非木浆漂白过程中生成AOX的前体物质与反应机制

Adsorbable organic halogen (AOX) is a group of chlorinated organic compounds as a persistent bio-accumulative toxin category. They have been found to accumulate in organisms and affect human health through the food chain, which attracts an increasing interests and concerns. High amounts of AOX are generated during pulp chlorine bleaching process and released into water environment. This project focuses on the formation of AOX compounds with high concerns during non-wood pulp chlorine bleaching process, such as polychlorinated biphenyls and chlorinated polycyclic aromatic hydrocarbons. A series of non-wood pulp raw materials including wheat straw and reeds will be studied. The precursor compounds of AOX will be separated step by step during the raw material extraction and pulp chlorine bleaching process. The possible precursor compounds will be identified and quantitatively analyzed. Spiked chlorination experiments will be conducted in order to explore the formation mechanism of AOX from the precursor compounds and the emission characteristic. The effects of bleaching conditions, including temperature, available chlorine dosage, initial pH value on the formation of AOX and their species will be discussed, as well as the formation kinetics mechanism. Meanwhile, hydroxylated AOX during the chlorine bleaching process will be screened while their analysis method will be further developed. This research will provide the theoretical foundation and data support in reducing the emission of AOX and their by-product in pulp mills and other similar chemical process.

有机卤化物（AOX）属于持久累积毒性物质（PBT），可以在生物体内的长期残留并通过食物链影响人类健康。本项目关注于造纸漂白制浆过程中生成氯代联苯、氯代多环芳烃等高关注度氯代有机污染物（AOX）的前体物质和AOX的生成机制，围绕麦草、芦苇等非木浆材料的制浆工艺，采用浆料分类提取-制浆漂白-色谱制备-化学表征相结合的技术手段，逐级分离生成AOX的前体物质；以分离到的前体物质或标准品为基质，通过漂白试验，剖析前体物质转化为AOX的反应机制和排放特征；考察AOX生成过程中温度、pH、氯浓度等对AOX生成种类、生成浓度的影响，研究AOX生成的动力学规律；筛选羟基化AOX，开发羟基化AOX的分析检测技术。揭示高关注度AOX的生成机制与关键控制因子，为制浆造纸的AOX减排和其它化工过程中AOX副产物研究提供参考。

非木浆氯漂可产生多氯二苯并对二恶英和二苯并呋喃(PCDD/Fs)。本研究探索了麦草浆氯漂过程中Cl1 - 8DD/Fs的来源、形成途径及形成动力学。13C同位素标记实验验证了纸浆中酚类物质氯化不能形成PCDD/Fs。80%以上的PCDFs来源于未漂白麦草浆中二苯并呋喃(DBF)的直接氯化，而约60%的PCDDs来源于纸浆中不可提取的前体的氯化。总PCDFs的产率比总PCDDs高2个数量级。动力学研究表明，DBF比二苯并对二恶英(DBD)更容易在纸浆溶液中氯化。拟一阶反应动力学方程较好地拟合了PCDD/Fs的形成和降解过程。DBD/F的直接氯化反应主要倾向于2位的选择性模式，其次是8位、7位和3位。未漂白纸浆中DBF含量越高，产率越高，分别为2,3,7,8- Cl4DF。为了进一步验证实验结果，创造性地将一系列酚类同位素实验和DBD/DBF加标漂白实验引入反应体系，追踪PCDD/Fs的来源。本报告提供的证据表明， DBD/DBF是PCDD/Fs形成的重要前体。在酚类物质存在的情况下，随着氯取代度的增加，形成PCDD/Fs的量大大减少，显示TCDD/F>PeCDD/F>HeCDD/F，甚至没有检测到HpCDD/F和OCDD/F。在DBD/F漂白体系中加入苯酚、愈创木酚或儿茶酚后，高氯取代的PCDD/Fs量急剧下降。在所有酚类物质的实验中，TCDFs、PeCDFs和HxCDFs的含量分别降低了98.9%、98.5%和65.1%，TCDDs、PeCDDs和HxCDDs的含量也分别下降了90.8%、95.4%和97.0%。氯代数大于4时，高氯代PCDD/Fs的浓度随着PCDD/Fs氯代数的增加而减小。可以看出，DBD/F漂白体系中添加酚类物质导致PCDD/Fs氯化取代度降低，这可能与氯化能力的改变以及高氯化PCDD/Fs的形成机理有关。