CS212582B1 - Process for the preparation of high-density pulps - Google Patents

Abstract

The preparation method consists in delignifying the wood after autohydrolysis or prehydrolysis in a caustic soda solution in the presence of an oxidation-reduction catalyst, usually anthraquinone and its derivatives. The method can be carried out in a continuous, discontinuous or combined process.

Description

The invention relates to a method for preparing highly concentrated pulps from any type of wood, intended for further chemical processing, including the preparation of cellulose derivatives.

The current method of preparing highly concentrated pulps intended for further chemical processing consists of delignification of pre-hydrolyzed chips with a sulfate cooking solution. The disadvantage of this delignification process is the formation of an enormous amount of toxic exhalates, poor whiteness of the produced pulp and environmental pollution with sulfur compounds.

The method of preparing highly concentrated pulps according to the invention eliminates the shortcomings of the method used so far.

The essence of the invention lies in the fact that the chips after autohydrolysis or prehydrolysis are further delignified in a caustic soda solution (sodium hydroxide) by applying 14 to 22% Na ₂ O, preferably 16 to 18% Na ₂ O, in the presence of an oxidation-reduction catalyst, usually anthraquinone and its derivatives in an amount of 0.01 to 2%, preferably 0.01 to 0.2%, calculated on the weight of the wood used. The application of the above process can be carried out by a continuous, discontinuous or combined process.

By eliminating the use of sulfur (as sodium sulfide) from the production process, as practiced in the present invention, there is no formation of toxic fumes and no pollution of the environment with sulfur compounds.

By removing sulfur from the production process, the regeneration of chemicals in the process of returning the concentrated liquor will also be simplified and the working conditions of the operating personnel will be significantly improved. The highly refined pulps prepared by the new sulfur-free process according to the invention exhibit better quality parameters than pulps prepared by the sulfate delignification process used so far.

Pulps prepared by the method according to the invention exhibit, after delignification, a lower Kappa number value (by approximately 10%) and a higher whiteness of the original unbleached pulp (by 4 to 5% MgO), as a result of which they are bleached significantly more easily than the corresponding kraft pulps prepared by the previously used process (see Table 1).

To achieve the same quality expressed in viscosity, average degree of polymerization and whiteness, they require a smaller amount of bleaching agents (approximately 10 to 12 %) than the corresponding equivalent kraft pulps.

The oxidation-reduction catalyst applied in the production of high-concentration pulps under the patent accelerates the alkaline delignification process to such an extent that it becomes equivalent to the sulphate delignification process.

In addition, the catalyst stabilizes the polysaccharide portion of the pulp, making it less soluble in cold alkalis (e.g. in 18% NaOH solution). The better quality of the highly concentrated pulps prepared according to the sulfur-free method, which is the subject of the invention, lies in the higher alpha-cellulose content and, above all, in the significantly lower solubility of the pulp in 18% NaOH solution (approximately 30% compared to the previously used process), which is particularly crucial in mercerization and further processing of cellulose into derivatives (see Table 2).

Example

Beech chips are subjected to autohydrolysis (prehydrolysis), e.g. 80 min at 170 °C in water at a hydromodule of 1:4, or in a steam environment. After the prehydrolysate is removed, the chips are boiled with a NaOH solution of the appropriate concentration so that the amount of Na^O applied to the wood is 17%.

0.1% anthraquinone is added to the alkaline cooking liquor as a catalyst (the amount of catalyst is calculated on the weight of the water-soluble wood). The unbleached pulp obtained after washing has the characteristics as shown in Table 1. The pulp after bleaching by a five-stage bleaching process, e.g. the CEDHH process (C = chlorination, E = hot alkaline extraction, D = chlorine dioxide stage, H = hypochlorite stage) has the characteristics as shown in Table 2.

For comparison, Table 1 and Table 2 also show the characteristics of pulp obtained using the sulphate delignification technology used so far.

The results shown in Table 1 and Table 2 show that the sulfur-free process, which is the subject of this invention, can produce highly refined pulps with a higher alpha-cellulose content, with lower solubility values in NaOH solutions of the appropriate concentration, and also with better values of viscosity, average degree of polymerization, whiteness and yield, as achieved by cooking pre-hydrolyzed pulps by the sulfate process.

Table 1

Beech wood chip processing method and characteristics of unbleached pulp

Number Pre-hydrolysis Into the batch Alkaline degree samples Spraying Yield Contents Extract Kappa PPS Whiteness % lignin % % number cnP/g % MgO 2 Water 80 min r _{Q 7} at . ^by >' 170 °C 27.7 Sulfate 17% Na ₂ 0 35.4 6.7 608 81 1 34.1 3 Sodium 17% _Na2O + 35.6 6.1 596 795 38.3

+0.1% AQ

5 Steam 80 min 70.0 29.7 Sulfate 17% Na ₂ 0 35.0 8.3 707 943 28.2 6 at _ 170 °C Sodium Bicarbonate 17% Na-0+ 35.3 7.4 674 898 33.8

+0.1% AQ

Table 2

Beech wood chip processing method, active chlorine consumption during bleaching by the CEDHH process and characteristics of bleached pulp

Number Spraying Consumption Whiteness cnP/g PPS Contents Solubility in % samples Auto- hydro- Delivery active Cl ₂ % % MgO alpha- cell-. i.,, in 5% solution in 10% solution in 18% solution lyza NaOH NaOH NaOH ^L 5 ^L 10 ^L 18 Sulfate 1.7 88.2 475 633 97.0 1.44 3.6 2.4 3 By water Sodium Bicarbonate +0.1% 1.5 88.5 462 616 97.1 1.45 4.1 1.7 AŮ 5 Steam Sulfate 2.1 88.5 532 709 97.1 1.09 4.0 1.7 Sodium 1.9 86.5 502 669 96.4 2.25 4.5 2.6

2.2582

Claims (1)

SUMMARY OF THE INVENTION A process for the preparation of high-temperature, pulverized pulps for further chemical processing by the wood grain detection by pre-hydrolysis or autohydrolysis followed by alkali treatment, characterized in that the chips after pre-hydrolysis or autohydrolysis are de-identified in NaOH solution, wherein the alkali level is, 4 to 22% Na 2 O, preferably 6 to 18% Na 2 O calculated on the weight of the wood, in the presence of an oxidation-reduction catalyst, usually anthraquinone and its derivatives in an amount of 0.01 to 2%, preferably 0.0 to 0.2% calculated on the weight of wood. Severografia, n. P. Plant 7, Most