Energy & Fuels 1997, 11, 385-391
385
Pyrolysis Analysis of Crude Oils and Their Fractions Ozgen Karacan and Mustafa Versan Kok* Petroleum Research Center (PAL), Department of Petroleum and Natural Gas Engineering, Middle East Technical University, 06531 Ankara, Turkey Received September 19, 1996. Revised Manuscript Received December 20, 1996X
This research was conducted to investigate the pyrolysis behavior of crude oils and their fractions using differential scanning calorimetry and thermogravimetry. Experiments were performed at 10 °C/min heating rate under nitrogen atmosphere. An examination of the fractions of crude oils shows that pyrolysis mechanisms depend on the chemical nature of the constituents. A study of the weight loss properties of SARA constituents suggests that each fraction in whole crude oil follows its own reaction (distillation and cracking) pathway independent of the presence of other fractions.
Introduction Differential scanning calorimetry (DSC) and thermogravimetry (TG/DTG) have not often been applied to the study of crude oil and its fraction pyrolysis due to their relatively recent development. Skala et al.1 used TG/ DTG and DSC to investigate the kinetics of nonisothermal pyrolysis of Aleksinae oil shale from the former Yugoslavia, and the influence of the addition of cracking catalyst addition was examined on the overall kinetics and conversion, in particular temperature regions. Del Bianco et al.2 used a vacuum residue of crude for thermal cracking to define a kinetic scheme and to calculate the kinetic parameters of thermal cracking of petroleum residues. They concluded that distillate production can be described as a simple first-order reaction, while coke formation seems to be the consequence of consecutive reactions, in particular those involving asphaltenes. Yoshida et al.3 investigated the thermal behavior of coal-derived asphaltenes by TG/ DTG. In their work, they conclude that weight loss is rapid from 300 to 500 °C and is slow above 500 °C. They also state that the asphaltene, which is comparatively low in molecular weight, shows greater weight loss. Rosenvold and Dubow4 analyzed the pyrolysis of bituminous coal samples by DSC. They have distinguished three regions of endothermic activity in the DSC scans in an inert atmosphere. Ranjbar5 investigated the influence of reservoir rock composition on the pyrolysis and combustion behavior of crude oils in porous media by thermal analysis techniques. Pyrolysis and combustion tests were performed to examine how clays affect the amount of fuel and its reactivity. He concluded that clay minerals present in the matrix enhance fuel deposition during the pyrolysis process and also catalyze the oxidation of fuel. Mianowski and Radko6 developed a method for evaluation of the temperature range to Abstract published in Advance ACS Abstracts, February 1, 1997. (1) Skala, D.; Kopsch, H.; Sokic, M.; Neumann, H. J.; Jovanovic, J. Fuel 1987, 66, 1185-1191. (2) Del Bianco, A.; Panariti, M. A.; Beltrame, P. L.; Carniti, P. Fuel 1993, 72, 75-85. (3) Yoshida, R.; Takeda, S.; Teramoto, S.; Matsushita, T.; Takeya, G. Fuel Process. Technol. 1984, 9, 307-313. (4) Rosenvold, R. J.; Dubow, J. B. Thermochim. Acta 1982, 53, 321326. (5) Ranjbar, M. J. Anal. Appl. Pyrolysis 1993, 27, 87-93. (6) Mianowski, A.; Radko, T. Fuel 1993, 72, 1537-1542. X
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calculate the kinetic parameters of coal pyrolysis. They concluded that pyrolysis is a first-order process for 12 coal samples of different rank. Ciajolo and Barbella7 used thermogravimetric techniques to investigate the pyrolysis and oxidation of some heavy fuel oils and their separate paraffinic, aromatic, polar, and asphaltene fractions. They also found that the thermal behavior of fuel oil can be interpreted in terms of a lowtemperature phase involving the volatilization of paraffinic and aromatic fractions and a high-temperature phase in which the polar and asphaltene fractions pyrolyze and leave a particulate carbon residue. Ranjbar and Pusch8 studied the effect of oil composition, characterized on the basis of light hydrocarbons, resin, and asphaltene contents and the pyrolysis kinetics of the oil. The results indicate that the colloidal composition of oil as well as the transferrability and heat transfer characteristics of the pyrolysis medium have a pronounced influence on fuel formation and composition. Ali and Saleem9 investigated the asphaltenes precipitated from crude oils by thermogravimetric analysis and pyrolysis-GC analysis. Under severe pyrolysis conditions 98-100% of asphaltenes are converted to the products. The evaluation of methane and other normal alkenes from all of the asphaltenes under mild pyrolysis conditions indicates that these asphaltenes contain thermally labile alkyl groups on the periphery of these asphaltenes. The aim of this study was to analyze the pyrolysis behavior of the fractions of crude oil by means of TG/ DTG and DSC and thus describe the complex whole oil via the less complex, chemically more representative constituents. Experimental Section Experiments were performed using the DuPont 9900 thermal analysis system with DSC and TG/DTG modules. The differential heat flow of the samples is monitored by DSC, whereas TG/DTG has the capability of measuring the weight loss as a function of either temperature or time in a varied but controlled atmosphere. Prior to the experiments the DSC (7) Ciajolo, A.; Barbella, R. Fuel 1984, 63, 657-662. (8) Ranjbar, M.; Pusch, G. J. Anal. Appl. Pyrolysis 1991, 20, 185192. (9) Ali, M. F.; Saleem, M. Fuel Sci. Technol. Int. 1991, 9, 461-468.
© 1997 American Chemical Society
386 Energy & Fuels, Vol. 11, No. 2, 1997
Karacan and Kok
Figure 1. TGA thermogram of B.Raman crude oil and its fractions. Table 1. Properties of Crude Oils property
Garzan crude oil
B.Raman crude oil
°API gravity (°API) viscosity (cP)
