Multi-scale analysis of liquid-based pretreatment in lignocellulosic biorefineries

  • Multiskalen-Analyse von flüssigkeitsbasierter Vorbehandlung in Lignocellulose-Bioraffinerien

Marks, Caroline; Mitsos, Alexander (Thesis advisor); Hallett, Jason (Thesis advisor)

Aachen : RWTH Aachen University (2021, 2022)
Book, Dissertation / PhD Thesis

In: Aachener Verfahrenstechnik series AVT.SVT - Process systems engineering 21 (2022)
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2021

Abstract

To reduce CO2 emissions, fossil-carbon-based fuels and chemicals can alternatively be produced from renewable carbon sources such as lignocellulosic biomass. The material conversion of biomass requires a pretreatment to cleave the composite-like structure of biomass, often followed by enzymatic hydrolysis to make sugars available for further processing. However, the mechanisms of liquid-based pretreatment concepts are not yet completely understood. Especially the role of the various mixtures of solvents and ions that are applied as pretreatment liquids remains unclear in many cases. In this thesis, pretreatment of biomass is investigated on multiple scales: from the molecular scale with interactions between components of pretreatment liquids to the process level with the influence of sugar yield on the production pathway performance of biofuels. In combination with enzymatic hydrolysis, the ionic liquid 1-ethyl-3-methylimidazolium acetate (EMIMAc) effectively pretreats and disintegrates beech wood, but sugar yields decrease with increasing water content in EMIMAc. In this work, molecular interactions between EMIMAc and water are characterized using low-field NMR spectroscopy and deuterated solvents. Model-based evaluation of the observed hydrogen-deuterium exchange allows for the determination of the underlying kinetics. Composition-dependent changes of exchange kinetics imply that strongly associated ion networks remain active down to 30 mol % EMIMAc. Hence, this investigation presents a first step towards the understanding of the effect of water in mixtures of EMIMAc. Analogously to EMIMAc pretreatment, acetic acid-based acetosolv pretreatment can effectively disintegrate beech wood, albeit with lower sugar yields. The experiments conducted for this thesis reveal that pretreatment phenomena such as the newly defined degree of disintegration and the non-recovered fraction of wood after pretreatment are not only interdependent but also relate to the type and concentration of catalyst acid in the pretreatment liquid. Furthermore, disintegration and non-recovered fraction correlate with the composition of pretreated biomass. Unlike with EMIMAc pretreatment, the presence of water in acetosolv pretreatment liquids facilitates both disintegration and delignification. To evaluate the influence of the effectiveness of both pretreatment and hydrolysis on the production pathway performance of two biofuels, carbon loss and fuel cost are estimated with reaction network flux analysis. The analysis of changing biomass composition in combination with pretreatment-specific fractionation effectiveness and sugar yield after hydrolysis shows that fuel cost and carbon loss correlate reciprocally. Below a threshold of 40 wt % sugars from wood, fuel costs increase strongly. Hence, this value describes the minimal viable sugar yield of biomass pretreatment.

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