【作者】 姚明辉；

【导师】 银建中；

【作者基本信息】 大连理工大学 ， 化工过程机械， 2012， 硕士

【摘要】 超临界流体萃取技术和膜分离技术是现代化工分离技术中倍受关注的新技术,将二者耦合有利于回收高压超临界流体、强化膜分离过程以及应用于超临界膜反应器等。目前,对于超临界流体在多孔膜内的渗透扩散机理研究并不多,因此,通过实验研究以及建立模型计算对此进行深入研究是非常有必要的。(1)为了避免传统焙烧法产生的大裂纹缺陷,本文首先用超临界萃取的方法脱除模板剂制得MCM48复合膜。之后在温度40-100℃,压力1-12MPa条件下,考察二氧化碳在介孔膜(MCM48复合膜,有效分离层理论孔径2.6nm)和大孔膜(商业化陶瓷管膜,平均孔径50nm)内的渗透扩散行为。实验发现,虽然孔径差别较大,但是温度和压力对于二氧化碳在两种膜内的渗透扩散行为的影响极为相似。压力和温度对渗透通率都有显著的影响,在低压区域二氧化碳的渗透通率随压力成线性变化；随着压力增加,渗透通率的变化率增大,特别是在临界点附近的增加更加明显；在高压区随着压力的增加,渗透通率的变化不太显著,特别是在低温区,渗透通率随着压力的增加不再增加甚至有下降趋势。(2)在实验的基础上,对二氧化碳在膜内的渗透扩散只考虑努森流和粘性流,忽略表面扩散的影响,建立理论模型对实验结果进行预测和拟合。由于二氧化碳在高压区粘度和密度会随温度压力发生变化,用P-R气体状态方程代替理想气体状态方程来建立理论模型,发现预测值在低压区与实验值吻合很好,但是在高压区都略高于实验值。这可能是由于膜参数和膜孔径的预测过程中只采用低压下的实验数据造成偏差；另外也有可能是由于二氧化碳在超临界区粘度和密度发生变化,导致渗透机理的改变。(3)基于从发酵液中提取多元醇的研究背景,本文用超临界流体萃取法提取乙醇稀水溶液中的乙醇,初步实验之后耦合NaA膜进行分离,研究了回收高压二氧化碳的可行性.结果表明,在稳态连续操作条件下,萃取率会随着温度的增加而显著增加,在萃取时间为120min时,萃取率从35℃条件下的10.27%提升到了55℃条件下的19.99%。耦合膜分离后,随着操作时间的增加,分离因子会逐渐减少,但是随着温度的增加,分离因子会逐渐增加。另外尝试采用超临界二氧化碳微乳耦合膜分离1,3-PDO水溶液,实验结果表明采用增溶1,3.PDO的超临界二氧化碳微乳可以实现1,3-PDO水溶液的分离,并且可以通过耦合膜分离过程实现高压二氧化碳的回收。更多还原

【Abstract】 Supercritical fluid extraction technology and membrane separation technology are highly concerned new technologies in the modern chemical separation techniques. A combination of these two technologies is beneficial for recycling the high-pressure supercritical fluid, strengthen the membrane separation process, as well as expand application in supercritical membrane reactor. Currently, few researches are reported on the diffusion and permeation mechanism of supercritical fluids in the porous membrane penetration. Thus, further studies using experiment method and model calculations are necessary.(1) In order to avoid large crack defects of the traditional method of calcinations, the method of supercritical fluid extraction are used to remove the template to obtain MCM48composite membrane. The mechanism of diffusion and permeation of CO2in mesoporous membrane (MCM48composite membrane with theoretical aperture of2.6nm in effective separation layer) and macroporous membrane (commercial ceramic membrane with average pore diameter of50nm) are investigated at40-100℃and1-12MPa. The results show that the effects of temperature and pressure on the diffusion and penetration behaviors of CO2in these two membranes are significant and almost the same. At low pressure range, the penetration rate increases linearly with the increase of pressure and increases sharply near the critical point. But at high pressure range, no significant changes of penetration rate are observed with an increase of pressure and even a downward trend appears at low temperature.(2) On the basis of experiment, theoretical model is established to predict and fit the effect of Knudsen diffusion and Viscous flow on the diffusion and permeation of CO2in membrane. The prediction results with P-R equation but not the ideal gas status equation show good agreement with the experimental results, though a little higher than experimental results at high pressure range. This may be result from only membrane parameters and diameters at low pressure range are used in the process of prediction or the change of diffusion and permeation mechanism at supercritical region of CO2.(3) Based on the research background of extracting polyalcohol from fermentation broth, extracting ethanol from ethanol dilute aqueous solution using the method of supercritical fluid extraction is studied in this article. In addition, the feasibility of recovering carbon dioxide at high pressure using the method of supercritical fluid extraction combining with NaA membrane is discussed. The results show that the extraction rate increases significantly with the increase of temperature under steady state continuous operating conditions. The extraction rate increases from10.27%at35℃to19.99%at55℃when the extracting time is120minutes. After membrane separation, the separation factor gradually decreases as the operation time increases but gradually increases as the temperature increases.更多还原