Ni/Ce_xZr_1-xO₂-CaO Catalyst Absorbs Enhanced Bio-oil Steam Reforming To Produce Hydrogen

Hydrogen is a kind of ideal secondary energy source,whose combustion product is just water and it will not only no polluting to the environment but also its calorific value is the highest among all of the current fuels.However,most of the hydrogen comes from fossil energy,which causes a double crisis of environment and resources.In recent years,the thermal-chemical conversion of biomass has become a new research hotspot.Among them,the biomass fast pyrolysis technology is the conversion of solid biomass into a liquid bio-oil,but due to the complex composition,poor stability,and strong corrosive properties of the bio-oil,so it needs to be upgraded and further transformed.However,the conversion of low-grade bio-oil to high-calorific-value hydrogen fuel is an attractive route to hydrogen production.In this paper,a series of bi-functional catalysts 10%Ni/CexZr1-xO2-CaO were prepared by sol-gel method and impregnation method using cerium-zirconium solid solution as carrier,nickel as active component and calcium oxide as absorbent.The 10%Ni/CexZr1-xO2-CaO characterized by BET,XRD,TPR and CO2 absorption was found mainly consist of Ni,CexZr1-xO2 and CaO.With the increase of CaO content,CaZrO3 with perovskite structure will form.Due to the presence of CaZrO3 in the catalyst,CaO grains are prevented from sintering under high temperature,thereby improving the stability of CO2 cycle absorption.The 10%Ni/CexZr1-xO2-CaO of bi-functional catalysts were used for the sorption-enhanced steam reforming(SESR)from acetic acid,mixed model compounds,and real sawdust bio-oil.It mainly studies from the following aspects:(1)The bi-functional catalyst of 10%Ni/CexZr1-xO2-CaO was firstly used in the steam reforming of acetic acid,a model compound of bio-oil.The effects of reaction temperature,space velocity and water-carbon ratio on hydrogen yield were investigated.At the same time,the influence of the ratio of calcium and cesium on the product concentration by SESR of acetic acid was investigated over 10%Ni/CexZr1-xO2-CaO.The results show that the hydrogen yield obtained was as high as 83%over 10%Ni/CexZr1-xO2-CaO when the molar ratio of Ce4+,Zr4+ and Ca2+ is 1.2:1:5,the temperature is 550℃,the space velocity is 0.48 h-1,and the water-carbon ratio is 2:1.The changes of hydrogen concentration in the acetic acid reforming reaction were compared among 10%Ni/CexZr1-xO2,physical mixed catalyst of 10%Ni/CexZri-xO2+CaO and bi-functional catalyst of 10%Ni/CZC-1.2:1:5.Among them,in the bi-functional catalyst of 10%Ni/CZC-1.2:1:5,hydrogen purity in the prebreakthrough was up to 99%,and after 15 carbonization calcination reaction the hydrogen concentration can still be maintained at 95%.(2)The typical bio-oil components of acetic acid,acetone,ethanol,ethyl acetate,phenol,and furfural were selected to be mixed into a simulated bio-oil,and sorption-enhanced steam reforming for simulated bio-oil was researched under the bifunctional catalyst of 10%Ni/CZC-1.2:1:5.The effects of reaction temperature and airspeed on SESR of mixed model compounds were explored,and found hydrogen yield of 82%and a raw material conversion rate of 99%at a water-carbon ratio of 6,a space velocity of 0.48 h-1 and a reaction temperature of 550℃.The results of multiple cycle reactions of 10%Ni/CexZr1-xO2+CaO and bi-functional catalyst 10%Ni/CZC-1.2:1:5 in mixed model compounds were compared,and were found that the bio-oil mixed model compound and the single model compound acetic acid have the same absorption pattem.Among them,in the 10%Ni/CZC-1.2:1:5 catalyst in the sorption-enhanced steam reforming for the mixed model compounds,the hydrogen concentration in prebreakthrough was up to 99%.After 15 cycles of reaction,the hydrogen purity can still be maintained above 90%in prebreakthrough.(3)Finally,the SESR of real wood chips bio-oil for hydrogen production was studied under the bi-functional catalyst of 10%Ni/CZC-1.2:1:5.The influence of temperature on the hydrogen yield of SESR for bio-oil was investigated.It was found that hydrogen yield reached 78%at a temperature of 550 ℃,at a water-carbon ratio of 15 and a space velocity of 0.72 h-1.The results of 15 cycle reactions were compared by SESR of bio-oil between 10%Ni/CexZr1-xO2+CaO and 10%Ni/CZC-1.2:1:5 catalysts.It was found that the bi-functional catalyst of 10%Ni/CZC-1.2:1:5 is also suitable for SESR of bio-oils.The hydrogen concentration prebreakthrough is 99%.Even after fifteen reaction calcination cycles,it can still be obtained 90%high purity hydrogen.The results show that SESR from bio-oil for hydrogen production is a very promising technology.