Coupling Between Catalytic Hydrolysis And Absorption Of HCN In Yellow Phosphorus Flue Gas

Hydrogen cyanide(HCN)is a colorless,poisonous liquid.It is a colorless and bitter gas under the standard state,which is poisonous and deadly with an almond odor.Based on the full analysis and comparison of existing processing methods for HCN,this paper proposed the functional coupling among the catalytic hydrolysis and oxidation of HCN in yellow phosphorus exhaust gas as well as NH3-SCR for the first time.The impregnation method,dipping precipitation method and sol-gel method were used for preparing HCN hydrolysis and oxidation catalysts during the experiment.The hydrolysis and oxidation ability of HCN were investigated on these catalysts respectively to selecte the optimal catalysts.On this basis,a functional integration was made between HCN hydrolysis catalyst and oxidation catalyst by mechanical mixing,so that the integration catalyst can possess both hydrolysis and oxidation activity and producd NH3 and NOx during reaction.By examining the different reaction conditions,the production of NH3 and NOx can be maintained at 1:1 as far as possible.Under this condition,the coupling properties among HCN hydrolysis and oxidation and NH3-SCR were evaluated and compared between segmented operation method and mechanically mixed method.The results showed that:In the space velocity of 52000h-1,HCN gas with concentration of 100ppm has a good hydrolysis effect on catalyst Nb-La-Ti prepared by sol-gel method.The Fe/La/Ti-Al2O3 catalyst prepared by dipping precipitation method preformed the best hydrolysis ability,HCN removal rate can be maintained more than 90%with a high production of ammonia in the temperature range of 150℃-350℃.Through the study of HCN oxidation,it can be found that catalyst Mn/Ti-Al2O3 maintained both a high yield of HCN removal and a relatively high level of NOx production,which ensured the supplment of feedstock gas for the following NH3-SCR reaction.So Mn/Ti-Al2O3 was choosed as HCN oxidation catalyst.The functional integration was made between HCN hydrolysis catalyst and oxidation catalyst by mechanical mixing,so that the integration catalyst can possess both hydrolysis and oxidation activity and producd NH3 and NOx during reaction and it was found that the generation of NH3 and NOx was approximately equal 1:1 when the temperature reached about 300℃.During the activity evaluation of coupled process among HCN hydrolysis,oxidation and NH3-SCR,it was found that segmented catalyst Fe/La-Mn/Ti+Ce/W preformed better on HCN and NH3-SCR coupling process,when the temperature reached about 300℃,NOx was almost removed completely with a small number of NH3 remaining.This showd that the NH3 and NOx produced in the hydrolysis and oxidation process of HCN occured NH3-SCR reaction in the second paragraph on catalyst Ce/W.There was some coupling effect on the mechanical mixing catalyst(Fe/La-Mn/Ti)-Ce/W as well,however the effect was not obvious as segmentation operation method,which may resulted from the poisoning of NH3-SCR catalyst Ce/W by HCN and lost some NH3-SCR catalytic activity.In this paper,the catalysts were characterized by means of methods such as the N2 adsorption-desorption(BET),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),transmission electron microscopy(TEM),Fourier transform infrared(FT-IR)and temperature-programmed desorption(TPD)to study the pore structure,crystal structure,morphology and the possible catalytic principle.The possible reaction mechanism was then speculated based on the products and characterization.Presumably,the hydrolysis process has adsorption effect under low temperature condition,with temperature increasing,the hydrolysis ability increased with the production of formamide and formic acid,and finally decomposed to NH3,CO and CO2 to complete the hydrolysis process;the oxidation process can produce water,and therefore the oxidation process is accompanied by hydrolysis reaction.Through a series of reactions,HCN converted to NOx,NH3,CO,CO2 ultimately;coupling process was on the basis of the previous two stages,the hydrolysis and oxidation of HCN coupling with NH3-SCR process,so that the NH3 and NOx generated during HCN hydrolysis and oxidation occured a further NH3-SCR reaction can be removed completely.