1. A process for the production of a Product Heavy Marine Fuel Oil, the process comprising: mixing a quantity of Feedstock Heavy Marine Fuel Oil, wherein Feedstock Heavy Marine Fuel Oil complies with Table 2 of ISO 8217 (2017) as a residual marine fuel and has a sulfur content (ISO 14596 or ISO 8754) greater than 0.5% wt., with a quantity of Activating Gas mixture to give a Feedstock Mixture; contacting the Feedstock Mixture with one or more hydrotreating catalysts under reactive distillation conditions in a reaction vessel, wherein the reactive distillation conditions promote the formation of a Process Mixture from said Feedstock Mixture, wherein said one or more catalysts are in the form of a structured catalyst bed, and wherein a majority by weight of the Process Mixture is comprised of a Product Heavy Marine Fuel Oil component and a minority by weight of the Process Mixture is comprised of bulk gaseous component and by-product hydrocarbon component; and wherein the reactive distillation conditions promote separating the Product Heavy Marine Fuel Oil portion of the Process Mixture from the bulk gaseous components of the Process Mixture; and the by-product hydrocarbon components from the Product Heavy Marine Fuel Oil; and discharging the Product Heavy Marine Fuel Oil from the bottom of the reaction vessel.
