CA1315233C - Process for the preparation of potassium nitrate - Google Patents
Process for the preparation of potassium nitrateInfo
- Publication number
- CA1315233C CA1315233C CA000541991A CA541991A CA1315233C CA 1315233 C CA1315233 C CA 1315233C CA 000541991 A CA000541991 A CA 000541991A CA 541991 A CA541991 A CA 541991A CA 1315233 C CA1315233 C CA 1315233C
- Authority
- CA
- Canada
- Prior art keywords
- potassium
- cell
- compartment
- catholyte
- aqueous solution
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D9/00—Nitrates of sodium, potassium or alkali metals in general
- C01D9/18—Preparation in the form of shaped products, e.g. granules
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D9/00—Nitrates of sodium, potassium or alkali metals in general
- C01D9/04—Preparation with liquid nitric acid
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/01—Products
- C25B1/14—Alkali metal compounds
Abstract
ABSTRACT OF THE DISCLOSURE:
A process is disclosed for the preparation of potassium nitrate by reaction of nitric acid with potassium carbonate, wherein potassium carbonate is obtained by means of an electrochemical process. In this process which is simple and cheap, and efficient to produce potassium nitrate of high purity, a saturated aqueous solution of potassium chloride (anolyte) is fed to the anodic compartment of a membrane cell, whereas an aqueous solution of potassium carbonate or bicarbonate (catholyte) is fed to the cathodic compartment of this cell. The anolyte is electrolysed inside the anodic cell compartment, so to cause chlorine gas to be generated at the anode, and potassium ion to migrate from the anodic compartment to the cathodic compartment of the cell through the membrane. From the anodic compartment of the cell, a depleted anolyte is discharged, which is saturated with potassium chloride, and is recycled back to the anodic compartment of the cell. The catholyte is electrolysed in the cathodic compartment so to cause hydrogen to be generated at the cathode, and thus transform, at least partially, potassium bicarbonate into potassium carbonate. From the cathodic compartment of the cell, a potassium-carbonate enriched catholyte is discharged. A
portion of the enriched catholyte is treated with nitric acid, for the purpose of forming an aqueous solution of potassium nitrate, and generating carbon dioxide gas whit the other portion is contacted with the evolved carbon dioxide, in order to convert, at least partially, the potassium carbonate therein contained into potassium bicarbonate that is recycled to the cathodic compartment of the cell.
A process is disclosed for the preparation of potassium nitrate by reaction of nitric acid with potassium carbonate, wherein potassium carbonate is obtained by means of an electrochemical process. In this process which is simple and cheap, and efficient to produce potassium nitrate of high purity, a saturated aqueous solution of potassium chloride (anolyte) is fed to the anodic compartment of a membrane cell, whereas an aqueous solution of potassium carbonate or bicarbonate (catholyte) is fed to the cathodic compartment of this cell. The anolyte is electrolysed inside the anodic cell compartment, so to cause chlorine gas to be generated at the anode, and potassium ion to migrate from the anodic compartment to the cathodic compartment of the cell through the membrane. From the anodic compartment of the cell, a depleted anolyte is discharged, which is saturated with potassium chloride, and is recycled back to the anodic compartment of the cell. The catholyte is electrolysed in the cathodic compartment so to cause hydrogen to be generated at the cathode, and thus transform, at least partially, potassium bicarbonate into potassium carbonate. From the cathodic compartment of the cell, a potassium-carbonate enriched catholyte is discharged. A
portion of the enriched catholyte is treated with nitric acid, for the purpose of forming an aqueous solution of potassium nitrate, and generating carbon dioxide gas whit the other portion is contacted with the evolved carbon dioxide, in order to convert, at least partially, the potassium carbonate therein contained into potassium bicarbonate that is recycled to the cathodic compartment of the cell.
Description
,3 1~ CASE 23 ~ 2 "PROCESS FOR THE PREPARATION OF POTASSIUM NITRATE"
The present invention relates to a process for ~he preparation of potassium nitrate from nitric acid and potassium carbonate, with this latter being obtained by means of an elec~rochemical process.
Most industrially manufactured potassium ni~rate is obtained by starting from potassium chloride and nitric acid.
In particular, according to a process of the prior art, potassium chloride and nitric acid are reacted at a 1n high temperature, to yield potassium nitrate according to the reaction scheme:
3 KCl + 4 HN03 ~ ~ 3 KN03 + Cl2 + NOCl + 2 H20 The nitrosyl chloride byproduct is of no commercial value, and is hence processed for being converted into chlorine - and nitrous anhydride; this latter being recycled to the nitric acid production unit.
The related chemical equations are the following:
The present invention relates to a process for ~he preparation of potassium nitrate from nitric acid and potassium carbonate, with this latter being obtained by means of an elec~rochemical process.
Most industrially manufactured potassium ni~rate is obtained by starting from potassium chloride and nitric acid.
In particular, according to a process of the prior art, potassium chloride and nitric acid are reacted at a 1n high temperature, to yield potassium nitrate according to the reaction scheme:
3 KCl + 4 HN03 ~ ~ 3 KN03 + Cl2 + NOCl + 2 H20 The nitrosyl chloride byproduct is of no commercial value, and is hence processed for being converted into chlorine - and nitrous anhydride; this latter being recycled to the nitric acid production unit.
The related chemical equations are the following:
2 NOCl ~ 4 HN03 ~ ~ 6 N02 + Cl2 + 2 H20 4 N02 + 2 + 2 H2U ---~ ~ 4 HN03 According to another process of the prior art, potassium chloride is d;rectly converted ;nto potassium nitrate, in a reaction step operating at room temperature, accord;ng to the equation:
KCl + HNO ~ ~ KN03 + HCl In this process, an organic liquid is used as an extracting agent for the purpose of removing hydrogen chloride and shifting the reaction towards the desired direction.
As relates to such known processes, reference is made in particular to: Southwest Potash Process, ~ C~
~ 2.
Phosphorus and Potassium, 52, March/April 1971, and IMI
Process, Phosphorus and Potassium, 52, March/April 1971.
These processes of the prior art are complex and economically burdensome, and to date they have not yet found an adequate commerc;al d;ffus;on.
On the other hand, d;ff;cuLties ex;st in producing a potassium nitrate of adequate purity for being used as fertilizer. For example, its chlorine content must be reduced to zero values, or, at least, to such low values as to be negligible.
A potassium nitrate endowed with such a high purity level is required in fact for being used as fertiLizer, e.g., in intensive cultivations, such as of tomato, potatoes, tobacco, citrus and peaches.
The need was hence felt for a process to be available for the production of potassium nitrate, ~hich is simple and cheap, and capable of producing a high-purity potassium nitrate.
Such a need is fulfilled by means of the process of the present invention, according to which potassium nitrate is prepared from nitric acid and potass;um carbonate, this latter being obtained by means of special electrochem;cal process~.
More particularly, according to the present invention, potassium carbonate is prepared by means of a process characterized in that:
- a saturated aqueous solution of potassium chloride tanoLyte) is fed to the anodic compartment of a membrane cell, which is provided with an anode, a cathode and a perm-selective cation-exchange membrane, interposed between the anode and the cathode, so to form an anodic compartment and a cathodic compartment;
- an aqueous solut;on of po~3ss;um carbonate or b;carbonate (catholyte) ;s fed to the cathodic compartment of said cel~;
- sa;d anolyte ;s electrolysed ;ns;de said anod;c cell compartment, so to cause chlor;ne gas to be generated at the anode, and potass;um ;on to m;gra,te from the anod;c compartment to ~he cathodic compartment of the cell through the membrane; from ~he anodic compartment 1û of the cell a depleted anolyte ;s discharged, sa;d depleted anolyte is satura~ed w;th potass;um chlor;de, and is recycled back to the anodic compartment of the ' cell;
- said catholyte is electrolysed, in said cathod;c compartment of the cell, so to cause hydrogen to be generated at the cathode, and thus transformO at least partially, potassium bicarbonate into potassium carbonate; from the cathodic compartment of the cell a potass;um carbonate-enriched catholyte is d;scharged; a port;on of sa;d enriched catholyte ;s treated w;th nitric acid, for the purpose of forming an aqueous solution of potassium n;trate, and generating carbon d;ox;de gas; the other portion of said enr;ched catholyte ;s contacted w;th the generated carbon d;ox;de, ;n order to convert, at least part;ally, the potass;um carbonate there;n contained ;nto potassium bicarbonate and is recycled to the cathodic compar~ment of the cell;
- solid potassium nitrate is recovered from the relevant aqueous solution~
The celL used ;n the process of the present .' ~ 3~
invention is a cell equipped with an anode and a cathode separatecl from each other by a perm-selective cat;on-exchange membrane, so to define an anodic compartment and a cathodic compartment~
The anodic compartment contains usually a titanium anode, in the form of an open-structure teither perforated or expanded) sheet, coated with an electoconductive coating endowed with catalytic activity for chlorine generation.
The cathodic compartment usually contains a metal with a low hydrogen overvoltage, such as iron, steel or nickel, in the form of a perforated or expanded sheet.
The sell can consist of a plastic material, such as poly(methyl methacrylate) or polypropylene, and generally has a vertically extended shape, and a rectangular cross section.
The anodic compartment and the cathodic compartment are separated from each other by a cation-permeable membrane, in particular a potassium ion-permeable membraneO The membranes obtained from a copolymer of perfluorosulphonic acid are particularly suitable for the intended purpose. Membranes of th;s type are known and available from the market, such as, e.g., those marketed by Du Pont ~U.S.A.) under the trade mark NAFIONo According to the process of the prPsent invention~
to the anodic compartment of the cell an anolyte is sent, ~hich is constituted by a saturated aqueous solution of potassium chloride. In particular, said anolyte can contain potassium chloride at a concentration of the order of 300-320 9tlr and that as a funct;on of the cell operating temperature.
,, .
During the electrolysis, at the anode chlorine gas is generated, and potass;um ion migrates through ~he membrane from the anodic compartment to the cathodic compartment, and from the anodic compartment of the cell a potassium chloride-depleted anolyte is discharged.
j The conditions are advantageously so adjusted that said depleted anolyte çontains potassium chloride at a concentration of the order of 180-200 g/l. Lower concentration values are unacc`eptable due to the overvoltages they generate in the cell. H;gher values are expensive, and in any case do not supply any advantages in cell operation.
The depleted anolyte is separated from chlorine at the outlet from the anodic compartment of the cell, and the so-separated chlorine can be submitted to the ususal treatments, such as ~ashing, drying, compression, liquefaction and storage inside suitable containers.
The depleted anolyte is made flow through a container containing solid potassium chloride, in order to bring the concentration of that salt back to ~he above indicated saturation values, and is then recycled to the anodic compartment of the cell. If necessary, the anolyte ;s submitted, before being recycled, to treatments of filtration and removal of the excess of such impurities as sulphate, calcium and magnesium ions.
According to the process of the present invention, to the anodic compartment of the cell a catholyte i5 sent, which~ is constituted by an aqueous solution of potassium carbonate and bicarbonate. Advantageously, this catholyte contains potassium carbonate at a concentration of from 30 to 5D% by weight, and potassium bicarbonate at ~ 3 ~
6.
a concentration of from 1 to 8% by weight, and that as a function of the cell operation temperature.
During the electrolysis~ at the cathode hydrogen gas is generated, ~hilst the bicarbonate contained in the catholyte is converted into bicarbonate.
The conditions are preferably so adjusted that potassium bicarbonate ;s completely, or substantially completely, converted into carbonate, and a potassium carbonate-enriched catholyte, at a potassium carbonate concentration of approximately 90-95% of the saturation value at the cell operation temperature, is discharged.
However~ useful results are still obtained when the catholyte discharged from the cell conta;ns unconverted bicarbonate, or sodium hydrox;de.
The potassium carbonate-enriched catholyte is separated from hydrogen at the outlet of the cathodic compartment of the cell, and is then subdivided into two portions.
A portion of the catholyte is contacted ~ith an 2Q amount of nitric acid corresponding to ~he required stoichiometric amount for the formation of potassium nitrate, so to form an aqueous solution of potassium nitrate.
In this reaction, carbon dioxide gas is generated, which is contacted, e.g., inside a carbonation tower, with the other portion of the enriched catholyte. In this way, a portion of the therein contained carbonate is converted into bicarbonate.
After the restoration of the cell ~eed conditions~
the catholyte is recycled to the cathodic compartment of the same cell.
7. ~ e,~
The operating temperatures of the cell can generally have values comprised within the range of from 50 to 100 C, with values of ~he order o~ 60-80 C being preferred.
The cell current densi~y is equal to, or higher than, 2,500 A/m2, with values of the order of 3,000 A/m being preferred, and the cell voltage is of ~he order of 3 V.
By operating under the above indicated conditions, current efficiencies generally higher than 99~87D are accomplished.
As it has been previously said, a portion of the catholyte, enriched with potassium carbonate, is treated with the amount of nitric acid ~hich is stoichiometrically necessary for form;ng potass;um nitrate.
This operation can be carr;ed out by contacting the high-temperature cathoLyte with nitr;c acid having a concentration higher than 507D by weight, and generally of the order of 72-1007D~ Furthermore, this step is carried out under adiabatic conditions, with water being evaporated, and the aqueous solution of potassium nitrate being thus concentrated.
From the so-obtained concentrated solution, solid potass;um nitrate crystals can be separated, by means of the customary operations of crystallization, crystal separation and drying thereof. By acting on the crystallization parameters, it is possible to make the crystals grow up to a desired size, usually of the order of OA5-1 mm.
Accord;ng to en eLeernative procedure, the '1 !
7 ~
8.
concentrated solution of potassium nitrate can be submitted to a prilling treatment, for the purpose of ~` obtaining a solid product in the form of free-flowing granules, having the desired size.
In any case, a potassium nitrate of exceptionally high purity is obtained~
In the overall, the process of the present invent;on ia simple and convenient.
' Besides mak;ng it possible ~o produce a solid potassium nitrate in pure form, the same process makes it possible to obtain a high current efficiency in the electrolysis cell, with a reduced cell voltage. We think that this particularly good result derives, above all, from the fact that to the electrolysis a catholyte of particular composition is submittedt and that the carbonation of potassium carbonate is carried out externally to the cathodic compartment of the electrolytic cell. This, differently from those processes of the known art~ wherein potassium carbonate is produced by electrolytic way, with carbon dioxide being directly fed to the cathodic compartment.
The particular operation of the electrolytic ce~l according to the present ;nvent;on supplies the additional advantages that part;cularly pure gaseous electrolysis products are obtained, with the life of the anodes and of the perm~selective membrane being increased.
The following experimental examples are illustrative and not limitative of the present invention.
Exa_~le 1 A pilot cell is used, which is constituted by an 9 . I~L ~
anodic compartment and a cathodic compartment, between which a membrane permeable for potassium ion is ;nterposed.
The anodic compar~ment has a parallel pipedon, S vertically extended~ shape and is made from polytmethyl methacrylate).
The anodic compartment contains furthermore an anode formed by an expanded titanium sheet~ of rectangular shape, with dimensions of 50 x 60 mm, and with a thickness of 1~5 mm~ coated with a coating endowed ~ith catalytic properties for chlorine generation.
The cathodic compartment has a parallelepipedon, vertically extended, shape and is made from poly(methyl methacrylate). The cathod;c compartment contains furthermore a cathode, in the form of a wire net of AISI
316 stainless steel~ of rectangular shape, and with dimensions of 50 x 60 mm. Said cathodic wire-net does not undergo any pre-treatments.
The anodic compartment and the cathodic compartment are separated from each other by a membrane of NAFION
325, marketed by Du Pont (U.S~A.), which is trea~ed, immed;ately before the ;nstallation, accord;ng to the directions of the supplier company.
The anodic and cathodic compartments are furthermore kept together by two plates theads) of 90 x 110 mm of dimensions, of an insulatin~ and ri~id material, by means of six cadmium-coated steel bolts. Suitable gaskets provide the tight sealing between the edges of the two compartments and the membrane, and at the same time keep the membrane 3Q fastened in its position.
The anodic and cathod;c compartments are furthermore ~ 3 ~ P~
provided, in correspondence of their upper and lower surfaces, ~ith two opposi~e openings, of 3 mm of diameter, respectively for the inlet and the outlet of the anolyte and of the catholyte.
The equipment comprises also an eLectrical power supply system, with relevant measuring instruments of current intensity, and of voltage drop.
In particular, in the present example, the process is carried out with a current intensity of 10 A, and with a cell voltage of 3 V, to the anodic compartment 0.55 l/hour being fed of an anolyte, constitu~ed by an aqueous solution containing 300 g/l of potassium chlorider at a temperature of 60 C and to the cathodic compartment n.8 l/hour being fed of a catholyte, constituted by an aqueous solution at 28% by weight of potassium carbonate and at 4.3% by ~eight of potassium bicarbonate, at a temperature of 60 C.
By operating under these conditions, at the anode 4.1 l/hour of chlorine (evaluated under normal conditions of temperature and pressure) are generated, and an anolite is recovered at a temperature of 65C, containing 249.5 g of potassium chloride.
This depleted anolyte is contacted with solid potassium chloride, operating at 60 C,So as torestore the feed concentration~ and is then recycled to the anodic compartment.
Furthermore, by operating under the above indicated conditions~ at the cathode 4.1 l/hour ~evaluated under normal conditions of temperature and pressure) of hydrogen are generated, and 0.8 l/hour are recovered of a catholyte, at a temperature of 65 C, containing 32.1% by , .. i~, .
s~ ~ r~
` 11., ~eight of potassium carbonate, and 0.6~ by weight of ~,.
potassium bicarbonate~ 80 mllhour of this catholyte are trea~ted ~ith S ml/hour of nitric acid at 54%, operating at 60C.
By so doing, 88 ml/hour are obtained of an aqueous solut;on at 33% by ~e;ght of potassium nitrate, from ~h;ch the solid potassium nitrate ;s separated by evaporation and crystall;zat;on~
In th;s way, 0.037 kg/hour are obta;ned of potassium nitrate with a purity of 99.9% and with a chloride content lower than 50 ppm.
During the treatment with nitric acid, as indicated ~ above, of the aqueous solution discharged from the ; cathodic compartment, 4 l/hour are generated of carbon d;ox;de, ~h;ch ;s contacted, at 40 C, ~;th the res;dual port;on of the aqueous solut;on d;scharged from the cathod;c compartment, by operat;ng ;n a tower packed with Rasch;g r;ngs. In th;s way, 0.75 lthour are obta;ned of a soLution contain;ng 29.2% by we;ght of potassium ~ 20 carbonate, and 4.5X by ~eight of potassium bicarbonate.
j This solution, after the addition of water and of potassium carbonate for restoring the feed composition, is recycled to the cathodic compartment of the celL~
8y operat;ng under the above indicated condit;ons, current efficiencies of 9~.8% and practicalLy unitary yields of potassium nitrate are obtained.
_xamel__2 The process is carried out anaLogously to as discLosed in Example 1~ with a piLot cell, to whose anodic compartment 10 lthour are fed of an anolyte at the temperature of 80t, conta;ning 310 g/L of potass;um .
.
2 ~ ;~
12.
chloride, and to whose cathodic compartment 26 l/hour are fed of a catholyte, at the temperature of 79 S, which is constituted by an aqueous solution at 38% by weight of potassium carbonate and at 7.2~ by weight of potassium bicarbonate~
At the cell outlet, a depleted anolyte is recovered, at the temperature of 88 C, which contains 205 g/L of potassium chloride, and a catholy~e is recovered, at the temperature of 86 C, which is constituted by an aqueous solution at 45.7% by weight of potassium carbonate and 1.6% by weight of potassium bicarbonate.
By operating ;n a similar way to as shown in Example 1, 190 gthour are obtained of potassium nitrate with a purity of 99.9%, w;th a chlorine content lower than 50 ppm, with a current eff;c;ency of 99.9%, and w;th a practically unitary y;eld relat;vely to the produced potassium nitrate.
KCl + HNO ~ ~ KN03 + HCl In this process, an organic liquid is used as an extracting agent for the purpose of removing hydrogen chloride and shifting the reaction towards the desired direction.
As relates to such known processes, reference is made in particular to: Southwest Potash Process, ~ C~
~ 2.
Phosphorus and Potassium, 52, March/April 1971, and IMI
Process, Phosphorus and Potassium, 52, March/April 1971.
These processes of the prior art are complex and economically burdensome, and to date they have not yet found an adequate commerc;al d;ffus;on.
On the other hand, d;ff;cuLties ex;st in producing a potassium nitrate of adequate purity for being used as fertilizer. For example, its chlorine content must be reduced to zero values, or, at least, to such low values as to be negligible.
A potassium nitrate endowed with such a high purity level is required in fact for being used as fertiLizer, e.g., in intensive cultivations, such as of tomato, potatoes, tobacco, citrus and peaches.
The need was hence felt for a process to be available for the production of potassium nitrate, ~hich is simple and cheap, and capable of producing a high-purity potassium nitrate.
Such a need is fulfilled by means of the process of the present invention, according to which potassium nitrate is prepared from nitric acid and potass;um carbonate, this latter being obtained by means of special electrochem;cal process~.
More particularly, according to the present invention, potassium carbonate is prepared by means of a process characterized in that:
- a saturated aqueous solution of potassium chloride tanoLyte) is fed to the anodic compartment of a membrane cell, which is provided with an anode, a cathode and a perm-selective cation-exchange membrane, interposed between the anode and the cathode, so to form an anodic compartment and a cathodic compartment;
- an aqueous solut;on of po~3ss;um carbonate or b;carbonate (catholyte) ;s fed to the cathodic compartment of said cel~;
- sa;d anolyte ;s electrolysed ;ns;de said anod;c cell compartment, so to cause chlor;ne gas to be generated at the anode, and potass;um ;on to m;gra,te from the anod;c compartment to ~he cathodic compartment of the cell through the membrane; from ~he anodic compartment 1û of the cell a depleted anolyte ;s discharged, sa;d depleted anolyte is satura~ed w;th potass;um chlor;de, and is recycled back to the anodic compartment of the ' cell;
- said catholyte is electrolysed, in said cathod;c compartment of the cell, so to cause hydrogen to be generated at the cathode, and thus transformO at least partially, potassium bicarbonate into potassium carbonate; from the cathodic compartment of the cell a potass;um carbonate-enriched catholyte is d;scharged; a port;on of sa;d enriched catholyte ;s treated w;th nitric acid, for the purpose of forming an aqueous solution of potassium n;trate, and generating carbon d;ox;de gas; the other portion of said enr;ched catholyte ;s contacted w;th the generated carbon d;ox;de, ;n order to convert, at least part;ally, the potass;um carbonate there;n contained ;nto potassium bicarbonate and is recycled to the cathodic compar~ment of the cell;
- solid potassium nitrate is recovered from the relevant aqueous solution~
The celL used ;n the process of the present .' ~ 3~
invention is a cell equipped with an anode and a cathode separatecl from each other by a perm-selective cat;on-exchange membrane, so to define an anodic compartment and a cathodic compartment~
The anodic compartment contains usually a titanium anode, in the form of an open-structure teither perforated or expanded) sheet, coated with an electoconductive coating endowed with catalytic activity for chlorine generation.
The cathodic compartment usually contains a metal with a low hydrogen overvoltage, such as iron, steel or nickel, in the form of a perforated or expanded sheet.
The sell can consist of a plastic material, such as poly(methyl methacrylate) or polypropylene, and generally has a vertically extended shape, and a rectangular cross section.
The anodic compartment and the cathodic compartment are separated from each other by a cation-permeable membrane, in particular a potassium ion-permeable membraneO The membranes obtained from a copolymer of perfluorosulphonic acid are particularly suitable for the intended purpose. Membranes of th;s type are known and available from the market, such as, e.g., those marketed by Du Pont ~U.S.A.) under the trade mark NAFIONo According to the process of the prPsent invention~
to the anodic compartment of the cell an anolyte is sent, ~hich is constituted by a saturated aqueous solution of potassium chloride. In particular, said anolyte can contain potassium chloride at a concentration of the order of 300-320 9tlr and that as a funct;on of the cell operating temperature.
,, .
During the electrolysis, at the anode chlorine gas is generated, and potass;um ion migrates through ~he membrane from the anodic compartment to the cathodic compartment, and from the anodic compartment of the cell a potassium chloride-depleted anolyte is discharged.
j The conditions are advantageously so adjusted that said depleted anolyte çontains potassium chloride at a concentration of the order of 180-200 g/l. Lower concentration values are unacc`eptable due to the overvoltages they generate in the cell. H;gher values are expensive, and in any case do not supply any advantages in cell operation.
The depleted anolyte is separated from chlorine at the outlet from the anodic compartment of the cell, and the so-separated chlorine can be submitted to the ususal treatments, such as ~ashing, drying, compression, liquefaction and storage inside suitable containers.
The depleted anolyte is made flow through a container containing solid potassium chloride, in order to bring the concentration of that salt back to ~he above indicated saturation values, and is then recycled to the anodic compartment of the cell. If necessary, the anolyte ;s submitted, before being recycled, to treatments of filtration and removal of the excess of such impurities as sulphate, calcium and magnesium ions.
According to the process of the present invention, to the anodic compartment of the cell a catholyte i5 sent, which~ is constituted by an aqueous solution of potassium carbonate and bicarbonate. Advantageously, this catholyte contains potassium carbonate at a concentration of from 30 to 5D% by weight, and potassium bicarbonate at ~ 3 ~
6.
a concentration of from 1 to 8% by weight, and that as a function of the cell operation temperature.
During the electrolysis~ at the cathode hydrogen gas is generated, ~hilst the bicarbonate contained in the catholyte is converted into bicarbonate.
The conditions are preferably so adjusted that potassium bicarbonate ;s completely, or substantially completely, converted into carbonate, and a potassium carbonate-enriched catholyte, at a potassium carbonate concentration of approximately 90-95% of the saturation value at the cell operation temperature, is discharged.
However~ useful results are still obtained when the catholyte discharged from the cell conta;ns unconverted bicarbonate, or sodium hydrox;de.
The potassium carbonate-enriched catholyte is separated from hydrogen at the outlet of the cathodic compartment of the cell, and is then subdivided into two portions.
A portion of the catholyte is contacted ~ith an 2Q amount of nitric acid corresponding to ~he required stoichiometric amount for the formation of potassium nitrate, so to form an aqueous solution of potassium nitrate.
In this reaction, carbon dioxide gas is generated, which is contacted, e.g., inside a carbonation tower, with the other portion of the enriched catholyte. In this way, a portion of the therein contained carbonate is converted into bicarbonate.
After the restoration of the cell ~eed conditions~
the catholyte is recycled to the cathodic compartment of the same cell.
7. ~ e,~
The operating temperatures of the cell can generally have values comprised within the range of from 50 to 100 C, with values of ~he order o~ 60-80 C being preferred.
The cell current densi~y is equal to, or higher than, 2,500 A/m2, with values of the order of 3,000 A/m being preferred, and the cell voltage is of ~he order of 3 V.
By operating under the above indicated conditions, current efficiencies generally higher than 99~87D are accomplished.
As it has been previously said, a portion of the catholyte, enriched with potassium carbonate, is treated with the amount of nitric acid ~hich is stoichiometrically necessary for form;ng potass;um nitrate.
This operation can be carr;ed out by contacting the high-temperature cathoLyte with nitr;c acid having a concentration higher than 507D by weight, and generally of the order of 72-1007D~ Furthermore, this step is carried out under adiabatic conditions, with water being evaporated, and the aqueous solution of potassium nitrate being thus concentrated.
From the so-obtained concentrated solution, solid potass;um nitrate crystals can be separated, by means of the customary operations of crystallization, crystal separation and drying thereof. By acting on the crystallization parameters, it is possible to make the crystals grow up to a desired size, usually of the order of OA5-1 mm.
Accord;ng to en eLeernative procedure, the '1 !
7 ~
8.
concentrated solution of potassium nitrate can be submitted to a prilling treatment, for the purpose of ~` obtaining a solid product in the form of free-flowing granules, having the desired size.
In any case, a potassium nitrate of exceptionally high purity is obtained~
In the overall, the process of the present invent;on ia simple and convenient.
' Besides mak;ng it possible ~o produce a solid potassium nitrate in pure form, the same process makes it possible to obtain a high current efficiency in the electrolysis cell, with a reduced cell voltage. We think that this particularly good result derives, above all, from the fact that to the electrolysis a catholyte of particular composition is submittedt and that the carbonation of potassium carbonate is carried out externally to the cathodic compartment of the electrolytic cell. This, differently from those processes of the known art~ wherein potassium carbonate is produced by electrolytic way, with carbon dioxide being directly fed to the cathodic compartment.
The particular operation of the electrolytic ce~l according to the present ;nvent;on supplies the additional advantages that part;cularly pure gaseous electrolysis products are obtained, with the life of the anodes and of the perm~selective membrane being increased.
The following experimental examples are illustrative and not limitative of the present invention.
Exa_~le 1 A pilot cell is used, which is constituted by an 9 . I~L ~
anodic compartment and a cathodic compartment, between which a membrane permeable for potassium ion is ;nterposed.
The anodic compar~ment has a parallel pipedon, S vertically extended~ shape and is made from polytmethyl methacrylate).
The anodic compartment contains furthermore an anode formed by an expanded titanium sheet~ of rectangular shape, with dimensions of 50 x 60 mm, and with a thickness of 1~5 mm~ coated with a coating endowed ~ith catalytic properties for chlorine generation.
The cathodic compartment has a parallelepipedon, vertically extended, shape and is made from poly(methyl methacrylate). The cathod;c compartment contains furthermore a cathode, in the form of a wire net of AISI
316 stainless steel~ of rectangular shape, and with dimensions of 50 x 60 mm. Said cathodic wire-net does not undergo any pre-treatments.
The anodic compartment and the cathodic compartment are separated from each other by a membrane of NAFION
325, marketed by Du Pont (U.S~A.), which is trea~ed, immed;ately before the ;nstallation, accord;ng to the directions of the supplier company.
The anodic and cathodic compartments are furthermore kept together by two plates theads) of 90 x 110 mm of dimensions, of an insulatin~ and ri~id material, by means of six cadmium-coated steel bolts. Suitable gaskets provide the tight sealing between the edges of the two compartments and the membrane, and at the same time keep the membrane 3Q fastened in its position.
The anodic and cathod;c compartments are furthermore ~ 3 ~ P~
provided, in correspondence of their upper and lower surfaces, ~ith two opposi~e openings, of 3 mm of diameter, respectively for the inlet and the outlet of the anolyte and of the catholyte.
The equipment comprises also an eLectrical power supply system, with relevant measuring instruments of current intensity, and of voltage drop.
In particular, in the present example, the process is carried out with a current intensity of 10 A, and with a cell voltage of 3 V, to the anodic compartment 0.55 l/hour being fed of an anolyte, constitu~ed by an aqueous solution containing 300 g/l of potassium chlorider at a temperature of 60 C and to the cathodic compartment n.8 l/hour being fed of a catholyte, constituted by an aqueous solution at 28% by weight of potassium carbonate and at 4.3% by ~eight of potassium bicarbonate, at a temperature of 60 C.
By operating under these conditions, at the anode 4.1 l/hour of chlorine (evaluated under normal conditions of temperature and pressure) are generated, and an anolite is recovered at a temperature of 65C, containing 249.5 g of potassium chloride.
This depleted anolyte is contacted with solid potassium chloride, operating at 60 C,So as torestore the feed concentration~ and is then recycled to the anodic compartment.
Furthermore, by operating under the above indicated conditions~ at the cathode 4.1 l/hour ~evaluated under normal conditions of temperature and pressure) of hydrogen are generated, and 0.8 l/hour are recovered of a catholyte, at a temperature of 65 C, containing 32.1% by , .. i~, .
s~ ~ r~
` 11., ~eight of potassium carbonate, and 0.6~ by weight of ~,.
potassium bicarbonate~ 80 mllhour of this catholyte are trea~ted ~ith S ml/hour of nitric acid at 54%, operating at 60C.
By so doing, 88 ml/hour are obtained of an aqueous solut;on at 33% by ~e;ght of potassium nitrate, from ~h;ch the solid potassium nitrate ;s separated by evaporation and crystall;zat;on~
In th;s way, 0.037 kg/hour are obta;ned of potassium nitrate with a purity of 99.9% and with a chloride content lower than 50 ppm.
During the treatment with nitric acid, as indicated ~ above, of the aqueous solution discharged from the ; cathodic compartment, 4 l/hour are generated of carbon d;ox;de, ~h;ch ;s contacted, at 40 C, ~;th the res;dual port;on of the aqueous solut;on d;scharged from the cathod;c compartment, by operat;ng ;n a tower packed with Rasch;g r;ngs. In th;s way, 0.75 lthour are obta;ned of a soLution contain;ng 29.2% by we;ght of potassium ~ 20 carbonate, and 4.5X by ~eight of potassium bicarbonate.
j This solution, after the addition of water and of potassium carbonate for restoring the feed composition, is recycled to the cathodic compartment of the celL~
8y operat;ng under the above indicated condit;ons, current efficiencies of 9~.8% and practicalLy unitary yields of potassium nitrate are obtained.
_xamel__2 The process is carried out anaLogously to as discLosed in Example 1~ with a piLot cell, to whose anodic compartment 10 lthour are fed of an anolyte at the temperature of 80t, conta;ning 310 g/L of potass;um .
.
2 ~ ;~
12.
chloride, and to whose cathodic compartment 26 l/hour are fed of a catholyte, at the temperature of 79 S, which is constituted by an aqueous solution at 38% by weight of potassium carbonate and at 7.2~ by weight of potassium bicarbonate~
At the cell outlet, a depleted anolyte is recovered, at the temperature of 88 C, which contains 205 g/L of potassium chloride, and a catholy~e is recovered, at the temperature of 86 C, which is constituted by an aqueous solution at 45.7% by weight of potassium carbonate and 1.6% by weight of potassium bicarbonate.
By operating ;n a similar way to as shown in Example 1, 190 gthour are obtained of potassium nitrate with a purity of 99.9%, w;th a chlorine content lower than 50 ppm, with a current eff;c;ency of 99.9%, and w;th a practically unitary y;eld relat;vely to the produced potassium nitrate.
Claims (3)
1. Process for the preparation of potassium nitrate, characterized in that:
- a saturated aqueous solution of potassium chloride (anolyte) is fed to the anodic compartment of a membrane cell, which is provided with an anode, a cathode and a perm-selective cation-exchange membrane, interposed between the anode and the cathode, so to form an anodic compartment and a cathodic compartment;
- an aqueous solution of potassium carbonate or bicarbonate (catholyte) is fed to the cathodic compartment of said cell;
- said anolyte is electrolysed inside said anodic cell compartment, so to cause chlorine gas to be generated at the anode, and potassium ion to migrate from the anodic compartment to the cathodic compartment of the cell through the membrane;
- from the anodic compartment of the cell a depleted anolyte is discharged, said depleted anolyte is saturated with potassium chloride, and is recycled back to the anodic compartment of the cell;
- said catholyte is electrolysed, in said cathodic compartment of the cell, so to cause hydrogen to be generated at the cathode, and thus transform, at least partially, potassium bicarbonate into potassium carbonate; from the cathodic compartment of the cell a potassium-carbonate enriched catholyte is discharged; a portion of said enriched catholyte is treated with nitric acid, for the purpose of forming an aqueous solution of potassium nitrate, and generating carbon dioxide gas; the other portion of said enriched catholyte is contacted with the evolved carbon dioxide, in order to convert, at least partially, the potassium carbonate therein contained into potassium bicarbonate and is recycled to the cathodic compartment of the cell;
- solid potassium nitrate is recovered from the relevant aqueous solution
- a saturated aqueous solution of potassium chloride (anolyte) is fed to the anodic compartment of a membrane cell, which is provided with an anode, a cathode and a perm-selective cation-exchange membrane, interposed between the anode and the cathode, so to form an anodic compartment and a cathodic compartment;
- an aqueous solution of potassium carbonate or bicarbonate (catholyte) is fed to the cathodic compartment of said cell;
- said anolyte is electrolysed inside said anodic cell compartment, so to cause chlorine gas to be generated at the anode, and potassium ion to migrate from the anodic compartment to the cathodic compartment of the cell through the membrane;
- from the anodic compartment of the cell a depleted anolyte is discharged, said depleted anolyte is saturated with potassium chloride, and is recycled back to the anodic compartment of the cell;
- said catholyte is electrolysed, in said cathodic compartment of the cell, so to cause hydrogen to be generated at the cathode, and thus transform, at least partially, potassium bicarbonate into potassium carbonate; from the cathodic compartment of the cell a potassium-carbonate enriched catholyte is discharged; a portion of said enriched catholyte is treated with nitric acid, for the purpose of forming an aqueous solution of potassium nitrate, and generating carbon dioxide gas; the other portion of said enriched catholyte is contacted with the evolved carbon dioxide, in order to convert, at least partially, the potassium carbonate therein contained into potassium bicarbonate and is recycled to the cathodic compartment of the cell;
- solid potassium nitrate is recovered from the relevant aqueous solution
2. Process according to claim 1, wherein to the anodic compartment of the cell an anolyte is fed, which is constituted by an aqueous solution containing 300-320 g/l of potassium chloride, and to the cathodic compartment of the cell a catholyte is fed, which is constituted by an aqueous solution containing from 30 to 50% by weight of potassium carbonate, and from 1 to 8% by weight of potassium bicarbonate; the electrolysis is carried out at a temperature comprised within the range of from 50 to 100°C, and an anolyte constituted by an aqueous solution containing 180-200 g/l of potassium chloride, as well as a catholyte free, or substantially free, from potassium bicarbonate, is discharged.
3. Process according to claim 1, wherein the solid potassium nitrate is recovered from the related aqueous solution by crystallization, or by submitting the same solution to a prilling treatment.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IT21229A/86 | 1986-07-23 | ||
| IT21229/86A IT1196984B (en) | 1986-07-23 | 1986-07-23 | PROCEDURE FOR THE PREPARATION OF POTASSIUM NITRATE |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1315233C true CA1315233C (en) | 1993-03-30 |
Family
ID=11178722
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000541991A Expired - Fee Related CA1315233C (en) | 1986-07-23 | 1987-07-14 | Process for the preparation of potassium nitrate |
Country Status (9)
| Country | Link |
|---|---|
| US (1) | US4776930A (en) |
| EP (1) | EP0254361B1 (en) |
| JP (1) | JPS6342386A (en) |
| AT (1) | ATE60092T1 (en) |
| CA (1) | CA1315233C (en) |
| DE (1) | DE3767397D1 (en) |
| ES (1) | ES2021347B3 (en) |
| GR (1) | GR3001508T3 (en) |
| IT (1) | IT1196984B (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3729669A1 (en) * | 1987-09-04 | 1989-03-16 | Basf Ag | METHOD FOR PRODUCING ALKALINE METAL NITRATES |
| JPH04305226A (en) * | 1991-01-25 | 1992-10-28 | Senichi Masuda | Method for decreasing nox in gas |
| DE19614645C1 (en) * | 1996-04-13 | 1997-10-30 | Durferrit Thermotechnik Gmbh | Process for the selective recovery of salt components from nitrate-nitrate-hydroxide-containing hardening agent salts |
| US6475457B2 (en) * | 1998-06-22 | 2002-11-05 | William J. Rigby | Process for manufacturing potassium nitrate fertilizer and other metal nitrates |
| JP4950056B2 (en) * | 2004-10-29 | 2012-06-13 | コーニンクレッカ フィリップス エレクトロニクス エヌ ヴィ | Electrodes and enclosures for cardiac monitoring and treatment |
| NZ597787A (en) * | 2009-06-25 | 2013-07-26 | Imi Tami Institute Research | Polyhalite imi process for kno3 production |
| CN102596856A (en) * | 2009-06-25 | 2012-07-18 | Imitami院研发有限公司 | Process for production of commercial quality potassium nitrate from polyhalite |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| BE621091A (en) * | 1961-08-11 | |||
| NL282666A (en) * | 1961-09-06 | |||
| DD104066A1 (en) * | 1973-05-09 | 1974-02-20 | ||
| AR205953A1 (en) * | 1975-01-22 | 1976-06-15 | Diamond Shamrock Corp | PRODUCTION OF CARBONATES FROM METALS TO CALINES IN A MEMBRANE CELL |
| US4465568A (en) * | 1981-11-16 | 1984-08-14 | Olin Corporation | Electrochemical production of KNO3 /NaNO3 salt mixture |
-
1986
- 1986-07-23 IT IT21229/86A patent/IT1196984B/en active
-
1987
- 1987-07-07 US US07/070,419 patent/US4776930A/en not_active Expired - Fee Related
- 1987-07-14 DE DE8787201343T patent/DE3767397D1/en not_active Expired - Fee Related
- 1987-07-14 AT AT87201343T patent/ATE60092T1/en active
- 1987-07-14 ES ES87201343T patent/ES2021347B3/en not_active Expired - Lifetime
- 1987-07-14 CA CA000541991A patent/CA1315233C/en not_active Expired - Fee Related
- 1987-07-14 EP EP87201343A patent/EP0254361B1/en not_active Expired - Lifetime
- 1987-07-23 JP JP62182428A patent/JPS6342386A/en active Pending
-
1991
- 1991-02-26 GR GR91400214T patent/GR3001508T3/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| ES2021347B3 (en) | 1991-11-01 |
| DE3767397D1 (en) | 1991-02-21 |
| EP0254361B1 (en) | 1991-01-16 |
| EP0254361A1 (en) | 1988-01-27 |
| IT8621229A0 (en) | 1986-07-23 |
| JPS6342386A (en) | 1988-02-23 |
| GR3001508T3 (en) | 1992-11-23 |
| US4776930A (en) | 1988-10-11 |
| IT8621229A1 (en) | 1988-01-23 |
| IT1196984B (en) | 1988-11-25 |
| ATE60092T1 (en) | 1991-02-15 |
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