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

Abstract

Methods, apparatuses, and systems for extracting lignin from non-wood black liquor are disclosed. The non-wood black liquor is heated to a first temperature to degrade hemicelluloses contained therein. The liquid is then cooled to a second temperature. The pH of the cooled liquid is chemically reduced to precipitate lignin from the liquid. The liquid is filtered to separate the precipitated lignin from the liquid.

Description

Technical Field

[0001] This disclosure generally relates to lignin extraction, and more specifically to the extraction of lignin from non-wood black liquor.

[0002] Related Applications

[0003] This application claims priority to U.S. Patent Application No. 63 / 534,666, filed August 25, 2023, entitled “Apparatus and Methods for Extracting Lignin from Non-Wood Black Liquor.” For the purposes of this application in the United States, U.S. Patent Application No. 63 / 534,666, filed August 25, 2023, entitled “Apparatus and Methods for Extracting Lignin from Non-Wood Black Liquor,” is claimed under 35 USC §119. The entire contents of U.S. Patent Application No. 63 / 534,666 are incorporated herein by reference for all purposes. Background Technology

[0004] Black liquor is a byproduct 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 feedstocks, black liquor can be burned in a recycling boiler to extract energy from the pulping residues and recover inorganic chemicals for future use in the pulp production process. In some cases, the recycling boiler becomes a bottleneck in black liquor treatment. In these cases, it may be desirable to pretreat the black liquor before combustion to precipitate lignin from it, thereby improving treatment efficiency.

[0005] Traditional techniques for extracting lignin from wood-based black liquor may involve precipitating and filtering lignin from the black liquor. The precipitated lignin can then be used as a valuable material for the production of chemical products that reduce the use of harmful substances or their generation. Lignin extraction lowers the calorific value of the remaining lignin-poor black liquor. The reduced calorific value results in a lower heat load on a recovery boiler, which can then be operated to process additional black liquor solids and support incremental pulp production.

[0006] Non-wood black liquor is a byproduct of pulp production using non-wood raw materials such as straw. Conventional lignin extraction processes for black liquor are infeasible for non-wood black liquor due to the high silica and hemicellulose content in non-wood raw materials (e.g., wheat straw). In particular, studies have shown that existing commercial wood-based processes are ineffective for non-wood black liquor due to the poor filterability of lignin. The elevated levels of silica present in non-wood black liquor will co-precipitate with lignin, impairing filtration and making lignin removal difficult. Furthermore, non-wood black liquor typically contains higher levels of hemicellulose, especially arabinoxylan, compared to conventional wood-based black liquor. The elevated hemicellulose content can lead to hydrogel formation, which further impairs the filterability and removal of precipitated lignin from the solution. These problems generally result in energy-inefficient processes for extracting lignin from non-wood black liquor.

[0007] Therefore, there is a need for improved methods and processes for the precipitation, filtration, and / or separation of lignin from non-wood black liquor. There is also a need for highly energy-efficient processes that can overcome the filterability problems caused by the elevated silica and hemicellulose content found in non-wood black liquor. Summary of the Invention

[0008] In general, this specification describes apparatus, systems, and processes for extracting lignin from non-wood black liquor.

[0009] One aspect of the present invention relates to a method for extracting lignin from non-wood black liquor. The non-wood black liquor may have a dissolved solids concentration in the range of 5% to 30%. The method includes the steps of: heating the non-wood black liquor to a first temperature to degrade hemicellulose contained therein, subsequently cooling the non-wood black liquor to a second temperature, subsequently chemically lowering the pH of the cooled non-wood black liquor to precipitate lignin from the non-wood black liquor, and subsequently filtering the non-wood black liquor to separate the precipitated lignin from the non-wood black liquor. The first temperature may be in the range of 150°C to 200°C. The second temperature may be in the range of 65°C to 95°C.

[0010] In some embodiments, the non-wood black liquor is oxidized under pressure before cooling. The non-wood black liquor can be oxidized at a pressure between 1 bar and 10 bar. The oxidation can also be performed while the non-wood black liquor is heated to a first temperature. In some embodiments, the separated lignin is washed and subsequently collected. The lignin can be washed with hot water.

[0011] In some embodiments, a filter press or belt filter is used to filter the non-wood black liquor. In some embodiments, the non-wood black liquor is heated at a first temperature for a period of time between 5 and 80 minutes. In some embodiments, the pH of the non-wood black liquor is chemically lowered to a value between 1 and 4 to precipitate lignin from the non-wood black liquor. The pH of the non-wood black liquor can be chemically lowered by adding an inorganic acid to the non-wood black liquor.

[0012] In some embodiments, non-wood black liquor is obtained from pulping non-wood feedstock that has already been desiliconized during a desiliconization process prior to pulping. In these embodiments, the non-wood black liquor can be cooled by indirectly preheating the cooking chemicals used in the non-wood feedstock pulping process. The desiliconization process may include mechanically separating silica from the non-wood feedstock using a mechanical pulper. The desiliconization process may include chemically treating the non-wood feedstock with a compound solution at a third temperature (e.g., between 50°C and 100°C) to selectively remove silica from the non-wood feedstock. The compound solution may include sodium carbonate, sodium hydroxide, or potassium hydroxide. The non-wood feedstock may include straw-based feedstock.

[0013] Further aspects of the invention will become apparent from the following description. Attached Figure Description

[0014] The features and advantages of embodiments of the present invention will become apparent from the following detailed description with reference to the accompanying drawings, in which:

[0015] Figure 1 This is a flowchart of a process for precipitating and extracting lignin from non-wood black liquor, based on an example implementation.

[0016] Figure 2 It is possible to be with Figure 1 The process is combined with a flowchart of a supplementary process for extracting lignin from non-wood black liquor. Detailed Implementation

[0017] The following description, and the embodiments described herein, are provided by way of example illustrating specific embodiments of the principles of the invention. These examples are provided for the purpose of explanation, and not limitation, of the principles of the invention.

[0018] This invention relates to apparatus, systems, and processes for precipitating and separating lignin from non-wood black liquor. For purposes of description, the term “non-wood” is used herein to refer to non-wood raw materials or agricultural-based fibers, such as straw and / or agricultural residues remaining after crop harvest. As used herein, the term “straw” includes, but is not limited to, wheat straw, barley straw, oat straw, flax straw, rice straw, hemp, bamboo, miscanthus, sorghum, switchgrass, ryegrass, corn stalks, bagasse, reed stems, and banana tree stalks. As used herein, the term “non-wood black liquor” refers to a black liquor byproduct produced according to the process of manufacturing pulp from non-wood raw materials. As described in more detail elsewhere herein, non-wood black liquor typically has a higher silica and hemicellulose content compared to wood-based black liquor, thereby making lignin extraction from it more challenging.

[0019] Now for reference Figure 1 The diagram illustrates a flowchart of a process 10 for extracting lignin 15 from non-wood black liquor 17 according to one embodiment. Process 10 utilizes a combination of chemical and mechanical means to precipitate, filter, and separate lignin 15 from the non-wood black liquor 17. Depending on factors such as the composition of the non-wood feedstock and the alkali addition rate, the non-wood black liquor 17 collected from the pulping process can typically have a dissolved solids concentration in the range of 5% to 30%. Compared to existing lignin precipitation and filtration systems that require the use of evaporators to increase the dissolved solids concentration of the black liquor to between 30% and 50%, process 10 can extract lignin 15 from non-wood black liquor 17 with a dissolved solids concentration of less than 30%.

[0020] Process 10 begins by heating the non-wood black liquor 17 to an elevated temperature in heat treatment step 20. Even with elevated levels of silica, heat treatment of the non-wood black liquor 17 can improve the filterability of the precipitated lignin 15 downstream. In some embodiments, step 20 is performed to raise the temperature of the non-wood black liquor 17 from, for example, room temperature (e.g., 20°C to 25°C) to between 150°C and 200°C. In some embodiments, the heating of the non-wood black liquor 17 is sustained for a period ranging from 5 minutes to 80 minutes. Since hemicellulose dissolves at temperatures above 150°C, raising the temperature of the non-wood black liquor 17 can help enhance the degradation of the hemicellulose it contains. It is desirable to degrade the hemicellulose in the non-wood black liquor 17 early in process 10 (i.e., in step 20) because hemicellulose content impairs the filterability of the precipitated lignin and its removal from the solution.

[0021] After heating the non-wood black liquor 17 to a desired temperature for a desired time period in heat treatment step 20, process 10 proceeds to an optional oxidation treatment step 30. In step 30, the heated non-wood black liquor 17 is oxidized under pressure to further enhance the filterability of the precipitated lignin downstream. Oxidation treatment can help further degrade the hemicellulose retained in the heated non-wood black liquor 17. Oxidation treatment can also help lower the pH of the heated non-wood black liquor 17, thereby improving lignin colloidal aggregation. The non-wood black liquor 17 can be oxidized under pressure (e.g., between 1 bar and 10 bar).

[0022] In addition to improving lignin filterability, the oxidation treatment in step 30 also helps reduce the molecular weight of organic acids and the levels of biochemical oxygen demand (BOD) and chemical oxygen demand (COD) in the non-wood black liquor 17, thereby improving the treatability of the downstream lignin-poor filtrate 18.

[0023] In some embodiments, the oxidation treatment step 30 may be performed before or simultaneously with the heating step 20. In these embodiments, the oxidation treatment of hemicellulose (i.e., an exothermic process) can help reduce the energy input required to heat the non-wood black liquor 17 in step 20.

[0024] After completing heating step 20 and optional oxidation treatment step 30, process 10 proceeds to step 40. In step 40, the non-wood black liquor 17 is cooled to a temperature below the elevated temperature. The non-wood black liquor 17 can be cooled to a temperature typically in the range of 65°C to 95°C. Lowering the temperature in step 40 promotes disposal of the heat-treated non-wood black liquor 17 in subsequent treatment steps, but it is generally still maintained at a slightly elevated temperature (e.g., relative to room temperature) to promote hemicellulose degradation. In some embodiments, the heat-treated non-wood black liquor 17 is cooled by indirectly preheating the cooking chemicals used in the non-wood pulping process. Cooling by indirectly preheating the cooking chemicals improves the energy efficiency of the process.

[0025] After cooling the non-wood black liquor 17 to the desired temperature in step 40, process 10 proceeds to precipitation step 50. In precipitation step 50, the pH of the cooled non-wood black liquor 17 is lowered to precipitate lignin from the non-wood black liquor 17. In some embodiments, the pH of the non-wood black liquor 17 is lowered to a value between 1 and 4. In some embodiments, in precipitation step 50, the pH of the non-wood black liquor 17 is lowered by adding a strong inorganic acid (such as sulfuric acid) to the cooled non-wood black liquor 17. Other acids, such as nitric acid, phosphoric acid, and hydrochloric acid, can also be used in precipitation step 50. Compared to existing wood-based lignin precipitation processes that require both carbon dioxide (CO2) and sulfuric acid for lignin precipitation and acid washing, step 50 only requires a strong acid (e.g., sulfuric acid), thereby reducing the amount of chemicals used for lignin precipitation. After completing step 50, a mixture of lignin-poor filtrate 18 and precipitated lignin 15 is obtained.

[0026] After completing precipitation step 50, process 10 proceeds to filtration step 60. In filtration step 60, the lignin-poor filtrate 18 and the precipitated lignin 15 are separated to complete the lignin extraction process. Filtration step 60 can be performed using a mechanical filter press, mechanical belt filter, etc. Compared to existing lignin precipitation systems that require two or more filter presses to separate and purify the precipitated lignin, step 60 can be performed using a single filter, thereby reducing the equipment required for separating and purifying the precipitated lignin. Filtration step 60 may optionally include washing the extracted lignin 15. The extracted lignin 15 can be washed using purified water and / or hot water.

[0027] The removal of lignin 15, along with the thermal and oxidative treatment of non-wood black liquor, significantly improved the treatability of lignin-poor filtrate 18. Aerobic treatment has been used to effectively treat lignin-poor filtrate 18 obtained from process 10. Oligolignin-poor filtrate 18 can also be anaerobically treated to produce biogas.

[0028] Within the scope of this invention, a wide range of variations and additions are possible. These include supplementary processes that can be performed in conjunction with the main process 10 described herein for the extraction of lignin 15 from non-wood black liquor 17.

[0029] For example, Figure 2 An additional exemplary process 80, which can be implemented prior to process 10 to assist in lignin separation, is depicted. For example... Figure 2As described, a desilication step 100 can be incorporated into the process of manufacturing pulp 92 from non-wood raw material 90 to improve the filterability of the precipitated lignin in black liquor and further enhance the efficiency of process 10. To the extent possible, it is desirable to minimize the silica content in the non-wood black liquor 17, as a mixture of lignin and silica can be difficult to manage in the lignin extraction process 10. In particular, silica may co-precipitate with lignin during precipitation step 50, thereby impairing the filterability and purity of the final lignin product.

[0030] Performing desilication step 100 can significantly reduce the level of silica present in non-wood black liquor 17. As an example, non-wood raw material 90 can be treated with hot water or a chemical solution (e.g., an alkaline solution) to pretreat and separate some of the silica from the non-wood raw material 90 during step 100. This treatment can last for a period of 10 to 30 minutes or longer. In some embodiments, non-wood raw material 90 is heated and chemically desilicated with compounds such as sodium carbonate, sodium hydroxide, potassium hydroxide, etc. Non-wood raw material 90 can also be treated with hot water in step 100 without the addition of alkaline chemicals. The compounds used in desilication step 100 can preferentially separate silica (relative to, for example, lignin) from non-wood raw material 90.

[0031] To preferentially separate silica from non-wood raw material 90, the desilication step 100 can be carried out at atmospheric pressure at a temperature ranging from 50°C to 100°C. If a strong base is used in step 100, a relatively low reaction temperature (e.g., about 60°C) may be sufficient to preferentially remove silica over the delignification reaction. If a weak base or hot water is used in step 100, a relatively high reaction temperature (e.g., about 90°C) may be required to preferentially remove silica over the delignification reaction.

[0032] As another example, mechanical desilication of the non-wood material 90 can be performed in step 100. In some embodiments, step 100 involves a combination of mechanical and chemical processes. In these embodiments, the desilication step 100 may include mechanically pulping the stream of non-wood material 90 after it has been heated and chemically reacted (e.g., in an alkaline solution) to mechanically separate more silica from the non-wood material 90.

[0033] After desilication step 100, a relatively large amount of silica will dissolve in the alkaline desilication liquor and be selectively removed from the non-wood feedstock 90. ​​The desilicationated non-wood feedstock 90 can then be processed by non-wood pulping process 200 to produce pulp 92. Due to the execution of desilication step 100, the remaining non-wood black liquor 17 from process 200 will have a relatively low silica content. It can then be used... Figure 1Process 10 treats this non-wood black liquor 17 to extract lignin 15.

[0034] The examples and corresponding figures used in this article are for illustrative purposes only. Different configurations and terminology may be used without departing from the principles expressed herein.

[0035] Although the invention has been described with reference to certain specific embodiments, various modifications 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 to the illustrative embodiments set forth in the examples, but should be given the broadest interpretation consistent with the entire specification. For example, various features are described herein as existing in “some embodiments” or “one embodiment.” Such features are not mandatory and may not be present in all embodiments. Embodiments of the invention may include zero, any, or any combination of two or more of such features. This is limited to the degree to which some features are incompatible with others in the same category of features in the sense that it would be impossible for someone of ordinary skill in the art to construct a practical embodiment combining such incompatible features. Therefore, the description that “some embodiments” have feature A and “some embodiments” have feature B should be understood as an explicit indication that the inventors also contemplate embodiments combining features A and B (unless otherwise stated in the description or features A and B are fundamentally incompatible).

Claims

1. A method for extracting lignin from a non-wood black liquor, the method comprising: heating the non-wood black liquor to a first temperature to degrade hemicellulose contained therein; cooling the non-wood black liquor to a second temperature; chemically reducing a pH of the cooled non-wood black liquor to precipitate the lignin in the non-wood black liquor; and filtering the non-wood black liquor to separate the precipitated lignin from the non-wood black liquor.

2. The method of claim 1 or any other claim herein, comprising oxidizing the non-wood black liquor under pressure prior to cooling the non-wood black liquor.

3. The method of claim 1 or any other claim herein, comprising oxidizing the non-wood black liquor while heating the non-wood black liquor to the first temperature.

4. The method of claim 2 or claim 3, or any other claim herein, comprising oxidizing the non-wood black liquor under a pressure of between 1 bar and 10 bar.

5. The method of claim 1 or any other claim herein, comprising washing the separated lignin and collecting the washed lignin. washing the lignin with hot water.

6. The method of claim 5 or any other claim herein, wherein, filtering the non-wood black liquor using a filter press or a belt filter.

7. The method of claim 1 or any other claim herein, wherein, the first temperature is between 150 °C and 200 °C.

8. The method of claim 1 or any other claim herein, wherein, heating the non-wood black liquor at the first temperature for a period of between 5 minutes and 80 minutes.

9. The method of claim 1 or any other claim herein, wherein, chemically reducing the pH of the non-wood black liquor to a value of between 1 and 4 to precipitate the lignin in the non-wood black liquor.

10. The method of claim 1 or any other claim herein, wherein, chemically reducing the pH of the non-wood black liquor by adding an inorganic acid to the non-wood black liquor.

11. The method of claim 10 or any other claim herein, wherein, obtaining the non-wood black liquor from a pulping non-wood feedstock that has been desilicated in a desilication process prior to pulping.

12. The method of claim 1 or any other claim herein, wherein, the desilication process comprises chemically treating the non-wood feedstock with a compound solution at a third temperature to selectively remove silica from the non-wood feedstock.

13. The method of claim 12 or any other claim herein, wherein, the third temperature is between 50 °C and 100 °C.

14. The method of claim 13 or any other claim, wherein, the compound solution comprises sodium carbonate, sodium hydroxide, or potassium hydroxide.

15. The method of claim 13 or any other claim herein, wherein, the desilication process comprises mechanically separating silica from the non-wood feedstock with a mechanical pulper.

16. The method of claim 12 or any other claim herein, wherein, cooling the non-wood black liquor by indirect preheating cooking chemicals used in a non-wood feedstock pulping process.

17. The method of claim 12, wherein, the non-wood feedstock comprises a straw-based feedstock.

18. The method of claim 12, wherein, the second temperature is in a range of 65 °C to 95 °C.

19. The method of claim 1 or any other claim herein, wherein, the non-wood black liquor has a dissolved solids concentration in a range of 5% to 30%.

20. The method of claim 1 or any other claim herein, wherein, 21. An apparatus having any new and inventive feature, combination of features, or sub-combination of features as described herein.

22. A method having any new and inventive step, combination of steps, or sub-combination of steps and / or actions as described herein. ​

Images