JP2009074234A - Method for treating slurry of comminuted cellulosic fibrous material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce fully bleached (typically having a whiteness degree of over 89 or more 90% ISO) cellulose pulp from an environmentally friendly (ECF), yet commercially viabled comminuted cellulosic fibrous material. <P>SOLUTION: A method for producing bleached chemical pulp from comminuted cellulosic fibrous material comprises: (a) treating the material in a chemical pulping process in the presence of chemical additive to produce a chemical pulp containing at least some of the additive; (b) treating the chemical pulp with at least one elemental-chlorine-free bleaching agent to produce a bleached chemical pulp having at least some discoloration due to the presence of the chemical additive; and (c) treating the bleached pulp with at least one oxidizing agent to remove the discoloration produced by the presence of the chemical additive. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for treating pulverized cellulose fiber material.

  In a situation where the environmental impacts of chemical pulp production and bleaching are increasingly concerned, attempts have been made to specifically limit chlorine-containing compounds in the processing of cellulosic materials used to make cellulose pulp used in papermaking. This is especially the case for bleaching cellulose pulp, where instead of using oxidative chlorine compounds, attempts to use more environmentally friendly oxygen compounds such as oxygen, peroxides and ozone. Has been made. For example, a regulation called “Cluster Rules” recently proposed and legislated by the US Environmental Protection Agency (EPA) includes inclusion in both gas and liquid effluents emitted from pulp mills. It limits the emission of certain chemicals related to chlorine bleach.

As a result, a wide variety of complete chlorine-free (TCF) or elemental chlorine-free (ECF) bleaching methods have been proposed, and some methods are used in commercial operation. For example, in TCF bleaching, chlorine-free compounds, particularly chlorine-free (Cl ₂ or abbreviated “C”) or chlorine-free (ClO ₂ , abbreviated “D”) agents are used for pulp bleaching. In ECF bleaching, simpler chlorine dioxide is expelled from the bleaching plant and more environmentally friendly chlorine dioxide is preferred and used. Usually, the TCF bleaching method uses oxygen gas (O ₂ , abbreviation “O”), ozone gas (O ₃ , abbreviation “Z”) and hydrogen peroxide (H ₂ O ₂ , abbreviation “P”), In the ECF bleaching method, chlorine dioxide (D) is also used.

  TCF and ECF bleaching methods are particularly susceptible to poisoning due to the presence of dissolved metal ions such as dissolved iron (Fe), copper (Cu), manganese (Mn) and the like. Not only can these “non-process elements” be concentrated in “closed cycle” bleaching effluents of TCF and ECF bleaching processes, but these metals, especially Mn, are chlorine-free bleaches, especially hydrogen peroxide and pulp. And is recognized as harmful to effective treatment. As a result, it is also desirable to limit the presence of such dissolved metals in the pulp and liquid treatment streams inside and around the pulp mill. A typical processing method used to minimize the presence of these metals is pickling and chelating, for example using conventional chelating agents, especially EDTA and DPTA.

Also, a sulfur-containing compound having a bad odor from a gas discharged from a pulp mill, such as hydrogen sulfide (H ₂ S), methyl mercaptan (CH ₃ SH), dimethyl sulfide (CH ₃ SCH ₃ ), dimethyl disulfide (CH) It is also interesting to reduce emissions of gases including ₃ S ₂ CH ₃ ) (collectively referred to as total reducing sulfur (TRS) gas). These sulfur-containing gases are usually generated in connection with “sulfate” or “kraft” pulp manufacturing methods, where the main pulp-making agents are sodium sulfide (Na ₂ S) and sodium hydroxide (NaOH). is there. An alternative to the kraft method is the “soda” method, in which the active pulp producing agent is limited to NaOH and sulfur-containing agents are not used in pulp production (although some sulfur is either via raw wood or from the factory) It may be introduced via oil that is made by a boiler).

  However, it is recognized that the soda method produces a product with slightly inferior quality compared to the craft method. That is, the soda process usually produces a pulp with a lower yield and inferior strength properties than the kraft process. In order to address this limitation of soda processes, attempts have been made to improve the quality of the pulp produced by introducing strength or yield improvers into the soda process. The most famous one is known as the “soda AQ” method of introducing anthraquinone (AQ), but the success has been limited.

  A recently recognized effect is the undesirable “yellowing” of pulp obtained by AQ treatment, the effect obtained by treating cellulose material, ie wood chips, with AQ. That is, the fact that the pulp produced in the presence of AQ had a yellow or orange color, which is undesirable for pulp that has been fully bleached. It has been recognized in the present invention that an effective way to reduce or eliminate this undesirable discoloration is to treat pulp treated with AQ with an oxidant such as air, oxygen gas, peroxide or most preferably. Treatment with ozone gas.

  Furthermore, recently recognized are US Pat. Nos. 5,489,363, 5,536,366, 5,547,012, 5,575,890, 620,562, 5,662,775, etc., and Andritz-Ahlstrom Inc. of Glens Falls, NY are trademarks of Low Solid (LO). -SOLIDS) the method of sale under the manufacture of cellulose pulp with improved strength properties (shown as increased viscosity), especially compared to pulp produced by conventional methods, compared to the soda method That is. It is also known that the use of ozone has a negative effect on pulp viscosity. Therefore, in the embodiment of the present invention that employs the low solid cooking method and the AQ treatment, it is possible to counteract the negative effects of soda cooking and ozone bleaching on the quality and strength of the produced pulp.

  Thus, the present invention eliminates or minimizes sulfur present in the pulp manufacturing process and chlorine present in the bleaching process while maintaining quality (ie, the strength and yield of the manufactured bleached pulp). Or, by modification, a method is provided for producing fully bleached cellulose pulp from comminuted cellulose fiber material that is environmentally friendly and commercially viable.

  One aspect of the present invention is: (a) a step of treating a cellulosic material using an ozone-containing gas in the first stage, and (b) a cellulosic material using a chlorine dioxide-containing liquid in the second stage. A process for producing a bleached chemical pulp, wherein a cellulosic material is provided between steps (a) and (b). Is treated with an alkaline solution, the pH of the cellulose material is raised before step (b), and no washing is performed between step (a) and step (b). Preferably, between step (a) and step (b), the pH of the cellulosic material is raised to at least about 6.0, preferably at least 7.0. The present invention can be expressed as a symbol (ZEND). Here, Z indicates that an acidification treatment is performed with an ozone-containing gas, EN indicates an alkali neutralization treatment, and D indicates an alkali neutralization treatment with chlorine dioxide. Of course, no washing is performed between these processing steps.

  In the present invention, the alkali neutralization treatment, EN, performs at least two recognized functions. First, raising the alkalinity to approximately neutral pH, i.e., in the range of about 6-8, preferably about 7, will solubilize the reaction product from the previous Z step. For example, the lignin-containing compound oxidized in the Z step is kept in a solution state by adding an alkali to the ozone-treated pulp. In the conventional alkaline extraction process, these solubilized compounds are removed before further processing in subsequent pulp washing, but in the present invention washing (the term “washing” may be compressed or concentrated). So that the solubilized lignin-containing compound is sent to the next alkaline chlorine dioxide treatment. The lignin-containing compound can be removed later in the washing step following the chlorine dioxide step. Second, when alkali is introduced in the neutralization step, the pH of the pulp can be raised to a range that is more suitable for the subsequent alkali D step. It is known in the art that it is preferable to start the chlorine dioxide treatment in an alkaline state, but during chlorine dioxide treatment the pH usually decreases as acid is generated. That is, the alkali introduced into the EN process partially offsets the amount of alkali that needs to be added to adjust the pH in the D process. In the present invention, not only a more effective treatment of the obtained pulp, that is, a more effective removal of the chromogenic compound, but also the need for an expensive washing device is eliminated.

  In a preferred embodiment, prior to step (a), the cellulosic material is treated in an alkaline chemical pulp manufacturing process, preferably a pulp manufacturing process that is substantially free of sulfur, such as a soda pulp manufacturing process. The alkaline pulp production process also preferably uses strength enhancers or yield improvers, such as anthraquinone or polysulfide, or equivalents or derivatives thereof. A preferred additive is anthraquinone, abbreviated AQ. This is because AQ is known to compensate for the yield reduction characteristic of the soda method compared to the kraft method. Further, the alkaline pulp production method preferably comprises a bulk delignification step, and the production method comprises at least one step before or during the bulk delignification step. In this step, the liquid containing the first level of dissolved organics is removed from the cellulosic material and replaced with a second liquid having a lower level (eg, at least 50% lower) of dissolved organics. These are described in the aforementioned patents (the disclosures of which are incorporated herein by reference).

  Further, it is preferable to provide a step (c) a step of treating the cellulose material with a chlorine dioxide-containing liquid before the treatment of step (a), and then a step (d) of treating the cellulose material with an alkaline solution. Specifically, the treatment step (c) is a chlorine dioxide (D) treatment, the step (d) is treated with an alkaline solution, and the oxidation product produced in the step (c) is solubilized and extracted ( E) is preferable. The alkaline liquid of step (d) is usually sodium hydroxide. That is, one of the preferred embodiments is the bleaching sequence D-E- (ZEND). Here, the washing is performed before, during and after the first D process and the first E process (as indicated by the hyphen in the bleaching sequence display above), but between the Z, EN and D processes. Is not done (as shown in the bleach sequence display above with these symbols in parentheses closed without hyphens). The initial treatment (E) with the alkaline liquid can involve the use of oxygen, peroxide or both. That is, this step may be Eo, Ep, or Eop.

  Another aspect of the present invention includes: (a) treating a cellulosic material with a chemical pulping process in the presence of a chemical additive to produce a chemical pulp containing at least some additive; and (b) at least Treating the chemical pulp with one single chlorine-free bleach to produce a bleached chemical pulp having at least some discoloration due to the presence of a chemical additive; and (c) at least the bleached pulp, A method is provided for producing bleached chemical pulp from comminuted cellulose fiber material comprising the step of treating with one oxidizing agent to remove discoloration in the presence of chemical additives. In a preferred embodiment, the chemical additive used in the pulp production process of step (a) is anthraquinone or an equivalent or derivative thereof. A characteristic of pulp discoloration due to the presence of an additive, usually AQ, is the yellow or orange hue applied to the pulp.

  The at least one bleach used in processing step (b) is preferably one or more of the following bleaches: oxygen, chlorine dioxide, sodium hydroxide, ozone, hydrogen peroxide, but at least chlorine dioxide Most preferably. The oxidant used in process step (c) is usually air, ozone, oxygen or peroxide, but is preferably an ozone-containing gas.

  According to another aspect of the present invention, a sequence for cooking soda / AQ followed by one of D-Ep- (ZEND), D-Eo- (ZEND) or D-Eop- (ZEND) A method of performing ECF treatment of a pulverized cellulose fiber material is provided. The pulp thus produced has a brightness of at least ISO 89% or 90% and a viscosity of more than 21 cP or 22 cP.

  Thus, according to the present invention, there is provided a method used to produce fully bleached cellulose pulp from comminuted cellulose fiber material that is environmentally friendly and commercially viable. Since the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, the invention is not limited to the disclosed embodiments, but on the contrary, various modifications. It is to be understood that only combinations and equivalent combinations and methods are included and are limited only by the prior art.

1 is a schematic diagram of one complete pulp production system according to an exemplary embodiment of the present invention. FIG. FIG. 2 is a detailed view of a subsystem of the pulp production system of FIG. 1. FIG. 3 is a graph of viscosity versus whiteness showing the properties of a pulp made according to the present invention compared to many prior art methods. It is a graph similar to FIG. 3, and is a graph which plots and shows whiteness versus chlorine dioxide consumption.

  FIG. 1 shows a schematic diagram of a typical fully environmentally friendly and commercially viable fiber or cellulosic material processing system 10 of the present invention. A comminuted cellulose fiber material 11, usually a hardwood or softwood chip, is introduced into the digester 12. Most forms of comminuted cellulose fiber material can be treated with the present invention. Although the present invention is most preferably processed in a continuous digester, the digester 12 can be a batch digester. According to a preferred embodiment of the present invention, the pulp production process is preferably a sulfur-free cooking process, preferably a soda / AQ process. Caustic soda, i.e. sodium hydroxide, is introduced into the digester 12 along with the chips via conduit 13 and AQ or its equivalent or derivative thereof is introduced via conduit 14. The treated pulp is discharged from the digester to the conduit 15.

  As is conventional, the digested pulp is processed in one or more brown coarse pulp washers 16 to recover a portion of the cooking chemical and clean the pulp slurry prior to subsequent processing. The cleaned pulp is optionally sent via conduit 17 to alkaline oxygen delignification step 18 and then via conduit 19 to post-oxygen delignification washing step 20. The oxygen treatment is preferably carried out in one or more stages with a moderate consistency, i.e. about 8-18% pulp consistency. The washed pulp is sent to the subsequent treatment through the conduit 21 regardless of whether it has been subjected to oxygen treatment.

The conduit 21 sends the pulp to the first formal bleaching step 22. Preferably, this step is an alkaline chlorine dioxide treatment D _0. This treatment 22 has a moderate or low consistency, i.e. about 0.5-18%, preferably about 2-8% (and all other narrow ranges within this wide range) of pulp consistency. Can be done in tensy. The treated pulp is then sent via a conduit 23 to a washer 24. The washer 24 can be any form of conventional washer, such as a vacuum drum washer, a washer press, a diffusion washer, or a belt washer. The cleaning with one or a plurality of cleaning machines 24 may be performed with a low or medium consistency as in the prior art.

  The washed pulp is then sent via conduit 25 to an alkaline extraction step (E) 26 (which can be an Eo, Ep or Eop step). This step is a conventional alkali treatment using sodium hydroxide to solubilize the reaction product of step 22. Pulp from the extraction step 26 is sent via conduit 27 to another conventional washing step 28 similar to step 24. The washed pulp is sent to the ozone treatment process 30 via the conduit 29.

  Process steps 30, 34 and 38 constitute the broadest aspect of the present invention. In step 29, the pulp is treated with ozone-containing gas introduced via conduit 31. The pulp has a medium consistency (eg, about 6-18%), but may be low consistency (0.5-5%) or high consistency (greater than 18%). This ozone-containing gas is usually generated and introduced at a concentration higher than 5%, usually in the range of about 5-15%, using a carrier gas such as oxygen or air. This ozone-containing gas is usually generated and used internally, but can be supplied from an external source. This ozone-containing gas is normally supplied under pressure to a high-strength mixer, such as an AMZ mixer manufactured by Andritz-Ahlstrom, Glens Falls, NY. The treatment of step 30 is usually performed in an acidic environment, usually at a pH below 5, preferably in the range of about 2-3. After the ozone treatment 30, the treated pulp is sent to the alkali treatment step 34 via the conduit 32. If desired, the amount of gas introduced into the pulp via conduit 31 is relatively large so that some degassing 33 can be performed after treatment 30 and before treatment 34, although washing (this term is Do not squeeze or concentrate).

Alkaline treatment 34 is usually the exposure of ozonated pulp to alkali introduced via conduit 35, usually NaOH, for a relatively short time. The residence time of treatment 34 is usually less than 30 minutes, preferably less than 15 minutes. As discussed above, the treatment 34, among other things, neutralizes the acidic pulp discharged from the treatment 30, so that the reaction product of the treatment 30 is maintained in a dissolved state. The pH of step 34 is usually in the range of about 6-8, preferably about 7. However, unlike the prior art, these solubilized compounds not washed off from the pulp even after the process 34 is sent directly to the alkali treatment 38, D ₁ via conduit 36. As before, some degree of deaeration 37 can be performed between steps 34 and 38 if desired. Unwashed pulp is sent to treatment 38 via conduit 36 and treated with chlorine dioxide, ClO ₂ . Chlorine dioxide is introduced into the pulp via a conduit 39 and a mixer (see mixer 59 in FIG. 2), for example a conventional high strength mixer.

  The treated pulp is then sent via conduit 40 to the conventional washing step of step 41 and then, if desired, via conduit 42, for example, a bleaching step that does not contain more elemental chlorine (as a result of the overall pulp processing). ECF), storage tank, if the factory is an integrated production paper mill, it is sent to the raw material preparation before the paper machine, or if the factory is a pulp sales factory, it is sent to the pulp dryer.

  FIG. 2 shows a special embodiment of steps 30, 34 and 38 shown in FIG. The structure of FIG. 2 that is similar to that of FIG. 1 is identified with a similar reference number, but in FIG. 2 the reference number is prefixed with the number “1”. For example, conduit 129 in FIG. 2 is substantially the same as conduit 29 in FIG.

  The pulp flowing from the washer 28 of FIG. 1 is introduced into the treatment 130 via the conduit 129 in FIG. Process 130 is preferably performed in mixer 50. Ozone-containing gas, usually ozone in oxygen carrier gas, is sent to the mixer 50 via a conduit 131. The ozonation step is usually performed at a temperature below 100 ° C., for example about 20-70 ° C., depending on the energy balance of the system. Acidic ozone treatment 130 is typically performed at a pH below 5, preferably between about pH 2-3. However, the ozone treatment 130 can be performed at pH higher than pH 5, or even pH higher than pH 7 if ozonolysis and cellulose damage can be avoided or minimized at such high pH values.

  The ozone-treated pulp is discharged from the mixer 50 to the conduit 132. The reaction of ozone with the pulp is very rapid, for example, this reaction usually occurs in less than 30 seconds, so a holding tank is usually not required after the mixer 50, and the ozonated pulp is an alkali neutralization step. Sent directly to 134. However, the holding tank 51 can be used after the mixer 50 if desired. Although not shown in FIG. 2, the pulp may be degassed after the mixer 50 and before step 134.

  The ozone-treated pulp is introduced into the alkali neutralization step 134 via the conduit 132. Treatment 134 is performed by introducing alkali, preferably NaOH, into conduit 52 via conduit 135, again preferably into a high intensity mixer. Again, because the reaction between ozone and pulp is rapid, especially at moderate consistency, the alkali in conduit 135 can be introduced directly into mixer 150 via conduit 62 and conduit 131. In a special embodiment of the present invention, the mixer 52 can be removed and ozone-containing gas and alkali can be introduced into the mixer 50.

  Given the embodiment shown using two mixers 50 and 52, the pulp is discharged from conduit 53 after introducing alkali into the pulp via mixer 52. The pulp is typically held in this alkaline state at a temperature of about 20-70 ° C, preferably about 50-70 ° C, for at least about 15 minutes, preferably at least about 30-60 minutes. This holding is performed in a normal holding tank (not shown) or the pump supply chute 54. In a preferred embodiment, any suitable conventional method may be used, but at least some degassing of the pulp 137 occurs when the pulp is introduced into the feed chute 54. The pulp can be degassed with a specially designed rotary degasser if desired.

  The pulp is pumped from the supply chute 54 or holding tank (not shown) via the pump 55 to the chlorine dioxide treatment 138. The pump 55 is preferably a degassing type pump from which gas is removed via a conduit 56. Pump 55 transfers pulp from conduit 57 to mixer 59. Again, this mixer is preferably a high-strength mixer, into which chlorine dioxide is introduced via conduit 139. If desired, the pulp in conduit 57 can be heated by introducing steam through conduit 58. The pH of the pulp discharged into the tank 61 is usually at least 5 and preferably at least 6. Further alkali can be added to the pulp, for example via conduit 63. Chlorine dioxide is thoroughly mixed with the pulp in the mixer 59 and discharged to the holding tank 61 via the conduit 60. The alkaline and chlorinated pulp is held in a conventional holding tank (eg, upward flow tank) 61 for at least one hour. The pulp is usually held at a temperature of about 20-70 ° C, preferably about 50-70 ° C for about 1.5-6 hours, preferably about 2-4 hours. The treated pulp is discharged via conduit 140 to a conventional washer 141, washed, and then sent via conduit 142 for further processing as previously discussed.

  FIG. 3 shows a graph plotted for three different processing scenarios. Reference numeral 70 indicates a D-Eop- (ZEND) processing sequence according to the present invention, 71 indicates D-Eop-DP, 72 indicates D-Eop-D. It is a kind of prior art procedure. As can be seen, the process 70 of the present invention achieves whiteness comparable to that of procedure 71, yet has a much higher viscosity and is actually equivalent to that shown at 72. In all of the procedures 70, 71 and 72 shown in FIG. 3, the raw pulp prior to the treatment sequence is a mixed solid-leaved pulp of LO-SOLIDS® cooked oxygen delignified up to 9 kappa. The exact same raw pulp was used for each treatment 70, 71 and 72.

  FIG. 4 is a graph of the same pulp and treatment sequence as in FIG. 3, in which the whiteness is graphically displayed with respect to chlorine dioxide consumption. As can also be seen here, the procedure 73 of the present invention is comparable in brightness to that of procedure 74, has a much higher brightness than procedure 75, and the consumption of chlorine dioxide is approximately the same (slightly higher). It is.

  As is apparent from FIGS. 3 and 4, the processing sequence DE (usually Eo, Ep or Eop)-(ZEND) of the present invention has a whiteness of at least ISO 89% or 90% and a viscosity of at least 21 cP or 22 cP.

  The present invention includes all specific narrow ranges within the broad range described above. For example, consistency 6-18% means 6-12%, 8-11%, 9-18%, and all other narrow ranges within this wide range.

  Thus, the present invention provides an environmentally friendly and commercially viable method for producing fully bleached cellulose pulp from comminuted cellulose fiber material. Since the present invention has been described with respect to what is presently considered to be the most practical and preferred embodiments, the present invention is not limited to the disclosed embodiments, and conversely, the spirit of the invention and the claims. It should be understood that it includes many partial modifications and equivalent combinations and methods that fall within the scope.

Claims (9)

A method for producing bleached chemical pulp from comminuted cellulose fiber material,
(A) treating the cellulosic material with a chemical pulp manufacturing method in the presence of a chemical additive to produce a chemical pulp containing at least some additive;
(B) treating the chemical pulp with at least one elemental chlorine-free bleach to produce a bleached chemical pulp having at least some discoloration due to the presence of chemical additives;
(C) treating the bleached pulp with at least one oxidizing agent to remove discoloration suffered in the presence of chemical additives;
A process for producing bleached chemical pulp from comminuted cellulose fiber material. 2. The method according to claim 1, wherein step (a) is performed using anthraquinone or an equivalent thereof or a derivative thereof as a chemical additive used in the pulp production method. 2. The method of claim 1, wherein step (b) is performed using at least one bleach as one or more of the following bleaches: oxygen, chlorine dioxide, sodium hydroxide, ozone, hydrogen peroxide. A method characterized by that. The method of claim 1, wherein step (b) is performed such that the discoloration is characterized by a yellow or orange hue applied to the pulp. The method of claim 1, wherein step (c) is performed using at least one of air, oxygen, peroxide, or ozone as the oxidant. 3. The method according to claim 2, wherein step (c) is performed using ozone-containing gas as an oxidizing agent, step (a) is a soda / AQ pulp manufacturing method, and step (b) is at least one bleaching agent as described below. Bleaching agent: A method characterized by being carried out using one or more of oxygen, chlorine dioxide, sodium hydroxide, ozone, hydrogen peroxide. A method for ECF treatment of comminuted cellulose fiber material includes a sequence of performing soda / AQ cooking followed by D-Ep- (ZEND), or D-Eo- (ZEND) or D-Eop- (ZEND). An ECF treatment method for a pulverized cellulose fiber material. 8. A method according to claim 7, characterized in that the treatment is carried out so as to produce pulp with a whiteness exceeding ISO 89%. 9. Pulp produced as claimed in claim 8, having a viscosity of over 21 cP.

Images