Influence of arsenic on light cycle oil hydrodesulfurization over a CoMo catalyst
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Influence of arsenic on light cycle oil hydrodesulfurization over a CoMo catalyst Mildred Rodriguez1 · Susana Pinto‑Castilla1,2 · Myloa Morgado‑Vargas3 · Paulino Betancourt1 Received: 5 August 2020 / Accepted: 25 August 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract Samples of a commercial hydrotreating catalyst with different initial arsenic content were used in the study light cycle oil (LCO) feed in a hydrotreating unit operating at high pressure (350 °C, 3 MPa) to evaluate the conversion and selectivity of the cata‑ lyst in the presence of arsenic. It was determined that arsenic in the catalyst modifies the textural properties and has the strongest influence on the conversion of the HDS reaction. For the first time, evidence is provided that the arsenic replaces cobalt in CoMoS phase. The incorporation of As is proposed to occur in “edge” sites of the molybdenum sulfide disfavoring the C–S cleavage during the HDS reaction, while hydrogenation sites would be favored. Graphic Abstract
Keywords Arsenic · Hydrodesulfurization · LCO feed · Deactivation · CoMo catalyst * Susana Pinto‑Castilla [email protected] Extended author information available on the last page of the article
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Reaction Kinetics, Mechanisms and Catalysis
Introduction The effects of permanent poisons on hydrotreating catalysts have demonstrated to be irreversible, and are generally determined at the end-of-cycle by an activity level too low to meet with the product specifications [1–3]. Different poisons originate from the feed (vanadium, nickel, copper, arsenic, sodium, and mercury), and additives used during refining operations (silicon, lead) or by corrosion (iron) [4–8]. The ini‑ tial refining process consists of distillation and fractionating the crude into separate hydrocarbon cuts. Distillation tends to concentrate any metallic components in the oil residue. However, some organometallic compounds are volatilized at distillation temperatures, therefore, distribute in some of the higher-boiling distillate fractions. The aforementioned metals have a significant deactivating effect on the catalysts, which has a severe impact on the economy of hydrotreating, and consequently, the catalyst must be replaced, because the poisons are so strongly absorbed that they cannot be removed adequately, even with aggressive corrective actions such as ther‑ mal regeneration or steaming. There is a wealth of information available about cata‑ lyst deactivation caused by coke and metals such as vanadium and nickel. While other poisons have been less studied in academic literature, such as arsenic (As). The presence of arsenic as arsine and organoarsenic compounds in crude oil has been recognized to have a significant impact on catalyst activity [9–13]. Also, the arsenic may be present in a range of chemical forms, including elemental, ionic, organic, and as suspended solids, in concentrations ranging from a few parts per billion (ppb) to several ppm. Hydrotreating catalysts consisting of Co(Ni)-promoted molybdenum sulfide sup‑
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