Research On Hydrogen Production From Reforming Reactions Based On High-temperature In-situ Separation Of Hydrogen In A Silica Membrane Reactor

The thermochemical reaction hydrogen production technology has attracted much attention in recent years because it can use various raw materials such as petrochemical energy,biomass and its derivatives,and organic waste,and the technology is relatively mature.Due to the limitation of thermodynamic equilibrium,the thermochemical reaction loses the driving force for continuous hydrogen production after the reaction reaches equilibrium.In situ separation of hydrogen under high temperature reaction conditions can break the thermodynamic equilibrium and promote the continuous hydrogen production of the reaction.Although a silica membrane reactor with H2 selectivity can improve the reaction efficiency of thermochemical hydrogen production and obtain high-purity hydrogen products at the same time,it is limited by the poor hydrothermal stability of the silica membrane and rarely used in steam reforming reactions.In this paper,a cobalt-doped silica composite membrane with hydrothermal stability was prepared,and a silica membrane reactor for hydrogen production by methane steam reforming was built.The main results of the study are as follows:(1)In this paper,cobalt-doped silica composite membranes were prepared by the sol-gel-dipping method.Through a series of material structure characterizations of sols,xerogels and composite membranes,the successful doping of cobalt metal to silica membranes was demonstrated,and the microstructural information of the composite membranes was obtained.(2)The permeance and selectivity of cobalt-doped silica membranes with different number of top layers are tested,and it is found that the He permeance of the prepared composite membranes can reach up to 1.21×10-7 mol m-2 s-1 Pa-1,the selectivity of He/N2 can reach up to 705.84,the selectivity of He/CO2 can reach up to 242.19,and the permeance and selectivity are excellent.A cobalt-doped silica composite membrane with 6 top layers was determined as the membrane element of the methane steam reforming membrane reactor.(3)A cobalt-doped silica composite membrane was used to build a membrane reactor for hydrogen production by methane steam reforming.By sequentially changing the conditions of temperature,pressure,S/C ratio and space velocity,the reaction characteristics and the boosting effect of the membrane reactor on the reforming reaction were investigated.It was confirmed that the temperature of 500°C,the pressure difference of 0.3 MPa,the S/C ratio of 3,and the space velocity of 30 ml-1g-1h-1 were the optimum process conditions of cobalt-doped silica composite membrane reactor for methane steam reforming reaction.The experimental results show that,compared with the traditional reactor,the methane conversion rate of the membrane reactor is up to 83.71%,and the purity of hydrogen in the product is up to 66.02%.(4)The influence of the hydrothermal conditions of the methane steam reforming reaction on the cobalt-doped silica composite membrane was studied.Through a series of material structure characterizations,it was found that although high temperature steam still caused some microscopic morphology changes in the cobalt-doped silica composite membrane,compared with pure silica,the pore volume change of cobalt-doped silica decreased by 48.12%,and the hydrothermal stability of the membrane was significantly improved.