THE REMOVAL OF WOOD COMPONENTS FROM HARDWOOD BY HOT WATER

THE REMOVAL OF WOOD COMPONENTS FROM HARDWOOD BY HOT WATER

By Rory Jara

Thesis Advisor: Dr. Adriaan R.P. van Heiningen

An Abstract of Thesis Presented

in Partial Fulfillment of the Requirements for the

Degree of Doctor of Philosophy

(in Chemical Engineering)

December, 2010

Hot-water extraction of hemicelluloses from wood is a promising technology in the integrated biorefinery concept. A particular case is where the pulp industry makes co-products such as ethanol and acetic acid besides pulp thereby maximizing the value of biomass. Similarly, the oriented strand board (OSB) industry appears to be suitable for this technical approach as it is composed of large centralized facilities.Many studies have been carried out on the kinetics and mechanism of hot-water extraction of lignocellulosics. However, most of these studies were performed in batch reactors which are not best suited to determine intrinsic kinetics of hemicellulose dissolution because of further reaction of the hemicelluloses in solution.

As a first approach to study the extraction yield for hydrothermal treatments on red maple (Acer rubrum) strands, a batch reactor (ASE-100, Dionex) was used. A complete mass balance on extracted wood and wood extracts has been obtained by determining cellulose, hemicellulose, and lignin content on both solid and liquid phases at different extraction temperatures and times, described by a combined parameter called the P-factor. In addition, a study was completed of the molecular weight distribution of dissolved polysaccharides in the liquid phase and of cellulose in the solid phase.

In the second part of this work a continuous mixed batch reactor was used to obtain the intrinsic kinetics of dissolution of hemicelluloses from hardwood (Acer rubrum) at three different temperatures (150°C, 160°C, and 170°C) and four constant pH values: 2, 3, 4 and 5. Wood-meal and a high flow rate (100 mL/min) were used to avoid mass transfer limitations during dissolution of the hemicelluloses. An improved mechanism for xylan dissolution is proposed which is in agreement with recent knowledge of the topochemistry of hardwood fibre cell walls. Finally, it is shown that a modified P_H-factor can describe the effect of pH and time and temperature on xylan dissolution during pH-controlled hot water extraction of red maple wood.