Heteroatom Removal as Pretreatment of Boiler Fuels

Heteroatom removal without the use of hydrogen was investigated for the pretreatment of heavy fuels to produce cleaner burning boiler fuels from petroleum residua and coal. This is relevant for applications, such as the production of marine bunker fuel oil, where the anticipated change in maximum sulfur specification in January 2020 is from 3.5 to 0.5 wt %. Processing challenges, such as fluidity, yield loss, and cost-effective reagents, were considered. The study drew primarily on published data; however, claims about key process steps were experimentally verified, and those results are also presented. An oxidative process that employed air as an oxidant was evaluated for oxidative liquefaction and heteroatom removal from coal and petroleum. It was found that this strategy was viable for coal conversion but not for petroleum. Oxidative coal liquefaction produced two potential boiler fuels, an oxidized partly desulfurized coal and a water-soluble coal product. This step was experimentally demonstrated. The experimental work indicated that product separation is potentially challenging. Oxidized sulfur- and nitrogen-rich material must be treated to remove sulfur and nitrogen from the bulk of the hydrocarbon mass, which would otherwise represent a substantial yield loss. This step was not demonstrated. The final processing step involved deoxygenation to improve the heating value of the cleaned boiler fuel. Catalytic deoxygenation over zinc oxide and copper oxide appeared to be promising. Copper oxide supported on a carbon catalyst was evaluated for deoxygenation. Substantial deoxygenation of a mixture of acids was achieved by conversion at 350 °C, with both ketonization and decarboxylation pathways being active for deoxygenation.