Purification and recovery of biofuels using inorganic membranes

对可再生燃料的兴趣促使了对从生物质生产乙醇的大量研究和投资。 从发酵液中纯化乙醇产物是一个显著的工艺障碍，这是由于存在反硝化物，显著阻碍了可再生的基于发酵的生物燃料的经济生产。 膜分离，特别是反渗透，代表了用于分离和纯化化学系统的常规蒸馏工艺的低能量替代方案。 不幸的是，用于化学分馏的常规反渗透膜技术的广泛应用还没有实现，这是因为两个主要的障碍：1）高浓度的有机化学品通常使常规聚合物反渗透膜降解;和2）在膜内产生极端的渗透背压，如果不是无法达到的，则需要过量的跨膜压力。 本工作提出了使用无机氧化铝膜结合逆流反渗透的选择性去除水从酒精发酵产品。 通过阳极铝氧化，然后原子层沉积合成的氧化铝膜，除了提供对高浓度有机化学品的优异稳定性之外，还提供反渗透分离所必需的均匀的纳米尺寸的孔。 原子层沉积以0.1 nm增量调节孔径的能力意味着任何两个尺寸差异> 0.1 nm的分子理论上可以使用膜分离。 为了克服在反渗透过程中产生的渗透压限制，将采用萃取剂在膜的渗透侧的逆流。 这种逆流可以由一部分高浓度渗余物的再循环（例如回流）组成，或者它可以是独立的萃取剂（称为渗透萃取的过程）。 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，脱盐，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.