| dc.contributor.author | Xu, Xuejun. | en_US |
| dc.date.accessioned | 2014-10-21T12:37:10Z | |
| dc.date.available | 2002 | |
| dc.date.issued | 2002 | en_US |
| dc.identifier.other | AAINQ67657 | en_US |
| dc.identifier.uri | http://hdl.handle.net/10222/55833 | |
| dc.description | Acetylene is believed to be a precursor of polycyclic aromatic hydrocarbons (PAHs) and soot in the industrial pyrolysis and combustion of various hydrocarbons. The first experiment on the pyrolysis of acetylene was performed by Berthelot in 1866. However, the mechanism below 1500 K is still the subject of sharp controversy. Free radical mechanisms and molecular mechanisms were proposed by previous workers. Published experimental results are limited and are subject to interference by secondary and even tertiary reactions, so neither proposed mechanism could be eliminated. Study of the pyrolysis of acetylene at low conversions should provide crucial information regarding the mechanism. | en_US |
| dc.description | A series of micro-reactors were developed to pyrolyse acetylene at temperatures between 854 and 971 K, pressures between 20.4 and 403 Torr, and residence times between 8 and 3320 milliseconds. Gaseous products were separated and characterized by gas chromatography, mass spectrometry, and gas chromatography-mass spectrometry (GC-MS). Solid products such as carbon nanotubes were examined by optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and were quantified by laser extinction. | en_US |
| dc.description | The effect of surface reactions is the most serious disadvantage of the micro-reactors and thus was thoroughly studied first. Carbon nanotubes were observed in the pyrolysis of acetylene without adding metal catalyst. The carbon deposit was found to inhibit the formation of gaseous products by a heterogeneous termination process. Washing the reactor with HF solution almost eliminated both the formation of carbon on the surface and the resulting inhibition of the formation of gaseous products. For the first time, acetylene and intermediates formed directly from acetylene were shown to be the main precursors of the formation of carbon nanotubes. | en_US |
| dc.description | Induction periods for the formation of vinylacetylene and benzene have been observed between 854 and 970 K for the first time in acetylene pyrolysis below 1600 K. This is crucial evidence for a free radical mechanism. The product of the rate constants for the initiation and termination steps was determined from the induction periods. For the first time, the orders and Arrhenius parameters for the formation of vinylacetylene and benzene were measured without significant effects from surface reactions. | en_US |
| dc.description | Trace amounts of neopentane were observed to accelerate the rates of formation of vinylacetylene and benzene by similar factors. This confirms that a free radical mechanism dominates the pyrolysis of acetylene. The rate constant for initiation in the pyrolysis of acetylene was experimentally determined for the first time in the present temperature range without effects by a surface termination. The rate constants for the termination reaction and for the formation of vinylacetylene and benzene from chain propagation steps were also determined. | en_US |
| dc.description | More than twenty-four minor products were observed. Of these products, fifteen species were found to be primary or partially primary products for the first time. The orders and the rate constants for the formation of eleven partially primary products were measured for the first time. A complete mechanism has been proposed to interpret the formation of all the primary and partially primary products. | en_US |
| dc.description | Thesis (Ph.D.)--Dalhousie University (Canada), 2002. | en_US |
| dc.language | eng | en_US |
| dc.publisher | Dalhousie University | en_US |
| dc.publisher | | en_US |
| dc.subject | Chemistry, Physical. | en_US |
| dc.title | An experimental study of the early stages of the pyrolysis of acetylene. | en_US |
| dc.type | text | en_US |
| dc.contributor.degree | Ph.D. | en_US |
