of crude oil include:
oAPI = (141.5/SG 15oF) – 131.5 The purpose of this equation was to extend the range of the specific gravity scale. Crude oil SG changes, although small, may be important.
Crude Oils oAPI = 10 – 50
Higher oAPI, more paraffinic crude, higher yields of gasoline.
Lower oAPI, more aromatic crude, lower yields of gasoline.
Resistance to flow, usually measured @ 100oF in centistokes (kinimatic viscosity)
Measured by ASTM D-97 – temperature at which oil ceases to flow. Diesel may contain waxes, smaller than candle wax, which could solidify in cold weather.
Temperature above which the oil will spontaneously combust. Fractions in vacuum tower are the least combustible. They are the heaviest.
Measured by ASTM D-323. Also know as Reid vapor pressure (RVP). True vapor pressure is usually 5-9% > RVP
The solid residue (%wt) remaining after heating to coking temperatures (700-800oC)
ASTM D-524 Ramsbottom Carbon
ASTM D-189 Conradson Carbon
CCR incr. then Asphaltene incr.
Measured by ASTM – 3230 (lb NaCl/1000 bbl)
Desalting is necessary because NaCl content > 10 lbs/1000 bbl leads to corrosion
Measured by EPA Method 3040 These include Ni, V, Ag, Hg, Na, and Ca. Metals can cause catalyst deactivation and corrosion.
Sediment and Water
Measured by ASTM D – 96 These inorganic particles can lead to operational problems.
Measured by ASTM – 664
Measured by ASTM D – 129, 1552, 2622
Sour crudes > 0.5 wt% and sweet crudes < 0.5 wt%. Today it is difficult to find crudes below 1% sulfur.
TBP Distillation Data
Butanes and lighter 55-175 oF
Light Gasoline 175-300 oF
Light naphtha 300-400 oF
Heavy naptha 400-500 oF
Kerosene 500-650 oF
Atmosphere Gas Oil 650-800 oF
Light Vacuum Gas Oil 800-1000 oF
Hvy. Vacuum Gas Oil 1000 oF
Vacuum Residue > 1000 oF
Specifications and Environmental Regulations for Gasoline and Diesel
Engine knock is caused by the spontaneous ignition of fuel (higher octane gas reduces engine knock). Gasoline engines use spark ignition. Octane number is determined by (Research Octane + Motor Octane)/2. Research octane is measured at low rpm, characteristic of city driving. Motor octane is measured at high rpm, characteristic of highway driving. The octane #s are reported by comparison of the gasoline’s performance to that of a binary mixture of:
2,2,4 – trimethylpentane (100)
Octane Rating Fuel Type Compression Ratio
87 regular 9
93 super 12
Octane # of straight run crude oil is ~ 40
EPA regulations limiting benzene to 1%, aromatics to 10%, and sulfur to 30 ppm
Diesel fuel is rated by a cetane number. The desirable range for the cetane number is between 40-50
EPA regulations limiting sulfur content to 50 ppm in diesel.