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T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMIST&Y
It is interesting to note under A that less total color was left a t pH = 7 (neutrality) than a t pH = 5.4,the natural acidity of the juice. The rest of the figures demonstrate clearly that increase of H-ion concentration brings about increase of decolorization. These results may be duplicated by using phosphoric in the place of acetic acid. I n this connection, when working with increase of H-ion concentration in sucrose solutions it is necessary to take into consideration the fact that the rate of inversion of sucrose increases in proportion to increase in the concantration of hydrogen ion. The extent of inversion was determined a t several p H values used in the decolorization tests. The results shown in Table I1 were obtained by boiling 200 cc. of juice under reflux after the H-ion concentration had been adjusted to the desired point by addition of acetic acid. The time factor for these inversions differs entirely from that of the decolorization tests, the experiments being made in the manner described more to accentuate the differences in rate of inversion with increase in p H value than to imitate the conditions of the decolorization experiments. At the end of 2 hrs.' boiling the juice was cooled, aliquot parts were taken, and the direct polarization was read after clarification with lead acetate. I n Table I1 are shown the H-ion concentration, the direct polarization after 2 hrs.' boiling, and the direct polarization of the original juice. This was 8.9" V. From these data were calculated tho percentages indicated. The sample
Vol. 13, No. 11
described in the first column under pH = 5 WRS the original juice without addition of acid. The loss of direct rotation here wap 3 . 4 per cent of the original. TABLE11-INVERSION OF SUCROSE Direct polar- P H - 5 p H = 4 . 8 p H = 4 6 p H ~ 4 . p 4 H=4.2 pH-4 ization ... 8.6 Polarization per cent of origin$ 96.6 Percentloss 3.4
.
Original Pokrization
8.5
7.0
6.5
6.6
5.0
8.9
95.5 4.5
78.6 21.4
73.0 27.0
74.2 25.8
56.2 43.5
... ...
In view of the amount of inversion that can be brought about even a t an acidity as low as pH = 5, about that of normal juice, it would appear to be somewhat doubtful that much advantage would be gained in practice by acidifying to improve decolorization unless conditions were very carefully controlled. Since fairly high acidity and a temperature a t or near the boiling point of the juice are required for best results, the third factor to be controlled is that of time of exposure to high acidity. The authors have obtained good results by heating the juice mixed with carbon to the boiling point, adding phosphoric acid to an acidity of pH = 4, allowing a short time for action, and neutralizing back with milk of lime. Calcium phosphate precipitates out and is removed with the carbon by filtration. One must be careful not to over-lime the mixt,ure and thus obtain an alkaline reaction. It is safe to stop the addition of lime a t about p H = 6 . 5 . By this procedure as good decolorization may be obtained as by carrying through the entire procedure a t p H = 4.
The Iodine Numbers of Unsaturated Hydrocarbons and Cracked Gasolines' By W. F. Faragher, W. A. Gruse and F. H. Gamer M E L ~ OINSTITUTE N OF INDUSTRIAL RESEARCH, PITTSBURGH, PENNSYLVANIA
The work here presented represents an att,empt to clear up, in small part, a t least, the uncertainties connected with the determination of the unsaturated constituents of cracked gasolines, and, if possible, to find the conditions under which unsaturation may be determined accurately. Such data are of interest, not only from the point of view of the derivatives obtainable, but also from that of the keeping qualitties of a gasoline itself. The methods ordinarily employed for this determination are, in the order of the frequency of their use, the sulfuric acid absorption method, the iodine number method, and the bromine absorption method. The sulfuric acid absorption method is the one most generally used, but it is practically useless from the standpoint of information obtainable, since sulfonation, polymerization, solution, and possibly oxidation occur along with the absorption of unsaturated compounds. The method has been standardized by Dean.2 The bromine absorption methodS is least employed because of its inconvenience, and it is useful chiefly when it is desirable to determine substitution as well as addition. The iodine number method is well known, chiefly in the field of animal and vegetable fats and oils. The literature on its use for mineral oils is scanty; for gasolines, the method has been standardized by Dean,2 who was interested in getting a rapid and reproducible technique. The results obtained were found to depend entirely upon uniform procedure. Dean used the Hanus solution, a 30-min. reaction period, and a quantity of gasoline so chosen (depending on its unsaturation) that from 10 to 30 per cent of the reagent was absorbed. The weight of the gasoline varied from 0.04 to 0.20 g. 1 Presented before the Petroleum Section at the 61st Meeting of the American Chemical Society, Rochester, N. Y.,April 26 to 29, 1921. a Bureau of Mines, Techni'al Paper 181. 8 McIlhiney, J . A m . Chem. Soc., 21 (1899), 1084;Schxeitzer and Lungewitz, J . .Tot. Chem. I n d . , 14 (1895), 130.
Smith and Tuttlel have determined iodine values of lubricating oils, using the Hanus solution and a 30-min. period of reaction. They believed it advisable to use as much as 1 g. of oil. This procedure gave a nearly constant value with slight variations in quantity of sample, but very low iodine numbers. Radcliff e and Polychronis2 have studied the action of Hubl, Hanus, and Wijs solutions on heavy mineral oils. They found that the numbers obtained were in the order Hanus > Wijs > Hubl, though the Hanus and Wijs values agreed fairly closely. All three solutions gave increasing values over a 24-hr. period, and the character of the curves for the three solutions was about the same. Radcliffe and Polychronis discarded the Hanus solution because, in the first place, a difference of 20" C. in temperature caused a variation of 5 units in an iodine number of 30, and because they found that the presence of a slight excess of bromine produced a considerable change in the iodine number of an oil determined. The Hubl solution gave an iodine number much below the theoretical value for an amylene a t the end of 2 hrs., while the Wijs solution gave a satisfactory number. Roderer3 has found that for heavy fractions of mineral and lignite tar oils the Hubl-Waller and Wijs solutions give maximum values, using five- to ten-fold excess of reagent and periods of 16 to 2 1 hrs. Grun and Ulberich,4 working with heavy fractions of lignite tar oils and using the Wijs reagent, found iodine numbers higher than the olefine content, as estimated by other reactions, would allow. They, therefore, took the bromine absorption and substitution numbers by the method of McIlhiney and found that the Wijs solution might give 1 2
8 4
Buseau of Standards, Technologzc Paper 87. J . SOG.Chem. I d . , 85 (1916). 341. Z angew. Chem., 88 (19201, 235. I b i d . , 38 (19201, I, 295.
T H E J O U R N A L OF I N D U S T R l A L .4ND ENGINEERING CHEMISTRY
Nov., 1921
aa iodine number of 27, while no bromine was added and 30 per cent of bromine was substituted. PREPARATION OF MATERIALS USEDI N TESTS Since practically no information was available on the results of the use of the Wijs, Hanus, and Hubl solutions with hydrocwbons of low molecular weight, such as are found in gasolines, i t seemed advisable to make comparative experiments with the two former reagents: the Hubl solution was not used. HANWS soLuTroN-In order to check up the effect of excess bromine in the reagent, reported by Radcliffe and Polychronis, two Hanus solutions were prepared: Hanus Solution 1, containing 12.7 g. of iodine and 2.88 cc. ( = 9.00 9.) of bromine per liter of glacial acetic acid. Hanus Solution 2, containing 12.7 g. of iodiue and 2.56 cc. (= 8.00 g.) of bromine.
It will be observed that Hanus Solution 2 contains the atomic proportions of bromine and iodine required for a 0.1 N solution of iodine monobromide, while the Hanus Solution 1 contains the same amount of iodine but the excess proportion of bromine ordinarily used, 13.2 g. iodine and 3 cc. (= 9.36 g. bromine).' It is probable that the extra amount of each of the reagents was originally used to compensate for impurities present. The original suggestion of Hanus2 was to prepare dry iodine monobromide and then to dissolve weighed amounts of it. WIJS soLmIoN-Only one Wijs solution was prepared: 8.50 g. iodine 7.80 g. iodine trichloride per liter of glacial acetic acid. These are the proportions for a 0.1 N solution of iodine monochloride, but it was found necessary to add more iodine trichloride in order to bring the titration value of the solution to the point where it was three times the value shown by the iodine solution before any IC13 had been added. For the particular sample of IC18 on hand, the proportions finally adopted were:
+
8.50 g. iodine 8.60 g. iodine trichloride
There is a great deal of misinformation in the literature on the proportions of materials to be used in preparing the Wijs reagent; this question has been commented on by Dubowitz3 and by Weigemann and K a y ~ e r . ~ Since slight variations in the weight of iodine trichloride used do not affect the resulting iodine numbers, it is suggested that the best way of making up this solution is as follows: Use 8.50 g. of resublimed iodine per liter of glacial acetic acid, determine the value of the solution in terms of standard thiosulfate solution, and then add iodine trichloride until the titration value of the solution is three times as great as that of ihe solution of iodine only. EABOLINES usm-Three gasolines were employed in this work: GasoTine A-An unrefined fraction to 150" of a pressure distillate made from Pennsylvania gas oil by cracking a t 550" C. a t 100 lbs. pressure. The cracking apparatus was such that local superheating was entirely avoided. The color and odor of the fraction were good and the material was entirely stable on standing. Gasoline B-An unrefined fraction to 150" of a pressure distillate produced commercially from a mid-continent oil in an ordinary pressure still. The exact pressure and temperature of the cracking process used are not known. Gasoline C-An unrefined fraction to 150" of a pressure distiUat,e made in a semi-commercial installation for vapor phase cracking. The pressure, temperature, and source of material are not known, but i t is known that it was cracked for 1 Hunt, J . SOL.Chem. Ind., 2 1 (1902). 454; Tolman and Munson, J. A m . Chcm. Soc., 26 (1903), 244. 2 Chem. Zcnfr., 1901, 11, 1217. * ChPm.-Ztg., 88 (1914), 1 1 1 1 . 4 I b M . , 89 (1915), 491.
'
1045
motor spirit rather than for unsaturated hydrocarbons and by-products, so that the pressure and temperature were probably low. The degummed Gasoline B was prepared by allowing a stoppered bottle containing 100 cc. of the material to stand exposed to a northern light for 9 mo. About 1 cc. (1 per cent) of clear, viscous, brown oil deposited during this time, and the color and odor of the gasoline were improved very markedly. All these gasolines were distilled through a 12-in. Hempel column filled with magnesium turnings. IxYDROCARBON+--The unsaturated hydrocarbons which were used in this investigation were prepared by different methods: amylene and isoprene from amyl alcohol, octylene from sec-octyl alcohol, heptine from heptaldehyde, and the other hydrocarbons from the corresponding saturated hydrocarbons. The trimethyl ethylene (Amylene I ) was isolated from amylene obtained from the Eabtnian Kodak Company by the method given by R. Adams.' The tertiary amyl alcohol obtained was dehydrated by mcans of anhydrous oxalic acid and carefully refractionated several times through a Vigreux column; the fraction used was that distilling from 36.3" to 37.3" C. (747 mm.). After fractionating the Eastman amylene several times, a fraction distilling from 28.8" to 31.8" C. was collected. This fraction corresponds to unsymmetrical methylethylethylene (Amylene 11). Octylene was obtained from sec-octyl alcohol (methylhexylcarbinol) distilling from 174" to 176" C., by a number of different methods. The use of phosphorus pentoxide as dehydrating agent was found to give the best results. The octylene obtained was purified by fractionation and distilled finally a t 122" to 124" C . The hexylenes, n-hexylene and isohexylene, and heptylene were prepared from n-hexane, isohexane, and n-heptane, respectively, all isolated from straight-run Pennsylvania gasoline. The n-hexane and n-heptane were fairly pure specimens, but the isohexane was a fraction boiling from 63" to 65" C. Monochloro compounds were prepared from these hydrocarbons and separated by repeated fractionations from unchanged hydrocarbons and the more highly chlorinated products. The olefines were prkpared from the chloro compounds by the method described in a previous paper.2 The products obtained by the elimination of hydrogen chloride were subjected to repeated fractionations through a Vigreux column; fractions distilling over a 1" or 2" range were collected after four or five fractionations.
-
l?raI.tinn - - -__. _. Collected (760 Mm.)
TABLEI
c.
Amylene I 36.3-37.3 28.8-31.8 Amylene I1 Isoprene 29.3-33.8 n-Hexylene 66-68 Isohexylene 64-65 Hexadiene 75-78 Cyclohexene 81-82 Cyclohexadiene 82-83 Heptylene 96-98 Heptadiene 100-105 Octylene 122-124 Cetene 125-145 (IO Mm.)
Specific Gravity 2Oo/O0
.,. . ..
o:i91
0.684
0.763 0,809 0.846 0.727 0.796 0.735
. ..
IODINE NUMBER Found Calculated 354 362 367 362 3S2 74 1 295.5 302 309 302 426 620 298 310 204 630 260 254 253 518 210 226 105 113
Hexadiene and heptadiene were prepared in a similar may from the dichloro compounds of n-hexane and n-heptane, but the products obtained were not as pure as the olefines, and undoubtedly were mixtures. Cyclohexene and cyclohexadiene were prepared from the mono- and dichloro derivatives of cyclohexane. The heptine used was kindly given by Prof. B. IT. Nicolet, University of Chicago, and was pure n-heptine, CaH12.C = CH. 1 2
J . A m . Chem. Soc., 40 (1918), 1950. W F. Faragher and F . H. Garner, Ibid., 48 (1921). 1715.
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T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
The isoprene, which was prepared from amyl alcohol through the dichloride, we owe to the kindness of Dr. E. F. Farnau, University of Cincinnati. It was refractionated before use and the fraction coming over from 29.3" to 33.8' was used. I n Table I are given the boiling points, specific gravities and maximum iodine numbers of the hydrocarbons used.
SIO,
Vol. 13, No. 11 1
I
340
300
EXPERIMENTAL DETAILS For weighing out the volatile materials used, special weighing bottles, 10 mm. X 40 mm. and having glass stoppers with ground joints 16 mm. long, were made of Pyrex glass. On a warm day these weighing bottles lost a volatile material, say, amylene (b. p. 3 l 0 ) , a t the rate of about 1 mg.in 3 min. By using ice baths and working quickly, these losses were minimized. The usual iodine absorption flasks made of Pyrex glass and fitted with ground glass stoppers were employed. PROCEDURE-The procedure was as follows: The stopper of the weighing bottle containing the material to be examined was loosened, and the weighing bottle dropped into the absorption flask, which contained 10 cc. of carbon tetrachloride. After shaking the closed flask, 25 cc. of the reagent were run in from an automatic pipet, and the flask was set in the dark for the time period chosen. The reaction was stopped by adding 10 cc. of 10 per cent potassium iodide solution and 200 cc. of distilled water. Titrations were made with 0.1 N thiosulfate, starch solution serving as indicator. By following a rigid procedure, two observers could check one another closely, and one observer could check himself closely over long time periods. Thus on octylene a t different quantity points: Observer A obtained Observer B obtained
208.7 209.0
212.4 210.0
The same observer obtained on a gasoline on August 17, 1920, 215.2, and on April 13, 1921, 215.2. A blank determination was made each day.
FXG. 1-QUANTITY CURVES FOR GASOLXNB A-30 MIN., AND OCTYLBNE TABLEI1 (Fig. 1) Period of contact with iodine solution in all cases = 30 min. Hanus 1 Hanus2 Wijs Iodine Iodine Iodine AMT. Number AMT. Number AMT. Number Gasoline A 0.0371 227 0.0308 238 0.0308 236 0.0605 219 0.0567 219 0.0835 209 206 209 0.1017 0.0922 210 0.0904 205 187 0.1154 0.1422 203 0.1656 0.1380 197 0.2028 186 Octyleme 0.0493 208.7 0.0491 211.8 0.0489 211.7 0 . 0 5 0 5 209 0.0499 210 0.0495 210.1 0.0994 208.8 0.1002 212.4 0.0975 209.8 0.1057 208.2 0.1000 210 0.1001 211 0.1707 203 0.1029 207 0.1586 211 0.1873 200 0.2194 203 The Hanus 2 and Wijs values for octylene are not shown on chart.
260
6
g
27-0
z w
r
lool GASCLINE
OUANTITY
USED (pm ZSCC IODINE SOLUTION)
FIG,2-QUANTITY
CURVB FOR OLERINES
TABLE111 (Fig. 2) Iodine Iodine Iodine AMT. Number AMT. Number AMT. Number Amylene I Amylene 11 (ansym-Methylethylethylene) (10 rnin.) (Trimethylethylene) (10 min.) 0.0250 367 0.0279 354.5 0.0484 356 0.0603 354.5 0.0979 337 0.0936 341.5 0.1515 272 0.1686 258.0
-
.
Hexvlene (30min.) 294 0.0231 295.5 0.0481 285 0.1051 243 0.1626
Hcblvlene (30 _ . mid 0.0188 253 251 0.0499 0.0968 237 0.1307 215.6
Isohervlene (30 min.) 0.0221 309 307 0.0534 0.0971 288 0.1718 226
Octylene (30 rnin.) 0.0493 208.7 0.0994 208.8 0.1707 203
Cetene (10 rnin.) 0.0472 105 0.1028 101 0.1529 101
Gasoline B (10 min.) 0.0371 120 0.0687 118 0.1023 115 0.1214 117 0.1547 112.5
Gasoline C (10 rnin.) 0.0304 112 0.0fi01 112 0.0840 114 0.0963 109.5 0.1483 108
Fig. 1 shows tthe change with quantity' of the iodine numbers of cracked Gasoline A and of octylene for the two Hanus solutions and the Wijs solut
