Chemical coprecipitation technique is proven to be a beneficial method to prepare uniformly mixed catalyst metal and Kraft lignin precursors. Coprecipitation is a simple, yet very complex process which is highly sensitive to the reaction conditions, particularly temperature. In an exothermic coprecipitation process, the reaction rate can become uncontrollable over certain temperatures which could lead to a thermal runaway reaction. In this work, metal-lignin nanocomposites were synthesized by coprecipitation of metal (M) salts and Kraft lignin. Kraft lignin and metal salts were dissolved in organic solvents and DI water, respectively, to make lignin solution/suspension and metal salt aqueous solution. The aqueous solutions of metal salts were then added to the lignin solutions/suspensions and mixed well, resulting in chelation of transition metal ions to the functional groups of lignin chains and co-precipitation of metal-lignin composites from the solvents. To develop a safe process for producing M-lignin composites in a large volume, potential reactions, exothermic or endothermic processes, hazards gases, and volatiles were evaluated during the coprecipitation process. The effects of transition metal type, solvent selection, concentration of metal salts, and initial solution temperature on the interactions between metal ions and Kraft lignin, metal uniformity in the lignin matrix, and morphology of the metal-lignin composites were investigated during the coprecipitation process. Cu, Mo, Ni, and Fe were investigated as the transition metals for the metal-lignin composites. Fenton or Fenton-like reactions were discovered to occur during the Fe- and Cu-lignin coprecipitation process and tremendous heat evolved, which lead to the overshoot of the reaction system temperature in a very short time (i.e. a few seconds). Significant amounts of CO₂ and toxic NO₂ gasses were released during the coprecipitation process when Fenton or Fenton-like reactions occurred. No interaction or a very weak interaction occurred between lignin and Mo(VI) ions when mixing both solutions. Ni ions were coordinated strongly to oxygen-containing functional groups in lignin, but no Fenton or Fenton-like reaction was detected during Ni-lignin coprecipitation. Fenton reaction or Fenton-like reaction occurred when tetrahydrofuran (THF) and acetone were used to dissolve Kraft lignin, and the reaction became highly fierce and unmanageable with increasing of iron content in the composite. The reaction initialization time was shortened with increase of initial solution temperature and thermal runaway reaction might occur if the initial mixing temperature reached 60 °C or above.

事实证明，化学共沉淀技术是制备均匀混合的催化剂金属和硫酸盐木质素前体的有益方法。共沉淀是简单但非常复杂的过程，其对反应条件特别是温度高度敏感。在放热共沉淀过程中，反应速度在某些温度下变得不可控制，这可能导致热失控反应。在这项工作中，金属-木质素纳米复合材料是通过金属（M）盐和硫酸盐木质素的共沉淀而合成的。将牛皮纸木质素和金属盐分别溶解在有机溶剂和去离子水中，制成木质素溶液/悬浮液和金属盐水溶液。然后将金属盐的水溶液添加到木质素溶液/悬浮液中，并充分混合，导致过渡金属离子与木质素链的官能团螯合，并导致金属-木质素复合物从溶剂中共沉淀。为了开发安全的大批量生产M-木质素复合材料的方法，在共沉淀过程中评估了潜在的反应，放热或吸热过程，有害气体和挥发物。研究了共沉淀过程中过渡金属类型，溶剂选择，金属盐浓度和初始溶液温度对金属离子与硫酸盐木质素之间相互作用，木质素基质中金属均匀性以及金属-木质素复合材料形态的影响。 。研究了Cu，Mo，Ni和Fe作为金属-木质素复合材料的过渡金属。发现在Fe和Cu木质素共沉淀过程中发生Fenton或类Fenton反应，并散发大量热量，这导致在非常短的时间内（即几秒钟）反应系统温度超调。大量的CO₂和有毒NO ₂当发生Fenton或类Fenton反应时，共沉淀过程中会释放出气体。混合两种溶液时，木质素和Mo（VI）离子之间没有相互作用或非常弱的相互作用发生。Ni离子与木质素中的含氧官能团密切配合，但在Ni-木质素共沉淀过程中未检测到Fenton或Fenton样反应。当使用四氢呋喃（THF）和丙酮溶解牛皮纸木质素时，发生Fenton反应或类Fenton反应，并且随着复合物中铁含量的增加，该反应变得非常剧烈且难以控制。随着初始溶液温度的升高，反应的初始化时间缩短，如果初始混合温度达到60°C或更高，则可能发生热失控反应。