Study On In-situ Preparation Of Functional Activated Carbon From Low Rank Coal And Its Desulfurization Performance At Room Temperature

Hydrogen sulfide（H₂S）is a toxic gas commonly found in natural gas,synthetic gas and coal-based gas.H₂S not only harms human health,corrodes process equipment,and pollutes the environment,but also poisons downstream catalysts,causing huge safety hazards and economic losses to industrial production.Therefore,the removal of H₂S is one of the most critical processes in many industrial processes involving the use of gasification products.However,a large number of current desulfurization methods and technologies have many limitations and shortcomings,such as high operating temperature,low desulfurization accuracy,Low sulfur capacity,poor selectivity,etc.The development of a new type of desulfurization material synthesis method with excellent performance and a low-temperature and high-efficiency H₂S removal technology has very important significance and broad application prospects.Considering both the environment and cost,by using a selective catalytic oxidant,reacting with H₂S at low temperature to generate elemental sulfur or metal sulfide is the preferred method for the removal of low-content H₂S gas.Among them,the new catalytic oxidation process of porous carbon material adsorbing low concentration of H₂S has gradually become a research hotspot.Research has found that under low-temperature aerobic conditions,the use of porous carbon material catalysts to catalytically oxidize H₂S can finely remove H₂S to below 10 ppm,and at the same time obtain elemental sulfur products and realize the recovery and utilization of sulfur resources,which is a kind of green economical new desulfurization technology.However,traditional activated carbon materials have a large number of microporous structures,the mass transfer resistance of gas is large,and the total pore volume is small.The deposition of elemental sulfur can easily lead to clogging of the pores,and the capacity of elemental sulfur generated in the desulfurization process is very limited.Although traditional activated carbon is chemically modified on its surface and loaded with active components for desulfurization,its sulfur capacity will be significantly increased,but the method of loading active components through post-impregnation will cause blockage of its pores,resulting in low desulfurization performance,which greatly limits its industrial application.Therefore,the preparation of mesoporous carbon materials with large pore volume and three-dimensional multi-channel structure and the improvement of the loading problem of active components on porous support are the focus of this research.Based on the above considerations,the work of this paper is devoted to the preparation of a new efficient modified activated carbon desulfurizer.Lignite is used as raw material,the impurities in the coal are removed after nitric acid pretreatment,zinc nitrate,urea or dicyandiamide is loaded by wet impregnation method,and the modified activated carbon room temperature desulfurizer is prepared by one-step method.This process combines the preparation and modification of activated carbon,which can independently control the loading of active components,and conveniently synthesize a carbon material desulfurizer with high loading and rich mesopores,so that it has a multi-stage pore structure mainly composed of mesoporous channels.It can improve the problem of blocking the pore structure caused by the post-impregnation and loading of active components,so as to promote the diffusion of H₂S in the catalyst and the adsorption and storage of product sulfur,so as to achieve high-efficiency removal and green conversion of H₂S at room temperature.Use XRD,BET,XPS,SEM and other methods to characterize the desulfurizer,analyze the sulfurization products of the desulfurizer,and infer the possible adsorption mechanism.The specific research results are as follows:（1）ZnO-based activated carbon room temperature desulfurizer is prepared in situ.When the amount of zinc nitrate added is 20 wt.%,the activation temperature is 850℃,and the activation time is 1 h,the desulfurization performance of the desulfurizer is the best,and the breakthrough time is 210 min,its corresponding breakthrough sulfur capacity is 71.4 mg/g,which is 5.3 times the desulfurization performance of commercial activated carbon loaded ZnO desulfurizer under the same experimental conditions.（2）The high desulfurization performance of the in-situ ZnO-based activated carbon desulfurizer is attributed to its developed mesoporous pores.On the one hand,it is conducive to mass transfer in the desulfurization process,and on the other hand,it is conducive to the storage of sulfide products（Zn S and elemental S）.The in-situ ZnO-based activated carbon desulfurizer mainly undergoes chemical reaction adsorption and H₂S catalytic oxidation during the desulfurization process.Oxygen-containing functional groups or chemically adsorbed oxygen on the surface of activated carbon can provide an oxygen source for H₂S catalytic oxidation in an oxygen-free atmosphere.（3）The N-modified activated carbon desulfurizer at room temperature was prepared in situ.When the amount of urea was 23 wt.%,the activation temperature was 850℃,and the oxygen concentration was 5%,the desulfurization performance of the desulfurizer was the best,the penetration time was 180 min,and the corresponding penetrating sulfur capacity was28.4 mg/g.When the amount of dicyandiamide is 9 wt.%,the activation temperature is 850℃,and the oxygen concentration is 5%,the desulfurization performance of the desulfurizer is the best,the penetration time is 550 min,and the corresponding penetrating sulfur capacity is79.6mg/g.（4）The dicyandiamide-N modified desulfurizer has a higher penetrating sulfur capacity,mainly because the dicyandiamide-N modified desulfurizer has a larger comparative area and a higher pore volume,which is conducive to adsorption and storage of more sulfide products;dicyandiamide-N modified desulfurizer has higher oxygen and nitrogen content,which can expose more alkaline active sites on its surface,promote the alkalinity of the water film on the surface of the catalyst,promote the dissociation of H₂S,and accelerate the reaction of HS^-with oxygen to generate more elemental sulfur.