Preparation of High‐Purity 2,6‐Naphthalenedicarboxylic Acid from Coal Tar Distillate

Using coal tar distillate as the starting material, a novel high‐purity 2,6‐naphthalenedicarboxylic acid (2,6‐NDA) preparation method was developed. Firstly, the 2,6‐dimethylnaphthalene (2,6‐DMN) precursor was separated by successive vacuum distillation, melt crystallization, and solvent crystallization from the 250–270 °C fraction of the coal tar distillate. Then, over Co‐Mn‐Br as catalysts, oxidation of 2,6‐DMN was carried out in acetic acid to produce crude 2,6‐NDA with molecular oxygen. By high‐temperature hydrogenation, the crude 2,6‐NDA was further purified to obtain high‐purity 2,6‐NDA. From the coal tar distillate to pure 2,6‐NDA, the operation parameters and reaction conditions of each process were optimized and evaluated, indicating that the proposed 2,6‐NDA synthesis method has great potential for industrial application to create cheap feedstock in viable yields. 2,6‐Dimethyl‐naphthalene precursor was separated from cheap coal tar distillate in order to prepare the high‐value‐added monomer 2,6‐naphthalenedicarboxylic acid (2,6‐NDA) in high purity (99.9 %). The whole process is applicable to bulk production of pure 2,6‐NDA due to its inexpensive feedstock and the relatively decent yield after separation, oxidation, and purification.