DE1098804B - Process for pretreating wood prior to sulphite boiling - Google Patents

Description

The invention relates to a method for the continuous pretreatment of wood before sulphite boiling with milk of lime, which results in considerably higher yields in the subsequent sulphite boil of cellulose with at the same time significantly improved parchment properties than with the boiling of untreated wood under otherwise identical conditions.

It is well known. Wood or other cellulosic Treat raw materials with aqueous alkalis or alkaline earths before sulphite boiling by adding either directly in the cooker or in another suitable container with a multiple of theirs Weight of such solutions are added and the lye is allowed to act for 1 or more hours to the wood to incorporate as much liquid and alkali or alkaline earth as possible. To do the soaking process favor, the lye is pumped around and the wood-lye mixture is sometimes subjected to pressure or vacuum treatment subject. The excess lye is then drained off. This intense treatment results in a practically complete impregnation of the wood by adding a degree of impregnation of about 2.0 is achieved, with the degree of impregnation after the treatment in 1 part by weight parts by weight of water contained in dry wood are to be understood.

It is obvious that this intensive treatment aimed at as complete a saturation as possible can only be carried out intermittently and that the same can be carried out continuously has not yet succeeded.

In contrast, the main feature of the invention is the continuous design of the pretreatment. This is made possible by the surprising finding that in just a few minutes of The small amounts of water absorbed by the wood chips are sufficient to absorb the Effect of increasing the yield and improving the parchment properties of the connected Sulphite boiling obtained pulps. This rapid absorption of milk of lime is made possible by demonstrated the experiment described below.

Spruce wood chips, as they are used in pulp production Common were with 10% moisture in a rotating cylindrical vessel with 0.9 parts of their weight were added to milk of lime and the time course of liquid intake was followed. The following picture emerged:

After minutes Degree of impregnation 0.5
1 0.60
0.65

Process for the pretreatment of wood
before the sulphite boil

Applicant:

As Chaffenburger Zellstoffwerke
Corporation,
Redenfelden (Obb.)

Dr. Alfred Ogait, Aschaffenburg,
has been named as the inventor

After minutes Degree of impregnation 1.5 0.70 2.5 0.75 6th 0.80 15th 0.86 60 1.00

As can be seen, a degree of saturation of 0.65 is already after one minute and it is after 6 minutes such of 0.8 has been achieved. This low degree of impregnation is, as already mentioned and from the Examples 1 to 3 can be seen, completely sufficient to produce a considerable amount in the subsequent sulphite boiling To achieve an increase in yield and improvement of the parchment properties.

The results reported above allow the pretreatment with milk of lime to be carried out continuously perform. According to the invention, the procedure can be, for example, that the wood chips lets pass a rotating drum and at the same time adds milk of lime. The amount of this is adapted to the moisture content of the wood and dimensioned so that this after the treatment has a degree of impregnation of, for example, 0.8. Pretreatment can be done in an even simpler way be made in such a way that the wood chips transported on the conveyor belt

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sprayed with milk of lime, preferably in the places where the wood chips transition from one conveyor belt to the other subjected to mechanical processing with the milk of lime will. Working with a drum is definitely preferable because of the better mixing.

The possibility of continuous pre-treatment is not the only advantage of the process after the invention. Another advantage is that with the connected sulphite boiling the cooking acid is nowhere near as much diluted as after the pretreatment after the already known procedures. This is explained below.

When impregnating with a multiple excess of milk of lime and at least 1 hour exposure with the aid of hydraulic pressure with simultaneous fluid circulation according to the known method, the wood chips absorb, as already mentioned, about twice the amount of their dry weight in water. Since the weight ratio of wood to liquid is about 1: 4.5 during the subsequent sulphite boiling, the cooker filled with the impregnated wood chips can only absorb 2.5 times the weight of the wood in cooking acid, i.e. only 55% of the normal amount. As a result, they are diluted by about 45%. In contrast, in the case of impregnation according to the method according to the invention, when a degree of impregnation of 0.8, for example, is reached, 3.7 parts of cooking acid per 1 part by weight of wood can be added to the cooker, so that the cooking acid is only diluted by just under 20%. _{So if you want to cook with an SO 2} content of the cooking acid of at least 4 to 5% SO ₂ required for normal cooking, the cooking acid to be fed to the cooker would have to contain 7.5 to 9% SO ₂ in the former case, while in the process according to the invention, an SO ₂ content of 5 to 6% would be sufficient. The production of a cooking acid with 5 to 6% SO ₂ with a normal lime content (about 1% CaO) does not cause any particular difficulties, while the production of one with more than 7% _{requires the use of liquid SO 2} , which makes it considerably more expensive.

Another feature of the invention is that the finished impregnated wood before the sulfite boiling is initially left to the action of the lime. In special tests it was found that that with increasing exposure time, the pulp yields in the one following the impregnation Sulphite boiling increase significantly, as can be seen from Examples 1 and 2.

example 1

Wood chips of spruce wood with 10% moisture were treated with 0.7 parts by weight of the absolutely dry wood weight of a milk of lime with 12.5 g CaO per liter for 15 minutes in a rotating cylindrical vessel, the liquid being completely absorbed. The wood then had a degree of impregnation of 0.8 and contained 1.0% CaO. The impregnated wood chips were left to the action of the lime at room temperature and then digested under exactly the same cooking conditions with a cooking acid containing 6.3% SO ₂ and 1.1% CaO at a maximum temperature of 127 ° C. and 5 atmospheres.

The results were the following: cellulose
yield Increased yield
opposite to
untreated . Exposure time Exposure
Degree from wood tem wood
in% of ^a of lime na.cn
Johnsen -
TNJ η 1 1 Fabric weight IN 011 53.7 _ Untreated ... 45 55.1 2.6 ίο 1 hour 46 56.0 4.3 3 hours .... 46.5 56.2 4.7 6 hours .... 46 56.4 5.0 9 hours .... 47 56.7 5.6 12 hours .... 47 56.8 5.8 15 16 hours .... 49

Example 2

Pretreatment as in Example 1, with the difference that the milk of lime 25 g CaO per liter

ao and the wood contained 2.0% Ca O after the treatment. The boilings were carried out with a cooking acid containing 5.5% SO ₂ and 1.1% CaO in 9.5 hours at 5.0 atmospheres and 129 ° C. maximum temperature. The results are shown in the table below

z5 emerges.

Exposure time
of lime
30th Exposure
Degree
after
Johnsen -
Noil cellulose
yield
in ° / o
from wood Increased yield
in%
from the fabric Untreated ...
1 hour
35 3 hours ....
6 hours ....
9 hours ....
12 hours ....
16 hours .... 61
65
66
66
61
63
63 54.6
57.1
57.9
58.4
58.6
58.7
59.0 4.6
6.0
6.9
7.3
7.5
8.1

As can be seen, at least 10 to 12 hours of exposure to the lime is required to achieve a To get maximum extra yield. In addition, it is apparent from the experiments that the yield increases depends considerably on the amount of lime incorporated into the wood during the pre-impregnation, in that at 1% CaO 5 to 6% and with 2% CaO 7 to 8% additional yield be achieved. The following shows how a further increase in the CaO content has an effect Example.

Example 3

Pretreatment also as in Example 1, but with 37.5 g CaO per liter of milk of lime, so that the wood contained 3.0% CaO after the treatment. After storage for 12 hours, the pre-impregnated wood was _{digested with a cooking acid containing 6.6% SO 2} and 0.84% CaO in 9.5 hours at a maximum of 126 ° C. A pulp with a Johnsen-Noll number of 73 was obtained in a yield of 65.7% of the weight of the wood.

Cooking with untreated wood under the same conditions gave a yield of 58.5% of the wood weight is a pulp with a Johnsen-Noll number of 70. The increase in yield as a result of the pretreatment with 3% CaO of the wood, this was about 12% of the pulp weight.

All of the pulps obtained after lime impregnation according to Examples 1 to 3 show this opposite those made of untreated wood are considerably

serte parchment properties, with a parallelism between yield and parchment ability was observed.

Finally, it should be mentioned that when the wood pretreated according to the invention is broken down with neutral or alkaline solutions of sulphites of sodium and ammonium are also considerably higher Yields are obtained than with similar cookings with untreated wood.

Claims (2)

Patent claims: 1. A method for pretreating wood prior to sulphite boiling with milk of lime, characterized in that that the pretreatment is carried out continuously by using the usual wood chips with simultaneous mechanical penetration working with so much milk of lime that 1 part by weight of the dry wood after treatment, including the original wood moisture content, does not contain more than 1 part by weight of water and the impregnated wood left to the action of the lime for some time, preferably several hours. 2. The method according to claim 1, characterized in that the added with the milk of lime Amount of lime 0.5 to 5%, preferably 1 to 2%, of dry wood, calculated as CaO, amounts to. Considered publications:
German Patent No. 665 959;
U.S. Patent No. 2,175,154.