Abstract
With the growing demand for energy and the depletion of conventional crude oil, heavy oil in huge reserve has attracted extensive attention. However, heavy oil cannot be directly refined by existing processes unless they are upgraded due to its complex composition and high concentration of heteroatoms (N, S, Ni, V, etc.). Of the variety of techniques for heavy oil upgrading, supercritical water (SCW) is gaining popularity because of its excellent ability to convert heavy oil into valued, clean light oil by the suppression of coke formation and the removal of heteroatoms. Based on the current status of this research around the world, heavy oil upgrading in SCW is summarized from three aspects: Transformation of hydrocarbons, suppression of coke, and removal of heteroatoms. In this work, the challenge and future development of the orientation of upgrading heavy oil in SCW are pointed out.
Highlights
Heavy oil is a collective term for unconventional crude oil with a gravity smaller than 20 API and a viscosity greater than 100 cP [1,2]
Funazukuri et al [30,37] studied supercritical fluid extraction of Chinese oil shale and found that polar components were more decomposed in supercritical water (SCW) than in supercritical toluene (SCT)
With the growing heavier of the crude oil, upgrading heavy oil in SCW may be a promising alternative technique to meet the constantly increasing demand for clean light oil, due to its relatively superior performance in the transformation of hydrocarbons, the suppression of coke, and the removal of heteroatoms
Summary
Heavy oil is a collective term for unconventional crude oil with a gravity smaller than 20 API and a viscosity greater than 100 cP [1,2]. The goal for upgrading heavy oil is to produce light oil suitable for further utilization, which can be realized through the cracking and removal of macromolecules, the elimination of the heteroatoms, the lowering of the viscosity, and the increasing of the H/C ratio [2,10]. Among the technologies for upgrading heavy oil, the technique of deasphalting is often used due to its effective removal of heteroatoms, along with the asphaltene, in the extraction processes [14]. Though the hydrogen addition processes can retard the formation of coke and convert heavy components into valuable light fraction, the cost of hydrogen is considerable [19]. Extensive research shows that upgrading heavy oil in SCW would produce cleaner light fractions and less coke than those in pyrolysis processes.
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