A process for operating a guard bed system in a reaction system for the production of ethylene carbonate and/or ethylene glycol, said reaction system comprising a catalytic ethylene oxide reactor, a guard bed system positioned upstream of the catalytic EO reactor, and an EO absorber positioned downstream of the catalytic EO reactor, wherein the gas composition from the catalytic EO reactor is passed to the EO absorber in which it is contacted with a lean absorbent in the presence of one or more catalysts that promote carboxylation and hydrolysis, wherein gases that are not absorbed in the EO absorber are removed from the top of the EO absorber and recycled to the EO reactor, and wherein the one or more catalysts that promote carboxylation and hydrolysis in the EO absorber comprise one or more iodides or bromides, and iodide-containing impurities or bromide-containing impurities are formed which exit the EO absorber with the recycle gas stream, said guard bed system comprising a feed line supplying a gaseous feed to be treated and an effluent line configured to remove the treated gaseous feed and two or more guard bed vessels arranged in series in sequential order, each guard bed vessel comprising an inlet, a bed of guard bed material and an outlet, wherein the inlet of each guard bed vessel is attached by means of valves to both the feed line and the outlet of the guard bed vessel preceding it in sequential order and wherein the outlet of each guard bed vessel is attached by means of valves to both the effluent line and to the inlet of the guard bed vessel following it in sequential order and wherein the guard bed vessel following the last guard bed vessel in sequential order is the first guard bed vessel in sequential order, said process comprising the steps of: (i) supplying the gaseous feed to be treated via the feed line, wherein the gaseous feed to be treated is the recycle gas from the EO absorber; (ii) feeding said gaseous feed through the two or more guard bed vessels arranged in series, wherein each guard bed vessel comprises a bed of guard bed material capable of removing impurities from the gaseous feed; (iii) contacting the gaseous feed with the guard bed material in each of the two or more guard bed vessels thereby removing impurities from the gaseous feed; (iv) removing a treated gaseous feed from the final guard bed vessel in series; (v) after a period of time, removing the first guard bed vessel from the flow of the gaseous feed and allowing the gaseous feed to continue to flow through the second and any subsequent guard bed vessels; (vi) refreshing the guard bed material present in the first guard bed vessel; and (vii) restoring flow of the gaseous feed through the first guard bed vessel such that it is the last guard bed vessel in series to be contacted with the gaseous feed. (i) supplying the gaseous feed to be treated via the feed line, wherein the gaseous feed to be treated is the recycle gas from the EO absorber; (ii) feeding said gaseous feed through the two or more guard bed vessels arranged in series, wherein each guard bed vessel comprises a bed of guard bed material capable of removing impurities from the gaseous feed; (iii) contacting the gaseous feed with the guard bed material in each of the two or more guard bed vessels thereby removing impurities from the gaseous feed; (iv) removing a treated gaseous feed from the final guard bed vessel in series; (v) after a period of time, removing the first guard bed vessel from the flow of the gaseous feed and allowing the gaseous feed to continue to flow through the second and any subsequent guard bed vessels; (vi) refreshing the guard bed material present in the first guard bed vessel; and (vii) restoring flow of the gaseous feed through the first guard bed vessel such that it is the last guard bed vessel in series to be contacted with the gaseous feed.