Chlorine (Cl-2) gas is an aggressive chemical used in various industries. Standard separation processes, or purification of chlorine, are energy demanding and complicated. This work focuses on the use of glass membranes as an alternative to the existing separation methods. Three families of glass membranes were considered: pure glass tubes (pore diameters (2-4 nm)), surface modified glass tubes (pore size similar to 1-2 nm), and glass fibres (pore size < 1 nm). Membrane performance for the gases Cl-2, N-2, O-2 was measured, as well as membrane stability towards chlorine exposure over time. A perfluorinated surface modified glass membrane showed the overall best performance and stability with a selectivity of similar to 9 for the gas pair Cl-2-N-2 and a permeance of 3.45 [10(-9) mol/(m(2) Pa s)]. It was however proved that longer acyl chains for the surface modifying component, will increase separation performance (a selectivity for Cl-2-N-2 = 11 and permeance of 6.86[10(-9) mol/(m(2) Pa s)] was achieved). Thinner capillary glass tubes of the same kind are available which will increase these permeances by a factor of 17. The selectivity is expected to increase for increased chain length of the perfluorinated compound, as documented in the current work. Hollow glass fibre membranes (not surface modified) are also promising candidates for the chlorine separation. A more detailed discussion of the governing transport mechanisms through the glass membranes is presented in the companion paper. (c) 2005 Elsevier B.V. All rights reserved.