Purification and recovery of biofuels using inorganic membranes

对可再生燃料的兴趣促使大量研究和投资从生物质中生产乙醇。由于共沸物的存在，从发酵液中纯化乙醇产品是一个重大的过程障碍，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，代表了一种低能耗的替代传统蒸馏过程分离和净化化学系统。不幸的是，由于两个主要障碍，传统的反渗透膜技术在化学分馏法中的广泛应用尚未实现：1)高浓度的有机化学品通常会降解传统的聚合物反渗透膜；2)膜内产生极端的渗透背压，需要过高的跨膜压力，如果不是无法达到的话。这项工作提出使用无机氧化铝膜与逆流反渗透相结合，选择性地去除酒精发酵产品中的水。氧化铝膜是由阳极铝氧化合成的，然后是原子层沉积，除了对高浓度有机化学物质具有优异的稳定性外，还提供了反渗透分离所需的均匀的纳米级孔。原子层沉积能够以0.1 nm的增量调整孔径，这意味着理论上任何两个大小相差为> 0.1 nm的分子都可以用膜分离。为了克服在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流动。这种逆流流动既可以由一部分高浓度滞留物的再循环（如回流）组成，也可以是一个独立的萃取剂（称为萃取的过程）。一旦完善，这种膜工艺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.