A Study on Preservation Treatment of Waterlogged Wood by Supercritical Drying

本文从化学工程的角度研究了超临界干燥技术在湿材防腐中的应用和PEG浸渍法的应用。PEG浸渍法：我们已经基于扩散模型对PEG浸渍法进行了分析，发现可以通过扩散模型预测处理时间。在这项研究中，我们发现木材种类，木材结构，温度，和PEG浓度对浸渍率的影响。进一步研究了木材干燥后的收缩率，发现当PEG的质量分数大于74%时，木材的体积收缩率小于5%。超临界干燥：采用二氧化碳作为超临界流体。由于木材在水-二氧化碳体系中的互溶度小，因此先用乙醇置换木材中的水，再用乙酸异戊酯置换乙醇。本文对乙醇和乙酸异戊酯的渗透速率进行了测定和分析 ...更多信息 d的基础上的扩散模型，以估计有效扩散系数。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-水体系的基本相同。因此，无论木材种类如何，在25 ° C下，两种系统的有效扩散系数均为0.3平方厘米/天。乙酸异戊酯在超临界二氧化碳中的分子扩散系数预计为11.5 cm^2/天。在这种情况下，有效扩散系数取为5.06 cm^2/天，这是分子扩散系数的44%，与乙醇-水系统的情况相同。预测PEG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PEG浸渍方法的四分之一。最后，测量木材干燥后的收缩率。超临界干燥后的体积收缩率小于20%，假设木材的各向同性收缩率为7%。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