Lignin has an enormous valorization potential as a sustainable raw material. The most common source of industrial lignin is black liquor, a byproduct from the kraft process. However, the variability in color and chemical characteristics of precipitated lignin is a constituent, hindering its use as a raw material. The structural complexity and heterogeneity of the lignin molecule make it challenging to determine the underlying mechanisms behind the chemical and physical changes that occur during precipitation. This work used a statistical design of experimental approach in Minitab to study how fractionation process variables influence the lignin mass yield and characteristics. The specific phenomena governing hardwood lignin solubility and precipitation in black liquor were investigated, and the relationships between chemical and physical properties and lignin color were analyzed. We found a positive correlation between temperature, mass yield, molecular weight, and dark coloration. For pH < 4, condensation of molecular fragments and sorption onto larger chains seem to drive the precipitation process.

中文翻译：

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了解降水过程变量对硬木木质素特性和黑液回收的影响

木质素作为可持续原料具有巨大的增值潜力。工业木质素的最常见来源是黑液，这是硫酸盐法制浆过程中产生的副产品。然而，沉淀的木质素的颜色和化学特性的变化是构成因素，从而阻碍了其用作原料。木质素分子的结构复杂性和异质性使其难以确定沉淀过程中发生的化学和物理变化背后的潜在机制。这项工作在Minitab中使用实验方法的统计设计来研究分馏过程变量如何影响木质素的产量和特性。研究了控制硬木木质素在黑液中的溶解度和沉淀的特定现象，分析了化学和物理性质与木质素颜色之间的关系。我们发现温度，质量产率，分子量和深色之间呈正相关。对于pH <4，分子片段的缩合和在较大链上的吸附似乎驱动了沉淀过程。