Washing column

Esterifica.tlon. The process flow sheet (Fig. 4) outlines the process and equipment of the esterification step in the manufacture of the lower acryflc esters (methyl, ethyl, or butyl). For typical art, see References 69—74. The part of the flow sheet containing the dotted lines is appropriate only for butyl acrylate, since the lower alcohols, methanol and ethanol, are removed in the wash column. Since the butanol is not removed by a water or dilute caustic wash, it is removed in the a2eotrope column as the butyl acrylate a2eotrope this material is recycled to the reactor. 

Acryflc acid, alcohol, and the catalyst, eg, sulfuric acid, together with the recycle streams are fed to the glass-lined ester reactor fitted with an external reboiler and a distillation column. Acrylate ester, excess alcohol, and water of esterification are taken overhead from the distillation column. The process is operated to give only traces of acryflc acid in the distillate. The bulk of the organic distillate is sent to the wash column for removal of alcohol and acryflc acid a portion is returned to the top of the distillation column. If required, some base may be added during the washing operation to remove traces of acryflc acid. 

Fig. 3. Schematic of toluene diamine phosgenation process A, cold phosgenator B, hot phosgenator C, wash column D, solvent distillation E, preflasher F, evaporator G, TDI distillation H, phosgene removal I, HCl absorber and K, phosgene decomposition.

The carbon monoxide-rich, Hquid condensate from the primary separator is expanded and exchanged against the incoming feed and is then sent to a distillation column where the carbon monoxide is purified. The bottoms Hquor from the methane wash column is expanded, heat-exchanged, and sent to the bottom section of the distillation column for methane rectification and carbon monoxide recovery. The methane bottom stream is recompressed and recycled to the top of the wash column after subcooling. A sidestream of methane is withdrawn to avoid a buildup of impurities in the system. 

A horizontal column is typified by the Brodie Purifier, which is shown schematically in Figure 26. Feed enters the column between recovery and refining sections, and crystals exit the refining section and pass through a purifying section. The purifying section is a wash column in which the crystals are contacted with melt generated at the bottom of the column. 

This ammonia is recycled to the reactor via a compressor and a heater. Liquid ammonia is used as reflux on the top of the absorber. The net amount of carbon dioxide formed in the reactor is removed as bottom product from the absorber in the form of a weak ammonium carbamate solution, which is concentrated in a desorber-washing column system. The bottom product of this washing column is a concentrated ammonium carbamate solution which is reprocessed in a urea plant. The top product, pure ammonia, is Hquefted and used as reflux together with Hquid makeup ammonia. The desorber bottom product, practically pure water, is used in the quench system in addition to the recycled mother Hquor. 

Fig. 59. Flow-sheet of washing nitroglycerine at Gyttorp —separator of acid wash-water, B—separator of alkaline wash-water, C—separator of warm wash-water, D—storage tanks, with. wash-equipment, E— storage tanks with refrigerating coils, F— nitroglycerine waggon on a balance, /, 4, 7—air separators, 2, 5—injectors, 3, 6, 9—wash-columns.

The basic process outline is depicted in Figure 5.2 moist un-roasted coffee beans and CO2 are fed counter-currently into the extractor under supercritical conditions. Caffeine is selectively extracted into the CO2 and this stream is led to a water-wash column to remove caffeine at a reduced pressure, the CO2 being recycled back to the extraction column. Extraction of the caffeine into water is necessary to avoid dropping the CO2 pressure too low, since compression is energy-intensive. There is now the problem of separating the caffeine (which is used in soft drinks and pharmaceu-... 

A comparison of the axial-dispersion coefficients obtained in oscil-lating-spiral and dense-bed crystallizers is given in Table 20-5. The dense-bed column approaches axial-dispersion coefficients similar to those of densely packed ice-washing columns. 

We have reported that Zr(IV) loaded phosphoric acid RGP exhibits high selectivity to arsenite when it is washed with water thoroughly after its alkaline treatment.14 The quite similar phenomenon was observed in the case of Zr(IV) loaded CRP200 as shown in Fig. 3. The pH of the effluent from incompletely washed column is nearly equal to or higher than 10, resulting in the incomplete removal of arsenite. On the other hand, the pH of the effluent from the well washed column was less than 9 and nearly equal to neutral pH. Clearly, arsenite was much more effectively removed by the well washed column than the incompletely washed case. 

Figure 3 Effect of washing of alkali-treated column on the adsorption of arsenite. Completely washed column . arsenite, pH (run 1-1 in Table 4).

Whilst the Schildknecht column is essentially a laboratory-scale unit, a melt-crystalliser of the wash-column type was developed by Phillips Petroleum Company in the 1960s for large-scale production of xylene. The key features of this Phillips pulsed-column crystalliser, as described by McKay et alSss are shown in Figure 15.27. A cold slurry... 

Wash column using intermediate solvent at low flow rate change eluent change chromatography system Replace with a suitable one... 

Use fixed oven temperature If due to previous solvent, wash column sufficiently, if due to stationary phase, wash column sufficiently if stationary phase is soluble in the eluent, change chromatographic system Fix recorder... 

Replace stationary phase or column if stationary phase soluble, change chromatographic system Wash column sufficiently... 

Change eluent, buffer components Wash column with water then methanol Wash and fix injector and pump Dilute cone, buffer and counter-ion Select appropriate wavelength Wash flow cell with water and methanol... 

The effluent from the reactor is cooled in a heat exchanger. The EO, byproducts, and unreacted ethylene are separated in a water-wash column in a manner just like the solvent recovery process described in Chapter 2. The EO is absorbed by the water while the by-products (mainly CO2, plus the everpresent cats and dogs in small quantities), and unreacted ethylene are not. The EO/water solution is then steam-stripped and purified by fractionation. 

Nitroglycerine is discharged from the separator (17) through an overflow (17a) and passing through injectors (22c) (23c), (24c) it enters in turn the washing columns (22), (23) and (24). 

The batch nitrator (1) is connected with a separator (2) and the drowning tank (3). The displacing acid tank (4) can produce a flow of nitroglycerine from the separator through the pipe (6) to the wash columns (7), (P) and (11). These columns... 

The method uses a batch nitrator but the separator (2) and the wash-columns run continuously. 

Processes with high mass-flow rates, for example more than 40 t/h, have energy demands of a very high level. Especially for the decaffeination processes, in which several hundred - up to a thousand tons of CO2 are in circulation, isobaric processes were developed. In these processes, the extraction step and the separation step have nearly the same pressure and temperature. The separation of the dissolved substance from the CO2 in circulation is maintained by adsorption on activated charcoal, with an ion-exchanger, or by absorption in a washing column. 

The separation in the isobaric decaffeination processes is executed with absorption of caffeine, that means, the caffeine dissolved in CO2 is carried over into water by means of a packed washing column, or by adsorption with activated charcoal, but without recovery therefrom. Other separation methods under investigation are the use of membranes, since the difference in molecular weight between extract and solvent is high enough, or by the addition of substances of low solvent power. It is questionable whether the advantage of the possible isobaric process can compensate for the investment for the additional process steps required. 

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. 

Overhead from D-l is called the raffinate. It is washed countercurrently with water in D-4 for the recovery of the solvent, and then proceeds beyond the battery limits for further conversion to isoprene. Both wash columns operate at substantially atmospheric pressure and 100°F. The product streams are delivered to the battery limits at 100 psig. 

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