| In recent years,with the increasingly severe national and international energy situation,the utilization of biomass resources has gradually attracted widespread attention of scholars at home and abroad.Among them,the heat treatment process represented by biomass catalytic pyrolysis and catalytic gasification can realize the high value utilization of waste biomass resources,and has the potential of industrialization.As a key factor to improve the overall economy of catalytic pyrolysis and gasification process,catalysts have been extensively studied in academia.According to a large number of literature research,this study used industrial solid waste,red mud,as a catalyst to produce high-quality reducing gas by in-situ catalytic pyrolysis and steam gasification of biomass.In order to preliminarily explore the catalytic mechanism and performance of red mud as a catalyst,XRD,XRF,thermogravimetry,DSC,BET and SEM characterization of red mud were carried out,and the corresponding physical and chemical properties of red mud were obtained.The results showed that Fe2O3 was the main component of red mud.Al,Si,Ca and other elements formed the basic skeleton of red mud in the form of silicate.Elements in red mud were doped with each other at the lattice level in the form of solid solution.Red mud particles had broken surface morphology and good pore structure,which could be destroyed by high temperature calcination.Firstly,in order to obtain the pyrolysis characteristics of corn straw,the thermogravimetry and DSC analysis of corn straw and its pyrolysis experiments under different reaction temperatures and N2 atmosphere were carried out.In order to explore the characteristics and mechanism of red mud to catalyze biomass pyrolysis,the experimental study of catalytic pyrolysis of corn straw by red mud and its three main components,Fe2O3,Al2O3 and CaCO3,was carried out.To further verify the catalytic mechanism of red mud,the red mud and Fe2O3 after catalyzing pyrolysis were obtained by magnetic separation,and were characterized and analyzed.It was found that the increase of reaction temperature was conduc ive to the release of volatile matter and the secondary decomposition of macromolecules,and was conducive to the production of H2 and CO.At 900℃,the maximum yield of H2 was 144.15 ml/g,and the maximum yield of CO was 229.79 ml/g.Fe2O3 was the most critical catalytic active component of red mud,which could not only be used as an oxygen carrier to promote the cracking of raw materials,but also catalyze the fracture and precipitation of carbonyl,carboxyl and other oxygen-containing groups,promote the dehydrogenation and condensation of hydrocarbons and the fracture and reorganization of carbon chain,thus improving the production of CO and H2.Al2O3 could promote the initial pyrolysis reaction and the fracture precipitation of methoxy,etc.thus increasing the CH4 output.When a small amount of CaCO3 was decomposed at high temperature,the CaO produced could promote the breakage of alkyl groups and oxygen-containing groups,and the small amount of CO2 produced could promote the gasification of carbon in the raw material.But the large amount of CO2 produced by excessive CaCO3 could inhibit the breakage of alkyl groups and oxygen-containing groups,etc.Red mud as a pyrolysis catalyst could effectively promote the production of CO,CO2,CH4 and H2,among which,the maximum yield of H2 at 800℃ reached 143.58 ml/g,an increase of 78.98%.The unique structure of red mud enhanced the catalytic performance of Fe2O3 in it and improved the stability of the red mud catalyst.Secondly,in order to obtain the steam gasification characteristics of corn straw,the steam gasification experiments of corn straw under different reaction temperature,steam flow rate and gasification time were carried out;In order to explore the characteristics of red mud catalytic biomass gasification,the experimental study of red mud and its three main components catalytic steam gasification of corn straw was carried out,and the catalytic mechanism of red mud was further explored by combining the characteristics analysis of catalysts before and after the reaction.It was found that the increase of reaction temperature promoted the production of CO,CO2 and H2,among which the yield of H2 reached 458.13 ml/g at 850℃,which was 445.00%higher than that at 700℃.The increase of steam flow rate influenced the relevant reaction equilibrium and improved the reaction rate by increasing the concentration of steam in the reaction system,thus promoting H2 output.Since the fixed carbon gasification reaction proceed with a long period,the amount of fixed carbon gasification can be increased by extending the gasification time,thus promoting the H2 output.Fe2O3 not only promoted the gas-phase reactions such as water-gas shift reaction,but also effectively catalyzed the fixed carbon gasification reaction as an intermediate reactant.Al2O3 as a catalyst facilitated the output of CH4 and H2,while inhibiting the output of CO.The CO2 produced by the high temperature decomposition of CaCO3 inhibited the water-gas shift reaction and methane-water steam reforming,so as to reduce the H2 output in the pyrolysis stage.The addition of red mud was beneficial to the production of H2 and CO2,and inhibited the production of CO.The maximum yield of H2 reached 496.34 ml/g,which was 70.90%higher than that under the condition without catalyst.Compared with pure Fe2O3,the superior pore structure of red mud provided a large gassolid contact area,and the doping of heteroatoms in the Fe2O3 crystal structure also made the surface lattice oxygen more active,improving the redox performance of Fe2O3 in red mud.Compared with pure Fe2O3,red mud catalyst showed more superior ability to prevent carbon deposition,which was conducive to improving its service life... |
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