Patent GB-723412-A (GB)
Title: Improvements relating to methods of treating the waste liquors obtained in the decomposition of lignified cellulose-containing materials
IPC: D21C11/02
Filed: 1950-05-31
Abstract: A method for the treatment, with subsequent recovery of the alkali salts of the sulphurous acid obtained, of the waste sulphite liquors containing lignin sulphonic acid or its salts which are obtained in the decomposition of lignified cellulose-containing materials, especially wood, by means of sulphurous acid, its neutral or acid salts, or mixtures of such agents is characterized by the fact that the sulphonated lignin contained in the waste sulphite liquor is first desulphonated therein by addition to the liquor of a solution of an alkali metal hydroxide at a temperature sufficiently above 100 DEG  C. to ensure complete desulphonation, after which the desulphonated lignin is precipitated from the resulting alkaline solution by addition thereto of sulphurous acid, the solution being thereupon separated from the precipitated lignin, the desulphonation being effected with such a quantity of alkali metal hydroxide and at such a temperature that on the one hand the lignin is precipitated completely and in a state in which it is fusible with boiling water, and on the other hand there is avoided decomposition of the lignin to such a degree that there are obtained water-soluble decomposition products which are not precipitated by sulphurous acid, and the step of precipitating the lignin being effected with such a quantity of sulphurous acid that an addition of sulphuric acid to the solution as separated from the precipitated lignin causes no resinifiable organic substances to be precipitated. The separated solution may be used for the decomposition of further amounts of lignified cellulose - containing materials.  As desulphonating agents may be used calcium-, barium-, lithium-, potassium-, sodium-, or tetramethylammonium - hydroxides to which may be added carbonates.  Solvents for the lignin, e.g. phenols, amines, or alcohols, may be added to the desulphonating solution. If the lignin sulphonic acid is originally present as its calcium salt, it may be decalcified as a preliminary step.  Precipitation of the lignin may be effected in stages at gradually decreasing temperatures, and increasing acidity, with separation of different lignin fractions, e.g. by collecting the lignin precipitated at 80 DEG  C. and pH 6, and then precipitating a further fraction at 15 DEG  to 20 DEG  C. and pH 3.  Precipitation with the sulphurous acid may be effected while the lignin sulphonate liquor is in a finely dispersed state.  The solution separated from the precipitated lignin may be treated for re-use by addition of sodium hydroxide, or converted by the addition of lime to calcium bisulphate and sulphite and sodium hydroxide.  The solution may alternatively be concentrated, and the salts allowed to crystallize. The precipitated lignin may be treated with mineral acids, e.g. whilst suspended in water.  It may be used as a binding agent with the optional addition of lignin-dissolving substances, e.g. mono- or polyvalent alcohols, esters, ethers or ketones and/or with synthetic resin components, e.g. phenols, amines, amides, aldehydes or ketones, and/or synthetic resins obtained separately therefrom.  Alkalis, e.g. alkali metal hydroxides, carbonates, or alkaline earth metal oxides or hydroxides may be added.  Such mixtures may be used in solution suspension or solid form for binding wood chips, wood waste, decomposed wood, wood pulp, veneer or veneer waste.  Calcium oxide is the preferred hardener. Aldehydes, e.g. formaldehyde, acetaldehyde or furfurol may also be added for this purpose.  Compositions containing synthetic resins may be used in moulding compositions or in making laminated wood.  Either acid- or alkaline-hardening resins may be used.  In examples: (1) non-decalcified 50 per cent sulphite waste liquor is heated at 165 DEG  C. with sodium hydroxide.  Sulphurous acid is added at 80 DEG  C. until the solution is neutral.  The precipitated lignin is separated, and a further liquid resin then obtained by adding sulphurous acid at 15 DEG  C. until the pH is 3. The solution is diluted with water to a 15 per cent sodium bisulphite content, adjusted to pH 4 with NaOH and re-used in the decomposition of wood.  The lignin is treated as a suspension in cold water with dilute sulphuric acid and fused.  It is again suspended in water, a cresol/formaldehyde (alkaline catalysed) reaction product is added, and the mixture heated to give a synthetic resin.  This is kneaded with wood meal and quicklime to form a moulding composition.  (2) Sulphite waste liquor is decalcified with sodium sulphate and desulphonated with sodium hydroxide at 175 DEG  C.  The lignin is precipitated with sulphurous acid, the separated solution treated with quicklime, and caustic soda lye is recovered.  (3) Decalcification spruce waste liquor is mixed with sodium hydroxide, concentrated to a 30 per cent solution, and finely-powdered lignin from the hydrochloric acid hydrolysis of wood is added.  After treatment in an autoclave, lignin is precipitated by addition of sulphurous acid to the solution at 70 DEG  to 80 DEG  C. until neutral.  The lignin is separated and a second batch of lignin is precipitated by the addition of more sulphurous acid in the cold. The second batch of lignin is dissolved in ammonia, added to the first batch and the mixture acidified with sulphuric acid.  The precipitated lignin is then fused by heating. Specification 693,760 is referred to.ALSO:A method for the treatment, with subsequent recovery of the alkali salts of the sulphurous acid obtained, of the waste sulphite liquors containing lignin sulphonic acid or its salts which are obtained in the decomposition of lignified cellulose-containing materials, especially wood, by means of sulphurous acid, its neutral or acid salts, or mixtures of such agents is characterized by the fact that the sulphonated lignin contained in the waste sulphite liquor is first desulphonated therein by addition to the liquor of a solution of an alkali metal hydroxide at a temperature sufficiently above 100 DEG C. to ensure complete desulphonation, after which the desulphonated lignin is precipitated from the resulting alkaline solution by addition thereto of sulphurous acid, the solution being thereupon separated from the precipitated lignin, the desulphonation being effected with such a quantity of alkali metal hydroxide and at such a temperature that on the one hand the lignin is precipitated completely and in a state in which it is fusible in boiling water, and on the other hand there is avoided decomposition of the lignin to such a degree that there are obtained water-soluble decomposition products which are not precipitated by sulphurous acid, and the step of precipitating the lignin being effected with such a quantity of sulphurous acid that an addition of sulphuric acid to the solution as separated from the precipitated lignin causes no resinifiable organic substances to be precipitated.  The separated solution may be used for the decomposition of further amounts of lignified cellulose-containing materials.  As desulphonating agents may be used calcium-, barium-, lithium, potassium-, sodium- or tetramethylammonium-hydroxides to which may be added carbonates.  Solvents for the lignin, e.g. phenols, amines or alcohols, may be added to the desulphonating solution. If the lignin sulphonic acid is originally present as its calcium salt, it may be decalcified as a preliminary step. Precipitation of the lignin may be effected in stages at gradually decreasing temperatures, and increasing acidity, with separation of different lignin fractions, e.g. by collecting the lignin precipitated at 80 DEG  C. and pH6, and then precipitating a further fraction at 15 DEG  to 20 DEG  C. and pH3.  Precipitation with the sulphurous acid may be effected while the lignin sulphonate liquor is in a finely dispersed state.  The solution separated from the precipitated lignin may be treated for re-use by addition of sodium hydroxide, or converted by the addition of lime to calcium bisulphate and sulphite and sodium hydroxide.  The solution may alternatively be concentrated, and the salts allowed to crystallize.  The precipitated lignin may be treated with mineral acids, e.g. whilst suspended in water.  It may be used as a binding agent with the optional addition of lignin-dissolving substances, e.g. mono- or polyvalent alcohols, esters, ethers or ketones and/or with synthetic resin components, e.g. phenols, amines, amides, aldehydes or ketones, and/or synthetic resins obtained separately therefrom.  Alkalis, e.g. alkali metal hydroxides, carbonates or alkaline earth metal oxides or hydroxides, may be added.  Such mixtures may be used in solution, suspension or solid form for binding wood chips, wood waste, decomposed wood, wood pulp, veneer or veneer waste.  Calcium oxide is the preferred hardener.  Aldehydes, e.g. formaldehyde, acetaldehyde or furfurol, may also be added for this purpose.  Compositions containing synthetic resins may be used in moulding compositions or in making laminated wood.  Either acid- or alkaline-hardening resins may be used.  In examples: (1) non-decalcified 50 per cent sulphite waste liquor is heated at 165 DEG  C. with sodium hydroxide. Sulphurous acid is added at 80 DEG  C. until the solution is neutral. The precipitated lignin is separated, and a further liquid resin then obtained by adding sulphurous acid at 15 DEG  C. until the pH is 3. The solution is diluted with water to a 15 per cent sodium bisulphite content, adjusted to pH4 with NaOH and re-used in the decomposition of wood.  The lignin is treated as a suspension in cold water with dilute sulphuric acid and fused.  It is again suspended in water, a cresol/formaldehyde (alkaline catalysed) reaction product is added, and the mixture heated to give a synthetic resin.  This is kneaded with wood meal and quicklime to form a moulding composition; (2) sulphite waste liquor is decalci