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Two-stage pyrolysis of heavy oils. 1. Pyrolysis of vacuum residues for olefin production in a batch-type reactor
Two-stage of vacuum batch-type
pyrolysis of heavy oils. I, Pyrolysis residues for olefin production in a reactor
Toshimitsu Suzuki, Maki and Yoshinobu Takegami
Itoh,
Department of Hydrocarbon Chemistry, 606, Japan (Received 9 February 1981)
Masaru Faculty
Mishima,
Yoshihisa
of Engineering,
Watanabe
Kyoto University,
Kyoto
Twostage pyrolysis of Iranian heavy and Taching vacuum residues using a batch-type reactor has been carried out to produce lower olefins. The reactor tube was constructed with two zones in which temperatures were controlled at ~440’C and 700-800°C. Vacuum residues (MW 900-1000) were pyrolysed into cracked oils (MW 300-4gO) in the first, low-temperature, stage, which were carried to the second, high-temperature, stage by an argon flow to undergo subsequent pyrolysis. In comparison with the vacuum residues pyrolysed directly at high temperature, the ethylene yield increased by a factor of 1.5-l .8 using the two-stage procedure. 26% of ethylene was obtained from the Taching vacuum residue and 15% from the Iranian Heavy residue. Pyrolysis residues can be recovered without carbonization under the conditions of the first stage.
Conversion of heavy oils such as atmospheric and vacuum residues to produce lighter products is of current industrial interest. These residues contain asphaltenes concentrated through distillation and have a tendency to coke on pyrolysis. Many devices have been introduced to overcome the problem. In Flexicoking’, atmospheric residues or vacuum residues are pyrolysed on fluidized cokes at high temperature to produce gases and oils, the resultant coke being gasified in air and steam. Crude oil is directly cracked into ethylene or acetylene by superheated steam in the process of Kureha Chemical Industry Co., Ltd., and the residue can be obtained as pitches’. In the KK-process using a fluidized-bed reactor containing carbon particles as a heat carrier, the pyrolysis of a wide range of heavy oils, crudes to vacuum residues, has been carried out to manufacture lower olefins3. The coke produced was gasified to provide heat to the carrier which returned to the fluidized-bed reactor. In the test plant, 14.4% yield of ethylene was obtained from Kafji vacuum residue. ‘Mitsui’ has reported the steam cracking of heavy oils using molten salts (COSMOS Process), showing relatively high yields of ethylene from Minas or Taching crudes4. In this process, carbon and pitch, produced via the thermal cracking, do not adhere to the internal wall of the reactor tube because of the wet wall effect. In the Ubeprocess5, a clean fuel gas can be obtained from heavy oils using partial oxidation in combination with pyrolysis. The structural investigation on vacuum residues using ’ 3C n.m.r. spectroscopy6 clearly shows that long paraIIinic straight-chains (-(CH,),-n = 14-20) are contained in vacuum residues. This type of residual oil is expected to produce a significant amount of lower olefins on pyrolysis. In Japan, because of the lack of strong caking coals, production of binder pitch as an additive to coals is required for the making of metallurgical coke. For this purpose, vacuum residues must be reformed by thermal treatment. 001fS2361/81/100961-0606%2.00 01981 IPC Business Press
This paper describes the pyrolysis of vacuum residues using a batch-type reactor having two different reaction zones controlled at different temperatures, ~444O’C and 700-800°C respectively. Vacuum residues are pyrolysed at the first, low-temperature, stage to produce cracked oils, and an argon flow carries the oils to the second, hightemperature, stage for subsequent pyrolysis. Pyrolysis residues obtained at the first stage are scarcely carbonized under these conditions. The procedure is defined as ‘twostage pyrolysis’. EXPERIMENTAL Materials
The oils used for the pyrolysis are Iranian heavy and Taching (from China) vacuum residues, supplied by Maruzen Oil Co. and Daikyo Oil Co., respectively. Properties of these oils are Iranian heavy vacuum residue: average molecular weight, 1000; C, 83.6; H, 10.2 wt%; aromaticity, 0.35. Taching vacuum residue: average molecular weight, 870; C, 87.0; H, 12.7 wtT/,; aromaticity, 0.20. Detailed structural data of these oils have been reported previously6. Procedures
The pyrolyses were carried out with a batch-type apparatus (Figure I). A quartz reactor tube (5) (500 mm long and 18-8 mm i.d.) was place horizontally through an electric furnace (1) (1 kW, 300 mm long, and 50 mm i.d.). A copper heat block (9) (50 mm long) was placed at the centre of the furnace, and the temperature of the reactor tube was held at 43G45O”C by controlling the electric current of the main heater. The end of the reactor tube had a narrower inner diameter in order to give shorter residence times. An auxiliary heater (4) was placed in this section of the reactor tube in the furnace to establish a hightemperature zone (700-800°C).
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1981,
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In order to obtain a rapid heating rate, 100 mg of vacuum residue in a platinum boat (2) (2.7 g) was inserted into the low-temperature zone with a glass rod (10) through a G-ring seal (6) under an argon flow (20 ml min-’ at room temperature). The cracked oils and gases produced at the first stage (~440°C) were carried to the second stage (70~800°C) by the argon flow to undergo subsequent pyrolysis. After a certain reaction time, the platinum boat was removed and the amount of the pyrolysis residue was weighed. The product gases were collected in a gas burette. Chromotographic analyses of the product gases were made using Shimadzu Model GC3BF and GC-3BT gas chromatographs. C,-C, hydrocarbon gases were analysed with Porapak Q(SCr 100 mesh, 3.0 mm i.d. x 2.0 m), and benzene and toluene with SE-30 (60-80 mesh, 3.0 mm id. x 2.9 m) at 80°C with a hydrogen flame ionization detector using nitrogen as a carrier gas. Hydrogen was analysed with active carbon (6&80 mesh, 3.0 mm i.d. x 2.9 m) at 30°C with a thermal conductivity detector using nitrogen as a carrier gas. Prior absolute calibrations of the analysis the to chromatographs were made against known amounts of pure hydrocarbons and hydrogen.
RESULTS AND DISCUSSION One-stage pyrolysis Table I summarizes the yields of hydrocarbon gases (expressed as weight percentage of feed) produced by the pyrolysis of Iranian heavy vacuum residue. In runs 1-3,
1. Ekc,m Pla,lnum
z
3 TC (0
6. 0 rang
1wmcc boat
4. Awhy
Apparatus
Tab/e 1 Hydrocarbon
‘I”
8. ICC trap 9. copperMat bl0d
heater
10. Glass
5 Quart* reaction tube Figure 7 residues
seat
7 Al ccollng
*,p,ta, nl” meter
used for the twostage
rod
pyrolysis
of vacuum
gas yield from the pyrolysis of Iranian
heat was only supplied by the main electric furnace, and the maximum temperature of the furnace was in the region of the copper heat block. The platinum boat containing vacuum residue was inserted directly into the zone of highest temperature. In runs 1 and 2, the vacuum residue was pyrolysed at 450°C for 20 min and 500°C for 10 min, respectively. Approximately 80 wt% of the sample was cracked into oil and gas, however, the total yield of C,-C, hydrocarbon gases was only 3-6 wt%. Thus, the main product was cracked oil. In contrast at a higher temperature, 705°C (run 3) the pyrolysis was completed very rapidly with evolution of large amounts of gases. The total yield of C,-C, gases increased to 36.9 wt%. Yields of methane (9.4 wt%), ethylene (8.1 wt%), and propylene (8.1 wt%) were much higher than those of the pyrolysis of Arabian medium vacuum residue using a vertical-type reactor reported by Morita et al.‘. This difference is due to the rapid heating rate and the short residence time in the onestage pyrolysis process. The yields of hydrocarbon gases from the pyrolysis of Taching vacuum residue are summarized in Table 2. The one-stage pyrolysis at 705°C and 765°C (runs 12 and 13) showed the influence of rapid heating rate, giving high yield of C,-C, hydrocarbon gases, i.e. ~50 wt%. The amount of residues after pyrolysis uersus reaction time at 430,440, and 450°C of both samples are plotted in Figure 2. The rate of pyrolysis increased with increasing followed temperature. The pyrolysis reaction approximately first-order kinetics up to 70 wt% conversion for Iranian heavy vacuum residue and 80 wt% for Taching residues. Values of the pyrolysis residues from Iranian heavy and Taching residues were w 20 and 5 wt%, respectively, and correspond to the Conradson carbon residue of these vacuum residues, 23 and 7 wt%, respectively. For Iranian heavy vacuum residues, the pyrolysis residue was completely soluble in carbon disulphide to conversions of 70 wt%, and was slightly carbonized (insoluble in carbon disulphide) when the conversion exceeded w 75 wt%. The time required for the conversion of 75 wt% was approximately 45 min at 430°C 30 min at 440°C 20 min at 450°C and 15 min at 460°C. The extent of carbonization at 75 wt% conversion, however, depended strongly on the pyrolysis temperature. At 75% conversion, the pyrolysis residue was completely soluble in carbon disulphide at 430°C and most of the
heavy vacuum residue Gas yield (wt %)b
Time Temp. (“Cl lststage 2nd stage (min)
Residuea fwt %I
1 2 3
450 500 705
20 10 10
24 20 -
0.6 1.1 9.4
4 5 6 7 8 9 10 11
440 430 440 450 460 500 440 440
25 45 30 20 15 10 30 30
24 25 24 24 21 19 23 23
7.8 8.2 9.4 9.3 9.7 9.9 10.3 10.5
Run
a b ’ o
705 765 765 765 765 765 BOO 825
CH,
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FUEL, 1981, Vol 60, October
Toluened
TotalC
-
0.8 1.3 4.5
3.0 5.8 36.9
_ -
-
0.5 0.3 0.3 0.2 0.2 0.4 0.3
6.3 3.1 2.9 3.2 3.0 3.1 1.7 1.2
39.8 34.3 34.8 36.2 37.4 37.5 33.2 30.6
3.1 3.6 3.8 2.4 4.0 3.7 4.0 3.6
1.4 1.2 1.3 0.8 1.3 1.3 1 .o 0.8
C3H6
C3’+3
C3”4
0.1 0.6 8.1
0.6 1.0 5.5
0.4 1.0 8.1
0.5 0.8 1.3
12.2 14.0 13.7 13.6 13.7 11.9 15.1 15.0
3.3 1.9 2.2 2.7 3.1 4.1 1.7 1.2
9.7 6.6 6.2 7.1 7.4 7.8 4.2 2.7
0.7 0.2 0.2 0.1 0.3 0.5 trace trace
Residue in the platinum boat after pyrolysis 0.5-0.9 wt % (5-9 ml) of Hz and trace amount of CO end CO2 were also present Total yield of Cr-C4 gases Benzene and toluene present in the gases collected
Benzened
C4
C2H6
C2H4
Two-stage pyrolysis of heavy oils (1): T. Suzuki et al. Table 2 Hydrocarbon
gas yield from the pyrolysis of Taching
vacuum residue Gas yield fwt %)b
Time
Residuea
Run
Temp. (“C) lststage 2ndstage
(min)
fwt %)
CH4
C2H4
C2H6
C3H6
12 13 14 15 16 17 18 19 20 21
705 765 440 430 440 450 460 480 500 440
10 5 30 45 30 20 15 10 10 30
14 17 12 13 10 5 6 15
8.6 10.3 8.4 9.4 11 .o 10.9 11.9 11.8 11.3 11.7
13.3 17.7 23.3 24.5 26.3 23.9 25.7 23.6 21.7 26.2
5.1 4.9 2.6 1.6 2.2 2.4 2.9 3.5 3.9 1.6
10.3 10.5 14.2 9.3 9.2 9.0 9.4 10.2 10.8 5.3
a b ’ d
_ 705 765 765 765 765 765 765 800
0.9 0.8 0.5 0.3 0.2 0.2 0.2 0.4 0.6 trace
Benzened
Toluened
C4
TotalC
-
5.9
44.3
_
-
_ 0.6 0.4 0.3 0.3 0.2 0.2 0.5
6.9 9.7 5.4 4.7 4.6 4.5 4.6 4.9 2.9
51.2 58.7 51.1 54.0 51.3 54.9 54.4 53.4 48.2
4.2 4.7 5.8 7.2 6.8 6.9 6.7 6.1 6.6
0.8 1.6 1.4 1.9 1.7 1.7 1.5 1.6 1.2
C3H4
C3’+3
Residue in the platinum boat after pyrolysis 0.5-0.7 wt % (6-8 ml) of Hz and trace amount of CO and CO2 were also present Total yield of C, to C4 gases Benzene and toluene present in the gases collected
a
b
180
160
140
120
100
SO
60
40
20
fppm from
- -A__ -A._
I 0
4
10
20
30 Reaction
40 time(min
)
Figure 3 (fa, 0.36) (fa, 0.64)
0
TMS)
13C n.m.r. spectra of (a) Arabian light vacuum residue and (b) its residue after pyrolysis at 440°C for 30 min
a
Figure 2 Pyrolysis behaviour of vacuum residues at various temperatures. The amount of pyrolysis residue versus reaction time. -, lranium heavy vacuum residue: A, 430°C; 0,440”C; 0,450”C; - - - -, Taching vacuum residue: *, 43O’C; l,44O”C; ., 450°C
pyrolysis residue was insoluble at 460°C. The temperature range 43S46O”C is the same as that used in the visbreaking process and a slight change in pyrolysis temperatures greatly affects the reaction rate and the properties of the pyrolysis residues. Taching vacuum residue gave a similar conversion to that for Iranian heavy, 87-88 wtY&at 430°C for 60 min, 440°C for 30 min, 450°C for 20 min, and 460°C for 15 min, respectively. However, no carbonization of the pyrolysis residue occurred. Properties of the pyrolysis residues and cracked oils produced by the low-temperature pyrolysis 13C n.m.r. spectra of Arabian light and Taching
vacuum residues and their pyrolysis residues produced at 440°C for 30 min are shown in Figure 3 and 4, respectively.
b
180
160
140
120
100
60
60
40 (ppm
Figure 4 (fa, 0.20) (fa, 0.39)
20 from
0 TMS)
13C n.m.r. spectra of (a) Taching vacuum residue and lb) its residue after pyrolysis at 449’C for 30 min
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1981,
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Two-stage pyrolysis of heavy oils (1):
T. Suzuki et al.
a
L CHCl3
X16--+----
1
9
6
7
6
5
160
140
120
100
4
:pprn
fL
449
0
b
160
80
60
40
20
O-
( ppm from TMS 1 1H and 1% n.m.r. spectra of the cracked oil from the Figure 5 pyrolysis of Taching vacuum residue at 440°C for 30 min (Mn, 405; H/C, 1.87; f,, 0.13). (a) proton spectrum; (bl carbon-13 spectrum
Properties of Arabian light vacuum residue are similar to those of Iranian heavy’s, and the i3C n.m.r. spectra of the pyrolysis residues were almost the same. As reported previously6, several sharp peaks appearing in the aliphatic region of the spectra of vacuum residues are assignable: +CH,),-n > 7, 29.7 ppm; CH,-(CH,),-n > 3, 14.1 ppm; CH,-CH,4CH,),n 22, 22.7 ppm, etc. One average molecule of Middle East vacuum residues contains a paraffinic straight-chain of cu. 15 carbon atoms, and for Taching vacuum residues >20 carbon atoms. Recently Simm and Steedman’ presented some evidence supporting this finding by isolating the straightchain alkane fraction as urea adducts from the liquid pyrolysate obtained from asphaltenes at 500°C. They showed that a long straight-chain alkane series was contained in asphaltenes, running from C, 1 to C,, for the Middle East asphaltene, and from C,, to C,s for a Venezuelan asphaltene’. These findings indicate that pyrolysis of vacuum residues to produce lower oletins is more effective than pyrolysing heavy oils from coal hydrogenation or tar sand bitumen containing only shorter methylene chains. The ’ 3C n.m.r. spectra of the Arabian light and Taching pyrolysis residues show some differences. As seen in Figure 3, the sharp characteristic peaks in the aliphatic region almost disappear in the spectrum of the Arabian light pyrolysis residue indicating that most of the alkyl chains attached to aromatic ring systems are broken off into cracked oil. The value of aromaticity of the pyrolysis residue was 0.64, even higher than that of the original asphaltene, 0.53 (original vacuum residue, 0.36). The ratio
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FUEL, 1981, Vol 60, October
of H/C was w 0.8. This pyrolysis residue can be considered to be similar to pitches obtained by the Eureka process’ or the Cherry-P process l”*ll judging from the H/C ratio, the solubility in carbon disulphide, the high aromaticity, and the fluidity at elevated temperature, and, therefore, can be used as an additive in the manufacture of metallurgical coke from non-caking coals. For the Taching vacuum residue, the aromaticity of the pyrolysis residue increased to 0.39 from the 0.20 of the original oil. However, the pattern of the spectrum was almost the same as that of the original oil. As mentioned previously, cracked oil was the main product of the pyrolysis at CQ.450°C. Average molecular weights of the cracked oils from Iranian heavy and Taching vacuum residues were 330 and 400, which were one third and one half of that of the original oil, respectively. As Taching vacuum residue contains a large amount of aliphatic carbon atoms, the cracked oil can be distilled easily even when its molecular weight is high: consequently the molecular weight of Taching cracked oil appeared higher than that of Iranian heavy. Figure 5 shows ‘H and 13C n.m.r. spectra of the cracked oil from the pyrolysis of Taching vacuum residue at 440°C for 30 min. The pattern of the peaks in the aliphatic region of the ’ 3C n.m.r. spectrum was similar to that of the original oil. The value of aromaticity decreased to 0.13 from the 0.20 of the original oil, indicating that fused aromatic ring systems remained in the pyrolysis residue. Also, some peaks can be seen in the olefin region of the ‘H n.m.r. spectrum and sharp peaks assignable to a terminal olefin, 139 and 114 ppm, can be seen in the 13C n.m.r. spectrum The ‘H and ’ 3C n.m.r. spectra of the cracked oil of Iranian heavy vacuum residue were similar to those of Taching vacuum residues. These findings suggest that the reaction occurring in the low-temperature zone is not simple distillation, but degradation of the large molecules of the vacuum residue to produce lighter cracked oils like vacuum gas oils. As seen from the 13C n.m.r. spectrum, this cracked oil contains long, paraflinic straight-chains similar to the original vacuum residue. Two-stage pyrolysis: comparison with one-stage pyrolysis
The twostage pyrolysis was carried out with the intention of producing lower olefins by pyrolysing the cracked oi< as obtained from the one-stage pyrolysis, at higher temperatures. Runs 4-l 1 in Table 1 and 14-21 in Table 2 show the results of the twc+stage pyrolysis of Iranian heavy and Taching vacuum residues, respectively. The temperature of the second, hightemperature zone given in the Tables indicates the maximum temperature of the zone, average temperature of the zone (80 mm long) was w20°C lower than the maximum temperature. The residence time of the lowtemperature pyrolysate at the second stage was estimated from the residence time of argon gas at this zone from the volume of the reactor tube, its flow rate, and the average temperature. In the present study, all the experiments were conducted at the residence time of ~3 s. Inserting the platinum boat containing the vacuum residues into the first, low-temperature zone, the residues gradually undergo low-temperature pyrolysis, and the cracked oil (in gas or vapour form) is carried to the second stage by an argon flow for subsequent pyrolysis, from which lower hydrocarbon gases are produced. Coke produced near the outlet of the reactor tube could be
Two-stage pyrolysis
430-765’C 45 min.
440-76SC 33 n-4”.
450-765T
m mln.
460-765-C 15 min.
WO-765T 10 min
Figure 6 Distribution of products obtained from the pyrolysis of lraniun heavy vacuum residue. 0, CH4; n, CZH4; 0, C2H6; A, C3H6; A, CsHa, X, C4; ( 1,yield in wt %
reduced by cooling the reactor tube with an aluminum cooling fin by air blowing. Comparing the gas yields from Iranian heavy vacuum residue by the one-stage pyrolysis at 705°C (run 3) with those by the two-stage pyrolysis at 440-705°C (run 4), the yields of ethylene and propylene increased from 8.1 to 12.2 wt% and from 8.1 to 9.7 wt%, respectively, whereas the methane yields decreased from 9.4 to 7.8 wt%. The total yield of C,-C, hydrocarbons slightly increased from 36.9 to 39.8 wt%. For the Taching vacuum residue, the trend was similar to that of Iranian heavy. Comparing the results of the one-stage pyrolysis (run 12, 705°C; run 13, 765°C) with those of the twestage pyrolysis (run 14,440705°C; run 15,44&765”C), yields of olefins increased and saturated hydrocarbons decreased. The ethylene yield increased markedly from 13.3 (run 12) to 23.3 wt% (run 14), particularly at 705°C. The pyrolysis residue of the one-stage pyrolysis at cu. 700°C was completely carbonized. The pyrolysis residue of the two-stage pyrolysis, however, was not carbonized. By pyrolysing the cracked oil the asphaltenes which would cause coking remain in the residue, whereas the lower olefins are obtained in high yield. Effect of the temperature of the first stage
The temperature of the first stage was varied from 430 to 500°C while the temperature of the second stage was fixed at 765°C (Table 1, runs 5-9; Table 2, runs 15-20). The product distribution in mol% of hydrocarbon gases from C,-C, is shown in Figures 6 and 7. In order to compare the yields of the hydrocarbon gases, conversion of the pyrolysis was kept constant by adjusting the reaction time. Pyrolysis of Iranian Heavy vacuum residue (Figure 6), yielded a pyrolysis residue of ~24% at 43o”C, 45 min; 44o”C, 30 min; 450°C 20 min; and 46o”C, 15 min; and was 19% at 5oo”C, 10 min. The total yield of C,-C, hydrocarbons was always ca. 36%. As shown in Figure 6, the proportion of ethylene decreased, and that of methane, ethane, and propylene increased with increase in the temperature of the’first stage. The trend was similar for the Taching vacuum residue, as shown in Figure 7. For both vacuum residues the ethylene yield decreased when the first stage was >45O”C and carbonization of the
of heavy oils (1): T. Suzuki et al.
pyrolysis residue was accelerated at higher temperatures. These changes in the product distribution can be explained as follows: (1) When a more severe reaction condition is applied by raising the temperature of the first stage, production of methane at the first stage increases. This methane does not undergo further pyrolysis at the second stage, thus the overall result is an increase in methane yield. (2) Pyrolysis at high temperature (500°C) of vacuum residue at the first stage causes extensive bond scission to give cracked oil containing shorter paraffinic straight-chains than that pyrolysed at a lower temperature (43&45O”C). Pyrolysis of oils containing shorter paraflinic straight-chains at high temperature (70CN300°C, the second stage) gives lower yields of ethylene. Yields of the hydrocarbon gases did not change greatly when the first stage was between 430°C and 460°C. For the Iranian heavy vacuum residue, the pyrolysis residue was greatly carbonized at >45O”C, and the rate of the reaction was very slow at ~430°C. Consequently, the optimum condition for the first stage in this procedure was determined to be 440°C for 30 min. For the Taching vacuum residue, the pyrolysis residue was scarcely carbonized even at 450°C for 20 min or 460°C for 15 min, as the yield of the pyrolysis residue (12-13 wt%) was significantly more than the ultimate yield (5 wt%). The conditions at the first stage, 450°C for 20 min or 460°C for 15 min, can be applied for this vacuum residue without excessive carbonization. Efict
of the temperature of the second stage
The temperature of the second stage was varied from 705°C to 825°C while the condition of the first stage was fixed at 440°C for 30 min. For the Iranian heavy vacuum residue, the ethylene yield was 12 wt% at 705°C (run 4), and increased to 14 wt% at 765°C (run 6), and 15 wt% at 800 and 825°C (runs 10 and 11). The total yield of C,-C, hydrocarbons, however, decreased from 40 to 31 wt%, because the yields of C, and C, hydrocarbons decreased with an increase in temperature. For the Taching vacuum residue, the ethylene yields were 23 wt% at 705°C (run 14) and 26 wto/, at 765°C (run 16) and also at 800°C (run 21). Yields of C, and C, hydrocarbons also decreased and the total yields of C,-C, gases were 59, 54 and 48 wt% at 705”C, 765°C and 8oo”C, respectively. Evidently, a high temperature, e.g. SOO”C,and a residence time of w 3 s are
60
I -(24.5)
?
40
(26 3)
(23 9)
+-----
(257)
I2361
(2171
Figure 7 Distribution of products obtained from the pyrolysis of Taching vacuum residue. 0, CH4; n, C2H4;0, C2He; ., C3H6; A, CaHa; X, C4; ( 1,yield in wt %
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sufficiently severe for the production of gaseous hydrocarbons in the two-stage pyrolysis procedure.
2 3 4
ACKNOWLEDGEMENT This work is supported in part by a Grant in Aid for Scientific Research, from the Ministry of Education, Japan (No. 411008).
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Kohno, H. Kagakukogaku 1974, 38, 710 Takegami, Y., Watanabe, Y., Suzuki,T., Mitsudo, T. and Itoh, M. Fuel 1980, 59, 253 Morita, Y., Ota, K., Izumi, K. and Yamazaki, T. J. Fuel Sot. Japan 1974,53,959
9
Simm, I. and Steedman, W. Fuel 1980, 59, 669 Takahashi, R. and Washimi, K. Hydrocarbon Processing 1976,
10 11
Ueda, K. and Sasaki, S. J. Japan Petrol. Inst. 1976, 19, 417 Oka, S., Kimoto, J., Matsui, H., Seki, H. and Kaneko, M. Am.
55, (1 1), 93
REFERENCES Blaser, D. E. and Edelman, A. M. 43 Midyear API Relining Meeting, Toronto, May 10, 1978
Kunugi, T., Kunii, D., Tominaga, H., Sakai, T., Mabuchi, S. and Takeshige, K. J. Japan Petrol. Inst. 1973, 16, 232, 238, 241 Yamaguchi, F., Sakai, A., Yoshitake, M. and Saegusa, H. Am. Chem. Sot. Div. Petrol. Chem. Preprints 1979, 24, 264
5 6
8
1
Wilkinson, L. A. and Gomi, S. Hydrocarbon Processing 1974,53, (5), 109
Chem. Sot. Diu. Petrol. Chem. Preprints 1979, 24, 678
pyrolysis of heavy oils. I, Pyrolysis residues for olefin production in a reactor
Toshimitsu Suzuki, Maki and Yoshinobu Takegami
Itoh,
Department of Hydrocarbon Chemistry, 606, Japan (Received 9 February 1981)
Masaru Faculty
Mishima,
Yoshihisa
of Engineering,
Watanabe
Kyoto University,
Kyoto
Twostage pyrolysis of Iranian heavy and Taching vacuum residues using a batch-type reactor has been carried out to produce lower olefins. The reactor tube was constructed with two zones in which temperatures were controlled at ~440’C and 700-800°C. Vacuum residues (MW 900-1000) were pyrolysed into cracked oils (MW 300-4gO) in the first, low-temperature, stage, which were carried to the second, high-temperature, stage by an argon flow to undergo subsequent pyrolysis. In comparison with the vacuum residues pyrolysed directly at high temperature, the ethylene yield increased by a factor of 1.5-l .8 using the two-stage procedure. 26% of ethylene was obtained from the Taching vacuum residue and 15% from the Iranian Heavy residue. Pyrolysis residues can be recovered without carbonization under the conditions of the first stage.
Conversion of heavy oils such as atmospheric and vacuum residues to produce lighter products is of current industrial interest. These residues contain asphaltenes concentrated through distillation and have a tendency to coke on pyrolysis. Many devices have been introduced to overcome the problem. In Flexicoking’, atmospheric residues or vacuum residues are pyrolysed on fluidized cokes at high temperature to produce gases and oils, the resultant coke being gasified in air and steam. Crude oil is directly cracked into ethylene or acetylene by superheated steam in the process of Kureha Chemical Industry Co., Ltd., and the residue can be obtained as pitches’. In the KK-process using a fluidized-bed reactor containing carbon particles as a heat carrier, the pyrolysis of a wide range of heavy oils, crudes to vacuum residues, has been carried out to manufacture lower olefins3. The coke produced was gasified to provide heat to the carrier which returned to the fluidized-bed reactor. In the test plant, 14.4% yield of ethylene was obtained from Kafji vacuum residue. ‘Mitsui’ has reported the steam cracking of heavy oils using molten salts (COSMOS Process), showing relatively high yields of ethylene from Minas or Taching crudes4. In this process, carbon and pitch, produced via the thermal cracking, do not adhere to the internal wall of the reactor tube because of the wet wall effect. In the Ubeprocess5, a clean fuel gas can be obtained from heavy oils using partial oxidation in combination with pyrolysis. The structural investigation on vacuum residues using ’ 3C n.m.r. spectroscopy6 clearly shows that long paraIIinic straight-chains (-(CH,),-n = 14-20) are contained in vacuum residues. This type of residual oil is expected to produce a significant amount of lower olefins on pyrolysis. In Japan, because of the lack of strong caking coals, production of binder pitch as an additive to coals is required for the making of metallurgical coke. For this purpose, vacuum residues must be reformed by thermal treatment. 001fS2361/81/100961-0606%2.00 01981 IPC Business Press
This paper describes the pyrolysis of vacuum residues using a batch-type reactor having two different reaction zones controlled at different temperatures, ~444O’C and 700-800°C respectively. Vacuum residues are pyrolysed at the first, low-temperature, stage to produce cracked oils, and an argon flow carries the oils to the second, hightemperature, stage for subsequent pyrolysis. Pyrolysis residues obtained at the first stage are scarcely carbonized under these conditions. The procedure is defined as ‘twostage pyrolysis’. EXPERIMENTAL Materials
The oils used for the pyrolysis are Iranian heavy and Taching (from China) vacuum residues, supplied by Maruzen Oil Co. and Daikyo Oil Co., respectively. Properties of these oils are Iranian heavy vacuum residue: average molecular weight, 1000; C, 83.6; H, 10.2 wt%; aromaticity, 0.35. Taching vacuum residue: average molecular weight, 870; C, 87.0; H, 12.7 wtT/,; aromaticity, 0.20. Detailed structural data of these oils have been reported previously6. Procedures
The pyrolyses were carried out with a batch-type apparatus (Figure I). A quartz reactor tube (5) (500 mm long and 18-8 mm i.d.) was place horizontally through an electric furnace (1) (1 kW, 300 mm long, and 50 mm i.d.). A copper heat block (9) (50 mm long) was placed at the centre of the furnace, and the temperature of the reactor tube was held at 43G45O”C by controlling the electric current of the main heater. The end of the reactor tube had a narrower inner diameter in order to give shorter residence times. An auxiliary heater (4) was placed in this section of the reactor tube in the furnace to establish a hightemperature zone (700-800°C).
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In order to obtain a rapid heating rate, 100 mg of vacuum residue in a platinum boat (2) (2.7 g) was inserted into the low-temperature zone with a glass rod (10) through a G-ring seal (6) under an argon flow (20 ml min-’ at room temperature). The cracked oils and gases produced at the first stage (~440°C) were carried to the second stage (70~800°C) by the argon flow to undergo subsequent pyrolysis. After a certain reaction time, the platinum boat was removed and the amount of the pyrolysis residue was weighed. The product gases were collected in a gas burette. Chromotographic analyses of the product gases were made using Shimadzu Model GC3BF and GC-3BT gas chromatographs. C,-C, hydrocarbon gases were analysed with Porapak Q(SCr 100 mesh, 3.0 mm i.d. x 2.0 m), and benzene and toluene with SE-30 (60-80 mesh, 3.0 mm id. x 2.9 m) at 80°C with a hydrogen flame ionization detector using nitrogen as a carrier gas. Hydrogen was analysed with active carbon (6&80 mesh, 3.0 mm i.d. x 2.9 m) at 30°C with a thermal conductivity detector using nitrogen as a carrier gas. Prior absolute calibrations of the analysis the to chromatographs were made against known amounts of pure hydrocarbons and hydrogen.
RESULTS AND DISCUSSION One-stage pyrolysis Table I summarizes the yields of hydrocarbon gases (expressed as weight percentage of feed) produced by the pyrolysis of Iranian heavy vacuum residue. In runs 1-3,
1. Ekc,m Pla,lnum
z
3 TC (0
6. 0 rang
1wmcc boat
4. Awhy
Apparatus
Tab/e 1 Hydrocarbon
‘I”
8. ICC trap 9. copperMat bl0d
heater
10. Glass
5 Quart* reaction tube Figure 7 residues
seat
7 Al ccollng
*,p,ta, nl” meter
used for the twostage
rod
pyrolysis
of vacuum
gas yield from the pyrolysis of Iranian
heat was only supplied by the main electric furnace, and the maximum temperature of the furnace was in the region of the copper heat block. The platinum boat containing vacuum residue was inserted directly into the zone of highest temperature. In runs 1 and 2, the vacuum residue was pyrolysed at 450°C for 20 min and 500°C for 10 min, respectively. Approximately 80 wt% of the sample was cracked into oil and gas, however, the total yield of C,-C, hydrocarbon gases was only 3-6 wt%. Thus, the main product was cracked oil. In contrast at a higher temperature, 705°C (run 3) the pyrolysis was completed very rapidly with evolution of large amounts of gases. The total yield of C,-C, gases increased to 36.9 wt%. Yields of methane (9.4 wt%), ethylene (8.1 wt%), and propylene (8.1 wt%) were much higher than those of the pyrolysis of Arabian medium vacuum residue using a vertical-type reactor reported by Morita et al.‘. This difference is due to the rapid heating rate and the short residence time in the onestage pyrolysis process. The yields of hydrocarbon gases from the pyrolysis of Taching vacuum residue are summarized in Table 2. The one-stage pyrolysis at 705°C and 765°C (runs 12 and 13) showed the influence of rapid heating rate, giving high yield of C,-C, hydrocarbon gases, i.e. ~50 wt%. The amount of residues after pyrolysis uersus reaction time at 430,440, and 450°C of both samples are plotted in Figure 2. The rate of pyrolysis increased with increasing followed temperature. The pyrolysis reaction approximately first-order kinetics up to 70 wt% conversion for Iranian heavy vacuum residue and 80 wt% for Taching residues. Values of the pyrolysis residues from Iranian heavy and Taching residues were w 20 and 5 wt%, respectively, and correspond to the Conradson carbon residue of these vacuum residues, 23 and 7 wt%, respectively. For Iranian heavy vacuum residues, the pyrolysis residue was completely soluble in carbon disulphide to conversions of 70 wt%, and was slightly carbonized (insoluble in carbon disulphide) when the conversion exceeded w 75 wt%. The time required for the conversion of 75 wt% was approximately 45 min at 430°C 30 min at 440°C 20 min at 450°C and 15 min at 460°C. The extent of carbonization at 75 wt% conversion, however, depended strongly on the pyrolysis temperature. At 75% conversion, the pyrolysis residue was completely soluble in carbon disulphide at 430°C and most of the
heavy vacuum residue Gas yield (wt %)b
Time Temp. (“Cl lststage 2nd stage (min)
Residuea fwt %I
1 2 3
450 500 705
20 10 10
24 20 -
0.6 1.1 9.4
4 5 6 7 8 9 10 11
440 430 440 450 460 500 440 440
25 45 30 20 15 10 30 30
24 25 24 24 21 19 23 23
7.8 8.2 9.4 9.3 9.7 9.9 10.3 10.5
Run
a b ’ o
705 765 765 765 765 765 BOO 825
CH,
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FUEL, 1981, Vol 60, October
Toluened
TotalC
-
0.8 1.3 4.5
3.0 5.8 36.9
_ -
-
0.5 0.3 0.3 0.2 0.2 0.4 0.3
6.3 3.1 2.9 3.2 3.0 3.1 1.7 1.2
39.8 34.3 34.8 36.2 37.4 37.5 33.2 30.6
3.1 3.6 3.8 2.4 4.0 3.7 4.0 3.6
1.4 1.2 1.3 0.8 1.3 1.3 1 .o 0.8
C3H6
C3’+3
C3”4
0.1 0.6 8.1
0.6 1.0 5.5
0.4 1.0 8.1
0.5 0.8 1.3
12.2 14.0 13.7 13.6 13.7 11.9 15.1 15.0
3.3 1.9 2.2 2.7 3.1 4.1 1.7 1.2
9.7 6.6 6.2 7.1 7.4 7.8 4.2 2.7
0.7 0.2 0.2 0.1 0.3 0.5 trace trace
Residue in the platinum boat after pyrolysis 0.5-0.9 wt % (5-9 ml) of Hz and trace amount of CO end CO2 were also present Total yield of Cr-C4 gases Benzene and toluene present in the gases collected
Benzened
C4
C2H6
C2H4
Two-stage pyrolysis of heavy oils (1): T. Suzuki et al. Table 2 Hydrocarbon
gas yield from the pyrolysis of Taching
vacuum residue Gas yield fwt %)b
Time
Residuea
Run
Temp. (“C) lststage 2ndstage
(min)
fwt %)
CH4
C2H4
C2H6
C3H6
12 13 14 15 16 17 18 19 20 21
705 765 440 430 440 450 460 480 500 440
10 5 30 45 30 20 15 10 10 30
14 17 12 13 10 5 6 15
8.6 10.3 8.4 9.4 11 .o 10.9 11.9 11.8 11.3 11.7
13.3 17.7 23.3 24.5 26.3 23.9 25.7 23.6 21.7 26.2
5.1 4.9 2.6 1.6 2.2 2.4 2.9 3.5 3.9 1.6
10.3 10.5 14.2 9.3 9.2 9.0 9.4 10.2 10.8 5.3
a b ’ d
_ 705 765 765 765 765 765 765 800
0.9 0.8 0.5 0.3 0.2 0.2 0.2 0.4 0.6 trace
Benzened
Toluened
C4
TotalC
-
5.9
44.3
_
-
_ 0.6 0.4 0.3 0.3 0.2 0.2 0.5
6.9 9.7 5.4 4.7 4.6 4.5 4.6 4.9 2.9
51.2 58.7 51.1 54.0 51.3 54.9 54.4 53.4 48.2
4.2 4.7 5.8 7.2 6.8 6.9 6.7 6.1 6.6
0.8 1.6 1.4 1.9 1.7 1.7 1.5 1.6 1.2
C3H4
C3’+3
Residue in the platinum boat after pyrolysis 0.5-0.7 wt % (6-8 ml) of Hz and trace amount of CO and CO2 were also present Total yield of C, to C4 gases Benzene and toluene present in the gases collected
a
b
180
160
140
120
100
SO
60
40
20
fppm from
- -A__ -A._
I 0
4
10
20
30 Reaction
40 time(min
)
Figure 3 (fa, 0.36) (fa, 0.64)
0
TMS)
13C n.m.r. spectra of (a) Arabian light vacuum residue and (b) its residue after pyrolysis at 440°C for 30 min
a
Figure 2 Pyrolysis behaviour of vacuum residues at various temperatures. The amount of pyrolysis residue versus reaction time. -, lranium heavy vacuum residue: A, 430°C; 0,440”C; 0,450”C; - - - -, Taching vacuum residue: *, 43O’C; l,44O”C; ., 450°C
pyrolysis residue was insoluble at 460°C. The temperature range 43S46O”C is the same as that used in the visbreaking process and a slight change in pyrolysis temperatures greatly affects the reaction rate and the properties of the pyrolysis residues. Taching vacuum residue gave a similar conversion to that for Iranian heavy, 87-88 wtY&at 430°C for 60 min, 440°C for 30 min, 450°C for 20 min, and 460°C for 15 min, respectively. However, no carbonization of the pyrolysis residue occurred. Properties of the pyrolysis residues and cracked oils produced by the low-temperature pyrolysis 13C n.m.r. spectra of Arabian light and Taching
vacuum residues and their pyrolysis residues produced at 440°C for 30 min are shown in Figure 3 and 4, respectively.
b
180
160
140
120
100
60
60
40 (ppm
Figure 4 (fa, 0.20) (fa, 0.39)
20 from
0 TMS)
13C n.m.r. spectra of (a) Taching vacuum residue and lb) its residue after pyrolysis at 449’C for 30 min
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1981,
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Two-stage pyrolysis of heavy oils (1):
T. Suzuki et al.
a
L CHCl3
X16--+----
1
9
6
7
6
5
160
140
120
100
4
:pprn
fL
449
0
b
160
80
60
40
20
O-
( ppm from TMS 1 1H and 1% n.m.r. spectra of the cracked oil from the Figure 5 pyrolysis of Taching vacuum residue at 440°C for 30 min (Mn, 405; H/C, 1.87; f,, 0.13). (a) proton spectrum; (bl carbon-13 spectrum
Properties of Arabian light vacuum residue are similar to those of Iranian heavy’s, and the i3C n.m.r. spectra of the pyrolysis residues were almost the same. As reported previously6, several sharp peaks appearing in the aliphatic region of the spectra of vacuum residues are assignable: +CH,),-n > 7, 29.7 ppm; CH,-(CH,),-n > 3, 14.1 ppm; CH,-CH,4CH,),n 22, 22.7 ppm, etc. One average molecule of Middle East vacuum residues contains a paraffinic straight-chain of cu. 15 carbon atoms, and for Taching vacuum residues >20 carbon atoms. Recently Simm and Steedman’ presented some evidence supporting this finding by isolating the straightchain alkane fraction as urea adducts from the liquid pyrolysate obtained from asphaltenes at 500°C. They showed that a long straight-chain alkane series was contained in asphaltenes, running from C, 1 to C,, for the Middle East asphaltene, and from C,, to C,s for a Venezuelan asphaltene’. These findings indicate that pyrolysis of vacuum residues to produce lower oletins is more effective than pyrolysing heavy oils from coal hydrogenation or tar sand bitumen containing only shorter methylene chains. The ’ 3C n.m.r. spectra of the Arabian light and Taching pyrolysis residues show some differences. As seen in Figure 3, the sharp characteristic peaks in the aliphatic region almost disappear in the spectrum of the Arabian light pyrolysis residue indicating that most of the alkyl chains attached to aromatic ring systems are broken off into cracked oil. The value of aromaticity of the pyrolysis residue was 0.64, even higher than that of the original asphaltene, 0.53 (original vacuum residue, 0.36). The ratio
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FUEL, 1981, Vol 60, October
of H/C was w 0.8. This pyrolysis residue can be considered to be similar to pitches obtained by the Eureka process’ or the Cherry-P process l”*ll judging from the H/C ratio, the solubility in carbon disulphide, the high aromaticity, and the fluidity at elevated temperature, and, therefore, can be used as an additive in the manufacture of metallurgical coke from non-caking coals. For the Taching vacuum residue, the aromaticity of the pyrolysis residue increased to 0.39 from the 0.20 of the original oil. However, the pattern of the spectrum was almost the same as that of the original oil. As mentioned previously, cracked oil was the main product of the pyrolysis at CQ.450°C. Average molecular weights of the cracked oils from Iranian heavy and Taching vacuum residues were 330 and 400, which were one third and one half of that of the original oil, respectively. As Taching vacuum residue contains a large amount of aliphatic carbon atoms, the cracked oil can be distilled easily even when its molecular weight is high: consequently the molecular weight of Taching cracked oil appeared higher than that of Iranian heavy. Figure 5 shows ‘H and 13C n.m.r. spectra of the cracked oil from the pyrolysis of Taching vacuum residue at 440°C for 30 min. The pattern of the peaks in the aliphatic region of the ’ 3C n.m.r. spectrum was similar to that of the original oil. The value of aromaticity decreased to 0.13 from the 0.20 of the original oil, indicating that fused aromatic ring systems remained in the pyrolysis residue. Also, some peaks can be seen in the olefin region of the ‘H n.m.r. spectrum and sharp peaks assignable to a terminal olefin, 139 and 114 ppm, can be seen in the 13C n.m.r. spectrum The ‘H and ’ 3C n.m.r. spectra of the cracked oil of Iranian heavy vacuum residue were similar to those of Taching vacuum residues. These findings suggest that the reaction occurring in the low-temperature zone is not simple distillation, but degradation of the large molecules of the vacuum residue to produce lighter cracked oils like vacuum gas oils. As seen from the 13C n.m.r. spectrum, this cracked oil contains long, paraflinic straight-chains similar to the original vacuum residue. Two-stage pyrolysis: comparison with one-stage pyrolysis
The twostage pyrolysis was carried out with the intention of producing lower olefins by pyrolysing the cracked oi< as obtained from the one-stage pyrolysis, at higher temperatures. Runs 4-l 1 in Table 1 and 14-21 in Table 2 show the results of the twc+stage pyrolysis of Iranian heavy and Taching vacuum residues, respectively. The temperature of the second, hightemperature zone given in the Tables indicates the maximum temperature of the zone, average temperature of the zone (80 mm long) was w20°C lower than the maximum temperature. The residence time of the lowtemperature pyrolysate at the second stage was estimated from the residence time of argon gas at this zone from the volume of the reactor tube, its flow rate, and the average temperature. In the present study, all the experiments were conducted at the residence time of ~3 s. Inserting the platinum boat containing the vacuum residues into the first, low-temperature zone, the residues gradually undergo low-temperature pyrolysis, and the cracked oil (in gas or vapour form) is carried to the second stage by an argon flow for subsequent pyrolysis, from which lower hydrocarbon gases are produced. Coke produced near the outlet of the reactor tube could be
Two-stage pyrolysis
430-765’C 45 min.
440-76SC 33 n-4”.
450-765T
m mln.
460-765-C 15 min.
WO-765T 10 min
Figure 6 Distribution of products obtained from the pyrolysis of lraniun heavy vacuum residue. 0, CH4; n, CZH4; 0, C2H6; A, C3H6; A, CsHa, X, C4; ( 1,yield in wt %
reduced by cooling the reactor tube with an aluminum cooling fin by air blowing. Comparing the gas yields from Iranian heavy vacuum residue by the one-stage pyrolysis at 705°C (run 3) with those by the two-stage pyrolysis at 440-705°C (run 4), the yields of ethylene and propylene increased from 8.1 to 12.2 wt% and from 8.1 to 9.7 wt%, respectively, whereas the methane yields decreased from 9.4 to 7.8 wt%. The total yield of C,-C, hydrocarbons slightly increased from 36.9 to 39.8 wt%. For the Taching vacuum residue, the trend was similar to that of Iranian heavy. Comparing the results of the one-stage pyrolysis (run 12, 705°C; run 13, 765°C) with those of the twestage pyrolysis (run 14,440705°C; run 15,44&765”C), yields of olefins increased and saturated hydrocarbons decreased. The ethylene yield increased markedly from 13.3 (run 12) to 23.3 wt% (run 14), particularly at 705°C. The pyrolysis residue of the one-stage pyrolysis at cu. 700°C was completely carbonized. The pyrolysis residue of the two-stage pyrolysis, however, was not carbonized. By pyrolysing the cracked oil the asphaltenes which would cause coking remain in the residue, whereas the lower olefins are obtained in high yield. Effect of the temperature of the first stage
The temperature of the first stage was varied from 430 to 500°C while the temperature of the second stage was fixed at 765°C (Table 1, runs 5-9; Table 2, runs 15-20). The product distribution in mol% of hydrocarbon gases from C,-C, is shown in Figures 6 and 7. In order to compare the yields of the hydrocarbon gases, conversion of the pyrolysis was kept constant by adjusting the reaction time. Pyrolysis of Iranian Heavy vacuum residue (Figure 6), yielded a pyrolysis residue of ~24% at 43o”C, 45 min; 44o”C, 30 min; 450°C 20 min; and 46o”C, 15 min; and was 19% at 5oo”C, 10 min. The total yield of C,-C, hydrocarbons was always ca. 36%. As shown in Figure 6, the proportion of ethylene decreased, and that of methane, ethane, and propylene increased with increase in the temperature of the’first stage. The trend was similar for the Taching vacuum residue, as shown in Figure 7. For both vacuum residues the ethylene yield decreased when the first stage was >45O”C and carbonization of the
of heavy oils (1): T. Suzuki et al.
pyrolysis residue was accelerated at higher temperatures. These changes in the product distribution can be explained as follows: (1) When a more severe reaction condition is applied by raising the temperature of the first stage, production of methane at the first stage increases. This methane does not undergo further pyrolysis at the second stage, thus the overall result is an increase in methane yield. (2) Pyrolysis at high temperature (500°C) of vacuum residue at the first stage causes extensive bond scission to give cracked oil containing shorter paraffinic straight-chains than that pyrolysed at a lower temperature (43&45O”C). Pyrolysis of oils containing shorter paraflinic straight-chains at high temperature (70CN300°C, the second stage) gives lower yields of ethylene. Yields of the hydrocarbon gases did not change greatly when the first stage was between 430°C and 460°C. For the Iranian heavy vacuum residue, the pyrolysis residue was greatly carbonized at >45O”C, and the rate of the reaction was very slow at ~430°C. Consequently, the optimum condition for the first stage in this procedure was determined to be 440°C for 30 min. For the Taching vacuum residue, the pyrolysis residue was scarcely carbonized even at 450°C for 20 min or 460°C for 15 min, as the yield of the pyrolysis residue (12-13 wt%) was significantly more than the ultimate yield (5 wt%). The conditions at the first stage, 450°C for 20 min or 460°C for 15 min, can be applied for this vacuum residue without excessive carbonization. Efict
of the temperature of the second stage
The temperature of the second stage was varied from 705°C to 825°C while the condition of the first stage was fixed at 440°C for 30 min. For the Iranian heavy vacuum residue, the ethylene yield was 12 wt% at 705°C (run 4), and increased to 14 wt% at 765°C (run 6), and 15 wt% at 800 and 825°C (runs 10 and 11). The total yield of C,-C, hydrocarbons, however, decreased from 40 to 31 wt%, because the yields of C, and C, hydrocarbons decreased with an increase in temperature. For the Taching vacuum residue, the ethylene yields were 23 wt% at 705°C (run 14) and 26 wto/, at 765°C (run 16) and also at 800°C (run 21). Yields of C, and C, hydrocarbons also decreased and the total yields of C,-C, gases were 59, 54 and 48 wt% at 705”C, 765°C and 8oo”C, respectively. Evidently, a high temperature, e.g. SOO”C,and a residence time of w 3 s are
60
I -(24.5)
?
40
(26 3)
(23 9)
+-----
(257)
I2361
(2171
Figure 7 Distribution of products obtained from the pyrolysis of Taching vacuum residue. 0, CH4; n, C2H4;0, C2He; ., C3H6; A, CaHa; X, C4; ( 1,yield in wt %
FUEL, 1981, Vol 60, October
965
Two-stage
pyrolysis
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sufficiently severe for the production of gaseous hydrocarbons in the two-stage pyrolysis procedure.
2 3 4
ACKNOWLEDGEMENT This work is supported in part by a Grant in Aid for Scientific Research, from the Ministry of Education, Japan (No. 411008).
7
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FUEL, 1981, Vol 60, October
Kohno, H. Kagakukogaku 1974, 38, 710 Takegami, Y., Watanabe, Y., Suzuki,T., Mitsudo, T. and Itoh, M. Fuel 1980, 59, 253 Morita, Y., Ota, K., Izumi, K. and Yamazaki, T. J. Fuel Sot. Japan 1974,53,959
9
Simm, I. and Steedman, W. Fuel 1980, 59, 669 Takahashi, R. and Washimi, K. Hydrocarbon Processing 1976,
10 11
Ueda, K. and Sasaki, S. J. Japan Petrol. Inst. 1976, 19, 417 Oka, S., Kimoto, J., Matsui, H., Seki, H. and Kaneko, M. Am.
55, (1 1), 93
REFERENCES Blaser, D. E. and Edelman, A. M. 43 Midyear API Relining Meeting, Toronto, May 10, 1978
Kunugi, T., Kunii, D., Tominaga, H., Sakai, T., Mabuchi, S. and Takeshige, K. J. Japan Petrol. Inst. 1973, 16, 232, 238, 241 Yamaguchi, F., Sakai, A., Yoshitake, M. and Saegusa, H. Am. Chem. Sot. Div. Petrol. Chem. Preprints 1979, 24, 264
5 6
8
1
Wilkinson, L. A. and Gomi, S. Hydrocarbon Processing 1974,53, (5), 109
Chem. Sot. Diu. Petrol. Chem. Preprints 1979, 24, 678