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
  • D21C9/10—Bleaching ; Apparatus therefor
  • D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
  • D21C9/153—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications with ozone
• • 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
  • D21C5/00—Other processes for obtaining cellulose, e.g. cooking cotton linters ; Processes characterised by the choice of cellulose-containing starting materials
  • D21C5/02—Working-up waste paper
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W30/00—Technologies for solid waste management
  • Y02W30/50—Reuse, recycling or recovery technologies
  • Y02W30/64—Paper recycling

Definitions

• the invention relates to a method for treating used paper.
• used paper There is currently a great demand in the world for the recycling of used paper, in particular to limit the exploitation of forests. Worn paper is collected and processed to make new sheets of paper or new paper or cardboard packaging, for example.
• the current process for treating used paper for recycling begins with pulping of the recovered paper to be recycled.
• One or more sieves of this paste are then carried out to remove coarse particles such as paper clips, staples, coarse ink particles, etc.
• One or more flotation steps are then carried out to more completely remove the ink used to print the old paper.
• used papers are generally printed.
• the printing ink consists of organic or mineral dyes and organic binders which, when dried, trap the dye particles and keep them on the paper.
• used papers are often coated with glues or adhesives, for example binding glues and adhesives ensuring the closure of the envelopes.
• Worn papers are also soiled with food and the like; the paper pulp obtained therefore contains microorganisms such as bacteria, fungi, yeasts, as well as enzymes such as the enzyme catalase.
• Soda is introduced in particular to swell the paper fibers and allow better separation of the solids.
• Peroxide hydrogen and / or chlorinated oxidizing products are also added to destroy microorganisms and to improve deinking.
• Complexing agents such as sodium silicate, the mode of action of which is not well known, are also added to further facilitate deinking. They form complexes with binders and dyes which are then more easily removed.
• Used paper to be recycled generally consists of a mixture of papers of different types: newspapers, glossy papers, magazines or higher quality papers.
• the differences in the quality of the papers mean that, once the preceding processing steps have been carried out, a paper pulp is obtained which is capable of producing a paper whose "whiteness" may not be satisfactory for the end use.
• This bleaching step is carried out, as for new paper pulps, by treatment with oxidants such as hydrogen peroxide or chlorinated products or with reducing agents such as sodium dithionite.
• Used papers can also contain papers that have been treated with optical brighteners (optical brighteners are fluorescent compounds making the paper appear whiter due to an optical phenomenon) these fluorescent compounds have been suspected of being carcinogenic; one may therefore want to carry out a defluorescence of the paper pulp, and here again, hydrogen peroxide is used.
• the pulp is then transformed into sheets of paper by known methods.
• ozone for the treatment of used paper.
• the ozone treatments are carried out after the flotation stages, that is to say during the possible stages of bleaching and defluorescence.
• ozone is still used there in addition to other chemicals, namely hydrogen peroxide, chlorinated products, soda, and complexing agents already present in the process.
• the flotation step for deinking purposes may not be sufficient, and as we have seen, it is then necessary to implement several kneading steps followed by flotation steps to perfect it. It is necessary here to emphasize the distinction between: the deinking step, which aims to eliminate the printing ink present on the used papers to be treated and makes it possible to obtain a corresponding whiteness close to that of the original papers and the 'proper bleaching step which is carried out on both pulp from used paper and on new pulp, that is to say obtained directly from cellulose. Bleaching as such consists in eliminating the lignin present in the pulp (new or recycled). The deinking step does not need to be implemented in the case of new paper pulps.
• the invention aims to overcome the drawbacks of the method of the prior art by proposing a method for treating used paper which makes it possible to reduce or even eliminate the overconsumption of hydrogen peroxide and to improve deinking. This allows a shorter treatment process comprising fewer or no kneading steps followed by flotation steps intended to perfect the deinking.
• the invention also proposes, in a variant, a method for treating waste paper which makes it possible to significantly reduce the pollution of the effluents discharged by the treatment plants.
• the invention provides a method for treating used paper of the type comprising the successive stages of: a) pulping used paper in an aqueous medium, b) at least one sieving to remove coarse particles, c) at least one flotation for deinking the dough, characterized in that it further comprises a step d) of ozonation carried out at the latest before step c) of flotation.
• step d) of ozonation is carried out at a consistency of the pulp of used paper of between 0.5 and 5%.
• step d) of ozonation is carried out at a consistency of the pulp of used paper of 0.5 to 3%.
• steps a), b), c) and d) are carried out in water, without adding chemicals other than ozone to the step d).
• steps a), b), c) and d) are implemented in the presence of soda, hydrogen peroxide and / or chlorinated products, of silicate. sodium and / or complexing agents.
• step d) is preferably implemented after step b) of sieving.
• step d) of ozonation is implemented in a two-phase tubular contactor of the gas-liquid type.
• step d) of ozonation is implemented in the tubular contactor operating in wave regime.
• step d) of ozonation is implemented in the tubular contactor operating in plug mode.
• step d) of ozonation is carried out with an air-ozone or oxygen-ozone gas mixture comprising between 50 and 200 g of ozone per m 3 of gas mixture.
• step d) of ozonation is implemented in a two-phase gas-liquid tubular contactor into which the ozone is introduced in the form of a gaseous mixture of air-ozone or oxygen-ozone at a speed greater than 0 , 5 m / s and less than or equal to 10 m / s while the used paper is introduced at a speed greater than 0.5 m / s and less than or equal to 10 m / s.
• step d) of ozonation is implemented in a two-phase tubular contactor into which the ozone is introduced in the form of a gaseous air-ozone or oxygen-ozone mixture at a speed between 0.5 and 2 m / s while the used paper pulp is introduced at a speed of between 0.5 and 2 m / s.
• FIG. 1 schematically represents an enlarged view of a particle of printing ink bonded to the surface of used paper
• FIG. 2 schematically represents an enlarged view of the ink particle of FIG. 1, on the same scale, after the deinking step of the method of the prior art,
• FIG. 3 schematically shows an enlarged view of the ink particle of Figure 1, on the same scale, after the deinking step of the process of the invention.
• FIG. 4 schematically represents a sectional view of a two-phase gas-liquid tubular contactor in segregated regime
• FIG. 5 schematically represents a sectional view of a two-phase liquid-gas tubular contactor in wave mode
• FIG. 6 schematically shows a sectional view of a two-phase gas-liquid tubular contactor in plug mode
• Figure 7 schematically shows a sectional view of a two-phase gas-liquid tubular contactor in dispersed bubble mode
• FIG. 8 shows in the form of bar graphs the number of ink dots remaining, depending on their sizes, in a pulp of used paper after the sieving step ( Figure 8A), the ozonization step (FIG. 8B), and the flotation step (FIG. 8C), according to a first mode of implementation of the method of the invention, and
• FIG. 9 shows in the form of bar graphs the number and size of the ink dots remaining in a used paper pulp after the sieving step (Figure 9A), flotation ( Figure 9B) and ozonation ( Figure 9C), implemented according to the method of the prior art.
• the process for treating used papers to be recycled according to the invention comprises, like the process for treating used papers of the prior art, a step of pulping the mass of papers to be recycled in an aqueous medium. The paper pulp then undergoes several solid-solid separation steps in order to remove undesirable elements such as paper clips, staples, coarse ink particles.
• At least one sieving step is carried out.
• one or more flotation steps make it possible to remove very fine ink particles.
• these steps are carried out in an aqueous medium in the presence of sodium hydroxide to adjust the pH and cause the paper fibers to swell in order to allow easier detachment of the ink particles and other impurities, hydrogen peroxide and / or sodium hypochlorite in order to facilitate the elimination of ink particles, eliminate microorganisms, such as bacteria, fungi and yeasts as well as enzymes such as the enzyme catalase in order to sanitize not only the paste itself but also the circuits of the installation in which the process is implemented.
• Complexing agents such as sodium silicate are also added to complex the metals, for example from dyes in printing inks so that they can then be removed with hydrogen peroxide or the chlorinated products already mentioned. Any other chemical can be added, as known in the art.
• the process for treating used paper of the invention differs from the process of the prior art in that, at the latest before the flotation steps, a step for ozonizing the paper pulp is implemented.
• This ozonization step makes it possible to improve the efficiency of the flotation steps for deinking the pulp, moreover it destroys the microorganisms and above all the enzyme catalase.
• the deinking step by flotation being made more efficient, the number and the duration of the subsequent processing steps intended to perfect the deinking, for example by implementing a series of kneading followed by flotation, are reduced compared to l prior art or even deleted.
• stickies which are present, for example as an adhesive for binding, for example blocks of paper or as an adhesive for envelopes, and
• the ozone used in the process of the invention will be used to react with the unsaturated products permeating the papers. worn and little with the lignin present because it is "covered” by these products and others such as mineral fillers.
• printing inks consist, in the liquid state, of particles of carbon or of another dye dispersed in a liquid binder. When the binder dries, it coats the carbon or other particles and attaches them to the surface of the sheet of paper.
• Figure 1 schematically shows an enlarged sectional view of a particle of dried printing ink on the surface of the paper.
• the carbon particle 2 is enveloped and bound to the surface of the paper 3 by the dried binder 1.
• FIG. 2 shows a schematic sectional view of the ink particle of Figure 1, on the same scale, after the steps of pulping, sieving and flotation according to the method of the prior art.
• the carbon particle 2 is still coated and bonded to the surface of the paper 3 by the binder l 'which has decreased in thickness.
• the mechanical action necessary to detach this particle of ink 2 from the surface of the paper 3 will be less than that necessary to separate the particle of ink 2 represented in FIG. 2.
• the number of mixing-flotation steps necessary for deinking totally the paper to be recycled according to the process of the invention will be less.
• ozone destroys microorganisms and especially the catalase enzyme.
• Ozone also makes it possible to clean up the circuits of the installation in which the used paper treatment process is implemented.
• ozone can be used without adding any of the reagents commonly used in the process of the prior art.
• the method of the invention in a particularly advantageous embodiment therefore consists in pulping the mass of paper to be recycled, in water, in carrying out the steps of solid-solid separation by sieving then in the steps of flotation, always only in water and without addition of no reagent, provided that an ozonation step is used at the latest before the flotation steps.
• This process using only ozone without other chemical reagents has great advantages, its simplicity and its economy, moreover, it is a process for treating used paper whose effluents are very little polluting.
• the ozonization step must be carried out at the latest before the flotation step for deinking. It can be carried out before, during or just after the pulping step or after the sieving step.
• ozone is used more efficiently and without overconsumption to remove fine ink particles, purify the system circuits and / or react with certain additives.
• the effectiveness and extent of degradation of the products to be removed from used paper for the same duration of contact depends on the extent and effectiveness of the contact of ozone with the products to be degraded. .
• the efficiency of the ozonation reaction depends on the rate of dissolution of the ozone in the pulp.
• ozone has already been used in paper pulp manufacturing processes to bleach virgin pulp. At present, these ozonization processes take place at a solids concentration of between 8 and 40 g of solids per 100 g of dough.
• Paper pulps can be likened to a liquid medium, generally an aqueous medium, in which solid particles are in suspension.
• Another process proposes, to increase the rate of dissolution of ozone in the liquid-solid phase, to conduct the ozonation reaction under pressure in apparatuses of the centrifugal pump type, which requires compressing the ozone.
• low consistency paper pulp denote a paper pulp whose paper concentration is between 0.5 and 5% by weight relative to the total weight of the pulp.
• very low consistency paper pulp denote a paper pulp whose paper concentration is approximately 1% by weight relative to the total weight of the pulp.
• the invention proposes to implement the ozonization step in a two-phase tubular contactor of the gas-liquid type and to introduce paper pulp at low or very low consistency.
• the tubular contactor for implementing the method of the invention can be a horizontal or vertical tubular contactor operating in co-current of liquid phase containing solids.
• the gas can be introduced by a simple pipe or by a more sophisticated system, for example a static mixer.
• the rate of dissolution of ozone in the pulp is a function of the gas-liquid mass transfer coefficients and more particularly of the interfacial area between the two phases.
• the goal here is to obtain a good gas-paste emulsion.
• FIG. 4 represents a diagrammatic section of a horizontal tubular contactor T operating in segregated regime in which the gas phase is denoted 4 and the dough is denoted 6.
• the interfacial area is represented by the contact surface 5 between the gas phase 4 and the paste 6. This contact surface 5, when the tubular contactor T is in segregated mode, as shown in FIG. 4, can be assimilated to a flat surface.
• the interfacial area corresponding to the contact surface 5 is less important than in the cases represented in FIGS. 5 to 7 which will be discussed below. For this reason, the ozone dissolution rate is less favorable.
• Such a segregated regime is obtained when the respective rates of introduction of the gas phase and of the paste are less than 1 m / s, more particularly greater than 0.5 m / s and less than 1 m / s.
• the contact surface between the gas phase and the liquid phase containing solids is improved when the contactor T operates in wave regimes, as shown in FIG. 5.
• the speed of dissolution of ozone, and therefore of the reaction of ozone with the paste is further improved when, as shown in FIG. 6, the tubular contactor T operates in plug mode.
• the paste 6 is animated by a movement which makes it touch the two internal horizontal walls of the contactor.
• the gas phase 4 therefore has a contact surface denoted 5 "high with the paste 6 when the contactor operates in such a plug regime.
• the contactor T operates in wave mode or in plug mode when the respective speeds of introduction of the gas phase and the paste are between 1 and 2 m / s.
• the contactor is in a dispersed bubble flow regime, as shown in FIG. 7.
• the paste 6 forms bubbles which are dispersed in the gas phase 1 and the contact surface 5 ′ "between the gas phase 4 and the paste 6 is very high.
• Such a dispersed bubble regime is obtained for respective introduction speeds of the gas and the paste greater than 2 m / s and which can range up to 10 m / s.
• the ozonization step can be implemented in the contactor T operating in segregated mode, in wave mode, in plug mode or in dispersed bubble mode, it will be preferably implemented in wave mode or in plug mode, that is to say with gas introduction speeds of between 0.5 and 2 m / s and pulp introduction speeds of between between 0.5 and 2 m / s.
• the introduction speeds mentioned above and in what follows are the speeds obtained when the contactor T is empty.
• the gas introduction rate will be calculated as a function of the internal section of the contactor used so as to obtain a gas introduction speed of between 0.5 and
• the speed of introduction of the dough will be calculated according to its rate of introduction into the empty contactor and according to the internal section of the contactor.
• ozone is very reactive and the quantities of ozone to consume are generally low.
• a carrier gas such as for example air.
• an ozone-air gas mixture containing between 50 and 200 g of ozone per m 3 of gas mixture is entirely suitable.
• an oxygen-ozone or nitrogen-ozone gas mixture or any other mixture of ozone in a carrier gas compatible with ozone may also be used.
• the mixture is stirred in a pulper sold by the company Lamort for 20 min.
• the pH is then close to 10.5.
• the paper pulp obtained is then sieved through sieves, according to the usual methods for the profession.
• the ozonation is carried out at a consistency of 3% in a glass reactor, the ozone is introduced in the form of a gaseous oxygen-ozone mixture containing 150 g of ozone per m 3 of gaseous mixture, until 10 kg of ozone per tonne of dry paper is consumed.
• Flotation step The paste obtained is diluted to a consistency of 1% and then transferred to a Lamort-type flotation cell. Flotation is carried out for 6 min and then extended by 4 min. A foaming agent is added.
• the number and size of the black dots per m 2 of surface was also measured on each sheet.
• the number of black dots remaining after the flotation is very small. This means that the ozonization step, when introduced before flotation improves the efficiency of the flotation step itself, that is to say deinking.
• the number of black dots per m 2 as well as the size in microns of these black dots were by image analysis.
• Example 2 The procedure was as in Example 1 but without adding hydrogen peroxide, soda and sodium silicate.
• the pH is around 7.5.
• the whiteness was measured with and without UV, the fluorescence and number of black dots per m 2 of sheets of paper obtained by this process as well as their size in microns, on each sheet of paper obtained after the sieving step, after 1 'flotation step and after the ozonation step.
• the results of Table 3 show, when compared with the results of the whiteness measurements with and without UV and of fluorescence carried out on the sheets of paper obtained in Example 1, that with the process of the invention, one obtains sheets of paper having in the end a higher whiteness and a lower fluorescence in the case of the sheets treated according to the process of the invention than in the case of the process of the prior art.
• the results of the measurements of the number of black dots per m 2 present on the sheets of paper obtained according to the method of the prior art as described in the present example as well as their sizes are given in FIG. 9.
• Example 2 The procedure was as in Example 2, without adding any chemical reagent other than ozone but by implementing the ozonization step after the flotation step.
• Example 2 The test of Example 2 was repeated using a horizontal tubular stainless steel contactor having an internal diameter of 4.5 cm and a length of 100 m supplied with a pulp of used paper having a consistency of 2.5%. .
• the rate of introduction of the paper pulp is chosen so as to obtain pulp speeds (in empty contactor) of between 1 and 2 m / s.
• the same speeds are used for the gas mixture consisting of a mixture of oxygen and ozone having an ozone content of 100 g / m3 of mixture.
• the ozone transfer capacity is then 1.5 to 3 kg / t of pasta for a residence time of one and a half minutes.

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• 2002
  • 2002-02-18 FR FR0202062A patent/FR2836162B1/fr not_active Expired - Fee Related
• 2003
  • 2003-02-13 JP JP2003569908A patent/JP2005517834A/ja active Pending
  • 2003-02-13 AU AU2003222375A patent/AU2003222375A1/en not_active Abandoned
  • 2003-02-13 WO PCT/FR2003/000460 patent/WO2003071024A2/fr not_active Ceased
  • 2003-02-13 US US10/504,806 patent/US20050155729A1/en not_active Abandoned
  • 2003-02-13 CA CA 2475689 patent/CA2475689A1/fr not_active Abandoned
  • 2003-02-13 EP EP03717397A patent/EP1478802A2/de not_active Withdrawn

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