Application of novel adsorbents in methanol removal from ethanol: Citric acid-modified 4A zeolites and Cu@ZIF-7

Abstract

Ethanol, as an important solvent and basic chemical feedstock, has widespread applications in the pharmaceutical, food, and fine chemical industries, including processes such as absorption, washing, and extraction. However, methanol and water are inevitable by-products in the industrial production of ethanol, whether through biological fermentation or chemical synthesis. Particularly methanol, which is harmful to both health and the environment, is typically present in ethanol products at low concentrations, posing a significant challenge for its effective removal. We designed citric acid-modified 4A zeolites and a bimetallic organic framework Cu@ZIF-7. Under optimal modification conditions, the modified 4A zeolite showed a 39.15 % and 37.21 % increase in selectivity for methanol and water, respectively, compared to the initial 4A zeolite. The yield of qualified products increased by 44.71 %. Furthermore, Cu@ZIF-7 exhibited a methanol adsorption capacity of 1.125 mg·g⁻¹, which is 3.42 times that of the initial 4A zeolites. Density Functional Theory (DFT) calculations confirmed that the introduced Cu sites are associated with this enhanced methanol adsorption capacity. Experimental evidence suggests that these adsorbents perform exceptionally in purifying ethanol, particularly in the removal of trace methanol. As a new, environmentally friendly separation method, it holds great potential for obtaining high-purity ethanol.