Cresylic Acids in Petroleum ASSAY RECOVERY AND CHARACTERIZATION S. C.GALLO1, C. S. CARLSON, AND F. A. BIRIBAUER Esso Laboratories, Standard Oil Development Co., Linden, N . 1.
RESYLIC acid is the T h e increasing demand for cresylic acids, particularly 1. Extraction of creqlicthe Cg to C8 phenols, has recently stimulated an appraisal acids from naphtha with condesignation used by the trade for a variety of of catalytic petroleum naphthas (Cj to 450’ F.) as a source sideration given to optimum c o n i m e r c i a l m i x t u r e s of for additional quantities of these materials. Naphthas caustic concentration and the phenolic materials. I n many from seven fluid catalytic crackers have been assayed for e x t e n t of c i r c u l a t i o n of these trace components and results compared with similar caustic soda solution. in s t a n c e s , t h e cresols (C, assays of thermal naphthas. From characterization stud2. Recovery of cresylic phenols) from which the term ies i t is found that these acids contain cresols, xylenols, was derived, are present in a c i d s f r o m t h e alkaline and phenol in decreasing order of abundance. Methods only minor amounts or are aqueous layer and means of were tested for reducing the concentration of thiophenols, entirely absent. The present acidification (carbon dioxide the only serious contaminant encountered in cresylic work is concerned with the versus mineral acids). acids from the catalytic naphthas examined. By air lower boiling phenols (C, to 3. P r o c e s s i n g requireblowing, distillation, limited neutralization, or combinaments for removing contamiC,) in which the cresols tions of these, “sweet-smelling” cresylic acids are obtainnants either prior to acidifica( o r t h o , m e t a , a n d para) able which are essentially equivalent in iundamental generally predominate. tion or follon-ing acidification properties to the corresponding ones obtained from It has been known for some or both. years that these materials coal tar. Normally, soda washing of occur in cracked petroleum naphtha is employed for the stocks, that they concentrate purpose of improving naphtha quality. Therefore, caustic concentration and extent of recircuin sodium hydroxide solutionscontacted with refinery streams, and that they are recoverable along with certain impurities by acidifilation are often predetermined without regard to the recovery of’ cation of the spent caustic sodas with mineral acids or flue gas. trace quantities of by-products such as cresylic acids OperaI n 1940, Field, Dempster, and Tilson (4)published the resulte tions 2 and 3, on the other hand, are carried out with the object of a detailed study and characterization of petroleum phenols of obtaining maximum quantities of these materials a t the highest derived presumably from thermally cracked naphthas. By purity levels consistent TT-ith economic considerations. chemical methods the presence of phenol, o- , m- , and p-cresols, The choice of the means of acidification of spent soda sohition depends primarily on what is most available. Flue gas can be and several higher phenols was established. Important contriused advantageously for this purpose as well as waste sulfurie butions were made also in elucidating the effect of composition acid which is usually available in oil refineries. of these phenol mixtures on germicidal activity. Aries and Savitt ( d ) in 1950 summarized the market situation with respect to I n addition to the studies on recovery and characterization of’ cresylic acid, an attempt is made in the present work to define the cresylic acids from both coal tar and petroleum sources, presentproblems of purification and to present the results of experiing the recent trend and extrapolating into the foreseeable future. mental work directed tovard their solution. All the evidence points to increasing demand for these materials for use in resins, plasticizers, adhesives, coatings, flotation agents, and a variety of other applications. Part of the additional deMETHODS mand is expected to be met from petroleum sources and the Assay of Naphthas for Extractable Cresylic Acids. I n view of balance by synthetic processes. I n view of the growth of catalytic cracking over the past the practical aspects of cresylic acid recovery, an assay procedure IT as devised which would employ extraction conditions thought decade, it seems desirable to review the matter of quantity and t o be feasible for plant operation. Accordingly, extractable quality of cresylic acids obtainable from catalytic naphthas and cresylic acids were determined by a single batch extraction of to determine the processing requirements for making comthe naphtha with 10 volume % of 10 weight % ’ caustic soda. mercially acceptable products. I n particular, it was of interest The procedure employed is represented schematically in Figure 1. to assay those stocks which promised to be richest in the lighter The difference between the acetyl value and the sulfur content (in phenols (C, to CJ for which the current demand is greatest. The present work includes in addition assays of several thermal consistent units) was taken as the hydroxyl content of the sample. naphthas for comparison purposes. The results of this survey are Assuming an average molecular weight of 112 and a density of 1.03 for the cresylic acids present the volume per cent on original shown in Table I. Nine catalytic naphthas from seven catalytic crackers are listed together with two thermal naphthas. naphtha mas calculated. This procedure is known to give low results with heavier stocks containing more highly substituted In the recovery of cresylic acids from petroleum naphthas three distinct operations must be considered: phenols (>C,), which are more difficult to extract and to This method Of assay was in preference 1 Present address, Standard Oil Co. (N. J.), 30 Rockefeller Plaza, New to photometric methods (11, 12, 16) because it yielded a finite Y o r k , N. Y . 2610
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Vol. 44, No. 11
PETROLEUM-COMPOSITION quantity of the actual compounds, which could be further examined and characterized. The simpler colorimetric methods have been found to give erroneous results because of interfering impurities (8).
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acetylated under these conditions. I n all cases cresylic acid concentrates (in benzene) were blanketed with nitrogen to prevent oxidation of thiophenols prior to acetylation. This procedure o jviously involves the assumption that the acidic sulfur compounds recovered by the caustic extraction consisted predominantly of mercapto-type compounds and therefore were susceptible to acetylation under the above conditions. A review of the known acidic sulfur compounds appears to lend validity to this assumption, Sulfur in excess of 0.2 weight % was determined by means of the Parr peroxide bomb (13) employing sugar as combustion promoter and gelatin capsules for samples. By limiting the time between weighing the sample and firing the bomb, it was possible to analyze certain sets of samples without removing some 9 to 10% dissolved water. When present in concentrations below 0.2 weight yo, sulfur was determined b y means of the ASTM oxygen bomb procedure (1). Neutral oil was measured by the method of Field and Steuerwald (6) which determines the volume of material insoluble in
C I D O I L CDilCiITRATE
Assay of Cresylic Acids in Petroleum Naphthaso
1 A C E T Y L VALUE
S U L W R CONTENT
Figure 1. Schematic Diagram of Procedure for Cresylic Acids in Petroleum Naphthas
Final boiling point, F. Volume % a c i d s
Light Naphtha 2 3 4 5 CATALYTIC NAPHTHAS
Heavy Naphtha 6 7 8
300 325 370 370 405 426 440 446 450 0 . 0 2 3 0.020 0 . 0 5 1 0.070 0 . 1 5 0 . 1 4 0 . 3 7 0 . 1 4 0 . 2 2 THERMAL NAPHTHAS 10 11
Final boiling point, F. 275 430 Volume % acids 0.002 0.040 a Catalytic naphthas were obtained from a total of seven fluid catalytic crackers; naphthas 1 . 3 , 6. and 8 were derived primarily from crudes originating in West Texas: naphthas 2 and 5 were obtained predominantly from Louisiana crudes: naphthas 4, 7, 9. 10, and 11 were produced from fairly broad mixtures of Texas crudes.
T o check the degree of cleanup of cresylic acids obtained with this single treat, a test was made wherein a second sample of the same naphtha was run concurrently, employing three successive 25 volume % treats of 15 weight % soda. The quantity of cresylic acids obtained with the more exhaustive extraction exceeded that of the single 10% treat by less than 10%. I n the presence of fatty acid impurities such as were encountered in some thermal naphthas, it was found necessary to effect a split between the cresylic PAFFI N A T E acids and the more acidic fatty acids. CHILL ACIDIFY T O pH'2 This was achieved by employing an exhaustive extraction of the liberated acid oil mixture with saturated sodium bicarbonate solution. The procedure is shown schematically in Figure 2. The aqueous overhead was found to contain a minor amount of organic EXTRACT I NATE m a t e r i a l , w h i c h w a s recovered by I I 5C$ A C E T I C A C I D BOTTOMS QVE R UL A 0 DISCARD I saturating with salt and topping. The 508 P R O P I O N I C A C I D H3P04 (8%) DISCARD FI NR AA C1T IX O45 NATE (CONTAINLD organic layer of the toppings was comC6H OH E Q U A L T O ?M O I P L . OLDERSUAW bined with the subsequent organic A a u ~ o u s L A Y E R( 8 ) O R G A N I CLA YE^ T D T A ~R ' ~ C , CRESYLIC layer obtained from the bottoms. The I DRY B Y MEK ANALYSES ACIDS) aqueous layer contained 15% of the E N T R A I N M E N T .( S E E T A B L E I I I ) FRAC;IONATE total recovered organic acids, which IN 1 X 45 P L . OLDERSHAW COLUMN were recovered by extraction with four 35 volume % methyl ethyl ketone A N A L Y S L ~ ( S E E TABLE v i i ) washes and combined with the organic layer prior to drying b y methyl ethyl Figure 2. Recovery and Purification of Cresylic Acids Occurring in the Presence of Fatty Acids ketone entrainment. An a 1 y t ical T e sting Hydroxyl content of cresvlic acid concentrates was determined by acetylation using a modification of the 2 to 2.5 N sodium hydroxide solution after refluxing for 15 classical pyridine-acetic anhydride method of Verley and BOISminutes. Carboxylic acid impurities were estimated from measurement of ing (16). A 1-hour refluxing period was employed and titration was accomplished with the aid of a Fisher Titrimeter. the infrared absorption peaks a t 5.6 to 5.8 microns, in which reAcetyl values were corrected for thiophenols, which are also gion the phenolic compounds were found to be reasonably trans-
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parent. Appropriate molecular weights must be assumed if it is desired to calculate the results on a weight basis When large concentrations of aliphatic acids were encountered, the sodium bicarbonate multiple-extraction procedure outlined in Figure 2 was used to remove them. It is estimated that in mixtures of roughly equal quantities of fatty acids and phenols the latter may be determined with an accuracy of 5% or better. Kitrogen content of typical samples was determined for the most part by the Kjeldahl procedure modified to pick up ring nitrogen (3). Phenol distribution in appropriate cresylic acid fractions Kas determined by infrared measurements a t 1 1 . 8 5 ~(0- or p-cresol), 1 2 . 3 ~(phenol or p-cresol), 1 2 . 9 ~(m-cresol), 1 3 . 3 ~(phenol), 1 4 . 1 ~(o-cresol), and 1 4 . 5 ~(phenol). Measurements were made with a Baird double-beam spectrophotometer using rock salt cells and Phillips pure grade cyclohexane as solvent. Infrared analyses of phenols up to the ethylphenols and four of the xylenols are described by Friedel, Pierce, and McGovern (7').
total yield of acid oils (including thiophenols) was estimated to be 0.18 volume % based on naphtha treated. Figure 3 shows a titration curve for a sample of the spent soda. The curve indicates a number of small plateaus as may be anticipated from the complexity of the mixture. The changeb in slope a t pH 9.5 and again a t 6.5 suggest the end points for phenols and thiophenols, respectively, although there is undoubtedly considerable overlapping. There is a suggestion of a break at pH 12 which might be associated with aliphatic mercaptans
I I 20 (c
Recovery, Purification, and Characterization of Cresylic Acids from Catalytic Naphtha. In order to obtain cresylic acids from a typical catalytic stock under well-controlled conditions, a 10barrel batch of the desired heavy naphtha (10 to 99% boiling range; 260' to 426' F.) was treated in successive portions in a 50-gallon Pfaudler kettle. Prior evaluation of the naphtha (4-liter sample) employing the procedure outlined in Figure 1 indicated a concentration of 0 41 volume % cresylic acids. On this basis, therefore, a 4.5-gallon batch of 10 weight % soda was considered ample for treating the entire 10 barrels of naphtha. Each batch of naphtha u a s contacted with the soda solution by agitating for hour, Following a 1-hour settling time, the phases were separated and the aqueous layer was returned to the kettle with fresh naphtha. This was repeated until all 10 barrels had been treated.
4.0 6.0 8.0 10.0 MILLIEQUIVALENTS Of K I D
Figure 3. Titration Curve for Spent Soda from 10Cycle Pfaudler Treat of Heavy Catalytic Naphtha
A check of the raffinate from the first and seventh barrels treated was made by the method illustrated in Figure 1 and a cleanup of 91 and SO%, respectively, was indicated. It appears, therefore, that an over-all average of 80% or more of the extractable phenols was recovered in treating the 475 gallons of naphtha. .4 Babcock bottle test of the extract layer by acidification indicated the presence of 16.4 volume % acid oils in the aqueous layer. Entrainment and handling accounted for a loss of 10.lyo of the aqueous layer. With appropriate correction for losses, the
," 3 I I
Sulfur Distribution on Distillation of Total Acid Oils in Spent Soda of Figure 3 Fractions 1 to 5 in Table 11
Sixteen liters of the soda solution out of a total of 17.5 litero recovered were acidified to various p H levels with the aid of a pH meter and several fractions nere separated as indicated in Table 11. All cresylic acid fractions segregated from aqueoue layers having a pH greater than 7 were recontacted with acidified brine t o p H 3 to 4 to ensure complete liberation of phenols and to reject significant quantities of emulsified water. A portion of the total dry acid oil mixture was subjected to anal>tical distillation. A 30-actual plate Oldershaw column was employed a t 10 mm. of mercury pressure or less a t the condenser and 10/1 reflux ratio. Temperatures were corrected to atmospheric pressure by means of the nomograph of Lippincott and Lyman (IO). The distillation curve is shown in Figure 4 together a i t h sulfur analyses of appropriate fractions. It can be seen that part of the sulfur is concentrated in the initial fractions, representing lower boiling thiophenols, while the remainder is concentrated in the high boiling cuts and bottoms apparently as disulfides. Analysis of the phenolic components of the individual fractions gives the over-all analysis shown in Table I11 for a full range catalytic naphtha (C, to 450" F.) Since the purity of the cresylic acids determines to a large extent their marketability, several procedures were investigated for reducing the major contaminants-namely, sulfur compounds neutral oil, and fatty acids. The data in Table I1 show that the initial fraction obtained on acidification contained the bulk of the cresylic acids with the least sulfur. The second fraction comprising another 10% of the cresylic acids was substantially higher in sulfur. The third fraction consisted mainly of thiophenols while the fourth and fifth fractions were essentially phenol in aqueous solution. Analytical distillations of the total acid oils and of the first fraction of Table I1 are plotted in Figures 4 and 5, respectively These plots illustrate the degree of desulfuiization that may be achieved by a combination of limited neutralization and distillation. The phenomenon of sulfur concentration in front ends and bottoms has been noted Jvith essentially all the crude cresylic acids studied in the course of thic work including those from Venezuelan naphthas. Figures 6 and 7 demonstrate a similar phenomenon as noted from distillation of
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Vol. 44, No. 11
PETROLEUM-COMPOSITION Table 11.
Fractionation of Cresylic Acids by Limited Neutralization Incremental Vol. of Dry Acid Oil, M1. 1800 260 280 50 60
Initial to p H 10.0 p H 10.0to 9.1 p H 9.1 to 3.5 Salted out (as. layer p H 3.5) Benzene extraoted (pH 3.5)
Wt. % s4 in Increments 1.61
4.7 (approx. av.)
Determined by Parr peroxide bomb method.
Composition of Crude Cresylic Acids from Cracked Naphtha (C,to 450' F.) Venezuelan Thermal Naphthaa, % 15 35 45
Catalytic Naphtha, %
Component Phenol Cresols C8+ phenols Impurities
45 2o 25 10
40 50 60 W T % CHARGE
Figure 6. Sulfur Distribution on Distillation of Acid Oils from Plant Treating of Light Naphtha (Predominantly Catalytic)
a The cresylic acids in this naphtha comprised only about 30 to 35% of the total acid oils, the balance being fatty acids and thiophenols.
some cresylic acids derived from full-scale plant caustic washing operations. The cresylic acids obtained predominantly from light naphthas (Figure 6) are indicated to be quite rich in phenol (CBH~OH) while those derived from heavy naphtha (Figure 7) are richer in the cresols. An alternate procedure for sulfur reduction is a sweetening operation such as may be achieved by a number of oxidative methods. Airblowing was investigated for this purpose both in the presence and in the absence of added catalyst. This work was confined to airblowing of alkaline cresylate solutions in light of the findings of Hund, Thomas, and Luten (Q),who noted that air oxidation of sulfur impurities in free cresylic acid mixtures is less effective than in alkaline solutions.
It may be noted from the above results that under these conditions maximum sulfur reduction appeared to be achieved in approximately 4 days (96 hours). Airblowing with catalyst was carried out on half-liter batches of high-sulfur spent soda to establish the effect of catalysts on the rate of sweetening. Five compounds were tested in all, including tannic acid which is known to catalyze this type of oxidation.
50 60 70 % OF CHARGE
Figure 7. Sulfur Distribution on Distillation of Acid Oils from Plant Treating of Heavy Catalytic Naphtha
c: I 1- c .3 .
W T . % CHARGE
Sulfur Distribution on Distillation of Acid Oils Liberated at pH 10.0 Fraction 1 in Table I1
Airblowing without catalyst was tested on a 20-liter batch of high-sulfur spent soda obtained from plant treating of heavy catalytic naphtha. The alkaline solution was air blown a t room temperature using an alundum disperser and an air rate of approximately 3 liters per minute while maintaining vigorous swirling of the charge. Samples were drawn daily, washed four times with 20 volume % hexane, and acidified with hydrochloric acid. The phenol layer was analyzed for sulfur by the peroxide bomb method. The results from samples taken over a period of 5 days are shown in Table IV.
I n these experiments a sample of the master batch of soda (naphtha-washed and stored under nitrogen) was blown in the presence of 0.2 weight %catalyst for a period of 6 hours in a 1-liter tall form scrubber fitted with an alundum thimble. The rate of blowing was kept constant throughout the series of tests. At the end of the blowing period the sample was washed three times with 40 volume % hexane, sprung, and analyzed for sulfur by the peroxide bomb method. The results obtained are shown in Table V. Consistent with published literature, tannic acid is found to be a most effective catalyst for the sweetening of spent soda Quinone was found to be next best. No attempt is made to differentiate between the various catalysts on a molar basis inasmuch as the compounds tested appear to be relatively ineffective except for tannic acid and quinone. Tannic acid appears to be capable of increasing the room temperature sweetening rate approximately tenfold. I n addition to the problem of sulfur contamination some thermal and virgin naphthas present further complications because
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Airblowing of Spent Soda i n Absence of Catalyst W t . % SQ in Cresylic Acids 5.78 5.08
Blowing Time, Hr. 0 24 48 72 96 120 Determined b y Parr peroxide bomb method. Sample
Catalyst (0.2 K t . %)
Desulfurization by Airblowing i n Presence of Catalysts
Test 1 (control) 2 (control) 3 5
0.89 0.86 0.19
Quinone Tannic acid (EK)
Wt. 75 s after 6 Hours (Peroxide Bomb) 6 . 3 2 initial value 5 07 5.28 4.98 4.82 2.30 0.65
of the presence of significant amounts of fatty acids. This is perhaps best illustrated by certain Venezuelan cracked naphthas examined in the course of these studies. The caustic extracts of a Quiriquire thermal naphtha were found to contain major proportions of fatty acids (>60% on free acid oils). I n preliminary experiments with naphtha of this type two different strengths of caustic were employed to establish the effect of caustic strength and the degree of caustic utilization on cresylic acid selectivity. The data shown in Table VI indicate no selectivity since essentially equal proportions 5f plienols and aliphatic acids were found in all the acid oils isolated.
Table VI. Extraction of Acids and Phenols from Venezuelan Thermal Naphtha with Aqueous Sodium Hydroxide Fresh Caustic Wt. % OBB. NaOH
wt.% SaOH Consumed
70of Extracted Acid Oils as Aliphatic Phenols acids Wt.
The analysis of the cresylic acid fraction (33 weight % of the total segregated by the procedure of Figure 2 ) is shown in Table 111. The balance of the material extracted (67%) consisted of aliphatic acids in the range Cz to Ce. The breakdown of the fatty acids is shown in Table S‘II.
Table VII. Analysis of Organic Material Extracted from Venezuelan Thermally Cracked Naphtha (100’ to 400’ F.) with Aqueous Caustic (Aliphatic acids 66.8 weight % of total) Wt. % 21.8 35.8 8.7 9.0 9.7 15.0
Component Acetic acid Propionic acid Butyric acid Valeric acid Caproic acid Higher acids
Keutral oil contamination and the methods of reducing it have been subjects of considerable controversy (14, I?), mainly as a result of inadequate definition. I n general, the problem is en2614
countered in strong caustic. ( > 2 5 % ) treating and in particular the treating of heavier petroleum fractions which mal contain significant amounts of less acidic, highly substituted phenols. Neutral oil contaminant is perhaps most commonlj- encountered as the result of entrainment because of poor settling of the spent soda prior to “springing.” However, in cases where strong caustic is employed and high concentrations of sodium phenolates allowed to build up, a certain amount of neutral oil may actually be held in solution. RIoreover, in strong caustic treating certain weakly acidic phenols may be extracted which subsequently may be measured as neutral oil by relatively milder neutral oil tests. I n either of these two cases. however, the bulk of the neutral oil may be rejected by dilution of the phenolate solution to an acid oil content of 20 to 25 volume yo or less and allowing sufficient time for proper settling if a light naphtha wash is not employed. I n the course of these studies, which \yere mainly concerned with weak caustic extraction of cresylic acids from relatively low boiling stocks, the problem of neutral oil contamination \$as not encountered. $nalyses of cresylic acid samples for neutral oil indicated in ever! case negligible neutral oil (