1148
Energy & Fuels 1998, 12, 1148-1152
Catalytic Conversion of Used Oil to Hydrocarbon Fuels in a Fractionating Pyrolysis Reactor Levent Dandik, H. Ayse Aksoy,* and Ayse Erdem-Senatalar Istanbul Technical University, Chemical Engineering Department, 80626 Maslak, Istanbul, Turkey Received January 21, 1998
Pyrolysis of used sunflower oil was carried out in the presence of different amounts of HZSM-5 at 400 and 420 °C in a reactor equipped with a fractionating packed column, the length of which was varied. The products consisted of gaseous and liquid hydrocarbons, acids, CO, CO2, water, and coke. The compositions of the gaseous and liquid products were studied by gas chromatography. The product yields and compositions were affected by catalyst content, temperature, and column length. Nearly complete conversion (96.6%) of the used oil and the maximum liquid hydrocarbon yield (33%) were obtained at the highest temperature (420 °C), highest catalyst content (20%), and the lowest column length (180 mm) employed. The aromatic hydrocarbon contents of the liquid hydrocarbon products, which consisted of hydrocarbons of gasoline range, were in general lower than those obtained using fixed bed reactors but increased parallel to the increase in catalyst content. Additional thermal reactions taking place in this type of reactor increased with the increase in column length. Although the total conversion and total liquid hydrocarbon yields were influenced adversely by these reactions, liquid products with higher isomeric hydrocarbon contents were obtained with longer columns.
Introduction Recently, increasing attention has been focused on biomass as a renewable source of fuels and chemicals due to environmental reasons and the problem of energy assurance.1 Because of their suitable properties (negligible sulfur, nitrogen, and metal content), plant oils have been suggested as important biomass sources for the production of synthetic fuels and useful chemicals.2,3 However, the plant oils have alternative uses and their initial costs are generally high. On the other hand, in several branches of industry, especially in the food industry and rendering plants, large quantities of oils are produced as waste. Also, the disposal of these waste oils is of environmental concern.4 Therefore, using the waste oils as feed materials to produce synthetic fuels and valuable chemicals would be advantageous. Various attempts have been made to use plant oils directly, but their use in the direct injection-type diesel engine has caused serious problems such as the formation of carbon deposits in the combustion chamber, crankcase oil dilution, and oxidation.5 One of the most promising ways for the production of liquid fuels and chemicals from plant oils is pyrolysis. The pyrolysis of plant oils to obtain products suitable for being used as * Author to whom all correspondence should be addressed. (1) Schwab, A. W.; Dykstra, G. J.; Selke, E.; Sorenson, S. C.; Pryde, E. H. J. Am. Oil Chem. Soc. 1988, 65, 1781-1786. (2) Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed.; Interscience Publishers: New York, 1980; Vol. 11, pp 344-345. (3) Sharma, R. K.; Bakhshi, N. N. Can. J. Chem. Eng. 1991, 69, 1071-1081. (4) Katikaneni, S. P. R.; Adjaye, J. D.; Bakhshi, N. N. Energy Fuels 1995, 9, 599-609. (5) Schwab, A. W.; Bagby, M. O.; Freedman, B. Fuel 1987, 66, 13721378.
fuels have been studied under different reaction conditions with and without addition of catalysts.1-14 Especially since the discovery of the high-silica zeolite catalyst HZSM-5 by Mobil workers, a number of investigations employing this catalyst have been reported.3,15-16 The shape-selective pentasil HZSM-5 catalyst was first used by Weisz et al.17 to convert plant oils to hydrocarbons. They achieved a complete conversion of jojoba oil at 400 °C over HZSM-5, whereas both castor and corn oils required a temperature of 500 °C for complete conversion. In all the cases, 42-78 wt % of the oil was converted to aromatic hydrocarbons. Weisz et al. proposed that the triglyceride molecule could penetrate into the zeolite pores at elevated temperatures (6) Chang, C. C.; Wan, S. W. Ind. Eng. Chem. 1947, 39, 1543-1548. (7) Crosley, A.; Heyes, T. D.; Hudson, B. J. F. J. Am. Oil Chem. Soc. 1962, 39, 9-14. (8) Nawar,W. W. J. Agric. Food Chem. 1969, 17, 18-21. (9) Alencar, W.; Alves, P. B.; Craveiro, A. A. J. Agric. Food Chem. 1983, 31, 1268-1270. (10) Konwer, D.; Taylor, S. E.; Gordon, B. E.; Otuos, J. W.; Calvin, M. J. Am. Oil Chem. Soc. 1989, 66, 223-226. (11) Filho, G. N. R.; Bentes, M. H. S.; Brodzki, D.; Mariadassou, G. D. J. Am. Oil Chem. Soc. 1992, 69, 266-271. (12) Agra, I. B.; Warnijati, S.; Pratama, M. S. Catalytic Pyrolysis of Nyamplung Seeds Oil to Mineral Oil-Like Fuel; Proceedings of 2nd World Renewable Energy Congress; Sayigh, A. A. M., Ed.; Pergamon Press: New York, 1992; pp 1346-1351. (13) Filho, G. N. R.; Brodzki, D.; Mariadassou, G. D. Fuel 1993, 72, 543-549. (14) Dandik, L.; Aksoy, H. A. Converting Used Oil to Fuel and Chemical Feedstock through the Use of a Fractionating Pyrolysis Reactor; Proceedings of the World Conference on Oilseed and Edible Oils Processing; Koseoglu, S. S., Rhee, K. C., Wilson, R. F., Eds.; AOCS Press: Champaign, 1998; Vol. 1, pp 126-129. (15) Prasad, Y. S.; Bakhshi, N. N. Appl. Catal. 1985, 18, 71-85. (16) Yarlagadda, P. S.; Yaollang, H.; Bakhshi, N. N. Ind. Eng. Chem. Prod. Res. Dev. 1986, 25, 251-257. (17) Weisz, P. B.; Haag, W. O.; Rodewald, P. G. Science 1979, 206, 57-58.
10.1021/ef980012u CCC: $15.00 © 1998 American Chemical Society Published on Web 09/19/1998
Catalytic Conversion of Used Oil
Energy & Fuels, Vol. 12, No. 6, 1998 1149
Table 1. Fatty Acid Composition and Main Characteristics of Used Oil acid value (mg of KOH/g) saponification value (mg of KOH/g) iodine value (g of I/100 g) density, 21 °C (g/mL) viscosity, 37.8 °C (mm2/s) refractive index (nD20) fatty acid composition (wt %) palmitic stearic oleic linoleic
2.32 194 117.82 0.9383 89.39 1.4785 9.49 5.62 31.14 53.75
Table 2. Conditions of Gas Chromatographic Analyses conditions detector detector temp, °C injector temp, °C gas flow, mL/min carrier gas, N2 hydrogen air split ratio column oven temp, °C
hydrocarbons
acids
gas
FID 280 250
FID 280 250
TCD 300 250
1.11 30 400 370/1 Ultra 1a temp prog.d
1.72 10.17 30 400 175/1 Ultra 2b Chromosorb 102c temp proge temp progf
Figure 1. Sample chromatogram for gaseous products.
a
a 25 m, 0.32 mm, 0.52 µm film thickness, 100% dimethyl polysiloxane. b 25 m, 0.32 mm, 0.52 µm film thickness, 5% diphenyl and 95% dimethyl polysiloxane. c 80/100 mesh, 2 m, 1/8 in., 2.2 mm. d 24 °C (5 min), 24-30 °C (1 °C/min, 5 min), 30-70 °C (1.5 °C/ min, 20 min), 70-200 °C (3 °C/min, 30 min). e 30 °C (5 min), 30170 °C (5 °C/min, 10 min), 170-200 °C (3 °C/min, 30 min). f 30 °C (2 min), 30-200 °C (10 °C/min, 10 min).
by assuming a slender configurational alignment. Another possibility was thought to be that the initial fragmentation occurs on the external surface of the catalyst followed by the diffusion of the intermediate products into the pores.18 The subsequent reactions, namely, cyclization, isomerization, and hydrogen transfer, leading to the formation of mainly aromatic hydrocarbons from the carbonium ions produced in the pores of the HZSM-5 catalyst are well-understood. Katikaneni et al.19 investigated the catalytic conversion of canola oil over various cracking catalysts. They observed that at 400 °C, among the six catalysts, HZSM-5 gave the highest amount of organic liquid product (63 wt %) and it was more selective for aromatic hydrocarbons compared with the other zeolitic and nonzeolitic catalysts. In another study, canola oil and steam were co-fed continuously to a fixed-bed reactor loaded with HZSM-5 catalyst at varying process conditions. The liquid hydrocarbon product contained 60-70 wt % aromatics. The gaseous product was reported to be highly olefinic.20 The compositions of the pyrolysis products with or without catalyst are known to depend on the characteristics of oils and catalysts.9,10 Catalytic conversion of saturated and unsaturated fatty acids and a plant oil using 1-20% Na2CO3 at the same conditions resulted in pyrolysis products consisting of hydrocarbons in different quantities.10 The liquid pyrolysis products of boiling range 60-320 °C of unsaturated fatty acids (C18:1 (18) Prasad, Y. S.; Bakhshi, N. N.; Mathews, J. F.; Eager, R. L. Can. J. Chem. Eng. 1986, 64, 278. (19) Katikaneni, S. P. R.; Adjaye, J. D.; Bakhshi, N. N. Can. J. Chem. Eng. 1995, 73, 484-497. (20) Prasad, Y. S.; Bakhshi, N. N.; Mathews, J. F.; Eager, R. L. Can. J. Chem. Eng. 1986, 64, 285-292.
b
c
Figure 2. Sample chromatogram for liquid products: (a) retention time 0-40 min, (b) retention time 40-80 min, and (c) retention time 80-120 min. Table 3. Overall Product Distribution at 400 °C (wt %) 1% HZSM-5 column (mm) products liquid hydrocarbon phase n-alkenes n-alkanes aromatics others C5-C11 hyrocarbons aqueous phase acid phase gas coke-residual oil conversion
180
360
540
5% HZSM-5 10% HZSM-5 column (mm) column (mm) 540
180
540
23.18 19.66 16.20
18.10
28.92 20.75
7.22 10.09 0.54 5.34 16.77 3.88 16.50 16.30 40.14 59.86
3.93 7.35 1.04 5.78 17.64 5.63 2.53 13.52 60.22 39.78
4.33 12.30 1.81 10.48 24.90 6.12 12.50 19.10 33.36 66.64
6.66 5.65 8.13 6.50 0.53 0.48 4.34 3.57 17.96 15.93 4.48 9.28 7.25 1.21 16.14 9.66 52.47 63.65 47.53 36.35
3.06 5.70 1.73 10.26 20.15 5.49 1.58 18.29 53.89 46.11
and C18:2) contained more aromatic hydrocarbons than those of the saturated fatty acids (C16:0 and C18:0). On the contrary, the pyrolytic oils of saturated fatty acids contained more olefinic hydrocarbons than aromatics. Information on the pyrolysis products of sunflower oil is not available in the literature. Expecting the characteristics of the oil to affect the composition of pyrolysis products, we have investigated the pyrolysis of this
1150 Energy & Fuels, Vol. 12, No. 6, 1998
Dandik et al.
Table 4. Overall Product Distribution at 420 °C (wt %) 1% HZSM-5 column (mm)
5% HZSM-5 column (mm)
10% HZSM-5 column (mm)
20% HZSM-5 column (mm)
products
180
360
540
540
180
540
180
liquid hydrocarbon phase n-alkenes n-alkanes aromatics others C5-C11 hyrocarbons aqueous phase acid phase gas coke-residual oil conversion
26.40 8.52 11.06 0.56 6.25 16.59 2.47 24.03 26.21 20.89 79.11
25.42 8.95 10.03 0.79 5.66 17.93 3.35 12.78 25.50 32.95 67.05
21.32 7.94 8.23 0.68 4.48 19.45 3.74 7.08 24.20 43.66 56.34
22.12 8.05 7.08 1.00 5.99 21.62 5.46 3.12 26.90 42.40 57.60
38.05 6.59 14.23 3.64 13.59 31.19 4.58 19.41 24.44 13.51 86.49
25.57 6.42 6.41 2.22 10.52 24.43 5.88 4.07 26.22 38.26 61.74
32.88 0.34 1.38 16.05 15.11 32.59 5.01 8.36 50.32 3.44 96.56
waste oil, which has a fatty acid composition similar to that of sunflower oil. The present study was, therefore, undertaken in order to investigate the conversion of used sunflower oil with HZSM-5 catalyst by using a special fractionating pyrolysis reactor and the effects of process parameters, i.e., temperature, catalyst content, and fractionating column length, on the nature and yield of the products obtained. Experimental Section Materials. The oil which was used twice for frying of vegetables, obtained from the campus cafeteria, was filtered to remove pieces of food and used directly without any special purification. The fatty acid composition and the main characteristics of used oil are shown in Table 1. HZSM-5 catalyst was synthesized following the procedure described elsewhere.21 The X-ray powder diffraction pattern confirmed that the zeolite synthesized was highly crystalline HZSM-5. The surface area of the catalyst was determined to be 338 m2 g-1 using BET analysis. HZSM-5 catalyst was found to consist of 1.32% Al, 0.79% Na, and 40.90% Si by inductively coupled plasma (ICP) analysis. The catalyst powder was dried overnight at 110 °C and under atmospheric pressure in air before being used in the experiments. Other reagents were of analytical grade (Merck, Darmstadt, Germany). Experimental Setup and Procedure. The pyrolysis reactor (#316 SS tubing, 210 mm long, 75 mm i.d.) was equipped with thermocouples, an inert gas connection, and a fractionating packed column (#316 SS tubing, 45 mm i.d., packed with ceramic rings having 7 mm i.d., length of 180, 360, or 540 mm). The reactor was heated using a tubular furnace (220 mm long, 78 mm i.d.). For the batch cracking experiments, the reactor was loaded with 100 g of oil. Then HZSM-5 catalyst (1%, 5%, 10%, or 20% based on the weight of oil) was added to the oil, and the mixture was stirred to disperse the catalyst in oil. After the air was purged with N2, the mixture was heated to the reaction temperature with a heating rate of 40 °C/min. Temperature was kept constant until the end of the experiments. The gaseous and liquid reaction products leaving the fractionating column were collected separately. The liquid product was collected in two glass traps cooled with an icesalt mixture and ice, respectively. The gaseous products were trapped over a saturated solution of NaCl in a gas holder. The reaction time was kept at 3 h. At the end of the experiments, the reactor was left to cool at ambient temperature. The amounts of the collected liquid, gas, and residual oil-coke were measured. The conversion was calculated from the difference between the weights of the feed and that of coke and residual oil. (21) Altun, M. Control of Si/Al Ratio, Crystal Size and Morphology in ZSM-5 Synthesis, M.S. Thesis, Istanbul Tecnical University, Istanbul, 1993.
Table 5. Compositions of the Liquid Hydrocarbon Products at 400 °C (wt %) 1% HZSM-5 column (mm)
5% HZSM-5 column (mm)
10% HZSM-5 column (mm)
carbon no.
180
360
540
540
180
540
C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15-C17 ∑n-alkenes ∑n-alkanes ∑aromatics ∑isomers
11.73 14.39 16.09 13.36 7.08 4.58 5.01 2.57 3.59 3.05 18.55 31.13 43.21 2.33 23.03
9.57 16.58 21.26 19.09 12.09 7.25 5.52 2.37 2.01 1.09 3.17 33.90 41.33 2.70 22.07
9.36 20.55 24.30 20.67 14.05 6.55 2.86 0.86 0.42 0.19 0.19 34.85 40.14 2.99 22.02
1.94 16.78 29.17 24.41 14.93 7.93 2.30 1.22 0.45 0.31 0.56 21.69 40.62 5.73 31.96
19.48 21.28 20.79 12.69 4.54 4.63 2.70 3.04 1.65 1.45 7.74 14.97 42.52 6.25 36.25
14.90 25.86 28.26 17.79 6.67 3.65 1.42 0.36 0.17 0.18 0.74 14.76 27.49 8.32 49.43
Liquid product was separated in a separatory funnel into aqueous and organic phases. The organic phase consisted of hydrocarbons and carboxylic acids. Using the acid value of the organic phase, as determined by base titration, a corresponding amount of base was added to the organic phase to separate it into a liquid hydrocarbon and an acid phase, the latter being converted to methyl esters by using the BF3methanol esterification procedure.22 The aqueous phase was discarded. Analysis. The analyses of the liquid hydrocarbon and acid phases were carried out quantitatively by using Ultra 1 (25 m, 0.32 mm, 0.52 µm film thickness of 100% dimethyl polysiloxane) and Ultra 2 (25 m, 0.32 mm, 0.52 µm film thickness of 5% diphenyl and 95% dimethyl polysiloxane) capillary columns with a Hewlett-Packard gas chromatograph (5890 Series II) fitted with a flame ionization detector (Waldron, Germany). The average molecular weight of component fatty acids was calculated, and the weight of the acid phase was determined. Standard mixtures of n- and i-alkanes (C5-C8) and aromatic hydrocarbons (benzene, toluene, and xylene) were used to calculate the response factors. The response factors of the alkanes changed between 0.98 and 1.22 and were slightly higher than those of the aromatic hydrocarbons (0.90-0.93). Since the response factors varied in a rather narrow range and since there were several unidentified peaks in the chromatograms, the area percents were considered as weight percents (wt %) for the components of the liquid products. The gas product was further analyzed by using a packed column (Chromosorb-102, 2 m, 1/8 in., 2.2 mm, 80/100 mesh) with a gas chromatograph equipped with a thermal conductivity detector. The conditions of the gas chromatographic analyses and sample choromatograms for gaseous and liquid products are presented in Table 2 and Figures 1 and 2, respectively. (22) AOCS Official Method Ce 2-66, Rev. 1969, reappeared 1973.
Catalytic Conversion of Used Oil
Energy & Fuels, Vol. 12, No. 6, 1998 1151
Table 6. Compositions of the Liquid Hydrocarbon Products at 420 °C (wt %) 1% HZSM-5 column (mm)
a
5% HZSM-5 column (mm)
10% HZSM-5 column (mm)
20% HZSM-5 column (mm)
carbon no.
180
360
540
540
180
540
180
C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15-C17 ∑n-alkenes ∑n-alkanes ∑aromatics ∑isomers
10.63 13.76 14.98 11.77 4.82 3.35 3.52 2.45 2.95 5.50 25.59 32.29 41.90 2.13 23.68
6.77 15.64 18.37 13.58 6.11 5.16 4.90 2.81 4.89 2.69 18.06 35.19 39.46 3.10 22.25
10.35 17.36 20.91 17.14 12.60 7.54 5.33 2.83 2.11 1.40 2.43 37.23 38.60 3.17 21.00
9.05 20.81 26.28 21.67 12.56 5.03 2.36 1.14 0.51 0.30 0.29 36.40 32.00 4.54 27.06
18.69 22.99 21.43 6.80 4.19 4.54 3.30 3.40 1.99 1.77 9.90 17.33 37.39 9.57 35.72
20.71 27.16 28.28 12.49 4.02 3.30 1.65 1.15 0.45 0.34 0.48 25.11 25.07 8.67 41.15
42.57 13.23 17.88 16.92a 7.18 1.33 0.44 0.44
1.02 4.20 45.97 48.81
4.47% Ethyl benzene and 12.45% o,m,p-xylenes.
Results and Discussion As expected, the pyrolysis products of used oil consisted of gaseous and liquid hydrocarbons, carboxylic acids, CO, CO2, H2, water, and coke. Although no information has been published on the mechanism of the conversion of the used vegetable oils to hydrocarbons, the reaction pathways previously suggested17-19 for the conversion of triacylglycerol molecules on zeolite catalysts are expected to be valid in this case too. Initially, cracking and deoxygenation may take place at the external surface of HZSM-5; then the heavy liquid hydrocarbons produced and the remaining oxygenates may undergo secondary cracking and deoxygenation reactions to produce light alkenes, alkanes, water, CO, and CO2 in the pores of HZSM-5 catalyst. Oligomerization of the alkenes may produce a mixture of C2C10 alkanes and alkenes, some of which may be converted to hydrocarbon gases and the remaining to aromatic hydrocarbons by cyclization, H-transfer, and isomerization reactions that occur via carbonium ion mechanisms. Additionally, coke is formed from the polymerization of some aromatic hydrocarbons. The conversions of used oil and the overall product distributions obtained from the reactions conducted with different amounts of HZSM-5 (1%, 5%, 10%, and 20% based on oil weight) at 400 and 420 °C by using a fractionating pyrolysis reactor equipped with a packed column of three different lengths (180, 360, and 540 mm) are shown in Tables 3 and 4, respectively. Reaction temperature, packed column length, and catalyst content were all found to have significant effects on the conversion and product distribution obtained from the oil. As seen from the tables, conversion was observed to increase significanly with the increase in the reaction temperature and catalyst content whereas it decreased with an increase in the column length. At 420 °C, with 20% HZSM-5 addition and a 180 mm column length, nearly complete conversion (96 wt %) was observed. An increase in reaction temperature increased the amount of liquid hydrocarbon and gaseous products and decreased the coke-residual oil yield. On the other hand, the major effects of increasing the column length were to increase the coke-residual oil yield and decrease the yields of acid and liquid hydrocarbon phases.
The distributions of the hydrocarbons in the liquid products are presented in Tables 5 and 6. As can be seen from the tables, the liquid product consisted mainly of alkanes, alkenes, and their isomers. It was very poor in aromatics (about 2-10 wt %) when 1%, 5%, and 10% of the catalyst was used in the reactions. This is contrary to the other results in the literature but can be explained by the fractionating batch reactor configuration used in our study. Prasad and co-workers 18 observed that the pyrolysis oil produced by the catalytic conversion of canola oil on HZSM-5 in a continuous fixed-bed reactor contained 60-70 wt % of aromatic hydrocarbons. A significant aromatic hydrocarbon content of the liquid product (46 wt %) was obtained only with the addition of 20% HZSM-5 at 420 °C in our fractionating pyrolysis reactor. The content of the hydrocarbons that have 5-11 carbon atoms, which are in the gasoline boiling range, also increased parallel to the increase in the catalyst content and reaction temperature. The liquid products mainly consisted of C5-C9 hydrocarbons in all cases. The effect of the column length on the composition of the liquid hydrocarbon phase was less pronounced at lower catalyst contents. At a relatively high catalyst content of 10%, the increase in the content of isomers in addition to the decrease in the content of n-alkanes became significant, parallel to the increase in column length. At 420 °C, the total content of n-alkenes was also seen to increase significantly with increasing column length. The gaseous product consisted of H2, CO, and CO2 in addition to saturated and unsaturated hydrocarbons consisting mostly of those in the C1-C3 range (Tables 7 and 8). Changes in the reaction conditions are also seen to affect the composition of the gaseous product to some extent. The most striking change was the increase in the alkenes/alkanes ratio of the gases with 20% catalyst addition at 420 °C. From the product distribution, it can be concluded that the relative importance of the thermal reactions with respect to the catalytic reactions is higher in the fractionating reactor used in this study than in the fixed-bed reactors used previously.18-20 This is especially true when longer column lengths are employed. In other words, secondary thermal reactions take place
1152 Energy & Fuels, Vol. 12, No. 6, 1998
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Table 7. Compositions of Gaseous Products at 400 °C (Area %) 1% HZSM-5 column (mm) 180 360 540
carbon no. H2 CO CO2 C1 C2d C2 C3d C3 C4d C4 C5d C5 C6+d ∑alkenes ∑alkanes
18.10 8.05 9.22 10.85 10.11 9.74 6.65 9.88 3.96 6.44 2.42 3.21 1.27 23.14 41.49
23.27 6.26 8.00 10.07 7.56 10.50 8.58 5.24 3.99 7.30 2.60 4.61 2.01 22.73 39.74
5% HZSM-5 column (mm) 540
32.11 6.93 7.15 7.30 3.44 7.46 9.45 5.43 3.51 7.11 1.73 6.29 2.09 18.13 35.68
20.18 6.90 5.85 8.21 5.19 8.76 12.08 12.59 3.25 8.54 1.24 5.84 1.37 21.76 45.31
10% HZSM-5 column (mm) 180 540 18.33 6.41 8.99 13.80 6.96 9.84 8.70 12.82 2.95 6.05 1.43 2.85 0.87 20.04 46.23
16.82 7.12 5.65 9.09 6.58 10.50 9.43 11.88 4.92 9.65 1.29 6.04 1.03 22.22 48.19
Table 8. Compositions of Gaseous Products at 420 °C (Area %) 1% HZSM-5 column (mm)
5% HZSM-5 10% HZSM-5 20% HZSM-5 column (mm) column (mm) column (mm)
carbon no.
180
360
540
540
180
540
180
H2 CO CO2 C1 C2d C2 C3d C3 C4d C4 C5d C5 C6+d ∑alkenes ∑alkanes
19.52 5.82 6.67 12.34 8.97 12.87 8.39 6.43 3.94 6.85 2.05 4.17 1.98 23.35 44.64
20.18 6.61 5.59 12.76 8.53 12.83 9.77 4.27 3.87 6.77 2.86 4.04 1.92 25.03 42.59
22.44 5.97 4.97 14.47 8.72 11.74 9.93 3.19 4.32 5.93 3.11 3.79 1.74 26.08 40.54
19.96 6.79 4.77 14.80 9.70 11.07 5.12 11.59 3.48 5.53 1.86 3.60 1.73 20.16 48.32
13.88 11.68 4.32 14.15 6.96 11.64 9.98 11.54 4.16 6.31 1.49 2.98 0.92 22.58 47.53
16.70 7.28 4.11 17.12 10.57 16.11 5.86 4.89 3.79 6.17 1.57 3.94 1.89 21.79 50.12
8.42 11.68 1.51 4.48 12.95 3.71 23.36 9.37 10.51 6.95 3.49 2.55 1.02 50.30 28.08
in the fractionator in this type of reactor, one obvious consequence of which is the increased coke yields. Although the total conversion and total liquid hydrocarbon yields are influenced adversely by these reactions, the lower aromatic and higher isomeric hydrocarbon contents of the liquid are advantages when the
recent requirements imposed on fuels are considered.23 It seems possible to choose appropriate values for column length, temperature, and catalyst content to optimize the yield and composition of the products by monitoring the relative importance of the catalytic and thermal reactions taking place in the system. Further processing requirements for these liquid products to be used as high-octane fuels may be decreased in this manner. Conclusions Used oil could be converted to liquid products containing gasoline-range hydrocarbons. The highest conversion (96.6%) of used oil and the maximum liquid hydrocarbon yield (33%) were obtained at the highest temperature (420 °C), highest catalyst content (20%), and the lowest column length (180 mm) employed. The aromatic contents of the liquid hydrocarbon product was, in general, lower than those obtained using fixedbed reactors. Using the fractionating column causes, in addition to the catalytic reactions on HZSM-5, additional thermal reactions to occur in the liquid and vapor phases. Thermal effects became more pronounced with increasing column length. Isomeric hydrocarbon content of the liquid hydrocarbon product increased with the increase in column length while the n-alkane content decreased. At 420 °C, n-alkene content increased significantly with increasing column length. It seems possible to employ the length of the fractionating column as an additional variable, in addition to the temperature and catalyst amount, to optimize the aromatic, paraffinic, and olefinic hydrocarbon contents of the liquid product in order to be used as high-octane fuels of acceptable composition. Acknowledgment. The authors are grateful to the Istanbul Technical University Research Fund for financial support. EF980012U (23) EFOA Newsletter, 1995, 13, 3.
