Hydrothermal Depolymerisation of Kraft Lignin: The Influence of Capping Agents and Residence Time
Doctoral thesis, 2023
In this work, the depolymerisation of softwood kraft lignin has been investigated under hydrothermal conditions, with additions isopropanol, glycerol and guaiacol, to investigate their potential of functioning as capping agents. A customised batch reactor (99 ml) enabling swift heating of the reaction mixture was employed at 290-335 °C and 250 bar with low residence times (1-12 min).
The result of the hydrothermal depolymerisation of lignin was an aqueous suspension with a strong smoky odour. No apparent separate liquid organic phase was formed, although a char fraction precipitated. Characterisation of the products indicated a rapid depolymerisation of the lignin, since inter-unit ether linkages were cleaved, which was later followed by a slower repolymerisation. Additions of isopropanol, glycerol and guaiacol, reduced the weight average molecular weights (Mw) of the product fractions. Only isopropanol appeared to be able to reduce the amount of char formed from the lignin. Subsequent aftertreatment of the product would be required to obtain a usable product.
isopropanol
depolymerisation
capping agents
kraft lignin
glycerol
guaiacol
hydrothermal liquefaction
Author
Anders Ahlbom
Chalmers, Chemistry and Chemical Engineering, Chemical Technology
Towards understanding kraft lignin depolymerisation under hydrothermal conditions
Holzforschung,;Vol. 76(2021)p. 37-48
Journal article
Using Isopropanol as a Capping Agent in the Hydrothermal Liquefaction of Kraft Lignin in Near-Critical Water
Energies,;Vol. 14(2021)
Journal article
On the hydrothermal depolymerisation of kraft lignin using glycerol as a capping agent
Holzforschung,;Vol. 77(2023)p. 159-169
Journal article
Ahlbom A., Maschietti M., Nielsen R., Hasani M., Theliander H.; Using Guaiacol as a Capping Agent in the Hydrothermal Depolymerisation of Kraft Lignin
There has been a long-desired goal to break down, i.e. depolymerise, lignin efficiently in order to access its aromatic units: hydrothermal depolymerisation, which employs water as a reaction medium and reactant, is suggested as being suitable for this end. As the lignin is broken down, the products, which are reactive, react and form unwanted char: this can be mitigated, however, by adding chemicals known as capping agents that scavenge reactive components.
In this work, hydrothermal depolymerisation of a type of lignin available on a large scale, namely LignoBoost kraft lignin, was investigated: focus was placed on the effect of adding capping agents as well as on short residence times in the reactor. Not only was it shown that adding isopropanol can reduce the amount of char formed as well as its molecular weight, and thus function as a capping agent, but also that bonds in the lignin structure break swiftly, i.e. the depolymerisation process appears to be very rapid. As such, this work is part of endeavours to valorise lignin.
Från lignin till biobränslen och specialkemikalier
Swedish Energy Agency (45395-1), 2018-01-01 -- 2021-12-31.
Subject Categories
Chemical Engineering
Infrastructure
Chalmers Materials Analysis Laboratory
ISBN
978-91-7905-808-1
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5274
Publisher
Chalmers
VasaA Lecture Hall, Vera Sandbergs Allé 8
Opponent: Prof. Lasse Rosendahl | The Faculty of Engineering and Science, AAU Energy | Aalborg University, Denmark