FR2459326A1 - Direct prodn. of cellulosic pulp or paper from wood - by impregnating with solvent soln. of alkali(ne earth) hydroxide and kneading mechanically at above 100 degrees Celsius - Google Patents

Abstract

Wood is converted into cellulose pulp or directly into Kraft paper or cardboard, by impregnating the wood chips with a soln. of an alkali(ne earth) hydroxide in a solvent and kneading the impregnated material mechanically at above 100 deg.C. The process is simple to operate, uses smaller amts. of solvent than previous processes, and is based on much smaller plant and investment costs than prior papermaking processes.

Description

In conventional processes, the wood is treated with aqueous chemical solutions such as alkaline or alkaline earth salts of sulphydrioue acid, or sulfurous acid.

These techniques have the following drawbacks: - cooking time of several hours, up to 10 - 12 hours - large dilution of lacquer solutions, hence the need
to have a large volume of water and spend a
large amount of energy.

- the black-colored by-product must be evaporated for collection
to handle chemicals, hence a new denense
energetic.

- high investments due to volumes and pressure from
reactor service - pollution of the atmospheric atmosphere of sulfur by-products
gaseous (dimethylsulfide, methylmercaptanj - water pollution by liquid cooking residues.

Other processes, which have not occurred on an industrial level, consisting in treating the wood with solvents such as alcohol, amine, amino alcohol, sulfoxide, in an acid medium or in the presence of alkaline or alkaline earth bases.

The processes which have certain advantages compared to conventional processes such as greater cooking speed (30 'to 3 hours), and absence of pollution, are however difficult to justify economically, due to the excessive consumption of the solvent used. compared to the price of the latter.

This consumption is itself partly linked to the volume of solvent used (2 to 6 times the weight of the wood).

The method according to the invention makes it possible to make the methods of treating wood with solvents economical by: - considerable reduction in the consumption of solvent - reduction in the investments required I1 has, in addition, other advantages: in a very simple way the manufacturing
cardboard or plain paper and therefore create units
profitable industrial buildings, even in small dimensions
compatible with the French forest massif.

- possibility of transforming the crude reaction product into
chemical products.

The process according to the invention is characterized in that the wood, in the form of chips, is first of all sprayed with a reduced quantity of solvent containing chemicals such as soda, potash, alkaline or alkaline earth salts or bases etc ..., the weight of solvent used being equal to 0.2 until once the wood of the initial wood.

This solid mass is then introduced into an apparatus of the mixer or extruder type with a single or double screw, or screw press, in which the mass is brought for a short time (2 'to 10') at a temperature of 150 to 200 C .

The essential discovery forming the subject of the invention is the surprising fact that, under the simultaneous action of a mechanical action and of the temperature, the time for delignification of the wood is considerably reduced: 2 'to 10' instead of 30 'to 3 hours.

- The reaction mass takes on a particular pasty consistency
particularly suitable for continuous processing in a device
lage such as twin screw extruder - The gross paste reaction mass is very homogeneous if the action
was sufficiently energetic and this homogeneity
avoids further refining operations such as
to the elimination of the knots or particles which are induced, which are
necessary in conventional processes.

= The last point allows us to consider the use of waste
plants of all kinds, in particular of clear wood
skinned.

- Similarly, the homogeneity of the gross reaction mass makes it
an ideal material as the basis of a transformation process
chemical or biochemical of cellulose or lignin.

If you want to get paper directly
Kraft or cardboard using this process, we do
as follows: the extruder used for the basic reaction of delignification is equinated at the head of a device making it possible to obtain the reaction pasty mass in the form of a continuous ribbon of determined width and thickness. This is first passed between pressing rollers which express a thick black bond. The ribbon is then transformed into a felt of cellulosic fiber which, thanks to its mechanical strength, can be continuously passed through successive washing to remove the alkali lignin products which have become soluble in water, then in bleaching baths.

Conventional drying, icing, etc.

made on this strip lead to finally obtain Kraft paper or cardboard.

 There is, in this case, considerable savings compared to the traditional process since it avoids the operations of drying the cellulose pulp and re-suspending it in aqueous suspension.

This is made possible thanks to the low investment required by the operation of delignification of wood in an extruder and therefore of authorizing industrial units of reduced dimensions compatible with those for manufacturing Kraft paper or cardboard.

Among the chemicals which can be used for the delignification phase, there may be mentioned, without limitation: - sodium hydroxide - potassium hydroxide - alkali or alkaline earth sulfides - acetate, stearate, sodium or potassium phenate,
alone or in combination.

Among the solvents and without limitation: - glycol - glycerol - ethanolamines (mono, di or tri) - benzyl alcohol - ethylene d1amin.

The process can be implemented as follows:
Preparation of the reaction mixture
The wood chips are placed, for example, in an open rotary device of the tilting type, such as is commonly used for cement (concrete mixers). In addition, a solution of chemicals in a suitable solvent was prepared.

Keeping the device containing the shavings in rotation, water the wood with the appropriate amount of the previous solution. I1 may be necessary to perform this watering at a temperature of about 1000 C to keep the chemicals contained in solution.

During this operation, the chemical solution is absorbed by the chips which appear at the end of the operation as simply moistened on the surface.

Reaction phase
The impregnated chips are fed continuously in a screw extruder which includes 4 zones: - a feeding zone in which the chips are introduced
duits. Bulk density in this area 0.5.

- a preheating zone gradually bringing the mass to
a temperature of around 1900 C. Temns approximately 4 minutes.

In this zone and the previous one, the apparent density gradually drops from about 0.5 to 0.95. The consistency of the reaction mass becomes that of a thick paste.

- a cooling zone up to around 1000 C (duration
about 2 minutes) allowing a safe final entry.

Treatment of reaction mass: a) Case of celulose paste
The extruder will preferably produce the pasty product of
reaction (brown color) in the form of a continuous ribbon.

The ribbon first passes between expressing rollers which
removes a viscous black liquor, containing compounds
lignin, solvent and initial chemicals.

The tape, after passing, takes on the appearance of fiber felt
cellulosic and still contains a fraction of liquor
black.

It takes four watering and systematic watering to receive
about 98% of the initial solvent and chemicals
combined lignin.

The cellulose tape, after washing and oressåe, is dried and
pressed into bales.

b) Kraft paper - cardboard
The previous ribbon is treated according to conventional techniques
finishing to obtain the desired end product.

Treatment of the black liquor phase:
this can be distilled and the solvent recovered in a
thin film evaporator type device. There is one
solid phase containing lignin derivatives and about
20% of sodium carbonate can be polished to re
to collect sodium carbonate and energy, or used
as a chemical raw material.

EXAMPLE I
100 kg of dry wood shavings are watered. with a solution of 37.5 kg of glycol and 7.5 kg of caustic soda.

These impregnated chips are introduced into a screw extruder, with a total passage time of 12 minutes, including 4 minutes of mixing at 190 C.

The extruder mass at the speed of 20 kg per hour (useful volume of the extruder 5 liters) is collected at the outlet in the form of a ribbon 2 mm thick and 250 mm wide.

2.5 kg of extruded ribbon are sprayed and treated by washing with water. The cellulosic mass is dried and the washing waters are evaporated and distilled to dryness.

We obtain: - 915 g of cellulose pulp (yield on dry wood 53%) t oIO g of glycol (losses 6t) - 850 g of solid residue.

This after combustion leaves approximately 170 g of CO3N a2 EXAMPLE II
100 kg of wood chips (counted dry) are sprayed with a solution of 38 kg of monoethanolamine and 6 kg of caustic soda.

We operate as before but at 1800 C in the mixing zone.

Analysis of an extruded sample of 3.4 kg gives:
Cellulose paste: 1,287 g (Yield 54.5%)
Monoethanolamine: 852 g (loss 5%)
Solid residue: I.210 g which leaves after combustion:
18 g of sodium carbonate.

EXAMPLE III
Same as example 1, but with 0.5 kg of sunplementary sodium stearate. We observe a more regular extrusion and an identical yield.

Claims (1)

CLAIM Process for obtaining, from wood, either the cellulosic tab, or directly from the nanier type Kraft or cardboard, characterized in that naked fragments of wood impregnated with an alkali metal hydroxide solution are treated in alkaline earth in a solvent at a temperature higher than 100 C and by exerting a mechanical kneading action during the treatment.