Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Patent
1999-02-04
2000-12-26
Killos, Paul J.
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
562600, C07C 5116, C07C24100
Patent
active
061662488
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for preparing acrylic acid by catalytic gas phase oxidation, in particular to recovery of acrylic acid from the acid water produced.
2. Description of the Background
Acrylic acid can be prepared from propene by catalytic gas phase oxidation. The propene to be oxidized can be mixed with a diluent gas or with a circulated gas containing unreacted starting materials. The gas-phase oxidation reaction mixture is passed to an absorption column to separate off the acrylic acid. There, the acrylic acid is substantially separated off from the mixture of reaction products using solvents such as lactams, for example methylpyrrolidone, or other organic acids, for example ethylhexanoic acid. The non-absorbed components are taken off from the absorption column in the gaseous state and fed to a condensation stage. The condensible and condensed part of this gas mixture is separated off and led off as what is termed acid water. The uncondensible gaseous part, in contrast, is in part recycled to the gas phase oxidation and forms the circulated gas. The acid water is generally incinerated. Thus, although many low- and medium-boilers are removed from the production cycle, acrylic acid present in the acid water is also destroyed.
This loss of acrylic acid can be avoided by distilling the acid water or extracting it with suitable compounds. Suitable compounds for extracting acrylic acid from aqueous solutions are specified by I. M. Korenman et al. in "Distribution of acrylic acid between organic solvents and water" (translation by Consultants Bureau, New York, from Zhurnal Prikladnoi Khimii, Vol. 45, No. 5, May 1972, pp. 1078-1082), including dimethyl phthalate. Distillation has the disadvantage of a high energy consumption, and extraction leads to a not inconsiderable additional use of equipment, since, in addition to extracting the acid water, it is necessary to distil or strip the solvent from the extract phase. This cycle for recovering acrylic acid from the acid water is complicated, especially, by the need to avoid as far as possible carrying over the solvent used there into the preparation cycle, since the presence of further organic solvents in the preparation cycle can adversely effect the quantitative yield and the quality of the acrylic acid present. It is highly complicated to exclude adverse effects of this type reliably.
SUMMARY OF THE INVENTION
It is an object of the present invention therefore to find an efficient process for preparing acrylic acid in which acrylic acid can be additionally recovered from the acid water in a simple and effective manner.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
We have found that this object is achieved by the process for preparing acrylic acid by catalytic gas phase oxidation of propene, acrylic acid being absorbed from the gas phase oxidation reaction mixture in an absorption stage using a first solvent, a gas mixture being taken off from the absorption stage which is low in the first solvent and in acrylic acid, the gas mixture being cooled in a condensation stage, preferably to a temperature of from 20.degree. C. to 60.degree. C., the condensed phase of the gas mixture from the condensation stage being taken off as acid water and the gaseous phase of the gas mixture being taken off from the condensation stage and at least in part recycled as circulated gas to the gas phase oxidation. In the process of the invention the first solvent comprises at least one substituted or unsubstituted biphenyl, a substituted or unsubstituted diphenyl ether or dimethyl phthalate, and acrylic acid is extracted from the acid water in an acid water-extraction stage using a second solvent which comprises at least one substituted or unsubstituted biphenyl, a substituted or unsubstituted diphenyl ether or dimethyl phthalate.
Preferably, the first solvent used is a mixture which comprises biphenyl and diphenyl ether and/or dimethyl phthalate, in particular a mixture which comprises from 60 t
REFERENCES:
patent: 3932500 (1976-01-01), Duembgen et al.
patent: 4110370 (1978-08-01), Engelbach et al.
patent: 5426221 (1995-06-01), Willersinn
I.M. Korenman, et al., Zhurnal Prikladnoi Khimii, vol. 45, No. 5, "Distribution of Acrylic Acid Between Organic Solvents and Water", May 1972, English Translation Only, pps. 1101-1105, (translated from the original transcript of pps. 1078-1082).
Dams Albrecht
Hammon Ulrich
Heida Bernd
Thiessen Fritz
BASF - Aktiengesellschaft
Killos Paul J.
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