Abstract:

In order to utilize the black liquor effectively, lignin was extracted from bagasse soda pulping black liquor by acid precipitation.The bagasse lignin(BL) was then characterized by Fourier transform infrared(FTIR), nuclear magnetic resonance(¹H NMR) and gel permeation chromatography(GPC).The results indicated that BL, which was consisting of syringyl(S) and guaiacyl(G) units and connected together by β-O-4 aryl ether linkages, β-5, β-1 and β-β condensed C-C linkages, was more similar to the broadleaf wood lignin than annual grass lignin.There was large variation among the molecular weight of the BL molecules.The GPC spectrum of BL contained two continuous peaks, and the number-average molecular weight(M_n) of these two peaks was 107106 g·mol^-1 and 11270 g·mol^-1, respectively.Thermogravimetric analysis(TG) was used to investigate the combustion characteristics of BL.The results showed that the combustion process undergoes four periods, i.e. dehydration(30-200℃), volatilization(200-300℃) releasing from cleavage of the C-O linkage and combustion, volatilization(300-500℃) releasing from cleavage of the highly condensed C-C linkage and combustion of coke, and burnout stage(500-800℃).The combustion of BL mainly occurred at the temperature range of 300-500℃ with above 80% mass loss, and the maximum mass loss rate reached its value of -142.75%·min^-1 at the temperature of 477℃(20℃·min^-1).The influences of different heating rates(5, 10, 15, 20℃·min^-1) on combustibility parameters of BL, which consisted of the ignition temperature, peak temperature at maximum mass loss rate, burnout temperature and maximum/mean mass loss rate were analyzed through computing the differential thermogravimetric(DTG) curves.It was shown that the thermal hysteresis would occur and all combustibility parameters were increased along with increasing heating rate.The bagasse lignin residues(BLR) were prepared by burning at 300, 600, 900 and 1100℃, and the surface morphology and elemental composition of those BLR were comprehensively analyzed by using the scanning electron microscopy(SEM) and the X-ray fluorescence(XRF) technique.The results showed that a majority of tight structure of granular with smooth surface were found in the BL, while most of loose and poriferous larger particles, which was caused by the volatilization releasing and melting of the BL, was found in the 300℃ BLR.The sporadically coke particles wrapped in the loose particles still existed in the 600℃ BLR, indicating that the incomplete combustion of the cake occurred.Then, the higher the burning temperature was, the smaller size and homogeneous of the BLR.The well-ordered lamellar particles were the majority surface morphology of BLR when burning temperature exceeded 600℃.The main composition elements of BLR were calcium(Ca), silicon(Si), aluminum(Al), phosphorus(P), sulphur(S) and ferrum(Fe).With the increase of burning temperature the Na and K contents decreased, while the other elements contents not obviously changed.

Key words: biomass, pulping black liquor, lignin, combustion characteristics, microstructure

摘要：

以酸析法从蔗渣碱法造纸黑液中回收蔗渣木质素（BL），通过红外光谱（FTIR），核磁共振氢谱（¹H NMR）和凝胶渗透色谱（GPC）对其进行了表征。结果表明，BL主要由愈创木基丙烷单元（G）和紫丁香基丙烷单元（S）通过C-O、C-C键合方式连接而成，其分子量分布较宽，分子之间存在较大差异。通过热重分析法（TG）研究了BL的燃烧特性，结果表明BL的燃烧主要发生在300~500℃的阶段，在此过程中BL分子中的C-C键发生断裂形成挥发分和焦炭，并迅速燃烧，失重率超过80%。通过扫描电子显微镜（SEM）和X射线荧光光谱（XRF）研究了BL在300、600、900和1100℃燃烧灰渣（BLR）的微观形貌和元素组成，结果表明BL呈结实、饱满的颗粒状，而BLR则表现为多孔的疏松堆积体或规则的片状结晶颗粒。随着燃烧温度的升高，BLR中的Na和K质量分数逐渐减少，而其他元素质量分数变化不大。

关键词: 生物质, 造纸黑液, 木质素, 燃烧特性, 显微结构