Ethanol entrainers

There have been only a few citations in the literature concerning the extraction and recovery of natural chlorophyll pigments. Chlorophylls, despite their high molecular weights, are soluble in pure CO2 (like pheophytin a at 500 bar and 55°C), or in the presence of an entrainer (like copper chlorophyllin at 60 bar and 20°C with 5% ethanol entrainer). The extraction of dried grass resulted in 1.56 wt.% yield of green components [79]. 

Carrots Fatty adds and volatiles Pressure 330 bar temperature 40 C CO2 flow 12 kg/h ethanol entrainer 50 ml [113]... 

The results reported by Calame and Steiner [13] are the most detailed, showing GLC and major component analysis for S.CO2 extraction alone, with ethanol entrainer added at once, and continuously added compared to the steam-distilled oil from the same batch of spice. No great differences were reported sensorically between the steam-distilled oil and extracts. 

Calame and Steiner reported a 5.3% yield from allspice by extracting at 300 bar and 40°C using ethanol entrainer, with subsequent separation at 55 bar and 37°C. This compared to a 2.5% yield by steam distillation [13]. 

Two separate studies on the S.COiz extraction of rosemary have been reported by Calame and Steiner [13]. In the first, a batch of herb which had a steam distillation yield of 1.44% was extracted using ethanol entrainer at 250 bar and 60°C with subsequent separation at subcritical conditions of 53 bar and 12°C, yield 7.5%. In the second, hexane entrainer and the same extraction and fractionation conditions also gave a 7.5% yield. 

Lawrence has reviewed vanilla extracts analyses [226]. Vanilla extraction with CO2 has been patented [227] with two stages of processing. Extraction at 400 bar and 45°C and separation at 65 bar and 25°C gave 10% yield. This was subsequently refuted by Calame and Steiner who used Bourbon beans, with 1.5% vanillin extracted at 300 bar and 40°C with ethanol entrainer to give a 3.44% yield at 37% vanillin [13]. The current author s results are in agreement with the Calame and Steiner work, when genuine quality beans are... 

Sasol Fischer-Tropsch Process. 1-Propanol is one of the products from Sasol s Fischer-Tropsch process (7). Coal (qv) is gasified ia Lurgi reactors to produce synthesis gas (H2/CO). After separation from gas Hquids and purification, the synthesis gas is fed iato the Sasol Synthol plant where it is entrained with a powdered iron-based catalyst within the fluid-bed reactors. The exothermic Fischer-Tropsch reaction produces a mixture of hydrocarbons (qv) and oxygenates. The condensation products from the process consist of hydrocarbon Hquids and an aqueous stream that contains a mixture of ketones (qv) and alcohols. The ketones and alcohols are recovered and most of the alcohols are used for the blending of high octane gasoline. Some of the alcohol streams are further purified by distillation to yield pure 1-propanol and ethanol ia a multiunit plant, which has a total capacity of 25,000-30,000 t/yr (see Coal conversion processes, gasification). 

Fig. 18. Separation of ethanol from an ethanol—water—benzene mixture using benzene as the entrainer. (a) Schematic representation of the azeo-column (b) material balance lines where I denotes the homogeneous and the heterogeneous azeotropes D, the end points of the Hquid tie-line and A, the overhead vapor leaving the top of the column. The distillate regions, I, II, and III, and the boundaries are marked. Other terms are defined in text.

Fig. 19. Separation of ethanol and water from an ethanol—water—benzene mixture. Bottoms and are water, B is ethanol, (a) Kubierschky three-column sequence where columns 1, 2, and 3 represent the preconcentration, azeotropic, and entrainer recovery columns, respectively, (b) Material balance lines from the azeotropic and the entrainer recovery columns, A and E, respectively, where represents the overall vapor composition from the azeo-column, 2 1SP Hquid in equiUbrium with overhead vapor composition from the azeo-column, Xj, distillate composition from entrainer...

Podebush Sequence forPthanol—Water Separation. When ethyl acetate is used as the entrainer to break the ethanol—water azeotrope the residue curve map is similar to the one shown in Figure 21d, ie, the ternary azeotrope is homogeneous. Otherwise the map is the same as for ethanol—water—benzene. In such... 

Diethoxymethanol-water-ethanol Minimiim-boiling azeotropes Self-entraining ... 

Water and ethanol form a low boiling point azeotrope. So, water cannot be completely separated from ethanol by straight distillation. To produce absolute (100 per cent) ethanol it is necessary to add an entraining agent to break the azeotrope. Benzene is an effective entrainer and is used where the product is not required for food products. Three columns are used in the benzene process. Column 1. This column separates the ethanol from the water. The bottom product is essentially pure ethanol. The water in the feed is carried overhead as the ternary azeotrope of ethanol, benzene and water (24 per cent ethanol, 54 per cent benzene, 22 per cent water). The overhead vapour is condensed and the condensate separated in a decanter into, a benzene-rich phase (22 per cent ethanol, 74 per cent benzene, 4 per cent water) and a water-rich phase (35 per cent ethanol, 4 per cent benzene, 61 per cent water). The benzene-rich phase is recycled to the column as reflux. A benzene make-up stream is added to the reflux to make good any loss of benzene from the process. The water-rich phase is fed to the second column. 

Consider a second example involving the separation of a mixture of ethanol and water that forms an azeotrope at around a mole fraction of ethanol of 0.88. It is proposed to use ethylene glycol as entrainer. An overall mass balance for the separation is shown in Figure 12.22a. As with the... 

Figure 12.22 Distillation sequence for the separation of an ethanol-water mixture using ethylene glycol as entrainer is infeasible using single-feed column.

One feature common to both designs in Figures 12.21 and 12.22 is that single-feed columns were used with the entrainer being mixed with the feed. In the case of the ethanol-water-ethylene glycol, the operation leaves for the top and bottom sections of the column do not meet, and there is a gap. In some systems, it is possible to bridge the gap between the operation leaves between the top and bottom sections by creating a middle section in the... 

Bottom Product B with a straight line joining the Distillate D and Entrainer Feed E, as shown in Figure 12.24. Pinch point curves for the middle section can now be constructed by drawing tangents to the residue curves from the difference point (net overhead product). This is shown in Figure 12.25 for the system ethanol-water-ethylene glycol. The area bounded by the pinch point curves defines the middle section operation leaf. 

Figure 11.44. Azeotropic distillation for the separation of ethanol from water using benzene as entrainer. Compositions are given in mole per cent. E = Ethanol, B = Benzene, W = Water, S = Steam...

The azeotrope in the ethanol-water binary system has a composition of 89 mole per cent of ethanol(14). Starting with a mixture containing a lower proportion of ethanol, it is not possible to obtain a product richer in ethanol than this by normal binary distillation. Near azeotropic conditions exist at points marked in Figure 11.44. The addition of the relatively non-polar benzene entrainer serves to volatilise water, a highly polar molecule,... 

Figure 11.45. Composition profile for the azeotropic distillation of ethanol and water, with benzene as entrainer...

Isomerization processes produce sour water and caustic wastewater. The ether manufacturing process utilizes a water wash to extract methanol or ethanol from the reactor effluent stream. After the alcohol is separated, this water is recycled back to the system and is not released. In those cases where chloride catalyst activation agents are added, a caustic wash is used to neutralize any entrained hydrogen chloride. This process generates a caustic wash water that must be treated before being released. This process also produces a calcium chloride neutralization sludge that must be disposed of off-site. 

The separation properties in SFE are dependent on the choice of solvents, as well as on the solutes. The most popular solvent, carbon dioxide, is a rather nonpolar solvent, which dissolves mainly nonpolar solutes. Solubilities of selected compounds in liquid carbon dioxide are given in Table 10.6. The solubility and selectivity can be altered by adding small amounts of polar solvents, called entrainers (e.g., water or ethanol). 

The VLB was also measured for binary and ternary systems of [ethanol + [C2Cilm][C2S04] and [ethanol + ethyl ferf-butyl ether + [C2Cilm][C2S04] at 101.3 kPa [151]. This ternary system does not exhibit a ternary azeotrope. The possibility of [C2Cilm][C2S04] use as a solvenf in liquid-liquid extraction or as an entrainer in extractive distillation for fhe separation of the mixture ethanol/ethyl fcrf-butyl ether was discussed [151]. 

Ethanol as a Co>Solvent with SC>C02 for Extracting Cholesterol from Beef Tallow. Figure 4 contains data for comparing the extraction of lipid and cholesterol with 5% ethanol as a co-solvent (entrainer) compared to extracting with SC-CO2 alone. 

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