SE1550127A1

SE1550127A1 - A method for the treatment of spent pulping liquor for the production of a stream of liquid depolymerised lignin

Info

Publication number: SE1550127A1
Application number: SE1550127A
Authority: SE
Inventors: Lars Stigsson
Original assignee: Kiram Ab
Priority date: 2013-05-29
Filing date: 2014-05-09
Publication date: 2015-02-05
Also published as: CA2913852A1; SE1751100A1; US20160130752A1; WO2014193289A1; SE1551720A1; EP3004455A1; BR112015029859A2; SE540451C2; SE1550117A1; EP3004455A4

Description

15 20 25 30 2 One objective of the present invention is to provide an efficient process for the production of depolymerised Iignin (without drying the Iignin throughout the process) for use in fine chemicals production or as precursor for production of renewable fuels.

Summarv of the invention The stated objectives above is achieved by a method for the treatment of spent pulping Iiquor for the production of a stream of depolymerised Iignin product and recovering or recycling of aqueous cooking chemicals to a pulp mi|| chemicals recovery cycle, said method comprising: - passing a spent pulping Iiquor discharged from a digester or an spent pulping Iiquor evaporator, or discharged from any other Iiquor treatment step in between the digester and the evaporator, through at least one separation step, e.g. a fiitration step, in which the flow is separated into one aqueous stream comprising cooking chemicals being recovered or recycled and into one stream concentrated with respect to Iignin; - passing the stream concentrated with respect to Iignin to a Iignin depolymerisation step consisting of one or more depolymerisation reactors in order to produce a stream of depolymerised Iignin. ln relation to the above description of the present invention and its high level of recirculation and recovery of aqueous cooking chemicals it may further be said that at least 75% of the total input of aqueous cooking chemicals present in the spent pulping Iiquor feed is recovered or recycled from the spent Iiquor treatment steps of the present invention. ln relation to some of the expressions used above, the following may be stated. The expression “recovered or recycled” implies that the aqueous stream comprising cooking chemicals may be both directly and indirectly used in other parts of the pulp mi|| processes. As an example, recycling may imply recycling the aqueous stream comprising cooking chemicals to a pulp mi|| recovery cycle.

According to one embodiment of the present invention, a catalytic Iignin depolymerisation step is integrated in the spent pulping Iiquor recovery system of a pulp mi||. 10 15 20 25 30 Brief description of the drawinqs Fig.1 shows a process flow set-up according to one embodiment of the present invention, wherein a catalytic depolymerisation step is integrated in the spent pulping liquor system of a pulp mill.

Specific embodiments of the invention Below, specific embodiments according to the present invention are disclosed.

The Iignin containing spent pulping liquor starting material used in the process of the invention may be of different types mainly depending on the pulping process and the wood raw material fed to the pulp mill. According to one specific embodiment, the spent pulping liquor is a kraft black liquor or a spent cellulose liquor originating from a soda pulping process.

Apart from Iignin the spent pulping liquor contains spent cooking chemicals which chemicals needs to be recycled and reformed to fresh cooking chemicals within the pulp mill .A kraft black liquor is highly alkaline and has a pH value between 11 and 13. The total content of inorganic salts dissolved in the kraft black liquor including the active cooking chemicals varies between 15 and 30 % by weight of the black liquor solids. The variation is mainly due to wood raw material and pulp product from the mill. lt is a key objective of the present invention to recycle a major portion of these dissolved inorganic salts to the pulp mill chemicals recovery cycle.

Furthermore, it is of great importance to ensure that the pH value in streams charged or recycled to a chemicals recovery cycle of a kraft pulp mill always is kept above about 11 in order to minimize evolution of toxic and odorous hydrogen sulphide gas. ln the following text and in the claims these dissolved salts present in the spent pulping liquor is referred to as aqueous cooking chemicals.

The separation step may e.g. involve different filter types, however membrane filters are one useful alternative. Therefore, according to one specific embodiment of the present invention, at least one of the filtration steps is based on using membranes. 10 15 20 25 30 4 According to one specific embodiment, the method comprises at least one separation step, e.g. a filtration step, such as a membrane filtration step, involving a separation of the input stream into one aqueous stream comprising cooking chemicals being recovered or recycled and one stream having a concentrated content of organic substances.

Furthermore, according to yet another specific embodiment, the method also comprises a pre-filtration step, said pre-filtration step involving a separation of the input stream of spent pulping Iiquor flow into one stream with large undesired molecules and one stream intended to be further filtrated.

Sulphuric acid can advantageously be used for acidulation in an acidulation step located downstream a lignin depolymerisation step , as sulphuric acid is used in kraft mills and any sulphates can be recycled to the chemicals recovery cycle. Nevertheless other acids can also be used for acidulation including mineral acids and organic acids.

According to one embodiment, the temperature in at least one of the separation steps, such as e.g. filtration steps, is held above 85°C, e.g. above 90°C and preferably above 100°C. Temperatures well above 100°C, such as up to 150°C are fully feasible. ln addition to the method, the present invention is also related to a system configuration. According to one embodiment, the present invention is directed to a system for the treatment of spent pulping liquorfor the removal and production of organic substances and recovering or recycling of aqueous inorganic cooking chemicals, said system optionally comprising a separation unit, such as a filter unit, arranged to separate a spent pulping Iiquor flow from a digester or an evaporator, or from any other step in between the digester and the evaporator in a pulp mill, into one aqueous stream comprising a major portion of the cooking chemicals present in the spent pulping Iiquor being recovered or recycled and one stream having a concentrated content of organic substances.

According to the present invention there is provided a method wherein lignin is depolymerized within the lignin separation process of the present invention. A lignin depolymerisation step is preferably performed on the 10 15 20 25 30 5 concentrated stream of organic substances from a spent cooking liquor separation unit, e.g. a filtration unit, wherein an aqueous solution comprising a major portion of the cooking chemicals have been separated and recycled to the chemicals recover cycle. The stream of organic substances from a spent cooking liquor separation unit or spent pulping liquor comprising lignin may be charged directly without prior concentration to the depolymerisation step and any alkali and sulphur compounds present in the feed so charged to the depolymerisation step act as catalysts in the depolymerisation step. By a preceding separation step, e.g. a filtration unit, the lignin concentration in the feed stream charged to a lignin depolymerisation step may be considerably increased relative to the concentration of lignin in the spent cooking liquor.

One or more catalysts may be added to the depolymerisation step in order to promote breakdown of the lignin macromolecule to smaller fragments. The catalyst may be composed of the inorganic chemicals present in the concentrated stream of organic substances from a spent cooking liquor separation unit (sodium and sulphur salts). Optionally alkali in the form of potassium carbonate can be added to present in the depolymerisation step. ln addition one or more heterogeneous catalysts may also be present during catalyzed depolymerisation of the lignin in a depolymerisation step. ln order to prevent undesired recondensation reactions during depolymerisation a capping agent or a solvent may be present in the depolymerisation step. Such solvents include recycled depolymerized lignin product, phenols, vinyl acetate, butyl acetate, ethyl acetate, turpentine, cresol, light gasoil and BTX solvent recovered from nafta cracking. ln addition formic acid, furans such as THF, organic acid rich hydrolysates from separation of hemicellulose from wood or C1 -C4 alcohols may be present during depolymerisation of lignin in a depolymerisation step. The depolymerisation step may be performed in continuous or batch reactors, preferably tubular reactors or CSTRs (continuous stirred tank reactors). Preferred solvents present during depolymerisation includes one or more of water, liquid carbon dioxide, hydrolysates, turpentine and/or methanol recovered in a chemical pulp mill or chemical dissolving pulp mill. lt is particularly advantageous to recycle a 10 15 20 25 30 6 portion of the depolymerised Iignin product stream to the depolymerisation step.

Particularly advantageous heterogeneous and sulphur tolerant catalysts that may be added to promote Iignin depolymerisation (and partial deoxygenation) include Ni based catalysts supported on Al and/or Si supports, calcium compounds and Zr, Mo (MoSg) and Cu compounds on support. Potassium carbonate is a preferred homogeneous catalyst. The heterogeneous catalysts can be separated from the Iignin streams by for example magnetic separation or filtration and be recycled to the reactor with or without reactivation (decoking).

Although specific process conditions in the depolymerisation step dependent on the catalyst and solvent selected may vary, typical reaction temperature in the catalytic step ranges from about 200 C to 375°C. The liquid hourly space velocity in a depolymerisation reactor is from 0.5 to 6 hours.

Gases formed in a depolymerisation reactor (mainly carbon dioxide and hydrogen sulphide) may be removed from time to time or continuously from the reactor.

Depolymerised Iignin which is discharged from the reactor with the solvent may be concentrated by any or more of liquid-liquid extraction with a solvent, acidulation with an acid such as carbon dioxide or a mineral acid, membrane separation or centrifugation. According to one specific embodiment of the present invention, depolymerised Iignin being discharged is concentrated by acidulation, preferably with carbon dioxide. ln a preferred embodiment the depolymerised Iignin is recovered in the form of a pumpable liquid .Any Iignin rich solids or aqueous streams comprising salts are recycled to the spent cooking liquor stream charged to the evaporators/recovery boiler. Acidic streams can be discharged to a crude tall oil acidulation plant or be neutralized and charged to the spent cooking liquor stream. Depolymerised Iignin (coming from a molecular weight of 10 000 or more in the spent liquor down to about 300-500 g/mol after the depolymerisation step) may be further upgraded by treatment with hydrogen 10 15 20 25 30 7 donor so|vents or hydrogen in one or more catalytic steps in order to form components suitable for use in renewable diesel or renewable gasoline.

Based on the disclosure above, according to one aspect of the present invention there is provided a method for the treatment of spent cooking Iiquor for the removal and production of a stream of depolymerised lignin and recovering or recycling of aqueous cooking chemicals, said method comprising: - passing a spent cooking Iiquor discharged from a digester or an evaporator in a pulp mill, orfrom any other step in between a digester and an evaporator, through at least one separation step, e.g. a filtration step, in which the spent cooking Iiquor is separated into one aqueous stream comprising cooking chemicals being recovered or recycled and one stream having a concentrated content of lignin; - passing the stream having a concentrated content of lignin to a lignin depolymerisation step consisting of one or more reactors in order to produce a stream of depolymerised lignin.

According to one embodiment one or more catalysts are added to be present during depolymerisation step. According to one specific embodiment, one or more so|vents are added to be present during the depolymerisation step.

One embodiment of one aspect of the present invention involves a method comprising: - providing a spent cooking Iiquorfeedstock; - separating aqueous cooking chemicals and lignin from the black Iiquor feedstock in one or more separation steps, e.g. by one or more filters; - contacting lignin with a solvent in order to form a stream comprising lignin and solvent; - contacting the stream of lignin and solvent with a catalyst in a reactor in order to form an intermediate liquid lignin stream wherein a first portion of the intermediate lignin stream is recycled to form the solvent; - processing at least a second portion of the liquid lignin intermediate to form a biofuel component. 10 15 20 25 30 8 According to yet another specific embodiment, the stream of depolymerised lignin is discharged from the depolymerisation reactor and directly or indirectly charged to an extraction step in which step a solvent is added dissolving the depolymerized lignin.

Furthermore, the process disclosed above relating to forming a stream of depolymerised lignin may also involve one or more filtration steps after the depolymerisation step. Therefore, according to one embodiment of the present invention, the stream of depolymerised lignin being discharged from a depolymerisation reactor and/or a lignin containing stream from a subsequent extraction and/or acidulation step is passed through a subsequent filtration step in which the stream is separated into one aqueous stream comprising cooking chemicals being recovered or recycled and one stream having a increased content of organic substances. A stream of organic substances originating in lignin obtained by any of the procedures described herein may be purified by for example an acid treatment step, optionally in the presence of a solvent.

According to yet another embodiment of the present invention, a stream of depolymerised lignin is discharged from the depolymerisation reactor and separated from inorganic compounds in a subsequent separation step in order to form a purified liquid lignin product. The lignin product can advantageously be treated with hydrogen or hydrogen donor solvents in order to provide a fully deoxygenated lignin material. According to one specific embodiment relating to this context, there is provided a method comprising: - providing a spent cooking liquorfeedstock - charging pumpable spent cooking liquorfeedstock comprising lignin to a depolymerisation reactor wherein lignin is depolymerised - separating depolymerised lignin from lignin particles and lignin oligomers - recycling lignin particles and lignin oligomers to a stream of aqueous cooking chemicals such as a spent cooking liquor - discharging depolymerised lignin in liquid form for optional further treatment by hydrogen or hydrogen donor solvents in order to provide deoxygenated lignin compounds. 10 15 20 25 30 9 Also in relation to the disclosed aspects of the present invention, the following embodiments should be further recognized. According to one embodiment, the spent cooking liquor is a kraft black liquor or origin from a kraft pulping process.

According to one specific embodiment, at least one of the separation steps and/or the subsequent separation steps is one or more filtration steps.

According to one embodiment, at least one of the separation steps is a membrane filtration step. Furthermore, the membrane filtration(s) may be e.g. nanofiltration and/or ultrafiltration.

Detailed description of the drawinq Fig.1 shows a process configuration for production of depolymerised liquid lignin from black liquor (spent cooking liquor from a kraft process) integrated in a kraft pulp mill chemicals recovery cycle. ln this particular embodiment a spent cooking liquor (weak black liquor) is discharged from a digester or an evaporator and passed through a first separation step (1) wherein the spent cooking liquor is separated into two streams wherein a first stream of the spent cooking liquor is diverted to black liquor evaporators (2) and a second stream of spent cooking liquor charged to an optional second separation step, e.g. a filtration step (3), in which second separation step spent cooking liquor is separated into one aqueous stream comprising cooking chemicals being recovered or recycled to black liquor evaporators (4) and one stream having a concentrated content of lignin (5). The lignin containing stream discharged from separation step (1) or (3) (e.g. retentate from a membrane filtration step (3) concentrated with respect to lignin concentration in weak black liquor), is pumped directly without prior drying to a depolymerisation reactor (6) in order to produce a stream of depolymerised lignin for export in liquid form (7) to for example a petroleum refinery. The depolymerisation reactor product stream (8) discharged from the lignin depolymerisation reactor (6) is charged to a separation step (9), said separation step including one or more of a carbon dioxide acidulation step, an extraction step, a sulphuric acid acidulation step and one or more filtration steps. A stream of inorganic spent cooking chemicals (comprising sodium and sulphur compounds) is discharged from separation step (9) and 10 15 20 25 10 passed to the black Iiquor evaporators (10). The depolymerised liquid Iignin product stream (7) discharged from the separation step (9) is exported from the pulp mill for further treatment for example by hydrogenation.

Precipitation and filtration of concentrated and base catalvsed black Iiquor Depolymerisation, acidulation and filtration trials using retentate from membrane filtration of black Iiquor have been performed. The retentate from membrane filtration of black Iiquor was subjected to a Iignin depolymerisation step involving base-catalytic heat-treatment before acidulation/filtration. No additional catalyst beyond the basic salts present in the retentates was added. The depolymerisation was conducted during 2 hours at a temperature of 250 °C. The Iignin average molecular weight was decreased by approximately 50 %.

Acidulation of depolymerised Iignin product was performed in a bench- scale heat-controlled stirred tank reactor with a volume of approximately one litre. Concentrated sulphuric acid was kept in a burette to ensure a controlled addition to the depolymerisation reactor product. The experiment was started when the target temperature was reached. The temperature was varied between 30°C and 100 °C. Different stirring rates and addition rates of sulphuric acid were also investigated. The addition of the acid stopped when the solution reached the desired pH-value of 7 - 2.

When the correct pH-value was achieved the solution was kept at the same temperature for a certain period of time ranging from 0 min to 1.5 hours.

The filtration unit consisted of a pressurized vessel with a volume of about 0.6 litres. The filter used had a mesh size of 60 pm. The pressure used was 0.5 bar. After filtration the liquid Iignin product was washed with washing Iiquor consisting of distilled water and acid in order to wash out some of the sodium in the Iignin.

Claims

10 15 20 25 30 11 Claims

1. A method for the production ofa stream of depolymerised Iignin in liquid form by the treatment of a spent cooking Iiquor/ black Iiquor, said method comprising: a) passing or pumping a spent cooking Iiquor stream comprising Iignin and catalytically active sodium compounds into a Iignin depolymerisation step comprising one or more depolymerisation reactor steps in order to produce a stream of depolymerised Iignin; b) further treating the stream of depolymerised Iignin in one or more acidulation steps and separation steps in order to separate spent cooking chemicals from a depolymerised Iignin product; and c) recycling the spent cooking chemicals from one or more acidulation steps and separation steps in b) to a pu|p mili chemicals recovery cycle.

2. A method according to claim 1, wherein the spent pulping Iiquor fed into a depolymerisation reactor is discharged from a digester or a spent cooking Iiquor evaporator, or is discharged from any other Iiquor treatment step in between a digester and a spent cooking Iiquor evaporator.

3. A method according to claim 1or 2, wherein a spent cooking Iiquor stream is passed through on or more separation steps prior to feeding into a Iignin depolymerisation reactor.

4. A method according to any of claims 1-3, wherein a separation step is dividing a spent pulping Iiquor stream in one stream of spent pulping Iiquor passed or pumped to a spent pulping Iiquor / black Iiquor evaporator and one stream passed or pumped directly or indirectiy to a Iignin depolymerisation reactor.

5. A method according to any of claims 1-3, wherein a separation step divides a stream of spent pulping Iiquor into one aqueous stream comprising cooking 10 15 20 25 30 12 chemicals being recovered or recycled to a pulp mi|| chemicals recovery cycle and into one stream concentrated with respect to Iignin which stream is charged into a Iignin depolymerisation reactor.

6. Method according to claim 5, wherein a separation step is a fiitration step.

7. Method according to claim 6, wherein a separation step is a membrane filtration step.

8. The method according to any of the preceding claims, wherein at least 75% (by weight) of the total input of aqueous cooking chemicals charged to a separation step is recovered or recycled to a pulp mi|| chemicals recovery cycle.

9. The method according to claim any of claims 1-8, wherein depolymerisation of Iignin is performed in a reactor at an elevated temperature in the range of 150 to 400° C and a pressure in the range from 5 bar to 400 bar.

10. The method according to any of claims 1-9, wherein depolymerisation of Iignin in a depolymerisation reactor is performed substantially without any catalyst added beyond catalytically active sodium compounds present in the feed stream to the Iignin depolymerisation reactor.

11. The method according to any of the preceding claims, wherein a fed stream to a Iignin depolymerisation reactor is the form the form of an aqueous slurry or aqueous solution. 12. The method according to any of claims 1-11, wherein one or more catalysts are added to be present during depolymerisation in the Iignin depolymerisation step, such catalysts preferably selected among heterogeneous Ni, Cu, Mo and Zr catalysts on support, calcium compounds or potassium carbonate. 10 15 20 25 30 13

12. The method according to any of the preceding claims, wherein hydrogen gas or a hydrogen donor solvent is added to a lignin depolymerisation reactor further supporting depolymerisation of Iignin and decreasing the oxygen content of depolymerised Iignin.

13. The method according to any of the preceding claims, wherein a solvent is added to be present during Iignin depolymerisation.

14. The method according to claim 13, wherein said solvent is selected from one or more of recycied depolymerised Iignin product, phenoi, cresoi or methanol.

15. The method according to any of the preceding claims, wherein a stream of depolymerised Iignin product in liquid and pumpabie form is discharged from a separation step arranged after the Iignin depolymerisation step form which separation step salty brines formed during depolymerisation, optionally after neutralization, is recycled to the pulp mi|| chemicals recovery cycle.

16. The method according to any of the preceding claims, wherein a stream of depolymerised Iignin is discharged from the depolymerisation step and directly or indirectly passed to an extraction step in which step a solvent is added.

17. The method according to any of the preceding claims, wherein depolymerised Iignin discharged from a depolymerisation reactor is concentrated by any or more of liquid-liquid extraction with a solvent, acidulation with an acid such as carbon dioxide or a mineral acid, membrane separation or centrifugation.

18. The method according to claim 16, wherein depolymerised Iignin being discharged from the depolymerisation reactor is acidulated with carbon dioxide. 10 15 20 25 30 14

19. The method according to any of the preceding claims, wherein a stream of depolymerised Iignin is treated with a mineral acid such as suiphuric acid.

20. The method according to any of the preceding claims, wherein the stream of depolymerised Iignin is discharged from the depolymerisation step and further treated to form a liquid Iignin containing oil which oil is exported from the pulp mill and further treated with hydrogen or hydrogen donor solvents in order to provide a stream of deoxygenated Iignin compounds.

21. The method according to any of claims 1-20, wherein the spent cooking liquor is a kraft black liquor or origin from a soda pulping process.

22. The method according to any of the preceding claims, wherein at least one of the separation step and/or the subsequent separation step is a membrane filtration.

23. The method according to claim 22, wherein the membrane filtration(s) is nanofiltration and/or ultrafiltration.

24. The method according to any of the preceding claims, wherein the temperature is held in the range of 30 - 100°C in an acid treatment step.

25. The method according to any of the preceding claims, wherein the pH value is held below 10 in any acid treatment step.

26. The method according to any of the preceding claims, wherein hydrolysates from separation of hemicellulose from wood or C1 -C4 alcohols is present during depolymerisation of Iignin in a depolymerisation step.