Research on the purification of the monoethylene glycol obtained by polyethylene terephtalate methanolysis

The monoethylene glycol obtained during the polyethylene terephtalate methanalysis process is purified with oiling and avivage substances from the preparation bath. This monoethylene glycol has to be purified previous to its re-use; but this purification cannot be done via the humid method, by using various chemical reagents; it is successful only if it is performed by the dry method, i.e. filtering, using those products capable to retain the impurities. The laboratory used following filtering products: silicagel, Th-zeolite type molecular sieves and micronized cellulose. Good results were obtained only with the last one on the above list. After determining the oiling and avivage products general properties, the paper presents the specific conditions for the monoethylene glycol purification, using micronized cellulose as a filtering material. The impurities retention on the micronized cellulose is explained by the possibility of having hydrogen bridges between the hydrophilic groups in the oiling and avivage products and the free alcoholic hydroxyls in the beta-glucose molecule, which is at the basis of the cellulose macromolecule. A physical adsorbtion is also possible. In order to further increase the micronized cellulose efficiency, the previous cooling of the impure monoethylene glycol and removal of the superficial only products layer are recommended. The filtering surface is established using the experimental determinations, together with the general filtering equation, at constant pressure. The used micronized cellulose can be regenerated by treating it with alcohol, at high temperature.