Process for synthesising hydrocarbons

A process for synthesising hydrocarbons comprising the steps of:

• (a) feeding a gas mixture comprising hydrogen and carbon dioxide to a reverse water-gas shift unit to form a crude synthesis gas comprising hydrogen, carbon monoxide carbon dioxide and steam, (b) cooling the crude synthesis gas to condense water and removing water from the crude synthesis gas to produce a feed stream comprising hydrogen and carbon monoxide, (c) passing the feed stream though a hydrocarbon synthesis unit comprising a reactor containing a Fischer-Tropsch catalyst to form a product stream comprising a mixture of liquid hydrocarbons, a co-produced water stream, and a tail gas stream containing hydrogen, carbon monoxide and gaseous hydrocarbons, and (d) upgrading the product stream in an upgrading unit to produce an upgraded product stream, the upgrading unit comprising a hydrotreating unit to perform one or more of hydroisomerization, hydrogenation, hydrodeoxygenation, and hydrocracking to produce the upgraded product stream, wherein a naphtha stream is separated from the product stream or the upgraded product stream, at least a portion of the tail gas stream is fed with steam to a first derichment vessel containing a derichment catalyst to form a first gas mixture containing methane, at least a portion of the naphtha stream is fed with hydrogen and steam to a second derichment vessel containing a derichment catalyst to form a second gas mixture containing methane, wherein the first and second derichment vessels containing derichment catalyst convert C2+ hydrocarbons to methane, wherein the first and second derichment vessels are operated at different conditions to produce the first and second gas mixtures containing methane, and the first and second gas mixtures containing methane are fed to the reverse water gas shift unit.