Purification and recovery of biofuels using inorganic membranes

对可再生燃料的兴趣促使人们在生物质生产乙醇方面进行了大量的研究和投资。由于共沸物的存在，从发酵液中提纯乙醇产品是一个重大的工艺障碍，严重阻碍了可再生发酵生物燃料的经济生产。膜分离，特别是反渗透，是分离和提纯化学体系的传统精馏过程的一种低能量替代方法。不幸的是，传统的反渗透膜技术在化学分级中的广泛应用还没有实现，因为两个主要障碍：1)高浓度的有机物通常会使传统的聚合物反渗透膜降解；2)膜内会产生极端的渗透背压，需要过高的跨膜压力。这项工作建议使用无机氧化铝膜与逆流反渗透相结合，选择性地从酒精发酵产品中去除水分。通过阳极铝氧化合成的氧化铝膜，然后原子层沉积，提供了反渗透分离所需的均匀的纳米尺寸的孔，此外还提供了针对高浓度有机化学品的出色稳定性。原子层沉积以0.1纳米为增量调整孔径的能力意味着，理论上可以使用膜分离尺寸相差&gt；0.1 nm的任何两个分子。为了克服反渗透过程中产生的渗透压限制，将在膜的渗透侧采用萃取剂的逆流。这种逆流既可以包括部分高浓度保留液的回流(例如回流)，也可以是独立的萃取剂(称为渗透过程)。一旦完善，这种膜过程可以适用于其他酒精-水分离、果汁浓缩、海水淡化以及许多其他非水化学系统。

Interest in renewable fuels has prompted a significant amount of research and investment in the production of ethanol from biomass. Purifying the ethanol product from fermentation broth represents a significant process hurdle as a result of the presence of azeotropes, significantly impeding the economic production of renewable, fermentation based biofuels. Membrane separation, and in particular reverse osmosis, represents a low-energy alternative to conventional distillation processes for separating and purifying chemical systems. Unfortunately, the widespread application of conventional reverse osmosis membrane technology for chemical fractionation has not materialized because of two main roadblocks: 1) High concentrations of organic chemicals generally degrade conventional polymeric reverse osmosis membranes; and 2) Extreme osmotic back pressures develop within the membrane requiring excessive if not unattainable trans-membrane pressures. This work proposes the use of inorganic alumina membranes in conjunction with countercurrent reverse osmosis for the selective removal of water from alcoholic fermentation products. Alumina membranes synthesized by anodic aluminum oxidation, followed by atomic layer deposition, provide uniform, nanometre sized pores necessary for reverse osmosis separations in addition to providing excellent stability against high concentrations of organic chemicals. The ability of atomic layer deposition to tune the pore size in 0.1 nm increments means that any two molecules with a size difference of > 0.1 nm can theoretically be separated using a membrane. In order to overcome the osmotic pressure limitations that develop during reverse osmosis, a countercurrent flow of an extractant on the permeate side of the membrane will be employed. This countercurrent flow can consist of either the recirculation of a portion of the high concentration retentate (e.g. reflux) or it may be an independent extractant (a process referred to as perstraction). Once perfected, this membrane process could be adapted to other alcohol-water separations, fruit juice concentration, desalination, as well as a multitude of other non-aqueous chemical systems.