U.S. patent application number 11/836858 was filed with the patent office on 2008-03-06 for processes for the electrolysis of alkali metal chloride brines.
This patent application is currently assigned to Bayer Material Science AG. Invention is credited to Klaus Geisler, Thorsten Leidig, Wolfgang Mentsches, Alfred Soppe.
Application Number | 20080053839 11/836858 |
Document ID | / |
Family ID | 38922024 |
Filed Date | 2008-03-06 |
United States Patent
Application |
20080053839 |
Kind Code |
A1 |
Mentsches; Wolfgang ; et
al. |
March 6, 2008 |
PROCESSES FOR THE ELECTROLYSIS OF ALKALI METAL CHLORIDE BRINES
Abstract
Processes are described which include: (a) providing an initial
crude alkali metal chloride brine; (b) mixing the initial crude
brine with a recirculated brine to form a process brine steam; (c)
subjecting the process brine stream to electrolysis to form
chlorine gas and an electrolyzed weak brine; and (d) subjecting the
electrolyzed weak brine to a post-electrolysis salt enrichment
comprising (i) diverting a substream of the electrolyzed weak brine
at a post-electrolysis diversion point; (ii) removing water from
the substream; (iii) crystallizing salt present in the substream;
(iv) separating the crystallized salt from the substream; and (v)
introducing the separated salt into the electrolyzed weak brine to
form the recirculated brine.
Inventors: |
Mentsches; Wolfgang; (Neuss,
DE) ; Geisler; Klaus; (Bergisch Gladbach, DE)
; Soppe; Alfred; (Issum, DE) ; Leidig;
Thorsten; (Shanghai, CN) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ, LLP
P O BOX 2207
WILMINGTON
DE
19899
US
|
Assignee: |
Bayer Material Science AG
Leverkusen
DE
|
Family ID: |
38922024 |
Appl. No.: |
11/836858 |
Filed: |
August 10, 2007 |
Current U.S.
Class: |
205/556 ;
205/349 |
Current CPC
Class: |
C25B 15/08 20130101;
C25B 1/34 20130101 |
Class at
Publication: |
205/556 ;
205/349 |
International
Class: |
C25B 1/26 20060101
C25B001/26; C25B 15/00 20060101 C25B015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 2006 |
DE |
102006037400.2 |
Claims
1. A process comprising: (a) providing an initial crude alkali
metal chloride brine; (b) mixing the initial crude brine with a
recirculated brine to form a process brine steam; (c) subjecting
the process brine stream to electrolysis to form chlorine gas and
an electrolyzed weak brine; and (d) subjecting the electrolyzed
weak brine to a post-electrolysis salt enrichment comprising (i)
diverting a substream of the electrolyzed weak brine at a
post-electrolysis diversion point; (ii) removing water from the
substream; (iii) crystallizing salt present in the substream; (iv)
separating the crystallized salt from the substream; and (v)
introducing the separated salt into the electrolyzed weak brine to
form the recirculated brine.
2. The process according to claim 1, further comprising a
purification selected from the group consisting of purifying the
initial brine, purifying the process brine stream, and combinations
thereof.
3. The process according to claim 2, wherein the purification
comprises precipitating one or more ions selected from the group
consisting of Ca, Mg, Fe, Al and mixtures thereof from one or both
of the initial brine and the process brine stream; and filtering
out the precipitated ions.
4. The process according to claim 1, further comprising subjecting
the process brine stream to a purification comprising precipitating
one or more ions selected from the group consisting of Ca, Mg, Fe,
Al and mixtures thereof; filtering out the precipitated ions; and
passing the filtered process brine stream over an ion exchange
resin.
5. The process according to claim 1, further comprising purifying
the initial brine and purifying the process brine stream.
6. The process according to claim 5, wherein purifying the initial
brine comprises precipitating one or more ions selected from the
group consisting of Ca, Mg, Fe, Al and mixtures thereof from the
initial brine and filtering out the precipitated ions; and wherein
purifying the process brine stream comprises precipitating one or
more ions selected from the group consisting of Ca, Mg, Fe, Al and
mixtures thereof; filtering out the precipitated ions; and passing
the filtered process brine stream over an ion exchange resin.
7. The process according to claim 1, further comprising removing at
least a portion of any residual chlorine present in the
electrolyzed weak brine prior to the salt enrichment.
8. The process according to claim 7, wherein removing at least a
portion of any residual chlorine comprises stripping the portion of
residual chlorine under a reduced pressure.
9. The process according to claim 2, further comprising removing at
least a portion of any residual chlorine present in the
electrolyzed weak brine prior to the salt enrichment.
10. The process according to claim 5, further comprising removing
at least a portion of any residual chlorine present in the
electrolyzed weak brine prior to the salt enrichment.
11. The process according to claim 1, wherein the substream of the
electrolyzed weak brine is diverted at a weight ratio of the
substream to a remainder of the electrolyzed weak brine of 1:1 to
1:20.
12. The process according to claim 1, further comprising subjecting
the initial crude brine to a pre-electrolysis salt enrichment
comprising (i) diverting a substream of the initial crude brine at
a pre-electrolysis diversion point; (ii) removing water from the
substream; (iii) crystallizing salt present in the substream; (iv)
separating the crystallized salt from the substream; and (v)
reintroducing the separated salt into one or both of the initial
crude brine after the pre-electrolysis diversion point and the
mixing of the initial crude brine and the recirculated brine.
13. The process according to claim 12, wherein the substream of the
initial crude brine is diverted at a weight ratio of the substream
to a remainder of the initial crude brine of 5:1 to 1:5.
14. The process according to claim 1, wherein the alkali metal
chloride comprises sodium chloride.
15. The process according to claim 1, wherein the electrolysis is
selected from membrane electrolysis, diaphragm electrolysis and
amalgam electrolysis.
16. The process according to claim 1, wherein the initial crude
brine has an alkali metal chloride concentration of at least 14 wt.
%.
17. The process according to claim 1, wherein the separated salt is
reintroduced at a reintroduction point after the post-electrolysis
diversion point.
18. The process according to claim 1, wherein the separated salt is
divided into two or more portions and one of the two or more
portions is reintroduced at a first reintroduction point after the
post-electrolysis diversion point, and another of the two or more
portions is reintroduced at a second reintroduction point before
the post-electrolysis diversion point.
19. A process comprising: (a) providing an initial crude sodium
chloride brine having a sodium chloride concentration of at least
14 wt. %; (b) precipitating one or more ions selected from the
group consisting of Ca, Mg, Fe, Al and mixtures thereof from the
initial brine and filtering out the precipitated ions to form a
pre-purified crude brine; (c) mixing the pre-purified crude brine
with a recirculated brine to form a process brine steam; (d)
precipitating one or more ions selected from the group consisting
of Ca, Mg, Fe, Al and mixtures thereof from the process brine
stream; filtering out the precipitated ions; and passing the
filtered process brine stream over an ion exchange resin; (e)
subjecting the filtered, ion-exchanged process brine stream to
electrolysis to form chlorine gas and an electrolyzed weak brine;
(f) removing at least a portion of any residual chlorine from the
electrolyzed weak brine; and (g) subjecting the electrolyzed weak
brine to a post-electrolysis salt enrichment comprising (i)
diverting a substream of the electrolyzed weak brine at a
post-electrolysis diversion point; (ii) removing water from the
substream; (iii) crystallizing salt present in the substream; (iv)
separating the crystallized salt from the substream; and (v)
introducing the separated salt into the electrolyzed weak brine to
form the recirculated brine.
20. The process according to claim 19, further comprising
subjecting the pre-purified crude brine to a pre-electrolysis salt
enrichment comprising (i) diverting a substream of the pre-purified
crude brine at a pre-electrolysis diversion point; (ii) removing
water from the substream; (iii) crystallizing salt present in the
substream; (iv) separating the crystallized salt from the
substream; and (v) reintroducing the separated salt into one or
both of the pre-purified crude brine after the pre-electrolysis
diversion point and the mixing of the pre-purified crude brine and
the recirculated brine.
Description
BACKGROUND OF THE INVENTION
[0001] In chlor-alkali electrolysis, the raw material salt is
conventionally supplied to the electrolysis process via a brine
circuit. The purified brine is usually introduced into the
electrolysis process in virtually saturated form. In the
conventional electrolysis processes, a portion of the salt content
is converted into the products (i.e., chlorine and alkali metal
hydroxide solution). Furthermore, the stream of brine in the
circuit loses a portion of its water content by mass transfer
through the electrolysis membrane, in the case of membrane
electrolysis, and via moisture discharged with the gaseous product,
such that the brine leaving the electrolytic cell is a smaller and
more dilute brine stream than what is introduced into the
electrolysis.
[0002] Water losses can be made up by the addition of water. The
brine stream is usually re-fortified by the addition of fresh
alkali chloride salt and, after purification, is reintroduced into
the electrolysis. Impurities in the salt which cannot be separated
during brine preparation are compensated by removing a sub-stream
of the diluted brine ("purge"). The purge quantity to be removed is
variable and can be determined based on the admissible
concentrations of impurities in the purified brine in the
electrolysis process and on the impurities which are introduced as
a function of salt purity. This results in a costly and thus
unwanted loss of the raw material salt.
[0003] Salt is generally introduced into the brine circuit, for
example in NaCl electrolysis, not only as purified evaporated salt,
but also as sea salt or rock salt. To this end, solid salt can be
dissolved in water (for example, by solution mining a salt dome).
The resultant brine stream can be pre-purified by a combination of
precipitation and filtration. Further purification then proceeds by
evaporating the brine and separating the salt as solid crystals
("evaporated salt"), wherein the predominant proportion of the
impurities remains dissolved in the mother liquor and may be
separated from the evaporated salt. This process demands an
elevated energy input. For example; for each ton of evaporated salt
transferred into the brine circuit, approx. 2.85 tons of water must
be evaporated in the salt works.
[0004] The provision of an electrolysis process which facilitates
using crude brine would therefore be advantageous. An electrolysis
using crude brine has been described wherein the weak brine from
electrolysis is concentrated in a vacuum installation, making use
of waste heat from electrolysis which is exhausted with the weak
brine. The vacuum-concentrated weak brine is then reintroduced into
the input brine stream for electrolysis. The crude brine from the
salt dome may be used directly.
[0005] However, in such a process, the weak brine is evaporated at
most up to its saturation point, specifically avoiding
crystallization of the salt. As a result, however, the impurities
introduced with the crude brine remain in the electrolysis circuit.
Moreover, an increase in temperature during electrolysis as
described in such a process for use in the vacuum concentration
does not occur in more energy-efficient electrolysis processes used
today, such that the described crude brine process would not be
economically sensible today.
[0006] Accordingly, there remains a need in the art for an
electrolysis process which makes use of crude brine in an economic
way and which avoids the concentration of impurities in the brine
circuit.
SUMMARY OF THE INVENTION
[0007] It has been found by the present inventors that electrolysis
of crude brine can be carried out economically and without
detrimental over-concentration of impurities in the brine circuit
by directly supplying the salt required for the electrolysis
process to the brine circuit and electrolysis cell as a mixture of
crude brine and a recirculated process brine stream, without
further purification by brine evaporation and evaporated salt
production.
[0008] More particularly, it has been found that crystallization of
a portion of the salt in an electrolyzed weak (diluted) brine
process stream, and re-introduction of the crystallized salt into
the weak brine before the combined recirculated brine and crude
brine enter the electrolysis cell can significantly improve the
economics and impurity levels of the overall electrolysis.
Advantageously, impurities are decreased by salt crystallization
while energy requirements are lowered via the evaporation of a
lower volume brine stream.
[0009] One embodiment of the present invention includes processes
which comprise: (a) providing an initial crude alkali metal
chloride brine; (b) mixing the initial crude brine with a
recirculated brine to form a process brine steam; (c) subjecting
the process brine stream to electrolysis to form chlorine gas and
an electrolyzed weak brine; and (d) subjecting the electrolyzed
weak brine to a post-electrolysis salt enrichment comprising (i)
diverting a substream of the electrolyzed weak brine at a
post-electrolysis diversion point; (ii) removing water from the
substream; (iii) crystallizing salt present in the substream; (iv)
separating the crystallized salt from the substream; and (v)
introducing the separated salt into the electrolyzed weak brine to
form the recirculated brine.
[0010] Another embodiment of the present invention includes
processes which comprise: (a) providing an initial crude sodium
chloride brine having a sodium chloride concentration of at least
14 wt. %; (b) precipitating one or more ions selected from the
group consisting of Ca, Mg, Fe, Al and mixtures thereof from the
initial brine and filtering out the precipitated ions to form a
pro-purified crude brine; (c) mixing the pre-purified crude brine
with a recirculated brine to form a process brine steam; (d)
precipitating one or more ions selected from the group consisting
of Ca, Mg, Fe, Al and mixtures thereof from the process brine
stream; filtering out the precipitated ions; and passing the
filtered process brine stream over an ion exchange resin; (e)
subjecting the filtered, ion-exchanged process brine stream to
electrolysis to form chlorine gas and an electrolyzed weak brine;
(f) removing at least a portion of any residual chlorine from the
electrolyzed weak brine; and (g) subjecting the electrolyzed weak
brine to a post-electrolysis salt enrichment comprising (i)
diverting a substream of the electrolyzed weak brine at a
post-electrolysis diversion point; (ii) removing water from the
substream; (iii) crystallizing salt present in the substream; (iv)
separating the crystallized salt from the substream; and (v)
introducing the separated salt into the electrolyzed weak brine to
form the recirculated brine.
[0011] Processes in accordance with various embodiments of the
present invention can also optionally include treatment of one or
more brine streams, (e.g., an initial crude brine, a combined crude
brine and recirculated brine, etc.) to remove at least some of
various constituents which can be disruptive to electrolysis, such
as, in particular, metal ions such as calcium, magnesium, iron,
aluminium, strontium, and barium. In various preferred embodiments,
one or more of the removal treatments can comprise precipitation of
such ions and subsequent filtration, and/or subsequent ion
exchange.
[0012] In various embodiments of the processes according to the
invention, an initial crude alkali chloride brine can be preferably
supplied as a 30 wt. % to saturated alkali metal chloride brine,
more preferably as a saturated alkali metal chloride brine.
[0013] In processes according to the invention, a portion of the
salt in the recirculating, electrolyzed weak brine is deliberately
crystallized out of the weak brine so as to be able to remove the
impurities which are concentrated in the mother liquor during
crystallization. As noted above, in previously suggested crude
brine electrolysis, all the impurities remain in the brine and have
to be separated and removed during brine purification, while
accepting economically damaging losses of salt. In comparison with
conventional methods using purified evaporated salt, a further
advantage of the invention resides in energy savings from the
removal of a proportion of the process water.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0014] The foregoing summary, as well as the following detailed
description of the invention, will be better understood when read
in conjunction with the appended drawings. For the purpose of
assisting in the explanation of the invention, there are shown in
the drawings representative embodiments which are considered
illustrative. It should be understood, however, that the invention
is not limited to the precise arrangements and instrumentalities
shown.
[0015] In the drawings:
[0016] FIG. 1 is a process flow diagram of a brine electrolysis
circuit in accordance with one embodiment of the present invention;
and
[0017] FIG. 2 is a process flow diagram of a brine electrolysis
circuit in accordance with another embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0018] As used herein, the singular terms "a" and "the" are
synonymous and used interchangeably with "one or more."
Accordingly, for example, reference to "a gas" herein or in the
appended claims can refer to a single gas or more than one gas.
Additionally, all numerical values, unless otherwise specifically
noted, are understood to be modified by the word "about."
[0019] Processes according to the invention include providing an
initial crude alkali metal chloride brine and mixing the initial
crude brine with a recirculated brine to form a process brine
steam. In various preferred embodiments of the invention, the
processes may further include treatment (e.g., purification) of one
or more process streams. Thus, for example, preferred embodiments
may include purifying the initial brine, purifying the process
brine stream, and combinations thereof.
[0020] Purification of a process stream can comprise precipitating
one or more ions selected from the group consisting of Ca, Mg, Fe,
Al and mixtures thereof from one or both of the initial brine and
the process brine stream; and filtering out the precipitated ions.
In various preferred embodiments, additional purification of the
filtered process brine can be carried out in order to remove
divalent ions, in particular metal ions from the range: calcium,
magnesium, strontium and barium. Thus, for example, purification
can comprise subjecting the process brine stream to a purification
comprising precipitating one or more ions selected from the group
consisting of Ca, Mg, Fe, Al and mixtures thereof; filtering out
the precipitated ions; and passing the filtered process brine
stream over an ion exchange resin.
[0021] In various particularly preferred embodiments, purification
can comprise purifying the initial brine and purifying the process
brine stream. Thus, for example, in such particularly preferred
embodiments, purification can include purifying the initial brine
via precipitation of one or more ions selected from the group
consisting of Ca, Mg, Fe, Al and mixtures thereof from the initial
brine and filtration of the precipitated ions; and purifying the
process brine stream via precipitation of one or more ions selected
from the group consisting of Ca, Mg, Fe, Al and mixtures thereof;
filtration of the precipitated ions; and passing the filtered
process brine stream over an ion exchange resin.
[0022] In various preferred embodiments of the processes according
to the invention, the substream of the electrolyzed weak brine is
diverted at a weight ratio of the substream to the remainder of the
electrolyzed weak brine of 1:1 to 1:20. Preferably, the separated
salt is reintroduced into the electrolyzed weak brine at a
reintroduction point after the post-electrolysis diversion point.
In various embodiments, the separated salt can be divided into two
or more portions and one of the portions can be reintroduced into
the electrolyzed weak brine at a first reintroduction point after
the post-electrolysis diversion point, and another portion can be
reintroduced at a second reintroduction point before the
post-electrolysis diversion point.
[0023] In various preferred embodiments, processes according to the
invention can further include subjecting the initial crude brine to
a pre-electrolysis salt enrichment comprising (i) diverting a
substream of the initial crude brine at a pre-electrolysis
diversion point; (ii) removing water from the substream; (iii)
crystallizing salt present in the substream; (iv) separating the
crystallized salt from the substream; and (v) reintroducing the
separated salt into one or both of the initial crude brine after
the pre-electrolysis diversion point and the mixing of the initial
crude brine and the recirculated brine. Subjecting a substream of
the crude brine to an evaporation before mixing with the
recirculated brine can further reduce impurities by removing
process water and separating crystallized salt from the remaining
residual liquor containing the impurities, and then re-introducing
the crystallized salt.
[0024] In such preferred embodiments of the invention, the
substream of the initial crude brine is preferably diverted at a
weight ratio of the substream to a remainder of the initial crude
brine of 5:1 to 1:5.
[0025] In various preferred embodiments of the present invention,
the processes can further include removing at least a portion of
any residual chlorine present in the electrolyzed weak brine prior
to salt enrichment. The removal of residual chlorine preferably
proceeds by stripping the chlorine under reduced pressure.
[0026] Electrolysis preferably comprises membrane electrolysis,
diaphragm electrolysis or amalgam electrolysis, more preferably
membrane electrolysis.
[0027] The alkali metal chloride present in the brine of the
present invention preferably comprises sodium chloride.
[0028] In various preferred embodiments, the alkali chloride
concentration of the initial crude brine is at least 14 wt. %, more
preferably 14 to 23 wt. %.
[0029] Chlorine obtained from the various embodiments of the
processes according to the invention can be further used in various
chemical production processes, such as for example, in the
production of plastics precursors.
[0030] The following examples, in conjunction with the Figures,
illustrate embodiments of processes according to the invention and
are for reference, and do not limit the invention described
herein.
EXAMPLES
[0031] In the Figures, the reference letters refer to the
following: [0032] A: salt dome [0033] B: crude brine treatment
(precipitation, filtration) [0034] C: extraction of evaporated salt
(from crude brine) [0035] D: extraction of evaporated salt (from
weak brine from electrolysis) [0036] E: restoration of the
(electrolysis) brine circuit [0037] F: brine purification
precipitation, filtration, ion exchanger) [0038] G: electrolysis
[0039] H: dechlorination of weak brine [0040] I: cooler/condenser
[0041] J: cooler/condenser
Example 1
[0042] Referring to FIG. 1, initial sodium chloride-containing
crude brine is obtained from a salt dome A and subjected to a
combination of precipitation and filtration B to remove Ca, Mg, Fe
and Al ions. The initial crude brine 11 is combined with
recirculated weak brine 9 to provide process brine stream 1. The
process brine stream 1 is supplied to a brine purification stage F,
in which contaminants are further removed by means of a combination
of precipitation and filtration and subsequent passage of the brine
through a membrane ion exchanger (Ca, Mg, Fe and Al, as well as Sr
and Ba ions). The filtered, ion-exchanged process brine stream 2 is
electrolysed in a membrane electrolysis stage G. The material flow
is indicated by 15. The resulting chlorine gas is separated and
water 12 is removed therefrom.
[0043] Any residual chlorine is removed from the resultant weak
brine 3 in an evaporator H. The chlorine is separated and water 13
removed therefrom, the chlorine is combined with the chlorine
stream from electrolysis and further used in another process.
[0044] In comparison with a purified evaporated salt brine, the
initial crude brine 11 introduces a certain quantity of impurities
into the brine circuit. In order to compensate this input and
comply with the specifications for the membrane electrolysis stage
G with regard to impurities, a substream 5 of the electrolyzed weak
brine 4 is diverted and supplied to a weak brine evaporation stage
D. Here, the weak brine substream 5 is concentrated to a solid
crystal state. The salt 6 obtained in this manner is redissolved in
the remaining weak brine 8 and recirculated as weak brine stream 9.
The recirculated weak brine 9 is mixed into the crude brine stream
11 in the restoration stage E.
[0045] The impurities present in the weak brine substream 5 are
likewise concentrated in the evaporation stage D and removed via a
purge substream 7 to be discharged from the evaporator. An
advantage is that, relative to the known process, the impurities
may be retained and discharged from a considerably larger substream
(approx. 10.times. larger), thus compensating for the increased
input of impurities via the crude brine stream 11.
[0046] A substantial advantage obtained by the process is that, for
each 1 ton of salt introduced into the brine circuit as crude
brine, only approx. 1.33 tons of water 14 are evaporated, which
amounts to a 53% reduction relative to prior process. Energy and
operating costs and capital costs for the necessary evaporation
plant and for steam generation or other energy sources are reduced
commensurately.
[0047] Depending on the impurities present in the initial
(optionally pre-purified, B) crude brine, it is possible with this
process to supply at most the entire required quantity of salt to
the electrolysis process; brine evaporation/evaporated salt
production is then no longer necessary in the course of raw
material preparation.
Example 2
[0048] Referring to FIG. 2, where individual impurities, which
cannot be separated either via crude brine preparation or via brine
purification of the brine circuit, such as for example bromine, do
not permit sole use of crude brine as described in Example 1, a
portion of the crude brine may also be pre-treated. Except as noted
below, the process described in this example including the
reference numerals and letters are the same as in FIG. 1 and
example 1. A portion 11a of the crude brine 11 is sent for
evaporation and crystallization C and the resultant salt 10 is
reintroduced into the crude brine. The size of the crude brine
stream 11, and the size of the crude brine sub-stream 5 to be
prepared in the weak brine evaporation stage is then determined in
accordance with the impurities admissible in the process brine
stream 2.
[0049] It will be appreciated by those skilled in the art that
changes could be made to the embodiments described above without
departing from the broad inventive concept thereof. It is
understood, therefore, that this invention is not limited to the
particular embodiments disclosed, but it is intended to cover
modifications within the spirit and scope of the present invention
as defined by the appended claims.
* * * * *