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US-12624477-B2 - Method for providing a filtered spinning dope

US12624477B2US 12624477 B2US12624477 B2US 12624477B2US-12624477-B2

Abstract

The present invention describes a method of dissolving cellulose, said method comprising: dissolving cellulose in an alkali solution: —filtering the dissolved cellulose, thereby forming a filtered dissolved cellulose solution and a filter reject; —mixing said filter reject having a first viscosity value with a dissolution liquid having a second viscosity value, wherein the second viscosity value is lower than the first viscosity value, to provide a diluted reject stream having a third viscosity value being lower than the first viscosity value of the filter reject; and—separating inhomogeneities from the diluted reject stream.

Inventors

  • Artur Hedlund

Assignees

  • TREETOTEXTILE AB

Dates

Publication Date
20260512
Application Date
20220708
Priority Date
20210708

Claims (20)

  1. 1 . A method of dissolving cellulose, said method comprising: dissolving cellulose in an alkali solution; filtering the dissolved cellulose, thereby forming a filtered dissolved cellulose solution and a filter reject; mixing said filter reject having a first viscosity value with a dissolution liquid having a second viscosity value, wherein the second viscosity value is lower than the first viscosity value, to provide a diluted reject stream having a third viscosity value being lower than the first viscosity value of the filter reject; and separating inhomogeneities from the diluted reject stream.
  2. 2 . The method according to claim 1 , wherein the cellulose concentration in the solution formed by the alkali solution, preferably being a first alkali dissolution liquid, after dissolving the cellulose therein is at least 4 wt. %, calculated on the total weight, and/or wherein the solubility of the cellulose in the solution formed by the alkali solution, preferably being a first alkali dissolution liquid, is kept at at least 95%.
  3. 3 . The method according to claim 1 , wherein the alkali solution is a first alkali dissolution liquid, and wherein the dissolution liquid is a second alkali dissolution liquid, and/or wherein the dissolution liquid is an alkaline aqueous solvent solution, and/or wherein the dissolution liquid has substantially the same composition with reference to main salt components of the filter reject, but which dissolution liquid is concentrated relative to the water content by a factor ranging from 0.9-1.8.
  4. 4 . The method according to claim 1 , wherein the method is implemented in or connected to a spinning dope preparation process, and/or wherein the method is implemented in or connected to a spinning dope preparation process comprising a step of homogenizing the cellulosic material in an alkali solution and a subsequent step of dissolving cellulose in the alkali solution to obtain a cellulose spinning dope composition.
  5. 5 . The method according to claim 1 , wherein the inhomogeneities comprise any of particles, aggregates, solid components, or impurities, and/or other insoluble material.
  6. 6 . The method according to claim 1 , wherein the second viscosity value of the dissolution liquid is at least 10 times lower than the first viscosity value of the filter reject, and/or wherein the second viscosity value of the dissolution liquid is at least 10 times lower than the first viscosity value of the filter reject, and wherein the filter reject is an aqueous sodium hydroxide solution with a sodium hydroxide concentration of at least 5 wt. %, calculated on the total weight of the filter reject, and wherein the second alkali dissolution liquid is an aqueous sodium hydroxide solution with a sodium hydroxide concentration of at least 5 wt. %, and/or wherein the third viscosity value of the diluted reject stream is at least 2 times lower than the first viscosity value of the filter reject, and/or wherein the third viscosity value of the diluted reject stream is maximum 500 mPa*s.
  7. 7 . The method according to claim 1 , wherein the step of separating inhomogeneities from the diluted reject stream provides a stream of purified dissolution liquid with dissolved cellulose, which stream of purified dissolution liquid with dissolved cellulose is recycled to a step of dissolving cellulose, and/or wherein the step of separating inhomogeneities from the diluted reject stream provides a stream of purified dissolution liquid with dissolved cellulose which is used in a spin dope preparation step for dissolving cellulose.
  8. 8 . The method according to claim 1 , wherein temperatures of the filter reject and the dissolution liquid are kept at temperatures below 30° C., and/or wherein the diluted reject stream is kept at a temperature below 30° C.
  9. 9 . The method according to claim 1 , wherein the filter reject is an aqueous sodium hydroxide solution with a sodium hydroxide concentration of at least 5 wt. %, and/or wherein the dissolution liquid is an aqueous sodium hydroxide solution with a sodium hydroxide concentration of at least 5 wt. %, and/or wherein the filter reject is an aqueous sodium hydroxide solution with a sodium hydroxide concentration of at least 5 wt. %, calculated on the total weight of the filter reject, and wherein the dissolution liquid, is an aqueous sodium hydroxide solution with a sodium hydroxide concentration of at least 5 wt. %.
  10. 10 . The method according to claim 1 , wherein the mixing of said filter reject with the dissolution liquid involves a total dilution of the filter reject by at least a factor 2, with respect to the cellulose content, and/or wherein the dilution of the filter reject by mixing with dissolution liquid is performed in at least two steps.
  11. 11 . The method according to claim 1 , wherein the dilution of the filter reject by mixing with dissolution liquid is performed by adding dissolution liquid gradually, preferably in a continuous manner, such that the dissolution liquid is added to the filter reject and continuously dispersed into the filter reject.
  12. 12 . The method according to claim 1 , wherein the step of separating inhomogeneities from the diluted reject stream involves centrifugation, filtration or sedimentation, or a combination thereof, and/or wherein the step of separating inhomogeneities from the diluted reject stream involves sedimentation and subsequent filtration.
  13. 13 . The method according to claim 1 , wherein the step of separating inhomogeneities from the diluted reject stream provides a stream of purified dissolution liquid with dissolved cellulose and a low amount of inhomogeneities.
  14. 14 . The method according to claim 1 , wherein the stream of purified dissolution liquid is mixed with another stream of dissolution liquid prior to being used for preparing cellulose spinning dope.
  15. 15 . The method according to claim 1 , wherein the cellulosic material in the alkali solution is spinning dope composed of cellulose, cellulose carbamate, carboxylated cellulose, hydroxy-ethoxylated cellulose, cellulose xanthate, another derivative of cellulose, or a mixture of cellulose and cellulose derivatives, in the range of 4-12 wt. %, calculated on the total weight of spinning dope, and/or wherein the cellulose spinning dope composition comprises at least one additive for gelation prevention, said additive preferably comprising urea, thiourea, PEG or zinc, and/or wherein the cellulose spinning dope composition comprises an being ZnO or Zn(OH) 2 added in a concentration range of 0.5-1.4 wt. % Zn calculated on the total weight of the cellulose spinning dope composition.
  16. 16 . The method according to claim 4 , wherein the spinning dope preparation process is followed by fiber spinning or film forming of the cellulose spinning dope composition in a coagulation bath, having a pH of more than 7.0 to produce a fiber tow, then passing the produced fiber tow through a sequence of consecutive stretching and washing steps, in which the fiber tow is washed with washing liquid having gradually lower alkalinity, and/or wherein the cellulosic material in an alkali solution is pre-treated prior to the step of homogenizing by derivatizing, hydrolysis, enzymatic treatment and/or mechanical treatment, and/or wherein the cellulosic material in an alkali solution is pre-treated prior to the step of homogenizing by shortening the chains of cellulose polymers by cleavage of cellulose chains.
  17. 17 . The method according to claim 1 , wherein the cellulose concentration in the solution formed by the alkali solution, being a first alkali dissolution liquid, after dissolving the cellulose therein is in a range of 4-12 wt. %, and/or wherein the solubility of the cellulose in the solution formed by the alkali solution, being a first alkali dissolution liquid, is kept at at least 95%.
  18. 18 . The method according to claim 1 , wherein the alkali solution is a first alkali dissolution liquid, and wherein the dissolution liquid is a second alkali dissolution liquid, and/or wherein the dissolution liquid is an alkaline aqueous sodium hydroxide solution, wherein the alkali solution is a first alkali dissolution liquid and the dissolution liquid is a second alkali dissolution liquid, and/or wherein the dissolution liquid is a second alkali dissolution liquid, and has substantially the same composition with reference to main salt components of the filter reject, but which dissolution liquid is concentrated relative to the water content by a factor ranging from 0.9-1.8.
  19. 19 . The method according to claim 1 , wherein the filter reject is an aqueous sodium hydroxide solution with a sodium hydroxide concentration of 7-9 wt. %.
  20. 20 . The method according to claim 1 , wherein the step of separating inhomogeneities from the diluted reject stream provides a stream of purified dissolution liquid with dissolved cellulose and a low amount of inhomogeneities, which stream of purified dissolution liquid with dissolved cellulose and a low amount of inhomogeneities is recycled to a step of dissolving cellulose in an alkali solution, wherein the stream of purified dissolution liquid with dissolved cellulose and a low amount of inhomogeneities is recycled to said step of dissolving cellulose in an alkali solution.

Description

FIELD OF THE INVENTION The present invention relates to a method for dissolving cellulose, e.g. as a complement to or in a spinning dope preparation process. TECHNICAL BACKGROUND Different forms of spinning dope production methods are known and have been described before. One such related process is described in WO2017/178531. In WO2017/178531 there is disclosed a method for the production of a spinning dope composition, which method comprises a homogenization involving vigorous mixing of a cellulosic pulp material in alkali solution and thereafter a dissolution involving mixing of the cellulosic pulp material in the alkali solution to obtain a spinning dope composition, wherein the cellulosic pulp material in alkali solution is kept at a temperature of less than 0° C. during the homogenization and during at least part of the dissolution. Spinning dope preparation process, such as the one disclosed above, includes a filtration step. One aim of the present invention is to provide a process resulting in an improved spinning dope filtration, and which process is intended as a complement to a spinning dope preparation process. SUMMARY OF THE INVENTION The stated purpose above is achieved by a method of dissolving cellulose, said method comprising: dissolving cellulose in an alkali solution;filtering the dissolved cellulose, thereby forming a filtered dissolved cellulose solution and a filter reject;mixing said filter reject having a first viscosity value with a dissolution liquid having a second viscosity value, wherein the second viscosity value is lower than the first viscosity value, to provide a diluted reject stream having a third viscosity value being lower than the first viscosity value of the filter reject; andseparating inhomogeneities from the diluted reject stream. As should be understood from the above, the method according to the present invention is directed to the reuse of a filter reject by the removal of inhomogeneities from the filter reject. In this context it should be mentioned that the filter reject also is a cellulose solution with a high concentration of inhomogeneities, and that the reuse implies a potential to reuse the solution part of the filter reject. According to one embodiment of the present invention, the method is implemented in or connected to a spinning dope preparation process. A filter reject being recovered in spinning dope preparations using cellulose in alkali contains particles and other insoluble solids, which are difficult to remove. The present invention is directed to a method enabling removal of this material being at least partly insoluble, or at least has not undergone optimal dissolution, in an efficient way so that the valuable content of the filter reject, i.e. the liquid fraction, then may be recovered and used in a subsequent step or steps in the cellulose dissolution, such as in a spinning dope preparation process. According to one embodiment, the method according to the present invention comprises the following steps: dissolving cellulose in an aqueous alkali dissolution liquid, to generate an alkaline cellulose solution, in which more than 97, preferably more than 99%, of the added cellulose has been dissolved;filtering the alkaline cellulose solution, thereby generating two fractions: a major fraction of filtered alkaline cellulose solution free of any particles larger than the filter-cut-off value, and a second minor reject fraction of alkaline cellulose solution which contains the particles captured by the filter;mixing said reject fraction having a first viscosity value, with another aqueous alkali dissolution liquid, preferably with the same or very similar composition to the above first mentioned aqueous alkali dissolution liquid, which has a second viscosity value being lower than the first viscosity value of the aqueous alkali dissolution liquid, to provide a diluted reject fraction which has a third viscosity value being lower than the first viscosity value. Furthermore, with reference to the above it may be mentioned that the expression “dissolution liquid” refers to a liquid that is a solvent which can be used to provide new solution and which as such lowers the viscosity of the obtained mixture when being mixed with the filter reject. In other words, when the filter reject, which is a polymer solution, is admixed with the dissolution liquid, the obtained viscosity is lowered, because the polymer concentration is reduced by dilution. As a reference to further prior art documents, in WO2013/124265 there is disclosed a method for regeneration of a cellulose containing material comprising exposing the cellulose containing material to oxygen with an alkali aqueous solution at a pH of at least 9 and at a temperature of at least 20° C., dispersing the cellulose containing material in the alkali aqueous solution, adding an organic solvent to the dispersion to precipitate cellulose and separating the precipitated cellulose by filtering or centrifugatio