Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B9/00—Cellulose xanthate; Viscose
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B11/00—Preparation of cellulose ethers
  • C08B11/02—Alkyl or cycloalkyl ethers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B11/00—Preparation of cellulose ethers
  • C08B11/02—Alkyl or cycloalkyl ethers
  • C08B11/04—Alkyl or cycloalkyl ethers with substituted hydrocarbon radicals
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B11/00—Preparation of cellulose ethers
  • C08B11/02—Alkyl or cycloalkyl ethers
  • C08B11/04—Alkyl or cycloalkyl ethers with substituted hydrocarbon radicals
  • C08B11/08—Alkyl or cycloalkyl ethers with substituted hydrocarbon radicals with hydroxylated hydrocarbon radicals; Esters, ethers, or acetals thereof
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B11/00—Preparation of cellulose ethers
  • C08B11/02—Alkyl or cycloalkyl ethers
  • C08B11/04—Alkyl or cycloalkyl ethers with substituted hydrocarbon radicals
  • C08B11/10—Alkyl or cycloalkyl ethers with substituted hydrocarbon radicals substituted with acid radicals
  • C08B11/12—Alkyl or cycloalkyl ethers with substituted hydrocarbon radicals substituted with acid radicals substituted with carboxylic radicals, e.g. carboxymethylcellulose [CMC]
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B15/00—Preparation of other cellulose derivatives or modified cellulose, e.g. complexes
  • C08B15/05—Derivatives containing elements other than carbon, hydrogen, oxygen, halogens or sulfur
  • C08B15/06—Derivatives containing elements other than carbon, hydrogen, oxygen, halogens or sulfur containing nitrogen, e.g. carbamates
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08H—DERIVATIVES OF NATURAL MACROMOLECULAR COMPOUNDS
  • C08H8/00—Macromolecular compounds derived from lignocellulosic materials
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L1/00—Compositions of cellulose, modified cellulose or cellulose derivatives
  • C08L1/08—Cellulose derivatives
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L1/00—Compositions of cellulose, modified cellulose or cellulose derivatives
  • C08L1/08—Cellulose derivatives
  • C08L1/22—Cellulose xanthate
  • C08L1/24—Viscose
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L1/00—Compositions of cellulose, modified cellulose or cellulose derivatives
  • C08L1/08—Cellulose derivatives
  • C08L1/26—Cellulose ethers
  • C08L1/28—Alkyl ethers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L1/00—Compositions of cellulose, modified cellulose or cellulose derivatives
  • C08L1/08—Cellulose derivatives
  • C08L1/26—Cellulose ethers
  • C08L1/28—Alkyl ethers
  • C08L1/284—Alkyl ethers with hydroxylated hydrocarbon radicals
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L1/00—Compositions of cellulose, modified cellulose or cellulose derivatives
  • C08L1/08—Cellulose derivatives
  • C08L1/26—Cellulose ethers
  • C08L1/28—Alkyl ethers
  • C08L1/286—Alkyl ethers substituted with acid radicals, e.g. carboxymethyl cellulose [CMC]
• • 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
  • D21C1/00—Pretreatment of the finely-divided materials before digesting
  • D21C1/04—Pretreatment of the finely-divided materials before digesting with acid reacting compounds
• • 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
  • D21C3/00—Pulping cellulose-containing materials
  • D21C3/04—Pulping cellulose-containing materials with acids, acid salts or acid anhydrides
• • 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
  • D21C9/001—Modification of pulp properties
• • 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
  • D21C9/001—Modification of pulp properties
  • D21C9/002—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives
• • 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
  • D21C9/001—Modification of pulp properties
  • D21C9/007—Modification of pulp properties by mechanical or physical means
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
  • D21H11/16—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only modified by a particular after-treatment
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2205/00—Polymer mixtures characterised by other features
  • C08L2205/14—Polymer mixtures characterised by other features containing polymeric additives characterised by shape
  • C08L2205/16—Fibres; Fibrils

Definitions

• the present invention relates to the field of production of regenerated cellulose and cellulose derivatives from dissolving pulps. Background
• Dissolving pulp is a cellulose pulp with a high cellulose content (above 90 % w/w) and low contents of lignin, hemicellulose and resin. These features make dissolving pulp suitable as a raw material for the production of regenerated cellulose. Dissolving pulp is mainly produced by the acid sulfite process or the prehydrolysis kraft processes. The acid sulfite process is the most common and benefits of this technique include high recovery rates of the inorganic cooking chemicals and a totally chlorine free bleaching. One disadvantage with the method is that it results in pulps with a broad molecular weight distribution of cellulose (Christofferson 2005, Sixta et al. 2004).
• Dissolving pulp is mainly used for production of regenerated cellulose and as a raw material in the production of different cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl cellulose (HPC) and hydroxyethyl cellulose (HEC).
• CMC carboxymethyl cellulose
• MC methyl cellulose
• HPC hydroxypropyl cellulose
• HEC hydroxyethyl cellulose
• the cellulose is dissolved in a solvent to form a cellulose dope which is processed to regenerate the cellulose fibers in different forms.
• the viscose process has been used industrially for many years for the production of rayon fibers, used in the textile industry.
• One advantage with the method is that it is possible to use wood as a starting material whereas several other methods need lignin-free cellulose as starting material.
• the viscose process can be divided into the following steps:
• the cellulose In the Mercerization step the cellulose is typically soaked in 17-20% (w/w) NaOH solution at room temperature for a few hours such that the cellulose is converted into alkali-cellulose.
• the cellulose fibers are activated by the swelling of the fibers leading to an increased accessibility of the cellulose fibers to the chemicals in the solvent (e.g. carbon disulfide) such that the reactivity of the cellulose fibers with the chemicals is increased.
• the breakage of intra- and inter molecular hydrogen bonds in and between the cellulose chains caused by the alkaline conditions also contributes to the increased reactivity of the swelled fibers.
• the alkali-cellulose will be degraded into desired degree of polymerization through depolymerization reaction with the oxygen in the air.
• the reaction can be catalyzed by cobalt or manganese.
• the pre-riped alkali-cellulose is mixed with carbon disulfide (CS2) resulting in a cellulose xanthate derivativewhich is dissolved in a dilute sodium hydroxide solution to from a cellulose xanthate solution (viscose solution).
• CS2 carbon disulfide
• a cellulose xanthate derivative which is dissolved in a dilute sodium hydroxide solution to from a cellulose xanthate solution (viscose solution).
• CS2 carbon disulfide
• a ripening step where some of the alkali xanthate groups are removed from the cellulose.
• the cellulose xanthate is applied to a coagulation bath.
• Lyocell process Another industrially established process for production of regenerated cellulose is the Lyocell process.
• the cellulose pulp is mixed with a water solution of N-methyl morpholine N-oxide (NMMO) in a heated vessel.
• NMMO N-methyl morpholine N-oxide
• NMMO is believed to be a direct solvent of cellulose which means it can dissolve cellulose without derivatization.
• Other methods for dissolving cellulose and for production of solutions comprising dissolved cellulose using amine oxides are known in the art, see e.g. US4196282 and US2179181 .
• the Lyocell process can be performed at neutral pH in a water/NMMO solution.
• cellulose acetate process wherein cellulose is reacted with acetic acid and acetic anhydride in the presence of sulfuric acid. The cellulose is thereafter partially hydrolyzed to remove sulfate and some of the formed acetate groups to give the produced cellulose acetate product the desired properties. Thereafter the cellulose acetate can be dissolved in acetone and cellulose acetate fibers can be regenerated by extrusion through spinnerets and evaporation of the acetone.
• Regenerated cellulose can also be produced by the cellulose carbamate process, see e.g. US6590095. This process includes reacting cellulose with urea at elevated temperatures to form cellulose carbamate. The formed cellulose carbamate can be dissolved in a sodium hydroxide solution such that a spinnable cellulose carbamate dope is formed.
• Preparation of regenerated cellulose usually involves reacting the cellulose to form cellulose derivatives such as for example cellulose xanthate, cellulose acetate and cellulose carbamate. To get a high yield in the reactions it is important that the reactivity of the cellulose and accessibility of the fibers to the solvent is high. This is also true for production of other cellulose derivatives such as cellulose sulfate, cellulose phosphate, cellulose nitrate, ethyl hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose and hydroxyethyl cellulose. In some processes such as the Lyocell process, the cellulose is dissolved without derivatization.
• cellulose derivatives such as for example cellulose xanthate, cellulose acetate and cellulose carbamate.
• the present inventors have further demonstrated that the solubility of the fibers in the over flow fraction in a cellulose acetate process is significantly higher than for the under flow fraction or the unfractionated dissolving pulp, most likely due to the increased accessibility of the fibers in the over flow pulp fraction.
• the present inventors have thus realized that a fraction of cellulose fibers with increased accessibility of the fibers to the solvent can be generated by fractionation of a cellulose pulp into an over flow fraction and an under flow fraction using a hydrocyclone.
• the over flow fraction, due to the increased accessibility of the fibers to the solvent is particularly suitable as a starting material in processes for production of cellulose products where the fibers are swelled at a pH below 9.0.
• one aspect of the present invention relates to a method for producing at least one cellulose product comprising the following steps:
• a) providing a cellulose pulp preferably by a method comprising pulping lignocellulosic biomass by a pulping process such that a cellulose pulp is obtained
• the at least one first cellulose product is a cellulose derivative and/or a cellulose dope.
• Dissolving pulp A cellulose pulp having a dry weight cellulose content of at least 90 % (w/w)
• Cellulose dope A liquid solution of dissolved cellulose fibers.
• Swellability Ability to swell in a solvent. A pulp sample of cellulose fibers with a high swellability in water will have a larger increase in volume after incubation in water than a pulp sample of cellulose fibers with a lower swellability in water.
• Over flow fraction A fraction of the pulp which exits the hydrocyclone at or near the top of the hydrocyclone (i.e. in the over flow).
• Under flow fraction A fraction of the pulp which exits the hydrocyclone at or near the bottom of the hydrocyclone (i.e. in the underflow).
• Methods for production of cellulose derivatives and cellulose dope usually involve swelling of cellulose fibers prior to dissolving and/or derivatization of the cellulose fibers.
• the swelling step is important for increasing the accessibility of chemicals and/or the solvent to the cellulose fibers and a sufficient swelling of the fibers are therefore highly beneficial for the reactivity in the derivatization reaction and for the dissolving of the cellulose fibers to a cellulose dope.
• the cellulose fibers needs to be swelled at an acidic or close to neutral pH or at least at a pH below 9.0.
• a drawback with these kinds of methods is that the swelling of the fibers are less effective compared to methods where the fibers are swelled in a more alkaline liquid, such as in liquids having a pH above 9.0. Therefore, some types and qualities of dissolving cellulose is presently not used in industrial processes for production of regenerated cellulose or cellulose derivatives by processes which requires swelling of fibers at pH below 9.0. Some of these methods are important industrial process, which are highly suitable for production of different high quality regenerated cellulose products and/or cellulose derivatives. It is therefore desired that also such types of dissolving pulps could be used as starting material in these kinds of methods and that the swelling of the fibers are as efficient as possible.
• the present invention relates to a method for isolation of a fraction of a dissolving pulp with an increased swellability in liquids having a pH below 9.0.
• a fraction of cellulose fibers which is more suitable for production of regenerated cellulose and/or cellulose derivatives, by methods including swelling of fibers at a pH below 9.0, can be obtained.
• This enables use of dissolving pulps which previously have been regarded as unsuitable or less suitable for these kinds of methods.
• the present invention also enables a more efficient swelling of the fibers at pH below 9.0.
• one aspect of the invention relates to a method for producing at least one cellulose product comprising the following steps:
• a) providing a cellulose pulp preferably by a method comprising pulping lignocellulosic biomass by a pulping process such that a cellulose pulp is obtained
• the at least one first cellulose product is a cellulose derivative and/or a cellulose dope.
• a hydrocyclone (often referred to in the shortened form cyclone) is a device to classify, separate or sort particles in a liquid suspension based on the ratio of their centripetal force to fluid resistance.
• a hydrocyclone will normally have a cylindrical section at the top where liquid is being fed tangentially, and a conical base. The angle, and hence length of the conical section, plays a role in determining operating characteristics.
• a hydrocyclone has two exits on the axis: ususally one smaller on the bottom (underflow exit) and a larger at the top (overflow exit).
• over flow fraction should be interpreted as a pulp fraction that exits the hydrocyclone through an exit located at or near the top of the hydrocyclone and the term “under flow fraction” should be interpreted as a fraction of the pulp which exits the hydrocyclone at or near the bottom of the hydrocyclone.
• under flow fraction should be interpreted as a fraction of the pulp which exits the hydrocyclone at or near the bottom of the hydrocyclone.
• hydrocyclone and cyclone is used interchangeably.
• the over flow fraction can also be referred to as the "long fiber fraction” and the under flow faction can be referred to as the "short fiber fraction”.
• regenerated cellulose such as e.g. viscose can be produced from a paper grade pulp, see US4210747A.
• regenerated cellulose, cellulose dopes and cellulose derivatives are usually produced from dissolving pulps which are fairly pure cellulose pulps with low levels of hemicellulose and lignin and wherein the dry weight proportion of cellulose is above 90 % (w/w). Therefore it is preferred that the cellulose product is prepared from a dissolving pulp.
• a dissolving pulp can be obtained directly after the digesters in the pulping step (i.e.
• step a) in the present invention or hemicellulose might need to be degraded and/or removed in a step subsequent to the pulping step to obtain the dissolving pulp.
• the pulping process in step a) is a pre-hydrolysis kraft pulping process hemicellulose have been removed in a pre-hydrolysis step, prior to the pulping step, and thus a dissolving pulp (i.e. a cellulose pulp having a dry weight cellulose content of at least 90 % (w/w)) can be obtained already at step a).
• a dissolving pulp i.e. a cellulose pulp having a dry weight cellulose content of at least 90 % (w/w)
• the dry weight cellulose content can some times be below 90 % (w/w) directly after the pulping step and thus hemicellulose can be degraded in a step
• hemicellulose is usually degraded subsequently of the pulping step in a bleaching step.
• a paper pulp can be upgraded to dissolving pulp by extracting and/or degrading hemicellulose from the paper pulp, see e.g. US6057438.
• the cellulose pulp provided in step a) and/or the over flow fraction swelled in step c) is a dissolving pulp.
• the cellulose pulp provided in step a) is a dissolving pulp having a dry weight cellulose content of at least 90 % (w/w).
• the cellulose pulp provided in step a) has a dry weight cellulose content below 90 % (w/w) and the method is further comprising a step:
• step a2) removing or degrading hemicellulose at a step prior to step c) such that the cellulose content in the over flow fraction is at least 90 % (w/w) in step c).
• the removing or degradation of hemicellulose in step a2) is performed prior to step b).
• the removing or degradation of hemicellulose in step a2) is performed subsequently of step b).
• the over flow fraction swelled in step c) and/or the pulp provided in step a) is a sulfite dissolving pulp.
• the pulping process in step a) is an acid sulfite pulping process.
• step a2) includes a bleaching step, such as hydrogen peroxide bleaching step, a chlorine dioxide bleaching step or a chlorine bleaching step.
• a bleaching step such as hydrogen peroxide bleaching step, a chlorine dioxide bleaching step or a chlorine bleaching step.
• the cellulose pulp provided in step a) is a pre-hydrolysis kraft dissolving pulp.
• the pulping process in step a) is a pre- hydrolysis kraft pulping process.
• the over flow fraction swelled in step c) is a dissolving pulp upgraded from a paper pulp.
• the under flow fraction is suitable for use in alkaline processes such as for example a viscose process or a cellulose carbamate process.
• the method further comprising the step of: e) swelling at least part of the cellulose fibers present in the under flow fraction by soaking at least part of the under flow fraction in a second liquid having a pH above 9.0, preferably above 10 such as above 1 1 , such that a second set of swelled cellulose fibers is obtained
• step e producing at least one second cellulose product from the second set of swelled cellulose fibers obtained in step e).
• the under flow fraction swelled in step e) is a dissolving pulp.
• the dry weight cellulose content of the under flow fraction swelled in step e) is at least 90 % (w/w).
• the first cellulose product is a cellulose dope having a pH of 9.0 or lower and in one embodiment the second cellulose product is a cellulose dope having a pH of above 9.0.
• the first cellulose product is selected from Lyocell dope, cellulose acetate dope, cellulose sulfate, cellulose phosphate and cellulose nitrate.
• the second cellulose product is selected from a viscose solution, solid cellulose carbamate, cellulose carbamate dope, Ethyl hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, ethyl cellulose, propyl cellulose and ethyl - hydroxymethyl cellulose.
• the pH of the first set of swelled fibers is not raised above 9.0 at any time in between step c) and step d).
• the pH of the second set of swelled fibers is not decreased below 9.0 at any time in between step e) and step f).
• at least 60 % (w/w) of the fibers present in the over flow fraction obtained in step b), preferably at least 75 % (w/w), preferably at least 90 % (w/w) is used in step c).
• at least 60 % (w/w) of the fibers present in the under flow fraction obtained in step b), preferably at least 75 % (w/w), preferably at least 90 % (w/w), preferably 95 % (w/w) is not used in step c).
• less than 40 % (w/w), preferably less than 30 % (w/w), preferably less than 20 % (w/w) of the fibers in the over flow fraction have a fiber length between 0.2-1 mm and more than 60 % (w/w) preferably more than 70 % (w/w) preferably more than 80 % (w/w) of the of fibers in the over flow fraction have a fiber length between 1 -5 mm.
• less than 40 % (w/w), preferably less than 30 % (w/w), preferably less than 20 % (w/w) of the fibers in the under flow fraction have a fiber length between 1 -5 mm and more than 60 % (w/w), preferably more than 70 % (w/w), preferably more than 80 % (w/w) of the fibers in the under flow fraction have a fiber length between 0.2-1 mm.
• the cellulose pulp is mixed with a water solution of NMMO in a heated vessel and incubated until the cellulose fibers are dissolved by the water/NMMO solvent. During this incubation, the fibers are initially swelled before they are dissolved, otherwise the fibers are not accessible to the solvent and can not be dissolved. However, in this method the swelling is not performed in a separate step but is rather performed in the same vessel, in parallel with the actual dissolving of the fibers. The same is also true for example in the production of cellulose phosphate, cellulose nitrate and cellulose sulfate. In the production of these cellulose derivatives, the cellulose pulp is incubated with phosphoric acid, nitric acid and sulfuric acid
• the fibers are first swelled and then derivatized. Again the swelling and the reaction is not performed in separate steps but rather in the same vessel in parallel.
• the swelling is performed at a step which is separate from the derivatization and/or dissolving step.
• the cellulose fibers are swelled by soaking of the fibers in 17-20% sodium hydroxide in the mercerization step.
• the formed alkali-cellulose is derivatized by reaction with carbon disulfide to form the cellulose xanthate derivative in the xanthation step and finally the viscose solution is formed by dissolving of the cellulose xanthate derivative in sodium hydroxide of a concentration of about 5-10 % (w/w) in the dissolving step.
• step c) the swelling in step c) is performed
• the swelling in step c) is performed prior to the production of the first cellulose product in step d) in a step separate from step d) and in one embodiment the swelling in step e) is performed prior to the production of the second cellulose product in step f) in a step separate from step f).
• the first product can be selected from Lyocell dope, cellulose acetated dope, cellulose sulfate, cellulose phosphate and cellulose nitrate.
• the fibers are preferably swelled in a mixture of water and an amine oxide such as NMMO.
• the fibers are preferable swelled in a mixture of acetic acid and sulfuric acid.
• the fibers are preferable swelled in sulfuric acid.
• the fibers are preferable swelled in nitric acid.
• the fibers are preferable swelled in phosphoric acid.
• the first liquid having a pH of 9.0 or lower comprises acetic acid, sulphuric acid, nitric acid, phosphoric acid or at least one amine oxide.
• the amine oxide is selected from NMMO, trimethylamine, triethylamine, tripropylamine, monomethyldiethylamine, dimethylmonoethylamine, monomethyldipropylamine, ⁇ , ⁇ -dimethyl-, N,N- diethyl- or ⁇ , ⁇ -dipropylcyclohexylamine, N,N-diemethylmethylcyclohexamine and pyridine,
• the amine oxide is NMMO.
• the first liquid having a pH of 9.0 or lower is acetic acid, sulphuric acid, nitric acid, phosphoric acid or a mixture of acetic acid and sulfuric acid.
• the first liquid having a pH of 9.0 or lower is a water solution comprising at least one amine oxide such as NMMO.
• the NMMO is NMMO-monohydrate. Suitable amine oxide concentration for swelling cellulose fibers is well known to the skilled person.
• the concentration of NMMO in the first liquid can be about 75 % (w/w ), such as between 60 % (w/w) and 85 % (w/w).
• the production of the first cellulose product in step d) comprises dissolving at least part of the swelled cellulose fibers obtained in step c) with at least one amine oxide, such as for example NMMO, trimethylamine, triethylamine, tripropylamine, monomethyldiethylamine, dimethylmonoethylamine, monomethyldipropylamine, ⁇ , ⁇ -dimethyl-, N,N- diethyl- or N,N-dipropylcyclohexylamine, N,N-diemethylmethylcyclohexamine or pyridine.
• the amine oxide is NMMO and in one embodiment the first cellulose product produced in step d) is Lyocell dope.
• the first liquid having a pH of 9.0 or lower comprises acetic acid and optionally sulfuric acid.
• the production of the first cellulose product produced in step d) comprises dissolving at least part of the swelled cellulose fibers obtained in step c) by acetylation of the cellulose.
• the first cellulose product produced in step d) comprises reacting the swelled cellulose fibers obtained in step c) with acetic anhydride.
• the first cellulose product produced in step d) is cellulose acetate dope.
• the first cellulose product produced in step d) is selected from cellulose sulfate, cellulose phosphate and cellulose nitrate.
• the second liquid having a pH of above 9 comprises sodium hydroxide. In one embodiment the second liquid having a pH of above 9 is sodium hydroxide. In a preferred embodiment the second liquid having a pH of above 9 comprises 15-25 % (w/w), such as 17-20% (w/w) sodium hydroxide.
• alkali-cellulose is formed in step e). In one embodiment the production of the second cellulose product in step f) comprises mixing at least part of the alkali-cellulose formed in step e) with carbon disulfide such that cellulose xanthate is formed. In one embodiment at least part of the cellulose xanthate is dissolved in a sodium hydroxide solution such that a viscose solution is formed.
• the cellulose xanthate is dissolved in a solution comprising 5-10 % (w/w) sodium hydroxide such that a viscose solution is formed.
• the second cellulose product produced in step f) is a cellulose xanthate derivative such as a viscose solution.
• the second cellulose product produced in step f) is produced by a cellulose carbamate process and in one embodiment the second cellulose product produced in step f) is cellulose carbamate. In one embodiment the second cellulose product produced in step f) is a cellulose carbamate dope.
• Pulp from the cooking step usually contains some unwanted solid material. If the starting material is wood chips, some of the chips may not have been fiberized properly, and some of the fibrous material may not be completely in the form of individual fibers. Furthermore, contaminants such as bark, sand or gravels might enter the cooker together with the wood chips. Therefore, this unwanted material is usually removed by a screening step prior to the production of cellulose dopes, cellulose derivatives or other cellulose products. In the present invention it is desirable that this screening step is performed prior to the fractionation in step b). However it is possible, even though less desirable to perform the screening subsequently of the
• step b fractionation in step b).
• the method further comprising a step
• step a3) screening the cellulose pulp provided in step a) wherein the screening preferably is performed prior to step b).
• the pulp screened in step a3) is the over flow fraction and/or the under flow fraction obtained in step b).
• the over flow fraction and the under flow fraction can preferably be dried prior to step c).
• the production of the cellulose dope or the cellulose derivative is performed at another site or in another plant than the production of the cellulose pulp. Therefore drying of the pulp is desired for transportation and storage of the pulps.
• the method further comprises the step
• step b2) drying the over flow fraction obtained in step b) prior to step c) and in another preferred embodiment the method comprises the step
• step b3) drying the under flow fraction obtained in step b) prior to step e).
• the regenerated cellulose produced in step g) is selected from cellulose fibers such as ryons and cellulose films, such as cellofan.
• cellulose fibers such as ryons and cellulose films, such as cellofan.
• the present inventors have demonstrated that in a cellulose acetate process, the mean reactivity with acetic anhydride of the fibers in the over flow fraction is higher than the mean reactivity with acetic anhydride of the fibers in the under flow fraction and the fibers in the unfractionated pulp, see table 2.
• the present inventors have further demonstrate that the swellability in water is higher (se table 3) and that the water retention value (WRV) is higher for the over flow fraction compared to the reference and the under flow fraction.
• WRV water retention value
• the mean reactivity with acetic anhydride, of the fibers in the over flow fraction is higher than the mean reactivity with acetic anhydride of the fibers in the under flow fraction and of the fibers in the unfractionated pulp provided in step a).
• the mean reactivity with acetic anhydride is measured as amount of produced and dissolved cellulose acetate in a cellulose acetate process.
• the mean swellability in a water solution, such as water, for the cellulose fibers in the over flow fraction is higher than the mean swellability in water for the cellulose fibers in the under flow fraction and in the unfractionated cellulose pulp provided in step a).
• the water retention value for the cellulose fibers in the over flow fraction is higher than the mean water retention value for the cellulose fibers in the under flow fraction and in the unfractionated cellulose pulp provided in step a).
• fibers of these characteristics have a lower density than other fibers and therefore end up in the over flow fraction.
• the average length of the fibers in the over flow fraction have also, in many cases, been longer than the fibers in the under flow fraction. It is therefore possible that longer fiber lengths also, to some extent, can be associated with increased accessibility.
• the lignocellulosic biomass is wood such as wood chips.
• the lignocellulosic biomass is softwood such as pine, spruce, cedar, fir, larch, douglas-fir, hemlock, cypress, redwood, or yew.
• the wood is hardwood such as birch, beech, eucalyptus, acacia, oak, ash, elm, aspen, poplar or maple.
• the lignocellulosic biomass is wood chips from spruce, pine, birch, beech, acacia and/or eucalyptus.
• the lignocellulosic biomass is wood chips from spruce or pine.
• the lignocellulosic biomass is wood chips from spruce,
• the present invention relates to an industrial process for production of cellulose products. Therefore in step a) an industrially relevant amount of pulp is produced, in step b) an industrially relevant amount of pulp is fractionated, in step c) an industrially relevant amount of the over flow fraction is swelled and in step d) and industrially relevant amount of first cellulose product is produced.
• at least 100 kg pulp preferably at least 1 ton, is produced in step a).
• at least 100 kg pulp/h such as at least 500 kg/h is produced in step a).
• at least 100 kg of pulp is fractionated in step b).
• at least 100 kg of pulp is swelled in step c).
• at least 100 kg of the first cellulose product is produced in step d).
• a sample of hydrogen peroxide bleached sulfite dissolving pulp was taken out at a position in an acid sulfite process prior to drying of the pulp.
• the cellulose concentration in the wet sample wasl .5 % (w/w) and the sample was further diluted with water to a concentration of 0.2 % (w/w).
• the sample was fractionated with a hydrocyclone at room temperature such that an over flow fraction and a under flow fraction were obtained.
• the pH at the fractionation was about 6, the ingoing pressure was 4.5 bar and the outgoing pressure was 0.2 bar.
• the over flow fraction, the under flow fraction and the unfractionated reference pulp was dewatered and dried for further experiments.
• Table 3 Swellability in water for the over flow fraction, the under flow fraction and the reference pulp, The volume incensement was measured after 5 minutes and 30 minutes.

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