Pretreatment of biomass using the OrganoCat process : characterization and valorization of product streams

• Aufschluss von Biomasse mit dem OrganoCat Prozess : Charakterisierung und Verwertung der Produktströme

Weidener, Dennis; Leitner, Walter (Thesis advisor); Schurr, Ulrich (Thesis advisor)

Aachen : RWTH Aachen University (2020, 2021)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020

Abstract

The production of bio-based fuels and fine chemicals in bio-refineries is a key step in a future bioeconomy. Sustainably grown lignocellulosic feedstocks need to be converted and fully valorized to provide a maximized sustainability. In this thesis, existing Biorefinery concepts were investigated, optimized and new pretreatment concepts for the conversion of lignocellulose were designed. They aim at producing valuable product streams that provide a high purity and should be ready to use for further applications, potentially boosting the pretreatments efficiency.The current state of the OrganoCat pretreatment, a biphasic oxalic acid catalyzed pretreatment, was evaluated and a new catalyst, 2,5-furandicarboxylic acid (FDCA) was tested. FDCA showed similar efficiency compared to oxalic acid but enables a more straightforward recovery and provides sufficient thermal stability. Both reaction systems were scaled up to 7 L, highlighting the impact of agitation, but also that comparable efficiency as in lab scale can be achieved. OrganoCat was then applied to different lignocellulosic feedstocks such as perennial plants, agricultural residues and wooden biomasses. The OrganoCat pretreatment proved to be robust and to process all provided substrates with good efficiency. To transfer the concept of OrganoCat from a batch reactor to a flow through mode, a reaction system was designed that uses a fixed bed reactor with continuous solvent flow. Similar efficiencies as in batch mode were observed when applying flow through pretreatment. Shorter reaction times, reducing contact times of solvent and catalyst, resulted in less side reactions. The flow thorugh setup showed promising results for future upscaling and application of the process.A novel approach for lignocellulose valorization was proposed, using phosphoric acid, aiming at the conversion of xylan into the platform molecule furfural, while providing high quality lignin and highly accessible cellulose pulp. Lignocellulose is swollen in phosphoric acid and afterwards treated with diluted phosphoric acid and 2-MTHF. Lignin and cellulose enriched pulp are separated and recovered to boost the economy of the process, both showing promising properties. In a second biphasic reaction step, the xylose is converted to furfural, the main product of the described process. The residual aqueous phase is concentrated, to recover the phosphoric acid for consecutive reactions. The processing efficiency was observed to be stable over four consecutive cycles. Having the potential to be a high-value feedstock, strategies for the purification and fractionation of lignin were evaluated based on its precipitation. Lignin precipitation from 2-MTHF solutions was achieved using either antisolvents or CO2 expansion of the solvent phase. The precipitation led to lignin fractions with different structures and sizes while separating furfural, formed during pretreatment. To make lignin more accessible for subsequent conversion, a depolymerization strategy was developed that aims at cleaving the β-O-4 linkage in the extracted lignin. A Mn(I) complex was used to successfully cleave the β-O-4 bond in lignin model compounds with full conversion and high selectivity.