1176
Energy & Fuels 2000, 14, 1176-1183
Major Products Obtained from the Pyrolysis of Oil Sludge Ching-Yuan Chang,*,† Je-Lueng Shie,† Jyh-Ping Lin,‡ Chao-Hsiung Wu,§ Duu-Jong Lee,| and Chiung-Fen Chang† Graduate Institute of Environmental Engineering, National Taiwan University, Taipei 106, Taiwan, Department of Environmental Engineering, Fu-Shin Institute of Technology, Tou-Cheng, I-Lan 261, Taiwan, Department of Environmental Engineering, Da-Yeh University, Chang-Hwa 515, Taiwan, and Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan Received March 15, 2000. Revised Manuscript Received August 9, 2000
Oil sludge, if unused, is one of the major industrial wastes that needs to be treated for the refinery or petrochemical industry. It contains a large portion of combustible components with high heating values. Obviously, the conversion of oil sludge to various useful materials such as lower molecular weight organic compounds and carbonaceous residue via pyrolysis not only solves the disposal problem but also matches the appeal of resource utilization. In this study, the oil sludge from the oil storage tank of a typical petroleum refinery plant located in northern Taiwan is used as the raw material of pyrolysis. Its heating value of dry basis and low heating value of wet basis are about 10681 and 5870 kcal/kg, respectively. The pyrolysis of oil sludge is conducted by using nitrogen as carrier gas in the temperature range 378-873 K. The pyrolytic reaction is complex and significant in the range 450-800 K. The residues of pyrolysis of oil sludge exhibit very high viscous form below 623 K (pyrolysis temperature), while low viscous or solid form above 713 K. The major gaseous products (noncondensable gases at 298 K) excluding N2 are CO2 (50.88 wt %), HCs (hydrocarbons, 25.23 wt %), H2O (17.78 wt %), and CO (6.11 wt %). The HCs mainly consist of low molecular weight paraffins and olefins (C1-C2, 51.61 wt % of HCs). The temperature corresponding to the maximum production rate of HCs is 713 K. The distillation characteristics of liquid product (condensate of gas at 298 K) from the pyrolysis of oil sludge is close to diesel oil. However, it contains a significant amount of vacuum residue of about 9.57 wt %. The heating value of liquid product is about 10840 kcal/kg. All this information is useful not only to the proper design of a pyrolysis system but also to the better utilization of liquid oil product and understanding of gaseous emission.
Introduction In the petroleum refineries, a lot of oil sludge accumulates from refining processes. The major sources of oil sludge include the oil storage tank sludge, the biological sludge, the dissolved air flotation (DAF) scum, the American Petroleum Institute (API) separator sludge, and the chemical sludge. In Taiwan, most of the oil sludges are from the oil storage tank sludge and the biological sludge of refinery wastewater treatment plant.1 Some of the oil sludges are included in the hazardous waste listings regarding the wastes originated from specific sources as regulated by the Resource Conservation and Recovery Act (RCRA). The hazardous waste listings include (1) DAF sludge (K048), (2) slop oil emulsion solids (SOES) (K049), (3) heat exchanger * Author to whom correspondence should be addressed. † Graduate Institute of Environmental Engineering, National Taiwan University. ‡ Department of Environmental Engineering, Fu-Shin Institute of Technology. § Department of Environmental Engineering, Da-Yeh University. | Department of Chemical Engineering, National Taiwan University. (1) AAECC (Asian American Environmental Control Corporation). Refinery Solid Wastes Treatment and Management; A Report Submitted to Chinese Petroleum Corp. (Taiwan) by AAECC; 1987.
bundle sludge (K050), (4) API separator sludge (K051) and (5) tank bottoms lead (K052).2 The other oil sludges not included in the hazardous waste listings are regulated depending on the results of the Toxicity Characteristics Leaching Procedure (TCLP). The previous study3 of this oil sludge showed that it contained approximately 39.15, 1.88, and 58.97 wt % moisture, ash, and combustible, respectively. Its heating value of dry basis and low heating value of wet basis were about 10681 and 5870 kcal/kg, respectively. The ultimate analysis of dry basis of oil sludge in wt % was 83.94 C, 12.01 H, 0.81 N, 0.96 O, 2.06 S, and 0.22 Cl. The concentrations of different metal elements in the wet basis of oil sludge in ppmw (ppm in wt/wt) were 7340.7 Fe, 1055.6 Ca, 348.6 Na, 118.3 Al, 95.3 Mg, 91.5 Zn, 64.4 Mn, 35.3 Hg, 28.3 Sr, 27.5 K, 19.6 Pb, 14.1 Cu, 13.7 Ba, 11.7 Ni, 6.5 Cr, 1.3 Mo, 0.96 As, 0.88 Co, 0.14 Cd, and 0.12 Se. (2) Guidance Manual for Hazardous Waste Permits; U. S. Environmental Protection Agency Office of Solid Waste and Emergency Response, PB 84-10057, Washington, DC, 1989. (3) Shie, J. L.; Chang, C. Y.; Lin, J. P.; Wu, C. H.; Lee, D. J. Resources Recovery of Oil Sludge by Pyrolysis: Kinetics Study. J. Chem. Technol. Biotechnol. 2000, 75, 1-8.
10.1021/ef0000532 CCC: $19.00 © 2000 American Chemical Society Published on Web 10/21/2000
Major Products from the Pyrolysis of Oil Sludge
One of the current major methods to dispose of oil sludge is incineration. The incinerators used are aggregate types such as fluidized bed combustion, circulating fluidized bed combustion (CFBC), kiln, rotary, and rack, and step-type furnaces with combustion temperatures of 1073-1173 K.4-9 However, during the runs conducted in the incineration, the following major problems are encountered: (1) excessive bed temperature, (2) frequent clinker formation, (3) high flue gas temperature, and (4) excessive pressure drop. The resolutions of these problems constitute the current major investigation.8 Incineration has been deemed an effective method for destroying the majority of organic constituents to innocuous carbon dioxide and water. But three polyaromatic hydrocarbons (PAHs)sphenanthrene (phA), fluoranthane (fluA), and pyrene (pyr)swere detected from a bench-scale study.10 The study indicated that with a small excess air of 20 vol % and short nominal gas residence times (0.7-1.2 s), the fluidizedbed incineration of an industrial waste at 773-1073 K (500-800 °C) emitted priority PAHs in the 2506-5930 µg/Nm3 range.10 Other methods considered for disposal of oil sludge include (1) landfarming with microbial treatment to convert the hydrocarbons (HCs) to combustible gases, (2) use in a delayed coker, (3) utilization for industrial bitumen, and (4) separation of water and sediment at elevated temperature by the use of diluents and emulsifiers with subsequent burning.7,10-14 Landfill has pollution risks if stabilization of oil sludge is not complete. It may pollute groundwater and cause health problem.11 Landfarming requires a large surface area and usually takes a long time to complete. It also causes air pollution problem.14 The organic compounds of oil sludge may include aromatics and PAHs that are carcinogenic, while the inorganic compounds may contain toxic heavy metals.13 Separation and Recovery Systems, Inc. (SRS) introduced a new generation of dryer technology, the MX2500, for the treatment of refinery wastes and secondary (4) Ayen, R. J.; Swanstrom, C. P. Low-Temperature Thermal Treatment of Petroleum Refinery Waste Sludges. Environ. Prog.; May, 1992, 11 (5), 127-133. (5) Chang, Y. M.; Lo, Y. F.; Chen, M. Y. Heat Transfer Measurements of a 1.0 Ton-steam/hr Circulating Fluidized Bed Combustor Burning Taiwan Coal. Partic. Sci. Technol. 1991, 8, 199-208. (6) Chang, Y. M.; Chen, M. Y. Industrial Waste to Energy by Circulating Fluidized Bed Combustion. Resources, Conservation, Recycling 1993, 9, 281-294. (7) Kuriakose, A. P.; Manjooran, S. K. B. Utilization of Refinery Sludge for Lighter Oils and Industrial Bitumen. Energy Fuels 1994, 8, 788-792. (8) Sankaran, S.; Pandey, S.; Sumathy K. Experimental Investigation on Waste Heat Recovery by Refinery Oil Sludge Incineration Using Fluidised-Bed Technique. J. Environ. Sci. Health 1998, A 33 (5), 829845. (9) Steger, M. T.; Meibner, W. Drying and Low-Temperature ConversionsA Process Combination to Treat Sewage Sludge Obtained From Oil Refineries. Wat. Sci. Technol. 1996, 34 (10), 133-139. (10) Wei, Y. L.; Wu, C. H. PAH Emissions from the Fluidized-Bed Incineration of an Industrial Sludge. J. Air Waste Manage. Assoc. 1997, 47, 953-960. (11) Aithal, U. S.; Aminabhavi, T. M.; Dhukla, S. S. Photomicroelectro-chemical Detoxification of Hazardous Materials. J. Hazard. Mater. 1993, 33 (3), 369∼400. (12) ElBagouri, I. H.; ElNawary, A. S. Mobility of Oil and other Sludge Constituents during Oily Sludge Treatment by Landfarming. Resour., Conserv. Recycl. 1994, 11, 93-100. (13) Karr, L. A.; Lysyj, I. Physical, Chemical and Toxicological Properties of Navy Oily Sludge; Naval Civil Engineering Lab.: Port Hueneme, CA, 1985; NCEL-TN-1739. (14) Milne, B. J.; Baheri, H. R.; Hill, G. A. Composting of a Heavy Oil Refinery Sludge. Environ. Prog. 1998, 17 (1), 24-27.
Energy & Fuels, Vol. 14, No. 6, 2000 1177
materials including API sludges, DAF float, and slop oil emulsion solids. The MX-2500 is an electrically heated dryer system for the objectives of waste minimization and oil recovery, while producing a solid residue meeting EPA Land Disposal Restriction (LDR) treatment levels.15 Ayen and Swanstrom4 tested a lowtemperature thermal treatment process for the petroleum refinery waste sludges with waste codes K048, K049, K050, K051, and K052 under the RCRA. The reaction temperatures of low-temperature thermal treatment process were between 588-698 K (laboratory unit) or 463 and 633 (pilot plant) under nitrogen atmosphere, providing effective waste minimization up to 40% decrease in the mass of sludge to be disposed of. The heating value of sludge was increased simultaneously by one-third and demonstrated the effectiveness of removal of organics of concern from the sludges to meet the RCRA best demonstrated available technology (BDAT) treatment standards.4 However, they did not report the quality of recovered liquids and the emissions of vent gas. For greater reduction of the residue solid and increase of the quality of liquid oil, it was necessary to divide the drying and pyrolysis processes. Steger and Meibner9 investigated a pilot plan combination of a drying process and a low-temperature conversion process to treat the sewage sludge obtained from oil refineries. Drying, followed by the low temperature conversion at 673 K, rendered the sludge to fuel oil and char. Halogenated organics and PAHs in the feed sludge were reduced during the conversion process by 98.4 and 83.7 wt %, respectively.9 In the previous study of pyrolysis of oil sludge,3 for the sake of simplicity and engineering use, a simple global reaction kinetic model was used to predict the experimental results. For precise use, the two- and three-reaction models were proposed to describe the pyrolysis.3 This was reasonable because of the complex compositions of oil sludge. The variations of instantaneous reaction rates of pyrolysis of oil sludge were significant at about 640-765 K.3 Comparing the references above, one can roughly note the different temperature ranges between the pyrolysis and incineration processes. Other studies included the utilizations of petroleum waste, waste oil, and petroleum vacuum resid in coal liquefaction.16-19 Coprocessing of coal with petroleum wastes that contained dispersant additives could improve the dispersion of the coal particles and the catalysts during liquefaction. Coal conversions in excess of 90% were obtained, with conversion to oil of 50%. Hydrocracking of vacuum residue by two-stage treatment suppressed the formation of sludge. Hahn20 used heavy oil dehydration facilities to treat crude oil (15) Swanberg, C. MX-2500 Thermal Processor for the Treatment of Petroleum Refinery Wastes and Contaminated Soils. Environ. Prog. 1993, 12 (2), 160-163. (16) Hajdu, P. E.; Tierney, J. W.; Wender, I. Effect of Catalytic Hydropretreatment of Petroleum Vacuum Resid on Coprocessing with Coal. Energy Fuels 1996, 10, 493-503. (17) Mochida, I.; Zhao, X. Z.; Sakanishi, K. Supressing of Sludge Formation by Two-Stage Hydrocracking of Vacuum Residue at High Conversion. Ind. Eng. Chem. Res. 1990, 29, 2324-2327. (18) Ramdoss, P. K.; Kuo, C. H.; Tarrer, A. R. Utilization of Petroleum Waste in Coal Liquefaction. Energy Fuels 1996, 10, 9961000. (19) Sanjay, H. G.; Tarrer, A. R.; Marks, C. Iron-Based Catalysts for Coal/Waste Oil Coprocessing. Energy Fuels 1994, 8, 99-104. (20) Hahn, W. J. High-Temperature Reprocessing of Petroleum Oily Sludges; Society of Petroleum Engineers (SPE): Richardson, TX, 1993; 41-49.
1178
Energy & Fuels, Vol. 14, No. 6, 2000
tank bottoms and other petroleum oily sludge for the residual hydrocarbon recovery and the volume reduction. Benito et al.21 upgraded an asphaltenic coal residue, which was obtained by direct coal liquefaction of a sub-bituminous Spanish coal, by thermal hydrotreatment. It was observed that the thermal cracking took place by two competitive first-order reactions with activation energies of 97 and 145 kJ/mol for the experimental temperatures, and yielded light distillates. The above studies provided some useful information of thermal treatment of oil sludge but gave no data about the pyrolysis products of oil sludge. It is thus the aim of the present work to deal with the pyrolysis of oil sludge with the viewpoint of providing products distribution of solid, liquid, and gas. The pyrolysis is performed by the use of a dynamic thermogravimetric analysis (TGA) reaction system at the temperatureprogrammed heating rate of 5.2 K/min in nitrogen atmosphere. The solid residues, liquid oils, and noncondensable gases at 298 K are collected and analyzed by elemental analyzer, inductively coupled plasmaatomic emission spectrometer (ICP/AES), gas chromatography analyzers with thermal conductivity detector (GC-TCD), and flame ionization detector (GC-FID). Experimental Section Materials. The oil sludge used in this study is sampled from the crude oil storage tank of a typical petroleum refinery plant located in the northern Taiwan. The oil storage tank sludge accumulates at the bottom of tanks where crude oil, product oil, vapor, slop, asphalt, etc., are stored, and it is taken out during periodic tank cleaning and dumped separately from other sludges in ponds with or without covers.3 Nitrogen gas for the purge gas, with 99.99% purity, is purchased from the Ching-Feng-Harng Co. Ltd. in Taipei, Taiwan. The oil sludge sample is dried in a recycle ventilation drier for 24 h at 378 K before use. Thermogravimetry (TG). The lab-scale apparatus used and the experimental procedures for the pyrolysis of oil sludge are the same as those of the previous study.3,22-24 Several duplicate experimental runs are performed in order to collect a suitable amount of solid residues and liquid oils for analysis.The heating rate employed for the analysis of pyrolysis products is 5.2 K/min. Sampling. The mass of oil sludge used for the experiments of study on the pyrolysis products is 300 ( 0.5 mg. The products of pyrolysis of oil sludge are divided into solid residues, liquid oils (condensable liquid, 298 K), and noncondensable gases (298 K). The program-raising temperatures for collecting solid residues are stopped at 533, 623, 713, 743, and 873 K. The pyrolysis gases are passed through two condensing tubes that are immersed in a 298 K water bath, and the condensates are the liquid oils. The pyrolytic temperature range for collecting products is 378-873 K. When the collection glass line between the pyrolysis furnace and condensing tube is exposed to atmosphere, or wrapped with a heating tape at (21) Benito, A. M.; Martinez, M. T.; Fernaudez, I.; Miranda, J. L. Upgrading of an Asphaltenic Coal Residue: Thermal Hydroprocessing. Energy Fuels 1996, 10, 401-408. (22) Lin, J. P.; Chang, C. Y.; Wu, C. H.; Shih, S. M. Thermal Degradation Kinetics of Polybutadiene Rubber. Polym. Degrad. Stab. 1996, 53, 295-300. (23) Wu, C. H.; Chang, C. Y.; Hor, J. L. On the Thermal Treatment of Plastic Mixtures of MSW: Pyrolysis Kinetics. Waste Manage. 1993, 13, 221-235. (24) Chen, K. C. An investigation of major products for pyrolysis of tire tread in nitrogen; M. S. Thesis, Graduate Institute of Environmental Engineering, National Taiwan University, Taipei, Taiwan, 1996.
Chang et al. 410 K, the total condensate collected is referred to as TLA or TLB, respectively. The purpose of performing the experiment with the 410 K heating tape is to reduce the amount of substances coated on the walls of the glass collection line. The liquid oils (TLA and TLB) are then subjected to simulation distillation and compared to the commercial oils. To study the temperature effects on the gaseous products, the noncondensable gases are discretely collected in the 1 L sampling bags for the temperature ranges of 400-425, 425-450, 450-475, 475-500, 500-525, 525-550, 550-575, 575-600, 600-625, 625-650, 650-675, 675-700, 700-725, 725-750, 750-775, 775-800, 800-825, 825-850, 850-875, and 875-900 K, respectively. The concentrations of gaseous products at the pyrolysis temperatures of 413, 438, 463, 488, 513, 538, 563, 588, 613, 638, 663, 688, 713, 738, 763, 788, 813, 838, 863, and 888 K correspond to above temperatures ranges. Analysis. A Hewlett-Packard (HP 5890 series II) GC-FID is used for the quantitative analyses of hydrocarbon (HC) gaseous products and liquid oils. The chromatographic column is a Supelco fused silica capillary column (SPB-5, 30 m long, 0.53 mm i.d., 1.5 µm film thickness). An integrator from Hewlett-Packard (HP 3395) is connected to the GC for graphing and integrating purposes. The conditions for analyzing gaseous products are set as follows: injector temperature 393 K, detector temperature 473 K, column temperature (following the sampling injection) being held at 303 K for 20 min, nitrogen carrier gas flow rate 3.2 mL/min, nitrogen makeup gas 24 mL/min, sample volume 250 µL. The operation conditions for simulation distillation of liquid oils and commercial oils are set as follows: injector temperature 393 K, detector temperature 473 K, column temperature (following the sampling injection) being held at 313 K for 1 min, programmed to 573 K at 10 K/min, and finally stayed at 573 K for 50 min, nitrogen carrier gas flow rate 3.2 mL/min, nitrogen makeup gas 24 mL/min, sample volume 0.5 µL. For the analysis of non-hydrocarbon gases (e. g., H2, CO, CO2), a China Chromatography 8900 GC-TCD with a Supelco packing column (60/80 carbonxen-1000, 15 ft long, 2.1 mm i.d.) is used. An integrator from Hewlett-Packard (HP 3396) is connected to the GC for graphing and integrating purposes. The operation conditions are set as follows: injector temperature 393 K, detector temperature 373 K, column temperature (following the sampling injection) being held at 373 K for 20 min, helium carrier gas flow rate 35 mL/min for A and B columns, sample volume 1000 µL. The concentrations of H2O in the gases products are analyzed by the psychrometer (HT3003, Lutron). The elemental analyses for the solid residues are made on a Perkin-Elmer, Norwalk, CT2400 elemental analyzer with 0.3 wt % accuracy, i.e., C, H, and N analyzed with Heraeus CHNO-RAPID, and S, Cl analyzed with Tacussel Coulomax 78 automatic coulometric titrator. The heavy metals in the solid residues are measured on the ICP/AES (Jarrel-Ash, ICAP 9000). The mass of sample used for the digestion experiment is 0.5 g. For the purposes of analysis, the samples are pretreated by mixing with 2 mL of concentrated HNO3, 0.5 mL of HClO4, and 1 mL of HF and digested at 443 K for 6 h. The heating values of solid residues and liquid oils are measured by the adiabatic bomb calorimeter (O.S.K., 150 Vacuum Flask Oxygen Bomb Calorimeter). Chemicals. The principal gas standards are 99.9999% N2, 99.9% CO2, CO, and H2, and 100 ppmv C1-C6 paraffin and C2-C6 olefins. The liquid standards for establishing calibration curves are listed at Table 1. The gasoline and diesel oil are supplied by the Chinese Petroleum Corp. (Taiwan). The liquid standards for elemental analyzer are sufonilic acid, 1-chloro-2, 4-dinitrobenzene, 3,5-dinitrobenzoic acid, acetanilide, benzoic acid, and stearic acid. Quantitative analysis of gaseous products is based on the calculation using the linear calibration response equations of standards. The equation is generated for each of gas and liquid
Major Products from the Pyrolysis of Oil Sludge
Energy & Fuels, Vol. 14, No. 6, 2000 1179
Table 1. Liquid Standards for Establishing Calibration Curves name
formula
supplier
grade
n-pentane n-hexane n-heptane n-octane n-nonane 1-decene benzene ethylbenze toluene iso-oxylene
C5H12 C6H14 C7H16 C8H18 C9H20 C10H20 C6H6 C8H10 C7H8 C8H10
Theta Merk Merk Merk Merk Merk Merk Merk Merk Merk
GRa GR GR GR GR GR GR GR GR GR
acetone
For Extraction CH3COCH3 Merk
GC
For Simulation Distillation D 2887 Quantitative Calibration Mix No. 4-8882: Supelco. This mixture consists of the following n-paraffins in the proportions (wt %/wt) indicated: hexane 6 dodecane 12 octacosane 1 heptane 6 tetradecane 12 dotriacontane 1 octane 8 hexadecane 10 hextracontane 1 nonane 8 octadecane 5 tetracontane 1 decane 12 eicosane 2 tetratetracontane 1 undecane 12 tetraconsane 2 a
gr: guaranteed reagent.
standards using a minimum of five different concentrations with three replicates at each concentration. All correlation coefficients (r2) of linear calibration response curves are great than 0.997.
Results and Discussion Characteristics of Solid Residues. The oil sludge used in this study is sampled from the crude oil storage tank of a typical petroleum refinery. Its high values of content of combustible substances (58.97 wt % of wet basis), heating value of dry basis (10681 k cal/kg), low heating value of wet basis (5870 k cal/kg) and C element (83.94 wt % of dry basis) suggest that the waste of oil sludge would be a valuable resource. From the TGA and reaction rate curves, the pyrolytic reaction is significant in the 450-800 K range.3 Under the constant heating rate (5.2 K/min), the contents of elemental components of solid residues at different pyrolysis temperatures can indicate the reaction degrees. The results of elemental analysis are summarized in Table 2. It indicates that carbon (C) and hydrogen (H) are the major elements in solid residues. The weight ratios of C/H in solid residues are about 6.99, 6.91, 7.04, 8.41, 11, and 25.2 at pyrolysis temperatures of 298, 533, 623, 713, 743, and 873 K, respectively. The residues of pyrolysis of oil sludge exhibit very high viscous form before 623 K (pyrolysis temperature), while low viscous or solid form after 713 K. This indicates that the pyrolysis processes before 623 K would include physical volatilation with the transformation reaction (the first reaction of the threereaction model of pyrolysis of oil sludge).3 In the temperature range of 623-713 K, the residues of oil sludge form aggregated solid residues (solid form). The C and H elements decrease while S and Cl elements increase between 713 and 873 K (column a). Also, after the pyrolysis temperature of 713 K, the wt C/H ratio increases rapidly. In this pyrolysis temperature range (713-873 K), the reaction mechanism includes two reactions of the three-reaction model.3 From the experimental results, the residual masses are about 96.2, 74.9,
40.6, 21.3, and 13.1 wt % for the heating rate of 5.2 K/min at the pyrolysis temperatures of 533, 623, 713, 743, and 873 K, respectively. The weight percent of C based on the initial sample decreased from 81.1% (533 K) to 5.57% (873 K), and this may be ascribed to the conversion of C to HCs, CO, and CO2. In the process of pyrolysis, some volatile trace metal species may be evaporated with the gaseous products and in parts condensed in the liquid oil. The presence of metal species may then affect the quality of liquid oil. Also, the concentrations of metal elements in the solid residues and TCLP leachates in turn decide the disposal methods. The results of metal element analysis of solid residues are summarized in Table 3. Note especially the dramatic reduction for Hg metal element, which, at 873 K, is reduced by 99 wt %, based on the mass of dry oil sludge. The other metal elements except Pb and Ba do not have significant reductions. The significant reduction of Hg (99 wt %) during the pyrolysis process is reasonable due to its low evaporating point (with boiling point (bp) of 629.6 K). From Table 2, it is noted that the weight percent of Cl decreases from 0.22 wt % in dry oil sludge to 0.08 wt % in solid residues of 873 K. The decrease of Cl in dry oil sludge in the pyrolysis temperature range of 378-873 K indicates that the reduction of Pb might be attributed to the volitilation of PbCl2 (with melting point (mp) and bp of 771 and 1223 K). The reasons for reduction of Ba are not clear (the mp of BaCl2 is 1233 K). For more precise reasons, further research would be needed in the future works. The concentration of total metal element (CMt) of initial dry basis oil sludge is 15728 mg/kg (ppmw). As the temperature increases, the values (column c) of CMt of solid residues (at different temperatures) also increase. The value of CMt of solid residues at 873 K is 83062 mg/kg and 5.28 times that of the initial dry basis oil sludge. Properties of Gaseous Products. Gaseous samples are collected by the discrete and accumulated sampling methods at the preset temperature (298 K) of the water bath. Quantitative analyses are made by GC-FID (for HCs), GC-TCD (for H2, CO, CO2), and psychrometer (for H2O). Retention times of major compounds are summarized in Tables 4 and 5. The components of HCs are classified into seven groups according to the retention times as shown in Table 4. The instantaneous concentrations of gaseous products (discrete samples) at various temperature ranges are shown in Figures 1 and 2. From Figure 1, the maximum instantaneous concentrations occur at about 863 K for CO and CO2, 763 K for H2O, and 713 K for HCs, respectively. The accumulated masses of the four major products (CO2, HCs, H2O, CO) relative to total mass of gaseous products, in wt %, are 50.88 (31595 µg/L) for CO2, 25.23 (15671 µg/L) for HCs, 17.78 (11040 µg/L) for H2O, and 6.11 (3793 µg/L) for CO, respectively. Hydrogen is almost not detected, and the conversion of C to CO2 would be an important reaction. It is noted that CO is not detected before 663 K and the formation of HCs could be neglected before 538 K. Among the seven groups of HCs, the accumulated masses of major HCs relative to the total HCs gases, in wt %, are about 51.61 for C1-2, 17.92 for C6, 11.53 for C5, 9.24 for C3-4, 7.29 for C7, 2.34 for C8, and 0.04 for C9, respectively. The HCs mainly consist of low molec-
1180
Energy & Fuels, Vol. 14, No. 6, 2000
Chang et al.
Table 2. Elemental Analysis of Oil Sludge and Solid Residues at Different Pyrolysis Temperaturesf 533 K
623 K
713 K
743 K
873 K
dry oil sludge
a
b
a
b
a
b
a
b
a
b
S
83.9 (0.90)c 12.0 (0.58) 0.81 (0.53) 2.06
84.3 (0.05) 12.2 (0.05) 0.22 (0.04) 1.3
81.1 (0.05) 11.7 (0.05) 0.19 (0.04) 1.25
32.4 (1.67) 3.86 (0.61) 0.22 (0.06) 0.63
67.4 (3.82) 6.13 (0.69) 0.66 (0.07) 5.04
14.3 (0.81) 1.3 (0.15) 0.14 (0.01) 1.1
0.22
0.19
0.18
59.0 (3.61) 8.37 (0.49) 1.06 (0.88) 0.91 [0.45] 0.11 [3.14]
79.89 (4.11) 9.5 (1.50) 0.54 (0.15) 1.54
Cl
0.14
0.06
0.64
0.14
6.99
6.91
42.55 (10.27) 1.69 (0.30) 0.65 (0.27) 6.17 [5.10] 0.64 [6.39] 25.2
5.57 (1.35) 0.22 (0.04) 0.09 (0.04) 0.81 [0.67] 0.08 [0.84]
wt C/H ratio
78.7 (4.82) 11.2 (0.66) 1.42 (1.17) 1.21 [0.60]d 0.15 [4.19] 7.04
C H N
8.41
96.2e
74.9e
11 40.6e
21.3e
13.1e
d Numbers a Based on mass of residue. b Based on mass of dry oil sludge. c Numbers in parentheses are standard deviations (σ n-1). in brackets are relative errors ((|X1 - X2|/(0.5(X1 + X2))) × 100, %). e Mass ratio of residue to dry oil sludge. Units: in wt % for C, H, N, S, Cl; in wt/wt for wt C/H ratio. f Heating rate (HR) ) 5.2 K/min.
Table 3. Analyses of Metal Elements in Oil Sludge and Solid Residues at Different Pyrolysis Temperaturesf,g oil sludge boiling point (K) Fe
3273
Ca
1760
Na
1156
Al
2720
Mg
1390
Zn
1180
Mn
2393
Hg
629.6
Sr
1639
K
1031
Pb
2024
Cu
2855
Ba
1810
Ni
3113
Cr
2913
Mo
5073
As
886
Co
3823
Cd
1040
Se
958
total e
713 K
743 K
873 K
a(3) wet
b dry
c
d
c
d
c
d
(ppmw)e
(ppmw)e
(ppmw)e
(ppmw)e
(ppmw)e
(ppmw)e
(ppmw)e
(ppmw)e
7340.7 (477.7) 1055.6 (107.9) 348.6 (2.57) 118.3 (3.67) 95.3 (8.99) 91.5 (2.11) 64.4 (9.26) 35.3 (0.01) 28.3 (5.6) 27.5 (3.62) 19.6 (1.87) 14.1 (0.45) 13.7 (0.25) 11.7 (0.12) 6.5 (0.14) 1.3 (0.01) 0.96 (0.02) 0.88 (0.27) 0.14 (0.01) 0.12 (0.001) 9275
12448.2 (810.07) 1790.1 (182.97) 591.15 (4.36) 200.61 (6.22) 161.61 (15.25) 155.16 (3.58) 109.21 (15.7) 59.86 (0.02) 47.99 (9.5) 46.63 (6.14) 33.24 (3.17) 23.91 (0.76) 23.23 (0.42) 19.84 (0.2) 11.02 (0.24) 2.2 (0.02) 1.63 (0.03) 1.49 (0.46) 0.24 (0.02) 0.2 (0.002) 15728
32075 (193.2) 4349.8 (33.1) 1816.5 (69.0) 714.9 (32.3) 369.7 (4.68) 503.4 (5.08) 224.5 (7.74) 0.79 (0.23) 71.01 (1.91) 65.37 (3.27) 23.03 (0.48) 63.91 (0.91) 9.34 (0.56) 62.78 (0.51) 29.98 (0.59) 40.36 (0.25) 3.27 (0.08) 1.98 (0.14) 0.78 (0.02) 3.43 (1.41) 40430
13023 (78.44) 1766 (13.44) 737.49 (28.01) 290.23 (13.11) 150.11 (1.9) 204.39 (2.06) 91.16 (3.14) 0.32 (0.09) 28.83 (0.78) 26.54 (1.33) 9.35 (0.19) 25.95 (0.37) 3.79 (0.23) 25.49 (0.21) 12.17 (0.24) 16.39 (0.1) 1.33 (0.03) 0.80 (0.06) 0.32 (0.008) 1.39 (0.57) 16415
59924 (310.1) 11157 (95.4) 3463.1 (76.95) 1038.6 (51.2) 964.9 (13.14) 2323.3 (18.84) 1238 (10.06) 2.09 (0.01) 355.9
12764 (66.05) 2376.3 (20.32) 737.65 (16.39) 221.23 (10.91) 205.52 (2.8) 494.86 (4.01) 263.73 (2.14) 0.44 (0.002) 75.81
58592 (595.9) 14850 (132.2) 4101.9 (174.8) 1284.6 (28.05) 1091.5 (19.06) 1193.7 (15.82) 625.6 (3.66) 4.58 (0.26) 359.83
7675.6 (78.06) 1945.3 (17.32) 537.4 (22.9) 168.3 (3.67) 143 (2.5) 156.4 (2.07) 81.95 (0.48) 0.60 (0.03) 47.14
246.6 (4.97) 35.08 (0.42) 163.0 (2.29) 21.41 (0.26) 160.4 (5.08) 61.99 (1.32) 13.76 (0.05) 13.47 (0.84) 7.12 (0.37) 2.38 (0.04) 2.66 (1.15) 81194
52.53 (1.06) 7.47 (0.09) 34.73 (0.49) 4.56 (0.06) 34.16 (1.08) 13.20 (0.28) 2.93 (0.01) 2.87 (0.18) 1.52 (0.08) 0.51 (0.008) 0.57 (0.24) 17294
332.7 (9.51) 49.26 (0.92) 239.7 (10.32) 35.0 (4.22) 169.9 (5.25) 80.44 (2.57) 17.85 (0.23) 18.97 (0.89) 8.76 (0.20) 2.32 (0.15) 3.55 (2.46) 83062
43.58 (1.24) 6.45 (0.12) 31.39 (1.35) 4.58 (0.55) 22.26 (0.69) 10.54 (0.34) 2.34 (0.03) 2.49 (0.12) 1.15 (0.03) 0.30 (0.02) 0.47 (0.32) 10881
a Wet basis (ref 3). b Dry basis. c Based on mass of solid residues at different temperatures. d Based on mass of initial dry oil sludge. ppmw: ppm in wt/wt, mg/kg. f Numbers in parentheses are standard deviations (σn-1). g Heating rate (HR) ) 5.2 K/min.
ular weight paraffins and olefins, especially C1-2. Quantitative analyses for the emissions of benzene (B), toluene (T), ethylbenzene (E), and xylene (X) are made and shown in Figure 3 at various temperatures. The accumulated masses of four BTEX gaseous products relative to total mass of BTEX gaseous products, in
wt %, are 63.19 (158.39 µg/L) for benzene, 29.42 (73.75 µg/L) for toluene, 3.96 (9.92 µg/L) for iso-xylene, and 3.43 (8.59 µg/L) for ethylbenzene, respectively. And the maximum instantaneous concentrations occur at about 763 K for benzene and ethylbenzene, 738 K for toluene, and 463 K for iso-xylene, respectively.
Major Products from the Pyrolysis of Oil Sludge
Energy & Fuels, Vol. 14, No. 6, 2000 1181
Table 4. Major Components of HCs and GC-FID Performance Conditions group
retention time (min)
species
average µg/L per area
1 2 3 4 5 6 7
0-2.343 2.343-2.609 2.609-3.114 3.114-5.09 5.09-9.751 9.751-21.036 21.036-
C1-2: methane, ethane, ethylene C3-4: propane, propylene, butane, butene C5: pentene, pentane, C6: hexene, hexane, benzene C7: heptane, toluene C8: octane, ethylbenzene, iso-xylene C9: nonane
3.00524 × 10-5 2.16732 × 10-5 2.32246 × 10-5 2.25522 × 10-5 2.33642 × 10-5 2.61745 × 10-5 1.91829 × 10-5
Figure 1. Instantaneous gaseous product concentrations of oil sludge pyrolysis. Heating rater (HR) ) 5.2 K/min. O, 0, 4, ]: CO2, HCs, H2O, CO.
Figure 2. Instantaneous gaseous product concentrations of HCs of oil sludge pyrolysis. HR ) 5.2 K/min. 1, 2, 3, 4, 5, 6, 7: C1-2, C3-4, C5, C6, C7, C8, C9.
Figure 3. Instantaneous gaseous product concentrations of BTEX of oil sludge pyrolysis. HR ) 5.2 K/min. 1, 2, 3, 4: benzene (B), toluene (T), ethylbenzene (E), iso-xylene (X). Table 5. Major Components of Non-HCs and GC-TCD Performance Conditions species
retention time (min)
average µg/L per area
hydrogen, H2 nitrogen, N2 carbon monoxide, CO carbon dioxide, CO2
1.120 2.897 4.159 17.671
0.3014 0.05143 0.06057 0.08037
Quality of Liquid Oils. The liquid oils are mostly collected in the first condensing tube immersed in 298 K water bath. The liquid oils are collected by two ways to test the efficiency of collection and referred as TLA and TLB. TLB is collected by passing the gaseous
products through a glass connecting line wrapped with a heating tape of 410 K before collecting at 298 K, while TLA is collected without the heating tape. The liquid oils and commercial oils are analyzed for the different boiling points by GC, according to the Standard Test Method for Boiling Range Distribution of Petroleum Fractions, proposed by the ASTM D-2887 method. Five portions of oils are cut apart as listed in Table 6. The simulated distillation results are shown in Figure 4. From Table 6 and Figure 4, TLA contains, in wt %, about 2.33 light naphtha, 0.45 heavy naphtha, 10.97 light gas oil, 65.7 heavy gas oil, and 20.55 vacuum residue, respectively. Therefore, TLA is close to the heavy oil. As for TLB, it contains, in wt %, about 0.72 light naphtha, 12.28 heavy naphtha, 66.58 light gas oil, 10.85 heavy gas oil, and 9.57 vacuum residue, respectively. Comparison of the distillation results indicates that TLB is close to the diesel oil. It is clearly that the quality of TLB liquid oil with a wrapped heating tape before collection has been improved. However, both TLA and TLB liquid oils have significant portion of vacuum residue, which affected the quality of liquid oils. For the oil of TLB with better quality, its heating value is about 10840 k cal/kg and the contents of elements, in wt %, are 84.06 C, 11.01 H, 0.31 N, 1.58 S, and 0.05 Cl, respectively. The mole H/C ratio of TLB oil is 1.57, close to No. 6 fuel oil of 1.56 mole H/C ratio. As for the initial dry oil sludge, its mole H/C ratio is 1.71. Under the pyrolysis process, the H/C of liquid oil of TLB is decreased. The mole H/C ratios of aromatics are between 1.0 and 2.0. Therefore, the mole H/C ratios of both initial dry oil sludge and TLB oil are in the range of aromatics. Mass Balance of Solid Residues, Gaseous Products, and Liquid Oils. Under the pyrolysis temperatures of 413-873 K, the variations of mass fractions of products with temperature for pyrolysis of dry oil sludge are shown in Figure 5. At 873 K, the final product distributions relative to the initial dry oil sludge, in wt %, are about 69.63 liquid oils, 3.57 gaseous products, and 13.1 solid residues, respectively. The total recovery is 86.3 wt % with 13.7 wt % unrecovered. The 13.7 wt % deficiency of recovery may include (1) uncollected substances coated on the walls of the collection line, (2) unidentified gaseous substances, and (3) experimental errors. In terms of the relative percentages to the sum of collected gaseous products, liquid oils, and solid residues, the final product distributions, in wt %, are about 80.68 liquid oils, 4.13 gaseous products, and 15.18 solid residues, respectively. Kinetic Models and Reaction Products. In the previous study,3 among the one-, two-, and threereaction kinetic models proposed for the pyrolysis of oil sludge, the three-reaction model gave the best fit. Based on the multi-reaction kinetic model, the reaction pathways would involve multi-reaction mechanism. Multi-
1182
Energy & Fuels, Vol. 14, No. 6, 2000
Chang et al.
Table 6. Distillation Characteristics of Total Pyrolysis Oil in This Study and Some Commercial Oilsa,b light naphtha 343-366 K heavy naphtha 366-477 K light gas oil 477-616 K heavy gas oil 616-811 K vacuum residue >811 K
DL
FL(24)
HL(24)
TLA
TLB
GL
2.33 (0.86)
0.72 (0.48)
10.07 (1.91)
0.04 (0)
0
0
0.45 (0.15)
12.28 (7.96)
62.93 (0.24)
7.84 (2.34)
4.03
0.29
10.97 (3.96)
66.58 (9.60)
26.15 (2.65)
87.27 (1.42)
46.01
23.88
65.7 (10.44)
10.85 (5.79)
0.85 (0.25)
4.78 (0.99)
49.59
75.19
20.55 (7.48)
9.57 (7.55)
0
0
0.38
0.64
a TL, GL, DL, FL, HL: total pyrolysis oil, gasoline, diesel oil, fuel oil, and heavy oil. Unit: in wt %. b Numbers in parentheses are standard deviations (σn-1).
Figure 4. Simulated distillation results of liquid oil products and commercial oils. TLA (]), TLB (0), HL (4), FL (*), DL (O), GL (×): total pyrolysis oil of A, total pyrolysis oil of B, heavy oil, fuel oil, diesel oil, gasoline.
Figure 5. Variations of mass ratios of products with temperature (T) for pyrolysis of oil sludge. HR ) 5.2 K/min. 0, 4, ×, ], O: residue, balance of residue, sum of liquid and gas collected, liquid collected, gas collected. W, Wo: masses of residue and initial sample.
gross categories of combustible reactants, which in turn yield their distinct products correspondingly, might exist in the oil sludge. The kinetic parameters of the three reactions (1, 2, and 3) proposed in the previous study3 are activation energies E1, E2, and E3 of 69.93, 93.79. and 123.22 kJ mol-1, reaction orders n1, n2, and n3 of 2.94, 2.42, and 1.24, and frequency factors A1, A2, and A3 of 7.69 × 105, 9.09 × 106, and 2.95 × 108 min-1, respectively. The temperature dependence for reaction 1 is weaker than those for reactions 2 and 3 (E1 < E2 < E3), while the trend in reactant amount dependence reverses (n1 > n2 > n3). Thus, the individual extents and amounts of products of three reactions are temperature dependent, which then result in the variation of overall products with temperature. The detailed intrinsic reaction scheme should be rather complex and would need further study to elucidate it. Restated, in this study, the pyrolysis gases are passed through two condensing tubes immersed in 298 K water bath before collection of gas. The condensates of the condensable gases at 298 K are referred as the liquid
oils. In the pyrolytic temperature range of 378-873 K, the compositions of the pyrolytic products of solid residues, condensate liquid oil, and non-condensable gases, which are associated with each other, vary with the temperature according to the multi-reaction kinetic model proposed in the previous study.3 Further from the previous study,3 a higher heating rate (HR) gives a higher value of the residue mass fraction of active reactant (M) at the same reaction temperature (T) and thus a lower conversion X (X ) 1 - M). A higher HR also results in a higher peak value of reaction rate (r, ) dX/dt) and a higher temperature for its occurrence. Noting that X and dX/dt correspond to the yields (Mv) and formation rate (dMv/dt) of products, one may reasonably expect that, at the same T, a higher HR also results in a lower Mv but a higher dMv/dt. For the oil sludge initially subjected to a high temperature (say 873 K), one may regard the situation as a special case of employing extremely high HR with a setting ceiling temperature. Thus, according to the three-reaction kinetic model and the role of HR on Mv and dMv/dt, the product spectrum would be different for the cases with different heating rates and pre-set ceiling temperatures. Recently, Lou et al.25 investigated the gas-products formation (CO, CO2, and HCs) in thermal decomposition of styrene-butadiene rubber (SBR) under various heating conditions (2, 5, 10, and 20 K/min) in oxygennitrogen atmosphere (5, 10, and 20 vol % O2). It is seen that the reaction zone shifts to the high-temperature region and the peak height increases with an increasing HR. That is, an increase of HR causes the temperature with vigorous reaction to increase and the gas formation curve to move toward a high-temperature region. The gas formation rate also increases with a higher HR. Thus, the results of the present study of oil sludge system are consistent with those of Lou et al.25 of SBR system. Conclusions Although the present work combining with the previous study3 of three-reaction kinetic model cannot conclude the completely detailed mechanisms that correspond to the observed pyrolysis behavior, nonetheless, the pyrolysis method not only effectively converts the oil sludge into fuels or primary chemicals, but also greatly reduces the waste residues. In addition, the (25) Lou, J. C.; Lee, G. F.; Chen, K. S. Incineration of styrenebutadiene rubber: the influence of heating rate and oxygen content on gas products formation. J. Hazard. Mater. 1998, 58, 165-178.
Major Products from the Pyrolysis of Oil Sludge
results provide the concluding information as follows. At nitrogen atmosphere with the heating rate of 5.2 K/min, the pyrolytic reaction is complex and significant in the range 450-800 K. The residues of pyrolysis of oil sludge exhibit very high viscous form below 623 K (pyrolysis temperature), while low viscous or solid form above 713 K. The major gaseous products (noncondensable gases at 298 K) excluding N2 are CO2 (50.88 wt %), HCs (hydrocarbons, 25.23 wt %), H2O (17.78 wt %), and CO (6.11 wt %). The HCs mainly consist of low molecular weight paraffins and olefins (C1-C2, 51.61 wt % of HCs). The temperature corresponding to the maximum production rate of HCs is about 713 K. The distillation characteristics of liquid product (TLB, con-
Energy & Fuels, Vol. 14, No. 6, 2000 1183
densate of gas at 298 K) from the pyrolysis of oil sludge is close to diesel oil. However, it contains a significant amount of vacuum residue of about 9.57 wt %. The heating value of liquid product is about 10840 k cal/kg. This study greatly assists the resource recovery of oil sludge. Acknowledgment. We express our thanks to the National Science Council of and the Chinese Petroleum Corp. (Taiwan) financial support, under the contract NSC86-CPC-E-002-002. EF0000532
sincere Taiwan for the number
