US2481816A - Method of finshing aromatic concentrates - Google Patents

Description

METHOD OF FINISHING AROMATIC CONCENTRATES Filed April 10, 1947 Fresh Sulfuric Acid |8 Aromatic Extract cuusi'c Fresh Guus1ic lnhibiior v s N I i I 42 my 07 as v mm? a" 5| l 4- e 52 4 5 l 39 Fresh/ v Cuusfic Finished Aromatic Concentrate 43 49 4 47 37 38' L 8 40 Hclner Spent Cushc M d 1/ INVENTORJ:

BY I

Qfl/W AT OR/NEY- Patented Sept. 13, 1949 UNITED STATES PATENT OFFICE METHOD OF FINISHING AROMATIC CONCENTRATES tion'of Delaware Application April 10, 1947., Serial No. 740,564

2 Claims.

This invention relates to a method of finishing aromatic concentratescontai'ning appreciable quantities (1.0% or over) of olefinic compounds.

This invention is particularly adaptable to the finishing of synthetic aromatics produced by the catalytic dehydrogenation of cyclonaphthenes in which process undesirable by-products such as .olefinic compounds are formed which. render the concentration and finishing of the aromatic concentrate a difficult operation.

synthetically produced aromatics resulting from a catalytic dehydrogenation process may be concentrated by distillation and then subjected to. liquid sulfur dioxide extraction wherein an extractis producedcontaining from 70% to 90% aromatics, from.5% to 29% of high boiling paraflinic compounds and from 1% to 5% olefinic may be treated to remove harmful olefinic bodies by acid-treating the oil, neutralizing the acidtreated' oil with a concentrated. aqueous solution of caustic alkali, heating the oil to an elevated temperature. and .hydrol'yzing it with an aqueous Ti;

solution of caustic alkali, and subsequently distilling the treated oilv under controlled conditions 'to. produce a stable nitration grade toluene concentrate. This process is disclosed and claimed in U. S. Patent 2,400,373;

Although the above-mentioned process has beenfbund to be particularly suitable for finishing nitration grade toluene concentrates, it is not applicable for finishing all types of aromatic concentrates. For example, the higher boiling aromatics such as the xylenes may be treated 'by the above-mentioned process to produce a concentrate which is not entirely satisfactory ,from thestandpoint of stability. It is also sometimes desired to produce an even more stable toluene concentrate than is produced by the above-described procedure.

It is the main object of the present invention to provide a method for treating an aromaticcontaining oil. I

It is a further object of this invention to trea aromatic-containing oils by a'procedure permit- ,tingtheproduction oi. an aromatic concentrate having improved stability characteristics.

Briefly, our invention comprises acid treating an aromatic-containing fraction under controlled conditions to remove substantial portions of olefinic compounds, separating acid sludge from. the treatedv material, neutralizing easily neutralized constituents in the acid treated material in the presence of an alkaline solution, hydrolyzing the alkaline washed material at elevated temperatures and carefully controlled contact times with an alkaline solution of carefully adjusted concentration, separating the hyclrolysed material, adding to it an alkaline material and distilling it under carefully controlled conditions such that acidic materials released during the distillation are neutralized and recovering an aromatic concentrate from the distillation operation which is inhibited with a phenolic material to obtain an aromatic concentrate of improved stability characteristics.

We have found that an aromatic containing fraction of the character above-described may be treated to improve its stability to a desired degree by a process including the following steps. The temperature of the extract from the sulfur dioxide extraction process is adjusted to approximately 80 F. and the extract is then acid treated in a two-stage acid treater, Fresh su'lfuric acid is employed in the second stage and acid sludge withdrawn from the second stage is utilized to pretreat the extract in the first stage. Following the acid treatment, caustic soda solution of from 18 to 20" B. is employed to neutralize the acid oil. The neutralized acid oil is then hydrolyzed at a temperature in the range of 300 to 325 F. in the presence of18 to 24 B. caustic soda solution and then separated fromthe caustic soda solution by settling. The hydrocarbon material withdrawn from the settling stage is admixed with saponified petroleum phenols or sodium naphthenates and distilled to remove an aromatic concentrate as a condensate fraction. The condensate fraction is then inhibited by the addition of petroleum phenols or other inhibitor and a finished aromatic concentrate of improved stability is thus obtained.

The operation of the hydrolyzing step in the above finishing procedure is of prime importance. Two different types of sulfonated material are contained in the finished extract charged-to this unitv These are the alkyl sulfates which are easily hydrolyzed in'thepresence of steam or hot caustic and the aromatic sulfonates and chemically neutral sulfonated compounds which are extremely difficult to hydrolyze by steam .or hot caustic. It is necessary to remove both types of sulfonated compounds or to neutralize them in pipe 35 to vessel 36.

the distillation step in order to prevent the liberation of free sulfur dioxide in the distillation step which will be contained in the finished aromatic concentrate and which will render this contaminated concentrate unstable in storage with respect to acid wash color and sometimes original color.

In order to explain the present invention more fully, the preferred treating procedure will be described in conjunction with the drawing in which the single sheet is in the form of a diagrammatic fiow sheet.

Referring now to the drawing, an aromaticcontaining mixture such as is obtained from a sulfur dioxide extraction plant is passed through line I I to incorporator I2, acid sludge being introduced into the liquid stream flowing through line II by means of line I3. An admixture of acid sludge and the aromatic-containing stock is withdrawn from incorporator I2 by line I4 and passed into settling vessel I5. An acid sludge layer is withdrawn from vessel I5 by line I6 and a hydrocarbon fraction is withdrawn by line H, admixed with fresh acid from line I8 and passed into incorporator I9. where thorough admixture of the .through line I3 containing pump 22 and the hydrocarbon fraction is withdrawn by line 23, has .an alkali metal hydroxide solution such as caustic solution added thereto by line 24 and passes into incorporator 25. A mixture of caustic and hydro carbons is withdrawn from the incorporator 25 by line 26 and passes into settling vessel 21. Caustic from the lower portion of vessel 21 is withdrawn through line 24 and is recycled by means of pump 28. If desired, spent caustic may ;be withdrawn from the recirculating line by outlet 29 and fresh caustic may be added to the recirculating line by inlet 30.

. The hydrocarbon fraction from vessel 21 may be withdrawn through line 3| to intermediate storage vessel 32. Hydrocarbon from vessel 32 is withdrawn through line 33, sent through preheater 34 where it is heated to a temperature in the range of 300 to 325 F. and then passed by Vessel 36 is arranged to allow intimate contacting .of immiscible fractions therein and the settling of said fractions and to this end is provided with recirculating line 31 containing pump 38, and heater 38; line 31 discharges into vessel 36 through spray nozzles 39.

Recirculating line 31 is provided with outlet 40 aromatic-containing fraction injected into vessel 36 with 18 to 24 Be. caustic which is dispersed through spray nozzles 39 at a high velocity.

4. Heater 38' may be used to maintain the temperature of the mixture in the drum at the desired operating temperature of 300 to 325 F. The retention time of the aromatic-containing fraction in the mixing section of the drum must be a minimum of ten minutes. After the mixing period the hydrocarbon caustic mixture is conducted to the settling section of the drum wherein. the two phases are allowed to separate. The aromatic-containing fraction is withdrawn from the vessel continuously by means of line 42.

To obtain an aromatic fraction of satisfactory stability, the charge within vessel must be maintained in intimate admixture with the caustic soda for a minimum period of ten minutes and the total time of contacting and settling must not be less than 1 hour at 300 F. or one-half hour at 325 F. It is preferable to renew the caustic soda solution'in vessel 36 when its total sulfate content has increased to 40,000 parts per million although, if desired, the sulfate content may be allowed to increase to 60,000 parts per million before the renewal step. In ordinary op-' erations the caustic must be renewed when from 300 to 500 barrels of aromatic extract have been treated per barrel of caustic. The aromatic containing fraction passing through line 42 has added to it a portion of saponified petroleum phenols, sodium naphthenates, or other basic material from line 41, pump 48, and line 49. The quantity of 'saponified petroleum phenols or other material added through line 49 will vary depending on the tendency of the material undergoing distillation to release sulfur dioxide. As a rule, it is desired to add from 30 to 50 gallons of such material per 1,000 barrels of concentrate. The concentrate containing the saponified material then passes into distillation zone 43 where it is separated by distillation. A light overhead fraction may be removed from the zone through line 44,.a side stream consisting of the desired aromatic concentrate is removed via outlet 45 and a bottoms fraction is removed through line 46. To prevent excessive decomposition of sulfonated compounds in the distillation column, it is desirable to heat the hydrocarbon fraction no higher than about 525 F. in the distillation zone. This is true even though an alkaline material is present in the hydrocarbons undergoing distillation.

It is to be understood that zone 43 may comprise one or more precise fractionation towers. For example, this zone may comprise two efiiclent distillation towers with the finished aromatic concentrate being recovered as an overhead fraction from the second of the two towers. Inhibitor, such as petroleum phenols, is withdrawn from tank through valve 5| and line 52 to combine with the aromatic concentrate passing through line 45.

' centrate may be withdrawn through line 53m a suitable storage means not shown. Usually approximately two to fifteen pounds of inhibitor per 1000 barrels of the finished aromatic concentrate is suflicient to insure the production of a stable product. 7

The amount of sulfuric acid employed in the acid treating step will depend on the molecular weight of the aromatics being treated and on the amount of olefinic materials. contained in the The finished stabilized aromatic conbromine number barrel. In other words. its. stock has a5 bromine number and is acid treated with 25 pounds of acid per barrel ofstock, the acid treat is 5 pounds of acid per bromine number barrel. A typical benzene concentrate usually requires as little as one to two pounds of acid per bromine number barrel and a toluene concentrate, from 2.5 to 3 pounds of acid per bromine number barrel. Cs and C9 aromatics usually require approximately 4 to 5 pounds of acid per bromine number barrel and the higher boiling aromatics will require more acid per bromine number barrel depending on their molecular weight and the ease with which they sulfonate.

As previously mentioned, the alkaline material added to the concentrate in line 42 may suitably be a partially or completely saponified petroleum phenols fraction such as sodium phenolates or may comprise alkali metal salts of naphthenic acids derived from petroleum fractions. The chief function of this material is to neutralize sulfur dioxide formed during the distillation step from acidic materials not removed during the hydrolysis operation. The inhibitor added to the distilled aromatic concentrate may suitably be petroleum phenols, an amino phenol, such as N- butyl-p-aminophenol, or a phenylenediamine, such as N,N-di-sec-butyl-p-phenylenediamine or their mixtures. V

A typical example of a treatment of an arcmatic-containing fraction comprising predominately Ca and C9, aromatics resulting from catalytic dehydrogenation will now be given. A fraction having a boiling range of 250 to 500 F. and consisting of 75.4% aromatics, 20% paraflinic compounds, and 4.6% olefinic compounds with a bromine number of 5.8 was treated with 25 pounds per barrel of 96% sulfuric acid. The acid-treated oil was then contacted with 20 B. caustic soda solution in an amount equivalent to about 4.3 pounds of sodium hydroxide per barrel of oil. The aromatic-containing charge was then heated to a temperature of about 315 F., admixed with 1.5 volumes of 20 B. sodium hydroxide solution at a temperature of 325 F. and kept in intimate contact therewith for ten minutes in the mixing zone of the hydrolyzer drum. The caustic was separated from the mixture in the settling drum of the hydrolyzer and the aromatic-containing fraction was withdrawn from the hot caustic solution after a total contact and settling time of about one-half hour at 325 F.

A portion of the aromatic concentrate was then distilled to separate a fraction containing 99% aromatics and having a bromine number of 0.1. The distilled aromatic concentrate was then tested for acid wash color. An accelerated oxidation test was then made in which the hydrocarbons were heated for various periods of time in the presence of an oxygen-containing gas under carefully controlled conditions, and the acid wash color was again tested. The results of these tests are shown as follows:

Acid wash color Original 1-2 Accelerated oxidation test-after- 4 hours 6-7 8 hours 8-9 12 hours 9-10 16 hours 9-10 20 hours 12-13 24 hours 14 A sample of the distilled aromatics was also placed in storage for a period of 19 days after whichtime' the acid-Wash color-divas found "to have increased from 1-2 to 11.

The acid wash color of the aromatic concentrate was determined by agitating 21 cc. of the concentrate with 7 cc. of Water white 96% sulfuric acid for 20 seconds in a 30 cc. square bottle. The mixture was then settled for 15 minutes and the color of the acid layer compared with the color of a series of standard solutions. An acid wash color of 6-7 indicates that the color of the acid layer is intermediate the color of standards 6 and 7. The higher the color, the poorer the stability of the oil being treated. l

The accelerated oxidation test-is carried out by placing 500 cc. of oil in a one liter, roundbottom flask and placing the flask in a bath maintained at a temperature of about 200 F. Air is bubbled through the oil in the flask at a carefully controlled rate for 24 hours. Every 4 hours during the oxidation perioda sample of the oil is removed and tested for acid wash color.

It is seen that the aromatic concentrate .-finished by the above procedure was very unstable since the acid wash color should not be above about 4 after 24 hours accelerated oxidation.

Another portion of the sample of distilled concentrate was inhibited with petroleum phenols and the acid wash color of the inhibited product was tested after being subjected to an accelerated oxidation test for various periods of time. The results of these tests are shown as follows:

Petroleum phenols, lb./1000 bbl. 2 10 a 7 Acid wash color Original .1 2 1-2 Accelerated oxidation test after- 4 hours 2' V 2 8 hours 3-4 2 12 hours 5 2 16 hours 5 2 20 hours 5-6 4 24 hours 6 I 4-5 It is seen that the addition of from 2 to 10 pounds of inhibitor per 1000 barrels of the arcmatic concentrate greatly improved the stability of this material.

A portion of the hydrocarbons subjected to the above caustic hydrolysis procedure was then distilled in the presence of 39 gallons of saponified petroleum phenols per 1,000 barrels of feed and the resulting aromatic concentrate removed from the distillation tower was inhibited with 10 pounds of petroleum phenols per 1000 barrels. The inhibited concentrate was then subjected to an accelerated oxidation test and the acid wash color of the concentrate was determined after various oxidation times. These tests are shown It is seen that the distillation of the concentrate in the presence of saponified petroleum phenols combined with the inhibiting operation produced a finished concentrate which is more stable than that produced by distilling without the addition of petroleum phenols followed by inhibiting the material.

ates-n t it is; mentioned. that increasing the acid treat. in the above example; 130144} pounds of acid per barrel produced a. concentrate which after caustic treating, hydrolysis, and distilling was not improved in acid wash color as compared to that treated with 25- pounds of acid per barrel. It is indicated, therefore; that the critical phase of the treating procedure is that of preventing sul fur dioxide from carrying over into the finished aromatic concentrate inappreciable quantities and of inhibiting the finished aromatic concentrate; to prevent any small. quantities of acidic materials therein from deleteriously effecting the stability of the finished product.

Having fully described. the present invention, what we wish to claim is:

1. A. process for the treatment oi a hydrocar bod. oil comprising a major portion of aromatics and a minor portion of olefins including the steps of admixing said oil with concentrated. sulfuric acid at approximatelyatmospheric temperature to form an acid sludge and separating the acid sludge: therefrom, subsequently admixing said oil. with. caustic soda solutionof 18 to- 200'B.at approximately atmospheric temperature and separating said oil: from said caustic soda solution, heating the oil to a temperature in the range of 300:to: 325 Eh, intimately contacting said oil with caustic soda solution. of 18: to 24 B; for less than ten: minutes and. subsequently separating the hot caustic soda. solution. from the oil. with. a total contacting and separating time of not less than one hour at 300 F;, adding to said separated oil an alkali metal salt of petroleum naphthenic acids, distilling said mixture at a temperature no higher than 525 F;, removing an aromatic concentrate as a side stream from said distillation, and inhibiting said aromatic concentrate.

2. A process for the treatment of a hydrocarbon oil comprising a major' portion Cs and C9 aromatics and a minorportion of olefi'ns inciuding the steps of admixing said oil with concentrated sulfuric acid at approximately atmospheric tem- Number 8i 7 perature: to term. an acid; sludge. andseparating the acid sludge therefrom, subsequently admixmg. said oil; with caustic soda solution, of 18 to 2(1 v at approximately atmospheric temperature: andseparati-ng said oilfrom said. caustic soda solution, heating the oilto: a temperaturei-n the range ofp300 to 325? R, intimately contacting said oil with. caustic soda solution of 18 to 241 B. for no less than ten minutes and subsequently separating the hot caustic soda solution. from the oil with a total contacting and separating. time oi not less than one-half hour at 325 F., admixing said separated oil with from 30 to 50 gallons of an alkali metal salt of petroleum. naphthenic acids per 1009 barrels of oil, distilling said oil. at a temperature no higher than 525 removing alow boiling fraction as overhead and a desired aromatic-containing fraction as a side stream, and addingto: said aromatic-containing fraction from 2 to 15- pounds of a phenolic inhibitor per 1000 barrels of said. fraction.

- 7 JOHN BROWDER...

ROBERT M. LOVE. HENRY G. SCHUTZE. RICHARDiE. TANNICH.

REFERENCES CITED The following references are of record in the file of this patent:

sTa'rEs PATENTS Name Date v Chappel'l June-3 i930 Pew July 2, 1 935 Pott Mar; l0, 1-936 Schutze May 14, 1 946 et Bil V Sept. 24-, 1946 FQREIGN- PATENTS 1 Comtry 7 Date Great Britainv n m. Aug. 7, 1934 Number 1,761,328" 2 30063407 2 ,033,297 2,400,373 24U80l3t Certificate of Correction Patent No. 2,481,816 September 13, 1949 JOHN G. BROWDER ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: 1 Column 7, line 24, for 18 to 200 Be. read 18 to 20 B.;

and that the said Letters Patent should be read with this correction therein th.aLthe/ same may conform to the record of the casein the Patent Ofiice. I

Signed and sealed this 31st day of January, A. D. 1950.

THOMAS F. MURPHY,

Assistant Oommz'sm'oner of Patents.

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