Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2001-05-31
2002-05-14
Davis, Brian J. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C564S475000
Reexamination Certificate
active
06388137
ABSTRACT:
The present invention relates to a method of purifying triethanolamine (TEA) prepared by reacting aqueous ammonia with ethylene oxide in the liquid phase under superatmospheric pressure and at elevated temperature.
Important fields of use of TEA are, for example, soaps, detergents and shampoos in the cosmetics industry or else dispersants and emulsifiers.
For these fields of use, it is desirable for the TEA to be water-clear and colorless and to retain these properties even over prolonged storage times.
It is known that pure TEA obtained by a fractional distillation of a TEA crude product which has been obtained by reacting aqueous ammonia with ethylene oxide and distilling off monoethanolamine (MEA) and diethanolamine (DEA), and initially colorless (color number: about 0 to 20 APHA according to DIN-ISO 6271(=Hazen)), can, after a storage time of from about 4 to 6 weeks, even in a sealed pack and with the exclusion of light, gradually turn pale pink and finally, particularly when left to stand in light, can turn yellow to brown. This effect is accelerated by the action of relatively high temperatures. (See e.g.: G. G. Smirnova et al., J. of Applied Chemistry of the USSR 61, (1988) p. 1508-9, and Chemical & Engineering News 1996, September 16, page 42, middle column).
According to Chemical & Engineering News 1996, September 16, page 42, one mole of TEA decomposes at elevated temperature to give one mole of ethanolamine and two moles of acetaldehyde. Acetaldehyde condenses to give crotonaldehyde which, in turn, forms a Schiff's base with ethanolamine. This unsaturated Schiff's base leads, with 1,4-polymerization, to colored products in the TEA.
As well as the time-consuming storage experiments in which the APHA color number (according to DIN-ISO 6271) of TEA is measured as a function of the storage time, another method which has proven successful for assessing the color quality of pure TEA is the “acid neutralization test”.
This “acid neutralization test” permits assessment of the shelf life as regards color of freshly prepared TEA within a few minutes.
The test is described in the Japanese documents JP-A-62 019 558 (Derwent Abstract No. 87-067647/10) and JP-A-62 005 939 (Derwent Abstract No. 87-047397/07), according to which the TEA is treated (neutralized) with acetic acid, citric acid, sulfuric acid, hydrochloric acid or phosphoric acid, and then the absorbance of the absorption bands at 420 nm and 530 nm is measured. If, during the test, the TEA does not develop any pink discoloration visible to the eye and if the measured values for the absorbance remain sufficiently low, then the TEA has a long shelf life as regards color, i.e. remains colorless over a period of several months.
The literature describes various processes for the preparation of pure and colorless to slightly colored TEA.
EP-A-4015 describes how ethanolamines with relatively low discoloration are prepared by adding phosphorous or hypophosphorous acid during or after the preparation of the ethanolamines.
EP-A-36 152 and EP-A-4015 illustrate the effect of the materials used in processes for the preparation of alkanolamines on the color quality of the process products and recommend nickel-free or low-nickel steels.
US-A-3 819 710 discloses a method of improving the color quality of ethanolamines by hydrogenating the crude ethanolamines in the presence of selected catalysts. The method is, however, technically complex and does not give TEA products which remain colorless over several months.
US-A-3 207 790 describes a method of improving the color quality of alkanolamines by adding a boron hydride of an alkali metal.
US-A-3 742 059 and DE-A-22 25 015 describe the improvement in the color quality of alkanolamines by adding an alkanolamine ester of boric acid or alkali metal/alkaline earth metal borates.
The presence of an auxiliary for stabilizing TEA is, however, undesirable in many important TEA application fields.
The subsequent addition of small amounts of ethylene oxide to freshly distilled TEA likewise leads, according to U.S. Pat. No. 4,673,762, to decoloration and color stability. However, the method appears hazardous for toxicological reasons.
GB-A-1 062 730 describes a method of purifying ethanolamines by carrying out the purification by distillation in the presence of silicates or aluminates.
JP-A-62 019 558 (Derwent Abstract No. 87-067647/10) reports on the preparation of high-quality TEA by treating crude TEA with inorganic oxides at from 170 to 250° C. and subsequently distilling the mixture in the absence of oxygen.
Similar results are achieved according to JP-A-62 005 939 (Derwent Abstract No. 87-047397/07) if crude TEA is heated with the exclusion of air for from 1 to 10 h at from 170 to 250° C., and then distilled under reduced pressure.
SU-A-326 178 (Derwent Abstract No. 63384T-AE) describes the preparation of TEA with good color quality by gently reacting anhydrous monoethanolamine (MEA) or diethanolamine (DEA) or mixtures of the two substances with ethylene oxide at temperatures less than 50° C.
Similar results are obtained according to SU-A-228 693 (Chem. Abstr. 70, 77305f (1969)) and GB-A-1 092 449 if ammonium is reacted with ethylene oxide at less than or equal to 35° C., and the resulting ethanolamine mixture is distilled with the exclusion of air.
For cost reasons, processes in which the reactions with ethylene oxide are carried out at low temperatures are unprofitable because of the long residence times and the low space-time yields associated therewith.
It is an object of the present invention to find an alternative, economic process for the preparation of pure, colorless (APHA color number less than or equal to 10) and color-stable triethanolamine (TEA) from aqueous ammonia and ethylene oxide.
We have found that this object is achieved by a method of purifying triethanolamine prepared by reacting aqueous ammonia with ethylene oxide in the liquid phase under superatmospheric pressure and at elevated temperature, which comprises removing excess ammonia, water and monoethanolamine (MEA) from the reaction product, reacting the resulting crude product with ethylene oxide at temperatures of from 110 to 180° C., and then rectifying the mixture in the presence of phosphorous or hypophosphorous acid or compounds thereof.
The method according to the invention can be carried out as follows:
Firstly, for example in accordance with GB-A-760 215 or EP-A-673 920, an ethanolamine mixture, comprising the main components monoethanolamine (MEA), diethanolamion [sic] (DEA) and triethanolamine (TEA), is prepared by reacting aqueous ammonia with ethylene oxide in the liquid phase under superatmospheric pressure and elevated temperature in a reactor provided with cooling. Preference is given here to the process as in EP-A-673 920.
The reaction temperatures here are generally from 110 to 160° C., preferably from 120 to 150° C., and the pressures are from 50 to 120 bar (5 to 12 MPa), preferably from 75 to 100 bar (7.5 to 10 MPa). The molar ratio of ammonia to ethylene oxide is from 1:1 to 100:1, preferably from 3:1 to 50:1, particularly preferably from 4:1 to 15:1, and the ammonia is used as a 60 to 99.99% strength, preferably 70 to 95% strength, aqueous solution. The ethylene oxide used can be added all at once or in from 2 to 10, preferably from 2 to 6, portions of in each case from 10 to 70% by weight (based on the total amount).
For example, the reaction of aqueous ammonia with ethylene oxide can be carried out in accordance with Example 15 on page 16 of GB-A-760 215 or, preferably, according to the two experiments No. 5 of Examples 1 and 2 in EP-A-673 920.
Then, in a manner known per se, the excess ammonia, together with some of the water, is distilled off from the resulting product under superatmospheric pressure, and then the remaining water is distilled off at reduced pressure.
This leaves a crude product comprising essentially MEA, DEA and TEA and having a water content of less than 0.3% by weight, preferably less than 0.1% by weight.
The monoethanolamine (MEA) is subsequen
Ross Karl-Heinz
Ruider Günther
BASF - Aktiengesellschaft
Davis Brian J.
Keil & Weinkauf
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