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Proof of commercial value requires further a n d largerscale demonstration on apparatus carefully designed in either full commercial size, or truly proportioned models of smaller size, b u t still large enough t o permit tests for reliable d a t a . This is usually a n expensive procedure t o be undertaken as a t r u e investment on t h e prospect of financial returns t o follow adoption a n d use. While in most cases i t is a proper thing for a n engineering research and development laboratory, it usually involves larger equipment t h a n a n y existing university laboratory can care for, a n d in some cases, due to t h e nature or t h e size of t h e equipment, must be carried out in a commercial establishment. Such commercial demonstrations, being financial enterprises of direct concern t o t h e industries, must have industrial support, even if t h e work is done by t h e university staff, b u t in every case this staff can render valuable assistance by bringing t o bear its broader scientific a n d engineering judgment unhampered b y commercial traditions a n d jealousies. At t h e present time some work of this kind is being undertaken a n d carried through, limited only by t h e number of available men a n d facilities on t h e one hand, or, on t h e other, by t h e willingness or unwillingness of t h e industrial interests t o use what is t o be had. The last step in t h e development of new apparatus for t h e industries is t h a t of commercial perfection a n d installation, all of which culminates in a working plant, in which t h e perfected apparatus is correctly associated with the existing apparatus in a n old plant,
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12
or in a complete new plant with standard equipment selected so as t o cooperate best with it for proper results in quality or product a n d economy of production. I n this last stage t h e university laboratory can play no part, b u t its staff can, a n d a t present does t o a limited degree, partly in t h e designing of t h e final form of t h e apparatus, partly in t h e selection of t h e standard equipment t o be associated with i t a n d in planning t h e connections a n d controls, a n d finally in testing for full scale performance d a t a , publication of which creates a n industrial document, a record of results achieved, a n d a standard by which further suggestions for improvement must be judged. Such test results of complete plants a n d t h e division of performance factors between t h e several units, is almost wholly lacking for t h e factories of t h e chemical industries, though quite common a n d even standard practice for other kinds of establishments, notably central power stations, shops a n d many of t h e non-chemical manuf actures. I n conclusion i t is believed t h a t a n y correct analysis of t h e relations between t h e university and t h e chemical industries will show t h a t the industries are receiving from t h e university t h e right kind of both direct a n d indirect contributions, though t o a n inadequate degree, limited only b y financial support, a n d this limit, i t would appear, could be removed by t h e industries themselves, by contributions in t h e reverse direction from t h e m t o t h e university. C H A R L E SE. L U C K E ~
ORIGINAL PAPERS THE UTILIZATION OF AROMATIC HYDROCARBONS DERIVED FROM CRACKED PETROLEUM1 BY W. F. RITTXAN Received October 10, 1915
I n t h e course of t h e commercial development of the vapor-phase cracking process for t h e production of benzene a n d toluene from petroleum, numerous chemical problems have arisen. One of t h e most important is t h e utilization of t h e products obtained, since these necessarily differ from those derived from coal. T h e idea is widely prevalent t h a t petroleum-derived products are inferior and a principal object of t h e present work has been t o show t h a t this prejudice is due entirely t o a lack of knowledge concerning proper methods of utilization. T h e immediate cause for the present work has been t h e necessity of demonstrating t h a t petroleum-derived toluene can be successfully converted into trinitrotoluene in a commercially practicable manner. . D I F F E R E N C E S B E T W E E N COAL-DERIVED A N D P E T R O L E U Y D E R I V E D H Y D R O C A R B O N MIXTURES
A brief consiaeration of t h e sources and methods of production of t h e t w o types of commercial hydrocarbon mixtures serves t o indicate t h e nature of t h e present problem. T h e coal-derived products are t h e results of decomposition of t h e original material a t high temperatures, which fact influences t o a large degree t h e composiPublished with the permission of the Director of the Bureau of Mines.
tion of these mixtures. The aromatics are associated with varying quantities of such impurities as sulfur, oxygen, and nitrogen bodies, as well as non-aromatic hydrocarbons of various degrees of unsaturation. Condensable paraffins are not, however, stable a t t h e temperatures which occur during t h e destructive distillation of coal a n d these hydrocarbons are, therefore, absent from products derived from this source. I t follows, therefore, t h a t aromatic products obtained from coal contain objectionable impurities, from which, however, they may be freed if subjected t o treatment b y proper physical and chemical processes. On t h e other h a n d , t h e cracking of petroleum yields aromatics which are entirely free from oxygen-containing impurities and which a t worst carry only minute quantities of sulfur a n d nitrogen bodies. T h e chief a n d practically t h e only impurities are olefins a n d paraffins. These paraffins are necessarily present because maximum yields of toluene a n d benzene cannot be obtained under conditions which entirely break down these saturated compounds and, furthermore, i t is difficult or even impossible t o get rid of t h e m completely. Methods of fractional distillation d o not effect complete separation a n d chemical methods are ineffective, since t h e aromatics are more reactive t h a n the paraffins. Thus, in attacking t h e present problem i t has been 1
Professor of Mechanical Engineering, Columbia Unive! sity
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
Dec., 1915
granted t h a t it m a y be difficult or even impossible t o obtain pure aromatics from cracked petroleum. Experiments have, therefore, aimed at devising methods of utilization suitable for t h e impure products a n d i t now appears t h a t these methods have commercial advantages over those in use for coal-derived products, although t h e latter substances cannot be treated in t h e same way as t h e petroleum products since t h e sulfur, oxygen, a n d nitrogen bodies a r e n o t chemically inactive, as are t h e paraffin hydrocarbons. METHODS
O F PREPARATIOh-
AND
OF
PROPERTIES
THE
NITROTOLUENES
Trinitrotoluene is obtained from toluene b y a process of nitration occurring in three successive stages a n d involving t h e intermediate formation of mononitrotoluene a n d dinitrotoluene. "03 Ir C7H7(hTO?) HzO (I) C7Hs Toluene Mononitrotoluene (2) C?H7(Noz) HxO3 C ~ H ~ ( N O Z4-) ZHzO M ononitrotol uene Dinitrotoluene (3) C ~ H S ( N O ~ )"03 ~ If C7Hb(N0?)3 HzO Dinitrotoluene Trinitrotoluene T h e extent t o which t h e nitration m a y proceed to a n y one of t h e above stages is controlled b y conditions of t r e a t m e n t a n d particularly b y t h e factor of acid concentration. This can be regulated b y a d j u s t m e n t of t h e q u a n t i t y of nitric acid employed a n d also b y varying t h e a m o u n t of sulfuric acid mixed with t h e nitric t o t a k e u p a n d render inactive t h e water which is one of t h e reaction products.
+
+ +
__
+
+
PROPERTIES O F T H E NITROTOLUENES
MONONITROTOLUENE, C7H7N02, exists isomeric forms, ortho- meta- a n d p a r a :
in
three
8 NO" -.
_.
o-Nitrotoluene m-Nitrotoluene $-Nitrotoluene T h e physical properties of these compounds are indicated below: MONONITROTOLUENE MELTING
. . . ...
Ortho.. Meta.. , ... P a r a . . . ., .. .
POINT
-10.5O 16.0' 54.0"
SPECIFIC G E AVITY
BOILING POINT
218' 231' 238'
1, 168(15"/1S0) 1 . 168(15°/150) 1.231 (54'/4O)
Direct nitration of toluene yields a mixture of t h e three isomers, which, however, contains little of t h e m e t a product. This is in accord with t h e law of substitution in t h e benzene ring, t h e methyl group being one which controls t h e ortho a n d para positions. DINITROTOLUENE exists in six possible isomeric forms, all solids. These are designated b y numbers, t h e position occupied b y t h e methyl group being
No.
I. DINITROTOLUENE Melting point
........ .
2:40 70.5
3:4,52:3, 60.0 63.0
2 ' 2
61.0
3:5,
93.0
2:5, 52.5
T h e dinitrotoluene produced b y t h e nitration of toluene or of t h e commercial mixture of 0- a n d p-nitrotoluenes consists chiefly of t h e 2:4 a n d 2:6 products. TRINITROTOLUENE is theoretically capable of ex-
IO1 j
isting in six isomeric forms. Of these t h e 2 : 4 : 6 , t h e 2 : 3 : 4 a n d 2 : 4 : 5 compounds have been prepared. T h e 2 : 4 : 6 , or "symmetrical" compound, is t h e best known a n d is b y far t h e chief constituent of t h e commercial product. TRINITROTOLUENE 2 : 4 : 6 Melting p o i n t . . . . . . . . . . . 80.6'
2 : 3 : 4 112.00
2 : 4 : 5 104.0.
P u r e nitrotoluene is a white solid of absolutely neutral reaction a n d of unusual stability. T h e commercial product is generally pale yellow. Trinitrotoluene is very slightly soluble in water, either hot or cold. It is sparingly soluble in cold alcohol, b u t readily in hot, this solvent being one commonly used for t h e process of recrystallization. Trinitrotoluene is b y far t h e most valuable explosive now used in military service for bursting charges. T h e substance m a y be manufactured with comparative safety a n d is free from danger of deterioration. It is non-acid a n d does not a c t upon metals with which i t m a y come in contact. T h e lowness of its melting point makes easy t h e filling of shells a n d containers, which is accomplished b y t h e simple process of pouring t h e molten explosive. Trinitrotoluene is sufficiently inert so t h a t t h e possibility of accidental explosion through concussion is practically nil. It is s t a t e d t h a t a shell filled with i t m a y be made t o penet r a t e steel plates without setting off t h e explosive through t h e shock. Detonation is accomplished after penetration b y means of a time fuse. COMMERCIAL
PREPARATION
OF
TRINITROTOLUENE
T h e commercial preparation of trinitrotoluene is accomplished in either of t w o general ways: ( I ) T h e process m a y be completed in one stage, or ( 2 ) i t m a y be accomplished in several successive stages. I n a n y event, i t has been found commercially undesirable, in this country at least, to purify t h e final product b y a n y process of crystallization or washing which involves t h e use of organic solvents. T h e purity of trinitrotoluene is generally determined b y its melting point a n d present specifications place t h i s a t 7 j o C., which is a b o u t 5 " below t h e melting point of t h e pure compound. It h a s been found possible t o a t t a i n t h e desired degree of purity b y a simple process of water washing, providing conditions of preparation are right. T H E SINGLE S T A G E P R O C E S S of nitration is of course simple in operation a n d requires a minimum of plant equipment. It has t h e decided disadvantage, however, of being uneconomical in acid consumption. T h e process requires a considerable concentration of acid a t t h e e n d of t h e reaction a n d t h e resulting spent acid cannot be utilized in t h e single stage method, although i t s strength is considerably greater t h a n would be necessary in t h e earlier stages of t h e other general process. P R O C E S S E S INVOLVING S E V E R A L S T A G E S , with complete or partial purification of intermediate products are, of course, expensive as regards costs of labor a n d plant equipment. T h e y do, however, permit economic utilization of acid, since t h e spent acid from t h e final stage m a y be employed in a n earlier stage of t h e next
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T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
cycle, obviating t h e necessity of discarding a n y b u t a thoroughly exhausted waste acid. I n addition, as has been shown by t h e results of t h e present experiments, t h e polystage process permits t h e use of a less expensively purified raw material. The preparation of trinitrotoluene involves t h e removal of water-insoluble impurities from t h e final product or from some one of the other substances, dinitrotoluene, mononitrotoluene, or toluene. Processes involving t h e use of coal-derived toluene have been dependent upon t h e purification of t h e initial substance. I n t h e past, when specifications were more exacting, a n d especially abroad, crystallization of t h e final product has been resorted t o b u t this is not practicable under present conditions. T h e purification of dinitrotoluene involves t h e same methods as need be applied t o trinitrotoluene a n d t h a t possible medium for purification is likewise eliminated. S C O P E A N D P L A N O F PRESENT W O R K
T h e present work has been based upon t h e device of purifying t h e mono-substitution product. T h e whole proposition may be stated concisely as follows: T h e preparation of satisfactory trinitrotoluene involves a purification from water-insoluble impurities of one of t h e four substances: toluene, mononitrotoluene, dinitrotoluene or trinitrotoluene. Both toluene a n d mononitrotoluene are liquids having boiling points sufficiently low t h a t their distillation is a matter involving no inherent difficulty. T h e purification of dinitrotoluene and trinitrotoluene can be accomplished only through commercially impracticable processes of crystallization or washing which involve the use of organic solvents. Toluene derived from petroleum cannot be brought t o a s t a t e of complete purity readily by any methods now known, b u t by means of simple processes of fractionation it is possible t o obtain, from cracked petroleum, toluene with no impurities save paraffin and olefin bodies. T h e olefins may be removed by extraction with sulfuric acid, a n d t h e resulting mixture, when nitrated under proper conditions of acid concentration, yields mononitrotoluene contaminated with t h e original paraffins, with resinous bodies formed b y t h e action of t h e acid, a n d possibly with a small quantity of dinitrotoluene. Mononitrotoluene boils between 218’ C. a n d 238’ C., t h e paraffins in t h e neighborhood of 1 1 0 ’ a n d t h e resins, etc., a t temperatures above 300’ C. Hence, a simple distillation, preferably in vacuo or with steam, gives a n easy a n d practically complete separation of mononitrotoluene from t h e low boiling paraffins a n d t h e high boiling resins. Since no water-insoluble impurities are present in t h e mononitrotoluene it may be converted readily into trinitrotoluene by commercially practicable methods. EXPERIMENTAL
Samples of toluene were obtained which had been prepared by simple distillation a n d redistillation of cracked petroleum from the commercial furnaces
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12
employed in t h e Bureau of Mines vapor-phase cracking process. MONONITROTOLUENE-The first section of t h e work involved t h e preparation of pure mononitrotoluene a n d this process was studied in detail. Large quantities were not used, but d a t a were obtained which can be applied with some exactness t o commercial work. It was shown conclusively t h a t no difficulties need be encountered in large scale operations. T h e mononitrotoluene prepared was analyzed carefully for its purity, as indicated by nitrogen content. Yields were also measured, although no emphasis is laid on these since t h e scale of operation made t h e m necessarily low. TRINITROTOLUEKE-The analyses of t h e mono product indicated t h a t it was almost chemically pure but it was thought desirable t o actually convert it into t h e higher substituted compound. Samples of trinitrotoluene were therefore prepared; these, when washed with water, showed melting points of 7 5 ’ and above. I n t h e course of these preparations valuable indications were obtained a s t o advantageous methods of procedure for large scale operations, although no final details were worked out. NITROBENZENE-Finally a simple experiment was performed t o verify t h e obvious conclusion t h a t benzene mixtures would behave in a manner identical with those containing toluene. Nitrobenzene was prepared by the method used for mononitrotoluene. The resulting product was tested by conversion into aniline by t h e method outlined by Gattermann.’ This section of the work was purely qualitative a n d no figures were obtained, but it may be stated t h a t t h e preparations involved no difficulty a n d t h a t t h e behavior of t h e benzene product was identical with t h a t of t h e toluene. ORIGINAL MATERIALS-The original materials were toluene fractions obtained from petroleum cracked b y the Bureau of Mines vapor-phase process. The oils were distilled in commercial Badger stills. Analyses of t h e products yielded t h e following figures: Sample No. 2 Sample No. 1 Distillation r a n g e . , . . . , , . . . . . . . . . . . 109°-1150 0,823 0.832 Specific gravity (15O/1So). . . . . . . . . . . . 6 6 . 4 per cent Toluene content (on basis of sp. gr.) ( a ) . 7 2 . 9 per cent ( a ) Rittman, Twomey and Egloff, M e t . Chem. Eng., 13 (1915). 682.
.
.
P R E P A R A T I O N O F MONONTROTOLUEIiE-The method employed for t h e preparation of mononitrotoluene was t h a t of Schultz and FlachslanderP The nitration is conducted in a wide-mouthed, round-bottomed flask fitted with a thermometer (bulb immersed in the liquid) and with a short condenser, through which is passed a motor-driven stirrer. The nitrating acid is introduced through the condenser, being run in from a dropping funnel. For each IOO grams of toluene a mixture of I I O grams of nitric acid (sp. gr. 1.456)and 143 grams of sulfuric acid (sp. gr. I .84) is required (the mixture made up in these proportions is hereafter designated as “mixed acid”). In the process of nitration the cold mixed acid is run in slowly from the dropping funnel. During the main course of the reaction the temperature is not allowed to rise above from 45’ to 5 5 ’ . At the end, when the concentration of excess acid is small, the mix1 “Practical Methods of Organic Chemistry,” second English from fourth German edition, 1907, p. 188. 2 J . grakf. Chem., [2] 66 (1902). 156.
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T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
ture is heated to 100’ in order to complete the nitration. I t is claimed that by this method it is possible to obtain a yield which is 95 per cent of the theoretical. After completing the process of nitration the mixture is cooled and then washed with water to remove the remaining acid. The resulting oil is dried and distilled i n vucuo. The use of vacuum or steam in the distillation does not permit the obtaining of actual boiling points but there is no necessity for this. A low boiling fraction comes over first, which includes the paraffins and any small residue of unnitrated toluene. The thermometer then starts to rise rapidly and at this point the receiver is changed. After the collection of a large fraction the temperature begins another sharp rise and the distillation is then stopped. The residue consists of resins and any di- or trinitrotoluene which may have been formed. T h e experiments with mononitrotoluene were conducted t o ascertain: I-The effects of various methods of preliminary deolefinization ; 2-The effect of variation in t h e q u a n t i t y of nitrating acid upon t h e degree of purity; 3-The quantitative yields of t h e samples of mononitrotoluene obtained. Details of these experiments are given in Table I. I n Experiment 2 , t h e sample of t h e toluene mixture was deolefinized b y t r e a t m e n t with quantities of
IO17
t r e a t m e n t with sulfuric acid. This is, however, undesirable from a commercial point of view. Mechanical difficulties arise on account of t h e formation of emulsions a n d , in addition, this t r e a t m e n t is unnecessary since t h e acid removed is immediately added again when t h e nitrating “mixed acid” is r u n in. T h e next best yield was obtained when there was no preliminary t r e a t m e n t a n d this result furnished t h e key t o a solution of this phase of t h e problem. T h e q u a n t i t y of mixed acid used was calculated for I O O grams of actual toluene a n d as this a m o u n t of aromatic hydrocarbon was not present there was some conversion t o dinitrotoluene, which substance is in t h e present course of procedure lost in t h e residue after distillation. When t h e preliminary deolefinizat i o n was omitted some of t h e nitric acid was t a k e n u p b y t h e unsaturated bodies a n d t h e excess reduced, which resulted in a n increased yield of mononitrotoluene. F r o m a commercial point of view this is a n undesirable mode of procedure since it involves allowing expensive nitric acid t o d o work which m a y b e performed equally well b y cheap sulfuric. It is obvious, however, t h a t t h e magnitude of t h e yield is controlled by this factor of acid concentration a n d i t appears t h a t a n excess is undesirable from t h e
TABLE I-MONONITROTOLUENE PROM TOLUENE(100-Gram Sample-Toluene
Content as Given)
The Preliminary Treatments for Removal of Olefins Are Described in the Text YIELDOB PURIFIED(DISTILLED) MONONITROTOLUENB Yield of MIXEDToluene crude monoPER CENT ACTUAL Exp. ACID used nitrotoluene GRAMS YIELD N I T R O G E N ( U ) PER CENT TYPEOF NITRATION No. Grams Grams Grams Actual Theoretical Actual Theoretical Yield Purity 10.21 72.7 99.5 108.5 10.16 79.0 72.9 95.0 OLEFINSPRESENT.. ................................. 1 253 144.5 10.19 10.21 73.2 99.8 104.5 OLEFINSREMOVED,sample washed and redistilled.. . . . . 2 253 97.0 127.0 10.19 10.21 6 6 . 6 99.8 8 6 . 4 131.8 253 8 8 . 5 1 2 7 . 0 OLEFINSREMOVED, no washing or redistillation. 10.17 10.21 65.3 99.6 ~ 6 . 8 118.0 253 79.2 126.0
........
Same as Experiment 3 . . .............................
200 79.2 126.0 90.7 118.0 10.21 77.3 .... 200 76.2 120.0 90.0 115.3 10:04 10.21 79.3 98.5 10.21 8 2 . 2 .... 180 6 8 . 8 126.0 8 4 . 4 102.5 Same as Experiment 3, but different sample.. 180 68.8 128.0 82.6 ... ... 10.21 80.7 .... ( a ) Nitrogen determinations were made under the direction of Mr. W. C. Cope of the Explosives Laboratory of the Bureau of Mines. Analyses were made by Mr. Cope‘s modification of the Kjeldahl method, which has been devised for nitro-substitution products. (Description about to be published.) The modification is characterized by a preliminary 12-hour cold digestion of the unknown substance with sulfuric acid, salicylic acid and zinc dust.
..........
I O a n d 5 per cent of i t s volume of ordinary concent r a t e d sulfuric acid. T h e product was washed with water a n d alkali, dried a n d redistilled. A fraction was collected, boiling between 105’ a n d 110’. This represented 7 j. z per cent of t h e original a n d , on t h e approximately correct assumption t h a t no toluene was lost in t h e preliminary t r e a t m e n t , i t contained 97 per cent of actual toluene. I n Experiment 3 t h e sample of the toluene mixture was deolefinized as in Experiment 2 , b u t t h e resulting mixture was nitrated immediately after drawing off t h e second lot of acid sludge. Experiments I , 2 a n d 3 established without a n y possible d o u b t t h e fact t h a t b y t h e simple process of nitrat,ion t o t h e mono-stage, with subsequent distillation, i t is possible t o get rid of t h e impurities which are associated with aromatic hydrocarbons produced b y t h e cracking of petroleum. T h e products obtained a r e pure within t h e limits of errors of analysis. Correct indications as t o t h e desirable method of preliminary t r e a t m e n t were obtained only b y careful interpretation of results. It appears on superficial examination of t h e d a t a obtained t h a t t h e most desirable method on t h e basis of percentage yield is t h a t which involves purification after t h e preliminary
...
point of view of yield of t h e desired product as well as cost of wasted nitric acid. T h e conditions of preliminary t r e a t m e n t seem t o have no effect upon t h e purity of t h e product, t h e general method of procedure being such as t o fix this at a high mark. On t h e basis of general considerations of expense a n d convenience t h e process involving a simple refining with sulfuric acid a n d n o intermediate washing before nitration seemed most desirable, even in face of t h e fact t h a t i t seemed t o give lower yields t h a n either of t h e two other methods. This low yield a p peared t o be explainable on t h e basis of excess of nitrating acid a n d Experiments q a a n d b were therefore conducted t o demonstrate whether o r not this was t h e case. T h e indications furnished b y these t w o experiments were clear-cut a n d satisfactory. T o show t h a t there was nothing accidental about t h e m , a n d t h a t t h e y mere not characteristic of t h e particular sample of toluene mixture used as original material, some supplementary preparations (Experiments sa a n d b ) were made, using a second sample of toluene, which h a d a lower content of t h e aromatic hydrocarbon. T h e q u a n t i t y of acid used was equivalent t o t h a t needed for 7 1 grams of toluene, so t h a t a 3 per cent excess was present.
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T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
C O N C L U S I O N S REGARDING T H E PREPARATION O F M O N O NITROTOLUENE
I-Mononitrotoluene of a high degree of purity may be prepared f r o m t h e paraffin-olefin-toluene mixtures. obtained b y t h e simple distillation of cracked petroleum. T h e purity of t h e nitro-product a n d , consequently, its utility for t h e preparation of waterwashed trinitrotoluene, is fixed b y t h e general method of t r e a t m e n t , which ensures a very sharp separation of mononitrotoluene from t h e impurities associated with it. 2-It is desirable t o remove olefins b y a preliminary extraction with sulfuric acid. Otherwise they consume expensive nitric acid and incidentally develop so much heat t h a t t h e process of nitration is difficult t o regulate. N o washing is necessary between t h e processes of deolefinization and nitration since such a treatment removes acid which must be added again a s soon as nitration is begun. 3-The q u a n t i t y of nitrating acid mixture should be based approximately on t h e actual toluene in t h e mixture t o be treated and not on t h e total quantity of t h e latter. An excess of acid causes t h e formation of dinitrotoluene, which under present conditions is a n undesirable occurrence. P R E P A R A T I O N OF TRINITROTOLUENE
Experiments on t h e preparation of trinitrotoluene were not conducted for t h e purpose of modifying or improving a n y of t h e numerous methods which have already been proposed. T h e work done was for t h e simple purpose of obtaining absolute verification of t h e results obtained by t h e analyses of t h e samples of mononitrotoluene prepared b y t h e method indicated above. T h e fact t o be established was t h a t t h e fraction of a per cent of impurities included in the mononitro product did not in a n y unexpected way interfere with its transformation into waterwashed trinitrotoluene of a satisfactory degree of purity. Preliminary experiments were performed according t o various sets of directions found in t h e literature, b u t t h e products obtained invariably melted below t h e required mark of 7 5 " C. A satisfactory product could always be obtained by a simple crystallization from alcohol b u t this fact was of little significance. It finally appeared necessary t o concentrate on t h e details of some specific method a n d for this purpose t h e poly-stage process employed by one of t h e large explosives companies in this country was selected as most promising. Translated into terms of quantities usable in t h e laboratory t h e method of procedure is as follows: FIRST STAGE-Transformation nitrotolaene
of mononitrotoluene into di-
Amount of mononitrotoluene., ... Acid concentration., . , , . , . , . , , .
.
50 g. 1 0 7 , 6 g. of a mixture of 1 part by weight of HNOa (sp. gr. 1 . 5 ) and 2 parts HzSOi (sp. gr. 1 .84)
Temperature during addition of a c i d . . . ...................... 88.0' C. Time of heating.. . . . . . . . . . . . . . . . 1/z hour at 88.0'
C.
The mixture is then cooled and the spent acid drawn off.
SECOND STAGE-Transformation into trinitrotoluene.
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12
of u n p u r i f e d dinitrotoluene
Acid concentration.. . . . . . . . . . . . .
Temperature during addition of acid ......................... Heating.. ......................
Below 8 8 . 0 ' Cg 1 hour at 8 8 . 0 11/z hours at 100'
The mixture is then cooled and the acid drawn off. The rernaining product is washed several times with hot water, being stirred with the latter while in a molten condition. It is finally dried. T h e first experiments were performed using t h e quantities of acids specified in these directions b u t with modifications in t h e time and degree of heating (Nos. I t o 4, Table 11): TABLE11-TRINITROTOLUENE FROM MONONITROTOLUENE FIRSTSTAGE SECOND STAGE: DI- to TRINITROTOLUENE Acid in Excess of Amount Specified NITROTOLUEHE % YIELD Acid specified ExHours heated at Melting Exp. Heated Temp. CESS Temperatures (" C.) In point (a) No. Hrs. C. ACID95 100 110 115 120 130 grams OC. 1 1 88 0 1'/z 0 0 1 0 0 5 7 -72 64 88 0 1 1 2 1 0 58 -69 61 '/* 0 0 88 3 1 0 1 55 -72 1 1 / z '/z 0 '/2 1/2 61 4 I, /, _ 115 0 1 0 0 0 ll/z 0 60 69 -77 25 1 i1/2 1 0 73.5-77.5 5 '/2 115 25 1 0 0 0 75 -79 6 115 50 1 11/2 0 0 0 0 60 74 -80 7 1 115 8 1 115 50 1 1'/2 0 0 0 0 56 75.5-79.5 1 115 50 1 4 0 0 0 0 60 75.5-79 9 10 1/2 115 50 1 0 0 0 11/z 0 60 78 -79.5
M O K O -t o DI-
~~~
I
-
?L
~~
2:
(a) Melting points were determined under the direction of Mr. Cope in the Explosives Laboratory of the Bureau of Mines. Thermometers were carefully standardized. The apparatus was that described by Mulliken, " A Method for the Identification of Pyre Organic Compounds," Vol. I (1908), p. 218.
This series of experiments was instructive, since i t appeared t h a t no improvement could be secured through increasing time of heating a n d temperature in the second stage of the process. A marked improvement, however, appeared by t h e modification of treatment in t h e first stage. Heating for one-half hour a t I I j instead of a n hour a t 88 resulted in a n increase of about 10' in t h e melting point of t h e product. T h e next series of experiments involved a z j per cent increase in t h e amount of acid used for t h e second stage of the nitration (Nos. j a n d 6 , Table 11). An improvement was shown here, the product obtained in one case being just above the satisfactory degree of purity. From a commercial point of view there seems t o be no inherent objection t o t h e employment of a considerable excess of acid a t t h e second stage of t h e reaction, since t h e spent acid m a y be utilized in a n earlier stage in t h e next cycle. Hence, instead of proceeding with experiments involving a 2 j per cent excess of acid, t h e quantity was increased t o a j o per cent excess a n d a third series of preparations made (Nos. 7-10, Table 11). Three of these four experiments yielded satisfactory products a n d there seemed t o be no doubt but t h a t with t h e higher concentration of acid there was little difficulty in producing a trinitrotoluene of a satisfactory degree of purity. The yields were all in t h e neighborhood of 60 grams, which is about 7 0 per cent of t h e theoretically possible amount. This is, of course, low, for commercial work, b u t conditions here were less favorable t h a n they would be on a large scale a n d , a t best, t h e work has only remotely approached completion in t h e matter of determining optimum conditions for t h e process of nitration. Here as well as in t h e earlier
T H E J O C R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
Dec., 1915
p a r t of the work, attention was given only t o t h e establishment of general principles a n d no a t t e m p t was made t o learn details. CONCLUSIOKS
REGARDING
THE
PREPARATION
OF
TRI-
&-ITR O T O L U E N E
1-Trinitrotoluene, of a satisfactory degree of purity, may be prepared from t h e mononitrotoluene obtained b y t h e nitration of t h e toluene-paraffinolefin mixtures produced b y the fractionation of “cracked” petroleum. a-From t h e laboratory point of view, at least, t h e poly-stage process seems best. T h e transformation from mono- t o di-product should involve a fair d e gree of heating a n d a moderate concentration of acid. T h e final stage of t h e nitration should be conducted with a considerable excess of strong acid, which acid need not be wasted since when drawn off i t m a y be used in a n earlier stage of t h e next cycle of nitration. GENERAL SGNMARY
I-The aromatic hydrocarbons produced b y t h e “cracking” of petroleum may be utilized for t h e preparation of nitro-products without being brought t o a high degree of purity. T h e foreign substances not easily removable are paraffins a n d these are not affected b y reagents of sufficient vigor t o transform t h e aromatics quantitatively into mono-nitro products. These compounds may be separated in a high degree of purity by a simple process of distillation. 11-The mononitrotoluene prepared b y t h e method indicated m a y be readily converted into trinitrotoluene which, when washed with h o t water, satisfies t h e ordinary commercial specification of a melting point of 7 j 0 C. C H E M I C A L S E C T I O N OF T H E P E T R O L E U M
u. s.BUREAUO F MINES
DIVISION
THERMAL REACTIONS OF AROMATIC HYDROCARBONS IN THE VAPOR PHASE’ By W. F. RITTMAN, 0. BYRONA N D G .
EGLOFS
Received September 8, 1915
I n connection with t h e phenomena of thermal decomposition or “cracking” of hydrocarbons a s t u d y has been outlined for t h e purpose of obtaining comprehensive d a t a regarding t h e whole field. A first series of experiments2 dealt with t h e production of gas a n d determined t h e influence of temperature, pressure a n d concentration on t h e yield a n d composition of t h e product. Another series of experiments3 dealt with liquid reaction products a n d indicated conditions favorable for t h e production of ( I ) open-chain hydrocarbons a n d ( 2 ) aromatic hydrocarbons; i t was shown t h a t t h e temperature range m a y be divided roughly as follows with regard t o t h e products of t h e cracking reaction: u p t o a b o u t 600’ C. t h e formation of low-gravity hydrocarbons of t h e open chain class is favored; from 600’ t o 800’ aromatic compounds are produced in large q u a n t i t y ; above 800’ t h e maximum products are carbon a n d gas. F r o m both a scientific a n d a commercial point of
’ Published
*
with t h e permission of t h e Director of t h e Bureau of Mines. R i t t m a n a n d Whitaker, THISJOURNAL, 6 (1914), 383 and 472. R i t t m a n , I b i d . , 7 (1915). 945.
1019
view t h e differences among various aromatic hydrocarbons are of almost, if not quite, as great importance as t h e differences among- classes. The present series of experiments has, therefore, been conducted for t h e purpose of establishing facts concerning t h e influence of conditions of temperature a n d pressure on interaromatic reactions. Four typical monocyclic hydrocarbons-cymene, xylene, toluene a n d b e n z e n e w e r e subjected t o cracking, each at three different temperatures a n d a t each temperature under four pressures. Some work has been done also with t h e solid hydrocarbons naphthalene a n d anthracene, b u t on account of experimental difficulties, t h e results obtained are only qualitative. F r o m t h e results of t h e s t u d y of reaction products, indications have been obtained which may be summarized in t h e following general way: T h e course of t h e reaction is in t h e direction I-(a) of decrease in size of molecule when t h e degree of saturation is unchanged. ( b ) Reactions may occur in t h e direction of de-hydrogenation either with increase or with decrease in size of molecule. a-Reverse reactions occur in practically negligible amount. HISTORICAL
More or less work seems t o have been done by previous investigators on t h e problem of thermal reactions of aromatic compounds b u t in no case has a systematic s t u d y been made. The information desired at present concerns t h e influence of conditions of temperature a n d pressure upon quantitative a n d qualitative relations a m o n g end products a n d this is not adequately supplied b y t h e literature. T h e classic researches of Bertholet’ have furnished a foundation for our knowledge in this general field. His series of thermal reactions is comprehensive a n d t h e results obtained are valuable, though not such as t o supply t h e needs of t h e present case. Ferko2 furnished some valuable information, particularly with regard t o t h e direction of reactions. He passed t h e vapors of several hydrocarbons, either pure, or mixed with ethylene gas, through a n iron t u b e heated over a 40 cm. length in a gas furnace. T h e products were condensed a n d their composition studied. The more important of t h e results obtained are summarized in Table I. Without attempting a TABLEI-SUMMARYOF RESULTSOBTAINEDB Y FERKO REACTIOX PRODUCTS PERCENTAGES OF ORIGINALMATERIAL
Benzene a n d ethylene 1320 Toluene . . . . . . . . . . . . . . 1300 Toluene and ethylene.. 1300 Naphthalene a n d ethyle n e . . . . . . . . . . . . . . . . 900 E t h y l b e n z e n e . . . . . . . . 500
6.0 0.0 1.3 0.0 11.5 13.8 0 . 5 0 . 0 15.4 12.3 0 . 8 0 . 0
0.0 22.7 0 . 0 2.1 0.0 0.0
0.0 0.0 0.0 0.0 1 3 . 3 15.0 1 . 0 2 . 0 4.0 0.0
0 . 0 0 . 8 1.1 3 . 0 1.1 1.0 0.0 0 . 0 1 . 5
0.0 44.5 0 . 1 0.0 0.6 2 . 2 2 . 6 0.4
detailed s t u d y of this table it m a y be seen t h a t no reaction products are obtained which are not in t h e order of decrease of saturation, or of molecular weight ‘ A n n . chim. p h y s . , [4] 9 (1866), 445; 12 (1867), 5; 16 (1869). 143. 2
Bn.,20 (1887).
660.
