Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a process for recovering steam-
volatile and/or water-soluble organic products from meltable residues or
suspensions by extraction. More particularly, it relates to a process for
the continuous separation of amines, alcohols, phenols, water-soluble
organic and inorganic salts, such as, for example, common salt, the sodium
salt of mercaptobenzthiazole (MBT) and mercaptobenzimidazole.
In many chemical reactions carried out industrially, a number of
undesirable by-products, resins and/or salts are formed in addition to the
desired end products.
In many cases, it is only possible to separate these residues in
part from the unreacted starting materials and the end product. Thus, for
example, the recovery of unreacted volatile starting materials by distil-
lation in a thin-film evaporator will depend upon the viscosity of the
residues. Non-volatile starting materials such as, for example salts of
organic acids may usually be recovered only by highly expensive processes
of extraction. If the residues contain inorganic salts, viscosity may only
be obtained by using large proportions of the liquid starting materials
even at high temperature.
The present invention now provides a process for recovering steam
volatile or water-soluble, organic or inorganic products from meltable
residues or suspensions containing these products by means of extraction,
characterised in that extraction is carried out at a temperature below 250C
in such a way that the molten residue or the suspension is fed into a trickle
plate column, extracted with steam or water condensate, the mixture issuing
at the top of the column is condensed and the remaining extracted melt or
suspension is drawn off together with the descending aqueous phase at the
column bottom and separated.
In the process according to the present invention, compounds which
form a homogeneous or heterogeneous azeotrope with water are designated as
steam-volatile products. Salts of mineral and organic acids such as common
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salt, sodium sulphate, the sodium salt of mercaptobenzthiazole and mercapto-
benzimidazole are designated as water-soluble inorganic or organic products.
The removal of the volatile and/or soluble fractions from the melt-
able residues or suspensions by means of steam distillation and extraction
with water, or the condensate of water and the volatile fraction is desig-
nated as extraction in the process according to the present invention.
In the accompanying drawings,
Figure 1 shows a detail from a trickle plate column, illustrating
the arrangement of the separating units; and
Figures 2a and 2b show two possible arrangements for using a trickle
plate column in the process of the invention.
The separator shown in Figure 1 is a trickle plate column which may
be employed in the process of the present invention and is characterised
by having a multiple arrangement of separating units ~c) consisting of a
conical distributor (a) and a collector ~b). The design of such a suitable
laboratory trickle plate column is described in for example the catalogue
published by the company Normag ~1976 edition, page 79). It is advantageous
for the process according to the present invention for the gas mixture
issuing at the head of the column to condense only after rectification, and
for the condensate
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draining at the foot of the rectifying column to be used
for the extraction. If the residues contain inorganic salts,
a higher degree of efficiency is obtained in the upper section
of the extr~ction column as a result of this step according
to the invention. With a smaller number of plates, quantitative
conversion of the salts from the resinous into the aqueous
phase is quite feasible.
Temperatures of from 70 to 150C and pressures of from
0.5 to 10 bar, preferably 100C nnd about 1 bar are gener~lly
convenient as extraction temperatures and pressures but
higher temperatures of up to 250C and pressures of up to 30
bar may also be used if this is necessitated, due to the
high melting point of the residue to be worked up.
However, the melting point of the residue or the
suspension is normally already reduced at the first extraction
stage plate by extracting the organic and inorganic salts
so that a lower temperature is thereby sufficient for
extraction.
The lower extraction temperature is generally influenced
by the viscosity, ~ the resin.
Resins which may be recovered in the process according
to the present invention include, for example, those organic
products which are formed as non-usable by-products during
the production of, for example, sulphenic
amides. The viscosity of these resins is important when
selecting the extraction temperature and also the temperature
in the apparatus separating the aqueous phase from the resinous
phase.`Thus, for example, resins having a viscosity ~= 1 - 30
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Poise at between 90 and 75C, and also resins having a viscosity of up to
200 Poise may be extracted and separated by a suitable choice of the tempera-
ture.
Quantitative conversion of the organic and inorganic salts into
the aqueous phase drawn off at the foot of the column together with the re-
sin, is obtained by suitable choice of the extraction stages (separating
units in the trickle plate column). Whereas the resins may be baked after
separating the phases, the organic acids may be recovered from the aqueous
phase, for example by known precipitation processes.
A separating vessel whose temperature may be controlled is part-
icularly convenient for separating the resinous phase from the aqueous phase.
However, other separating means such as, for example, centrifugal separators
may be used.
The process according to the present invention is preferably
carried out continuously.
A possible manner of carrying out the process according to the
present invention is shown diagrammatically in Figure 2 and is described be-
low.
The molten residue 1 is fed into, for example, from a trickle
plate column 8. Steam 2 is simultaneously supplied at the bottom of the
trickle plate column and extracts the steam volatile constituents from melt
in the counter-flow. The gas mixture leaving the trickle plate column is
then either condensed 3 (variation a) by flowing through a stripper 9 or is
rectified (variation b) in a column 10. In this case, an enriched conden-
sate may be drawn off as condensate 7 in variation b. In order to extract
the organic and inorganic salts from the melt, either steam condensate 6
(variation a) or the condensate draining at the bottom of the rectification
column 10 (variation b) is fed onto the top plate of the trickle plate
column. The condensate draining at the bottom of the column 8 and contain-
ing the salts is drawn off together with the remaining resin and is intro-
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duced into the separating vessel 11. After separating the phases, theaqueous and resinous phases may be removed continuously (via 5 and 4 respect-
ively).
The proportions given in the following illustrative examples are
parts by weight.
Example 1
The apparatus used corresponded to the embodiment shown dia-
grammatically in Figure 2a.
650 parts of a melt of the average composition;
20.3 % of cyclohexylamine (CHA)
41.6 % of sodium salt of mercaptobenzthiazole (NaMBT)
31.4 % of resins which were formed by reacting
NaMBT with CHA and chlorine at about 50 C;
viscosity at 80C about 15 Poise,
6.7 % of NaCl
were fed each hour via the feed pipe 1 onto a trickle plate column having 20
separating units (plates) at a temperature of 130C.
On average, about 1956 parts of steam condensate at about 98C and
810 parts of steam at about 1.2 bar were simultaneously added each hour via
the feed pipes 6 and 2 respectively.
The vapours leaving at the head of the trickle plate column were
condensed after passing through a 50 cm high packed column 9 and, subsequently,
removed via the pipe 3.
The resinous and aqueous phases draining at the foot of the -
trickle plate column flowed into the separating vessel 11 which was cooled
sufficiently for the resin to still just be drawn off in liquid form at a
temperature of 80C, for improving separation of the phase.
At the beginning of the extraction process, water containing about
2 % of NaCl was placed in the separating bottle 11 to make it easier to
start up the equipment.
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On average, about 835 parts of distillate and 192 parts of resin
from the separating vessel as well as 2389 parts of aqueous phase of the
following average composition were drawn off hourly.
Distillate: 15.8 % of CHA
0.1 % of unknown
84.1 % of H20
Resins containing about: 0.2 % of NaMBT
0.5 % of NaCl
Aqueous Phase: 1.8 % of NaCl
11.8 % of NaMBT + resins
86.4 % of H20
Example 2
An apparatus of the type shown diagrammatically in the embodiment
in Figure 2b was used for this example.
1150 parts of a melt drawn from the bottom of a thin-film evapor-
ator having the average composition:
8.8 % of CHA
33.0 % of NaMBT
33.7 % of resins which were formed by reacting NaMBT with CHA and
chlorine at about 50C; viscosity at 80C about 15 Poise
24.5 % of NaCl
was fed each hour via the feed pipe 1 on to a trickle plate column 8 having
15 separating units at a temperature of about 150C.
An average of 3000 parts of steam at a pressure of 6 bar was
simultaneously added hourly at the bottom of the trickle plate column via
the pipe 6.
The vapours leaving the column 8 flowed into a 2 m packed column
10 and were rectified at a reflux ratio of about 4. The operating pressure
(pressure at the top of the column 10) was 5 bar, and the temperature at the
column top was about 140C. The distillate was removed via the pipe 7. The
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condensate draining from the packed column 10 was fed onto the trickle plate
column as an extraction agent.
The resinous and aqueous phases draining at the bottom of the
trickle plate column 8 were then fed into a cooled separating vessel (about
80C) which had been filled before beginning the experiment with 10 % common
salt solution.
On average, about 383 parts of distillate and 369 parts of resin
from the separating vessel and 3397 parts of aqueous phase of the following
average composition were drawn off hourly:
Distillate: 26.4 % of C~IA
about 0.2 % of unknown
73.4 % of H20
Resins: <0.1 % of NaMBT
<0.01 % of NaCl
Aqueous Phase: ~ 11.7 % of NaMBT + resins
~ 8.3 % of NaCl
~ 80.0 % of H20
Example 3
The apparatus used in Example 2 was used.
1100 parts of a melt having the average composition:
19.2 % of CHA
35.5 % of NaMBT
29.4 % of resins which were formed by reacting NaMBT with CHA and
chlorine at about 50C;
viscosity at 80C about 15 Poise
15.9 % of NaCl
was fed each hour via the feed pipe 1 on to the trickle plate column 8 at a
temperature of about 130C. An average of 2615 parts of steam at 1.2 bar
was added via the pipe 2.
At a head temperature of about 96C, a pressure of about 1 bar
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(measured at the condensor) and a reflux ratio of about 6, the following
products were obtained on average:
Products Average Composition
Distillate r~ 480 Parts 44 % CHA, 56 % H20
Resins: ~ 310 Parts NaMBT<0.2 %, NaCl<0.01 %
Aqueous Phase: ~ 2925 Parts about 14 % NaMBT + Resins,
about 6 % NaCl
about 80 % H2O
Example 4
The apparatus described in the Example 1 was employed but was
modified by use of an additional separating vessel for separating the phases
of the distillate. After placing water in this additional separating vessel
and an approximately 10 % common salt solution in the separating vessel 11,
about 2000 parts of a suspension of the average composition:
51 % of NaCl
20 % of sodium salt of mercaptobenzimidazole (NaMb)
19.7 % of isopropylphenol
9.3 % of resins (Elementary analysis: C = 56.7 %, H = 6.5 %,
N = 10.3 %, O = 3 %, S = 23.5 %.
Viscosity 5 Poise at 80C)
was fed hourly via feed pipe 1 onto the column 8 at a temperature of 80C.
About 4720 parts of steam at 1.2 bar was simultaneously added via
the feed pipe 2. The vapours leaving the stripper 9 flowed after condensa-
tion (temperature about 90C, pressure at the head of the column about 1 bar)
into a separating vessel in which the isopropylphenol phase was separated
from the aqueous phase. Although the isopropylphenol phase was drawn off as
distillate, the aqueous phase flowed via the pipe 6 back into the trickle
plate column again.
On average, about 397 parts of distillate and about 186 parts of
resin from the separating vessel 11 and 6137 parts of aqueous phase of the
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following average composition were drawn off hourly:
Distillate: about 99.0 % of isopropylphenol
about 1.0 % of H20
Resins containing about: 0.1 % of NaCl, 0.1 % NaMB
Aqueous Phase: about 16.6 % of NaCl
76.9 % of H20
6.5 % of NaMB + Resins
Example 5
The modified apparatus according to Figure 2a and described in
Example 4 was used. After placing water and a 10 % common salt solution in
the separating vessel, about 1500 parts of a suspension of the average com-
position:
51.6 % NaCl
20.2 % of NaMB-Salz
17.4 % of hexanol
1.4 % of H20
9.4 % of resins ~Elementary analysis: C = 56.7 %
H = 6.5 %, N = 10.3 %, O = 3 %, S = 23.5 %;
Viscosity 5 Poise at 80C
was fed hourly via the pipe 1 onto the colùmn 8 at a temperature of 80 C.
About 1850 parts of steam at 1.2 bar was simultaneously added via the pipe 2.
The vapours leaving the stripper 9 flowed after condensation (about 50C,
pressure at column top about 1 bar) into a separating vessel in which the
hexanol phase was separated from the aqueous phase. Although the hexanol
phase was drawn off as distillate, the aqueous phase and about another 2.002
parts of hot water at 98C flowed back via the pipe 6 into the trickle plate
column.
On average, about 281.7 parts of hexanol phase and about 134 parts
of resin from the separating vessel 11 and about 4936 parts of aqueous
phase of the following average composition were drawn off:
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Distillate: 92.5 % of hexanol
7-5 % of H20
Aqueous Phase: 15.7 % of NaCl
6.3 % of NaMB + Resins :-
78-0 % of H20 :
.Resins: <0.1 % of NaCl, <0.1 % of NaMB.
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6. 3% of NaMB ~ resins
78. 0,~ of H20
Resins: ~ O. l,~ of NaCl ,~O. l,~ of N~IMB.
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