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Coupling refining, chemical and enzymatic treatments for improved purification and dissolution of cellulose

Published on April 21, 2022
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PhD Defense March 11, 2022

Gloria Ifunanya Ngene, doctoral student at LGP2, defended her thesis: "Coupling refining, chemical and enzymatic treatments for improved purification and dissolution of cellulose".

This doctoral thesis was prepared at the University of Grenoble Alpes under the supervision of Professor Jean-Claude Roux and Professor Emeritus Dominique Lachenal (Grenoble INP-Pagora / LGP2).

Gloria Ifunanya Ngene presented the results of her research entitled Coupling refining, chemical and enzymatic treatments for improved purification and dissolution of cellulose.
In this study, mechanical refining was used in conjunction with cold caustic extraction and xylanase treatments. The purpose was to increase the accessibility of chemical and enzymatic agents in the hard-to-reach regions of the fiber for more complete xylan extraction and to improve the reactivity of the pulp to dissolution.

The first part examined the morphological changes resulting from mechanical refining with three different technologies (Valley beater, PFI and pilot disc refiner) and the impact on the elimination of hemicelluloses when performing CCE and xylanase treatments. A good correlation between the modification of fibers induced by refining, namely the increase in the water retention value (WRV), the increase in the specific surface, the shortening of fibers, the generation of fines, and the CCE performance was found.  At a soda concentration of 100 g/L, the xylan removal for the Valley beater, PFI, and disc refined pulp were 84%, 82%, and 79%, respectively. This corresponds to 3.3%, 3.6%, and 4.3% residual xylan in the extracted pulp, starting from 20% in the reference paper pulp. Roughly, residual xylan was 50% less in refined pulp compared to unrefined pulp. In terms of upscaling, it was determined that though the laboratory refiners performed slightly better than the industrial-like refiner, the difference was marginal. Therefore, the risks associated with upscaling would be minimal in this process.

In order to further improve the CCE extraction performance, certain strategies were examined in the second part of this study. The most promising was to perform simultaneous refining / CCE with the Valley beater and the PFI refiners. The response of residual xylan in the pulp to simultaneous refining / CCE was already high at 60 g /L NaOH, with for example a xylan reduction of 79% for the Valley beater. This strategy makes it possible to achieve a good xylan extraction without formation of cellulose II

In the third part of this thesis, the influence of the hemicellulose elimination treatment on the reactivity of the resulting pulp was studied. Reactivity was evaluated on the basis of the degree of swelling in NaOH and dilute cupriethylene diamine solution (CUEN), the solubility in 8% NaOH at -10 ° C and the Fock measurement. The result obtained showed that hemicellulose removal strategies that included mechanical refining led to better pulp reactivity than unrefined pulp. The best result was obtained with the refined pulps extracted with 6% soda (no cellulose II formed in the pulp). In addition, we obtained a Fock reactivity ranging from 60 to 70% which exceeded that obtained for reference prehydrolysis kraft dissolving pulp . The good correlations found between swelling measurements, solubility in caustic soda, and Fock reactivity suggest that the tedious Fock test could be substituted by the much simpler swelling and solubility measurements.

In the last part of this study, the xylans recovered from the CCE treatment of unrefined and refined pulps at 6% and 10% NaOH concentrations were characterized. The average DPn ranged from 70 to 177. The DP of xylan extracted from the pulp after refining was higher than for the unrefined pulp.

In conclusion, the results obtained in this study show that the production of dissolving grade pulp from conventional hardwood kraft pulp is feasible with the use of existing technologies (refining, CCE). This represents a major advantage since a kraft pulp mill may easily shift from paper pulp to dissolving pulp production and vice versa, depending on the market conditions.
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Date of update April 21, 2022

Université Grenoble Alpes