杏壳纤维素结构表征及热解特性分析

为研究生物质中单一组分的分离和热解特性,以杏壳为原料通过碱法分离制备了杏壳纤维素,采用红外光谱、X射线衍射、扫描电子显微镜对其组成结构、微观形貌进行表征,通过热重分析和热重红外联用分析,研究其热解特性及挥发性产物的形成规律。结果表明:碱法杏壳纤维素的分离得率为24.59%; 纤维素的红外光谱图在895和1 162 cm-1有β-(1→4)-糖苷键的特征吸收峰,1 058 cm-1处为糖苷键连接的C―O弯曲振动,3 419 cm-1处吸收峰表明分子间的氢键作用较强; X射线衍射谱图中22.13°的结晶区衍射峰最强,结晶度为48.38%; 扫描电子显微镜的结果表明杏壳纤维素为条状且有团聚现象。热重分析结果显示,杏壳纤维素热解质量损失主要经历了物理水脱除、玻璃化转变、主质量损失和煅烧4个阶段,最后进入焦炭生成阶段,主要质量损失温区为270～420 ℃,其质量损失率为70%。800 ℃时质量损失曲线相对平稳,热解残炭率为15.78%。随着温度的升高,挥发分的浓度呈先增大后降低的趋势,各产物析出量在362 ℃时达到最高值,热解气体产物主要以CO2和CO为主,CO2的生成伴随着H2O、烷烃类、醛类、酮类等化合物生成。研究结果可为杏壳纤维素的分离及热解利用提供理论基础。
The complex composition of biomass makes the chemical reaction in pyrolysis complex. In this study, the structure and microstructure of cellulose from apricot shell were analyzed, and its pyrolysis behaviors were also studied. The apricot shell cellulose was separated from apricot shell by alkali treatment. The resulting cellulose was characterized by infrared spectroscopy, X-ray diffraction and scanning electron microscope, and then the pyrolysis behaviors of apricot shell-cellulose were studied by thermogravimetric and thermogravimetric infrared analysis. The results showed that the yield of apricot shell cellulose was 24.59%. In the infrared spectrogram of cellulose, there were absorption peaks of β-(1→4)-glycosidic bond at 895 cm-1 and 1 162 cm-1, and the C―O bend vibration presented at 1 058 cm-1. The absorption peak of 3 419 cm-1 indicated that hydrogen bonds between molecules were strong. The diffraction peak at 22.13° was derived from the 002 plane of cellulose I and the calculated crystallinity index was 48.38%. The images of scanning electron microscope showed that the apricot shell cellulose was about 100 μm long and 10 μm wide, and it had a trend to aggregate. According to the results of thermogravimetric analysis, the weight loss of apricot shell cellulose mainly occurred between 270-420 ℃, where the weight lose was 70%. The pyrolysis weight losses were mainly due to the loss of water, vitrification transformation, calcination, and finally the char generation. The weightlessness curve was relatively flat and stable. When the temperature reached 800 ℃, pyrolytic char residue content was 15.78%. The content of aldehydes, ketones and acids in the pyrolysis gas products of apricot shell cellulose was high at wavelength of 2 400-2 260 cm-1 and 1 900-1 650 cm-1. As the pyrolysis temperature increased, the concentration of volatile first increased and then decreased, and the maximum amount of volatile product was produced at 362 ℃. The pyrolysis gas products were mainly CO2 and CO. With the increase of