Middle oils

A typical primary distillation product pattern at a coke-oven tar-processing plant is given in Table 1. At some coke-oven distilleries, only one fraction, designated naphthalene oil, is taken between 180 and 240°C. Two fractions, light creosote or middle oil (230—300°C) and heavy creosote or heavy oil (above 300°C), are taken between the naphthalene oil and pitch. 

Carbolic Oils and Tow Temperature Tar Middle Oil, TarMcids. The fractions of some coke-oven tars, distilling in the range of 180—240°C, and the middle oil fraction (180—310°C) from low temperature tars are treated for the recovery of tar acids (19). 

Imperial Chemical Industries in Great Britain hydrogenated coal to produce gasoline until the start of World War II. The process then operated on creosote middle oil until 1958. As of this writing none of these plants is being used to make Hquid fuels for economic reasons. The present prices of coal and hydrogen from coal have not made synthetic Hquid fuels competitive. Exceptions are those cases, as in South Africa, where there is availabiHty of cheap coal, and fuel Hquids are very important. 

At one time the requirement for phenol (melting point 41°C), eould be met by distillation of eoal tar and subsequent treatment of the middle oil with eaustic soda to extraet the phenols. Such tar acid distillation products, sometimes containing up to 20% o-cresol, are still used in resin manufacture but the bulk of phenol available today is obtained synthetically from benzene or other chemicals by such processes as the sulphonation process, the Raschig process and the cumene process. Synthetic phenol is a purer product and thus has the advantage of giving rise to less variability in the condensation reactions. 

Chemical Designations - Synonyms Middle Oil Liquefied Phenol Chemical Formula CijH OH. Observable Characteristics - Physical State (as twrmally shipped) Liquid Color Colorless, darkens on exposure to light Odor Sweet, tar-like. 

Naphthalene is obtained from the middle oil in the distillation of coal-tar. It crystallises in colourless, glistening plates, which have a characteristic smell. 

The technical method for obtaining phenol is by shaking out with caustic soda the middle oil of the coal-tar distill ate,. after some of the naphthalene has crystallised out. The phenol dis-soKes m the alkali, and is then lemoved fiom insoluble oils. The alkaline liquid is acidified, the phenol separated, distilled, and finally purified by freezing. 

Mittel-ol, n. middle oil medium-heavy oil. -ost, m. Middle East, -produkt, n. middle product intermediate middlings, -punkt, m. center, central point, mittels, prep, by means of,... 

Figure 1 Space-time-yield (volume/volume reactor/100 hours) of gasoline and middle oil for brown and bituminous coals as a function of composition of starting coal. Data from continuous coal hydrogenation facilities operating in Germany during the 1930 s.

CARBOLIC OIL Middle Oil, Liquefied Phenol Poisonous Liquid or Solid, Class B 3 2 0 ... 

Gases and vapors from the hot catchpot are cooled and passed to a cold catchpot. The condensate is discharged at atmospheric pressure and topped to provide middle oil for the second stage of hydrogenation and distillate heavy oil, which is recycled for dilution of the heavy oil slurry and for paste preparation. 

Distillation of coal tar yields light oil (contg benzene, toluene 8c xylene), middle oil (contg phenol, cresol naphthalene), heavy oil (contg impure cresol other phenols) and green oil (contg anthracene) (Refs 4,9,11 13)... 

Middle Oil—yielding about 40 lb. of phenol and cresols, and 80-120 lb. of naphthalene. 

Liquid-phase hydrogenation for the conversion of coal, tar, or heavy oil into an intermediate product—the middle oil—with a boiling range up to about 325°C. (In this stage finely divided catalysts distributed in the liquid or liquefiable feed were used.)... 

Vapor-phase hydrogenation using a fixed-bed catalyst for the conversion of middle oil into gasoline whereby the middle oil was vaporized under pressure in a stream of hydrogen. 

Pilot plant results indicated that satisfactory catalyst life could be realized by gradual temperature increase to offset the decrease in activity with time. This decrease in activity was caused mainly by the formation of more refractory aromatic recycle oils. In commercial operation the activity loss of the catalyst was more rapid. The decline in catalyst activity could be slowed down by decreasing the end point of the feed middle oil or by withdrawing small amounts of heavy ends formed. Commercial operation indicated further that the use of recycle hydrogen was a cause of the more rapid loss of catalyst activity. Ammonia and volatile ammonium salts formed by the reduction of tar bases in the feedstock might have been a factor in the accelerated-catalyst-activity loss. 

Prehydrogenation of bitu- Splitting hydrogenation minous-coal middle oil of petroleum gas oil... 

For the splitting hydrogenation of petroleum gas oil, a lower temperature than that required for the prehydrogenation of bituminous-coal middle oil with smaller conversion to gasoline was sufficient. This is caused mainly by the higher nitrogen content of the bituminous-coal middle oil, which decreases catalyst activity. As shown in Table IV, aromatic rings like naphthalene are saturated with WS2 catalyst at a temperature of 335°C. 

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