| Cellulose is the main component of lignocellulosic biomass.The study of combustion and pyrolysis characteristics of cellulose plays an important role in the overall utilization of biomass.Nature cellulose exhibits semi-crystalline structure,and the crystallinity is a crucial factor affecting the properties of cellulose.In this paper,the influence of different extraction methods on the microstructure of cellulose were studied comparatively,and an extraction method with minimal influence on the microstructure of cellulose was determined.The combustion and pyrolysis behavior and product distribution of cellulose with different crystallinity were explored by thermogravimetric analysis(TG),microscale combustion calorimeter(MCC),thermogravimetric analyzer coupled with Fourier transform infrared spectrometry(TG-FTIR)and pyrolysis coupled with gas chromatography/mass spectrometry(Py-GC/MS).The primary studies of this thesis are as following:1.The cellulose of flue-cured and oriental tobacco leaves were extracted by neutral detergent method,acid hydrolysis method and alkali treatment method;The microstructure of tobacco cellulose extracted by different methods was characterized by solid-state cross-polarization magic angle spinning carbon-13 nuclear magnetic resonance(CP/MAS 13C NMR).The yields and purity of tobacco cellulose extracted by the three methods were comparatively analyzed.The results showed that:?The purity of tobacco cellulose extracted by neutral detergent method(81.2%)was the highest.?The crystal form of cellulose Ip was dominant in the tobacco cellulose obtained by the three extraction methods.?The crystallinity of tobacco cellulose obtained by the neutral detergent method(43.8%)was the largest,and the size of elementary fibrils(3.4 nm)and elementary fibrils aggregate(8.9 nm)were the largest.Thus,the influence of neutral detergent method on the microstructure of tobacco cellulose was the slightest.2.Two batches of cellulose samples with different crystallinity were obtained by ball-milling microcrystalline cellulose and extracting from different plant cellulose by neutral detergent method.The combustion and pyrolysis behavior of cellulose with different crystallinity was analyzed by TG and MCC.The results show that:?During the pyrolysis process at the nitrogen atmosphere,when the crystallinity of microcrystalline cellulose was reduced from 54.4%to 23.1%,the onset temperature,the maximum weight loss rate and the temperature at the maximum weight loss ratedecreased by 16.0 ?,10.08%/min and 19.0 ?,respectively;for plant cellulose,when tme crystallinity was reduced from 68.8%to 38.9%,the above parameters were reduced by 18.4 ?,17.24%/min and 2.4 0C,respectively;(?During the combustion and pyrolysis process at 10%oxygen atmosphere,when the crystallinity of microcrystalline cellulose decreased from 54.4%to 23.1%,the onset temperature,the maximum weight loss rate and the temperature at the maximum weight loss rate decreased by 19.2 ?,17.83%/min,and 22.1 0C,respectively.When the crystallinity of plant cellulose was reduced from 68.8%to 38.9%,the above parameters were reduced by 27.8 ?,24.44%/min and 23.6 °C,respectively.?At 10%oxygen atmosphere,when the crystallinity of microcrystalline cellulose decreased from 54.4%to 23.1%,the ignition temperature,peak of heat release rate and total heat release decreased by 37.3?,295.4 W/g and 10.3 KJ/g,severally.When the plant cellulose's crystallinity was reduced from 68.8%to 38.9%,the above parameters were reduced by 40 ?,323.1 W/g and 8.9 KJ/g,respectively.Therefore,cellulose crystallinity has a significant effect on the combustion and pyrolysis behavior,the onset temperature,the maximum weight loss rate and the temperature at the maximum weight loss rate decrease with the reduction of cellulose crystallinity,and the ignition temperature,peak of heat release rate and total heat release also decrease with the decreasing crystallinity.Cellulose with higher crystallinity has better thermal stability.3.TG-FTIR and Py-GC/MS were used to study the formation of pyrolysis products of cellulose with different crystallinity.(1)TG-FTIR results show that:?At temperature range of 290~410 0C,the relative content of CO,CO2 and H2O decreased with the decrease of cellulose crystallinity.Under nitrogen atmosphere,when the crystallinity of microcrystalline cellulose decreased from 54.4%to 23.1%,the maximum absorbance of CO,CO2 and H2O produced by pyrolysis decreased by 44.7%,63.1%and 36.8%,respectively.For plant cellulose,when the crystallinity decreased from 68.6%to 42.6%,the maximum absorbance of the above products decreased by 48.1%,55.4%and 72.7%,severally;?When the crystallinity of microcrystalline cellulose decreased from 54.4%to 23.1%under 10%oxygen atmosphere,the maximum absorbance of CO,CO2 and H2O produced during the combustion and pyrolysis process decreased by 38.6%,28.6%and 28.2%,respectively.For plant cellulose,when the crystallinity decreased from 68.6%to 42.6%,the maximum absorbance of the above products was severally reduced by 8.2%,65.3%and 74.3%.?The relative content of carbonyl compounds showed a decreasing trend with decreasing crystallinity.Under nitrogen atmosphere,when the crystallinity of microcrystalline cellulose decreased from 54.4%to 23.1%,the maximum absorbance of carbonyl compound produced by pyrolysis decreased by 11.9%;when the cellulose crystallinity of plant decreased from 68.6%to 42.6%,there was no significant change in the maximum absorbance of the carbonyl compound.Under 10%oxygen atmosphere,when the crystallinity of microcrystalline cellulose decreased from 54.4%to 23.1%,the maximum absorbance of carbonyl compound decreased by 25.6%;when the crystallinity of plant cellulose decreased from 68.6%to 42.6%,the maximum absorbance of the carbonyl compound decreased by 23.2%.(2)Py-GC/MS results show that:When the crystallinity of microcrystalline cellulose was reduced from 54.4%to 23.1%,the relative content of phenol produced by pyrolysis at 800 ? was reduced by 10.7%,and the relative content of benzenes also decreased;For plant cellulose,when the crystallinity decreased from 68.6%to 42.6%,the relative content of phenol and benzenes produced decreased by 63.9%and 61.0%,respectively.Hence,as the crystallinity of cellulose decreased,the relative content of CO,CO2,H2O,carbonyl compounds,phenol and benzenes during the main combustion and pyrolysis process were reduced.This paper reveals the influence of cellulose crystallinity on its combustion and pyrolysis characteristics,and clarifies the relationship between the formation of harmful components such as CO,CO2,carbonyl compounds and phenol in cellulose combustion and pyrolysis process and crystallinity.This work has the potential to provide regulatory guidance for the biomass utilization and provide vital experimental support for the tobacco's harm reduction. |
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