GB1093917A - Removal of non-sugars from syrups comprising sugars - Google Patents

Abstract

Sedimental impurities and divalent metal cation impurities comprising both Ca and Mg are removed from sugar-cane syrups, e.g. low-grade mill syrups, by a process comprising the following steps:- (1) lowering the pH of the syrup to below 4, e.g. to about 3, by the addition of a selected acid capable of forming with Ca ions a salt insoluble in sugar solutions, (2) removing suspended solids comprising flocculated and precipitated material, (3) in the presence of orthophosphate and ammonium ions raising the pH to about 7 by the addition of a suitable base and (4) removing precipitated material. In step (2) sedimentable material is flocculated and calcium impurity is precipitated and in step (3) magnesium impurity is precipitated as magnesium ammonium phosphate. The removal of the flocculated and precipitated material from step (2) may be effected by a pressure filter or a continuously operating centrifuge suitable acids for use in step (1) are sulphuric and orthophosphoric acids or a mixture of sulphuric acid with a phosphate salt (e.g. superphosphate) may be used. If phosphoric acid has not been used in step (1) there must be a subsequent addition of phosphate ions, suitably after step (2). The base added in step (3) may be ammonium hydroxide or (if the Mg content is not high) a mixture of sodium carbonate and NH4OH. The purified syrup from step (4) may be further purified by passage through an ion exchange column.ALSO:Sedimental impurities and divalent metal cation impurities comprising both Ca and Mg are removed from sugar cane syrups, e.g. lowgrade mill syrups or low-grade invert syrups derived therefrom, by a process comprising the following steps:-(1) lowering the pH of the syrup to below 4, e.g. to about 3, by the addition of a selected acid capable of forming with Ca ions a salt insoluble in sugar solutions, (2) removing suspended solids comprising flocculated and precipitated material, (3) in the presence of orthophosphate and ammonium ions raising the pH to about 7 by the addition of a suitable base and (4) removing precipitated material. In step (2) sedimentable material is flocculated and calcium impurity is precipitated and in step (3) magnesium impurity is precipitated as magnesium ammonium phosphate. The removal of the flocculated and precipitated material from step (2) may be effected by a pressure filter or a continuously operating centrifuge. Suitable acids for use in step (1) are sulphuric and orthophosphoric acids or a mixture of sulphuric acid with a phosphate salt (e.g. superphosphate) may be used. If phosphoric acid has not been used in step (1) there must be a subsequent addition of phosphate ions, suitably after step (2). The base added in step (3) may be ammonium hydroxide or (if the Mg content is not high) a mixture of sodium carbonate and NH4OH. The sugar content of the treated syrup may be sucrose or invert sugar and inversion can be effected by heating the mixture in step (1) in a non-corrodible container. Alternatively, the inversion may be performed by invertase catalysis at a pH between 5 and 7, this inversion being conveniently carried out before step (1) at 60-65 DEG C. in a holding vessel fabricated of inexpensive material, e.g. mild steel. The purified syrup from step (4) may be further purified by passage through an ion-exchange column.