MXPA94006557A - Deinking wastepaper printed with water-based ink - Google Patents

Abstract

A process is disclosed for deinking pulp which has been made from paper printed with flexographic ink. The process uses a surfactant component made from a fatty acid or a fatty acid blend and at least one alkoxylated diamine selected from Formula I:Formula I where X, Y, W and Z may be alike or different and are each independently selected from the group consisting of (i) -(CH2-CH(CH3)-O)a(CH2-CH2-O)b-;(ii) -(CH2-CH2)-O)c(CH2-CH(CH3)-O)d-;and (iii) random copolymers of ethylene oxide and propylene oxide, wherein a, b, c and d are each selected independently to be a number between 1 and 30 so as to give an HLB value between 5-15.

Description

"PROCEDURE TO DISINFECT PRINTED WASTE PAPER WITH AQUEOUS BASE INK" Inventor (s): MEAN-3ENG HOU and NARAYANASAMY SEENIVASAN, Taiwanese, Hindi, respectively, residing at: 12062 Spinna er Drive, Tega Cay, South Carolina 29715 and 7531 Claiborne Woods Road, Charlotte, North Carolina 26216, respectively E.U.A.

Causaire: HOECHST CELANESE CORPORATION, a North American corporation, organized and existing in accordance with the laws of the State of Delaware, E.U.A., located at: Route 202-206 North, Somerville, New Jersey 06676, E.U.A.

SUMMARY A method for de-inking pulp that has been made from paper printed with flexographic ink is described. The process uses a surfactant component made from a fatty acid or a mixture of fatty acid and at least one alkylated diamine, selected from the formula I: HX-0 0-WH \ / N - - C = C - - N Formula I / \ HY-0 0-ZH wherein X, Y, W and Z may be the same or different and each of them is independently selected from the group consisting of: (i) ~ (CHa-CH (CH3) -0). (CH5a-CHSI-0) to-; < ii) - < CHa-CHa .. < (CHßCH < CHB3 > -0) cl; AND (iii) - random copolymers of ethylene oxide and propylene oxide; where a, b, c and d are each independently selected to be a number between 1 and 30, in order to give an eHL value between 5 and 15.

BACKGROUND OF THE INVENTION The recycling of paper is having increasing importance as the demands on resources increase. One of the aspects of recycling, which is particularly challenging, is the de-inking area. Various aspects of de-inking are described in the literature. See, for example, L. D. Ferguson, "Deinking Chemistry: Part 1", TAPPI Journal, pages 75-63 (July 1992), and "Deinking Chemistry: Part 2", TAPPI Journal. pages .9-56 (August 1992); B. R. Read, "The Chemistry of Flotation Deinking", TAPPI Proceedinqs. 1991 Pulpinq Conference, pages 651-656; J. Jossinet, "Custom Deinking of Newsprint", 77th Annual Meetina Technical Section Canadian Pulp 8. Paper Association, pages 369-372 (1991); L. D. Ferguson, "The Role of Pulper Chemistry in Deinking", TAPPI Froceedinqs, 1991 Pulpinq Con erence. pages 793-799; T. W. Woodward, "Appropriate Chemical Additives Are Key to I proved Deinking Operations", Pulp & Paper. pages 59-63 (November 1966); and T. W. Woodward, "Deinking Chemistry", 1991 Chemical Processing Aids Short Course. pages 65-105. De-inking by washing and de-inking by flotation are the two main types of deinentation procedures. Some preference is given to de-inking by flotation, because it uses less water. One of the biggest challenges in the area of flotation technology is the increasing amount of waste paper that has been printed with water based inks. The change to water-based inks has been largely due to concern about the environmental impact of oily base inks and the desire to reduce or eliminate the use of solvents in printing. As will be appreciated, the # Separation of oily base inks from the pulp during a recycling process in a water-based environment is easier than separating water-based inks from water-based pulp. The two greatest problems in the use of flotation for physical inks are: (a) the particle size is small after the formation of new pulp, at 0.2-1.0 micras and (b), the ink is hydrophilic and seeks to remain with the water. (See the discussion in Ferguson's August 1992 article, mentioned above, on page 53-5.) Additionally, systems that have been used by recyclers for the separation of oily base ink are not always immediately adaptable to separations involving water based inks. Regular supply contamination by water based inks has caused major problems by degrading the operation of deinking systems. Various approaches have been tried to adapt the flotation processes to the physical inks. These approaches have included the search for chemical substances that give improved results. These chemicals have included collectors to remove the ink that has been released from the fiber (which include fatty acids), such as stearic acid), surfactants, "disks" (combination of dispersants and collectors), water hardeners and chelates. In contrast to the oily base ink, the water-based ink has a water-soluble polymer that carries and binds the ink to the substrate. A typical flexographic ink formulation (water based) for newspaper printing can be of the order of 15. pigment, 70 percent water, 1 * acrylic polymer and 5- amines, defoamers and other components. When paper pulp is formed, these polymers (such as acrylic polymers) dissolve in the water, carry the ink throughout the pulp suspension and redeposit on the pulp fibers. Flotation is not always useful for treating pulps that contain water-based inks. The washing steps, even the multiple washing steps, are also not totally reliable to eliminate the pulp residue. For example, gray water (filtered water from washing or thickening) can be recycled to the system and often the resulting pulp is darker than desirable. Bleaching steps have been used in conjunction with the de-inking of photographic materials to obtain brighter pulps. Thus, it is an object of the present invention to provide an improved method for de-inking pulp that comes from sources containing flexographic (water-based) ink. It is another object of this invention to provide a deinking process and deinking chemicals for flexographic ink that allow the use, in part, of the float. These and other objects of the invention will be apparent from the description that follows.

BRIEF DESCRIPTION OF THE INVENTION This invention provides a method for detecting pulp that has been made from paper printed with lexical ink. The method comprises pulping the paper with water at a temperature of 25 to 65 ° C, in particular 35 to 55 ° C, in a neutral to moderately alkaline environment diluting the pulp to the desired consistency; mix the pulp with 0.5 to 3.0 weight percent, based on the kiln-dried weight (SH) of the pulp, of a surfactant component made by combining 5 to 95_ fatty acid or fatty acid mixtures selected from acids fatty acids of 12 to 22 carbon atoms (carboxylic acids) and 95 to 5 of one or more alkoxylated diamines, selected from the group consisting of formula I: H-X-0 0-W-H \ / N - C = C - N Formula I / \ H-Y-0 0-Z-H wherein X, Y, W and Z may be the same or different and each of them is independently selected from the group consisting of: (i) - (CHa-CH (CH3) -Q) m (CHa-CHa-0) b-; (ii) - (CHa-CHa) (= (CHaCH (CHB3) -0); and (iii) - random copolymers of ethylene oxide and propylene oxide, where a, b, c and d are each independently selected so that be a number between 1 and 30, in order to give an EHL value between 5 and 15. The mixture is then treated in a flotation cell and drained using familiar methods for those who are experts in the flotation cell technology, In order to obtain the recycled product, during the process, the alkalinity is adjusted and the pulp formation is controlled so that the reduction in the size of the ink particles is minimized or prevented, the reasonable swelling of the pulp is obtained. the pulp fiber and the entrapment of the ink particles in the fibers is reduced or prevented It is convenient that the flexographic ink particles are agglomerated and hydrophobicized to facilitate the separation from the pulp fibers Suitable particle sizes pa These agglomerated materials are in the range of 10 to 200 microns. The process of this invention can be put into practice in order to minimize the solids lost during the flotation process and it is preferred that this be done.

DESCRIPTION OF THE DRAWINGS Figure 1 shows a schematic diagram of a simpler deinking process, suitable for use at a pilot plant level. In Figure 1, hot water 10, de-inerting chemicals 11 (such as caustic, surfactants and CaCla) and the supply 12 of paper material, made with paper printed with flexographic ink, are loaded into a pulp former 13, . at a temperature. between .5 and 50 ° C (for example, from "+6 to .9 ° C) and a consistency of 7.5 to 15- (for example, 15-). If the hardness of the water is more than 350 ppm (as CaCla), the addition of CaCla is not necessary. The preferred hardness is on the scale of 200 to 600 ppm (as CaCla). After the pulp formation is completed for the desired time of 2 to 5 minutes, the suspension is transferred to a dilution tank. Dilution water 15 is added which is sufficient to reduce the pulp consistency to approximately 1 * and the temperature is maintained at approximately l + 6 -? + 90C. The pulp suspension is then transferred to a flotation cell 16 and the flotation process is operated for the desired time. The rejected material 17 is removed during flotation and placed in a suitable container. The de-inked pulp 16 is transferred to a receiving tank 19, where the temperature is maintained at approximately 45-. Β ° C and the consistency is approximately 1%. The pulp is then transferred to a rotary drum washer, approximately at .5 - .6 ° C and a consistency of 1%. The receiving pulp 21 is then dewatered and the filtrate 22 discarded or recirculated after clarification.

DETAILED DESCRIPTION OF THE INVENTION AND DESCRIPTION OF THE PREFERRED MODALITY The process of this invention provides a method for de-inking pulp containing flexographic ink, wherein the method comprises first forming paper pulp (which, optionally, can be pre-shredded) with water at a temperature of 25 to 65 ° C, such as water. at 55 ° C, in an aqueous alkaline environment. The alkaline environment is formed by adding up to 0.5 weight percent (based on the oven-dried weight of the fiber) of a base, such as NaOH or anhydrous sodium carbonate. A pH scale of 6.5 to 9.5 is particularly suitable. The aqueous suspension may also contain other additives, such as chelates, sodium silicate, builders, bleaching agents, such as hydrogen peroxide, which has been added to the pulp suspension at various points in the pulp formation process.

The alkali pulp suspension is then diluted to form a pulp of the desired consistency. It is preferred that consistencies of 0.6% to 3.0% are used, such as 0.6% to 1.2% and, especially, of 0.9% to 1.1%, since they appear to give good results in the currently available desentheter equipment. The pulp suspension is then mixed with 0.5 to 3.0% of a surfactant component made with 5 to 95% of one or more fatty acids or fatty acid mixtures, such as those described above, such as those selected from 14 to 20 atoms carbon (and, preferably, selected to be oleic acid or stearic acid) and from 95 to 5 percent of at least one alkoxylated diamine of the formula I described above. More particularly, from 65 to 50% of fatty acid or fatty acid mixture can be used, with 15 to 50% of a compound of formula I. Preferably, the fatty acid portion is 60 75% and the compound of the formula I is from 20 to 25%. An example of a suitable material is Genapol < R > PN-30 (Hoechst Celanese Corporation, So erville, New Jersey). Genapol < p, > PN-30 is a block copolymer of ethylene oxide / propylene oxide, based on ethylene diamine with a total of 47 moles of ethylene oxide and 47 moles of propylene oxide. Genapol < R > PN-30 can be described as a compound of the formula I with: W = - (CHa- (Ha-O). (CHa-CH (_Ha) -0> t - X = - (CHa-ÍHa-O) , (CHa-CH (CHa) -0) j- Y = - (CHa- (H -.- 0) ß (CHa-CH (CHa) -0) k- Z = - (CHa- (H _, - 0 ) (CHa-CH (CHa) -0) m-, where e + f + g + h = 47 and i + j + k + m = 47. It is particularly suitable to add a compound of formula I above, charging the pulper former with waste paper and other chemicals Preferred compounds are those compounds of formula I wherein each of a, b, c and d are independently selected from the integers 5 to 15. The number of EHL (hydrophilic balance) -lipophile or EHL system) is a quantitative way, known to those skilled in the art, of correlating the chemical structure of surfactant molecules with their surface activity For the compounds of formula I, the EHL number is preferably selected so that it is a number from 5 to 15. It is also important that the process be conducted to minimize the loss of solid pulp during the flotation step. Care must be taken in selecting the degree of alkalinity so that the fibers swell enough to be free of ink, but not so much that the fibers come out in the waste with the ink. The excessive reduction in particle size decreases the deinking efficiency. After the pulp formation the mixture is then processed by means of a flotation cell, drum washing machine, etc., as shown in the diagram in Figure 1. The flotation process can be repeated until a product with the desired brightness or until it is no longer affordable to repeat the process. A washing process (eg, drum washing) is then used to ignite the product additionally and to raise the consistency. Finally the suspension is drained and can be dried in a drum dryer to obtain a final product. Such methods are known in the art, including references cited in the background of the invention. With respect to the flotation cell, the diluted pulp is treated cyclically and recirculated through the cell for 2 to 10 minutes. All of the deinking surfactants described above can be obtained commercially, although any of the mixtures referred to herein may have to be mixed. Other compounds of formula I that are not commercially available can be prepared by techniques known to those skilled in the art. The equipment useful for practicing the method of this invention is described in greater detail in the examples. Some parts of the equipment were obtainable in commerce; some more were made to order, and still others are modi ications of artifacts obtainable in commerce. Commercially available equipment can be used. Note that Lionsu ^ fM ,, is a proprietary brand of nonionic surfactants.

EXAMPLES The following examples are offered as illustrative of the invention, but should not be considered as limitations therefor. All chemical symbols and abbreviations have the ordinary and customary meanings, unless otherwise indicated. So, mm is millimeter, cm is centimeter, is meter, g is grams, ° C means degrees Celsius, ppm means parts per million, min is minute, lpm is liters per minute, kg / cma is kilograms per square centimeter, SH is Oven-dried, DTPA is diethylenetriaminepentaacetic acid. Note that the washing process involves diluting and then thickening the pulp (by dewatering). EXAMPLE 1 PREPARATION OF DISTINGUISHING AGENTS A formulation is prepared for these examples of two components: (a) a fatty acid or a mixture of fatty acid (examples being oleic acid and stearic acid); and (b) a diamine alkoxylate (Senapol "» PN-30 from Hoechst Celanese Corporation, Somerville, New Jersey.) For the purposes of the examples, "agent A" is formulated by mixing a portion of Genapol < R > PN-30 directly with two parts of oleic acid in a container, followed by mixing with a stirrer to obtain a clear amber solution "Agent B" is formulated by adding a part of Genapol < R > PN-30 to 2 parts of molten stearic acid, followed by mixing with a stirrer and cooling the mixture to obtain a paste.

EXAMPLE 2 STUDY OF LAYOUT IN LABORATORY Printed newspaper was shredded by a water-based printing process (Charlotte Qbserver, North Carolina), to approximately 3 x 3 cm pieces as a waste paper supply. A modified Hobart mixer was used as the pulper former for temperature control. The pulp former was charged with 1020 g of hot water (at 50 ° C), then with 0.5% NaOH (based on the oven-dried weight of the paper) and then 160 g of waste paper. The pulp was formed at 50 ° C for 10 minutes to obtain a very dark suspension. After forming the pulp, the suspension was diluted to 0.6-1.0% consistency, 3% agent A was added (based on the oven-dried weight of the fiber), and the hardness of the water suspension was adjusted / pulp at 200 ppm CaCla, adding 0.24 g of CaCla • After moderately mixing the suspension for a few minutes, the diluted suspension was loaded in a Denver-type flotation cell, manufactured at home, and floated for 10 minutes . After flotation, the suspension was drained through a modified dynamic drainage jar, under a house vacuum, with a regular vacuum pump outlet. The dynamic drainage jug was modified by replacing the mesh with 100 mesh wire cloth. Brilliance pads were formed for the post-pulper, post-floated and post-washed the samples using the procedure described in the Technical Association of the Pulp and Paper Industry (TAPPI) standard T 216 om-91 (incorporated here as a reference in its entirety), except that the pads of brilliance were formed to a consistency of 0.5%, to avoid excess washing. The brightness was determined from these pads using a Technidyne brightness meter and the data are found in Table I.

• EXAMPLE 3 SE6UND0 LABORATORY UNINTENDED STUDY A low consistency pulp former of the type described in Example 2 was used. Hot tap water (760 g at 50 ° C) was charged to the stainless steel beaker. To the water present in the pulp former 0.6 g of agent B (as described in example 1), 0.06 g of naOH and sufficient CaCla were added to adjust the hardness of the aqueous solution to 200 ppm of CaCla-S added slowly shredded newspaper, of the type described in example 2 (40 g), to the pulper, while the stirrer was rotated. The pulp was formed at 50 ° C for 25 minutes. The pulp was then diluted to a consistency of 1% with hot tap water, approximately 50 ° C; the hardness was adjusted to 200 ppm of CaCla and the pulp was stirred moderately at 50 ° C for 5 hours.

«Minutes before starting the flotation. Flotation was carried out in a Denver-type flotation cell, as described in example 2, for 10 minutes. After the flotation was finished, the washing was performed in the modified dynamic draining jar, described in example 2. Brilliance pads were made from samples after the pulp former, after flotation and after washing. The brilliance of these pads was measured by the Technidyne brightness meter and the data are shown in Table I. The fiber loss, as determined from the weight of waste solids, was 14% and the water loss was of 7%. The data are found in table I.

TABLE I BRILLANTEZ DATA After After After form of pulp. ford.- 2 37.6 44.4 46.96 3 51.11 52.41 EXAMPLE 4 STUDY OF DETNINTING IN PILOT PLANT The de-inking process of this example was carried out with 100% of the type of newsprint described in Example 2, except that the newsprint was not shredded prior to its addition to the pulper former. The schematic representation of figure 1 shows the general diagram of the steps in the process. A large-scale pilot scale pulper (Formax 1600, from Adirondack Machine • ^ Corporation, Glens Falls, New York) was connected to a 26.5 liter capacity custom made flotation cell, and a 0.3 by 0.9 pilot drum washer, from Komline-Sandersop »New Jersey. The flotation cell has four inlets, located tangentially to a cylindrical vessel, to bubble fine air bubbles in the pulp. Depending on the size of the camera, the 4 inputs should not be used at the same time. The pulp rises to the acceptance zone while it is circulating in the zone of • food. The foam containing the ink is removed through the waste tube in the center of the cell, while the acceptable pulp is removed through the bottom of the acceptance zone. Hot water (24.9 liters at 46-49 ° CX in the pulp former was charged, followed by 2.6 g of NaOH, 32.5 g of sodium silicate and 20.5 g of agent A, as described in Example 1. After the contents of the pulp former were thoroughly mixed and dispersed and 1300 g of newsprint, as described earlier in this example, were added directly to the pulper, a slurry of newspaper was formed in the pulper at speed reduced 70-% of the design speed) for 3 to 5 minutes, and then the contents of the pulp former were described in a tank, where the suspension was diluted to an approximate consistency of 1 percent with hot water to 46- 49 ° C. The diluted suspension was allowed to remain in the feed tank for five minutes to ensure complete de-scaling of the high consistency pulp. During the flotation process, this suspension was pumped at 1% through two entrances that were each constructed to let the contents pass from the entrances to the flotation cell, at an angle that was tangential to the cell. It is also preferred that the entries used at any given time be through the cell, one with respect to the other. When the suspension was pumped into the cell, through two entrances, the suspension was mixed with very fine air bubbles, before entering the cell, at 56.7 bpm. The accepted portion of the suspension from the flotation cell ("acceptance") was recirculated continuously through the cell to the feed tank, again through the cell to the feed tank and so on, for a period of 32 to 40 minutes. The acceptance from the flotation cell was subjected to this flotation process until the desired time had elapsed. The flotation time was calculated using the following equation: F = t? (v / V), where F = flotation time (the retention time of the suspension in the flotation cell); t = total operating time; v = capacity of the cell and V = volume of the cell. For this example, F = 40 x (7.5 / 30) = • 10 minutes. During the flotation »sampling was carried out at different times and the degree of de-inking was also monitored visually. After the flotation had been completed, the pulp suspension was washed by pumping the slurry to a consistency of about 1% to a drum washer so that it would drain and thicken to an approximate consistency of 20%. The vacuum applied during the collection and thickening of the pulp is approximately 506 mm of mercury. To prepare brightness pads, a thickened sample was diluted 63.5 g of fiber, based on oven-dried weight (SH)) to a consistency of 0.5% and filtered through a No. 230 filter paper from Reeve Angel, in a Büchner fritted glass funnel under a domestic vacuum pump, such as that described above. Brilliance pads were placed on pressure plates and pressed at 3.4 kg / cm5 * for 2.5 minutes, before being placed in drying rings which are to be dried overnight »in a common conditioning atmosphere, such as it was described in TAPPI T 402 om-66, incorporated herein by reference, in its entirety. The ISO brightness was measured by the Technidyne brightness meter on both the felt side and the wire side of the brilliancy pads after the drying was completed. Four readings were taken on each side of the samples and four samples were used for each data point. The results of the measurements are recorded in table II.

TABLE II Brilliance Brilliance on the side of the piece Wire felt samples After the pulper 43. .9 41.5 2 min of flotation 50., 1 46.4 4 min of flotation 52. .4 50.6 6 min of flotation 54., 6 52.3 6 min of flotation 54. .0 52.7 10 min of flotation 54. 2 53.1 After washing 55. .6 53.2 • EXAMPLE 5 SESUNDO STUDY OF DETNINTING IN PILOT PLANT In order to compare the use of a different surfactant, the same equipment described in example 4 was used. The pulp former was charged with 6.7 liters of water, hot at 46-49 ° C, 19.5 g of NaOH, 32.5 g of sodium silicate, 26 g of Ha0a (50% hydrogen peroxide), 1.95 g of DTPA and 13.0 g of Lionsurf ™ "727" from Lion Industries, Vancouver, Washington. The pulp was formed at an approximate temperature of 46-49 ° C and an approximate consistency of 15%, for 3 to 5 minutes. The remainder of the procedure is the same as that described in example 4. ISO brightness determinations were carried out as described in the example and the data were recorded in Table III. In contrast to the results obtained in example 4, the deinking used in this example 5 gave poorer results than those obtained in example 4. This indicates that a typical deinking agent is not satisfactory for use with newsprint paper. Even with the use of 1% hydrogen peroxide and .15% DTPA, noted above, used to increase the brightness of the pulp, the pulp disentangled in this example 5 was much darker than the de-inked pulp in example 4. see this effect particularly in the data for the wire side of the samples.

TABLE III Brilliance Brilliance on the side of the side Wirewire samples After the pulp former 46.6 30.95 2 minutes of flotation 46.66 35.7 4 minutes of flotation 50.01 36.39 6 minutes of flotation 49.49 35.26 6 minutes of flotation 50. 19 34.32 10 minutes of flotation 49.32 36.19 after washing 54.56 36.29 EXAMPLE 6 MIXED PULP This example describes the effectiveness of the process of this invention when applied to de-inert pulp comprising a mixture of newspaper, some of which was printed with flexographic (water-based) ink and some of which was printed with offset ink (based on of oil). For this example, the waste paper used was 50 percent by weight of the newsprint of the type described in Example 2 and 50 percent newspaper from the Wall Street Journal. All other conditions and procedures are as described in example 4. The results are registered

Claims (7)

In table IV. TABLE IV Brilliance Brilliance on the side of the side Wirewire samples After the pulper 43.9 41.5 2 min of flotation 50.1 46.4 4 min of flotation 52.4 50.6 6 min of flotation 53.2 52.3 6 min of flotation 54 52.7 10 min of flotation 54.2 53.1 after washing 55.6 53.2 NOVELTY OF THE INVENTION CLAIMS

1. A method for de-inking pulp, which has been made from paper printed with flexographic ink, characterized said method because it comprises: a) forming paper pulp with water at a temperature of 25 to 65 ° C under neutral to moderately alkaline conditions; b) dilute the pulp to a consistency of 0.6 to 3.0%; c) mixing the pulp with 0.5 to 3.0 weight percent (based on the oven-dried weight of the pulp) of a surfactant component made by combining from 5 to 95% of a fatty acid or a mixture of fatty acids, selected from the group consisting of fatty acid of 12 to 22 carbon atoms and 95 to 5% of at least one alkoxylated diamine of the formula I: H-X-0 O-W-H \ / N - C = C - N Formula I / \ H-Y-0 O-Z-H wherein X, Y, W and Z may be the same or different and each of them is independently selected from the group consisting of: (i) - (CHa-CH (CHa) -0) m (CHa-CHa-0) t, -; (ii) - (CHa-CHa) e (CHaCH (CHB3) -0) cl; AND (iii) - random copolymers of ethylene oxide and propylene oxide wherein a, b, c and d are each independently selected to be a number between 1 and 30, so as to give a EHL value between 5 and 15; and d) treating said pulp in a flotation cell.

2. A process according to claim 1, further characterized in that the surfactant component comprises from 65 to 50 percent of the fatty acid or mixture of fatty acid and from 15 to 50 percent of said compound of the formula I

3. A process according to claim 1, further characterized in that the surfactant component comprises from 60 to 75% of the fatty acid or fatty acid mixture, and from 20 to 25 percent of said compound of the formula I

4. A process according to claim 1, further characterized in that said fatty acid component is selected from fatty acids of 14 to 20 carbon atoms.

5. A process according to claim 1, further characterized in that the fatty acid component is selected from the group consisting of oleic acid and stearic acid.

6. A process according to claim 1, further characterized in that the consistency of the pulp is between 0.6 and 1.2 percent during the process.

7. A process according to claim 1 »further characterized in that the compound of formula I is a copolymer of ethylene oxide / propylene oxide, based on ethylenediamine, with a total of 47 moles of ethylene oxide and 47 moles of propylene oxide. 6. A process according to claim 1, further characterized in that the process is carried out at a pH of 6.5 to 9.5. 9. A process according to claim 1, further characterized in that the process is carried out at a temperature of 35 to 55 ° C. In testimony of which I sign the above in this City of Mexico, D.F., on the 26th day of the month of August of 1994. BY HOECHST CELANESE CORPORATION ATTORNEY CR / CRG *