SE468644B - PREPARATION OF CHEMISTRY MECHANICAL MASS AND IMPROVEMENT SOLUTION CONTAINING BORHYDRIDE AND SULPHITE - Google Patents

Description

10 15 20 468 644 2 freeness number should be above 600 ml CSF, preferably over 700 ml CSF, and the tip content should not exceed 10%, preferably it should be below 6%.

Description of the invention and its objects According to the present invention, it is now possible to carry out a refining at elevated temperature - i energy-saving purpose - without the brightness of the mass deteriorating.

The pulp produced is also bleachable in a subsequent bleach step with peroxide. The method according to the invention is characterized by the chips being pre-impregnated with an impregnation liquid comprising borohydride, at least one compound selected from the group of sodium sulphite, sodium hydrogen sulphate and sodium di- sulphite, and optionally one or more complexing agents, wherein the impregnating liquid has a slightly acidic pH value, after which the impregnated chip is preheated to 160-180 ° C and refined the operation is carried out while maintaining the temperature.

The borohydride is suitably added in the form of a alkaline aqueous solution, such as the borohydride solution sold commercially under the BOROL® brand and which contains 12% by weight of NaBH4. The borohydride is added in the form of the said aqueous solution in an amount of about 5 - 15 kg BOROL® per tonne of chips, preferably about 10 kg per tonne of chips.

The added active amount of borohydride should thus be correspond to about 0.6-1.8 kg NaBH4 per tonne of chips, preferably about 1.2 kg per ton of chips.

The sulfite-containing compound consists of natural sodium sulfite, sodium hydrogen sulfite, sodium disulfite or a mixture of two or more of these compounds. Total- the sulphite charge calculated in the form of the amount of sodium added sulphite, Na2SO3, amounts to approximately 20 - 40 kg per tonne chips, preferably about 30 kg per tonne of chips, or stoichiometric amounts of SO 2, HSO 3 'and / or S2O52 '. In order to achieve maximum brightness on the pulp, impregnation the pH of the curing fluid is adjusted to a slightly acidic pH i.e. The pH should be between about 5 and 6.5, preferably desvis 5.5-6.5. This setting of the pH value can be done for example with the aid of an acid such as sulfuric acid, H¿SO4, 10 15 20 25 30 35 468 644 3 or with sulfur dioxide often available in pulp mills, SO2.

If SO2 is used for the acidification of the impregnation liquid or however, if HS03 'or S2052' is used instead of S032 'must the total sulphite investment is adjusted so that it is within it the above range. How this sulfite venture and that recommended pH is reached, however, is insignificant for invention and can be applied to any application of the invention. the procedure in an appropriate manner.

In addition, the impregnating liquid should be one or more complexing agents are added to bind in the pulp possibly present metal ions, which may give rise to discoloration. A suitable complexing agent is the sodium salt of diethylenetriaminepentaacetic acid (DTPA), or ethylenediamine tetraacetic acid (EDTA), which are added in an amount of approx. 2 - 4 kg per ton of chips.

The invention also comprises an impregnating liquid for impregnating a lignocellulosic material at production of chemithermomechanical pulp. Impregnation the liquid comprises borohydride, at least one compound selected from the group of sodium sulphite, sodium hydrogen sulphite and sodium disulfite, and possibly complexing agents. The weight ratio between the active components boron hydride contained in the liquid and total sulfite is between 20:80 and 30:70, preferably ca 25:75. Furthermore, the impregnation liquid is set to a weak one acidic pH value, ie the pH value of the liquid should be between approx 5 and 6.5, preferably 5.5-6.5.

According to the process of the invention, thus by impregnating wood chips with an impregnated ring fluid comprising borohydride and at least one compound selected from the group of sodium sulfite, sodium hydrogen sulfite and sodium disulfite, and possibly complexing agents. Then the impregnated chip is preheated for a period of time by about 1-3 minutes, preferably about 1 minute, at one temperature of 160-180 ° C, preferably about 165-170 ° C, and defibrated / refined into pulp with essentially retained kept pressure and temperature from the preheating. Mass suitably washed under pressure and high temperature 10 15 468 644 4 without air access in direct connection to the refining whereby it is dewatered to a concentration of 25 - 40%, after which bleaching is done with peroxide. After bleaching, pulp can be washed again if required.

The refining was carried out with an energy consumption of about 500 kWh / ton to a freeness figure above 700 ml CSF.

With the above procedure it is possible to produce a mass with high temperature refining an unbleached brightness before the peroxide bleaching which is comparable with the brightness of conventionally prepared CTMP pulps.

In the event of a subsequent peroxide bleaching of the the pulp produced mass is also obtained an equivalent bleach response and a brightness maximum of the same magnitude as for masses produced in a conventional manner at lower temperatures.

Exemplary embodiments Example 1. (High temperature refining with boron hydride).

Spruce chips were impregnated with impregnating liquids containing 30 kg of sodium sulphite, 10 kg of BOROL® (12%) aqueous sodium borohydride solution) and 3 kg DTPA per tonne wood chips. The impregnation liquid had pH = 11 or had alternate neutralized or acidified with H 2 SO 4 to pH = 8 resp. pH = 6. The chips were preheated at 165 ° C for 1 minute.

The refining was then carried out while maintaining the temperature.

After refining, it was washed and dewatered the pulp in direct connection with the refining under pressure and high temperature, about 150 - 180 ° C, without air access.

For further process conditions, please refer to the following table 1.

The brightness of the prepared, unbleached masses was measured according to SCAN-C 11 at a wavelength of 457 nm.

The pulps produced were then bleached at conventional by 40 kg peroxide per tonne of pulp. They faded the brightness of the masses was measured in the same way as the unbleached ones the masses. The results from the brightness measurements are shown in table 1 below. 10 15 20 25 30 35 468 644 5 Example 2 (High temperature refining without borohydride) Spruce chips were impregnated with an impregnating liquid with pH = 9.5 and containing 30 kg Na2SO3 and 3 kg DTPA per tons of chips. The chips were preheated to 165 ° C for 1 minute. and be- was otherwise traded according to Example 1. The unbleached mass brightness and the brightness of the peroxide bleached pulp were measured according to SCAN-C11 and the results are shown in Table 1, below.

Example 3 (Conventional refining) Spruce chips were impregnated with the same impregnation liquid used in ex. The chips were preheated to 130 ° C under 3 min. and refined while maintaining the temperature.

After refining, the pulp was washed and dewatered conventional way at about 130 ° C and without air access.

The brightness of the unbleached mass and the peroxide bleached the brightness of the mass was measured and the results are shown in Table 1, below.

Results from and process conditions for the three the procedures described above in Examples 1 to 3 are employees in Table 1. 10 15 20 25 30 xx (D 468 644 _ 6 IâhQLL_l EX.

Brnnassbefinsslaerr Preheating temp. ° C 155 my time 1 Energy consumption kWh / h 550 'm n' n - Nazsos kg / h 30 Borol solution (12 wt-% Nassa) kg / h 10 DTPA kg / h pH value .lleailrari Freeness CSF ml 740 Unbleached brightness after refining ISO% 59 Faded brightness after peroxide pale. (Hzoz 40 kg / h) Iso s 78.5 Of the results from the brightness measurements, EX. 165 600 740 57.5 55 54 77 75 73 EX.3 13ø i 900 730 57 78 performed on the pulps produced, it appears that high-temperature refining to reduce energy consumption during refining is possible while maintaining the brightness of the masses produced if the chips are pre-impregnated with an impregnating liquid according to the invention. Furthermore, the measured brightness values show that the pH of the impregnation liquid has an effect on the result.

Claims (9)

10 15 20 25 30 35 7 468 644 PATENTKRAY Process for the preparation of chemithermomechanical pulp of lignocellulosic material by preheating and refining at elevated temperature after pre-impregnation of the chips with a liquid containing borohydride and at least one compound selected from the group of sodium sulphite, sodium hydrogen sulphite and sodium disulphite, and optionally one or more complexing agents, characterized in that the impregnation liquid has a slightly acidic pH value between 5 and 6.5 and the impregnated chips are preheated to a temperature between 160-180 ° C and the refining is carried out with a substantially maintained temperature. Process according to Claim 1, characterized in that the chips per tonne are impregnated with 0.6-1.8 kg of sodium borohydride and 20-40 kg of sodium sulphite or the corresponding stoichiometric amount of sodium hydrogen sulphite and / or sodium disulphite or a mixture of at least two of the mentioned compounds. 3. A method according to any one of claims 1-2, characterized in that the impregnating liquid is acidified to a pH between approximately 5.5 and 6.5, possibly by means of acid addition. 4. A method according to any one of claims 1-3, characterized in that the preheating takes place at a temperature between 160-180 ° C for a time period of about 1-3 minutes. Process according to any one of claims 1 to 4, characterized in that the chips are impregnated with an aqueous solution containing about 1.2 kg of borohydride, about 30 kg of sodium sulfite and about 3 kg of DTPA per ton of chips, after which the chips are preheated to about 165 - 170 ° C for about 1 minute and refined with substantially maintained temperature. Process according to any one of the preceding claims, characterized in that the pulp produced is subjected to a conventional bleaching with peroxide. 10 15 20 468 644 g Impregnating liquid containing borohydride and at least one compound selected from the group of sodium sulphite, sodium hydrogen sulphite and sodium disulphite, and optionally one or more complexing agents for impregnating a lignocellulosic material in the production of chemithermomechanical pulp, characterized in that the impregnating liquid has a slightly acidic pH between 5 and 6.5. Impregnating liquid according to claim 7, characterized in that the liquid has a pH value between 5.5 and 6.5. Impregnating liquid according to one of Claims 7 to 8, characterized in that the active components boron hydride and total sulphite present in the liquid are present in a quantity ratio of between 20:80 and 30:70.