Azeotropic distillation acetonitrile/water separation

Because a large amount of water is entrained in the side stream, this is removed in the column C-3. Raw acetonitrile, namely a binary azeotrope with 20% water, separates in top. The bottom stream contains water with heavy impurities. Vacuum distillation at 0.5 bar is adequate to limit the bottom temperature. In the next step pure acetonitrile can be obtained by using pressure-swing distillation. 

Axial flow pumps, 134, 136, 140 applicafion range, 150 Azeotrope separation, 387,388,420-426 Azeotropic distillation, 420-426 acetonitrile/water separation, 422 commercial examples, 421-424 design method, 424 ethanol/water/benzene process, 424 n-heptane/toluene/MEK process, 424 vapor-liquid equilibrium data, 421, 423, 425,426... 

The separation of acetonitrile from acetonitrile by extractive distillation with water can be done in a more efficient two-column heat integrated setup. The separation of acrylonitrile from water, which is hindered by the existence of an azeotrope, can actually take advantage of the large immiscibility gap. Valuable byproducts, such as HCN and acetonitrile can be efficiently separated. Chemical conversion can solve the separation of difficult impurities, such as acroleine. 

In specific cases when the vapor-liquid equilibrium favors distillation at the side of the organic component of an azeotrope and a high purity of the organic component is specified the membrane system may be used just to split the azeotrope. For the separation of the system acetonitrile-water a hybrid system as shown in Fig. 3.19 may be economically advantageous. Here the membrane system is used to cross the azeotropic point the partially dehydrated vapor enters the second column in which final dehydration is effected. Again it is necessary to determine the economical optimum between the size of both columns, the energy consumption of the first one and the volume of the recycle stream from the second column at one side, and the size of the membrane system and its outlet concentration on the other side. 

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). 

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... 

Table 11.2 presents fundamental physical properties for the key components implied in separations. The difference in the boiling points favors the separation, except of acrylonitrile and acetonitrile. The differences in the freezing point are also sensitive, but they did not justify the investment in a separation by crystallization. It remains that distillation-based separation methods should be tried in the first place. However, the formation of azeotropes of components with water will present difficulties. 

Acetonitrile. CH3CN, b.p. 81.6° [1, 7, before a-Acetoxyacrylonitrile]. Aprotic. water-miscible Diels-Alder solvent (1, 239). Supplier of pure solvent. 1, 1110. For polara-graphic use. Moe1 notes that the main impurity is acrylonitrile, which differs from it in b.p. by only 4.2°, and recommends separation by distillation of the ternary and secondary azeotropes which the two liquids form with ethanol and with water. Ethanol (95%) is added to practical acetonitrile and the mixture is distilled through an H. Stedman column of 60-65 theoretical plates. The purified material is suitable also for U V spectroscopy. 

G4. The system water-acetonitrile (C2H3N) forms an azeotrope. This system can be separated using a two-pressure distillation system. Both columns have total condensers and ketde-type reboilers. Valid phases are vapor-liquid. Use NRTL for VLE data. The feed to the system is at 1.0 atm and 60°C. The feed is 15 mol% water and 85 mol% acetonitrile, and the flow rate of the feed is 200 kmol/h. This feed and the recycle stream labeled D2 in Figure 8-6 are input into column 1 (see... 

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