Brine purification process
The present application claims benefit of French patent application n°
1056820 filed on August 27, 2010, the content of which is incorporated herein
by reference for all purposes.
Should the disclosure of any of the patents, patent applications, and
publications which are incorporated herein by reference conflict with the
description of the present application to the extent that it may render a term
unclear, the present description shall take precedence.
The present invention relates to a process for purifying a brine. The present
invention relates more specifically to a process for purifying a brine of organic
compounds.
International application WO 2008/152043 filed in the name of SOLVAY
SA discloses the stripping of a brine comprising organic compounds. The
temperature conditions disclosed for the stripping operation may be a source of
problems in the stripping zone. Thus, temperatures that are too high may lead to
degradations of the organic products and the use of costly materials that are
resistant to the brine under these conditions, and temperatures that are too low
may make it necessary to use uncommon and expensive coolants.
The present invention aims to overcome these problems by providing a
process for purifying a brine of organic compounds comprising:
(a) supplying a brine that comprises at least one organic compound;
(b) feeding at least one stripping zone with the brine from (a) and at least one
stripping agent;
(c) withdrawing from the stripping zone at least one fraction (I) essentially
constituted of brine, the content of organic compound of which is lower than
in the brine from (a) and at least one fraction (II) essentially constituted of
stripping agent;
in which the temperature, expressed in degrees Celsius (Ti), of the hottest
fraction of the two fractions (I) and (II) and the temperature, expressed in
degrees Celsius (T2), of the coldest fraction of the two fractions (I) and (II), said
temperatures being the temperatures measured before any possible thermal
conditioning which might be carried out before and/or during the withdrawal
thereof, correspond to the following formula:
6 10 () • 2 4 2 < 
In the process according to the invention, the temperature T2 is preferably
less than or equal to 0.9752 (Ti)° 1 and more preferably less than or equal to
0.8967 (Ti) 10147 .
In the process according to the invention, the temperature T2 is preferably
greater than or equal to 510 5 (Ti) 2 8779 , more preferably greater than or equal to
0.0058 (Ti) 1 9415 , even more preferably greater than or equal to 0.0593 (Ti) 1 4859,
more preferably still greater than or equal to 0.5342 (Ti) 1 and very
particularly preferably greater than or equal to 0.7535 (Ti) 1 325.
In one embodiment of the process according to the invention that is very
suitable, the stripping zone consists of a stripping column.
The essential feature of the present invention lies in the combination of the
values of the temperatures of the hottest fraction and of the coldest fraction
withdrawn from the stripping zone.
By carrying out the stripping under the temperature conditions mentioned:
less degradation of the organic products in the stripping zone is observed;
it is not necessary to use specific and costly materials for producing the
equipment of the stripping zone; and
it is not necessary to use specific and expensive coolants for the
stripping zone.
In the embodiment of the process according to the invention that is very
suitable, where the stripping zone consists of a stripping column, the
combination of the values of the temperatures of the hottest fraction and of the
coldest fraction withdrawn from the stripping zone has the following advantages:
less degradation of the organic products in the stripping column is observed;
it is not necessary to use specific and costly materials for producing the
stripping column and its internals;
it is not necessary to use specific and expensive coolants for the
stripping column;
it is possible to work with columns of reasonable height; and
the mechanical stresses in the column are minimized.
In the process according to the invention, the term "brine" is understood to
mean an aqueous composition containing at least one salt. The salt may be an
organic salt, an inorganic salt or a mixture of the two. An inorganic salt is a salt
whose constituent anions and cations do not contain a carbon-hydrogen bond.
The inorganic salt may be chosen from the group constituted of metal chlorides,
metal sulphates, metal hydrogen sulphates, metal hydroxides, metal carbonates,
metal hydrogen carbonates, metal phosphates, metal hydrogen phosphates, metal
borates and mixtures of at least two thereof. Alkali and alkaline-earth metal
chlorides are preferred. Sodium and potassium chlorides are more particularly
preferred and sodium chloride is very particularly preferred.
The salt content of the brine is generally greater than or equal to 5 g of
salt/kg of brine, often greater than or equal to 10 g/kg, frequently greater than or
equal to 50 g/kg, commonly greater than or equal to 80 g/kg, preferably greater
than or equal to 90 g/kg, more preferably greater than or equal to 100 g/kg, even
more preferably greater than or equal to 140 g/kg, more preferably still greater
than or equal to 160 g/kg, and very particularly preferably greater than or equal
to 180 g/kg. This salt content is habitually less than or equal to 270 g of salt/kg
of brine, preferably less than or equal to 250 g/kg and very particularly
preferably less than or equal to 230 g/kg.
A brine for which the sodium chloride content is greater than or equal to
190 g/kg of brine and less than or equal to 220 g/kg is very particularly suitable.
A brine for which the content of sodium salts is greater than or equal to
200 g/kg is also very particularly suitable.
The brine may have a neutral, acid or basic pH.
In the process according to the invention, the organic compound may be
chosen from the group constituted of aliphatic compounds, aromatic compounds
or mixtures of at least two thereof. These compounds may optionally contain at
least one heteroatom chosen from the group constituted of halogens, preferably
fluorine, chlorine, bromine and iodine, chalcogens, preferably oxygen or
sulphur, nitrogen, phosphorus and mixtures of at least two thereof. The
heteroatom is preferably oxygen.
The organic compound may be as described in application
WO 2009/095429 in the name of SOLVAY (Societe Anonyme), of which the
content, and more specifically the passage from page 2, line 16, to page 3, line
11, is incorporated by reference.
The organic compound is preferably chosen from the group constituted of
epichlorohydrin, dichloropropanols and mixtures of at least two thereof. Among
the dichloropropanols, l,3-dichloropropan-2-ol and 2,3-dichloropropan-l-ol are
often encountered. The organic compound is often chosen from mixtures of
epichlorohydrin and of dichloropropanols.
In the process according to the invention the content of organic compound
in the brine before the stripping operation is generally greater than or equal to
0 .1 g/kg of brine, often greater than or equal to 1 g/kg, in a lot of cases greater
than or equal to 5 g/kg, frequently greater than or equal to 10 g/kg and more
specifically greater than or equal to 20 g/kg. This content is generally less than
or equal to 250 g/kg, often less than or equal to 150 g/kg and frequently less than
or equal to 100 g/kg.
In the process according to the invention, when the organic compound is
chosen from mixtures of epichlorohydrin and of dichloropropanols, the content
of epichlorohydrin in the brine before the stripping operation is generally greater
than or equal to 0 .1 g/kg of brine, often greater than or equal to 1 g/kg, in a lot of
cases greater than or equal to 5 g/kg, frequently greater than or equal to 8 g/kg
and more specifically greater than or equal to 10 g/kg. This content is generally
less than or equal to 100 g/kg, often less than or equal to 50 g/kg and frequently
less than or equal to 25 g/kg.
In the process according to the invention, when the organic compound is
chosen from mixtures of epichlorohydrin and of dichloropropanols, the sum of
the contents of l,3-dichloropropan-2-ol and 2,3-dichloropropan-l-ol in the brine
before the stripping operation is generally greater than or equal to 0.2 g/kg of
brine, often greater than or equal to 0.5 g/kg, in a lot of cases greater than or
equal to 0.7 g/kg, frequently greater than or equal to 1 g/kg and more specifically
greater than or equal to 1.5 g/kg. This content is generally less than or equal to
100 g/kg, often less than or equal to 50 g/kg and frequently less than or equal to
25 g/kg. In this case, the content of l,3-dichloropropan-2-ol in the brine before
the stripping operation is generally greater than or equal to 0 .1 g/kg of brine,
often greater than or equal to 0.3 g/kg, frequently greater than or equal to
0.4 g/kg, in a lot of cases greater than or equal to 0.6 g/kg and more specifically
greater than or equal to 0.8 g/kg. This content is generally less than or equal to
50 g/kg, often less than or equal to 30 g/kg, frequently less than or equal to 20
g/kg and more specifically less than or equal to 10 g/kg. In this case, the content
of 2,3-dichloropropan-l-ol in the brine before the stripping operation is generally
greater than or equal to 0 .1 g/kg of brine, often greater than or equal to 1 g/kg, in
a lot of cases greater than or equal to 2 g/kg and more specifically greater than or
equal to 4 g/kg. This content is generally less than or equal to 50 g/kg, often less
than or equal to 30 g/kg and frequently less than or equal to 20 g/kg.
In the process according to the invention, the brine may originate from any
process that generates a brine containing an organic compound. Examples of
such processes are the processes for manufacturing epoxides, in particular
ethylene oxide, propylene oxide, butylene oxide or epichlorohydrin, the
processes for manufacturing a derivative of an epoxide, in particular epoxy
resins, the processes for manufacturing chlorinated organic products, in
particular 1,2-dichloroethane, the processes for manufacturing monoisocyanates
and polyisocyanates, in particular 4,4'-methylenediphenyl diisocyanate (MDI),
toluene diisocyanate (TDI) or hexamethylene-l,6-diisocyanate (HDI) and the
processes for manufacturing polycarbonates, in particular 2,2-bis(4-
hydroxyphenyl)propane polycarbonate (bisphenol A polycarbonate). The brine
may be a combination of brines originating from at least two of these processes.
The derivatives of an epoxide, in particular of epichlorohydrin, and the epoxy
resins, may be as described in application WO 2008/152044 in the name of
SOLVAY (Societe Anonyme), of which the content, and more specifically the
passage from page 13, line 22, to page 44, line 8, is incorporated herein by
reference.
In the process according to the invention, the brine preferably originates
from a process for manufacturing epichlorohydrin, from a process for
manufacturing epoxy resins, from a process for manufacturing 1,2-
dichloroethane, or from a combination of at least two of these processes.
In the process according to the invention, the brine more preferably
originates from a process for manufacturing epichlorohydrin, more preferably
still from a process for manufacturing epichlorohydrin by dehydrochlorination of
dichloropropanol, and very particularly preferably from a process for
manufacturing epichlorohydrin by dehydrochlorination of dichloropropanol in
which at least one portion of the dichloropropanol was obtained from glycerol
and of which at least one fraction of said glycerol is natural glycerol. The
expression "natural glycerol" is understood to mean glycerol which has been
obtained from renewable raw materials. Natural glycerol is as described in
application WO 2006/1003 12 in the name of SOLVAY (Societe Anonyme), of
which the content, and more specifically the passage from page 4, line 22, to
page 5, line 24, is incorporated herein by reference. In this case, the organic
compound present in the brine is preferably chosen from the group constituted of
epichlorohydrin, dichloropropanols and mixtures of at least two thereof. In this
case, the brine may contain at least one other organic compound chosen from the
group constituted of acetone, acrolein, 2-butanone, isopropanol, 3-methoxy-l,2-
epoxypropane, cyclopentanone, epichlorohydrin, chloroacetone, hydroxyacetone
(acetol), the compound of empirical formula: C O, 1,2,3-trichloropropane,
2,3-epoxy-l-propanol (glycidol), 2-chloro-2-propen-l-ol, c 5-3-chloro-2-propenl-
ol, l-methoxy-3-chloropropan-2-ol, 3-chloro-l-propan-l-ol, tra«s-3-chloro-2-
propen-l-ol, the compound of empirical formula: C6H 02, the compound of
empirical formula: C6H12OCI2, the compound of empirical formula: C6H10O2CI2,
l,3-dichloro-2-propanol, the compound of empirical formula: C9H10O2, 2,3-
dichloro-l-propanol, phenol, glycerol, l-chloro-2,3 -propanediol, 2-chloro-l,3-
propanediol, cyclic diglycerols, glyceraldehyde, formaldehyde, acetaldehyde,
propionaldehyde, butyraldehyde, acetic acid, propionic acid, formic acid,
glycolic acid, oxalic acid, lactic acid, capric acid, caprylic acid, valeric acid,
caproic acid, lauric acid, and mixtures of at least two thereof.
The processes for preparing epoxy resins, dichloropropanol and
epichlorohydrin can be such as disclosed in International applications
WO2005/054167, WO2006/10031 1, WO2006/100312, WO2006/100313,
WO2006/100314, WO2006/100315, WO2006/100316, WO2006/100317,
WO2006/106153, WO2007/054505, WO 2006/100318, WO2006/100319,
WO2006/1 00320, WO 2006/106154, WO2006/106155, WO 2007/144335, WO
2008/107468, WO 2008/101866, WO 2008/145729, WO 2008/1 10588, WO
2008/152045, WO 2008/152043, WO 2009/000773, WO 2009/043796, WO
2009/121853, WO 2008/152044, WO 2009/077528, WO 2010/066660, WO
2010/029039, WO 2010/029153, WO 201 1/054769 and WO 201 1/054770, filed
in the name of SOLVAY, the contents of which are incorporated herein by
reference.
In the process according to the invention, when the brine originates from a
process for manufacturing epichlorohydrin by dehydrochlorination of
dichloropropanol, the brine purification process makes it possible both to recover
valuable epichlorohydrin and to obtain a brine that is purified of organic
compounds which may feed an electrolysis process, in particular a process for
the electrolysis of brines of alkali metal chlorides, in particular sodium chloride,
such as a chlor-alkali electrolysis process.
In the process according to the invention, at least one stripping zone is fed
with a brine comprising at least one organic compound and at least one stripping
agent.
The expression "stripping zone" is understood to mean the zone between
the feeding and the withdrawal of the brine and of the stripping agent.
The term "stripping" is understood to mean the separation of a substance
by entrainment using a gas, the vapour of a pure material or a mixture thereof,
denoted by the term "stripping agent", which dissolves or does not dissolve said
substance.
In the process according to the invention, the stripping agent may be
chosen from the group constituted of air, oxygen-depleted air, nitrogen, oxygen,
steam and mixtures of at least two thereof. Steam, air, oxygen-depleted air and
nitrogen are preferred stripping agents and steam is a more preferred stripping
agent. A mixture of steam and oxygen-depleted air may also be suitable.
When the stripping agent contains steam, the stripping agent may feed the
stripping zone independently of the brine or from the brine itself, or via a
combination of the two. Feeding the stripping agent from the brine is very
suitable. When the stripping agent feeds the stripping zone independently of the
brine, in part or wholly, said part or whole may be of any origin. In particular,
when the brine originates at least partly from a process for manufacturing
epichlorohydrin, the stripping agent may originate from any step of the process
for manufacturing epichlorohydrin, in particular from the step of producing
dichloropropanol from glycerol. In this case, the vapour is generated in the steps
of cooling and/or condensing the streams from the dichloropropanol production
plant.
In the process according to the invention, when the stripping zone is
constituted of a stripping column, when the stripping agent is steam that feeds
the stripping zone from the brine, the steam is generated from the brine and this
generation may take place in the column either by virtue of an internal heat
exchanger such as a coil, for example, or via an external heat exchanger such as
a reboiler for example. In the process according to the invention, when the
stripping zone is constituted of a stripping column, when the stripping agent is
steam, the steam is preferably introduced independently of the brine directly into
the column with no reboiler via a steam distribution network.
In the process according to the invention, when the stripping agent is
steam, the temperature of the coldest fraction of the two fractions withdrawn
from the stripping zone (T2) is generally greater than or equal to 10°C, often
greater than or equal to 30°C, frequently greater than or equal to 50°C and more
specifically greater than or equal to 80°C. This temperature is generally less than
160°C, often less than or equal to 150°C, frequently less than or equal to 140°C,
more specifically less than or equal to 120°C and in particular less than or equal
to 100°C.
In the process according to the invention, when the stripping agent is
oxygen-depleted air or nitrogen, the temperature of the coldest fraction of the
two fractions withdrawn from the stripping zone (T2) is generally greater than or
equal to 10°C, often greater than or equal to 15°C, frequently greater than or
equal to 20°C and more specifically greater than or equal to 25°C. This
temperature is generally less than 160°C, often less than or equal to 120°C,
frequently less than or equal to 100°C, more specifically less than or equal to
80°C and in particular less than or equal to 60°C.
In the process according to the invention, when the stripping zone consists
of a stripping column, and when the stripping agent is steam, the temperature of
the coldest fraction of the two fractions withdrawn from the stripping column is
as mentioned in the preceding paragraph for the temperature of the coldest
fraction of the two fractions withdrawn from the stripping zone when the
stripping agent is steam. The coldest fraction may be withdrawn at the top or at
the bottom of the column, and is preferably withdrawn at the top of the stripping
column.
In the process according to the invention, when the stripping zone consists
of a stripping column, and when the stripping agent is oxygen-depleted air or
nitrogen, the temperature of the coldest fraction of the two fractions withdrawn
from the stripping column is as mentioned in the preceding paragraph for the
temperature of the coldest fraction of the two fractions withdrawn from the
stripping zone when the stripping agent is oxygen-depleted air or nitrogen. The
coldest fraction may be withdrawn at the top or at the bottom of the column, and
is preferably withdrawn at the bottom of the stripping column.
In the process according to the invention, when the stripping agent is
steam, the temperature of the hottest fraction of the two fractions withdrawn
from the stripping zone is generally greater than 40°C, often greater than or
equal to 50°C, frequently greater than or equal to 60°C and more specifically
greater than or equal to 90°C. This temperature is generally less than or equal to
160°C, often less than or equal to 150°C, frequently less than or equal to 140°C,
more specifically less than or equal to 130°C and in particular less than or equal
to 120°C.
In the process according to the invention, when the stripping agent is
oxygen-depleted air or nitrogen, the temperature of the hottest fraction of the two
fractions withdrawn from the stripping zone is generally greater than 15°C, often
greater than or equal to 25°C, frequently greater than or equal to 40°C and more
specifically greater than or equal to 60°C. This temperature is generally less than
or equal to 160°C, often less than or equal to 150°C, frequently less than or equal
to 140°C, more specifically less than or equal to 130°C and in particular less than
or equal to 120°C.
In the process according to the invention, when the stripping zone is a
stripping column, and when the stripping agent is steam, the temperature of the
hottest fraction of the two fractions withdrawn from the stripping column is as
mentioned in the preceding paragraph for the temperature of the hottest fraction
of the two fractions withdrawn from the stripping zone when the stripping agent
is steam. The hottest fraction may be withdrawn at the top or at the bottom of
the column, and is preferably withdrawn at the bottom of the stripping column.
In the process according to the invention, when the stripping zone is a
stripping column, and when the stripping agent is oxygen-depleted air or
nitrogen, the temperature of the hottest fraction of the two fractions withdrawn
from the stripping column is as mentioned in the preceding paragraph for the
temperature of the hottest fraction of the two fractions withdrawn from the
stripping zone when the stripping agent is oxygen-depleted air or nitrogen. The
hottest fraction may be withdrawn at the top or at the bottom of the column, and
is preferably withdrawn at the top of the stripping column.
In the process according to the invention, when the stripping agent is
chosen from the group constituted of air, oxygen-depleted air, nitrogen, oxygen,
and mixtures of at least two thereof, and also mixtures thereof with steam, the
temperature of the coldest fraction of the two fractions withdrawn from the
stripping zone (T2) is generally greater than or equal to 10°C, often greater than
or equal to 25°C, frequently greater than or equal to 40°C and more specifically
greater than or equal to 50°C. This temperature is generally less than 120°C,
often less than or equal to 110°C, frequently less than or equal to 105°C and
more specifically less than or equal to 100°C.
In the process according to the invention, when the stripping zone is a
stripping column, and when the stripping agent is chosen from the group
constituted of air, oxygen-depleted air, nitrogen, oxygen, and mixtures of at least
two thereof, and also mixtures thereof with steam, the temperature of the coldest
fraction of the two fractions withdrawn from the stripping column is as
mentioned in the preceding paragraph for the temperature of the coldest fraction
of the two fractions withdrawn from the stripping zone when the stripping agent
is chosen from the group constituted of air, oxygen-depleted air, nitrogen,
oxygen, and mixtures of at least two thereof, and also mixtures thereof with
steam.
In the process according to the invention, when the stripping agent is
chosen from the group constituted of air, oxygen-depleted air, nitrogen, oxygen,
and mixtures of at least two thereof, and also mixtures thereof with steam, the
temperature of the hottest fraction of the two fractions withdrawn from the
stripping zone is generally greater than or equal to 15°C, often greater than or
equal to 30°C, frequently greater than or equal to 40°C and more specifically
greater than or equal to 60°C. This temperature is generally less than 120°C,
often less than or equal to 110°C, frequently less than or equal to 105°C and
more specifically less than or equal to 100°C.
In the process according to the invention, when the stripping zone consists
of a stripping column, and when the stripping agent is chosen from the group
constituted of air, oxygen-depleted air, nitrogen, oxygen, and mixtures of at least
two thereof, and also mixtures thereof with steam, the temperature of the hottest
fraction of the two fractions withdrawn from the stripping column is as
mentioned in the preceding paragraph for the temperature of the hottest fraction
of the two fractions withdrawn from the stripping zone when the stripping agent
is chosen from the group constituted of air, oxygen-depleted air, nitrogen,
oxygen, and mixtures of at least two thereof, and also mixtures thereof with
steam.
In the process according to the invention, the temperatures Ti and T2 of the
hottest fraction and of the coldest fraction withdrawn from the stripping zone are
the temperatures measured before any possible thermal conditioning which
might be carried out before and/or during the withdrawal thereof.
These temperatures may be measured using any known type of temperature
probe: thermocouple sensor, thermoresi stive sensor, infrared sensor, bimetallic
sensor, thermometers, etc. Such types of probe are for example described in
"Perry's Chemical Engineers' Handbook", Sixth Edition, McGraw Hill, 1984,
Section 22-32 to 22-37.
In the process according to the invention, the fraction (I) essentially
constituted of brine contains more than 500 g of brine per kg of fraction (I), often
at least 750 g/kg, frequently at least 900 g/kg and more specifically at least
990 g/kg.
In the process according to the invention, the fraction (II) essentially
constituted of stripping agent contains more than 50 mol% of stripping agent per
mole of fraction (II), often at least 75 mol%, frequently at least 90 mol%,
specifically at least 99 mol%.
The temperature may be measured at any location of the fractions
withdrawn from the stripping zone. This measurement is preferably carried out
within the fractions withdrawn.
In the process according to the invention, the pressure in the stripping zone
is generally greater than or equal to 20 mbar absolute, in a lot of cases greater
than or equal to 50 mbar absolute, often greater than or equal to 100 mbar
absolute, frequently greater than or equal to 200 mbar absolute, more specifically
greater than or equal to 400 mbar absolute and in particular greater than or equal
to 500 mbar absolute. This pressure is generally less than or equal to 10 bar
absolute, often less than or equal to 5 bar absolute, frequently less than or equal
to 2 bar absolute, more specifically less than or equal to 1.5 bar absolute and in
particular less than or equal to 1.2 bar absolute. A pressure greater than or equal
to 600 mbar absolute and less than or equal to 1.1 bar absolute is very suitable.
In the process according to the invention, when the stripping zone is a
stripping column, the pressure in the stripping column is as mentioned in the
preceding paragraph for the pressure in the stripping zone.
In the process according to the invention, when the stripping zone is a
stripping column, the pressure drop i.e. the difference between the pressure at the
bottom of the column and the pressure at the top of the column is generally less
than or equal to 2 bar, in a lot of cases less than or equal to 1.5 bar, often less
than or equal to 1.2 bar, frequently less than or equal to 1 bar, in many cases less
than or equal to 0.7 bar and in particular less than or equal to 0.5 bar. This
pressure difference is generally greater than or equal to 10 mbar, often greater
than or equal to 20 mbar, frequently greater than or equal to 30 mbar, and in
particular greater than or equal to 50 mbar.
In the process according to the invention, the stripping may be carried out
in continuous mode or in batch mode. The expression "continuous mode" is
understood to mean a mode in which the brine and the stripping agent feed the
stripping zone in an uninterrupted manner over a period of time covering at least
50% of the duration of the stripping operation, preferably at least 90% of this
duration and more preferably at least 95% of this duration. The duration of the
stripping operation is the time elapsed between the moment when the feeding of
the stripping zone with brine and with stripping agent begins and the moment
when this feeding is interrupted. The expression "batch mode" is understood to
mean any other operating mode. The stripping is preferably carried out in
continuous mode.
In the process according to the invention when the stripping is carried out
continuously, the stripping agent and the brine may feed the stripping zone co
currently or counter currently or in a crossed current manner. Countercurrent
feeding of the stripping zone is preferred.
In the process according to the invention, the stripping agent is preferably
steam and the stripping zone from (b) is fed continuously and counter currently
with brine and with stripping agent.
In the process according to the invention, when the stripping operation is
carried out continuously, the direction of movement of the streams of stripping
agent and of brine may be vertical or horizontal, or vertical for the stream of
brine and horizontal for the stream of stripping agent or horizontal for the stream
of brine and vertical for the stream of stripping agent. A vertical direction of
movement for the two streams is preferred.
In the process according to the invention, the ratio between the total
amount of stripping agent that is introduced during the stripping operation,
expressed in kmol, and the amount of brine that is introduced during the
stripping operation, expressed in kmol, is generally greater than or equal to
0.0001, frequently greater than or equal to 0.001, often greater than or equal to
0.01, in particular greater than or equal to 0.05 and more specifically greater than
or equal to 0.1. This ratio is generally less than or equal to 10, frequently less
than or equal to 5, often less than or equal to 1, in particular less than or equal to
0.5 and more specifically less than or equal to 0.3. The number of kmol of brine
corresponds to the sum of the numbers of moles of the constituents of the brine.
In one particular embodiment of the process according to the invention, it
is possible to feed the stripping zone or the stripping column with, besides the
stripping agent and the brine, at least one basic compound. The basic compound
may be an organic basic compound or an inorganic basic compound or a mixture
of the two. Organic basic compounds are, for example, amines, such as for
example imidazole and derivatives thereof, pyridine and derivatives thereof,
phosphines and ammonium, phosphonium or arsonium hydroxides. Inorganic
basic compounds are preferred. The expression "inorganic compounds" is
understood to mean compounds which do not contain a carbon-hydrogen bond.
The inorganic basic compound may be chosen from alkali metal oxides,
hydroxides, carbonates, hydrogen carbonates, phosphates, hydrogen phosphates
and borates, alkaline-earth metal oxides, hydroxides, carbonates, hydrogen
carbonates, phosphates, hydrogen phosphates and borates, and mixtures of at
least two thereof. Alkali metal oxides, alkali metal hydroxides, alkaline-earth
metal oxides, alkaline-earth metal hydroxides, and mixtures of at least two
thereof, are preferred.
In the process according to the invention, the basic compound may be in
the form of a liquid, an essentially anhydrous solid, a hydrated solid, an aqueous
and/or organic solution or an aqueous and/or organic suspension. The basic
compound is preferably in the form of an essentially anhydrous solid, a hydrated
solid, an aqueous solution or an aqueous suspension.
The expression "essentially anhydrous solid" is understood to mean a solid
for which the water content is less than or equal to 20 g/kg, preferably less than
or equal to 10 g/kg and more preferably less than or equal to 1 g/kg.
The expression "hydrated solid" is understood to mean a solid for which
the water content is at least 20 g/kg and at most 700 g/kg, preferably at least 50
g/kg and at most 650 g/kg and very particularly preferably at least 130 g/kg and
at most 630 g/kg. The hydrates which denote solid combinations of substances
with one or more water molecules are examples of hydrated solids.
When the basic compound is used in the form of an aqueous solution, its
content in the aqueous solution is generally greater than 20 g/kg, preferably
greater than or equal to 70 g/kg and more preferably greater than or equal to
150 g/kg. This content is generally less than or equal to the solubility of the
basic solid in the brine at the temperature of the stripping treatment.
When the basic compound is used in the form of an aqueous solution of
sodium hydroxide, the content of sodium hydroxide is preferably greater than or
equal to 150 g/kg.
When the basic compound is used in the form of an aqueous suspension, its
content in the aqueous suspension is generally greater than the solubility of the
basic solid in the brine at the temperature of the stripping treatment, preferably
greater than or equal to 20 g/kg and more preferably greater than or equal to 70
g/kg. This content is generally less than or equal to 400 g/kg, preferably less
than 300 g/kg.
The preferred basic compounds are in the form of concentrated aqueous
solutions or suspensions of sodium hydroxide or calcium hydroxide or in the
form of purified caustic brine. The expression "purified caustic brine" here
means sodium hydroxide which contains sodium chloride such as, for example,
that produced in a diaphragm electrolysis process. The sodium hydroxide
content of the purified caustic brine is generally greater than or equal to 30 g/kg,
preferably greater than or equal to 40 g/kg and more preferably greater than or
equal to 60 g/kg. This sodium hydroxide content is generally less than or equal
to 300 g/kg, preferably less than or equal to 250 g/kg and more preferably less
than or equal to 200 g/kg. The sodium chloride content of the purified caustic
brine is generally greater than or equal to 30 g/kg, preferably greater than or
equal to 50 g/kg and more preferably greater than or equal to 70 g/kg. This
sodium chloride content is generally less than or equal to 250 g/kg, preferably
less than or equal to 200 g/kg and more preferably less than or equal to 180 g/kg.
It is also possible to use a mixture of several basic agents depending on the
availabilities and on the economic optimization of the industrial site where the
process according to the invention is established. The basic agents preferred for
producing these mixtures are limewater and solutions of sodium hydroxide and
of purified caustic brine, for example, a mixture of limewater and a sodium
hydroxide solution or a mixture of limewater and purified caustic brine. These
mixtures may be produced in any relative proportion of at least two of these
basic agents. They may be produced both before introduction into the stripping
zone and also in this stripping zone.
The use of a basic agent is very suitable when, in the process according to
the invention, the brine originates from a process for manufacturing
epichlorohydrin by dehydrochlorination of dichloropropanol and when the
organic compound in the brine is chosen from mixtures of epichlorohydrin and
dichloropropanols. In this case the addition of a basic agent makes it possible to
convert at least one portion of the dichloropropanols present in the brine to
epichlorohydrin, a valuable product that is also more easily stripped. In this
case, not only is the brine purified of organic compounds but in addition a
valuable organic product is recovered. In this case, the brine generally contains,
before stripping, organic compounds other than epichlorohydrin and
dichloropropanols, such as for example monochloropropanediols, glycidol and
chloroacetone. These other organic compounds may be converted to glycerol
and to hydroxyacetone, which are less readily stripped, less toxic and more
readily degradable, via a biological route and/or via a chemical route. The risk
of contamination of the stripped epichlorohydrin by these other organic
compounds is reduced and the reuse of the epichlorohydrin recovered there from
is facilitated.
In the process according to the invention, when the stripping zone or the
stripping column is fed with at least one basic agent, and when the organic
compound in the brine is chosen from mixtures of epichlorohydrin and
dichloropropanols, the ratio between the total amount of basic agent that is
introduced during the stripping operation, expressed in equivalents, and the
amount of dichloropropanol contained in the brine before the stripping,
expressed in moles, is generally greater than or equal to 0.1, frequently greater
than or equal to 0.5 and often greater than or equal to 1. This ratio is generally
less than or equal to 20, frequently less than or equal to 10, often less than or
equal to 5 and in particular less than or equal to 2 .
In this embodiment, the epichlorohydrin present in the brine may react
with the alkaline agent added. One preferred operating mode consists in dividing
the stripping into two parts: a first part where the epichlorohydrin fed into the
brine is stripped, then a second reactive part where the dichloropropanol reacts
with the alkaline agent and the epichlorohydrin formed is stripped. The alkaline
agent is introduced between the two parts. These two parts may be carried out in
one and the same device, by way of non-limiting example, a two-section column,
or in different devices, by way of non-limiting example, two separate columns.
When the stripping zone or the stripping column is fed with at least one
basic compound, the basic compound may feed the stripping zone independently
of the brine or from the brine itself, or via a combination of the two. Feeding of
the basic agent from the brine is carried out by addition of the basic agent to the
brine before the latter is fed into the stripping zone. Any type of mixer may be
used to homogenize the resulting mixture, such as for example, a static mixer, a
dynamic mixer, a stirred tank, etc.
In the process according to the invention, the stripping zone may comprise
any type of apparatus or combination of apparatus as described in "Perry's
Chemical Engineers' Handbook", Sixth Edition, McGraw Hill, 1984, Section 14.
In one particular embodiment of the process of the invention, the stripping
zone consists of a stripping column.
In a first aspect of this particular embodiment, a single stripping column is
fed with the brine and the stripping agent, counter currently, and the direction of
movement of the streams of brine and stripping agent is vertical. The brine is
introduced at the top of the column and withdrawn from the bottom of the
column. The stripping agent, preferably steam, is introduced at the bottom of the
column and withdrawn from the top of the column.
In a second aspect of this particular embodiment, at least two stripping
columns are fed in series with the brine and the stripping agent, counter
currently, and the direction of movement of the streams of brine and stripping
agent is vertical. The brine is introduced at the top of the columns and
withdrawn from the bottom of the columns. The stripping agent, preferably
steam, is introduced at the bottom of the columns and withdrawn from the top of
the columns.
In a third aspect of this particular embodiment, at least two stripping
columns are fed in parallel with the brine and the stripping agent, counter
currently, and the direction of movement of the streams of brine and stripping
agent is vertical. The brine is introduced at the top of the columns and
withdrawn from the bottom of the columns. The stripping agent, preferably
steam, is introduced at the bottom of the columns and withdrawn from the top of
the columns.
In a fourth aspect of this particular embodiment, at least two stripping
columns are fed with the brine and the stripping agent, counter currently, and the
direction of movement of the streams of brine and stripping agent is vertical.
The columns are fed in parallel by the brine and in series by the stripping agent.
The brine is introduced at the top of the columns and withdrawn from the bottom
of the columns. The stripping agent, preferably steam, is introduced at the
bottom of the columns and withdrawn from the top of the columns.
In a fifth aspect of this particular embodiment, at least two stripping
columns are fed with the brine and the stripping agent, counter currently, and the
direction of movement of the streams of brine and stripping agent is vertical.
The columns are fed in series by the brine and in parallel by the stripping agent.
The brine is introduced at the top of the columns and withdrawn from the bottom
of the columns. The stripping agent, preferably steam, is introduced at the
bottom of the columns and withdrawn from the top of the columns.
In a sixth aspect of this particular embodiment, a single stripping column is
fed with the brine and the stripping agent, counter currently, and the direction of
movement of the streams of brine and stripping agent is vertical. The brine is
introduced at the top of the column at various levels and withdrawn from the
bottom of the column at various levels. The stripping agent, preferably steam, is
introduced at the bottom of the column at various levels and withdrawn from the
top of the column at various levels.
When a basic agent is used, this agent is habitually added at one or more
intermediate levels, and often at a single level, to the stripping column. When
the basic agent is added at a single level, said level is more specifically located
above or below the brine feed point. When the basic agent is added at several
levels, said levels are more specifically located below the brine feed point, it
being possible for one of the levels to be located above the brine feed point and
the others below.
The basic agent may also be introduced into the brine feeding the stripping
column.
When the stripping zone consists of a stripping column, this generally
comprises plates or packing or both. The stripping column preferably comprises
packing in its upper part and plates in its lower part. More preferably, the
packing extends from a level located below the brine feed point to the top of the
column and the plates are located below the packing. More preferably still, the
retention of the plates increases on descending the column.
In the process according to the invention, the stripping column very
particularly preferably comprises packing in its upper part and plates in its lower
part, and the brine is fed into the top of the column and the packing is located
below the brine feed point and the retention of the plates increases towards the
bottom of the column.
The plates may be of any type known to a person skilled in the art, for
example perforated plates, bubble-cap trays, valve trays, and "doughnut" trays.
Perforated plates are very suitable.
The number of plates is generally greater than or equal to 3, often greater
than or equal to 5, frequently greater than or equal to 8 and in particular greater
than or equal to 12. This number of plates is generally less than or equal to 100,
often less than or equal to 80, frequently less than or equal to 50 and in particular
less than or equal to 40. A number of plates between 18 and 25 is very suitable.
The packings may be of any type known to a person skilled in the art such
as random packings and structured packings. Random packings are very
suitable.
The packing height is generally greater than or equal to 0.5 m, often greater
than or equal to 1m and frequently greater than or equal to 2 m. This height is
generally less than or equal to 10 m, often less than or equal to 8 m, frequently
less than or equal to 5 m and in particular less than or equal to 4 m. A height
between 2.5 and 3.5 m is very suitable.
The apparatus in which the stripping treatment is carried out, such as for
example the stripping column, the packing and the plates of the column, is
generally made from or covered with a material that withstands the stripping
conditions. This material may be chosen from the group constituted of carbon
steels, stainless steels, enamelled steels, compressed steels, titanium, titanium
alloys and nickel alloys, polymers, such as polyolefins, for instance
polypropylene and polyethylene, such as chlorinated polymers, for instance
polyvinyl chloride and chlorinated polyvinyl chloride, such as fluorinated
polymers, for instance perfluorinated polymers including, for example,
polytetrafluoroethylene, copolymers of tetrafluorethylene and
hexafluoropropylene, and poly(perfluoropropyl vinyl ether), for instance
partially fluorinated polymers including, for example, polyvinylidene fluoride
and copolymers of ethylene and chlorotrifluoroethylene, such as sulphurcontaining
polymers, for instance polysulphones and polysulphides, in particular
that are aromatic, coatings using resins such as epoxy resins and phenolic resins,
and combinations of at least two thereof. The polymers may be used in bulk or
shrunk-fit form or in the form of a coating.
In the process according to the invention, the fraction of stripping agent
withdrawn (II) comprises the stripping agent and a first portion of the organic
compound present in the brine before the feeding of the stripping zone. The
fraction of brine withdrawn (I), the content of organic compound of which is
lower than in the brine which feeds the stripping zone, comprises brine and a
second portion of the organic compound present in the brine before the stripping
operation.
In the process according to the invention, the amount of organic compound
present in the fraction withdrawn (II) is generally greater than or equal to 80% of
the amount of organic compound present in the brine which feeds the stripping
zone, often greater than or equal to 85%, frequently greater than or equal to 90%
and in many cases greater than or equal to 94%.
In the process according to the invention, when the organic compound in
the brine is chosen from mixtures of epichlorohydrin and of dichloropropanols,
the amount of dichloropropanols present in the fraction withdrawn (I) relative to
the amount of dichloropropanols present in the brine which feeds the stripping
zone is generally less than or equal to 5%, often less than or equal to 1%,
frequently less than or equal to 0 .1% and in many cases less than or equal to
0.05%.
In the process according to the invention, the content of organic compound
in the fraction withdrawn (I) expressed as g of carbon per kg of fraction
withdrawn (I) is generally less than or equal to 10 g/kg, preferably less than or
equal to 5 g/kg, more preferably less than or equal to 2 g/kg, even more
preferably less than or equal to 1 g/kg, and more preferably still less than or
equal to 0.8 g/kg. This amount is generally greater than or equal to 0.0001 g/kg.
In the process according to the invention, when the organic compound is
chosen from the group constituted of epichlorohydrin, dichloropropanols and
mixtures of at least two thereof and in particular when the organic compound is a
mixture of epichlorohydrin and dichloropropanols, the content of organic
compound in the fraction withdrawn (I) expressed as g of carbon per kg of
fraction withdrawn (I) is generally less than or equal to 10 g/kg, preferably less
than or equal to 5 g/kg, more preferably less than or equal to 2 g/kg, even more
preferably less than or equal to 1 g/kg, and more preferably still less than or
equal to 0.8 g/kg. This amount is generally greater than or equal to 0.0001 g/kg.
In this case, the content of epichlorohydrin in the fraction withdrawn (I)
expressed as g of carbon per kg of fraction withdrawn (I) is generally less than
0.5 g of carbon/kg of fraction withdrawn (I) and preferably less than or equal to
0.1 g/kg. In this case, the content of dichloropropanols in the fraction
withdrawn (I) expressed as g of carbon per kg of fraction withdrawn (I) is
generally less than 0.5 g/kg, and preferably less than or equal to 0 .1 g/kg.
In the process according to the invention, the fraction withdrawn (II) may
be subjected to any subsequent treatment. This treatment may be chosen from
the group constituted of distillation, evaporation, stripping, liquid/liquid
extraction, settling, adsorption and absorption operations and any combination of
at least two thereof. This subsequent treatment is generally intended to recover,
in a first portion, the majority of the organic compound present in the fraction
withdrawn (II) before the subsequent treatment and, in a second portion, the
majority of the stripping agent present in the fraction withdrawn (II) before the
subsequent treatment. The second portion may be recycled to the stripping zone.
When the stripping agent comprises steam, a condensation operation followed by
a liquid/liquid phase separation operation, for example by centrifugation, by
coalescence or by gravity settling, is preferred. In certain cases, the settling
operation may be preceded by a coalescence operation. This operation is
preferred when the organic compound is chosen from the group constituted of
epichlorohydrin, dichloropropanols or mixtures of epichlorohydrin and
dichloropropanol. When the stripping agent is chosen from the group constituted
of air, nitrogen, oxygen, oxygen-depleted air, and mixtures of at least two
thereof, an adsorption of the organic compound onto an adsorbent solid, such as
for example activated carbon or a resin is a preferred variant. Another preferred
variant is sending to a high-temperature oxidation treatment.
In the process according to the invention, the fraction withdrawn (I) may
be subjected to any subsequent treatment. This treatment may be chosen from
the group constituted of thermal conditioning, dilution, concentration,
distillation, evaporation, settling, coalescence, liquid/liquid extraction, filtration,
crystallization, adsorption, oxidation, reduction, neutralization, complexation,
precipitation and salt addition operations and combinations of at least two
thereof. These treatments are as described in application WO 2008/152043 by
SOLVAY (Societe Anonyme), of which the content, and more specifically the
passage from page 11, line 13 to page 29, line 7, is incorporated herein by
reference and in application WO 2009/095429 by SOLVAY (Societe Anonyme),
of which the content, and more specifically the passage from page 1, line 24 to
page 27, line 26, is incorporated herein by reference. A treatment that is very
suitable is as described in French patent application No. 10/56360 filed on 02
August 2010 in the name of Solvay S.A. and the content of which is incorporated
herein by reference. The fraction (I) thus treated is a brine purified of organic
compounds that may feed an electrolysis process, in particular a process for the
electrolysis of brines of alkali metal chlorides, in particular sodium chloride,
such as a chlor-alkali electrolysis process.
In the process according to the invention, particularly when the stripping
zone is a stripping column, a brine depleted in organic compounds is withdrawn
from the stripping zone, particularly from the stripping column, and it is possible
to subject said depleted brine to at least one treatment chosen from the group
constituted of thermal conditioning, dilution, concentration, distillation,
evaporation, liquid/liquid extraction, filtration, crystallization, adsorption,
oxidation, reduction, neutralization, complexation, precipitation, salt addition,
aerobic bacterial treatment and anaerobic bacterial treatment operations, and
combinations of at least two thereof, and to feed a mercury electrolysis cell or a
diaphragm electrolysis cell or a membrane electrolysis cell, preferably a
membrane electrolysis cell, of a process for the electrolysis of alkali metal
chloride brines, with said thus treated brine.
The invention also relates to a process of electrolysis of brines of alkali
metal chlorides, in which a mercury electrolysis cell or a diaphragm electrolysis
cell or a membrane electrolysis cell, preferably a membrane electrolysis cell, of a
process for the electrolysis of alkali metal chloride brines, is fed with a brine
obtained by subj ecting to at least one treatment chosen from the group
constituted of thermal conditioning, dilution, concentration, distillation,
evaporation, liquid/liquid extraction, filtration, crystallization, adsorption,
oxidation, reduction, neutralization, complexation, precipitation, salt addition,
aerobic bacterial treatment and anaerobic bacterial treatment operations, and
combinations of at least two thereof, a brine depleted in organic compounds, the
brine being withdrawn from the stripping zone, preferably from the stripping
column, of the epuration process according to the invention.
In the process according to the invention, the brine that feeds the stripping
zone may be subjected to at least one treatment before feeding the stripping zone.
This treatment may be chosen from the group constituted of dilution,
concentration, distillation, evaporation, settling, coalescence, liquid/liquid
extraction, filtration, crystallization, adsorption, oxidation, reduction,
neutralization, complexation and precipitation operations and combinations of at
least two thereof. These treatments are as described in application WO
2008/152043 by SOLVAY (Societe Anonyme), of which the content, and more
specifically the passage from page 11, line 13 to page 29, line 7, is incorporated
herein by reference and in application WO 2009/095429 by SOLVAY (Societe
Anonyme), of which the content, and more specifically the passage from page 1,
line 24 to page 27, line 26, is incorporated herein by reference.
Examples 1 to 2 1 below are intended to illustrate the invention without
however limiting it.
Examples 1 and 2
A stripping column comprising 27 plates is fed with a brine comprising,
per kg of brine, 20 g of epichlorohydrin, 12 g of l,3-dichloro-2-propanol, 8 g of
2,3-dichloro-l-propanol and 200 g of sodium chloride, at the fifth plate counting
from the top of the column, and with 3 bar absolute saturated steam at the bottom
of the column.
The flow of steam that feeds the column relative to the flow of brine that
feeds the column is 6/40 kg/kg.
The residence time of the liquid in the column is 45 s on the feed plate,
18 s per plate on the plates located below the feed plate and 4.5 s on the plate at
the top of the column.
The brine is withdrawn from the bottom of the column and the steam at the
top of the column.
Example 3
The procedure from Example 2 is followed except that the stripping
column is also fed with a solution containing 320 g/kg of sodium hydroxide.
The flow of sodium hydroxide is adjusted in order to obtain an amount of
dichloropropanols present in the brine at the bottom of the column relative to the
amount of dichloropropanols present in the brine feeding the column of 0.01%.
Examples 4, 10, 11, 12, 13 and 14
The procedure from example 3 is followed except that the stripping is
made with 4 bar absolute saturated steam at the bottom of the column.
Examples 5, 6, 7, 8, 9,15, 16, 17, 18, 19, 20 and 2 1
The procedure from example 2 is followed except that the stripping is
made with 4 bar absolute saturated steam at the bottom of the column.
For Examples 1 to 21, the values of the residual contents of organic
compounds in the brine withdrawn, expressed as mg of carbon per kg of brine
withdrawn from the bottom of the column and the various values of the pressure
at the top of the column, of the pressure drop in the column, of the temperature
of the brine withdrawn from the bottom of the column and of the temperature of
the steam withdrawn at the top of the column are presented in the table below.
Table 1
Example P(top) Pressure T(brine T(steam Residual According
(mbar) drop withdrawn) withdrawn) content of to the
(mbar) (°C) (°C) organic invention
compounds
(mg of
C/kg)
1 40 1700 118.2 29.7 4925 no
2 40 1200 107.9 29.7 4914 yes
3 40 1200 108 29.4 2 11 Yes
4 30 300 71.7 23.7 23 Yes
5 30 1400 112.2 24.8 4951 No
6 50 2100 124.9 33.5 4918 No
7 70 2500 130.8 39.6 4920 No
8 100 2700 133.7 46.3 4917 No
9 200 3000 138.3 60.5 4935 No
10 50 300 73.1 32.5 26 Yes
11 70 1400 113.1 39.4 268 Yes
12 100 300 76.3 45.3 32 Yes
13 200 300 81.8 59.5 48 Yes
14 300 300 86.4 68.5 66 Yes
15 300 3600 145.3 69.4 5237 No
16 200 1900 124.2 60.7 4806 Yes
17 150 1500 118.4 54.7 4806 Yes
18 150 400 84.6 54.9 4721 Yes
19 100 600 91.9 46.7 4785 Yes
20 50 1800 120.1 33.5 4906 Yes
2 1 50 1000 103.1 33.7 4884 Yes
C L A I M S
1. Process for purifying a brine of organic compounds comprising:
(a) supplying a brine that comprises at least one organic compound;
(b) feeding at least one stripping zone with the brine from (a) and at least one
stripping agent;
(c) withdrawing from the stripping zone at least one fraction (I) essentially
constituted of brine, the content of organic compound of which is lower than
in the brine from (a) and at least one fraction (II) essentially constituted of
stripping agent;
in which the temperature, expressed in degrees Celsius (Ti), of the hottest
fraction of the two fractions (I) and (II) and the temperature, expressed in
degrees Celsius (T2), of the coldest fraction of the two fractions (I) and (II), said
temperatures being the temperatures measured before any possible thermal
conditioning which might be carried out before and/or during the withdrawal
thereof, correspond to the following formula:
6 10 (Ti) 2 4 T2 < Ti
2 . Process according to claim 1, in which the temperature T2 is less than or
equal to 0.9752 (Ti)0 9991 .
3 . Process according to claim 1, in which the temperature T2 is less than or
equal to 0.8967 (Ti) 10147 .
4 . Process according to any one of claims 1 to 3, in which the temperature
T2 is greater than or equal to 5 10 5 (Ti)2 8779.
5 . Process according to any one of claims 1 to 3, in which the temperature
T2 is greater than or equal to 0.0593 (Ti) 1 4859.
6 . Process according to any one of claims 1 to 3, in which the temperature
T2 is greater than or equal to 0.5342 (Ti) 1 88.
7 . Process according to any one of claims 1 to 3, in which the temperature
T2 is greater than or equal to 0.7535 (Ti) 1 325.
8 . Process according to any one of Claims 1 to 7, in which the stripping
zone (b) consists of a stripping column.
9 . Process according to claim 8, in which the difference between the
pressure at the bottom of the column and the pressure at the top of the column is
less than or equal to 2 bar and greater than or equal to 10 mbar.
10. Process according to claim 9, in which the difference between the
pressure at the bottom of the column and the pressure at the top of the column is
less than or equal to 1.5 bar and greater than or equal to 30 mbar.
11. Process according to any one of Claims 1 to 10, in which the brine
contains at least sodium chloride at a content greater than or equal to 5 g of NaCl
per kg of brine.
12. Process according to Claim 12, in which the sodium chloride content of
the brine is greater than or equal to 180 g of NaCl per kg of brine.
13. Process according to any one of Claims 1 to 12, in which the organic
compound is chosen from the group constituted of epichlorohydrin,
dichloropropanols and any mixture thereof.
14. Process according to claim 13, in which the content of epichlorohydrin
in the brine before the stripping operation is greater than 0.1 g/kg of brine and
less than or equal to 100 g/kg of brine.
15. Process according to claim 14, in which the content of epichlorohydrin
in the brine before the stripping operation is greater than 10 g/kg of brine and
less than or equal to 25 g/kg of brine.
16. Process according to any one of claims 13 to 15, in which the
dichloropropanols are l,3-dichloropropan-2-ol and 2,3-dichloropropan-l-ol and
in which the content of l,3-dichloropropan-2-ol in the brine before the stripping
operation is greater than or equal to 0.1 g/kg and less than or equal to 50 g/kg.
17. Process according to any one of claims 13 to 16, in which the
dichloropropanols are l,3-dichloropropan-2-ol and 2,3-dichloropropan-l-ol and
in which the content of 2,3-dichloropropan-l-ol in the brine before the stripping
operation is greater than or equal to 0.1 g/kg and less than or equal to 50 g/kg.
18. Process according to any one of Claims 1 to 17, in which the stripping
agent is chosen from the group constituted of air, oxygen-depleted air, nitrogen,
steam, and mixtures of at least two thereof.
19. Process according to Claim 18, in which the stripping agent is steam
and the stripping zone from (b) is fed continuously and counter currently with
brine and with stripping agent.
20. Process according to any one of Claims 1 to 19, in which the stripping
zone from (b) is also fed with at least one basic compound chosen from the
group constituted of alkali metal oxides, alkaline-earth metal oxides, alkali metal
hydroxides, alkaline-earth metal hydroxides and mixtures of at least two thereof.
21. Process according to claim 20, in which the at least one basic agent is
an aqueous solution of sodium hydroxide and in which the content of sodium
hydroxide is greater than or equal to 150 g/kg.
22. Process according to claim 20, in which the organic compound is a
mixture of epichlorohydrin and dichloropropanols and in which the ratio
between the total amount of basic agent that is introduced during the stripping
operation, expressed in equivalents, and the amount of dichloropropanol
contained in the brine before the stripping, expressed in moles, is greater than or
equal to 0 .1 and less than or equal to 20.
23. Process according to any one of Claims 8 to 22, in which the stripping
column from (2) comprises packing in its upper part and plates in its lower part,
in which the brine is fed into the top of the column, the packing is located below
the brine feed point and in which the retention of the plates increases towards the
bottom of the column.
24. Process according to any one of Claims 1 to 23, in which the brine
originates from a process for manufacturing epichlorohydrin by
dehydrochlorination of dichloropropanol in which at least one portion of the
dichloropropanol was obtained from glycerol and of which at least one fraction
of the glycerol is natural glycerol.
25. Process of electrolysis of brines of alkali metal chlorides, in which a
membrane electrolysis cell of a process for the electrolysis of alkali metal
chloride brines, is fed with a brine obtained by subjecting to at least one
treatment chosen from the group constituted of thermal conditioning, dilution,
concentration, distillation, evaporation, liquid/liquid extraction, filtration,
crystallization, adsorption, oxidation, reduction, neutralization, complexation,
precipitation, salt addition, aerobic bacterial treatment and anaerobic bacterial
treatment operations, and combinations of at least two thereof, a brine depleted
in organic compounds, the brine being withdrawn from the stripping zone of the
epuration process according to any one of Claims 1 to 24.