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Lignin is a renewable and abundant source for production of bio-based chemicals and is a valuable alternative to crude oil to obtain aromatic building blocks. It is built from aromatic units with strong chemical linkages, which need to be cleaved to enable the use of the aromatic compounds in industrial applications. In addition to depolymerizing lignin, efficient fractionation and conversion of the resulting complex mixtures is an essential step in the valorization of lignin derivatives for different applications. In this work, we studied the separation of a lignin oil obtained by catalytic cleavage in supercritical ethanol (scEtOH) of technical lignin produced by means of soda pulping of wheat straw. The use of six commercial polymeric nanofiltration (NF) membranes and one in-house developed Grignard-functionalized ceramic membrane was investigated for the fractionation of a mixture of lignin derivatives. Separation by molecular weight (MW) was observed with the polymeric NP030 membrane but not with the other membranes tested. The development of a protocol using this membrane in the diafiltration mode for fractionation of crude lignin oils (CLOs) is discussed.

We optimized the solvolysis step in methanol for two-step lignin-first upgrading of woody biomass. Birchwood was first converted via sulfuric acid methanolysis to cellulose pulp and a lignin oil intermediate, which comprises a mixture of lignin oligomers and C5 sugars in the methanol solvent. The impact of reaction temperature (140–200 °C), acid loading (0.24–0.81 wt%, dry biomass), methanol/biomass ratio (2.3/1–15.8/1 w/w) and reaction time (2 h and 0.5 h) was investigated. At high biomass loadings (ratio &lt, 6.3/1 w/w), operation at elevated pressure facilitates delignification by keeping methanol in the liquid phase. A high degree of delignification goes together to a large extent with C5 sugar release, mostly in the form of methyl xylosides. Gel permeation chromatography and heteronuclear single quantum coherence NMR of lignin fractions obtained at high acid (0.81 wt%) and low biomass (15.8/1 w/w) loading revealed extensive cleavage of β-O-4′ bonds during acidolysis at 180 °C for 2 h. At an optimized methanol/biomass ratio of 2.3/1 w/w and acid loading (0.24 wt%), more β-O-4′ bonds could be preserved, i.e., about 33% after 2 h and 47% after 0.5 h. The high reactivity of the extracted lignin fragments was confirmed by a second hydrogenolysis step. Reductive treatment with Pd/C under mild conditions led to disappearance of ether linkages and molecular weight reduction in the hydrotreated lignin oil.

The thermal profile of solvent liquefaction experiments must be well-controlled to generate data suitable for process scaling and technoeconomic analysis. Acknowledging the differences in small-scale batch systems compared to continuous commercial processes is important. In particular, many experiments have long heating and cooling periods, which influence rates of reaction in ways that would not occur in commercial continuous reactors. To overcome this problem, a novel semi-batch autoclave (SBA) system was built to rapidly heat reactants and cool products while maintaining constant pressure during solvent liquefaction experiments. In this study, the performance of the SBA reactor was compared to an isobaric conventional batch autoclave (ICBA) reactor in the solvent liquefaction of lignin in n-butanol. Heat transfer affected both the apparent reaction rate and measured product yields. Solvent liquefaction limited by slow heating gave the misperception that reaction rates were faster than was actually the case and promoted the formation of char-like solids. Experiments constrained by slow heat transfer are of limited use in process modeling and reactor design, which would otherwise result in undersized reactors for desired processing rates. The SBA system facilitates the design and scale-up of commercial SL plants as it approximates the thermal profile of a continuous system.

Much scientific research has been carried to convert lignin into valuable biobased chemicals or fuels. Most of these studies had the objective to develop active and selective catalysts for effective lignin depolymerization; this with little regard for the parameters that are necessary for later commercialization of these technologies. In this work, we have chosen as a case study a process that has been extensively studied and reported on earlier by our group. This process converts (technical) lignin into mainly aromatic compounds, using supercritical ethanol and a Cu–Mg–Al mixed oxide catalyst. Here, we investigate the impact of scaling up this process from lab to bench scale. More specifically, we study the influence of higher lignin loadings than previously reported on, amongst other parameters, monomer yield, solvent losses and catalyst fouling; all of which being critical performance parameters for industrial operation. After we examined the technical feasibility of our process at 4 L scale, we further looked into the economic viability of this technology, by introducing two performance criteria, both of which being a function of lignin monomer yield. The ratios (g/g) of yield over total feed, and yield over ethanol losses are presented as qualitative indicators for capital expenditure (CAPEX) and operational expenditure (OPEX), respectively. This exercise sheds some much needed light on the trade-off between yield optimization and cost minimization.