US1945376A - Extraction of phenols - Google Patents

Description

Patented Jan. 30, 1934 STATES PATENT OFFICE EXTRACTION OF PHENOLS Wales No Drawing. Application March 5, 1931, Serial No. 520,479, and in Australia April 4, 1930 3 Claims.

In the known process of extracting phenols, phenol homologues, and other hydroxy aromatic compounds from oils, crude phenates, cresylates, and like compounds obtained by washing the oil with caustic soda or other alkali hydroxide, are decomposed with acid and settled out and the crude tar acids thus liberated are separated by distillation. In the distillation step, neutral oils, pyridine, naphthalene, and certain other substances come overwith the acids, and the products are thus rendered impure. The impurities unfit the acids for many uses, as for instance in the manufacture of synthetic resins and fine antiseptic s.

The impurities are frequently found to amount to as much as in a crude acid prepared as above. In the known method of purification, the crude phenate or cresylate or like compound is heated with steam and simultaneously blown with air, which process removes naphthalene and neutral oil, but must be continued for a considerable period in the most favourable circumstances to obtain the desired result, and in some cases is carried on for as long as forty-eight hours, and is attended by a considerable loss of tar acids as hydrolysis is considerable at the temperature at which blowing is conducted.

Phenates, cresylates, and like compounds derived from horizontal retort and coke oven tars contain impurities which have a relatively high vapor pressure. The known process is more or less effective for the treatment of those products; but the phenates, cresylates, and like compounds obtained from low temperature tar oils, cracked mineral oils, or shale oil contain impurities which have a relatively low vapor pressure, and for the treatment of these oils it has been found necessary to prolong the process of purification by steam or air blowing, with the consequence that loss of tar acid product is substantially increased; the degree of refinement attained is also unsatisfactory.

The present invention consists in distilling the phenates, cresylates, or like compounds in aqueous solution containing the impurities, un-

der high vacuum, before the tar acids are liberated from it by treatment with mineral acid, carbonic acid, or other reagent. The neutral oils and other impurities which will distil at subsequent stages of refining are thus taken ofi. The tar acids are held in combination with the alkali, and as they are not volatile when in such combination, they remain in the still with a proportion of heavy and gummy impurities which do not pass over; these heavy and gummy impurities, however, cause no difliculty in the later steps in the process.

The known process is then again followed, and the still liquor from which the impurities have been removed in the distillation step are treated with sulphuric acid or carbon dioxide, following known practice, to liberate the tar acids. The mixed acid product thus obtained is fractionated under appropriate temperature and pressure conditions to obtain the particular phenols or other tar acids required. The distillate acids may be treated by air blowing or with a metallic oxide and subjected to final redistillation to obtain them in a condition of great purity.

The removal of the impurities by distillation prior to the decomposing of the alkali phenolic or similar compounds is efiected under high vacuum. It is desirable that the vacuum should be as high as practicable; the results are less satisfactory as the vacuum falls.

In practice the process is operated as follows:

Sodium cresylate solution of specific gravity about 1.075 obtained from washing tar oil is run to settling tanks where any oil that settles out on standing for twelve hours is skimmed off.

The cresylate solution is then pumped to a vacuum pan; a single effect pan such as used for concentration of weak caustic soda liquor is suitable for this operation. The charge is boiled vigorously under a vacuum of 27-28" vacuum; the bulk of the oil and bases come away in the first five minutes. However, to obtain acid which gives a completely miscible solution in caustic soda it is necessary to prolong the process; when so prolonged the process is generally completed in forty-five minutes.

The completeness of the operation can be determined by decomposing a small sample of the cresylate with sulphuric acid, distilling the separated cresylic acid, and re-dissolving in 10% caustic soda solution.

The refined sodium cresylate can then be decomposed by known process and distilled.

What I claim as my invention and desire to secure by Letters Patent is:-

1. In the recovery of phenols from tar oils by extraction with a solution of a hydroxide of an alkali metal, the step of removing neutral oils and other alkali insoluble bodies from the solution which step comprises distilling the solution of phenols in the hydroxide of an alkali metal at a pressure substantially below atmospheric pressure.

2. In the recovery of phenols from tar oils by 3. The herein described method of removing neutral oils from a caustic soda phenolate solution, comprising distilling the solution at a pressure substantially below atmospheric pressure.

JVOHN GRIFFITH PEAKE.

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