Different types of membranes can operate at different temperatures. The most common polymeric membranes can operate between 1 to 45 deg C. Normal operating temperature is 15 to 25degC. If a membrane is operated above the maximum allowable temperature, the membrane will quickly degrade resulting in poor product quality.
At lower temperature, the operating pressure will by higher, mostly due to increased viscosity of the process fluid. Conversely, as temperature increases, operating pressure will reduce.
In the case of Reverse Osmosis membranes, rejection of dissolved substances will increase as temperature decreases, and decrease as temperature increases.
There are special polymeric membranes that can operate at much higher temperatures (e.g. 85degC). This characteristic is normally used to allow heat sanitisation of membranes in specialty applications such as pharmaceuticals. These membranes are much more expensive so are only used when absolutely necessary.
Other types of membrane that can operate at very high temperature are ceramic and metallic membranes. Although the costs of these membranes are gradually reducing, they are still very expensive and normally only used for special applications.