Method for producing electronic-grade pyromellitic dianhydride from secondary trapped coarse anhydride

The invention relates to a method for producing electronic-grade pyromellitic dianhydride from secondary trapped coarse anhydride, which belongs to the technical field of preparing pyromellitic dianhydride. The method comprises the following steps: secondary trapped coarse anhydride washing; dehydration and decoloration; recrystallization; and drying. The method has the following advantages: firstly, the process flow is simple and short so that energy sources can be saved; secondly, because the refining process is performed in a closed device, the environment is not damaged; thirdly, because the separated out crystallization mother solution can be recycled, not only the yield of the PMDA can be improved and the dosages of a dehydrating agent and a discoloring agent are saved to embody the economical efficiency, but also the energy consumption is saved; fourthly, the purity of the obtained PMDA can reach over 99 percent; and fifth, the PMDA produced by the method can reach the purity grade requirement of synth