| Mercury has become one of the most hazardous environmental pollutants due to its high toxicity,volatility,persistence and bio-accumulation.Its control technologies for releasing emission have caused considerable worldwide concerns in recent years.The mercury removal technology of coal-fired flue gas has been widely studied,but the research on mercury removal from natural gas is still not deep enough.Furthermore,the accumulation of mercury would erode aluminum heat exchangers and valves then led to serious accidents.At the same time mercury will endanger human health with the release of natural gas combustion.A large number of studies have shown that one of the most effective methods to remove Hg0 is adsorption with solid adsorbents.Therefore,it is of great practical significance for the research and development of natural gas mercury removal adsorbents.This study focused on chemical reduction methods in aqueous solutions to synthesize Ag/4A zeolite,and the influences of ultrasonic and protective additives were investigated to reduce the size of silver particles.According to the results of xrd,xps and hrtem,silver nanoparticles exist as highly dispersed elements on the surface of 4A molecular sieves,and the particle size is between 14-17 nm The Hg0 removal efficiency of prepared Ag/4A zeolite adsorbents was higher than 97%at 70000 h-1,and at 5%breakthrough,the Hg0 capture capacity of 1.5%(wt%)silver loaded C-AgNPs/4A-zeolite was as high as 1.82 mgg-1.Furthermore,the regeneration and reutilization results indicated that the Hg0 adsorption performance remained stable after 5 reuse cycles.However,water vapor obviously inhibited the Hg0 capture performance of Ag/4A adsorbents.At present,most of the silver-based adsorbents have the disadvantages of low utilization of silver atoms and deactivation of water.In order to improve the water resistance of the adsorbents,the performance of the adsorbents is further enhanced.A simple passivation and amino functionalization method was established to prepare an efficient and water-resistant N-Ag/MCM-41 composite adsorbent for the removal of Hg0 in natural gas.According to the results of XRD,XPS characterization,methyl was successfully loaded on MCM-41 molecular sieves,and silver nanoparticles existed in the form of simple substances.It can be seen from the analysis of HRTEM and mapping.The Ag nanoparticles were successively confined inside the mesoporous channels of MCM-41 molecule sieve with an average diameter of 1-3 nm.The synthesized sorbent was found to achieve a complete removal of Hg0 at high space velocity of 50000 h-1 in ambient temperature.At 5%breakthrough,the Hg0 capture capacity of 1%(wt%)silver loaded N-Ag/MCM-41 was as high as 6.64 mg·g-1,which is much higher than the sample of Ag loaded outside of the pore channels(S-Ag/MCM-41)and other existing commercial sorbents.The H2O has negligible inhibitory effect on Hg0 removal performance of N-Ag/MCM-41.In addition,the spent N-Ag/MCM-41 could be easily regenerated without significant performance degradation over five cycles.In order to elucidate the adsorption process of mercury removal by silver bearing molecular sieves,the adsorption behavior of mercury atoms on ag(111),(200),(220)and(311)crystal planes was studied by DFT simulation.The results show that mercury atoms first adsorb mercury on Ag(111)crystal planes.It can react with Ag to form silver amalgam,which provides a theoretical basis for the next development of silver-loaded adsorbents. |
