Construction Of Bifunctional Catalyst And Tailoring Its Enhancement On Steam Reforming Coke Oven Gas

The steel industry in China is in large scale.,so the coke output for steelmaking is also large and the yield is stable.As a by-product of the coking process,coke oven gas has not been utilized efficiently,thus resulted in waste of resources and environmental pollution.In this research,sorption enhanced steam reforming coke oven gas was utilized to prepare high-purity hydrogen as well as carbon fixation,forcusing on preparation and performance tailoring of bifunctional catalyst.The main content of this research included:The effects on partical structure of different preparation methods for NiO-CaO based bifunctional catalysts was studied.NiO-CaO based bifunctional catalysts with different NiO loading were prepared by hydrothermal precipitation method,sol-gel method and hydrothermal-impregnation method.The composition,surface morphology and elements distribution of the samples were analyzed by XRD,SEM and EDS characterization methods.Finding that the carrier Al₂O₃ in samples prepared by the sol-gel and hydrothermal precipitation method is mostly in an amorphous status,and the surface porosity of these samples is lower than those prepared by hydrothermal-impregnation method.What's more,the elements distribution insamples prepared by hydrothermal precipitation method is obviously uneven,and Ni cannot be completely precipitated.For these reasons,hydrothermal-impregnation method was prefered for preparation,and a 20%NiO-loaded,70%CaO-loaded,bifunctional catalyst NiO-CaO/Ca₁₂Al₁₄O₃₃ made by this method was applied to CO₂ adsorption and steam reforming coke oven gas experiments.The sorption performance and cyclic stability of this NiO-CaO/Ca₁₂Al₁₄O₃₃bifunctional catalyst were obtained by bench test and thermogravimetric analysis which lead to qualitative and quantitative analysis respectively.In the qualitative analysis,CO₂ sorption process in bench test showed effects by heat and mass transfer in some degree.During the first 6 sorption cycles,the appearance that CO₂concentration increased to the end before reaching the peak,indicating that there was no obvious sintering and carbon deposition in the first 6 cycles.The peak concentration of CO₂ gradually became stable after 20 cycles,indicating the sample is capable of efficiently CO₂ sorption in first 20 cycles and maintaining a stable CO₂sorption capacity between 20 to 50 cycles.The CO₂ sorption capacity of fresh sample and 50 sorption cycles used sample were compared by a thermogravimetric analyzer quantitatively.Finding that 50 sorption cycles used sample was relatively low in terms of the CO₂ sorption rate.However,the mass increase ratios were similar with fresh sample's 43.79%,and 50 sorption cycles used sample's 41.98%when reaching sorption saturation.The bifunctional catalyst NiO-CaO/Ca₁₂Al₁₄O₃₃3 was applied to steam reforming coke oven gas compared with NiO-CaO/Al₂O₃ catalyst mixing CaO under the condition of steam carbon ratio equals 3,700?,COG inlet 100nmL/min.However,this bifunctional catalyst didn't show an effect as excepted.Relying on experimental research,it was concluded that the space velocity,NiO loading and loading mode of Ni were not the main reasons for the inhibition of its activity,but the sulfur poisoning,carbon deposition,nickel-aluminum combination and Ni encapsulated by CaCO₃.Considering of problems exhibited by the bifunctional catalyst,performance improvement were studied in both catalyst and adsorbent respectively.As for catalysts,Fe doping modification and loading increasement of Ca₁₂Al₁₄O₃₃ measures were taken to achieve the purpose of nickel-iron combination instead of nickel-aluminum combination to enhance catalyst's activity,as well as resisting carbon deposition and sulfur poisoning.Then,steam reforming CH₄,steam reforming coke oven gas,and sorption enhanced steam reforming coke oven gas experiments were carried out at 700°C to study the reforming efficiency of NiO/Ca₁₂Al₁₄O₃₃ catalyst which is in the original bifunctional catalyst,Fe doping modified NiO-FeO/Ca₁₂Al₁₄O₃₃ catalyst,and compared with NiO-CaO/Al₂O₃catalyst.In the steam reforming CH₄ experiment,it was found that the Ca₁₂Al₁₄O₃₃loading increased NiO/Ca₁₂Al₁₄O₃₃ catalyst group exhibited 50%-70%CH₄conversion rate at 3,4.5 and 6 steam carbon ratios,while both Ca₁₂Al₁₄O₃₃ loading increased and Fe-modified NiO-FeO/Ca₁₂Al₁₄O₃₃ catalyst group achieved 95%CH₄conversion rate at the same level of NiO-CaO/Al₂O₃ catalyst group under 3 steam carbon ratios.In the steam reforming coke oven gas experiment,CH₄ conversion rate in NiO/Ca₁₂Al₁₄O₃₃ catalyst group is less than 30%,while in NiO-FeO/Ca₁₂Al₁₄O₃₃catalyst group and NiO-CaO/Al₂O₃ catalyst group floating between 50%-70%similarly.All three groups showed the effect of sulfur poisoning,but NiO-FeO/Ca₁₂Al₁₄O₃₃ catalyst and NiO-CaO/Al₂O₃ catalyst are less affected with a low degree of activity decline observed.In the sorption enhanced steam reforming coke oven gas experiment,CH₄ conversion rate decreased in turn amount CaO/Al₂O₃ catalyst group,NiO-FeO/Ca₁₂Al₁₄O₃₃ catalyst group and NiO/Ca₁₂Al₁₄O₃₃ catalyst group.But NiO/Ca₁₂Al₁₄O₃₃ catalyst group and NiO-FeO/Ca₁₂Al₁₄O₃₃ catalyst group exhibited a much lower CO selectivity.With CO₂ adsorbed by CaO,the catalytic efficiency of three catalysts were significantly suppressed.In the aspect of adsorbent,the effects of precursors for CaO adsorbent were investigated by comparing CaO adsorbents prepared from calcium acetate monohydrate and steel slag,respectively.It was found by SEM that the CaO sorbent particles prepared from steel slag appeared a flocculent combination with a diameter less than 0.5?m would be more effective on CO₂ sorption while reducing CaCO₃reunion than that prepared from calcium acetate monohydrate with an 1?m diameter and layered accumulation.Two different adsorbents were mixed with NiO-CaO/Al₂O₃catalyst respectively for sorption enhanced steam reforming coke oven gas under the condition of steam carbon ratio equals 4,700°C.The improved adsorbent didn't appear obvious inhibition on Ni activity after CO₂ adsorped.The modified bifunctional catalyst's efficiency is significantly improved and higher than that of NiO-CaO/Al₂O₃ catalyst.