WO2004061224A1

WO2004061224A1 - Paper pulp, method for the production thereof, and use of the paper pulp

Info

Publication number: WO2004061224A1
Application number: PCT/CH2003/000792
Authority: WO
Inventors: Urs Domeisen
Original assignee: Gmpv Ineta Ag
Priority date: 2003-01-07
Filing date: 2003-12-02
Publication date: 2004-07-22
Also published as: AU2003281896A1

Abstract

A paper pulp is produced from a non-woodlike lignocellulose-containing biomass and has the following characteristics: the proportion of holocellulose is greater than 90 percent by mass with regard to the dry mass of the paper pulp; the proportion of hemicelluloses to the proportion of cellulose does not fall below a mass ratio of 0.4: 1; the lignin content is no greater than 2.5 % by mass with regard to the dry mass of the paper pulp, and; the pulp yield is determined, in essence, by the removal of lignin. A method for producing the paper pulp by delignifying a starting material formed by a non-woodlike lignocellulose-containing biomass comprises the following steps: mixing the biomass with a delignification agent containing an organic decomposing agent for lignin, whereby the decomposing agent has a base constant KB > 10-6; thermally treating the mixed biomass in order to decompose the lignin; separating the delignification agent containing the decomposition products of the lignin out from the delignified biomass, and; extracting the paper pulp from the delignified biomass.

Description

Paper pulp, process for its production and use of the paper pulp

TECHNICAL FIELD The invention relates to a paper pulp according to the preamble of claim 1, a method for its production and a use of the paper pulp.

State of the art

The known processes for producing chemical pulp from agricultural waste or from annual plants mostly use sodium hydroxide solution and / or sodium carbonate for the digestion. The Arbokem process uses potassium hydroxide instead of caustic soda. Some sodium sulfide is also used. In the so-called Soda-AQ process, small amounts of anthraquinone are added to the sodium hydroxide solution. Examples of the known processes can thus be listed: the soda pulping, the soda AQ process, the "steam explosion" process, the Kraft process, the Naco process and the Bivis process.

All these processes have in common that not only lignin but also hemicellulose are dissolved in the cooking liquor during the digestion. The consequence of this is that the yield of paper pulp is limited to the range 45-55% by mass.

The processing of black liquor from the digestion of agricultural waste is problematic; because the silica contained in all types of straw, for example, largely passes into the cooking liquor. The high silica or silicate content increases the viscosity of the black liquor and requires special precautions with regard to the apparatus and processes involved in evaporating and burning the black liquor. The silicic acid content in the black liquor is responsible for a number of side effects such as deposits in the recovery boilers, colloidal gels in the caustification system and the formation of glass-like deposits. The removal of silica is associated with additional effort the, whereby the silica from the black liquor with carbon dioxide or from the fresh cooking liquor must be precipitated by adding lime.

In many pulp mills - especially small and medium-sized ones - an expensive conventional recovery of the caustic soda is not common. No chemical recovery systems are installed there due to these problems. Rather, the black liquor is introduced into water courses after appropriate dilution. In addition to the environmental impact, there are considerable NaOH losses, which with a share of 15% NaOH are economically significant when soda pulping straw, especially since the costs for caustic soda have risen sharply in recent years. However, the pressure to install recovery systems is also growing strongly from an ecological point of view.

In processes that use acids for digestion (Milox, Natural Pulping), the silica is not removed. The problems in the recovery that arise when using alkalis in the digestion are avoided. However, the acidic digestion conditions also lead to a considerable breakdown of hemicelluloses, which also keeps the pulp yield low (45-50%). In addition, the acidic processes require the use of special steels in order to keep the corrosion under the digestion conditions to a reasonable extent. From this point of view, the Alcell process can also be classified as an acid process because alcohol in the mixture with water has acidic properties at the high temperatures used in the Alcell process.

It is disadvantageous that the proportion of hemicelluloses is greatly reduced both in the processes which work with alkali metal lye and in the processes which work with acids as digestion chemicals. Compared to the raw materials used, this leads to considerable mass decreases, ie the yields are far below the mass loss, which corresponds to the removal of the lignin. Too much loss of hemicelluloses due to chemical degradation does not only have a negative impact on the yield, because hemicelluloses contribute to the binding and thus to the strength in cellulose, which is advantageous for paper production. Another disadvantage of the known methods is that the extraction and utilization of by-products such as lignin is not feasible with reasonable effort. Neither the hemicelluloses that are mostly broken down to sugar nor the lignin can be used as such, because the effort to cleanly separate these components from the black liquor is high.

Chemical digestion of non-woody agricultural waste has to face some additional difficulties compared to wood digestion. Depending on the climate zone, only one harvest (or possibly a few harvests) is possible per year. This limits direct processing to a few weeks during the harvest. There are also additional storage and preservation costs. Transport only makes economic sense within a certain logistical radius. For straw in the USA, for example, this is a maximum of 100 to 150 km around the cellulose plant. The low packing density of straw also has a negative impact on transport. These circumstances mean that the size of a pulp mill according to a state-of-the-art process should have a production capacity of more than 50,000 tons per year due to process-related reasons, and on the other hand should be as small as possible for logistical reasons. The infrastructure in straw-processing countries such as India and China, however, is not in line with this requirement in that most pulp mills have large pulp pulps with less than 10,000 tons a year.

Presentation of the invention

The object of the invention is to provide an improved paper pulp and a method for its production. In particular, the disadvantages mentioned above should be avoided. Another object of the invention is to specify a use of the paper pulp according to the invention. These tasks are solved by the paper pulp defined in claim 1, the method defined in claim 2 and the use defined in claim 10.

The paper pulp according to the invention is produced from a non-woody, lignocellulosic biomass and has the following features:

a) the proportion of holocellulose is more than 90% by mass based on the dry mass of the paper pulp; b) the proportion of hemicelluloses to the proportion of cellulose does not fall below a mass ratio of 0.4: 1; c) the lignin content is at most 2.5% by mass based on the dry mass of the paper pulp; and d) the pulp yield is essentially determined by the removal of the lignin.

The method according to the invention for producing the paper pulp according to the invention, by delignifying a starting material formed by a non-woody lignocellulosic biomass, comprises the following steps:

a) adding a delignifying agent containing an organic disintegrant for lignin to the biomass, the disintegrant having a base constant K _B > 10 ^-6 ; b) thermal treatment of the added biomass to break down the lignin; c) separating the delignifying agent containing the degradation products of the lignin from the delignified biomass; and d) obtaining the paper pulp from the delignified biomass.

An organic base is therefore used as a disintegrant for lignin. This eliminates the disadvantages that arise when using strongly basic alkali lyes such as sodium or potassium hydroxide or avoided by acidic disintegrants.

In the use according to the invention for the production of chemical pulp, the paper pulp is subjected to a treatment with an at least 10% aqueous sodium hydroxide solution at a temperature of at least 35 ° C. for at least 20 minutes without prior drying.

Advantageous developments of the invention are defined in the dependent claims.

According to the preferred embodiment of claim 3, air-dried, comminuted non-woody agricultural waste and / or annual plants with a moisture content of less than 20 mass%, in particular with a moisture content of less than 15 mass% and very particularly with a moisture content of less, are used as the starting material used as 10 mass%. Since such agricultural waste is dry in air and has a significantly lower moisture content than wood, it is not necessary to reduce the water content by dewatering. Agricultural waste can therefore be used as raw materials without further pretreatment. The lignin breakdown agent is eagerly absorbed by this agricultural waste.

Various organic substances per se can be used as disintegrating agents for lignin. It is particularly advantageous if an alkanolamine, preferably monoethanolamine, is used for this purpose. Monethanolamine in aqueous solution at 25 ° C has a base constant κ _B = 3.2 10 ^-5 (corresponding to an acid dissociation constant K _A = 3.16 10 ^-10 ; source: CRC Handbook of Chemistry and Physics, 57th Ed., RC Weast, Ed., CRC Press, Cleveland, 1976, page D147). In the particularly preferred embodiment according to claim 5, the delignifying agent further contains a primary amine, preferably ammonia, or a diamine or a betaine. Surprisingly, it was found that it is favorable to add a small amount of a primary organic or inorganic amine or diamine before delignification. On the one hand, this obviously serves to accelerate the lignin degradation, or the delignification can be carried out at a lower temperature than without this addition. On the other hand, reactions between the delignifying agent, such as, in particular, aminoethanol, and functional groups in the lignin are restricted by the primary amine competing in this regard with the delignifying agent. All primary amines, diamines or derivatives such as betaines which are soluble in water or in aminoethanol are suitable for this. According to claim 6, the alkanolamine to the primary amine or diamine or betaine is preferably in a molar ratio of 99.9: 0.1 to 90: 1.

According to claim 7, the starting material is mixed with the delignifying agent in a mass ratio of approximately 10:90 to 90:10, in particular approximately 20:80 to 80:20 and very particularly 40:60 to 60:40, the total moisture content not being given can drop below the water content of the starting material and then thermally treated this mixture at a temperature of about 100 to 200 ° C until the lignin content in the delignified biomass is less than 10% by mass of that in the starting material.

According to the process defined in claim 8, a separated delignifying agent and a lignin-containing residue, in particular an organosolvlignin, are obtained from the separated delignifying agent by distillation. The lignin recovered has a nitrogen content of 2 to 6%, which depends on both the agricultural waste used and the process conditions. Lignins with such a high nitrogen content can advantageously be used as fertilizers. It is also advantageous according to claim 9 that silicates or silicas separated from the starting material remain mainly in the residue during the distillation.

WAYS OF CARRYING OUT THE INVENTION General Remarks

The present invention avoids the disadvantages of the prior art, such as low yields, low hemicellulose contents, complex recovery of the digestion chemicals, measures for the silicification of the digestion chemicals, and the compromises with plant sizes of at least 30,000 to 50,000 tons annually.

The paper pulp obtained has a carbohydrate content of more than 90% and the mass ratio of pentosans (xylans) to α-cellulose in the pulp after removal of most of the lignin is similar to the ratio of these substances in the starting material. Neither with sodium hydroxide solution nor with acids as a constituent of the digestion chemical for removing lignin can pulps be produced which have such properties.

Example 1: Delignified Wheat Straw

Twenty kg of chopped wheat straw with a moisture content of 8.3 mass% is mixed in a mixer with 0.2 kg of 25% ammonia water in 20 kg of aminoethanol at room temperature. The mixer is equipped with a homogenizer (knife unit), a double jacket for heating with steam and with a direct steam supply. After filling, the mixer and knife unit are started and steam is fed into the heating jacket and directly into the mixer for heating. When the temperature reaches 140 ° C, a pressure of 3 bar is established. After a dwell time of 20 minutes at 140 ° C., the mixture is decompressed and the mixer is opened to remove the delignified wheat straw. The straws have completely broken down into individual fibers. The analysis data of the wheat straw used and the delignified wheat straw are compared in the following table.

After the delignifying treatment, the relative proportions of the carbohydrates have shifted compared to the starting material. This is primarily due to the decrease in lignin content. Accordingly, the yield after removing the lignin is over 80%.

Example 2: Holocellulose content of wheat straw before and after delignification

After the delignification of wheat straw, the proportion of holocellulose rises sharply due to the delignification:

"): based on sample (atro) after extraction with ethanol / cyclohexane

Example 3: Oil fruit waste (EFB)

a) Process parameters:

b) Composition:

The EFB oil palm waste shows the following composition before and after lignin removal:

After delignification, the kappa number is 4.7.

Example 4: Holocellulose fraction

The holocellulose content of oil palm waste (empty fruit bunches; EFB) is 95.8% after treatment of the mechanically roughly shredded oil palm waste with EFB: MEA = 1: 1 at 160 ° C for 20 minutes in a mixer with homogenizer and stirrer.

Example 5: Manufacture of chemical pulp

The delignified sample from Example 3, which was thoroughly freed from the extractant and lignin by washing, was additionally subjected to a treatment with 10% sodium hydroxide solution at 35 ° C. for 45 minutes. The following carbohydrate composition was found:

The delignified sample can thus be converted into a chemical pulp for use as a dissolving pulp with little effort. Example 6: Comparison with the prior art

As a comparative example with example 3 above, the result of a soda-AQ digestion of oil palm waste (empty fruit bunches, cf. with example 3) is given:

a) Process parameters:

b) Properties of the pulp after delignification:

Lit .: Ryohei, Tanaka et al. "Preparation of cellulose pulp from oil palm empty fruit bunches (EFB) by processes including pre-hydrolysis and ozone bleaching".

Claims

claims

1. Paper pulp made from a non-woody lignocellulosic biomass, characterized in that:

a) the proportion of holocellulose is more than 90 mass% based on the dry mass of the paper pulp;

b) the proportion of hemicelluloses to the proportion of cellulose does not fall below a mass ratio of 0.4: 1;

c) the lignin content is at most 2.5% by mass based on the dry mass of the paper pulp; and

d) the pulp yield is essentially determined by the removal of the lignin.

2. A process for producing the paper pulp as claimed in claim 1, by delignifying a starting material formed by a non-woody lignocellulosic biomass, characterized by the following steps:

a) adding a delignifying agent containing an organic disintegrant for lignin to the biomass, the disintegrant having a base constant K _B > 10 ^-6 ;

b) thermal treatment of the added biomass to break down the lignin;

c) separating the delignifying agent containing the degradation products of the lignin from the delignified biomass; and

d) Obtaining the paper pulp from the delignified biomass.

3. The method according to claim 2, characterized in that air-dried, crushed non-woody agricultural waste and / or annual plants with a moisture content of less than 20% by mass, in particular with a moisture content of less than 15% by mass and very particularly as a starting material a moisture of less than 10 mass%.

4. The method according to claim 2 or 3, characterized in that the disintegrant is an alkanolamine, preferably monoethanolamine.

5. The method according to any one of claims 2 to 4, characterized in that the delignifying agent further contains a primary amine, preferably ammonia, or a diamine or a betaine.

6. The method according to claims 4 and 5, characterized in that the alkanolamine to the primary amine or diamine or betaine is present in a molar ratio of 99.9: 0.1 to 90: 1.

7. The method according to any one of claims 3 to 6, characterized in that the starting material with the delignifying agent in a mass ratio of about 10: 90 to 90: 10, in particular from about 20: 80 to 80: 20 and very particularly of 40: 60 to 60: 40 mixes, whereby the total moisture content is not allowed to drop below the water content of the starting material, and then this mixture is thermally treated at a temperature of about 100 to 200 ° C. until the lignin content in the delignified biomass is less than 10% by mass. % of that in the starting material.

8. The method according to any one of claims 3 to 7, characterized in that from the separated delignifying agent by distillation, a recycled delignifying agent and a lignin-containing residue, in particular an organosolvlignin, are obtained.

9. The method according to claim 8, characterized in that from the starting material separated silicates or silicas mainly remain in the residue during the distillation.

10. Use of the paper pulp according to claim 1 for the production of chemical pulp, characterized in that the paper pulp is subjected to a treatment with an at least 10% aqueous sodium hydroxide solution at a temperature of at least 35 ° C for at least 20 minutes without prior drying.