Vacuum distillation glycol separation

The ethylene glycol, bp 198°C, is readily vacuum distilled and separated from the DEG, bp 246°C, and TEG, bp 288°C. The mechanism of the reaction follows the general scheme for acid-catalyzed ring openings of epoxides. 

Diethylene glycol is produced as a by-product in the manufacture of ethylene glycol from hydrolysis of ethylene oxide. It is separated from the ethylene glycol by vacuum distillation. 

It is separated from the ethylene glycol and from triethylene glycol by vacuum distillation. 

Due to the high boiling point of the di-or tri-glycol ethers, production of EGME requires its separation from the glycol ether mixture in a vacuum distillation process. In a CD process, the cooling system and vacuum distillation process... 

The effluent in the individual tubes was pooled into five bands, as indicated by the peaks on the chart. These bands, which contained cyclohexane, methylene chloride, a small amount of ethylene glycol stripped from the colunm, and a separated steroid, were first subjected to vacuum distillation to remove the volatile solvents. The remaining glycol-steroid residue was then mixed with about ten volumes of water. The glycol was trapped in the aqueous solution, and the steroid was removed by extracting three times with an equal volume of ethylene chloride. When this solvent was removed by distillation, the steroid remained as a crystalline residue and was dissolved in 10 ml. of acetone for further identification by narrow-strip paper chromatograms. Evaporation of the acetone and recrystallization from cold ethanol or anhydrous ethyl ether produced the individual steroids, of anal3rtical purity, in recovery yields that exceeded 85%. 

The aqueous solution rich in ethylene oxide is sent to purification. It passes through a stripping column, which operates under vacuum and separates the ethylene oxide at the top. The aqueous effluent leaving at the bottom is recycled to the absorption stage. It can be treated in an auxiliary unit to recover the glycol it contains. The top effluent which, in addition to carbon dioxide, contains acetaldehyde and hydrocarbon traces, is sent to two distillation columns in series, one for dehydration ( = 20 trays), and the second for purification (S 50 trays). These columns produce high-purity ethylene oxide with a very low acetaldehyde content. The product is stored in liquid form in tanks under nitrogen pressure. 

The stream from the reaction section is first distilled to remove unconverted propylene, whose recycle, added to the make-up, represents the feed of the first epoxidation stage. Excess propane is also removed by distillation (—50 to 60 trays) to prevent its buildup in tfie synthesis loop. The heavy end of the first column is sent to the purification train for products for which the temperatures cannot exceed 100°C to avoid undesirable degradation. On account of the boiling points at standard pressure of the components present, this makes operation under vacuum necessary. Crude propylene oxide is collected at the top of the first distillation column (50 trays), and r-butyl alcohol at the1bottom, with some hydroperoxide, the catalyst, propylene glycol, aldehydes, esters etc. This stream is sent to a r-butyl alcohol separation column (35 to 40 trays), where the alcohol is recovered at the top. 

The reaction requires an initial heat-up. Typical heat-up rates are 70 - 90 °C per hour initially followed by a phase where water distillation starts and further heats up at rates of around 15 - 25 °C per hour. Heating is continued until a predetermined batch temperature above 200 °C is reached. The equilibrium is shifted to the right by reaction water removal. For this purpose, the reactor is equipped with a distillation column (for the purpose of separating glycols and reaction water), a condenser and a receiver to collect the reaction water. Water removal is facilitated by applying nitrogen as the inert gas or a vacuum. Alternatively, an azeotropic distillation process may be applied. A solvent is used for water removal, e.g. xylene. In a separator, the xylene-water mixture is separated, the xylene is recirculated back into the reactor and the reaction water is collected in the receiver. 

Dibutyl formal (0.2 mole) with a 5% excess of decamethylene glycol and 0.1 gm of ferric chloride gives a fairly rapid reaction at 165°C (bath). The temperature is raised to 200°C during 2 hr and heating continued for 1 j hr in a good vacuum. The distillate is of the theoretical yield calculated as butyl alcohol the yield of residual a-polymer is 103%. When cold the latter is a light brown, rather hard wax. When dissolved in hot ethyl acetate (150 ml for 17.5 gm), it separates in the form of a microcrystalline powder that is soluble in chloroform, benzene, carbon tetrachloride, and xylene, and insoluble in alcohol, ether, petoleum, hydrocarbons, and acetone. 

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