生物焦微观特性及分子结构研究

Microscopic characteristics and molecular structure of biomass char

本文利用多种表征手段,研究了汞吸附剂核桃壳生物焦的热解特性、孔隙结构与官能团等微观特性,并基于所获得的化学结构利用ChemBioOffice构建了生物焦的分子结构单体模型.结果表明,生物质的热解过程分为三个阶段,所形成的生物焦孔隙发达,并含有丰富的表面官能团.生物焦的大分子结构中芳香碳是主要组成部分,而脂肪碳则起到联结芳香结构单元的作用.而且生物焦是一种短程有序的非晶态物质,结构中存在一定数量的石墨微晶结构.基于表征结果,所构建的分子模型以芳香结构为主,并含有1个甲基、4个羟基以及8个羰基,分子式为C_(55)H_(37)NO_(14),M_r=935.同时对模型进行了验证.另外,基于分子力学,在UFF、Dreiding和MM2,3种力场下对三维模型进行了结构优化,其中UFF力场优化后的三维结构的总势能最大,而MM2力场势能最小.利用量子化学半经验PM6方法对3种优化后构象的生成热进行了研究,其中Dreiding力场下优化的结构更稳定.

Mercury adsorbent bio-chars prepared in N2 were investigated.The pyrolysis characteristics,pore structures and functional groups of the bio-chars were characterized.The two-dimensional molecular structure of bio-char was built by ChemBioOffice in combination with the chemical structure obtained.The results showed that the pyrolysis process of biomass could be divided into three stages.The pore structures of bio-char were well developed.There were abundant functional groups on the surface of bio-char.Aromatic carbon was the main component of the bio-char molecular structure,while aliphatic carbon was linked to aromatic structural units.And the bio-char was a short-range ordered amorphous substance,which contained graphite microcrystalline structures.Based on the characterization results,the molecular structure model was mainly constituted by aromatic structure,including a methyl,4 hydroxyls and 8 carbonyls.The molecular formula was C55H37NO14,Mr=935.The model was verified.Based on the molecular mechanics,the three-dimensional molecular structure was optimized in the UFF,Dreiding and MM2 force fields.After the optimization,the total potential energy was the maximum in the UFF force field.The SE method PM6 was also applied to obtain the formation heat of the bio-char molecular in the three force fields.And the molecular was the most stable in the Dreiding force field.