U.S. patent application number 10/017816 was filed with the patent office on 2002-06-20 for process for preparing trimethylol compounds and formic acid.
Invention is credited to Dobert, Frank, Eymann, Wolfgang, Feller, Rolf, Klausener, Alexander, Wagner, Paul.
Application Number | 20020077502 10/017816 |
Document ID | / |
Family ID | 7668250 |
Filed Date | 2002-06-20 |
United States Patent
Application |
20020077502 |
Kind Code |
A1 |
Dobert, Frank ; et
al. |
June 20, 2002 |
PROCESS FOR PREPARING TRIMETHYLOL COMPOUNDS AND FORMIC ACID
Abstract
The present invention relates to a process for preparing
trimethylol compounds and formic acid by reaction of formaldehyde
and aldehydes in the presence of a nitrogen base and distillation
of the resulting reaction mixture in the presence of an
auxiliary.
Inventors: |
Dobert, Frank; (Koln,
DE) ; Wagner, Paul; (Dusseldorf, DE) ;
Klausener, Alexander; (Pulheim, DE) ; Eymann,
Wolfgang; (Koln, DE) ; Feller, Rolf;
(Korschenbroich, DE) |
Correspondence
Address: |
BAYER CORPORATION
PATENT DEPARTMENT
100 BAYER ROAD
PITTSBURGH
PA
15205
US
|
Family ID: |
7668250 |
Appl. No.: |
10/017816 |
Filed: |
December 13, 2001 |
Current U.S.
Class: |
562/531 ;
568/595 |
Current CPC
Class: |
C07C 51/02 20130101;
C07C 51/02 20130101; C07C 51/16 20130101; C07C 51/16 20130101; C07C
53/06 20130101; C07C 31/22 20130101; C07C 53/02 20130101; C07C
29/38 20130101; C07C 29/38 20130101 |
Class at
Publication: |
562/531 ;
568/595 |
International
Class: |
C07C 051/16; C07C
041/60 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 20, 2000 |
DE |
10063937.2 |
Claims
What is claimed is:
1. A process for preparing trimethylol compounds and formic acid
comprising (a) reacting formaldehyde and an aldehyde in the
presence of a nitrogen base to form a product mixture containing
the trimethylol compound and a formate salt of the nitrogen base,
(b) removing the trimethylol compound from the product mixture
after the reaction, and (c) cleaving the formate salts into the
free nitrogen base and formic acid by distillation in the presence
of an auxiliary.
2. A process according to claim 1 wherein the aldehyde has the
formula (I), 5where R represents methylol, straight-chain or
branched C.sub.1-C.sub.12-alkyl, C.sub.3-C.sub.8-cycloalkyl,
C.sub.6-C.sub.10-aryl, or C.sub.7-C.sub.22-aralkyl, wherein each
such radical is optionally further substituted with groups that are
inert under the reaction conditions.
3. A process according to claim 1 wherein the aldehyde is
n-butyraldehyde.
4. A process according to claim 1 wherein the trimethylol compound
is removed from the product mixture by extraction.
5. A process according to claim 4 wherein the extraction is carried
out using an extractant selected from the group consisting of
alkanes, cycloalkanes, alcohols, ethers, aldehydes, ketones, and
esters.
6. A process according to claim 4 wherein the extraction is carried
out using as the extractant the aldehyde that was reacted with
formaldehyde according to claim 1 to form the trimethylol
compound.
7. A process according to claim 1 wherein the auxiliary comprises
compounds that have a lower basicity than the nitrogen base used
and form adducts with formic acid that can be decomposed thermally
at a temperature above the boiling point of the nitrogen base.
8. A process according to claim 1 wherein the auxiliary is a
nitrogen-containing compound having a pK.sub.b of 10 to 3.
9. A process according to claim 1 wherein the auxiliary is (i) a
cyclic nitrogen base selected from the group consisting of
imidazoles, quinolines, pyridines, pyrimidines, pyrroles,
pyrazoles, isoquinolines, pyrazines, pyridazines, piperidines,
pyrrolidines, and morpholines, P1 (ii) an amide of the formula
(III), 6where R.sup.3 and R.sup.4 each represent, independently of
one another, straight-chain or branched C.sub.1-C.sub.24-alkyl,
C.sub.6-C.sub.10-aryl, or C.sub.7-C.sub.22-aralky- l, and R.sup.5
represents hydrogen or is as defined for R.sup.3 and R.sup.4, or
(iii) a cyclic amide of the formula (IV), 7where R.sup.6 represents
straight-chain or branched C.sub.1-C.sub.20-alkyl or a
C.sub.2-C.sub.20-alkenyl radical, and n represents a number from 3
to 6.
10. A process according to claim 1 wherein the auxiliary is
N-methylpyrrolidone.
11. A process according to claim 1 wherein the distillation in the
presence of an auxiliary is carried out in such a way that a stream
containing the free nitrogen base is obtained as a top fraction and
a stream containing the auxiliary and formic acid is obtained as a
bottom fraction.
12. A process according to claim 11 wherein the bottom fraction is
separated into the auxiliary and formic acid in a subsequent
distillation and the separated auxiliary is returned to the
distillation for cleavage of the formate salt.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a process for preparing
trimethylol compounds and formic acid by reaction of formaldehyde
and aldehydes in the presence of a nitrogen base followed by
distillation of the resulting reaction mixture in the presence of
an auxiliary.
[0002] Trimethylol compounds are widely used in the plastics sector
for producing surface coatings, urethanes, and polyesters.
Important trimethylol compounds are, for example, trimethylolethane
and trimethylolbutane, but especially trimethylolpropane.
[0003] The industrial preparation of trimethylolpropane (TMP)
starts out from n-butyraldehyde and formaldehyde that are reacted
in a two-stage reaction process. In a first reaction step,
2,2-dimethylolbutanal is formed first in a base-catalyzed aldol
condensation via the intermediate 2-methylolbutanal. In a
subsequent cross Cannizzaro reaction, trimethylol-propane together
with formate salts are formed in the presence of stoichiometric
amounts of a base.
[0004] As base, use is usually made of inorganic compounds such as
sodium hydroxide or calcium hydroxide. If calcium hydroxide is used
as base in the process, the calcium formate obtained as coproduct
can, for example, be used further for producing various animal
fodder products and additives for animal fodder products. However,
the sodium formate formed when sodium hydroxide is used is less
desirable. In any case, the formation of an inorganic formate salt
as coproduct is associated with disadvantages even when it can be
utilized: first, the separation of the salt from TMP is complicated
and incurs additional costs, while, second, the salt has to be
worked up and purified if it is to be utilized in a beneficial
fashion.
[0005] In an alternative process variant, the reaction of
n-butyraldehyde with formaldehyde is carried out in the presence of
a tertiary amine, usually a trialkylamine. However, the excesses of
formaldehyde and -trialkylamine used result in stoichiometric
amounts of trialkylammonium formate being formed in addition to
TMP. To improve the economics of such a process, it is necessary to
recover the amine used from trialkylammonium formate and preferably
pass the formate to a purposeful use.
[0006] DE 25 07 461 A describes a process for preparing
2,2-dimethylolalkanals that are converted into the corresponding
trimethylol compound in a subsequent hydrogenation. Thus, for
example, TMP is prepared by reaction of n-butyraldehyde with
formaldehyde in the presence of catalytic amounts of tertiary
amines and subsequent hydrogenation of the reaction product. A
disadvantage of this process is that only unsatisfactory yields of
trimethylolpropane are achieved.
[0007] DE 1 952 738 A describes a process for preparing TMP by
reaction of n-butyraldehyde with formaldehyde in the presence of
tertiary amines. The formate salts formed in the process are
separated from TMP by distillation. It is proposed that the
trialkylammonium formates thus formed be reacted with an aqueous
calcium hydroxide solution to give calcium formate and liberate the
amine, which is returned to the reaction circuit. A disadvantage of
this process is that, once again, it results in formation of an
organic formate salt that, if it is to be utilized further, has to
be separated off and purified in a further reaction step. In
addition, calcium hydroxide has to be used as additional starting
material in order to convert the formate into a usable product.
[0008] In EP 142 090 A, TMP is prepared by reacting one mol of
n-butyraldehyde with from 2.2 to 4.5 mol of formaldehyde and from
0.6 to 3 mol of trialkylamine and catalytically hydrogenating the
resulting 2,2-dimethylolbutanal. A disadvantage is that the high
amine concentrations in the aldol reaction result in formation of
considerable amounts of trialkylammonium formates that have to be
separated off by distillation prior to the hydrogenation.
Liberation of trialkylamine from the formates formed and
recirculation of the base to the process is not described.
[0009] In the method of reducing the amount of formate formed
described in DE 28 13 201 A, formaldehyde is used in excess but the
amine is used only as catalyst for the aldol reaction to form
2,2-dimethylolbutanal. The aldehyde formed is subsequently
catalytically hydrogenated. The process is not very suitable for
industrial use since the excess of formaldehyde has to be separated
off prior to the hydrogenation because of possible poisoning of the
hydrogenation catalyst.
[0010] EP 289 921 A describes a process for preparing
trimethylolalkanes which is similar to that described in EP 142 090
A and in which 1 mol of aldehyde is reacted with from 2.2 to 4.5
mol of formaldehyde in aqueous solution in the presence of from 0.6
to 3 mol of trialkylamine and the product is subsequently
hydrogenated. To work up the trialkylammonium formate obtained, two
process variants are reported. In variant (a), the crude
hydrogenation mixture is heated to 100-200.degree. C. and water and
excess trialkylamine are separated off by distillation. The
trialkylammonium formate remaining in the bottoms reacts with the
alcohol present to give trimethylolalkane formate, thus liberating
the amine used. The trimethylolalkane formate is subsequently
transesterified with methanol to give methyl formate and
trimethylolalkane. In process variant (b), the hydrogenation
product is first substantially dewatered and the trialkylammonium
formate remaining in the bottoms is subsequently esterified
directly with methanol to form methyl formate. A disadvantage of
both variants is that a loss of formaldehyde due to catalytic
hydrogenation has to be accepted in order to achieve economical
yields.
[0011] In DE 195 42 036 A, the recirculation of the tertiary amine
used as base is carried out via esterification of the
trialkylammonium formate formed with polymethylolalkane. A
disadvantage of this method is that the ester formed has to be
transesterified with a further, lower-boiling alcohol in a further
step in order to liberate the polymethylolalkane.
[0012] WO 98/28253 A describes a process for preparing TMP without
producing a coproduct. Here, n-butyraldehyde is reacted with from 2
to 8 times its molar amount of formaldehyde in a first reaction
step in the presence of a tertiary amine as catalyst. The reaction
mixture obtained is fractionally distilled in a second stage, where
the distillate stream consisting predominantly of unreacted or
partially reacted starting materials is returned to the first stage
and the bottoms comprising predominantly 2,2-dimethylolalkanal are
separated off or the reaction mixture from the first stage is
separated by phase separation into an aqueous phase and an organic
phase and the organic phase is returned to the first stage. In a
third after-reaction stage, the bottoms fraction that has been
separated off in the second stage or the aqueous phase obtained by
phase separation in the second stage is subjected to a catalytic
and/or thermal treatment in which the incompletely reacted
compounds are converted into 2,2-dimethyolalkanal and starting
materials that are returned to the first stage. Subsequently,
2,2-dimethylolalkanal is hydrogenated in a known manner to produce
the corresponding trimethylol compound. However, this process has
the disadvantage that the mono-methylolalkanal formed has to be
eliminated from the reaction mixture by complicated measures since
otherwise relatively large amounts of by-products are formed in the
catalytic hydrogenation.
[0013] A further process for recovering the amines used is
disclosed in DE 198 48 568 A and DE 198 48 569 A. After reaction of
the aldehyde with aqueous formaldehyde in the presence of a
tertiary amine, the reaction mixture is first freed of free amine
and water by distillation. The trialkylammonium formate remaining
in the bottoms is concentrated by distillation at a pH of 5 until
trimethylolalkane formate and free amine are formed, with the
latter being separated off as distillate. The trimethylolalkane
formate is decomposed catalytically under pressure at temperatures
of about 280.degree. C. into trimethylolalkane, hydrogen, carbon
dioxide, water, and carbon monoxide. A disadvantage of this process
is that at least 1 mol equivalent of formaldehyde per mole of
alkanal is not utilized economically.
[0014] It is therefore an object of the invention to provide a
process for preparing trimethylol compounds in the presence of
tertiary amines as base that allows the formate salts obtained to
be converted into a usable form with recirculation of the amine
used.
SUMMARY OF THE INVENTION
[0015] We have now surprisingly found a process for preparing
trimethylol compounds and formic acid comprising
[0016] (a) reacting formaldehyde and an aldehyde in the presence of
a nitrogen base to form a product mixture containing the
trimethylol compound and a formate salt of the nitrogen base,
[0017] (b) removing the trimethylol compound from the product
mixture after the reaction, and
[0018] (c) cleaving the formate salt into the free nitrogen base
and formic acid by distillation in the presence of an
auxiliary.
BRIEF DESCRIPTION OF THE DRAWING
[0019] FIG. 1 shows a preferred embodiment of the process of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0020] In the process of the invention, the formate salts formed
are cleaved by distillation in the presence of an auxiliary into
formic acid and the free nitrogen base, which can advantageously be
returned to the process. Furthermore, the prior removal of the
trimethylol compound from the product mixture ensures that no
trimethylol formate esters are formed during the cleavage of the
formate salts into formic acid and the free nitrogen base.
[0021] Formic acid is an important product that is used, for
example, in the tanning of leather, for adjusting pH values, in dye
manufacture, and for producing pharmaceutical products. In
addition, formic acid is used in the coagulation of latex, as an
additive for producing silage, and as promoter in fermentation
processes.
[0022] The aldehydes used in the process of the invention are
preferably those of the formula (I) 1
[0023] where
[0024] R represents methylol, straight-chain or branched
C.sub.1-C.sub.12-alkyl, C.sub.3-C.sub.8-cycloalkyl,
C.sub.6-C.sub.10-aryl or C.sub.7-C.sub.22-aralkyl, wherein each
such radical is optionally further substituted with groups that are
inert under the reaction conditions (e.g., alkyl groups or alkoxy
groups having 1-3 carbon atoms).
[0025] If R represents a straight-chain or branched
C.sub.1-C.sub.12-alkyl radical, R may be, for example, methyl,
ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl,
or hexyl. If R is a C.sub.3-C.sub.8-cycloalkyl radical, R may be,
for example, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl,
cycloheptyl, or cyclooctyl. If R is a C.sub.6-C.sub.10-aryl
radical, R may be, for example, phenyl or naphthyl. If R is a
C.sub.7-C.sub.22-aralkyl radical, R may be, for example,
benzyl.
[0026] In the process of the invention, the aldehydes of the
formula (I) are, in particular, aldehydes in which R is methylol or
straight-chain or branched C.sub.1-C.sub.6-alkyl. Particular
preference is given to using aldehydes of the formula (I) in which
R is methylol, methyl, ethyl, n-propyl, or isopropyl, very
particularly preferably ethyl.
[0027] The formaldehyde used in the process of the invention can be
used in gaseous form, in polymeric form, or in the form of an
aqueous solution. If formaldehyde is used in polymeric form in the
process of the invention, preference is given to using
paraformaldehyde. Formaldehyde is preferably used in the process of
the invention in the form of an aqueous solution, preferably a 1 to
55% strength by weight aqueous solution, more preferably a 5 to 35%
strength by weight solution, particularly preferably a 10 to 32%
strength by weight solution.
[0028] In the process of the invention, formaldehyde is preferably
used in an excess over the aldehyde used. The molar ratio of
aldehyde to formaldehyde is preferably 1:(3-10), particularly
preferably 1:(3-5), very particularly preferably 1:(3-3.5).
[0029] Nitrogen bases that can be used in the process of the
invention are those which are known as basic catalysts for aldol
condensations and additionally make possible a Cannizzaro reaction
between the aldehyde used and formaldehyde. Examples of such
nitrogen bases are symmetrical trialkylamines such as
trimethylamine, triethylamine, tri-n-propylamine,
triisopropylamine, tri-n-butylamine, triisobutylamine, or
tri-tert-butylamine; unsymmetrical trialkylamines such as
ethyldimethylamine, isopropyldimethylamine, diethylmethylamine,
dimethylpropylamine, isobutyldimethylamine, butyldimethylamine,
tert-butyldimethylamine, dimethylpentylamine,
(2,2-dimethylpropyl)dimethy- lamine, hexyldimethylamine, or
dibutylheptylamine; diamines such as
N,N,N',N'-tetramethylbutane-1,3-diamine, ethyldiisopropyldiamine,
or N,N,N',N'-tetramethylethane-1,2-diamine; allylamines such as
allyldimethylamine, allyldiethylamine, or triallylamine;
aminoalcohols such as 4-dimethylaminoethanol,
2-dimethylaminobutanol, 2-diisopropylaminoethanol,
diethylaminomethanol, diethylaminoethanol,
3-dimethylaminopropan-1-ol, or dimethylamino-2-methyl-propan-1-ol;
alkoxy-substituted amines such as (2-methoxyethyl)dimethylamine,
(3-methoxypropyl)dimethylamine, or diethylmethoxymethylamine; and
hydroxylamines such as N,N-dimethylhydroxylamine.
[0030] Preference is given to using symmetrical tri-n-alkylamines
such as trimethylamine, triethylamine, tri-n-propylamine, or
tri-n-butylamine, particularly preferably trimethylamine and
triethylamine.
[0031] Mixtures of various nitrogen bases can also be used in the
process of the invention.
[0032] In the process of the invention, the nitrogen base is
preferably used in an amount of from 1 to 10 mol, particularly
preferably from 1 to 5 mol, very particularly preferably from 1 to
3 mol, per 1 mol of aldehyde.
[0033] In the first step of the process of the invention, an
aldehyde, preferably an aldehyde of the formula (I), is reacted
with formaldehyde, preferably with an aqueous formaldehyde
solution, in the presence of a nitrogen base to form a trimethylol
compound and the formate salt of the nitrogen base used.
[0034] The reaction preferably takes place at temperatures of from
10 to 150.degree. C., particularly preferably from 30 to
130.degree. C., very particularly preferably from 40 to 100.degree.
C.
[0035] The reaction can be carried out at atmospheric pressure,
under subatmospheric pressure, or under superatmospheric pressure.
If the reaction temperature chosen is above the boiling point of
the components of the reaction mixture, the reaction can be carried
out under super-atmospheric pressure. It is preferably carried out
at atmospheric pressure.
[0036] The reaction can be carried out batchwise, semibatchwise, or
continuously, preferably continuously. Possible reaction
apparatuses are all reaction apparatuses that are known to those
skilled in the art and are suitable for reacting liquid reactants.
The reaction is preferably carried out in stirred tank reactors,
cascades of stirred tanks, flow tubes, or multichamber
reactors.
[0037] The residence time of the reaction mixture in the reactor
can be, for example, from 10 minutes to 50 hours.
[0038] In a second step of the process of the invention, the
trimethylol compound that is formed is removed from the product
mixture. The trimethylol compound is preferably removed from the
product mixture by extraction.
[0039] If the trimethylol compound is removed from the product
mixture by extraction, it is possible to use alkanes, cycloalkanes,
alcohols, ethers, aldehydes, ketones, or esters as extractants.
Preference is given to using hexane, cyclohexane, isopropyl
alcohol, isobutyl alcohol, 2-ethylhexanol, 2-ethyl-2-hexenol,
cyclohexanol, tert-butyl methyl ether, butyraldehyde,
propionaldehyde, methyl ethyl ketone, methyl isobutyl ketone, ethyl
acetate, or butyl acetate. The extractant is particularly
preferably the aldehyde that is reacted in the process of the
invention to form the trimethylol compound. Very particular
preference is given to using butyraldehyde as extractant.
[0040] The extraction can be carried out continuously or batchwise
in any extraction apparatus known to those skilled in the art. The
extraction is preferably carried out continuously, preferably in a
mixer-settler apparatus, sieve tray column or packed column, pulsed
sieve tray column or packed column, Karr column, Kuhni column, or
spray column or in a centrifugal extractor.
[0041] The mixture of extractant and trimethylol compound obtained
in the extraction is preferably separated by distillation,
particularly preferably by rectification.
[0042] After removal of the trimethylol compound, the remaining
formate solution is, in the process of the invention, admixed with
an auxiliary that has the task of binding the formic acid, as a
result of which the nitrogen base is liberated.
[0043] The cleavage of formate salts of a nitrogen base into formic
acid and the nitrogen base by use of bases is described, for
example, in EP181078A.
[0044] In the process of the invention, auxiliaries used are
preferably substances that have a lower basicity than the nitrogen
base used, that form adducts with formic acid that can be
decomposed thermally at a temperature above the boiling point of
the nitrogen base, and that have a low volatility. Auxiliaries are
preferably compounds containing nitrogen and having a pK.sub.b of
from 10 to 3.
[0045] Auxiliaries used in the process of the invention are
preferably cyclic nitrogen compounds selected from the group
consisting of imidazoles, quinolines, pyridines, pyrimidines,
pyrroles, pyrazoles, isoquinolines, pyrazines, pyridazines,
piperidines, pyrrolidines, and morpholines, each of which may bear
one or more substituents selected from the group consisting of
C.sub.1-C.sub.6-alkyl (preferably methyl, formyl or phenyl), for
example, 2-, 3- and 4-methylpyridine, N-methylmorpholine,
N-formylmorpholine, or N-phenylmorpholine. Preferred cyclic
nitrogen compounds are N-formylmorpholine, dimorpholinoethane,
quinoline, and imidazoles of the formula (II) 2
[0046] where
[0047] R.sup.1 and R.sup.2 each represent, independently of one
another, hydrogen or straight-chain or branched
C.sub.1-C.sub.24-alkyl (preferably straight-chain or branched
C.sub.1-C.sub.10-alkyl such as methyl, ethyl, propyl, isopropyl,
n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, or
n-heptyl).
[0048] In a further preferred embodiment, auxiliaries used are
amides of the formula (III), 3
[0049] where
[0050] R.sup.3 and R.sup.4 each represent, independently of one
another, straight-chain or branched C.sub.1-C.sub.24-alkyl
(preferably straight-chain or branched C.sub.1-C.sub.10-alkyl such
as methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl,
tert-butyl, n-pentyl, n-hexyl, or n-heptyl), C.sub.6-C.sub.10-aryl
such as phenyl or naphthyl, or C.sub.7-C.sub.22-aralkyl such as
benzyl, and
[0051] R.sup.5 represents hydrogen or is as defined for R.sup.3 and
R.sup.4.
[0052] In a further preferred embodiment, auxiliaries used are
cyclic amides of the formula (IV), 4
[0053] where
[0054] R.sup.6 represents straight-chain or branched
C.sub.1-C.sub.20-alkyl such as methyl, ethyl, propyl, isopropyl,
n-butyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, hexyl,
isohexyl, nonyl, n-decyl, dodecyl, tridecyl, tetradecyl, hexadecyl,
octadecyl, or 2-methylbutyl or a C.sub.2-C.sub.20-alkenyl radical
such as vinyl, allyl, or buten-2-yl, and n represents a number from
3 to 6.
[0055] Auxiliaries used in the process of the invention are
preferably cyclic amides of the formula (IV) in which n represents
3, particularly preferably cyclic amides of the formula (IV) in
which n represents 3 and R.sup.6 represents methyl or ethyl.
[0056] Further preferred auxiliaries are cyclic amides of the
formula (IV) in which n represents 4, particularly preferably
cyclic amides of the formula (IV) in which n represents 4 and
R.sup.6 represents methyl or ethyl.
[0057] Very particularly preferred compounds used as auxiliaries in
the process of the invention are N-methylpyrrolidone,
1,2-dimorpholinoethane, N-formylmorpholine, N-methylacetamide,
N,N-dimethylacetamide, N-ethylacetamide, N-butylimidazole, and
N,N-diethylacetamide.
[0058] In the process of the invention, the auxiliaries are
preferably used in an excess relative to the formic acid.
Particular preference is given to using 1.1 to 5 mol of auxiliary
per mol of formic acid.
[0059] After the cleavage of the formate salt of the nitrogen base
formed in. the process of the invention into the free nitrogen base
and formic acid by distillation in the presence of an auxiliary,
the nitrogen base is preferably returned to the reaction
process.
[0060] The distillation is preferably carried out at temperatures
of from 10 to 300.degree. C. (particularly preferably from 50 to
250.degree. C.) and preferably at a pressure of from 1 mbar to 5
bar (particularly preferably from 1 mbar to 1 bar).
[0061] After the base, which is preferably returned to the reaction
process, has been separated off by distillation, the formic acid is
preferably separated thermally from the auxiliary. In a
particularly preferred embodiment, this separation is achieved by
extractive rectification since this enables a very pure formic acid
to be obtained.
[0062] The separation of the formic acid from the auxiliary is
preferably carried out at a temperature of from 100 to 300.degree.
C. and a pressure of from 1 to 200 mbar.
[0063] The bottoms comprising auxiliary and possibly small
proportions of formic acid is preferably returned to the
process.
[0064] FIG. 1 shows a preferred embodiment of the process of the
invention. In this embodiment, the aldehyde used in the process of
the invention is fed via stream 1 together with formaldehyde
(stream 2) and nitrogen base, which comes mostly from the recycle
stream 10 and to a lesser extent is added fresh via stream 3 to a
reaction stage 4. In this reaction stage, the aldehyde is
preferably reacted at temperatures of from 10 to 150.degree. C. The
resulting reaction mixture is passed as stream 5 to a separation
stage 6 in which the trimethylol compound formed is removed from
the product mixture, preferably by extraction. If desired, low
boilers and/or part of the water can be removed beforehand from the
product stream by distillation, a variant that is not shown in FIG.
1. The low boilers mentioned include, for example, incompletely
reacted aldehyde, formaldehyde, or nitrogen base, as well as
by-products such as acroleins and in the case of the preparation of
trimethylolpropane .alpha.-ethylacrolein. If low boilers are
removed from the product stream by distillation, all or some of the
distillate may, if desired, be returned to reaction stage 4.
[0065] If the trimethylol compound has been, in a preferred
embodiment, removed from the product mixture by extraction, the
extract is separated into the trimethylol compound (stream 16) and
the extractant in a subsequent process stage 15, this separation
preferably being carried out by rectification. The extractant used
is preferably returned as stream 18 to the extraction stage 6 or,
if the aldehyde employed in the process of the invention is used as
extractant, wholly or partly returned as stream 17 to the reaction
stage 4. If the aldehyde employed in the process of the invention
is used as extractant, the fresh aldehyde fed in as stream 1 is, in
a further preferred embodiment, firstly introduced into the
extraction step 6.
[0066] The aqueous raffinate phase 8 that is obtained in the
removal of the trimethylol compound from the product mixture and
contains the formate salt is, according to the invention, converted
into the free nitrogen base and formic acid by distillation in the
presence of an auxiliary. For this purpose, the raffinate is
preferably brought into contact with the auxiliary in a
rectification column 9. The auxiliary is preferably fed as stream
14 into the upper part of the column. In a preferred embodiment,
the aqueous raffinate phase 8 is fed into the middle part of a
rectification column 9, so that the auxiliary stream 14 which is
preferably fed into the upper part of the column is conveyed in
countercurrent to the aqueous raffinate phase. In a preferred
embodiment, the rectification column 9 is operated at pressures of
100 to 1,000 mbar. The distillate obtained in 9, which contains the
nitrogen base used in the process and possibly residual water and
low boilers, is preferably returned directly or after purification
by distillation, a variant that is not shown in FIG. 1, as stream
10 to the reaction stage 4.
[0067] The bottom product from 9 consists essentially of the
auxiliary used in the process of the invention and formic acid. The
bottoms are preferably fed as stream 13 into a second rectification
column 11, preferably in the middle region of the column.
Rectification in the rectification column 11 separates the bottom
product from 9 into the free formic acid as top product (stream 12)
and auxiliary as bottom product (stream 14). The rectification can
be carried out batchwise or continuously. The rectification is
preferably carried out continuously. The rectification can be
carried out in all rectification apparatuses known to those skilled
in the art but preference is given to using columns provided with
sieve trays, bubble cap trays, random packing, or ordered packing.
The pure formic acid is usually obtained at a pressure of from 50
to 250 mbar and a temperature of from 20 to 60.degree. C. The
auxiliary obtained as bottom product is preferably returned to the
distillation 9.
[0068] The following examples further illustrate details for the
process of this invention. The invention, which is set forth in the
foregoing disclosure, is not to be limited either in spirit or
scope by these examples. Those skilled in the art will readily
understand that known variations of the conditions of the following
procedures can be used. Unless otherwise noted, all temperatures
are degrees Celsius and all percentages are percentages by
weight.
EXAMPLES
[0069] Preparation of Trimethylolpropane
Example 1
[0070] 117.90 g of distilled water, 250.25 g (2.5 mol) of 30%
strength aqueous formaldehyde solution, and 154.88 g (1.5 mol) of
triethylamine were placed in a 1 liter glass reactor at 25.degree.
C. 36.46 g (0.5 mol) of butyraldehyde were subsequently metered in
over a period of 45 minutes and the reactor temperature was at the
same time increased linearly to 70.degree. C. After the metered
addition was complete, the mixture was stirred under reflux for
another 3 hours. According to GC analysis, trimethylolpropane was
obtained in a yield of 81.59% of theory.
Example 2
[0071] 117.90 g of distilled water, 250.25 g (2.5 mol) of 30%
strength aqueous formaldehyde solution, and 77.44 g (0.75 mol) of
triethylamine were placed in a 1 liter glass reactor at 25.degree.
C. 36.46 g (0.5 mol) of butyraldehyde were subsequently metered in
over a period of 45 minutes and the reactor temperature was at the
same time increased linearly to 70.degree. C. After the metered
addition was complete, the mixture was stirred under reflux for
another 3 hours. According to GC analysis, trimethylolpropane was
obtained in a yield of 82.77% of theory.
Example 3
[0072] 231.75 g of distilled water, 175.18 g (1.75 mol) of 30%
strength aqueous formaldehyde solution, and 72.28 g (0.70 mol) of
triethylamine were placed in a 1 liter glass reactor at 25.degree.
C. 36.46 g (0.5 mol) of butyraldehyde were subsequently metered in
over a period of 45 minutes and the reactor temperature was at the
same time increased linearly to 70.degree. C. After the metered
addition was complete, the mixture was stirred under reflux for
another 4 hours. According to GC analysis, trimethylolpropane was
obtained in a yield of 76.34% of theory.
[0073] Extraction of Trimethylolpropane
Example 4
[0074] 100 g of an aqueous trimethylolpropane solution containing
10% by weight of trimethylolpropane and 15.4% by weight of
triethylammonium formate were extracted three times in succession
with 50 g of n-butyraldehyde. The combined organic phases (157.1 g)
contained 7.7 g of TMP and 0.1 g of triethylammonium formate.
[0075] Recovery of Triethylamine
Example 5
[0076] A mixture of N-methylpyrrolidone (NMP), water and
triethylammonium-formate was distilled in a distillation apparatus
comprising a 1.6 m high silvered column filled with 4 mm mesh rings
and a 1 liter still part. 623.8 g of a mixture consisting of 62.9%
by weight of NMP, 22.3% by weight of triethylammonium formate, and
14.8% by weight of water were first placed in the apparatus and
distilled at atmospheric pressure. At a reflux ratio of 10,104.6 g
of distillate were separated off at a temperature at the top of
76.degree. C. The temperature at the bottom was 127-136.degree. C.
The distillate consisted of 88.3% by weight of triethylamine and
11.7% by weight of water. The recovery of triethylamine was thus
92%. Formic acid and NMP remained in the bottoms.
Example 6
[0077] 560.7 g of a mixture consisting of 66.4% by weight of
N-butylimidazole, 20.8% by weight of triethylammonium formate, and
12.8% by weight of water were placed in the apparatus described in
Example 5. At a reflux ratio of 10, 79.2 g of distillate were
separated off at a temperature at the top of 76.degree. C. The
distillates contained 82.3% by weight of triethylamine and 17.7% by
weight of water. The recovery rate of triethylamine was thus 85.8%.
Formic acid and N-butylimidazole remained in the bottoms.
[0078] Isolation of Formic Acid
Example 7
[0079] 600 g of a mixture of 16.7% by weight of formic acid and
83.3% by weight of NMP were placed in the apparatus described in
Example 5. At 200 mbar and a reflux ratio of 10, 52.6 g of
distillate were obtained at a temperature at the top of 56.degree.
C. The temperature at the bottom was 150-152.degree. C. The
distillate contained 98.6% by weight of formic acid and 1.4% by
weight of NMP.
* * * * *