WO2023015325A1 - System and method for obtaining lignin and carboxylic acid from byproducts of pulping processes - Google Patents

Abstract

The invention provides a system and method for obtaining lignin and carboxylic acid from a byproduct of a pulping process for digesting a source of lignin, such as the Kraft process or the soda pulping process. A spent liquor obtained from the pulping process is acidified by adding at least one organic acid to the liquor, thereby to precipitate a lignin component from the liquor and yield a suspension of precipitated lignin particles in the liquor. This suspension is filtered to separate a lignin-containing filter cake from a first filtrate of the suspension, and the carboxylic acid is extracted from the first filtrate. The carboxylic acid may, for example, comprise tartaric acid.

Description

SYSTEM AND METHOD FOR OBTAINING LIGNIN AND CARBOXYLIC ACID FROM BYPRODUCTS OF PULPING PROCESSES

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from South African provisional patent application number 2021/05810 filed on 6 August 2021 , which is incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to the production of lignin and carboxylic acids from byproducts of pulping processes used to digest lignin sources such as, but not limited to, wood pulp.

BACKGROUND TO THE INVENTION

Pulping processes are used to produce paper pulp by digesting wood or other sources of lignin. Such processes remove lignin, hemicelluloses, and other compounds from the wood to free the cellulose fibres in the wood. The Kraft process and the soda pulping process are examples of pulping processes.

The Kraft process is used to convert wood into wood pulp, which consists of almost pure cellulose fibres, the main component of paper. The kraft process entails treatment of wood chips with a hot mixture of water, sodium hydroxide, and sodium sulphide (Na2S), known as white liquor. This treatment breaks the bonds that link lignin, hemicellulose, and cellulose. The Kraft process is the dominant method of producing paper.

Soda pulping is a chemical process for making wood pulp with sodium hydroxide as the cooking chemical. The soda process gives pulp with lower tear strength than other chemical pulping processes. It is typically used for easily pulped materials like straw and some hardwoods.

Black liquor is produced by pulp mills as a byproduct of the Kraft and soda pulping processes. It is typically present in the form of a liquid or slurry. Black liquor that is derived from the Kraft process comprises an aqueous solution containing the inorganic chemicals used for cooking, as well as the degraded, dissolved wood substance. This has hundreds of components, including carboxylic acids, lignin residues, dissolved hemicelluloses, and methanol. The liquor typically contains around 15% w/w solids, of which 10% are inorganic and 5% are organic. Typically, the organic constituents in black liquor are 40%-45% soaps, 35%-45% lignin, and 10%— 15% miscellaneous other organic materials. Black liquor from the soda pulping process includes residual soda, lignin derivatives, low molecular weight organics, anthraquinone and sulphides.

More than 1.3 billion tons of black liquor are produced annually. Therefore, methods for the extraction of useful compounds found in black liquor may offer important economic benefits.

Conventional methods for lignin extraction include the LignoBoost® process described in US 2010/0325947 and in an earlier, related patent publication, W02006/031175. The process includes separation and washing steps. In the separation step, lignin is precipitated by acidifying the black liquor, preferably by using CO₂. The resultant lignin suspension is filtered to produce a lignin filter cake, which is then suspended again to form a second lignin suspension. The pH of this suspension is reduced to below 8 and it is filtered to form a second lignin filter cake. The washing step is then carried out. It involves purifying the second lignin cake by displacement washing in a low pH solution. Acidified wash water, virgin acid, or clean water may be used for this step. The filter cake is then dried to a level specified for different uses of the lignin. The filtrate remaining after the formation of the second lignin filter cake can be recycled back to suspend the first lignin filter cake and optionally wash it. The pH of the filtrate can be adjusted before doing so, to allow control to be exercised over the sodium and sulphur balance in the pulp mill.

The LignoForce™ process described in US8771464 is another way of separating lignin from black liquor. This process addresses problems of filtration resistance in conventional lignin recovery processes. Filterability is improved by oxidizing the black liquor under controlled conditions before the acidification step. The LignoForce™ process uses a filter press instead of a belt filter for lignin cake filtration and washing.

In addition to the above methods for recovering lignin, there are methods for producing carboxylic acids from the byproducts of pulping processes. Conventional methods for doing so involve depolymerization of the obtained lignin to produce the carboxylic acids. Such processes therefore require a separate treatment to be performed on the lignin after it has been extracted.

The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application. SUMMARY OF THE INVENTION

In accordance with an aspect of the invention there is provided a method for obtaining lignin and carboxylic acid from a byproduct of a pulping process for digesting a source of lignin, the method comprising the steps of acidifying a spent liquor obtained from the pulping process by adding at least one organic acid to the liquor, thereby to precipitate a lignin component from the liquor yielding a first lignin suspension of precipitated lignin particles in the liquor; filtering the first lignin suspension to separate a first lignin-containing filtrand or filter cake from a first filtrate of the suspension; and extracting the carboxylic acid from the first filtrate.

The spent liquor may comprise a black liquor from a pulping process.

The extracted carboxylic acid may comprise tartaric acid; therefore, the method may include extracting tartaric acid from the first filtrate. However, it will be appreciated that a plurality of other types of carboxylic acids may be extracted and recovered using the disclosed method.

The method may include a step of pre-heating the liquor prior to the acidification step. The step of pre-heating the liquor may comprise heating it to a temperature in a range from 30-70 °C.

The method may include holding or maintaining the liquor at a substantially isothermal temperature while the acidification and precipitation are carried out. The isothermal temperature may be > 40 °C.

The step of extracting the carboxylic acid from the first filtrate may comprise a first crystallization step wherein the carboxylic acid in the first filtrate is subjected to crystal formation. The first crystallization step may include lowering the temperature of the first filtrate.

The carboxylic acid yielded by the first crystallization step may be subjected to an acid purification or washing process involving at least one dissolution and re-crystallization step. The method may thus include dissolving the crystallized carboxylic acid in water and re-crystallizing it. The crystals may be washed multiple times by dissolution and recrystallization in water, thereby to increase further the purity of the carboxylic acid.

The step of acidifying the liquor may comprise adjusting its pH level to a pH < 8. The organic acid that is added to the liquor may be provided as a solution having an acid concentration of at least 5% w/v. In some modes of performing the disclosed method, the organic acid may be provided as a solution having an acid concentration > 8% w/v. For example, the solution may have an acid concentration of about 10% w/v.

The organic acid solution may be added to the liquor in a ratio of liquor to solution ranging from about 1 :3 to about 1 :4.5 v/v, i.e. , 3 to 4.5 volume units of the organic acid solution for every one volume unit of the liquor. This ratio is variable, however, and can be adjusted depending upon the desired pH level of the resultant mixture of acid and liquor.

The method may include recovering the first lignin-containing filter cake. The method may further include subjecting the first filter cake to a lignin purification or washing process. The lignin washing process may comprise one or more steps of dispersing or suspending the first filter cake in water and filtering the resultant dispersion to yield a washed lignin-containing filtrand or filter cake.

The lignin washing process may include one or more additional washing steps in which the washed lignin-containing filter cake is further washed with alcohol. The alcohol used for the lignin washing step may be added by way of an alcohol solution. The alcohol solution may be a dilute aqueous solution. It may have an alcohol concentration of 10%-50% v/v inclusive.

The alcohol may be selected from the group consisting of methanol, ethanol, propanol, and mixtures thereof.

The lignin washing process may yield a final lignin cake. The final lignin cake may be dried in a drying step before the lignin is stored. The drying step may comprise air-drying the lignin.

The pulping process from which the spent liquor is derived may be selected from the group consisting of a Kraft process, a soda pulping process, and a mild alkaline process.

Without limitation thereto, the source of the lignin may be selected from the group consisting of pulp wood, straw, jute, hemp, and cotton.

In accordance with a further aspect of the invention there is provided a system for obtaining lignin and carboxylic acid from a byproduct of a pulping process for digesting a source of lignin, the system comprising a source of spent liquor from the pulping process; an acidification component configured to acidify the liquor by adding at least one organic acid to the liquor, thereby to precipitate a lignin component from the liquor yielding a first lignin suspension of precipitated lignin particles in the liquor; a filtration component configured to filter the first lignin suspension to separate a first lignin-containing filtrand or filter cake from a first filtrate of the suspension; and a carboxylic acid extraction component configured to extract the carboxylic acid from the first filtrate of the liquor.

The spent liquor may comprise a black liquor from a pulping process.

The carboxylic acid may comprise tartaric acid.

The system may further include a heating component configured to pre-heat the liquor and to maintain the liquor at a substantially isothermal temperature while the liquor undergoes acidification and precipitation. The heating component may be configured to pre-heat the liquor to a temperature in a range from 30-70 °C. It may be configured to maintain the liquor at an isothermal temperature > 40 °C during acidification thereof by the acidification component.

The carboxylic acid extraction component may be configured to perform a first crystallization step wherein the carboxylic acid in the first filtrate is subjected to crystal formation, thereby to yield crystals of the carboxylic acid. The system may further include a carboxylic acid purification or washing component configured to purify or wash the resultant carboxylic acid crystals by dissolution and re-crystallization.

The acidification component may be configured to perform a pH adjustment operation whereby the pH level of the liquor is adjusted to a pH < 8.

The acidification component may be configured to add the organic acid to the liquor as a solution having an acid concentration of at least 5% w/v. The acidification component may be configured to add the organic acid to the liquor as a solution having an acid concentration > 8% w/v, for example, about 10% w/v.

The acidification component may be configured to add the organic acid solution to the liquor in a ratio of liquor to solution ranging from about 1 :3 to about 1 :4.5 v/v, i.e. , 3 to 4.5 volume units of the organic acid solution for every one volume unit of the liquor. This ratio is variable, however, and can be adjusted depending upon the desired pH level of the resultant mixture of acid and liquor. The system may include additional components configured to perform ancillary steps of the method of the invention as detailed above.

The system may include recovery means for recovering the final carboxylic acid and lignin products of the system for downstream use or processing, or for chemical reactions.

The pulping process and the source of the lignin may be as described above.

The present invention extends to carboxylic acid obtained by the disclosed method, including but not limited to tartaric acid. The invention also extends to the use of a carboxylic acid obtained by the disclosed method as a reactant in a downstream chemical reaction.

The present invention extends, further, to lignin or an intermediate lignin product obtained by the disclosed method. The invention extends further to the use of lignin or an intermediate lignin product obtained by the disclosed method to produce heat or as a reactant in a downstream chemical reaction.

Embodiments and modes of performing the invention will now be described, by way of example only, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Figure 1 is a schematic process flow diagram illustrating an exemplary mode of performing the disclosed method for obtaining lignin and carboxylic acid from a black liquor byproduct of a pulping process.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

Modes of performing the disclosed method are explained in greater detail in the following description.

A method is provided for obtaining lignin and carboxylic acid from a byproduct of a pulping process used to digest a source of lignin. The byproduct may be a spent liquor such as black liquor. Without limiting the generality thereof, the pulping process may be selected from the group consisting of a Kraft process, a soda pulping process, and a mild alkaline process.

The disclosed method may facilitate dual separation and extraction of the lignin and carboxylic acid using a bifurcated processing stream. Recovery of the two products by separation and extraction may accordingly be carried out simultaneously and concurrently, as opposed to consecutively as in conventional methods of obtaining carboxylic acid from lignin sources. Additionally, the carboxylic acid may be extracted at a lower temperature than is typically used in conventional processes to obtain carboxylic acid from lignin sources.

The method addresses a need, previously unmet, for methods which are less complex, and which have lower energy demands than other methods of producing lignin and carboxylic acid from byproducts of pulp processing. Amongst the carboxylic acids in black liquor, the inventor has identified tartaric acid as a viable compound for extraction. Previously, the related compounds succinic acid and methylsuccinic acid have been identified in black liquor. Tartaric acid has not, however, been identified or targeted for recovery by extraction.

Referring to Figure 1 , reference numeral 100 indicates, generally, an exemplary process for carrying out the disclosed method for recovering lignin and carboxylic acid from a spent liquor such as black liquor.

The method (100) may include preheating (101) the black liquor. The liquor may be preheated to a temperature in a range from 30-70 °C.

The lignin may be precipitated (103) while the liquor is maintained at a substantially isothermal temperature. This temperature may be > 40 °C. The period for which the liquor is maintained at the substantially isothermal temperature may range from 40-80 minutes.

The precipitation step may involve acidifying the liquor by adding at least one organic acid to it. This step may be carried out while the liquor is maintained at the substantially isothermal temperature referred to above. The acidification step may comprise adjusting the pH level of the liquor to a pH < 8. The organic acid used for the acidification step may be selected from the group consisting of citric acid, oxalic acid, formic acid, acetic acid, and combinations thereof. Instead, or in addition, it may comprise any other type of organic acid capable of precipitating at least one type of lignin. The organic acid may be provided as a solution having an acid concentration of at least 5% w/v, and in some cases > 8% w/v. For example, the solution may have an acid concentration of 10% w/v.

The organic acid solution may be added to the black liquor in a ratio of liquor to solution ranging from about 1 :3 to about 1 :4.5 v/v, i.e. , 3 to 4.5 volume units of the organic acid solution for every one volume unit of the liquor. This ratio is variable, however, and can be adjusted depending upon the desired pH level of the resultant mixture of acid and liquor.

The addition of the organic acid to the liquor may be performed in a gradual, continuous, or stepwise manner.

The acidification step causes a lignin component to be precipitated from the liquor, yielding a first lignin suspension of precipitated lignin particles in the liquor. This suspension may also be referred to as a lignin precipitation solution. The step of precipitating the lignin component may include coagulating the precipitated lignin particles to promote their subsequent filtration. The coagulating step may include a secondary heating step wherein the first lignin suspension is heated to a temperature < 100 °C.

The first lignin suspension may then be filtered in a first filtration step (105 / Filtration 1), producing a first lignin-containing filtrand and a first filtrate which may contain the carboxylic acid. The step of filtering the lignin suspension may be performed using a high pressure filter press. The filtrand may be obtained as a lignin filter cake.

The process (100) then bifurcates into two separate and concurrent sub-processes (107; 109). These two sub-processes relate, respectively, to the extraction, filtration and washing of the carboxylic acid on the one hand; and to the separation, purification, and recovery of the lignin on the other hand.

In the first sub-process (107), carboxylic acids may be extracted from the first filtrate of the black liquor. It will be appreciated that a plurality of different types of carboxylic acids may be recovered using the disclosed method. As mentioned, the disclosed method may be used for extracting tartaric acid, provided the liquor that is being processed contains that acid. Exemplary modes of performing the disclosed method may yield 25-35 g of tartaric acid for every 10 g of organic acid used for precipitation of the lignin.

The step of extracting the carboxylic acid from the first filtrate may comprise a first carboxylic acid crystallization step (111) wherein the carboxylic acid in the first filtrate is subjected to crystal formation by dissolution and crystallization, typically carried out following the addition of water to the filtrate. The first crystallization step may involve lowering the temperature of the first filtrate.

Raw carboxylic acid crystals produced by the first crystallization step may be filtered in a first carboxylic acid filtration step (113 / Filtration 4) to yield a carboxylic acid filtrand. The carboxylic acid filtrand yielded by the first crystallization step may be subjected to at least one purification or washing process (115) involving further dissolution and re-crystallization. The method may thus include dissolving the filtrand of the raw crystallized carboxylic acid in water and recrystallizing it. The resultant crystals may be washed multiple further times by dissolution and recrystallization in water, thereby progressively increasing the purity of the carboxylic acid product.

The washed crystals from the washing step (115) may be filtered out (117 / Filtration 5) and recovered.

The filtrates from the carboxylic acid filtration steps (113; 117) may serve as a feedstock for further processing downstream (119), to yield other products that are not discussed herein.

In the other sub-process (109), the raw lignin filtered out of the black liquor may be washed or purified. In a first lignin-washing step (121), the first lignin-containing filtrand or filter cake obtained from the first filtration (105) may be re-dispersed or re-suspended in water. Subsequent washing may be carried out in alcohol, as discussed further below.

The suspension of lignin in water may be filtered (123 / Filtration 2) to yield a water-washed lignin filtrand. This may then be subjected to a further washing step (125), this time using alcohol. The alcohol used for this washing step may be provided as a dilute aqueous solution of alcohol. The alcohol solution may have a concentration in a range from 10%-50% v/v. The alcohol used for the washing may be selected from the group consisting of methanol, ethanol, propanol, and mixtures thereof.

A further filtration step (127 / Filtration 3) may be used to separate out the alcohol-washed lignin, producing a final lignin filter cake (129) and a final filtrate. The final filtrate may be joined with the filtrate from the first filtration step (105) and the filtrate from the downstream lignin filtration step (123) and may be added to the first carboxylic acid crystallization step (111 ). Meanwhile, purification of the lignin may include further alcohol washing processes (not shown), each using a fresh volume of aqueous alcohol solution.

The method may include a drying step (not shown) for drying the lignin of the final lignin cake (129) before recovering it and storing it as a dried lignin product. The drying step may comprise air-drying the lignin. The air-drying may be performed at ambient atmospheric conditions.

A system (not shown) for separating lignin and extracting carboxylic acid from a byproduct of a pulping processes is also disclosed. The byproduct may comprise spent liquor from the pulping process concerned. As in the case of the method of the invention, described above, the spent liquor may be a black liquor derived from one of the types of pulping processes listed previously.

The system may include a heating component configured to pre-heat the liquor and to maintain the liquor at a substantially isothermal temperature. The heating component may be configured to pre-heat the liquor to a temperature in a range from 30-70 °C. It may be configured to maintain the liquor at an isothermal temperature > 40 °C.

The system may include an acidification component configured to acidify the liquor by adding at least one organic acid thereto. It may be configured to do so while the liquor is held at the substantially isothermal temperature by the heating component. The acidification component may be configured to adjust the pH level of the liquor to a pH < 8.

The acidification component may be configured to add the organic acid to the liquor as a solution having an acid concentration of at least 5% w/v. The acidification component may be configured to add the organic acid to the liquor as a solution having an acid concentration > 8% w/v, for example, about 10% w/v.

The acidification component may be configured to add the organic acid solution to the black liquor in a ratio of liquor to solution ranging from about 1 :3 to about 1 :4.5 v/v, i.e., 3 to 4.5 volume units of the organic acid solution for every one volume unit of the liquor. This ratio is variable, however, and can be adjusted depending upon the desired pH level of the resultant mixture of acid and liquor.

The organic acid may be selected from the group of organic acids described above,

In use of the system, acidification carried out by the acidification component may precipitate a lignin component from the liquor yielding a first lignin suspension of precipitated lignin particles in the liquor. This suspension may also be referred to as a lignin precipitation solution.

The system may further include a filtration component for filtering the first lignin suspension to separate a first lignin-containing filtrand or filter cake from a first filtrate of the suspension.

The system may further include a carboxylic acid extraction component configured to extract the carboxylic acid from the first filtrate of the liquor.

The carboxylic acid extraction component may be configured to perform a first crystallization step wherein the carboxylic acid in the first filtrate is subjected to crystal formation, thereby to yield crystals of the carboxylic acid. The system may further include a carboxylic acid purification or washing component configured to purify or wash the resultant carboxylic acid crystals by dissolution and re-crystallization.

The system may further include a lignin washing component. This component may be configured to perform the steps of sub-process (109) set out above.

Feed means may be provided for feeding the black liquor to the system for processing.

The system may include additional components configured to perform ancillary steps of the method of the invention as detailed above.

The carboxylic acid extracted by the process may comprise tartaric acid.

The system may include recovery means for recovering the final carboxylic acid and lignin products of the system for downstream use.

The disclosed method and system may have several benefits. They may permit lignin and carboxylic acid to be separated or extracted simultaneously from black liquor. Lignin and carboxylic acid may be obtained without the need to depolymerize the lignin to produce the carboxylic acids, which has been the process used in previous technologies used for production of carboxylic acids from lignin sources. This is an important advantage of the presently disclosed method since it facilitates extraction of the lignin in an ongoing single process, which has benefits for scaling the method up to industrial levels of production.

The disclosed method may also permit carboxylic acid recovery to be carried out at relatively low temperatures, which in turn provides advantages of energy savings and relative simplicity.

Moreover, the disclosed method involves the use of organic acids as opposed to potentially harmful and corrosive mineral acids.

The disclosed method also addresses a need for practical methods of extracting high-value products such as tartaric acid from lignocellulosic material on an industrial scale. Biorefinery viability is promoted since the extraction of carboxylic acids as by-products provides a valueadding proposition to increase production profitability. The disclosed method gives at least two valuable products from a single concurrent process, whereas in the past, as mentioned, lignin has been required as an intermediate towards producing carboxylic acids.

Additionally, the method and system are adapted to produce lignin having good levels of purity because of the step of washing the lignin with dilute alcohol.

There are multiple industrial uses for the products of the disclosed method. For example, the extracted lignin may be used in the production of fuels, materials, and chemicals, and the extracted carboxylic acid may be used in the food and chemical industries, amongst others.

The foregoing description has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure.

The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention.

Finally, throughout the specification, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising” will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

CLAIMS:

1 . A method for obtaining lignin and carboxylic acid from a byproduct of a pulping process for digesting a source of lignin, the method comprising the steps of acidifying a spent liquor obtained from the pulping process by adding at least one organic acid to the liquor, thereby to precipitate a lignin component from the liquor yielding a first lignin suspension of precipitated lignin particles in the liquor; filtering the first lignin suspension to separate a first lignin-containing filter cake from a first filtrate of the suspension; and extracting the carboxylic acid from the first filtrate.

2. The method according to claim 1 , wherein the spent liquor comprises a black liquor from a pulping process.

3. The method according to either one of claims 1 and 2, which comprises extracting tartaric acid from the first filtrate.

4. The method according to any one of claims 1 to 3, which includes pre-heating the liquor prior to the acidification step and maintaining the liquor at a substantially isothermal temperature while the acidification and precipitation steps are carried out.

5. The method according to any one of claims 1 to 4, wherein the organic acid is provided as a solution having an acid concentration > 8% w/v and the solution is added to the liquor in a ratio of liquor to solution ranging from about 1 :3 to about 1 :4.5 v/v.

6. The method according to any one of claims 1 to 5, wherein the step of extracting the carboxylic acid from the first filtrate comprises a first crystallization step wherein the carboxylic acid in the first filtrate is subjected to crystal formation, the first crystallization step including lowering the temperature of the first filtrate; and wherein the carboxylic acid yielded by the first crystallization step is subjected to an acid washing process involving at least one dissolution and re-crystallization step.

7. The method according to any one of claims 1 to 6, which further includes recovering the first lignin-containing filter cake and subjecting it to a lignin washing process which comprises dispersing the first filter cake in water, filtering the resultant dispersion to yield a washed lignin-containing filter cake, and further washing the washed lignin-containing filter cake with alcohol. A system for obtaining lignin and carboxylic acid from a byproduct of a pulping process for digesting a source of lignin, the system comprising a source of spent liquor from the pulping process; an acidification component configured to acidify the liquor by adding at least one organic acid to the liquor, thereby to precipitate a lignin component from the liquor yielding a first lignin suspension of precipitated lignin particles in the liquor; a filtration component configured to filter the first lignin suspension to separate a first lignin-containing filter cake from a first filtrate of the suspension; and a carboxylic acid extraction component configured to extract the carboxylic acid from the first filtrate of the liquor. The system according to claim 8, wherein the spent liquor comprises a black liquor from a pulping process. The system according to either one of claims 8 and 9, wherein the carboxylic acid comprises tartaric acid. The system according to any one of claims 8 to 10, which includes a heating component configured to pre-heat the liquor and to maintain the liquor at a substantially isothermal temperature while the liquor undergoes acidification and precipitation. The system according to any one of claims 8 to 11 , wherein the acidification component is configured to add a solution of the organic acid to the liquor, the organic acid solution having an acid concentration > 8% w/v; and wherein the acidification component is further configured to add the solution to the liquor in a ratio of liquor to solution ranging from about 1 :3 to about 1 :4.5 v/v. The system according to any one of claims 8 to 12, which further includes components configured to recover the first lignin-containing filter cake and subject it to a washing process which comprises dispersing the first filter cake in water, filtering the resultant dispersion to yield a washed lignin-containing filter cake, and further washing the washed lignin-containing filter cake with alcohol. Lignin obtained by the method according to any one of claims 1 to 7. Carboxylic acid obtained by the method according to any one of claims 1 to 7.