U.S. patent application number 09/935024 was filed with the patent office on 2002-06-06 for tmp/vapor pressure filtration.
Invention is credited to Klausener, Alexander, Wagner, Paul.
Application Number | 20020066703 09/935024 |
Document ID | / |
Family ID | 7653402 |
Filed Date | 2002-06-06 |
United States Patent
Application |
20020066703 |
Kind Code |
A1 |
Wagner, Paul ; et
al. |
June 6, 2002 |
TMP/Vapor pressure filtration
Abstract
The invention relates to a process for preparing
trimethylolpropane with simultaneous formation of formate salts of
the formula M(OOCH).sub.n (I), where M represents the alkali metals
lithium, sodium, potassium, rubidium, caesium and/or the alkaline
earth metals beryllium, calcium, strontium, barium and n is 1 when
M is an alkali metal and is 2 when M is an alkaline earth metal,
where n-butyraldehyde, formaldehyde and a base are reacted by the
inorganic Cannizzaro process and the reaction mixture formed is
subjected to vapour pressure filtration as a suspension, if
appropriate after partly removing distillable constituents, such as
water.
Inventors: |
Wagner, Paul; (Dusseldorf,
DE) ; Klausener, Alexander; (Pulheim, DE) |
Correspondence
Address: |
BAYER CORPORATION
PATENT DEPARTMENT
100 BAYER ROAD
PITTSBURGH
PA
15205
US
|
Family ID: |
7653402 |
Appl. No.: |
09/935024 |
Filed: |
August 22, 2001 |
Current U.S.
Class: |
210/768 ;
210/634; 210/771; 210/772; 210/774; 210/806 |
Current CPC
Class: |
C07C 29/38 20130101;
C07C 51/41 20130101; C07C 29/76 20130101; C07C 51/41 20130101; C07C
53/06 20130101; C07C 29/38 20130101; C07C 31/22 20130101; C07C
29/76 20130101; C07C 31/22 20130101 |
Class at
Publication: |
210/768 ;
210/771; 210/772; 210/774; 210/634; 210/806 |
International
Class: |
B01D 037/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 23, 2000 |
DE |
10041197.5 |
Claims
What is claimed is:
1. A process for preparing trimethylolpropane with simultaneous
formation of formate salts of the formula (I):M(OOCH).sub.n
(I),wherein M is a metal selected from the group consisting of
alkali metals, alkaline earth metals, and mixtures thereof, wherein
n is 1 when M is an alkali metal and n is 2 when M is an alkaline
earth metal, the process comprising reacting n-butyraldehyde and
formaldehyde by an inorganic Cannizzaro process, forming a reaction
mixture, and subjecting the reaction mixture formed to vapor
pressure filtration.
2. The process according to claim 1, wherein M represents sodium or
calcium.
3. The process according to claim 1, wherein formate salt is
isolated and has a residual moisture content of <3.5% by
weight.
4. The process according to claim 1, wherein the vapor pressure
filtration is carried out continuously.
5. The process according to claim 1, wherein the differential
pressure in the vapor pressure filtration is from 0 to 6 bar.
6. The process according to claim 1, wherein a filter cake is
formed in the vapor pressure filtration and the filter cake is
subjected to at least one washing step during the filtration
procedure.
7. The process according to claim 6, wherein the washing of the
cake is carried out using a fully saturated or partially saturated
aqueous solution of the formate salt to be isolated.
8. The process according to claim 7, wherein distillable
constituents are partly separated from the resulting reaction
mixture prior to the formate salt being separated off.
9. The process according to claim 6, wherein cake formation, cake
washing, vapor treatment of the cake and demoisterizataion of the
cake are carried out during the vapor pressure filtration.
10. The process according to claim 9, wherein in the vapor
treatment of the cake, the filter cake of formate salt to be
separated off formed on the filter area is treated with a gaseous
treatment fluid whose pressure and temperature are set so that the
treatment fluid condenses in the filter cake, optionally initially
in the uppermost layer of the filter cake farthest from the filter
area, so that a condensation front is formed along this layer and
that, in addition, the filter cake is heated to the temperature of
the gaseous treatment fluid progressively from the uppermost layer
in the direction of the filter area, so that the condensation front
at the phase boundary between the gaseous treatment fluid and the
liquid is shifted towards the filter area.
11. The process according to claim 9, wherein in the
demoisturization of the cake, the filter cake of formate salt to be
separated off formed on the filter area is treated with compressed
inert gas and/or compressed air.
12. The process according to claim 1, wherein the reaction mixture
after the vapor pressure filtration is subjected to at least one
further purification and drying step which comprises a
recrystallization from and redispersion in a solvent, or
redispersion in a solvent.
13. The process according to claim 12, wherein the solvent is water
or a water-containing mixture.
Description
BACKGROUND
[0001] The present invention relates to a process for preparing
trimethylolpropane with simultaneous formation of a formate salt
and to the separation of the formate salt from the reaction
mixture, if appropriate, after prior concentration of this reaction
mixture by evaporation.
[0002] Both trimethylolalkanes, and formate salts are products of
industrial interest. Thus, trimethylolpropane is used in the
production of surface coating resins, powder coatings, foams and a
variety of polyesters. Formate salts can be utilized, for example,
for producing formic acid. Calcium formate is particularly
versatile and is used commercially in, for example, the following
fields: additive in the field of animal nutrition (pig, cattle and
turkey feed), use in the building materials industry (improving the
curing of cement, gypsum plaster and jointing compositions and also
as frost protection agent for mortar), auxiliary in the leather
industry, auxiliary in the production of high-gloss papers,
treatment of scrubbing water in flue gas de-sulphurization,
auxiliary in silage production.
[0003] The industrial preparation of trimethylolpropane (TMP) is at
present carried out by means of the inorganic Cannizzaro process, a
process which simultaneously forms a formate salt. This process
makes use of n-butyraldehyde and formaldehyde as starting
materials. According to the generally accepted view,
2,2-dimethylolbutanal is initially formed in a base-catalysed aldol
reaction via the intermediate 2-methylolbutanal. In the presence of
stoichiometric amounts of a base, preferably sodium hydroxide or
calcium hydroxide, across-Cannizzaro reaction occurs in the final
step to form trimethylolpropane with simultaneous liberation of the
corresponding formate salts. For example, calcium formate is formed
when calcium hydroxide is used as base.
[0004] The formate salts formed have to be removed as completely as
possible from the reaction mixture before the work-up by
distillation to isolate the trimethylolpropane, since formate salts
catalyse the decomposition of trimethylolpropane under distillation
conditions. Furthermore, the formate salt has to be freed of
organic residues and dried so as to be able to be used in a further
application. Numerous methods of separating off the formate salt
are known.
[0005] Thus, according to Ullmann's Encyclopaedia of Industrial
Chemistry, 5th Edition 1985, p. 315, trimethylolpropane can be
extracted by means of a suitable organic solvent from the reaction
solution after the latter has been concentrated. The solvent is
subsequently removed under reduced pressure and the crude
trimethylolpropane obtained is purified by distillation.
Alternatively, the aqueous reaction solution can be evaporated
until the formate crystallizes. The mixture is subsequently
filtered hot to remove the crystallized material.
[0006] DE-B 1 052 383 describes a process in which the
trimethylolpropane is separated off by driving off the
trimethylolpropane by means of superheated steam in a thin film
evaporator. The process is advantageously carried out under reduced
pressure and steam temperatures of from 120.degree. C. to
220.degree. C.
[0007] DE-A 32 07 746 describes a process for preparing
trimethylolpropane using formaldehyde having a particularly low
methanol content. To work up the reaction mixture, acid is added to
it so as to give a pH of from 5 to 7. Excess formaldehyde is
subsequently separated off by distillation. The trimethylolpropane
is isolated by distillation or extraction.
[0008] The processes mentioned display technological difficulties
in respect of the fractionation of reaction mixtures obtained in
the preparation of trimethylolpropane by the Cannizzaro process. No
optimal solution has yet been found for separating off the formates
formed. This can also be seen from the fact that great efforts have
been made in recent times to develop or to improve processes for
the preparation of trimethylolpropane which proceed without
formation of alkali metal formates or alkaline earth metal formates
in the product mixture.
[0009] According to DE-A 1 952 738, the reaction of n-butyraldehyde
and formaldehyde can be carried out in the presence of a lower
tertiary amine. An approximately 6-fold excess of formaldyhyde and
an approximately 1.5-fold excess of trialkylamine are used. Apart
from the desired product trimethylolpropane, the process produces
stoichiometric amounts of trialkylammonium formate which can easily
be removed from the reaction mixture by distillation. However,
unlike alkali metal formates or alkaline earth metal formates, this
cannot be used further, so that it is proposed that the
trialkylammonium formate be converted into calcium formate in a
separate reaction step and the amine liberated in this step be
returned to the circuit. This procedure makes the process
economically unattractive.
[0010] According to DE-A 196 53 093, 2,2-dimethylolbutanal is
firstly prepared by condensation of n-butyraldehyde and
formaldehyde in the presence of catalytic amounts of a tertiary
amine in three steps, with unreacted starting material and
by-products formed being recycled and reacted further. The
condensation product (2,2-dimethylolbutanal) obtained in this way
is subsequently hydrogenated to give trimethylpropane. A usable
formate is not obtained in this process.
[0011] EP-A 860 419, too, proposes carrying out the preparation of
2,2-dimethylolbutanal from n-butyraldehyde and formaldehyde in a
plurality of stages, with the actual reaction occurring in the
first stage and the 2-ethylacrolein obtained as by-product being
reacted with further formaldehyde in the second stage. The
2,2-dimethylolbutanal prepared in this way can then be hydrogenated
to give trimethylolpropane. Once again, no formate is isolated.
[0012] The known processes for preparing trimethylolpropane without
formation of a formate salt have hitherto been inferior to the
inorganic Cannizzaro process. This is firstly because formate salts
are interesting and marketable products and secondly because a
hydrogenation reaction can only be carried out in expensive
equipment designed for this purpose.
[0013] It is an object of the present invention to provide a
process for the simultaneous preparation of trimethylolpropane and
a formate salt and for the effective isolation of both products,
which process allows a high space-time yield and gives both
products in very pure form. This object is achieved by means of the
process of the invention.
SUMMARY
[0014] The invention relates to a process for preparing
trimethylolpropane with simultaneous formation of formate salts of
the formula (I):
M(OOCH).sub.n (I),
[0015] wherein M is a metal component selected from the group
consisting of alkali metals (e.g., lithium, sodium, potassium,
rubidium, caesium) and alkaline earth metals (e.g., beryllium,
calcium, strontium, barium), and mixtures thereof, wherein n is 1
when M is an alkali metal and n is 2 when M is an alkaline earth
metal. The process comprises reacting n-butyraldehyde and
formaldehyde by an inorganic Cannizzaro process, forming a reaction
mixture, and subjecting the reaction mixture formed to vapor
pressure filtration. These and other features, aspects, and
advantages of the present invention will become better understood
with reference to the following description and appended
claims.
DESCRIPTION
[0016] The invention provides a process for preparing
trimethylolpropane with simultaneous formation of formate salts of
the formula
M(OOCH).sub.n (I),
[0017] where M represents the alkali metals lithium, sodium,
potassium, rubidium, caesium and/or the alkaline earth metals
beryllium, calcium, strontium, barium and n is 1 when M is an
alkali metal and is 2 when M is an alkaline earth metal,
characterized in that n-butyraldehyde, formaldehyde and a base are
reacted by the inorganic Cannizzaro process and the reaction
mixture formed is subjected to vapor pressure filtration.
[0018] Distillable constituents may optionally be partly removed in
part from the reaction mixture prior to the vapor pressure
filtration.
[0019] Further purification and drying steps can optionally be
carried out after the vapour pressure filtration.
[0020] The process of the invention gives good space-time yields.
As regards the formate isolated, degrees of purity and dryness
which are not obtained by means of simple filtration,
centrifugation or evaporative crystallization are achieved. The
formate salts isolated are very substantially freed of adhering
organic substances and of moisture without a plurality of process
steps having to be carried out in succession in physically separate
apparatuses.
[0021] The principles of the vapor pressure filtration method are
described in DE-C 42 38 087 and in R. Bott, Th. Langeloh,
Aufarbeitungstechnik 37, No. 4, 1996, 163-170. Fields of
application mentioned are the filtration of coal slurries, pigment
filtration, starch filtration, sugar filtration and
hydrometallurgy. Thus, insoluble solids are always separated off
from a suspension. Surprisingly, vapor pressure filtration can also
be utilized for an extremely effective separation of formate salts
in good quality from the mixtures formed in the course of the
preparation and isolation of trimethylolpropane by the inorganic
Cannizzaro process. This was not to be readily expected since in
vapor pressure filtration, the filter cake formed is brought into
contact with a gaseous treatment fluid, preferably steam and it was
thus to be feared that appreciable amounts of the formate salt
would be lost. However, residual formate salts in
trimethylolpropane-containing filtrates have the disadvantages
described above. In addition, it would have to have been feared
that, in view of the comparatively high vapor temperatures, there
would be adverse effects on the quality of the formate salt
isolated due, for example, to thermal decomposition of organic
components present in the mixture to be filtered.
[0022] In the process of the invention, n-butyraldehyde is firstly
reacted with formaldehyde in the presence of a base. This reaction
can be carried out in one or more stages. In the single-stage
variant, the starting materials are reacted directly to form
trimethylolpropane and a formate salt. In a two-stage variant,
n-butyraldehyde and formaldehyde are firstly reacted in the
presence of catalytic amounts of base to form
2,2-dimethylolbutanal, purification or separation steps are carried
out if desired and only then is the 2,2-dimethylolbutanal reacted
with further formaldehyde in the presence of stoichiometric amounts
of base to form trimethylolpropane and formate salt.
[0023] The process of the invention produces, apart from
trimethylolpropane, the formate salts of the formula
M(OOCH).sub.n (I)
[0024] where M represents the alkali metals lithium, sodium,
potassium, rubidium, caesium and/or the alkaline earth metals
beryllium, calcium, strontium, barium and n is 1 when M is an
alkali metal and is 2 when M is an alkaline earth metal.
[0025] M preferably represents sodium, potassium, rubidium,
caesium, calcium, strontium and/or barium, particularly preferably
sodium, potassium, caesium and/or calcium and very particularly
preferably sodium and/or calcium.
[0026] Suitable bases are compounds selected from the group
consisting of alkali metal hydroxides, alkaline earth metal
hydroxides, alkali metal hydrogencarbonates and alkaline earth
metal hydrogencarbonates and alkali metal carbonates and alkaline
earth metal carbonates, with the base used naturally having to
contain the alkali metal or alkaline earth metal ion which is to be
present in the desired formate salt. Preferred bases are sodium
hydroxide, calcium hydroxide, sodium hydrogencarbonate and sodium
carbonate. The compounds can in each case be used alone or else as
mixtures of two or more basic components of the substances
mentioned. However, it is advisable to use only bases having an
identical cation so as to obtain a uniform formate salt.
[0027] Formaldehyde is preferably used in the form of an aqueous
solution which contains, for example, from about 5 to 99% by
weight, preferably from 5 to 75% by weight, particularly preferably
from 10 to 55% by weight, of formaldehyde. Formaldehyde is
particularly preferably used in the form in which it is obtained in
customary industrial processes for the preparation of
formaldehyde.
[0028] The molar ratio of n-butyraldehyde to formaldehyde is, for
example, from 1:2 to 1:10, preferably from 1:2 to 1:5, particularly
preferably from 1:2 to 1:4.
[0029] The reaction can generally be carried out at a temperature
of from 0 to 100.degree. C., preferably from 10 to 90.degree. C.,
particularly preferably from 15 to 70.degree. C.
[0030] The residence time of the reaction mixture in the reactor
can generally be from 0.15 to 10 hours.
[0031] The reaction can be carried out batchwise, in a semibatch
mode or continuously. Possible reaction apparatuses are all
reaction apparatuses known to those skilled in the art which are
suitable for reaction of liquid reactants. Particular mention may
be made of stirred tank reactors, cascades of stirred tanks, flow
tubes and multichamber reactors.
[0032] The resulting product mixture comprising trimethylolpropane,
formate salt and possibly further components such as water,
alcohols, unreacted starting materials and by-products formed is,
optionally after partial removal of distillable constituents,
subjected, according to the invention, as a liquid/solid suspension
to a vapor pressure filtration in which the formate salt is
separated from the mixture, freed of organic impurities and
demoisturized. This procedure can optionally be followed by further
downstream purification and drying steps.
[0033] The above-mentioned partial removal of distillable
constituents is preferably the partial removal of water by
distillation and/or the partial or complete removal of further
volatile components such as unreacted starting materials,
relatively low-boiling by-products or small amounts of the
trimethylolpropane product formed by distillation.
[0034] Suitable filtration apparatuses are described, for example,
in DE-C 42 38 087. Such a filtration apparatus consists essentially
of a filter area located in a housing, with the filter area being
surrounded by a pressure-tight housing configured as a pressure
chamber. The pressure chamber is filled with a gas under
superatmospheric pressure. At least part of the filter area is
surrounded by a hood which together with the filter area encloses a
second pressure chamber containing the vapor treatment fluid in the
gaseous state. The filtration apparatus contains washing devices
for washing the filter cake, preferably tubes and nozzles, which
may be located both under the hood and before or after it over the
filter area.
[0035] According to the process of the invention, the formate salts
can be separated off either continuously or batchwise. For
continuous operation, it is possible to use, for example, drum,
disc, belt or plate filters. For batchwise operation, suitable
filters are, for example, suction filters. The separation is
preferably carried out continuously using a rotating drum or disc
filter, particularly preferably using a rotating drum filter.
[0036] The mixture to be filtered which is fed to the vapor
pressure filtration generally contains, for example, from 5 to 95%
by weight, preferably from 6 to 90% by weight, particularly
preferably from 7 to 85% by weight and very particularly preferably
from 8 to 75% by weight, of trimethylolpropane. It additionally
contains, for example, from 5 to 95% by weight, preferably from 6
to 90% by weight, particularly preferably from 7 to 85% by weight
and very particularly preferably from 8 to 75% by weight, of the
formate salt and from 5 to 95% by weight, preferably from 6 to 90%
by weight, particularly preferably from 7 to 85% by weight and very
particularly preferably from 8 to 80% by weight, of water. In
addition, further components such as unreacted starting materials
or organic impurities may be present.
[0037] The temperature of the mixture fed to the vapor pressure
filtration can be, for example, from 0.degree. C. to 150.degree.
C., preferably from 5.degree. C. to 120.degree. C. and particularly
preferably from 10.degree. C. to 110.degree. C.
[0038] In vapor pressure filtration, 4 phases, namely cake
formation, cake washing, vapor treatment of the cake and
demoisturization of the cake, are generally carried out. Cake
washing can be carried out before, during and/or after vapor
treatment of the cake. However, it is also possible to carry out
vapor pressure filtration without cake washing, since the vapor
treatment of the cake likewise effects washing. Preference is given
to carrying out the phase of cake washing.
[0039] The reaction mixture obtained in the preparation of
trimethylolpropane by the inorganic Cannizzaro process is,
optionally after preliminary partial evaporation to separate off
low-boiling impurities, for example unreacted formaldehyde and part
of the water present in the reaction mixture, fed to the vapor
pressure filtration apparatus. A filter cake of the formate salt is
formed on the filter area.
[0040] During the cake formation phase, it is advantageous to apply
a differential pressure. This is, for example, in the range from 0
to 6 bar, preferably from 0.3 to 4 bar particularly preferably from
0.5 to 3 bar.
[0041] The cake formation phase generally lasts for from 2 to 420
seconds, preferably from 3 to 360 seconds and particularly
preferably from 4 to 300 seconds.
[0042] Filter media which can be used are, for example, woven metal
meshes or heat-resistant polymer materials.
[0043] Cake formation can be followed by cake washing and vapor
treatment of the cake in any order; cake washing is preferably
carried out first.
[0044] Cake washing can consist of one or more washing steps. For
this purpose, the filter cake is treated with one or more identical
or different washing liquids. For washing a formate salt cake
obtained according to the invention, the following washing liquids
have been found to be particularly useful: pure water and/or steam
or its condensate, and/or the water containing the formate salt to
be isolated, preferably water partially saturated, saturated or
supersaturated with the formate salt to be isolated and/or a
filtrate obtained in the vapor pressure filtration, with the
washing liquids being able to be used in pure form or as mixtures
of any of them.
[0045] The filtrates from different regions of the filter are
advantageously discharged separately and collected separately. The
filtrates can then be directed to specific further processing. To
optimize washing, it is advantageous, as mentioned above, to return
one or more of these filtrates to the vapor pressure filtration as
washing liquid.
[0046] The temperatures of the washing liquids are, for example, in
the range from 0.degree. C. to 165.degree. C., preferably from
5.degree. C. to 155.degree. C. and particularly preferably from
10.degree. C. to 145.degree. C.
[0047] The differential pressure across the filter cake during cake
washing is, for example, from 0 to 6 bar, preferably from 0.3 to 4
bar, particularly preferably from 0.5 to 3 bar.
[0048] The cake washing phase lasts, for example, for from 0 to 420
seconds, preferably from 1 to 360 seconds and particularly
preferably from 2 to 300 seconds.
[0049] In the vapor treatment of the cake, the filter cake of
formate salt formed on the filter area is treated with a gaseous
treatment fluid whose pressure and temperature are set so that the
treatment fluid condenses in the filter cake, preferably initially
in the uppermost layer of the filter cake farthest from the filter
area, so that a condensation front is formed along this layer and
that, in addition, the filter cake is heated to the temperature of
the gaseous treatment fluid progressively from the uppermost layer
in the direction of the filter area, so that the condensation front
at the phase boundary between the gaseous treatment fluid and the
liquid is shifted towards the filter area. The gaseous phase of the
treatment fluid can be used as pressure medium for generating a
differential pressure. The cake can once again be washed, heated
and mechanically and thermally demoisturized by means of the vapor
treatment of the cake.
[0050] As treatment fluid, preference is given to using deionized
water. However, it is also possible to use other treatment fluids,
for example organic solvents.
[0051] The temperature of the vapor which is fed to the vapor
pressure filtration can be, for example, from 100.degree. C. to
250.degree. C., preferably from 105.degree. C. to 220.degree. C.
and particularly preferably from 110.degree. C. to 200.degree.
C.
[0052] The differential pressure across the filter cake during the
vapor treatment of the cake is, for example, in the range from 0 to
6 bar, preferably from 0.3 to 4 bar, particularly preferably from
0.5 to 3 bar.
[0053] The vapor treatment of the cake lasts, for example, for from
0.5 to 300 seconds, preferably from 0.5 to 240 seconds and
particularly preferably from 0.5 to 180 seconds.
[0054] Cake washing and vapor treatment of the cake can be followed
by demoisturization of the cake. Here, the filter cake is, for
example, demoisturized mechanically and thermally by means of
superheated steam, by means of compressed inert gas and/or
compressed air. Air which has been compressed and optionally heated
is preferably used for demoisturizing the formate salt cake.
[0055] The differential pressure in the cake demoisturization phase
is, for example, in the range from 0 to 6 bar, preferably from 0.3
to 4 bar, particularly preferably from 0.5 to 3 bar.
[0056] The temperature of the compressed inert gas or the
compressed air is, for example, in the range from 0.degree. C. to
250.degree. C., preferably from 10.degree. C. to 220.degree. C. and
particularly preferably from 20.degree. C. to 200.degree. C.
[0057] The cake demoisturization phase lasts, for example, for from
0 to 300 seconds, preferably from 0.5 to 260 seconds and
particularly preferably from 0.5 to 180 seconds.
[0058] The washed, vapor-treated and demoisturized formate filter
cake can be taken from the filter cloth and conveyed out of the
pressure chamber via a cake discharge lock.
[0059] The formate salt obtained in this way generally has a
residual moisture content of 0.1-3.5% by weight, preferably
0.1-3.0% by weight. The content of organic impurities is, for
example, <500 ppm, preferably <300 ppm.
[0060] In contrast to the methods known hitherto for working up
mixtures containing trimethylolpropane and a formate salt, vapor
pressure filtration allows not only the separation of the formate
salt from the mixtures obtained in the course of the preparation
and isolation of trimethylolpropane but also the removal of
adhering organic residues and the demoisturization of the formate
salt. This leads to a further improvement in the purity of the
formate salt.
[0061] The trimethylolpropane-containing filtrates obtained in the
vapor pressure filtration are largely free of formate salts, so
that trimethylolpropane can be isolated in a manner known per se.
The filtrates are generally worked up by distillation.
[0062] The vapor condensate obtained and the washing filtrates can,
optionally after prior work-up, be passed to regulated disposal.
However, it may be more economically advantageous to return some or
all of these, continuously or discontinuously, to a suitable point
in the process, for example, as washing liquids.
[0063] The formate salt obtained can be used further in the form as
discharged, but it is also possible, if desired, for it to be
passed to one or more further isolated or combined purification and
drying steps. For this purpose, all known purification and drying
processes suitable for the present case can be employed. Examples
of purification processes are: recrystallization from water or a
water-containing solvent mixture or redispersion in water or a
water-containing solvent mixture. Examples of drying processes are:
convection drying (circulated air drying, belt drying,
fluidized-bed drying, stream drying or atomization drying), contact
drying (plate dryers, double cone dryers, blade dryers), freeze
drying or radiation drying.
[0064] The following example illustrates the process of the
invention without implying any restriction of the scope of the
invention, in which all parts and percentages are by weight unless
otherwise indicated.
EXAMPLE
[0065] 240 g of a mixture containing about 45% by weight of
trimethylolpropane, about 28% by weight of calcium formate, about
20% of water and further organic components was fed to a laboratory
pressure filter cell having a filter area of 22 cm.sup.2 (filter
material: polypropylene filter cloth, 25 .mu.m). A pressure of 2
bar was applied by means of compressed air to the mixture to be
filtered; the pressure on the filtrate side was about 1 bar. The
cake formation time was 26 seconds. The filter cake was
subsequently washed on the filter for 25 seconds using 80 g of a
saturated aqueous solution of calcium formate. The filter cake was
then treated for 9.3 seconds with steam which had been
depressurized to 2 bar. The hot filter cake was subsequently dried
for 26 seconds by means of compressed air.
[0066] This gave 65 g of calcium formate which had a residual
moisture content of 1.95% by weight (K. Fischer) and a residual
organics content of 77 mg/kg.
[0067] Although the present invention has been described in detail
with reference to certain preferred versions thereof, other
variations are possible. Therefore, the spirit and scope of the
appended claims should not be limited to the description of the
versions contained therein.
* * * * *