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Lignin as a Chemical Feedstock. Ian Suckling APPI May 2012. Introduction. Chemical processing of wood mainly targets carbohydrates, e.g. pulp, bioethanol Large amounts of process lignins potentially available as “co-product” in NZ ~380,000 tpa kraft lignin

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Lignin as a Chemical Feedstock


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    1. Lignin as a Chemical Feedstock Ian Suckling APPI May 2012

    2. Introduction • Chemical processing of wood mainly targets carbohydrates, e.g. pulp, bioethanol • Large amounts of process lignins potentially available as “co-product” • in NZ ~380,000 tpa kraft lignin • Lignin structure → potential sustainable source of aromatic and aliphatic chemicals • Only ~1% of lignin processed through pulp mills is currently recovered for uses other than energy • nearly all as lignosulfonates (1 – 1.2m tpa)

    3. in-situ radical polymerisation (enzyme-initiated) Softwood lignin • Potential feedstock for: • aromatic and aliphatic chemicals • biopolymers

    4. Introduction ctd • chemical feedstocks potentially a higher value use

    5. Agenda • Issues with lignin utilisation • why is lignin such a difficult feedstock? • Current technical lignins • Isolation • Structures • Current uses • Potential uses for lignin • Combustion for energy • Gasification to fuels and chemicals • As a polymeric material • Feedstock for low molecular weight chemicals

    6. Issues • Structural complexity & variability of lignin

    7. Cellulose -basis for comparison 1 chemistry >95% yield

    8. 26 C-9 units 7 different chemistries monomers Breakdown of softwood lignin

    9. Lignin heterogeneity in reality it is even worse…. • 3 lignin precursors – species dependent • process lignins heavily modified • reactive -ether interunit links cleaved • new interunit bonds formed • sulfonate or thiol groups can be introduced • lignin structure depends on process

    10. Issues • structural complexity & variability of lignin • need to isolate & purify the process lignins • degradation processes tend to require severe conditions • products often more reactive than starting lignin • generally complex mixtures of products • low yields, purification required • what happens to the rest?

    11. Issues • costs vs petrochemical alternatives • lignin often has existing value as fuel • lignin isolation • high Capex & Opex • product isolation • low saleable product yields “you can make anything you want out of lignin ………except money” • huge amounts of lignin potentially available • markets for the products?

    12. In summary Lignin as a feedstock for chemical production represents: • both a major opportunity… • large amounts available & currently poorly utilised • sustainable source of biopolymers and aromatic & phenolic feedstocks • and a major challenge… • technical • economic

    13. Isolated lignins • Kraft lignin • Lignosulfonates • Organosolv lignins • Hydrolytic lignins • “Native wood” lignins • Not possible to isolate an unmodifed wood lignin • Best lignins (research purposes only): • Milled wood lignin (MWL) • Cellulolytic enzyme lignins (CELs)

    14. Kraft lignin • Large amounts of black liquor produced worldwide • Lignin has current value as a fuel • Only small amounts currently isolated • e.g. Indulin (MeadWestvaco) • Main use after sulfonation • Benefit of lignin removal = increased pulp production in recovery-limited mill • lignin then used as fuel in lime kiln or for combustion

    15. Kraft black liquor Typical composition of the dry matter of Scots pine and silver birch Kraft black liquors % of total dry matter)

    16. Isolation of kraft lignin • By acidification of black liquor • Many variants • Issues: • Lignin purity • Obtaining an easily filterable product • H2S emitted on acidification • Foaming (CO2 release on acidification) • Restricted to CO2 or H2SO4 for acidification as residue → recovery cycle

    17. Lignoboost process

    18. Sequential Liquid-Lignin Recovery & Purification (SLRP)

    19. Kraft lignin structure Zakzeski, J. et al. Chem. Rev. 110:3552 (2010)

    20. Lignosulfonates • Major use of lignin (~1,000,000 tpa) • Wide variety of grades/purities • Derived from: • Acid sulfite pulping of hardwoods, softwoods and bagasse • NSSC pulping • Sulfonation or sulfomethylation of kraft lignin

    21. Sulfite pulping liquor Typical composition of Norway spruce and silver birch spent acid sulfite liquors (kg/ton pulp).

    22. Isolation of lignosulfonates • Depends on the cooking base and purity required • Commonly sold as powders/40-60% solutions in water • By evaporation and/or spray drying of pulping liquors • Directly → impure product • Or following purification • By precipitation as the Ca salt with Ca(OH)2 • Step 1: recovers Ca sulfite • Step 2: separate lignin as the calcium lignosulfonate • Step 3: precipitate remaining lignin & return to step 1

    23. Lignosulfonates Zakzeski, J. et al. Chem. Rev. 110:3552 (2010)

    24. Performance of lignosulfonates • Application-specific and can depend on: • Feedstock processed, e.g. hardwood or softwood • Pulping process used • Base of lignosulfonate, e.g. Ca, Na, NH4, Fe, Cr • Level of impurities – commercial products often only 60-80% pure – sugars, sugar acids, extractives, inorganics • Level of sulfonation • Molecular weight distribution • Types of functional groups present • Modifications to the lignosulfonates • Multiple grades for different applications

    25. Commercial lignosulfonates – an example • BorregaardLignoTech – just for agricultural chemicals

    26. Modification of lignosulfonates • Cation exchange • or from a Na base by ion exchange • Ultrafiltration to remove low MWt fractions • Sugar removal by: • fermentation, yeast production • ion exchange • oxidation in alkali • Desulfonation by treatment with NaOH or ammonia

    27. Sulfonation of kraft lignin • Treatment of kraft lignin at ~100ºC with chemicals used during sulfite pulping • Introduces sulfonate functionality into sidechain • recovery by evaporation or precipitation as Ca salt • At higher temperatures (150-200ºC) get ring sulfonation • Acid-induced hydroxymethylation of the aromatic rings • then sulfonation of hydroxymethyl groups

    28. Applications of lignosulfonates • Concrete admixtures [Large] • Reduce amount of water needed → stronger concrete • Dust control [Large] • Animal feed [Large] • Use as binder in animal feed pellets • Added to feed molasses to reduce viscosity • Vanillin manufacture [Medium] • Gypsum wallboard dispersant [Medium] • Oil well drilling mud additive [Medium to Small] • Dye dispersants [Medium] • Resins [Small to medium] • Binders [Small to medium] Ek – The status of applied lignin research Processum Report (2002).

    29. Organosolv lignins • Not currently available on commercial scale • Renewed interest in organosolv process for biofuel production with lignin as a potentially valuable co-product • Lignin easily separated from pulping solvent by: • Solvent removal and recovery • Precipitation with water + distillation to recover solvent • Organosolv lignin: • Low molecular weight • Low sulfur and ash content • Low water solubility • Readily soluble in alkali and organic solvents Attractive for low MWt phenols or aromatics

    30. Hydrolytic (dilute acid) lignins • Still produced commercially in Russia • Hydrolytic lignin ~1/3 of initial wood • Low value • Low purity (typically only 60-70% lignin) • Highly condensed lignin (condensation reactions) • Can be used as a source of process heat Ethanol + Ferment Yeast Monomeric sugars 0.4-0.7% H2SO4 120-190ºC + Wood + Furfural Hydrolytic lignin

    31. Analysis of hydrolysis lignins Composition of commercial technical hydrolytic lignins from various Russian commercial plants (% of oven-dried sample). Krutov et al. Proceedings of 16th ISWFPC, Tianjin (2011)

    32. Comparison of commercial lignins

    33. Other potential uses of lignin • Combustion for energy - current major use • Gasification to fuels and chemicals • As a polymeric material • as dispersant, emulsifier, stabiliser or sequestrant • in material systems • adhesives, thermosetresins • polymer modifier • carbon fibre • As a feedstock for low molecular weight chemicals • aromatic & aliphatic chemical feedstocks

    34. Combustion • Lignoboost kraft lignin proposed as fuel for co-firing in coal-fired power plants

    35. Gasification • Gasification to synthesis gas (CO, H2 and CO2) • Forest & other biomass residues • Lignin • Black liquor • Synthesis gas then converted to chemicals or burnt for energy

    36. Gasification - ctd

    37. Gasification - ctd • Fisher Tropsch chemistry • H2/CO ratio may need to be adjusted using water gas shift reaction

    38. CHEMREC black liquor gasification • Pilot plant uses black liquor as feedstock • Syngas then used to produce DME (H3COCH3)

    39. Dimethyl ether production

    40. Carbon fibre production • Lignin a potential low-cost source of carbon suitable for displacing polyacrylonitrile in carbon fibre production • 10% of US lignin could displace half steel in domestic passenger vehicles • reduce vehicle weight & improve fuel economy • Requires C fibre cost to be reduced

    41. Carbon fibre production from polyacrylonitrile (PAN)

    42. Carbon fibre production from lignin • Range of lignins have been melt-spun and carbonised • sometimes with added plasticising agent

    43. Carbon fibre production from lignin - issues • Requires melt-spinning of lignin at high rates • Low-cost purification of lignin • need to remove polysaccharides, salts, particulates, water and volatiles • Lignin molecular weight polydispersity • low and high MWt fractions may need to be removed • Methods to process, stabilise and derivatise lignin to optimise its thermal (Tg), melt flow and melting point • Maximise yields of carbon fibre from thermal conversion of melt-spun lignins • Application to varied lignin sources

    44. Polymer modifiers • Low-cost fillers • Focus of much research, e.g. incorporation into adhesives • High-value additives to improve polymer performance, e.g. • High-strength engineering plastics • Heat-resistant polymers • Under-the-hood uses • Antibacterial surfaces • High-strength formaldehyde-free adhesives

    45. Polymer modifiers • Area of active research, including: • Epoxies • UV stabilisers for plastics • Polyurethanes • Issues: • Economical modifications to improve solubility and compatibility with other polymers • Controllable alteration of molecular weight • Lignin colour • Control of polyelectrolyte character • Functional group enhancement

    46. Phenolic resins • Chemistry of phenol-formaldehyde (PF) resins

    47. Lignin as a phenol substitute • Lignin extensively investigated as phenol substitute in PF resins • Ready availability and low cost (vs phenol) • Issue: much lower reactivity as fewer phenolic groups • E.g. kraft lignin 0.3 reactive aromatic sites/C-9 unit vs 3 for phenol

    48. Means to enhance reactivity to formaldehyde • Demethylation • Hydroxymethylation • Phenolation • Use of novel lignins, e.g. organosolv lignins • By extensive lignin degradation (see later)

    49. Low MWt chemicals from lignin

    50. Options for low MWt chemicals