Title : Applying unreacted-core model analysis for delignification during a water/1-butanol co-solvent treatment
Abstract:
Lignocellulose is attractive as carbon resource for substituting fossil resource because of their carbon neutrality. In utilizing lignocellulose, fractionation of its components, such as cellulose, hemicellulose, and lignin, is necessary to accomplish high valuable use of them. Cellulose and hemicellulose are polysaccharides, and lignin is polymer of alkyl phenols. As usual, the fractionation is carried out by kraft method, in which lignin and hemicellulose is removed, but the strong base employed in the method converts lignin into residual material, which is difficult to be depolymerized and utilized as high-value added products. Thus, novel technique for the fractionation is desired for utilization of lignin. On the other hand, our previous study revealed that lignocellulose could be fractionated via water/1- butanol co-solvent treatment at around 473 K. Lignin with less structure changes is recovered in the treatment compared with that from kraft method, so the co-solvent treatment is expected the novel fractionation technique. In present work, we tried to analyse kinetics of delignification of cedar wood during the co-solvent treatment by applying unreacted- core model. This model is used to express situations in which solid particles are being consumed by reactions with forming product layer, and the amount of the reactant material being consumed is shrinking, and the model used for predicting the rate-controlling step, such as reaction on the unreacted core, diffusion of the product molecule within the product layer (remained cellulose layer) between unreacted core and film, and diffusion of the molecule within the film. As a result, the diffusion within the remained cellulose layer was indicated to be the rate-controlling step. Moreover, the result was could be supported by following results; there were no isotope effect on hydrolysis of lignin and no rotation speed effect on the delignification. These results mean the reaction and diffusion within film were not rate- controlling step. On the other hand, the size of lignin molecule obtained the delignification was approximately 3.8 nm and the pore size of remained cellulose layer was 3-10 nm, indicating diffusivity of the molecule within the layer seemed to be enough low that the diffusion step could be the rate-controlling step.
