Note: Descriptions are shown in the official language in which they were submitted.
2 ~'7~
Process for the preparation of storaae-stable
levulinic _cid
The invention relates to a proce~s for the
preparation of storage-stable levulinic acid by saponif-
ication of acetylsuccinates.
Levulinic acid is a startin~ product for the
preparation of organic chemicals, dyestuffs, polymers,
pharmaceutically active compounds and f~avour substances.
Particularly in the use of levulinic acid for the prepar-
ation of polymers, pharmaceutically active compounds and
flavour substances, stringent requirements regarding
purity, colour and stability of the levulinic acid are
laid down.
Several processeq for the preparation of levu-
linic acid, on the basis of different starting compounds,
are already known.
The preparation of levulinic acid from carbo-
hydrates by the action of mineral acids is known from
G.J. Mulder, J.prakt.Chem. 21, 219 ~1840~, cited in
~.F. Wiggins, Research 3, (1950), 140. In addition to
formic acid, further by-products, of which some are
insoluble and som0 are deeply coloured and which cannot
be co~pletely separated off, are formed in yields of
40-60%. Levulinic acid prepared in thi~ way already show~
a marked brown to reddish-tinged coloration and rapidly
darkens further on storage, that is to say it is not
colour-stable.
DE-A 2,112,726 has disclosed the preparation of
levulinic acid starting from furfuryl alcohol by ring
cleavage with hydrochloric acid or oxalic acid. To
~mprove the yield, thi~ process i8 carried out in a very
dilute solution, which entails a high energy consumption
in ~eparating off the solvent. Levulinic acid prepared in
this way, however, shows very rapid dark discoloration
eve~ under a brief thermal stress, that i8 to say it has
a low colour stability.
EP-A 0,028,234 ha~ disclosed a proces~ for the
preparation of levulinic acid, wherein furfuryl alcohol
is firqt e~terified in the presence of an acid catalyst
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to give a levulinic acid ester, this e~ter i8 purified by
distillation in the presence of a high-boiling solvent
and then hydrolysed in the presence of water and a strong
lacid, an aqueou~ levulinic acid ~olution being formed.
This levulinic acid ~olution show~ a slight coloration,
]but the le w linic acid likewise darkens rapidly under a
brief thermal stress.
In spite of its disadvantages, the preparation of
levulinic acid from urfuryl alcohol i~ the only proces~
which has so far been carried out industrially.
In M. Conrad, Ber.Dt.Chem.Ges. 11, 211 (1878) and
M. Conrad, Ann. 188, 1216 (1877), the saponification of
diethyl ace~ylsuccinate with concentrated hydrochloric
acid or with Ba~OH)2 or KOH to give levulinic acid i8
described. In the acidic saponification, ethyl levu~
linate i8 formed as a by-product. In the alkaline saponi-
fication, elimination of the acetyl group takes place, 80
that succinic acid is formed as a by-product. Levulinic
acid prepared in this way by ~aponification of diethyl
acetylsuccinate show~ a dark coloration even after
isolation by distlllation under the slightest possible
temperature stress, and this rapidly deteriorates on
storage.
Surprisingly, a process for the preparation of
levulinic acid, ~tarting from acstyl~uccinates, has now
been found, wherein colour-stable lew linic acid i8
obtained in high purity with a good yield.
The invention therefore relate~ to a process for
the preparAtion of colour-stable levulinic acid by
saponification of acetylsuccinate~ with aqueQus mineral
acid~, which i8 characterized in that the starting
products are continuously trested with ~team in counter-
current in a reactor ca~cade, the reaction being carried
out above the boiling point of the alcohol being formed
in the reaction or above the boiling point of th~ aqueous
azeotrope being formed.
The starting compounds used are acetylsuccinates
whiCh are dQrivsd from alcohols whose boiling point or
who~o boiling point in the azeotrope with water i8 below
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100C. Examples of ~uch alcohols are methanol, ethanol,propanol, i-propanol, n-butanol and t-butanol. Prefer-
ably, dimethyl acetylsuccinate or diethyl acetylsuccinate
and, particularly preferably, dLmethyl acetylsuccinate i~
used. Hydrochloric acid or ~ulphuric acid can be u~ed as
1;he mineral acids, and preferably aqueous hydrochloric
clCid i8 used.
For carrying out the process, the star~ing
compound~ are mixed, the acetylsuccinate : miner2i acid
molar ratio being 1 : 1 to 7 : 1, preferably 3 : 1.
The starting compounds are fed to the upper part
of the reactor cascade, which is preferably constructed
as a tray column, and treated with steam in counter-
current, at least 0.85 kg of steam being fed per kg of
acetylsuccinate.
The residence time in the reactor cascade ~hould
allow as quantitative as possible a decarbo~ylation of
the acetylsuccinate and hydroly~is of the resulting
levulinic acid esters to give levulinic acid. The re3i-
dence time required for this purpo~e depends on the
liquid level on the trays and on the number of trays.
Preferably, a tray column with a defined liquid level on
the tray~ (hold-up) i8 used, it being intended that the
trays do not run empty. A~ a rule, re~idence times of
30-60 minute~ ~re sufficient.
~he top and bottom temperatures of the reactor
cascade are controlled in such a way that the alcohol
formed in the reaction is stripped out of the column
together with water and CO2, but the mineral acid remains
in the column, a temperature difference of at lea~t lO-C
between the top and bottom temperatures being preferably
maintained. When hydrochloric acid is used as the mineral
a¢id, a top temperature o~ 90-lOO-C and a bottom temper-
ature of 110-140C are preferably maintained.
Due to the continuou~ removal of the alcohol
being formed in the hydrolysis of the levulinic acid
ester resul~ing after the decarboxylation, the levulinic
acid ester content in the end product is minimized.
At the bottom of the column, crude lew linic acid
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is taken off and then purified by distillation under the
~lightest posQible tempsrature stre~. The hydrochloric
acid thus separated off can be fed ba~k to the column if
de~ired.
SPigure 1 show~ a preferred embodiment of the
proces~ according to the invention~ In Figure 1, 1 is the
re~lctor cascade, for example a bubble-cap tray column,
2 is the heat exchanger, 3 i~ a dephlegma~or, 4 i~ the
acetylsucci~ate feed line, 5 is the mineral acid feed
10line, 6 is the feed line for the mixed starting com-
pounds, 7 i-~ the vapour line, 8 i8 the steam feed and
9 is the take-off line for crude levulinic acid.
Acetyl~uccinate from line 4 is mixed with mineral
acid from line 5 and the mixture is fed via line 6 to the
15upper part of the colu~n at a temperature of about 100.
Superheated steam i~ blown in via line 8 and p~ssed
upwards through the column.
}n the bottom of the column, the reaction mixture
running off from the lowest tray of the column is con-
20centrstsd via heat exchanger 2 by evaporation of water.
The crude levulinic acid formed is discharged via line 9
and purified in a down~tream vacuum di~tillation at the
~lightest pos~ible temperature stress. At the top of the
column, the t~mperature iB controlled by the dephleg-
25mator 3 in such a way that the mineral acid i8 not
discharged via the vapour line 7 together with the
alcohol, water and CO2, but predominantly remain~ in tha
crude levulinic acid. Depending on the bottom tempera-
tur~, the crude levulinic acid taken off via line 9
30contains differing guantitie~ of mineral acid, which can
be separated off in the vacuum distillation and fed back
to the column via line 5.
By the proce~s according to the invention,
levulinic acid i~ obtainad at short re~idence times in
35high yield and ex~ellen~ colour stability. A~ a rule,
yields of 85-95% of theory, relative to acetylsuccinate,
are achieved. ?he re~idence time i8 in general only
between 30 and 60 mi~utes, wheroby the formation of by-
products, which are in~oluble or cannot be separated off
5 ~7~
and which impair the purity, colour and colour ~tability,
i~ avoided. The total reaction time i~ about 1-2 hour~.
After purification by di~tillation, the levulinic
acLd prepared according to the invention shows a Gardener
coLour number of about 2 according to ASTM D1544-8,
which, even under strong thermal stress, deteriorates
only 810wly and to a far smaller extent as compared with
levulinic acid prepared by known proce~ses.
ExamPle 1:
In a reactor cascade, shown in Figure 1, with 28
bubble-capped trays and a diameter of 300 mm, 87.5 kg of
reaction mixture were fed per hour to tray 23. The
mixture consisted of 57.5 kg of dimethyl acetylsuccinate
and 30 kg of a 12~ hydrochloric acid. 50 kg of steam per
hour were blown into the column below the bottom tray.
The bottom temperature was maintained at 115C. 84.3 kg
per hour of a vapour mixture consisting of methanol,
water, CO2 and a little hydrochloric acid escaped over
the top. The temperature of this mixture escaping through
line 5 wa~ maintained at 99 100C by mean~ of the
dephlegmator 3.
53.2 kg per hour of crude levulinlc acid of the
following chemical composition:
65.8% of levulinic acid
1.2~ of methyl levulinate
0.2% of dimethyl acatyl~uccinate
O.5% of unknown by-product~ (which were introduced
with the technical dim~thyl acetylsucci-
nate employed)
28.0% of water
4.3% of HCl
left the bottom of the column via line 9.
The crude levulinic acid was purified by frac-
tional vacuu~ di~tillation, 33.8 kg of pure levulinic
acld being obtained per hour, corresponding to a ~ield of
95.2%. The levulinic acid purified in thi~ way had a
~ardener colour number of 1-2 and showed no colo~r
deterioration on storag~.
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Example 2:
In the apparatus described in Example 1 and
~igure 1, 87.5 kg/hour of reaction mixture were f~d to
tray 23. The mixture con~isted of 57.5 kg of dimethyl
acetylsuccinate and 30 kg of the first distillate frac-
tion from the pure levulinic acid distillation, and this
wa~ made up with 36~ HCl, so that the HCl concentration
was about 11-12~.
The~e 30 kg were compo3ed of
57.7% of water
23.0% of levulinic acid
12.0% of HCl
6.7~ of methyl levulinate
O.6~ of methanol and unknown by-product~. _
50 kg per hour of steam were blown into the
column below the bottom tray. The bottom temperature was
maintained at 115C. 71.5 kg~hour of vapour mixture
con~isting of methanol, water, C02 and a little hydro-
chloric acid escapad over the top. The temperature o~
this e~caping mixture i~ maintained at lOO-C by means of
the dephlegmator.
66 kg per hour of crude levulinic acid of the
following chemical compo~itions
64.2% of levulinic acid
3.0% of methyl levulinate
0.2% of dimethyl acetylsuccinate
0.4% of unknown by-products twhich are introduced
with the technical dimethyl acetyl-
succinate used)
28.0~ of water
4.2% of HCl
left the bottom of the column.
This crude levulinic acid was purified by frac-
tional vacuum distillation, 33.5 kg per hour of pure
levulinic acid being ubtained, corresponding to a yield
of 94.6%. The~lew linic acid purified in this way had a
Gardener colour number of 1-2 and -showed no colour
deterioration on storage.
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Comparison Exampl~
244.6 g of dimethyl acetylsuccinate and 520 ml of
HCl (17~) were heated under reflux until the end of the
reaction had been reached at the end of CO2 evolution.
The reaction tLme was 5 hours. The reaction mixture was
concentrated and the residue was then distilled at
O.013 bar. 86 g (57~ of theory) of levulinic acid were
obtained.
Boiling point 138-140C at 0.013 bar.
The levulinic acid thus obtained showed a
Gardener colour number of 2, which deteriorated to a
Gardener colour number of 6 after ~torage for one month
at room temperature.
To investigate the colour stability, levulinic
lS acid prepared according to Example 1 was sub~ected to
different thermal stresses and compared with a levulinic
acid prepared (by Otsuka) from furfuryl alcohol according
to DE-A 2,112,726. The results are shown in Table 1:
a levulinic acid prepared according to Example 1
b levulinic acid prepared (by Otsuka) from furfuryl
alcohol
c levulinic acid prepared according to the comparison
example
~able 1
Gardener colour number under different thermal ~treYses
T(DC) 35 100 150
h a b c a b c a b c
1 2 1 3 3 l 3 5 13 10
2 2 1 3 3 1 3 6 14 12
3 2 1 3 3 2 4 7 15 13
4 2 1 3 3 3 4 8 16 15
2 1 3 4 3 4 8 17 }6
6 2 1 3 4 3 4 9 17 17
7 2 1 3 4 3 4 9 18 18
8 2 1 3 5 4 5
9 2 1 3 S 4 6
24 2 1 5 6
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