HU185045B - Method for producing cellulose from annual plants chiefly from straw - Google Patents

Abstract

In the one-stage alkaline oxygenation of annual plants, preferably straw, the goal is to save energy, water and chemicals and to reduce the expenditure on equipment by reducing the hydromodule to values below 2.5. This is achieved by supplying the decomposition vessel with air preferably up to an excess pressure of 1.0 to 1.4 MPa before the decomposition is started, and then digesting under the usual conditions.

Description

The present invention relates to a process for the production of cellulose from annual plants, in particular straw, by digestion in a single step in an aqueous alkaline solution in the presence of oxygen.

Until now, there has been no known process for the alkaline digestion of cellulosic plant material with oxygen, which would yield a fully digested, bleachable cellulose in a single step. Although a process has been known for digesting straw with sodium carbonate as an excipient in the presence of oxygen, Revue, J. T. T. P. Paris 31, 4, 131-135 (1977), however, only a very hard, semi-cellulosic cellulose product could be obtained.

It has therefore been proposed to digest the straw in an aqueous solution of sodium hydroxide and sodium carbonate in the presence of oxygen by introducing pure oxygen at a partial pressure of 0.8 MPa into the digester; v. D 21 C / 209 744 German patent application description. Although this process was able to produce 20 fully digested, bleachable cellulose with good strength properties, it also had various disadvantages. Thus, the introduction of pure oxygen into the process necessitated special safety measures which required the use of more expensive equipment 25 and increased the hydro modulus in the boiler to 4 to 5, which increased the energy, water and chemical requirements. .

SUMMARY OF THE INVENTION The object of the present invention was to provide a method for alkaline digestion of annual plants which can be carried out in relatively simple equipment with less energy, water and chemicals than previously known. In addition, we aimed to reduce hydro-modulus to less than 2.5 during one-step alkaline digestion in the presence of oxygen. 35

These objects are accomplished in accordance with the present invention by introducing air into the digestion vessel prior to the commencement of the digestion process, preferably to a pressure of 1.0 to 1.4 MPa, and then to the digestion under spray conditions. The total amount of alkali to be added to the digestion process is preferably 10 to 16% Na ₂ O based on the dry weight of the starting material used. The digestion is preferably carried out at a temperature between 413 K and 433 K. In a particularly preferred embodiment of the process of the invention, the alkaline disintegrant is a mixture of sodium hydroxide and sodium carbonate in a ratio of 1: 3 to 3: 1.

In addition to reducing the hydro modulus below 2.5, the process of the present invention results in significant energy, water and chemical savings and requires simple equipment, and, surprisingly, the partial pressure of oxygen can be substantially compared to the smoldering processes in the presence of oxygen, which also has very significant economic benefits. A further advantage is that the process according to the invention does not require any special safety precautions for known processes using pure oxygen. Due to the smaller hydro-modulus of the process according to the invention, the amount of litter produced is also reduced.

Practical embodiments of the process of the invention are illustrated by the following examples. In addition to the Examples illustrating the process of the present invention, comparative examples of prior art processes are provided below to illustrate more clearly the advantages of the process of the invention. The measured values for the properties of the cellulose products 35 obtained by each method are summarized in the attached table.

Table I

Example Kappa- song Average degree of polymerization (glucose units) Yield (%) breaking length (M) Strain (%) Dual- folding burst index pressure (MPa) COD (Chemical Oxygen Demand) (gO ₂ / l) First 35.7 1173 45.8 7276 3.60 715 0.262 126.6 Second 26.9 1171 46.5 7329 3.80 1399 0.279 134.6 Third 17.9 929 42.1 6390 3.10 298 0.249 152.2 4th 28.3 985 50.9 6585 3.20 624 0.260 181.5 5th 26.9 - 930 37.7 6740 2.63 282 0.262 167.0 6th 34.5 973 51.9 6910 3.13 593 0.282 118.0 7th 26.4 868 42.3 6320 2.76 177 0.263 162.6 8th 42.7 1042 46.0 6500 3.03 540 0,270 136.2

comparative

example First 23.5 662 37.8 4815 2.30 10 0,145 135.7 Second 22.7 969 49.0 6370 3.60 795 0.258 106.3 Third 29.2 911 47.5 5880 4.41 738 0.216 116.7 4th 17.1 923 45.6 6200 3.51 540 0.252 104.5

-2185,045

Example 1

Chopped wheat straw from wheat grown in the German Democratic Republic is treated with an aqueous solution of 10% Na ₂ O 1 and an appropriate amount of a protective colloid of 1% magnesium sulfate in such a proportion that the mixture contains 25% straw chips. Air was introduced into the digestion vessel at a partial pressure of 1.0 MPa and subsequently the digestion reaction mixture was heated to 423 ° C for 60 minutes. The digestion is then completed within 60 minutes of cooking time. After separation of the leach liquor, completely digested cellulose is obtained. The properties of the cellulose thus obtained, together with the properties of the cellulose product of the following examples, are shown in the accompanying table.

Example 2

An aqueous solution containing 12% Na ₂ O in sodium hydroxide (12% Na ₂ O) is added to the chopped wheat straw produced in the German Democratic Republic and subjected to the digestion as described in Example 1.

Example 3

An aqueous solution containing 16% Na ₂ O in sodium hydroxide (16% Na ₂ O) was added to the chopped wheat straw produced in the German Democratic Republic and subjected to the digestion as described in Example 1.

Example 4

An aqueous solution containing 12% sodium hydroxide equivalent to 12% Na ₂ O is added to chopped wheat straw produced in the German Democratic Republic, and the digestion is continued under the conditions described in Example 1. juice.

Example 5

An aqueous solution containing 16% sodium hydroxide equivalent to 16% Na ₂ O is added to chopped wheat straw produced in the German Democratic Republic, and the digestion is continued under the conditions described in Example 1. juice.

Example 6

To a shredded wheat straw produced in the German Democratic Republic, an aqueous solution containing sodium hydroxide equivalent to 12% Wa ₂ O and 1% magnesium sulfate as a protective colloid is added to a density of 33%. Air is introduced into the digestion vessel up to a partial pressure of 0.9 MPa and oxygen up to a partial pressure of 0.1 MPa, while the total partial oxygen pressure corresponds to an air pressure of 1.4 MPa. The digestion reaction mixture was heated to 413 ° C for 60 minutes and then subjected to digestion for 60 minutes.

Example 7

To a chopped straw of wheat produced in the German Democratic Republic, an aqueous solution containing sodium hydroxide equivalent to 16% Na ₂ O is added to a density of 40%. The digestion was carried out as described in Example 6 but at 423 ° K.

Example 8

An aqueous solution of 11.8% Na ₂ O and 11.8% Na ₂ O in sodium hydroxide is added to 25% wheat straw of wheat straw produced in the German Democratic Republic contain. The digestion was carried out under the conditions described in Example 1 as described therein.

Comparative Example 1

An aqueous solution of sodium hydroxide corresponding to 12% Na ₂ O and 1% magnesium sulfate as a protective colloid is added to a chopped straw of wheat produced in the German Democratic Republic according to a known method to a density of 25%. Oxygen was introduced into the digestion vessel at a partial pressure of 0.8 MPa and the digestion reaction mixture was heated to 423 ° C for 60 minutes. The digestion is then carried out at reflux for 40 minutes.

Comparative Example 2

Produced in the German Democratic Republic, chopped wheat straw in a 25% aqueous solution was added to a density of material, containing 6% of Na ₂ O has a suitable amount of sodium hydroxide and 6% Na ₂ O equivalent amount of sodium carbonate. The digestion was carried out under the conditions described in Example 1 as described therein.

Comparative Example 3

An aqueous solution of sodium hydroxide and sodium carbonate equivalent to 16% Na ₂ O is added to 25% wheat straw of wheat straw produced in the German Democratic Republic, with a relative proportion of sodium hydroxide and 1: 3rd The digestion was carried out under the conditions described in Example 1 as described therein.

185,045

Comparative Example 4

An aqueous solution of sodium hydroxide and sodium carbonate equivalent to 16% Na ₂ O is added to 25% wheat straw of wheat straw produced in the German Democratic Republic, with a relative proportion of sodium hydroxide and 3: 1. The digestion was carried out under the conditions described in Example 1 as described therein.

Claims (2)

1. Process for the production of cellulose from annual plants, in particular straw, in aqueous alkaline solution, oxygen 5 in one step, characterized in that air is introduced into the digestion vessel prior to the commencement of the digestion process, preferably up to an excess pressure of 1, 4, 4 MPa and then digested under alkaline conditions 10 to 16 in the presence of an alkaline compound corresponding to 1% sodium oxide at a temperature of 413-433 ° K. 2. A process according to claim 1 wherein the alkali compound is a mixture of sodium hydroxide and sodium carbonate in a ratio of 1: 3 to 3: 1.