Preparation Of Sorbent For Ultra-deep Removal Of Thiophene In Coke Oven Gas And The Desulfurization Mechanism

The production of natural gas from coke oven gas is one of the important ways for its efficient utilization,but the presence of thiophene in it will lead to the irreversible poisoning of nickel-based catalyst in the synthesis section.In order to meet the requirements of industrial production,the thiophene in coke oven gas is required to be ultra-deep removed to ppbv level.Among many desulfurization methods,the adsorption desulfurization（ADS）and reactive adsorption desulfurization（RADS）have attracted much attention due to their advantages of mild reaction conditions,simple operation,and high desulfurization accuracy.The key to adsorption desulfurization lies in the preparation of sorbent.Previous studies have shown that modified Y zeolite and Cu/ZnO sorbent have good selectivity for the ultra-deep removal of thiophene,but their applicability in complex coke oven gas atmosphere needs to be further improved.Through the analysis of desulfurization mechanism,optimizing and improving the performance of Y zeolite and Cu/ZnO sorbent for the ultra-deep removal of thiophene is an urgent problem to be solved.Based on this,in the thesis the acid sites with different types and strengths in Na Y zeolite were regulated,the metal active sites were modified.The adsorption mechanism of acid sites and metal active sites in Y zeolite on the removal of thiophene was explored,and the structure-activity relationship of Y zeolite was investigated.The desulfurization performance of Cu/ZnO sorbent was improved by means of the optimization of preparation conditions,the regulation of support structure and the modification of metal promoters.The combination of theoretical calculation and experiment was used to analyze the reactive adsorption desulfurization mechanism on Cu/ZnO sorbent,which would provide theoretical basis and technical support for the development of sorbent.The main research contents and conclusions are as follows:（1）Sorbents with different types and strengths of acids were prepared by modifying Na Y zeolite in ammonium nitrate and citric acid solutions.Their desulfurization performances in simulated coke oven gas were correlated with the acid properties.The results show that both ammonium nitrate and citric acid modification on Na Y are beneficial to the Q_b-thiophene.Y zeolite after modified in 0.10 mol/L citric acid solution has higher Q_b-thiophene at 100°C.Ammonium nitrate modification could significantly increase B acid in Y zeolite,whereas citric acid modification mainly increases weak L acid.The increase of L acid is conducive to the thiophene removal.On B acid sites,thiophene polymerization reaction can occur,which would result in the acid sites covering and micropores blocking by thiophene oligomer,and thereby the decrease of Q_b-thiophene.（2）Series of metal modified MY zeolite（M=Ce,Ni,Ag and Zn）were prepared via ion-exchanged with Na⁺of Na Y,and their desulfurization performances in different temperatures were investigated.The results show that Ag Y sorbent has the highest Q_b-thiophene（144 mg/g）at100°C,and Ce Y has the best desulfurization performance at 200°C compared with other sorbents.Thiophene could be adsorbed viaπ-complexation over Ni Y,Ag Y and Zn Y sorbents,however mainly through S–Ce bond over Ce Y sorbent.S–Ce bond has higher thermal stability thanπ-complexation,which makes Ce Y have better temperature adaptability.And the variation in thiophene adsorption capacity of Ce Y is relatively low in the range of 100–200°C.Moreover,Ce（IV）species is more favorable for thiophene adsorption than Ce（III）in coke oven gas.Although H₂ and CO in coke oven gas would reduce the adsorption capacity of Ce Y for thiophene,Ce Y still has thiophene adsorption capacity of 31.7 mg/g at 200°C.（3）The preparation conditions of Cu/ZnO sorbent were optimized through single-factor experiments.The optimal preparation conditions are p H value 7.5,Cu/Zn molar ratio 1:1 and calcination temperature 300 ^oC.The Q_b-thiophene of Cu/ZnO sorbent obtained under optimal preparation conditions is 25.1 mg/g.The Cu/Zn molar ratio（1:3–3:1）and the calcination temperature（250–550 ^oC）had a great influence on the Q_b-thiophene of sorbent.The calcination temperature mainly affects the specific surface area,pore volume,active component dispersion and grain size of sorbent.In the range of 300–550 ^oC,with the calcination temperature increases,the Cu Zn solid solution in sorbent decreases continuously until it disappears and Cu agglomerates,resulting in the increase of Cu grains and the decrease of Cu dispersion,and thereby the decrease of desulfurization performance.（4）The RADS mechanism of Cu/ZnO sorbent was investigated by combining in-situ infrared experiment and quantitative calculation.The results show that the active site of Cu/ZnO sorbent for thiophene ultra-deep removal could be identified as a combination of Cu⁰ and ZnO.The parallel adsorption at the hexagonal closest packing site is the most stable.Cu⁰ can adsorb H₂ and activate it into hydrogen atoms,and can also cleave thiophene molecules into C₄compounds by breaking the C–S bond.ZnO in Cu/ZnO sorbent is an ingredient for sulfur accepting,and its presence affects the adsorption properties by enhancing the hydrogen spillover.Other sulfur-containing gases are not generated during thiophene removal and the sulfur in thiophene could transfer directly from active Cu to ZnO and generate into Zn S.（5）Cu Zn Al O_x sorbents with aluminum nitrate,γ-Al₂O₃ and pseudo boehmite as aluminium sources were prepared and their desulfurization performances were correlated with their physicochemical structure.The results show that aurichalcite is a better precursor for Cu Zn Al O_x sorbent.The sorbent prepared withγ-Al₂O₃ or pseudo boehmite as aluminum source has more surface active components,larger specific surface area,smaller average pore size,higher Cu dispersion and higher Cu specific surface area,which is the main reason for the desulfurization performance is better than that of the sorbent prepared with aluminum nitrate as the aluminum source.（6）To enhance the desulfurization performance,Cu Zn Al O_x sorbents with the addition of metal promoters Ni and Zr were prepared.The results show that an appropriate amount of Ni could increase the specific surface area,pore volume,Cu dispersion and Cu Zn interactions of sorbent,thus improving the desulfurization activity of sorbent.Metal promoter Ni or Zr could increase the content of oxygen-ligated unsaturated Zn^δ+on sorbent surface.Metal promoter Zr mainly exists in the form of oxygen-ligated unsaturated Zr³⁺,which could enhance the hydrogen spillover of sorbent.The bimetallic promoters Ni and Zr could improve the Cu Zn interactions of sorbent,enhance the hydrogen spillover and reduce the grain size,resulting in the increase of the desulfurization performance of sorbent.