Effect of the type of precipitation on the process to obtain sodium alginate: Calcium alginate method and alginic acid method

The precipitation step of the process to obtain alginate from the alga Macrocystis pyrifera was studied in order to find the most economical process and best conditions to handle the product. We compared the two processes known to produce alginate: the calcium alginate process, in which precipitation is carried out with calcium chloride, and the alginic acid process, in which precipitation is obtained with hydrochloric acid. The yield was statistically the same in both processes, but the viscosity of the alginate was 33% higher in the precipitation with calcium chloride. The calcium alginate process reduced by 90.8% the consumption of hydrochloric acid and by 53.1% the consump-tion of alcohol, compared with the acid precipitation method. In spite of the additional cost of calcium chloride in the calcium alginate method, the total cost is lower than the cost of the reagents used in the alginic acid method. In a second experiment, the reduction of the amount of calcium chloride was studied. The calcium chloride concentration was changed from 6.76 to 3.61 milliequivalents of calcium per gram of dry alga used (meq/g). The response variables were yield, viscosity, amount of calcium retained and consistency of the precipitate. It was found that the minimum concentration of calcium chloride that can be used without affecting these variables was 4.51 meq/g. This amount reduced by 19.3% the amount of calcium chloride, compared with the amount used in the control treatment (6.76 meq/g).