442 MINERALS YEARBOOK

 Low-temperature carbonization has possible interest only to the coal operator
who seeks to produce a premium domestic fuel from his slack coal. A commercially
successful process must produce a reasonably dense and strong lump fuel,
which must be sold at a price that will bear most of the costs of the operation.
The returns from tar and light oil will not be any greater than the prevailing
price of the corresponding products from petroleum, which, under present
con-. ditions, means a very low return from the byproducts. In general, low-temperature
processes will have to meet severe competition from anthracite and high-temperature
coke, even though it is granted that easier ignitabiity and ability to hold
a fire are real advantages for the low-temperature product. At present no
low-temperature process has demonstrated that it can operate at lower cost
than existing high-temperature plants.

HYDROGENATION AND LIQUEFACTION OF COAL

 Bergius process.—Dr. Frederich Bergius, inventor of the~ process for
the hydrogenation and liquefaction of coal, states that the direct addition
of hydrogen to coal was first carried out in his laboratory in Hanover in
1913, as a result of some 3 years' study of the chemical nature of coal.6°
In his first experiments a product resembling anthracite was obtained by
subjecting cellulose to very high pressures in steel bombs at elevated temperatures.
In 1912 and 1913 he found~ that under certain conditions of temperatures
and pressures the chemical compounds in coal could be made to take up hydrogen
and be converted into liquid and gaseous compounds and pressures of 100 atmospheres
at temperatures of 3500 to 400° C. Parallel experiments with oil instead
of coal showed that heavy oils and tars could be cracked and hydrogenated
under pressure with large yields of light, saturated hydrocarbons. Even in
these early experiments as much as 85 percent of the coal was converted to
gaseous liquids and benzene-soluble products. It was not until 1921 that
the principal difficulties in developing high-pressure apparatus on a technical
scale were overcome and a systematic examination of various types of coal
and lignite was undertaken.
 In normal bituminous coal the ratiO of hydrogen to carbon is approximately
16 to 1, while in petroleum the ratio is about 8 to 1, hence in the conversion
of coal to oil it is necessary to double the quantity of hydrogen. The process
of liquefaction of coal consists in cracking coal molecules with simultaneous
absorption of hydrogen, or possibly absorption of hydrogen, followed by splitting
up of large molecules into smaller ones, with continued addition of hydrogen.
 In the large-scale process as finally developed in 1926 at Rheinau by Bergius,
a paste of finely pulverized coal mixed with about 40 percent of its weight
of oil from a previous cycle and 5 percent of iron oxide was pumped through
a heat exchanger into a thick-walled steel reaction cylinder, where it was
subjected to the action of hydrogen at a pressure of 150 to 200 atmospheres
and a temperature of 450° to 490° C. The effluent was a black, mobile
liquid containing the residual inorganic matter and unconverted carbonaceous
matter of the charge. The oil was distified from the solid residue, which
60 Bergius, F., The Transformation of Coal into Oil by Means of Hydrogenation:
Proc. 1st Interriat. Q~nf. Bit. Coal, Carnegie Inst. Technol., 1926, pp.
102—131.