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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
the viscosity remained approximately constant, rising only three points during a further three months' ageing. The changes in other physical and chemical characteristics which accompany this interesting viscosity change in lithographic linseed oils are being further investigated a n d additional information will be published as soon as t h e results are complete. With many varnishes very great viscosity changes occur during the first 2 4 hrs. Surprise has often been expressed t h a t a batch of varnish. a sample from which was removed and tested when hot, did not have t h e proper viscosity when t h e entire batch h a d cooled, say about 24 hrs. later. A sample removed from a fresh batch a n d cooled rapidly almost invariably shows a much lower viscosity t h a n one taken later when t h e entire batch has fallen t o room temperature. This is undoubtedly merely an extreme case of t h e general phenomena which occur during t h e ageing of varnishes. I n general a review of t h e ageing processes shows t h a t with stable varnishes viscosity approaches a constant value at t h e end of about one month's time. If viscosity continues t o rise t o a n y considerable extent for longer t h a n this period trouble with the varnish must be feared as it will usually be found t h a t this increase will go on for a long time until finally t h e consistency of t h e varnish will become such as t o make i t unsuitable for general use. The results quoted above have shown in a very brief way some of t h e values of viscosity determinations. It is not intended t o intimate t h a t these are b y a n y means t h e only lines along which this determination can prove of value. They merely indicate t h a t continued study of such factors as this can teach t h e varnish manufacturer t h e general nature of t h e products occurring in t h e various materials which he manufactures, and can also show him in what direction changes in t h e physical nature of t h e constituents will influence t h e practical characteristics which he is attempting t o obtain. The generally recognized fact t h a t varnish drying is closely related t o t h e phenomena of jell formation shows a t once how important a knowledge of t h e nature a n d amount of colloidal matter present in t h e liquid varnish is. Study of this and other factors will end b y proving t h e most instructive work possible and will well repay all t h e time a n d expense spent on i t , as it will enable t h e producer t o construct varnish formulas a n d indicate heat treatments which will give him practically any characteristic which he desires in t h e completed product. RSSEARCHLABORATORIES. T H E ARCOCOMPANY CLEVELAND, OHIO
THE CRACKING OF AN AROMATIC BASE OIL THE TEMPERATURE FACTOR AT CONSTANT RATE UNDER PRESSURE B y GUSTAVEGLOPF AND ROBERTJ. MOORE Received November 10, 1916
T h e greatly increased demand for t h e aromatic hydrocarbons, benzene a n d toluene, due t o , their use in explosives a n d dyes, has led t o a systematic review of their sources with t h e object o€ obtaining new or greater yields of these two fundamental sub-
Vol. 9 , No.
I
stances in t h e production of picric acid a n d trinitrotoluene, a n d t h e varied dye compounds. This activity towards increased efficiency in method and better utilization of by-products, although fostered by present immediate demands brought on by war conditions, has nevertheless been in accord with the ideals of conservation of resource$, lately taking root in our American industries. A number of communications for t h e production of t h e above-mentioned hydrocarbons from paraffin and naphthene base oils have already appeared.' I n t h e present paper t h e formation of benzene a n d toluene from a n aromatic base oil-solvent naphtha-at temperatures from 500 t o 800' C. at t h e r a t e of oil flow of 15 gals. per hr. a n d 11 atmospheres pressure has been s t u d ied. These results are then compared with t h e percentage yields of benzene and toluene from other hydrocarbon oils. E X P E R I M E N T A L PROCEDURE
The apparatus used in t h e following series of experiments was one which has been described in some detail.2 It consisted essentially of a n 8 in. diameter steel tube II~,'~feet in length, gas-heated in a muffle t y p e furnace. The temperature, pressure a n d rate of oil flow was controlled with care, since any change t a k ing place in one of these factors would give widely different percentage yields of products resulting from t h e reaction. The temperatures used were joo, jjo, 600, 6 j 0 , 700, 7 j o and 800' C., a t a pressure of 11 atmospheres a n d r a t e of oil flow of 1 5 gals. per hr.; 2 0 gals. of solvent naphtha were used in each experiment. The analyses of t h e recovered oils for their benzene a n d toluene content were made b y means of fractional distillation in a Hempel column, specific gravity determinations a n d nitrations of t h e fractions. Three hundred cc. of t h e oil were distilled t o 170' C. This cut was redistilled t o I o j ' and 105 t o 135'. The cut t o 105' redistilled t o 95'. This 9;' cut was t h e benzene fraction. The residue from this distillation was then added t o t h e IO; t o 135' cut. T h e latter fraction, IO; t o 13j0, was in t u r n redistilled from 95 t o 120'. This cut represented t h e toluene. T h e benzene was further determined as t h e dinitrocompound, and t h e toluene as trinitrotoluene. TYPE O F O I L U S E D
The oil used in t h e following experiments was one derived from the thermal decomposition of coal, and was t h e cut known as solvent naphtha. T h e solvent naphtha gave upon sulfuric acid treatment only a slight yellow-lemon in t h e acid layer. The per cent of 0- m-,and &xylenes was 7 0 per cent; t h e other 3 0 per cent was composed of higher methyl and isopropyl derivatives of benzene. A trace of naphthalene was also present a n d was detected as a white solid a t t h e end of t h e condenser at t h e completion of t h e distillation. T h e melting point of t h e naphthalene was 79.8' C. 1 E g l o f f ,Met. & Chem. Eng.. 1 5 (1916), 125; Egloff, Twomey and Moore, THIS JOURNAL, 8 (1916), 1102; Egloff and Twomey, J . Phys. Chcm., 80 (1916). 597; LOC.cit.: Met &' Chem. Eng., 16 (1916). 523. 2 Egloff and Twomey, Met. & Chem. E n g . , 16 (1916), 15.
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
Jan., 1917
T h e distillation analysis (Table I) was made by means of a Hempel distilling head a n d conducted at t h e r a t e of 2 drops per sec. at t h e end of a 24 in. Liebig condenser. T h e s p . gr. of t h e oil a n d fractions were taken by means of a Westphal balance a t 15.5' c.
have been formed a t a lower temperature in greater quantities. The toluene formation from t h e starting oil a t temperatures from j j o t o 7 j o Oshows a higher percentage yield t h a n benzene, while a thange of jo' between 7 j o t o 800' shows a percentage increase of benzene of 23.4 per cent and a drop of toluene formation of 22.6 per cent, this drop of 22.6 per cent of toluene formation clearlyforming part of t h e 23.4 per cent increase of benzene formation. This phenomenon gives added experimental evidence as t o the course of t h e aromatic hydrocarbon reaction; in short, t h e higher alkyl derivatives of benzene of t h e dimethyl, trimethyl and isopropyl groups, go t o toluene a n d toluene t o benzene. The percentage yield of benzene a t j o o ' was zero a n d with increase in 50' increments, gave a maximum The formation of toluene of 4 2 . j per cent a t 800'. reached a maximum of 39.9 per cent at 7jo' and decreased t o 17.3 per cent a t 800' during a change of 50'. The d a t a have been graphically shown in Fig. 2 , which indicates t h e smoothness of t h e curve for benzene formation, while a sharp break is t o be noted for toluene formation a t 7 50".
TABLEI-DISTILLATIONANALYSIS OF OIL ~ J S B D Specific Gravity 0.868/15.5° C. Specific Temperature Per cent Gravity O c. by Vol. 7 0 . 1 0,866 135 to 145 15.0 0.869 145 to 160 160 t o 170 170 t o 183
Loss
12.0 1.6 1.3
0.869
...
...
oxs-The general phenomena of t h e thermal decomposition of hydrocarbons is t o give a lower percentage yield of recovery of the starting oil with increase of temperature. A temperature change from j o o t o 650' changed t h e percentage yield only 2 per cent, whereas a similar change of I jo' ( 6 j o t o 800') gave a decomposition of 39.3 per cent (Table 11). T h e greatest decomposition took place between temperatures of 7 0 0 a n d 7 j o o , where a percentage change of z j per cent is t o be noted. THE RECOVERED
TABLE I1 TEMP. C.
500 550 600 650 700
750 800
RECOVEWDOIL Per cent Sp. Gr. 100 99.5 99.0 98.0 76.6 51.6 37.3
PERCSNTACES BENZENE A K D TOL'UENG Basis of Recovered Oil Basis of Oil Used Benzene Toluene Benzene Toluene 0.0
1.4
1.6
2.4
8.0 19.1 42.5
0.0 6.5 8.0 13.0 23.3 39.9 17.3
0.0 1.3 1.5 2.3 6.1 9.8 15.9
o,o 6.4
7.9 12.7 17.8 20.6 6.5
T h e specific gravity of t h e recovered oils increased
high molecular weight. T h e specific gravity changed from 0 . 8 6 8 at joo' t o 0.989 a t 800'. The d a t a are expressed graphically in Fig. I . BENZENE AND TOLCENE I N
THE
RECOVERED
OILS-
I n t h e thermal decomposition of hydrocarbon oils t h e formation of benzene apparently invariably increases a t a more rapid rate in t h e recovered oil t h a n toluene, particularly a t t h e higher temperatures (Table 11). This is no doubt due t o t h e decomposition of t h e higher alkyl derivatires of benzene which
41
B E N Z E N E A N D T O L U E N E OK THE BASIS
OF
OIL USED
PRODUCTION-upon t h e basis of I O O gals. of oil used, t h e percentage yield of toluene, within t h e limits of practical experimentation, exceeds t h a t of benzene b y 4.7 per cent (Table 11). The maximum yield of 20.6 per cent of toluene occurred at 7 j o o , whereas a t 800' benzene showed a maximum of 15.9 FOR
tures of 7 j o and 800' C. Between these temperature limits a drop of 14.1 per cent of toluene is t o be noted. This fact indicates t h e temperature control necessary when maximum conditions are required for a particular hydrocarbon. A slight increase in temperature above 7jo' C. changes greatly the percentage yield of toluene on t h e basis of oil used for production, as is shown in Fig. 3. I n t h e recovered oil, benzene shows a higher per cent, b u t , v h e n the factor of percentage of recovered
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
42
oil is taken into consideration, t h e conditions reverse and toluene reaches a higher percentage yield, when taken on t h e basis of oil required for t h e production of benzene and toluene. MECHANISM OF T H E REACTION
I n the thermal decomposition of paraffin and naphthene base oils t h e mechanism of t h e reaction is very complex and not thoroughly understood a t t h e prese n t time. But with an aromatic base oil of t h e type utilized in t h e present series of experiments t h e mechanism of t h e reaction is relatively simple. The course of t h e reaction has been already worked out in t h e case of the effect of aluminum chloride upon t h e methyl derivatives of benzene as t h e xylenes, trimethyl benzenes and higher derivatives. -4nschatz a n d Immendorff , l and Jacobsen2 found t h e following reaction taking place in general when xylene and aluminum chloride reacted: C Ha ,CHI C ~ H ~ + C ~ H S - - C H ~ + CsH4 + C6H3--CH3 'CH3 No quantitative yields are noted in t h e above experiments. I n t h e present communication, dependent upon t h e temperature, t h e percentage yields of benzene and toluene varied. Now since the starting oil was composed mainly of alkyl derivatives of benzene of the methyl group, the course of t h e reaction was found t o go mainly in the direction of: ,CHI CsH4\ CeHs.CH3 --3 C6H6 CH3 ( 0 ) ( m ) ( P I From two entirely different methods it has been shown t h a t t h e mechanism of t h e reaction is essentially as shown above.
