FI80730C - Mass cooking process and composition used therein - Google Patents

Description

1 80730

This invention relates to alkaline cooking and in particular to the use of additives in alkaline cooking to increase pulp yield.

Alkaline cooking comprises methods in which a plant material containing cellulosic fibers is treated with temporal aqueous solutions. Since the most common alkali method is the sulfate or kraft method, in which wood is treated at a temperature above 160 ° C with a solution containing Na 2 S and NaOH, a preferred embodiment of the present invention will be presented according to the kraft method, although it can be applied to any alkaline cooking. .

In the conventional kraft process, lignocellulosic materials, such as wood chips, are treated with a fresh cooking solution (white liquor) consisting of an aqueous solution of Na 2 S and NaOH under certain temperature, pressure and time conditions. By completing the cooking diagram, the cooked pulp is washed to remove used chemicals and dissolved wood. The washed mass is screened and / or ground to remove or decompose the undercooked material. The pulp is stored until it is pulled directly into paper products as required or is brought to produce conventionally bleached paper products.

The waste liquor from the cooking process is called weak black liquor, which contains spoiled or dissolved wood and inorganic salts. Some black liquor can be used. *** for regulating the volume and concentration of cooking liquor.

The purpose of the cooking process is to chemically decompose and dissolve the binder lignin and on the other hand to preserve the carbohydrate fraction. Lignin is a high molecular weight polymer that gives wood its structural strength by bonding cellulose fibers together. In the Kraft process, during delignification, the other components of the fibrous raw material are dissolved to a degree determined by the process conditions. Ideally, the cooking should be performed so that the lignin dissolves selectively without dissolving or degrading cellulose or other carbohydrates.

Numerous chemical additives and broth modifications have been used to achieve some increase in pulp yield. When talking about an increase in yield, it should be remembered that the goal is to increase the yield of ingredients other than lignin. It is entirely possible and practically common to increase the yield by terminating the cooking reactions at an early stage. Thus, more starting material remains, including lignin. Increasing the yield by this method involves a discrepancy between the yield and the quality of the pulp. Virtually any end product has a limit value for residual lignin above which the quality of the product is rejected.

Among the additives and modifications that achieve increased yield at the same lignin content are polysulfide, hydrogen sulfide pretreatment, and numerous other agents that stop the "peeling reaction" in which carbohydrates decompose and dissolve.

Much interest has been focused on the finding that anthraquinone, when added to kraft broth, facilitates the dissolution of lignin and suppresses the dissolution of carbohydrates. This finding is disclosed in U.S. Patent 4,012,280. It is believed that anthraquinone acts as a catalyst, intermittently in a form that facilitates delignification and occasionally in a form that stabilizes carbohydrates from alkaline degradation. While the use of anthraquinone in alkaline cooking represents an improvement in efficient cooking by providing an increase in yield with a given lignin content, anthraquinone does not provide complete protection for carbohydrates.

3,80730 U.S. Patents 4,115,186 and 4,080,248 disclose that molecular oxygen and a salt of a divalent or monovalent metal, especially Ca 2 O 4 in the former and Na 2 CO 2 in the latter, whiten the pulp and improve overall cooking performance.

In particular, the above patents do not disclose an increase in pulp yield due to the addition of a calcium salt and an oxidizing agent. U.S. Patents 3,695,994 and 3,384,533, on the other hand, disclose that the simultaneous addition of molecular oxygen and CaCl 2 increases pulp yield in calcium-depleted pulping systems where the need for a stabilizer occurs.

A paper was recently presented at a scientific meeting in Europe attended by researchers in the paper and pulp industry who underlined the unexpected and advantageous nature of the current invention (Johnson, Eckert and Mark ... Factors Influencing Performance of Quinone Promoters in Alkaline Delignification of Douglas Fir ... Stockholm , Sweden, International Symposium on Wood and Pulping Chemistry -The Ekman Days, June 1981). In the text of this publication (Figure 5 and its comments), the Cu, Co, Ni and Mg complexes of 1-hydroxy-anthraquinone are discussed by experts. These complexes were prepared according to the method of Johnson et al. with the aim of increasing the catalytic activity of 1-hydroxyanthraquinone in alkaline cooking. The summary of their report was that such complexes did not prove to be superior to 1-hydroxyanthraquinone alone, which in itself is a relatively ineffective cooking catalyst.

Therefore, the simultaneous finding of a new broth additive that increases the pulp yield from the lignocellulosic material proves the fact that the broth additive analogs of the invention, in increasing the pulp yield, do not appear to work as achieved by the present invention. This actually leads 4,80730 experts in the field out of the observation that certain metal salts with anthraquinone provide unexpected and beneficial effects.

With reference to the above, the aims and purposes of the research work will now be described in general terms and in detail, as well as how it achieved an unexpected and cost-effective improvement in pulp production.

The main object of the invention is to provide a new and unique catalytic additive * for cooking solution, the main advantage of which is an unexpected increase in the mass yield from the raw material.

It is a very specific object of the invention to provide a novel and unique broth catalytic additive containing anthraquinone and a divalent metal cation selected from the group consisting of Ca, Ba, Mg, Sr and Zn.

A secondary object of the invention is to provide a new and improved process for the production of pulp from a number of available raw materials, in particular pine chips, in a manner which allows the use of the currently available vegetable material without major modification.

More particularly, the present invention comprises a method in which a ligno-cellulosic material is boiled in an alkaline cooking solution containing anthraquinone and a metal salt selected from the group consisting of Ca, Ba, Sr, Mg and Zn, and further waste liquor obtained from the digester.

These and other relevant objects will become apparent from the following description of the invention in more detail and from the new examples of embodiments of the invention and the results and conclusions obtained therefrom.

Numerous drawings are further presented to illustrate the method that has resulted in the improved result. These drawings 5 80730 will be explained during the general presentation of the invention, which will appear in the examples of the new method.

Figures 1 and 2 show the effect of the addition of CafOH 2 to anthraquinone on the kappa / yield ratio in the kraft method.

Figures 3 and 4 show the effect of kraft black liquor feedback on the magnitude of the increase in yield achieved with kraft / anthraquinone and kraft / anthraquinone / Ca (OH) 2 soups.

Figure 5 shows the effect of the addition of CafOH® with anthraquinone on the kappa / yield ratio in soda soup.

Figures 6 and 7 show the effect of metal cations other than Ca with anthraquinone in alkaline cooking.

Figure 8 shows the effect of metal cations in alkaline cooking without anthraquinone.

The present invention relates to the finding that the ability of anthraquinone to increase yield in alkaline cooking can be increased simultaneously by the addition of a divalent metal salt, which increases the effectiveness of anthraquinone in protecting carbohydrates during alkaline cooking and thus provides increased wood fiber yield by several percentage points. Comparing this to the conventional kraft method, the combined effect of anthraquinone and the divalent metal salt results in a significant increase in mass yield. Since the addition of a divalent metal salt to the kraft cooking liquor has little or no effect on pulp yield, the divalent metal salt is said to catalyze anthraquinone in the process of the invention.

The amounts of the various substances in the cooking solution according to the invention are not very critical and can vary, for example, between 0.01 and 1.5% by weight of the 6 80730 lignocellulosic material to be treated for anthraquinone and between 0.01 and 10.0% by weight for the metal salt selected. from the group: Ca, Ba, Sr, Mg and Zn. Waste liquor can be added up to 50% by volume. The addition of anthraquinone and the metal salt has no upper limit, but in practice the point of decreasing yield is reached by these limit values. With respect to the lower limits, there should be sufficient anthraquinone and a metal salt to ensure the use of these additives to provide a sufficient increase in yield.

Preferably, the divalent metal salt is Ca (OH) 2 and the anthraquinone is generally 0.05-0.15% of kiln-dried wood and Ca (OH) 2 0.1-0.5% of kiln-dried wood. The relative amounts of these additives can be varied to some extent without loss of additional benefit in the yield obtained by using these additives together, although the amount of increase in yield may vary. To achieve the optimal result, black liquor, i.e. soup waste liquor, is used with additives. A small increase in yield is obtained when black liquor recycling is used and this is due to the increased solubility of the calcium salt in the early stages of the cooking process. Black liquor recycling is normal in practice when using intermittent digesters and amounts to 10-50% by volume of the total broth. In this case, the desired liquid / wood ratio is achieved without the addition of additional water. Thus, when the additives of the invention are used, the recycling of black liquor provides an additional advantage by dissolving the metal salt.

The use of a divalent metal cation with anthraquinone is apparently critical, as demonstrated by the finding that other metal cations were either not as effective or completely ineffective with respect to calcium in terms of yield increase when used with anthraquinone. For example, the monovalent lithium cation and the trivalent aluminum and boron cations did not show an increase in yield, which was obtained with anthraquinone alone, while the divalent metal cations showed an increase in yield. Ba, Zn and, to a lesser extent, Mg and Sr were effective in increasing the yield of 7,80730 with anthraquinone when used in kraft cooking. Ca was most effective when compared to the equimolar addition of the metal cation.

It is hypothesized that quinones other than anthraquinone, such as tetrahydroanthraquinone, which act like anthraquinone, would also have the ability to stabilize carbohydrates during alkaline cooking while the Ca cation is added simultaneously. Compounds that act similarly to anthraquinone, including those that oxidize carbohydrates and reduce lignin intermediates that are formed during cooking and thus prevent condensation of lignin intermediates during cooking. Such compounds include cyclic keto compounds, as disclosed in U.S. Patent 4,012,280. The source of the addition of anthraquinone to the divalent metal and its versatility in use with similar quinones is believed to be the ability of calcium to catalyze rearranged dicarbonyl sugars to alkali-stable aldonic acids. It has been shown in the literature that alpha-dicarbonyl sugar, glucosone, treated with CatOH® is converted primarily to mannonic acid, whereas treatment with NaOH favors the formation of arabinonic and erythronic acids, which are not as stable as mannonic acid in an alkaline medium (Lindberg, B, Acta Chem Scand 22 1968 p. 1782). In the anthraquinone-catalyzed case, the yield increases, which is believed to be due in part to the cyclic mechanism in which anthraquinone catalyzes the oxidation of decreasing end groups of carbohydrates to form dicarbonyl sugar as intermediates, which then rearrange in the presence of alkali to form aldonic acid groups. The formation of these acid end groups stabilizes the carbohydrates from degradation that would otherwise occur. These acids, whose stability varies during the cooking process, can decompose and re-subject carbohydrates to alkaline decomposition. The ability of calcium and apparently also the ability of other divalent metal cations to react with these dicarbonyl sugar intermediates in favor of the formation of more alkali stable acids is thus believed to be the reason for the increase in yield. Therefore, the yield, also catalyzed by other quinones that behave chemically like anthraquinone, increases in the presence of calcium.

This should therefore be taken into account when emphasizing the results of the present invention using anthraquinone and C aOH® together, the scope of the invention including: (1) The use of anthraquinone in combination with CaiOH 2, including calcium salts such as CaCl 2.

(2) Use of anthraquinone with another divalent metal cation such as Zn, Ba, Sr and Mg.

(3) Use of the above grain metal cations with quinones other than anthraquinone, which in themselves have a yield-increasing effect.

The tabulated data in Table 1 below illustrate the relationship between pulp yield and kappa number in kraft and soda soups. The data are obtained from several of the following examples as well as the proportional curves of the improvements in pulp yield described in the drawings. The data show the reaction conditions of several pilot plant runs in relation to varying reaction conditions, both in kraft or soda soup and unmodified or modified according to the present invention. The process conditions for each run are proportional to the mass yield versus the number of pieces and can be compared to a control run in which an additional quinone promoter combination for which a patent is sought was used.

The runs marked "kraft" in Figure 1 and Example 1 were, for example, control runs. Similarly, runs labeled "kraft / Ca" and "kraft / AQ" were control runs where each of the components of the new broth additive was used alone.

"Kraft / AQ / Ca" represents the runs of the invention and the improved pulp yield conditions.

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Example 1

Effect of anthraquinone and CaOr-catalyzed broth in the kraft method

To illustrate the additional effect of the new practical combination in the kraft cooking method, runs were performed on a pilot paint cooker using the new cooking method. This example shows the best or preferred operating model of the cooking method. 17,000 g of southern pine chips with a moisture content of about 48% were placed in a 67.5 l draw digester. The chips were screened and thoroughly mixed. Chips larger than 2.86 cm and smaller than 0.48 cm were discarded. To the digester were added: a) 33.3 l of conventional kraft white liquor with 42.9 g / l of active alkali and 29% sulphidity; b) 3.5 l of kraft black liquor obtained after separation of the soap with a solids content of 25% and NaOH calculated as Na 2 O of about 5.3 g / l and Na 2 S calculated as Na 2 O of about 10.7 g / 1; c) 8.73 g of anthraquinone and; d) 61 g of lime (CaO). The anthra-quinone was added to a digester filled with chips, followed by the addition of a mixture of lime and black liquor, followed by the addition of white liquor. Taking into account the wood moisture, the total volume of the liquid was 45 l, corresponding to a liquid / wood ratio of 5.2.

The digester was heated to 173 ° C for 60 minutes and maintained at this temperature for a predetermined time (10-70 min) depending on the desired Kappa number. After cooking, the chips were blown into a blow tank; followed by chip washing.

The pulp yields in this way were 2-3% higher than those obtained with kraft boil without additives and 1-1.5% higher than those obtained when only anthraquinone was used as an additive.

It was rather unexpected that the addition of the AQ / CaO combination gave results which the addition of the individual components could not achieve. CafOH ^ sn or 15 80730

The addition of CaO to the white liquor does not significantly increase the mass yield, nor does the known addition of anthraquinone achieve the same synergistic effect as that obtained with the combination of additives. The combination of additives appears to inhibit the formation of arabinonic and erytric acids, and cause the formation of mannonic acid end groups. Mannic acid is much more alkali stable and is believed to prevent carbohydrates from "hatching" and alkaline acidification during cooking, resulting in increased pulp yield.

Example 2

Effect of CaCOH 2 sn addition on kappa / yield ratio, in the presence of anthraquinone, in kraft cooking.

The effect of CafOH® sn as a cooking additive on the kappa / yield ratio in kraft and kraft / AQ cooking is shown in Figures 1 and 2. Anthraquinone was used in 0.1% kiln dry wood and Ca (OH) 2 0/5% kiln dry wood calculated as Ca ++: as. Cooking was performed in a 67.5 L pull-plant pilot kitchen using 16.8-18.1 kg of wood chips with a moisture content of about 50%. The data / shown in Figures 1 and 2 were obtained by cooking two different Southern pine species. Cooking conditions and results are shown in Table 1.

In both cases, the ability to increase the yield with small amounts of Ca (OH) 2 is clearly detectable. The increase in pulp yield, with a kappa number of 50-100, is 2-3% points in kraft soup and 1-1.5% points when anthraquinone was used alone,

Comparing the results obtained from two different tree species, it can be seen that the total addition with the lignin content given in the yield differs slightly. Differences in final yield obtained for different wood species in alkaline cooking are quite common and such differences can be considered as characteristic differences in wood chemistry. It should also be noted that the increase obtained with anthraquinone alone differs slightly for the two wood species, as did the kraft pulp yield compared to the given number of pieces.

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Example 3

Effect of Kraft Black Liquid on Yield Increase in Kraft / AQ and Kraft / AQ / Ca Soups Using the same cooking conditions as in the previous examples, cooking experiments were performed using additives with and without kraft black liquor. In soups using kraft black liquor, the amount of black liquor was 7% by volume of the total cooking solution. Black liquor was obtained from kraft soup and contained 25% solids. Soap had first been removed from the black liquor before being used for these studies.

The results of this study are shown in Figures 3 and 4, which show that the use of black liquor had no effect in kraft / AQ cooking, which is consistent with observations from the literature, but in kraft / AQ / Ca cooking, black liquor had an obvious effect on pulp yield.

1 Since this additional advantage may be due to the increased solubility of the Ca cation by forming complexes with organic compounds such as phenol, acids, sugar, etc., it could be that introducing black liquor into a pilot plant digester produces small amounts of polysulfide which can affect pulp yields.

The purpose of this presentation is to show that the optimum benefits are obtained by using black liquor with anthraquinone and CaiOH 2.

Example 4

Effect of addition of CaiOH on the kappa / yield ratio with anthraquinone in soda broth

By proceeding in the same manner as in the previous examples, cooking experiments were performed using a combination of anthraquinone 17 80730 and Ca (OH) 2 seedlings in temporal soups than in kraft cooking and comparing the results obtained when anthraquinone was used alone and no additives were used at all. The results of this experiment are shown in Figure 5. To achieve the optimal result, soda soup black liquor was used.

These results suggest that the benefits are obtained by using both additives together in an alkaline cooking other than kraft cooking.

Example 5

Effect of metal cations other than Ca with anthraquinone in alkaline cooking

In order to determine whether metal cations other than calcium had similar activity to anthraquinone, or whether calcium had a unique ability to synergistically with anthraquinone to increase pulp yield, cooking experiments were performed with other divalent metal cations and also monovalent and multivalent metal cations.

The procedure was similar to that in several previous examples, in which the amount of metal cation was kept constant. Comparison of different metals was made based on equimolarity.

Among the metals used were: Mg in the form of MgO,

Ba Ba (in the form of OH ^, Zn in the form of ZnCOgtn, Sr in the form of SriOH ^ sn, in the form of BH ^ BO ^ n, Li in the form of LiCl and Al in the form of AKOHl. Ca as CaO and AQ without metal additives were also as control. kraft black liquor was used.

The effect of different divalent metal compounds on the kappa / yield ratio of kraft / AQ fiber is shown in Figure 6 and the effect of monovalent and multivalent metals in Figure 7. In these figures, pulp yields were corrected for ash content. is 80730 den by removing any ash precipitate contained in the pulp in determining the final pulp yields obtained.

These results indicate that although Carlia did not have the unique ability to synergistically co-anthraquinone increase pulp yield, it was nonetheless most effective when compared to other metals, based on equimolarity.

Barn and Zn were found to be effective while Mg and Sr were less so. Monovalent Li and trivalent B and AI were not effective, thus indicating that the nature of the cation used is critical.

Example 6

Effect of the use of metal cations without anthraquinone in alkaline cooking

As an indication that this invention relates to the combined use of a divalent metal and anthraquinone, and not to the use of metals alone, the following example shows that the addition of metal alone to alkaline cooking has little or no effect on pulp yields at a given lignin content.

Again, as before, the procedures were in line with the examples above. The soups were performed using different metal cations in the kraft soup but without the simultaneous addition of anthraquinone. As in the previous example, pulp yields were corrected for ash content.

The results of this experiment, shown in Figure 8, show that the addition of metal alone had no significant effect on the lignin content given in the pulp yield. These results, when compared to the increase in yield when anthraquinone was present, show that the ability of the metal cation, especially calcium, to act synergistically with anthraquinone increases pulp yield. The scope of the invention is not limited to the above description, but its scope can be determined within the scope of the following claims.

Claims (9)

20 80730 A one-step alkaline cooking process for cellulose, wherein the lignocellulosic material is boiled in a digester to produce pulp with alkaline cooking broth without the addition of oxygen-containing gas, characterized in that a mixture containing a) about 0.01-1.5% by weight of lignocellulose anthra-quinone, and b) about 0.01-10.0% by weight of a lignocellulosic material of a divalent metal salt which is calcium, barium, strontium or magnesium. Single-stage alkaline cellulose cooking process according to Claim 1, characterized in that the lignocellulosic material is boiled to produce pulp with an alkaline cooking broth and up to 50% by volume of waste liquor derived from the effluent of the digester. A single-stage alkaline cellulose cooking process according to claim 1, characterized in that the divalent metal salt is a calcium salt. A single-stage alkaline cellulose cooking process according to claim 2, characterized in that the divalent metal salt is a calcium salt. A one-step alkaline cooking process for cellulose according to claim 3, characterized in that the calcium salt is calcium hydroxide. A one-step alkaline cooking process for cellulose according to claim 4, characterized in that the calcium salt is calcium hydroxide. 21 80730 A single-stage alkaline cellulose cooking process according to claim 1, characterized in that the process is a single-stage kraft cooking process. A single-stage alkaline cellulose cooking process according to claim 2, characterized in that the process is a single-stage kraft cooking process. Single-stage alkaline cellulose cooking process according to Claim 5 or 6, characterized in that the amount of anthraquinone is between 0.05 and 0.15% by weight of the lignocellulosic material and the amount of calcium hydroxide is between 0.1 and 0.5% by weight of the lignocellulosic material. 22 80730