Aqueous extraction of hemicelluloses from spruce--From hot to warm.

Aqueous extraction of hemicelluloses from spruce sapwood was performed at 90°C and 110°C. One of the main goals was to study if the same reaction mechanisms are valid at low temperatures as the ones observed previously at higher temperatures. An intensified cascade reactor system with a high liquid-solid ratio (∼ 180) was used in the experiments. Differences between the sugar specific extraction rates were observed especially in the beginning of the extraction processes. The experimental results fitted well to a kinetic model developed at higher temperatures, which confirms that the dissolution occurs with the same mechanisms at low temperature. Moreover, the correlation of the pH with the amount of sugars dissolved concurred with previous observations. The results contradict the assumption that low temperature dissolution would not occur and they help in studying the early stages of extraction as the kinetics are considerably slowed down.