Method For Producing Stabilized Lignin Having A High Specific Surface

Abstract

The invention relates to a method for producing stabilized lignin from lignin-containing raw materials, comprising two process steps. The invention also relates to the stabilized lignin produced in this way.

Claims

1. A process for producing an undissolved stabilized lignin having a statistical thickness surface area (STSA) of at least 10 m.sup.2/g from lignin-containing raw materials, the process comprising: reacting a lignin dissolved in a liquid and a crosslinker, thereby producing a dissolved modified lignin, and converting the dissolved modified lignin is converted into an undissolved stabilized lignin.

2. The process as claimed in claim 1, wherein: the lignin containing phenolic aromatics, aromatic and aliphatic hydroxy groups and/or carboxy groups as crosslinkable units, and the crosslinker containing at least one functional group as a crosslinkable unit that can react with the crosslinkable units in the lignin, are reacted at a first temperature T1 that is less than or equal to a first maximum temperature T1max and greater than or equal to a first minimum temperature T1min for a defined period of time, thereby producing the dissolved modified lignin, and the dissolved modified lignin is converted into the undissolved stabilized lignin at a second temperature T2 that is less than or equal to a second maximum temperature T2max and greater than or equal to a second minimum temperature T2min for a defined period of time.

3. The process as claimed in claim 1, wherein an amount of the crosslinker reacted with the lignin corresponds to a maximum of 4 mol of crosslinkable units in the crosslinker per mole of crosslinkable units in the lignin.

4. The process as claimed in claim 1, wherein an amount of the crosslinker reacted with the lignin corresponds to at least 0.5 mol of crosslinkable units in the crosslinker per mole of crosslinkable units in the lignin.

5. A process for producing a stabilized lignin from lignin-containing raw materials, comprising: reacting a lignin dissolved in a first liquid, the lignin containing phenolic aromatics, aromatic and aliphatic hydroxy groups and/or carboxy groups as crosslinkable units, and the crosslinker containing at least one functional group as a crosslinkable unit that can react with the crosslinkable units in the lignin, and an amount of crosslinkable units in the crosslinker being greater than or equal to 0.5 and less than or equal to 4 mol per mol of crosslinkable units in the lignin, thereby producing a dissolved modified lignin in a second liquid, and converting the dissolved modified lignin into an undissolved stabilized lignin in a third liquid at a second temperature T2 that is less than or equal to a second maximum temperature T2max and greater than or equal to a second minimum temperature T2min for a defined period of time.

6. The process as claimed in claim 5, wherein the amount of the crosslinker is a maximum of 35 g/100 g lignin.

7. The process as claimed in claim 5, wherein the crosslinker comprise aldehydes or bifunctional compounds.

8. The process as claimed in claim 5, wherein the reacting of the lignin with the crosslinker is conducted at a temperature more than 50° C. and less than 180° C.

9. The process as claimed in claim 5, wherein an average residence time for the reacting of the lignin with the crosslinker is at least 5 minutes and less than 300 minutes.

10. The process as claimed in claim 5, wherein the second maximum temperature T2max is 270° C.

11. The process as claimed in claim 5, wherein an average residence time for the converting of the dissolved modified lignin is at least 10 minutes and less than 600 minutes.

12. The process as claimed in claim 5, further comprising prior to the reacting, dissolving the lignin in the first liquid having a pH of at least 7.5 and above the pH of the second liquid containing the modified dissolved lignin.

13. The process as claimed in claim 5, wherein a pH of the second liquid containing the modified dissolved lignin is at least 7 and above the pH of the third liquid containing the undissolved stabilized lignin.

14. The process as claimed in claim 5, wherein: a carbohydrate-based crosslinker is obtained from carbohydrates dissolved or dispersed in the first liquid containing the dissolved lignin, and the lignin dissolved in the first liquid and the carbohydrate-based crosslinker are reacted, thereby producing the dissolved modified lignin.

15. The process as claimed in claim 5, wherein: a lignin-based crosslinker is obtained from the lignin dissolved or dispersed in the first liquid containing the dissolved lignin, and remaining lignin dissolved in the liquid and the lignin-based crosslinker are reacted, thereby producing the dissolved modified lignin.

16. An undissolved stabilized lignin made by a process as claimed in claim 5, comprising a statistical thickness surface area (STSA) of at least 10 m.sup.2/g.

17. The undissolved stabilized lignin as claimed in claim 16 comprising a pore volume of <0.1 cm.sup.3/g.

18. The undissolved stabilized lignin as claimed in claim 16 comprising a solubility in alkaline liquids of less than 30%.

19. The undissolved stabilized lignin as claimed in claim 16 comprising a glass transition temperature of more than 160° C.

20. The undissolved stabilized lignin as claimed in claim 16 comprising: the STSA of at least 20 m.sup.2/g and less than 200 m.sup.2/g; a signal in a solid-state .sup.13C-NMR at of 0 to 50 ppm, having an intensity relative to a signal of methoxy groups at 54 to 58 ppm of 1-80%, and a .sup.13C-NMR signal at 125 to 135 ppm that is higher than that of the lignin; a .sup.14C content that is greater than 0.20 Bq/g carbon; and/or a carbon content based on the ash-free dry substance of greater than or equal to 60% by mass and less than or equal to 80% by mass.

Description

[0127] The present invention is elucidated in more detail hereinbelow on the basis of exemplary embodiments with reference to the figures. In the figures:

[0128] FIG. 1 shows a schematic representation of the results for a first embodiment according to exemplary embodiment 1;

[0129] FIG. 2 shows a .sup.13C-NMR spectrum of a stabilized lignin obtained according to exemplary embodiment 1;

[0130] FIG. 3 shows a schematic representation of the results for a second embodiment according to exemplary embodiment 2;

[0131] FIG. 4 shows a schematic representation of the temperature profiles from exemplary embodiments 1 and 2;

[0132] FIG. 5 shows a schematic representation for depicting the influence of the amount of the employed crosslinker on the yield and BET value of a stabilized lignin produced according to exemplary embodiment 3; and

[0133] FIG. 6 shows a .sup.13C-NMR spectrum of a stabilized lignin obtained according to exemplary embodiment 3.

EXEMPLARY EMBODIMENTS

[0134] In the examples that follow, the BET is stated instead of the STSA. For the undissolved stabilized lignins produced here, BET and STSA do not however differ by more than 10% from one another.

Example 1

[0135] The raw material for this example is the solid from an enzymatic hydrolysis of woody biomass (hardwood). The solid was converted into a liquid containing dissolved lignin through addition of water and sodium hydroxide solution.

[0136] To each 30 g of the liquid containing dissolved lignin and having a dry matter content of 15% and a pH of 10.9 was added, in the first process step of reactions with the crosslinker formaldehyde, an amount of 23.5% formaldehyde solution as defined in Table 1. The liquid containing the dissolved lignin and the formaldehyde solution were homogenized and in the first process step treated for the times and temperatures stated in Table 1, producing a modified dissolved lignin, and then treated in the second process step, producing an undissolved stabilized lignin. The undissolved stabilized lignin was obtained by centrifugation. After washing twice with demineralized water and drying in an air-circulation drying oven, the yields given in Table 1 and FIG. 1 were obtained. The specific surface area (BET) in Table 1 and FIG. 1 was determined after heating at 150° C. under reduced pressure.

[0137] The dry matter used has a lignin content of 88%. The lignin fraction of the dry matter used has 1.3 mmol/g of phenolic guaiacyl groups and 0.1 mmol/g of p-hydroxyphenyl groups and thus 1.5 mmol/g of crosslinkable units.

[0138] The formaldehyde used has 66.6 mmol of crosslinkable units per g of dry formaldehyde.

TABLE-US-00001 TABLE 1 Variants of the experiments in example 1 with varying additive concentrations Yield Crosslinkable units [undissolved Crosslinker/ in crosslinker/ Temperature stabilized crosslinkable crosslinkable Temperature and time lignin/dissolved units in lignin units in lignin Crosslinker/lignin and time in second lignin in BET No. [mol/mol] [mol/mol] [g/100 g lignin] in first step step percent] [m.sup.2/g] A 0 0 0 70-130° C., 190° C., 3 h 54 0.2 12 min 50-180° C., 26 min B 0.25 0.5 1.2 70-130° C., 190° C., 3 h 59 1.8 12 min 50-180° C., 26 min C 0.75 1.5 3.6 70-130° C., 190° C., 3 h 74 8.9 12 min 50-180° C., 26 min D 1.25 2.5 6.1 70-130° C., 190° C., 3 h 82 10.2 12 min 50-180° C., 26 min E 1.25 2.5 6.1 70-130° C., 190° C., 3 h 71 21.0 71 min 50-180° C., 85 min F 1.25 2.5 6.1 70-130° C., 190° C., 4 h 69 10.0 12 min 50-180° C., 26 min G 1.75 3.5 8.6 70-130° C., 190° C., 3 h 71 2.6 12 min 50-180° C., 26 min E2 1.25 2.5 6.1 70-130° C., 190° C., 3 h 72 20.9 71 min 50-180° C., 85 min

[0139] As can be seen from Table 1 above, the yield and BET of the lignin material produced depend on the amount of crosslinker used and on the use of an upstream, first reaction step.

[0140] Thus, examples D, E, and F show that the use of a first process step while leaving the amount of crosslinker unchanged results in an increase in the BET of the material obtained. When the first reaction step is carried out for a period of 71 min or 85 min, the BET value (example E) is doubled by comparison with a shortened first reaction step.

[0141] The BET also initially increases with increasing amount of crosslinker (examples B-F), but falls when the amount of crosslinker is increased further (example G).

[0142] A similar effect can be seen in exemplary embodiment 2 (see Table 2 below). Here, doubling the amount of crosslinker results in a reduction in BET and in the yield of the stabilized lignin (examples I and L).

[0143] Thus an optimum clearly arises for the amount of crosslinker used.

[0144] In example E2, .sup.13C-formaldehyde was used and analyzed by solid-state NMR spectroscopy. The spectra of the lignin used and stabilized lignin are presented in FIG. 2 and show at 11 to 36 ppm the preferential formation of methylene groups with the central signal at 24 to 32 ppm with two guaiacyl units as a structure of the stabilized lignin.

Example 2

[0145] The raw material for this example is LignoBoost lignin obtained from a black liquor from a kraft digestion. The solid was converted into a liquid containing the dissolved lignin through addition of water and sodium hydroxide solution. To each 30 g of a liquid containing dissolved lignin and having a dry matter content of 15% and a pH of 9.2 was added, in the first process step of reactions with the crosslinker formaldehyde, an amount of 23.5% formaldehyde solution as defined in Table 2. The liquid containing the dissolved lignin and the formaldehyde solution were homogenized and in the first process step treated for the times and temperatures stated in Table 2, producing a modified dissolved lignin, and then treated in the second process step, producing an undissolved stabilized lignin. The undissolved stabilized lignin was obtained by centrifugation. After washing twice with demineralized water and drying in an air-circulation drying oven, the yields given in Table 2 and FIG. 3 were obtained. The specific surface area (BET) in Table 2 and FIG. 3 of the undissolved stabilized lignin was determined after heating at 150° C. under reduced pressure.

[0146] The lignin used has 1.9 mmol/g of phenolic guaiacyl groups and 0.3 mmol/g of p-hydroxyphenyl groups and thus 2.5 mmol/g of crosslinkable units.

[0147] The formaldehyde used has 66.6 mmol of crosslinkable units per g of dry formaldehyde.

TABLE-US-00002 TABLE 2 Variants of the experiments in example 2 with varying additive concentrations Yield Crosslinker/ Crosslinkable units [undissolved crosslinkable in crosslinker/ Crosslinker/ Temperature stabilized units in crosslinkable lignin Temperature and time lignin/dissolved lignin units in lignin [g/100 g and time in second lignin in BET No. [mol/mol] [mol/mol] lignin] in first step step percent] [m.sup.2/g] H 0 0 0 70-130° C., 225° C., 8 h 59 34.4 12 min 50-180° C., 26 min I 1.0 2.0 8 70-130° C., 225° C., 8 h 88 61.4 12 min 50-180° C., 26 min K 0 0 0 70-130° C., 225° C., 4 h 58 35.0 12 min 50-180° C., 26 min L 2.0 3.9 16 70-130° C., 225° C., 4 h 77 39.7 12 min 50-180° C., 26 min

[0148] The temperature curves from examples 1 and 2 are summarized in the diagram in FIG. 4.

Example 3

[0149] The raw material for this example is LignoBoost lignin obtained from a black liquor from a kraft digestion. The solid was converted into a liquid containing the dissolved lignin through addition of water and sodium hydroxide solution.

[0150] To each 30 g of a liquid containing dissolved lignin and having a dry matter content of 15% and a pH of 8.7 was added, in the first process step of reactions with the crosslinker formaldehyde, an amount of 23.5% formaldehyde solution as defined in Table 3. The liquid containing the dissolved lignin and the formaldehyde solution were homogenized and in the first process step treated for the times and temperatures stated in Table 3, producing a modified dissolved lignin, and then treated in the second process step, producing an undissolved stabilized lignin. The undissolved stabilized lignin was obtained by filtration. After washing with demineralized water in an amount twice that of the filtrate and drying in an air-circulation drying oven, the yields given in Table 3 and FIG. 5 were obtained. The specific surface area (BET) in Table 3 and FIG. 5 of the undissolved stabilized lignin was determined after heating at 150° C. under reduced pressure.

[0151] The lignin used has 1.9 mmol/g of phenolic guaiacyl groups and 0.3 mmol/g of p-hydroxyphenyl groups and thus 2.5 mmol/g of crosslinkable units.

[0152] The formaldehyde used has 66.6 mmol of crosslinkable units per g of dry formaldehyde.

TABLE-US-00003 TABLE 3 Variants of the experiments in example 3 with varying additive concentrations Yield [undissolved Crosslinker/ stabilized crosslinkable Crosslinkable units in Crosslinker/ Temperature lignin/ units in crosslinker/crosslinkable lignin Temperature and time dissolved lignin units in lignin [g/100 g and time in second lignin in BET No. [mol/mol] [mol/mol] lignin] in first step step percent] [m.sup.2/g] M 0 0 0 70-130° C., 240° C., 4 h 64.3 0.7 12 min 50-180° C., 26 min N 0.25 0.5 2 70-130° C., 240° C., 4 h 76.8 20.5 12 min 50-180° C., 26 min O 0.5 1.0 4 70-130° C., 240° C., 4 h 67.3 65.0 12 min 50-180° C., 26 min P 1.0 2.0 8 70-130° C., 240° C., 4 h 80.6 88.6 12 min 50-180° C., 26 min Q 2.0 4.0 16 70-130° C., 240° C., 4 h 83.2 91.0 12 min 50-180° C., 26 min P2 1.0 2.0 8 70-130° C., 240° C., 4 h 81.4 82.2 12 min 50-180° C., 26 min

[0153] As can be seen from Table 3 above and FIG. 5, the yield and BET of the lignin material produced depend on the amount of crosslinker used.

[0154] Thus, examples M to Q show that the BET initially increases with increasing amount of crosslinker (examples M to P), but increasing the amount of crosslinker further does not result in any further increase in BET (example Q).

[0155] Thus an optimum clearly arises for the amount of crosslinker used.

[0156] In example P2, .sup.13C-formaldehyde was used and analyzed by solid-state NMR spectroscopy. The spectra of the lignin used and stabilized lignin are presented in FIG. 6 and show at 11 to 35 ppm the preferential formation of methylene groups with the central signal at 24 to 32 ppm with two guaiacyl units as a structure of the stabilized lignin.

Example 4

[0157] The raw material for this example is LignoBoost lignin obtained from a black liquor from a kraft digestion. The solid was converted into a liquid containing the dissolved lignin through addition of water and sodium hydroxide solution.

[0158] To each 30 g of a liquid containing dissolved lignin and having a dry matter content of 15% and a pH of 9.0 was added, in the first process step of reactions with the crosslinker glyoxal, an amount of 40% glyoxal solution as defined in Table 4. The liquid containing the dissolved lignin and the glyoxal solution were homogenized and in the first process step treated for the times and temperatures stated in Table 4, producing a modified dissolved lignin, and then treated in the second process step, producing an undissolved stabilized lignin. The undissolved stabilized lignin was obtained by centrifugation. After washing twice with demineralized water and drying in an air-circulation drying oven, the yields given in Table 4 were obtained. The specific surface area (BET) in Table 4 of the undissolved stabilized lignin was determined after heating at 150° C. under reduced pressure.

[0159] The lignin used has 1.9 mmol/g of phenolic guaiacyl groups and 0.3 mmol/g of p-hydroxyphenyl groups and thus 2.5 mmol/g of crosslinkable units.

[0160] The glyoxal used has 68.9 mmol of crosslinkable units per g.

TABLE-US-00004 TABLE 4 Variants of the experiments in example 4 with varying additive concentrations Yield Crosslinker/ Crosslinkable units [undissolved crosslinkable in crosslinker/ Temperature stabilized units crosslinkable Crosslinker/ Temperature and time lignin/dissolved in lignin units in lignin lignin and time in second lignin in BET No. [mol/mol] [mol/mol] [g/100 g lignin] in first step step percent] [m.sup.2/g] R 0 0 0 70-130° C., 200° C., 4 h 54.3 0.7 12 min 50-180° C., 26 min S 1 3.9 14.3 70-130° C., 200° C., 4 h 71.2 45.3 12 min 50-180° C., 26 min

Example 5

[0161] The raw material for this example is LignoBoost lignin obtained from a black liquor from a kraft digestion. The solid was converted into a liquid containing the dissolved lignin through addition of water and sodium hydroxide solution.

[0162] To each 30 g of a liquid containing dissolved lignin and having a dry matter content of 15% and a pH of 9.0 was added, in the first process step of reactions with the crosslinker glyceraldehyde, an amount defined in Table 5. The liquid containing the dissolved lignin and the glyceraldehyde were homogenized and in the first process step treated for the times and temperatures stated in Table 5, producing a modified dissolved lignin, and then treated in the second process step, producing an undissolved stabilized lignin. The undissolved stabilized lignin was obtained by centrifugation. After washing twice with demineralized water and drying in an air-circulation drying oven, the yields given in Table 5 were obtained. The specific surface area (BET) in Table 5 of the undissolved stabilized lignin was determined after heating at 150° C. under reduced pressure.

[0163] The lignin used has 1.9 mmol/g of phenolic guaiacyl groups and 0.3 mmol/g of p-hydroxyphenyl groups and thus 2.5 mmol/g of crosslinkable units.

[0164] The glyceraldehyde used has 22.2 mmol of crosslinkable units per g.

TABLE-US-00005 TABLE 5 Variants of the experiments in example 5 with varying additive concentrations Crosslinkable Yield units in [undissolved Crosslinker/ crosslinker/ Temperature stabilized crosslinkable units crosslinkable Crosslinker/ Temperature and time lignin/dissolved in lignin units in lignin lignin and time in in second lignin in BET No. [mol/mol] [mol/mol] [g/100 g lignin] first step step percent] [m.sup.2/g] T 0 0 0 70-130° C., 240° C., 4 h 54.3 0.7 12 min 50-180° C., 26 min U 1 2 22.2 70-130° C., 240° C., 4 h 75.3 48.5 12 min 50-180° C., 26 min

Example 6

[0165] The raw material for this example is a lignosulfonate in the form of black liquor from the digestion with sulfite. The starting material was converted into a liquid containing the dissolved lignin through addition of water and sodium hydroxide solution. To each 30 g of a liquid containing dissolved lignin and having a dry matter content of 12.4% and a pH of 10.4 was added, in the first process step of reactions with the crosslinker formaldehyde, an amount of 23.5% formaldehyde solution as defined in Table 6. The liquid containing the dissolved lignin and the formaldehyde solution were homogenized and in the first process step treated for the times and temperatures stated in Table 6, producing a modified dissolved lignin, and then treated in the second process step, producing an undissolved stabilized lignin. The undissolved stabilized lignin was obtained by centrifugation. After washing twice with demineralized water and drying in an air-circulation drying oven, the yields given in Table 6 were obtained. The specific surface area (BET) in Table 6 of the undissolved stabilized lignin was determined after heating at 150° C. under reduced pressure.

[0166] The dry matter of the black liquor used has a lignin content of 70%. The lignin fraction of the dry matter used has 0.6 mmol/g of phenolic guaiacyl groups and thus crosslinkable units.

[0167] The formaldehyde used has 66.6 mmol of crosslinkable units per g of dry formaldehyde.

TABLE-US-00006 TABLE 6 Variants of the experiments in example 6 with varying additive concentrations Crosslinkable units in Yield crosslinker/ [undissolved Crosslinker/ crosslinkable Temperature stabilized crosslinkable units in Temperature and time lignin/dissolved units in lignin lignin Crosslinker/lignin and time in second lignin in BET No. [mol/mol] [mol/mol] [g/100 g lignin] in first step step percent] [m.sup.2/g] V 0 0 0 70-130° C., 230° C., 6 h 58 7.0 12 min 50-230° C., 26 min W 4.3 8.6 7.7 70-130° C., 230° C., 6 h 74 22.4 12 min 50-230° C., 26 min