JPH0532686A - Sulfonated lignin and its preparation - Google Patents

Abstract

PURPOSE: To obtain sulfonated lignin that exhibits superior water solubility in all pH ranges and to provide its preparation method.

CONSTITUTION: Lignin raw material is allowed to react with fuming sulfuric acid by dissolving the former in the latter. The reaction temp. is maintained at below 40°C. The lignin raw material may be sulfonated lignin or unsulphonated lignin. In the thus obtained sulfonated lignin, at least 4.2 moles of sulfonic acid is bonded organically per 1000 g of the lignin raw material.

COPYRIGHT: (C)1993,JPO

Description

Detailed Description of the Invention

[0001]

This invention relates to sulfonated lignin suitable as an additive to chemical formulations and a process for its preparation. More specifically, the present invention relates to a sulfonated lignin having a high sulfonation rate and exhibiting almost complete solubility in an aqueous solvent in the entire pH range.

[0002]

BACKGROUND OF THE INVENTION Lignin is a naturally occurring polymer having a complex and large molecular weight, which occurs with cellulose contained in plants and wood. Lignin is extracted as a by-product of cellulose obtained by two major processes in the paper industry, the sulfite process and the Kraft process. In the sulfite method, lignin is solubilized from the cellulose portion of wood pulp by direct sulfonation. on the other hand,
The Kraft method is based on the alkali decomposition mechanism. This decomposition mechanism is to cleave the beta allyl ether bond in the lignin polymer, thereby generating a phenol group and a carboxyl group. Kraft lignin is precipitated and separated from Kraft black liquor by acidification to pH values below the pKa of the phenol group.

Depending on the conditions under which the lignin is precipitated, the precipitated form of lignin is obtained as the free acid lignin or lignin salt. Lignin has a high pH value (about 9.5-1
When precipitated in 0), lignin is obtained as a salt. This lignin is further washed to obtain a low pH value (about 2-
Acidification to 5) and further washing until the salt and ash-forming components are free, yields free lignin known as A-lignin. Monovalent salts of lignin (alkali metal salts and ammonium salts) are water-soluble, while free acid lignin and polyvalent metal salts of lignin are water-insoluble.

Lignin products are widely used as additives in various chemical formulations and chemical processing methods. Since lignin has high chemical activity, it can be used as a surfactant or extender (exten
der), dispersant, toughener, absorbent, binder, sequestering agent, emulsifier, emulsion stabilizer, etc., and also as a colloid for stabilization and protection. Lignin is the applicant of this application, Westvaco
It is sold by the corporation under the trade name Indulin. Sulfonated lignins or lignosulfonates (particularly their sodium salts) are widely used as additives and dispersants for textile dyes and printing ink pigments. Such sulfonated lignin is available from Westvaco Corporation
It has been sold for many years under the trade names of olyfon and LEAX. The sulfonation rate of lignin is a factor that affects the water solubility at various pH values. For example, the sodium salt of sulfonated lignin is generally water-soluble in the alkaline range (high pH range), but is acidic (low pH range).
It is insoluble in the pH range.

The lignosulfonate obtained from the lignin by-product of the Kraft process is a methylol solution obtained by treating an aqueous solution of lignin with an aldehyde in an alkaline region,
It is produced by treatment with sodium sulfite or sodium bisulfite in an acidic region to sulfomethylate the methylol group of the phenol nucleus of the lignin molecule. The long side chains of lignin molecules can also be sulfonated by treatment with sulfite or bisulfite.

Naphthylene sulfonates suitable as additives and dispersants in chemical formulations have been produced by sulfonation of naphthylene with sulfuric acid. Benzene and other aromatic compounds can be sulfonated with concentrated sulfuric acid, but as the water content increases during the reaction, the sulfonation rate decreases and the reaction rate is inversely proportional to the square of the water content. The reaction is stopped when the acid concentration reaches a certain value (depending on the type of compound, 78% for benzene).

Much research has been done on methods for completing the sulfonation reaction. One of them is a method of removing water generated during the reaction and using a hydrocarbon and an acid. Lignin is treated with various concentrations of sulfuric acid, gaseous sulfur trioxide, fuming sulfuric acid, etc. to be sulfonated, but the sulfonated lignin produced by this treatment does not have sufficient water solubility and is chemically prepared. It was not suitable as an additive in the preparation of products. Thus, the conventional method of sulfonating lignin with sulfuric acid is not suitable as a method for producing a water-soluble lignin product suitable as a dispersant and an additive.

[0008]

The object of the present invention is to provide a method for producing a sulfonated lignin suitable as an additive for chemical preparations, that is, a sulfone having almost complete water solubility and a high sulfonation rate in the entire pH range. A method for producing activated lignin is provided.

Another object of the present invention is to provide a method for producing a water-soluble sulfonated lignin by directly sulfonation of lignin with fuming sulfuric acid.

Another object of the present invention is to provide a method for producing a water-soluble sulfonated lignin by increasing the sulfonation rate of lignin using fuming sulfuric acid.

Yet another object of this invention is to provide a sulfonated lignin suitable as an additive in chemical formulations.

[0012]

The lignin feedstock is reacted with fuming sulfuric acid (ie concentrated sulfuric acid containing sulfur trioxide).
The reaction temperature is maintained at 40 ° C or lower (preferably 20 ° C or lower). By this reaction, sulfonated lignin (lignosulfonate), which is almost completely water-soluble and has a high sulfonation rate, can be used as an additive for chemical formulations.
Is generated. This sulfonated lignin is a lithium salt,
It is neutralized with a compound selected from the group consisting of sodium salt, calcium salt, ammonium salt and amine salt and converted to the alkali metal salt of sulfonated lignin.

By treating lignin (in the case of sulfate lignin such as Kraft lignin) with sulfuric acid, water-soluble sulfonated lignin containing sulfonic acid organically bonded at a ratio of at least 4.2 mol per 1000 g of lignin raw material. Was found to be generated. If the starting lignin is a non-sulphonated lignin, then when such lignin is sulphonated by fuming sulfuric acid the product will contain at least 4.2 moles of organically bound sulphonic acid. On the other hand, when the raw material kraft lignin is lignin previously sulfomethylated with formaldehyde and sulfite or bisulfite, when such lignin is treated with fuming sulfuric acid, the sulfonation rate is further improved. A product is produced. The lignin product contains up to 4.7 moles of organically bound sulfonic acid per 1000 grams of lignin feed. In addition, this lignin product shows almost complete water solubility in the entire pH range.

[0014]

Examples Examples of lignin that has been previously sulfomethylated or sulfonated, and lignin that has not been sulfonated at all,
It can be sulfonated by treatment with fuming sulfuric acid (concentrated sulfuric acid containing sulfur trioxide). This reaction is carried out at a temperature of 40 ° C or lower (preferably 20 ° C or lower) for a sufficient time. The sulfonated lignin obtained by this reaction is almost completely water-soluble in the entire pH range.

The degree of water solubility of the sulfonated lignin can be measured by comparing the acid precipitation values or acid precipitation values of these lignins. The acid precipitation value of lignin is represented by the number of grams of 50% sulfuric acid added until 50% sulfuric acid was added to 37 ml of a 0.5% by weight lignin solution to form a precipitate. The method of the present invention will be described below based on experimental examples.

Experimental Example 20 g of previously dried A-lignin (not sulfonated) are dissolved in 80 g of fuming sulfuric acid (sulfuric acid containing 30% of sulfur trioxide) for 2 hours. Reaction temperature is 40
The temperature is kept below ° C (preferably below 20 ° C). The temperature is adjusted by adjusting the addition rate of lignin or using an external cooler. After 10 minutes, increase the temperature to 4
The fuming sulfuric acid / lignosulfonate composition is poured into 500 g of a mixture of ice and water, keeping below 0 ° C. To remove excess sulfuric acid, the completely dissolved solution is diluted 3 times with water and then neutralized with Lime. This operation is performed as needed. The neutralized slurry is filtered to remove the calcium sulfate precipitate produced by the reaction of sulfuric acid and slaked lime that did not participate in the sulfonation reaction.
Then, a necessary amount of sodium carbonate is added to the filtrate to convert the calcium salt of sulfonic acid into a sodium salt. The resulting precipitate of calcium carbonate is then removed by filtration and the filtrate containing the required lignin salt is recovered. Next, the filtrate is dried by a conventional drying method to obtain a sodium salt of sulfonated lignin. This sodium salt of lignin shows almost complete water solubility in the entire pH range.

The sulfonation test with fuming sulfuric acid was carried out on many types of lignin, and the sulfonated lignin thus obtained and the lignin product sulfonated with sulfuric acid and the non-sulfonated conventional lignin product were tested. And compared. Comparative tests of the samples were carried out on acid precipitation values (solubility) and sulphonic acid content. The acid precipitation values and sulfonic acid contents obtained for various lignin samples are shown in Tables 1 and 2.

[0018]

[Table 1] Sample No. Lignin acid precipitation value Sulfonic acid content (grams of 50% sulfuric acid) ( moles per 1000 grams of lignin ) 1 Indurin 0.2 0.0 Non-sulfonated 2 Indurin 10.5 1. 7 Sulfonated with sulfuric acid (water content 8%) 3 Indulin 12.5 1.85 Sulfonated with sulfuric acid (water content 2%) 4 Indulin (no precipitation formation) 4.35 / 4.40 Sulfonated with fuming sulfuric acid (water content 8%) 5 Reax 83 9.2 1.6 (sulfomethylated) 6 Reax 83 (no precipitation) 4.35 / 4.40 (sulfomethylated) Sulfonated with fuming sulfuric acid 7 Polyphone 0 3.4 1.1 Sulfonated with Na ₂ SO ₃ 8 Polyphone 0 (No precipitation) 4.25 / 4.40 (Sulfonated with Na ₂ SO ₃ ) Sulfonated with fuming sulfuric acid 9 Reax 88 15.0 2.4 Sulfonated / sulfomethylated

[0019]

[Table 2] Sample No. Lignin acid sedimentation value Sulfonic acid content (grams of 50% sulfuric acid) ( moles per 1000 grams of lignin ) 10 Reax 88 (no precipitate formation) 4.5 (Sulfonation / sulfomethylation) Sulfonating with fuming sulfuric acid 11 Liax 100M 65 3.1 (sulfonation / sulfomethylation) 12 Liax 100M (no precipitation) 4.72 (sulfonation / sulfomethylation) Sulfonating with fuming sulfuric acid 13 Vanisperse CB 1. 7 0.7 (Partially desulfonated sulphite lignin) 14 Vanisperse CB 95.5 3.3 (Partially desulphonated sulphite lignin) Sulfonated with fuming sulfuric acid 15 Lignosol NSX110 10.9 1.83 Sulfite lignin 16 LIGNOSOL NSX110 (no precipitation) 4.1 / 4.14 Sulfite Sulfonated with Nin fuming sulfuric acid

As shown in Tables 1 and 2, the sample No.
1-4 used indulin (lignin not sulfonated) as a lignin raw material. Sample No. 5-
No. 6 uses Reax 83 as a lignin raw material. This is lignin sulfomethylated with formaldehyde and sulfite. Sample No. Nos. 7 to 8 use polyphone 0 as a lignin raw material. This is Westvaco's sulfonated lignin (treated with sodium sulfite). Sample No. 9-10 uses Reax 88 as a lignin raw material. This is a sulfonated and sulfomethylated lignin obtained by methylolating and sulfonation of lignin with sulfite or bisulfite. Sample No. 11-12 uses West Vaco-made Reax 100M as a lignin raw material. This is a sulfonated and sulfomethylated lignin obtained by methylolating and sulfonation of lignin with sulfite or bisulfite. sample
No. Nos. 13-14 use vanisperth as a lignin raw material. This is lignin obtained by partially desulfonation of sulfite lignin, which is a by-product of the sulfite method. Lignosol NSX 110 is a sulfite lignin manufactured by Lignosol Corporation. Sample Nos. In Table 1 and Table 2 4, 6, 8, 10,
12, 14 and 16 are sulfonated lignin products sulfonated with fuming sulfuric acid by the method of the present invention. The lignin raw material of Samples 1-12 is lignin sulfate produced as a by-product of the Kraft process. Sample No. 14 and 1
No. 6 shows the effectiveness of the method of the present invention for lignin sulfite. Acid precipitation values (Sample No. 1
, Which is 2, which is a value at which a precipitate is gently formed at a pH of about 6.5). However, as is clear from the table, sulfonic acid sulfonated with fuming sulfuric acid is shown. Lignin does not produce a precipitate. However, vanisper lignin shows an extremely high acid precipitation value when sulfonated with fuming sulfuric acid. From these results, it can be seen that the sulfonated lignin produced by the treatment with fuming sulfuric acid exhibits excellent water solubility in both acidic and alkaline pH ranges. Similarly, sample No. The sulfonic acid content of the oleum of 16 treated with fuming sulfuric acid is somewhat lower than the sulfonic acid content of the lignin of sulfuric acid treated with fuming sulfuric acid. Sample No. 2-4 shows the influence of the water content on the sedimentation value and the sulfonic acid content.

Claims (8)

[Claims] 1. A method for producing a water-soluble sulfonated lignin, which comprises reacting a dry lignin raw material recovered as a by-product of the Kraft method or the sulfite method by dissolving it in fuming sulfuric acid. Including stages,
A method in which the reaction temperature is maintained at 40 ° C or lower. 2. The method according to claim 1, wherein the reaction temperature is maintained at 20 ° C. or lower. 3. The organically bound sulfonic acid in the sulfonated lignin produced is the lignin feedstock 10.
The method of claim 1, wherein the amount is at least 4.2 mol per 00 g. 4. The lignin raw material is sulfomethylated lignin, and the organically bound sulfonic acid in the sulfonated lignin produced is at most 4.7 mol per 1000 g of sulfomethylated lignin. the method of. 5. The method of claim 1 including the step of neutralizing the sulfonated lignin produced with an alkali salt selected from the group consisting of lithium, sodium, potassium, ammonium and amine salts. . 6. The lignin raw material is lignin presulfonated and / or sulfomethylated with sulfite or bisulfite, and the sulfonated lignin solution produced by dissolving this lignin in fuming sulfuric acid is slaked lime. After neutralization and filtration, the sulfonated lignin is converted to the sodium salt of sulfonated lignin by reacting the filtrate with sodium carbonate, and the precipitated calcium carbonate is removed by filtering the solution. The method according to Item 1. 7. A lignin raw material 1000 g produced by dissolving a dry lignin raw material recovered as a by-product of the Kraft method or the sulfite method in fuming sulfuric acid while maintaining the temperature at 40 ° C. or lower. A sulfonated lignin which contains at least 4.2 mol of organically bound sulfonic acid per unit and is almost completely water-soluble in the entire pH range. 8. The dried lignin raw material is sulfomethylated lignin, and the sulfonic acid bound to the lignin raw material is at most 4.7 per 1000 g of the lignin raw material.
The sulfonated lignin according to claim 7, which is molar.