Lignin as a renewable aromatic resource for the chemical industry

lignin is recovered by an alternative recovery process by acid precipitation, maturation and filtration giving novel types of sulfur-free lignin (Abächerli and Doppenberg 1998;Abächerli and Doppenberg 2000; Lora and Glasser 2002). Organosolv pulping and/or fractionation processesThe use of organic solvents, e.g.ethanol, allows avoiding the formation of sulfated byproducts.Organosolv pulping or fractionation enables the production of high quality cellulose AND high quality lignin.The water insoluble organosolv lignins are more pure containing a higher percentage of lignin.The major organosolv processes are the following: Lignol process, based on the Alcell ethanol/water pulping process,  ASAM, Alkaline Sulfite Anthraquinone Methanol pulping,  Organocell, Methanol pulping followed by anthraquinone/NaOH pulping,  Acetosolv, an acetic acid/HCl pulping,  Milox, formic acid/hydrogen peroxide delignification,  Avidel, formic/acetic acid pulping.These processes are not commercial yet, but have been demonstrated at pilot and demonstration scale.Organosolv pulping or fractionation of lignocellulosic biomass is nowadays one of the selected pretreatments to produce high quality cellulose for pulp and/or biofuel production together with a high purity lignin for materials and chemicals.Both the Canadian company Lignol (former Alcell process; Hallberg et al. 2010) and the French company CIMV (Avidel process; Delmas 2008) are using an organosolv fractionation technology (Table 1.3).In this thesis, high purity organosolv lignins obtained from ethanol/water fractionations of mixed hardwoods (Alcell tm lignin) and wheat straw are studied for the production of aromatic chemicals described in Chapter 5. Biomass pretreatment and conversion (biorefinery)Examples of these biomass pretreatment and conversion processes are strong or dilute acid pretreated lignocellulosic biomass followed by enzymatic hydrolysis of the carbohydrates.The resulting lignin fraction contains a considerable amount of residual carbohydrates (Vishtal and Kraslawski 2011).In a modern lignocellulosic biorefinery plant about 40% of the dried lignin-rich stream is necessary to meet the thermal requirements of 2G bioethanol production in particular for the biomass pretreatment step and the ethanol distillation part.The remaining 60% excess of lignin could be utilized as a feedstock for green chemicals and materials giving additional revenues to the biorefinery plant (Sannigrahi et al., 2010).The directives of the EC in 2020 to replace 10% of transportation fuels by biofuels (Table 1.1) will likely result in the generation of large amounts of lignin in the biofuel production from lignocellulosic biomass.In 2020 10% of the annual use of about 300 Mtonnes of transportation fuels must be generated from biomass in the EU-25.If 50% will consist of bioethanol and the other half of biodiesel for both 15 Mt will be needed.To produce 15 Mt of bioethanol, approximately double the amount 2x15=30 Mt of carbohydrates (fermentable sugars) are necessary.Assuming that half of this amount will be produced from lignocellulosic biomass as so-called 2G bioethanol, together with 15 Mt of carbohydrates (C6 and C5) from lignocellulose 5 Mt of (pure) lignin will be generated per annum.In practise, this potentially enormous lignin stream will not be highly pure but associated with other biomass components such as undigested carbohydrates, proteins and minerals.Therefore this lignin-rich stream will be even higher in amount up to 7.5 Mt/annum.In 2030 the production of 2G biofuels will further increase by a factor 2.5 to substitute 25% of the fossil-based transportation fuels.This will lead to the generation of slightly less than 20Mt/annum of biorefinery lignin.40% of this amount needs to be used for the energy requirements of the biorefinery, which means that about 60% = 12 Mt can be potentially produced as a lignin product.Together with the additional lignin from the pulp and paper industry (2-4 Mt/year) potentially about 14-16 Mt/annum lignin will become available in the coming years in Europe.In this section it is shown that a variety of technical lignins are available or will become available in the future.As these lignins differ in purity, properties and costs these materials will be used for different applications as described in the next section.In this thesis, in particular the high purity lignins such as kraft, soda and organosolv lignin from different raw materials (wood, grass and agro residues) were studied for development of applications.These lignins were selected to minimize the influence of impurities on the behavior of the lignin in the chosen applications.However, for analytical purposes the other less pure lignins (steam explosion, hydrolysis lignin, and lignosulfonates) were used in the characterization work to show the broad applicability No Medium l) Gnansounou (2010) m) Zimbardi et al. (1999) 1) Impurities are generally residual carbohydrates, ash and proteins and largely depends on feedstock and process 2) Former technology of Repap.Technologies, Canada (Alcell tm ) However, in oxidising atmosphere the char yields are lower.Carbonisation and solidification with maximum surface area of the char is obtained at 350-400°C (Sharma et al. 2004).Below 300°C no significant lignin degradation occurs, but volatile products are released due to dehydration, dehydrogenation, deoxygenation and decarboxylation reactions resulting from the breaking of weaker bonds and condensation reactions (Órfão et al. 1999).At higher temperatures rearrangements take place producing volatiles (syngas: CO and H 2 ) and reactive free radicals reactions occur when also stronger bonds are broken (Ferdous et al. 2002).Phenolic components are the main volatile products that are released during the pyrolysis stage between 250-400 along Supercritical depolymerization Biorefinery processes aimed at liquefaction of lignocellulosic biomass and the extraction of valuable components for fermentation or recovery of chemicals are currently studied extensively.Different fluids were used to solubilize biomass and lignin for conversion and extraction of valuable compounds.47 47Goyal, G.C., Lora, J.H., Pye, E.K. (1992) Autocatalyzed organosolv pulping of hardwoods: effect of pulping conditions on pulp properties and characteristics of soluble and residual lignin.Tappi J.

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