This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present invention. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present invention. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of any prior art.
Marine vessels used in global shipping typically run on marine fuels, which can also be referred to as bunker fuels. Marine fuels include distillate-based and residues-based (“resid-based”) marine fuels. Resid-based marine fuels are usually preferred because they tend to cost less than other fuels, but they often, and typically, have higher sulfur levels due to the cracked and/or residual hydrocarbon components that typically make up the resid-based marine fuels. The International Maritime Organization (IMO), however, imposes increasingly more stringent requirements on sulfur content of marine fuels used globally. In addition, IMO imposes more strict marine fuel sulfur levels in specific regions known as Emission Control Areas, or ECAs. The regulations will require a low-sulfur marine fuel with a maximum sulfur content of 0.1 wt % (1000 wppm) for the ECA in the near future. One conventional way of meeting the lower sulfur requirements for marine vessels is through the use of distillate-based fuels (e.g., diesel) with sulfur levels typically significantly below the sulfur levels specified in the IMO regulations. The distillate-based fuels, however, typically have a high cost premium and limited flexibility in blending components. For instance, use of heavy and highly aromatic components in a distillate-based low-sulfur marine fuel is limited because of the density, MCR content, appearance (color), and cetane specifications imposed on marine distillate fuels. A distinct advantage that resid-based marine fuel oils have over distillate-based marine fuels is that they can incorporate heavy and aromatic components into their formulations because of their product specifications. This allows more flexible use of available blending components for marine fuel oil production and results in lower cost fuels. Further, the use of heavy and highly aromatic components possible in resid-based marine fuel blends allows higher density fuels to be produced.
While there are some publications that disclose the desirability of lowering the sulfur content of marine fuels, there is still a need for low-sulfur marine fuels with at least one residual hydrocarbon component. Exemplary publications include U.S. Pat. Nos. 4,006,076, and 7,651,605, and WO2012135247.