分子筛材料在煤气脱H_(2)S中的研究进展

Research advances on H_(2)S removing over zeolites and its application in coal gas

焦炉煤气和高炉煤气是重要的二次能源,其中的含硫化合物不仅会造成环境污染,还会导致后续加工利用中的催化剂中毒,很大程度上限制了其后续利用,因此H_(2)S的高效脱除是实现煤气清洁利用的必需途径。分子筛吸附脱硫技术因操作简单、运行费用低、循环再生性好、使用寿命长等优点,在煤气脱硫领域应用前景广阔。对分子筛脱除H_(2)S的相关研究和应用进行了综述,总结了脱除H_(2)S的分子筛种类和特点,归纳了分子筛脱除H_(2)S的机理,探讨了分子筛改性对脱硫性能的影响,分析了煤气中的CO、CO_(2)、H_(2) O和O_(2)等气体组分对H_(2)S的竞争吸附作用,并基于分子筛脱硫机理及与其结构特性间的关联提出了分子筛吸附材料用于煤气净化的相关建议。结果表明,分子筛具有优异的择形选择性以及酸碱位、金属位可调性,被广泛应用于H_(2)S的吸附脱除,用于脱除H_(2)S的沸石分子筛主要有斜发沸石、LTA型分子筛、FAU型分子筛、MFI型沸石分子筛、钛硅分子筛等;H_(2)S在分子筛上的吸附机理与活性位密切相关,根据活性位点的不同,分子筛吸附剂可通过羟基吸附机理、碱金属解离机理、过渡金属配位机理和表面酸碱反应机理有效脱除H_(2)S;分子筛晶体结构和表面物化性质不同,吸附H_(2)S的机理也不相同;金属元素改性和表面酸碱位调控可有效提升其脱硫性能。煤气成分也会影响分子筛脱硫性能:H_(2)O分子与H_(2)S分子结构相似,产生较强的竞争吸附;CO可与过渡金属离子,如Cu^(+)等进行配位,从而产生竞争吸附;酸性气体CO_(2)会与分子筛表面碱性位结合产生竞争吸附,此外还会与H_(2)S反应生成COS;O_(2)可引起单质硫的生成,为吸附剂再生带来困难。基于对已有研究分析,指出今后需进一步明确吸附剂的构效关系、竞争吸附的内在机制和规模化气体净化中吸附H_(2)S的动力学行为;在分子筛吸附剂应用开发过程中,需针对不同脱硫工况,匹配合适的吸附机理,使脱硫性能和再生性能达到最佳,避免或抑制煤气中其他组分对H_(2)S的竞争吸附,同时兼顾成本是其未来发展方向。

Coke oven gas and blast furnace gas are important secondary energy sources.The sulfur compounds not only cause environmental pollution,but also lead to catalyst poisoning in the subsequent processing and utilization,which largely limits their further utilization.Therefore,it is necessary to efficiently remove H_(2)S from these gas for their clean utilization.Zeolite adsorption desulfurization technology has the advantages of easy operation,low operating costs,excellent regeneration ability and long service life,so it has great application potential in desulfurization field.This paper made a review on the investigation and application of H_(2)S removal over zeolite.The types and characteristics of zeolites used for H_(2)S removal were summarized.The mechanisms of H_(2)S removing by zeolite were investigated.The influences of zeolite modification on desulfurization performance were discussed.And the competitive effects on H_(2)S adsorption caused by the components contained in coal gases,e.g.,CO,CO_(2),H_(2) O and O_(2) were analyzed.Some suggestions on the development of zeolite desulfurizer were proposed based on the correlation between the mechanism of desulphurisation and the structural properties of molecular sieve.The results show that zeolites have excellent selective shape as well as acid-base site and metal site adjustability,and are widely used in the adsorption and removal of H_(2)S.The zeolites used for H_(2)S removal mainly include clinoptilolite,LTA,FAU,MFI and titanium silicon zeolites.The mechanism of H_(2)S adsorption on zeolites is closely related to the active site.Depending on the active site,H_(2)S adsorption mechanisms include Si—OH adsorption mechanism,alkali metal dissociation mechanism,transition metal coordination mechanism and surface acid-base interaction mechanism,which are closely related with the crystal structure and surface physical and chemical properties of zeolites.Metal element modification and surface acid-base modification can effectively improve their desulfurization performance.Gas composition can also affect the desulphurisation performance of zeolites:H_(2)O molecules and H_(2)S molecular structural similarity,resulting in strong competition for adsorption;CO can be coordinated with transition metal ions,such as Cu^(+),resulting in competition for adsorption;acidic gas CO_(2) will combine with the molecular sieve surface alkaline sites to produce competition for adsorption,in addition to the reaction with H_(2)S to generate COS;O_(2) can cause the generation of singlet sulphur,giving O_(2) can cause the formation of singlet sulphur,making the regeneration of the adsorbent difficult.Based on the analysis of existing research,further clarification of the structure-activity relationship of the adsorbent and the intrinsic mechanism of competitive adsorption,as well as the kinetic behavior of H_(2)S adsorption in gas purification will be the focus of future research.In the process of developing the application of zeolite adsorbent for H_(2)S removal,the following aspects should be taken into consideration:operation conditions,proper adsorption mechanism and the corresponding modification,avoiding and inhibiting the competitive adsorption,improving regeneration ability and reducing preparing costs.