(Aromatizing Cracking of Hydrocarbon Oils)
INFLUENCE OF THE NATURE OF CHARGING STOCIC CHAIM WEIZMANN, ERNST BERGMANN, W. E. HUGGETT, HERBERT STEINEK, AND MAX SULZBACHER WITH K. 0. MICHAELIS, FELIX POPPER, SYDNEY WHIKCUP, AND EMANUEL ZIMKIN The Weizmann Institute of Science, Rehovoth, Israel
I
F T H E aromatizing cracking of hydrocarbon oils is, a t least to a certain extent, due to a breakdown into small units, particulady olefins and diolefins, and a subsequent resynthesis by a Diels-Alder mechanism, one viould expect that the results reflect the proneness of the various types of hydrocarbons to such breakdown-i.e., will depend on the chemical nature of the charging stock. In Table I, a number of charging stocks of roughly similar boiling range but varying nature are compared as to the yield in liquid aromatized product.
will have a value of 0.16. Statistical evaluation of the fairly large experimental material has led from this fixed point to the following additional numerical values: p = 0.25; y = 0.50; 6 = 0.80, therefore
+
y = 0 . 1 6 ~ 0.250
+ 0.50n + 0 . 8 0 ~
(2)
The coefficients show reasonably well that olefins are aromatized more easily than paraffins [for the cracking velocity of olefins see (7, 11, l a ) ] , that naphthenes give a still higher yield-here the possible straight dehydrogenation to the corTABLEI. COMPOSITION OF VARIOUS CHARGING STOCKS (APPROXIMATE BOILIKG responding aromatics (16) expresses RANGE100-200" C.) AND YIELDOF AROXATICS (LIQUIDPRODUCTS) itself-and that aromatics of the boiling Liquid Yield, Composition, % ' b y Vol. 7 by Wt. of range 100" to 200" C. give only 80% Charge Paraffins Olefins Naphthenes Aromatics Chirging Stock "liquid" aromatization product. The 64 36 22 Fischer-Tropsch distillate ILL .. original charge TI ill consist of alkylated Fischer-Tropsch distillate I1 .. (hydrogenated) 94 6 16 benzene derivatives and, therefore, on 56 3 28 13 44 Iranian naphtha 48 .. 37 15 East Texas naphtha 36 cracking, partly lose the side rhains 41 24 5 37 30 Cracked East Texas naphtha
Naphthenic naphtha 8 77 11 4 53 East Texas naphtha SO1 extract 11 1 18 65 70 Coal oil I distillateb 31 9 45 15 70 55 20 14 24 Coal oil I1 distillateb 36 a I n its distillation, the plateaus corresponding to the boiling points of the constituent straightchain paraffins were fairly noticeable. From low temperature carbonization of bituminous coal.
Equation 2 presupposes that branched and straight chain paraffins give the same yield of aromatics. Experiments nith iso-octane have shown this not to be the caw; branched paraffins gave a considerablv better vield than FischerTropsch oil (Table 111). If one assumes on the basis of such experiments that a' = 0.21 (instead of a = 0.16), one arrives empirically a t the following equation :
DENSITY OF HYDROCARBON OILS AS FUNCTlON OF COMPOSlTION
As the density of a hydrocarbon oil is dependent on its composition, one will also expect a close relationship between these two properties. This is graphically expressed in Figure 1 for the same charging stocks to which Table I refers; the relationship is approximately linear. This linearity can easily be understood as the densities (dzo) of hydrocarbons boiling at about 150" C. are (4): paraffins, 0.73; olefins, 0.75; naphthenes, 0.81; aromatics, 0.86; one can express the density, d, of a charging stock by an additive function, thus
+
d = 0 . 7 3 ~ 0.750
+ O.8ln + 0 . 8 6 ~
+
y' = 0 . 2 1 ~ 0.320
(3)
TABLE11. DENSITIES OF VARIOUS CHARGING STOCKS
(1
(Approximate boiling range, 100-200° C.) Density a t 2OyC. Charge Calcd. Exptl. 0.74 0 732 0 731 0.73 0 768 0.77 0 771 0.77 0.76 0 773 Naphthenic naphtha 0.80 0 795 East Texas naphtha SO1 extract 0.83 0 815 Coal oil I 0 820 0.80 Coal oil I1 0 814 0.78
YIELD OF AROMATIZED CRACKING PRODUCT AS FUNCTION OF COMPOSITION OF CHARGE
Similarly, one may assume that the yield of aromatics, y-i.e., the yield of fully aromatized liquid product expressed as per cent by weight of charge-from a given charging stock can be expressed by a function additive in the contributions from the various hydrocarbon types present, thus: = ap
+ 0.50n + 0.75a
Table IV compares the calculated figures and the experiinental yields for the charging stocks used in Table I. The agreement aith the figures calculated from Equations 2 and 3 is reasonable.
in which p , a, n,and a are the content of paraffins, olefins, naphthenes, and aromatics, respectively, given in fractions of unity. Table I1 s h o m the reasonable agreement between the calculated and the experimental figures for the charging stocks of Table I.
Y
(16).
TABLEI n .
+ Pa + y n + 6a
OF FISCHER-TROPSCH OIL .4Pil> ISO-OCTAKE
COXPARISOX
Cracking te,mp., C. Space velocity Liquid yield, % by wt. of charge
As the hydrogenated Fischer-Tropsch oil is nearly purely paraffinic in nature (a = n = a = 0; p = I), a, according to Table I, 2322
FischerTropsch Oil 675 0 23 16
Iso-
octane fiRO
0 10 2Y
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1951
At any rate, the conclusion seems justified that this empirical method permits an approximate estimation of the yield of aromatics (liquid yield) which can be expected from a given charging stock. The only case in which the agreement is unsatisfactory is that of coal oil. It is noted that in Table I1 the agreement between the calculated and the experimental density is worse in this case than in all the other ones; this is believed to be due to the fact that the olefins of coal oil are likely to be of a cyclic nature. Now, cyclo-olefins of boiling point of about 150" C. have a density of 0.83 (4). Also on cracking they will give a yield of aromatics higher than that from either olefins or naphthenes. With a figure of 0.83 for the density and 0.70 for the coefficient of o in Equations 2 and 3, respectively, one obtains the yield figures given in parentheses in Table IV; these are in much better agreement with the observed yields. As long as no evidence for the chemical nature of the olefins in coal oil is available from other sources, the present hypothesis may be accepted as satisfactory.
TABLEIV. YIELD OF AROMATICS (LIQUID PRODUCT)FROM VARIOUSCHARGING STOCKS (Boiling range, 100-200" C.) Yield % b y Wt. of Charge Chlcd. Aocording t o Charge Found Equation 2 Equation 3 Fischer-Tropsch distillate I 22 19 25 Fischer-Tropsch distillate I1 (hydrogenated) 16 Iranian naphtha 44 East Texas naphtha 36 Cracked East Texas naphtha 37 Naphthenic naphtha 52 East Texas naphtha Son extract 65 Coal oil distillate I 71 Coal oil distillate I1 55 0 Figures in parentheses were calculated assuming coal oil to contain cyclo-olefins.
2323
tent of the charge is considerably reduced. After processing, the isolation of the aromatics is easy: toluene, for example, is obtained from the product in a purity of 98 to 99%; its amount has risen to 18010, presumably through reactions of the following type-
This is evidenced by the experiments summarized later in the experimental part especially from the decrease in percentage of the alkylbenzene fraction. According to Coulson and Handley ( 2 ) the toluene cut of low temperature coal-carbonization oil (52.9% toluene) can be converted into very pure toluene over a silver-pumice catalyst (675" C.; contact time, 0.53 minute), but without an increase in the absolute quantity of toluene.
Barring this deviation, Equations 1 and 2 and I and 3 can be combined as follows:
+ 5.3~) + 1.60 + 3.0n f 5.0a) d - 0.68 - 0.05 ( 1 . 0 ~+ 1.40 + 2.6n + 3.6a) -0.21 ( L o p + 1.50 + 3.4n + 3 . 8 ~ ) 9' d
- 0.70 - 0.03 ( 1 . 0 ~+ 1.30 + 3.3n Y
0.16 ( L o p
_L)
To a first approximation, the expressions in brackets on the right-hand side of these equations are equal to unity whatever the individual values for p , 0, n, and a are, and one obtains d = 0.18521
+ 0.70 +
d' = 0 . 2 4 ~ ' 0.68
% AROMA'IICS
FORMED
Figure 1. Yield of Liquid Product (Aromatics) as Function of Density of Charging Stock A. B. C.
(4)
D.
E.
F. G. H.
(5)
These linear relations are compared in Figure 1with the experimental results on the charging stocks to which Table I refers.
Fischer-Tropsch distillate I Fischer-Tropsch distillate I1 (hydrogenated) Iranian naphtha East Texas naphtha East Texas naphtha (cracked) Naphthenic naphtha East Texas naphtha So2 extract Coal oil distillate I
EXPERIMENTS WITH HIGHLY AROMATIC CHARGING STOCKS
TABLE V.
It appears worthwhile to dwell somewhat longer on the experiments with highly aromatic charging stocks. I n addition to the already discussed coal oil (IO), the product of low temperature carbonization, the authors had at their disposal (a)the so-called C.V.R. benzole-i.e., the highly aromatic crude benzene derived from coal carbonization in continuous vertical retorts, ( b ) a product originating from their own experiments with petroleum fractions carried out under conditions at which aromatization is still incomplete, ( c ) the alkylbenzene fraction (150" to 200" C.) of the fully aromatized product (I6), and ( d ) coal tar "solvent naphtha." C.V.R. benzole contains 60% aromatics, among them toluene to an extent of 13 to 14% by weight. Its aromatization under the standard conditions of the process gives a yield of 84% of liquid product and 16% gas, and, as in most cases, the sulfur con-
Charge Density a t 20° C. Engler distillation (5-95%), O C. Composition of charge, % ' b y vol. Boiling below 130° 130-150' (xylenes) 150-18O0 (alkylbenzenes) Above 180° Cracking conditions Temp., C. Space velocity, cc./cc./hour Product Liquid yield wt. % of charge Density a t 20. C. Composition vol. % of liquid product Boiling beiow 95O C. 95-125O (toluene) 125-150° (x lenes) 150-180° (agylbenaenes)
CRACKING OF LIGHTAND HEAVYSOLVENT NAPHTHA Light Naphtha Heavy Naphtha
0.862 134-159
0.887 164-192
02: 5 12.5
8:4 37 55
680 0.12
680 0.11
77 0,890
56 0,965
2.8 14.2 54.2 9.4
11.0 23.0 22.5
6.0
INDUSTRIAL AND ENGINEERING CHEMISTRY
2324
TABLE VI.
CRACKING EXPERIMENT8 WITH VARIOUS CHARGING STOCKS
FischerTropsoh Distillate
I
Charge Density a t 20' C. Boiling range (5-:52), C Cracking temp Space velocity,'bc./oc./bour Liquid yield, % by wt. of charge Density a t 20° C. of liquid product
0.732 100-195 680 0.20 22 0.923
Composition of liquid products, of liquid product Gp t o 750 c. 75-95' (benzene) 95-125" (toluene) 125-150° (xylenes) 150-180'' (alkylbenzenes lbove 180"
Vol. 43, No. 10
(Approximate boiling range 100-200' C.) FischerTropsch Distillate Cracked XaphEast Texas I1 (HydroIranian East Texas East Texas theme Naphtha genated) Naphtha Kaphtha Naphtha Naphtha 802 Extract 0,730 0,768 0.771 0.773 0.795 0.815 166-235 118-186 115-184 102-203 101-204 116-160 675 690 680 680 680 680 0.23 0.11 0.26 0.19 0.24 0.14 16 44 37 45 53 67 0.870 0.910 0.916 0.901 0.933 0 907
2.6 25.0 23.5 15.6 10.6 21 . o
4.0 21.1 12.4 12.2
I . .
34.9 12 8 6.9 12 0 33 4
8.t
41 .-l
2.2 23.8 20.2 10.6 13.1 30 I
2.0 18.2 21.0 11.1 13.7
31 6
3 5 23 6 21 4 13.6 0 9 31 0
...
11.5 23.0 30.8 9.6 25.1
Coal Oil Distillate
Coal Oil Distillate
0.820 107-213 685 0.26 70 0.926
0.814 110-205 680 0.20 55 0 936
I
3.6
11.4 21.0 21.0 15.5 27 2
I1
...
11.6 23.8 19.4 14.4
31 0
of gaseoue produols "/c by vol
I+butadiene
VII.
TABLE Engler 1.b.p.
CHARACTERIST'ICS OF
250 C.
79 80
5% 10 20
30 40 50 60 70 80 90 95 F.b.y. Density a t 20' C.
S?
YU
95 101 106 116 132 158 179 200 0.810
Content, % by Wt. Benzene 32 Toluene 13.5 Sulfur 1.2
4.7 46.8 27.3 9.0 9.0 0.7 2.3 0.2
8 3 39.2 30 2 9 9 0 7 0 9 1 5 0 2
C.V.R. BENZOLE
Group Analysis, % ' by Vol. F G a x Olefins Naphthenes Aromatics 13 22 7 59 Fractionation on Column of Medium Fraction Up to 70' 70-95O (benzene fraction) 96-125' (toluene fraction) 125-150' (xylene fraction) Above 150° Characteristics of Benzene (70-95' _-__ Toluene (96-125O C.) Benzene Bromine S o . , g./lOO g. n Lo Aromatic content, % Toluene Bromine No., g./100 g n2rP .Gonutic content, %
Total
C.V.R.
Charge Temp O C. Yield gf liquid product % by wt. Density at 20' C. of liduid product
Crude 650 84 0.879
Efficiency
% by VoI 8.6 43.2 21.8 13.6 12.0 C.) an?
c.
g
.Approx. so benzene content, %;
Toluene Bromine KO., g./100 g
nsa
Approx. toluene contenx,
c;,
...
...
l.i
...
1.3
4 9 8
8 2 0 5
14 4 46 0 20 3 9 7 8 0 O R
0 4
The experiments wit,li a partly aromatized produd; from it naphthenic naphtha (aromatic content 70%) have led to thr same results. In both cases, a serious operational diffic,ulty was experienced due to the formation, at relatively low temperatures, of a nonvolatile resin Fhich carbonized. The resin originates most' likely from dienic or similar constituent,s in the charging stock, as treatment of the charge with activated clay, or heating at 200" C. and subsequent distillation, removes the cause of the difficulty. The same degradation and condensation reactioiis could also be observed with coal tar eolvent naphtha, as shown b y Table V (1-3).
28 3 1 4602
In all expeiinients conditions \%ereadjusted to give a liquid produLt of an aromatic content of at least 85 to 90%. Oncr a concentration of aromatic hydrocarbons of 85 to 90% has been icached in the liquid product, its absolute quantity does not ch.inge anv further h ~ iiiing . longrr contart time. or higher l(tw
62
Fraction -_____ Benzene Toluene (75(10595O C.) 125O C.) 650 650 90 85 0.878 0,878
EXPERIMEkTAL
170 160150-
140
-
120-
0.8 42.7 19.2 8.8; 12,5j
13 42 15 9 12 2 3
20.5 1.4728 71
3.0 64.2 9.6 13.2
1.0 16.7 44.0 20.3
5 0 1 4966 94
10.5 1.4930 92
1 4910
6 0 1 4962
10 0 1 4926
97
93
Characteristics of benzene (7695') and toluene (95-126") fractions of cracked prodiicts Benzene Bromine No., g./lOO
... ... ...
17.0 11.6 10.8 0.g
130
Composition of liquid product, % b y wt. of charge u p t o 750 75-950 95-125O 125-150" Above 150°
... ...
16.1 40.6
15 90 4 1 4950 98
110
-
October 1951
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
TABLE IX. RECYCLING OF PARTLY AROMATIZED PRODUCT FROM CRACKING NAPHTHENIC NAPHTHA Recycle Charge Material boiling Material boiling below 150° C. below 125O C. Space velocity cc./co./hour Yield of liquid'product, % by wt. on charge
Density a t 20' C. of liquid product Composition of liquid product, % by vol. 75-95' C. (benzene) 95-125O (toluene) 125-150" (xylenes) Above 150° Aromatic content of benzene and toluene fraction, 7 by.vol. Benzene fraction Toluene fraction
0.050 61
0.064
60
0.050 85
0.042
66
After After After After Before Recy- Recy- Before Recy- RecyRecy- elins a t cling a t Recy- cling a t cling a t cling 680 C. 700 C. cling 68OOC. 700° C. 0.826 0 . 8 8 2 0 . 8 8 9 0 . 8 4 7 0.870 0 . 8 8 3 42.5
38:/) .. 68 71
20.6 26.4 8.2
96 98
24.5 26.3
44.7 32.3 11.9
..
98 99
peratures. Whenever possible, charges boiling over the full range from 100"to 200" C. were used. In a few cases-e.g., the sulfur dioxide extract of East Texas naphtha-narrower boiling fractions had to be used. ANALYSISOF CHARGING STOCKS. The charging stocks were distilled in a long column fitted with a Podbielniak spiral. Fractions were taken from 95" to 120' C., 120' to 150' C., and 150" to 180" C., and analyzed separately. The olefins were determined by bromine titration, the combined quantity of olefins and aromatics by treatment with Kattwinkel solution (concentrated sulfuric acid saturated with phosphorus pentoxide) and subsequent distillation (in order to remove any oil-soluble polymers and copolymers). From the aniline points of these distillates their naphthene content was calculated (19). The paraffins were obtained by difference to 100. The data so obtained are in good agreement with those derived from other recent analytical procedures based on physical constants (6, 6, 8, 9,1.4). CRACKING EXPERIMENTS. Table VI summarizes the cracking experiments with the charging stocks, to which Table I refers. The purity of the aromatized liquid can be judged from the example given in Figure 2, referring to Fischer-Tropsch oil. EXPERIMENTS WITH C.V.R. BENBOLE.Table VI1 gives the characteristics of the charging stock and Table VI11 summarizes the aromatizing cracking experiments. The sulfur content in a representative experiment had fallen from 1.20 to 0.63%, while that of the toluene cut was reduced from 0.63 to 0.38%. It was not possible to desulfurize the charge completely, perhaps because of the presence of thiophene derivatives.
68 70
34.7 23.6 7.1 13.6
31.8 20.0 4.8 12.4
96 98
99.5 99.6
2325
EXPERIMENTS WITH INCOMPLETELY AROMATIZEDXAPHTHENICNAPHTHA. Exneriments were carried out with two fractions-one in which the material boiling below 125' C. was used, and one in which all the material boiling up to 150" C. was taken. The former did not contain the xylene fraction, whereas the latter did. The characteristics of the two materials and the results of some representative experiments are presented in Table IX. ACKNOWLEDGMENT
The Fischer-Tropsch distillate in Table I was supplied by the National Chemical Laboratory (Teddington). The coal tar solvent naphtha- was made available bv the courtesv of Yorkshire Tar Distillers. LITERATURE CITED
Ashmore, S. A., and Penny, E. E., U. S. Patent 2,395,161 (Fob. 19, 1946).
Coulson, E. A., and Handley, R., J. Soc. Chem. Ind., 65, 398 (1946).
Coulson', E. A., Handley, R., Holt, E. C., and Stonestreet, D. A., Ibid., 65, 396 (1946).
Dunstan, A. E., et al., "Science of Petroleum." Vol. 11. D. 1173. London, Oxford University Press, 1938. Gooding, R. M., Adam, N. G., and R a l l , H. T., IND. ENO.CHEM., ANAI,. ED., 18, 2 (1946). Grosse, A. V., and Wackher, R. C., Ibdd., 11, 614 (1939). Krause, M. W., Nemzow, M. S., and Ssosakina, J. A., J. G ~ L . Chem. U.S.S.R., 5, 343, 356, 382 (1935); C h m . Zentr., 1936, I, 2722, 2729. Kurtz, S. S., Mills, I. W., Martin, C. C., Harvey, W. T., and Lipkin, M. R., IND.ENQ.CHEM.,ANAL. ED., 19, 175 (1947). Losowoi, A. W., Djakowa, M. K., and Stepanzew, T. G., J. Gen. Chem. U.S.S.R., 7, 1119 (1937); Chem. Zentr., 1938, 11, 1755. National Research Council Committee, "Chemistry of Coal Utilization," p. 1291, 1293, 1396 ff., New York, 1945. Nemzow, M. S., and Poletajew, A. W., J. Gen. Chem. U.S.S.R., 6, 892 (1936); Chem. Zentr. 1936, 11, 2878.
Rosen, Oil Gas J., 39 (Feb. 13, 1941). Saohanen, A. N., "The Chemical Constituents of Petroleum," p. 99, New York, Reinhold Publishing Corp., 1945. Starr, C. E., Jr., Tilton, J. A., and Hockberger, W. G., IND. ENG.CHEM.,39, 195 (1947). Weizmann, C., et al., IND.ENG.CHIM., 43, 2312 (1951). RE~CEIVED August 2, 1949. Contribution from the laboratories of The Weiemann Institute of Science, Rehovoth, Iarael; Petrooarbon Ltd., London Bridge, London E.C. 4, England; and the Grosvenor Laboratory, 25 Grosvenor Crescent Mews, London S.W. 1 , England.
(Aromatizing Cracking of Hydrocarbon Oils)
CONVERSION 'OF BUTYLENE INTO AROMATICS CHAIM WEIZMANN, VICTOR HENRI', AND ERNST BERGMANN The Weismann Institute of Science, Rehovoth, Israel
T
HE observation that in the high temperature formation of aromatic hydrocarbons from mineral oils butadiene plays a central part has led to experiments on the behavior of butylene (I-butylene) under dehydrogenating conditions. Obviously, the formation of the whole range of aromatics is less easy in this case than for mineral oil as their formation requires not only butadiene but other low molecular oleiins ( l a ) which are formed from 1
Deceased,
butylene less easily and not without the danger of concomitant carbonization, The conversion of low molecular olefins into aromatics has been studied before. Dunstan, Hague, and Wheeler (3, see also 1 , 3) observed in experiments in quartz tubes with a space velocity of 80 liters (gas) per hour and liter reactor volume the following yields of an aromatic liquid (no indication being given as to whether the liquid was fully aromatic or not),
