NO813257L - PROCEDURE FOR DELIGNIFICATION OF LIGNOCELLULOS MATERIALS - Google Patents

Description

The invention relates to a method for delignification of lignocellulosic material, such as e.g. wood, straw, reeds, bagasse, hemp and the like using a chemical digestion process. The method is characterized in that the digestion is carried out at a bath ratio of 1:3 to 1:50 in the presence of a thioamide, thiourea, thiocarbamate or dithiocarbamate compound.

The thiourea and dithiocarbamate compounds are cyclic as well as preferably acyclic compounds. Thereby, the acyclic thiourea derivatives are particularly preferred.

In particular, compounds with the formula are used

in which

X means alkyl with 1-12 carbon atoms, cycloalkyl, aryl, aralkyl,

R-^, R2, R^ and R^ independently of each other mean hydrogen-alkyl with 1-12 carbon atoms, lower alkoxy-lower alkyl, phenyl, benzyl or with halogen, lower alkyl, lower alkoxy, lower alkoxy-lower alkyl or sulfo-substituted phenyl or benzyl or the pairs of substituents ( R^ and R2) and (R^ and R^) independently of each other, each time together with the nitrogen atom connecting them, means a five- or six-ringed hetrocyclic residue or R^ and R2 together mean the alkylene with 2 or 3 carbon atoms or the phenylene and M .means a cation.

In the definition of the residues of the compounds of formula (1) and in the following formulas, lower alkyl and lower alkyl usually mean such groups or group constituents which have 1-5, especially 1-3 carbon atoms such as e.g. methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl. or amyl respectively methoxy, ethoxy or isopropoxy. Halogen is, for example, fluorine, bromine or preferably chlorine.

The term "sulfo" means the sulfonic acid group. Aryl preferably includes phenyl and aralkyl is especially benzyl.

If the substituents X, R-^, R2, R^ and R^ mean an alkyl group, then they can be linear or branched. These alkyl groups can have 1-12 carbon atoms, preferably however 1-5 and especially 1-3 carbon atoms. Examples of such alkyl residues are methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, n-hexyl, n-octyl or d-dodecyl.

If R 1 , R 2 , R 2 and R 2 mean a lower alkoxy-lower alkyl group, then it is above all alkoxyalkyl with a total of 2-4 carba atoms, such as e.g. 3-methoxyethyl or 3-ethoxyethyl.

The example of cycloalkyl in the sense of X is cyclopentyl or preferably cyclohexyl.

X in the sense of aralkyl usually means phenyl-

ethyl or primarily benzyl, while aryl conveniently means naphthyl, diphenyl or above all phenyl. Aralkyl-

and the aryl residues may be substituted with halogen, lower alkyl, lower alkoxy or sulfo.

Preferred substituents in the phenyl and benzyl group of the residue X and the R residues are e.g. halogen, lower alkyl or lower alkoxy such as e.g. chlorine, methyl or methoxy.

When the substituent pairs (R^ and P^) and (R^ and R^)

together rncd the common nitrogen atom means a heterocyclic residue, then this is, for example, pyrrolidino, piperidino, pipe-colino, morpholino or thiomorpholino.

Means and R^together the alkylene with 2 or 3 carbon atoms, then they form with the connecting nitrogen atom a cyclic thiourea compound, which e.g. ethylenethiourea or propylenethiourea. If R^ and R^ together mean phenyl, then with the thiourido group they form phenylenethio-urea which can be substituted by R2 and R^. Thioura-sil-2 can also be used as cyclic thiourea compounds.

The substituent X is preferably a lower alkyl or especially one R3R4N group. R 1 , R 2 , R 3 and R 4 are preferably hydrogen or each time a lower alkyl group such as methyl or ethyl.

As a cation, M can for example mean hydrogen, an alkali metal, especially sodium or potassium, an alkaline earth metal, especially magnesium or calcium or an ammonium group. The term "ammonium group" as used here refers both to ammonium (NH^+J) and also to substituted ammonium groups.

The latter derives, e.g. from aliphatic amines such as di- or triethyl- or mono-, di- or triethanolamine or cycloaliphatic amines such as cyclohexylamine. Preferably, M represents hydrogen, an alkali metal or ammonium.

Preferably, according to the invention, compounds with the formula are used

in which

X represents lower alkyl or

and R5, R6, R7 and

Rg independently means hydrogen or lower alkyl. Thereby, X can preferably also mean phenyl.

Among the compounds of formula (2), those where X± means methyl, NH 2 or -N(CH 3 ) 2 and R 5 and R 6 mean hydrogen or methyl are particularly preferred. Typical representatives here are thioacetamide, thiobenzamide, tetramethylthiourea and above all thiourea.

Dithiocarbamates with the formula are also particularly suitable

wherein R₁ and R₂ have the indicated meaning and mean an alkali metal or ammonium.

In formula (3), R 1 and R 2 preferably mean lower alkyl such as methyl or ethyl. The most important representative of this group is sodium diethyldithiocarbamate. Further thiocarbamates are e.g. piperidine sodium dithiocarbamate or diethylammonium diethyldithiocarbamate.

According to the invention, the compounds of formula (1) to (3) are primarily used as additives for the production of ac cellulose from lignocellulosic materials, with which satisfactory cellulose yields are obtained at a given Kappa number (TAPPI method T-236 M-60).

The amounts used in which the compounds of formulas (1) to (3) are added to the pulp liquid range between 0.001 and 5% by weight, preferably 0.001 and 2.5% by weight, referred to lignocellulosic material.

They mentioned thioamines, thiocarbamides, thiocarbamates

and dithiocarbamates are used alone or preferably in combination with an organic, cyclic keto- and/or hydroxy group-containing compound.

As organic cyclic keto- and/or hydroxy group-containing compounds, for example, mono-, di- and/or polycyclic, especially di-, tri- and/or tetracyclic compounds containing two keto groups and/or two hydroxy groups come into consideration. Preferably, 1,4-naphthaquinone, 9,10-anthraquinone, Diels-Alder adducts of 1,3-diene, e.g. of unsubstituted or substituted butadienes to p-benzoquinone and/or 1,4-naphthoquinone and/or their monoalkyl-, dialkyl-, hydroxy-, amino-, alkyloxy-, alkylamino, halogen and/or sulpho derivatives.

For example, according to the invention, 0,10-anthraquinone, 2-methyl-anthraquinone, 2-ethylanthraquinone, dichloro-anthraquinone, 2,3-dimethylanthraquinone, 2,6-dimethylanthraquinone, 2,7-dimethylanthraquinone, 2-aminoanthraquinone, 1- methoxyanthraquinone, 2-methoxyanthraquinone, anthraquinone-2-sulfonic acid or

.anthraquinone-disulfonic acid (as alkali metal salts), 1,2-benz-anthraquinone, phenanthrenequinone, anthrone, 10-methyleneanthrone, di^hydroxyanthracene, dihydroxyanthracene sulfonate, tetrahydro-9,10-diketoanthracene, or 1,3-dimethyl-tetrahydro-9,10 -diketoanthracene. According to the invention, two or more of these keto compounds can be used. Preferably use

es only one of these substances and especially preferred

becomes 9,10-anthraquinone or 2-methyl-9,10-anthraquinone together with the aforementioned thioamines, thiocarbamides or dithiocarbamates.

According to the invention, mixtures of, for example, 50-95% by weight of one or more organic cyclic keto- and/or hydroxy group-containing compounds, especially 9,10-anthraquinone and 5-50% by weight of one or more of the compounds with the formula (1) can be used to (3). Mixtures of 60 or preferably 70-90% by weight of a cyclic keto- and/or hydroxy group-containing compound, especially 9,10-anthraquinone or 2-methylquinone and 10-40, preferably 10-30% by weight of a compound with the formula (1) to (3), especially thiourea, thioacetamide, tetramethylthiourea or sodium diethyldithiocarbamate. Of interest are mixtures of thiourea and anthraquinone which are used in a mixture ratio of 1:3 or i:4, or preferably from 1:9 to 3:7.

The amounts used in which the mixtures of compounds

one with the formulas (1) to (3) and the cyclic keto- and/or

hydroxy compounds for pulp liquids ranges between 0.001 and 1% by weight, preferably 0.001 and 0.2% by weight, referred to lignocellulosic material.

Wood is preferably used as lignocellulosic material. This is usually transferred first in cuts or chips. The tree can consist of conifers, such as balsam fir, spruce or pine, or of hardwood, e.g. maple, birch, beech, oak, aspen or poplar. The lignocellulose material can, however, also be available in fiber form.

The chemical digestion for cellulose production conveniently takes place in an alkaline medium, e.g. according to the sulphate or kraft digestion method, the soda digestion method, sulphite boiling under semi-alkaline conditions or the so-called oxygen-alkali method.

In the latter case, oxygen can be used before, during or after the alkali treatment. The polysulphide method can be considered as a further digestion method for the cellulose removal according to the invention.

This can be carried out both alkaline and neutral.

The neutral sulphite digestion method can in particular be carried out using said mixtures of thiofor compounds etc. and the cyclic keto compounds. Furthermore, one can boil the lignocellulosic material in a first cooking stage in the presence of sodium hydroxide, the fibrous treated material and subject the fibrous material to a second cooking stage,

the second boiling step being carried out in the presence of an alkaline solution of a peroxide, e.g. hydrogen peroxide or alkali peroxide.

The digestion method according to the invention can be carried out at a temperature from 50 to 250°C, preferably 120 to 200°C. The digestion takes place in a bath ratio between lignocellulosic material and pulp liquid of 1:3 to 1:50, preferably 1:3 to 1:10.

Preferably, the lignocellulosic material is treated in

a closed container in a bath ratio of 1:3 to 1:10 with an alkaline preparation containing 0.001 to 0.2% by weight

of a mixture of a compound of formula (1) to (3) and an anthraquinone compound referred to lignocellulosic material. The alkali used is preferably sodium hydroxide and/or magnesium hydroxide, which is usually used in the form of a 2 to 15% aqueous solution. Very good regulators are also achieved with a combination of the aforementioned sodium hydroxide solution with sodium sulphide according to the so-called lraft method. Sodium sulphide is used, preferably in an amount of 0.01 to 40 g/litre, preferably 0.1 to 25 g/litre.

In relation to the use of anthraquinone alone as a known delignifier, the method according to the invention excels especially when using said mixture in that it produces pulp which leads to a paper with better firmness properties. Above all, thanks to the synergistic effect of the mixture used, it is possible to achieve a reduction of expensive anthraquinone derivatives with practically the same yield and dewooding rate.

In the following examples, the chlorine number is determined as a measure of the lignin residue content and the obtained yields. Thereby the percentages are percentage by weight and the parts are parts by weight. Atro equals absolutely dry.

Example 1-3; Each time three samples of wood cuttings (Picea Abies, max. thickness equal to 3 mm) of each 25 g are mixed in an autoclave at 80°C with 100 ml of an aqueous 1,18-N-sodium hydroxide solution and flushed with nitrogen. Then each time the alkaline mixture is mixed with one of the mixtures listed in the following table (2nd column) of thiourea and 9,10-anthraquinone in the indicated percentages (3rd column) and mixing ratio (4th column), after which the temperature is increased to 173°C and the digestion mixture is kept at this temperature for two hours. After cooling, the raw pulp is filtered off, washed with warm water and rinsed with deionized water. The pulp is then defibrated and compressed into a leaf. The average chlorine number and the average yields of the three trials of individual examples are then determined. The obtained data are listed according to table 1. The yields of obtained pulp in % by weight referred to the wood used are indicated in the last column of the table. The pulp's equation content is calculated by multiplying the chlorine consumption by a factor of 0.90 according to the "Scandinavian pulp, paper and board testing committee (Scan-C 29:72)". The corresponding chlorine number is indicated in the table's 5th column. The carbon hydrate content in the pulp is determined by the difference between pulp yield and equation content. In the last column of the table, the equation-free substance yield is thus listed. Example 4-6: Each time three samples of wood cuts for each. 25 g are mixed in an autoclave at 80°C with 100 ml of an aqueous 1,11-N-sodium hydroxide solution and 1.13 g of sodium sulphide and sparged with nitrogen. Then each time the alkaline mixture is mixed with one of the mixtures listed in the following table 2 (column 2) of thiourea and 9,10-anthraquinone in the percentage amounts (column three) and mixing ratio (column 4) indicated there, after which the temperature! is increased to 168°C and the digestion mixture is kept at this temperature for 2 hours. After cooling, the raw pulp is filtered off, washed with warm water and rinsed with deionized water. The pulp is then defibrated and compressed into a sheet. The chlorine number and the yields of individual trials and the mean value of the three corresponding trials are then determined. The results are listed in table 2. The chlorine number is indicated in the table's column 5, while in columns 6 and 7, respectively, the pulp yield and the equation-free substance yield in % are listed, referred to the wood used.

Examples 7 - 9: Each time three samples of wood cuts of 25 g each are mixed in an autoclave at 80°C with 100 ml of an aqueous 1-N sodium hydroxide solution and 2 g! sodium sulphide and flushed with nitrogen. The alkaline mixture is then mixed each time. ing with one of the mixtures listed in the following table 3 (column 2) of thiourea and 9,10-anthraquinone in the percentage amounts (column 3) and mixing ratio (column 4) indicated there, whereupon the temperature increases to 168°C and the slurry mixture is kept 2 hours at this temperature. After cooling, the raw pulp is filtered off, washed with warm water and rinsed with deionized water. The pulp is then fiberized and compressed into a leaf. The chlorine number and yield of individual trials and the mean value of the three corresponding trials are then determined. The results are listed in table 3. The chlorine number is indicated in column 5 of the table, while in columns 6 and 7, respectively, the pulp yield and the lignin-free substance yield are listed in percent, referred to the wood used. Example 10: Each time three samples of wood cuts of 25 g each are mixed in an autoclave at 80°C with 100 ml of an aqueous 1,18-N-sodium hydroxide solution and flushed with nitrogen. Then each time the alkaline mixture is mixed on the one hand without additive and on the other with thiourea, respectively 9,10-anthraquinone in the percentage amounts indicated there (column 2), after which the temperature1 is increased to 173°C and the digestion mixture is kept for two hours at this temperature. After cooling, the raw pulp is filtered off, washed with warm water and rinsed with deionized water. The pulp is then defibrated and compressed into a sheet. The chlorine number and the yields of individual trials and the average of the three corresponding trials are then determined. The results are listed in table 4. The chlorine figure is indicated in column 3 of the table, while in columns 4 and 5 respectively, the pulp yield and the non-equation material yield are listed in percent, referred to the wood used.

As can be seen from example 10, thiourea

also used alone to increase the selectivity of the process.

However, approx. 40 times more thiourea than anthraquinone to achieve the same effect. The fact that with a mixture of up to 30% thiourea and 70% anthraquinone the same effect is achieved as with pure anthraquinone (see examples 1-9), therefore shows that the combination of these additives shows a synergistic effect.

Example 11-20: Each time two samples of woodcuts on each

25 g are mixed in an autoclave at 80°C with 100 ml of an aqueous 1.118 or 1.12 3-H sodium hydroxide solution and rinsed

with nitrogen. Then each time the alkaline mixture is mixed on the one hand without additive or with the addition of anthraquinone and on the other hand with tetramethylthiourea, ethylenethiourea, benzothioamide, respectively sodium diethyldithiocarbamate in the indicated percentage amounts (table 5, column 3), after which the temperature is increased to 173°C

and the digestion mixture is kept for two hours at this temperature. After cooling, the raw pulp is filtered off, washed with warm water and rinsed with deionized water. The pulp is then defibrated and compressed into a leaf. The chlorine number is then determined and the yields of individual trials and the average value of the two corresponding trials are calculated. the results are listed in table 5. The chlorine number is indicated in the table's column 5, while in columns 6 and 7, respectively, the pulp yield and the equation-free substance yield are listed in percent, referred to the wood used.

Example 21 - 35: Each time two samples of woodcuts on each

25 g are mixed in an autoclave at 80°C with 100 ml of an aqueous 1.116-W or 1.126-N sodium hydroxide solution and flushed with nitrogen. Then each time the alkaline mixture is mixed on the one hand with the addition of anthraquinone and on the other hand with ethylenethiourea, thioacetamide, thiobenzamide, respectively thiouracil-2 in the percentage amounts indicated there (column 3, table 6), after which the temperature is increased to 173°C and the digestion mixture is kept at this temperature for two hours. After cooling, the raw pulp is filtered off and washed with warm water and rinse with deionized water. The pulp is then defibrated and compressed into a leaf. The chlorine number and yields of the individual trials and the average value of the two corresponding trials are then determined. The results are listed in table 6. The chlorine number is indicated in column 6 of the table, while in column 6 and column 7, respectively, the pulp yield and the equation-free material yield are indicated in percent, with reference to the wood used. Examples 36 - 41; Each time three samples of wood cuts of 25 g each are mixed in an autoclave at 80°C with 100 ml of an aqueous 1.10 W sodium hydroxide solution (Example 39-41 in addition 11 g/l ice phase 2 S) and flushed with nitrogen. Then each time the alkaline mixture is mixed on the one hand with the addition of anthraquinone or 2-methylanthraquinone and on the other hand with thiourea, thiourea/2-methylanthraquinone (1:4), thiourea/anthraquinone 1:3, thioacetamide/anthraquinone (1:3) in the percentage amounts indicated there (column 3 in Table 7), after which the temperature is increased to 173°C (Example 39.41: 168°C) and the slurry mixture is kept for two hours ( example 39 - 41: 53 minutes). After cooling, the raw pulp is filtered, washed with warm water and rinsed with deionized water. The pulp is then defibrated and compressed into a leaf. Then, the chlorine number and the conversions of the individual trials and the average value of the three corresponding trials are determined. The results are listed in table 7. The chlorine number is indicated in column 5 of the table, while in column 6 and column 7, respectively, the pulp yield and the equation-free material yield in percent are listed based on the amount of wood used.

Example 4 2 - 53: Each time three samples of wood cuts on each

25 g are mixed in an autoclave at 80°G with 100 ml of an aqueous 1.10 N sodium hydroxide solution (examples 46 - 49 in addition 11 g/l Na2S, examples 50 - 53 in addition 40.6 g/l Na2S) and rinsed with nitrogen. The alkaline mixture is then mixed on one side with anthraquinone and on the other side with thiourea, respectively thiourea/anthraquinone (1:3)

in the quantities indicated there (column 3, table 8), after which the temperature is increased to 160°C (example 46 - 53 150oc) and the digestion mixture is kept for 90 minutes (example 46 - 53 45 min.) at this temperature. After cooling, the raw pulp is filtered off, washed with warm water and rinsed with deionized water. The pulp is then defibrated and pressed into a leaf. The chlorine number and the yields of the individual trials are then determined and average values of the three corresponding trials are calculated. The results are listed in table 8. The chlorine number is indicated in column 5 of the table, while in column 6 and column 7, respectively, the pulp yield and the lignin-free substance yield are indicated in percent, referred to the amount of wood used.

In addition, part of the raw pulp and viscosity is bleached

of the cellulose is determined. The value is indicated in column 8 of the table.

Example 54-57: Each time 700 g (atro) wood chips (Mill chips) of spruce wood (picea excelsa) are rinsed with boiling water at 80°C in an autoclave. The boiling liquor is specified in table 9. It is heated l°c per minute to 173°C (Example 54 - 56) or 168°C (Example 57), respectively, and the digestion mixture is held for two hours (Example 54 - 56) or one hour (Example 57) respectively at this temperature. It is then cooled and the cellulose thus formed is prepared in the usual way and analyzed. The data is shown in the following table 9. In addition, cellulose ground (each time 6 different degrees of grounding) and the corresponding physical properties are determined. The results are summarized in subsequent tables 10 - 13, as tear values are listed in relation to the corresponding tear length for comparison purposes.

From the ratio of tear values to the corresponding tear lengths, it appears that the cellulose from examples 54 and 55 gives roughly equal strengths, although the Kappa number of example 55 is somewhat higher. In addition, it should be noted that the sorted yields of example 55 are around approx. 3.7% higher. As seen by the difference in lignin-free yields (2.6%)

is this dividend increase attributable to a larger coal-new-drate dividend. The raw material part from example 55 is somewhat better than from example 54. The viscosity is also improved.

If one compares the tear value with the corresponding tear length of the cellulose from examples 54 and 57 (kraft process: 20% sulphidity), the following can be established. The cellulose boiled with thiourea shows better firmness properties than that with anthraquinone, although the lignin content is higher. This is also in line with the higher viscosity, the yield is improved. The firmness properties, viscosity and lignin-free yield of the cellulose from example 56 are comparable to the corresponding properties from the cellulose from a kraft process as described in example 57 (sulfidity approx. 20%), although a similar sulfidity is given in all cases in the case of thiourea, it is only half as large (approx. 10%).

Claims (15)

1. Method for delignification of lignocellulosic material by a digestion method, characterized in that the digestion is carried out at a bath ratio of 1:3 to 1:50 in the presence of a thioamide, thiourea, thiocarbamate or dithiocarbamate compound. 2. Method according to claim 1, characterized in that cyclic or acyclic thiourea or dithiocarbamate compounds are used. 3. Method according to one of claims 1 and 2, characterized in that an acyclic thiourea compound is used. 4. Method according to claim 1, characterized in that a compound of formula is used: wherein X means alkyl of 1-12 carbon atoms, cycloalkyl, aryl, aralkyl, R-^, R^, R^ and R^ independently mean hydrogen, alkyl with 1-12 carbon atoms, lower alkoxy-lower alkyl, phenyl, benzyl or with halogen, lower alkyl, lower alkoxy, lower alkoxy-lower alkyl or sulfo-substituted phenyl or benzyl or the pairs of substituents (R^ and R^ ) and (R^ and R^) mean independently of each other, each time together with 1' the connecting nitrogen atom a five- or six-membered hetrocyclic residue or and R2 together mean the alkylene with 2 or 3 carbon atoms or, the phenyl and M means a cation. 5. Method according to claim 4, characterized in that a compound of formula is used: 7 wherein means lower alkyl or -N and 8 R 1 , R 2 , R 2 and R 2 independently mean hydrogen or lower alkyl. 6. Method according to claim 4, characterized in that a compound of formula is used: in which R^ and R^ independently of each other mean hydrogen, alkyl of 1-12 carbon atoms, lower alkoxy-lower alkyl, phenyl, benzyl or with halogen, lower alkyl, lower alkoxy, lower alkoxy-lower alkyl or sulfo-substituted phenyl or benzyl or R^ and R 2 mean together with the connecting nitrogen atom a five- or six-membered hetrocyclic residue and M. means an alkali metal or ammonium. 7. Method according to claim 6, characterized in that a compound of formula (3) is used in which R-1 and R2 mean lower alkyl. 8. Method according to claim 1, characterized in that, in addition to the thioamide, thiourea, thiocarbamate or dithiocarbamate compound, an organic, cyclic compound containing keto and/or hydroxy groups is used. 9. Method according to claim 8, characterized in that the additional compound is a di-, tri- and/or tetracyclic compound containing two keto groups and/or two hydroxy groups. 10. Method according to claim 9, characterized in that the additional compound is anthraquinone or 2-methylanthraquinone. 11. Method according to claim 8, characterized in that the digestion preparation contains a mixture of 50-95% by weight of one or more organic, cyclic keto- and/or hydroxy group-containing compounds and 5-50% by weight of one or more of the compounds of formula (1 ). 12. Method according to claim 8, characterized in that the digestion preparation contains 70-90% by weight of a cyclic keto- and/or hydroxy group-containing compound and 10-30% by weight of a compound of formula (1). 13. Method according to claim 8, characterized in that the digestion preparation contains a mixture of thiourea and anthraquinone or 2-methylanthraquinone in the mixing ratio 1:3 or 1:4. 14. Method according to claim 8, characterized in that the digestion preparation contains a mixture of thiourea and anthraquinone in a mixture ratio of 1:9 to 3:3. 15. Method according to one of claims 1-14, characterized in that the digestion is carried out at a temperature from 50 - 250°C, preferably 120 - 200°C.