US2035696A - Purification of naphthenic acids - Google Patents

Description

Patentedlllar. 31, 1936 UNITED STATES:

YUBIFIGATION F NAPHTHENIG ACIDS Frederick J. Ewing, Pasadena, Calif assignor to Union Oil Company of California, Los Angeles, Calii.,-a co p ration oi California 1 No Drawing. Application Must 12. 1933,

V Serial No. 684,929

15 Claims. (or. 200-108) This invention relates tothe purification of naphthenic acids. A primary object thereof is to present a simple and thoroughly satisfactory process for effecting the permanent removal of 5 substantially all of the dark coloration and pungent odor which usually accompany these acids. 4

Naphthenic acids, asmight be obtained from the alkali waste arising during the refining of petroleum or shale oil fractions, constitute a complex mixture of acidic compounds containing principally carbon, hydrogen and oxygen. They range from comparatively low boiling liquids to compounds which are solid or semi-solid at ordinary temperatures. Their viscosity in most instances is directly proportional to the viscosity of the hydrocarbon fractions in which they were originally present. The acidic character of the naphthenic acids is believed to be due to the presence of one or more carboxyi (COOK) groups in association with the remainder of a molecule.

, Naphthenic acids, as originally obtained from the alkaline refining wastes of various hydrocarbon fractions including those stated above, possess a dark red to black color and this color subslsts whether or not the acids be substantially free from associated phenolic and hydrocarbon materials. When such acids are distilled, which may or may not be performed under reduced pressure, the overhead product is substantially colorless at first but it rapidly reverts to a dark amber or black color on standing, therebyrendering the acids unfit for use in many instances.

Therefore, it is desirable to obtain colorless naphthenic acids which do not darken on standing even over a long prolonged period oftime and which also possess a bland to sweet odor.

I have discovered that such a decolorization and deodorization may be brought about by contacting the naphthenic acids with non-volatile oxidizing agents. This treatment maybe carried out with the acids in either the liquid or vapor phase although from an economical standpoint it is preferable to resort to the former which in 7 its simplest exemplification consists in adding 'the oxidizing agent directly to the still charge either before or during distillation. The non-volatile oxidizing agents which I pro- 50 pose to use in this invention are metallic oxides .tvhich are capable of being-transformed to the naphthenate salt ofth'e metal or else reduced to the metal itself, in which latteroase the naphthenate salt may be formed as an intermediate product. p

Practically all metallic oxides may be used for the decolorization and deodorization, of the 'naphthenic acids. Typical examples thereof are: magnesium oxide, MgO, mercin'lc oxide, HgO. 30 aluminum'oxide A120: and Vanadium oxide V205.

The following metallic oxides have been found to be especially suitablefor use inthis invention: cupric oxide, guO, ferric oxide F9203, litharge Pbao manganese dioxide MnOa and chromic oxide, 0110a. The naphthenate salts of these 5 metals which may be reduced to the free metal itself are themselves capable of ringing about the desired' color stability and deodorization.

. Thus cupric oxide or cupric naphthenate, when added to a naphthenic acid still charge havel proved to be equally eiiective in the production of naphthenic acids of high color stability and bland odor.

The treatment as hereinafter more fullydescribed, is carried out in the absence of any ap- 15 preciable quantities of water and thereby'avoids the emulsification difiiculties which arise on purifying naphthenicacids with aqueous solutions of various reagents. Another one ofthe advantages inherent in the use of any or all of the previously 20 mentioned metallic oxides resides in the fact that the naphthenate salts of the metals are quite readily soluble in the naphthenic acids at the temperatures prevailing during the purification process thereby providing an excellent'contact 25 between the refining agent and the product to be purified. These naphthenate salts are nonvolatile and remain in the still together with small amounts of the free metal itself, after distillationhas been completed. As the amount of $0 the metallic omde addedis usually very small. these naphthenates may be discarded along with the dark colored viscous residue. Should it be deemed desirable to obtain the free naphthenic acids from the still residue, this may be accomplished by the addition d1 small amounts of an inorganic acid such as sulphuric acid.

The finished product, obtained according to my invention is substantially free from phenolic material which is believed to be due to the distil- 40 lation in the presence of the oxidizing agent at.

A elevated temperatures; however I do not wish to be limited by any such theory. It is a known fact however, that the absence of phenols in naphthenic acid mixtures accounts for high acid num- 45 bers such as those indicated in the specific exam ples hereinafter described.

In practice, the crude naphthenic acids which have been preferablyfreed from the major fraction of the phenolic material are distilled in the 50 presence of asmall amount of dry steam or hydrocarbon gas in order to eliminate the admixed asphaltic and carbonaceous material. The partially purified naphthenic acids. are then redistilled .in the presence of small amounts of 'a 56 metallic'oxide'such as cupric oxide or anyof the; metallic oxides set out above or of the metallic naphthenates which are capable or bringing .about the desired result. Whflejthis preliminary distillation process in the presence of steam or 00 gas has been found to be helpful in a number of cases, especially in such cases where it is desirable to avoid the useof sub-atmosphericpressures, it is not considered to be essential in the obtadnment of the final result.

Therefore, my invention resides in the process for deodorizing and deoolorizing naphthenic acid naphthenate which will accomplish the purpose which comprises treatment with metallic oxides during distillation whereby a finished product is obtained which possesses a stablewater-white to straw color and abland odor. My invention also extends to the distillation of naphthenic acids in the presence of cupric oxide or to distillation with a non-volatile oxidizing agent such as cupric intended. 4

Considering the process in greater detail, a caustic liquor, such as might be obtained-by treating crude kerosene or a liquid sulphur dioxide extract thereof, with sodium hydroxide, is neutralized in such a manner that it is only slightly basiotoward phenolphthalein. By so operating,

admixed hydrocarbons. These crude naphthenjc the naphthenic acids, in contrast to the phenols, are not liberated from their alkali metal salt but remain as sodium naphthenates. The resulting mixture of sodium naphthenates, phenols and admixed hydrocarbons is then steam distilled. The sodium .naphthenates remain behindin the stilland when dissolved in water and treated with sulphuric acid, produce naphth'enic acids which contain only very small amounts of phenols and acids are of a poor color and contain considerable amounts of insoluble carbonaceous material. They are preferably subjected to a preliminary distillation in the presence of dry steam or some vcellent color, possess a do'not darken on standing even for a period as of the normally gaseous hydrocarbons. such as ethane or methane,- to removethe above-mentioned undesirable fractions. The effect of the introduction of the steam or gasis to lower the.

temperature necessary to distill the mixture and thereby avoid any undue cracldng and eliminates the necessity of carrying out the distillation under reduced pressure.

The overhead when first condensed is a clear light yellow liquid but acquires a deep red color so rapidly that in a few hours, layers greater than an.inch in depth are virtually-opaque; Small amounts of water usually come over during the initial stages ofthe distillation and may be removed by a simple settling or centrifuging process. The semi-refined naphthenic ,acids which were condensed as an overhead product are subse- 'quently introduced into a still into which small amounts of the oxidizing agent, ranging from 1 to 6% by weight, have been placed. The mixture is then redistilled underatmospheric pressure until. substantially. all of. the purified naphthenic acidsareremoved as an overhead product; The so obtained finished naphthenic acidsare of exbland to sweet odor and long-as six months. In addition, they possess an acaaeae sure so as to avoid any substantial amount of decomposition.

The following example is illustrative of my process: T

Example 1 A mixture of crude naphthenic acids derived from the caustic liquor obtained in the refining of a kerosene fraction and which has been substantially freed from admixed phenols by: careful acidification, steam distillation and acidification of the sodium naphthenate residue as previously described, had the'following properties:

Acid number- 283mgs.KOHpergramofsubstance ,Saponificationnumber 283mgs.KOHpergramofsubstance v Specific grav- 0.97 Dark brown ity Color. Sulphur content Boiling range 480-580 F. Sediment 1 to 2% These acids were subsequently distilled in the presence of small amount of dry steam or hydrocarbon gas which was introduced into the still during the distillation. The semi-refined naphthenic acids which were condensed as an overhead product had the following properties:

Acid number- 284 mgs.KOHpergramof substance 'Saponificationnumber ZSGmgsKOHpeI-gramoisubstance Specific grav- Sulphur con- 4 tent- 0.12%

Boiling e- 480-575 F.

Sediment; None The naphthe'nic acids condensed as an overhead product had a clear straw like color which deepened into a dark red after standing for only a few hours. i Y .Four hundred (400) cubic centimeters of these acids were introduced into a still to which four grams ofcupric oxide had ben added. The overhead fraction comprising the finished naphthenic acids had the fdllowingcharacteristics:

Acid number 295 mgs.KOHper gramof substance Saponii'icationnumber 298mgs.KOHpergramoisubstance Specific lgra'v ity 0.948' Sulphur. content; 0.08% Color 1 to 1% N. P. A.= Color of same m a t e r 1 al aiterstanding 1 o r 6 months 1 to 1% N.'P. A.

' point range 480 5'l0f1.

Odor Bland The stilY b ottoms which of a' carbona'ceous residue together with, small amounts of metallic copper and copper naphthenates (both cuprous andcupric naphthenates) were discarded. A total amount of 380 cubic centimeters 'of purified naphthenic acids were obtained as an overhead product during the distillation. They had an excellent color which did-not change on standing,

together with a small amount of the oxidizing bland odor as previously described.

Although the above mentioned process has been I n 'a,oeo,eeo 3- even for a period oi: six months as may be seen be equally wellcarried out in thei'puriflcation of from the table, higher boiling naphthenic acids derived from' Example 2 heavier hydrocarbon fractions such as stove oil or The same "amount 01' naphthenic acids med in Example lwasredistilledint-he presenceoii grams of cupric naphthenatc. 'lhe finished product obtained on condensation of the naphthenic acid vapors had properties very analogous to the product obtained on distillation with cupric oxide as may lie-seen from the iollowing table:

Acid number- 296mgs.KOHpergramotsubstance Saponirication number 301 Specific gravity 0.948

tent 0.10% Color 1 to 1% N. P. A.- 1 Color a! t er standingfor 6 months; lto 1% N. P. A. Boiling point range 480-570 F. Odor Bland As a modification of the process described above, I may pas the vapors of the semi-refined naphthenic acids through a tower filled with clay or other adsorptive substance which has been im-. pregnat'ed with cupric oxide or cupric naphthenate or any other oxide or naphthenate which is capable of improving the color and odor of naph; thenic acids. The adsorption tower should be preferably quipped with a dephlesmator to throw down any metallic naphthenates or metallic oxide which might otherwise be'carried over with the 'naphthenic acid vapors and contaminate the iinished product. The adsorption tower should preferably be equipped with means for introducing fresh reagent and for removing the waste products. 1 A multiplicity of towers each fllled with an edsol'ptive agent and using only one tower at any ,particular time has proved to be very successful one of the towers may be-recharged while the others are being used.

I, may also heat the above mentioned "se refined"- naphthenic acids in a pressure vessel mgsKOHpergramotsubstance agent which I propose'to use. The heating is continued at a temperature of about 450 to 550 F.- under the pressure generated by the vaporization of the-naphthenic acids for about one to two hours whereupon the vessel is cooled and-anyprevailing presurareleasedas soon as room temperature hasbeen reached. Mechanical agitators placed withinthe pressurevessel are found to be very efiective in obtaining a more eflicient contact between the naphthenic acids and the oxidizing agent during heating. The cooled liquid Y 'nafihthenic acids together with small amounts of metallic'naphthenates dissolved therein, are decanted and treated with a suilicient amount of sulphuric acid to liberate the tree naphthenic acids from the naphthenate salts.- The acid reaction products areremoved by settling or centriiuging from the supernatant naphthenic acids. The latter are preferably distilled to remove any dissolved impurities and the naphth enic acids, condensed overhead, constitute the finishedprodnot and possess the desired color stability ani A more particularly described in connection with naphthenic acids derived from kerosene, itlnay'i to the naphthenic acid still charge and produce capable oi decolorizing and deodorizing the naph- N. P. A. 3 a yellow to the metal oxide used has been completed, distilling the said free-crude Y tioned naphthenicacids 'it is desirable to purifynaphthenic acids with copper naphthenates, I may add cupric carbonate my cupric naphthenat by the action of the naphthenic acids on this reagent. However, I prefer to use cup'ricoxide as this compound itself is thenic acids.

The term N. P. A. color referred to in this specification relates to a color grade of a liquid obtaineddiy means of the Union Betroleum Company calorimeter adapted as a standard by the National Petroleum Association in 1915. A detailed description-oi the apparatus, method of test and significance of the scale readings is found' in David T. Day, Handbook .of Petroleum Industry, 1922', vol. 1, page 665. For example, N. P. A. 0.5 indicates a light, almost white color, straw color and N. P. A. 7 or 8 a dark reddish to brown color. I

This invention is not restricted to any specific example described therein, the examples being merely illustrative of the generic invention here-- in disclosed and many variations may be made within the scope of the appended claims;

l. A process for deodoriz'ing and dccolorizingnaphthenic acids which comprises distilling a mixture of crude naphthenic acids to remove the admixed carbonaceous materials-present thereinand redistillingthe overheadproduct in-the presa light color of high stability and a bland'oddr to the aforesaid naphthenic acids.

2. A process for deodorizing and decolorizing naphthenic acids according to claim 1 in which.

is copper oxide.

3. A process for deodorizing and decolorizing naphthenic acids which comprises distilling a mixture of crude naphthenic acids to remove the admixed carbonaceous materials present therein and redistilling, the overhead product in the presence of a metal naphthenate whereby there'is imparted a light color oi-high stability and a bland odor to the aforesaid naphthenic acids.

4. A process. for deodorizing and decolorizing naphthenic acids according to claim '3 iii which the metal naphthenate ,used is copper napthen ate.

5. A process for deodorizing and decolorizing naphthenic acids which comprises extracting a petroleum fraction with alkali, neutralizing the resulting extract to liberate the phenols from their akaline salts without attacking the alkali naphthenates, distilling the phenols overhead, liberating the free crude naphthenic acids from the alkali naphthenates remaining'in the still after; the said distillation for the removal of phenols naphthenic acids to remove the admixed carbonaceous materials present therein and redistilling the overhead product in the presence of a metal oxide whereby there is imparted a light color of. 70

high Stability and a bland oder to the aforemen-v 6. A process for deodorizing anddecolorlzing naphthenic acids according v the metaloxide used is cupric omde. -1

' naphthenic acids which comprises extracting a petroleum fraction with alkali, neutralizing theresulting extract to liberate the phenols irom their alkaline salts without attacking the alkali naphthenates, distilling thphenols overhead, liberating the treecrude naphthenlc acids from the alkali naphthenates remaining in the still after the said distillation for the removal of phenols has been completed, distillingthe said free crude naphthenic acids to remove the admixed carbonaceous materials present therein and redistilling the overhead product in the presence of a metal naphthenate'whereby there is imparted a light color of high stability and a bland odor to the aforesaid naphthenic acids.

8. A process tor deodorizing and decolorizing naphthenic acids according to claim 7 in which the metal naphthenateused is copper naphthenate, e

9. As a new and useful composition or matter, naphthenic acids which do not exhibit any tendency to discolor on standing and which are substantially free from phenolic material and having a boiling point in excess of 480 F.

10. As a new and useful composition of matter, naphthenic acids of-a bla'ndodor which do not exhibit any tendency to become discolored on standing and which have an acid number greater than 250 mgs. KOH per gram of substance and having a boiling point in excess of 480 F.

11. As a new and useful composition of matter, naphthenic acids of a bland odor which do not exhibit any tendency to become discolored on standing and which have an acid number of 295 mgs. KOH per gram of substance orbetter and having a boiling point in excess of 480 F.

12. As a new and useful composition of matter. naphthenic acids of a"blai'1d odor having a permanent color of 1 to 1% N. RA. and having a boiling point in excess of 480 F.

13. As a new and useful composition oi. matter, naphthenic acids which do not exhibit any tendency to discolor on standing and substantially free from carbonaceous materials and having a boiling point ranging from approximately 480 F. to 570 F. r

- 14. As a new and useful composition of matter,

naphthenic acids ot a bland odor, which do notexhibit any tendency to become discolored on standing and which have an acid numben in excess of 250 mgs. KOH per gram'of acid and a boiling point ranging from approximately 480 F. e to 570 F.

15. As a new and useful composition or matter, naphthenic acids of a bland odor, which do not exhibit any tendency to become discolored on standing and which have an acid number of 295 ms. KOH per gram of acid or better, and a boiling point ranging from approximately 480 to