 |
Claims  |
|
|
We claim:
1. A method of converting amine hydrohalide into free amine comprising:
(a) providing an electrolytic cell having a catholyte compartment
containing a cathode assembly; an anode compartment containing an anode
assembly; and an intermediate compartment separating said catholyte and
anode compartments; said cathode assembly comprising a cathode and an
anion exchange membrane, said anode assembly comprising a hydrogen
consuming gas diffusion anode and a current collecting electrode, said
intermediate compartment being separated from said catholyte and said
anode compartments by said anion exchange membrane and said hydrogen
consuming gas diffusion anode;
(b) introducing an aqueous solution of amine hydrohalide into said
catholyte compartment;
(c) introducing hydrogen gas into said anode compartment;
(d) introducing an aqueous conductive electrolyte solution into said
intermediate compartment;
(e) passing direct current through said electrolytic cell; and
(f) removing an aqueous solution comprising free amine from said catholyte
compartment.
2. The method of claim 1 wherein said anode assembly further comprises a
hydraulic barrier, said hydrogen consuming gas diffusion anode being
fixedly held between said hydraulic barrier and said current collecting
electrode, and said intermediate compartment is separated from said anode
compartment by said hydraulic barrier.
3. The method of claim 2 wherein the amine hydrohalide is an amine
hydrochloride.
4. The method of claim 3 wherein the amine of the amine hydrochloride is
selected from the group consisting of ammonia, monoalkylamines,
dialkylamines, trialkylamines, ethyleneamines, alkyl ethylenediamines,
propylenediamines, alkyl propylenediamines, monoalkanolamines,
dialkanolamines, trialkanolamines, cycloaliphatic amines, aromatic amines
and mixtures thereof.
5. The method of claim 4 wherein the amine of the amine hydrochloride is an
ethyleneamine which is selected from the group consisting of
ethylenediamine, diethylenetriamine, triethylenetetramine,
tetraethylenepentamine, pentaethylenehexamine, piperazine,
1-(2-aminoethyl)piperazine and mixtures thereof.
6. The method of claim 2 wherein said aqueous conductive electrolyte
solution comprises a hydrogen halide aqueous solution having a
concentration of from 1% by weight to 25% by weight hydrogen halide, based
on the total weight of said aqueous conductive electrolyte solution.
7. The method of claim 6 wherein the concentration of hydrogen halide in
said aqueous conductive electrolyte solution is maintained below 25% by
weight by introducing an aqueous stream selected from the group consisting
of water, aqueous alkali metal hydroxide and a mixture of aqueous alkali
metal hydroxide and alkali metal halide into said intermediate
compartment.
8. The method of claim 2 wherein said aqueous conductive electrolyte
solution comprises a hydrogen halide aqueous solution and wherein the
hydrogen halide concentration of said aqueous hydrogen halide solution is
maintained below 25% by weight, based on the total weight of said aqueous
conductive electrolyte solution.
9. The method of claim 7 wherein the concentration of hydrogen halide in
said aqueous hydrogen halide solution is maintained below 25% by weight by
distilling aqueous hydrogen halide solution removed from said intermediate
compartment to produce a concentrated hydrogen halide distillate product
and bottoms product; and either (a) returning bottoms product to said
intermediate compartment or (b) introducing an aqueous stream selected
from the group consisting of water and an aqueous hydrogen halide solution
having a concentration of hydrogen halide of less than 25% by weight into
said intermediate compartment.
10. The method of claim 2 wherein a positive internal pressure difference
of from 0.07 kg/cm.sup.2 to 1.40 kg/cm.sup.2 exists between said
intermediate compartment and each of said catholyte and anode
compartments.
11. The method of claim 2 wherein said hydrogen consuming gas diffusion
anode comprises platinum supported on carbon dispersed in
polytetrafluoroethylene.
12. The method of claim 11 wherein said anion exchange membrane comprises a
copolymer of styrene and divinylbenzene having pendent quaternary ammonium
salt groups, and said hydraulic barrier is a cation exchange membrane
comprising a perfluoropolymer having pendent sulfonic acid groups.
13. The method of claim 12 wherein said cathode and said current collecting
electrode each comprises a material selected from the group consisting of
graphite, platinum, titanium coated with platinum, titanium coated with an
oxide of ruthenium, nickel, stainless steel, high alloy steel and
appropriate combinations thereof.
14. The method of claim 2 further comprising the step of passing aqueous
solution comprising free amine removed from said catholyte compartment
through an anion exchange resin.
15. The method of claim 2 wherein the anion exchange membrane of said
cathode assembly comprises a copolymer of styrene and divinylbenzene
having pendent quaternary ammonium salt groups; said hydrogen consuming
gas diffusion anode of said anode assembly comprises platinum supported on
carbon dispersed in polytetrafluoroethylene; said hydraulic barrier is a
cation exchange membrane comprising a perfluoropolymer having pendent
sulfonic acid groups; and the amine hydrohalide is an amine hydrochloride.
16. The method of claim 15 wherein the amine of the amine hydrochloride is
an ethyleneamine which is from the group consisting of ethylenediamine,
diethylenetriamine, triethylenetetramine, tetraethylenepentamine,
pentaethylenehexamine, piperazine, 1-(2-aminoethyl)piperazine and mixtures
thereof; and said cathode and said current collecting electrode each
comprises a material selected from the group consisting of graphite,
platinum, titanium coated with platinum, titanium coated with an oxide of
ruthenium, nickel, stainless steel, high alloy steel and appropriate
combinations thereof.
17. The method of claim 16 wherein a positive internal pressure difference
of from 0.07 kg/cm.sup.2 to 1.40 kg/cm.sup.2 exists between said
intermediate compartment and each of said catholyte and anode
compartments.
18. The method of claim 17 wherein said aqueous conductive electrolyte
solution comprises a hydrogen chloride aqueous solution and wherein the
hydrogen chloride concentration of said aqueous hydrogen chloride solution
is maintained below 25% by weight, based on the total weight of said
aqueous conductive electrolyte solution.
19. The method of claim 18 wherein the concentration of said hydrogen
chloride in said aqueous hydrogen chloride solution is maintained below
25% by weight by introducing an aqueous stream selected from the group
consisting of water, aqueous alkali metal hydroxide and a mixture of
aqueous alkali metal hydroxide and alkali metal halide into said
intermediate compartment.
20. The method of claim 18 wherein the concentration of said hydrogen
chloride in said aqueous hydrogen chloride solution is maintained below
25% by weight by distilling aqueous hydrogen chloride solution removed
from said intermediate compartment to produce a concentrated hydrogen
chloride distillate product and bottoms product; and either (a) returning
bottoms product to said intermediate compartment or (b) introducing an
aqueous stream selected from the group consisting of water and an aqueous
hydrogen chloride solution having a concentration of hydrogen chloride of
less than 25% by weight into said intermediate compartment.
21. The method of claim 15 further comprising the step of passing aqueous
solution comprising free amine removed from said catholyte compartment
through an anion exchange resin.
22. An electrolytic cell comprising: a catholyte compartment containing a
cathode assembly; an anode compartment containing an anode assembly; and
an intermediate compartment separating said catholyte and anode
compartments; said cathode assembly comprising a cathode and an anion
exchange membrane, said anode assembly comprising a hydrogen consuming gas
diffusion anode fixedly held between a cation exchange membrane and a
current collecting electrode, said intermediate compartment being
separated from said catholyte and said anode compartments by said anion
exchange membrane and said cation exchange membrane. |
|
 |
|
 |
Claims |
|
|
|
Description |
|
|
DESCRIPTION OF THE INVENTION
The present invention relates to a method of electrochemically converting
amine hydrohalide into free amine. Particularly the present invention
relates to an electrochemical method of converting ethyleneamine
hydrohalides, and more particularly ethyleneamine hydrochlorides, into
free ethyleneamines. The present invention also relates to electrolytic
cells having an intermediate compartment separated from a catholyte
compartment by an anion exchange membrane and from an anode compartment by
either a hydraulic barrier or a hydrogen consuming gas diffusion anode.
A major commercial method of producing free amines, particularly free
alkyleneamines, and more particularly free ethyleneamines, involves the
reaction of a 1,2-dihaloethane, e.g., 1,2-dichloroethane (EDC), with
ammonia to produce the entire family of ethyleneamines, including:
ethylenediamine (EDA) , diethylenetriamine (DETA), triethylenetetramine
(TETA), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA),
piperazine, i.e., diethylenediamine (DEDA), and 2-amino-1-ethylpiperazine.
The reaction of EDC and ammonia is well known and is described in U.S.
Pat. Nos. 2,049,467, 2,760,979, 2,769,841, 3,183,269, 3,484,488, and
4,980,507.
When the 1,2-dihaloethane reactant is 1,2-dichloroethane, the
ethyleneamines are produced as their hydrochloride salts which are
subsequently neutralized, typically with an aqueous alkali metal
hydroxide, e.g., sodium hydroxide. The neutralization reaction results in
the formation of a mixture of free ethyleneamines and by-product alkali
metal halide salt, e.g., sodium chloride. The by-product alkali metal
halide is typically separated from the mixture of free ethyleneamines by
an evaporative or distillation process. The mixture of free ethyleneamines
is further separated into its individual components by fractional
distillation. The presence of halide anion, e.g., chloride anion, in the
free ethyleneamines requires that the distillation column(s) be fabricated
from expensive corrosion resistant materials, such as titanium and
stainless steel. The waste water resulting from the distillation process
is typically treated further for the removal of trace amounts of amines
prior to disposal. The formation of ethyleneamines from the treatment of
ethyleneamine hydrochlorides with an alkali metal hydroxide, e.g., sodium
hydroxide, is described in U.S. Pat. Nos. 3,202,713, 3,862,234, 3,337,630,
and 4,582,937.
The commercial method described above can be expensive, particularly with
regard to the cost of distillation equipment, utility costs, raw material
costs, and the required treatment of waste streams. As a result, such
commercial method is typically dedicated to relatively high volume
production of free amines, can be expensive to expand, and may not be cost
effective for relatively low volume production of free amines.
International patent publication WO 93/00460 describes an apparatus and
process for electrochemically decomposing salt solutions to form the
relevant base and acid, and relates to an electrolyzer comprising at least
one elementary cell equipped with a novel hydrogen-depolarized anode
assembly. The hydrogen depolarized anode assembly comprises a
cation-exchange membrane, an electrocatalytic sheet and a rigid current
collector which provides a multiplicity of contact points with the
electrocatalytic sheet. The electrolyzer described has a cathodic
compartment, a hydrogen gas chamber, and a central compartment separated
from the cathodic compartment and the hydrogen gas chamber by cation
exchange membranes.
U.S. Pat. No. 4,561,945 describes a process for producing sulfuric acid and
caustic soda by the electrolysis of an alkali metal sulfate in a membrane
cell having a hydrogen depolarized anode. An electrolysis cell having an
anode chamber, a cathode chamber, and a central or buffer chamber, which
is separated from the anode and cathode chambers by cation exchange
membranes is described.
Because of the drawbacks of current commercial methods, alternative methods
for producing free amines, e.g., free ethyleneamines, that are lower in
cost with regard to capital investment for equipment, raw material costs,
and costs for the treatment of waste streams are continually being sought.
It has now been discovered that amine hydrohalides can be electrochemically
converted to free amines using a three compartment electrolytic cell in
which the intermediate compartment is separated from the catholyte
compartment by an anion exchange membrane, and is separated from the anode
compartment by either a hydraulic barrier or a hydrogen consuming gas
diffusion anode. The hydrogen consuming gas diffusion anode is either (a)
fixedly held between a hydraulic barrier and a current collecting
electrode or (b) alone in contact with the current collecting electrode.
In accordance with an embodiment of the present invention, there is
provided a method of converting amine hydrohalide into free amine
comprising:
(a) providing an electrolytic cell having a catholyte compartment
containing a cathode assembly; an anode compartment containing an anode
assembly; and an intermediate compartment separating the catholyte and
anode compartments; the cathode assembly comprising a cathode and an anion
exchange membrane, the anode assembly comprising a hydrogen consuming gas
diffusion anode and a current collecting electrode, the intermediate
compartment being separated from the catholyte and the anode compartments
by the anion exchange membrane and the hydrogen consuming gas diffusion
anode;
(b) introducing an aqueous solution of amine hydrohalide into the catholyte
compartment;
(c) introducing hydrogen gas into the anode compartment;
(d) introducing an aqueous conductive electrolyte solution into the
intermediate compartment;
(e) passing direct current through the electrolytic cell; and
(f) removing an aqueous solution comprising free amine from the catholyte
compartment.
In accordance with another embodiment of the present invention, there is
provided a method of converting amine hydrohalide into free amine as
recited above wherein the anode assembly further comprises a hydraulic
barrier, the hydrogen consuming gas diffusion anode being fixedly held
between the hydraulic barrier and the current collecting electrode, and
the intermediate compartment is separated from the anode compartment by
the hydraulic barrier.
In accordance with a further embodiment of the present invention, there is
provided an electrolytic cell comprising: a catholyte compartment
containing a cathode assembly; an anode compartment containing an anode
assembly; and an intermediate compartment separating the catholyte and
anode compartments; the cathode assembly comprising a cathode and an anion
exchange membrane, the anode assembly comprising a hydrogen consuming gas
diffusion anode and a current collecting electrode, the intermediate
compartment being separated from the catholyte and the anode compartments
by the anion exchange membrane and the hydrogen consuming gas diffusion
anode.
In accordance with yet a further embodiment of the present invention, there
is provided an electrolytic cell as recited above wherein the anode
assembly further comprises a hydraulic barrier, the hydrogen consuming gas
diffusion anode being fixedly held between the hydraulic barrier and the
current collecting electrode, and the intermediate compartment is
separated from the anode compartment by the hydraulic barrier.
The features that characterize the present invention are pointed out with
particularity in the claims which are annexed to and form a part of this
disclosure. These and other features of the invention, its operating
advantages and the specific objects obtained by its use will be more fully
understood from the following detailed description and the accompanying
drawings in which preferred embodiments of the invention are illustrated
and described.
Other than in the operating examples, or where otherwise indicated, all
numbers expressing quantities of ingredients or reaction conditions used
in the specification and claims are to be understood as modified in all
instances by the term about.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of an electrolytic cell useful for
converting amine hydrohalide into free amine in accordance with an
embodiment of the method of the present invention;
FIG. 2 is a schematic of the electrolytic cell depicted in FIG. 1 further
illustrating the flow of circulating process streams around the catholyte,
anode and intermediate compartments;
FIG. 3 is a schematic of the electrolytic cell depicted in FIG. 2 further
illustrating the treatment of a process stream removed from the
intermediate compartment; and
FIG. 4 is a schematic of an electrolytic cell similar to the electrolytic
cell of FIG. 1, but in which the hydraulic barrier is not present.
In FIGS. 1-4, like reference numerals represent the same structural parts,
the same process streams and the same conduits.
DETAILED DESCRIPTION OF THE INVENTION
In the practice of the present invention, electrolytic cells, such as those
represented in FIGS. 1 through 4, are provided for the conversion of amine
hydrohalide to free amine. Referring now to FIG. 1, electrolytic cell 6
comprises a housing 70 having therein a catholyte compartment 13, an anode
compartment 10, and an intermediate compartment 16. The catholyte
compartment 13 has an inlet 46 and an outlet 49, and also has therein a
cathode assembly comprising a cathode 31, which is substantially rigid and
provides support for anion exchange membrane 28. The anode compartment has
an inlet 34 and an outlet 37, and also has therein an anode assembly
comprising a hydrogen consuming gas diffusion anode 22 which is fixedly
held between current collecting electrode 19 and hydraulic barrier 25. The
intermediate compartment 16 has an inlet 40 and an outlet 43 and is
separated from the catholyte compartment 13 by anion exchange membrane 28,
and from the anode compartment 10 by hydraulic barrier 25, more
particularly, the anode assembly.
The electrolytic cells of FIGS. 1-4 may be assembled by any appropriate
method as long as the basic structural arrangements of component parts, as
depicted in FIGS. 1-4, are maintained. For example, the catholyte, anode
and intermediate compartments may each be fabricated separately and then
assembled by clamping or otherwise fastening the compartments together.
Housing 70 may be fabricated from any of the known conventional materials
for electrolytic cells, or combinations of these known materials, that are
preferably at least corrosion resistant to, and compatible with the
materials being circulated through the catholyte, anode and intermediate
compartments or formed in these compartments. Examples of materials from
which housing 70 may be fabricated include, but are not limited to: metal,
e.g., stainless steel, titanium and nickel; and plastics, e.g.,
poly(vinylidenefluoride), polytetrafluoroethylene which is sold under the
trademark "TEFLON", and which is commercially available from E. I. du Pont
de Nemours and Company of Wilmington, Del., glass filled
polytetrafluoroethylene, polypropylene, polyvinylchloride, chlorinated
polyvinylchloride and high density polyethylene. Preferred materials from
which the housing 70 may be fabricated include: poly(vinylidenefluoride)
and stainless steel.
If housing 70 is fabricated from an electrically conductive material, such
as stainless steel, then appropriately positioned nonconductive gaskets
would typically also be present as is known to those of ordinary skill in
the art. For example, if the various compartments of the cell are
prefabricated separately from stainless steel, such gaskets would
typically be placed between those portions of the prefabricated
compartments that would otherwise abut each other upon assemblage of the
electrolytic cell. Such nonconductive gaskets may be fabricated from
synthetic polymeric materials, e.g., copolymers of ethylene and propylene,
and fluorinated polymers.
Cathode 31 and current collecting electrode 19 each may be fabricated from
any appropriate material that is at least both corrosion resistant to the
environments to which they are exposed and electrically conductive. In
electrolytic cells 6 and 3, it is also desirable that cathode 31 and
current collecting electrode 19 be substantially rigid so as to provide
support for, respectively, anion exchange membrane 28, and either hydrogen
consuming gas diffusion anode 22 alone or the combination of hydrogen
consuming gas diffusion anode 22 and hydraulic barrier 25. Materials from
which cathode 31 and current collecting electrode 19 may be fabricated
include, but are not limited to: graphite; platinum; titanium coated with
platinum; titanium coated with an oxide of ruthenium; nickel; stainless
steel; specialty steels including high alloy steels containing nickel,
chromium, and molybdenum, e.g., HASTELLOY.RTM. C-2000.TM. alloy and
HASTELLOY.RTM. C-276.TM. alloy from Haynes International, Inc. While
current collecting electrode 19 may be fabricated from stainless steel, it
is preferred to use a more corrosion resistant material such as a high
| | |
