Processes and systems for forming ethanol from methanol. The process involves carbonylating the methanol to form acetic acid and hydrogenating the acetic acid to form ethanol. In a first aspect, at least some hydrogen for the hydrogenating step is derived from a tail gas stream formed in the carbonylation step. In a second aspect, at least some carbon monoxide for the carbonylation step is derived from a vapor stream in the hydrogenation system. In a third aspect, a syngas stream is separated to form a hydrogen stream and a carbon monoxide stream, and the hydrogen stream is methanated to remove residual carbon monoxide prior to being introduced into the hydrogenation system.