WO2020089655A1

WO2020089655A1 - Adsorption of lignin

Info

Publication number: WO2020089655A1
Application number: PCT/GB2019/053114
Authority: WO
Inventors: Roberto Rinaldi; Robert Woodward
Original assignee: Imperial College Of Science, Technology And Medicine
Priority date: 2018-11-02
Filing date: 2019-11-01
Publication date: 2020-05-07
Also published as: GB201817972D0

Abstract

Disclosed is a process of adsorption of lignin, or a derivative thereof, comprising contacting lignin, or a derivative thereof, with a porous organic polymer (POP) comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings or a metal organic framework (MOF) comprising ligands each independently comprising one or more aromatic and/or heteroaromatic rings.

Description

ADSORPTION OF LIGNIN

FIELD

The disclosure relates to a process of adsorption of lignin, or a derivative thereof, using porous organic polymers (POPs) comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings or metal organic frameworks (MOFs) comprising ligands each independently comprising one or more aromatic and/or heteroaromatic rings.

BACKGROUND TO THE INVENTION

As the second most abundant biopolymer on earth, lignin is an important structural material in vascular plants, providing mechanical resistance to the organism and protection from microbial degradation, due to its unique properties. Lignin is a complex, water-insoluble polymer that can be removed from lignocellulosic substrates during the pulping process by various extraction techniques (e.g. steam explosion treatment and Kraft and Organosolv processes), which are known to significantly alter the structure and chemistry of the native lignin, depending on the severity of the depolymerisation method.

As a result, technical lignins are obtained from such processes as mixtures of polymeric, oligomeric and monomeric materials with a variety of chemistries and molecular weights, depending on the source of the lignin and the extraction technique employed. Recently, more advanced techniques in the extraction and passivation of lignin fragments have been described, such as catalytic upstream biorefining (CUB) (Ferrini et al., Angewandte Chemie, 2014, 53, 8634-8639 and European Patent Application No. 2,891 ,748 A1 , the entire contents of which are herein incorporated by reference in their entirety) or lignin-first biorefining or reductive catalytic fractionation (RCF) (Schutyser et al., Chemical Society Reviews, 2018, 47, 852-908), producing increased individual yields of low molecular weight compounds from lignin and forming lignin-derived bio-oils rather than solid polymeric materials. Nonetheless, these most advanced methods still produce a residual lignin polymeric fraction, which may account up to 30-50% of the lignin stream.

Owing to its high-carbon and high aromatic content, coupled with its varied chemistry, lignin is widely regarded as having excellent potential as a sustainable alternative source for both the fuel and chemical industries. However, despite this potential, lignin remains the most poorly-utilised lignocellulosic biopolymer due to the complexity of technical lignins obtained after extraction. As a result, technical lignin is often used or sold as a low-value fuel, e.g. Kraft lignins, providing power to the pulping mill it is produced in (Rinaldi et al., Angewandte Chemie, 2016, 55, 8164-8215, the entire content of which is herein incorporated by reference in its entirety). The structural heterogeneity and broad molecular weight distribution of technical lignins have a significant impact on its reactivity, leading to unpredictable reactivity and a lack of control over the obtained products in the downstream processing. Such undefined structural features and broad molecular weight distribution pose problems for the monetization of lignin as a raw-material for the production of chemicals, additives, and biofuels.

Despite the progress made in recent years, so far the production of uniform technical lignins upon extraction has proven difficult and the resulting technical lignins can be considered as mixtures of valuable compounds as opposed to a valuable mixture of compounds. For the production of uniform technical lignin materials, the refinement and purification of technical lignins using downstream processes are being keenly sought, using techniques such as precipitation, filtration, and fractionation (International patent application WO 2015/178771 , the entire content of which is herein incorporated by reference in its entirety). However, there remains a need for simpler, energy-efficient processes to provide uniform technical lignins.

SUMMARY OF THE INVENTION

This disclosure relates to a process by which lignin, or a derivative thereof, can be refined by adsorption. The adsorption process may lead to fractionation and/or sequestration of lignin in a simple energy-efficient way, which can be performed in a continuous process and can be easily scaled up.

In a first aspect, the invention provides a process for adsorption of lignin or a derivative thereof, the process comprising:

contacting lignin, or a derivative thereof, with:

a porous organic polymer comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings; and/or a metal organic framework comprising ligands each independently comprising one or more aromatic and/or heteroaromatic rings.

Optionally, the invention provides a process for adsorption of lignin or a derivative thereof, the process comprising:

contacting lignin, or a derivative thereof, with a porous organic polymer comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings. The lignin may be a derivative of lignin, such as a non-native lignin, for example technical lignin, such as that obtained from the pulping of lignocellulosic materials, or products of lignin conversion such as chemical (e.g. acid hydrolysis), biological (e.g. enzymatic degradation), mechanical, or thermal (e.g., pyrolysis oils and lignin oils). Optionally, the lignin is technical lignin. The lignin, or a derivative thereof, may be obtained by thermal treatment of lignocellulose by pyrolysis in the presence or in the absence of a catalyst.

The lignin, or a derivative thereof, may be a mixture of lignin products obtained from a treatment by chemical and/or enzymatic catalysis, or a lignin product mixture obtained from reactions in the absence of a catalyst. The lignin product mixture may comprise aromatic compounds of molecular weight ranging from 100 to 10,000,000 Da, optionally 100 to 1 ,000,000 Da, optionally 100 to 100,000 Da.

Technical lignin may be obtained from pulping of lignocellulosic materials by Kraft, soda, sulphite or mechanical processes, or from acid-hydrolysis or enzymatic hydrolysis of lignocellulosic materials, or from solvent pulping, that is, Organosolv pulping processes, or pulping processes carried out in the presence of a hydrogenation catalyst or a capping agent. The technical lignin may be an Organosolv lignin, soda lignin, Kraft lignin, enzymatic lignin, depolymerised lignin streams from lignocellulose deconstruction enhanced by hydrogenation catalysts or capping agents or a mixture thereof. The lignocellulosic source of the technical lignin may be softwood, hardwood, grass, straw, waste wood, lignocellulosic crop residues, or a mixture thereof. The technical lignin may be Organosolv straw lignin, soda straw lignin, Kraft pine lignin, Organosolv hardwood lignin, softwood Kraft lignin, sarkanda grass soda lignin, hardwood soda lignin, milled wood lignin or a mixture thereof.

The lignin may be a derivative of lignin such as lignin streams obtained from the lignin-first biorefining methods (as described in Schutyser et al., Chemical Society Reviews, 2018, 47, 852— 908, the entire contents of which are herein incorporated by reference in their entirety) in which reactive lignin species are passivated by reductive processes or reacted with protecting agents (e.g. aldehydes, such as formaldehyde, acetaldehyde, or diols, such as ethylene glycol, propylene glycol) or depolymerized.

The one or more aromatic and/or heteroaromatic rings of the porous organic polymer or metal organic framework may each independently be benzene, pyridine, thiophene, pyrrole, furan, imidazole or a mixture thereof, such as benzene, pyridine, thiophene, pyrrole, furan, triptycene, phenanthrene, naphthalene, pyrene, anthracene, phenanthroline, imidazole or a mixture thereof. For example, the one or more aromatic and/or heteroaromatic rings of the porous organic polymer or metal organic framework may each independently be benzene, pyridine, phenol, aniline, benzenethiol, thiophene, pyrrole, furan, 1 ,3,5- triphenylbenzene, biphenyl, triphenylmethane, tetraphenylmethane, triptycene, phenanthrene, naphthalene, pyrene, anthracene, triphenylene, phenanthroline, triphenylmethylamine, triphenylmethanethiol, triphenylmethanol or imidazole.

The monomer units or ligands of the porous organic polymer or metal organic framework may each independently be:

wherein each A is independently C-i-s alkyl, C2-8 alkenyl, C2-8 alkynyl, C1-6 haloalkyl, C1-6 hydroxyalkyl, carboxyl, hydroxy, Ci-₆ alkoxy or halo; and each a is independently an integer, for example, an integer from 0 to 6, depending on the number of possible sites for substitution a may be an integer from 0-1 , 0-2, 0-3, 0-4, 0-5 or 0-6. Optionally, a is 0.

The one or more aromatic and/or heteroaromatic rings of the porous organic polymer or metal organic framework may be linked by covalent or ionic bonds. For example, the monomer units may be linked by covalent or ionic bonds.

The porous organic polymer may be formed from a single type of monomer unit, i.e., the porous organic polymer may be a homopolymer. Alternatively, the porous organic polymer may be formed from a mixture of two or more (for example, two) different types of monomer unit, i.e., the porous organic polymer may be a co-polymer.

The porous organic polymer may be formed by cross-linking aromatic and/or heteroaromatic ring-containing monomers by transition metal or noble-metal catalysed cross-coupling techniques, such as Friedel-Crafts alkylation coupling, Sonogashira- Hagihara coupling and Yamamoto coupling. The porous organic polymer may be formed by cross-linking aromatic and/or heteroaromatic ring-containing monomers by condensation reactions. The porous organic polymer may be formed by radical polymerization or any other cross-coupling technique known to a skilled person.

The monomer units of the porous organic polymer may be cross-linked by any suitable group. For example, C-i-salkylene, C2-salkenylene or C2-salkynylene or arylene or heteroarylene linkers, optionally Ci-₆alkylene, C2-6alkenylene, C2-6alkynylene or arylene linkers, optionally a Ci-₆alkylene linker.

The metal organic framework may comprise ligands (also referred to herein as monomer units) each independently comprising one or more aromatic and/or heteroaromatic rings linked by coordination to metal centres (for example, copper). The metal organic framework may be formed from a single type of monomer unit. Alternatively, the porous organic polymer may be formed from a mixture of two or more (for example, two) different types of monomer unit. The metal organic framework may comprise monomer units (also referred to herein as ligands) each independently comprising one or more aromatic and/or heteroaromatic rings, wherein each monomer unit is substituted with two or more carboxy groups, linked by coordination to copper centres. For example, copper benzene-1 ,3,5- tricarboxylate

The porous organic polymer and/or metal organic framework may have a surface area of at least about 50 m²g^_1, optionally at least about 200 m²g^_1, optionally at least about 500 m²g^_ ¹. Surface area of the porous organic polymer or metal organic framework may be calculated using the Brunauer Emmett-Teller (BET) method by measuring N₂ adsorption, as described in the Examples.

The lignin, or a derivative thereof, may be provided in a liquid medium. The lignin, or a derivative thereof, may be provided in as a solution and/or a suspension. For example, the lignin, or a derivative thereof, may be technical lignin and the technical lignin may be provided in the pulping solvent solution (known as a liquor), following extraction from the lignocellulosic substrates.

The lignin, or a derivative thereof, may be a mixture of lignin products obtained from lignin treatment by chemical and/or enzymatic catalysis or a lignin product mixture from reactions in the absence of a catalyst.

The process may be a batch process.

The process may be a continuous process. For example, the porous organic polymer and/or metal organic framework may be provided in a column (e.g., as the stationary phase) and the technical lignin may be passed through the column so as to contact the porous organic polymer. This process may enable sequestration of the lignin, or a derivative thereof, onto the porous organic polymer and/or metal organic framework via a solid state extraction. Use of such a flow-through process is particularly advantageous where complete sequestration of the technical lignin is desired.

The process may further comprise the step of washing the porous organic polymer and/or metal organic framework with a solvent to extract the adsorbed lignin or a derivative thereof (i.e., desorption of the lignin or a derivative thereof). Thus, the adsorption of lignin or a derivative thereof is reversible, allowing for the reutilisation of the porous organic polymer and/or metal organic framework. Where the process is a continuous process, this may involve passing the solvent through the column containing the porous organic polymer and/or metal organic framework.

By controlling the wash solvent used, fractionation of lignin or a derivative thereof may be achieved. The selectivity towards desorption of specific components of the lignin mixture can be tuneable by the choice of solvent polarity.

The process may comprise multiple, adsorption-desorption cycles, for example using a continuous flow-through setup, in which a porous organic polymer and/or metal organic framework is loaded with lignin or a derivative thereof from a liquor or other liquid medium during adsorption and upon saturation of the porous organic polymer and/or metal organic framework, the eluent may be changed to a wash solvent in order to extract the lignin and concentrate the adsorbed material from the column. Successful adsorption-desorption processes may enable recycling of adsorbent porous organic polymers and/or metal organic frameworks without significant detriment to the adsorption performance. By monitoring UV- adsorption at fixed wavelengths, the repeated uptake-desorption can be monitored.

The process may be for complete sequestration of lignin, or a derivative thereof, from a liquor, thus, providing a route to pulping liquor solvent recycling and the concentrating of lignin upon subsequent desorption from the porous organic polymer and/or metal organic framework sorbent

The lignin, or a derivative thereof, may be selectively separated from sugars or non- aromatic materials via solid state adsorption using a porous organic polymer and/or metal organic framework comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings. Accordingly, the process may be for separation of lignin or a derivative thereof from pulping liquor by selective adsorption of the lignin or a derivative thereof over other components of the liquor (for example, sugars). Thus, the process may be for selective adsorption of lignin, or a derivative thereof, from pulping liquor, the process comprising:

contacting pulping liquor comprising lignin, or a derivative thereof, with: a porous organic polymer comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings; and/or a metal organic framework comprising ligands each independently comprising one or more aromatic and/or heteroaromatic rings, such that lignin or a derivative thereof is adsorbed.

The process may be for fractionation of lignin or a derivative thereof (e.g., technical lignin), for example by molecular weight. By controlling (i) the relative loading of porous organic polymer and/or metal organic framework (for example, the relative concentration) to the lignin or a derivative thereof; and/or (ii) the polarity of the monomers forming the porous organic polymer and/or metal organic framework used, selective adsorption of lignin or a derivative thereof by molecular weight may be achieved (iii) By controlling the polarity of the solvent used to desorb the lignin, or a derivative thereof, from the porous organic polymer and/or metal organic framework selective desorption of lignin or a derivative thereof may be achieved. Thus, the invention may enable the separation of the lignin or a derivative thereof into fractions of varied molecular weight with low polydispersity index. For example, this may enable the fractionation of technical lignin.

Accordingly, in a second aspect, the invention provides a process for fractionation of lignin or a derivative thereof (for example, technical lignin), the process comprising: contacting lignin or a derivative thereof with: a porous organic polymer comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings; and/or a metal organic framework comprising ligands each independently comprising one or more aromatic and/or heteroaromatic rings (optionally a porous organic polymer), such that lignin or a derivative thereof is adsorbed.

The process may further comprise the step of washing the porous organic polymer and/or metal organic framework with a solvent to extract the adsorbed lignin or a derivative thereof.

The step of contacting lignin or a derivative thereof with a porous organic polymer and/or metal organic framework may be such that a molecular weight fraction of the lignin or a derivative thereof is adsorbed. This may be achieved by:

(i) decreasing the loading (e.g concentration) of the porous organic polymer and/or metal organic framework relative to lignin or a derivative thereof (for example, the relative concentration) to provide increased selectively towards adsorption of molecular weight fractions of lignin or a derivative thereof; and/or

(ii) increasing the polarity of the surface of the porous organic polymer and/or metal organic framework to vary the selectivity towards different fractions of lignin or a derivative thereof.

Decreasing the loading (e.g., concentration) of the porous organic polymer and/or metal organic framework relative to lignin or a derivative thereof, may provide increased selectively towards adsorption of fractions of lignin or a derivative thereof (for example, higher molecular weight fractions of lignin or a derivative thereof). Increasing the loading of porous organic polymer relative to lignin or a derivative thereof, may result in decreased selectivity and a wider range of molecular weight material may also be adsorbed. A skilled person would be able to determine a suitable loading (e.g. concentration) of porous organic polymer to achieve selective adsorption of the fraction of lignin desired. Accordingly, the loading of porous organic polymer may be selected to achieve selective desorption of the fraction of lignin desired.

The process may comprise:

contacting lignin or a derivative thereof with: a porous organic polymer comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings; and/or a metal organic framework comprising ligands each independently comprising one or more aromatic and/or heteroaromatic rings (optionally a porous organic polymer), such that a molecular weight fraction of the lignin or a derivative thereof is adsorbed; and

optionally washing the porous organic polymer and/or metal organic framework with a solvent to extract the fraction of adsorbed lignin or a derivative thereof; and

optionally repeating the contacting and washing steps one or more times, optionally wherein each subsequent step of contacting is carried out with a higher loading (e.g. concentration) of porous organic polymer and/or metal organic framework to lignin or a derivative thereof.

Each subsequent cycle may provide a fraction of lignin or a derivative thereof having a lower average molecular weight than the preceding cycle. A skilled person will appreciate that each subsequent cycle may use a lower loading of porous organic polymer to lignin or a derivative thereof to produce a series of fractions having increasing average molecular weights.

Increasing the polarity of the porous organic polymer and/or metal organic framework may increase selectivity towards lower molecular weight fractions of lignin or a derivative thereof. For example, a porous organic polymer and/or metal organic framework formed from phenol monomers may favour the adsorption of low molecular weight fractions of lignin or a derivative thereof, compared to a porous organic polymer and/or metal organic framework formed from benzene monomers, which may favour the adsorption of high molecular weight fractions. A skilled person would be able to determine a suitable polarity for the monomer units of the porous organic polymer and/or metal organic framework to achieve selective adsorption of the fraction of lignin desired. Accordingly, the polarity for the monomer units of the porous organic polymer and/or metal organic framework may be selected to achieve selective adsorption of the fraction of lignin desired.

The step of washing the porous organic polymer with a solvent to extract the adsorbed lignin or a derivative thereof may be such that a molecular weight fraction of the lignin or a derivative thereof is extracted (i.e., desorbed). This may be achieved by:

(iii) increasing the polarity of the wash solvent to provide increased selectivity towards fractions (for example, lower molecular weight fractions) of adsorbed lignin or a derivative thereof

Increasing the polarity of the wash solvent may increase selectivity towards fractions of adsorbed lignin or a derivative thereof (for example, lower molecular weight fractions). A skilled person would be able to determine a suitable polarity for the solvent to achieve selective desorption of the fraction of lignin desired. Accordingly, the solvent may be selected to achieve selective desorption of the fraction of lignin desired.

The process may comprise:

contacting lignin or a derivative thereof with: a porous organic polymer comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings; and/or a metal organic framework comprising ligands each independently comprising one or more aromatic and/or heteroaromatic rings (optionally a porous organic polymer), such that lignin or a derivative thereof is adsorbed; and

washing the porous organic polymer and/or metal organic framework with a solvent to extract a molecular weight fraction of the adsorbed lignin or a derivative thereof;

optionally conducting one or more further washes of the porous organic polymer and/or metal organic framework with a solvent to extract further molecular weight fractions of the adsorbed lignin or a derivative thereof, optionally wherein each subsequent step of washing is carried out with a solvent of increased polarity relative to the solvent used in the preceding wash step.

Each subsequent wash cycle may provide a fraction of lignin or a derivative thereof having a lower average molecular weight than the preceding cycle. A skilled person will appreciate that each subsequent wash cycle may use a solvent of decreased polarity to produce a series of fractions having increasing average molecular weights.

The solvents may be selected from: alcohols, ethers, ketones, esters, halogenated solvents or mixtures thereof, and mixtures of one or more of said solvents and water, in order of increasing polarity. Optionally, the solvent may be selected from: ethyl acetate, methyl ethyl ketone, methanol, acetone, tetrahydrofuran, 2-methyltetrahydrofuran, dichloromethane, and mixtures of any of these with water.

The polarity of a solvent is known to the skilled person. The polarity of mixtures of solvent, or of mixtures of a solvent and water, can be easily calculated or determined by the skilled person. In case one of the solvents is a mixture with water, sequence is determined by the polarity of the mixture.

In a third aspect, the invention provides a lignin composition obtained by a process comprising:

contacting lignin, or a derivative thereof, with: a porous organic polymer comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings; and/or a metal organic framework comprising ligands each independently comprising one or more aromatic and/or heteroaromatic rings (optionally a porous organic polymer); and

washing the porous organic polymer and/or metal organic framework with a solvent to extract the adsorbed lignin to obtain the lignin composition.

In a fourth aspect, the invention provides a composite material comprising:

a porous organic polymer comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings; and/or a metal organic framework comprising ligands each independently comprising one or more aromatic and/or heteroaromatic rings (optionally a porous organic polymer); and

lignin, or a derivative thereof, adsorbed to the porous organic polymer and/or metal organic framework.

In a fifth aspect, the invention provides the use of: a porous organic polymer comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings; and/or a metal organic framework comprising ligands each independently comprising one or more aromatic and/or heteroaromatic rings (optionally a porous organic polymer) for adsorption of lignin or a derivative thereof.

In a sixth aspect, the invention provides the use of: a porous organic polymer comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings; and/or a metal organic framework comprising ligands each independently comprising one or more aromatic and/or heteroaromatic rings (optionally a porous organic polymer) for the separation of lignin from non-adsorbed trace sugars, or a derivative thereof, in lignin liquors.

In a seventh aspect, the invention provides a process, lignin, composite material or use as substantially herein described, with reference to the accompanying description and figures.

Embodiments described herein in relation to the first aspect of the invention apply mutatis mutandis to the second to seventh aspects of the invention

BRIEF DESCRIPTION OF FIGURES

Figure 1 - GPC chromatograms of poplar-derived CUB lignin liquor as obtained from extraction (solid black line), fraction extracted and recovered from a benzene-derived POP (dashed black line) and the non-adsorbed lignin fraction remaining after extraction (dotted grey line).

Figure 2 - GPC chromatograms of a poplar-derived Organosolv lignin liquor (solid black line), fraction extracted and recovered from a benzene-derived POP (dashed black line) and the non-adsorbed lignin fraction remaining after extraction (dotted grey line).

Figure 3 - GPC chromatograms of a spruce-derived CUB lignin liquor as obtained from extraction (solid black line), fraction extracted and recovered from a benzene-derived POP (dashed black line) and the non-adsorbed lignin fraction remaining after extraction (dotted grey line).

Figure 4 - GPC chromatograms of a CUB lignin (solid black line), fraction extracted from methanol and recovered from a benzene-derived POP (dashed black line) and the non- adsorbed lignin fraction remaining after extraction (dotted grey line).

Figure 5 - GPC chromatograms for 5 extractions of a CUB lignin, removed by and recovered from a benzene-derived POP with each extraction and the remaining lignin post- extraction accompanied by Mw and PDI data for each fraction. Arrows indicate peak shift with each successive fractionation.

Figure 6 - GPC chromatograms of a CUB lignin (solid black line), fraction extracted and recovered from a phenol-derived POP (dashed black line) and the non-adsorbed lignin fraction remaining after extraction (dotted grey line).

Figure 7 - GPC chromatograms of a CUB lignin (solid black line), fraction extracted and recovered from a thiophene-derived POP (dashed black line) and the non-adsorbed lignin fraction remaining after extraction (dotted grey line).

Figure 8 - GPC chromatograms of a CUB lignin (solid black line), fraction extracted and recovered from a pyrrole-derived POP (dashed black line) and the non-adsorbed lignin fraction remaining after extraction (dotted grey line).

Figure 9 - GPC chromatograms of a CUB lignin (solid black line), fraction extracted and recovered from a naphthalene-derived POP (dashed black line) and the non-adsorbed lignin fraction remaining after extraction (dotted grey line).

Figure 10 - GPC chromatograms of a CUB lignin (solid black line), fraction extracted and recovered from a anthracene-derived POP (dashed black line) and the non-adsorbed lignin fraction remaining after extraction (dotted grey line).

Figure 11 - GPC chromatograms of a CUB lignin (solid black line), fraction extracted and recovered from a benzene- and phenol-derived porous organic co-polymer (dashed black line) and the non-adsorbed lignin fraction remaining after extraction (dotted grey line). Figure 12 - GPC chromatograms of untreated Kraft lignin (solid black line), fraction extracted and recovered from a benzene-derived POP (dashed black line) and the non- adsorbed lignin fraction remaining after extraction (dotted grey line). Figure 13 - GPC chromatograms of untreated Kraft lignin (solid black line), and the fraction extracted and recovered from a benzene-derived POP (dashed black line) after sequestration.

Figure 14 - Organosolv liquor solution before and after passing through a column of a benzene-derived POP was compared in UV-Vis spectroscopy, which showed 95 % or higher removal of lignin from the solvent.

Figure 15 - Adsorption-desorption cycles of an Organosolv liquor onto a benzene-derived POP, monitored using UV-spectroscopy (204 nm).

Figure 16 - GPC chromatograms of an OS lignin liquor (solid black line), fraction desorbed from a benzene-derived POP column using methanol (dashed black line) and the fraction desorbed from the same POP column using acetone (dotted grey line).

DETAILED DESCRIPTION

The disclosure provides a process by which lignin, or a derivative thereof, can be refined via fractionation and/or sequestered in a simple energy-efficient way, which can be performed in a continuous process and can be easily scaled up.

Disclosed herein is a process for adsorption of lignin or a derivative thereof, the process comprising:

contacting lignin, or a derivative thereof, with

Preferably, the process is a process for adsorption of lignin or a derivative thereof comprising:

contacting lignin, or a derivative thereof, with a porous organic polymer comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings.

The application of porous organic polymers and/or metal organic frameworks of various chemical and textural properties to lignin or a derivative thereof may lead to selective adsorption of the lignin, or a derivative thereof, by molecular weight or polarity. Efficient adsorption may lead to fractionation and/or sequestration of the lignin, or a derivative thereof, via solid state extraction. Furthermore, selective adsorption may lead to the separation of lignin, or a derivative thereof, from sugars or sugar derivatives in complex liquors

The disclosure makes use of porous organic polymers (MOPs) and/or metal organic frameworks (MOFs), for example but not only limited to porous organic polymers produced via Friedel-Crafts alkylation (Li et al., Macromolecules, 201 1 , 44 (8), 2410-2414; Woodward et al., J. Am. Chem. Soc., 2014, 136 (25), 9028-9035, the entire contents of which are herein incorporated by reference in their entirety), to adsorb lignin, or a derivative thereof, thus providing for the solid-state sequestration, fractionation, and/or refining of lignin, or a derivative thereof.

The porous organic polymers or metal organic frameworks comprise linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings. Therefore, the sorbents are rich in tt-electrons, meaning they harbour potential for adsorption of aromatics compounds via tt-p interactions, in much the same way as carbon materials, such as graphene and carbon nanotubes, but at a fraction of the costs associated with those materials. The porous organic polymers and metal organic frameworks may have varied chemistries, allowing for adsorption by hydrogen-bonding, Van der Waals interactions and ion-pairing. The porous organic polymers and/or metal organic frameworks described herein are excellent sorbents enabling the sequestration and/or molecular-weight fractionation of lignin, or a derivative thereof, via adsorption. Advantageously, the porous organic polymers and metal organic frameworks are selective towards lignin and so may be used for selective adsorption of lignin, or a derivative thereof, from the pulping liquor, over other components that may be present (such as sugars).

The porous organic polymers or metal organic frameworks may be formed from a plurality of linked aromatic and/or heteroaromatic rings such as benzene, pyridine, thiophene, pyrrole, furan, triptycene, phenanthrene, naphthalene, pyrene, anthracene, phenanthroline, imidazole or a mixture thereof. For example, the one or more aromatic and/or heteroaromatic rings of the porous organic polymer and/or metal organic framework may each independently be benzene, pyridine, phenol, aniline, benzenethiol, thiophene, pyrrole, furan, 1 ,3,5-triphenylbenzene, biphenyl, triphenylmethane, tetraphenylmethane, triptycene, phenanthrene, naphthalene, pyrene, anthracene, triphenylene, phenanthroline, triphenylmethylamine, triphenylmethanethiol, triphenylmethanol or imidazole. This feature renders porous organic polymers or metal organic frameworks with tuneable and well- defined surface chemistry, which is advantageous compared to the undefined-surfaces or activated carbons or charcoals. The porous organic polymer may be formed by cross-linking aromatic and/or heteroaromatic ring-containing monomers by transition-metal or noble-metal-catalysed cross-coupling reactions, such as Friedel-Crafts alkylation, for example resulting in C-i-s alkylene cross-linkers. The porous organic polymer may be formed by cross-linking aromatic and/or heteroaromatic ring-containing styrene polymers (e.g,, formed by polymerising aromatic and/or heteroaromatic ring-containing monomers) by Friedel-Crafts alkylation, for example resulting in C-i-s alkylene cross-linkers. Alternatively, the porous organic polymer may be formed by any other cross-linking technique known to a skilled person. For example, porous organic polymers may be formed from conventional free- radical polymerisation of aromatic vinyl monomers, such as styrene and divinylbenzene. Porous organic polymers may be formed by condensation reactions by using formaldehyde or compounds that decompose to form formaldehyde (e.g. hexamethylenetetramine) as a cross-linking agent. Porous organic polymers may be formed from other transition-metal or noble-metal-catalysed cross coupling reactions (for example, palladium catalysed Sonogashira coupling or nickel catalysed Yamamoto coupling reactions). Porous organic polymers may also be cross-linked by coordination to a metal, such as in metal-organic frameworks (MOFs). The porous organic polymer may be formed from a single type of monomer unit, i.e., the porous organic polymer may be a homopolymer. For example, the porous organic polymer may have a structure such as:

wherein each of m, n and o are independently integers. Alternatively, the porous organic polymer may be formed from a mixture of two or more (for example, two) different types of monomer unit, i.e., the porous organic polymer may be a co-polymer.

L. Tan et al., Chem. Soc. Rev., 2017,46, 3322-3356 and S. Xu et al., Macromol. Rapid Comm., 2013, 34(6), 471-484, the entire contents of which are herein incorporated by reference in their entirety, set out reviews of suitable porous organic polymers that may be used in the present invention. Suitable porous organic polymers include:

• Polymers formed from cross-linking triptycene (C. Zhang et al., Macromolecules, 2015, 48 (23), 8509-8514, the entire contents of which is herein incorporated by reference in its entirety);

• Polymers formed from cross-linking bicarbazole (X. Zhu et al., Chem. Commun., 2014, 50, 7933-7936, the entire contents of which is herein incorporated by reference in its entirety);

• Polymers formed from cross-linking 1 , 1 '-Bi-2-naphthol, 1-napthol or bisphenol (R Dawson et al., J. Am. Chem. Soc., 2012, 134 (26), 10741-10744, the entire contents of which is herein incorporated by reference in its entirety);

• Polymers formed from cross-linking tetraphenylmethane or triphenylmethane (R.

Woodward et al., J. Am. Chem. Soc., 2014, 136 (25), 9028-9035, the entire contents of which is herein incorporated by reference in its entirety);

• Polymers formed from cross-linking silole (Y. Zhang et al., Polymer, 2014, 55 (22) 5746-5750, the entire contents of which is herein incorporated by reference in its entirety);

• Polymers formed from cross-linking carbazole (X. Yang et al., RSC Adv., 2014, 4, 61051-61055, the entire contents of which is herein incorporated by reference in its entirety);

• Polymers formed from cross-linking indolo[3,2-b]carbazole (D. Chang et al., Microporous and Mesoporous Materials, 2016, 228, 231-236, the entire contents of which is herein incorporated by reference in its entirety);

• Polymers formed from cross-linking thiophene, pyrrole or furan (Y. Luo et al., Advanced Materials, 2012, 24 (42), 5703-5707, the entire contents of which is herein incorporated by reference in its entirety)

• Polymers formed from cross-linking triphenylphosphine (B. Li et al., Advanced Materials, 2012, 24 (25), 3390-3395, the entire contents of which is herein incorporated by reference in its entirety);

• Polymers formed from cross-linking aniline and copolymers formed from cross- linking aniline and benzene (R. Dawson et al., Polym. Chem., 2012,3, 2034-2038, the entire contents of which is herein incorporated by reference in its entirety);

• Polymers formed from cross-linking phenol and copolymers formed from cross- linking phenol and benzene (R. Woodward et al., Green Chem., 2018,20, 2374- 2381 , the entire contents of which is herein incorporated by reference in its entirety). The monomer units of the porous organic polymer may be cross-linked by any suitable group. For example, Friedel-Crafts alkylation may be carried out using dihaloalkane, dihaloalkane, dihaloakyne, dihaloaryl or dihaloheteroaryl groups, i.e, to form alkylene, alkenylene, alkynylene, arylene or heteroarylene linkers.

L. Tan et al., Chem. Soc. Rev., 2017,46, 3322-3356 discloses further suitable crosslinking groups that may be used to prepare porous organic polymers via Friedel-Crafts alkylation for use herein, such as trimethyl orthoformate, trimethyl orthoacetate, triethyl orthoacetate, triisopropyl orthoformate, dimethoxy 1 ,4-benzene and trichlorotriazine:

The porous organic polymer may be formed from the cross-coupling of polystyrene of polydivinylbenzene (V. Davankov et al., Reactive Polymers, 1990, 13(1-2), 27-42 and T. Ratvijtvech et al., Polym. Chem., 2015, 6, 7280-7285, the entire contents of which are herein incorporated by reference in their entirety).

Suitable porous organic polymers formed by Pd-catalysed coupling reactions include:

• Microporous poly(aryleneethynylene) (J-X Jiang et al., Angewandte Chemie, 2007, 46 (45), 8574-8578 and J-X Jiang et al., J. Am. Chem. Soc., 2008, 130 (24), 7710- 7720, the entire contents of which are herein incorporated by reference in their entirety), synthesized using Sonogashira-Hagihara coupling;

• Microporous poly(p-phenylene) and poly(phenyleneethynylene) (J. Weber et al., J.

Am. Chem. Soc., 2008, 130 (20), 6334-6335, the entire contents of which is herein incorporated by reference in its entirety) synthesized using Suzuki coupling;

• Polymers formed from cross-linking aryl chlorides by Suzuki coupling (B. Li et al., Advanced Materials, 2012, 24 (25), 3390-3395, the entire contents of which is herein incorporated by reference in its entirety). Suitable porous organic polymers formed by Ni-catalysed coupling reactions, such as in Yamamoto coupling which employs a Ni(COD) catalyst, include:

• Polymers formed from cross-linking spirobifluorene or benzene using Yamamoto coupling (J. Schmidt et al., Macromolecules, 2009, 42 (13), 4426-4429, the entire contents of which is herein incorporated by reference in its entirety);

• Polymers formed from cross-linking tetraphenyl methane using Yamamoto coupling (T. Ben et al., Angewandte Chemie, 2009, 48 (50), 9457-9460, the entire contents of which is herein incorporated by reference in its entirety).

Porous organic polymers formed by condensation reactions may also be of use in the present invention, such as an aminophenol positional isomer cross-linked using ammonia and formaldehyde (G.-H. Wang et al., Angewandte Chemie, 2016, 55 (31 ), 8850-8855, the entire contents of which is herein incorporated by reference in its entirety)

The metal organic framework may comprise ligands each independently comprising one or more aromatic and/or heteroaromatic rings linked by coordination to metal centres (for example, copper). The monomer units may be linked by a bond between the metal centre and a carboxy substituent on each monomer unit. The metal organic framework may be formed from a single type of monomer unit. Alternatively, the porous organic polymer may be formed from a mixture of two or more (for example, two) different types of monomer unit. The metal organic framework may comprise monomer units each independently comprising one or more aromatic and/or heteroaromatic rings linked by coordination to copper centres, wherein each monomer unit is substituted with two or more carboxy groups. For example, copper benzene-1 ,3,5-tricarboxylate (Cu-BTC MOF, HKUST-1 ):

Further suitable metal organic frameworks are set out in Z. Hu et al., Chem. Soc. Rev., 2014, 43, 5815-5840, the entire contents of which are herein incorporated by reference. The wide synthetic design of porous organic polymers and metal organic frameworks means that a huge array of sorbent materials are possible, broadening the scope of this invention greatly towards the fractionation and sequestration of lignin.

Lignin is a class of complex, naturally-occurring, cross-linked phenolic polymers. Derivatives of lignin as described herein include phenolic monomers, oligomers and polymers produced from processing native lignin. Technical lignins are derivatives of lignin and are isolated as by-streams of the pulp and paper industry and lignocellulosic bio refineries, including e.g. Kraft, soda, sulfite, Organosolv, hydrolysis lignins, and lignosulfonates. They have a modified structure compared to native lignin and contain impurities that are dependent on the extraction process. Technical lignins are obtained from such processes as mixtures of polymeric, oligomeric and monomeric materials with a variety of chemistries and a broad molecular weight distribution, depending on the source of the lignin and the extraction technique employed. Unlike native lignins, technical lignins are not contained in a biomass matrix, but are isolated therefrom. Hence, technical lignins, although isolated, can still be present in a composition remaining from biomass but are at least not chemically bound thereto.

After extraction of lignin from lignocellulosic substrates, the technical lignin liquors are typically dried (i.e. the extraction solvent is removed), to isolate the technical lignins. Solid- state extraction, therefore, allows for the removal of technical lignins from the pulping solvent without the need for energy-intensive drying steps, which is particularly important as water is often employing as a component of the pulping solvent. The solvent reclamation is found to be the bottleneck in technical-economic assessments of pulping processes based on lignin extraction by organic solvents (Gurgel da Silva et al., Clean Technologies and Environmental Policy, 2018, 20 (7), 1401-1412 and Viell et al., Bioresource Technology, 2013, 150, 89-97, the entire contents of which are herein incorporated by reference in their entirety).

The broad molecular weight distributions and chemistries of lignin and derivatives thereof presents significant obstacles in its further utilisation as a chemical commodity. By the simple and cost-effective refinement of lignin, the present invention opens the door to more controllable and predictable downstream processes, allowing for the production of fractions of lignin defined by molecular weight and polarity.

The fractionation of lignin and derivatives thereof using porous organic polymers shows promise for further valorisation of the material due to the production of materials with more uniform molar masses and narrower polydispersity, helping to reduce the heterogeneity within lignins and improve further processing techniques.

This solid-state extraction of lignin, or a derivative thereof, holds advantages over other common methods, such as solvent extraction (International patent application WO 2014/179777, the entire content of which is herein incorporated by reference in its entirety) and/or successive solvent extraction (WO 2015/178771 ) as it allows for the refinement of lignin immediately after extraction from pulps while still in the liquor, without any further processing such as solvent removal or purification. This opens to door to significant reductions in processing costs as energy intensive drying steps of the liquors are avoided prior to fractionation.

By controlling the loading of lignin in the liquid, the loading of the porous organic polymer or the duration of contact, the separation of the polymeric, oligomeric and monomeric fragments of the lignin is possible, beginning the refinement of these materials and the isolation of fractions of lignin by molecular weight. The application of porous organic polymer sorbents to lignins or derivatives thereof obtained immediately after extraction from a lignocellulosic substrate, may lead to the refining of lignin into fractions containing various molar masses and decreasing polydispersity by successful adsorption of lignin compounds onto porous organic polymers.

Porous organic polymers are able to successfully fractionate a variety of technical lignins (such as CUB and Organosolv lignins) and technical lignins derived from various lignocellulosic substrates (such as hardwoods such as Poplar and softwoods such as Spruce), despite differences in chemical composition and molecular weight distributions, demonstrating the versatility and robustness of this refinement technique.

Refinement by molecular weight has further implications, as technical lignin fractions of various molecular weight also have varying chemistries. Lower molecular weight fragments of technical lignin generally have higher oxygen content, therefore the refinement of technical lignins can be viewed as not only by molecular weight but also by polarity, giving rise to chemical refinement in addition to separation by molecular weight. By increasing the polarity of the porous organic polymer adsorbent, such as one derived from a phenol monomeric component, low molecular weight fractions can be collected preferentially, owing to the increased polarity of the low molecular weight lignin derived material. For a cross-linked benzene porous organic polymer, selective adsorption of higher molecular weight material may be observed, resulting in an adsorbed fraction with higher average molecular weight and narrower polydispersity. The non-adsorbed fraction has a lower average molecular weight than the initial lignin, again a narrower polydispersity, and a higher O content, resulting in some basic chemical refinement in addition to molecular weight refinement.

By varying the chemistries and textural properties of the porous organic polymers, fractionation performance may be tailored. By careful design of cross-coupled porous organic polymer sorbents, a bottom-up design approach for the adsorption of selected components of lignin or derivatives thereof is realised, i.e. fractionation. For example, the application of a phenol-derived porous organic polymers to technical lignin may result in the selective adsorption of a lower molecular weight fraction of the lignin, in contrast to a benzene-derived porous organic polymer.

The recovery of adsorbed lignin, or a derivative thereof, from the sorbent materials involves a simple solvent wash (using, e.g., acetone), yielding >95 % lignin recovery and allowing for the recycling of the porous organic polymer adsorbent, without any reduction in the porous organic polymer’s performance. Employing the methods of the invention are more environment-friendly owing to increased energy efficiency and are beneficial with regards to time and/or costs.

In addition, lignin, or a derivative thereof, can be recovered from the porous organic polymer, for example by washing the porous organic polymer with a solvent, in a more concentrated solution, again leading to less energy intensive processes for the isolation of lignin or lignin fractions. Furthermore, by careful solvent selection, narrower molecular weight fractions of the technical lignin can be washed from the adsorbent POP due to varying chemistries and/or polarities of the wash solvent, allowing for fractionation of the lignin in the desorption stage. This not only provides a route to lignin sequestration but also the fractionation of technical lignin upon desorption.

The disclosure provides processes that, in some embodiments, may provide one or more of the following advantages:

• POPs allow for the use of tt-p interactions to selectively adsorb aromatic compounds, favouring lignin adsorption in complex systems as demonstrated by the non-adsorbed glucose in Example 16. • The plethora of design options for synthetic POPs of high surface area allows for the application of many varied POPs to lignins and derivatives thereof, permitting preferential adsorption and/or sequestration.

• POPs are able to refine a variety of lignins and derivatives thereof from a number of different pulping solvents by selective adsorption, owing to a robust solid state extraction technique.

• Percolating solutions of lignin or derivatives thereof through a POP stationary phase results in lignin sequestration, allowing for simple solvent recycling and further lignin refining via solvent extraction.

• Solid-phase extraction enables the sequestration of lignins and derivatives thereof directly from liquors obtained upon pulping processes without further treatments.

• Solid-phase extraction allows for improvements in energy efficiency and cost effectiveness compared to current techniques due to the preconcentration of lignin onto POP sorbents, leading to efficient solvent recycling and less solvent removal in the isolation of technical lignins.

• Facile washing and regeneration of POPs after adsorption opens the door to efficient recycling of the sorbents, reducing costs.

The term“halide”,“halo” and“halogen” are used interchangeably and, as used herein mean a fluorine atom, a chlorine atom, a bromine atom, an iodine atom and the like, preferably a fluorine atom, a bromine atom or a chlorine atom, and more preferably a fluorine atom.

As used herein, an alkyl group is a straight chain or branched, substituted or unsubstituted group (preferably unsubstituted) containing from 1 to 40 carbon atoms. An alkyl group may optionally be substituted at any position. The term "alkenyl," as used herein, denotes a group derived from the removal of a single hydrogen atom from a straight- or branched- chain aliphatic moiety having at least one carbon-carbon double bond. The term "alkynyl," as used herein, refers to a group derived from the removal of a single hydrogen atom from a straight- or branched-chain aliphatic moiety having at least one carbon-carbon triple bond.

The term‘alkyl’,‘aryl’,‘heteroaryl’ etc also include multivalent species, for example alkylene, arylene,‘heteroarylene’ etc. Examples of alkylene groups include ethylene (-CH2-CH2-), and propylene (-CH2-CH2-CH2-). An exemplary arylene group is phenylene (-C6H4-), and an exemplary heteroarylene group is pyridinylene (-C5H3N-). Aromatic rings are cyclic aromatic groups that may have 0, 1 , 2 or more, preferably 0, 1 or 2 ring heteroatoms. If an aromatic ring contains 1 or more heteroatoms it may be referred to as a heteroaromatic ring. Aromatic or heteroaromatic rings may be optionally substituted and/or may be fused to one or more aromatic or non-aromatic rings (preferably aromatic), which may contain 0, 1 , 2, or more ring heteroatoms, to form a polycyclic ring system.

As used herein, the term“fused” refers to a cyclic group, for example an aryl or heteroaryl group, in which two adjacent ring atoms, together with additional atoms, form a fused ring to give a polycyclic (for example, a bicyclic or tricyclic) ring system.

A haloalkyl group is an alkyl group substituted with at least one halogen atom. The term “haloalkyl” encompasses fluorinated or chlorinated groups, including perfluorinated compounds. Specifically, examples of “haloalkyl group” include fluoromethyl group, difluoromethyl group, trifluoromethyl group, fluoroethyl group, difluroethyl group, trifluoroethyl group, chloromethyl group, bromomethyl group, iodomethyl group and the like.

A haloaryl group is an aryl group substituted with at least one halogen atom.

An alkoxy group is an alkyl group that is bonded via an oxy group. Specifically, examples of “alkoxy group” include methoxy group, ethoxy group, n-propoxy group, iso- propoxy group, n-butoxy group, iso- butoxy group, sec-butoxy group, ferf-butoxy group, n-pentyloxy group, /^'so-pentyloxy group, sec-pentyloxy group, n-hexyloxy group, iso-hexyloxy group, n- hexyloxy group, n-heptyloxy group, n-octyloxy group, n-nonyloxy group, n-decyloxy group, n-undecyloxy group, n-dodecyloxy group, n-tridecyloxy group, n-tetradecyloxy group, n- pentadecyloxy group, n-hexadecyloxy group, n-heptadecyloxy group, n-octadecyloxy group, n-nonadecyloxy group, n-eicosyloxy group, 1 ,1 -dimethylpropoxy group, 1 ,2- dimethylpropoxy group, 2,2-dimethylpropoxy group, 2-methylbutoxy group, 1 -ethyl-2- methylpropoxy group, 1 ,1 ,2-trimethylpropoxy group, 1 ,1-dimethylbutoxy group, 1 ,2- dimethylbutoxy group, 2,2-dimethylbutoxy group, 2,3-dimethylbutoxy group, 1 ,3- dimethylbutoxy group, 2-ethylbutoxy group, 2-methylpentyloxy group, 3-methylpentyloxy group and the like.

As used herein, the term“optionally substituted” means that one or more of the hydrogen atoms in the optionally substituted moiety is replaced by a suitable substituent. Unless otherwise indicated, an "optionally substituted” group may have a suitable substituent at each substitutable position of the group, and when more than one position in any given structure may be substituted with more than one substituent selected from a specified group, the substituent may be either the same or different at every position. Combinations of substituents envisioned by this invention are preferably those that result in the formation of stable compounds. The term "stable", as used herein, refers to compounds that are chemically feasible and can exist for long enough at room temperature (i.e. 16-25°C) to allow for their detection, isolation and/or use in chemical synthesis.

Any of the above groups (for example, those referred to herein as“optionally substituted”, including alkyl, aryl and heteroaryl groups) may optionally comprise one or more substituents, preferably selected from silyl, sulfo, sulfonyl, formyl, amino, imino, nitrilo, mercapto, cyano, nitro, halogen, -NCO, -NCS, -OCN, -SCN, -C(=O)NR⁰R⁰⁰, -C(=O)X⁰, - C(=O)R⁰, -NR°R⁰⁰, C-i-12 alkyl, C1-12 alkenyl, C1-12 alkynyl, C6-12 aryl, C3-12 cycloalkyl, heterocycloalkyl having 4 to 12 ring atoms, heteroaryl having 5 to 12 ring atoms, C1-12 alkoxy, hydroxy, C1-12 alkylcarbonyl, C1-12 alkoxy-carbonyl, C1-12 alkylcarbonyloxy or C1-12 alkoxycarbonyloxy wherein one or more H atoms are optionally replaced by F or Cl and/or combinations thereof; wherein X° is halogen and R° and R⁰⁰ are, independently, H or optionally substituted C1-12 alkyl. The optional substituents may comprise all chemically possible combinations in the same group and/or a plurality of the aforementioned groups (for example amino and sulfonyl if directly attached to each other represent a sulfamoyl radical).

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", mean "including but not limited to", and are not intended to (and do not) exclude other components. In any of the embodiment described herein, reference to“comprising” also encompasses“consisting essentially of”.

It will be appreciated that variations to the foregoing embodiments of the invention can be made while still falling within the scope of the invention. Each feature disclosed in this specification, unless stated otherwise, may be replaced by alternative features serving the same, equivalent or similar purpose. Thus, unless stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

All of the features disclosed in this specification may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. In particular, the preferred features of the invention are applicable to all aspects of the invention and may be used in any combination. Likewise, features described in non- essential combinations may be used separately (not in combination). It will be appreciated that many of the features described above, particularly of the preferred embodiments, are inventive in their own right and not just as part of an embodiment of the present invention. Independent protection may be sought for these features in addition to or alternative to any invention presently claimed.

Reference is now made to the following examples, which illustrate the invention in a non- limiting fashion.

EXAMPLES

Experimental

Materials

Poplar wood (2 mm pellets) was purchased from J. Rettenmaier & Sohne. Benzene, thiophene, naphthalene, anthracene, phenol, pyrrole, dimethoxymethane, iron(lll) chloride, 1 ,2-dichloroethane and Raney®Ni 2800 slurry were all purchased from Sigma Aldrich and used as received. Acetone, methanol, D-glucose and 2-propanol were purchased from VWR and used as received. Eucalyptus-derived Kraft lignin was kindly provided by Suzano Pulp and Paper.

Production of Organosolv and CUB lignin liquors and isolated lignins

For Organosolv lignin, wood chips (16-17 g) was suspended in a mixture of 2-propanol and water (70:30 vol/vol) (140 mL) in a 250 mL autoclave equipped with a mechanical stirrer; in the case of CUB lignins the process remains the same but additionally wet Raney® Ni catalyst (10 g) was also added to the mixture. The suspensions were then heated at 180 °C for three hours under autonomous pressure. After heating, the mixture was allowed to cool to room temperature. In the case of the Organosolv lignin, the remaining solid residue (the pulp) was simply filtered off and a dark-brown solution (the lignin liquor) was obtained. For the CUB lignin, first the Raney® Ni catalyst was removed over stirring using a magnet and the remaining solid residue (the pulp) was filtered off, yielding a reddish-brown solution (the liquor)

To obtain isolated Organosolv or CUB lignin, the 2-propanol solvent was partially evaporated from the solution at 60 °C using a Heidolph rotoevaporator, leading to either a solid lignin (Organosolv) or an oil suspension (CUB). The lignin was collected by filtration and further residual lignin was obtained after the remaining 2-propanol solution was fully evaporated. Finally, the lignin oil was dried in a vacuum oven at 40 °C overnight. Porous organic polymers via Friedel-Crafts alkylation (can be adapted to various aromatic monomers)

In a typical polymerisation, the monomeric material (i.e. benzene) (20 mmol) was added to a two-necked round bottom flask fitted with a reflux condenser. The flask was then charged with dimethoxymethane crosslinker (60 mmol) and anhydrous 1 ,2-dichloroethane solvent (50 mL) before purging with N₂ for a minimum of 30 min. Under continuous N₂ flow, the iron(lll) chloride catalyst (60 mmol) was added. The reactor was quickly sealed and heated under reflux at 80 °C overnight. The resulting brown solid material was then washed with methanol in a Buchner funnel before more extensive washing via Soxhlet extraction in methanol for 24 h. Finally, residual solvent was removed from the material in a vacuum oven under reduced pressure at least 60 °C overnight, yielding the microporous polymer.

If an alternate aromatic compound is used as a monomeric unit, the amount of crosslinker used relates to the number of aromatic carbons available for crosslinking in the monomeric compound in the following way: n = C_Ar/2

Where n is the molar ratio of crosslinker to monomer and C_Ar is the amount of unsubstituted aromatic carbons available for crosslinking in the monomer.

Lignin adsorption/desorption procedure

For the treatment of lignin liquors, the liquor was separated from the cellulosic pulp via filtration immediately after extraction. The liquors usually contained a lignin concentration of around 30 g/L, although this varies between batches. A sample of POP (5 wt%) is then added to the liquor and agitated on a shaker (at 300 rpm) plate for at least 2 hours. The POP is then simply removed via filtration and both the filtrate and the polymer are dried to isolate non-adsorbed lignin and the lignin-loaded polymer, respectively. The non-adsorbed material is then weighed before analysis. The lignin-loaded POP is weighed before the polymer is washed in a Buchner funnel using acetone, removing the adsorbed lignin material. The acetone is then removed in vacuuo from the filtrate and the adsorbed lignin, which has been removed from the adsorbent, is isolated, weighed and analysed.

If an isolated technical lignin is treated (i.e. it has already been removed from the pulping liquor prior to any POP treatment) the process remains the same, although the lignin is first dissolved in a solvent for separation, usually a 2-propanol and water mixture (70:30 vol/vol) or methanol at a concentration of 25 g/L. In the case of Eucalyptus-derived Kraft lignin the lignin is dissolved in a 0.01 M NaOH aqueous solution, in order to mimic is a typical liquor formed in the Kraft process and owing to its poor solubility in organic solvents.

Finally in the flow through experiments, a column was loaded with a benzene-derived POP and an Organosolv liquor was diluted to 1 mg/mL in order to avoid saturating the UV-Vis signal upon elution. The Organosolv solution was then flowed through the POP using a HPLC pump (described below) and the lignin adsorption monitored via UV-Visible spectra of the eluent, taken every 60 s. Desorption of the lignin from the POP was achieved by simply changing the eluent to the wash solvent and continuing to monitor the UV-Vis spectra of the eluent until it appeared clean - i.e. free of desorbed lignin.

Fine fractionation (such as in Example 5)

In order to fractionate a lignin into narrower, more well-defined fractions, a CUB lignin solution (25 mg/mL) in methanol was exposed to five smaller samples of the same benzene- derived POP (1 wt% in each adsorption process) one after another. After each adsorption the POP was removed and treated as described above before more‘fresh’ POP was added for the next adsorption stage, without any further treatment to the lignin solution. By limiting the amount of adsorbent in each adsorption process, the highest molar mass fraction is removed each time, producing more well-defined fractions with each extraction process. After five extractions again the solvent was removed from the non-adsorbed material, allowing for analysis of the remaining lignin.

Characterisation

Surface area determination by gas sorption isotherms

The textural properties and pore size distribution of POPs were measured using a porosity analyser (Micromeritics 3Flex) at -196 °C. The sample (-100 mg) was degassed under vacuum (0.2 mbar) at 120 °C overnight and then further degassed for 4 h (0.003 mbar) in- situ at 120 °C prior to measurement. Surface areas were calculated using the Brunauer Emmett-Teller (BET) method. The total volume of pores was calculated from the volume of N₂ adsorbed at P/Po 0.97, while the micropore volume was determined using the t-plot method.

UV-Visible spectroscopy

All UV-Visible spectroscopy were measured at 25 °C using a UV-Vis spectrometer (Agilent Technologies, UV-Vis 01 ) over a 200-900 nm spectral range, using a cuvette with a path- length of 0.1 mm. Concentrations were determined using UV by the plotting of calibration curves. The continuous flow experiments, i.e. sequestration in Examples 14 and 15, were conducted using a high performance liquid chromatography (HPLC) pump (Alltech HPLC pump, Model 426) and a column (8 mm x 30 mm) filled with the hypercrosslinked benzene polymer. During the experiments, the column was stored at 30 °C in a HPLC column thermostat (Spark Holland SPH99). The lignin liquor was eluted through the column at 0.1 mL/min, before passing through the UV-Visible spectrometer, which was setup to continuously take a measurement every minute. For desorption steps the eluent was simply changed to the wash solvent (either methanol or acetone) in order to wash the adsorbed lignin from the adsorbent POP.

Chemical composition (i.e. CHNO %) by elemental analysis

CHN/O analysis of materials was performed on an Elementar VarioMICRO Cube. Samples (~2 mg) was weighed and sealed in an aluminium boat prior to analysis. Each sample was measured at least in triplicate and oxygen content was determined by subtraction (%0 = 100 - %C - %H - %N - %S - %ash).

Molecular weight distribution determination by gel permeation chromatography (GPC)

To analyse the molecular weight distribution of lignins before and after fractionation, dried samples (10 mg) were dissolved in a 1 mL sample of the GPC eluent, which was anhydrous dimethylformamide containing lithium bromide (0.1 wt%). Samples were filtered (13 mm syringe filter, w / 0.45pm PTFE Membrane) prior to analysis. A high performance liquid chromatography system (Shimadzu, Prominence system) equipped with a pump (Shimadzu, LC-20AD), 3 columns including a guard column (Agilent Technologies, guard column: 1xPolarGel-M, separation columns: 1 xPolarGel-M and 1xPolarGel-L), a refractive index detector (Shimadzu, RID-20A) and a photodiode array detector (Shimadzu, SPD- M20A) was used to perform the GPC analyses at 60 °C.

Determination of glucose concentrations by liquid chromatography-mass spectrometry (LC- MS)

Samples were analyzed in a Shimadzu LC-MS 2020 system using an electrospray ionization (ESI) MS ion source and operating in Selected Ion Monitoring (SIM) mode for the detection glucose. The system was equipped with a TSKgel Amide-80 3.0x100 mm column operating at 70 °C. The mobile phase was a mixture of acetonitrile and water (ACN/H2O: 75:25 v/v) at a flow rate of 0.35 mL min ¹. A gradient method for the mobile phase was applied. Within the initial 5 min, the mobile phase was maintained at an ACN/H2O of 75:25 (v/v); between 5-10 min, it was decreased to 40:60 (v/v) ACN/H2O. Finally, the mobile phase ACN/H2O ratio was increased to 75:25 (v/v) from 10-14 min, remaining at this ACN/H2O ratio until the end of the run (15 min). To allow for high sensitivity for quantification of the glucose, a post-column addition of a solution of methanol and chloroform (4:1 v/v, 0.075 mi_¬ min ¹) was made. This procedure allows for the formation of the corresponding [carbohydrate-CI] ions, dramatically increasing the sensitivity for sugars and sugars alcohols.

Example 1

A CUB lignin liquor as obtained, i.e. in a 2-propanol:water solution (7:3 v/v) after successful extraction from a Poplar (hardwood) substrate, is exposed to a benzene-derived POP produced via Friedel-Crafts alkylation and agitated for ~1 h to allow for adsorption. After adsorption, the sorbent is filtered out, washed with water, and both the polymer and the filtrate collected. The lignin-loaded polymer is then washed with acetone to recover the adsorbed lignin (recovery >95 %), and both the adsorbed lignin (in acetone) and the filtrate (i.e. non-adsorbed lignin in propanol and water) are dried for analysis. GPC chromatograms, indicating the molecular weight of the lignin and its fractions are shown in Figure 1. The calculated CUB lignin capacity of the benzene-derived POP was 40 wt%.

Molecular weight data derived from GPC analysis and elemental analysis results are shown in Table 1 , indicating differences in apparent molecular weight, narrowing polydispersity indices and varying chemistries of the lignin fractions after refinement.

Table 1. Elemental analysis (H/C and O/C molar ratios) and molecular weight data of CUB lignin liquor and subsequent fractions, including number average molecular weight, M_n, weight average molecular weight, M_w, polydispersity index (PDI), M_wIM_n.

M_n (g/mol) M_w (g/mol) M_w/M_n (PDI) H/C O/C

CUB (Poplar) lignin

160 1003 6.27 1.66 0.43 liquor

CUB adsorbed fraction 201 1 180 5.87 1.44 0.33

CUB non-adsorbed

143 397 2.78 1.70 0.48 fraction

Example 2

In the same manner as in Example 1 , an Organosolv hardwood lignin liquor produced from a Poplar substrate is fractionated using a benzene-derived POP produced via Friedel-Crafts alkylation. Again, GPC chromatograms for obtained fractions and the OS lignin liquor are shown in Figure 2. The calculated OS lignin capacity of the benzene-derived POP was 46 wt%. Molecular weight data derived from GPC analysis and elemental analysis results are shown in Table 2, indicating differences in apparent molecular weight, narrowing polydispersity indices and varying chemistries of the lignin fractions after refinement.

Table 2. Elemental analysis (H/C and O/C molar ratios) and molecular weight data of OS lignin liquor and subsequent fractions, including number average molecular weight, M_n, weight average molecular weight, M_w, polydispersity index (PDI), MJM_n.

M_n (g/mol) M_w (g/mol) Mw/Mn (PDI) H/C O/C

OS (Poplar) lignin

105 1250 1 1 .93 1.19 0.40 liquor

Adsorbed fraction 147 1523 10.35 1.17 0.35

Non-adsorbed fraction 65 574 5.78 1.31 0.55

Example 3

In the same manner as in Example 1 , a CUB lignin (extracted from Spruce, softwood) is fractionated using a benzene-derived POP produced via Friedel-Crafts alkylation. GPC chromatograms for obtained fractions and the CUB lignin liquor are shown in Figure 3. The calculated lignin capacity of the benzene-derived POP in this instance was 40 wt%. Molecular weight data derived from GPC analysis are shown in Table 3, indicating differences in apparent molecular weight and narrowing polydispersity indices in the lignin fractions after refinement.

Table 3. Molecular weight data derived from GPC analysis, including number average molecular weight, M_n, weight average molecular weight, M_w, and polydispersity index (PDI), MJ Mn·

M_n (g/mol) M_w (g/mol) MJM_n (PDI)

CUB (spruce) lignin liquor 142 679 4.80

Adsorbed fraction 235 761 3.24

Non-adsorbed fraction 145 400 2.78

Example 4

In the same manner as in Example 1 , a CUB lignin (extracted from Poplar) is fractionated from a methanol solution (2.5 w/v%) in place of 2-propanol/water. GPC chromatograms for obtained fractions and the CUB lignin are shown in Figure 4. The calculated lignin capacity of the benzene-derived POP was 49 wt%. Molecular weight data derived from GPC analysis and elemental analysis results are shown in Table 4, indicating differences in apparent molecular weight, narrowing polydispersity indices and varying chemistries of the lignin fractions after refinement. Table 4. Elemental analysis (H/C and O/C molar ratios) and molecular weight data of CUB lignin adsorption from methanol and subsequent fractions, including number average molecular weight, M_n, weight average molecular weight, M_w, polydispersity index (PDI), MJ Mn·

M_n (g/mol) M_w (g/mol) M_w/M_n (PDI) H/C O/C CUB lignin 238 1780 7.49 1.60 0.53

Adsorbed fraction 448 2630 5.87 1.42 0.45

Non-adsorbed fraction 174 546 3.14 1.76 0.65 Example 5

In the same manner as in Example 4, a CUB hardwood lignin is fractionated from a methanol solution (2.5 w/v%) using subsequent treatments of the lignin solution with smaller amounts of a benzene-derived POP produced via Friedel-Crafts alkylation (5 x 1 wt%). GPC chromatograms for each extractive fraction and the remaining lignin fraction are shown in Figure 5.

Molecular weight data derived from GPC analysis are shown in Table 5, indicating differences in apparent molecular weight and narrowing polydispersity indices of lignin fractions with each subsequent fractionation.

Table 5. Molecular weight data derived from GPC analysis, including number average molecular weight, M_n, weight average molecular weight, M_w, and polydispersity index (PDI), MJ Mn·

M_n (g/mol) M_w (g/mol) MwIMn (PDI)

Extractive 1 365 2,533 6^95

Extractive 2 312 1 ,787 5.72

Extractive 3 266 1 ,180 4.43

Extractive 4 229 794 3.47

Extractive 5 199 585 2.94

Lignin bio-oil post-extraction 179 382 2.13 Example 6 In the same manner as in Example 1 , a CUB hardwood lignin liquor (extracted from Poplar) is fractionated, in this case using a phenol-derived POP produced via Friedel-Crafts alkylation. Again, GPC chromatograms for obtained fractions and the CUB lignin liquor are shown in Figure 6. The calculated CUB lignin capacity of the phenol-derived POP was 5 wt%, in good agreement with the reductions in surface area associated with the phenol POP.

Molecular weight data derived from GPC analysis are shown in Table 6, indicating differences in apparent molecular weight and narrowing polydispersity indices of lignin fractions.

Table 6. Molecular weight data derived from GPC analysis, including number average molecular weight, M_n, weight average molecular weight, M_w, and polydispersity index (PDI), M Mn·

M_n (g/mol) M_w (g/mol) MJM_n (PDI)

CUB lignin liquor 160 1003 6.27

Adsorbed fraction (phenol-based

154 878 5.71 sorbent)

Non-adsorbed fraction 170 1052 6.19

Example 7

In the same manner as in Example 6, a CUB hardwood lignin liquor (extracted from Poplar) is fractionated, in this case using a thiophene-derived POP produced via Friedel-Crafts alkylation. GPC chromatograms for obtained fractions and the CUB lignin liquor are shown in Figure 7. The calculated CUB lignin capacity of the thiophene-derived POP was 9 wt%.

Molecular weight data derived from GPC analysis are shown in Table 7, indicating differences in apparent molecular weight and polydispersity indices of lignin fractions. Table 7. Molecular weight data derived from GPC analysis, including number average molecular weight, M_n, weight average molecular weight, M_w, and polydispersity index (PDI), MJ Mn·

M_n (g/mol) M_w (g/mol) M_w/M_n (PDI)

CUB lignin liquor 160 1003 6.27

Adsorbed fraction (thiophene-based

167 1228 7.34 sorbent) Non-adsorbed fraction 185 1 172 6.32

Example 8

In the same manner as in Example 6, a CUB hardwood lignin liquor (extracted from Poplar) is fractionated, in this case using a pyrrole-derived POP produced via Friedel-Crafts alkylation. GPC chromatograms for obtained fractions and the CUB lignin liquor are shown in Figure 8. The calculated capacity of the pyrrole-derived POP was 5 wt%.

Molecular weight data derived from GPC analysis are shown in Table 8, indicating differences in apparent molecular weight and polydispersity indices of lignin fractions.

Table 8. Molecular weight data derived from GPC analysis, including number average molecular weight, M_n, weight average molecular weight, M_w, and polydispersity index (PDI), M Mn·

M_n (g/mol) M_w (g/mol) MJM_n (PDI)

CUB lignin liquor 160 1003 6.27

Adsorbed fraction (pyrrole-based

150 907 6.05 sorbent)

Non-adsorbed fraction 166 959 5.77 Example 9

In the same manner as in Example 6, a CUB hardwood lignin liquor (extracted from Poplar) is fractionated, in this case using a naphthalene-derived POP produced via Friedel-Crafts alkylation. GPC chromatograms for obtained fractions and the CUB lignin liquor are shown in Figure 9. The calculated capacity of the naphthalene-derived POP was 9 wt%.

Molecular weight data derived from GPC analysis are shown in Table 9, indicating differences in apparent molecular weight and polydispersity indices of lignin fractions.

Table 9. Molecular weight data derived from GPC analysis, including number average molecular weight, M_n, weight average molecular weight, M_w, and polydispersity index (PDI), MJ Mn·

M_n (g/mol) M_w (g/mol) M_w/M_n (PDI)

CUB lignin liquor 160 1003 6.27

Adsorbed fraction (naphthalene-based

187 1 158 6.20 sorbent) Non-adsorbed fraction 154 731 4.74

Example 10

In the same manner as in Example 6, a CUB hardwood lignin liquor (extracted from Poplar) is fractionated, in this case using an anthracene-derived POP produced via Friedel-Crafts alkylation. GPC chromatograms for obtained fractions and the CUB lignin liquor are shown in Figure 10. The calculated capacity of the anthracene-derived POP was 15 wt%.

Molecular weight data derived from GPC analysis are shown in Table 10, indicating differences in apparent molecular weight and polydispersity indices of lignin fractions.

Table 10. Molecular weight data derived from GPC analysis, including number average molecular weight, M_n, weight average molecular weight, M_w, and polydispersity index (PDI), MJ Mn·

M_n (g/mol) M_w (g/mol) M_w/M_n (PDI)

CUB lignin liquor 160 1003 6.27

Adsorbed fraction (anthracene-based

155 965 6.24 sorbent)

Non-adsorbed fraction 156 834 5.35 Example 11

In the same manner as in Example 6, a CUB hardwood lignin liquor (extracted from Poplar) is fractionated, in this case using a benzene- and phenol- derived porous organic co- polymer produced via Friedel-Crafts alkylation (molar ratios 60:40 for benzene:phenol, respectively). GPC chromatograms for obtained fractions and the CUB lignin liquor are shown in Figure 11. The calculated capacity of the benzene- and phenol- derived co- polymer was 14 wt%.

Molecular weight data derived from GPC analysis are shown in Table 11 , indicating differences in apparent molecular weight and polydispersity indices of lignin fractions.

Table 11. Molecular weight data derived from GPC analysis, including number average molecular weight, M_n, weight average molecular weight, M_w, and polydispersity index (PDI), M Mn·

M_n (g/mol) M_w (g/mol) MJM_n (PDI) CUB lignin liquor 160 1003 6.27 Adsorbed fraction (benzene-phenol co-

225 1345 5.98 polymer sorbent)

Non-adsorbed fraction 143 554 3.88

Example 12

In this example a Eucalyptus-derived Kraft lignin (kindly provided by Suzano Pulp and Paper) is fractionated from a basic aqueous solution (10 mg/mL of Kraft lignin, 0.01 M NaOH aqueous solution), in order to mimic a liquor formed during the Kraft process. A benzene- derived POP (5 w/v%) produced via Friedel-Crafts alkylation was used as adsorbent. GPC chromatograms for obtained adsorbed and non-adsorbed fractions and the original Kraft lignin are shown in Figure 12. The calculated Kraft lignin capacity of the benzene-derived POP was 15 wt%.

Molecular weight data derived from GPC analysis and elemental analysis results are shown in Table 12, indicating differences in apparent molecular weight, polydispersity indices and varying chemistries of the lignin fractions after refinement. Surprisingly, the benzene- derived POP appeared to selectively adsorb a low molecular weight portion of the Kraft lignin, meaning the non-adsorbed fraction had a much larger average molecular weight, M_w.

Table 12. Elemental analysis (C, H and S %) and molecular weight data of untreated Kraft lignin and subsequent fractions, including number average molecular weight, M_n, weight average molecular weight, M_w, polydispersity index (PDI), M_wIM_n.

ML H (%)

M_n (g/mol) M M„ (PDI) C (%) S (%)

(g/mol)

Kraft lignin 148 2126 14.37 61.2 5.6 1.8

Kraft adsorbed 5 5

1 1 1 1864 16.8 59.6 1.4 fraction

Kraft non-adsorbed 5.7

190 3839 20.3 61.1 1.5 fraction

Example 13

In the same manner as in Example 12, a Eucalyptus-derived Kraft lignin (kindly provided by Suzano Pulp and Paper) is almost completely sequestered from a basic aqueous solution (7.5 mg/mL of Kraft lignin, 0.01 M NaOH aqueous solution), in order to mimic a liquor formed during the Kraft process. In this example a benzene-derived POP (5 w/v%) produced via Friedel-Crafts alkylation was used as adsorbent and exposed to the model Kraft liquor in a batch process for 48 hours. It was ensured that enough polymer was present to allow full sequestration without exceeding the polymer’s adsorption capacity calculated from the previous example. GPC chromatograms for the untreated Kraft lignin and the Kraft lignin recovered from the adsorbent polymer are shown in Figure 13. The calculated lignin capacity of the benzene-derived POP in this case was 14 wt%, although this may be unrepresentative of the true value as an excess of the polymer was added. Around 97 % of the Kraft lignin was removed from solution, of which 89 % was successfully recovered from the adsorbent benzene polymer.

Molecular weight data derived from GPC analysis are shown in Table 13. The adsorbed and recovered fraction of the Kraft lignin appeared to show a slight difference with respect to the highest molecular weight materials, i.e. at lower retention times. As 97 % of the Kraft was sequestered but only around 89 % of that material was recovered, this fraction likely remained adsorbed to the POP adsorbent.

Table 13. Molecular weight data of untreated Kraft lignin and the lignin recovered from the POP sorbent, including number average molecular weight, M_n, weight average molecular weight, M_w, polydispersity index (PDI), MJM_n.

M_n (g/mol) M_w (g/mol) M_w/M_n (PDI)

Kraft lignin 133 2139 16.10

Kraft adsorbed

109 1495 13.75

fraction

Example 14

A column was packed with a benzene-derived POP (293 mg) produced via Friedel-Crafts alkylation, and an Organosolv lignin liquor (in 2-propanol:water, 7:3 v/v ratio and diluted to 1 mg/mL, so as to avoid saturation of the UV absorbance signal) was passed through the column at a flow rate of 0.1 mL/min. The first 1 mL of the Organosolv liquor pass over the sorbent was collected and the lignin content compared using UV spectroscopy, as shown in Figure 14.

The liquor that eluted from the column was then continuously monitored using UV- spectroscopy absorbance at a wavelength of 204 nm, the absorbance of which increases with time in the UV as the column becomes increasingly saturated and more lignin begins to elute. Figure 15 shows two repeated uptake-desorption cycles, in which to desorb the lignin, the eluent was changed to acetone. It is also demonstrated that changing the eluent to methanol produced some desorption but was not able to concentrate the lignin, emphasising the need for good lignin solvents as desorption eluents. It was found that uptake capacities for a benzene-derived POP of 15 wt% was achievable on repeated uptake-desorption processes. As a result of efficient acetone desorption, lignin could be concentrated in solution by around a factor of 3-4 times.

Example 15

In the same manner as in Example 14, an Organosolv lignin liquor (Poplar substrate) was adsorbed onto a benzene-derived POP produced via Friedel-Crafts alkylation and fractionation was attempted upon desorption by varying the desorption eluent. Upon saturation of the column, as measured by UV spectroscopy of the eluting sample, the eluent was changed to methanol and the eluent collected. After 1 h, equating to the elution of 6 mL, the eluent was changed to acetone and once again the eluent was collected. The GPC chromatograms of the two desorption eluents are compared to the OS lignin liquor in Figure

16.

Molecular weight data derived from GPC analysis are shown in Table 14, indicating differences in apparent molecular weight and narrowing polydispersity indices of lignin fractions. Methanol selectively desorbed more high molar mass material in comparison to acetone.

Table 14. Molecular weight data derived from GPC analysis, including number average molecular weight, M_n, weight average molecular weight, M_w, and polydispersity index (PDI), M Mn·

M_n (g/mol) M_w (g/mol) M_w/Mn (PDI)

OS lignin liquor 145 1305 8.97

Desorbed by methanol 204 3939 19.29 Desorbed by acetone 159 1460 9.17

Example 16

An aqueous solution of D-glucose (5 mg/L) was made up and exposed to a benzene-derived POP (2.5 w/v%) produced via Friedel-Crafts alkylation for at least 2 hours. After 2 hours the POP was filtered out and the D-glucose content of the solution was measured using LC-MS and compared to the initial solution (measured in the same manner) (Table 15). It was clear that the glucose concentration did not decrease, indicating the lack of any adsorption of the glucose by the POP.

Table 15. Glucose concentration derived from LC-MS analysis of untreated glucose solutions and the same solutions after 2 h exposure of a benzene-derived POP. Glucose concentration (mg/L)

Initial glucose solution 4.55 ± 0.21

After exposure to benzene-derived POP 4.64 ± 0.22

Example 17

In the same manner as in Example 2, an Organosolv hardwood lignin liquor produced from a Poplar substrate is fractionated using a benzene-derived POP produced via Friedel-Crafts alkylation. In this case glucose (5 mg/L) was added to the lignin solution and the concentration of glucose before and after adsorption of lignin by the benzene-derived POP was determined using liquid chromatography-mass spectrometry in order to demonstrate the POP’s selectivity toward the lignin. Although lignin adsorption occurred as in previous examples, the glucose concentration remained constant. The glucose content prior to lignin adsorption was determined by LC-MS (Table 16) from at least three repeated adsorption processes. The slightly increased numbers are owing to slight concentration during the adsorption process.

Table 15. Glucose concentration derived from LC-MS analysis of untreated Organosolv lignin solutions containing added glucose and the same solutions after 2 h exposure of a benzene-derived POP.

Glucose concentration (mg/L)

Initial Organosolv lignin/glucose solution 4.53

After exposure to benzene-derived POP 4.87 ± 0.15

Embodiments of the invention have been described by way of example only. It will be appreciated that variations of the described embodiments may be made which are still within the scope of the invention.

Claims

1. A process for adsorption of lignin, or a derivative thereof, the process comprising:

contacting lignin, or a derivative thereof, with:

a porous organic polymer comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings; and/or

a metal organic framework comprising ligands each independently comprising one or more aromatic and/or heteroaromatic rings.

2. The process of claim 1 , wherein the lignin, or a derivative thereof, is technical lignin or lignin oil or pyrolysis oil obtained from lignocellulose or a mixture thereof, optionally where the lignin or a derivative thereof is technical lignin.

3. The process of claim 2, wherein the source of lignocellulose is a softwood, hardwood, grass, straw, waste wood, lignocellulosic crop residues, or a mixture thereof.

4. The process of claim 2 or 3, wherein the technical lignin is lignin from acid- hydrolysis, organosolv lignin, soda lignin, kraft lignin, enzymatic lignin,

depolymerised lignin streams from lignocellulose deconstruction enhanced by hydrogenation catalysts or capping agents, or a mixture thereof.

5. The process of any of claims 2-4, wherein the technical lignin is Organosolv straw lignin, soda straw lignin, Kraft pine lignin, Organosolv hardwood lignin, softwood Kraft lignin, sarkanda grass soda lignin, hardwood soda lignin, milled wood lignin or a mixture thereof.

6. The process of claim 1 or 2, wherein the lignin, or a derivative thereof, is obtained by thermal treatment of lignocellulose by pyrolysis in the presence or in the absence of a catalyst, or a mixture of lignin products obtained from a treatment by chemical and/or enzymatic catalysis, or a lignin product mixture from reactions in the absence of a catalyst.

7. The process of any preceding claim, wherein the process comprises: contacting lignin, or a derivative thereof, with a porous organic polymer comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings.

8. The process of any preceding claim, wherein the one or more aromatic and/or heteroaromatic rings are each independently benzene, pyridine, thiophene, pyrrole, furan, imidazole or a mixture thereof.

9. The process of any preceding claim, wherein the monomer units or ligands are each independently:

wherein each A is independently C-i-s alkyl, C_2-8 alkenyl, C_2-8 alkynyl, Ci-6 haloalkyl, Ci-6 hydroxyalkyl, carboxyl, hydroxy, Ci-6 alkoxy or halo; and each a is

independently an integer.

10. The process of any preceding claim, wherein the porous organic polymer is formed by cross-linking aromatic and/or heteroaromatic ring-containing monomers by transition-metal or noble metal catalysed cross-coupling reactions, free radical polymerisation or condensation reactions.

1 1. The process of any preceding claim, wherein the monomer units are cross-linked by C-i-salkylene, C2-salkenylene or C2-salkynylene or arylene or heteroarylene linkers, optionally Ci-₆alkylene, C2-6alkenylene, C2-6alkynylene or arylene linkers, optionally a Ci-₆alkylene linker.

12. The process of any preceding claim, wherein the metal organic framework comprises ligands each independently comprising one or more aromatic and/or heteroaromatic rings coordinated to metal centres (for example, copper).

13. The process of any preceding claim, wherein the porous organic polymer and/or metal organic framework has a surface area of at least about 50 m²g ¹, optionally at least about 200 m²g ¹, optionally at least about 500 m²g ¹.

14. The process of any preceding claim, wherein lignin, or a derivative thereof, is provided in a liquid medium.

15. The process of any preceding claim, wherein the process is a batch process.

16. The process of any of claims 1-14 wherein the process is a continuous process.

17. The process of any preceding claim further comprising the step of washing the porous organic polymer and/or metal organic framework with a solvent to extract the adsorbed lignin or a derivative thereof.

18. The process of any preceding claim wherein the process is for selective adsorption of lignin, or a derivative thereof, from pulping liquor, optionally the process comprising:

19. The process of any preceding claim wherein the process is for fractionation of lignin or a derivative thereof.

20. A process for fractionation of lignin or a derivative thereof, the process comprising:

contacting lignin or a derivative thereof with: a porous organic polymer comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings; and/or a metal organic framework comprising ligands each independently comprising one or more aromatic and/or heteroaromatic rings, such that lignin or a derivative thereof is adsorbed; and

optionally further comprising the step of washing the porous organic polymer and/or the metal organic framework with a solvent to extract the adsorbed lignin or a derivative thereof.

21. The process of claim 19 or 20, wherein the step of contacting lignin or a derivative thereof with a porous organic polymer and/or a metal organic framework is such that a molecular weight fraction of the lignin or a derivative thereof is adsorbed; and/or the step of washing the porous organic polymer and/or metal organic framework with a solvent to extract the adsorbed lignin or a derivative thereof is such that a molecular weight fraction of the lignin or a derivative thereof is extracted.

22. The process of any of claims 19 to 20, the process comprises:

a) contacting lignin or a derivative thereof with: a porous organic polymer comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings; and/or a metal organic framework comprising ligands each independently comprising one or more aromatic and/or heteroaromatic rings, such that a molecular weight fraction of the lignin or a derivative thereof is adsorbed; and

optionally repeating the contacting and washing steps one or more times, optionally wherein each subsequent step of contacting is carried out with a higher loading (e.g. concentration) of porous organic polymer and/or metal organic framework to lignin or a derivative thereof; or b) contacting lignin or a derivative thereof with: a porous organic polymer comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings; and/or a metal organic framework comprising ligands each independently comprising one or more aromatic and/or heteroaromatic rings, such that lignin or a derivative thereof is adsorbed; and

23. A lignin, or a derivative thereof, obtained by the process of any preceding claim.

24. A composite material comprising:

a porous organic polymer comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings; and/or a metal organic framework comprising ligands each independently comprising one or more aromatic and/or heteroaromatic rings; and

25. Use of a porous organic polymer comprising cross-linked monomer units each independently comprising one or more aromatic and/or heteroaromatic rings; and/or a metal organic framework comprising ligands each independently comprising one or more aromatic and/or heteroaromatic rings for:

a) adsorption of lignin, or a derivative thereof; or

b) separation of lignin from non-adsorbed trace sugars, or a derivative thereof, in lignin liquors.