Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/08—Removal of fats, resins, pitch or waxes; Chemical or physical purification, i.e. refining, of crude cellulose by removing non-cellulosic contaminants, optionally combined with bleaching
  • D21C9/086—Removal of fats, resins, pitch or waxes; Chemical or physical purification, i.e. refining, of crude cellulose by removing non-cellulosic contaminants, optionally combined with bleaching with organic compounds or compositions comprising organic compounds

Definitions

• This invention relates to the removal of coloring matter from wood pulp and it is particularly directed to the actual removal from wood pulp of those materials which are responsible for or cause undesired colors in the pulp or the products produced therefrom.
• Ordinary wood pulps contain materials of varying character, such as waxes, resins, fats, pigments, lignin residues, etc., and these constitute impurities which are more or less colored. While the actual percentages of such impurities present may be very small they are able to produce or cause undesirable effects altogether out of proportion to the percentages 15 of the materials present in the pulp. Such materials are largely responsible for the so-called "pitch troubles in thepaper mill and they confer a dark color to rayon, 'films, cellulose derivatives and like materials manufactured from the pulp.
• a preferred method of determining the amount of such coloring matter in a pulp is provided by molding the pulp with a colorless resin and comparing the same colorimetrical ly with a standard similarly prepared by molding purified cotton linters or a wood pulp completely free from coloring matter. Pulps which appear perfectly white to the eye and which yield no material when extracted with organic solvents frequently display undesired color when so molded.
• the chief object of the present invention is thus to provide 'a method whereby these impurities may be economically and efiiciently re- 10 moved from wood pulp in commercial practice with a view to making such pulp available for further uses as previously indicated.
• the pulp at low density is impregnated with an emulsifier in solution containing an excess of caustic soda or the like, then concentrated to high density, in which condition it is maintained at elevated temperature for completion of the reaction, and then thoroughly washed.
• the method is preferably carried out in a continuous or cyclic manner in which the impregnation liquor is recovered, strengthened as required, and reused for impregnating further quantities of pulp.
• Suitable emulsifiers are those which dissolve to practically clear solutions in dilute caustic soda at ordinary temperatures, say up to 25 C.
• Oleic acid, linoleic acid, sulphonated oils, sulphonated fatty alcohols and the like are suitable but eco-' nomically oleic acid is preferred.
• Ordinary soaps are not advantageous. They dissolve to clear solutions only in hot water and on cooling coagulation of colloidal masses occurs. This renders the handling of soap solutions in the mill difficult, as pipe lines, storage tanks and the like are not easily kept free from deposits, particularly during shut downs or interruption of the operation.
• dilute soap solutions are inclined to undergo hydrolytic splitting, precipitating insoluble fatty acid compounds on or within the fibres of the pulp.
• the impregnation liquor containing the emulsifier should have an excess of free caustic soda which enhances the dissolving and dispersing power of the emulsifier and maintains an equilibrium in the liquor during its use. Some of this caustic soda disappears owing to the acid character of some of the impurities dissolved from the pulp.
• caustic soda and emulsifier is added to renew the'liquor and compensate for what has been removed in first use. The liquor reaches a stateof substantially stable equilibrium after several repeated usages, in which condition it may be used to best advantage.
• the density during impregnation and the extent of purification desired depending upon the character of the pulp to be treated, the density during impregnation and the extent of purification desired. Assuming, for example, that 10% of the liquor is carried away in the pulp, then 0.3-5.0% of sodium oleate and 03-50% of NaOH should be added before or during reuse of the 90% of the recovered liquor. In the continuous operation of theprocess the liquor in circulation is kept well balanced. The pulp under impregnation should have a slightly higher consistency than the pulp concentrated after impregnation, in order to compensate for the volume of solutions added in renewing the liquor. It is apparent that the higher the density to which the pulp is concentrated after impregnation the smaller will be the loss of chemical reagents. I
• the impregnated pulp After the impregnated pulp has been concentrated it is subjected to a mild heat treatment, usually by the introduction of steam. Normally a temperature of to 75 C. maintained for onehalf to two hours is suflicient to permit the reac- 35 tion to proceed to the desired point. The conditions will of course vary with the character of the coloring matter remaining in the pulp after impregnation.
• the pulp is then washed from the liquor thus removing the rest of the coloring mat- 40 ter.
• the useof warm water usually available in the mill, reduces the amount of wash water required. In some cases it is preferable to have the wash water slightly alkaline and for this purpose there may be added thereto, for example, not more than 0.5% of NaOH or the like calculated on the weight of the pulp being washed.
• the wash water should be low in lime, magnesium,
• the lime content of the pulp to be treated be low, particularly if the emulsifying agent used forms, with lime, salts-which are. insoluble or difilcultly soluble or dispersible. U nder these conditions the lime content of the pulp is preferably not more than about 0.02%. With such a pulp the impregnating liquor, containing sodium oleate as the emulsifier, withdrawn after impregnation remains practically clear whereas with a relatively high lime bearing pulp it becomes decidedly turbid. Low lime pulps may be closed in copending application Serial Number 735,437, filed July 16, 1934. It should be mentioned that some emulsifiers, such as sulphonated fatty alcohols, form calcium salts which are soluble and when using such emulsifiers the absence of lime in the pulp is not of particular importance. I
• the low density pulp then enters a mixing tank where it is kept in agitation to make the impregnation complete and. uniform.
• the size of this mixing tank need not be greater than to provide for a total impregnation time of about 30 minutes.
• the pulp mixture is conveyed to another thickener where its density is raised to a point slightly lower than the original density before maceration.
• the waste liquor is returned to the mix box where with added strengthening materials it is ready for reuse.
• pulp passes to a mixer where the desired temperature is obtained by the introduction of steam or'otherwise as desired and thence to a container where it remains until the reaction is complete when it is removed from the container and thoroughly washed.
• a mixer where the desired temperature is obtained by the introduction of steam or'otherwise as desired and thence to a container where it remains until the reaction is complete when it is removed from the container and thoroughly washed.
• material extractable with organic solvents was impregnated at a density of 1.5% with a previously used strengthened liquor containing 8% sodium oleate and 6% caustic soda calculated on the pulp for fifteen minutes with thorough mixing.
• the pulp was concentrated on a wet machine into laps of 30% density, the waste liquor being returned for reuse, and the moist laps were brought to a temperature of 65 C. for 30 minutes,
• the concentrated pared from unbleached pulp by chlorination in the presence of sodium. chloride and not containing more than .01% CaO and 1.1% of material extractable with organic solvents was impregnated at 1% density with a previously used liquor containing 12% sodium oieate and 60% caustic soda, calculated on fibre weight, for a period of 15 minutes under normal temperature and with thorough mixing.
• the pulp was con- 10 centrated to a density of 30%, containing in this condition 28% of sodium oleate and 1.91% caustic soda which are lost during washing, the removed liquor being returned to the cycle for reuse.
• the concentrated pulp'was heated to 65? C. for 90 minutesi'and after washing was bleached with a soda bleach liquor at a pH of above 8.5 to complete whiteness.
• the bleached pulp contained substantia1ly 90% alpha cellulose and its color was stable -under the severest light treatment.
• a pulp of the invention having an alpha-cellulose content of say 91% will provide rayon the equivalent of that produced from known pulps having an aiphacellulose content of 94 or 95%. It will produce an unbleached rayon as white as a bleached rayon produced from ordinary puips now in use. Thus in the production of rayon from this pulp less handling is required and a larger proportion of number one grade material is obtained.
• a continuous method of purifying wood pulp which comprises impregnating the pulp at low density and at ordinary temperature with a liquor containing an emulsifying agent and an excess of caustic soda, thickening the pulp to high density, returning the used liquor for reuse, subjecting the thickened pulp to a temperature not in excess of 75 C. to dissolve and disperse remaining impurities and washing-the pulp.
• a method of purifying low lime wood pulp which comprises impregnating the pulp at low density and ordinary temperature with a liq-' uor containing sodium oleate and-an excess of caustic soda, thickening the pulp to a density up to 30%, recovering the impregnating liquor, raising the temperature ofthe thickened pulp to about C. to dissolve and disperse impurities and washing the pulp.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)

Priority Applications (5)

Applications Claiming Priority (1)

Publications (1)

Family

ID=10018795

Family Applications (1)

Country Status (5)

Cited By (5)

• 1934
  • 1934-07-16 US US735438A patent/US2074473A/en not_active Expired - Lifetime
• 1936
  • 1936-05-09 GB GB13208/36A patent/GB468306A/en not_active Expired
  • 1936-05-16 FR FR807159D patent/FR807159A/fr not_active Expired
  • 1936-05-19 BE BE415620D patent/BE415620A/xx unknown
  • 1936-05-30 CH CH191024D patent/CH191024A/de unknown

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