Preparation And Properties Of Adsorbent For Removing Trace Ammonia From Hydrogen

Proton exchange membrane fuel cell and its supporting technology are international cutting-edge technologies that have attracted much attention.The purity of hydrogen used in proton membrane fuel cell will directly affect the service life of the cell.At present,there are many sources of industrial pure hydrogen,among which low-temperature ammonia decomposition to produce hydrogen has a broad application prospect because NH₃ can be used as an ideal hydrogen storage material.However,when ammonia decomposition is incomplete,there will be a certain concentration of NH₃ residue.Trace amounts of NH₃ are alkaline and will corrode the proton membrane,resulting in irreversible effects.Therefore,it is of great practical significance to study the removal of trace NH₃ from high-purity hydrogen in order to prolong the service life of fuel cell.In this paper,the dynamic adsorption evaluation was carried out on a fixed bed reactor with the mixture of H₂ and NH₃（NH₃ concentration is 300 ppm）.The removal ability of coal-based activated carbon and 13X molecular sieve for trace NH₃ in hydrogen was discussed,and the coal-based activated carbon was selected as the appropriate adsorbent carrier.As NH₃ is alkaline,nitric acid modified activated carbon adsorbent is selected from nitric acid,sulfuric acid,oxalic acid and boric acid to remove ammonia with the best effect.The adsorption time is 44 h and the adsorption capacity is 18.4 mg/g.By optimizing the preparation conditions,it was found that 1 mol/L nitric acid was the best concentration for the preparation of acid modified activated carbon.After that,activated carbon was modified with seven metal chlorides:Cr Cl₃,Cu Cl₂,Fe Cl₂,Fe Cl₃,Zn Cl₂,Ni Cl₂ and Co Cl₂,and the selectivity of adsorbent to NH₃ was also improved.Compared with the dynamic adsorption evaluation results,it was found that Cu Cl₂/AC had the best effect.Although roasting will contribute to the dispersion of copper salt,too high temperature will collapse the pores of activated carbon,so it is most suitable to roast at 350℃for 2 h.Combining the advantages of the above two methods,the acid Cu Cl₂/AC adsorbent was prepared by acid treatment combined with metal salt loading modification.The adsorbent was characterized by bet and XRD.It was found that copper salt as a strong adsorption center was evenly dispersed on the surface of the carrier.After comparing the type of acidic solution,the concentration of acidic solution and the load of Cu Cl₂,it is found that the activated carbon co impregnated with 1 mol/L sulfuric acid and Cu Cl₂mixed solution prepared according to 5%of the load of copper salt has the best ammonia removal effect.The adsorption time is 50 h and the adsorption capacity is 20.8 mg/g.