DYNAMIC POLYMER LAYERS ON MEMBRANES AS ANTIFOULANTS IN MEMBRANE FILTRATION: Antifouling Effect of Sulphate Lignin in Separation of Low Molecular Mass Organic Solutes with Cellulose A cetate Membranes

摘要

Using the concept of fouling control that consists in the substitution of a high resistance deposit, being formed in membrane pores of components of a filtered solution, by a low resistance deposit of an auxiliary polymer with larger molecules, the antifouling effect of dynamic layer of a compact polymer, well-defined sulphate lignin (SL), on an UAM-50 CA-membrane in filtration of low molecular mass dyes and surfactants has been studied. The filtration kinetics has been analysed in terms of constant-pressure dead-end filtration to detect the forms of membrane fouling by the low molecular mass organic solutes and to diagnose the mechanism of antifouling effect of the polymer. Three different conditions of membrane filtration have been studied: (1) Filtration of the model solution containing low molecular mass organic foulants (2) Filtration of the model solution with the SL additive through the membrane pre-treated by SL; (3) Filtration of the model solution with the SL additive through the untreated (clean) membrane. The main results are as follows: l. Pore narrowing and posterior pore plugging are the dominant mechanisms of irreversible fouling of an UAM-50 membrane in filtration of the model solution used in this study. This form of fouling yields the great loss in permeate flux (84.7%). Introduction into the model solution of SL does not effect on the flux in filtration through the fouled membrane. 2. Pre-treatment of the membrane by SL results in the formation of low resistance SL dynamic layer (a deposit of type 1) that causes the small flux decline (17%) at the parameters accepted. In filtration of the model solution with the SL additive through the pre-treated membrane the form of fouling changes (now it corresponds to the formation of a type 2 deposit), and the total flux decline, including the membrane pre-treatment, makes up 42.6% that is twice less than that for the condition (1). 3. For the untreated UAM-50 membrane and the model solution, in which the SL additive is preliminarily introduced, the form of fouling corresponds to a low resistance deposit of type 1. This filtration condition yields the least flux decline (21.7%), i.e. the antifouling effect of SL is the greatest. The mechanism of this effect consists in ⅰ) partial blocking the pore entrances by the SL macrosolutes and ⅱ) the adsorption ability of SL with respect to the membrane foulants used here. These protect the pore space against deep penetration of low molecular mass dyes and surfactants and, therefore, against the formation of high resistance intrapore deposits.