Pre-Extraction of Wood Components Mild hydrothermal methods for a future materials biorefinery
Doktorsavhandling, 2020

Today there is an increasing urgency in discovering new, and more sustainable, replacements for fossil-based materials and chemicals. The biorefinery concept is promising in this context in that it relies on transforming biomass into a spectrum of commercial products. Wood is the primary bioresource in Scandinavia. It is mostly processed in the kraft pulping process used in the huge and important pulp and paper industry, thereby providing a suitable platform for future material biorefineries. This process allows for the efficient separation of lignin and cellulose, along with the option of adding a pretreatment step for the recovery of hemicelluloses.

Among existing pretreatments, mild hydrothermal methods, such as hot water extraction and steam explosion, are promising since they allow recovery of hemicelluloses with minimal degradation. They are based on the acidic hydrolysis (autohydrolysis) of wood components and diffusive transport through the wood tissue. In steam explosion, the latter is enhanced by the advective transport in the pore system of the wood caused by the rapid release of the pressure. The focus of this work was to explore the possibility of using steam explosion and hot water extraction on different types of forest biomass, as well as to improve understanding of the underlying mechanisms.

Performed in different experimental set ups, the work included determining the local composition of wood chips pretreated in different ways, continuous extraction of spruce and birch wood meal and a stepwise treatment of forest residues. The influence of autohydrolysis on the wood components, hemicelluloses (decreasing molar weight, deacetylation, cleavage of side groups, extraction and degradation), lignin (partial degradation and extraction) and cellulose (introduction of chain scissions) was analyzed. Moreover, the mechanism of acidification and the contribution of acetic acid were also investigated. The variations in the local composition of the wood chips obtained by steam explosion and hot water extraction were determined and related to the differences in mass transport and severity of the treatment. Finally, it was shown that the impact of steam explosion had a limited effect on refined wood residues, likely due to the relatively small size of the material.


forest residues



soda cooking

hot water extraction

steam explosion



kraft cooking

KB-salen, Kemigården 4, Göteborg
Opponent: Prof. Mats Galbe


Joanna Wojtasz-Mucha

Chalmers, Kemi och kemiteknik, Kemiteknik

Dissolution of wood components during hot water extraction of spruce

Tappi Journal,; Vol. 22(2023)p. 329-343

Artikel i vetenskaplig tidskrift

Dissolution of wood components during hot water extraction of birch

Wood Science and Technology,; Vol. 55(2021)p. 811-835

Artikel i vetenskaplig tidskrift

Pretreatment and Cooking of Forest Residues

BioResources,; Vol. 14(2019)p. 9454-9471

Artikel i vetenskaplig tidskrift

Hydrothermal pretreatment of wood by mild steam explosion and hot water extraction

Bioresource Technology,; Vol. 241(2017)p. 120-126

Artikel i vetenskaplig tidskrift

In Scandinavia the most abundant bioresource is wood. Today it is the main raw material  for the large and important industry producing sawn timber as well as pulp and paper. These are products needed in the future, but wood consists of various components that when separated can be transformed into spectrum of various products in a biorefinery.

Wood has a complex chemical and morphological structure and is resistant toward separation of its structural elements (i.e. cellulose, lignin and various hemicelluloses).  The most used separation process today is the kraft process, with this process the cellulose is separated from the lignin, but at the same time most of the hemicelluloses are broken down despite them being an attractive feedstock for future materials.  In order to combine production of paper pulp and biorefinery products an additional step enabling recovery of hemicelluloses prior to pulping in needed.

Among the existing pretreatments mild hydrothermal methods are promising, as they allow recovery of hemicelluloses with minimal degradation. The focus in this work was on investigating the possibility of using two of such methods, namely hot water extraction and steam explosion, on different types of forest biomass. Both of those methods rely on hot water causing a self-mediated partial degradation  of the hemicelluloses  (autohydrolysis) and transport of the solubilized structures  out of the wood tissue. The steam explosion involves also a rapid pressure release that stimulates the transport.

The wood meal, wood chips and mixed forest residues were pretreated in different experimental set-ups and the resulting structural changes  were analysed by a variety of characterization methods. The results include improved knowledge on: the course of autohydrolysis in the cell wall,  variation in the local composition of the pretreated wood chips , and pretreatment impact on  the pulping of  forest residues.


Hållbar utveckling





Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4800



KB-salen, Kemigården 4, Göteborg


Opponent: Prof. Mats Galbe

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