A Study on Preservation Treatment of Waterlogged Wood by Supercritical Drying

本文从化学工程的角度出发，对超临界干燥技术在浸渍木材保鲜中的应用和聚乙二醇浸渍方法进行了研究。聚乙二醇浸渍方法：基于扩散模型对聚乙二醇浸渍过程进行了分析，发现可以通过该模型预测浸渍时间。在这项研究中，我们发现了木材种类、木材结构、温度和聚乙二醇浓度对浸渍速率的影响。此外，我们对木材干燥后的收缩进行了研究，发现当聚乙二醇的质量分数大于74%时，木材的体积收缩小于5%。超临界干燥：以二氧化碳为超临界流体。由于木材在水-二氧化碳体系中的互溶度较小，所以用乙醇代替木材中的水，然后用乙酸异戊酯代替乙醇。在本工作中，测量了乙醇和乙酸异戊酯的渗透速率，并分析了…更多地基于扩散模型来估计有效扩散系数。乙醇-水体系的有效扩散系数为分子扩散系数的44%。乙酸异戊酯-乙醇体系的有效扩散系数与乙醇-水体系的有效扩散系数相当。结果发现，在25ﾟC下，这两个系统的有效扩散系数为0.3cm2/天，与木材种类无关。预测了乙酸异戊酯在超临界二氧化碳中的分子扩散系数为11.5cm2/d。在这种情况下，有效扩散系数取为5.06 cm~2/d，是分子扩散系数的44%，与乙醇-水体系相同。预测了聚乙二醇浸渍和超临界干燥方法的处理时间，发现超临界干燥方法所需的时间是聚乙二醇浸渍方法的四分之一。最后，测定了木材干燥后的干缩率。超临界干燥后的体积收缩小于20%，假设木材各向同性收缩，则体积收缩长度为7%。较少

In the present study, application of supercritical drying to preservation of waterlogged wood and PEG impregnation method were investigated from the view poit of chemical engineering.PEG impregnation method : We have already analyzed the impregnation with PEG based on the diffusion model and found that the processing time can be predicted through the model. In this study, we found the effects of wood species, wood structure, temperature, and PEG concentration on the impregnation rate. Further, we investigated the shrinkage of woods after drying and found that the volumetric shrinkage is lower than 5% if the concentration of PEG is larger than 74% in mass fraction.Supercritical drying : Carbon dioxide was used as the supercritical fluid. Since the mutual solubility in water-carbon dioxide system is small, water in the wood was replaced by ethanol and then the ethanol was replaced by isoamyl acetate. In this work, penetration rates of ethanol and isoamyl acetate were measured and analyze … More d based on the diffusion model to estimate effective diffusion coefficients. The effective diffusion coefficient was 44% of the molecular diffusion coefficient for ethanol-water system. For isoamylacetate-ethanol system the effective diffusion coefficient was about the same as that for the ethanol-water system. Consequently, the effective diffusion coefficients for the both systems were found to be 0.3 cm^2/day at 25ﾟC,regardless of wood species. The molecular diffusion coefficient of isoamylacetate in supercritical carbon dioxide was predicted to be 11.5 cm^2/day. In this case, the effective diffusion coefficient was taken to be 5.06 cm^2/day which is 44% of the molecular diffusion coefficient, as in the case of ethanol-water system. Predicting the processing times for both of the PEG impregnation and supercritical drying methods, the time required for the supercritical drying method was found to be a quarter of that for the PEG impregnation method. Finally, the shrinkage of wood after drying was measured. The volumetric shrinkage after supercritical drying was less than 20%, which is 7% in length assuming isotropic shrinkage of wood. Less