U.S. patent application number 09/805725 was filed with the patent office on 2001-10-18 for process for the preparation of alkanolamines having improved color quality.
Invention is credited to Buskens, Philip, Gutschoven, Frank, Melder, Johann-Peter, Robeta, Karl-Heinz, Ruider, Gunther, Schulz, Gerhard.
Application Number | 20010031897 09/805725 |
Document ID | / |
Family ID | 7634383 |
Filed Date | 2001-10-18 |
United States Patent
Application |
20010031897 |
Kind Code |
A1 |
Ruider, Gunther ; et
al. |
October 18, 2001 |
Process for the preparation of alkanolamines having improved color
quality
Abstract
Preparation of alkanolamines having improved color quality by
treating the alkanolamine with an effective amount of phosphorous
acid or hypophosphorous acid or compounds thereof initially at
elevated temperature over a period of at least 5 min (step a), and
then distilling it in the presence of an effective amount of one of
these phosphorus compounds (step b).
Inventors: |
Ruider, Gunther;
(Wachenheim, DE) ; Robeta, Karl-Heinz; (Grunstadt,
DE) ; Melder, Johann-Peter; (Bohl-Iggelheim, DE)
; Schulz, Gerhard; (Ludwigshafen, DE) ;
Gutschoven, Frank; (Antwerpen, BE) ; Buskens,
Philip; (Hoogstraten, BE) |
Correspondence
Address: |
Herbert B. Keil
KEIL & WEINKAUF
1101 Connecticut Ave., N.W.
Washington
DC
20036
US
|
Family ID: |
7634383 |
Appl. No.: |
09/805725 |
Filed: |
March 7, 2001 |
Current U.S.
Class: |
564/497 ;
564/503 |
Current CPC
Class: |
C07C 213/10 20130101;
C07C 213/10 20130101; C07C 215/12 20130101 |
Class at
Publication: |
564/497 ;
564/503 |
International
Class: |
C07C 29/84 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 11, 2000 |
DE |
10011942.5 |
Claims
We claim:
1. A process for the preparation of alkanolamines having improved
color quality, which comprises treating the alkanolamine with an
effective amount of phosphorous acid or hypophosphorous acid or
compounds thereof initially at elevated temperature over a period
of at least 5 min (step a), and then distilling it in the presence
of an effective amount of one of these phosphorus compounds (step
b).
2. A process as claimed in claim 1, wherein the phosphorus
compounds are disodium hydrogenphosphite (Na.sub.2HPO.sub.3),
triethyl phosphite, triphenyl phosphite or disodium
hydrogenhypophosphite (Na.sub.2HPO.sub.2).
3. A process as claimed in claim 1 or 2, wherein the alkanolamine
is an ethanolamine or propanolamine.
4. A process as claimed in claim 1 or 2, wherein the alkanolamine
is monoethanolamine, diethanolamine or triethanolamine.
5. A process as claimed in claim 1, wherein the alkanolamine is
N-(2-aminoethyl)ethanolamine and the phosphorus compounds are
phosphorous acid or hypophosphorous acid.
6. A process as claimed in any of claims 1 to 5, wherein the
treatment of the alkanolamine in step a is carried out over a
period of from 10 min to 50 hours.
7. A process as claimed in any of claims 1 to 6, wherein the
treatment of the alkanolamine in step a is carried out at
temperatures of from 40 to 250.degree. C.
8. A process as claimed in any of claims 1 to 7, wherein the
treatment of the alkanolamine in step a and the distillation of the
alkanolamine (step b) are in each case carried out in the presence
of from 0.01 to 2% by weight of the phosphorus compound.
9. A process as claimed in any of claims 1 to 8, wherein the
prepared alkanolamine, following treatment for three hours with
1000 ppm of glacial acetic acid at 100.degree. C., has an APHA
color number (DIN ISO 6271) of from 0 to 100, an absolute value for
the numerical measure a* according to the CIE Lab system of from 0
to 4 and an absolute value for the numerical measure b* according
to the CIE Lab system of from 0 to 8, or following treatment for
one hour with 1.25 times the amount by weight of 32% strength
aqueous hydrochloric acid at 70.degree. C., a Gardner color number
(DIN ISO 4630) of from 0 to 3.
Description
[0001] The present invention relates to a process for the
preparation of alkanolamines having improved color quality.
[0002] Important fields of use of alkanolamines, such as, for
example, triethanolamine (TEA), or secondary products thereof, are,
for example, soaps, cleansers and shampoos in the cosmetics
industry, and also dispersants and emulsifiers.
[0003] For these and other fields of use, water-clear, colorless
alkanolamines having as little discoloration as possible, e.g.
measured as APHA or Gardner color number, which retain these
properties even over relatively long storage periods (of, for
example, 6, 12 or more months) are desired.
[0004] A known problem is that a pure alkanolamine obtained
following fractional distillation of an alkanolamine crude product
which has been obtained, for example, by reacting ammonia with
ethylene oxide or propylene oxide has a yellowish to brownish
discoloration (color number e.g. about 10 to 500 APHA in accordance
with DIN ISO 6271(=Hazen)). This discoloration arises particularly
in processes involving high temperatures.
[0005] During storage of the alkanolamine, including in sealed
packs or with the exclusion of light, this discoloration is further
intensified. (See e.g.: T. I. MacMillan, Ethylene Oxide
Derivatives, Report No. 193, chapter 6, pages 6-5 and 6-9 to 6-13,
1991, SRI International, Menlo Park, Calif. 94025; G. G. Smirnova
et al., J. of Applied Chemistry of the USSR 61, pp. 1508-9 (1988),
and Chemical & Engineering News 1996, September 16, page 42,
middle column).
[0006] A number of processes for the preparation of alkanolamines
having improved color quality are described in the literature.
[0007] EP-A-36 152 and EP-A-4015 describe 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.
[0008] U.S. Pat. No. 3,207,790 describes a process for improving
the color quality of alkanolamines by the addition of a borohydride
of an alkali metal to the alkanolamine.
[0009] However, the presence of an auxiliary (stabilizer) for
improving the color quality of alkanolamines is undesirable in many
important areas of application.
[0010] The earlier German Application No. 19942300.8 from 04.09.99
relates to a process for the preparation of alkanolamines having
improved color quality by treating the alkanolamine with hydrogen
in the presence of a hydrogenation catalyst at elevated
temperature.
[0011] JP-A-04 29 0850 (Derwent Abstract No. 92-393250/48; Chem.
Abstr. 118: 101513e) describes the decoloration of
triethylenetetramine by heating in the presence of phosphorous acid
and water.
[0012] JP-A-49 07 6804 (Derwent Abstract No. 76608V 44; Chem.
Abstr. 82:3766h) relates to the purification of ethyleneamines,
such as triethylenetetramine or pentaethylenehexamine by
distillation in the presence of esters of phosphorous acid.
[0013] EP-A-4015 describes how mono-, di- and triethanolamine
having reduced discoloration are obtained by the addition of
phosphorous or hypophosphorous acid or derivatives thereof before,
during or directly after the stepwise reaction of ethylene oxide
with ammonia and subsequent isolation by distillation. Page 2,
lines 14 to 18 teach that it is not possible to decolorize to a
satisfactory degree ethanolamines which already have a greater or
lesser degree of discoloration by a distillation carried out in the
presence of phosphorous acid. EP-A-4015 teaches that it is instead
necessary for the phosphorous or hypophosphorous acid to be present
during the preparation of the ethanolamine or at least be added to
the crude reaction mixture comprising the ethanolamines, water and
ammonia directly after the reaction (cf. the examples and the
patent claim).
[0014] The earlier German Application No. 19855383.8 from 01.12.98
relates to a process for the purification of TEA prepared by
reacting aqueous ammonia with ethylene oxide in liquid phase under
pressure and at elevated temperature by separating off excess
ammonia, water and monoethanolamine from the reaction product,
reacting the resulting crude product with ethylene oxide at
temperatures of from 110 to 180.degree. C., and then rectifying the
mixture in the presence of phosphorous or hypophosphorous acid or
compounds thereof.
[0015] It is an object of the present invention to find an
economic, selective, efficient and technically noncomplex process
for the preparation of alkanolamines having improved color quality.
The process should, by overcoming the disadvantages of the prior
art, permit the discoloration of alkanolamines (such as, for
example, triethanolamine or aminoethylethanolamine), e.g. measured
as APHA color number, to be reduced and the color stability to be
improved (undesired increase in color number over the storage
period).
[0016] We have found that this object is achieved by a process for
the preparation of alkanolamines having improved color quality,
which comprises treating the alkanolamine with an effective amount
of phosphorous acid or hypophosphorous acid or compounds thereof
initially at elevated temperature over a period of at least 5 min
(step a), and then distilling it in the presence of an effective
amount of one of these phosphorus compounds (step b).
[0017] The alkanolamine used in the process according to the
invention, preferably ethanolamine or propanolamine, can be
obtained by known processes, e.g. by the reaction of ammonia or of
a primary or secondary amine with ethylene oxide or propylene oxide
(e.g. as in EP-A-673 920), by the 1,4-addition of ammonia or of a
primary or secondary amine to an .alpha.,.gamma.-unsaturated
aldehyde (e.g. acrolein) and subsequent reduction (e.g.
hydrogenation), by the 1,4-addition of ammonia or of a primary or
secondary amine to an .alpha.,.gamma.-unsaturated acid (e.g.
acrylic acid) or an .alpha.,.gamma.-unsaturated ester (e.g. acrylic
ester) and subsequent reduction (e.g. hydrogenation), by the
1,4-addition of water to an .alpha.,.beta.-unsaturated nitrile
(e.g. acrylonitrile) and subsequent reduction (e.g. hydrogenation),
amination of corresponding primary or secondary alcohols, or
aminating hydrogenation of corresponding hydroxyaldehydes or
hydroxyketones.
[0018] N-(2-Aminoethyl)ethanolamine (AEEA) can be obtained by the
reaction of monoethanolamine or ammonia with ethylene oxide in the
presence of hydrogen and a hydrogenating, dehydrogenating or
aminating catalyst.
[0019] The purity of the alkanolamines used in the process
according to the invention, preferably ethanolamines or
propanolamines, is generally greater than 70% by weight, in
particular greater than 80% by weight. As well as distilled or
undistilled crude alkanolamines, which can also be removed directly
in crude form from the corresponding precursors from a plant for
the preparation of the alkanolamine, it is also possible to use
distilled alkanolamines having a purity of greater than 90% by
weight, particularly .gtoreq.97% by weight, in particular
.gtoreq.98% by weight, very particularly .gtoreq.99% by weight.
[0020] It is also possible to use mixtures of alkanolamines, in
which case the purities given above are based on each alkanolamine
of this mixture, or solutions of alkanolamines in an inert solvent,
such as, for example, alcohols (methanol, ethanol, isopropanol,
n-propanol, n-butanol, 2-ethylhexanol), ethers (tetrahydrofuran,
1,4-dioxane), hydrocarbons (benzene, pentane, petroleum ether,
toluene, xylene, hexane, heptane, Mihagol) and water.
[0021] The APHA color number of the alkanolamines used (based on
the non-acid-treated alkanolamine) is generally .ltoreq.100, in
particular .ltoreq.50, for example .ltoreq.20.
[0022] The alkanolamines which are preferably used in the process
according to the invention are ethanolamines and propanolamines
such as, for example, monoethanolamine (MEA), diethanolamine (DEA),
triethanolamine (TEA), O,N,N-tris(2-hydroxyethyl)ethanolamine,
N-(2-aminoethyl)ethanolamine (AEEA), N-(2-hydroxyethyl)piperazine,
N-(2-hydroxyethyl)morpholine, N,N'-bis(2-hydroxyethyl)piperazine,
monoisopropanolamine, diisopropanolamine, triisopropanolamine and
1,3-propanolamine, particularly preferably the ethanolamines MEA,
DEA, TEA and AEEA.
[0023] The process according to the invention can be carried out as
follows:
[0024] In a first process step (step a), the alkanolamine whose
color quality is to be improved, or a mixture of the alkanolamines
in liquid phase, optionally in the presence of an inert solvent, in
a suitable (stirred) container, which may be fitted with a reflux
condenser, is treated with an effective amount of phosphorous acid
(H.sub.3PO.sub.3), hypophosphorous acid (H.sub.3PO.sub.2) or
compounds of these acids, advantageously with stirring or
recirculation, and the mixture is heated over a period of generally
at least 1 minute, particularly at least 5 min, in particular at
least 10 min (for example 10 min to 50 hours, in particular 10 min
to 24 hours), very particularly at least 15 min (for example 15 min
to 2 hours), particularly preferably at least 30 min (for example
30 min to 2 hours), at temperatures of from 40 to 250.degree. C.,
in particular 100 to 250.degree. C., very particularly 120 to
220.degree. C., particularly preferably 150 to 220.degree. C.
[0025] For better handlability, it may be advantageous to meter in
the effective amount of phosphorous acid, hypophosphorous acid or
compounds of these acids in a suitable inert diluent or solvent,
such as, for example, water, alcohols (methanol, ethanol,
isopropanol, n-propanol), ethers (tetrahydrofuran, 1,4-dioxane) or
an alkanolamine (e.g. an ethanolamine, such as monoethanolamine,
diethanolamine, triethanolamine, N-(2-aminoethyl)ethanolamine),
where the alkanolamine can here also be the same as the
alkanolamine process product, in the form of a solution or
suspension.
[0026] The required treatment time of the alkanolamine (or of the
mixture of the alkanolamines) with the phosphorus compound is
determined inter alia from the degree of discoloration of the
alkanolamine used and the extent of desired decoloration and/or
color stability of the alkanolamine. As a rule, for a given
temperature, the higher the degree of decoloration of the
alkanolamine used in the process according to the invention and the
higher the requirements on the color quality of the process
product, the longer the treatment time.
[0027] The temperature must not, however, be chosen to be too high,
i.e. as a rule no greater than 250.degree. C., since otherwise
acid-induced degradation of the alkanolamine occurs, which has a
negative effect on the color quality of the alkanolamine ultimately
obtained.
[0028] The most favorable temperatures and treatment times for the
alkanolamine in question can be readily determined in simple
preliminary experiments.
[0029] During this treatment of the alkanolamine with the
phosphorus compound, it is advantageous if the mixture is further
stirred throughout the entire treatment period or occasionally
(e.g. stirred or recirculated).
[0030] It is also advantageous if the treatment of the alkanolamine
is carried out under a protective-gas atmosphere (e.g. N.sub.2 or
Ar).
[0031] The treatment of the alkanolamine with the phosphorus
compound can also be carried out continuously in suitable
containers, e.g. in a tubular reactor or in a cascade of stirred
containers.
[0032] The treatment of the alkanolamine can advantageously be
carried out in the still container of a distillation column or in a
distillation receiver vessel.
[0033] In one particular embodiment of this first process step,
during the treatment of the alkanolamine, an inert gas (e.g.
N.sub.2 or Ar) is passed as stripping stream through the
alkanolamine in order to remove from the mixture low-boiling
components which form and which may have a negative effect on the
color quality, such as, for example, acetaldehyde or secondary
products thereof.
[0034] In another particular embodiment of this first process step,
the alkanolamine to be treated is circulated in liquid form via a
eat exchanger, and low-boiling components which form, which may
have a negative effect on the color quality, such as, for example,
acetaldehyde, are drawn off in the process.
[0035] The heat exchanger here can be an open heat exchanger such
as, for example, a falling-film evaporator or wiper-blade
evaporator, or a sealed heat exchanger, such as, for example, a
plate-type heat exchanger or shell-and-tube heat exchanger.
[0036] Depending on the reaction conditions chosen, it may be
necessary to carry out the treatment of the alkanolamine at
superatmospheric pressure (e.g. 0.1 to 50 bar) in order to avoid
the undesired escape of one or more components from the
mixture.
[0037] The phosphorous acid or hypophosphorous acid can be used in
the process according to the invention in monomeric or else in
polymeric form, in hydrous form (hydrates) or as an addition
compound (e.g. on an inorganic or organic support such as
SiO.sub.2, Al.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2)
[0038] Suitable for the process according to the invention are also
compounds of phosphorous or hypophosphorous acid, such as salts
(e.g. disodium hydrogenphosphite (Na.sub.2HPO.sub.3), disodium
hydrogenhypophosphite (Na.sub.2HPO.sub.2)), dipotassium
hydrogenphosphite (K.sub.2HPO.sub.3), diammonium hydrogenphosphite
((NH.sub.4).sub.2HPO.sub- .3)), amides, esters (e.g. triethyl
phosphite or triphenyl phosphite) or anhydrides thereof (e.g.
P.sub.2O.sub.3) or mixtures of the abovementioned phosphorus
compounds.
[0039] Here, the salts can either be used directly as such, or be
obtained by mixing, either in situ or prior to use in the
treatment, a basic, organic or inorganic salt, such as NaOH, KOH,
Ca(OH).sub.2, NH.sub.4OH, Na.sub.2CO.sub.3, K.sub.2CO.sub.3, NaOMe
or NaOEt, optionally in a suitable solvent, with the phosphorous
acid or hypophosphorous acid.
[0040] Preference is given to phosphorous acid (H.sub.3Po.sub.3),
hypophosphorous acid (H.sub.3PO.sub.2), disodium hydrogenphosphite
(Na.sub.2HPO.sub.3), triethyl phosphite, triphenyl phosphite and
disodium hydrogenhypophosphite (Na.sub.2HPO.sub.2).
[0041] The amount of phosphorus compounds added is usually at least
0.01% by weight, preferably 0.01 to 2% by weight, particularly
preferably 0.02 to 1.0% by weight, very particularly preferably
0.02 to 0.5% by weight, based on the amount of alkanolamine used,
although the effect also occurs if the amounts are larger.
[0042] If the phosphorus compounds added are acidic, i.e. have a
pK.sub.a value of less than 4, the amount is generally 0.01 to 0.5%
by weight (based on the amount of alkanolamine used) in order to
largely avoid the induction of acid-catalyzed decomposition
reactions of the alkanolamine.
[0043] Following the above-described treatment of the alkanolamine
(or the mixture of the alkanolamines), the alkanolamine (or the
mixture of the alkanolamines) is distilled or rectified in a second
process step (step b) in the presence of an effective amount of one
or more of the abovementioned phosphorus compounds at reduced
pressure.
[0044] The amounts of phosphorus compounds in this second process
step are in the same range as in the first process step.
[0045] In a particular embodiment process, the distillation or
rectification of the alkanolamine takes place in the presence of
the phosphorus compound or phosphorus compounds already added in
the first process step.
[0046] The distillation or rectification of the alkanolamine is
carried out discontinuously or continuously at a pressure of, as a
rule, less than 100 mbar (100 hPa), for example at about 10 to 50
mbar, and at still temperatures of, generally, from 100 to
250.degree. C., where, in the case of the continuous procedure, in
a particular embodiment, low-boiling fractions which may be present
are drawn off overhead, and the alkanolamine is obtained in a
sidestream takeoff.
[0047] Some or all of the residue from the distillation or
rectification which comprises the added phosphorus compound or
reaction products thereof can, in a particular embodiment, be
returned to the process.
[0048] The process according to the invention produces an
alkanolamine having improved color quality which, directly after it
has been obtained, has an APHA color number of from 0 to 30, in
particular from 0 to 20, very particularly from 0 to 10, and which,
after acid treatment, which is carried out as described below under
2a) within 0.5 to 3 hours after it has been obtained, has an APHA
color number of from 0 to 100, in particular from 0 to 60, very
particularly from 0 to 40, and an absolute value for the numerical
measure a* according to the CIE Lab system of from 0 to 4, in
particular from 0 to 3, very particularly from 0 to 2.5, and an
absolute value for the numerical measure b* according to the CIE
Lab system of from 0 to 8, in particular from 0 to 5, very
particularly from 0 to 4, or which, after acid treatment, which is
carried out as described below under 2b) within 0.5 to 3 hours
after it has been obtained, has a Gardner color number of from 0 to
3, in particular from 0 to 2.5, very particularly from 0 to 2.
EXAMPLES
[0049] Preliminary Remarks
[0050] 1a) Heat Treatment and Distillation (Examples 1 to 11)
[0051] The crude triethanolamine (TEA) used in Examples 1 to 11
consisted of a technical-grade stream from the preparation of
ethanolamine, consisting of 71% by weight of triethanolamine, 27%
by weight of diethanolamine and 2% by weight of other substances
(predominantly O,N,N-tris(2-hydroxyethyl)ethanolamine,
O,N-bis(2-hydroxyethyl)ethanolami- ne and
bishydroxyethylpiperazine).
[0052] A sample of the crude TEA as described above and used in
Examples 1 to 11 had, following an industrial distillation, a
purity of >99% by weight and, after acid treatment as in 2a) and
subsequent measurement as in 2c) in a LICO 200 instrument, values
between 4 and 5 both for a* and for b*.
[0053] The heat treatment (=process step a) was carried out by
heating the crude ethanolamine mixture in a distillation receiver
vessel in the presence of the phosphorus compound listed in Table 1
at atmospheric pressure (temperature and duration see Table 1).
[0054] Subsequent distillation of the crude triethanolamine in the
presence of the phosphorus compound (=process step b) was carried
out on a 1 1 scale discontinuously at 0.4 to 1.0 mbar using a
single-stage laboratory bridge, the still temperature being
maintained throughout between 160 and 190.degree. C. and the 45
head temperature between 140 and 170.degree. C.
[0055] During the distillation, the distillate was collected in
four equal fractions, the first of which typically consisted of
approximately 66% by weight of DEA and 33% by weight of TEA, the
second of which consisted of 38% by weight of DEA and 61% by weight
of TEA, and the third and fourth of which each consisted of >97%
by weight of TEA. Since the first two fractions did not comprise
representative TEA, they were discarded and not taken into
consideration for the color number measurement.
[0056] 1b) Heat Treatment and Distillation (Examples 12 to 23)
[0057] The phosphorus compound given in Table 2 was dissolved, with
stirring for approximately 12 hours and where necessary slight
warming (max. 40 to 60.degree. C.), in pure AEEA (purity >99% by
weight of AEEA; impurities: diethylenetriamine (DETA) and
hydroxyethylpiperazine (HEP); color quality: Gardner color number
after acid treatment as described under 2b): 6.0, Gardner color
number after thermal treatment as described under 2d) and
subsequent acid treatment as described under 2b): 6.0).
[0058] The feed material prepared in this way and kept under a
blanket of nitrogen was pumped through a pipe coil (volume:
[0059] 50 ml) thermostated in an oil bath, the residence time,
amount of additive and temperature being varied as given in Table 2
(=process step a).
[0060] The discharge from the pipe coil was passed to a wiper-film
evaporator operated at a pressure of 50 mbar and an oil temperature
between 150 and 170.degree. C., meaning that a sufficiently high
still discharge (about 10 to 20% of the volume stream) was retained
in order to avoid deposits on the heating surface. At the top of
the wiper-film evaporator, the vaporous AEEA was stripped off and
obtained as distillate in a condenser (process step b). To improve
separation, a nitrogen stripping stream of 1 1 of N.sub.2/h was
passed upward from below through the wiper-film evaporator.
[0061] 1c) Heat Treatment and Distillation (Examples 24 to 32)
[0062] The phosphorus compound (H.sub.3PO.sub.3 or H.sub.3PO.sub.2)
given in Table 3 was dissolved, with stirring for approximately 12
hours, in pure AEEA (purity >99% by weight of AEEA; impurities:
diethylenetriamine (DETA) and hydroxyethylpiperazine (HEP); color
quality: Gardner color number after acid treatment as described
under 2b): 4.6).
[0063] The other process steps were carried out as described under
1b).
[0064] 2. Determination of the Color Quality of the
Alkanolamines
[0065] 2a) Acid treatment of the alkanolamines (Examples 1 to
11)
[0066] To amplify the color effects which occur, 20 ml of the
alkanolamine sample to be investigated were treated with 1000 ppm
of glacial acetic acid and carefully mixed. The mixture was
thoroughly stirred and transferred to a test tube, which was left
for 3 h in an oil bath thermostated at 100.degree. C. Here, the
vessel was sealed with a stopper and kept under nitrogen. The
stopper was pierced by a cannula in order to ensure pressure
compensation. After 3 h, the vessel was cooled in an ice bath, and
directly afterward the color number was measured (see 2c).
[0067] 2b) Acid Treatment of the Alkanolamines (Examples 12 to 23
and Examples 24 to 32)
[0068] 10 g of the alkanolamine (e.g. aminoethylethanolamine
(AEEA)) were weighed into a 100 ml Erlenmeyer flask and, with
stirring (magnetic stirrer) and cooling (ice bath), 12.5 g of 32%
strength aqueous hydrochloric acid were introduced over the course
of one minute in three portions, initially dropwise, then more
quickly, the solution heating up (max. about 30.degree. C.). After
a post-cooling period of 2 minutes, a sample of the solution was
transferred to a test tube and sealed with a rubber stopper pierced
by a cannula. The test tube was heated in a heating bath at
70.degree. C. for one hour. The test tube was then cooled in an ice
bath, the ingredients were immediately transferred to a cuvette and
the color number was measured (see 2c).
[0069] [An acid treatment of an alkanolamine for intensifying color
effects has been described generally in 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 TEA is treated (neutralized)
with acetic acid, citric acid, sulfuric acid, hydrochloric acid or
phosphoric acid.]
[0070] 2c) Color number measurement (Examples 1 to 32)
[0071] In general, the color number of the previously acid-treated
sample was measured at a max. of 3 h after cooling in order to keep
post-coloration following acid treatment (as a result of aging) as
low as possible.
[0072] In a spectral color measurement, the values for the
numerical measures a* and b* in accordance with the CIE Lab system
(according to Judd and Hunter (CIE = Comission International
d'Eclairage, Paris); (cf. DIN 6174)), the APHA value (corresponding
to DIN-ISO 6271) and the Gardner color number (DIN ISO 4630) were
determined.
[0073] The a*, b* and APHA values (APHA color number =Hazen color
number =Pt/Co color number) in Examples 1 to 11 were determined in
the standard manner in a LICO 200 instrument from Dr. Lange in a 5
cm (path length) curette (volume .apprxeq.10 ml).
[0074] The Gardner and APHA values in Examples 12 to 32 were
determined in the standard manner in an LTM1 Liquid Tester from Dr.
Lange in an 11 mm (internal diameter) round curette.
[0075] The a* value gives the red/green coloration of the sample (a
positive a* value gives the red color content, and a negative a*
value the green color content) and the b* value gives the
yellow/blue content (a positive b* value gives the yellow color
content, a negative b* value gives the blue color content). A
particularly desirable result is an absolute a* value which is
lower than that in the starting material prior to carrying out the
process according to the invention.
[0076] The a*, b*, Gardner and APHA values given in Tables Nos. 1,
2 and 3 refer in every case to the samples after acid treatment
carried out in the appropriate manner.
[0077] 2d) Storage Experiments (Examples 12 to 23)
[0078] In order to investigate the color stability of AEEA, 50 g of
the AEEA obtained at the distillation were heated at an internal
temperature of 90.degree. C. for 3 hours under nitrogen in a
three-necked flask with attached water condenser. After cooling to
room temperature, the mixture was acid-treated as described above
under 2b), and the color number was measured as described above
under 2c). This thermal treatment of the AEEA at 90.degree. C. for
3 h simulated storage over about 40 days at 20.degree. C.
Results
[0079] The results of Example Nos. 1 to 11, 12 to 23 and 24 to 32
are given in Tables 1, 2 and 3.
Examples 1 to 4, 12, 24 to 27 and 30 are Comparative Examples
[0080] Example 1 represents distillation of the TEA crude mixture
without prior heat treatment as comparative value, whereas Example
2 is with heat treatment (60 min, 180.degree. C.), but in each case
without the addition according to the invention of the phosphorus
compound.
[0081] In both cases, the a* and b* absolute value of the product
is unacceptably high.
[0082] By adding H.sub.3PO.sub.3 or Na.sub.2HPO.sub.3 during the
distillation, but without prior heat treatment, the color quality
was not sufficiently improved (Examples 3 and 4): the a* and/or b*
absolute values remained unacceptably high.
Examples 5 to 11
[0083] As a result of prior thermal treatment of the alkanolamine
in the presence of the phosphorus compounds described, it is
possible to achieve an improvement in the color quality to the
required color numbers and a* and b* values. In this connection,
H.sub.3PO.sub.3 is more effective than Na.sub.2HPO.sub.3, lowering
both the a* and also the b* absolute values. Na.sub.2HPO.sub.3 is
more effective in reducing the a* absolute value on its own, but
has less influence on the b* value.
Examples 13 to 23
[0084] The treatment according to the invention of the AEEA with
H.sub.3PO.sub.3 in each case significantly improved the color
quality (compare with Example 12).
[0085] The longer the AEEA was pretreated in the presence of
H.sub.3PO.sub.3, the more favorable the color number of the process
product (Example 14 vs. 13, 17 vs. 16 vs. 15 and 20 vs. 19 vs.
18).
[0086] Moreover, as the temperatures in the first process step
increase, a positive effect is established (Example 18 vs. 13 and
19 vs. 14).
[0087] Furthermore, the amount of H.sub.3PO.sub.3 added has a
positive effect on the color quality (Example 21 vs. 18 vs. 15, and
22 vs. 19 vs. 16).
[0088] If AEEA is heat-treated (=process step a) for too long in
the presence of amounts of H.sub.3PO.sub.3 which are too great at
too high a temperature (Example 23 vs. 22), then an impairment in
the color number is observed (acid-induced degradation).
Examples 24 to 32
[0089] Example 24 shows, as comparison, the result with regard to
the color number of a simple distillation of the AEEA over a Sambay
evaporator.
[0090] According to Examples 24, 27 and 30, distillation of the
AEEA in the presence of the phosphorus compound without prior heat
treatment according to the invention (step a) does not lead to an
improvement in the color number of the alkanolamine.
[0091] Examples 28, 29, 31 and 32 are in accordance with the
invention and show the improvement in color quality.
1 TABLE 1 Heat treatment (process step a) Fraction 3 Fraction 4
Example Duration Temperature (of the distillation) (of the
distillation) No. Additive [min] [.degree. C.] a* b* APHA a* b*
APHA 1 -- -- -- -9.3 65.6 530 -6.1 24.6 168 2 -- 60 180 -10.7 71.2
567 -8.8 30.5 254 3 2500 ppm of H.sub.3PO.sub.3 -- -- 4.3 3.0 35
5.1 3.3 39 4 2200 ppm of Na.sub.2HPO.sub.3 -- -- 2.4 16.3 130 3.3
14.1 118 5 2500 ppm of H.sub.3PO.sub.3 30 180 1.7 1.4 15 2.0 2.2 22
6 2500 ppm of H.sub.3PO.sub.3 60 180 1.3 1.2 13 1.7 1.6 17 7 4000
ppm of H.sub.3PO.sub.3 60 180 1.0 0.9 10 1.4 1.1 12 8 4000 ppm of
H.sub.3PO.sub.3 10 180 2.2 2.7 26 2.1 3.0 28 9 4000 ppm of
H.sub.3PO.sub.3 60 150 2.0 2.6 25 2.2 2.9 28 10 2200 ppm of
Na.sub.2HPO.sub.3 60 180 0.9 6.8 54 0.4 7.3 56 11 2000 ppm of
P(OPh).sub.3 60 180 1.7 3.2 29 2.1 4.6 41
[0092]
2 TABLE 2 After storage Pipe coil Sambay Color number Color number
Res. distillation (after acid (after acid Example Temp. time Temp.
Pressure treatment) treatment) No. Additive (min) (min) (.degree.
C.) (mbar) APHA Gardner APHA Gardner 12 -- 180 30 160 50 714 3.7
762 3.9 13 4000 ppm of H.sub.3PO.sub.3 150 10 170 50 430 2.5 502
2.8 14 4000 ppm of H.sub.3PO.sub.3 150 30 160 50 165 1.1 312 1.9 15
2000 ppm of H.sub.3PO.sub.3 180 10 170 50 198 1.2 252 1.6 16 2000
ppm of H.sub.3PO.sub.3 180 30 160 50 145 0.9 177 1.1 17 2000 ppm of
H.sub.3PO.sub.3 180 60 153 50 35 0.2 75 0.4 18 4000 ppm of
H.sub.3PO.sub.3 180 10 170 50 100 0.7 125 0.8 19 4000 ppm of
H.sub.3PO.sub.3 180 30 160 50 100 0.6 110 0.7 20 4000 ppm of
H.sub.3PO.sub.3 180 60 153 50 25 0.1 46 0.3 21 10,000 ppm of
H.sub.3PO.sub.3 180 10 170 50 36 0.2 40 0.3 22 10,000 ppm of
H.sub.3PO.sub.3 180 30 160 50 14 0.2 48 0.3 23 10,000 ppm of
H.sub.3PO.sub.3 180 60 153 50 70 0.4 101 0.6 (Res. time = residence
time)
[0093]
3TABLE 3 Color numbers after Pipe coil Sambay distillation (step a)
and acid treatment Temp. Res. time (HCl) Example No. Additive
(.degree. C.) (min) APHA Gardner 24 -- RT 30 505 2.9 25 -- 180 30
578 3.3 26 -- 180 10 541 3.1 27 4000 ppm of H.sub.3PO.sub.3 RT 30
515 2.9 28 4000 ppm of H.sub.3PO.sub.3 180 30 131 0.5 29 4000 ppm
of H.sub.3PO.sub.3 180 10 149 0.6 30 4000 ppm of H.sub.3PO.sub.2*)
RT 30 521 3.0 31 4000 ppm of H.sub.3PO.sub.2*) 180 30 216 1.0 32
4000 ppm of H.sub.3PO.sub.2*) 180 10 464 2.6 (Res. time = residence
time) (RT = room temperature = 22.degree. C.) *)as 50% strength
aqueous solution
* * * * *