Apparatus and method for extracting lignin from non-wood black liquor.

Abstract

Disclosed are a method, apparatus, and system for extracting lignin from non-wood black liquor. The non-wood black liquor is heated to a first temperature to decompose the hemicellulose contained therein. The liquor is then cooled to a second temperature. The pH of the cooled liquor is chemically reduced to precipitate the lignin in the liquor. The liquor is filtered to separate the precipitated lignin from the liquor.

Description

Technical Field

[0001] The present invention relates generally to lignin extraction, and more specifically to lignin extraction from non-wood black liquor.

[0002] (Related Application) This application claims the priority of U.S. Patent Application No. 63 / 534,666 entitled "Apparatus and Method for Lignin Extraction from Non-Wood Black Liquor" filed on August 25, 2023. In the United States, this application claims the benefit under 35 USC §119 of U.S. Patent Application No. 63 / 534,666 entitled "Apparatus and Method for Lignin Extraction from Non-Wood Black Liquor" filed on August 25, 2023. U.S. Patent Application No. 63 / 534,666 is incorporated herein by reference in its entirety for all purposes.

Background Art

[0003] Black liquor is a by-product of pulp production. It is a mixture of pulping residues such as lignin and hemicellulose, and inorganic chemicals used to facilitate the pulping process. In conventional pulp production using wood-based raw materials, black liquor is combusted in a recovery boiler for reuse in subsequent pulping processes, whereby energy can be extracted from pulping residues and inorganic chemicals can be recovered. In some cases, the recovery boiler becomes a bottleneck for black liquor treatment. In such cases, it may be desirable to pretreat black liquor to precipitate lignin before combustion in order to improve treatment efficiency.

[0004] Conventional techniques for extracting lignin from wood-based black liquor include precipitation and filtration of lignin from wood-based black liquor. Precipitated lignin can be used as a useful raw material for the production of chemical products to reduce the use or generation of hazardous substances. Lignin extraction reduces the calorific value of black liquor with a low residual lignin content. The reduction in calorific value reduces the heat load on the recovery boiler, which consequently leads to processing more black liquor solids and driving an increase in pulp production.

[0005] Non-wood black liquor is a by-product of pulp production using non-wood raw materials such as straw. Because non-wood raw materials (e.g., wheat straw) contain high concentrations of silica and hemicellulose, conventional lignin extraction processes for black liquor are not applicable to non-wood black liquor. In particular, studies have shown that existing commercial wood-based processes are ineffective for non-wood black liquor due to its poor filterability. The high concentration of silica in non-wood black liquor co-precipitates with lignin, inhibiting filtration and making lignin removal difficult. Furthermore, non-wood black liquor typically contains higher concentrations of hemicellulose, especially arabinoxylan, compared to conventional wood-based black liquor. High hemicellulose content leads to hydrogel formation, further complicating the filtration and removal of precipitated lignin from the solution. Due to these problems, processes for extracting lignin from non-wood black liquor are generally energy-inefficient.

[0006] Therefore, improved methods and processes are needed for precipitation, filtration, and / or separation of lignin from non-wood black liquor. More energy-efficient processes are needed that can overcome the filterability problems caused by the high silica and hemicellulose content present in non-wood black liquor. [Overview of the project]

[0007] Generally speaking, this specification describes apparatus, systems and products for extracting lignin from non-wood black liquor. Let me explain about Rothes.

[0008] One aspect of the present invention relates to a method for extracting lignin from non-wood liquor. The non-wood liquor may have a dissolved solids concentration in the range of 5% to 30%. The method includes the steps of: heating the non-wood liquor to a first temperature to decompose the hemicellulose contained therein; subsequently cooling the non-wood liquor to a second temperature; subsequently chemically lowering the pH of the cooled non-wood liquor to precipitate the lignin in the non-wood liquor; and subsequently filtering the non-wood liquor to separate the precipitated lignin from the non-wood liquor. The first temperature can be in the range of 150°C to 200°C. The second temperature can be in the range of 65°C to 95°C.

[0009] In some embodiments, the non-wood liquor is oxidized under pressure before cooling. The non-wood liquor may be oxidized under a pressure of 1 bar to 10 bar. The non-wood liquor may be oxidized at the same time as heating it to the first temperature. In some embodiments, the separated lignin is washed, and then the washed lignin is recovered. The lignin may be washed with hot water.

[0010] In some embodiments, the non-wood liquor is filtered by a filter press (press filtration) or a belt filter (belt filtration). In some embodiments, the non-wood liquor is heated at the first temperature for 5 to 80 minutes. In some embodiments, the pH of the non-wood liquor is chemically reduced to a value of 1 to 4 to precipitate lignin in the non-wood liquor. The pH of the non-wood liquor can be chemically reduced by adding a mineral acid to the non-wood liquor.

[0011] In some embodiments, the non-wood black liquor is obtained by pulping a non-wood raw material that has been desilicated in a desilicate process prior to pulping. In such embodiments, the non-wood black liquor may be cooled by indirectly preheating the pulping chemicals used in the pulping process of the non-wood raw material. The desilicate process may include mechanically separating silica from the non-wood raw material using a mechanical pulper. The desilicate process may include chemically treating the non-wood raw material with a compound solution at a third temperature (e.g., in the range of 50°C to 100°C) to selectively remove silica from the non-wood raw material. The compound solution may include sodium carbonate, sodium hydroxide, or potassium hydroxide. The non-wood raw material may include straw-based raw materials.

[0012] Further aspects of the present invention will become apparent from the following description.

[0013] The features and advantages of embodiments of the present invention will become apparent from the following detailed description with reference to the accompanying drawings. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a flowchart of a process for precipitating and extracting lignin from non-wood black liquor according to one embodiment.

[0015] [Figure 2] Figure 2 is a flowchart of a supplementary process for extracting lignin from non-wood black liquor, which can be used in combination with the process in Figure 1. [Modes for carrying out the invention]

[0016] The following description and embodiments are provided to illustrate examples of specific embodiments of the principles of the present invention. These examples are provided to illustrate those principles and the present invention, and are not intended to limit the invention.

[0017] Aspects of the present invention relate to apparatus, systems, and processes for precipitating and separating lignin from non-wood black liquor. For ease of explanation, the term “non-wood” as used herein refers to non-wood raw materials or agricultural fibers, such as straw and / or agricultural residues left after the harvest of crops. The term “straw” as used herein includes, but is not limited to, wheat straw, barley straw, oat straw, flax straw, rice straw, hemp, bamboo, miscanthus, sorghum, switchgrass, ryegrass, corn stalks and leaves, bagasse, reed stalks, and banana trees. The term “non-wood black liquor” as used herein refers to black liquor, a by-product produced in the process of manufacturing pulp from non-wood raw materials. As described in more detail elsewhere in this specification, non-wood black liquor typically has a higher silica and hemicellulose content compared to wood-based black liquor, which makes it more difficult to extract lignin from them.

[0018] Referring to Figure 1, a flowchart of a process 10 for extracting lignin 15 from non-wood black liquor 17 according to one embodiment is shown. Process 10 combines chemical and mechanical means to precipitate, filter, and separate lignin 15 from non-wood black liquor 17. Depending on factors such as the composition of the non-wood raw material and the alkali addition rate, non-wood black liquor 17 recovered from the pulping process can typically have a dissolved solids concentration in the range of 5% to 30%. In contrast to existing lignin precipitation and filtration systems that require the use of evaporators to increase the dissolved solids concentration of the black liquor to the range of 30% to 50%, process 10 can extract lignin 15 from non-wood black liquor 17 with a dissolved solids concentration of less than 30%.

[0019] Process 10 begins with heating the non-wood liquor 17 to a high temperature in the heat treatment step 20. Heat treatment of the non-wood liquor 17 can improve the filterability of the downstream precipitated lignin 15, even if the silica content is high. In some embodiments, step 20 is carried out to raise the temperature of the non-wood liquor 17 from, for example, room temperature (e.g., 20°C to 25°C) to 150°C to 200°C. In some embodiments, the non-wood liquor 17 is heated for 5 to 80 minutes. Since hemicellulose dissolves at temperatures above 150°C, raising the temperature of the non-wood liquor 17 can accelerate the decomposition of the hemicellulose contained therein. Since hemicellulose content inhibits filterability and the removal of precipitated lignin from the solution, it is desirable to decompose the hemicellulose in the non-wood liquor 17 in the early stages of process 10 (e.g., step 20).

[0020] In the heat treatment step 20, after heating the non-wood liquor 17 at a desired temperature for a desired time, process 10 proceeds to an optional oxidation step 30. In step 30, the heated non-wood liquor 17 is oxidized under pressure to further improve the filterability of the precipitated lignin downstream. Oxidation contributes to the further decomposition of hemicellulose remaining in the heated non-wood liquor 17. Oxidation also contributes to lowering the pH of the heated non-wood liquor 17 and improving the aggregation of lignin colloids. The non-wood liquor 17 may be oxidized under pressure (e.g., 1 to 10 bar).

[0021] In addition to improving the filterability of lignin, the oxidation in step 30 reduces the levels of biochemical oxygen demand (BOD) and chemical oxygen demand (COD) along with the molecular weight of organic acids in the non-wood black liquor 17, thereby improving the processability of the filtrate 18 with a low lignin content obtained downstream.

[0022] In some embodiments, the oxidation step 30 may be carried out before or simultaneously with the heating step 20. In such embodiments, the oxidation of hemicellulose (i.e., an exothermic process) contributes to reducing the energy input required to heat the non-wood black liquor 17 in step 20.

[0023] After completion of the heating step 20 and the optional oxidation step 30, the process 10 proceeds to step 40. In step 40, the non-wood black liquor 17 is cooled to a temperature lower than the high temperature. For example, the non-wood black liquor 17 can typically be cooled to a temperature in the range of 65°C to 95°C. The purpose of lowering the temperature in step 40 is to facilitate the handling of the heat-treated non-wood black liquor 17 in subsequent processing steps, but the temperature is usually maintained slightly higher (e.g., compared to room temperature) to promote the decomposition of hemicellulose. In some embodiments, the heat-treated non-wood black liquor 17 is cooled by indirectly preheating cooking chemicals used in the pulping process of non-wood raw materials. Cooling by indirectly preheating the cooking chemicals improves the energy efficiency of the present process.

[0024] After cooling the non-wood black liquor 17 to a desired temperature in step 40, the process 10 proceeds to the precipitation step 50. In the precipitation step 50, the pH of the cooled non-wood black liquor 17 is lowered to precipitate lignin in the non-wood black liquor 17. In some embodiments, the pH of the non-wood black liquor 17 is lowered to a value of 1 to 4. In some embodiments, in the precipitation step 50, the pH of the non-wood black liquor 17 is lowered by adding a strong mineral acid such as sulfuric acid to the cooled non-wood black liquor 17. In the precipitation step 50, other acids such as nitric acid, phosphoric acid and hydrochloric acid can also be used. In contrast to existing wood-based lignin precipitation processes that require the use of both carbon dioxide (CO₂) and sulfuric acid for lignin precipitation and acid washing, step 50 requires only a strong acid (e.g., sulfuric acid), thereby reducing the consumption of chemicals required for lignin precipitation. After completion of step 50, a mixture of a filtrate 18 with low lignin content and precipitated lignin 15 is obtained.

[0025] After completion of step 50, process 10 proceeds to filtration step 60. In filtration step 60, filtrate 18 with low lignin content and precipitated lignin 15 are separated, completing the lignin extraction process. Filtration step 60 may be carried out using a mechanical filter press (press filtration) or a mechanical belt filter (belt filtration), or the like. Whereas existing lignin precipitation systems require the use of two or more filtration presses for the separation and purification of precipitated lignin, step 60 can be performed using a single filter, which allows reduction of the equipment required for separation and purification of precipitated lignin. Filtration step 60 can optionally include washing of the extracted lignin 15. The extracted lignin 15 can be washed with purified water and / or warm water.

[0026] Removal of lignin 15, as well as heat treatment and oxidation of non-wood black liquor, significantly improves the treatability of the filtrate 18 with low lignin content. The low-lignin filtrate 18 obtained from process 10 is effectively treated using aerobic treatment. The filtrate 18 with low lignin content can also produce biogas through anaerobic treatment.

[0027] A wide range of modifications and additions are possible within the scope of the present invention. These include supplementary processes that can be carried out in conjunction with the main process 10 for extracting lignin 15 from non-wood black liquor 17 described herein.

[0028] For example, FIG. 2 shows an additional exemplary process 80 that can be implemented before process 10 to assist lignin separation. As shown in FIG. 2, incorporating a desilication step 100 during the process of producing pulp 92 from non-wood raw material 90 can improve the filterability of precipitated lignin in black liquor and further enhance the efficiency of process 10. Since a mixture of lignin and silica can make the control of lignin extraction process 10 difficult, it is desirable to minimize the silica content in the non-wood black liquor 17 as much as possible. In particular, silica can co-precipitate with lignin during precipitation step 50, which may impair filterability and the purity of the final lignin product .

[0029] By performing the desilicate process 100, the silica level present in the non-wood black liquor 17 can be significantly reduced. For example, in process 100, the non-wood raw material 90 can be pretreated by treating it with hot water or a chemical solution (e.g., an alkaline solution) and a portion of the silica can be separated from the non-wood raw material 90. This treatment can be carried out for 10 to 30 minutes or more. In some embodiments, the non-wood raw material 90 is heated and chemically desilicated using compounds such as sodium carbonate, sodium hydroxide, or potassium hydroxide. The non-wood raw material 90 can also be treated with hot water in process 100 without the addition of alkaline chemicals. The compounds used in the desilicate process 100 can preferentially separate silica from the non-wood raw material 90 (over lignin, for example).

[0030] To selectively separate silica from the non-wood raw material 90, the desilicate step 100 can be carried out under atmospheric pressure at a temperature in the range of 50°C to 100°C. When a strong alkali is used in step 100, a relatively low reaction temperature (e.g., ~60°C) is sufficient to prioritize silica removal over the delignin reaction. When a weak alkali or hot water is used in step 100, a relatively high reaction temperature (e.g., ~90°C) may be required to prioritize silica removal over the delignin reaction.

[0031] As another example, in step 100, the non-wood raw material 90 can be mechanically desilicated. In some embodiments, step 100 includes a combination of mechanical and chemical processes. In such embodiments, the desilicate step 100 may include heating the non-wood raw material 90 and subjecting it to a chemical reaction (e.g., in an alkaline solution), followed by mechanically pulping a stream of the non-wood raw material 90 to mechanically separate more silica from the non-wood raw material 90.

[0032] Upon completion of the desilicate process 100, a relatively large amount of silica dissolves in the alkaline desilicate solution and is selectively removed from the stream of non-wood raw material 90. The desilicated non-wood raw material 90 can then be processed through a non-wood pulping process 200 to produce pulp 92. As a result of performing the desilicate process 100, the non-wood black liquor 17, a by-product remaining from process 200, has a relatively low silica content. This non-wood black liquor 17 is processed using process 10 in Figure 1 to extract lignin 15.

[0033] The examples and corresponding diagrams used herein are for illustrative purposes only. Different structures and terminology may be used without deviating from the principles expressed herein.

[0034] While the present invention is described with reference to specific embodiments, various modifications thereto will be apparent to those skilled in the art without departing from the scope of the invention. The scope of the claims should not be limited by the exemplary embodiments described in the examples, but rather should be given the broadest interpretation consistent with the entire specification. For example, various features are described herein as being present in “several embodiments” or “one embodiment.” Such features are not essential and are not necessarily present in all embodiments. Embodiments of the present invention may include zero, any one, or any combination of two or more such features. This is only the case if certain of these features are so limited that they are incompatible with others, and it is impossible for those skilled in the art to construct a practical embodiment combining such incompatible features. Therefore, a statement that “several embodiments” have feature A, or “several embodiments” have feature B, should be interpreted as an explicit indication that the inventor has also considered embodiments combining feature A and feature B (unless otherwise stated in the description, or if feature A and feature B are fundamentally incompatible).

Claims

1. A method for extracting lignin from non-wood black liquor, The aforementioned method, The black liquor of the non-wood is heated to a first temperature to decompose the hemicellulose contained therein; The non-wood black liquor is cooled to a second temperature; Chemically lower the pH of the cooled non-wood liquor to precipitate the lignin in the non-wood liquor; and The black liquor of the non-wood is filtered to separate the precipitated lignin from the black liquor of the non-wood. A method that includes doing so.

2. The process includes oxidizing the non-wood black liquor under pressure before cooling the said non-wood black liquor, The method according to claim 1.

3. The method according to claim 1 or 2, comprising heating the non-wood black liquor to a first temperature and simultaneously oxidizing the non-wood black liquor.

4. The method according to claim 2 or 3, comprising oxidizing the non-wood black liquor under a pressure of 1 bar to 10 bar.

5. The process includes washing the separated lignin and recovering the washed lignin. The method according to any one of claims 1 to 4.

6. The method according to claim 5, wherein the lignin is washed with hot water.

7. The method according to any one of claims 1 to 6, wherein the non-wood black liquor is filtered by a filter press (press filtration) or a belt filter (belt filtration).

8. The method according to any one of claims 1 to 7, wherein the first temperature is in the range of 150°C to 200°C.

9. The method according to any one of claims 1 to 8, wherein the non-wood black liquor is heated at the first temperature for 5 to 80 minutes.

10. The method according to any one of claims 1 to 9, wherein the pH of the non-wood black liquor is chemically reduced to a value of 1 to 4 to precipitate the lignin in the non-wood black liquor.

11. The method according to claim 10, wherein the pH of the non-wood black liquor is chemically reduced by adding a mineral acid to the non-wood black liquor.

12. The method according to claim 1, wherein the non-wood black liquor is obtained by pulping a non-wood raw material that has been desilicated in a desilicate process prior to pulping.

13. The method according to claim 12, wherein the desilicate process comprises chemically treating the non-wood raw material with a compound solution at a third temperature to selectively remove silica from the non-wood raw material.

14. The method according to claim 13, wherein the third temperature is in the range of 50°C to 100°C.

15. The method according to claim 13, wherein the compound solution comprises sodium carbonate, sodium hydroxide, or potassium hydroxide.

16. The method according to claim 12, wherein the desilicate process includes mechanically separating silica from the non-wood raw material using a mechanical pulper.

17. The method according to claim 12, wherein the non-wood black liquor is cooled by indirectly preheating the pulping chemicals used in the pulping process of the non-wood raw material.

18. The method according to claim 12, wherein the non-wood raw material includes a straw-based raw material.

19. The method according to any one of claims 1 to 18, wherein the second temperature is in the range of 65°C to 95°C.

20. The method according to any one of claims 1 to 19, wherein the non-wood black liquor has a dissolved solids concentration in the range of 5% to 30%.

21. Apparatus having novel and inventive features, combinations of features, or subcombinations of features as described herein.

22. A method having a novel and inventive step, action, combination of steps and / or actions, or subcombination of steps and / or actions as described herein.

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