EP0494214B1 - Process for manufacturing chemo-mechanical and/or chemo-thermo-mechanical wood pulps - Google Patents

Abstract

PCT No. PCT/EP90/01622 Sec. 371 Date May 18, 1992 Sec. 102(e) Date May 18, 1992 PCT Filed Sep. 25, 1990 PCT Pub. No. WO91/05102 PCT Pub. Date Apr. 18, 1991.In a process for manufacturing chemo-mechanical and/or chemothermal-mechanical wood pulps, raw materials containing lignocellulose, such as wood shavings, wood chips, pre-ground wood or sawdust, are first impregnated with an aqueous alcoholic SO2 solution and then heated to a temperature between 50 DEG and 170 DEG C. for a period of 1 to 300 minutes. The wood shavings are then ground to the desired degree of fineness in a defibrinating device. The process makes it possible to achieve up to 50% reduction in grinding energy in comparison with known chemothermal-mechanical processes.

Description

The invention relates to a method according to the preamble of claim 1 for the production of chemo-mechanical and / or chemo-thermo-mechanical wood materials from lignocellulose-containing raw materials, such as wood chips, wood chips, pre-fiberized wood or sawdust.

The production of wood pulp in refiners enables better qualities under optimized conditions than in stone grinding production. However, this requires a thermal or thermal and chemical treatment of the wood before defibration. The aim of such a pretreatment is to soften the lignin, which reduces the energy required to detach the fibers from the tissue and creates predetermined breaking points in the area of the primary wall and S1. The resulting fiber surfaces are high in carbohydrates and therefore have good prerequisites for the formation of hydrogen bonds between the surfaces of these fibers. The temperatures to be used in the thermal pretreatment are between 125 and 150 ° C. With a treatment duration of a few minutes, the aforementioned goal of lignin plastification should be achieved, but the latter should not be so extensive that the fibers are separated in the area of the middle lamella, which would result in an intact fiber, but with a hydrophobic lignin layer would be provided on the surface. Higher temperatures or a longer treatment time also have the disadvantage that the lignin structure changes due to condensation reactions and the fibers darken considerably.

By sulfonating the wood in the area of the predetermined breaking points, a targeted defibrillation of the wood is achieved, loss of whiteness is prevented and a more hydrophilic lignin is generated in the area of the later fiber surface. Another positive aspect of sulfonation is the production of flexible fibers.

The energy required to isolate fibers from the wood fabric is reduced by thermal or chemical pretreatment of the wood. However, in order to produce high-quality fibrous materials for paper and cardboard production, these have to be mechanically defibrillated further. In this case, wall layers or fibrils are peeled off from the surface of the fibers by mechanical force, which increases the specific surface area of the fibers and thus improves their binding capacity and flexibility. Such methods are described in detail in the reference "Pulp and Paper Manufacture, Volume 2, Mechanical Pulping, Tappi, Atlanta 1987 ".

Compared to the stone grinding process, the energy requirement for all refiner pulp processes is significantly higher. In the stone grinding process, the defibration energy is deliberately released to the wood layer, which lies directly on the stone surface. In refiner processes, the energy transfer is less targeted because energy is used to accelerate the material, to rub the wood particles against each other and on the panes, to form the particles and for fluid friction. In the stone grinding process, the forces always attack at right angles to the grain where the wood has lower strength. Since the wood chips in the refiner are not always aligned parallel to the centrifugal force with their fiber direction, the energy expenditure for the defibration is higher here. The thermal and chemical pretreatment can reduce the energy required to remove the fibers from the wood fabric, but the total energy requirement for producing a more or less largely defibrillated wood pulp does not decrease, since the fiber has become more flexible due to the pretreatment and the influence of the refiner's grinding segments can dodge, so that a more targeted defibrillation is possible, but this requires more loading and relief procedures.

If around 1,500 kWh / t have to be spent on high-quality softwood stone grinding, this is around 2,000 for TMP and 2,500 kWh / t for CTMP.

As already mentioned, lignin must be sulfonated to produce high-quality wood pulps. This is usually done by using sodium sulfite in an alkaline medium, since the fibers swell at the same time, which creates favorable conditions for the subsequent defibrillation. As is well known, a sulfonation reaction also takes place in the acidic pH range; the lower the pH, the faster it takes place. Competing condensation reactions of the lignin are also favored by low pH values. Lignosulfonates with a higher degree of sulfonation are water-soluble and therefore reduce the fiber yield. On the other hand, acids attack the carbohydrates, depolymerize them and weaken the fiber structure.

The high energy demand, especially of the CTMP substances, limits their production to countries with low energy prices. The future development in the field of wood pulp production is therefore largely dependent on the energy requirements of the processes. A significant reduction in energy consumption seems essential.

It is therefore the task of a newly developed, energetically favorable wood pulp production process to find conditions that allow targeted sulfonation to a small extent, prevent condensation of the lignin, avoid losses in yield and significantly reduce the energy required to defibrate the wood and defibrillate the fibers that are produced. For environmental friendliness Such a process would also be very advantageous if the pretreatment chemicals used could be completely or at least largely recovered. The object is solved by the characterizing part of claim 1. Further advantageous developments are specified in the subclaims.

In M. Jackson et. al. "Chemithermomechanical pulp production and end-uses in Scandinavian", Tappi Journal vol. 85, no. 2 Feb. -85, EASTON US pages 64-68, CTMP / CMP methods according to the preamble of claim 1 are disclosed.

The use of aqueous, acidic digestion solutions of aliphatic, water-miscible alcohols and sulfur dioxide in the production of paper has long been known from US-A-2060068. Schorning has also reported on base-free sulfite digestion using methanol to produce pulp in the reference "Fiber Research and Textile Technology 12 , 487 to 494, 1957". In spite of the described advantages, the stated solution has not been able to prevail in practice. Although the Schorning process had already been published in 1956, the attempts to pulp-alcohol digestion were only taken up again in the mid-1970s and only then were they partially successful. B. DE-A-32 17 767 proves.

On the basis of the results reported by Schorning, the aim of all the investigations carried out was to find a formulation for pulping which would provide a largely delignified pulp for further processing into synthetic pulp. The yields for the pulps found to be good were in the range from 40 to 50% by weight. Digestions with higher yields were discarded. This reference does not indicate that such pulps may also be suitable for the purposes of papermaking. In particular, information about is missing Strength tests that would have made it possible to draw any conclusions about the suitability of such pulps for paper purposes.

If milder temperature conditions and / or shorter reaction times are selected, the lignin can surprisingly be sulfonated without major losses in yield, without the feared condensation reactions occurring. The power required during the subsequent defibrillation of the wood can then be reduced to approximately 50% depending on the pretreatment conditions, the resulting wood materials having excellent technological properties. The specific grinding work is selected depending on the desired degree of fineness or grinding in a range from 1,200 to 1,900 kWh / t of fiber.

The use of the acidic system aliphatic alcohol / water / SO₂ is not only able to sulfonate lignin, the alcohol taking over the function of the base, but the presence of the alcohol also improves the impregnation, condensation reactions in the lignin are suppressed and resin and fatty acids are dissolved . The alcohol also increases the solubility of SO₂ in water. This system is effective at temperatures below 100 ° C, but higher temperatures can also be used. It should be noted, however, that the sulfonation is only carried out until the lignin softens at the predetermined breaking points between the primary wall and S1 of the fiber structure. A further sulfonation results from lignin release Loss of yield and fiber damage.

A major advantage of this type of pretreatment is that the chemicals used can be easily recovered. For alcohol this is possible quantitatively, while with SO₂ only the portion that does not react with the wood can be traced. This is a significant advantage compared to base-containing, neutral or alkaline sulfite systems with their complicated recovery.

The aqueous digestion solution used in the process according to the invention contains 10 to 70 vol.% Aliphatic, water-miscible alcohols and 1.0 to 100.0 g / l sulfur dioxide. The pH of the digestion solutions is between 1.0 and 2.0 depending on the SO₂ content. The wood chips are suspended in this solution, a liquor ratio of 1: 3 to 1: 6 being selected, ie 1 kg of dry wood chips are suspended in 3 to 6 kg of solution. When choosing the liquor ratio, the wood chip moisture measured in each case must be taken into account, which lowers the concentration of the digestion solution. The proportion of sulfur dioxide contained in the digestion solution depends on the vol.% Content of alcohol. Further considerations for the choice of the sulfur dioxide concentration are the extent of the desired lignin sulfonation with regard to the desired yield, the temperature and the time which are chosen for the lignin sulfonation. After soaking the wood chips with the digestion solution, they are used to initiate the Lignin sulfonation reaction heated to 50-170 ° C. Possibly. Excess digestion solution can be removed after soaking, especially if the lignin sulfonation is to take place in the vapor phase. The heating can take place indirectly by circulating the digestion solution via a heat exchanger or directly by introducing steam.

The final temperature is again selected depending on the desired yield, the concentration of the digestion solutions and the digestion time. With short digestion times, a higher final temperature and vice versa can be aimed for. If the final temperature is chosen above 70 ° C, the reaction must be carried out in a pressure-resistant reaction vessel to avoid premature outgassing of the alcohol and sulfur dioxide.

After reaching the preselected final temperature, it is maintained for a period of 1 to 300 minutes. At low final temperatures, longer holding times and vice versa, again depending on the desired yield, are required.

After the holding time, the existing mixture of alcohol, steam and unused SO₂ gas can first be withdrawn and reprocessed, e.g. B. by condensation. Alcohol and sulfur dioxide still present in the liquid can also be evaporated and recovered by lowering the pressure or blowing in steam. The recovery of the Alcohol and the unused sulfur dioxide can also take place after the defibrating device in a downstream, known heat recovery system with a condensation stage.

Then the wood chips are conveyed by known conveying devices of a known defibrating device, such as, for. B. disc refiner, supplied and mechanically defibrated. Possibly. a wood chip washing device can be connected upstream of the defibrating device. A preselected degree of fineness of the chips to be defibrated is achieved by the throughput quantity per unit of time and the work input of the drive of the disc refiner in kwh / t of fiber.

For the alcohols used in the digestion solution, those with straight or branched chains, individually or in mixtures, are preferred.

In order to ensure complete and technically simple recovery of the alcohols after the lignin sulfonation has ended, preference is given to alcohols whose boiling point is below 100 ° C. under normal pressure. These alcohols include methanol, ethanol, propanol, isopropanol and tertiary butyl alcohol. Because of its high availability and low price, methanol is preferred.

The mixing ratio between water and alcohol can be varied within wide limits, but the alcohol content between 20 and 50 is preferred Vol.%, In particular between 20 to 40 vol.%, Selected.

Since the rate of lignin sulfonation is dependent on the concentration of sulfur dioxide, high concentrations per se are desirable. However, this can lead to undesirable losses in yield at elevated temperature during the holding time, so that a sulfur dioxide content of the digestion solution of 5 to 40 g / l is preferred.

The specified end temperature range during the holding time can be freely selected within the specified limits in coordination with the residence time and the concentration of the digestion solution. However, higher temperatures require additional heat and additional design measures on the reaction vessel because of the pressure that builds up in the process. It is therefore preferred to heat the digestion solution containing the wood chips to a temperature of 80 to 120 ° C. If alcohols with a boiling point close to 100 ° C are used, a temperature of 100 to 120 ° C is selected.

The holding time at the final temperature influences the degree of yield on the one hand and is determined on the other hand by the volume of the reaction vessel as a function of the mass flow of digestion solution and wood chips to be carried out. For this reason, a holding time at a final temperature of 2 to 120 minutes is preferred, particularly in the case of continuous processes.

If the possibility of energy reduction in the production of chemical-thermo-mechanical wood pulps by impregnation with an alcohol-water-sulfur dioxide solution is to be combined with a very gentle defribration, the actual impregnation stage can be preceded by a treatment, the wood chips being pretreated with an alcoholic aqueous solution be that contains a neutral and / or alkaline sodium compound.

Such sodium compounds can consist of sodium sulfite and / or sodium hydroxide and / or sodium carbonate, the solution preferably containing a concentration of 1 to 10 g / l total alkali, calculated as NaOH.

The purpose of these sodium compounds is to buffer the organic acids, such as formic and acetic acid, which arise from the wood during the holding time at the final temperature during the actual lignin sulfonation reaction, to avoid lignin condensation due to a low pH value and to promote the swelling of the wood. Another advantage of adding the sodium compounds is the maintenance of the white content of the wood chips to be defibrated, especially when sodium sulfite is added.

Treatment of the wood chips with an aqueous solution containing a sodium compound can also be carried out after the lignin sulfonation reaction in the reaction vessel and after being driven off and drawn off the alcohol and sulfur dioxide gas from the remaining digestion solution. For this purpose, the wood chips are first separated from the remaining digestion solution with the aid of devices known per se and then treated with a solution containing the sodium compound at a temperature of 20 to 150 ° C. A solution which contains 1 to 10 g / l of sodium sulfite, sodium hydroxide or sodium carbonate, calculated as NaOH, alone or in a mixture is preferred. In this way it is also possible to positively influence the paper technology properties of the wood pulp to be produced.

The present method can also be applied to mechanically defibrated fibrous materials, such as. B. sauerkraut obtained in the production of wood chips.

The process according to the invention is explained in more detail in the examples below.

Example 1:

Spruce wood chips are treated at 120 ° C for 10 minutes with a methanol / water mixture of 40:60 vol.%, Which contains 12.5 g / l SO₂. The liquor ratio is 1: 4. After the treatment time, the methanol and the unused SO₂ are recovered in the gas phase and the wood is defibrated in a refiner. When grinding to 70 ° SR, the grinding energy requirement is only 1,400 kWh / t, while 25 g / l Na₂SO₃ pretreated spruce wood chips to achieve the same Freeness 2,500 kWh / t required. The energy saving is 44%.

The yield is 95%, the fiber has the following technological values: Tear length 3,260 m Tear resistance (Brecht / Imset) 1.04 J / m spec. volume 2.30 cc / g Light scattering coefficient according to SCAN C27: 69 42.5 m² / kg

Example 2:

Spruce wood chips are first treated for 15 minutes at 100 ° C with a methanol-water mixture containing 5 g / l Na₂SO₃, then an aqueous SO₂ solution with 50.0 g / l is added and 60 minutes at 100 ° C . The liquor ratio is 1: 4 after the addition of the SO₂ solution. After recovery of the gaseous pulping chemicals, the wood chips are defibrated in the refiner to a freeness of 70 ° SR. The energy requirement is 1,850 kWh / t, which means a saving of 26% compared to a standard CTMP.

The yield is 96%, the fiber has the following technological values at 70 ° SR: Tear length 4,320 m Tear resistance (Brecht / Imset) 1.23 J / m spec. volume 2.22 cc / g Light scattering coefficient according to SCAN C27: 69 46.7 m² / kg

Example 3:

A pulp pulped in the refiner without pretreatment to a freeness of 15 ° SR is treated for 10 min at 100 ° C with the methanol / water / SO₂ solution described in Example 1 and then further ground in a Jokro mill under standard conditions. 6,750 revolutions were required to achieve a freeness of 70 ° SR. The untreated reference material required 15,750 revolutions to achieve a freeness of 63 ° SR.

Example 4:

Spruce wood chips are treated at 100 ° C for 60 minutes with a methanol-water mixture of 30: 70 vol.%, Which contains 50 g / l SO₂. After the treatment time, the methanol and the unused SO₂ are recovered and the wood chips are shredded in a refiner. 1,390 kWh / t are required to achieve a freeness of 77 ° SR.

The yield is 92.0%, the fiber has the following technological values: Tear length 4,070 m Tear resistance (Brecht / Imset) 0.96 J / m spec. Volume 2.03 cc / g Light scattering coefficient according to SCAN C27: 69 39.9 m² / kg

Example 5:

Spruce wood chips are steamed for 20 minutes and entered into a methanol / water mixture of 50:50 vol.%, Which contains 100 g / l SO₂. After a Impregnation time of 30 minutes, the excess amount of liquid is removed. The wood chips impregnated in this way are treated in a defibrator with steam at 150 ° C. for 5 minutes and then defibrated under pressure. The grinding energy to achieve a grinding degree of 68 ° SR is 1,510 kWh / t.

The fiber material produced has the following technological properties: Tear length 4,130 m Tear resistance (Brecht / Imset) 1.02 J / m spec. volume 2.28 cc / g Light scattering coefficient according to SCAN C27: 69 41.5 m² / kg

Example 6:

A further digestion experiment was carried out according to the invention with a methanol / SO₂ solution which contained 70% by volume of methanol and 23 g / l SO₂ at a temperature of 160 ° C. for a digestion period of 8 minutes. These chips were then defibrated in a disc refiner.

The results of the paper technological investigations are contained in Table 1 including the digestion parameters.

Comparative Examples 7 and 8:

For this purpose, digestions on spruce wood chips similar to Schorning with a methanol / SO₂ solution containing 50% by volume of methanol and 55 g / l SO₂ were carried out at a temperature of 130 ° C. for a digestion time of 205 min, example 7 and 300 min. Example 8.

The yield, whiteness, tear length and tear resistance are surprisingly low in the Schorning tests. Such a fibrous material is absolutely unsuitable for paper production. Even the very high splinter content, according to Schorning the fiber should be splinter-free, does not permit use for paper purposes. Table 1 example 6 7 8th temperature ° C 160 130 130 Digestion time min 8th 205 300 SO₂ use % / l 2.3 5.5 5.5 % / atro 13.9 33.0 33.0 Methanol content Vol .-% 70 50 50 Initial pH - 1.1 1.0 0.9 yield % 92.5 43.5 39.2 Splinter content % 0.8 13.1 10.6 Shatter-free yield % 91.5 April 30 28.6 Whiteness % ISO 61.6 22.8 19.0 Residual lignin content % 22.2 7.8 7.4 Kappa number - 148 51.7 49.5 Intrinsic viscosity dm³ / kg - 544 458 Freeness SR 70 20th 19th Tear length km 4480 1970 1670 Burst resistance kPa - 50 40 Tear resistance cN 70.2 13.2 11.3

Claims (14)

1. A method for the manufacture of chemo-mechanical and/or chemo-thermo-mechanical wood pulps from lignocellulose-containing raw materials for the manufacture of paper, card or cardboard having the following sequence of operations:
   mechanical comminution, sorting and homogenization of the lignocellulose-containing raw materials,
   impregnation with a digestion solution,
   digestion of the raw materials,
   grinding in one or more parallel or series-connected pulping devices,
   sorting of the fibrous material produced,
   characterized by the combination of the following features:

   a) combining the lignocellulose-containing raw materials with an aqueous, acid digestion solution having a pH from 1.0 to 2.0, which contains

   aa) 10 to 70 volume % of aliphatic, water-miscible alcohols,

   ab) 1.0 to 100 g/l of sulphur dioxide,

   b) initiating the lignosulphonation reaction by heating the mixture from a) to a temperature between 50 and 170 °C,

   c) maintaining the final temperature for a period of 1 to 300 minutes,

   d) driving off and recovering the alcohol and the unconsumed sulphur dioxide,

   e) grinding the lignocellulose-containing raw material in pulping devices known per se to a pre-selected degree of fineness by means of preselected specific grinding in a range from 1,200 to 1900 kWh/t of fibrous material.
2. A method according to claim 1, characterized in that the digestion solution contains alcohols having straight or branched chains.
3. A method according to one of claims 1 and 2, characterized in that the boiling point of the alcohols at normal pressure is below 100 °C.
4. A method according to one of claims 1 to 3, characterized in that the digestion solution contains 20 to 50 volume % of aliphatic water-miscible alcohols.
5. A method according to one of claims 1 to 4, characterized in that the digestion solution contains 20 to 40 volume % of aliphatic water-miscible alcohols.
6. A method according to one of claims 1 to 5, characterized in that the digestion solution contains 5 to 40 g/l of dissolved SO₂.
7. A method according to one of claims 1 to 6, characterized in that the mixture of digestion solution and lignocellulose-containing raw material is heated to a temperature of 70 to 120 °C.
8. A method according to one of claims 1 to 7, characterized in that the mixture of digestion solution and lignocellulose-containing raw material is heated to a temperature of 70 to 100 °C.
9. A method according to one of claims 1 to 8, characterized in that the final temperature is maintained for a period of 2 to 120 minutes.
10. A method according to one of claims 1 to 9, characterized in that, before being mixed with the digestion solution, the lignocellulose-containing raw material is pre-treated with a further solution containing a water-miscible, aliphatic alcohol and/or water and a neutral and/or alkaline sodium compound.
11. A method according to claim 10, characterized in that the further solution contains sodium sulphite and/or sodium hydroxide and/or sodium carbonate in a proportion of 1 to 10 g/l of total alkali, calculated as NaOH.
12. A method according to one of claims 1 to 11, characterized in that, after the alcohol and SO₂ gas has been driven off and removed, the lignocellulose-containing raw material is separated from the remaining digestion solution and treated subsequently with an aqueous solution of a neutral or alkaline sodium compound at a temperature from 20 to 150 °C.
13. A method according to claim 12, characterized in that the solution for subsequently treating the lignocellulose-containing raw material contains sodium sulphite, sodium hydroxide or sodium carbonate in a proportion of 1 to 10 g/l of total alkali, calculated as NAOH.
14. A method according to one of claims 1 to 13, characterized in that, before being combined with the digestion solution, the lignocellulose-containing raw material is pre-pulped mechanically to a coarse pulp.