Method for stabilizing lignin fiber for further conversion to carbon fiber

Abstract

A method for producing a stabilized lignin fiber from softwood alkaline lignin by heat treatment in the absence of oxidant is disclosed. The stabilized lignin fiber can be further treated to obtain carbon fiber.

Claims

1. Method of producing a stabilized lignin fiber comprising the following steps: a) providing a material consisting of fractionated softwood alkaline lignin and/or unfractionated softwood alkaline lignin in an amount of 10-100% by weight of the material, the balance being constituted by unfractionated hardwood alkali lignin, fractionated hardwood alkali lignin, or a mixture thereof; b) spinning the material obtained by step (a), whereby an alkaline lignin fiber is obtained; c) stabilizing the alkaline lignin fiber, wherein the complete process of stabilization is performed under inert conditions and entirely in the absence of oxidative conditions, wherein the stabilizing is performed by isothermally treating the alkaline lignin fiber at 220-300° C. for from 1 to 60 minutes, and d) carbonizing the stabilized lignin fiber under inert conditions, wherein the stabilizing of the alkaline lignin fiber under inert conditions and the carbonizing under inert conditions proceed as a one-step operation.

2. Method according to claim 1, wherein in a) the fractionated softwood alkaline lignin is produced by ultrafiltration.

3. Method according to claim 1, wherein the spinning in b) is melt extrusion and is performed at a temperature exceeding the glass transition temperature of the material by 20-75° C.

4. Method according to claim 1, wherein the inert conditions are provided by the use of any one of nitrogen, helium, neon, argon, krypton, xenon.

5. Method according to claim 1, wherein in c) the stabilizing is performed at a heating rate from 1 to 200° C. per minute from ambient temperature up to 250° C.

6. Method according to claim 5, wherein the stabilizing is performed at a heating rate from 4 to 70° C. per minute from ambient temperature up to 220° C.

7. Method according to claim 6, wherein the lignin fiber is isothermally treated at 220° C. for from 1 to 60 minutes.

8. Method according to claim 5, wherein the lignin fiber is isothermally treated at 250° C. for from 1 to 60 minutes.

9. Method according to claim 1, further comprising purifying the softwood alkaline lignin prior to spinning.

Description

EXAMPLES

(1) In the following, preparation of the alkaline lignins used is described in Examples 1 to 3. The melt extrusion conditions for obtaining a continuous lignin fiber are described in Examples 4 to 6. Stabilization conditions for the lignin fibers are described in Examples 7-16. The last two examples describe applicable carbonization conditions to obtain a structural carbon fiber.

(2) 1. Preparation of Fractionated and Purified Softwood Kraft Lignin

(3) Black liquor, obtained from kraft pulping of a mixture of pine and spruce wood, was subjected to ultra filtration using ceramic membrane (15 kDa) at a temperature of 120° C. The collected permeate was acidified by gaseous carbon dioxide at 70° C. to pH ˜9. After filtration, the lignin cake was suspended in water and acidified to pH ˜2 with sulfuric acid. Filtration of the lignin followed by washing with water and drying afforded purified softwood kraft lignin with the following characteristics: ash 0.9%, carbohydrates 0.4%, glass transition temperature (T.sub.g) 140° C., decomposition temperature (T.sub.d) 280° C.

(4) 2. Preparation of Softwood Kraft Lignin

(5) Softwood kraft lignin was isolated from black liquor obtained through pulping of a mixture of pine and spruce wood with kraft pulping liquor. The lignin isolation procedure was done following the steps described in EP 1794363. The following characteristics were obtained: Ash 0.9%, carbohydrates 2%, glass transition temperature (T.sub.g) 140° C., decomposition temperature (T.sub.d) 273° C.

(6) 3. Preparation of Fractionated and Purified Hardwood Kraft Lignin

(7) Black liquor, obtained from kraft pulping of a mixture of birch and aspen wood, was subjected to ultra filtration using ceramic membrane (15 kDa) at a temperature of 120° C. The collected permeate was acidified by gaseous carbon dioxide at 60° C. to pH ˜9. After filtration, the lignin cake was suspended in water and acidified to pH ˜2 with sulfuric acid. Filtration of the lignin followed by washing with water and drying afforded purified hardwood kraft lignin with the following characteristics: ash 0.9%, carbohydrates 0.4%, glass transition temperature (T.sub.g) 114° C., decomposition temperature (T.sub.d) 274° C.

(8) 4. Preparation of Lignin Fiber from Purified Softwood Lignin at 200° C.

(9) Dry purified softwood kraft lignin (7 grams) was prepared as described in Example 1 and introduced in a laboratory extruder kept at 200° C. The lignin was homogenized at that temperature in the extruder by rotating the two screws at a speed of ˜25 rpm for at least 10 minutes before extrusion of the lignin fiber through a die of 0.5 mm in diameter. The resulting continuous lignin fiber was collected on a bobbin using a winding speed of 30 m/min.

(10) 5. Preparation of Softwood Lignin Fiber Containing 5% Purified Hardwood Lignin at 200° C.

(11) A total of 7 grams of dry kraft lignin from Example 2 and Example 3 were mixed in the proportions 95:5 (by weight) and introduced in a laboratory extruder kept at 200° C. Lignin fibers were produced as described in Example 4.

(12) 6. Preparation of Softwood Lignin Fiber Containing 10% Purified Hardwood Lignin at 200° C.

(13) A total of 7 grams of dry kraft lignin from Example 2 and Example 3 were mixed in the proportions 9:1 (by weight) and introduced in a laboratory extruder kept at 200° C. Lignin fibers were produced as described in Example 4.

(14) 7. Stabilization of Purified Softwood Kraft Lignin Fibers Using 4° C./min from Ambient Temperature to 250° C., Isothermally Treated for 30 Minutes.

(15) Softwood kraft lignin fibers from Example 4 were placed in a sealed glass tube filled with nitrogen (>99.999%) and thermally stabilized in a temperature controlled oven using a heating rate of 4° C./min from ambient temperature to 250° C., where it was isothermally treated for 30 min.

(16) 8. Stabilization of Single Purified Softwood Kraft Lignin Fiber Using 10° C./Min from Ambient Temperature to 250° C., Isothermally Treated for 60 Minutes.

(17) Softwood kraft lignin fibers from Example 4 were stabilized according to Example 7 using a heating rate of 10° C./min from ambient temperature to 250° C., where it was isothermally treated for 60 minutes.

(18) 9. Stabilization of Single Purified Softwood Kraft Lignin Fiber Using 70° C./Min from Ambient Temperature to 250° C., Isothermally Treated for 10 Minutes.

(19) Softwood kraft lignin fibers from Example 4 were stabilized according to Example 7 using a heating rate of 70° C./min from ambient temperature to 250° C., where it was isothermally treated for 10 min.

(20) 10. Stabilization of Single Purified Softwood Kraft Lignin Fiber Using 70° C./Min from Ambient Temperature to 200° C., Isothermally Treated for 30 Minutes.

(21) Softwood kraft lignin fibers from Example 4 were stabilized according to Example 7 using a heating rate of 70° C./min from ambient temperature to 200° C., where it was isothermally treated for 30 min.

(22) 11. Stabilization of Single Purified Softwood Kraft Lignin Fiber Using 70° C./Min from Ambient Temperature to 220° C., Isothermally Treated for 20 Minutes.

(23) Softwood kraft lignin fibers from Example 4 were stabilized according to Example 7 using a heating rate of 70° C./min from ambient temperature to 220° C., where it was isothermally treated for 20 min.

(24) 12. Stabilization of Single Softwood Lignin Fiber Containing 5% Purified Hardwood Lignin Using 10° C./Min from Ambient Temperature to 250° C., Where it was Isothermally Treated for 60 Minutes.

(25) Kraft lignin fibers from Example 5 were stabilized according to Example 7 using a heating rate of 10° C./min from ambient temperature to 250° C., where it was isothermally treated for 60 min.

(26) 13. Stabilization of Softwood Lignin Fiber Containing 10% Purified Hardwood Lignin Using 1° C./Min from Ambient Temperature to 250° C., Isothermally Treated for 30 Minutes.

(27) Kraft lignin fibers from Example 6 were stabilized according to Example 7 using a heating rate of 1° C./min from ambient temperature to 250° C., where it was isothermally treated for 30 min.

(28) 14. Stabilization of Single Softwood Lignin Fiber Containing 10% Purified Hardwood Lignin Using 70° C./Min from Ambient Temperature to 250° C., where it was Isothermally Treated for 10 Minutes.

(29) Kraft lignin fibers from Example 6 were stabilized according to Example 7 using a heating rate of 70° C./min from ambient temperature to 250° C., where it was isothermally treated for 10 min.

(30) 15. Stabilization of Single Softwood Lignin Fiber Containing 10% Purified Hardwood Lignin Using 70° C./Min from Ambient Temperature to 200° C., where it was Isothermally Treated for 30 Minutes.

(31) Kraft lignin fibers from Example 6 were stabilized according to Example 7 using a heating rate of 70° C./min from ambient temperature to 200° C., where it was isothermally treated for 30 min.

(32) 16. Stabilization of Single Softwood Lignin Fiber Containing 10% Purified Hardwood Lignin Using 70° C./Min from Ambient Temperature to 220° C., where it was Isothermally Treated for 20 Minutes.

(33) Kraft lignin fibers from Example 6 were stabilized according to Example 7 using a heating rate of 70° C./min from ambient temperature to 220° C., where it was isothermally treated for 20 min.

(34) 17. Preparation of Carbon Fibers by Carbonization Subsequent to the Stabilization Step.

(35) Stabilized lignin fibers from Example 7-16 were carbonized in nitrogen atmosphere using a tube furnace with a heating rate of 20° C./min from ambient temperature to 250° C. followed by a heating rate of 1° C./min to 600° C. and subsequently 3° C./min to 1000° C. Solid and homogeneous carbon fibers were obtained as revealed by EM analysis. Furthermore, the fibers did not fuse and retained their shape.

(36) 18. Preparation of Carbon Fibers when Stabilization and Carbonization of Lignin Fibers Proceed as a One-Step Operation.

(37) Softwood kraft lignin fibers from Example 4 were placed in a ceramic sample holder and placed in a tube furnace filled with nitrogen (>99.999%). The lignin fibres were thermally stabilized and carbonized in a one-step operation using a heating rate of 10° C./min to 250° C. and isothermal for 10 min followed by a heating rate of 3° C./min to 1000° C. Solid and homogeneous carbon fibers were obtained as revealed by EM analysis. Furthermore, the fibers did not fuse and retained their shape.