T H E PRODUCTIOS O F AROMATIC HYDROCARBOKS FROM PARAFFIN WAX BY GUSTXV EGLOFF AND THOMAS J. T W O X E Y
The cracking of paraffin wax into lower boiling hydrocarbons has been made a study of in a number of investigations which are widely quoted. The first workers in this field were Thorpe and Uoung,l who cracked paraffin wax by distillation under pressure. In the distillate there was identified pentane, hexane, heptane, octane, nonane, probably also decane and undecane, as well as amylene, hexylene, etc., up to nonylene. Gawalowski? has found recently that paraffin wax (m. p. 4 j ' C) by prolonged heating in an autoclave may be decomposed into gaseous and liquid products which in both cases are said to belong to the ethylene and acetylene series. At any rate the decomposition oils contain also methane and homologues, cyclical saturated (naphthenes) and unsaturated hydrocarbons. Brooks and co-workers3 cracked pure commercial paraffin wax a t temperatures not exceeding 420' C and under IOO pounds' pressure, thus obtaining gasolene entirely aliphatic in composition. The phenomena of the decomposition of wax is also very familiar to those persons who have distilled crude petroleum, as well as t o the refiners of the oil. The cracking of paraffin wax in the oil takes place usually between 300 and 400' C under ordinary conditions of distillation a t atmospheric pressure. These conditions do not produce such extensive cracking as distillation under pressure and only yield increased amounts of kerosene and not an appreciable amount of gasolene. There is found nowhere in the literature that aromatic hydrocarbons such as benzene, toluene and xylenes have been produced in the decomposition of pure paraffin wax. The Liebig's .4nn., 165,2 8 ; Chem. News, 23, 174 (1871). Oesterr. Chem. Techn. Ztg., 70 (1910). Jour. Ind. Eng. Chem., 7, 180 (1915); Jour. Franklin Inst., 180, 653 (1915); Jour. Am. Chem. SOC.,38, 393 (1916). l
products of the reaction were always found to be those of the aliphatic group. Special effort to find aromatic compounds, especially by Brooks and co-workers' showed that they were not produced by distillation under roo pounds' pressure and 420° In view of these results and the development of cracking processes for the production of benzene and toluene from petroleum a t the present day, the question has arisen whether or not oils containing paraffin wax are suited for the production of benzene and toluene. That such oils are adapted for gasolene formation is universally accepted. If oils containing paraffin wax are to be used, it should be known if the wax is desirable, otherwise the wax should be removed. The authors saw no apparent reason why benzene and toluene should not be formed when paraffin wax is cracked, provided the proper conditions for the formation reaction were obtained. It was realized that the decomposition of paraffin wax by distillation under pressure as conducted by other investigators would produce only aliphatic compounds since the proper conditions were not obtainable by this method. It was also recognized t h a t other investigators were seriously handicapped by using this liquid-gas phase method of cracking which automatically fixes both conditions of temperature and pressure, as is well known from the laws of physical chemistry. From a study? of the kinetics of the decomposition of the paraffin series, it is indicated t h a t decomposition of paraffin wax would tend toward the formation of aromatic hydrocarbons such as benzene, toluene and xylene. The formation was also foreseen by Kramer and Bottcher.3 In commenting on the work of Thorpe and Young, they stated t h a t if a higher temperature had been used, the higher boiling olefins would have changed into benzene hydrocarbons but not naphthenes. For this reason the cracking of paraffin wax by the gas
c.
l
2
LOC.cit. R i t t m a n . Jour. Ind. Eng. Chem., 7, 945 (1915) Ber. deutsch. chem. Ges., 2 0 , 604 (18871.
phase method, t h a t is, the cracking of paraffin wax by passing through a heated tube, was undertaken to confirm the authors' opinion that it is possible to form benzene, toluene and xylenes from paraffin wax under similar conditions which result in the formation of the same compounds from petroleum cracking As might be expected. positive data to this effect were obtained. The results are interesting in that they show ( I that oils containing paraffin wax are adapted for the production of aromatic hydrocarbons as far as the wax is concerned, ( 2 ) t h a t there is a close relationship between the members of the aliphatic and aromatic series of hydrocarbons, ( 3 ) that the production of aromatic hydrocarbons formed by the cracking of petroleum may not be ascribed entirely to the presence of compounds in the petroleum containing the phenyl radical, and (4) the advantage of cracking in the gas phase system for the obtaining of desired results For the experiments pure commercial paraffin wax, m. p 37' C, and containing 0 . 0 5 ' ; of oil, was used. It was cracked by passing through a heated tube, in an apparatus which has been described in detail in other artic1es.l The wax was melted and placed in the lubricator in this condition. It was kept in this state by heating the lubricator gently with a flame. It was admitted to the cracking area a t a constant rate of 246 grams per hour, a rate of flow which has been used in all of the experimental work on the cracking of oils. Only two temperatures and pressures were employed -500 and 600' C and atmospheric and 1 5 0 pounds' pressure. The work was undertaken primarily for the purpose of showing that it was possible to produce aromatic hydrocarbons from paraffin wax and not in order to show the effect of temperature and pressure These effects in view of the present knowledge of the cracking reaction may he readily deduced from the results produced bj- experiments a t a few temperatures and pressures The accompanying tables show the effect of temperature _ _ Rittman Jour. Ind Eng Chem , 6 , 4 j z (1914)
and pressure on the percent of recovered oil, the percent to 170' C of the recovered oil with the specific gravities, the distillation with gravities of the cuts of this light oil fraction, and the percentage of benzene, toluene and xylenes in the recovered oil as well as on the basis of wax required for the production.
ABLE LE
I
The Effect of Temperature and Pressure on the Percent of Recovered Oil -
I
Temp ~~
~~~~~
~
Pressure
joo' C
Percent recovered
1
46 3 78 0
-A t mospheri c
Goo0 C
92 3
*Atmospheric I j o lbs.
joo' C
C
600'
1
~
Ijo
Ibs.
39 7
'r.4BL.E
2
The Effect of Temperature and Pressure on the Distillate t o 170' C and the Specific Gravity -
-
Temp.
Pressure
I
I joo' C
1 ;itmospheric
C C 600'C
Atmospheric
600' 500'
1 I j o Ibs. I 150lbs.
'
Percent to 1 7 0 ' C
I
0
Specific giavity
os
723 o 762 0 753 o 830 0
15 40 1 2 90 28 80
1
TABLE3
I
The Effect of Temperature and Pressure on the Specific Gravity and Percent of the Benzene Cut to 9 j ' C, on the Specific Gravity of the Toluene Cut 9 j ' C to 120' C and the Specific Gravity of the Xylene Cut 1 2 0 ' C to ~
-~~
Temperature
500' C 600'C joOo C 600' C
~
Pressure
'
' ,Itmospheric 1 1 ,Atmospheric
I
150 lbs. I j o lbs.
IjOO
C
-
Percent s p gr. 12o0to sp gr. CI 150' -_
Percent 950 t o
~ercen~ to 95
120°
I
I o o , o o 2 96 o 747 3 84 j 80 0 762 3 I4 I O 60 I o 820 7 20
1
I
~
o 768 0
788
o 83j
0 0
-
773 790 3 8 o 824
5
0
0
I
8
0
Temp
Pressure
benzene _ _ ~
toluene
~
xylene ~
Used for Their Production Pressure
Temp
' ~
500'
C
600' C
joo' C 600'C
1
1
Xtrnospheric -4tmospheric 150 lbs. 150lbs.
Percent benzene
'
0 0
'
1 2
o
2
2 6
, ' ~
~
Percent toluene
Percent xylene
0 0
0.0
o j 1 7
0.3 0.4 0.9
2 2
The analysis of the recovered oil was made by means of fractional distillation and specific gravities. However, the benzene, toluene and xylene formed were also identified by chemical means. The fractions were first deolefinized completely with concentrated sulphuric acid, and then nitrated to the mononitro stage. The paraffins associated with the mononitro compounds were separated by dissolving the mixture in concentrated sulphuric acid. A two-layer system resulted -paraffins and a mixture of mononitro compounds and sulphuric acid. The mixture of sulphuric acid and mononitro compounds was then nitrated to the dinitro state. The dinitro compounds were washed free from acid, recrystallized from alcohol and then identified by means of their melting point. KO attempt was made to distil or analyze the fraction of Rittman, Tmomey and Egloff
Met and Chem Eng., 13, 682 (1915).
520
Gustall EglofJ aiid Thonms J . Twowey
oil boiling above I i o o C, as it was considered that no naphthalene or anthracene was formed. At atmospheric pressure and j O O o C under the conditions of the experiment, but very little cracking of the paraffin wax took place. and to all appearances what cracking occurred produced members onlj- of the aliphatic series. Cnder the other conditions which were obtained, benzene, toluene and xylene as shown b y phqsical and chemical tests were formed in appreciable amounts, although contaminated to a large extent by other compounds such as olefins and paraffins. The aromatic formation increased with increase of temperature and pressure. This phenomena is shown by all cracking experiments in the gas phase method. The temperatures and pressures used in these experiments do not necessarily represent the critical temperatures and pressures for the formation of aromatic hydrocarbons from paraffin wax. They represent only a few of the many conditions possible for production. Due to the rate a t which the paraffin wax was admitted to the tube, it did not necessarily reach equilibrium. V3th a lower rate of feed, conditions approaching the true equilibrium would have been obtained, and in this way, data would have been obtained from which the absolute conditions of temperature and pressure required for the formation might have been deduced At the present time, we are not so intensely interested in this side of the question. Hence a rate was employed which has been made the standard for a comparative study of oils. Compared t o a distillate oil boiling between 2 j 0 and 3 j o o C derived from Pennsylvania petroleum, the paraffin wax is not so stable, and does not produce as much benzene, toluene and xylene. S o explanation is offered a t the present time. The results of this paper may be summarized as follows: I . It is possible t o produce benzene, toluene and xylene by the cracking of paraffin wax a t 600' C and atmospheric pressure: and at 500 and 600' C and I j o pounds' pressure. 2 . Under the same conditions of cracking aromatic hydro-
carbons also result from petroleum oils of the paraffin t?-pe. 3 . That the formation of aromatic h?Tdrocarbons produced by the cracking of petroleum may not be ascribed entirely t o the decomposition of the constituents of the petroleum which contain the phenyl group. 4. That there is a very close relationship between the members of aliphatic and aromatic series of h>-drocarbons. j. That oils containing paraffin wax are adapted for the commercial production of benzene and toluene P I / f A / ~ l / l ’ g hDit I S 2017 C l i e ? i i i ~ i i lCo P7!fabirvgi2 Po . l p i i l 9 , 1916
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