Tray column Solvent extraction

The crude C4 mixture is charged to a 70 tray extractive distillation column T-l that employs acetonitrile as solvent. Trays are numbered from the bottom. Feed enters on tray 20, solvent enters on tray 60, and reflux is returned to the top tray. Net overhead product goes beyond the battery limits. Butadiene dissolved in acetonitrile leaves at the bottom. This stream is pumped to a 25-tray solvent recovery column T-2 which it enters on tray 20. Butadiene is recovered overhead as liquid and proceeds to the BDS reactor. Acetonitrile is the bottom product which is cooled to 100°F and returned to T-l. Both columns have the usual condensing and reboiling provisions. 

Correlations for Estimating fob Purchased Costs for Internals (e.g., Distillation Trays, Absorber Packings, Solvent Extraction Columns, and Others. Referenced to Mid-1968 Dollars with (M S = 273.1). Correlated Using Information from Guthrie [71]... 

Four solvents were evaluated for the recovery of 1 -butadiene from crude Ch fractions by extractive distillation. Furfural [5 wt % water], methyl CeUosolve [10% water], acetonitrile [10% water] and p-methoxypropionitrile [5% water] solvents were studied at comparable operating conditions in a 2 inch diameter, 140 tray column. Furfural and methyl Cellosolve solvents performed the desired separation between 1,3-butadiene and trans-2-butene only at high solvent-to-Ch feed ratios. Acetonitrile and p-methoxypro-pionitrtle solvents were far superior to furfural and methyl Cellosolve at equivalent solvent-to-Cfeed ratios. The superior solvents could perform the desired separation at half the solvent ratio. When related to a plant scale operation, p-methoxypropionitrile solvent could double the capacity of an existing butadiene plant using furfural... 

Description The feedstock enters the extractive distillation column in its middle section while the solvent, N-methylpyrrolidone (NMP), is fed on the top tray of its extractive distillation section. The NMP solvent allows the separation of aromatic and non-aromatic components by enhancing their relative volatilities. 

The static packed column, shown in Fig. 6.3-1, is more efficient with respect to mass transfer. Its design is similar to that of gas/hquid systems (e.g., absorption and distillation). In contrast, the design of a static tray column, used for solvent extraction, is completely different from the corresponding column for gas/liquid service. The sieve trays have very small hole diameters (2-4 mm) and a very small free area 2-4%) (Fig. 6.3-1). 

Chlorobenzene Solvent System. Selecting an appropriate tray in the extractive column in the chlorobenzene system is a little less obvious than in the previous cases. As Figure 11.21a shows, the sharpest temperature profile is near the base, but this is caused by the rapid increase in chlorobenzene concentration and decrease in the acetone concentration (see Fig. 11.214 ). Remember that in this system the methanol goes overhead in the... 

Another dehydration process is the Drizo gas dehydration process that uses high glycol concentrations to give low due point temperatures and uses a solvent to recover extracted aromatics [30]. Trayed columns with a variety of structured proprietary packings have also been used for dehydration of natural gas in arctic gas production [31]. 

The thermal quality of the solvent feed has no effect on the value of (S/F)mjn, but does affect the minimum reflux to some extent, especially as the (S/F) ratio increases. R nax occurs at higher values of the reflux ratio as the upper-feed quality decreases a subcooled upper feed provides additional refluxing capacity and less external reflux is required for the same separation. It is also sometimes advantageous to introduce the primary feed to the extractive distillation column as a vapor to help maintain a higher solvent concentration on the feed tray and the trays immediately below... 

The process equipment consists mainly of two extraction columns with pulsating trays and four distillation columns according to Fig. 10.4 [7]. The feed, with a high content of aromatics, is pumped to the middle of the first extraction column where the aromatics are extracted with the solvent SI (tetraethylene glycol). In the lower part, the extracted aromatics are washed with S2 (dodecane). The outgoing raffinate phase R1 (containing aliphatics,... 

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. 

The C4 acetylenes, which have higher solubilities in NMP than 1,3-butadiene, are removed by the solvent in the bottoms and returned to the rectifier. A crude butadiene (BD) stream, from the overhead of the second extractive distillation column, is fed into the BD purification train. Both extractive distillation columns have a number of trays above the solvent addition point to allow for the removal of solvent traces from the overheads. 

An absorption zone in which the acetylenic compounds, butadiene and a certain quantity of butenes are extracted from the feedstock in countercurrent gas/Iiquid treatment with N methylp TTolidone, containing about 8 per cent weight water. This operation takes place in a column with about 80 trays operating betw een 45 and 55 at M to 0.6.10 Pa. on a feedstock previously vaporized by heat exchange with the hot solvent recycle and introduced at the bottom, llte N-methylpynolidone is inuodoced at the top, where the unabsorbed gases, chiefly butanes and butenes, leave the column. 

TTie feed C4 cut is first treated in countercurrent flow by the solvent in an extractive distillation column with about 90 trays, operating between 45 and 70"C, at 0,5 to 0.6.10 Pa. Butenes and unabsorbed butanes leave at the top. 

The extract is then flashed to liberate, the dissolved olefins and. after recompression, to return them to the extractive distillation step. The liquid fraction rich in butadiene and acetylenic compounds is preheated and sent to a regeneration column with 20 trays operating at about 0.2.10 Pa, at 90°C at the top and 150°C at the bottom. The solvent drawn off is recycled, possibly after purification if required. The distillate is partly condensed. The liquid fraction sei es as a reflux, and that in the gas phase is recompressed and partly returned to the absorption step. The crude butadiene remaining is rid of methyiacetylene and heavier compounds in two simple distillation columns, with about 40 and 110 trays respectively, in the presence of r-butylpyrocatechol. 

In principle, the flow sheet of such a facility (Fig 5.14) comprises the cooling of the C cut in gaseous form, followed by its countercurrent pass into an absorption column (20 trays), where the solvent flows, and which operates at about 2.10 Pa absolme. The extract, containing nearly all the initial acetylene, is sent to a stripping column (25 trays), operating at 0.105.10 Pa absolute to remove the other absorbed gases, which are recycled to the previous column after recompresston. A desorber (25 trays) then separates the dimethylfonnamide at the bottom and the acet ene at the top (Fig 5.11). 

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