Method for producing carbon from heat-treated lignin

Abstract

The present invention relates to the production of granular carbon prepared from lignin, the method comprising the steps of providing agglomerated lignin, heating the agglomerated lignin to obtain thermally stabilized lignin, and subjecting the thermally stabilized agglomerated lignin to a heat treatment to obtain the granular carbon.

Description

[Technical Field]

[0001] The present invention relates to the production of granular carbon prepared from lignin. [Background technology]

[0002] The carbon-rich material can be used in a variety of end uses, such as biochar, activated carbon, and electrode materials.

[0003] In conventional processes for converting biomass to carbon-rich intermediates, powders are often avoided. The direct use of finely powdered lignin is not preferred because it exhibits undesirable thermoplastic behavior.

[0004] During the thermal conversion of lignin powder to carbon-rich intermediates, lignin undergoes plastic deformation / melting, erosive swelling, and foaming. Combined with its strong tendency to form dust during handling, this severely limits the processability of lignin on an industrial scale in terms of equipment sizing and process throughput, as well as the need for intermediate processing.

[0005] It is desirable to use lignin as a replacement for petroleum-based carbon-containing materials. Lignin, an aromatic polymer, is the second most abundant carbon source on Earth, second only to cellulose, the primary constituent of wood, for example. In recent years, the development and commercialization of techniques for extracting lignin in a highly purified, solid, and particulate form from the pulp manufacturing process has attracted significant attention as a promising renewable alternative to the major aromatic chemical precursors currently supplied by the petrochemical industry.

[0006] However, in order to use lignin as a feedstock for the economical production of carbon-rich materials such as biochar, activated carbon, and electrode materials, it appears necessary to avoid lignin undergoing plastic deformation / melting, erosive swelling, and foaming upon heating.

[0007] US6099990 describes a method for making carbon materials, which includes mixing lignin powder with salt and then heating the mixture in several steps, including a carbonization step. According to US6099990, foaming is reduced during heating. However, the salt used is expensive and not suitable for large-scale processes. In addition, the salt may remain in the carbon material unless it is removed by a washing step.

[0008] Methods to make lignin less soluble during heating also include modification of lignin powder with maleic acid, as described in JP2015067514, and hydrothermal carbonization of lignin solutions prior to carbonization, as described in US2016230099 and JP2011178851.

[0009] However, there remains a need for a simple and scalable method for obtaining lignin that can be heat treated to obtain granular carbon while retaining its shape and size. Summary of the Invention

[0010] Surprisingly, it has been found that lignin that has been agglomerated into particles visible to the naked eye and thermally stabilized can be heat-treated while retaining its shape and dimensions and avoiding melting / swelling deformation. This facilitates the production of carbon-rich materials for a variety of end uses, such as biochar and activated carbon, and the method avoids dust. It has been found that the thermally stabilized, once agglomerated, lignin continues to retain its dimensional integrity during further processing into a carbon-rich product. In addition, the resulting granular carbon is substantially spherical, making it suitable for use in, for example, filters and other applications where substantially spherical granular carbon is advantageous.

[0011] The present invention provides a method for producing granular carbon, comprising the steps of: a) providing an agglomerated lignin having a particle size distribution such that at least 80% by weight of the agglomerates have a diameter within the range of 0.2 mm to 5.0 mm; b) heating the agglomerated lignin to a temperature in the range of 140°C to 250°C for at least 1.5 hours to obtain a thermally stabilized agglomerated lignin. c) subjecting the thermally stabilized agglomerated lignin to a heat treatment at one or more temperatures in the range of 300°C to 1500°C to obtain granular carbon, said heat treatment being carried out for a total time of 30 minutes to 10 hours. The present invention relates to a method, including:

[0012] Preferably, the agglomerated lignin obtained in step b) has a particle size distribution such that at least 80% by weight of the agglomerates have a diameter within the range of 0.2 mm to 5.0 mm.

[0013] Preferably, the agglomerated lignin used in step a) is i. providing a powdered lignin, the powdered lignin having a particle size distribution such that at least 80% by weight of the particles have a diameter of less than 0.2 mm and a moisture content of less than 45% by weight; ii. compressing the lignin powder of step i); iii. crushing the compressed lignin obtained in step ii); iv. Optionally, sieving the compacted lignin obtained in step iii) to remove particles having a particle size of less than 100 μm, thereby obtaining an agglomerated lignin having a particle size distribution in which at least 80% by weight of the particles have a size within the range of 0.2 mm to 5.0 mm. Manufactured by

[0014] Preferably, the product obtained in step iii is sieved according to step iv. Preferably, in step iv, the sieving is carried out so that the resulting agglomerated lignin has a particle size distribution such that at least 80% by weight of the particles have a diameter in the range of 0.5 mm to 2.0 mm, more preferably 0.5 mm to 1.5 mm.

[0015] Compaction can be carried out without adding any additives to the material to be compacted. In the context of the present invention, an additive is a substance added to the process to improve adhesion between lignin particles. Thus, an additive is a substance that is added but is not present in the starting lignin material in step a). Thus, neither moisture, such as water, nor other components already present in the starting lignin material in step i) are considered additives in the context of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] Throughout this specification, the term "lignin" is intended to encompass any type of lignin, for example, lignin derived from hardwood, softwood, or annual plants. Preferably, the lignin is alkaline lignin, such as that produced in the Kraft process. Preferably, the lignin has been purified or isolated before use in the process of the present invention. Lignin can be isolated from black liquor and, optionally, further purified before use in the process of the present invention. Purification typically results in a lignin purity of at least 90%, preferably at least 95%, more preferably at least 98%, and most preferably at least 99%, 99.5%, or 99.9%. Thus, the lignin used in the process of the present invention preferably contains less than 10%, preferably less than 5%, and more preferably less than 2% impurities. Lignin can be separated from black liquor using the method disclosed in WO2006031175.

[0017] In the context of the present invention, particle size is the equivalent spherical diameter of the particle if the particle is not spherical. The equivalent spherical diameter is the spherical diameter of an equivalent volume.

[0018] Preferably, the agglomerated lignin is i. providing a powdered lignin, the powdered lignin having a particle size distribution such that at least 80% by weight of the particles have a diameter of less than 0.2 mm and a moisture content of less than 45% by weight; ii. compressing the lignin powder of step i); iii. crushing the compressed lignin obtained in step ii); Optionally, sieving the compacted lignin obtained in step iii) to remove particles having a particle size of less than 100 μm, thereby obtaining an agglomerated lignin having a particle size distribution such that at least 80% by weight of the particles have a size within the range of 0.2 mm to 5.0 mm, preferably 0.2 mm to 2.0 mm, more preferably 0.5 mm to 1.5 mm. It is prepared by a method comprising:

[0019] Preferably, the powdered lignin is dried before compaction. Drying of the lignin is carried out by methods and apparatus known in the art. The powdered lignin used in step i) has a moisture content of less than 45% by weight. Preferably, the moisture content of the lignin before compaction according to the invention is less than 25% by weight, preferably less than 10% by weight, more preferably less than 8% by weight. In one embodiment, the moisture content of the lignin before compaction according to the invention is at least 1% by weight, for example at least 5% by weight. The temperature during drying is preferably in the range of 80°C to 160°C, more preferably in the range of 100°C to 120°C.

[0020] The lignin powder obtained after drying has a broad particle size distribution ranging from 1 μm to 2 mm, with a strong bias towards the micrometer range, meaning that a significant proportion of the particles have diameters within the range of 1 to 200 micrometers.

[0021] The compression of the lignin is preferably carried out by roll compression.

[0022] Roll compaction of the lignin can be carried out by a roll compactor, which can agglomerate the lignin particles.

[0023] In the compaction process, an intermediate product is produced. Here, lignin fine powder is typically fed through a hopper and transported to the compaction zone, where compaction rollers with a defined gap compress the material into flakes, using a horizontal or vertical feed screw. Controlling the feed screw speed and pressure generation in the compaction zone results in flakes with uniform density. Pressure generation in the compaction zone can be monitored and controlled by the rotational speed of the compaction rolls. As the powder is pulled between the rollers, it enters a nip area, which increases the material's density and converts it into flakes or ribbons. The rolls used have cavities. The depth of each cavity used in roll compaction is 0.1 mm to 10 mm, preferably 1 mm to 8 mm, more preferably 1 mm to 5 mm or 1 mm to 3 mm. The predetermined pressing force exerted during compaction can vary depending on the device used for compaction, but may be in the range of 1 kN / cm to 100 kN / cm. Suitable devices for performing compaction are known in the art.

[0024] After compression, crushing is preferably carried out.

[0025] In the crushing step, the intermediate product from the compaction step is crushed or comminuted, for example, by means of a rotary granulator, a cage mill, a beater mill, a hammer mill, or a crushing mill and / or a combination thereof. During this step, further intermediate products are produced.

[0026] After crushing, the crushed material is preferably subjected to a sieving process to remove fine material. Additionally, large material, e.g., agglomerates greater than 5.0 mm in diameter, can be removed and / or recycled back into the crushing process.

[0027] In the sieving step, the intermediate product from the crushing step is screened by physical fractionation, such as sieving, also called screening, to obtain a product that is an agglomerated lignin with a defined particle size distribution set by the porosity of the sieve or screen in this step. The sieve or screen is selected so that most of the particles less than 100 (or 500) μm in diameter pass through the screen, are removed, and preferably returned to the compaction step, while most of the particles greater than 100 (or 500) μm in diameter are retained and subjected to subsequent heating in the method according to the invention. Sieving can be carried out in two or more steps, i.e., sieving can be carried out so that the crushed material from the crushing step passes through two or more screens or sieves in succession.

[0028] In one embodiment of roll compaction, the roll configuration is such that the first roll has a periphery configured such that the powder in the nip region is sealed axially along the roller surface.

[0029] In one embodiment, the roll configuration is such that the nip region is axially sealed along the roller surface with the electrostatic plate.

[0030] By ensuring that the nip area is sealed, powder loss at the ends of the roller shaft is minimized compared to nip rollers that are entirely cylindrical.

[0031] It is particularly advantageous to carry out the compaction according to the present invention on a substantially lignin-only material, i.e., in the absence of additives, because the compacted product is easier to use due to the absence of binders or other components that may adversely affect the applications for which the compacted, crushed, and optionally sieved lignin is intended.

[0032] Due to the compaction of lignin powder in the preparation of agglomerated lignin, the bulk density of the lignin increases when pressure is applied to the lignin powder. This means that the agglomerated lignin will have a higher bulk density than the lignin powder. The more compacted lignin particles have been found to retain their shape and dimensions without fusing or swelling, which may be advantageous in subsequent processing into carbon-rich materials. The agglomerated lignin particles also have a relatively high hardness after compaction. Hard particles are advantageous in subsequent processing because they can withstand physical impacts during processing. Furthermore, processing problems that can arise when using hard, compacted particles due to the presence of lignin dust on the particle surface are avoided. This may be particularly important in large-scale processes, as the dust can form explosive mixtures with air and can also cause blockages in processing equipment.

[0033] The agglomerated lignin is preferably 0.5 g / cm 3 to 0.7 g / cm 3 , more preferably 0.5 g / cm 3 to 0.6 g / cm 3 The lignin powder before agglomeration has a bulk density in the range of 0.3 g / cm 3 to 0.4 g / cm 3 The thermally stabilized agglomerated lignin preferably has a bulk density in the range of 0.5 g / cm 3 to 0.7 g / cm 3 in the range of 0.5 g / cm 3 to 0.6 g / cm 3 It is also preferred that the lignin have a bulk density in the range of 0.1 to 0.25. Heat stabilization may induce a slight increase or decrease in the bulk density of the lignin. However, it is preferred that the bulk density be maintained in a similar range as before heat stabilization.

[0034] The agglomerated lignin has a particle size distribution such that at least 80% of the particles by weight have a diameter within the range of 0.2 mm to 5.0 mm. Preferably, at least 90%, more preferably at least 95%, by weight of the particles have a diameter within the range of 0.2 mm to 5.0 mm. More preferably, at least 90%, more preferably at least 95%, by weight of the particles have a diameter within the range of 0.5 mm to 2 mm.

[0035] The step of heating the agglomerated lignin to produce thermally stabilized agglomerated lignin can be carried out in a continuous or batch mode. Heating can be carried out using methods known in the art and can be carried out in the presence of air or fully or partially under an inert gas. Preferably, heating is carried out in a rotary kiln, moving bed furnace, or rotary hearth furnace.

[0036] Heating to produce thermally stabilized agglomerated lignin is carried out so as to heat the agglomerated lignin to a temperature in the range of 140°C to 250°C, preferably 180 to 230°C. Heating is carried out for at least 1.5 hours, i.e., the residence time of the agglomerated lignin in the equipment used for heating is at least 1.5 hours. Preferably, heating is carried out for less than 12 hours. Heating may be carried out at the same temperature throughout the heating stage or at a varying temperature, for example, using a temperature step increase or temperature gradient. More preferably, heating is carried out so as to first heat the agglomerated lignin to a temperature of 140°C to 175°C for at least 1 hour, and then to a temperature of 175°C to 250°C for at least 1 hour.

[0037] By controlling and optimizing parameters such as temperature and time during the thermal stabilization process, it is possible to obtain a thermally stabilized agglomerated lignin that retains its shape and dimensions without fusing or swelling during subsequent processing. The described process is highly compatible with conventional process requirements for continuous production using, for example, a rotary kiln due to the mechanical stability and relatively short residence time of the agglomerated lignin. This is particularly important for achieving an economical, large-scale industrial process for producing carbon-rich materials.

[0038] The color of the thermally stabilized agglomerated lignin differs from the color of the agglomerated lignin before heat stabilization. Color can be measured, for example, by using a spectrophotometer and reported according to the CIELAB color space. In the CIELAB color space, color is expressed as lightness (L * ), green to red (a * ) and blue to yellow (b * ) component of the surface of the thermally stabilized agglomerated lignin. * ) is in the range of 37 to 39, preferably in the range of 37 to 38. The surface brightness of the agglomerated lignin before heat stabilization is greater than 44, for example in the range of 44 to 52. Thus, the brightness of the agglomerated lignin decreases during heat stabilization.

[0039] The thermally stabilized agglomerated lignin obtained in step b) is subjected to a heat treatment at one or more temperatures in the range of 300°C to 1500°C to obtain granular carbon, wherein said heat treatment is carried out for a total time of 30 minutes to 10 hours.

[0040] Preferably, the heat treatment includes a preheating step followed by a final heating step. The preheating step is carried out in an inert atmosphere, preferably a nitrogen atmosphere, at a temperature preferably between 300°C and 800°C, for example between 500°C and 700°C. The duration of the preheating step is at least 30 minutes, preferably less than 10 hours. The preheating and final heating steps can be carried out as separate steps or as one single, serial step. The surface area of ​​the product obtained after the preheating step is typically between 300 and 700 m 2 / g, as measured by BET using nitrogen gas.

[0041] The final heating step is carried out in an inert atmosphere, preferably a nitrogen atmosphere, at a temperature preferably between 800°C and 1500°C. The duration of the final heating step is at least 30 minutes, preferably less than 10 hours. After the final heating step, the surface area of ​​the resulting product is typically less than 10 m 2 / g or less.

[0042] Preferably, the heat treatment is carried out in stages. Preferably, the preheating starts at about 300° C. and is then increased to about 500° C. The final heating step is preferably carried out at between 900° C. and 1300° C., for example at about 1000° C.

[0043] The heat-treated material, i.e., the particulate carbon product of step c), is useful, for example, as biochar or as a precursor to activated carbon or electrode materials.

[0044] The heat-treated material, i.e. the product of step c), granular carbon, has a density of 0.2 g / cm 3 to 0.4 g / cm 3 It is preferred that the bulk density of the agglomerated lignin is in the range of 0.05 to 0.15, which is lower than the bulk density of the agglomerated lignin and the thermally stabilized lignin obtained in step b) and is mainly due to the mass loss during the heat treatment.

[0045] The color of the granular carbon differs from the color of the previously thermally stabilized agglomerated lignin. Color can be measured, for example, by using a spectrophotometer and reported according to the CIELAB color space. In the CIELAB color space, color is expressed as lightness (L * ), green to red (a * ) and blue to yellow (b * ) component of the surface of the granular carbon. * ) is in the range of 34 to 37, preferably in the range of 34 to 36. Thus, the brightness of the agglomerated lignin decreases during step c). [Example]

[0046] Example 1 Lignin powder from the LignoBoost process was agglomerated by roller compaction into particles with a particle size distribution of 0.2 to 2 mm. The agglomerated lignin was slowly heated to 200°C and held for 12 hours. During this process, the agglomerated lignin did not exhibit any melting behavior and completely retained its original shape. Surprisingly, it was found that the individual granules did not fuse together and remained highly fluid. During processing, the material gradually darkened in color until it was completely black and odorless.

[0047] The thermally stabilized agglomerated lignin was then heated in an inert atmosphere at 500 to 1000°C. In this process, the granular carbon formed remained round in shape and had good flowability.

[0048] Example 2 Lignin powder from the LignoBoost process was agglomerated by roller compaction and then crushed and sieved into particles with a particle size distribution of 0.5 to 1.5 mm.

[0049] The agglomerated lignin was placed in a laboratory rotary furnace and heated using airflow to 160 °C for 2 hours, then to 225 °C for 2 hours. During this process, the agglomerated lignin did not exhibit any melting behavior. Surprisingly, it was found that the individual granules did not fuse to each other or to the inner walls of the reactor, and remained fluid. During processing, the material gradually darkened in color until it was completely black.

[0050] The thermally stabilized agglomerated lignin was then heated to 300-350°C for 1 hour, and then to 500°C for 1 hour under an inert nitrogen atmosphere. Finally, the material was heated to 1000°C under nitrogen for 1 hour. The resulting carbon material remained in an unagglomerated granular form.

[0051] Example 3 This experiment was carried out in the same manner as in Example 2, except that the agglomerated lignin was heated to 200°C.

[0052] The resulting carbon material had good fluidity but some melting and fusion. This indicates that the thermally stabilized lignin obtained by heating at 225°C was able to resist melting and fusion during thermal processing in a better way, as shown in Example 2. This further emphasizes the importance of selecting the right combination of temperature and time for the thermal stabilization step.

[0053] Example 4 (Comparative Example) In this experiment, conventional heat exchange of lignin powder was carried out.

[0054] Lignin powder from the LignoBoost process was slowly heated to 200°C and held for 12 hours. After heating, the lignin was found to melt / fuse into a solid, odorless black cake. This experiment demonstrates the importance of agglomeration of the lignin powder prior to the thermal stabilization step.

[0055] Example 5 In this experiment, a larger-scale, continuous method for producing granular carbon was evaluated. Lignin powder from the LignoBoost process was agglomerated by roller compaction, then crushed and sieved into particles with a particle size distribution of 0.5 to 1.5 mm. The bulk density of the lignin was 0.60 g / cm. 3 The thermal stabilization of the agglomerated lignin was carried out in a rotary kiln in air with a feed rate of 3 kg / h. The temperature was increased from 170 to 230 °C in separate heating zones, with an average residence time in the rotary kiln of 2.5 h.

[0056] The bulk density of thermally stabilized agglomerated lignin is 0.66 g / cm 3 , which was slightly increased compared to the agglomerated lignin before stabilization.

[0057] The color of the samples was measured using a Konica Minolta CM-5 spectrophotometer. No sample pretreatment was performed. The measurements provided color in the CIELAB color space index. The L of the aggregated kraft lignin was used as the starting value. * The value was 49.4. After heat stabilization, L * The values ​​were measured six times over a five-day period and ranged from 37.4 to 37.9.

[0058] A matte black aggregate was obtained. The thermally stabilized lignin aggregate had good flowability and showed a small amount of melting during the stabilization process. The total feed amount of agglomerated lignin was 441 kg, and the total output was 390 kg, resulting in an overall yield of 93%. The total duration of the test was 172 hours.

[0059] A continuous pre-carbonization heat treatment of the thermally stabilized agglomerated lignin was then carried out in a rotary kiln under nitrogen atmosphere. The feed rate was 3 kg / h and the average residence time in the rotary kiln was 2.5 h. In a separate heating zone, the temperature was increased from 250 to 525 °C. The bulk density of the pre-carbonized lignin was 160 g / cm. 3 The L of pre-carbonized lignin *The values ​​were measured four times over a four day period. Values ​​ranged from 39.8 to 40.7. Shiny gray aggregates were obtained. The aggregates showed a small amount of melting and fusion during the pre-carbonization process. The total feed amount of thermally stabilized agglomerated lignin was 339 kg and the total output was 183 kg, resulting in an overall yield of 54%. The total duration of the test was 121 hours.

[0060] Finally, a continuous carbonization process of the pre-carbonized lignin was carried out in a rotary kiln under nitrogen atmosphere. The feed rate was 2 kg / h and the average residence time in the rotary kiln was 1 h. The temperature was set at 1000 °C. The bulk density of the obtained carbonized lignin was 190 g / cm. 3 The increase compared to pre-carbonized lignin may be due to the shrinkage of aggregates. * The values ​​were measured four times over a three day period. Values ​​ranged from 35.2 to 35.9. Matte black aggregates were obtained after carbonization. No further melting or fusion of the aggregates was observed during carbonization. The total feed amount of pre-carbonized lignin was 169 kg and the total output was 134 kg, resulting in an overall yield of 80%. The total duration of the test was 76 hours.

[0061] This demonstrates that large-scale processing is possible.

[0062] In view of the above detailed description of the invention, other changes and modifications will be apparent to those skilled in the art, but it is evident that such other changes and modifications can be accomplished without departing from the spirit and scope of the invention.

Claims

1. 1. A method for producing granular carbon from lignin, comprising: a) providing an agglomerated lignin produced by a process comprising compressing lignin powder having a particle size distribution such that at least 80% by weight of the agglomerates have a diameter within the range of 0.2 mm to 5.0 mm; b) heating the agglomerated lignin to a temperature in the range of 180°C to 250°C for at least 1.5 hours and less than 12 hours to obtain a thermally stabilized agglomerated lignin; c) subjecting the thermally stabilized agglomerated lignin to a heat treatment at one or more temperatures in the range of 300°C to 1500°C to obtain granular carbon, the heat treatment being carried out for a total time of 30 minutes to 10 hours. and wherein the agglomerated lignin used in step a) comprises i. providing a powdered lignin having a particle size distribution such that at least 80% by weight of the particles have a diameter less than 0.2 mm and a moisture content of less than 45% by weight; ii. Compressing the lignin powder of step i); iii. Crushing the compressed lignin obtained in step ii); iv. Optionally, sieving the compacted lignin obtained in step iii) to remove particles having a particle size of less than 100 μm, thereby obtaining an agglomerated lignin having a particle size distribution in which at least 80% by weight of the agglomerates have a size within the range of 0.2 mm to 5.0 mm. The method of manufacturing the

2. Agglomerated lignin is 0.5 g / cm ３ to 0.7 g / cm ３ , preferably 0.5 g / cm ３ to 0.6 g / cm ３ 2. The method of claim 1, wherein the bulk density is in the range of

3. 3. The method of claim 1 or 2, wherein the heating of the agglomerated lignin in step b) is carried out by first heating the agglomerated lignin to a temperature of from 140°C to 175°C for at least 1 hour, and subsequently heating the agglomerated lignin to a temperature of from 180°C to 250°C for at least 1.5 hours.

4. 4. The method of any one of claims 1 to 3, wherein step c) comprises a pre-heating step followed by a final heating step.

5. 5. The method of claim 4, wherein the preheating step c) is carried out at a temperature between 400°C and 800°C for at least 30 minutes.

6. 6. The method of claim 5, wherein the preheating step is carried out in an inert atmosphere.

7. 7. The method according to any one of claims 4 to 6, wherein the final heating step is carried out at a temperature between 800°C and 1500°C for at least 30 minutes.

8. 8. The method of claim 7, wherein the final heating step is carried out in an inert atmosphere.

9. The CIELAB lightness (L ＊ 9. The method of claim 1, wherein the β-amino acid saturates ...

10. The CIELAB lightness (L ＊ 10. The method of claim 1, wherein the saturation factor is in the range of 34 to 37.

11. The granular carbon obtained in step c) has a density of 0.2 g / cm ３ to 0.4 g / cm ３ 11. The method of claim 1, wherein the bulk density is in the range of

12. 12. The method of any one of claims 1 to 11, wherein the lignin is kraft lignin.

13. 13. The method of claim 12, wherein the lignin has a purity of at least 98%.