Aspects of the invention relate to systems and processes for recovering methanesulfonic acid, in a purified form, from a composition additionally including sulfur trioxide. In accordance with one aspect, the invention provides a process that includes separating a feed stream comprised of hydrocarbons, methanesulfonic acid, sulfur trioxide, and optionally sulfuric acid to produce a light stream comprised of hydrocarbons and a heavy stream comprised of methanesulfonic acid and sulfur trioxide; contacting (e.g., by mixing) the heavy stream with a reactive additive capable of reacting with sulfur trioxide, under conditions effective to cause reaction of the reactive additive with the sulfur trioxide to produce a heavy reaction product having a boiling point higher than the boiling point of methanesulfonic acid; and separating the heavy stream using a distillation column to produce a distillate stream consisting essentially of methanesulfonic acid and a bottoms stream comprising the heavy reaction product.