Thermodynamic And Kinetic Analysis On The Mainly Reactions In The Conversion Of Methane With The Coal Char Act As The Catalyst

A tubular reactor system has been used to study the conversion of themethane to produce syngas with the coal char or modified coal char holding inthe reactor, the effect of H₂ and CO atmosphere (the most important componentsof coke-oven gas) on the convesion of sulfur in the coal char was also evaluated.Then, the thermodynamics and kinetic analysis for the mainly-reactions havebeen discussed in this paper.The mainly results are:(1) The decomposition temperature of methane thermal cracking can bedecreased when the coal char holds in the reactor (from 800℃to 600℃); andthe conversion of methane could be increased. The experimental results showthat the conversion of methane is about 80% at 1000℃with the coal char actingas a catalyst. Compared with the reference experiment, it is only 10% for the uncatalysis experiment using an empty tubar reactor. So, it is concluded that thecoal char can act as a catalyst for the thermal cracking of methane.(2) The decomposition temperature of methane can be also decreased underthe modified coal char holding in the reactor, but the results show that theconversion of methane is less than that of the coal char. At 1000℃, theconversion of methane is about 80% holding with the coal char, but it is only20% holding with the modified coal char. And moreover, the experimentalresults show that CH₄ can be produced at the temperatures more than 1000℃.After the analysis of the experimental results, it can be regarded that themodified coal char can act as the catalyst for both CH₄ thermal cracking and thereaction of CO and H₂ produce CH₄.(3) Some experimental results reveal that the coal char can act as thecatalyst for methane thermal cracking reaction. And the coal char pretreated byH₂ don't influence the catalysis of the coal char to the decomposition of methane.But the coal char pretreated by H₂ could release a lot of CH₄ under the highertemperature (higher than 1000℃). And under the temperature of 1000℃～1060℃, 7mL CH₄ could be released from 1g coal char pretreated by H₂.(4) The tendency of producing CH₄ from H₂ and CO maybe happens whenthe concentrations of H₂ and CO are high and there was an appropriate catalysiscondition. And the result is that the conversion rate of methane was decreasing.(5) Both H₂ and CO could convert the sulfur in the coal char to gaseous to acertain extent. Under the atmosphere of H₂, the sulfur in the coal char mainly release in the form of H₂S with the proportion of 0.6% and COS made from thecoal char pyrolysis process; Under the atmosphere of CO, the sulfur in the coalchar mainly released in the form of COS with the proportion of 2%～4%. Moreexperimental have been done using both TGA and the tubular reactor systemincluding the samples that after the pretreatment by HNO₃ or NaOH. But furtherresearches will fosus on the patterns of sulfur in the coal char, to understandwhether the inorganic sulfur or organic sulfur can react with H₂ and CO underthe experimental conditions.(6) During the experiment, a large number of reductive atmosphere such asH₂ and CO hold in the reactor. These gases could make the sulfur in coal charreleased in the form of gaseous sulfur which decreased the contents of sulfur inthe coal char and enhance the contents of gaseous sulfur in the gaseous products.But the influence of gaseous sulfur on the contents of sulfur in the generatedsyngas is slight for the low rate of desulfuration in the polygeneration systerms.According to the kinetic analysis, for the reaction of H₂ and sulfur and the thereaction of CO and sulfur in the coal char, the reaction orders were 1 and 2respectively. And the activity energies were 89.8kJ/mol and 111.7kJ/mol,respectively.