离线式的热化学降解技术研究Pahokee泥炭腐殖酸

离线式封闭体系下大分子的热化学降解通常在较低的温度下进行,很少讨论较高反应温度下的情况。本文以前期研究较深入的Pahokee腐殖酸作为对象进行了离线式热化学降解研究,结果表明,若反应时间相同,中等反应温度(350～400℃)下Pahokee腐殖酸的离线式热化学降解产物与较低温度(250～300℃)下的结果十分一致,在较低温度下反应时间对降解产物的分布没有明显的影响。尽管在较高的温度条件(500～600℃)下反应时间为30min时,可能导致严重的裂解与缩合反应。但是当反应时间减少至1min,可以获得与较低温度条件下类似的热化学降解产物。本文在离线方式下获得的Pahokee腐殖酸的热化学降解产物与已经报道的在线方式下得到的结果基本类似,主要差别在于离线方式下降解产物中长链脂肪酸甲脂相对含量较高并且检出了木质素芳环β-醚键降解的结构单元。因此,离线式封闭体系下的热化学降解方法可以在中等以及相对较高的温度条件下进行。这一结论有待于不同来源和结构的大分子样品的进一步证实。

Characterization of Humic Acid Extracted from Pahokee Peat by Off-line Thermochemolysis

Thermochemolysis of macromolecules performed in off-line closed systems are usually carried out at relatively low temperatures, and little attention was paid to off-line thermochemolysis at relatively high temperatures. Off-line thermochemolysis of a Pahokee humic acid (HA) sample, which was well characterized in the pervious studies, was carried out in this study. Off-line thermochemolysis of Pahokee humic acid at moderate temperatures (350℃~400℃) could yield similar products as to that at sub-pyrolysis temperatures (250℃~300℃) at the same reaction time, and reaction time seemed to have little effect on the yielded products from off-line thermochemolysis at sub-pyrolysis temperatures. Although off-line thermochemolysis of humic acid at pyrolytic temperatures (500℃~600℃) for 30 minutes seemed to have led to serious cracking and condense reactions and reaction time was significantly decreased to 1 min, similar products could still be obtained from off-line thermochemolysis at 600℃ to those yielded at relatively lower temperatures. Products resulting from off-line thermochemolysis of Pahokee humic acid in this work are comparable with those from on-line thermochemolysis at 610℃ as reported by a previous study. Notable differences exist in relatively higher amounts of long-chain fatty acid esters and identification of some fragments of β-aryl ether subunits of lignins in the off-line thermochemolysis products of humic acid. Hence, off-line thermochemolysis in closed systems could be considered as being carried out at pyrolytic or moderate temperatures. However, this conclusion requires further test of more macromolecule samples of various origins and structures.