Azeotropes acetonitrile

The separation of the azeotrope acetonitrile/water can be accomplished without an entrainer as shown in Figure 13.26(a). Two columns are required, operating at two different pressures. A single column suffices if trichloroethylene is added as an entrainer, shown in Figure 13.26(b). 

Most, if not all, of the acetonitrile that was produced commercially in the United States in 1995 was isolated as a by-product from the manufacture of acrylonitrile by propylene ammoxidation. The amount of acetonitrile produced in an acrylonitrile plant depends on the ammoxidation catalyst that is used, but the ratio of acetonitrile acrylonitrile usually is ca 2—3 100. The acetonitrile is recovered as the water azeotrope, dried, and purified by distillation (28). U.S. capacity (1994) is ca 23,000 t/yr. 

Isoprene [78-79-5] (2-methyl-1,3-butadiene) is a colorless, volatile Hquid that is soluble in most hydrocarbons but is practically insoluble in water. Isoprene forms binary azeotropes with water, methanol, methylamine, acetonitrile, methyl formate, bromoethane, ethyl alcohol, methyl sulfide, acetone, propylene oxide, ethyl formate, isopropyl nitrate, methyla1 (dimethoxymethane), ethyl ether, and / -pentane. Ternary azeotropes form with water—acetone, water—acetonitrile, and methyl formate—ethyl bromide (8). Typical properties of isoprene are Hsted in Table 1. 

Isoprene-pentane Minimum-hoiling azeotrope Furfural, DMF, acetonitrile ... 

Traces of unsaturated nitriles can be removed by an initial refluxing with a small amount of aq KOH (ImL of 1% solution per L). Acetonitrile can be dried by azeotropic distn with dichloromethane, benzene or trichloroethylene. Isonitrile impurities can be removed by treatment with cone HCl until the odour of isonitrile has gone, followed by drying with K2CO3 and distn. 

The bottom product from column (G) passes to the hydroextractive distillation column (H). The water feed rate to column (H) is five times that of the bottom product flow from column (G). It may be assumed that the acetonitrile and other by-products are discharged as bottom product from column (H) and discarded. The overhead product from column (H), consisting of the acrylonitrile water azeotrope, is condensed and passed to a separator. The lower aqueous layer is returned to column (H). 

PRATT, H. R. C. Trans. Inst. Chem. Eng. 25 (1947) 43. Continuous purification and azeotropic dehydration of acetonitrile produced by the catalytic acetic acid-ammonia reaction. 

Since non-bound or non-coordinated nucleophiles are even more reactive, crown-ethers [138] and cryptands (polyaminoethers) [139,140] have been used to chelate the alkali metal cations, notably the potassium ion of K[ F]F. This allows the [ F]fluoride anion to be less tightly paired with the cation and therefore to be more reactive, which has been coined the naked ion effect. In practice, the crown-ether (e.g. 18-crown-6) or better the polyaminoether Kryptofix-222 (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) is added to the aqueous K[ F]F/K2C03 solution which is then concentrated to dryness [139,140]. The complex (KP FIF-K ) can be further dried, if needed, by one or more cycles of addition of dry acetonitrile and azeotropic evaporation. 

Dilution of urine with acetonitrile, azeotropic distillation for water removal, evaporation of solvent, redissolution in acetone and derivatization using pentafluorobenzyl bromide. 

Ref 3a). Miscible with w, ale eth. Can be prepd by dehydration of acetamide or by other methods. Used as a solvent for many org compdsfamong them RDX, HMX, etc) and as a starting material for the prepo of some org compds. Its toxicity and fire hazard are discussed in Ref 6. The expl hazard is great when acetonitrile is exposed to heat, flame or cnem reactions with oxidizers. It forms an azeotrope with water... 

Samples were eluted in the reverse direction by using the Milton-Roy pump with the pulse dampener removed. The eluant flow (50-75 mL/min at 200-300 lb/in.2) was monitored at 254 nm by using an Altex 153 detector with a biochemical flow cell. Elution with each solvent was continued until the detector response returned to base line. All columns were eluted with acetonitrile this solvent was preceded by 4.5 M NaCl/0.04 M HC1 and 0.04 M HC1 elutions on the MP-1 column and by 4.5 M NaCl and distilled water elutions on the MP-50 column. The aqueous column effluents were adjusted to pH 2 (MP-1) or pH 11 (MP-50) and then extracted three times with dichloromethane. The acetonitrile column effluents were saturated with NaCl to separate the water, which was extracted twice more with acetonitrile. Fifty percent aliquots of the processed organic solvents from each respective column were concentrated in Kudema-Danish evaporators to a final volume of about 10 mL (any remaining water was removed as the low-boiling azeotrope in the process) to give 25,000 1... 

The extract is pumped from the bottom of D-l to a stripper D-2 with 35 trays. The stripped solvent is cooled with water and returned to D-l. An isoprene-acetonitrile azeotrope goes overhead, condenses, and is partly returned as top tray reflux. The net overhead proceeds to an extract wash column D-3 with 20 trays where the solvent is recovered by countercurrent washing with water. The overhead from D-3 is the finished product isoprene. The bottoms is combined with the bottoms from the raffinate wash column D-4 (20 trays) and sent to the solvent recovery column D-5 with 15 trays. 

Two feasible methods for removal of as much water as desired from the azeotrope are depicted on Figure 13.27. The dual pressure process takes advantage of the fact that the azeotropic composition is shifted by change of pressure operations at 100 and 760Torr result in the desired concentration of the mixture. In the other method, trichlorethylene serves as an entrainer for the water. A ternary azeotrope is formed that separates into two phases upon condensation. The aqueous layer is rejected, and the solvent layer is recycled to the tower. For economic reasons, some processing beyond that shown will be necessary since the aqueous layer contains some acetonitrile that is worth recovering or may be regarded as a pollutant. 

Figure 13.27. Separation of the azeotropic mixture of acetonitrile and water which contains approximately 69 mol % or 79.3 wt % of acetonitrile. (Pratt, Countercurrent Separation Processes, Elsevier, New York, 1967, pp. 194, 497). (a) A dual pressure process with the first column at 100 Torr and the second at 760 Torr. (b) Process employing trichlorethylene as entrainer which carries over the water in a ternary azeotrope that in turn separates into two phases upon condensation.

Most, if not all, of the acetonitrile produced commercially in the United States recently was isolated as a by-product from the manufacture of acrylonitrile by propylene ammoxidation. The acetonitrile is recovered as the water azeotrope, dried, and purified by distillation. 

The principal route for production of isoprene monomer outside of the CIS is recovery from ethylene by-product C5 streams. This route is most viable where ethylene is produced from naphtha or gas oil and where several ethylene plants are located in relatively dose proximity to the isoprene plant. Although the yield of isoprene per mass of ethylene is quite low, there is enough ethylene produced to provide a large portion of demand. Because of the presence of -pentane in these streams which azeotropes with isoprene, extractive distillation must be used to recover pure isoprene. Acetonitrile is the most common solvent, but dimethylformamide is also used commercially. 

As seen in Table 1, the boiling temperature of the possible entrainers is either lower or higher than that of the original components. All candidates form a binary heterogeneous azeotrope with -hexane. Methanol and acetonitrile... 

Nitromethane shows the simplest residue curve map with one unstable curved separatrix dividing the triangle in two basic distillation regions. Methanol and acetonitrile give rise two binary azeotropic mixtures and three distillation regions that are bounded by two unstable curved separatrices. Water shows the most complicated residue curve maps, due to the presence of a ternary azeotrope and a miscibility gap with both the n-hexane and the ethyl acetate component. In all four cases, the heteroazeotrope (binary or ternary) has the lowest boiling temperature of the system. As it can be seen in Table 3, all entrainers except water provide the n-hexane-rich phase Zw as distillate product with a purity better than 0.91. Water is not a desirable entrainer because of the existence of ternary azeotrope whose n-hexane-rich phase has a water purity much lower (0.70). Considering in Table 3 the split... 

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