Parameters afecting the conversion of alginic acid to sodium alginate

Abstract

The step to convert alginic acid to sodium alginate on the alginate extraction process was studied, using the brown seaweed Macrocystis pyrifera as raw material. The effect of alcohol volume, alcohol-water proportion, pH, and treatment time on the yield and viscosity of the alginate obtained was analyzed. Seven volumes of the mixture alcohol-water in proportion 50:50 were experimented, from 9 to 15 mL g^–1 alga. The yield and viscosity were not significantly different in any of the volumes used, however, the stirring with the volume of 9 mL g^–1 alga was less efficient, therefore the minimum volume to use in this step was 10 mL g^–1 alga. The appropriated proportion of the mixture alcohol-water was determined using five proportions: 50:50, 47:53, 44:56, 40:60, and 37:63. The highest yield and viscosity were obtained using the proportion 50:50. Five pH values from 6 to 10 were experimented to determine the optimum pH for the conversion reaction. The best results were obtained using a pH from 7 to 8 in the alcoholic solution of the conversion step. To determine the minimum time required for the conversion reaction, the fibers of sodium alginate were stirred in an alcoholic solution for 20, 30, 40, 50 and 60 min. The yield and viscosity obtained were not significantly different, therefore, the minimum time to carry out the conversion reaction was 30 minutes to assure a complete reaction. The use of a double planetary mixer is proposed to carry out this step at other level.