WO2014174152A1 - Procédé d'oxydation catalytique de la cellulose - Google Patents

Procédé d'oxydation catalytique de la cellulose Download PDF

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Publication number
WO2014174152A1
WO2014174152A1 PCT/FI2014/050295 FI2014050295W WO2014174152A1 WO 2014174152 A1 WO2014174152 A1 WO 2014174152A1 FI 2014050295 W FI2014050295 W FI 2014050295W WO 2014174152 A1 WO2014174152 A1 WO 2014174152A1
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Prior art keywords
cellulose
oxidized
pulp
oxidation
nitroxyl compound
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Ceased
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PCT/FI2014/050295
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English (en)
Inventor
Markus Nuopponen
Lauri Kuutti
Heikki Pajari
Timo PÄÄKKÖNEN
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UPM Kymmene Oy
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UPM Kymmene Oy
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Priority to EP14726181.2A priority Critical patent/EP2989127A1/fr
Publication of WO2014174152A1 publication Critical patent/WO2014174152A1/fr
Anticipated expiration legal-status Critical
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B3/00—Electrolytic production of organic compounds
    • 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
    • C08B15/02—Oxycellulose; Hydrocellulose; Cellulosehydrate, e.g. microcrystalline cellulose
    • 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
    • C08B15/02—Oxycellulose; Hydrocellulose; Cellulosehydrate, e.g. microcrystalline cellulose
    • C08B15/04—Carboxycellulose, e.g. prepared by oxidation with nitrogen dioxide
    • 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
    • C08L1/02—Cellulose; Modified cellulose
    • C08L1/04—Oxycellulose; Hydrocellulose, e.g. microcrystalline cellulose
    • 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
    • D21C1/08—Pretreatment of the finely-divided materials before digesting with oxygen-generating 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
    • D21C3/16—Pulping cellulose-containing materials with acids, acid salts or acid anhydrides nitrogen oxides; nitric acid nitrates, nitrites
    • 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
    • D21C9/002—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives
    • D21C9/005—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives organic compounds
    • 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
    • D21H11/18—Highly hydrated, swollen or fibrillatable fibres
    • 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
    • D21H11/20—Chemically or biochemically modified fibres

Definitions

  • the invention relates to a method for catalytic oxidation of cellulose. Background of the invention
  • Heterocyclic nitroxyl compounds are known as catalysts that participate in the selective oxidation of C-6 hydroxyl groups of cellulose molecules to aldehydes and carboxylic acids, the corresponding oxoammonium salt being known as the active direct oxidant in the reaction series.
  • One of these chemical oxidation catalysts known for a long time is "TEMPO", i.e. 2,2,6,6- tetramethylpiperidinyl-1 -oxy free radical.
  • the oxidized forms of the nitroxyl radicals, N-oxoammoniumions act as direct oxidants in the oxidation of the target cellulose molecule, whereas a main oxidant is used to bring oxygen to the reaction chain and to convert the nitroxyl compound back to the oxidized form.
  • WO01/29309 recommends using 3 parts by weight NaBr to 4 parts of NaOCI.
  • the bromide ion acts as oxygen mediator between the main oxidant and the nitroxyl radical by oxidation to hypobromite and reduction back to bromide.
  • bromine compounds in the oxidation reaction is problematic because of environmental concerns.
  • Sodium bromide is usually used in the reaction mixture in relatively large amounts (conventionally 100-125 kg / 1000 kg pulp) and it is difficult to remove bromide residues from the final cellulose product by washing.
  • Bromine compounds also accumulate in process waters. Further, the use of bromine in industrial scale is undesirable. Use of large amounts of sodium bromide cause also corrosion problems in the equipment.
  • Bromine compounds are generally recognized as hazardous to health, for example bromate anion which is formed as a result of side reactions is a suspected carcinogen.
  • One purpose of the invention is to provide a method for activating the catalyst for the catalytic oxidation of cellulose.
  • Still one purpose of the invention is to provide a method for making nano- fibrillar cellulose.
  • the heterocyclic nitroxyl compound is activated by electrolysis to oxidized form; whereafter the catalytic oxidation of cellulose is performed.
  • heterocyclic nitroxyl radicals such as 2,2,6,6-tetra- methylpiperidinyl-1 -oxy radical (TEMPO) can be activated by electrolysis from the stable radical form to the active oxidized form, whereafter the catalytic oxidation of cellulose can proceed to the desired degree of oxidation by means of the catalyst and a main oxidant (such as hypochlorite), which is the oxygen source.
  • TEMPO 2,2,6,6-tetra- methylpiperidinyl-1 -oxy radical
  • the heterocyclic nitroxyl radical can be activated by electrolysis without the use of bromide or iodide.
  • the catalytic oxidation of cellulose by means of the catalyst can be performed in optimum conditions in regard to structural integrity (DP value) of the cellulose.
  • the catalyst is activated by passing a solution containing the heterocyclic nitroxyl compound in the radical through an electrochemical cell, where the compound is oxidized by the anode to the oxidized nitrosonium form, which can be used for starting the catalytic oxidation. It is also possible that in the electrolytic treatment the compound is converted to a mixture of the oxidized form and the reduced hydroxylamine forms, which are different from the radical form and can start the catalytic activity in the reaction conditions in the presence of main oxidant and cellulose.
  • the cellulose is oxidized at C-6 carbons to carboxyl groups through the catalytic activity using a main oxidant, which provides the oxygen for the reaction and whose amount in relation to the amount of cellulose can be used to adjust the degree of conversion of the cellulose.
  • Hypochlorite such as sodium hypochlorite
  • Residual aldehyde groups may be oxidized to carboxyl groups in a second step to complete the oxidation process and to attain a desired oxidation degree.
  • the cellulose After the cellulose is subjected to oxidation, it can be processed to a final cellulose product.
  • the starting material is pulp derived from plants, especially wood, the cellulose exists in fiber form.
  • the fibers that contain the cellulose in oxidized form as a result of the oxidation process are easy to disintegrate by mechanical methods to small-scaled fragments, nanofibrillar cellulose (NFC).
  • the method for forming the cellulose product comprises the first process of catalytic oxidation of the fibrous starting material and the second process of disintegration the oxidized starting material to nanofibrillar cellulose.
  • Figure 1 shows schematically the activation step of the catalyst.
  • the primary hydroxyl groups of cellulose are oxidized cataly- tically by a heterocyclic nitroxyl compound, for example 2,2,6,6-tetramethyl- piperidinyl-1 -oxy free radical, "TEMPO".
  • a heterocyclic nitroxyl compound for example 2,2,6,6-tetramethyl- piperidinyl-1 -oxy free radical, "TEMPO”.
  • Other heterocyclic nitroxyl compounds known to have selectivity in the oxidation of the hydroxyl groups of C- 6 carbon of the glucose units of the cellulose may also be used, and these compounds are widely cited in the literature.
  • the oxidation of cellulose refers to the oxidation of these hydroxyl groups to aldehydes and/or carboxyl groups. It is preferred that the hydroxyl groups are oxidized to carboxyl groups, that is, the oxidation is complete.
  • catalytic oxidation refers to nitroxyl-mediated (such as " ⁇ ''-mediated) oxidation of hydroxyl groups.
  • the catalytic oxidation of fibers or fibrous material in turn refers to material which contains cellulose that is oxidized by nitroxyl-mediated (such as " ⁇ ''-mediated) oxidation of hydroxyl groups of the cellulose.
  • nanofibrillar cellulose refers to a collection of isolated cellulose microfibrils or microfibril bundles derived from cellulose raw material.
  • Micro- fibrils have typically high aspect ratio: the length might exceed one micrometer while the number-average diameter is typically below 200 nm.
  • the diameter of microfibril bundles may also be larger but generally less than 1 ⁇ .
  • the smallest microfibrils are similar to so called elementary fibrils, which are typically 2-12 nm in diameter. The dimensions of the fibrils or fibril bundles are dependent on raw material and disintegration method.
  • Nanofibrillar cellulose may be characterized as a cellulose-based material, in which the median length of particles (fibrils or fibril bundles) is not greater than 50 ⁇ , for example in the range of 1-50 ⁇ , and the particle diameter is smaller than 1 ⁇ , suitably in the range of 2- 500 nm.
  • the average diameter of a fibril is in the range of 5-100 nm, for example in the range of 10-50 nm.
  • non-ionic grades have such wider fibril diameter while the chemically modified grades are a lot thinner (for example in the range of 5-20 nm).
  • Nanofibrillar cellulose is characterized by a large specific surface area and a strong ability to form hydrogen bonds.
  • the nanofibrillar cellulose described herein typically appears as either light or turbid gel-like material.
  • the nanofibrillar cellulose may also contain some hemicelluloses; the amount is dependent on the plant source.
  • Mechanical disintegration of the oxidized cellulose raw material is carried out with suitable equipment such as a refiner, grinder, homogenizer, colloider, friction grinder, ultrasound sonicator, fluidizer such as microfluidizer, macrofluidizer or fluidizer-type homogenizer.
  • the heterocyclic nitroxyl compound used as catalyst in the oxidation process (such as "TEMPO") is stable in its neutral, radical form, and it can be stored in that form.
  • the catalyst is activated electrolytically to oxidized form, which can participate at once in the reaction, and the oxidation process of the cellulose starts quickly.
  • the structural formula of "TEMPO" in its radical form is given below
  • the oxidation reaction can be started and performed to completion to a desired conversion degree in a reaction medium in the presence of the catalyst, cellulose and main oxidant.
  • the reaction medium may be water-based medium where the materials are dissolved and suspended. In the case of pulp raw material, the cellulose exists in fiber form as suspension in water in a suitable consistency, whereas the catalyst and the main oxidant are dissolved in the water.
  • the pH of the reaction medium is controlled during the reaction to keep it in the optimum range. Temperature of the reaction medium may also be controlled.
  • the catalyst is activated before the oxidation of cellulose by passing the catalyst in an electrolyte solution through an electrolytic cell comprising an anode and a cathode and an electrolysis space between the anode and the cathode.
  • the cell may have several parallel spaces between an anode and a cathode for parallel passage of different electrolytes.
  • the electrolyte undergoes electrolysis when passing through the electrolysis space.
  • the anode oxidizes the radical form of the catalyst to the oxidized form.
  • the electrolyte is preferably an aqueous solution. The principle is shown in Figure 1 .
  • Figure 1 shows the anode, the cathode, and the electrolysis space between the anode and cathode for passing the electrolyte with the catalyst dissolved therein.
  • the space is preferably divided by a membrane to two compartments, the cathode compartment and the anode compartment.
  • the membrane prevents the passage of at least some substances of the electrolyte from one compartment to the other.
  • the electrolyte in contact with the anode contains in addition to the heterocyclic nitroxyl radical some dissolved salt to increase the conductivity.
  • the salt should be preferably inert and not reactive to the anode so that there are no anions or cations producing additional oxidizers and competing with the nitroxyl radical.
  • sodium sulfate can be used.
  • FIG. 1 different electrolytes are passed through the anode compartment and the cathode compartment.
  • a salt that is inert towards the anode is used in the anode compartment and alkali metal hydroxide in the cathode compartment.
  • the inert salt is sodium sulfate and the alkali metal hydroxide is sodium hydroxide.
  • the membrane is cation exchange membrane which allows cations to pass from the anode compartment to the cathode compartment.
  • the radical, neutral form of the catalyst is denoted with TE * and the oxidized form with TE + .
  • the oxidized form of the catalyst may pass through the membrane, depending on the permeability of the membrane for cations of this molecular size. However, if the concentration of other cations that can pass through the membrane is higher than that of the catalyst (expressed in M) in the anode compartment, the losses of the oxidized catalyst are not significant.
  • the salt used in the electrolyte passed through the anode compartment need not be an inert salt.
  • a chloride salt produces chlorine or hypochlorite, depending on pH, through the reactions at the anode.
  • These oxidative species can be used as oxidant or catalyst activator in the catalytic oxidation step of cellulose, and the electric current can be used more efficiently in the electrolysis.
  • sodium chloride may be used in the electrolyte.
  • the anode material is DSA (dimensionally stable anode) and the cathode material is titanium.
  • DSA dimensionally stable anode
  • the cathode material is titanium.
  • Other known electrode materials suitable for the electrolysis may also be used.
  • anion exchange membrane which allows the passage of anions from the cathode department but blocks the passage of cations (incl. oxidized catalyst) from the anode department.
  • a neutral membrane which only separates the solutions of the anode compartment and the cathode compartment allows the passage of both ionic species (anions and cations) may also be used.
  • the electrolytic activation can take place without a membrane, but in an undivided cell, part of the oxidized form reduces back to radical form at the cathode.
  • the composition of the electrolyte is not in two fractions, and it may be used as such in the subsequent oxidation step.
  • only the electrolyte passed through the anode compartment and containing the catalyst in the oxidized form is preferably used.
  • the reaction medium for oxidation of the cellulose comprises activated heterocyclic nitroxyl catalyst, cellulose, and main oxidant, which is preferably sodium hypochlorite.
  • the oxidation process is performed in a reactor which is equipped with mixing of the reactions medium and control of reaction conditions.
  • the catalyst and the main oxidant are added preferably to a fibrous suspension of cellulose fibers to achieve a desired starting consis- tency of the reaction medium.
  • the activated catalyst may be added by adding the whole volume of the electrolyte to the reaction medium, without the need to separate the catalyst.
  • the main oxidant may be added portionwise during the reaction. It is advantageous to add the main oxidant, such as hypochlorite, continuously as the oxidation of cellulose proceeds to avoid excess concentrations which may cause unwanted side reactions.
  • the fibrous starting material which is suspended in the reaction medium may be any of the above mentioned materials, especially fibers of plant origin which form, when suspended in aqueous reaction medium, a pulp of given consistency.
  • the fibers may be especially from wood.
  • Chemical pulp such as softwood or hardwood pulp, for example bleached birch pulp, may be used.
  • the oxidation reaction is allowed to proceed till a required conversion degree (oxidation level has been achieved. As expressed in carboxylate groups generated as the result of oxidation, this is normally 0.5-1 .4 mmol COOH/g pulp.
  • the oxidation level (conversion degree) of 0.5-1 .1 mmol COOH/g pulp preferably 0.6-0.95 and most preferably 0.7-0.9 is already sufficient that the cellulose fibers can be easily disintegrated to fibrils by mechanical energy.
  • the dosage of hypochlorite to cellulose, to reach the above-mentioned conversions, may be 1 .7 to 5 mmol/g pulp, preferably 2.2-2.7 mmol/g pulp.
  • the consistency of the pulp in the reaction medium where the oxidation is performed is preferably above 3%.
  • the reaction is performed at medium consistency of the pulp to increase selectivity.
  • medium consistency of the pulp is used, the selectivity of the cellulose oxidation can be improved, because the desired reactions take place in the fiber, whereas the unwanted side reactions take place in the solution phase.
  • the medium consistency is initial consistency of the cellulosic raw material that is higher than normally used.
  • the consistency of the pulp is above 6%, especially above 6% and at the most 12%, more preferably equal to or higher than 8%, and most preferably in the range of 8-12% by weight. Within the last-mentioned range, the optimum consistency is supposed to be in the range of 9-1 1 %.
  • the consistency values are the initial consistency at the beginning of the oxidation.
  • the catalytic oxidation may be performed without the use of bromide. Sodium bromide, which is conventionally used as activator and cocatalyst because of the faster reaction rate and high degree of oxidation, can be avoided in the catalytic oxidation process according to still one embodiment.
  • the catalytic non-bromine oxidation with the heterocyclic nitroxyl catalyst initially activated by electrolysis may be performed by using carefully defined conditions with regard to pH and temperature.
  • the reaction is performed in neutral or slightly alkaline pH, at 7- 10, more preferably in the range of 7-9, most preferably in the range of 7.5- 8.5, and at room temperature or slightly elevated temperature, in the range of 15-50°C, preferably in the range of 20-40°C, most preferably in the range of 26-35°C, in the absence of added alkali metal halide.
  • the selectivity (less C- 2 and C-3 reactions) is improved, and bromine compounds are avoided.
  • the slower oxidation reaction rate due to the lower pH is compensated by the temperature, which does not increase the side reactions as much as the higher pH.
  • Temperature control may be used to keep the temperature within the above ranges during the reaction. Because the oxidation is exothermic, the temperature of the reaction medium will rise if cooling is not provided. The rise is about 10°C between the start and the end point. Thus, in the range of 15-50°C the reaction can start at below 30°C and end at below 40°C, for example start at 24-26°C and end at 34-36°C.
  • the oxidation may be completed by oxidizing the aldehyde groups to carboxylate groups in a second step, using different reaction conditions.
  • the first step using the electrolytically activated catalyst has proceeded so that a desired conversion degree is reached, the first step is stopped.
  • the partly oxidized cellulose may be washed and the second step for converting the residual aldehydes to carboxylates to reach the final carboxylate content is performed in a reaction medium where the pH is clearly on acidic side, about 1 .5-4, preferably 2-3.
  • the second step is performed at a pH below 3.
  • the stop point of the first step may be chosen according to the consumption of the main oxidant or any other way.
  • the pH of the reaction medium of the first step may be lowered directly to the pH range of the second step at the stop point of the first step.
  • chlorite for example NaCIO2
  • DMSO dimethyl sulfoxide
  • aldehyde groups are reduced back to hydroxyl groups by using a suitable reducing agent, such NaBH .
  • the reaction medium is taken out from the reactor.
  • the fibers containing the oxidized cellulose are separated from the reaction medium, and the reaction medium is possibly reused. Regeneration measures making it possible to reuse at least some of the constituents of the reaction medium are not described herein in closer detail.
  • the fibers are washed to remove the remnants of the chemicals and processed further, especially to NFC.
  • Turbidity may be measured quantitatively using optical turbidity measuring instruments.
  • turbidometers There are several commercial turbidometers available for measuring quantitatively turbidity. In the present case the method based on nephelometry is used.
  • the units of turbidity from a calibrated nephelometer are called Nephelometric Turbidity Units (NTU).
  • NTU Nephelometric Turbidity Units
  • a nanofibrillar cellulose sample is diluted in water, to a concentration below the gel point of said nanofibrillar cellulose, and turbidity of the diluted sample is measured. Said concentration where the turbidity of the nanofibrillar cellulose samples is measured is 0.1 %.
  • HACH P2100 Turbidometer with a 50 ml measuring vessel was used for turbidity measurements. The dry matter of the nanofibrillar cellulose sample was determined and 0.5 g of the sample, calculated as dry matter, was loaded in the measuring vessel, which was filled with tap water to 500 g and vigorously mixed by shaking for about 30 s. Without delay the aqueous mixture was divided into 5 measuring vessels, which were inserted in the turbidometer. Three measurements on each vessel were carried out. The mean value and standard deviation are calculated from the obtained results, and the final result is given as NTU units.
  • the NFC was diluted with deionised water to a concentration of 0.5 w% and 200 g of the mixture was homogenised with a Buchi-mixer (B-400, max 2100 W, Buchi Labortechnik AG, Switzerland) for 3 x 10 s.
  • the apparent viscosity of NFC is measured with a Brookfield viscometer (Brookfield viscosity) or another corresponding apparatus. Suitably a vane spindle (number 73) is used. There are several commercial Brookfield viscometers available for measuring apparent viscosity, which all are based on the same principle. Suitably RVDV spring (Brookfield RVDV-III) is used in the apparatus. A sample of the nanofibrillar cellulose was diluted to a concentration of 0.8% by weight in water and mixed for 10 min. The diluted sample mass was added to a 250 ml beaker and the temperature was adjusted to 20°C ⁇ 1 °C, heated if necessary and mixed. A low rotational speed 10 rpm was used.
  • TEMPO TEMPO
  • the activation of "TEMPO" molecule by electrolysis was done.
  • the catalyst was initially in its radical form.
  • the used equipment, materials and concentrations are those shown in Fig. 1 .
  • a cation exchange membrane (area 100 cm 2 ) prevented the reduction of TEMPO+ (the oxidized form) at the cathode.
  • the electrolysis volume was 0.5 liter and the current was constant 0.9 A and the voltage was 2.5 V and temperature 20°C.
  • Electrolysis took 4 hour activation time (to ensure total oxidation of TEMPO) and the pH dropped during the electrolysis to pH 2.0 due to the decomposition of water at the anode. The most of the electric current was consumed to oxygen evolution.
  • Turbidity was 44 NTU.
  • the zero shear viscosity was 28 000 Pa s and yield stress 1 1 Pa.
  • the sample was disintegrated to nanofibrillar cellulose in Atrex dispergator.
  • the sample was diluted to 2.5 w% and run through the dispergator four times. Characterization was done by measuring turbidity and Brookfield viscosity.
  • NFC gel a clear gel consisting of microfibrils in water
  • the fibril cellulose is preferably made of plant material that has been subjected to the oxidation to convert the hydroxyl groups of the cellulose to carboxyl groups with a conversion degree that enhances the disintegration of the material to nanofibrillar cellulose.
  • One preferred alternative is to obtain the microfibrils form non-parenchymal plant material where the fibrils are obtained from secondary cell walls.
  • One abundant source of cellulose fibrils is wood fibers.
  • the nanofibrillar cellulose is manufactured by homogenizing oxidized wood-derived fibrous raw material, which may be chemical pulp. The pulp can be for example softwood pulp or hardwood pulp or a mixture of these.
  • the fibrils originating in secondary cell walls are essentially crystalline with degree of crystallinity of at least 55%.
  • the carboxylate content of 0.5- 1 .1 mmol COOH/ g starting pulp (on dry matter), preferably 0.7-0.9 mmol COOH/ g pulp is desirable so that the gel formation as a result of mechanical disintegration would be easy.
  • the pH of the medium is adjusted to 7-10, preferably 7-9, and most preferably to 7-8.5, which lowers the energy needed.
  • the obtained NFC gel is characterized by shear thinning behaviour.
  • the mean diameter of the microfibrils is 2-20 nm, preferably 2-6 nm, and the mean length is in the range of 0.3-5 ⁇ , preferably 0.5-2 ⁇ .
  • the turbidity of the NFC is 3-90, preferably 10-70, more preferably 20-60 NTU (0.1 % concentration, nephelometric measurement).
  • the gel has zero shear viscosity ("plateau" of constant viscosity at small shearing stresses approaching zero) of 5000-50000 Pa s and yield stress (shear stress where shear thinning begins) of 5-40 Pa, preferably 10-30 Pa.

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Abstract

La présente invention concerne un procédé d'oxydation catalytique de la cellulose faisant appel à un composé nitroxyle hétérocyclique comme catalyseur et à un oxydant principal agissant comme source d'oxygène, le composé nitroxyle hétérocyclique étant activé par électrolyse en sa forme oxydée, effectuant ainsi l'oxydation catalytique de la cellulose.
PCT/FI2014/050295 2013-04-25 2014-04-24 Procédé d'oxydation catalytique de la cellulose Ceased WO2014174152A1 (fr)

Priority Applications (1)

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EP14726181.2A EP2989127A1 (fr) 2013-04-25 2014-04-24 Procédé d'oxydation catalytique de la cellulose

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FI20135423 2013-04-25
FI20135423A FI126386B (en) 2013-04-25 2013-04-25 A process for catalytic oxidation of cellulose

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Cited By (4)

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