TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Process: The step (f) is carried out at 470-515 K. The gel is aged for at least 24 hours. The gel is aged at 10-75degreesC. The process further comprises: repeating steps (e) and (f) at least once. The steps (e) and (f) are repeated until the SAPO layer is substantially impermeable to nitrogen, before performing step (g); and washing and drying the support and the SAPO layer after step (f). The composition of the SAPO-34 crystals applied to the surface in step (b) is substantially similar to composition of the crystalline material formed in step (f). The average size of the crystals applied to the surface is step (b) is 100-1000 nm. The pore size of the support is greater than the size of the SAPO-34 crystals applied in step (b). Preferred Components: The ratio of silicon to aluminum is 0.15-0.3, preferably 0.15. The gel composition comprises 1 aluminum oxide:a phosphorus pentoxide:b silicon dioxide:c R:d water (where R is a quaternary organic ammonium templating agent, a is 0.01-52, b is 0.3-0.6, c is 0.2-5, and d is 20-300). The pore size of the support is 0.1-6 microns. The support surface comprises non-porous and porous portions. The first quantity of crystalline material does not form a complete or nearly complete layer over the non-porous portion of the surface. The support is in the form of a tube having an inner and an outer surface, and the SAPO layer is formed on only one of the inner or outer surface. The support has an upper and a lower surface and the SAPO layer is formed on only one of the upper or lower surface. The thickness of the SAPO layer is less than about 5 microns.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The templating agent is a quaternary organic ammonium templating agent. EXAMPLE - Silicoaluminophosphate-34 crystals were applied on to the porous stainless steel tubes. Phosphoric acid (85 wt.% aqueous solution), aluminum triisopropoxide and water were stirred for 12 hours, then tetra-ethyl ammonium hydroxide (35 wt.% aqueous solution) was added, and the mixture was stirred for 30 minutes before the Ludox AS40 (RTM: Colloidal silica solution) was added to give a solution. The solution was sealed and stirred during storage to give the gel composition comprising aluminum oxide:phosphorus pentaoxide: b silicon dioxide:1.2 tetra-ethyl ammonium hydroxide:55 water. The gel was aged for at least 24 hours. The outside of the tube was wrapped in Teflon tape. The tube was then placed vertically in an autoclave and the autoclave was filled with synthesis gel. The hydrothermal synthesis was carried at 473 K for 24 hours. Then the membrane was washed with purified water at 297 K, dried at about 373 K for 10 minutes and calcined at 663 K for 10 hours to give the crystalline silicoaluminophosphate-34 (SAPO-34) membrane.