<p>Disclosed herein is a process comprising introducing a chlorine-containing gas through an adsorbent to adsorb chlorine and thereafter reducing the pressure of the adsorbent to a pressure lower than that during the introduction, thereby obtaining an effluent gas with a higher chlorine concentration than that of the introduced gas. Among preferably usable adsorbents are zeolite, non-zeolite type porous acidic oxides and active carbon.</p>
