Study On High Temperature Separation Of Hydrogen In Reforming Gas By Metal Nickel Hollow Fiber Membrane

Hydrogen is an ideal clean energy,widely used in metallurgy,petrochemical,electronics,aerospace and other fields.The main source of hydrogen is fossil fuels and exists in the form of a mixture that must be separated from its mixture.Other than PSA and cryogenic distillation,membrane separation techniques have attracted the widest interest.However,the Pd-based membranes also have the unavoidable shortcomings such as high price of precious metal palladium,susceptibility to damage by CO and sulfur contaminants and coking,and hydrogen embrittlement as a consequence of the phase transition caused by cycling at different temperatures or hydrogen pressures.Compared with the palladium,nickel-based membrane is superior due to its lower material cost and high stability to withstand the presence of CO and sulfur in the hydrogen-containing atmosphere at high temperatures.However,the hydrogen permeability of the currently reported nickel membranes is much lower than the Pd-based membranes at similar operation temperatures as both the hydrogen solubility and the solid-phase diffusion coefficient in nickel are much lower than those in palladium.A strategy to improve the hydrogen flux of the nickel membranes is to reduce the membrane thickness by forming a composite or asymmetric structure.Metallic nickel hollow fiber membranes with a thin wall thickness were fabricated by a dry-wet spinning and programmed sintering process are used to separate hydrogen from the simulated reformate mixtures at elevated temperatures.Effects of the feed composition and the sweeping gas flow rate on the separation performance of the hollow fibers were investigated both experimentally and theoretically.The results indicate that the as-prepared nickel hollow fiber membranes possessed infinite H₂-permselectivity,only allowed the hydrogen in reformate mixtures to permeate through the membrane at experimental conditions.The nickel membrane exhibited excellent thermal and chemical stability in the reformate gas atmosphere.The presence of CO favors the hydrogen recovery due to the water gas shift reaction to provide more hydrogen,whereas the CO₂ in the feed reduced the hydrogen recovery by the reverse water gas shift reaction.The nickel hollow fiber membranes also demonstrate a high tolerance to H₂S poisoning.By controlling the core liquid flow rate and air distance spinning conditions such as the preparation of thinner netal nickel hollow fiber membrane thickness.The dense metal nickel hollow fiber membranes were modified by physical grinding,chemical nitric acid etching and electroless palladium plating to improve the hydrogen permeability.After sanding the outer surface,the wall thickness of nickel hollow fiber decreased from 0.09 to 0.04 mm,which reduced the penetration resistance and the permeation flux reached 20.48 mmol m^-2 s^-1 at 1000 ?.After 40 min of nitric acid etching,the thickness of nickel hollow fiber was reduced to 0.05 mm,which accelerated the diffusion process of hydrogen and the hydrogen flux increased by 68%to 24.11 mmol m^-2 s^-1.The surface of the nickel membrane was electroless by plated with palladium to accelerated the hydrogen dissolved accelerated,the hydrogen permeation flux up to 23.15 mmol m^-2 s^-1.