Study On Preparation And Properties Of Porous Ti Metal Supported Pd-Au Alloy Composite Membranes

As a clean renewable energy source,H₂ is widely used in various industrial fields due to its good combustion performance,non-toxicity and so on.At present,most of the high purity H₂ is obtained by coal gasification.Pd composite membrane has been widely used in coal gasification to separate H₂ because of its strong mechanical strength,high permeation flux and high selectivity.Compared with other Pd composite membranes,Pd-Au alloy composite membrane has the advantages of better hydrogen permeability and excellent sulfur resistance,which has become a research hotspot gradually.However,the Pd-Au alloy composite membrane has not yet achieved large-scale industrialization,and the most critical one is the stability of the Pd alloy composite membrane at high temperatures.The factors affecting the stabilit y mainly include:the support material,the interdiffusion between the metals at high temperature,the stability of the membrane material,and the preparation method of the membrane.Therefore,this paper uses the porous Ti as the support,and the ceramic layer prepared by in-situ oxidation as the transition layer to solve the problem of bonding between the layers.Based on this,a new Pd-Au alloy composite membrane material is developed.The performance of the porous Ti,which is selected as the Pd composite membrane support,was studied.The results are as follows:the porous Ti support has a symmetrical structure and the surface of the membrane is relatively regular;the pore size distribution is relatively uniform,and the optimum aperture is around 11?m.When the temperature is not higher than 700?,it has good oxidation resistance.It is preliminarily determined that the in-situ oxidation temperature of the porous Ti support ranges from 700°C to 800°C.Compared with ceramics,the thermal expansio n coefficients of porous Ti and Pd are closer,which is beneficial to improve the stabilit y of Pd-Au alloy composite membran at high temperature.The TiO₂/Ti composite membrane is prepared by in-situ oxidation method.The effects of oxygen concentration,oxidation temperature and oxidation time on the thickness,pore size and microstructure of the prepared ceramic membrane are investigated.The results show that with the increase of oxygen concentration,oxidation temperature and oxidation time,the thickness of the prepared ceramic membrane increases gradually,but the pore size decreases gradually.The optimum preparation conditions are:oxygen concentration of N ₂:O₂ is 2:1,oxidation temperature is 800?and oxidation time is 60min.The prepared TiO₂/Ti composite membrane surface is smooth with uniform membrane thickness,and only the rutile TiO₂ characteristic peak is formed on the surface of the membrane.The prepared TiO₂/Ti composite membrane has a narrow pore size distribution,and the optimum aperture is about 0.312?m.Stability experiments show that the prepared TiO₂/Ti composite membrane has good stability.The microstructure and permeability of the Pd-Au/TiO₂/Ti alloy composite membrane prepared by continuous electroless plating are characterized.The results show that the surface of prepared Pd-Au alloy composite membrane is smooth,the membrane thickness is about 20?m,and the bonding between the membrane layers is good.The BES and EDS analysis show that the TiO₂ transition membrane prevents interdiffusion between metals effectively.XRD analysis shows that Pd and Au are alloyed to form Pd-Au alloy membrane after heat ing in 773K for 10h at N₂ and H₂atmospheres.With the increase of temperature and pressure difference,the hydrogen permeation amount increases gradually.When the temperature is higher than 773K and the pressure difference is greater than 0.09MPa,the hydrogen permeation flux reaches to 13.4cm³/?cm²min?,indicating that the prepared Pd-Au alloy membrane has higher H₂ permeate flux.However,the H₂/N₂ selectivity of the prepared composite membrane is only 2000,which needs to be further improved.The hydrogen permeation stability test shows that the prepared Pd-Au/TiO₂/Ti alloy composite membrane has good hydrogen permeation stability.