Pott-Broche Process

The Pott-Broche process is now mainly of historical interest (Donath, 1963 Dryden, 1963) but several of the processes described previously actually employ the basic Pott-Broche concepts. In the process, bituminous coal is dissolved in a process-derived solvent at 450°C (840°F) and 2200 psi whaeupon approximately 15% (daf) of the feed coal can be dissolved and the products are a light oil and aheavy oil. 

Yields for Liquefaction of Illinois No. 6 Bituminous Coal from the Exxon Donor Solvent Process 

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The Pott-Broche process (101) was best known as an early industrial use of solvent extraction of coal but was ended owing to war damage. The coal was extracted at about 400°C for 1—1.5 h under a hydrogen pressure of 10—15 MPa (100—150 atm) using a coal-derived solvent. Plant capacity was only 5 t/h with an 80% yield of extract. The product contained less than 0.05% mineral matter and had limited use, mainly in electrodes. 

Exxon Donor Solvent Also known as EDS. A coal liquifaction process in which coal in solution in tetrahydronaphthalene is hydrogenated, using a cobalt/molybdenum/alumina catalyst. So-called because the hydrogen is donated by the tetrahydronaphthalene to the coal. Developed from the Pott-Broche process. Piloted by Exxon Research Engineering Company in the 1970s and operated at 250 ton/day in the Exxon refinery in Baytown, TX, from 1980 to 1982. 

Solvent-Refined Coal Process. In the 1920s the anthracene oil fraction recovered from pyrolysis, or coking, of coal was utilized to extract 35—40% of bituminous coals at low pressures for the purpose of manufacturing low cost newspaper inks (113). Tetralin was found to have higher solvent power for coals, and the I. G. Farben Pott-Broche process (114) was developed, wherein a mixture of cresol and tetralin was used to dissolve ca 75% of brown coals at 13.8 MPa (2000 psi) and 427°C. The extract was filtered, and the filtrate vacuum distilled. The overhead was distilled a second time at atmospheric pressure to separate solvent, which was recycled to extraction, and a heavier liquid, which was sent to hydrogenation. The bottoms product from vacuum distillation, or solvent-extracted coal, was carbonized to produce electrode carbon. Filter cake from the filters was coked in rotary kilns for tar and oil recovery. A variety of liquid products were obtained from the solvent extraction-hydrogenation system (113). A similar process was employed in Japan during Wodd War II to produce electrode coke, asphalt (qv), and carbonized fuel briquettes (115). 

H.Lowry, Chemistry of Coal Utilization , Vols 1 2, Wiley, NY (1945) 3)H.H.Lowry H.J.Rose, USBurMinesInfoCirc 7420 (1947) (Description of Pott-Broche process and the plant of Ruhrol GmbH, Bottrop-Welheim, Ger-... 

The Bergius process (Storch, 1945), like the Pott-Broche process, is more of historical interest than current commercial interest but it was a process that literally paved the way for the development of catalytic liquefaction of coal. 

High-pressure (ref. 31), 1, 84-85 Warren (ref. 18), 12-13, Germany (ref. 76) J.H. Howell and R.M. Crawford, The production of synthetic fuels by the hydrogenation of solid and liquid carbonaceous materials. IX the Pott-Broche process, U.S. Naval Technical Mission, Ministry of Fuel and Power, 217-245 (1945), 65-70. 

In the Pott-Broche process, tetralin was used as a solvent for coal extraction in a mixture with cresols (80/20). This method was used to produce 30,000 tpa of coal extract in a plant operated by Ruhrol in Welheim (Bottrop), Germany between 1938 and 1944. Extraction was carried out under a pressure of around 100 bar at a temperature of 415 to 435 °C. The coal extract was used as a low-sulfur fuel, for the production of electrode coke, or refined by hydrogenation to yield benzole, middle oil and heavy oil. The solvent had to be regenerated, i.e. hydrogenated, before each extraction. 

Pott-Broche A coal liquifaction process in which coal is dissolved in a mixture of tetrahy-dronaphthalene and cresols, and then hydrogenated. Invented by A. Pott and H. Broche at IG Farbenindustrie, Germany in 1927 used by the Ruhrol Company in Germany between 1938 and 1944. See also Exxon Donor Solvent. 

The SRC (solvent refined coal) process of Pittsburgh Midway Coal Mining Gulf Oil) is an advanced version of the Pott-Broche extraction process. The purpose of the SRC method is to desulfurize coal to yield a solid, low-sulfur fuel. 

There are two types of processes available for coal liquefaction, namely direct conversion of coal with hydrogen, invented by Friedrich Bergius in 1913, and coal extraction with hydrogenating solvents, first tested in a pilot plant by Alfred Pott and Hans Broche in 1935. The products from both processes can be further hydrogenated in a second stage to obtain fuels. 

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