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Investigation of the reaction mechanism of a carbocation scavenger with lignin during autohydrolysis pretreatment
In this the project, the reaction behaviour of lignin and the carbocation scavenger 2-naphthol is investigated. This will be studied on the basis of selected lignin model compounds.
Second generation biofuels (e.g. bioethanol) produced from lignocellulosic materials like wood or agricultural residues, show energetic, economic and environmental advantages in comparison to biofuels from starch or sugar. However, physical and chemical barriers caused by the entanglement of the main components of lignocellulosic biomass hinder the enzymatic hydrolysis of cellulose and hemicellulose to fermentable sugars. Therefore, pretreatment steps aim at breaking down the lignin structure and disrupting the crystallinity of cellulose to enhance enzyme accessibility to the cellulose. A possible pretreatment of lignocellulosic biomass is a hot water pretreatment, which can provoke alterations in the structure of lignocellulose. The difficultiy in this processing, however, are repolymerisation reactions of lignin fragments, which are formed during the pretreatment and hinder the desintegration of the wood structure. This can be prevented by carbocation scavengers that can suppress the repolymerisation reactions. We could already show that this approach enhances the pretreatment and greatly increases the enzymatic digestibility of the cellulose1. Nevertheless, the detailed reaction mechanism/path of the carbocation scavenger reacting with lignin has still to be elucidated. Since natural lignin structures are complex and difficult to isolate, reaction mechanisms are often studied with specific model compounds for lignin.
Second generation biofuels (e.g. bioethanol) produced from lignocellulosic materials like wood or agricultural residues, show energetic, economic and environmental advantages in comparison to biofuels from starch or sugar. However, physical and chemical barriers caused by the entanglement of the main components of lignocellulosic biomass hinder the enzymatic hydrolysis of cellulose and hemicellulose to fermentable sugars. Therefore, pretreatment steps aim at breaking down the lignin structure and disrupting the crystallinity of cellulose to enhance enzyme accessibility to the cellulose. A possible pretreatment of lignocellulosic biomass is a hot water pretreatment, which can provoke alterations in the structure of lignocellulose. The difficultiy in this processing, however, are repolymerisation reactions of lignin fragments, which are formed during the pretreatment and hinder the desintegration of the wood structure. This can be prevented by carbocation scavengers that can suppress the repolymerisation reactions. We could already show that this approach enhances the pretreatment and greatly increases the enzymatic digestibility of the cellulose1. Nevertheless, the detailed reaction mechanism/path of the carbocation scavenger reacting with lignin has still to be elucidated. Since natural lignin structures are complex and difficult to isolate, reaction mechanisms are often studied with specific model compounds for lignin.
The main objective of this thesis is to elucidate the reaction behaviour of lignin with the carbocation scavenger 2-naphthol. This will be studied on the basis of selected lignin model compounds. Autohydrolysis will be studied in a multi reactor system in our laboratory. For the analysis of the reaction products a GC/MS system and NMR spectroscopy will be used.
The specific tasks of the thesis are:
- Literature study and selection of appropriate lignin model compounds
- Autohydrolysis experiments with different model compounds with and without scavenger
- Analysis of the reaction products by GC/MS and NMR
- Evaluation of the results and assessment of the reaction path by the aid of reaction products
The main objective of this thesis is to elucidate the reaction behaviour of lignin with the carbocation scavenger 2-naphthol. This will be studied on the basis of selected lignin model compounds. Autohydrolysis will be studied in a multi reactor system in our laboratory. For the analysis of the reaction products a GC/MS system and NMR spectroscopy will be used.
The specific tasks of the thesis are:
- Literature study and selection of appropriate lignin model compounds
- Autohydrolysis experiments with different model compounds with and without scavenger
- Analysis of the reaction products by GC/MS and NMR
- Evaluation of the results and assessment of the reaction path by the aid of reaction products
Christoph-Maximilian Seidel
ML H14
044 632 24 99
seidel@ipe.mavt.ethz.ch
Christoph-Maximilian Seidel ML H14 044 632 24 99 seidel@ipe.mavt.ethz.ch
MA_modelcompound.pdf
