ISDUSTRIAL AND ENGINEERING CHEMISTRY
April, 1928
ency to form methane, as do the contact substances containing metals of the iron group. Furthermore, the useful products from the oxide catalysts consist mainly, if not wholly, of alcohols, while the iron-alkali catalysts are more uncontrolled in their action, yielding complex mixtures of practically all of the simpler types of oxygenated aliphatic hydrocarbons as well as straight paraffins.
359
Acknowledgment
The experimental data reported in this paper are the outcome of investigations conducted by the Research Laboratory of Applied Chemistry, and the writers wish to acknowledge the active participation of a number of members of the laboratory staff.
Phenols in Petroleum Distillates' LeRoy G. Story and Robert D. Snow M I D - C O N T I N E N T P E T R O L E U M CORPORATION, T U L S A , O K L A .
The writers have recently examined the oil extracted from HE alkaline solutions used for treating petroleum discracked gasoline by washing with caustic soda prior to treating tillates have been found to contain phenolic with acid, and find that this oil, precipitated from the aquepounds which are readily detected by a strong Odor ous alkali by dilute sulfuric acid, consists chiefly of cresols and resembling cresols when such solutions are neutralized. phenol. illthough the phenols comprise a very small percentage of most distillates, they may accumulate to the extent that Catlin3 has published a brief description of cresylic acid sepathe disposal of waste liquors around refineries may become rated from caustic soda which had been used in the first stage no small problem. The pollution of small streams or larger of a continuous unit treating cracked distiilates. Table I bodies of water near city water supplies and the odors arising shows a 500-cc. distillation in an Engler flask on the product from caustic wash waters, especially those used in treating as given by Catlin. He says: cracked distillates, are some All these fractions reacted of the c o m p l a i n t s w i t h p o s i t i v e l y to the tests for which refiners have already Phenols have been separated from petroleum discresylic acid as outlined by been confronted. A 11e n . 4 The fractions betillates and studied. The larger quantity present in tween 195' and 205" C. and A solution to the problem cracked distillates shows that the reaction producing between 205 and 210' C. had of a means for disposal of these compounds occurs primarily in the cracking a specific gravity of 0.9951 such materials is reached in process. Results of the investigation indicate that the and 1.052 (15'/15' C.), remany refineries by one of spectively, thus showing the product is composed chiefly of high-boiling compounds, a b s e n c e of 0-, m-, and pthe following methods: with very little or no carbolic acid, but the cresols have
T
(1) Seutralization of acid
been isolated and identified. A comparison is made of the petroleum phenols with those from other sources and a resemblance to those from low-temperature carbonization of coal pointed out. Low-boiling cracked distillates may be selected which yield phenols approaching the composition of commercial cresylic acid although the yield is too small to be commercially attractive under normal refinery conditions.
s 1u d g e , resulting from acid treatment of distillates, with alkaline p h e n o 1 - b e a r i n g liquors and burning of the neutralized fuel. (2) Treatment of the alkaline phenol liquors with flue or exhaust e n g i n e e a s e s . thereby convertkg thecaustic to sodium carbonate and liberating the phenols, which are then collected and disposed of by burning or some other suitable means.
It is apparent that burning has been the simp!est and prevalent means of disposing of petroleum phenols. The small quantity available might curtail any elaborate process of recovery and refining; yet in cases where sanitary conditions prohibit dumping into sewage, separation may be necessary and the most economical method of disposal of the recovered product become an important issue. Fuel is relatively cheap, and the use of phenols for this purpose may be regarded as a means of getting rid of an undesirable by-product. A better use will probably be found after the composition and nature of the product is fully understood. For this reason the present investigation was undertaken. Previous Work A survey of the literature disclosed that little work had been done on the investigation of petroleum phenols. Other chemists have noted the presence of phenols in cracked distillates, but are not in entire agreement concerning the nature of the compounds. Brooks and Parker2 state: 1 1
Received October 24, 1927. I n d . En& Chcm., 16, 587 (1924).
cresols.
Catlin further states: T h e r e l a t i o n of specsc gravity to the boiling point on the petroleum acid suggests methylphenylcarbinol, (K) CHa(CeHs)CHOH, spec s c gravity 1.003 (25O0/25" C.), boiling point 218 to 220" c.
Table I (from Catlin) (Specific gravity of sample, 1.058) SPBCIFIC GRAVITY
TEMPERATURE P E R C E N T O F F OF 10 P E R C E N T F R A C T I O N S 101 10 (water) 195 16 (water and oil) 0.9951 205 25 1.0052 210 35 212 45 219 55 1.0262 226 65 227 75 1.0270 82 232 1.0134 Average (195-227" C.)
The conclusion of Catlin that 0-, p-, and m-cresols are absent is probably not justified, because the presence of hydrocarbons, either from cracking during distillation or held in solution by the sodium phenolate, may have accounted for the low gravity of the particular fractions. On the other hand, it is very unlikely that the fraction aescribed by Catlin was methylphenylcarbinol, as alcohols of this type should not be extracted by aqueous caustic soda. Brooks and Parker give no data to substantiate their conclusion that the product extracted from gasoline was chiefly phenol and cresol. The high-boiling character of Eng. Chcm., 18, 743 (1926). Allen's Commercial Organic Analysis, 4th ed., Vol. 111, p. 316.
Ilnd. 4
ILVDUSTRIALA N D ENGINEERING C H E X I S T R Y
360
the products tested by Catlin s h o w that such products are not chiefly phenol and cresol, also that phenol (C6HsOH) is probably not present to any appreciable extent. Green6 in describing the method of abolishing offensive odors from cracked distillates a t the Richfield Oil Company, Rioco, Calif., quotes from John H. Loomis: I found that the odors were caused by chemical soaps formed in the caustic wash waters of the cracked distillates. They consisted of complex phenols and caustic soda***. It was discovered that carbon dioxide would break up the soaps almost quantitatively*** During the course of the .reaction, all the sodium hydroxide is converted into sodium carbonate* * *. After an hour's settling, the sodium carbonate is drawn off to the cooling pond and the recovered oils are drawn off to storage These oils will amount to as much as 15 per cent by volume of the sodium hydroxide solution used in washing the cracked distillates and have a specific gravity of approximately 1.02 to 1.04 with about 50 per cent distilling over between 400' and 430' F., the remainder breaking down above 445 O F.
The Richfield Oil Company apparently uses the second method, outlined above, for disposing of the phenols, which cause an offensii-e odor to residents of the city of Long Beach, Calif .
was shaken with 20 per cent aqueous caustic and the solution diluted with water until no further oily material separated. The mixture was then allowed to stand for some time and the aqueous layer separated. The same treatment of the oily layer with caustic soda was repeated until the 20 per cent solution extracted no more phenols from the oil. The small amount of insoluble material remaining suspended in the caustic solution was extracted with ether and added to the main body of oil. The hydrocarbons obtained after extraction of the phenols amounted to approximately 25 per cent of the original distillate, the larger portions coming from the high-boiling phenol fractions. The composite sample was distilled in an Engler flask and 5 per cent cuts made. The data for the distillation are gi\-en in Table 11. Fifty per cent of the hydrocarbon distillate, or that portion distilling under 232.2" c.,was analyzed according to the method outlined by Egloff and Morrell.' The analyses are also given in Table 11. Table 11-Hydrocarbons Separated from Phenol Distillate (Specific gravity 0.8681, 15.5O/15.5O C.) TEMPERATURE DISTILLED TEMPERATURE DISTILLED O c. Per cent c. Per cent 82.2 234.4 First drop 55 181.1 60 237.7 5 65 196.1 241.6 10 202.1 245.5 15 70 207.2 251.1 20 75 212.2 257.7 25 80 218.8 266.6 30 85 222.2 282.2 35 90 225.0 301.6 40 95 228.3 321.1 45 End point 232.2 50 Analysis of 0 l o .50 Oer cent fraction (Specific gravity 0.8473,15.5'/15.5' C.) P e r cent Unsaturated 47.3 Aromatic 13.3 Naphthenes 33.3 Paraffins 6.1 100.0
PRESENT INVESTIGATION
Previous work on petroleum phenols has been done on products derived from cracking. The formation of cracked distillates from high-boiling petroleum products affords a means for phenols to be formed by decomposition of primary tars, and for this reason larger quantities are present in cracked distillates than are ordinarily found in distillates straight from crude oil. The contact of crude oils with underground waters also tends toward elimination of watersoluble phenols. It has been found, however, that distillates straight from crude do contain traces of phenols and are included in this investigation as vel1 as those derived from cracked products. Phenols from High-Boiling Cracked Distillates
A sample of caustic soda, used in treating pressure distillate with a maximum boiling point of about 300" C., was neutralized with dilute sulfuric acid. The acid tars separated as a brownish black liquid, slightly heavier than water. Owing to the high-boiling character of the distillate; the tar acid contained considerable sludge and high-boiling compounds, and for this reason the method of examination is somewhat different from those to be described later. The tar acids thus separated were heated to drive off most of the water and then distilled, using a water-jet vacuum in order to separate the volatile phenols from the sludge and pitch with a minimum degree of decomposition. The distillate was of light yellow color with a strong odor of cresols. A slight odor of mercaptans and other sulfur compounds could be detected, but these had been mostly removed by previous treatment in the refining operations. Several regular fractional distillations of the phenol mixture were made using a Hempel column, and the water was separated as completely as possible from the first cuts. Considerable pitch was formed a t the end of the first operation but very little thereafter. Some cracking, accompanied by the liberation of water, was also noted in the first fractionations, and for that reason it was decided to separate the hydrocarbons insoluble in caustic before going further. Most of the fractions were completely soluble in 20 per cent caustic a t this stage. Some of the phenols were more soluble in strong than in dilute alkali, which is similar to the results of Morgan and Meighan.6 Each of the fractions 8
Natl. Petroleum News, 19, 92 (1927). Eng. Chem , 17, 696 (1925).
1Ind.
Yol. 20, N o . 4
-
The phenolate solutions, resulting from the 20 per cent caustic extraction and separation of the hydrocarbons, were acidified with dilute acid and the phenols separated from the salt solution. The phenols were refractionated twice, using a Hempel column. Practically no cracking or pitch formation occurred. No further fractionation was attempted as it was realized that a phenol mixture was present which could not be separated by simple fractionation.* The boiling points and other physical properties of the phenols are shown in Table 111. All fractions were practically colorless liquids showing no tendency to crystallize a t - 15" C., were very corrosive to the skin, and had a phenol-like odor. The high degree of purity is shown by the complete solubility in 5 per cent caustic and the low sulfur content. The distillation data given in Table I11 are plotted in Figure 1. Curves for Hydrogas and Carbocoal taken from the work of Morgan and Meighang are included for comparison. The specific gravities are plotted in Figure 2 in comparison with the Hydrogas and Carbocoal of Morgan and Meighan. The gravities of these investigators were determined a t 25" C., but this does not substantially afTect the comparison with gravities at 15"/15" C. of the petroleum phenols. The average formula weights of the phenols, determined by the sodium method developed by Morgan and Meighan'O are shown in Table I11 and Figure 3. The 240-250' C. fractions had a decided tendency to froth as a result of a violent reaction with sodium during the formula weight Ind Eng Chem., 18,354 (1926). Rhodes, Wells, and Murray, Ibid., 17, 1199 (1925). 0 I b i d . , 17, 864 (1925). 10 I b i d . , 17, 626 (1925). 7
E
April, 1928
INDUSTRIAL AND ENGINEERING CHEMISTRY
determinations, also abnormally low values for the formula weights of these fractions were obtained. Curves for t h e indices of refraction are not included as they are of the same type as those for specific gravities. Table 111-Properties of Petroleum Phenols from High-Boiling Cracked Distillates INDEXos REFRACAV. Av. TION BOILING BOILING DISSP. GR. FORMULA (40' C., RANGE POINT TILLED ( 1 5 ' / 1 5 O c.)WEIGHT DAYLIGHT)SULFUR 0 c. C. Per cent 121.3 1.5292 h-one 1,0330 1.8 192.2-195 193.6 121.8 1.5292 1,0290 3.1 185.0-197.1 1 9 6 . 5 124.3 1.5277 1.0274 4.4 197.1-198.9 198.0 125.4 1.5272 1.0230 8.4 198.9-201.8 200.3 127.1 1.5270 1.0200 11.8 201.8-203.3 2 0 2 . 5 127,6 1.5262 Sone 1.0199 15.0 203.3-204.4 203.8 129.6 1,0194 1.5254 17.6 204.4-205.5 204.9 1.5249 130.2 1.0183 205.5-207.2 2 0 6 , 3 2 1 . 6 1,5244 130.9 1.0155 28.0 207.2-208.8 208.0 1.5243 141.6 1.0149 31.3 208.8-210.5 209.6 1.0115 130.8 1.5237 35.8 210.5-212.2 2 1 1 . 3 1,0109 136.0 1,5226 212.2-214.4 2 1 3 . 3 4 0 . 5 138.2 1.5223 43.1 1.0107 214.4-215.5 214.9 139.8 1.5213 None 50.3 1.0065 215.5-218.8 2 1 7 . 1 142.9 1.5203 1.0050 52.8 218.8-220.5 219.6 145.4 1,5183 1,0013 59.0 220.5-223.3 221.9 148,4 1.5168 1.0005 223.3-225.5 2 2 4 , 4 6 2 . 0 150.3 1.5155 0.9993 225.5-217.2 226,3 6 5 , 3 1S5.3 0.9974 1. i151 70.3 227.2-231.1 229.1 156.8 1.5126 Trace 0,9947 73.2 231.1-233.3 232.2 1.5126 162.7 0.9968 76.8 233.3-237.2 2 3 5 . 2 158.8 0,9976 1.5116 80.3 237.2-243.3 240.2 1.0020 163.5 1.5120 Slight trace 82.8 243.3-248.8 246.0 158.4 1,0054 1.5141 84.4 248.8-253.3 251.0 185.3 1.0139 1.5203 253.3-260.0 2 5 6 . 6 85.9 1.0310 1.5313 Trace 196.1 87.7 260.0-271.1 265.5 1.0698 1.5710 Small amount 214.9 91.3 271.1-298.8 284.9 8.7 Pitch and loss ~~
~
~~
C O ~ ~ P O S I T I O NOF FRACTIOSS-An attempt to determine the composition of certain fractions w'as undertaken, since this first sample m-as fractionated rather extensively and also because it contained the phenols from cracked distillate of wide boiling range. The fractions boiling a t 192-195' C., 201.8-203.3' C., and 207.2-208.8' C. were tested for mcresol (b. p. 202.8' C.) by the Raschigll method of nitration and 10-gram samples of the fractions gave, respectively, 0.00, 0.97, and 6.03 grams of the nitration product. This product, instead of exhibiting the characteristic light yellow crystals of trinitro-nz-cresol, was a dark brown, viscous liquid in all cases. Assuming that the product was entirely trinitrom-cresol, the corresponding percentages of m-cresol in the fractions tested would be 0.00, 4.3, and 26.8 per cent; however, the nature of the product indicated that m-cresol was present in much smaller quantities. A 10.3-gram sample of Eastman's technical cresol gave, by the same procedure, 11.08 grams of pale yellow crystalline t~init;o-?n-cresol,corresponding to 47.8 per cent m-cresol. A portion of the 198.9-201.8' C. fraction was treated with acetyl chloride to prepare the acetates. The product had a boiling range between 212.2' and 218.3' C. and the fraction of this boiling from 212.2"to 215'C. had aspecific gravity of 1.025 a t 15'/15' C. p-Cresyl acetate boils a t 212.5' C. and has a specific gravity of 1.050.12 This indicates that p-cresol was present. I n order to determine if any of the methyl ethers of dior tri-hydric phenols were present, the following fractions204.4-206' C., 220.5-223.3' C., 237.2-243.3" C., 253.3260' C., and 271.1-298.8" C.-were subjected to the Zeisel test, but negative results were obtained in every case. Bromination yielded a liquid product for every fraction tested. When a dilute solution of ferric chloride was added dropwise to a saturated aqueous solution of any of the fractions boiling below 250' C., a violet color was produced which faded in a very few seconds through blue to a greenish yellow. The higher fractions gave blue and violet colors which persisted for several hours. All fractions gave red colors by 11
Z. angcw. Chcm., S1, 795 (1900).
1:
International Critical Tables, Vol. I, p. 227.
361
the phthalein fusion test, the shades varying from violet-red in the lower fractions to orange-red in the higher. A 2-gram sample of the 187.8-191.7' C. fraction and 2.4 grams of phenyl isocyanate were dissolved in 20 cc. of a paraffin hydrocarbon fraction boiling between 170" and 204.4' C. and were refluxed for 15 minutes. On cooling, the phenylurethan derivative crystallized in colorless needles. The product was repeatedly crystallized until it gave a sharp melting point of 139.4' C. (uncorrected). A composite sample slo of f r a c t i o n s bo ili n g b e t w e e n 194.4' and 204.4' C. was mixed with an equal weight of anhydrous oxalic acid and gently boiled under a reflux condenser for a b o u t half an hour. y z 2 6 0 The mixture was cooled e t o room temperature 2 240 and about three vol- : umes of benzene were added a s a d i l u e n t . The solid material was ZM separated by filtration and washed with ben-
&
was distilled in steamy The oily distillate was separated and dried over anhydrous calcium chloride. The phenylurethan, prepared from the dry oil and purified as described previously, melted a t 114' C., which corresponds to p-cresol phenylurethan. A small amount of m-cresol was similarly separated from the mixture by means of the addition compound formed with anhydrous sodium acetate. The phenylurethan prepared from this sample melted sharply a t 120.6' C. The following values for the melting points of phenylurethan of cresols were found in the literature: o-cresol phenylurethan 141' C., m-cresol phenylurethan 121-122' C., p-cresol phenylurethan 110115" C.
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The fractions boiling within the range corresponding to the boiling points of three xylenols known t o occur in coaltar cresylic acids-namely, 1, 2, 4-xylenol (b. p. 225' C.); 1. 3, 4-xylenol (b. p. 211.5' (2.); and 1, 3, 5-xylenol (b. p.
INDUSTRIAL AND ENGI NEERING CHEiMISTRY
362
219.5' C.)-were dissolved in naphtha and refluxed with the equivalent amount of phenyl isocyanate. No crystalline products corresponding to the phenylurethans were obtained. Further purification by the use of anhydrous salts was not attempted. Phenols from Low-Boiling Cracked Distillate
An untreated cracked gasoline of maximum boiling point of about 210' C. was scrubbed with 20 per cent aqueous caustic soda. The alkali containing the phenols was allowed to settle until free from oil and other suspended material, then drawn off and acidified with dilute sulfuric acid. The acid aqueous solution was extracted with benzene and the benzene extract containing the phenols and carboxylic acids was separated from the water layer.
Averaqe Boilinq Rmf of fraction:,
fqure 3 ' M o l e c u l a r Wciqhf
D Boding
c.
C'
DISTILLGD Per cent
The acid distillate was refractionated four times through a 6-inch (15-cm.) Hempel column and separated into the fractions shown in Table IV. Specific gravities of the fractions were determined with a pycnometer and the neutralization equivalents were obtained by titrating with 0.1 N potassium hydroxide using phenolphthalein as an indicator. Table IV-Properties
of Carbox Hc Acids from Low-Boiling Cracked DZtillate SP. GR. NEUTRALIZATION BOILING (15'/15' C.J EQUIVALENT RANGE 0
c-. .
0.9692 0.9577 0,9670 0.9508 0.9495 0.9596 0.9687
Table V-Phenols from Low-Boiling Cracked Distillate Av. Av. BOILING SP. GR. FORMULA REFRACTIVE POINT (15"/15O C.) WEIGHT INDEX 0
c.
1.0399 1.0350 1.0315 1.0290 1.0251 1.0230 1.0197 1.0181 1.0114 1.0040
110 112 119 123 125 126 130 131 134 143
1.5317 1.5308 1.6302 1.5287 1.5270 1.5267 1.5263 1,5240 1,5224 1.5140
Fbrnf of Phenol Tracfions
182 196 204 213 224 232 Residue
100.0-190 190.0-200 200.0-215.5 215.6-208.3 208.3-232.2 232.2-240.5 240.5
The benzene solution, from which the carboxylic acids had been separated, was washed free of phenols with 23 per cent caustic soda solution. The resulting caustic extract was steam-distilled until free from benzene or other hydrocarbons and, after cooling, neutralized with dilute acid. The phenols were taken up with ether and the ether was finally evaporated. Table V shows the results obtained after four fractionations of the phenols through a 20-disk Young's fractionating column.
I n Figure 4 are plotted the results on phenols from highand low-boiling cracked distillates taken from data in Tables I11 and IV. Curves (1) and (2) are specific gravity us. boiling point for low-boiling and high-boiling phenols, respectively, while curves (3) and (4) are average formula weight us. average boiling point for the same products. Curves for refractive indices are not included, as they are of the same general type as those for specific gravities. In Table VI and Figure 5 are the data for the distillation of phenols from low-boiling cracked distillate compared with distillations on commercial samples of 95 per cent cresylic acid, 97 per cent cresylic acid, and U. S. P. cresol.
The carboxylic acids were removed from the benzene solution by repeated extraction with a saturated water solution of sodium bicarbonate. The bicarbonate extract was acidified, the acids were taken up in ether, and after distilling off the ether a light yellow oil remained, having a speczc gravity of 0.958 a t 15'/15O C. and a strong odor of a mixture of lower fatty acids, such as butyric, valeric, caproic, etc. Small amounts of sulfur compounds-for example, lower mercaptans-were probably present in these acids, but most of them had been volatilized or decomposed. The original distillation of the carboxylic acids was as follows: TEMPERATURE
Vol. 20, No. 4
121.9 122.2 128.4 130.6 143,4 147.4 159.7
Table VI-Distillation of Petroleum Phenols from Low-Boiling Cracked Distillates and Commercial Samples of Phenols PETRO~EUM 95% CRESYLIC97% CRESYLIC u. s. P. DISTILLED PHENOLS ACIDS ACIDS CRESOL Per cent c. O c. O c. c. 15°$1.\0 Sp. gr. at C. 1.0278 1.027 1.0330 1.0391 191.5 178 179.5 3.1 198:3 197.0 5.0 194.5 189.0 7 n 200.0 201.5 192.0 197.0 202.0 201.5 198.5 193.0 203.0 193.5 199.0 204.0 200.5 204.0 194.0 205.0 202.0 194.5 51.1 207.0 206.5 203.5 195.0 60.0 62.5 208.8 208.5 196.0 205.5 70.0 71.7 211.1 78.0 213.8 210.0 209.0 197.0 80.0 214.5 90.0 216.5 199.0 94.8 227.2 200.5 220.0 95.0 218.0 242.2 96.8 212.2 250 238.0 Dry point ... 1.4 3.2 Residue 1.6 1.6
Phenols from Straight-Run Distillates
The question arose whether phenols were formed in the cracking still or whether they were present as such in the crude oil. I n order to learn more about this problem, samples of gasoline and gas oil straight-distilled from midcontinent crude were extracted with 23 per cent caustic soda solution. The yields of phenols were very small and no attempt was made to study the carboxylic acids or to fractionate the phenols. The procedure was to filter the caustic soda solution through asbestos, carefully neutralize with dilute sulfuric acid, extract three times with ether, distil off the ether, and dehydrate the resulting phenols by distillation. The results are shown in Table VII.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
April, 1928 Table VII-Distillation
Tests o n Phenols from Straight-Run Distillates STRAIGHT-RUN G A SOIL F R O MSTRAIGHT-RUN GASOLINE FROM (63.8" A . P. I.); SP. GR. 1.0283 AT (39'A. P . 1 . ) : SP. GR. 1.034 A T 1 5 0 j l 5 0 c. 1 5 ' / 1 5 O C. TemDerature Distilled Temperature Distilled c. Per cenf c. Per cenf 188 First drop 193 First drop 204 30 203 12 214 50 209 31 218 70 212 44 260 90 216 50 227 62.5 243 75 261 88 293 95 Residue 10 Residue 5
The yield of phenols from straight-run distillates is very .mall and no attempt was made to determine further propert'es of the samples; however, the above samples gave positive reactions for all tests for cresylic acids, and i t is probable that they resemble very much those obtained from the cracked distillates. Discussion
The distillation and analysis shown in Table I1 of the hydrocarbons separated from the phenol distillate indicate a mixture probably derived from cracking of the phenols rather than hydrocarbons originally held in solution by the sodium phenolates at the time of the extraction of the phenols from the cracked distillate. The high percentage of olefins may be due to cracking of high-molecular-weight phenols containing long side chains. The presence of these hydrocarbons substantiates the probable reason, mentioned in an earlier part of this paper, for Catlin's conclusion that the cresols are absent in petroleum phenols. The similarity of the distillation curves for Carbocoal and petroleum phenols shown in Figure 1 indicates that these
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products may be similar in composition. The curve for Hydrogas shows it to be a tar of more primary order than the other two. The curves also suggest that the phenols from the cracked distillates may have arisen from decomposition conditions similar to those taking place in low-temperature carbonization of coal. The specific gravities plotted in Figure 2 show a marked similarity in the ranges between 1.030 and 1.010. The maximum gravity of 1.033 for the low-boiling fractions of the petroleum phenols indicates that carbolic acid (C6HsOH, sp. gr. 1.071 a t 25'/4' C.) is absent or present only in very small amounts. This would account for the low minimum
363
point of the curve, since the presence of appreciable amounts of phenol would raise the curve in its entirety, thus tending to approach the curves for Carbocoal or Hydrogas which contain considerable amounts of carbolic acid. The decrease in gravity with increase in boiling point of the lower fractions shows increase in the length or number of side chains on the aromatic nucleus, while the increase with boiling point of the higher boiling fractions indicates condensed ring compounds. The minimum point of the curves in Figure 2 of the petroleum phenols a t 232.2' C. suggests that p-n-propylphenol, b. p. 232.2' C., sp. gr. 1009,13 may contain the longest side chain of any compound p r e s e n t , b u t the low gravity of 0.9947 for the compounds boiling a t 232.2' C. shows that butyl or amylphenols may also be present. I n Figure 3 the petroleum phenols are shown to differ from those of Carbocoal and Hydrogas in having a minimum formula weight of the lowest boiling fraction of 121.3, w h i c h again indicates the absence of carbolic acid. While t h i s minimum value is approximately that for the formula weight of the xylenols (122.1), the boiling point shows the presence of lower formula weight materials, such as cresols. The average formula weights of the petroleum phenols are much higher than those of Carbocoal for the higher boiling fractions, but if these had been fractionated to the same extent as the petroleum product the similarity would probably have been much more pronounced. Whether the abnormal results experienced with the fractions from 240' to 250' C. were due to dihydroxy compounds has not been determined. Bogert and Caplan14 have concluded that dimethyldihydroxy naphthols are present in the high-boiling phenols from Carbocoal. The values for the indices of refraction in Table I11 show the same general trend as those of specific gravity, with a minimum point around 240' C. boiling point. The decrease of refractive index with increase in boiling point of the lowmolecular-weight phenols indicates again a gradual lengthening of substituted aliphatic side chains on the aromatic nucleus. The experiments on identification show that a very complex mixture of phenols is present, which must be very carefully separated in order to identify the constituents. The urethans of the cresols were successfully prepared, but the xylenols were not obtained in a sufficiently purified condition to identify the urethans. The absence of phenol (C6H50H) to any extent is conclusive. The phenols from the low-boiling cracked distillates differ from those from the high-boiling distillates in being free from the higher molecular weight phenols. The curves in Figure 4 show that the phenols from the low-boiling cracked distillate are similar in composition to the lower boiling portions of the phenol from the high-boiling cracked distillates. The boiling point of the phenols can thus be controlled by choice of the cracked distillate. Figure 5 shows that the distillation of phenols from the cracked distillate used in this exInternational Critical Tables, Vol. I, p. 228. Unpublished work mentioned by Morgan and Meighan, I n d . En& Chern., 17, 854 (1925). 13
14
INDUSTRIAL A N D ENGINEERING CHEMISTRY
364
periment resemble closely the distillation for 95 per cent cresylic acid. The presence of the cresols is evident and also the presence of a larger percentage of higher boiling products is indicated by the divergence of the curves in the regions of higher boiling points. The presence of phenols in the straight-run distillates indicates the existence of such materials in crude oil. The very small quantity, however, indicates that the major reaction, producing the phenols, takes place in the cracking still. The similarity of the products produced from petroleum in the cracking still and the products produced by low-temperature carbonization of coal would indicate the same origin of petroleum and coal-namely, vegetation. It is more likely,
Vol. 20, No. 4
however, that the reaction taking place in a cracking still to produce phenols is dehydrogenation of cyclic hydrogenated hydroxy compounds such as homologs of cyclo hexanol. The quantity of phenols present jn the average cracked distillate is very small, usually less than 0.01 per cent; yet where sanitary conditions demand that they be separated from waste liquors, sufficient volumes may acccumlate to be useful as disinfectants, wood preservatives, or for other purposes for which high-boiling tar acids are suitable. Cracked distillates of sufficiently low-boiling end point may be selected which yield phenol products approximating 95 per cent cresylic acid.
Strength of Curved Walls Exposed to External Pressure' C. A. Andsten E. R. SQUIB% & SONS, BROOKLYN. N. Y.
CANT attention has been paid by the compilers of the standard engineering handbooks to the complex problem of designing spherical and cylindrical walls to withstand pressure applied to their outer surfaces, and it is all too common practice t o build equipment of this kind by guess and by rule of thumb. The estimation of a maximum safe steam pressure for a given jacketed kettle, of a safe thickness of material to be used in constructing a jacket or vessel to withstand a predetermined pressure, and other related problems are often presented to the chemical engineer for solution, but the data in the literature to guide one to a proper solution of such a problem are practically negligible. Although many industrial workers have collected valuable and reliable data, practically none of them have been published, and this secretiveness has forced many builders of equipment to resort to rule-of-thumb methods with consequent waste of labor and material or, what is of greater consequence, the collapse of apparatus used or designed improperly. The thickness of material used is only one of the variables involved in the strength of a spherical or cylindrical vessel exposed to external pressure, and it is the object of this paper to present a graphic method of reducing these variables to a workable minimum. I n this, as in other engineering calculations of the kind, certain assumptions must be made as to workmanship, etc., which have a serious significance in the result that no method of calculation can avoid. The method of calculation here given is based upon the graphic solution of the equations derived by Bach2s3 from a n extensive series of experiments with the actual collapse of the kind of vessels under consideration. By plotting equations derived from those given by Bach, a set of curves is obtained which is of immediate application to design problems.
S
Spherical Shells
To determine the strength of a spherical shell exposed to external pressure, Bach gives the following equations:
1
Received November 2, 1927.
:Z. Vcr. dcct. Ing., 46, 333, 375 (1902).
:"Maschinen Elemente."
K
K K
= 0.3 to 0.4 K O(for cold-worked copper) = 0.25 to 0.35 K , , (for wrought iron)
=E,
2sK orp = -
(2b)
(3) where K O = tension in kg. per sq. cm. a t which wall will collapse K = safe tension in kg. per sq. cm. A and B = empirical constants based on material used p = pressure in absolute atmospheres r = radius of curvature of the spherical surface, in cm. s = thickness of wall, in cm.
The values of the constants A and B as determined by Bach for different materials are as follows: For cold-worked copper, A = 2550 and B = 120 For wrought iron, A = 2600 and B = 118
As an example of the application of these formulas, let us assume that one is to determine the safe pressure to be applied to a spherical shell of cold-worked copper having a radius of 41.1 cm. and a thickness of 0.57 cm., and in other respects properly built. Substituting in (l), K O = 2850 - 120d\/72.1 = 1531 kg. per sq. cm. K = 0.3 X 1531 = 459.3
Substituting in (3),
='
0'57 459'3 41.1
=
12.73 absolute atmospheres
I n applying these formulas to design, one must assume that: (1) the material and workmanship will be first class; (2) the ratio of the radius of the spherical surface and the diameter of its plane face (d = 2a) has been properly selected (see below); (3) no temperature differences exist in different parts of the wall; (4)temperatures used will not seriously affect the tensile strength of the material used; and ( 5 ) no undue strains are set up in fabricating the material. I n good design, the ratio r/2a (2a being the inside diameter of the vessel) should be selected so that 0 . 5 5 ~to 0 . 6 5 ~is equal to the height, h, of the spherical segment. The relation between the radius of curvature of the sphere, the diameter of the segment, and its height are given by the following equation: a2
A
r = s + z
