Effect of molecular mass and surface charge of anionic polyacrylamide on pectin precipitation

Abstract

In sugar industry, separation of undesirable compounds in sugar beet juice is done mostly by CaO and carbon dioxide. In order to reduce the amount of lime, a new method of pectin separation based on the application CaSO 4 with the addition of various types of anionic polyacrylamides (PAMs) is presented. The effects of molecular weight (MW) and the surface charge type of anionic polyacrylamides on the pectin precipitation were investigated. These compounds cause the process of charge neutralization of pectin macromolecules, followed by two mechanisms of polymeric bridging effect: Ca 2+ bridges between anionic polymer molecules and pectin particles that promote the coagulation of pectin and Ca 2+ bridges between anionic polymers that hinder coagulation of pectin. The aim of this paper was to examine the effect of CaSO 4 mixture and anionic PAMs of different molecular weights and degree of ionizaton to increase the efficiency of removal of pectin from sugar beet juice. Two pectin preparations were isolated from sugar beet pulp. CaSO 4 was added to 100 cm 3 (0.1 % wt) pectin solution. Studies were performed with 10 different concentrations of CaSO 4 solution (50-500 mg/dm 3) with the addition of anionic PAM with two ionization degree and three molecular weight, concentrations of 3 mg/dm 3. The efficiency of pectin precipitation was monitored by measuring the zeta potential. The bridging effect of Ca 2+ ions between anionic PAMs and pectin has increased with an increase in the MW of the anionic PAMs. Using anionic PAM of the largest MW (1500 • 10 6 g/mol) and a lower degree of ionization (30%), the optimal amounts of CaSO 4 were measured: 340-355 mg/dm 3. These optimal concentrations were achieved at the zero value of the potential zeta when the pectin particles were discharged.