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Jalan, B. P.; Rao, Y. K. Carbon 1878, 16, 175-84. R. Soc.London Ser. A 1848, 193, 377-99. Long, F. J.; Sykes. K. W. ROC. Otto, K.; Bartoslewlcz. L.; Shelef. M. Fuel 1878 58, 85-91. Otto, K.; Bartosiewicz. L.; Shelef, M. Fuel 1878, 58, 565-72. Peter, S.; Woyke, 0.;Baumghrtei, G. Chem. Ing. Tech. 1878, 48, 742-49. Veraa, M. J.; Bell, A. T. Fuel 1878, 57, 194-200. Wicke, E.; Hedden, K.; Rossberg, M. "Beltrage der reaktionskinetischenForschung zur Technik der Vergasung und Verbrennung"; B.W.K., Band a, No. 6, June 1956. Yokohama, S.; Miyahara, K.; Tanaka, K.; Takakuwa, I.; Tashiro, J, Fuel 1878, 58, 510-14.
Berggren, JC.; Eklund, H.; Karlsson, H.; Svensson, 0. Chem. Eng. Sci. 1880. 35. 446-55. Bernando. C. A.; Trimm, D. L. Carbon 1878, 17, 115-20. BJerle, I.; Eklund, H.; Svensson, 0. 'Gasification of Swedish 011 Shale In a Fiuldlzed Bed Reactor"; paper presented at the Symposlum on the Gaslflcatbn and Liquefaction of Coal, U.N.-Economical Commission for Europe, Katowice, Poland, Apr 23-27, 1979. BJerle, I.; Eklund, H.; Svensson 0. Ind. Eng. Chem. Process Des. D e v . 1880. 19, 345-51. Bwnham. A. K. Fuel 1878, 58, 285-92. Carslaw, H. S.; Jaeger, J. C. "Conduction of Heat In Solids"; Oxford Universky Press, 1 9 5 9 p 234. Gadsby, J.; Hinshelwood, C. N.; Sykes, K. W. Roc. R. Soc. London Ser. A 1848, 787, 129-52. Hedden, K.; Kppper. H. H.; Schulze, V. Z . phvs. Chem. 1858, 22, 23. Hedden. K.; Lowe, A. Carbon 1867, 5 , 339-53.
Received for review February 4 , 1980 Revised manuscript received July 31, 1981 Accepted August 12,1981
Two-Stage Pyrolysis of Heavy Oils. 2. Pyrolysis of Taching Vacuum Residue and Arabian Light Atmospheric Residue for the Production of Olefins in a Flow-Type Reactor ToshlmHsu Suzukl, Maki Itoh, Masaru Mishlma, Yoshinobu Takegaml, and Yoshlhisa Watanabe Department of Hydrocarbon Chemlstty, Faculty of Engineering, Kyoto University, Kyoto 606, Japan
Two-stage pyrolysis of Taching vacuum residue and Arabian Light atmospheric residue was carried out using a flow-type reactor to manufacture lower olefins. I n this method, heavy oils were pyrolyzed at 440 "C to produce cracked oils, which were carried to a high-temperature zone (700-800 "C) to undergo subsequent pyrolysis. The operating Conditions at the high-temperature zone, temperature range of 700-825 "C and residence time of 0.35-1.5 s, were examined on the effect of the respective yield of olefins and aromatics. The highest ethylene yield of 27 wt % against feed was obtained at 800 O C , 0.4-0.7 s for the Taching sample and 23 wt % at 800 "C,1.0 s for the Arabian Light sample. The highest propylene yield was about 12 wt % for both samples. Total yield of C, to C, hydrocarbon gases showed a maximum, about 60%, both at 800 "C,0.35 s and 750 O C , 1.0 s for the Tachlng residue.
Table I. Properties of Sample Oils
Introduction
In a previous paper, we have demonstrated that the two-stage pyrolysis of vacuum residues using a batch-type reactor provides an excellent method for production of C2-C4 olefins (Suzuki et al., 1981). In this method, the reactor tube has two different reaction zones controlled at about 440 "C and 700-800 "C,respectively. Vacuum residues (mol wt 900-1OOO) are pyrolyzed into cracked oils at the first stage (the low temperature zone, 440 "C),which are carried to the second stage (the high-temperature zone) by an argon flow to undergo subsequent pyrolysis. Two distinct features of the procedure were apparent: (1)C2-C4 olefins and methane were obtained in high yields compared to the results of a direct pyrolysis of vacuum residues at high temperatures (700-800 "C); (2) pyrolysis residues obtained at the first stage below 440 "C were scarcely carbonized. The present paper deals with a two-stage pyrolysis of Taching vacuum residue and Arabian Light atmospheric residue with a semiflow system, and optimum conditions for the production of olefins are studied.
Arabian Light a.r.
41.7 870
48.3 420
wt % crude molecular weight a elemental analysis
c, %
H, %
s, %
N, % V, p p m b Ni, ppm Conradson carbon residue, wt % aromaticity
87.0 12.7 0.19 0.33 1.7 6.6 7.4
84.8 11.7 3.2 0.38 26 10 7.5
0.20
0.28
a Number-average molecular weight determined by vapor pressure osmometry. b Typical values from references. Determined by 13CNMR spectra.
atmospheric residue remains as vacuum residue by vacuum distillation; i.e., about 60% of vacuum gas oil is contained in it. Procedures. Figure 1 illustrates the experimental apparatus. A quartz reactor tube, 300 mm long, 18 mm i.d. at the lower section, and 8 mm at the upper section, was placed vertically in an electric furnace. The lower and the upper sections were heated independently and were set at 440 "C and 700-800 "C, respectively, by adjusting the
Experimental Section Materials. Properties of the oils used for pyrolysis are
shown in Table I. Detailed structural investigation of Taching vacuum residue has been described previously (Takegami et al., 1980). About 40 wt % of Arabian Light 0196-4305/82/1121-0149$01.25/0
Taching v.r.
0
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Table 11. Typical Material Balances for the Two-Stage Pyrolysis at 800 "C Taching Arabian v.r. Light ax. residence time, s
I Heater
2 Micro feeder 3 Quartz reaction tube
4 Thermocouple to digital mV meter 5 Inner tube with Pt wire helix
Figure 1. Apparatus used for the two-stage pyrolysis.
electric current. An inner tube on which platinum wire (0.3 "4) was wound helically was inserted in the lower section from the bottom of the reactor tube. A heavy oil was fed from the micro feeder through a hypodermic needle (1.0 mm 0.d.) to the top of the inner tube and was pyrolyzed during the down stream on the surface of the inner tube to give cracked oil. The cracked oil was carried to the upper section by argon flow to undergo subsequent pyrolysis. The oil not decomposed together with pyrolysis residue at the first stage further went down to a low-temperature area where no further cracking occurs. Taching vacuum residue and Arabian Light atmospheric residue were fed at 3.8 mg/min and 4.7 mg/min, respectively, for 30 min. The hot product was quenched by cooling the outlet of the reactor tube by air blowing. Condensable materials were collected with a glass wool plug and gaseous materials were collected for 20 min in the steady-state performance. Product gases were analyzed as described in part 1 (Suzuki et al., 1981), using a Shimadzu GC-3BF gas chromatograph (F.I.D.) with a 2.0 X 3 mm stainless steel column packed with Porapak Q, 80/lOO mesh, for mesh, for C,-C4 hydrocarbon gases, and with SE-30,60/80 benzene and toluene. Residence time at the second stage was controlled by changing the flow rate of argon gas. Typical material balances are shown in Table 11. Results and Discussion In the pyrolysis using the batch-type reactor described in part 1 (Suzuki et al., 1981),all the oils to be cracked were placed in the first stage in a platinum boat, so that the amount of the cracked oil carried to the second stage in a unit time could not be kept constant during the course of the reaction; heat transfer to the oil and residence time at the second stage were not uniform. Thus a systematic experimental approach with a variation of detailed reaction conditions was not carried out. In the present study, the effect of pyrolysis conditions at the second stage, temperature and residence time, on the yields of C2 to C4 olefins and aromatics were examined using a flow-type reactor. Temperature at the second stage described in this paper represent the maximum temperature of the zone. If the temperature profile of the high-temperature zone was plotted, temperature gradient was fairly small up to a maximum temperature minus 50". Therefore this zone was assigned to the high-temperature zone, and the calculated average temperature of the zone was about 15' lower than the maximum temperature. The residence time at the second stage was calculated from the volume of this zone.
product yields, wt % CH4 C*H4 C2H6 C3H4 C3H6 C3H.a C,H, + C4H8 CPlO C, -C4 total benzene toluene hydrogen oil, tar, and coke residue mass balancea
0.35
1.0
5.2 26.5 1.4 1.5 11.7 trace 9.8 0.1 56.3 3.8 1.0 0.5 13.9 19.0 94.5
10.6 22.8 1.6 0.9 9.1 trace 5.2 0.2 50.4 4.5 1 .o 0.7 33.1 7.0 96.0
Losses mainly consist of C,+ alkanes and alkenes which do not condense at the end of the reactor tube and hydrogen sulfide.
C,
I
-C4
total
60 L ,
0'
'
700 750 800 Temperature of the 2nd Stage ('c )
Figure 2. Hydrocarbon gas yields from the two-stage pyrolysis of Taching vacuum residue. Effect of the temperature at the residence time of 1.0 s.
The temperature of the first stage was set at 440 "C, the highest temperature at which residues underwent pyrolysis without severe carbonization. Effect of the Temperature of the Second Stage on the Pyrolysis of Taching Vacuum Residue. In the present reactor system, the low-temperature pyrolysis zone was slightly affected by the heat radiation from the hightemperature zone. The zone set at 440 "C was only about 1 cm of the top of the inner tube. Oils that went down below this zone did not undergo further pyrolysis, so that the oils that went down below the zone contained not only pyrolysis residues but also unreacted oils. The amount of pyrolysis residue deviated 20 f 5% in the pyrolysis of the Taching vacuum residue. Therefore yields of hydrocarbon gases were corrected against the amount of the pyrolysis residue and were expressed as weight percent of the low temperature pyrolyzate (eq 1). corrected yield = (wt % of gas x 100)/(100 - w t % of residue) (1)
Ind. Eng. Chem. Process Des. Dev., Vol. 21, No. 1, 1982 151
40
2 0
I
I
0
I
1
0'
I 05 10 15 Residence time at the 2nd stage (sec)
Figure 3. Methane and ethylene yields from the two-stage pyrolysis
v
0.5 10 15 Residence time at the 2nd stage (sec)
of Taching vacuum residue. Effect of the residence time at temperatures of 750 and 800 O C .
Figure 4. Propylene and C4 olefins yields from the two-stage pyrolysis of Taching vacuum residue. Effect of the residence time at temperatures of 750 and 800 O C .
Figure 2 shows the yields of C1 to C4hydrocarbon gases produced by the pyrolysis of Taching vacuum residue, in which the residence time was kept at about 1.0 s and the temperature of the second stage was varied from 700 to 825 "C. Methane yield was 5.9% at 700 "C, and 11.4% at 825 "C. Ethylene yield increased from 24% to 30% in the temperature range of 700-750 "C, and was slightly increased to about 33% as the temperature increased to 825 "C. Ethane yield was only 1.5-1.7% and was almost constant in these conditions. Propylene yield showed a maximum (15.5%) at about 750 "C and rapidly decreased a t over 750 "C. Propane was formed in only 0.1-0.5%. Methylacetylene appeared notably at over 750 "C and amounted to 1.0-1.3%. C4 olefins consisted mainly of 1,3-butadiene, followed by 1-butene, and their yield also decreased with an increase in temperatures. Butanes were also produced in 0.3-1.0% yield. Total yield of C1 to C4 hydrocarbon gases showed a maximum at about 750 "C and amounted to 69%. Hydrogen yield was about 0.4% a t 700 "C and 0.8% at 800 "C. As discussed later, 3-7% benzene and about 1%toluene were identified. Pyrolysis residue was obtained in 1525% yield. Besides C1-C4 hydrocarbons, benzene, and toluene, 12-18% oil and tar were condensed at the reactor outlet, and around 4% coke was formed on the wall of the reactor tube at the second stage. Consequently the material balance of about 95% was obtained. The loss of material was considered to be due to aliphatic hydrocarbons higher than Cg,xylenes, and hydrogen sulfide. Effect of t h e Residence Time at t h e Second Stage on the Pyrolysis of Taching Vacuum Residue. Figures 3 and 4 show the yields of C1 to C4hydrocarbons produced by the pyrolysis of Taching vacuum residue, in which the residence time (further denoted as 7)at the second stage was varied from 0.35 to 1.5 s a t 750 and 800 "C, respectively. As the residence time was controlled by changing the flow rate of argon gas, the dilution ratio was also varied in a strict sense. The dilution ratio, however, was not considered in the present study as the amount of argon gas was extremely larger than the low-temperature pyrolysate, that is close to infinite dilution. Methane yield was 6.5% both at 800 "C, 0.35 s and 750 "C, 0.7 s, and reached almost 12% at 800 "C, 1.4 s. Ethylene yield showed maxima at about 7 0.5 s at 800 "C,
and at 7 1.0 s at 750 "C. Propylene yield also showed maximum at 7 1.0 s at 750 "C. At 800 "C; however, maximum propylene yield was obtained at extremely shorter residence time (
