AS-4 LYTICAL EDITION
18
(l), 0.14 per cent of the N204is undecomposed; or, for 150 cc. of a 10 per cent mixture, about 0.02 cc. is present as this gas. This introduces an error of only 0.01 cc. As 0.2 per cent of the NO2 decomposes, the 02 from the NO2 dissociation is present to the extent of 0.01 per cent, which makes an error of only 0.015 cc. These two corrections are negligible and tend to neutralize each other. In the present study water vapor was carefully eliminated from the gas mixture, as its absorption by the sulfuric acid employed to remove the nitrogen peroxide would have introduced an error. It is hoped that later this apparatus can
Vol. 2, s o . 1
be adapted to the analysis of nitrogen peroxide mixtures containing water vapor. In addition to the usual precautions exercised in gas analysis, such as keeping the buret clean and changing the reagents frequently, it is necessary to be sure that the pipet with its content of oil has reached the temperature of the vapor jacket before the sample is drawn, and to run the sample at once into the sulfuric acid, as an appreciable error is introduced if the NO2 is in contact with the oil for longer than 1 or 2 minutes. ( 1 ) Z. p h y s i k . Cizem
,
100, 68 (1922)
Determination of Olefin and Aromatic Hydrocarbond W. F. Faragher, J. C. Morrell, and I. M . Levine RESEARCH LABORATORIES, UXIVERSAL OIL PRODKXTSCOXPINY, CHICAGO, ILL
A n analytical procedure for the determination of AKY methods for the FORMOLITE hhTHOD-The olefin and aromatic hydrocarbons is described. It condetermination of aroformolite method (71) desists of two steps: (1) Determination of the total matic and olefin hypends upon the formation of olefin-aromatic content by treatment with 91 per cent a resin when an oil containing drocarbons have been pubsulfuric acid, distillation to remove polymers, and final olefins is refluxed with formallished, but in general they treatment with 98 per cent sulfuric acid; (2) removal of have not been entirely satisdehyde and a strong acid. It olefins with sulfur monochloride, distillation to remove factory. The present analyhas been shown (74,81),howthe olefin-free oil, and determination of aromatic hyever, that the resin formed sis is based on the removal drocarbons in the olefin-free oil by means of nitration. does not account for all the of the olefins by means of sulfur monochloride, which reolefins present. Furthermore, acts quantitatively with these hydrocarbons, and the deter- the reagent reacts with aromatic hydrocarbons also (96). mination of the aromatic hydrocarbons in the olefin-free oil. MERCURICACETATE-&krCUriC salts react with olefins It is also necessary to determine the sum of the olefin and (103) to give derivatives of various compositions. Upon aromatic hydrocarbons in order to calculate the percentage the basis of these reactions, a method was devised for the determination (66, 95, 97‘) of oIefins. It has been found of olefins by difference. recently, however, that a large excess (86) of mercuric aceExisting Methods for Determination of Olefins tate has to be used to cause all the olefins to react and also HALOGENATION-The method most commonly used to that refluxing is necessary (8). Some of the unchanged determine olefins is halogenation. Modifications of the oil is retained mechanically by the flocculent precipitate procedures used for fatty oils are employed, but they have formed (8). HEATOF REACTION WITH SULFURIC ACID-olefins react not proved successful. One of the principal difficulties is that substitution takes place concurrentIy with addition a t with sulfuric acid, with the evolution of heat. Attempts the double bond, but even when the extent of substitution have been made to determine the relationship between the per(47, 62, 89) is taken into consideration the results are not centage of olefins present and the quantity of heat evolved satisfactory. When a reagent (31) with which no substi- (16, 23, 36, 60, 61). Although it has been reported (16) that tution apparently takes place is used, addition is not com- a useful relationship exists for olefins in cracked gasolines, plete (89). Furthermore, diolefins complicate the problem, tests made in this laboratory show that the method cannot be for, while some react with halogens as if there were one double used as an accurate index of the content of olefins. Even bond (%), it would be expected that if the two double bonds for a single olefin the interpretation of the result is difficult, were separated by several carbon atoms both would become as the increase in temperature is not a straight-line function saturated. Moreover, the results depend upon the ratio of the concentration of the olefin, the heat evolved varies with of the amounts of oil and reagent used (2U, 66). It has been the initial temperature, and the acid reacts also with aromatic shown that a constant result can be obtained only when hydrocarbons and, to a slight extent a t least, with naphthenes and some paraffins, so that the increase in temperature this ratio is kept constant (20). Apparently, good results can be obtained by the use of depends in part on the nonolefinic portion of the oil. The the bromide-bromate mixture (28,29, 50), as the conditions problem becomes more complicated when it is considered are such that very little bromine is present a t any time that cracked products contain a mixture of olefins and that and substitution is largely prevented. However, the figure each olefin has its own heat of reaction with sulfuric acid. SoLvmTs-Many solvents have been used t o separate obtained represents a t best the “concentration” of double bonds rather than of olefinic hydrocarbons. The olefin olefins and aromatic hydrocarbons from other hydrocarbons, content, of course, may be calculated by determining the but generally the results have not been successful. The average molecular weight of the oil and by assuming that separation of the olefins and the aromatic hydrocarbons is the average molecular weight of the olefins is the same as usually incomplete and the paraffin and naphthenc hydrocarbons are dissolved to some extent. Some of the solvents that of the oil as a whole. nhich have been used are liquid sulfur dioxide (6, 18, 19, Received June 11, 1929. Presented before t h e Division of Petroleum 24, 64,66),a solution of sulfur dioxide in acetone or other Chemistry a t the 75th Meeting of the American Chemical Society, St Louis, ketones (44, 78, 100, 82), sulfoacetic acid (49),methyl sulMo., April 16 to 19, 1928.
M
1
I,YDCSTRIdL AND ENGINEERIXG CHEMISTRY
January 15, 1930
fate (34, 35, 101), selenium oxychloride (53, &), methanol (8, 92), acetic anhydride (94),aniline (8, 33, &), nitrobenzene (8),dimethylaniline (8, SS), ethyl tartrate, ethyl oxalate, acetoacetic ester, levulinic acid, phenylhydrazine, and furfural (33). I n some instances fairly sharp separations are made if the correct quantity of reagent is used and the percentage of olefin and aromatic hydrocarbons lies within certain limit-. PERBENZOIC hD-Perbenzoic acid reacts with olefins, diolefins, and other unsaturated compounds (80) a t 0" C. to give olefin oxides, which upon hydrolysis yield glycols. This reaction was used as the basis of a method for the quantitative estimation of olefins (69, 70). h known quantity of perbenzoic acid is allowed to react with a known weight of oil. A solution of potassium iodide is then added and the liberated iodine titrated with sodium thiosulfate. This method has some of the disadvantages of the bromine-addition method. The reagent has to remain in contact with the oil for 40-48 hours; hence the method requires more time than the halogen method. Furthermore, the oil must be free from substances that are easily oxidized. Lubricating oils give values much higher than those calculated from the iodine numbers, owing to the fact that hydrocarbons other than olefins react with perbenzoic acid. It is knonii that aromatic hydrocarbons decompose hydrogen peroxide with the liberation of oxygen (67). It is possible that they have the same action upon perbenzoic acid, as this acid is the benzoyl derivative of hydrogen peroxide. SULFURIC ~4CID-sUlfUriC acid reacts with olefins to give five types of products: alcohols, esters, polymers, oxidation products] ( I O ) , and saturated hydrocarbons by reduction (59>77, 83). coxcs. OF A C I D
Per cent 95 90 85 80
Table I
c____Loss
Benzene P e r cenf 32.5 12.0
k5
----
7
Xylene P e r cent 96.5 85.3 28.5 0
Table I1 coxcw. ACID
OF
Per cent 98 90 80
Benzene P e r cent 100 5 tow
Toluenexylene (1:3) Per c e n t 100 32 5 7 5
Aromatics from cracked kerosene Under 210' C. 210-270O C P e r cent Per cenl 100 100 20.23 30 5 10
Sulfuric acid is not the only oxidizing agent in the presence of which reduction has been shown to take place, for pentane has been found among the products of the reaction between amylene and benzoyl peroxide (55). The extent t o which each of these five reactions takes place is a function of the molecular weight and the structure of the olefin and the concentration of the acid (10). Polymerization increases with increase in molecular weight and, up to a certain point, with increase in the concentration of the acid, the maximum polymerization taking place in the presence of 91 per cent acid (45). The alcohols that are formed directly are tertiary alcohols. They originate from tertiary olefins, which have been shown to be the most reactive (73). Sulfuric acid m-ould be a good reagent for removing olefins were it not for the fact that it dissolves or reacts with aromatic hydrocarbons also, as may be seen in Tables I (22) and I1 ( I I ) , which shorn the results obtained by shaking solutions of aromatic hydrocarbons with various concentrations of sulfuric acid. The results in Table I1 are the higher because a larger volume of acid was used for a longer period. The problem of the separation of olefins and aromatic hydrocarbons by means of this reagent becomes even more
19
complicated in viea, of the reports of various workers that hydrocarbons of these two classes condense with the formation of alkyl derivatives of the aromatic hydrocarbons (7, 9, 52, 90). However, various concentrations of acid have been proposed to make a t least an approximate separation. Acid having a strength of 80 per cent has been used frequently (17, 21, 7'5). Although it has but little action on aromatic hydrocarbons, all the olefins (63) are not removed, even after distillation to separate the polymers. In one case (57) a cracked distillate mas treated with 80 per cent acid, distilled to the original end boiling point, treated with 98 per cent acid, and redistilled to the original end boiling point. ilfter the last distillation a considerable residue remained, indicating that the treatment with 80 per cent acid did not react with all the olefins. Acid solutions stronger than 80 per cent have been proposed (8, 85),but it is evident from the results in Tables I and 11, and also from other work, that sulfuric acid cannot be used for the accurate determination of olefins. SULFURhIorioCHLoRIDE-Ethy1ene reacts with sulfur monochloride to yield mainly two types of compounds, dichlorodiethyl sulfide (mustard gas) and dichlorodiethyl disulfide. The latter was obtained about 1860 by Niemann (72) and Guthrie (38). It was proved to be a disulfide by showing that upon oxidation (91) it yielded the compound CH2C1CH2S03H. Further proof was the fact that upon reduction with zinc the corresponding amylene compound gave diamyl disulfide (37, 39). Guthrie carried out the reaction on the Tater bath, whereas Pope and hi's collaborators found that a t temperatures between 30" and 70" C. mustard gas was obtained (32). It is for this reason that Pope and his collaborators claim priority in the discovery of the reaction. These investigators also obtained the monosulfide derivative from propylene and butylene ( 7 9 ) . Propylene has also yielded the disulfide (13). The monosulfide derivatives have high boiling points. The disulfides decompose but may be heated to a temperature of 180" C. before decomposition is evident. hloreover, as both reactions are practically quantitative, sulfur monochloride is a suitable reagent for the removal of olefins from a mixture of hydrocarbons. It has been used in the determination of hydrocarbons of this class (58),but the proposer of the method admitted that it gave comparative figures only. There are fen. published reports on the action of sulfur monochloride on the other hydrocarbons. The compound has been used to purify commercial benzene by warming the mixture on the water bath for a long tirne (56). This fact would indicate that there is little or no reaction with the benzene itself. HoweTer, there is evidence that a slight reaction takes place when paraffins are so treated (58). The reaction with paraffins seems to be a chlorination. On the other hand, anthracene reacts almost quantitatively (30). In the presence of aluminum chloride (4, 5 ) or an aluminum-mercury couple (14), aromatic hydrocarbons react to yield sulfides. Even heptane has been found to react under these conditions. However, as will be shown, reaction with hydrocarbons other than the olefins can be practically preTented. Existing Analytical Methods for Aromatic Hydrocarbons
The methods used for the determination of aromatic hydrocarbons may be divided into two classes, physical and chemical. Among the physical properties used are density (15, 87, 98),index of refraction (1, /tG, 48), and the critical solution temperature in various organic liquids. DENSITYAND REFRACTION-,b-OmatiC hydrocarbons have a much higher density and index of refraction than the other
20
ANALYTICAL EDITION
hydrocarbons, and this fact has been used to determine their content in a mixture. It has been found, however, that increase in total volume occurs when aromatic hydrocarbons are mixed with paraffins. This increase in volume varies for each aromatic hydrocarbon, for its concentration, and even with the nature of the paraffins (15). The index of refraction differs also for each aromatic hydrocarbon. Methods based on these properties are not accurate, except for small concentrations. TEMPERATURE OF MIscIBILITY-substances with which paraffins and naphthenes are not miscible a t room temperature but in which the aromatic hydrocarbons dissolve have been found. If aromatic hydrocarbons are dissolved in a mixture of paraffins and naphthenes, the temperature a t which miscibility with the solvent is complete is lowered. The higher the concentration of the aromatic hydrocarbons the greater is the lowering of the solution temperature. The solvent most widely used for this test is aniline. The experimental procedure has been changed slightly since the time that the method was proposed (12). In the method generally used now (99) 1 volume of oil, ordinarily 5 cc., is mixed with an equal volume of aniline and the mixture heated until complete miscibility results. The mixture is then allowed to cool and the temperature a t which cloudiness first appears is noted. This temperature is known as the aniline point. The aniline is taken and is determined again after washing with 98 per cent sulfuric acid to remove the aromatic hydrocarbons. The percentage of aromatic hydrocarbons is calculated from the difference of the two temperature readings. Solutions containing high concentrations of aromatic hydrocarbons cannot be analyzed in this way, as an oil that contains more than 50 per cent of aromatic hydrocarbons is completely miscible vith aniline (8, 104). Furthermore, the aniline point varies somewhat with the non-aromatic base and also with the individual aromatic hydrocarbons (93, 99, 102). The variation is especially large for the higher boiling substances (11). Among other substances used in the place of aniline are nitrobenzene (25) and benzyl alcohol ( 3 ) . A method has been developed in which the critical solution temperature is obtained in two different solvents and the aromatic content calculated from the two temperatures ( 2 ) . The removal of the aromatic hydrocarbons from the oil is not necessary. Benzyl alcohol is proposed as one of the solvents. The objection to all proposed solvents, including aniline is that the temperature lowering is not the same for all the aromatic hydrocarbons and that it is not proportional to the concentration of even a single hydrocarbon. CHEMICAL hfETHoDS-The chemical methods used for the determination of aromatic hydrocarbons employ chiefly sulfonation and nitration. Sulfuric acid of 98 per cent strength has been used consistently in the removal of aromatic hydrocarbons (65, 98, 99). I n one of the methods, the concentration of aromatic hydrocarbons is determined by the conversion of the sulfonic acids in the acid sludge to barium sulfonates, and the precipitation of barium sulfate by addition of sulfuric acid. The weight of the barium sulfate is an indirect measure of the content of aromatic hydrocarbons. More often 100 per cent acid has been used and the loss of volume measured (11, 41, 68, 84) or the excess of acid determined by titration (105). It has been shown and verified in this laboratory that the loss to 98 per cent sulfuric acid is greater than the volume of the aromatic hydrocarbons (77). It would be expected, then, that the decrease in volume of oil would be greater still when 100 per cent acid is used, especially if unusual care is not taken in the preparation of the acid, as 100.5 and 101
Vol. 2 , No. 1
per cent acids remove naphthene and paraffin hydrocarbons (57, re). Nitration is also a commonly used process for the determination of aromatic hydrocarbons. Fuming nitric acid has been used and the nitrated products dissolved in a known volume of sulfuric acid, the content of aromatic hydrocarbons being calculated from the increase in volume of the acid layer (40). This method is not accurate, as a change in total volume occurs when nitrated aromatic compounds are dissolved in sulfuric acid, and each nitrated hydrocarbon not only gives a different volume change but also a different volume of nitrated products. The nitro compounds m-ere weighed after the nonaromatic substances were removed (27,43). This method cannot be accurate for reasons similar to those just given. A more reliable method was proposed by Hess (42). The aromatic hydrocarbons are nitrated in a vessel with a graduated neck and the nitro compounds are then dissolved in 66' Be. sulfuric acid added in such quantity that the unchanged oil appears in the graduated portions, where its volume can be read. A unique method developed in this laboratory (21) consists in the nitration of the aromatic hydrocarbons by a special nitration mixture, so chosen that the nitro compounds concentrate in a separate layer, the volume of which is proportional to the concentration of aromatic hydrocarbons in the oil. This method will be discussed later. Experimental Procedure
The new analytical procedure developed in this laboratory consists of two steps: (1) determination of the total olefinaromatic content by means of sulfuric acid; and (2) removal of olefins with sulfur monochloride and distillation to recover the olefin-free oil, followed by determination of the aromatic hydrocarbons in the olefin-free oil. STEP I-Shake 100 cc. of the oil with 3 volumes of 91 per cent sulfuric acid for 30 minutes. Withdraw the acid and note the reduction in volume of the oil. Distil the oil t o a point 5 degrees above the former end point of the oil to separate the unchanged oil from the polymers formed in the acid treatment. Finally, shake the distillate with 3 volumes of 98 per cent acid to remove the small amount of olefins and aromatic hydrocarbons that escaped the previous treatment. The total reduction in volume represents the olefins and aromatic. hydrocarbons in the oil. STEP 2-Add sulfur monochloride to the oil and allow them to remain in contact overnight. Distil the mixture a t an atmospheric pressure for the low-boiling portions and then under reduced pressure. This procedure separates the olefin-sulfur monochloride reaction products from the oil. The content of aromatic hydrocarbons in the distillate is then determined by nitration. The olefin and aromatic contents are calculated by means of the formulas 1OO(S - A ' ) U= 100 - A ' A = S - U
where U and A are the actual percentages of olefin and aromatic hydrocarbons, respectively, in the oil, S is the sum of the olefin and aromatic hydrocarbons (Step I), and A' is the aromatic content of the olefin-free oil (Step 2 ) . Analysis of Known Mixtures
The details of the method for the analysis'of known mixtures are as follows: Shake the oil (100 cc.) with 3 volumes of 91 per cent sulfuric acid for 30 minutes with thorough cooling. Add the acid a t first in 50-cc. portions to prevent loss of the low-
IA-D USTRIAL AXD ENGINEERI,VG CHEMISTRY
January 15, 1930
boiling substances. Allow the mixture to settle for 1 hour, withdraw the acid, and let the oil stand for 1 hour longer. From time to time remove the acid sludge which collects. Run the oil into the graduate that was used for measuring the sample, allowing about 5 minutes for drainage before reading the volume. Record the loss in volume ( L I )and the volume of the oil remaining (VI). The next step is the separation by distillation of the unchanged oil from polymers and the olefin-aromatic condensation products. In order to take into account the distillation loss, this step is carried out in the following manner: Pour a volume of the oil (1-2) into a weighed 100-cc. graduate and take the weight of the graduate and oil. Then transfer the oil to the distillation apparatus, consisting of a weighed 200-cc. round-bottom short-neck flask fitted with a 6-inch (15-cm.) Hempel column containing approximately 4 inches (10 cm.) of small Raschig rings. (The graduate is used as a receiver, so that no oil is lost except by evaporation.) Allow the distillation to proceed a t the rate of about 2 drops per second and stop it a t a temperature 5 degrees above the end point of the untreated oil. Cool the receiver in ice or cold water and allow the distillate to come to room temperature before the volume is read. Weigh it immediately after the distillation and then stopper. The loss of weight must be converted into a loss of volume. It is assumed that the oil lost has the specific gravity of the distillate, and, as the loss is usually less than 0.5 gram, the error is negligible. The specific gravity of the distillate is calculated to three places from the known weight and volume. This loss of volume is added to the measured volume of the distillate. Generally a loss of 0.5 cc. is sustained. The corrected volume of distillate is subtracted from the volume of oil distilled to obtain the volume reduction ( 1 2 ) caused by the removal of the olefin polymers and alkylated aromatic hydrocarbons. The following equation gives the actual polymerization loss suffered by the oil remaining after the acid treatment that had the volume VI: L1
x v, -
12
=
(1)
vz
The total loss to the 91 per cent sulfuric acid, i. e., the solution loss plus the polymerization loss, is, of course, given by the expression L1 L2. Disregarding mechanical loss a t this stage in the procedure, the volume of the oil that reLz). mains, UO, is given by the expression 100 - (Ll The oil is now ready for the third step, which is the determination of the loss upon treatment with 3 volumes of 98 per cent sulfuric acid, as follows: Transfer the measured volume of oil (V3) to a separatory funnel from the graduate, which is later used to receive the oil after the acid treatment. Stopper this graduate to prevent evaporation of adhering oil. The periods for reaction and settling are the same as those used during the treatment with 91 per cent sulfuric acid. The volume of the treated oil is subtracted from V s , and the apparent loss (&) is recorded. This loss also must be calculated on the basis of no mechanical loss, and the formula 13 x L'o L3 =
+
+
~
v3
(2)
is used to find the real loss. The sum of the aromatic hydrocarbons and the olefins is, of course, equal to the total loss sustained in the three steps A U = S = L1+ LL + La (3) A representing the percentage of aromatic hydrocarbons and U the pcrcentage of olefins. The manipulation of this method is easy, but care must be taken to prevent the loss of the low-boiling components or light ends. In the treatment with 91 per cent sulfuric
+
21
acid, the acid is added during 10 minutes in small quantities. After each addition the mixture is shaken while cooling. The first acid reacts quite vigorously. Subsequent additions raise the temperature of the oil slightly, so that the shaking can be done a t room temperature with occasional cooling. During the treatment with the 98 per cent acid the reaction is not violent, as most of the olefins and aromatic hydrocarbons have been removed, and the loss of light ends is small. REMOVAL OF OLEFINS-Fit a 500-cc. round-bottom shortneck flask containing 100 cc. of the oil with a reflux condenser and a dropping funnel from which sulfur monochloride (30 cc.) is added drop by drop. Allow the mixture to stand overnight. Cool the solution by addition of ice and n-ash two or three times with a 10 per cent solution of alkali and finally with water. An oil which does not have the sharp odor of hydrochloric acid is finally obtained. Dry it over calcium chloride and filter. Then distil to 120-125' C. at atmospheric pressure, allow to cool to 30' C., and further distil in vacuum. Stop the distillation when the end point is indicated in any one of the following ways-dark brown or red color of the oil dropping from the neck of the distillation flask, rise in the pressure due to a liberation of hydrogen chloride, or fall of temperature. Combine the distillates, wash with alkali, and dry over calcium chloride. The oil at this stage contains less than 1 per cent of olefins. The quantity can be determined by bromine titration2 and later taken into consideration in the determination of the aromatic hydrocarbons. Mixtures with known quantities of olefins and aromatic hydrocarbons were analyzed. The mixture contained amylene, heptylene, octylene, methylcyclohexene, limonene, pinene, benzene, toluene, and xylene. The results are shown in Table 111. U
MIX-
A
T a b l e 111
S
F O U N D A' PRESEXTPRESENT 1 20.0 20.0 39.6 24.07 2 20.0 10.0 , , 12.76 6 20.50 10.5 , . 12.63 9 26.22 9.74 13.2 12.13 10 18.18 9.09 2 8 : 6 3.88 11 24.90 2 . 4 7 27.10
TURB
..
U A ERROR .1 FOCNDF O U N D U 20.45 19.15 t 0 . 4 5 - 0 . 8 5 ,. 10.21 . . . . + 0 . 2 1 ,. , 10.04 . . . . - 0 . 4 6 9.57 -0.13 18174 9.86 +0:;6 +0.77 24.16 2.91 -0.74 +0.44
.
TOTALOLEFIN-A~ROR.fATICCOXCEI~TRATION-A prehllinary experiment proved that 98 per cent sulfuric acid does not remove all the olefins and aromatic hydrocarbons from a mixture containing them, as part of the polymers and olefinaromatic condensation products are soluble in the oil. The foregoing method was applied to the known mixtures already mentioned. The results are shown in Table IV. MIXTURE A 1 20.0 3 2.0 4 10.42 11 2.47
Table IV A + U A + U INSOLK. F O U N D 40.0 39.6 20 0 17.3 15,s 17.8 27.09 27.4 16.67 24.9 27.37 27.1
U
ERROR -0.4 -0.5
+0.31 -0.27
DETERMINATIOK O F AROMATIC HYDROCARBONS-The method for the determination of aromatic hydrocarbons adopted is a modification of that of Hess (41). Pour 20 cc. of the oil into a nitration tube and place it in a thermostat maintained a t 25' C. Read the volume after about 5 minutes. Add 50 cc. of acid mixture (25 per cent by weight of nitric acid, 58 per cent by weight of sulfuric acid, and 17 per cent by weight of water) (21), shake under running water for one minute, and continue the shaking a t room temperature for 9 minutes more. Withdraw the acid after standing for 30 minutes. Add 50 cc. of approximately 95 per cent sulfuric acid and shake vigorously for about a minute. Rithdraw the acid, place the tube in the thermostat, and read the volume of the oil layer after allowing one hour for set2
To be described in a later paper.
22
AiVA L Y TICAL EDI T I O S
tling. The loss in volume is corrected for the solution of the nonaromatic constituents. This correction is 0.62 per cent; Hess reported 0.5 per cent. Results with known mixtures are given in Table V. AROMATICS Per cent 20.00 (benzene) 16.60 (mixed) 3.33 (mixed) 28.57 (mixed) 23.68 (mixed) 55.24 (mixed) 69.33 (mixed) 74.92 (mixed) 84.78 (mixed) 100.00 (mixed)
Table V AROMATICS
AROMATICS FOUND ERROR CORRECTED ERROR Per cent Per cent -1.32 18.68 .... 16.90 16:28 -0 39 4-0.23 4.00 +0.67 +0.05 3.38 20.15 +0.58 28.53 -0.04 24.25 +0.57 23.63 -0.05 55.95 55.33 +0.71 +0.09 69.90 69.28 -0.05 +o 57 76,13 75.53 f1.21 4-0.61 85.80 +1.02 85.18 ~ 0 . 4 0 100.00 .... ... .. ,
AROMATICS
INOIL Per cent 8.53 10 0 11.0 12.36 15.35 17,68
19.80
20.00
20.00 23.00 29.5 30.0 30 31.9 34.1 38.1 40.0 40 44.6 47.0 50.0 54.1 56.8 60.7 63.6 67.0 70.0 70 73.1 76.6
.
When 91 per cent sulfuric acid was used to dissolve the nitro-compounds a smaller loss of the nonaromatic hydrocarbons was sustained, namely, 0.22 instead of 0.62 per cent. The results are shown in Table VI. AROMATICS Per cent
0 3 , 3 3 (mixed) 4.08 16.67 20.00 28.57 50.0 55.24 60.0 74.92 78.23 84.78 88.89 96.0 100.0 2 0 . 0 (benzene) 3 0 . 0 (benzene) 1 2 . 0 (toluene) 3 0 . 0 (toluene)
T a b l e VI AROMATICS AROI~ATICS FOUND CORRECTED Per cent Per cent 0.0s 0.30 3.50 3.18 4.01 4.23 16.78 17.0 20.12 20.34 28.60 28.38 49.94 50.16 55.14 55.36 59.85 60.07 75.17 75,39 77.96 78.18 86.0 84.78 88.96 88.73 95.92 96.14 100.0 ... 18.60 30:i3 30.35 11.96 12.18 30.13 30,35
ERROR +0.08 +0.15 -0.07 +0.11 +0.12 -0.19 -0.06 -0.10 -0.15 +0.25 -0.27 0.0 -0.16 -0.08
++ 7.8 for 8 to 20 per cent + = 2.888V + 7.0 for 40 t o 70 per cent = 2.3V + 19.8 for 70 to 76 per cent =
2.609V
= 2.806V 6.95 for 20 t o 30 per cent = 3.2V 3.8 for 30 t o 40 per cent
a
Per
ERROR
ceiit
... . . ,
C0.31 f0.46 -0.03
..
+o. 1 2
... ...
f0.01
..
-0 10 -0.02 -0.07 0
...
.,.
. . . .
.. .. .. ..
t0.11 +0.01 -0.04
f0.01
.. .. ..
...
...
... ...
.. ..
... ... .. ... 6 9 : 85 73.37 76,50
0 -0.06 + O 52 -0.01 0.40 0 -0.61 0 10.23 -0.27 +0.25 +0.09 -0.07 -0.16 -0.15 C0.27 - @ 10
0.9
or
+0:i3 -0.04
+0.14
ERROR +0.06 +1,55 -0.19 +1.20 -1.06
When the nitration method was used the function that connects the concentration of the aromatic hydrocarbons with the volume of nitric products varied with both the concentration and the particular aromatic hydrocarbons present. For oils containing 8 to 80 per cent of a mixture of equal volumes of benzene, toluene, and xylene, five equations have been developed: A
Equatipn
A = -A ' - 10
Two other methods, the reduction in volume effected by shaking with 3 volumes of 98 per cent sulfuric acid and the nitration method of Egloff and Ptforrell (21) were tried. Application of the reduction in volume method gave the results shown in Table VII.
A A A A
T a b l e VI11 -----AROMATICS CALCD.----VOLUME Equa- Equa- EquaEquaNITRO tion tion tion tion LAYER 1 2 3 4 Cc. Per cent Per cent Per cent Per cent 0.40 8.84 1.02 10.46 1.215 10.97 ... 1.75 12.37 ... 2 . 9 4 6 15.47 ... 3.75 17.58 .. 4 59 ... 19.78 4.65 ... 19.93 4.65 ... 20.0 5.76 23 11 ... 8 04 .. 29 51 8.19 29.96 .,. 8.19 ... . . 30 01 8.78 , . . ... 31 90 9.45 ... ... 34 04 10,88 .. ... 38 62 11.31 ... , . . 39 99 11.31 , . . , . 39 60 13.02 , . . ... 44 60 13.64 ... . . 46 39 14.89 ... ... 50 0 16.39 ... ... 54 33 17.15 ... 56 53 18.68 ... 60 95 19.63 ... 63 69 20.75 , . 66 93 .. 21.76 69 84 21,76 , . . 23,29 ... 24.65 . .
so. 1
The equat'ion to be used in this case is
...
T a b l e VI1 AROMATICS .~ROM~TICS AROMATIC HYDROCARBONS IXSOLN. FOUXD Per cent Per cent 12.0 12.06 Benzene 30.0 31.55 Benzene 12.0 11.81 Benzene, toluene, and xylene ( 1 : l : l ) 20.0 21.20 Toluene 20.0 21.06 Xylene
Yol. 2,
(1) (2) (3)
(4) (5)
The results are shown in Table VIII. For all concentrations higher than 80 per cent the volume of the nitro layer was constant and all the nonaromatic oil was dissolved in it. On the other hand, for concentrations lower than 7 per cent, there was no nitro layer, because the nitro products were dissolved in the oil. This behavior was observed also by Riesenfeld and Bandte (84). The method can be used, however, for these small concentrations if 2 cc. of aromatic hydrocarbons are added to 18 cc. of the oil.
where A' represents the total concentration of aromatic hydrocarbons in the enriched oil, t represents the volume of oil that is analyzed, and y represents the volume of aromatic hydrocarbons that was added. The results are shown in Table IX.
AROMATICS
Percent 1.24 2.3 4.4 7.63 7.63 8.53
Table IX VOL.OF MATICS NITRO ADDED LAYER A' Cc. Cc. 11.22 2 1.27 12.00 2 1.61 13.06 2 2.36 2 3.39 16.64 40.82 7.2 11.50 2 3.75 17.58 ARO-
ERROR
A 1.21 2.22 4.40 7.38 7,53 8.42
-0.03 -0.08 0.2-o.,o
-0.10 11
-0
The principal objection to this method is the fact that the volume of the nitro layer varies with the particular aromatic hydrocarbons in the mixture. This variability is illustrated in Table X. Table X
SUBSTANCE
VOLUZrE OF ?;ITRO
For 20% s o h .
For 307, soln.
0 90 1.06 2 55 1.55
4 41 4.45 5.44 3.93
6 44 7 86 S i8
cc.
Benzene Toluene Xylene Cymene
L.4YER
For 12% s o h .
cc.
cc ..
Analysis of Cracked Gasolines
Cracked gasoline from eight American oils was analyzed. The results are shown in Table XI. A study was made also of the distribution of olefins and aromatic hydrocarbons in a cracked gasoline. Sinackover oil was chosen for the experiment. It was fractionated by means of a Hempel column and each fraction was analyzed. The two fractions of lowest boiling points were titrated with bromine and the olefins calculated as amylene and hexylene. The other fractions were analyzed by the method given in this paper. The results are shown in Table XII.
A-EERI,YG CHEJIISTRY
January 15, 1930 Table X I Av. S S A ' 45.3 45.5 21.13 20.56 38.6 38.4 22.53 22,23 43.2 42.9 20.63 21.23 43.4 43.3 15.33 15.93 44.4 44.1 19.13 19.33 35.6 35,5 17.68 18.13 37.9 38.1 1 2 . 7 8 12.63 34.9 35.4 13.28 13.28 41.9 41.7 10.78 10.83
23
of aromatic hydrocarbons was added. The agreement of the observed values with the theoretical now seems fortuitous. 45.7 31.1 14.4 In the method proposed by Riesenfeld and Bandte 85 per cent sulfuric acid is used for t'he olefin determination. 17.8 Venezuela 38.2 22.38 20.6 The objections to this procedure have been discussed. The 20.93 27.8 15.1 Panuco 42.6 aromatic hydrocarbons are determined by treatment with Panhandle 43.2 15.63 3 2 . 8 1 0 . 5 2 volumes of 100 per cent sulfuric acid, a caution against 19.23 30.8 13.1 Pecos 43.9 shaking the mixture in order to prevent reaction with the 21 4 14.1 17.90 California 35.4 reactive paraffins and naphthenes that may be present being given. These investigators state that the value for the 9.0 12.70 29.1 Seminole 38.3 naphthene content obtained by the Egloff and Morrell method 25.5 9.9 Pennsyl\.ania 1 35.9 13.28 is too high because of the presence of nitro compounds in Pennsylvania 7 41.5 10.80 34.6 7.1 the oil, but the value that they obtain by their method is even higher in one of the two cases cited by them. This fact Table X I 1 signifies that, aromatic hydrocarbons are not removed by the FRACTION U A sulfuric acid as applied, and thus the values would tend to c. be too low, not only on account of this but also on account of their removal in the olefin determination. I n the method outlined by the writers the value for the aromatic hydrocarbons would be a little high on account of the inclusion of a small amount of olefins not removed The olefins reach a maximum percentage in the benzene by the sulfur chloride. The error due to inclusion, as was fraction. The aromatic hydrocarbons are present in small shown, may be decreased by bromine titrat'ion to determine quant'ity in the benzene and toluene fractions, but the per- the olefin content of the distillate. The necessary correccentage increases as the boiling point of the fraction rises. tion can then be applied. The value for the tot'al olefinThe amount of benzene in the oil as a whole is only 0.5 per aromatic content may also be a little high on account of the cent. mechanical loss of low-boiling material. Special care would A comparison of the results obtained by this method and tend to reduce this error. by the method described by Egloff and Morrell is shown Such compounds as di- and tetrahydroaromatic hydroin Table SIII. carbons are included among the olefins, for they behave like the chain olefins. The same may be said of the aromatic Table XI11 EGLOFB-MORRELL FARAGHER-MORRELL- and naphthene hydrocarbons that have olefin side chains. OIL Smackover
S
ORIGIN O F OIL \Vest Texas topped crude oil Panhandle gas oil Seminole fuel oil Smackover crude oil Panuco crude oil Pennsylvania crude oil a Unchecked results.
METHOD Aromatic Per cent 18.8 18.0 15.3 21.2 17.7 13.8
Unsatd. Per cent 27.1 28.0 22.3 22.g 29.1 25,l
A:. A 20.85
U
A
LEVINE METHOD Aromatic Per cent 13.1 10.5 9.0 16.0" 15.6 7.1
Unsatd. Per c e n t 30.8 32.8 29.1 29.15 27.3 34.6
Thus it seems that the older method gives low values for the olefins and high values for the aromatic hydrocarbons. This observation was made also by Riesenfeld and Bandte (84), whose results are repeated in Table XIV. Table XIV BENZENE1 SGBSTANCE E . & M . R.&B. Per cent Per cent Olefins 17.5 33.4 Aromatics 25.1 8.2 Saphthenes 7.9 4.1
BEXZENE 2 E.&M. R.&B. Per cent Per c e n t 9.1 37.6 20.4 4.9 3.5 4.0
Egloff and Morrell were aware that this error might be made and in their own criticism they state that some of the olefins would collect in the distillate obtained during the removal of the polymers and that this incomplete separation would give low results for the olefins and high results for the aromatic hydrocarbons. In experiments made shortly after their paper was published, these authors showed that when an 18 per cent octylene solution was treated with 80 per cent sulfuric acid and distilled to the original end point, the results indicated that approximately one-half of the octylene remained in the distillate. I n the synthetic mixtures employed by the writers amylene was the chief olefin, and these relations would not obtain. It may be pointed out, however, that the nitro volume that would show the presence of 12.7 per cent of aromatic hydrocarbons according to the formula used (89) really represents a concentration of 15.5 per cent. This signifies that some olefins were present in the distillate, as only 12.5 per cent
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Modification of Lamp Method for Determination of Total Sulfur in Petroleum Distillates’ A. E. Wood and William Mattox CHENIISTRY
DEPARTMEST, >
