Patent GB-806652-A (GB)
Title: Process for the fractionating of sulphite lye
IPC: C07H3/04
Filed: 1955-12-23
Abstract: Ammonium sulphite lye is fractionated by extracting the dried waste lye with a polar solvent having a dielectric constant between 27 and 42 and being miscible with water, isolating the extracted low-molecular lignin sulphonic acids from any carbohydrates which may be dissolved simultaneously, either by (1) precipitation with a polar organic liquid having a dielectric constant lower than 27 which is miscible with water and also with the extraction liquid without forming an azeotrope therewith, preferably a C3 and C4 alcohol; or (2) by precipitation with bases and/or inorganic or metal-organic salts soluble in the prevailing liquid system, the cations of said precipitating agents being able to form salts with the low-molecular acids which are difficulty soluble in said liquid system and the anions being able to form compounds with the cations of the low molecular acids which are soluble in said liquid system, or by a combination of (1) and (2), if necessary after previous partial evaporation, preferably under vacuum, removing from the filtrate after this precipitation the organic liquids by fractional distillation, preferably under vacuum, after any base and/or salt excess has first been removed by precipitation and/or ion exchange, obtaining as distillation nest any carbohydrates present, and processing separately the residue from the original extraction consisting of high-molecular lignin-sulphonic acids.  The extracting agent may be methanol, or it may be ethanol, which only extracts carbohydrates and sulphocarboxylic acids, the high- and low-molecular lignin sulphonic acids which are left being separated by extraction of the latter with methanol, or other polar solvent having a dielectric constant between 30 and 40.  The carbohydrate-containing residual extract solution may be used, after purification but before evaporation, for the extraction of further quantities of lye powder. The salts of the acids may be precipitated in portions.  When the low-molecular lignin-sulphonic acids have been extracted with methanol and then precipitated with a low-polar liquid such as n-propanol, if desired in combination with addition of sodium hydroxide to slight alkalinity, the simultaneously-extracted low-molecular sulphocarboxylic acids may be precipitated as calcium salts by the addition of calcium chloride, while adjusting pH to about 8, or by addition of sodium hydroxide to a pH of 10-11. Alternatively the low-molecular lignin-sulphonic acids may be precipitated as calcium salts by adding calcium chloride to the methanolic solution while adjusting the pH to about 5, and then isolating the sulphocarboxylic acids as calcium salts by adjusting the pH to about 8.7.  Again, the low-molecular lignin sulphonic acids may be precipitated by adding sodium hydroxide to the methanolic solution to a pH of 11.5-12, and after precipitation of the base excess to give a slightly alkaline or neutral pH, adding calcium chloride to precipitate the sulphocarboxylic acids as calcium salts. When ethanol is used as extraction agent, the extract may be adjusted to a pH of 9.5-10, preferably together with the addition of n-propanol, to precipitate the sulphocarboxylic acids, and subquently the aldonic acids are isolated by adding calcium chloride or by adjusting the pH to 11-12, preferably with more alcoholic precipitation liquid. Specific examples of the above procedures are given.