Investigations on hydrodesulfurization reactions using slurry catalysts and supercritical water

Depletion of easily accessed and light crude oil sources is shifting future crude oil supply to less attractive heavier oil fractions. Vacuum residue, as the heaviest fraction found in crude oil and the bottom product of the vacuum distillation column in a refinery, has therefore been gaining more and more attention in the past years. It is mostly used as heavy fuel oil in the shipping sector on open seas. Globalization and rising demand of international transportation of goods has led to a strong increase of heavy fuel oil consumption. Sulfur, present in vacuum residue to high extent, forms environmentally hazardous sulfur oxides (SO2 and SO3) when being burnt in the ships engines. In order to counteract rising sulfur oxide emissions, the International Maritime Organization has released a number of restrictions of which the last reduces the maximum allowed sulfur content in fuel for ships on open seas from 3.5% to 0.5%. These new sulfur regulations have come into force on January 1st 2020 and have led to increasing prices for fuels that comply with the sulfur regulations. On the other hand, high sulfur fuels exceeding the sulfur cap of 0.5% are declining in price, also affecting refineries margins when selling high sulfur vacuum residue. Developing a solution for removing sulfur directly from vacuum residue therefore bears large economic potential. Existing hydrodesulfurization technologies severely suffer from catalyst deactivation, coking and plugging as a result of high asphaltenes, heavy metals, and Conradson Carbon present in the viscous vacuum residue. Slurry phase hydrodesulfurization presents potentials for overcoming some of these downsides by using unsupported, highly dispersed catalysts and additives. In this work, process conditions, catalysts, and additives were tested and evaluated with respect to their activity in enhancing desulfurization of high sulfur vacuum residue. Experiments were conducted in a 2 l semi-batch slurry reactor that had the possibility of collecting oil and residue fractions separately. At low temperature, long residence time, and high H2 partial pressure, undesired conversion reactions could be minimized while desulfurization reactions could be maximized. Screening of active substances that influence the reactions, revealed a catalyst and an additive that showed very different effects on conversion and desulfurization reactions than the majority of the tested catalysts. Supercritical water, as very cheap additive, supported solely conversion reactions yielding large amounts of oil, while leaving a high sulfur residue behind. Investigations on sulfur containing model compounds underlined the absence of desulfurization reactions with supercritical water. The novel catalyst showed a strong hydrogenation activity thus destabilizing the sulfur bonds and enabling desulfurization of the high sulfur vacuum residue. Desulfurization of above 90% was achieved while at 400◦C and 310 bar undesired conversion reactions could be kept below 30%. Both mechanistic pathways behind supercritical water hydroconversion and hydrodesulfurization with the novel catalyst were investigated intensively and laid basis for an economic assessment of both hydrotreating routes. On basis of a 50,000 barrels per day vacuum residue upgrading plant, the two cases were calculated. Catalyst cost displayed a large penalty on the economic performance in case of the hydrodesulfurization with the novel catalyst. High sulfur content of the remaining residue in case of the supercritical water process presented the downside of the investigated hydroconversion path. The potential of utilizing the novel catalyst in direct hydrodesulfurization of vacuum residue for the production of Very Low Sulfur Fuel Oil is given though at the current state of research, catalyst cost make the process economically unfeasible. The long term price trends for heavy fuel oils as well as future research on improvement of the novel catalyst will show the potential for commercial applications.

Author dc:creator

• Risse, Stephan

Advisor dc:contributor.advisor

• Behrendt, Frank

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Identifier URI

http://dx.doi.org/10.14279/depositonce-11110

OAI identifier oai:identifier

oai:depositonce.tu-berlin.de:11303/12238