The invention provides a reaction system for the production of ethylene carbonate and/or ethylene glycol. The reaction system having a guard bed system upstream of a catalytic EO reactor. The guard bed system having a feed line supplying a gaseous feed and an effluent line configured to remove the treated gaseous feed. The guard bed system has two or more guard bed vessels arranged in series in sequential order, each having an inlet, a bed of guard bed material and an outlet. 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. 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.