Esterification ester column

The aqueous layer from the ester column distillate, the raffinate from washing the ester, and the aqueous phase from the dehydration step are combined and distilled in the alcohol stripper. The wet alcohol distillate containing a low level of acrylate is recycled to the esterification reactor. The aqueous column bottoms are incinerated or sent to biological treatment. Biological treatment is common. 

The oxidation reactor effluent and methanol ate sent to the esterification reactor, which operates at up to 250°C and a pressure sufficient to maintain the Hquid phase. This latter is about 2500 kPa (25 atm). The oxidation products are converted to methyl -toluate and dimethyl terephthalate without a catalyst. Excess methanol is suppHed, and steam and vaporized methanol ate removed and enter a methanol recovery column. The esterification products flow to a cmde ester column, which separates the toluate from the terephthalate. The overhead stream of methyl -toluate is returned to the oxidation reactor, and the bottoms stream of dimethyl terephthalate goes to a primary distillation. The distillate is dissolved in methanol, crystallized, and sohd dimethyl terephthalate is recovered. The dimethyl terephthalate can then be either recrystallized or distilled to yield the highly pure material needed for the polyesterification reaction. 

Esterification—Continued by azeotropic distillation with benzene, 22, 38 by nitric acid, 22, 65 of desoxycholic acid, 24, 41 of lactic acid, 26, 4 of linoleic acid, 22, 77 of linolenic acid, 22, 83 of pyruvic acid with use of methyl ester column, 24, 72 Ester interchange, 26, 5, 19 between polylactic acid and allyl alcohol, 26, 5... 

Description A slurry composed of PTA and EG, or molten DMT and EG is fed to the first esterification/ester-interchange reactor (1) in which main reaction occurs at elevated pressure and temperatures (200°C-270°C). Reaction vapors—water or methanol—are sent to a low/high boiler separation column. High boilers are reused as feedstock. 

Oxidation reactor 2 Off gas purification 3 Esterification reactor 4 Methanol-dewatering column 5 p-Methylbenzoic acid methyl ester column 6 Dimethyl terephthalate column 7 and 8 Crystallizers 9 Melting pot 10 Distillation column... 

In the Chemische Werke Witten process, which was further developed by Dynamit Nobel and Hercules, p-xylene, air and the catalyst are fed continuously into the oxidation reactor, to which recirculated p-methylbenzoic acid methyl ester is also added. Oxidation is effected at a temperature of 140 to 170 °C and a pressure of 4 to 7 bar. The heat of reaction is removed by the vaporization of water and excess p-xylene. The further reaction with methanol is carried out at 200 to 250 °C under slightly raised pressure (20 bar) in the esterification reactor, to keep the reaction mixture in the liquid-phase. The esterification products flow to the crude ester column, where p-methylbenzoic add methyl ester is separated from the crude dimethyl terephthalate. p-Methylbenzoic acid methyl ester is recycled to the oxidation reactor, where oxidation of the second methyl group occurs. The crude dimethyl terephthalate is purified to fiber grade quality by distillation and crystallization from methanol, and subsequent redistillation in a column with around 30 trays. The yield of dimethyl terephthalate (m.p. 141 °C) is generally about 87 mol%. 

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. 

Pure dry reactants are needed to prevent catalyst deactivation effective inhibitor systems are also desirable as weU as high reaction rates, since many of the specialty monomers are less stable than the lower alkyl acrylates. The alcohol—ester azeotrope (8) should be removed rapidly from the reaction mixture and an efficient column used to minimize reactant loss to the distillate. After the reaction is completed, the catalyst may be removed and the mixture distilled to obtain the ester. The method is particularly useful for the preparation of functional monomers which caimot be prepared by direct esterification. 

In typical processes, the gaseous effluent from the second-stage oxidation is cooled and fed to an absorber to isolate the MAA as a 20—40% aqueous solution. The MAA may then be concentrated by extraction into a suitable organic solvent such as butyl acetate, toluene, or dibutyl ketone. Azeotropic dehydration and solvent recovery, followed by fractional distillation, is used to obtain the pure product. Water, solvent, and low boiling by-products are removed in a first-stage column. The column bottoms are then fed to a second column where MAA is taken overhead. Esterification to MMA or other esters is readily achieved using acid catalysis. 

Activated esters of A-alkoxycarbonylamino acids are prepared by two approaches, activation of the acid followed by reaction with the hydroxy compound, and trans-esterification. Most of the products are stable enough to be purified by washing a solution of the ester in an organic solvent with aqueous solutions. A few that are not crystalline are purified by passage through a column of silica. The commonly used method for their preparation is addition of dicyclohexylcarbodiimide to a cold mixture of the reactants in dimethylformamide or ethyl acetate. The first Boc-amino acid nitrophenyl esters were obtained using pyridine as solvent. Pyridine generates the nitrophenoxide ion that is more reactive. For one type of ester, 2-hydroxypyridino... 

One fact to keep in mind with such phases is that weak acid cation-exchange materials based on carboxylic acid functional groups are subject to esterification in the presence of alcohol containing eluents. Even thongh typical eluent conditions (i.e., weakly acidic aqneous eluents containing alcohol) do not favor ester formation, such stationary phases typically exhibit slowly declining capacity when operated in the presence of alcohol-containing eluents. Consequently, such columns are normally operated with acetonitrile, tetrahydrofuran or acetone rather than with methanol, in order to avoid this problem. 

Following extraction/cleanup, quinoxaline-2-carboxylic acid can be detected by electron capture, or mass spectrometric techniques, after gas chromatographic separation on capillary or conventional columns. A prerequisite of quin-oxaline-2-carboxylic acid analysis by gas chromatography is the derivatization of the molecule by means of esterification. Esterification has been accomplished with methanol (419, 420, 422), ethanol (421), or propanol (423) under sulfuric acid catalysis. Further purification of the alkyl ester derivative with solid-phase extraction on a silica gel column (422), thin-layer chromatography on silica gel plate (420), or liquid chromatography on Hypersil-ODS, 3 m, column (423), has been reported. 

Nordstrom (19) demonstrated that esters are formed primarily by a direct biosynthetic process during fermentation in which acyl-CoA compounds containing the particular fatty acid moiety combine with alcohols of the medium, which explains the predominance of ethyl esters. Ester formation during fermentation does not appear to be direct esterification between alcohols and free fattty acids. However, some direct esterification may occur on the plates of a distilling column where acids and alcohols are most concentrated. 

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