Sulfonation *Productsof Mineral Oil REUBEN SPERLIIVG Chemical Research Department, Manchester Oil Rejhery, Ltd., Manchester, England During the treatment of petroleum oil with fuming sulfuric acid in the production of highly refined transformer and low viscosity technical white oils, a complex mixture of sulfonation products is formed. As a result of separation and examination of these sulfonation products, a new classification of the petroleum sulfonic acids has been established, based on differences in their constitution. Further light has been thrown on the mode of action of fuming sulfuric acid on petroleum hydrocarbons afid on the nature of the deleterious compounds removed by refining.
0
K E of the principal reagents employed in the refining of
lubricatiqg oils is sulfuric acid, which removes highly colored asphaltic and resinous compounds together with other deleterious impurities. The production of t,ransformer oil, and technical and medicinal white oils entails more drastic treatment ivith stronger acid, and considerable quantities of fuming sulfuric acid are required to effect, as complete a removal of reactive and colored components as possible. These react to form a complex mixture of sulfonation products, most of which collect in the oilinsoluble,.tarlike, acid sludge which separates out after treatment, while a small proportion remain in the oil layer. The action of fuming sulfuric a,cid on the higher boiling petroleum fractions is so complex that, despite the considerable amount of int,erest taken in the mechanism of their sulfonation and the nature of the sulfonation products, litt,le progress has hitherto resulted. Petroff (21) and Schestakoff (2.5) were among the first to investigate those petroleum sulfonic acids which remained in the oil layer and are generally referred t o as “mahogany” sulfonic acids. The examination of the sulfonic acids from the acid sludge, the so-called “green” acids, was more difficult, but von Pilat, Sereda, and Szankowski (2W)were able as a result of their investigations to classify the petroleum sulfonic acids on the basis of the solubilities of the calcium salts in ether and water (Table I). This classification gave no indicat.ion of the constit,ution of these sulfonic acids, how they are formed, or the cause of the different, solubilities of the calcium salts.
viscosity white oil, the same classification has been found to apply t o products formed during the production of medicinai white oil from a higher boiling distillate. REFINING OF LOW VISCOSITY WHITE OIL
.
The basic work was carried out on the sulfonation products formed during the production of low viscosity white oil. .it the Barton Refinery of Manchestcr Oil Refinery, Ltd., low viscosity white oil is prepared by subjecting a liquid sulfur dioxide extracted distillate, originating from a napht hene-base West Beaumont (Texas) crude oil, t o four successive treatment,s v5th a total of by weight of fuming sulfuric acid containing 207, free sulfur trioxide. After each treatment the acid sludge is allowed to set,tle out, and is subsequent’ly removed; the oil-soluble sulfonic acids are neutralized after the final acid treatment and removed by extraction with alcohol. All the acid sludges consist of three principal components, spent sulfuric acid, oil-insoluble acids, and a dark tarlike oil generally referred t o as a neutral oil. The analyses of the oils and acid sludges formed during the various stages of refining low viscosity m-hite oil are given in Tables I11 and ITT. Though the Waterman method (27) for analyzing petroleum hydrocarbons gives only an a.pproximate indication of the average composit,ion of the petroleum oils, it suffices to shorv that solvent extraction with liquid sulfur dioxide removes most of the constituents containing aromatic rings; the remaining undesirable aromatic and naphthenic compounds in the rafihate are removed by treatment Tvith fuming acid. The action of fuming sulfuric acid can be summarized as follows: The reactive aromatic hydrocarbons in the raffinate after solvent extraction arc convort,ed predominantly into the oil-soluble sulfonic acids by the action of the fuming sulfuric acid, while the oil-insoluble acids are produced principally by the dehydrogenation of deleterious reactive naphthenes to compounds which are subsequently sulfonated. A portion of these hydrocarbons are simultaneously converted to oxygenated and polymerized compounds during sulfonation, while the action of excess fuming acid results in the formation of disulfonic acids. PURIFICATION OF
TABLE I. CLASSIFICATIOK O F PETROLEUM STLFONIC ACIDS Sulfonic Acids or-Sulfonic acids
Occurrence Acid sludge layer
p-Sulfonic acids
Oil layer
y-Sulfonic acids
Acid sludge layer
pErKomu.w
SULFOKIC ACII)S
The petroleum sulfonic acids themselves cannot be prepared in a state even approaching purity; coiisequently they are isolated, and purified, in the form of their sodium SalTs. The separation of the sludge acids is a rather inore difficult problem and advantage has been ta,lren of the comparative solubilities of the acids in dilute sulfuric acid and of the barium salts in various solvents. I n this way a separation of the oil-insoluble sulfonic acids into the main groups of monosalfonic acids and disulfonic acids can be effected. They are ultimately converted into the corresponding sodium salts to facilitate final purificat,iori and analysis. The separation of the acids into subgroups is difficult; the solvent extraction of selected derivatives is the simplest method. OIL-SOLUBLE SULFOXIC ACIDS. The oil layer containing the dissolved sulfonic acids is neutralized with caustic soda and the sodium salts are extracted with dilute ethyl alcohol. The alcohol content of the crude ext’ract is then adjusted so as to precipitate most of the inorganic salts, mainly sodium sulfate and sulfite. The mixture is filtered and the filtrate is subsequently deoiled by prolonged extraction with petroleum ether. On removal of the
Solubility of Calcium Salts Calcium salts insolublc in ether and water Calcium salts soluble in ether, insoluble in water Calcium salts insoluble in ether, soluble in water
As a result of investigations into the whole range of sulfonation products formed during the production of white oils by the acid t r e a h e n t of the higher boiling petroleum fractions, it is now possible to classify t.he petroleum sulfonic acids according t o their constitution and properties. This classification is shown in Table 11,which divides the sulfonic acids into three main groups, similar atfirst glance t o the older classification but based instead on constitut,ionaldifferences. These main groups are further subdivided according t o modifications in the nature of the radical attached t o the sulfonic acid group-modifications mainly due t o oxidation and condensation. Although most of the work was carried out on t’he sulfonation products formed during the production of low
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TABLE11. CLASSIFICATION OF PETROLEUM SULFONICACIDS Subgroups Hydrocarbon sulfonic acids
Aromatic-naphthenio nucleus attached t o long paraffinic chains
Resin sulfonic acids
Oxygenated compounds derived from above
Hydrocarbon sulfonic acids
Aromatic-naphthenic nucleus with short paraffinic chains
Resin sulfonic acids
Oxygenated compounds derived from above
Asphaltene fonic acid
sul-
Oxygenated polymers of high molecular weight
Less aromatic disulfonic acids
Aromatic-naphthenic nucleus with short paraffinic chains ,
Highly aromatic disulfonic acids
Highly aromatic nucleus with no paraffinic chains 0
C o r r e s ponding
Corresponding oxygenated a n d polymerized compounds derived from above two hydrocarbon types
resin and asphal, tene disulfonic acids
.
.
N a t u r e of Radical
Characteristic Properties Source Oil-Soluble Monosulfonic Acids Oil layer Soluble in hydrocarbon oils
Soluble i n hydrocarbon oils
Oil layer
Oil-Insoluble Monosulfonic Acids Insoluble in hydrocarbon oil Acid sludge a n d dilute mineral acids. upper layer Soluble i n benzene on diluting sludge with water Insoluble in hydrocarbon oils Acid sludge and dilute mineral acids. upper layer Soluble in benzene o n diluting sludge with water Insoluble i n dilute mineral Acid sludge acids a n d benzene. Soluupper layer ble in chloroform on diluting sludge with water Oil-Insoluble Disulfonic Acids Soluble in dilute mineral Acid sludge acids b u t readily extracted upper layer b y a A y l alcohol. Barium on diluting salt soluble in water sludge with water Soluble in dilute mineral Acid sludge acids, b u t extracted with lower layer difficulty b y amyl alcohol. on diluting Barium salt soluble in sludge with water water Similar properties to disulfonic acids of parent compound
solvent, the sodium salts of t h e oil-soluble sulfonic acids are obtained as a yellowish hygroscopic powder. It is difficult t o remove the last traces of inorganic salts and mineral oil, but it is possible to estimate these impurities with accuracy. OIL-INSOLUBLE SLUDGESULFONIC ACIDS. The acid sludge is treated with an equal weight of water and separates into two layers: an upper tarry layer rich in organic matter, and a lower aqueous layer containing most of the spent sulfuric acid. The lower aqueous layer, consisting of a weak solution of highly aromatic disulfonic acids in dilute sulfuric acid, is neutralized with caustic soda, dehydrated, ahd then extracted with 75Oj, aqueous alcohol. The alcoholic extract contains the sodium salts of the disulfonic acids together with a little sodium sulfate. All attempts t o separate these highly aromatic disulfonic acids into different components by solvent extraction have so far been unsuccessful. The upper organic layer is neutralized with caustic soda and is then desalted and deoiled in a manner similsr t o t h a t employed for t,he oil-soluble sulfonates, except that benzene instead of petroleum ether is used for deoiling. After the solvent is removed from the purified alcoholic extract, a dark brown powder is obtained, consisting principally of a mixture of the sodium salts of the oil-insoluble monosulfonic acids and of the less aromatic disulfonic acids. Separation is effected by converting the sodium salts t o the corresponding barium salts; the barium monosulfonates are insoluble in water but soluble in chloroform, while the barium disulfonates are soluble in water. The sodium salts are dissolved in water and a n excess of 10% barium chloride solution is added. The mixture is then shaken up with chloroform, which dissolves the precipitated barium salts. The aqueous layer, containing most of the resulting sodium chloride together with any excess barium chloride, is carefully separated and rejected. The chloroform solution is washed several times with water until the aqueous washings are almost colorless, and the aqueous wash-
......
Remarks Correspond t o highly purified mahogany acids. Produced by action of fuming acid on aromatic compounds containing long paraffinic chains Produced b y action of fuming acid on oxygenated aromatic compounds containing long paraffinic chains a n d b y mild, oxidation of oil-soluble hydrocarbon acids Produced b y action of concentrated sulfuric acid on aromatic compounds containing either short or no paraffinic chains Formed b y action of concentrated sulfuric acid on oxygenated aromatic compounds containing either short or no paraffinic chains, also b y mild oxidation of oilinsoluble monosulfonic acids Produced b v action of sulfuric acid on asDha1tene compounds formed b y oxidking a n d condensing action of fuming acid on aromatic hydrocarbons. These acids are responsible for dark color of acid sludge Produced by action of excess fuming acid on correspoading hydrocarbon or hydrocarbon monosulfonic acids Correspond to y o r yellow-green scribed by von Pilat et al.
acids de-
......
ings are then concentrated and re-extracted with chloroform The chloroform extract is washed several times with 50% aqueous alcohol, and the alcoholic washings are concentrated and reextracted with chloroform. The aqueous and alcoholic extracts are evaporated t o dryness and extracted with hot water. This aqueous extract is allowed t o cool and after standing for 24 hours is filtered. The filtrate is then treated with excess sodium sulfate t o convert any barium salts present to the corresponding sodium salts. The precipitated barium sulfate is removed by centrifuging and filtering, and the filtrate is treated with excess alcohol t o precipitate sodium sulfate, which is then removed by filtration. After removal of the solvent, the sodium salts of the less aromatic disulfonic acids are obtained a s a brown hygroscopic powder. The chloroform extract obtained in the above process contains the barium salts of the various oil-insoluble sludge monosulfonic acids together with very small amounts of entrained oil-soluble acids. The separation of these acids is difficult because of the adsorption of one salt by another; thus, the sodium or barium oil-insoluble sulfonates when mixed with 10 or 20y0of the corresponding oil-soluble salts produEe a mixture which is completely insoluble in oil, the oil-soluble salt being adsorbed by the insoluble salt. It is also possible that an adsorbed protective film of oil-insoluble salt is formed over the surface of the soluble salt. This phenomenon is frequently encountered with mixtures of the petroleum sulfonic acids or their salts. A technique has been evolved by means of which it is possible to separate mixtures of oil-soluble and insoluble acids almost quantitatively. It is very similar in principle to the technique employed in chromatographic analysis for the selective elution of adsorbed materials, in which successive mixtures of aqueous alcohol are employed with solvents of varying polarity. Attempts to use other means for the separation of these mixtures of sulfonic acids have proved unsuccessful. It is possible in this way to separate all the entrained oil-soluble
INDUSTRIAL AND ENGINEERING CHEMISTRY
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ganic salts. KO. 42 Whatman filter papers are employed for filtration, and a combination of heating and high vacuum is required for thorough drying of the sodium salts.
TABLE 111. h A L Y S E S OF FINAL A S U ISTERJIEDIA4TE OILS PRODUCED IN REFINIBG OF Low VISCOSITYWHITEOIL Raffinate (after Original Solvent Distillate Extraction)
Extract from Solvent Extraction
Final Product after Acid Treatment ow Viscosity (LR%ite Oil)
22
62
Yield by weight&,
7.
Boiling range (converted t o 760 mm. of merc u r y ) , C. Density a t 20’ C. Aniline point, ’ C . Refractive index a t 200 C. Mean molecular weight Waterman analysis Aromatic rings, % S a p h t h e n i c rings,
’%
Paraffinic
%
chains,
100
78
300-360 0,8844 75.25
0.8690 86.25
Same as dis. tillate 0 9324 34.25
0.8867 93.0
1.4916
1.4810
1,5280
1.4732
312
329
276
320
16 15
10.37
42.32
22.16
22.93
9.08
22.54
4.96
61.7
66.7
48 6
72.5
Viscosity Redwood a t 70’ F., 111 154 sec. 116 Saybolt a t 100’ F., see. ... ... ... a All yields based on original chai’ge of disitillate
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-‘NALYSIS
OF SODIUM SALTS O F PETROLEUM SULFONIC A i C I D S .
The purified sodium salts were analyzed for carbon, hydrogen, sulfur, and sulfated ash, and the accompanying impurities were determined, these being mainly small percentages of sodium sulfate, neutral oil, and in some cases sodium chloride. The mean equivalent weight is first calculated from the corrected sulfated ash and the mean molecular formula can be subsequently determined when the basicity of the acids has been ascertained from mean molecular weight determinations of the derivatives. These formulas represent the mean of a large number of components including hydrocarbon sulfonates, and oxygenated and polymerized sulfonates, and they thus do not convey a great deal of information. Table V gives the analyses and properties of the sodium salts of the main sulfonic acid groups. HYDROLYSIS O F P E T R O L E U M SULFONIC ACIDS
The determination of the mean equivalent weights of the sodium salts having throrvn little light on the constitution of the components of these groups, it was decided to hydrolyze the sulfonic acids under such conditions that as little modification as possible of the radical took‘place.
102 65
RSOaH acids in the acid sludge, but they rarely exceed more than a very small percentage. By the same technique, the sludge monosulfonic acids can be partially separated into the asphaltene and hydrocarbon acids, but the results obtained by the employment of this long and tedious separation process do not warrant the trouble incurred, and a more effective separation can be obtained by solvent extraction of the methyl esters. The chloroform solution of the barium monosulfonates is freed from entrained oil-soluble sulfonates in the following manner. The chloroform extract is dried to remove solvent and then dissolved in a mixture of benzene and alcohol. The solution is freed from alcohol by careful washing n i t h water, when most of the asphaltene monosulfonates together with some oil-insoluble hydrocarbon sulfonates are precipitated. The benzene solution is filtered and dried, and the diied extract dissolved in 6 O 0 / S O 0 petroleum ether containing a little alcohol. On the careful addition of water, the oil-insoluble sulfonates are precipitated, and after washing with water, the petroleum ether solution contains onlv the entrained oil-soluble sulfonates. The precipitated barium salts are treated with a mixture of sulfuric acid and dilute alcohol. The alcoholic extract is neutralized with caustic soda and the inorganic salts are precipitated by the addition of alcohol. The mixture is filtered, washed with benzene, and finally dried. The sodium salts of the oil-insoluble monosulfonic acids are thus obtained as a dark brown hygroscopic powder. In the above separation of the sulfonic acids, 75y0alcohol is used for extracting the sodium salts substantially free from inor-
+ HzO
=
RH
+ H2S04
A considerable amo;nt of work was first carried out on the sulfonic acids t o ascertain the most suitable reagents and the optimum conditions for hydrolysis. Stability tests were carried out on aromatic petroleum extracts of similar mean molecular weights and constitution, in which they were subjected to the same conditions as were employed to hydrolyze the petroleum sulfonic acids; they showed no change in mean molecular weight, densitv, refractive index, or appearance. Refluxing the sulfonic acids with phosphoric acid solutions of 50y0 and higher concentrations ( 2 3 ) resulted in hydrolysis of the acids, the rate of hydrolysis being more dependent on teinperature than on phosphoric acid concentration. This method was rejected as unsatisfactory, for it iyas found that combination
TABLEIV. BXALY~ES OF ACID SLUDGES PRODUCED DURIKG TREATVENT OF Low VISCOSITY WHITEOILP Water, Iieutral oil, Sulfuric acid, 70 Sulfonic acid, % ’
First 19.0 12.1 49.3 19.6
.4fter Acid Second 15.5 7.0 54.1 23.4
Treatment Third Fourth 12.0 11.0 3.7 1.0 65.1 74.2 13.8 19.2
OF SODIUM SALTS OF MAIX GROUPS OF PETROLEUM SULFONICACIDS TABLE V. ANALYSESAND PROPERTIES
8.02
5.37
Mean Equivalent Wt. of Salt 429
9.05
5.61
410
20.68
12.04
8.19
281
27.34
16.22
11.57
199
Carbon,
Hydrogen,
Oxygen,
64.62
8,823
13.17
61 .82
6.78
Disulfonic acids containing paraff i n k chains
53.40
5.69
Highly aromatic disulfonic acids
40.72
4.15
Sodium Salts Oil-soluble monosulfonic acids Oil-insoluble monosulfonic acids
%
%
%
16.74
Sulfur,
%
Sodium,
%
Solubility of Mean Molecular Corresponding Barium Salts Weight Formula 429 Cz~HssOa.sS03h’a So1,uble in petroleum ethei , insoluble in water 410 C ~ H z 8 0 S 0 s N a Soluble i n , chloroform, insoluble in water and petroleum ether 562 Cz~H3zO(S03- Insolublein chloroform, soluNa)z ble in water, insoluble in 10% barium chloride solution 398 C~s.sHie.aOo.u- Insoluble in chloroform, sol(S03Na)z uble in water, soluble in 10% barium chloride solution
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acid by extracting the product with a mixture of equal parts of petroleum ether and benzene; this mixture was found to be a suitable solvent for all oxygenated products present. The solution is washed free from acid by repeated extraction with 50% aqueous alcohol, washed with 0 B water, and dried with anhydrous sodium sulfate. After filtration, the solution is evaporated to dryness at 80 "C. and the residue is dried in vacuo. The dried hydrolysis products are then separated into hydrocarbons, neutral resins, and asphaltenes, Time in Hours according to the method of M a r c u s s o n ( 1 1 ' ) . F i g u r e 1. Hydrolysis of Petroleum Sulfonic Acid in Boiling M i n e r a l Acids They are dissolved in a @ Oil-soluble monosulfonic acids in 50% H8POa Less aromatic disulfonic acids,in 2 N HC1 little benzene and excess Highly aromatic disulfonic acids in 2 N HCI 0 Oil-soluble monosulfonic acid? in ,2 N HC1 X Oil-insoluble monosulfonic acids in 2 N HCl 60"/80" p e t r o l e u m ether is added, when most of the dark polymerized asphaltenes are precipitated. occurred between the phosphoric acid and oxygenated compounds After standing overnight they are filtered off and well washed present in the sulfonic acids. The use of hydrochloric acid ( 2 A7) with petroleum ether. The petroleum ether solution is evapowas found preferable. rated to dryness and the residue is redissolved in excess The hydrolysis rates of the various sulfonic acids are shown in aromatic-free 60 "/80 O petroleum ether and allowed to stand Figure 1. I t can be seen that the petroleum sulfonic acids are overnight, when any further insoluble matter is precipitated very stable, as they are very slowly hydrolyzed by mineral acids. and removed by filtration. The insoluble asphaltenes are disThere is little preferential hydrolysis of the components of the solved in benzene and dried. The petroleum ether solution various sulfonic acids; the mean molecular weights of the residual containing neutral resins and hydrocarbons is then treated acids remain unchanged, even after 750/, of the sulfonic acids have with a considerable excess of activated fuller's earth, filtered, been hydrolyzed. The curve of the logarithm of percentage of and well washed with petroleum ether. The light colored residual sulfonic acid plotted against time shows a steep initial filtrate is evaporated to dryness a t 80 a C. and dried in vacuo to slope for both oil-soluble and insoluble monosulfonic acids; this yield pale oily hydrocarbons. is probably due t o a small percentage of sulfated compounds, The washed fuller's earth is then shaken up with a mixture of the presence of which has been confirmed by the determination benzene and alcohol, when most of the adsorbed neutral resins are of the acetyl values on the hydrolysis products. eluted (6). The solution is filtered and evaporated to dryness and The most satisfactory method for hydrolyzing the sulfonic the resulting neutral resins are dried in vacuo. acids, in order to prepare sufficient of the parent compounds for The hydrolPsis products of the petroleum sulfonic acids are examination, is to heat a mixture of the sulfonic acid or salt with very sensitive to heat and oxidation, so that in the processes 2 A; hydrochloric acid at 120" to 150" C. for 4 to 6 days in sealed described above, solvents are removed and the products dried air-free glass tubes. Even under these conditions, the rate of either in an atmosphere of nitrogen or in vacuo. hydrolysis of the disulfonic acids is very slow indeed. The hyTo determine the amount of hydrolysis which has taken place drolysis products are then separated into hydrocarbons, neutral in a mixture, the reaction products are dissolved in a suitable resins, and asphaltenes as described below. Table VI gives the solvent-chloroform for the monosulfonic acids, and amyl alcoproportions of these constituents in various sulfonic acid groups, hol for the disulfonic acids-and the mineral acid layer is sepaalthough these vary to a certain extent from sludge t o sludge and rated. The sulfonic acid solutions are washed with a little dilute with the treatment accorded these salts; prolonged heating in hydrochloric acid and the mineral acid washings are combined, air results in conversion of hydrocarbon and resin ,sulfonates to heated t o boiling, and treated with excess 10% barium chloride asphaltene sulfonates. solution. After cooling and standing for 24 hours the precipitated SEPARATION OF HYDROLYSIS PRODUCTS. The hydrolysis prodbarium sulfate is filtered, washed, and ashed. From the amount ucts are first freed from unchanged sulfonic acids and mineral of barium sulfate formed, it is possible t o determine the amount of hydrolysis which has occurred. TABLEVI. COMPOSITION OF HYDROLYSIS PRODUCTS OF HYDROLYSIS PRODUCTS. Hydrocarbons. These are pale oils PETROLEUM SULFONIC ACIDS soluble in petroleum ether. They were examined for mean moHydroNeutral Asphallecular weight, density, aniline point, refractive index, and elecarbons, Resins, tenes, Sulfonic Acid % % % mental analysis. The mean molecular weight determinations Oil-soluble monosulfonic acids 97.24 2.76 Nil were carried out cryoscopically in benzene with 5 , 10, and 20% Oil-insoluble monosulfonio acids 63.85 15.76 18.88 Disulfonic acids with paraffinic solutions, and the results were then extrapolated t o zero concenchains 67.80 15.93 12.65 tration. Highly aromatic disulfonic acids 44.5 27.5 28.0 The mean molecular weight of the mixed hydrolysis products I
t
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one or two hydrocarbon molecules. Oil-Soluble Oil-Insoluble Disulfonic Acids Highly Aromati< A s p h a 1 t e n e s. LIonosulfonic Monosulfonic Containing Short Disulfonic These are precipiAcids Acids Paraffinic Chains Acids tated from benzene Density a t 20° C. 0 9206 0 . 9835 0.984 1.02 Re::tc,$ve index a t 1.5140 1 5495 1,5605 1 ,5779 solution by means i v of aromatic-free Aniline point, C. 45.5 6.0
