Acetylene Production From Coal In Plasma Pyrolysis And Analysis Of Thermodynamics And Kinetics

Plasma technology is a novel one which owns a series of advantages in high-temperature chemistry. Coal pyrolysis in arc plasma jet to produce acetylene is an embodying application. It is well known that acetylene is an important chemical material, its traditional process using coal led to serious pollution and higher energy consumption. Thus, it forces researchers to explore a new technical means. Coal pyrolysis in arc plasma jet to produce acetylene is the most promising process, which substitutes for conventional coal -based yielding means. Currently it is still on the developing stage. Based on situation of the present developing researches at home and abroad, some important problems in this field are selected as research topics in this dissertation. They include such contents, as follows:1. To select 12 coals with different coal rank were investigated experimentally, according to their metamorphosing extents, oxygen contents, ash yields and coal granularities. At the same time, the value of acyclic carbon to aromatic one in raw coal and that in residue after pyrolysis were analyzed. Additionally some other researches were carried out, for instance changes of characteristic of coking matters with axial position, main factors affecting coking amount and effect of additive of SiO₂ and sands on coking amount and configuration of coke. The demands for the characters of coals used to produce acetylene in arc jet were summarized, thus there was theoretical foundation for the rational selection of coal kind.2. Using theoretical analysis, methods to calculate the plasma temperature and concentration of different species were established. Temperatures of arc plasma used experimentally in different power were calculated, moreover concentration distributions of different species were also analysized.3. C₆H₆,C₁₀H₈,.C₆H₁₂(cyclohexane),CH₄ ,C₂H₆, C₃H₈ and graphite were selected as model compounds, then some reactions on these compounds to produce acetylene were designed.Through the analysis of possibility and trend to produce acetylene in thermal plasma using thermodynamics theory, some conclusions were deduced.Smaller molecular acyclic hydrocarbons, for example CH₄, C₂H₆, C₃H₈ etc are the easiest to yield acetylene. The second is cyclo-hydrocarbon, such as cyclohexane. The third is unsaturated alkene. The fourth is cyclic compounds (naphthalene). The fifth is benzene. The most difficult is graphite. At the same time, the mathematical expression of Gibbs function of coal was deduced on the base of determination of Gibbs function and characteristic of enthalpy. Based on the above expression, the reactions by which coal is converted into acetylene were analyzed. The results indicated that coal could be converted into acetylene thermodynamically in H2 atmosphere and into acetylene mixture in non-H₂ atmosphere.4. According to chemical reaction kinetics, statistical mechanics and quantum chemistry etc, the pyrolysis mechanisms of model compounds in Ar-H₂ plasma were investigated, and then the mechanism of acetylene production from coal was studied on the foundation of big molecular structure of coal.5. Based on the above mentioned works, some conclusions were drawn. The model compounds have similar pyrolysis mechanism. The active species in plasma-H atoms firstly assault reactant molecules, thus they transfer into free radicals which are in excited state, then these high energy particles crack further or dehydrate to yield acetylene in high temperature. The covalent bonds in big molecule structure in coal have different bond energies, but yield of acetylene is dependent on the fraction of stronger and higher bond energy covalent bond. So it is necessary to supply higher temperature. Furthermore, the producing mechanism of acetylene can be detected that fragile chemical bonds in coal firstly rupture and emit the volatile, then the volatile decompose further, at last smaller molecules such as acetylene are produced.6. From the experime...