Kraft lignin is water insoluble and has limited end-use applications. To produce water soluble lignin-based products, the modification of softwood kraft lignin through phenolation followed by sulfonation of sulfuric acid or sodium sulfite treatment were investigated in this work. Fourier transform infrared (FTIR) spectrophotometer, nuclear magnetic resonance (NMR), and thermo-gravimetric analysis were also considered for characterizing the lignin-based products. The results showed that phenolation pretreatment was effective to generate sulfonated lignin (SAP-lignin) by sulfuric acid treatment with a high charge density (3.12 meq/g) and solubility, which is due to the addition of sulfonation sites on the phenolic ring. However, sodium sulfite treatment of phenolated lignin generated sulfonated lignin (SSP-lignin) with the charge density of 1.20 meq/g due to hindered sulfonation by occupation of reactive α-position. SAP-lignin was soluble across the tested pH range of 1–13, but SSP became insoluble at a pH lower than 3. Thermogravimetric analysis revealed that phenolation pretreatment reduced the thermal resistance of modified lignin when compared to kraft lignin, while SAP-lignin exhibited the highest thermal resistance due to condensation under sulfuric acid treatment. SAP- and SSP-lignin were successfully used as a coagulant for dye removal from simulated solutions as they could remove 72.1 and 90.4% of ethyl violet from a simulated dye solution, respectively.

中文翻译：

---

酚化硫酸盐木质素磺化生产水溶性产品

牛皮纸木质素不溶于水，最终用途有限。为了生产水溶性木质素基产品，本文研究了通过酚化、硫酸磺化或亚硫酸钠处理对针叶木硫酸盐木质素进行改性。傅里叶变换红外 (FTIR) 分光光度计、核磁共振 (NMR) 和热重分析也被考虑用于表征基于木质素的产品。结果表明，酚化预处理可有效地通过硫酸处理生成具有高电荷密度（3.12 meq/g）和溶解度的磺化木质素（SAP-木质素），这是由于在酚环上添加了磺化位点。然而，酚化木质素的亚硫酸钠处理产生电荷密度为1的磺化木质素（SSP-木质素）。20 meq/g 由于占据反应性 α 位受阻磺化。SAP-木质素在 1-13 的测试 pH 范围内可溶，但 SSP 在 pH 低于 3 时变得不溶。热重分析表明，与硫酸盐木质素相比，酚化预处理降低了改性木质素的耐热性，而 SAP-木质素表现出由于在硫酸处理下冷凝，具有最高的耐热性。SAP-和SSP-木质素成功地用作从模拟溶液中去除染料的凝结剂，因为它们可以分别从模拟染料溶液中去除72.1%和90.4%的乙基紫。热重分析表明，与硫酸盐处理的木质素相比，酚化预处理降低了改性木质素的耐热性，而 SAP-木质素由于在硫酸处理下缩合而表现出最高的耐热性。SAP-和SSP-木质素成功地用作从模拟溶液中去除染料的凝结剂，因为它们可以分别从模拟染料溶液中去除72.1%和90.4%的乙基紫。热重分析表明，与硫酸盐处理的木质素相比，酚化预处理降低了改性木质素的耐热性，而 SAP-木质素由于在硫酸处理下缩合而表现出最高的耐热性。SAP-和SSP-木质素成功地用作从模拟溶液中去除染料的凝结剂，因为它们可以分别从模拟染料溶液中去除72.1%和90.4%的乙基紫。