GB417075A - Improvements in or relating to the purification of sugar factory and refinery juices - Google Patents

Abstract

Sugar factory or refinery juices are purified by adding lime or equivalent alkali, and if necessary sulphur dioxide or an electrolytic equivalent in amounts sufficient to bring the juices to the optimum isoelectric point in the alkaline range of the colloidal impurities to be flocculated, adding a small amount of lime or equivalent alkali so that the soluble alkalinity of the juices is an optimum for the subsequent removal of the flocculated impurities, heating the juices to the flocculating temperature and, after separating the flocculated impurities, treating the juices with carbon dioxide or sulphur dioxide in order to reduce the alkalinity to factory requirements, defecation by further addition of lime being dispensed with. After the juice has been brought to the optimum isoelectric point, which is defined as that at which the conditions of pH and alkalinity are such as to render the total amount of colloidal impurities flocculated a maximum, test of the soluble alkalinity may be made to determine the amount of lime or equivalent alkali required for the next step. Details of the tests employed, quantities of lime required, definitions of the expressions "sulphur dioxide or electrolytically equivalent substance," "lime or equivalent alkali," and "factory requirements" are included. The optimum isoelectric point lies between pH values of 10,6 and 12,0, and the flocculating temperatures in general lie between 80 and 95 DEG C. for beet sugar juice. Dilute sulphuric acid and phosphorus pentoxide are included among the electrolytic equivalents of sulphur dioxide. The sulphur dioxide may be added in liquid form or as a gas under relatively high pressure. The carbon dioxide employed may be obtained from boiler flues. The scums obtained by clarification of the juices with sulphur dioxide, carbon dioxide, phosphoric acid or other acid are added to other juices from which the impurities have not been removed. The removal of the flocculated colloids may be effected either by filtration, centrifuging, or decantation. Examples are given. Specifications 351,160 and 394,498 are referred to.