Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Patent
1998-07-16
2000-10-17
McKane, Joseph K.
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
568920, C07C 2726, C07C 2974, C07C 2980, C07C 2988
Patent
active
061334898
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for obtaining glycols of low aldehyde content and to products prepared using these glycols.
Glycols of low molecular mass, such as mono-, di- and triethylene glycol, are important products of the chemical industry. Monoethylene glycol in particular (also referred to as 1,2-ethanediol, ethylene glycol or simply MEG) is among the principal products of the chemical industry worldwide, and is used predominantly as antifreeze for vehicle radiators and as raw material for the production of polyesters.
The only process currently used for the large-scale industrial production of ethylene glycol comprises the hydrolysis of ethylene oxide and the subsequent working up of the resulting reaction mixture. Worldwide production capacity for ethylene glycol produced by ethylene oxide hydrolysis is currently estimated at 7.times.10.sup.6 metric tons per annum. In this preparation process, the ethylene oxide is reacted continuously or in batches with water, in special reactors and under appropriate conditions. The resulting aqueous reaction mixture is then concentrated over several stages, and the crude glycol, finally, is purified by fractionation (cf. eg.: K. Weissermel, H.-J. Arpe, Industrielle Organische Chemie [Industrial Organic Chemistry], 3rd ed., VCH 1988, p. 159 ff.). The principal components of the reaction mixture are typically mono-, di- and triethylene glycol. Tetraethylene glycol and higher homologs are usually present in quantities so small that they are generally not worth recovering.
Distillation processes and apparatus for the purification of glycols, of various design, are known (cf. eg.: Ullmanns Encyklopadie der technischen Chemie [Ullmann's Encyclopedia of Industrial Chemistry], 4th edition, VCH 1974, Volume 8, p. 200 ff.). In the majority of cases, in serial distillation columns, first water and then ethylene glycol and, finally, the higher glycol ethers are recovered continuously. Various units can be used as evaporators for the distillations; modern continuous plants, however, employ falling-film evaporators for energy reasons. For reasons of cost, these plant components are commonly made from carbon steel.
Owing to the high boiling points of ethylene glycol and its homologs, the distillations always take place under reduced pressure. Any vacuum distillation unit, whether industrial-scale or laboratory-scale, possesses a certain leakage rate, ie. leaks which to a minor extent allow the surrounding atmosphere to enter the unit. Thus, in the course of operation, atmospheric oxygen finds its way into the vacuum distillation.
Like all alcohols, glycols can readily be oxidized both thermally (autoxidation) and catalytically. The reaction products of ethylene glycol with oxygen or other oxidizing agents are aldehydes (glycol aldehyde, glyoxal, formaldehyde, acetaldehyde) and the corresponding acids. On the other hand, however, especially when ethylene glycol is used to produce polyester films, there are particularly high purity requirements. Films produced using aldehyde-rich ethylene glycol prove to be highly sensitive to light. In particular, slight yellowing can be observed. Therefore, in the course of polyester production but also in other sectors, the presence of these oxidation products is extremely undesirable, so that the users are attempting to limit the aldehyde content by means of strict specification. For example, the aldehyde content of ethylene glycol intended for film production should be less than 20 ppm.
Provided no particular effects occur in the course of ethylene glycol production, the quantity of oxidation products formed is normally unimportant. However, it has been observed in industrial plants that a rise in the proportion of aldehyde in the distilled glycol may occur which was not readily explainable. At the same time, unusually large quantities of rust particles (magnetite) were found in the liquid phases of the distillation.
The problem set out above of increased aldehyde formation should also exist in the context of the distillative p
Mohr Jurgen
Vansant Frans
BASF - Aktiengesellschaft
McKane Joseph K.
Oswecki Jane C.
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