US2284460A - Purification of coal tab bases - Google Patents

Description

Patented May 26, 1942 PURIFICATION OF COAL TAR BASES Joseph H. Wells and Philip J. Wilson, Jr., Pittsburgh, Pa., assignors to Carnegie-Illinois Steel Corporation, a corporation of New Jersey No Drawing. Application July 22, 1941, Serial No. 403,586

2 Claims.

This invention is concerned with the problem of recovering pyridine bases from coal tar distillation oil fractions containing these bases along with at least 2% phenol and small volumes of other constituents that are soluble in the phenol. It is, of course, necessary to recover the pyridine bases so that they are relatively free from the phenol and the other constituents men tioned, these other constituents being impurities, neutral oils and gummy compounds.

According to the invention, this problem is solved by washing such a fraction with dilute sulphuric acid at an elevated temperature of from 60 to 100 C., until a solution is obtained containing in equilibrium concentration pyridine sulphate and the phenol with the described constituents dissolved therein. In addition to the pyridine, this solution will contain in sulphate form any other coal tar base that was present in the fraction when it was washed.

The elevated temperature of the above washing is the cause of the sulphate solution obtained containing the phenol with the phenol-soluble constituents dissolved therein. However, the elevated temperature of the washing has been found necessary in the case of the fractions con taining 2% or more of phenol, since in such instances the phenol combines with the pyridine bases to form complexes which cannot be easily decomposed by the prior art lower temperature acid washing successfully used in the case of fractions containing lower percentages of phenol.

The sulphate solution obtained by the prior art practice of acid washing at room temperature the fractions containing relatively little phenol, is 1 customarily purified by steam rectification. This produces an adequately pure pyridine su phate solution for pyridine recovery purposes, it serving to largely remove the relatively small amounts of contamination resulting from such acid washing. However, the sulphate solution obtained by the practice of the present invention cannot be treated in this manner, because it contains such large volumes of phenol and the described constituents that so much steam and time would be required as to make the practice economically impractical.

With the above in mind, the sulphate solution resulting from the elevated temperature acid washing, is cooled to a temperature no higher than 40 C. and is then washed with a relatively small volume of the original oil fraction, or any similar fractions; for instance, it being possible to use the acid-washed fraction low in pyridine for this purpose, providing it is cooled to a temperature not greater than 40 C. The result of this washing is to unbalance the equilibrium between the concentration of the phenol carrying the dissolved constituents and the pyridine sulphate solution, whereby this contamination passes back into the washing oil fraction. Therefore, separation of the pyridine sulphate solution from the washing oil results in a solution that is sufficiently free from contamination to permit, it to be rectified with steam without an excessive consumption of either steam or time. The washing oil fraction will contain, in addition to the phenol and the phenol-soluble constituents, some pyridine bases which may, however, be recovered by returning the washing oil fraction to the system so that it can be subjected to the elevated temperature acid washing.

As a specific example of the invention, 500 gallons of a coal tar distillation oil fraction, containing 4% by volume of pyridine and 21% by volume of phenol, along with the usual amounts of phenol-soluble constituents, is washed with three successive portions of 90 gallons each of a 25% sulphuric acid solution at 80 C. The pyridine in the oil fraction is thereby reduced to by volume.

This results in 110 gallons of a black, cloudy pyridine sulphate solution containing 33% by volume of pyridine and 110 grams per liter of phenol. It is to be understood that the pyridine sulphate solution also contains, in sulphate form, any tar bases that were in the washed fraction, and that the phenol includes the neutral oils and gummy compounds previously discussed. This solution is then. cooled to from to 35 C.

Fifteen gallons of the acid washed oil fraction are then cooled to from 20 to 35 0., and are added to the cooled pyridine sulphate solution, and the mixture thoroughly agitated for 15 minutes. Agitation is then stopped and the mixture settles into two layers, the bottom layer being a clear, amber pyridine sulphate solution, with a volume of from to gallons and containing 42 grams per liter of phenol, and the top layer being a dark red oil.

This pyridine sulphate solution thus obtained is suitable for rectification with steam for the purpose of reducing the phenol to the low concentration necessary to permit recovery of pyridine from the sulphate solution by springing it with an alkali.

We claim:

1. A method of recovering pyridine bases from a coal tar distillation oil fraction containing said bases along with at least 2% phenol and small Volumes of other constituents that are soluble in said phenol; said method comprising washing said fraction with dilute sulphuric acid at a temperature of from 60 to 100 C. until a solution is obtained containing in equilibrium concentration pyridine sulphate and said phenol with said constituents dissolved therein, cooling said solution to a temperature of not more than 40 C., washing said cooled solution at a temperature of not more than 40 C. with a relatively small volume of said fraction to unbalance the equilibrium concentration between said pyridine sulphate and said phenol and cause material volumes of the latter to dissolve in said washing fraction along with said constituents dissolved in said phenol, separating said solution from said small volume of said fraction and rectifying said solution with steam to produce relatively pure pyridine sulphate from which the pyridine bases may be recovered.

2. A method of recovering coal tar bases from a solution containing the same and sufficient phenol to combine with said bases and form complexes, said method comprising washing said solution With dilute sulphuric acid at temperatures sufiiciently high to decompose said complexes and produce a sulphate solution of said bases containing phenol, cooling said sulphate solution and Washing it with a coal tar distillation oil fraction to absorb said phenol, and separating said sulphate solution from said fraction as a solution suitable for easy purification by steam rectification.

JOSEPH H. WELLS.

PHILIP J WILSON, JR.