A gas separation membrane module includes a seal between a higher pressure gas and a lower pressure gas. The seal includes a compressible sealing member in between sealing surfaces. At least one of the sealing surfaces has corrosion-resistant cladding provided over either low alloy steel or high alloy steel. The cladding reduce the possibility of a seal failure due to corrosion of low alloy or high alloy steel exposed to acid gases or condensed moisture containing acid gases dissolved therein while at the same not requiring that all surfaces of the membrane module exposed to acid gases be provided with cladding.

A filter medium of the present disclosure has a laminate structure composed of a first polytetrafluoroethylene (PTFE) porous membrane, a first air-permeable supporting member, a second PTFE porous membrane, and a second air-permeable supporting member laminated in this order. The first PTFE porous membrane constitutes an exposed surface of the filter medium. A ratio of a transmittance of the first PTFE porous membrane to a transmittance of the second PTFE porous membrane is 100 or more. The filter medium of the present disclosure is a filter medium which includes the PTFE porous membranes, from which dust deposited on a surface over a period of use can be easily removed, and which has excellent reusability demonstrated by reduction of a filtration performance decrease caused by removal of dust.

The present disclosure is directed to a membrane vessel, the membrane vessel comprising: a cylindrical tube for holding a membrane element, the cylindrical tube having a first end and a second end; at least one flared end of the cylindrical tube wherein the tube flares outward at an angle from the end of the cylindrical tube; a cap configured to fit into the end of the cylindrical tube, the cap comprising an inclined distal perimeter surface configured to contact the inner surface of the flared tube.