Hydrocracking of vacuum residue with activated carbon in supercritical hydrocarbon solvents Tran Tan Viet a , Jae-Hyuk Lee a , Jae Wook Ryu b , Ik-Sung Ahn a , Chang-Ha Lee a,⇑ a Department of Chemical and Biomolecular Engineering, Yonsei University, Seoul, Republic of Korea b Global Technology, SK Innovation, Daejun, Republic of Korea article info Article history: Received 2 June 2011 Received in revised form 17 August 2011 Accepted 3 September 2011 Available online 18 September 2011 Keywords: Vacuum residue Supercritical reaction m-Xylene Activated carbon Hydrocracking abstract Hydrocracking of vacuum residue with activated carbon was conducted in a batch reactor with two types of supercritical hydrocarbon solvents, aromatic hydrocarbons (m-xylene and toluene) and normal alkane hydrocarbons (n-hexane and n-dodecane). The supercritical reactions were performed at 400 °C with H 2 partial pressures of 3.45 MPa and 6.89 MPa. The supercritical hydrocarbon solvent affected the levels of conversion and coke formation as well as the distribution of oil products (naphtha, middle distillate, vac- uum gas oil, and residue). The mass ratio of each oil product to the unreacted residue differed among the supercritical solvents. Compared to the product profile in n-alkane solvents, aromatic solvents yielded much smaller naphtha fractions and larger middle distillate fractions. An increase of surface acidity of the activated carbon led to the conversion improvement observed in the supercritical reactions. However, the increased partial pressure of hydrogen was not associated with significant changes in conversion. High conversion (69.2 wt.%) with low coke (13.5 wt.%), and high quality oil products (13.0 wt.% of naph- tha, 34.9 wt.% of middle distillate, 27.1 wt.% of vacuum gas oil, and 11.2 wt.% of residue) could be obtained with supercritical m-xylene and acid-treated activated carbon. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Recently, rising demand for conventional light petroleum prod- ucts has prompted the petroleum industry to refine heavier crude oils of lower quality. In addition, due to the dwindling reserves of sweet crude oil and environmental concerns, a greater amount of petroleum residue has to be converted into lighter fractions [1]. Among petroleum residue fractions, vacuum residue (VR) is the heaviest fraction of refinery processing. VR is obtained from the bottom of the vacuum distillation column tower at 3.33– 13.33 kPa, which has an atmospheric equivalent boiling point above 535 °C. Therefore, VR is characterized by a high density, high molecular weight, low atomic hydrogen to carbon ration (H/C ra- tio), and an extremely high viscosity. Furthermore, VR contains higher portions of asphaltenes/resins and higher concentrations of sulfur, nitrogen, and oxygen compounds and heavy metals such as vanadium, nickel, and iron [2,3]. The most difficult challenges encountered during residue conversion are coke formation and fouling, which not only deactivate the solid catalyst but also dam- age the surfaces of refining equipment [4,5]. Various strategies have been proposed to convert VR into light fractions with fewer contaminants such as carbon rejection processes [6], pyrolysis in supercritical water [7,8], solvent deasp- halting [9], and hydrogen addition processes [10]. Compared with carbon rejection processes, hydrogen addition processes such as hydrocracking and hydrotreating require moderate temperatures for reactions and provide high conversion levels with less coke for- mation. The standard hydrocracking process uses an alumina-base supported Ni, Mo, or Co catalyst [11,12], but is subject to the crit- ical problem of catalyst deactivation caused by coking and deposi- tion of heavy metals [13]. To address catalyst deactivation, other types of catalysts have been adopted such as the homogeneous cat- alyst HFÁBF 3 [14] or dispersed metal catalyst [15]. However, corro- sion of the reactor and the difficulty in separating catalysts from solution has limited the applications of these catalysts. Develop- ment of more durable and less expensive catalysts and additives for high conversion and prevention of coke has been an imperative in the petroleum industry. To achieve high conversion of residue with a relatively inexpen- sive catalyst, activated carbon (AC) has received a great deal of attention as a catalyst or catalyst support because of its high sur- face area, variable pore structure, and surface functional groups [16–18]. In addition, it has relatively better resistance to coke deposition and allows easy recovery of heavy metals by combus- tion. In addition, AC can act as a hydrogen transfer agent in hydro- cracking and leads to high conversion levels [19]. The cracking mechanism of AC is different from that of metallic catalysts [20]. Since the carbon catalyst has high selectivity for the thermal cleav- age of alkylene bridges between naphthyl moieties, bond cleavage 0016-2361/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2011.09.007 ⇑ Corresponding author. Tel.: +82 2 2123 2762; fax: +82 2 312 6401. E-mail address: leech@yonsei.ac.kr (C.-H. Lee). Fuel 94 (2012) 556–562 Contents lists available at SciVerse ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel