Frasch process

Frasch process

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The Frasch process is a method to extract sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

 from underground deposits. It is the only economic method of recovering sulfur from elemental deposits. Most of the world's sulfur was obtained this way until the late 20th century, when sulfur recovered from petroleum and gas sources (recovered sulfur) became more commonplace (see Claus process
Claus process
The Claus process is the most significant gas desulfurizing process, recovering elemental sulfur from gaseous hydrogen sulfide. First patented in 1883 by the scientist Carl Friedrich Claus, the Claus process has become the industry standard....

).

In the Frasch process, superheated water is pumped into the sulfur deposit; the sulfur melts and is extracted. The Frasch process is able to produce high purity sulfur.

As of 2011, the only operating Frasch mines worldwide are in Poland and since 2010 in Mexico. The last mine operating in the United States closed in 2000. A Frasch mine in Iraq closed in 2003 due to the U.S. invasion of Iraq.

History


In 1867, miners discovered sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

 in the caprock of a salt dome
Salt dome
A salt dome is a type of structural dome formed when a thick bed of evaporite minerals found at depth intrudes vertically into surrounding rock strata, forming a diapir....

 in Calcasieu Parish, Louisiana
Calcasieu Parish, Louisiana
Calcasieu Parish[p] is a parish located in the U.S. state of Louisiana. The parish seat is Lake Charles. As of 2010, the parish population was 192,768...

, but it was beneath quicksand
Quicksand
Quicksand is a colloid hydrogel consisting of fine granular matter , clay, and water.Water circulation underground can focus in an area with the optimal mixture of fine sands and other materials such as clay. The water moves up and then down slowly in a convection-like manner throughout a column...

, which prevented mining. In 1894 the German-born American chemist, Herman Frasch
Herman Frasch
Herman Frasch [or Hermann Frasch] was a mining engineer and inventor known for his work with petroleum and sulphur.-Biography:...

 (1852–1914), devised his Frasch method of sulfur removal using pipes to bypass the quicksand. The process proved successful, on December 24, 1894, when the first molten sulfur was brought to the surface. However, the high cost of fuel needed to heat the water made the process uneconomic until the 1901 discovery of the Spindletop
Spindletop
Spindletop is a salt dome oil field located in the southern portion of Beaumont, Texas in the United States. The Spindletop dome was derived from the Louann Salt evaporite layer of the Jurassic geologic period. On January 10, 1901, a well at Spindletop struck oil . The new oil field soon produced...

 oil field in Texas provided cheap fuel oil to the region. The Frasch process began economic production at Sulfur Mine, Louisiana in 1903.

When Frasch's patent expired, the process was widely applied to similar salt-dome sulfur deposits along the US Gulf Coast. The second Frasch-process mine opened in 1912 in Brazoria County, Texas
Brazoria County, Texas
Brazoria County[p] is a county in the U.S. state of Texas, located on the Gulf Coast within the Houston–Sugar Land–Baytown metropolitan area. Regionally, parts of the county are within the extreme southern-most fringe of the regions locally known as Southeast Texas. Brazoria County is among a...

. The US Gulf Coast came to dominate world sulfur production in the early and middle 20th century. However, starting in the 1970s, byproduct sulfur recovery from oil and natural gas lowered the price of sulfur and drove many Frasch-process mines out of business. The last US Frasch sulfur mine closed in 2000. A Frasch mine in Iraq closed in 2003 due to the U.S. invasion of Iraq.

The Frasch process is used to work sulfur deposits in the United States, Mexico, Poland, and Iraq.

Process



In the Frasch process, three concentric tubes are introduced into the sulfur deposit. Superheated water (165 °C, 2.5-3 MPa) is injected into the deposit via the outermost tube. Sulfur (m.p. 115 °C) melts and flows into the middle tube. Water pressure alone is unable to force the sulfur to the surface due to the molten sulfur's greater density, so hot air is introduced via the innermost tube to froth the sulfur, making it less dense, and pushing it to the surface.

The sulfur obtained can be very pure (99.7 - 99.8 %). In this form, it is light yellow in color. If contaminated by organic compounds, it can be dark-colored; further purification is not economic, and usually unnecessary. Using this method, the United States produced 3.89 million tonnes of sulfur in 1989, and Mexico produced 1.02 million tonnes of sulfur in 1991.
The Frasch process can be used for deposits 50–800 meters deep. 3-38 cubic meters of superheated water are required to produce every tonne of sulfur, and the associated energy cost is significant. A working demonstration model of the Frasch process suitable for the classroom has been described.