Construction Of Dual Functional Materials And Process Optimization On Chemical Looping CO₂ Capture And CH₄ In-situ Reforming Process In Syngas Production

CO₂ capture and utilization are important measures to complete double carbon target in China.Chemical looping,as a novel process intensification technology,divides one main reaction into specific sub-reactions through circulating medium,which can complete the directed transformation of materials and the separation of products with low energy consumption.Based on the concept of chemical looping,a reasonable reaction path was designed with the simplest carbon-hydrocarbon CH₄ as the reactant,so as to realize the integration process of syngas synthesis coupled CO₂ capture and utilization.The physicochemical properties of the circulating medium determine the efficiency of CO₂ capture and utilization.This work intends to analyze the thermodynamic properties through theoretical calculation,to explore the influencing factors via process simulation,and to test the conversion efficiency through fixed-bed experiments.Further,blank control method is adopted to explore the synergistic effect between solid carriers,the essence of the reaction process is innovatively analyzed by using the changes of gas-solid components in different reaction periods,micro-morphology regulation on solid carriers is conducted to improve the reaction activity,and a suitable single material is sought to achieve dual functions,thus providing theoretical and data support for the realization of chemical looping CO₂ capture and utilization.The main research achievements of this work are as follows:（1）Based on the thermodynamic equilibrium state theory,the H₂/CO ratio,methane conversion and product gas selectivity of Ca O,Fe₂O₃ and Al₂O₃ obtained by coprecipitation method as solid materials during carbonation,oxidation and methane reforming were analyzed to seek optimal operating conditions.It was found that Fe/Al weight ratio,CH₄ amount,Ca:Fe mole ratio and the packing manner would affect reforming performance.Meanwhile,the carbon accumulation amount under different feeding conditions was analyzed to explore the influence of solid carrier on carbon deposit.The distribution of gas products shows that the degree of carbon deposition and oxidation is closely related to the amount of methane feed.The spatial packing manner between the reforming of Ca CO₃ and Fe₂O₃ is very essential to obtain the desired reforming products.The difference of Fe O component between theoretical and experimental phases indicates that the reaction degree is affected by the dose of reducing agent.It is found that the presence of Ca CO₃ is conducive to the acceleration of Fe-based methane reforming from CH₄-TPR process.This study provides a simple way to enhance reaction degree and improve process characteristic for chemical looping process.（2）Based on thermodynamic theory analysis and fixed bed experiment optimized operating conditions,the synergistic effect between calcium and iron materials was explored through comparative analysis of blank experiments.For each single experiment,the changes of total gas content and solid composition were explored in different phases to speculate the potential reaction process mechanism.The reactivity of the dual-function material is significantly improved due to the interact effect between Ca-Fe solids and gas side reactions.Based on the Le Chatelier’s principle,oxygen carriers’addition accelerates the decomposition of Ca CO₃,while the availability of[O]from CO₂ replenishes the oxygen carriers and improves the reactivity.During the reforming process,Fe Al₂O₄ formation degrades the O content.By characterizing the samples,it was found that particle aggregation and C generation were important reasons for material deactivation.（3）To enhance the reactivity of Ca-Fe materials,the hydrotalcite precursor was used to construct highly dispersed Ca-Fe materials with large specific surface area.Meanwhile,alkaline earth metal Mg was introduced to replace Al element to avoid the formation of Fe Al₂O₄.The initial temperature research shows that 900 ^oC reforming temperature is more appropriate and its synthesis gas production is 2.5 times of that at800 ^oC.The presence of Ca induces an interact effect between Ca and Fe,and promotes syngas production and stable H₂/CO ratio,and Mg addition increases the reduction rate.The decreased redox performance can be attributed to the conversion of highly reactive Ca₂Fe₂O₅ to low-reactive Mg Fe₂O₄,crystal size changes,and material sintering during the redox process.The syngas production of hydrotalcites is better than that of physical mixed materials.It is expected that materials with related functions can be expanded to synthesize various metal oxide composites applied in new high temperature chemical looping,so as to achieve CO₂ capture and resource conversion into syngas.（4）Because of the complex reaction process caused by multiple complex elements,it is a good way to simultaneously achieve CO₂ capture and conversion to seek for Mn-based oxides with good carbonation and redox ability in chemical looping process.The application of single Mn-based material can effectively prevent the formation of spinel materials with weak activity between active substance and inert carrier,doping element and inert carrier,which reduce the reaction performance.From thermodynamic analysis,the gaseous O₂ from MnO₂ is the prerequisite for its reactivity and is the important step for MnO₂-CH₄ reforming from experiment aspect.The Mn₂O₃-CH₄ reforming activity is limited from thermodynamic hierarchy and the[O]capacity of Mn₃O₄ influences its reactivity with CH₄.Mn₂O₃exhibits the best syngas selectivity under higher reforming temperature.The[O]is replenished with a final product of MnO₂:Mn₂O₃ as 0.12:0.03 after air oxidation.41.6mol.%CO₂ capture ability of Mn O is obtained.The CH₄-O₂-CO₂ looping experiment suggests the realization of the integrated CO₂ capture and utilization with one material via chemical looping route.