Effect of cyclohexane as hydrogen-donor in ultradispersed catalytic upgrading of heavy oil

Abstract

The incorporation of catalysts to enhance downhole upgrading in the Toe-to-Heel Air Injection (THAI) process is limited by deactivation due to coking arising from the cracking of heavy oil. This study aims to reduce the catalyst deactivation problems that can occur with upgrading of heavy oils. Ultradispersed catalyst particles could potentially replace pelleted catalysts which may be difficult to regenerate once deactivated during the THAI operation. The dispersed particles could potentially be applied once through, down-hole for in situ upgrading of heavy oil. The catalyst studied was finely crushed pelleted Ni-Mo/Al 2 O 3 catalyst (2.4 μm). The product distribution of liquid, coke and gas may be influenced by the presence of a suitable hydrogen source which promotes hydroconversion reactions rather than simple cracking. In order to improve liquid yield whilst suppressing coke formation, the effect of cyclohexane as hydrogen-donor solvent was studied in a stirred batch reactor (100 mL) at temperature 425°C, initial pressure 17.5 bar, agitation 500 rpm, and a short reaction time of 10 min. The use of cyclohexane was evaluated against that of hydrogen gas. The reaction under hydrogen atmosphere significantly reduced coke yield by 41.3% compared with a nitrogen environment under the same conditions. Also, the coke decreased by 6.2-45.4% as the cyclohexane:oil ratio increased from 0.01 to 0.08 (g·g −1 ) relative to 4.67 wt.% of coke observed without added cyclohexane in ultradispersed catalytic upgrading under nitrogen environment. As the cyclohexane:oil ratio increases, the produced oil API gravity and middle distillate fractions (200-343°C) increase whilst the viscosity decreases. An estimated 0.073 CH:oil ratio was found to suppress coke formation in a similar manner to upgrading under hydrogen atmosphere at the same conditions.

Tetralin and Decalin H-Donor Effect on Catalytic Upgrading of Heavy Oil Inductively Heated with Steel Balls

“…The pressure inside the reactor was controlled by back pressure regulator (Swagelok, Manchester, UK), through the regulation of gas holdup inside the reactor. The ratio of H-donor solvent to oil used was 0.045 (g/g), which is within the range of the optimum reported by Hart et al [22]. The addition of the H-donor solvent caused negligible impact on the API gravity of the THAI feed oil, while the resultant effect on viscosity due to thinning was less than a 10% decrease.…”

“…The risk associated with hydrogen gas has shifted attention to hydrogen carriers such as polycyclic organic compounds, which are known to store, transport and liberate hydrogen in a safer and cost-effective means [21]. Moreover, it is well-known that asphaltene is soluble in aromatic solvents, so the presence of polycyclic organic solvent in the catalytic upgrading medium would keep the asphaltene solubilized, while undergoing cracking into smaller fragments which are readily hydrogenated by the liberated hydrogen [22]. On the other hand, the injection of steam has been reported as an alternative technique to supply hydrogen in situ through the water-gas shift (WGS) reaction and can also help to suppress coke formation [10,23].…”

“…However, to produce appreciable hydrogen, the WGS reaction needs to be conducted at high temperatures, i.e., 400-750 • C [24], and at a temperature above 425 • C, the catalytic upgrading of heavy oil has been shown to suffer more coke deposition, and as a consequence, severe catalyst deactivation and bed plugging can occur [8]. Unlike WGS reaction, where carbon monoxide and steam must be present as reagents, polycyclic organic compounds such as cyclohexane, decalin and tetralin liberate significant amounts of hydrogen in the temperature range 250-425 • C, via dehydrogenation [17,22]. Herein, the effect of tetralin and decalin polycyclic organic solvents as H-donors in an inductively heated catalytic upgrading of heavy oil is reported.…”

Inductive Heating Assisted-Catalytic Dehydrogenation of Tetralin as a Hydrogen Source for Downhole Catalytic Upgrading of Heavy Oil

“…Coke formation can be suppressed when the catalytic upgrading is carried out under a hydrogen rich environment [15]. The difficulty, safety and cost associated with transporting hydrogen gas itself into the reservoir have shifted attention to hydrogen-donor solvents such as polycyclic compounds (i.e., cyclohexane, decalin and tetralin) [16]. These organic liquids potentially store and transport hydrogen in a safer and less challenging manner when compared to external transport of hydrogen gas itself into the reservoir.…”

“…The dehydrogenation of tetralin to naphthalene can be used as a hydrogen source to promote in situ hydrocracking and hydrogenation reactions in the catalytic addon (CAPRI) to THAI. Hart et al [16] reported that the use of cyclohexane as hydrogen-donor solvent for downhole catalytic upgrading of heavy oil suppressed coke formation. Many studies have reported the use of tetralin as H-donor solvent [14,17,18], and the findings showed that coke formation is suppressed and upgraded oil quality improved.…”