Distillation Oil Refining

Crude oil, also called petroleum, is a complex mixture of carbon and hydrogen (hydrocarbons), which exist as a liquid in the earth's crust. Crude oil has many compositions, some is black, thick and tar like, while other crude oils are lighter in color and thinner. The carbon and hydrogen in crude oil are thought to have originated from the remains of microscopic marine organisms that were deposited at the bottom of seas and oceans and was transformed at high temperature and pressure into crude oil and natural gas.

This oil and gas migrates upward through the porous rock, as it is less dense than the water which fills the pores. The oil and gas is trapped by a layer of impermeable rock through which they can't flow. Several different types of oil and gas "traps" exist; a common dome formed by folded sedimentary rocks. Crude oil is obtained by drilling a hole into the reservoir rock (sandstone, limestone etc.) and pumping it out.

Petroleum refining is the process of separating the many compounds present in crude petroleum. This process is called fractional distillation where the crude oil is heated; the various of the compounds boil at different temperatures and change to gases; and are later recondensed back into liquids. Fossil Fuels

The principle which is used is that the longer the carbon chain, the higher the temperature at which the compounds will boil.
Boiling Points and Hydrocarbons

The crude petroleum is heated and changed into a gas. The gases are passed through a distillation column which becomes cooler as the height increases. See the figure on the left. When a compound in the gaseous state cools below its boiling point, it condenses into a liquid. The liquids may be drawn off the distilling column at various heights.
Although all fractions of petroleum find uses, the greatest demand is for gasoline. One barrel of crude petroleum contains only 25-35% gasoline. Transportation demands require that over 50% of the crude oil be converted into gasoline. To meet this demand some petroleum fractions must be converted to gasoline. This may be done by "cracking" - breaking down large molecules of heavy heating oil; "reforming" - changing molecular structures of low quality gasoline molecules; or "polymerization" - forming longer molecules from smaller ones. Conversion Oil Refining
For example if decane is heated to about 500 C the covalent carbon-carbon bonds begin to break during the cracking process. Many kinds of compounds including alkenes are made during the cracking process. Alkenes are formed because there are not enough hydrogens to saturate all bonding positions after the carbon-carbon bonds are broken.

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Cupellation

Cupellation is a process used to separate noble metals such as gold or silver from base metals such as lead. It is often used to assay gold in order to test its purity. Sometimes cupellation is called "fire assaying." It was formerly the usual process for extracting silver from lead.

In this process, an alloy consisting of both noble and base metals is placed in a crucible. This mixture is then melted and allowed to freeze. When solidified, a button consisting of precious metals and lead can be removed from the slag of metal oxides and other materials. When assaying ores this slag layer can be quite massive, but when assaying karat gold, it is virtually non-existent. After cooling, the metals are placed in a special pot made of bone ash or clay called a cupel. Under high heat, lead turns to litharge, a lead oxide, which is absorbed by the cupel or lost to the atmosphere. At the end of the cupellation process, a button of pure gold and silver remains in the bottom of the cupel. The button is then placed in nitric acid to dissolve the silver, and the remaining pure (24k) gold weighed to determine the gold content present in the original starting material.

Loss of lead to the larger atmosphere creates an environmental hazard, and so this larger loss should be restrained by appropriate equipment and lead recovery means.

Historically, cupellation was not merely a method of assaying, but also the main means of extracting silver from lead. It produced litharge in large quantities which was usually resmelted to lead.

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Petroleum

Petroleum (L. petroleum, from Greek πετρέλαιον, lit. "rock oil") or crude oil is a naturally occurring, flammable liquid found in rock formations in the Earth consisting of a complex mixture of hydrocarbons of various molecular weights, plus other organic compounds.

The term "petroleum" was first used in the treatise De Natura Fossilium, published in 1546 by the German mineralogist Georg Bauer, also known as Georgius Agricola.

Composition

The proportion of hydrocarbons in the mixture is highly variable and ranges from as much as 97% by weight in the lighter oils to as little as 50% in the heavier oils and bitumens.

The hydrocarbons in crude oil are mostly alkanes, cycloalkanes and various aromatic hydrocarbons while the other organic compounds contain nitrogen, oxygen and sulfur, and trace amounts of metals such as iron, nickel, copper and vanadium. The exact molecular composition varies widely from formation to formation but the proportion of chemical elements vary over fairly narrow limits as follows:

omposition by weight

Element	Percent range
Carbon	83 to 87%
Hydrogen	10 to 14%
Nitrogen	0.1 to 2%
Oxygen	0.1 to 1.5%
Sulfur	0.5 to 6%
Metals	less than 1000 ppm

Four different types of hydrocarbon molecules appear in crude oil. The relative percentage of each varies from oil to oil, determining the properties of each oil.