| As a very important fossil fuel,coal plays a pivotal role in China's energy structure.The application of coal has a long history.A series of environmental problems generated by the rude and extensive utilization of coal cannot be ignored.The clean and efficient use of coal is attracting the attention of governments,enterprises and scientific research scholars.Coal pyrolysis is the initial and important step of other thermochemical conversion processes,which is a clean utilization technology of coal.Coal pyrolysis produces gas,liquid and solid products simultaneously,which can realize the multiple utilization of coal and play an important role in the new chemical industry of coal.Coal structure is complex,and there are many factors affecting coal pyrolysis.Many works focus on the macroscopic pyrolysis characteristics and product distribution of coal pyrolysis process.However,on-line study of coal pyrolysis is not adequate.In this dissertation,online photoionization mass spectrometry was utilized to study coal pyrolysis,realizing rapid detection of pyrolysis products and providing real-time information of products during pyrolysis process.Pyrolysis and catalytic pyrolysis of bituminous coal,pyrolysis of high sulfur coal and co-pyrolysis of bituminous coal and biomass were systematically studied.The dissertation consists of the following chapters:The first chapter introduced current world energy situation,and explained the important role of coal in China's energy structure and the necessity of clean coal utilization.Thermal/chemical conversion methods of coal and its industrial application were introduced.The research status of coal pyrolysis was overviewed.The goal and significance of this dissertation was proposed.The second chapter mainly introduced the experimental devices and methods used in this dissertation.Photoionization mass spectrometry(Py-PI-MS)devices and experimental parameters were introduced.Some traditional analytical methods were used,including thermogravimetry(TG),pyrolysis-gas/mass spectrometry(Py-GC/MS),Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS).The third chapter focused on the pyrolysis of bituminous coal using Py-PI-MS.Pyrolysis products of bituminous coal were abundant,mainly including alkenes,alkanes,phenols,aromatics,and a small amount of H2S and NH3.The intensities of hydrocarbons and phenols were very weak,but sulfur-containing products were rich because of the high sulfur content of anthracite coal.In addition,the effects of some factors on pyrolysis of bituminous coal were studied,including temperature,heating rate and atmosphere.The release rate of the product was faster at higher temperature,and high temperature was favorable for the formation of alkenes and aromatics.At higher heating rate,intensities of products were increased,the initial releasing temperature of products was lower,and the temperature range of the product releasing curve was widened.Aromatics released at low temperature confirmed the presence of aromatic hydrocarbon guest molecules in coal structure.Py-PI-MS can also be applied to the study of oxidation and reduction of coal.The oxidation products of coal included high value-added hydrocarbons,such as alcohols,aldehydes,ketones,furans and phenols.Compared with the inert atmosphere,the amounts of alkenes increased under the reducing atmosphere,mainly because hydrogen was beneficial to stabilize the active free radicals generated by the coal pyrolysis.In the fourth chapter,the pyrolysis behaviors of Huainan coal(HN coal)with three particle sizes,i.e.,<40 ?m(HN-S),224-500 ?m(HN-M)and 1600-2000 ?m(HN-L),were investigated by thermogravimetry(TG)and online Py-PI-MS using a krypton discharge lamp(10.6 eV)and synchrotron radiation vacuum ultraviolet light(SVUV)(14.2 eV and 15.5 eV)as the ionization sources.The fragment-free mass spectra of coal pyrolysis products were obtained at 600 °C in real time.The released organic volatiles were characterized as alkenes,phenols and aromatics,and their evolved profiles were measured as a function of time in fixed temperature mode and as a function of temperature in programmed-temperature mode.A higher weight loss ratio of the TG curves was obtained when the particle size was increased.The intensities of the individual volatiles in the mass spectra were all enhanced following the increase in the particle size of HN coal.With regard to the time-evolved profiles,by increasing the particle size,the appearance times of volatiles were delayed.Tricyclic aromatics showed multi-releasing processes in both time-evolved and temperature-programmed profiles.The release of the guest molecules lagged within the higher temperature region as the coal particle size increased.To explain the evolution trends of most organic volatiles,a mechanism combining intraparticle and interparticle mechanisms was presented.In the fifth chapter,catalytic pyrolysis of bituminous coal over two commercial zeolites,i.e.HZSM-5 and HUSY,was investigated with Py-PI-MS in real time.The fragment-free mass spectra of coal pyrolysis products at different pyrolysis temperatures were measured.Products such as alkanes,alkenes,dienes,phenols,aromatics as well as small amounts of NH3 and H2S could be detected.The abundant products at a relatively low temperature(500-600 ?)were phenols.With the presence of zeolites,the products distribution could be observed from the mass spectra.Temperature effects for pyrolysis products showed some different tendencies with and without HZSM-5 and HUSY,due to different acidities and pore sizes of the catalysts.Time-evolved profiles of major products were also measured during the pyrolysis processes.Temperature and catalyst can both dramatically affect the reaction rates.In the sixth chapter,pyrolysis and hydro-pyrolysis of high sulfur coal were studied by Py-PI-MS.The effects of pyrolysis atmosphere and temperature on sulfur conversion were studied.Under the inert and reducing atmosphere,the pyrolysis products of high-sulfur coal mainly included H2S,elemental sulfur,alkenes and aromatics.High temperature was beneficial to remove sulfur in high-sulfur coal.Compared with the inert atmosphere,the reducing atmosphere was more favorable for the conversion of sulfur in high-sulfur coal to H2S,and the higher of H2 ratio showed the better desulfurization effect.Conversion of sulfur in high-sulfur coal exhibited different temperature zones,showing the conversion process of different types of sulfur.In the inert atmosphere,the sulfur-containing products were mainly elemental sulfur,and the distribution temperature was mainly at 450-600 ?.In the reducing atmosphere,H2S was the prominent sulfur-containing product,and its distribution temperature range was 450-600 ? and>600 ?.X-ray photoelectron spectroscopy(XPS)was used to analyze the sulfur type and content of raw coal and different chars,which showed the hydro-pyrolysis was beneficial to remove sulfur.Sulfur conversion processes under inert and reducing atmosphere were analyzed according to the release characteristics of sulfur-containing products.The seventh chapter mainly introduced the co-pyrolysis of bituminous coal and biomass.Py-PI-MS was used to analyze the pyrolysis products of coal,pine,coal/pine blends and three characteristic components of pine,i.e.,lignin,cellulose and hemicellulose.It was observed that the total peak area for co-pyrolysis of coal and pine was slightly higher than that of individual pyrolysis,which indicating the occurrence of interactions and synergistic effect.In addition,by increasing the ratio of pine in the blends,the intensities of the characteristic products of coal were increased.Coal had a similar effect on the characteristic products of pine.From the time evolved profiles,it was found that the initial appearance time of co-pyrolysis product can be reduced.Co-pyrolysis of coal and pine can play a mutually reinforcing role. |
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