1. A Quick Lesson On Crude Oil
Crude oil is composed of thousands of different chemical compounds, all with different boiling points.
A typical crude oil may begin to boil ~150°F; at 1000°F there is still crude oil which has not boiled.
Crude oil is generally described as being light/heavy or sweet/sour.
There are no strict definitions describing these measures.
In general a heavy crude is <25°API while a light crude is >30°API.
API is an index which is a relative measure of weight; the lower the number the heavier the material.
In general sour crude has more than 2% sulfur, while sweet has less than 0.5%.
The majority of Venezuelan oil is heavy and sour.

2. Value Creation At The Refineries
Refineries add value in two primary ways:
Separating oil into its more valuable components
The primary process is fractionation.
Another widely used process is extraction.
Chemically reacting the components to create more valuable products
Primary examples are:
Hydrodesulfurization
Reforming
Cat Cracking
Coking

3. Separation Processes
Most refinery equipment is for separation, which exploits the chemical differences of the compounds in crude oil.
Separation Processes
Fractionation (atmospheric and vacuum) takes advantage of the fact that different compounds have different boiling points.
Extraction takes advantage of the solubility of different compounds for a solvent.
Other separation processes (less common): crystallization, etc.

4. The Refining Process

5. Atmospheric Fractionation
The crude oil is heated to over 700°F at atmospheric pressure.
The smaller/lighter compounds come out of the top, the heaviest out of the bottom.
For CITGO’s complex refineries, the products are further processed in the refinery:
Butane and lighter are further processed.
Propane is recovered and sold.
Butane is blended to gasoline during the winter.
Naphtha is sent to the Reformers.
Kerosene & light gas oil are hydrotreated and blended turbine & diesel respectively.
Heavy gas oil is sent to the Cat Crackers.
Straight run resid is further processed in the Vacuum Units.

6. Vacuum Fractionation Extraction
Further processing of straight run resid (50% of the yield) in the atmospheric unit would tend to crack it and form coke at elevated temperatures.
Since boiling points are reduced as pressure decreases, we can boil the atmospheric residue in a vacuum at temperatures low enough to prevent cracking and coking.
The vacuum unit separates about half its feed into vacuum gas oil, which is further processed at the Cat Cracker. The residue (“bottom of the barrel”) is sent to the Coking Unit for further processing.
Extraction
CITGO’’s main uses of extraction: petrochemicals and lubricants.
Oil and water are not mutually soluble. Likewise, certain solvents dissolve different oil compounds better than in the original oil.
Taking advantage of this allows us to separate aromatics from reformates and lube base oils and waxes from vacuum gas oils.

7. Chemical Reactions
The value addition so far has only come through the separation of the molecules created by nature. Changing the chemical composition of the crude oil is the main source of value addition in the refining business.
Numerous catalysts are used throughout the refining process to facilitate the chemical reactions.
Crude oil itself will yield only ~30-40% of gasoline/diesel fuels.
When our refineries are finished processing the oil, we are able to yield ~90% as gasoline/diesel fuels.

8. Chemical Reactions
Reforming changes the molecular structure of naphtha to produce reformate (a primary gasoline blending stock).
Fluid catalytic cracking mixes vacuum gas oil with a catalyst at temperatures over 1000°f, promoting numerous chemical reactions. By breaking long molecules down into shorter ones (“cracking”), over 75% of the feed is converted to more valuable gasoline and lighter products.
Cokers process vacuum resid, which is heated to over 900°f and put into the coke drums, where it undergoes thermal cracking as the oil decomposes under the extreme heat. Products include butanes and lighter, naphtha for the Reformers, turbine and diesel fuel, gas oil for the Cat Crackers, and petroleum coke, which is sold as a fuel.

9. Chemical Reactions
Alkylation combines small molecules into larger ones to create alkylate, a high-octane gasoline component.
Hydrocracking also converts big molecules to smaller ones, but can process a much wider range of feedstocks. Expensive to operate, but very flexible. Operarions can be tailored to suit economic oportunities.
Hydrotreating removes impurities (primarily sulfur and nitrogen) by combining hydrogen with refined products over special catalysts at high temperatures.
Sulfur recovery converts H2S from the coking, cracking and hydrotreating processes and converts it to pure sulfur for sale.

10. Putting It All Together
The simplest refineries generally consist of crude, vacuum, reforming and some hydrotreating capacity.
If a refinery such as this would process heavy sour crudes, it would at best be able to produce ~35% of finished gasoline, turbine and diesel. The majority of the balance would be vacuum gas oil and asphalt type material.
These refineries, therefore, are usually limited to light, sweet crudes.
Most of these refineries have already ceased operations due to poor profitability. The remaining refineries of similar configuration are usually operating in a niche.

11. Putting It All Together
The next level of complexity adds cat crackers and some additional hydrotreating.
If a refinery like this processed heavy, sour crude, it would at best be able to produce ~65% of finished gasoline, turbine and diesel, with the majority of the balance being asphalt type material.
These refineries, therefore, usually process lighter sweet crudes. However, they can process heavy sour if they can obtain a secure outlet for the large volumes of asphalt they produce

12. Putting It All Together
The most complex refineries add cokers, more hydrotreating and possibly hydrocracking.
Refineries like this can process heavy sour crude with the capability of yielding ~85% as finished gasoline, turbine and diesel. Petroleum coke and petrochemicals make up most of the balance