Ch3 Flashcards
What is crude oil essentially a mixture of?
Hydrocarbons
Petroleum also contains small quantities of oxygen, sulphur, nitrogen, and metals.
What are the implications of differences in composition and types of hydrocarbons in petroleum?
They can greatly affect the physical properties and the processing required to produce salable products.
Why is sulfur considered an undesirable impurity in crude oil?
Due to pollution and corrosion concerns.
How is sulfur content in crude oil measured?
In terms of weight percentage.
What sulfur content generally requires more extensive processing?
Greater than 0.5 wt% sulfur.
What distinguishes sour crude from sweet crude?
Sour crude contains appreciable quantities of hydrogen sulfide or other reactive sulfur compounds; sweet crude is low in sulfur.
What is the criterion often used to distinguish between sour and sweet crudes?
0.5% sulfur content.
What forms can sulfur compounds take in crude oil?
Non-organic and organic compounds.
Fill in the blank: Crudes with salt content greater than ______ generally require desalting before processing.
It is economical to desalt crude oils to _____
10 lb/1000 bbl.
Less than 0.5 lb/1000 bbl.
What can happen if salt is not removed from crude oil?
Severe corrosion problems may be encountered.
What is the typical nitrogen content in crude oil compared to sulfur compounds?
Generally less than that for the sulfur compounds.
Why is high nitrogen content undesirable in crude oils?
It causes severe poisoning of catalysts used in processing and leads to corrosion problems.
What nitrogen content requires special processing to remove nitrogen?
Above 0.25% by weight.
What are the most important nitrogen compounds present in crude oil?
Amides, amines, derivatives of pyrrol, indol, carbazol, pyridine, and qinolean.
What is the Total Acid Number (TAN) of crude oils a measure of?
Potential corrosivity.
What is TAN? What TAN value is usually considered corrosive? Lowest concentration that corrosions can occur?
Total Acid Number: a measure of corrosivity. Quantifies the mg of KOH needed to neutralize 1g of crude oil
Greater than 1 mg KOH/g.
As low as 0.3
What is the general formula for paraffins?
C_nH_(2n+2).
What are isomers in the context of hydrocarbons?
Molecules that contain the same number of carbon and hydrogen atoms but have different structures.
What characterizes naphthenes in crude oil?
Cycloparaffin hydrocarbons where all available bonds of the carbon atoms are saturated with hydrogen.
What do aromatic hydrocarbons contain?
A benzene ring.
What is the general formula for olefins?
C_nH_(2n).
Why are olefins generally undesirable in finished products?
Because the double bonds are reactive and the compounds are more easily oxidized.
What does API gravity measure?
The density of crude oil relative to water.
What is the typical range of API gravity for most crudes?
20 to 45 °API.
Fill in the blank: The lowest temperature at which a material will flow or pour is known as the ______.
pour point.
What does the Watson characterization factor (K_W) indicate?
The paraffinicity of the oil.
What does a correlation index (CI) indicate?
The aromaticity of the oil.
What is the Watson characterization factor for a paraffinic base crude?
12.9
The Watson characterization factor is used to characterize crude oil based on its molecular structure.
What does the Correlation Index (CI) indicate?
The aromaticity of the oil
The CI scale ranges from 0 for straight-chain paraffins to 100 for benzene.
What is the mean average boiling point denoted by?
T_B
T_B is measured in degrees Rankine (°R).
What does specific gravity at 60°F denote?
G
Specific gravity is a measure of the density of a substance compared to the density of water.
What is the CI value for straight-chain paraffins?
0
What is the CI value for benzene?
100
What is the relationship between CI value and concentrations of naphthenes and aromatics?
The higher the CI value, the greater the concentrations of naphthenes and aromatics.
What are the criteria for crude oil to be suitable for asphalt manufacture?
The fraction with T_B = 750°F has a K_W of less than 11.8 and a gravity of less than 35 API, and the difference between K_W for T_B = 750°F and T_B = 550°F is less than 0.15.
What is the API gravity classification for light crudes?
o API > 38
What is the API gravity classification for intermediate crudes?
o API: 22-38
What is the API gravity classification for heavy crudes?
o API < 22
What is the API gravity classification for extra-heavy crudes?
o API < 10
What does the API gravity of bitumen approach?
Zero
What does the boiling range of crude indicate?
Quantities of various products present.
What type of distillation is known as true boiling point (TBP) distillation?
Distillation performed in equipment that accomplishes a reasonable degree of fractionation.
What are Hempel data sheets commonly used for?
Distillation Range analysis.
How is the Hempel analysis reported?
In two parts: at 1 atm pressure up to 527°F and at 40 mmHg total pressure to 572°F.
Why is the portion of distillation at reduced pressure necessary?
To prevent excessive pot temperatures that cause cracking of the crude oil.
What can the distillation temperatures at 40 mmHg pressure be converted to?
760 mmHg.
What were the overall gravity and sulfur content of the Hastings Field, TX crude oil discussed?
Overall gravity: 31.7° API; Sulfur: 0.15 wt%.
Find the specific gravity of a fraction of Hastings Field, TX crude oil with a true boiling point of 295°F.
Specific Gravity = 0.780
What is the formula for calculating specific gravity from API gravity?
Specific Gravity = 141.5/(°API + 131.5)
Metal content range in crude oils
Few ppm to more than 1000ppm
3 metals that can affect catalyst
Nickel, vanadium, and copper
Concentration of vanadium that leads to corrosion
> 2ppm
How are metallic contents dealt with
Distillation leaves them in the residues. Organometallic compounds are volatilized
Can also be reduced by solvent extraction with propane or similar solvents. Organometallic compounds are precipitated with asphaltenes and resins
