Processes for converting methane into methanol are disclosed in which methane, water, and a supported chromium (VI) catalyst are contacted with a light beam at a wavelength in the UV-visible spectrum in an oxidizing atmosphere in a single reactor to form a reaction product comprising methanol, followed by discharging a reactor effluent containing the reaction product from the single reactor, and then separating methanol from the reaction product. Processes to produce methanol using additional reactors also are described, as well as related methanol production systems.