Removing sulfur from hydroprocessed fischer-tropsch products

Abstract

An integrated process for producing desulfurized hydroprocessed products from Fischer-Tropsch synthesis is disclosed. The process involves isolating and desulfurizing a methane-rich stream from a natural gas source in a first separation zone and a desulfurization zone. The methane-rich stream is converted to syngas and subjected to a hydrocarbon synthesis step, for example, a Fischer-Tropsch synthesis step. The products from the hydrocarbon synthesis step typically include a C − fraction, a C fraction, and a C + wax fraction. These fractions are isolated in a second separation zone, typically via fractional distillation. The C − fraction can be recycled through the first separation zone to provide a second methane-rich fraction for conversion to synthesis gas. The C − fraction can optionally be treated, for example, with hydrotreatment or hydroisomerization catalysts and conditions before or after passage through the first separation zone. The hydrocarbons in the C and C + wax fractions are subjected to additional process steps, for example, hydrotreatment, hydroisomerization, hydrocracking (particularly in the case of the wax fraction), preferably in the presence of sulfur-containing compounds. The products of the additional process steps are sent to a third separation zone, and yield one or more fractions useful, for example, in fuel-related products (preferably C hydrocarbons) as well as an additional C4− fraction. The additional C4− fraction, which can include sulfur impurities resulting from the hydroconversion reaction, can also be desulfurized in the desulfurization zone along with the natural gas. This eliminates the need for a second desulfurization zone. The desulfurization zone can be scaled up from its normal size, if desired, to accommodate the additional sulfur removal resulting from the hydroconversion.