A breathing air purification device and method having a carbon-monoxide free sweep stream. Water vapor is removed from a compressed air stream using a membrane dryer, comprising, a membrane having a permeate portion and a non-permeate portion, a membrane housing which encases the membrane, a membrane feed inlet conduit connected to the membrane and a non-permeate gas outlet conduit fluidly connected to the non-permeate portion of the membrane. The sweep stream used to cleanse the outer permeate portion of the membrane dryer is taken from a catalyst filter. The catalyst filter includes a cartridge containing a bed of catalyst, two end pieces maintaining the cartridge within a catalyst bed housing and having outlet holes, a catalyst inlet conduit connected to the bed of catalyst and a product gas outlet conduit connected to the outlet holes. A sweep inlet tube provides a gas connection from the catalyst filter component to the permeate portion of the membrane.