Spruce Hemicellulose for Chemicals Using Aqueous Extraction: Kinetics, Mass Transfer, and Modeling Jussi V. Rissanen, † Henrik Gre ́ nman,* ,† Stefan Willfö r, ‡ Dmitry Yu. Murzin, † and Tapio Salmi † † Laboratory of Industrial Chemistry and Reaction Engineering, Process Chemistry Centre, Department of Chemical Engineering, Åbo Akademi University, Biskopsgatan 8, FI-20500 Åbo/Turku, Finland ‡ Laboratory of Wood and Paper Chemistry, Process Chemistry Centre, Åbo Akademi University, Porthansgatan 3, FI-20500 Åbo/Turku, Finland ABSTRACT: Pressurized hot water extraction of hemicelluloses from spruce sapwood was studied at 120-170 °C using a batchwise-operated cascade reactor, which enables precise sampling as well as very accurate and rapid temperature control. The extraction was performed under identical conditions for two different chip sizes, a 1.25-2.0-mm sieved fraction and handmade 10-mm cubic blocks, to evaluate the influence of chip size on the overall extraction kinetics. The results showed that the extraction rate increases significantly with temperature and that the pH decreases during the extraction, as a result of the liberation of acid groups. The concentration of hydronium ions in the liquid phase was observed to have a linear correlation with conversion depending, however, on the chip size, which shows that the mass transfer of the acid groups differs significantly from that of the bulky hemicelluloses. It also shows that significant amounts of acetyl groups are liberated inside the chips before the hemicelluloses enter the liquid phase, as the slopes would otherwise be identical. The extraction temperature did not influence the selectivity of dissolution significantly, which means that temperature cannot be used to influence the sugar composition of the obtained liquid phase. Mathematical modeling was performed on the overall extraction data using a simple first-order model, which corresponds to porous solid particles. An excellent fit of the model to the experimental data was obtained. The activation energy was determined to be about 120 kJ mol -1 for both chip sizes even though the reaction rates differed significantly, wheeras the pre-exponential factor was substantially lower for the larger chips. This somewhat surprising result can be explained by the fact that the diffusion inside the chips differs because of changes in viscosity and not only distance. The results contribute to the quantitative and qualitative understanding of the extraction process and shed light on the correlation of the experimental parameters used during extraction. 1. INTRODUCTION: SEPARATION OF HEMICELLULOSES In the biomass-based industry, the novel biorefinery concept has increased interest in utilizing the large resources of available biomass in new ways. Wood is one of the largest available resources being utilized industrially at present. In recent years, various carbon-neutral processes have been increasingly studied. The main components of biomass, namely, cellulose, hemicelluloses, and lignin, can be utilized for various purposes because of their different reactivities. 1 Norway spruce (Picea abies), also referred to as European spruce, covers considerable parts of central and northern Europe, as well as vast areas in Russia. This wide distribution, combined with its unique properties, makes spruce one of the corner stones of the biobased industries in Europe today. Spruce is mainly utilized for the production of pulp and sawn timber. In the pulp industry, the cellulose and part of the hemicelluloses are used for pulp production, and the remaining fraction, consisting mainly of hemicelluloses and lignin, is commonly burned for energy production. The basic goal of the modern biorefinery concept is the versatile utilization of all of the different wood fractions to obtain a diversified value-added product portfolio. In addition to the further processing of the versatile hemicelluloses, the valorization of lignin and utilization of cellulose for dissolving pulp, for example, is crucial for obtaining sustainable economics in the overall process. However, to be able to make use of the different properties of all of the main fractions, separation needs to be performed, and the separation kinetics/thermodynamics must be under- stood for the success of the process. The production of biofuels is a rapidly growing field. Industry already produces ethanol and some other alcohols by fermentation, and new alternative routes for fuel production are emerging at an increasing pace. 2 In alcohol production, wood-based hemicelluloses are hydrolyzed to sugar monomers before the fermentation step. 3-6 In addition to fermentation, the monomeric sugars obtained from the hemicelluloses can be utilized as platform molecules for the production of value- added chemicals, for example, through oxidation, hydro- genation, and dehydrogenation to further conversion steps. 7 Oligomeric hemicelluloses are desired for various applications outside the field of fuel production; for example, spruce-derived galactoglucomannan (GGM), the main hemicellulose in spruce, has the potential to be utilized in a wide assortment of products, ranging from the food industry to cosmetics, fine chemicals, and biocomposites. 8-10 Received: January 17, 2014 Revised: March 20, 2014 Accepted: March 21, 2014 Published: March 21, 2014 Article pubs.acs.org/IECR © 2014 American Chemical Society 6341 dx.doi.org/10.1021/ie500234t | Ind. Eng. Chem. Res. 2014, 53, 6341-6350