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Study on Hydrothermal Cracking of Heavy Oils: Formation of Radical Under Lower Reaction Temperature

ע⣺ՓAnal. Rep. Eng. Res. Inst. Facul. Eng. Univ. Tokyo, vol.59, pp.111l
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Jie CHANG, Noritatsu TSUBAKI and Kaoru FUJIMOTO

SYNOPSIS

The hydrothermal cracking of heavy oils, Canadian oil sand bitumen and Arabian heavy vacuum resid, as well as their model compound were performed over Ni/Al2O3 and NiMo/Al2O3 catalysts under 663-703 K and 5.0 MPa of hydrogen pressure in a autoclave reactor. The conversions of heavy oils and their model compound were remarkably enhanced by adding some free radical initiators, such as peroxide and sulfur. The reaction mechanism on model compound, 1-phenyldodecane (PhDD), suggested that the hydrogen in hydrocarbon was easily abstracted by free radicals that were formed from initiators under lower temperature, and the chain reactions were readily initiated. Therefore, the conversion was obviously increased even at lower reaction temperature.
1. Introduction

With the growing demand for high quality transportation fuels and middle distillate products, to obtain high conversion from heavy oil and bitumen is becoming the predominant research target of resid upgrading processes. Hydrothermal cracking has been developed to obtain maximum middle distillate yield (kerosene + gas oil) from residual oil 1-3). It involves free radical chain reactions and catalytic hydrogenation reactions: (1) C-C and C-X (heteroatom) bonds rupture to produce free radicals; (2) free radical dissociation to produce low-boiling products; (3) catalytic hydrogenation to terminate radicals, remove heteroelements and saturate C-C bonds such as olefin and aromatic etc 4,5).
The decomposition of resid is thermodynamically favored at high reaction temperature. With the increase of temperature, the selectivity of by-products, coke and gaseous hydrocarbon, will be increased, and therefore the selectivity of middle distillate will be lowered. How to obtain high conversion at low reaction temperature is the key point to resolve this contradiction. According to the mechanism of free radical chain reactions, some effective initiators may enhance the conversion of residue by increasing the concentration of free radicals. The present work showed the effect of the addition of free radical initiators, di-tert-butyl-peroxide (DTBP) and sulfur, on the decomposition of resids and model compound. Both remarkably enhanced the conversion of heavy oil.(
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Reference

[1] Nakamura I, Aimoto K, Fujimoto K. AIChE Symp., 1989, 85 (237), 15.
[2] Aimoto K, Nakamura I, Fujimoto K. Energy & Fuels, 1991, 5, 739.
[3] Chang J, Fan L, Fujimoto K. Energy & Fuels, 1999, 13, 1107. 
[4] Beaton WI, Bertolacini R. Catal. Rev.-Sci. Eng., 1991, 34 (3&4), 281.
[5] Fujimoto K, Chang J, Tsubaki N. Sekiyu Gakkaishi, 2000, 43 (1), 25.
[6] Speight J.G. The Chemistry and Technology of Petroleum, Marcel Dekkere, Inc. 1980, p. 229.

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1Effect of Addition of K to Ni/SiO2 and Ni/Al2O3 Catalysts on Hydrothermal Cracking of Bitumen

2Initiation Effect of Local Heating in Hydro-Thermal Cracking of Resids

3The Promotional Effect of Initiators in Hydro-thermal Cracking of Resids

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5Enhancement effect of free radical initiator on hydro-thermal cracking of heavy oil and model compound

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