For the separation of hydrogen and impurities.
The principle of hydrogen purification by palladium tube is that, at 300-500 ℃, hydrogen is adsorbed on the Palladium tube wall when hydrogen is purified to the side of the Palladium tube, because The 4d electron layer of palladium lacks two electrons, it can produce unstable chemical bonds with hydrogen (this reaction of palladium and hydrogen is reversible), under the action of Palladium, hydrogen is ionized to proton its radius is 1.5x1015m, and the lattice constant of palladium is 3.88x10-10m (20 ℃), so it can pass through the Palladium tube, Under the action of Palladium, protons are combined with electrons to form hydrogen molecules, escaping from the other side of the Palladium tube. In the Palladium tube surface, the gas that is not dissociated is not able to penetrate, so the high purity hydrogen can be obtained by the Palladium tube. Although palladium has a unique performance of hydrogen, but the mechanical properties of pure palladium, oxidation at high temperature, recrystallization temperature is low, easy to make the Palladium tube deformation and embrittlement, it can not use pure palladium as a membrane.
The mechanical properties of palladium can be improved by adding appropriate IB and Ⅷ elements in palladium and making palladium alloy. The current application of palladium alloy, silver accounted for 20-30%, other components (such as gold) content of 5%. The rate of hydrogen transmission through the Palladium alloy is related to the pressure difference (P) between the temperature, the thickness of the film and the material hydrogen and pure hydrogen on both sides of the osmotic touch. Increasing the temperature, increasing p and reducing the thickness of the film will increase the rate of hydrogen permeation. However, the tensile strength of the osmotic film will be reduced by increasing temperature.
Therefore, the use temperature of the palladium tube is usually controlled at about 450 ℃. Some impurities can lead to palladium poisoning, so that the permeability deterioration, and even can make the membrane damaged. The substances that can cause palladium poisoning are mercury, arsenic, halide, oil vapor, sulfur and ammonia-containing substances, and dust. Palladium alloy can be made into tubular (called Palladium tubes) or diaphragm (called palladium membrane).