Lignin as a renewable aromatic resource for the chemical industry (2011)

5-513 3 4-O-5 3 3nds to 1-position 1-3 3 Technical lignin types and their availabilityThe variation in technical lignin structure is partly caused by the botanical origin of the polyphenol but equally important is the method of extraction (Lora et al. 2008; Lora and Glasser 2002).Common pulping processes used for the extraction of lignin from lignocellulosic raw materials for the production of paper are listed below.The worldwide availability of technical lignins is presented in Table 1.3. Kraft pulping processThe most common chemical pulping process of wood today is the sulfate or kraft pulping process, a process using sodium sulfide under alkaline conditions.The lignin is partly cleaved and thiol groups were introduced at the -position of the propane side chain (Figure 1.8) resulting in a solubilized lignin.Kraft pulp mills have evolved in large efficient integrated facilities in which the recovery of pulping chemicals and 19 19 lignin is recovered by an alternative recovery process by acid precipitation, maturation and filtration giving novel types of sulfur-free lignin (Abcherli and Doppenberg 1998; Abcherli 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).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 350-400C (Sharma et al. 2004).Below 300C 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 (rfo 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 Hydrodeoxygenation (HDO)In the early 80's kraft lignin was converted in a two-step "Lignol" process including hydrocracking and hydrodealkylation over an catalyst bed in hydrogen into 20% phenol and 14% benzene (Huibers and Parkhurst 1982).This process was highly selective but Supercritical depolymerizationBiorefinery 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.is the production of monomeric phenolic compounds and these depolymerized aromatic chemicals are soluble in CO 2 .By selection of a CO 2 based fluid separation of the residual lignin and the produced mono-and oligomeric aromatic compounds can be accomplished.In this novel process the aromatic products were separated from insoluble residual lignin fragments and char by adiabatic pressure release.