Ethanol/water separation

Bowen et al. [94] made a B-MFI membrane on a monohthic support. The pervaporation fluxes and selectivities of several alcohol/water mixtures were comparable to similar tubular-based B-MFI membranes, demonstrating the scale-up, although, for pervaporation, the quality requirements are much more forgiving. Kuhn etal. tested a multicharuiel high-silica MFI membrane for ethanol/water separation. The membrane was supphed by NGK Insulators and, also, in this case, the multicharuiel membrane measures up to its tubular counterparts [95] (Figure 10.8). 

Silicalite-1 Selective layer PDMS Support PEI NA Thin-film composite fiat sheet Gas separations (e.g., O2/N2) Liquid separations (e.g., ethanol/water separation) [82]... 

Another type of mixed-matrix membranes for alcohol/water pervaporation applications was developed utilizing hydrophiUc poly(vinyl alcohol) (PVA) and ZSM-5. The ZSM-5/PVA mixed-matrix membranes demonstrated increased selectivity and flux, compared to pure PVA, for the water/isopropyl alcohol separation [97]. This type of mixed-matrix membranes, however, may have membrane swelling issue due to the hydrophilic nature of the PVA polymer. Mixed-matrix membranes comprising modifled poly(vinyl chloride) and NaA zeolite have shown both enhanced flux and selectivity for the ethanol/water separation at high NaA loadings [98]. 

A general scheme of the extractive alcoholic fermentation proposed by Silva et al. (3) is shown in Fig. 1. The process consists of four interlinked units the fermentor (ethanol production unit), the centrifuge (cell separation unit), the cell treatment unit, and the vacuum flash vessel (ethanol-water separation unit). A detailed description of the process and mathematical model can be found in ref. 5. 

Ethanol-water separation was the first industrial-scale application of pervaporation. It remains the dominant use of... 

ETBE is recovered as the bottoms product of the distillation unit. The ethanol-rich C4 distillate is sent to the ethanol recovery section. Water is used to extract excess ethanol and recycle it back to process. At the top of the ethanol/water separation column, an ethanol/water azeotrope is recycled to the reactor section. The isobutene-depleted C4 stream may be sent to a raffinate stripper or to a molsieve-based unit to remove oxygenates such as DEE, ETBE, ethanol and tert-butanol. 

Ethanol/water separation distillation. 387, 394, 424 reverse osmosis, 642 Ethylene... 

Cadotte ( ) presents a comprehensive review of the development of the composite membrane with emphasis on the pros and cons of the four preparation methods mentioned above and on the polymer chemistry Involved. Cadotte points out that while each of the four methods continues to receive some attention, the Interfaclal polymerization method appears to be the most versatile. This method can be used to produce skin layers from polyamines, polylmlnes, polyurethanes, polyesters and other polymers. Elsewhere In this volume, Lee and co-workers (45) discuss the advantages and problems associated with using these composite membranes for ethanol-water separations via counter-current reverse osmosis. Also, Cabasso (44) discusses double-layer composite membranes. 

Ethanol-Water Separation by Countercurrent Reverse Osmosis... 

Ethanol produced by fermentation is conventionally dehydrated by distillation, an inefficient process that consumes energy equivalent to a large fraction of the energy content of the product ethanol.(X) Reverse osmosis (RO) has been considered before for ethanol-water separation because of its inherent energy efficiency. However, a difficulty encountered in using RO is the high osmotic pressures associated with concentrated ethanol solutions. For example, the osmotic pressure of a 15-volX ethanol solution is about 960 psi, and that of a 50-volX solution is about 3700 psi.(2,) Because most... 

When the ethanol is not blended but used as such as fuel, hydrous ethanol (e.g. 95%) can be applied. In a cascade-type continuous set-up [27] a partial evaporation of the fermentation liquid was carried out and the ethanol-water mixture was passed over a H-ZSM5 zeolite (350 °C, 1 atm). As in the MTG (methanol to gasoline) [28, 29] process a mixture of alkanes (mainly C3-C5) and aromatics (mainly toluene, xylenes and C<)-compounds) was obtained. In this approach the ethanol-water separation is avoided the hydrocarbons and water are non-miscible and separate by gravity. Though its octane number is good there is no future in MTG-gasoline because of the trend to lower the aromatics content. 

This simplified equation is more generally employed by the groups discussing ethanol-water separation studies and we use it in the subsequent discussion. 

For the ethanol-water separation, the requirement of thorough removal of ethanol from the recycled CO2 represents a technical challenge that increases the complexity and cost of the process relative to the simplified diagram shown in figure 8.10. The reasons for the increased complexity are explained below. Figure 8.13 illustrates the ethanol extraction process in the instance where the recycled CO2 has an ethanol concentration of 0.1 wt%. At the raffinate section of the extractor the ethanol concentration in the water-rich phase is now dictated by considerations of equilibrium and by the value of the distribution coefficient. The limitation attributed to equilibrium is indicated by the... 

The first commercial application of pervaporation was for ethanol-water separation. The dilute solution produced by fermentation is distilled to produce an overhead product with 90 to 95 percent alcohol (close to the azeotrope), and this solution is fed to the membrane unit to give nearly pure ethanol (99.9 percent). The permeate stream with about 20 to 40 percent alcohol is recyled to the distillation column. The vapor-liquid equilibrium curve and the vapor and liquid compositions for a poly(vinyl alcohol) membrane are shown in Fig. 26.16. The membrane gives a permeate that is always richer in water than the liquid, in contrast to distillation, where alcohol is the more volatile component over most of the range. The shape of the curve for permeate composition indicates strongly... 

The following factors are considered important for selection of an appropriate MSA (adapted from factors for liquid—liquid extraction for ethanol/water separation [37-40]) ... 

Figure 2.11 Comparison of the primary energy usage for ethanol/water separation using traditionai distillation/adsorption process (Fig. 2.9) and hybrid membrane-assisted vapor stripping (MAVS Fig. 2.10) process. Minimum energy (from minimum work calculation) shown as reference. Assumptions 37% and 85% efficient conversion of primary energy to electrical energy and thermal energy, respectively, 0.02 wt% ethanol in stripping column bottoms, and 99.5 wt% ethanol product (0.5 wt% water).

Vane LM, Alvarez FR, Huang Y, Baker RW. Experimental validation of hybrid distiUation-vapor permeation process for energy efficient ethanol-water separation. J Chem Tech Biotechnol 2010 85 502-11. 

If a desired ethanol-water separation by distillation requires a minimum of 17 theoretical stages at total reflux, how many theoretical stages would be recommended for a first-pass design of a plant column using a computer simulation ... 

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