Shale oil or kerogen oil is a unconventional oil produced by the destructive distillation of oil shale. This process, a controlled form of pyrolysis, converts the organic matter within the rock (kerogen) into synthetic oil and gas. The resulting oil can be used immediately as a fuel or upgraded to meet refinery feedstock specifications by adding hydrogen and removing impurities such as sulfur and nitrogen. The refined products can be used for the same purposes as those derived from crude oil.

Contents 1 History 2 Retorting process 3 Properties 4 Upgrading 5 Usage 6 Reserves and production 7 References

[edit] History

Oil shale was one of the first sources of mineral oil used by humans.^[1] Its earliest recorded use was in Switzerland and Austria in the early 1300s.^[2] In 1596, the personal physician of Frederick I, Duke of Württemberg wrote of its healing properties.^[3] Shale oil was used to light the streets of Modena, Italy at the turn of the 17th century.^[3] The British Crown granted a patent in 1694 to three persons who had "found a way to extract and make great quantities of pitch, tarr, and oyle out of a sort of stone."^[3][4][5] Later sold as Betton's British Oil, the distilled product was said to have been "tried by divers persons in Aches and Pains with much benefit."^[6] Modern shale oil extraction industries were established in France during the 1830s and in Scotland during the 1840s.^[7] The oil was used as fuel, as a lubricant, and as lamp oil; the Industrial Revolution had created additional demand for lighting. It served as a substitute for the increasingly scarce and expensive whale oil.^[3][8][9]

During the late 19th century, shale oil extraction plants were built in Australia, Brazil and the United States. China (Manchuria), Estonia, New Zealand, South Africa, Spain, Sweden, and Switzerland produced shale oil in the early 20th century. The discovery of crude oil in the Middle East during mid-century brought most of these industries to a halt, although Estonia and Manchuria maintained their extraction industries into the early 21st century.^[7][10][11] Worldwide exploitation of oil shale peaked in 1980 when 47 million tons were mined, over 70% of it in Estonia.^[7] In response to rising petroleum costs at the turn of the 20th century, extraction operations have commenced, been explored, or been renewed in the United States, China, Australia, and Jordan.^[11]

[edit] Retorting process

The pyrolysis of the rock is performed in a retort, situated either above ground or within the rock formation itself. As of 2008, most oil shale industries perform the shale oil extraction process after the rock is mined, crushed, and transported to a retorting facility, although several experimental technologies perform the process in place (in-situ). The temperature at which the kerogen decomposes into usable hydrocarbons varies with the time-scale of the process; in the above-ground retorting process decomposition begins at 300 °C (570 °F), but proceeds more rapidly and completely at higher temperatures. Decomposition takes place most quickly at a temperature between 480 °C/900 °F and 520 °C/970 °F.^[12]

The amount of oil that can be recovered during retorting varies with the shale and the technology used.^[11] About 16% of the Green River Formation shales yield 25 to 100 U.S. gallons of oil per ton of shale; about 33% yield 10 to 25 gallons per ton; and about 50% yield 5 to 10 gallons per ton.^[13]

[edit] Properties

The properties of raw shale oil vary with the shale's composition and the extraction technology from aromatic to aliphatic.^[14] Typically it contains 0.5 to 1% oxygen, 1.5 to 2% nitrogen, and 0.15 to 1% sulfur. Mineral particles are often present as well.^[15][16] The oil is less fluid than crude oil, becoming pourable at temperatures between 75 °F (24 °C) and 80 °F (27 °C), while conventional crude oil is pourable at temperatures between −60 °C (−76.0 °F) to 30 °C (86 °F); this property affects shale oil's ability to be transported in existing pipelines.^[15][17][18]

[edit] Upgrading

Although raw shale oil can be immediately burnt as a fuel oil, many of its applications require that it be upgraded. The differing properties of the raw oils call for correspondingly various pre-treatments before it can be sent to a conventional oil refinery.^[19]

Particulates in the raw oil clog downstream processes; sulfur and nitrogen create air pollution. Sulfur and nitrogen, along with the arsenic and iron that may be present, also destroy the catalysts used in refining.^[20][21] Olefins form insoluble sediments and cause instability. The oxygen within the oil, present at higher levels than in crude oil, lends itself to the formation of destructive free radicals.^[16] Hydrodesulfurization and hydrodenitrogenation can address these problems and result in a product comparable to benchmark crude oil.^{[15][16][22][23]} Phenols can be first be removed by water extraction.^[23] Upgrading shale oil into transport fuels requires adjusting hydrogen-carbon ratios by adding hydrogen (hydrocracking) or removing carbon (coking).^[22][23]

Shale oil produced by some technologies, such as the Kiviter process, can be used without further upgrading as an oil constituent and as a phenolic compound. Distillate oils from the Kiviter process can also be used as diluents for petroleum-originated heavy oils and as an adhesive-enhancing additive in bituminous materials such as asphalt.^[23]

[edit] Usage

Before World War II, most shale oil was upgraded for use as transport fuels. Afterwards, it was used as a raw material for chemical intermediates, pure chemicals and industrial resins, and as a railroad wood preservative. As of 2008, it is primarily used as a heating oil and marine fuel, and to a lesser extent in the production of various chemicals.^[19]

Shale oil's concentration of high-boiling point compounds is suited for the production of middle distillates such as kerosene, jet fuel, and diesel fuel.^[16][24][25] Additional cracking can create the lighter hydrocarbons used in gasoline.^[16][26]

[edit] Reserves and production

Global technically-recoverable oil shale reserves have recently been estimated at about 2.8-3.3 trillion barrels of shale oil, with the largest reserves in the United States, which is thought to have 1.5-2.6 trillion barrels.^{[10][24][27][28]} Worldwide production of shale oil was estimated at 11,600 barrels per day (1,840 m³/d) in 2002. The leading producers were Estonia (5,500 barrels per day (870 m³/d)), Brazil (3,100 barrels per day (490 m³/d)), and China (2,000 barrels per day (320 m³/d)).^[29] The production of shale oil has been hindered because of technical difficulties and costs.^[30]

[edit] References