A review of Scion research using supercritical carbon dioxide

Authors: Bernard Dawson
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 2019, Issue N.Z.J.For. 64(3) 2019, pp 8-12, Nov 2019
Publisher: New Zealand Institute of Forestry

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Abstract: Scion has researched the application of supercritical CO₂ to remove water from timber. For CO₂ to become a supercritical fluid, a pressure of 7.4 MPa and a temperature of 31°C is required. Timber species that have been treated include a range of New Zealand softwoods and hardwoods, with radiata pine being most widely studied. Supercritical CO₂ offers advantages of being less energy intensive than thermal drying, it leaves no residue as the fluid reverts to gas below 7.4 MPa, and it can penetrate wet timber as a consequence of high pressure. Supercritical CO₂ can be used to remove water in radiata pine down to about 40% cycling from gas to supercritical fluid multiple times. At this moisture content chemicals or fluids can be added to radiata pine without water (sap) in the cell lumens to improve or add properties such as stiffness or decay resistance. For difficult-to-dry collapse-prone hardwoods, such as eucalypts, dewatering prevents timber collapse and has the potential to increase conversion rates from green timber into product. Following the supercritical CO₂ dewatering process, a kiln drying schedule will be required to achieve a moisture content of 10-14% in the timber. However, the effect of the supercritical CO₂ dewatering process is retained and collapse will not occur on kiln drying.

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