Design And Regulation Of Bi-functional Catalysts For Hydrogen Production From Sorption-enhanced Steam Reforming Of Glycerol

The production of biodiesel is most commonly done through the transesterification method,which produces about 10%glycerol as the by-product.With the rapid development of biodiesel,the glycerol has been a serious surplus.Hydrogen is widely used in the chemical and petroleum industries.Meanwhile,hydrogen is also a clean energy carrier with good combustion performance,high calorific value,producing water as the only emission to the environment.It is not only in favor of improving the economics of biodiesel and solving the problems caused by excess glycerol,but also in favor of easing the dependence of the current hydrogen production process on fossil energy,to utilize glycerol for hydrogen production.Sorption-enhanced steam reforming?SESR?processes can produce high purity hydrogen in one single step by in-situ capturing CO₂ which is stored in adsorbent for further processing.A bi-functional catalyst integrates catalyst and sorbent into one particle,mitigating the problem of mixing catalyst and adsorbent,and reducing the reactor volume.In this work,bi-functional catalysts were designed for SESR of glycerol?SESRG?.The hydrogen purity,CO content and stability in the SESRG process were further optimized through regulating the bi-functional catalysts.Firstly,a Co-CaO-Ca₁₂Al₁₄O₃₃ bi-functional catalyst was synthesized by co-precipitation method.In this catalyst,Co as active component of catalyst and CaO as an adsorbent to capture CO₂ are to complete the SESR process.The results indicated the hydrogen purity could reach 96.40%at 525^oC and S/C of 4,and the concentrations of CO,CH₄ and CO₂ were 1.85%,1.53%and 0.21%,respectively.After 50 reaction-calcination cycles,the purity of hydrogen stabilized at 96%.Since the methanation reaction is the main hydrogen-consuming reaction,the suppression of the methanation reaction could increase the purity of hydrogen.After introduction of Cu into the Co-CaO bi-functional catalyst,the purity of hydrogen can be increased from about 97%to99.23%.Because CO can easily poison the Pt catalyst in the proton exchange membrane fuel cell?PEMFC?,if considering the hydrogen is used in PEMFC,the existing techniques requires that the content of CO in hydrogen should not exceed 30 ppm.To this end,combining the characteristics of high hydrogen and low CO in SESR process,the small amount of CO was in situ removed by enhancing the methanation capacity of the catalyst.With Ni-Cu as the active component,a hydrogen purity of 97.15%and a CO content of 28ppm could be directly obtained.The practical application of SESRG is severely limited by the deactivation caused by the sintering of adsorbents and catalysts under high temperature conditions.The reversible phase transition of calcium cobaltate and Co and Ca species in the SESRG-regeneration cycle could effectively solve the sintering problem.The calcium cobaltate was reduced during the reaction,and Co and CaO were released to participate in the SESRG reaction.After entering the decarburization stage,the material would return to the state of calcium cobaltate under the oxidizing conditions.The reversible transformation of the calcium cobaltate and the change in morphology ensured the stability of the calcium cobaltate in the cycles,resulting in a very good stability of SESRG performance.The hydrogen purity remained⁹5%and the pre-breakthrough time was stable at 7.5 minutes in the whole 120 cycles.The combination of SESRG and the CH₄ reforming reaction could obtain high-purity hydrogen without CO₂ emissions.Under optimized reaction conditions,the 10 SESRG-CH₄reforming reaction cycles showed that the hydrogen in the SESRG process was retained at above 97%,while the conversion of glycerol was above 99%.At the same time,CH₄ conversion,R_H2/CO,and CO₂ selectivity were also stable at⁹5%,<2,and<17%,respectively,during the methane reforming.This work is instructive for using SESR technology to produce high-purity hydrogen without CO₂ emissions.