Preparation method of N-methyl piperazine

The invention relates to a preparation method of N-methyl piperazine. The preparation method comprises the following steps: (1) carrying out reaction on iminodiacetonitrile (IDAN) and methanal under the acidic condition to prepare N-methyl iminodiacetonitrile; and (2) carrying out hydrogenation reaction on N-methyl iminodiacetonitrile at the temperature of 70-140 DEG C and the pressure of 2-8MPa, wherein a molecular-sieve modified zirconium-based superacid serves a carrier, and one or two or more of the active metals of Fe, Co, Ni, Ru and Rh serves/serve as a hydrogenation catalyst. Compared with the prior art, the preparation method provided by the invention has the advantages of high yield due to the adoption of the catalyst and low equipment investment. In addition, the raw materials for preparing the N-methyl piperazine are low in cost and are easy to obtain.