The separation and especially the removal of morpholine (MOR) impurities from N-ethyl morpholine (NEM) is of great significance in the fine chemical industry. Herein, we offer a novel strategy for the selective adsorption of MOR over NEM by tetralactam solids. The adsorbent realized the purification of NEM by adsorbing traces of MOR impurities, such that the purity can be improved from around 98% to over 99.5%. Single crystal structures indicate that N-H⋯O and N-H⋯N hydrogen bonding interactions are essential in the selective separation.