Experiment And Mechanism Research On The Catalytic Cracking Of Coal

Coal is an organism mainly composed of C,H and O elements,which has both the properties of energy and resources.At present,the utilization of coal mainly exerts its energy properties and does not fully utilize its resource value.Through coal chemical technology,coal is converted into fuels or chemical products such as syngas,tar,semi-coke,etc,which can effectively increase the added value of coal.Directional pyrolysis is a promising technology for the utilization of coal resource value and catalytic pyrolysis is an important means of coal directional pyrolysis.On the one hand,the appropriate catalyst can reduce the energy barrier required for the reaction,and on the other hand,it can regulate the product yield and distribution of coal cracking.It is beneficial to regulate the products of coal cracking by using catalyst.Therefore,catalytic pyrolysis has attracted extensive attention.For catalytic pyrolysis,current researches focus on the effects of catalyst such as alkali and alkaline earth metal catalysts,transition metal catalysts and other catalysts on coal cracking characteristics.Exploring the catalytic effect of the catalyst by analyzing the changement of the pyrolysis products at the macro level has obtained some achievements,but the micro-catalytic mechanism of coal cracking needs further research.Moreover,the results of the study are relatively fragmented and difficult to be a coherent and systematic conclusion,so it is difficult to provide strong guidance for subsequent research.In view of this,based on previous researches,this paper focuses on the catalytic pyrolysis technology in the utilization of coal resource value,and mainly studies the core issues of coal catalytic pyrolysis co-produced syngas and semi-coke.Firstly,this paper used some characterization techniques and experimental methods such as SEM,BET,XRD,FTIR,TGA,tube furnace,etc.to study the effect of demineralization by acid washing on the physical and chemical properties of coal comprehensively for the first time.It can be concluded that acid washing does not change the main structure of coal.XRD experiments show that the phase structure of coal does not change significantly.FTIR data implies that the organic functional group changes not too much.TG experiments reveal that the temperature Tp at the maximum weight loss rate which reflectes the main structure of coal does change too much.Tube furnace experiments show that acid washing does not change the variation of coal pyrolysis products.Therefore,acid washing mainly removes the minerals and some oxygen-containing components of the coal.The structure of coal has not undergone qualitative changes and the tendency of coal pyrolysis reaction also does not change.Such results are the basis of catalytic pyrolysis experiments and data analysis in a large number of literatures.The results of the study provide data support and theoretical basis for the research methods of using acid-washed coal supported catalysts.Based on the study of the physical and chemical properties of acid washed coal,five metal chlorides,KCl,CaCl2,NiCl2,MnCl2,and ZnCl2,were selected as catalyst carrying the metal cations of K+?Ca2+?Ni2+?Mn2+ and Zn2+.The catalytic pyrolysis and gasification characteristics,reaction kinetics and catalytic mechanism of coal were comparatively studied by means of thermogravimetry as the key means,supplemented by XRD,FTIR,EDS and P Y-GC/MS methods.Results show that the order of the activation energies in catalytic pyrolysis is AW>RAW>AW+K>AW+Ni>AW+Mn>AW+Zn>AW+Ca and the order in gasification is AW>RAW>AW+Zn>AW+Ni>AW+K>AW+Ca.It indicates that both the catalyst and the minerals in the coal can reduce the energy barriers for both pyrolysis and gasification and are favorable for the reaction.The characterization by XRD experiments shows that K+,Ca2+/CaCO3,Ni and MnO play catalytic role during the pyrolysis process for the catalyst of KCl,CaCl2,NiCl2 and MnCl2 respectively,while K+,Ca2+/CaCO3,Ni/NiO and MnO/MnO2 play catalytic role during the gasification process.So the catalytic mechanism of KCl is supported by new data,the catalytic mechanism of CaCl2 is further developed,and the catalytic mechanism of NiCl2 and MnCl2 is innovatively revealed.It provides a theoretical basis for the subsequent study on the products regulation of catalytic cracking and the development of new novel catalyst for the directional cracking of coal.Finally,the macro-level research was carried out using fixed bed and entrained-flow bed experimental platform on the products regulation of catalytic pyrolysis of coal.The optimal reaction conditions for directional regulation of coal pyrolysis were explored,and the effects of pyrolysis temperature,catalyst type and catalyst concentration on the products characteristics were studied.Results show that in a fixed-bed experimental system,Ni2+ has the best effect on increasing pyrolysis gas production,and it is 7.5%,3.4%,4.1%,7.0%,and 7.3%higher than raw coal at 800-1200?,respectively.The increase of syngas(H2+CO)production by Ni2+ is also the most obvious,increasing by 21.1%,13.9%,15.1%,19.3%,and 19.9%from 800? to 1200?,respectively.Zn2+ is the most favorable for the production of H2,and the yield increases by 16.8%,29.1%,19.8%,19.7%and 19.2%at 800-1200?,respectively.Mn2+ and Zn2+ help to increase tar yield.In the entrained-flow bed experimental system,the influence of the catalyst on the pyrolysis gas composition is similar.Ni2+ has the most obvious catalytic effect on pyrolysis gas and syngas production and from 800? to 1200?,pyrolysis gas production increases 13.7%,12.5%,2.9%,3.6%,and 5.1%,compared to raw coal,and syngas production increases by 21.3%,16.1%,0.5%,3.5%and 4.5%respectively.Mn2+,Zn2+ and K+ can increase the yield of H2,and Ca2+ is beneficial to increase the yield of CH4.Both fixed bed and entrained-flow bed experiments show that the catalyst can affect the product yield and regulate the distribution of components,and the catalytic effects of different catalysts are different.The experimental results provide experimental and data support for the directional pyrolysis of coal.