Developing A Novel Calcium-based Composite Absorbent For Enhanced Multiple-cycle Hydrogen Production Via Promoted Tar Reforming With Integrated CO₂ Capture

The development of biomass calcium looping gasification?CLG?is limited by the lack of tar removal activity,poor mechanical strength and decaying carbonation performance of natural absorbent.It is of great significance for the development of CLG gasification theory and technical application to develop a novel calcium-based absorbent with stable cyclic carbonation performance,wear resistance and efficient cyclic tar removal for calcium looping gasification?CLG?of biomass and explain the mechanism of performance improvement of cyclic carbonation reaction and enhancement of hydrogen production from tar cyclic reforming.A two-step sol-gel method is adopted to prepare an iron-calcium hybrid absorbent?Ca-Al-Fe?integrating brownmillerite?Ca₂Fe₂O₅?and mayenite(Ca₁₂Al₁₄O₃₃)with CaO for calcium looping gasification.Ca₁₂Al₁₄O₃₃ significantly increased the mechanical strength of Ca-Al-Fe absorbers up to 29.46N,which was 191%,23.3%and 195%higher than that of Ca,Ca-Al and Ca-Fe absorbers,respectively.The influence of preparation conditions on the cycle CO₂ capture performance and mechanical strength of Ca-Al-Fe is investigated,and the preparation method of novel absorbent is optimized.The optimization method of preparation of absorbent was put forward,which consisted of pure CaO,Fe?NO₃?₃·9H₂O,calcination temperature of 900?,calcination time of 4h and p H value of 3.3.The prepared Ca-Al-Fe absorbers show excellent multi cycle carbonation performance and mechanical strength under the closed to the actual conditions of long period,severe calcination temperature,large particle size and so on.For example,under the condition of long cycle,the conversion of CaO in Ca-Al-Fe absorbent is still as high as 79.5%.According to the characteristics of CLG steam gasification,the effect of steam activation on the multi cycle CO₂ capture activity of Ca-Al-Fe absorbent was studied,and the effect of steam on the multi cycle carbonation activity was verified.Compared with three reference absorbers?Ca,Ca-Al and Ca-Fe?,the performance of Ca-Al-Fe multi cycle CO₂ capture and its enhancement of hydrogen production from typical biomass tar?toluene?by multi cycle reforming were systematically studied.Ca₁₂Al₁₄O₃₃ plays a key role in maintaining the cyclic carbonation stability of the new absorbent,improving the pore structure and inhibiting the sintering of the absorbent.After 20 cycles,the absorption capacity of the new absorbent is 0.40 mg_-CO2·mg^-1_-absorbent,which is 18.4%,6.2%and 72%higher than that of Ca,Ca-Al and Ca-Fe respectively.At the same time,Ca-Al-Fe sorbent has excellent performance in hydrogen production by cyclic reforming:the novel absorbent not only has the highest H₂ yield(up to 0.238 mol·h^-1·g^-1),but also has good hydrogen production stability,the H₂ concentration is higher than 68%in 5 cycles.Under the condition of high concentration tar input,the toluene conversion rate is the highest?53.23%?,and the amount of coke deposited was the lowest(12.69 mg·g^-1).The residual tar was analyzed by gas chromatography-mass spectrometry?GC-MS?,and the potential reaction mechanism of toluene was speculated.It is found that Ca-Al-Fe absorbent is beneficial to the deep dehydrogenation of toluene in the reforming process.The results show that Ca-Al-Fe absorbent can improve the performance of multi cycle CO₂ capture and toluene reforming for hydrogen production.