Vane Leland M
U.S. Environmental Protection Agency, Office of Research and Development, Center for Environmental Solutions and Emergency Response, Cincinnati, OH, USA.
J Chem Technol Biotechnol. 2022 Jun 15;97(10):2706-2719. doi: 10.1002/jctb.7161.
The presence of water in organic solvents and biofuels can complicate their production and reuse because many hydrophilic solvents form difficult-to-separate mixtures with water (e.g., azeotropes). Pervaporation (PV) and vapor permeation (V⋅P) remove water from such mixtures via selective solution-diffusion transport through a membrane material. A recent article reviewed design factors that impact the effectiveness of PV/V⋅P solvent dehydration processes ( 95: 495-512 (2020)). For the sake of simplicity, the earlier work assumed constant membrane permeabilities. The objective here is to explore the impact of variable permeabilities on predictions of PV/V⋅P system performance.
A multiparameter expression relating permeability to process conditions was incorporated into the spreadsheet calculators from the previous work. Use of the expression was demonstrated with literature ethanol/water PV data for a NaA zeolite material and two poly (vinyl alcohol) (PVA) membranes. The variable permeabilities of the membranes yielded membrane area requirements that were 20-30% different from those calculated using permeances fixed at either end of the target water range. The impact of composition-dependent permeabilities was most pronounced on the fraction of ethanol transferred to the permeate for the NaA membrane.
The inclusion of membrane permeabilities that vary with fluid composition and temperature noticeably altered predictions of the membrane area required to carry out water removal from ethanol by PV and of the transfer of ethanol to the permeate stream. Unless a PV/V⋅P process is expected to operate at a constant temperature and in a narrow concentration range, process performance estimates would be improved by inclusion of concentration- and temperature-dependent permeabilities or permeances.
有机溶剂和生物燃料中存在水分会使其生产和再利用变得复杂，因为许多亲水性溶剂会与水形成难以分离的混合物（例如共沸物）。渗透蒸发（PV）和蒸汽渗透（V⋅P）通过选择性的溶解 - 扩散传输穿过膜材料，从这类混合物中除去水分。最近有一篇文章综述了影响PV/V⋅P溶剂脱水过程有效性的设计因素（《95: 495 - 512 (2020)》）。为了简单起见，早期的工作假设膜渗透率是恒定的。这里的目标是探讨可变渗透率对PV/V⋅P系统性能预测的影响。
将一个将渗透率与工艺条件相关联的多参数表达式纳入了先前工作中的电子表格计算器。使用一种NaA沸石材料和两种聚乙烯醇（PVA）膜的文献乙醇/水PV数据证明了该表达式的用途。膜的可变渗透率产生的膜面积需求与使用目标水含量范围两端固定的渗透通量计算出的膜面积需求相差20 - 30%。对于NaA膜，组成依赖性渗透率对转移到渗透物中的乙醇分数影响最为显著。
纳入随流体组成和温度变化的膜渗透率，显著改变了通过PV从乙醇中去除水分所需膜面积以及乙醇向渗透物流转移的预测。除非预计PV/V⋅P过程在恒定温度和狭窄浓度范围内运行，否则通过纳入浓度和温度依赖性渗透率或渗透通量，可改进过程性能估计。
