Coal liquefaction

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Coal liquefaction (also coal hydrogenation ; English coal-to-liquid - or CtL process) describes chemical processes that produce liquid hydrocarbons from solid coal .

The Bergius-Pier process of direct hydrogenation of coal was used to produce gases, carburetor and diesel fuels . The hydrogen required for this is obtained through coal gasification . Liquid hydrocarbon products are also obtained by extracting coal with hydrogen-transferring solvents under pressure, as in the Pott-Broche process . Indirect processes such as the Fischer-Tropsch synthesis use synthesis gas , a mixture of carbon monoxide and hydrogen from coal gasification, to produce hydrocarbons .

Both methods differ significantly. In the Bergius-Pier process, the carbon structure is broken down into simpler molecules through hydrogenation with hydrogen, while in the Fischer-Tropsch process, hydrocarbons are built up from carbon monoxide and hydrogen. The products of the Bergius-Pier process have a higher aromatic content and a higher octane number, while the products of the Fischer-Tropsch process are more paraffinic and the higher molecular weight components are suitable as a basic product for the chemical industry.

The motivation for the large-scale use of coal liquefaction is the replacement of crude oil as a raw material for the petrochemical and energy sectors. The processes become more important when crude oil is not available in sufficient quantities, for example in Germany during the time of National Socialism .

history

Friedrich Bergius

As early as 1913, Friedrich Bergius received a patent for a process for the production of liquid or soluble organic compounds from coal and the like , for which he was awarded the Nobel Prize in Chemistry in 1931. Bergius' coal liquefaction process yielded “100 kg of hard coal and 40 kg of heavy oil from the process, with the addition of 5 kg of iron oxide and 5 kg of hydrogen at 120-150 atm and 450 to 480 ° C, about 30 kg of light oil and 50 kg of heavy oil and asphalt, in addition to 20 kg of gas, mainly methane and ethane. ” In the 1920s, the German chemical industry developed the process to industrial maturity. The lead factory was the Leuna works of IG Farben near Merseburg , which went into operation in 1927.

The Bergius process gained greater importance for the first time during the National Socialist era for the production of synthetic gasoline. In addition to the low, but at that time still notable, German oil production, only crude oil reserves were conditionally available in Romania . Between 1936 and 1943, eleven further hydrogenation plants were built in Germany, which together with the plant in Leuna had a total capacity of around 4 million tons. Lignite or lignite tar were used as raw materials in the Leuna , Böhlen , Magdeburg , Zeitz , Wesseling and Brüx plants , while coal , oil, pitch or tar were used in the Scholven , Gelsenberg , Pölitz , Welheim and Blechhammer plants .

In 1925 Franz Fischer and Hans Tropsch registered a patent for a process for indirect liquefaction. According to the Fischer-Tropsch process , nine plants were built in Germany between 1935 and 1939; the largest Fischer-Tropsch plant with a capacity of 210,000 t / a was located in Ruhland-Schwarzheide . The total capacity of the nine plants was around 740,000 t / a.

After the systematic destruction of the facilities by Allied air raids in May 1944, facilities were also built underground ( Geilenberg program ). Some of the production took place with forced laborers and in satellite camps.

In West Germany, coal liquefaction was discontinued after the war because of the unrivaled low oil prices. In the GDR, the last coal hydrogenation chamber in Leuna, although also "intolerably uneconomical", was not finally shut down until the mid-1950s, when the subsidies for the so-called "coal preference" introduced in Germany in the thirties were lifted by the Federal Republic and thus no longer how up until then all fuel deliveries from the GDR to the Federal Republic were subsidized. However, due to the rise in oil prices shortly afterwards, a resumption of fuel synthesis from lignite for export purposes with improved processes was part of the strategic planning of the Council of Ministers from the end of the 1970s until the collapse of the GDR.

In the Federal Republic of Germany, as a result of the first “oil crisis” in 1973, the energy research program adopted by the Federal Government in 1974 saw the establishment of seven pilot plants for coal refining (gasification and liquefaction), which went into operation from 1977 to 1980. From 1980, 14 large-scale plants with a total consumption of 22 million tons of hard and lignite per year were planned. However, the decline in oil prices in the mid-1980s made these plans obsolete. The pilot plants subsequently went out of operation step by step. The Bottrop coal oil plant was initially converted to the hydrogenation of chemical and plastic waste. The last very small plant still in operation in Essen with a production of approx. 200 kg / day was dismantled in 2004 and rebuilt for China Shenhua Energy in China.

Inspired by the development of high-temperature reactor technology, it was discussed how to generate the necessary process heat using nuclear reactors and thus to achieve higher levels of efficiency. Among other things, the HTR / CtL relationship explains why HTR technology is being further developed in China and South Africa. HTR development in South Africa was completely stopped in autumn 2010. Recent scientific results raise doubts that the temperatures required for CtL can be achieved with pebble bed reactors, the variant of high-temperature reactors promoted in Germany until 1990.

In the South African Union , whose industry had access to very large coal resources but had to import crude oil, the first modern CtL plant in South Africa near Sasolburg was put into operation in 1955 as a result of politically motivated self-sufficiency efforts . It was built by Suid Afrikaanse Steenkool en Olie (Sasol) with the participation of the German Lurgi AG . The Sasol 1 pilot plant was designed for around 6,000 barrels of fuel per day. Despite the low costs for the coal mined in what was then the Transvaal , the fuel produced had to be subsidized until the 1960s. The process was continuously improved and finally it could be operated economically.

Further production facilities, called Sasol II, were planned for the city of Secunda as a consequence of the oil crisis around 1973 and built from 1976. Its commissioning took place in mid-1981. The planning of Sasol III took place under the impression of the 1979 collapse of the regime of Mohammad Reza Pahlavi in Iran as a result of the Islamic Revolution . Sasol III was a copy of the Sasol II equipment and reached full production capacity in 1985. The reasons for the expansion of capacities are complex and mainly to be found in the growing militarization of South Africa, the increasing foreign policy confrontation within the framework of the total strategy and in the continued international embargoes against apartheid policy . A capacity of 104,000 barrels per day was now available in South Africa. With the political opening after 1994, the program was expanded to include natural gas as a raw material source, and in 1995 and 1998 additional capacities for 124,000 barrels / day of CtL and GtL fuel were created.

Procedure

A distinction is made between indirect processes, which are preceded by coal gasification , and those that hydrogenate coal directly, and extraction processes.

Bergius Pier Procedure

Ruins of a plant on the site of the former Pölitz hydrogenation plant near Stettin, now Police (Poland)

The Bergius Pier process is a large-scale process in which hydrocarbons are produced by hydrogenating coal with hydrogen in an exothermic chemical reaction . It is named after Friedrich Bergius and Matthias Pier . With highly active catalysts such as ammonium chloride and tin oxalate , the coal is heated at a hydrogen pressure of around 300 bar and temperatures of 470 to 490 ° C. Inexpensive catalysts such as iron oxide , so-called Bayer mass, require pressures of up to 700 bar. Other sources also quote lower pressures, depending on the catalyst. The range of products depends on the reaction conditions (hydrogen pressure, temperature, residence time) and the way in which the reaction is carried out (liquid phase hydrogenation or gas phase hydrogenation). The result is primarily liquid fractions that are used as fuel or heating oil. The coal used must be mechanically brought to an ash content of around 4 to 6%. Bituminous coals can be used undried, brown coals must first be dried to a water content of 5 to 10%.

Scheme of the Bergius-Pier procedure

In the sump phase hydrogenation, the catalyst is added to finely ground coal that has been suspended in a solvent and pressurized with hydrogen. Gas, petrol and coal oils are produced as light, medium and heavy oil, which are separated by distillation. The solid components are centrifuged off. The resulting oil, the so-called thin run, is used for mashing in the coal preparation. The solid components are smoldered for further extraction of oils. Smoldering coke is a solid product.

Fischer-Tropsch synthesis

In the Fischer-Tropsch process is initially at very high temperatures (over 1000 ° C) in the gasification of coal with steam and air or oxygen to the coal synthesis gas reacted, which is reacted, after removal of nitrogen oxides and sulfur dioxide catalytically converted to hydrocarbons and water. End products are gasoline ( synthetic gasoline ), diesel and heating oil as well as aromatics for the chemical industry.

This indirect coal liquefaction is more economical than direct coal liquefaction. Because of the high energy consumption and the associated CO 2 release during production - with the Fischer-Tropsch process about twice as high as with petroleum - the substances produced are significantly more harmful to the climate than corresponding petroleum products.

There are currently 25 indirect coal hydrogenation plants being planned worldwide, including 13 in the USA and 7 in China.

Coal extraction

For coal extraction, solvents are used which, under the selected extraction conditions , can transfer hydrogen to the coal in a transfer hydrogenation . Tetralin , which is oxidized to naphthalene during the extraction, has proven itself . Naphthalene can be separated off and converted back into tetralin by hydrogenation. The process is carried out under pressure at specific temperatures and residence times of around three hours, depending on the type of coal. The latest research includes the reactive extraction of lignite with, among other things, ethanol.

meaning

For reasons of cost, the processes of coal liquefaction are currently of no great economic importance. If oil prices persist, this situation could possibly change.

The coal liquefaction plants in South Africa are of particular commercial importance, with a production of 160,000 barrels / day they cover roughly one third of South African fuel consumption. There are three Fischer-Tropsch plants operated by the Sasol company; the construction of a fourth plant is planned. The synthesis product can be produced here at a price of approx. $ 25 / barrel. In addition to process engineering that has been developed over decades, the low coal production costs in the immediate vicinity of the site and low wage costs are decisive.

In the People's Republic of China there are plans to build two coal liquefaction plants in the provinces of Ningxia and Shaanxi . The plants should each have a capacity of 80,000  barrels / day (approx. 12,720 m 3 / day) and work with the technology of the South African company Sasol. In Australia, Monash Energy, a cooperation between Anglo American and Shell , is planning a major long-term project that will include newly developed coal mining, coal liquefaction and CO 2 sequestration and which could ultimately supply around a quarter of Australian fuel requirements .

Coal liquefaction costs around US $ 25–45 per barrel of oil equivalent. This made them competitive at oil prices in 2010, but no longer at prices in 2016.

Again, strategic considerations can play a role. The American Air Force ( USAF ) started test flights in 2006 with B-52 bombers , some of which are powered by synthetic fuel. The aim is to reduce the dependency of national defense on oil imports.
A facility for 18,000 barrels of gasoline per day is currently under construction in Mingo County, West Virginia. The plant is to work according to the PRENFLO process, a print version of the Koppers-Totzek process.

literature

  • Daniel Vallentin: Coal liquefaction, opportunities and limits , PdN-ChiS, Aulis-Verlag, 1/2009, pp. 17-19
  • Traa Yvonne: "Is a renaissance of coal imminent? -Challenges for catalysis", Chem. Commun. (2010) 46, pp. 2175-2187

Web links

Individual evidence

  1. ↑ a b Robert Haul: The Portrait: Friedrich Bergius (1884-1949). In: Chemistry in Our Time. 19, 1985, pp. 59-67, doi: 10.1002 / ciuz.19850190205 .
  2. ^ A b c d e f Karl-Heinz Schmidt, Ingo Romey, Fritz Mensch: Coal, petroleum, natural gas: chemistry and technology. Vogel, Würzburg 1981, ISBN 3-8023-0684-8 .
  3. ↑ Henry Ludmer: Oil in Germany ( Memento of 8 September 2006 at the Internet Archive ).
  4. ↑ vfkk.de: Forced Labor ( Memento from June 22, 2007 in the Internet Archive ).
  5. ↑ Marlies Mrotzek: The concentration camp subcamp of Gelsenberg Petrol AG . Germinal, Fernwald (Annerod) 2002, ISBN 3-88663-527-9 .
  6. ↑ Answer to a small question in the Bundestag on the energy research program - especially on coal liquefaction ( BT-Drs. 10/459 ).
  7. ^ Sigurd Schulien: The energy supply of Germany in the 21st century . In: AGAFE communications . tape 24 , no. 2 , 2005, p. 10-13 ( PDF ).
  8. ^ John T. Wolan, Faustino L. (Tino) Prado: Production of synthetic fuel hydrocarbons from biomass using the Prado-Wolan Fischer-Tropsch process . Technical Paper Presentation, conference paper June 7, 2008 Clearwater (Florida), American Institute of Chemical Engineers PDF document p. 4
  9. ↑ a b D. Valentin: Coal liquefaction - opportunities and limits. In: Practice of the natural sciences - chemistry in school . Volume 58, No. 1, 2009, pp. 17-19.
  10. ↑ H. Wollmerstädt: Reactive extraction of lignite for the production of chemical raw materials and fuels In: Chemie Ingenieur Technik 86, 2014, pp. 1363–1364, doi: 10.1002 / cite.201450427 .
  11. ↑ Demand drives the price of coal up . In: Frankfurter Allgemeine Zeitung . July 31, 2008.