DE4326539A1 - Process for the preparation of ammonia or alkali solutions and peroxodisulfates - Google Patents

Description

The present invention relates to a process for the preparation of ammonia, caustic alkalis and peroxodisulfates from neutral Ammonium or Alkalisulfathaltigen solutions in one by a Cation exchange membrane divided into two electrolysis cell Oxidation of sulfate solutions at the anode in the presence of thio cyanates, rhodanilic acid, dirhodan and organic stick substance carbon-sulfur group-containing compounds and / or nitrogen-containing heteroaromatics, wherein the ammonium or Alkali cations with high current yields in the cathode compartment over lead and form ammonia or alkali solutions.

In the production of peroxodisulphates, sulphate contents are  250 g / l required to achieve current efficiencies of <50%, whereby a maximum of 70% of the sulfate used are implemented can. The anodic oxidation of sulfates to peroxosulfates can only on smooth platinum electrodes and not on Metalloxidelek be carried out with economic electricity yields. In dilute sodium sulfate solutions of 20 wt .-% are peroxo sulfates depending on the temperature also on platinum anodes only with Stromaus obtained from 5%. An exception is dilute potassium and ammonium sulfate solutions in which Peroxidsulfate with Stromaus can be produced up to 18%. In the chemical Industry, most wastewaters usually consist of dilute sodium sulfate solutions or are sulfuric acid-containing, so that it was previously not possible Peroxosulfate with high Stromaus and at the same time to produce alkali or ammonia and thereby aufzu sulfate solutions or wastewater economically BEITEN. The electrolysis of acidic solutions or wastewater leads by the hydronium ion migration in the cation exchange membranes bran to low current yields for the alkali and ammonium ion transfer and thus becomes uneconomical. At the Elek trolysis of neutral sodium sulfate solutions, their economics high current yields for the ammonium or alkali over Due to the low tem temperatures of + 35 ° C for peroxodisulfate formation only max. 20gew .-% sodium sulfate solutions are used. hereby the current yields for peroxodisulfate formation decrease 5%, as the sulphate content is insufficient. Additions to the known potential-increasing substances such as hydrogen fluoride acid, hydrochloric acid, thiourea, cyanides and rhodanides, the at concentrations of 1500 ppm in the sulphate solution  become; do not give sufficient current yields and condition significant corrosion problems at the anodes.

Object of the present invention is ammonia or alkali lyes and peroxodisulphates from low-concentration sulphate solutions with high power yields and low energy consumption cost-effective to produce and thus highly concentrated To be able to implement sulfate solutions largely, so that the rest sulphate content in the peroxodisulphate solution according to the direct elec Trochemical implementation is as low as possible.

The object has been achieved by the Ammonium or alkali sulfates in the anode compartment by a Cation exchange membrane two-part electrolytic cell with a smooth platinum anode that has a high oxygen overvoltage has, electrolyzed and the electrolysis of the sulfate-containing Solutions or effluents in the presence of thiocyanates and / or Hydroxydic acid and / or dirhodane and thioamides and / or Thioaldehydes and / or thiocarboxylic acids and / or thiocarboxylic acid esters and / or thioalkanols and / or thioketals and / or Dithio compounds and / or nitrogen-containing heteroaromatics performs.

As anode materials come with high oxygen overvoltage preferably smooth platinum on titanium substrates, Niobium or tantalum or platinum on supports of alloys of these Metals into consideration. Particularly preferred is smooth platinum sheet on tantalum or niobium-tantalum alloys.

For the formation of peroxosulphates with economic Stromausbeu at low sulfate levels of <20% in use Sulfate-containing solutions and effluents are inhibitor combinations tions consisting of thiocyanates and / or Rhodanwasserstoffsäure and / or Dirhodan having the claimed in claim 1 Invention appropriate additions absolutely necessary.

The thiocyanates are in the form of their potassium, sodium or Ammonium salts used while the Rhodanwasserstoffsäure as aqueous solution is used.

As thioamides can thioformamide, thiourea and thiosemi carbazide can be used.

Suitable thioaldehydes are those which are prepared from aldehydes and Produces hydrogen sulfide.  

Thiocarboxylic, Thiocarbonsäureesther, thioalkanols or Thioketals are preferably aliphatic C₁ to C₄ compounds suitable, while thiocarbonic acid as Dithioverbindungen and / or dimercaproalkanols.

Advantageous organic thio compounds are the derivatives of Thiocarbonic acid such. Thiourea, thiosemicarbazide, thio carbohydrazide, bis-thiourea, thiosemicarbazone, dithizone and S-alkyl-isothiuronium salts, thiosemicarbazide being as be has proved particularly suitable.

Besides these compounds, thioglycols, thiomorpholine, thio ether, thiocyanic acid, thiocyanic acid ester, thiocarboxylic acid ester and rhodanine are used.

As nitrogen-containing heteroaromatics z. For example, pyridine and / or Derivatives of pyridine and / or fused ring systems of Pyridine and / or pyrimidine and / or pyrimidine derivatives and / or Pyridazine derivatives and / or pyrazine and / or pyrazine derivatives and / or pyrazone and / or pyrazone derivatives. Prefers come the benzene-fused ring systems of pyridine, or their descendants, such as Quinoline, isoquinoline, 1,2-dihydro quinoline, quinoline-8-sulfonic acid, aminoquinolines, 3-chloroquinol lin, quinolinic acid and hydroquinolines into consideration.

Furthermore, chlorinated derivatives of pyridine and / or chino lins and / or pyrimidine and / or pyridazine and / or pyrazine and / or pyrazones in combination with thiocyanates and / or Dirhodan and / or other organic thio compounds use bar, wherein the sulfate solutions additionally small amounts of Chlorides can add.

To protect the anode and reduce corrosion of the anode Platinum is used the chlorinated derivatives of pyridine and / or pyrimidine and / or pyridazine and / or pyrazine and / or pyrazones in combination with hexamethylenetetramine and Thiocyanates and / or rhodanilic acid and / or dirhodan.

The hexamethylenetetramine may also be used in combination with all other claimed inhibitor additives are used as it leads to a reduction of platinum losses.

The concentration of thiocyanates and / or rhodanilic acid and / or dirhodane in the sulphate solution or in the effluent may be 0.5 to 2000 ppm, preferably 50 to 800 ppm. To stabili The current efficiency can reduce this concentration during the  Electrolysis continuously by thiocyanates and / or Rhodan Hydrogenic acid and / or Dirhodan be supplemented.

The addition of nitrogen-carbon-sulfur group-containing organic compounds and / or nitrogen-containing hetero-aroma should be between 10 and 2000 ppm, preferably 50 to 500 ppm lie and are continuously supplemented during the electrolysis. The ammonium or alkali sulfate content of the electrolyte can 5 to 44 wt .-%, preferably 15 to 22 wt .-% with alkali sulfates and 5 to 44 wt .-% with ammonium sulfate. Especially Sulphate concentrations between 8 and 20 wt .-% are favorable at Alkalisulfat- and 8 to 40 wt .-% with ammonium sulfate solutions.

Suitable cathode materials are low-carbon electrodes Have hydrogen overvoltage. It comes with platinum metals and / or platinum metal mixed oxides doped titanium or nickel or doped copper or doped metallic silver into consideration. Preference is given to Raney nickel coated nickel and also coated with iron-nickel or iron-cobalt alloys Iron or nickel according to DPB 3102306. The hydrogen overvoltage the cathode should be less than 200 mV, preferably 10 to 80 mV to save energy costs.

For separating the anode and cathode compartments of the electrolytic cell cation exchange membranes or diaphragms are used. As cation exchange membranes, polymers are preferred Base of perfluorinated olefins or copolymers of tetrafluoro ethylene with unsaturated perfluorinated ethers or copolymers from styrene and divinylbenzene used as charge-carrying Groups sulfonic acid and carboxyl groups or only sulfonic acid groups included. Cation exchange membranes containing only sulfone contain acid groups, are much more resistant to Storage and contamination by polyvalent cations and therefore when using sulphate-containing process and wastewater before suitable.

For separation of the anode and cathode space can also Diaphrag used. Suitable diaphragms are such hydrophilized perfluorinated and / or perchlorinated art materials or sintered ceramics based on alumina and / or Zirconia. Preferably, diaphragms made of polymers are suitable consist of perfluorinated olefins and with Zirconia are hydrophilized.  

The electrochemical synthesis of peroxodisulfates and of Ammonia or the alkali can be continuous or in the Batch operation to be performed. In continuous operation the electrolysis cells are connected in series as a cascade. The electrochemical conversion of the neutral ammonium or Alkalisulfatlösungen is preferably carried out in such a way that the electrolysis cell is operated as a continuous cascade, wherein the sulphate solution or the sulphate-containing wastewater the Anode spaces flowed through the entire cascade. To stabili The current efficiency is determined in different sections of the Cascade continuously dosed the claimed additives. It has proved to be advantageous when the sulfate solution or the sulphate wastewater in the last third of the cascade no additives such as thiocyanates, rhodanilic acid, Dirhodan and organic nitrogen-carbon sulfur compounds gene or heteroaromatic added. In this mode of operation receives pure peroxosulphates which are free of inhibitor impurities included. On the cathode side is preferably used dilute alkali solutions as feed to the cascade. In addition to alkali solutions It is also possible to use aqueous ammonia solution as the conducting electrolyte become. The inflow concentrations for the cascade can be 0.25 to 25 wt .-%, preferably 4 to 8 wt .-% amount. As a process 5 to 40 wt .-% solutions, preferably 8 to 30gew .-% solutions suitable.

The anodes and cathodes on which gases evolve can be obtained in the form of gas lift electrodes. With these electrodes the buoyancy forces are used, which are in the electrolyte compared to the gas loading by adjusting the density differences Adjust the gas-free electrolyte. The buoyancy forces are by constructive design of the electrodes and circulation systems so directed that a directed electrolyte flow with minimal Gas content arises in the electrode space. The flow rate speeds should be 0.15 m / s and 10 m / s, preferably 2 to 5 m / s be. Particularly favorable is the subdivision of Elek between the electrodes in vertical, flowed through by the electrolyte Channels. In this way, a minimization of the gas bubbles caused a voltage drop.

The electrolysis of the ammonium or alkali sulfate solutions can at Current densities of 0.3 to 25 kA / m² are performed. virtue wise works at current densities of 1 to 8 kA / m².

The temperature in the electrochemical synthesis should be -5 to 45 ° C, preferably 10 to + 30 ° C. But it is also possible Lich, especially at higher sulfate concentrations, the electric  lysis with the claimed additives at higher temperatures perform.

The inventive method is particularly suitable for elek trochemical reaction of neutral or weakly alkaline Solutions or sulphate-containing effluents, the ammonium or Alkalisulfate, to ammonia or alkali solutions and Peroxodisulfaten. In the presence of thiocyanates and / or rhodan hydrochloric acid and / or dirhodane and thioamides and / or thio aldehydes and / or thiocarboxylic acids and / or thiocarboxylic acids star and / or thioalkanols and / or thioketals and / or Dithio compounds and / or nitrogen-containing heteroaromatics obtained in diluted as well as in highly concentrated solutions high current yields for the peroxodisulfate and ammonia or Caustic education. With the claimed combination of Inhibitors which are used in much lower concentrations it is possible to use diluted neutral ammonium or alkali sulfate solutions economically to ammonia, alkali lyes and peroxodisulfates and highly concentrated solutions reacting so that the peroxodisulfate solutions produced have only low residual sulfate levels.

example 1

In a two-part electrolysis cell, the anode and Cathode space through a cation exchange membrane of the type Neosepta CMH / 2 (Tokuyama soda) is disconnected, an anode becomes off Platinum plate on a tantalum carrier and a cathode made of nickel built-in.

In the cathode compartment of the electrolytic cell is aqueous 5gew .-% Sodium hydroxide used, while in the anode compartment, the following Electrolytes are tested:

• 1. 15gew .-% aqueous sodium sulfate solution
• 2. 15% strength by weight aqueous sodium sulfate solution + 500 ppm sodium thiocyanate
• 3. 15 wt .-% aqueous sodium sulfate solution with 500 ppm of sodium thiocyanate and 100 ppm thiourea
• 4. 15 wt .-% aqueous sodium sulfate solution with 500 ppm sodium thiocyanate + 100 ppm thiosemicarbazide
• 5. 11gew .-% aqueous potassium sulfate solution
• 6. 11gew .-% aqueous potassium sulfate solution with 500 ppm of potassium thiocyanate
• 7. 11gew .-% aqueous potassium sulfate solution with 500 ppm of potassium thiocyanate and 100 ppm thiourea
• 8. 15% strength by weight ammonium sulfate solution  
• 9. 15% strength by weight ammonium sulfate solution with 500 ppm ammonium thio cyanate
• 10. 15% strength by weight ammonium sulfate solution + 500 ppm ammonium thiocyanate + 100 ppm thiourea
• 11. 15gew .-% strength ammonium sulfate solution with 500 ppm thiocyanate and 100 ppm thiosemicarbazide.

The electrolysis of the electrolytes becomes under the following process conditions:

- temperature +28 to 30 ° C - Anodic current density 5 kA / m² - Electricity supply 30 Ah / l - Flow rate at the anode 1.2 m / s

After the electrolysis in the individual electrolytes listed contents of S₂O₈⁻⁻ and current yields determined:

From the results it is clear that without additives in the Elek trolysis of dilute, neutral sodium sulfate solutions barely peroxo compounds arise (experiment 1), while in ammonium and Potassium Sulphate Solutions Peroxo compounds with current yields of  20% (experiments 5 and 8). The additions of Thio cyanate lead to an increase in current efficiency in the sodium sulfate solution to 30% (Experiment 2) in the potassium sulfate solution 33% (experiment 6) and in the ammonium sulfate solution to 32% (Ver 9), while the simultaneous addition of thiourea or Thiosemicarbazide current yields of 50% for the S₂O₈⁻⁻ formation results (experiments 3, 4, 7, 10 and 11).  

If one uses instead of a platinum anode electrodes made of tin dioxide, lead dioxide and manganese dioxide are obtained without additives the electrolyte and with those in experiments 2, 3, 4, 6, 7, 9, 10 and 11 listed additions current yields for the S₂O₈⁻⁻- Education that is well below 1%.

This example shows that peroxo compounds only on smooth Platinum anodes and not metal oxide electrodes in the absence and in the presence of carbon-nitrogen-sulfur group containing compounds with technically interesting current yields be formed.

Example 2

In an electrolytic cell as in Example 1 is in the anodes room 43gew .-% ammonium sulfate solution used while Conducting electrolyte in the cathode compartment aqueous 5 wt .-% sodium hydroxide solution is used. The pH solution is about 6.

The electrolysis is at a cell voltage of 4.1 V and a Current density of 5 kA / m² anode surface performed. In the anode room the flow velocity is 1.2 m / s. The temperature will be kept between +28 and + 30 ° C. During the electrolysis will be the sulphate solution according to different electricity offered samples taken and the current yields for Peroxosulfatbildung and Ammonia transfer determined.

Depending on the electricity supply, the following current yields for peroxodisulfate formation and ammonium ion transfer th.

If the ammonium sulfate solution is additionally added during the oxidation 135 ppm of ammonium thiocyanate, the following results are obtained.

Electrolyzed to the ammonium sulfate solution with an addition 135 ppm sodium thiocyanate and 100 ppm thiosemicarbazide received the following results.

The example shows that the simultaneous addition of thiocyanate and thiosemicarbazide to a substantial improvement of Current yields in the electrochemical oxidation leads. lowers If you lower the temperature to +20 to + 21 ° C, then the increase Current yields for peroxodisulfate recovery by 5 to 8%, while the current efficiency for the ammonium transfer by 2 to 3% sinks.

Example 3

In an electrolytic cell as in Example 1 is 20 wt .-% pure Sodium sulfate used in the anode compartment.

In the cathode compartment, aqueous 5 wt .-% sodium hydroxide solution as Leit electrolyte used. The electrolysis is at a pH of 6.2, a current density of 5 kA / m² and a cell voltage of 4.08 V and a temperature of +28 and + 30 ° C.  

The following results are obtained.

Electrolyzed the sodium sulfate solution with an addition of 500 ppm sodium thiocyanate in the electrolysis cell, we obtain depending on the electricity supply the following results.

From the example it is clear that the addition of thiocyanate the Current efficiency significantly increased.

Adding the sulfate solution additionally 200 ppm Thiosemicarbazid to, the following changes in the current yields result.

This shows that the current efficiency for the S₂O₈⁻⁻ formation almost doubled and additionally increased for Na⁺ carryover.  

If you increase the flow rate to 4.3 m / s at the Anode, the results change as follows.

When lowering the temperature to +15 to + 18 ° C results An increase in the current efficiency for the Peroxodisulfatbil from 5 to 6%, while the current efficiency for the sodium transfer by 4 to 5%.

Claims (17)

1. A process for the preparation of ammonia or alkali solutions and peroxodisulfates from ammonium or alkali sulfate electrolytes by electrolysis of ammonium or alkali sulfate in the anode compartment of a membrane by a cation exchanger split electrolysis cell with a smooth platinum anode, which has a high oxygen overvoltage, characterized in that sulphate-containing solutions or wastewaters in the presence of thiocyanates and / or rhodanic acid and / or dirhodane and thioamides and / or thio aldehydes and / or thiocarboxylic acids and / or thiocarboxylic esters and / or thioalkanols and / or thioketals and / or dithio compounds and / or nitrogen-containing heteroaromatics electrolyzed. 2. A process for the preparation of ammonia or alkali solutions and Peroxodisulfates according to claim 1, characterized in that as anode material smooth platinum sheet on titanium and / or Niobium and / or tantalum is used. 3. Process for the preparation of ammonia or alkali and Peroxodisulfates according to claims 1 and 2, characterized net, that neutral sulphate-containing solutions or wastewater electrolysed at temperatures up to + 45 ° C. 4. Process for the preparation of ammonia or caustic solutions and Peroxodisulfates according to Claims 1 to 3, characterized net, that 5- to 44gew .-% ammonium or ammonium sulfate containing solutions or sewage electrolyzed. 5. Process for the preparation of ammonia or caustic solutions and Peroxodisulfates according to Claims 1 to 4, characterized net, that as Thioamide thiosemicarbazide and / or thio formamide and / or thiourea used. 6. A process for the preparation of ammonia or alkali solutions and Peroxodisulfates according to claims 1 to 5, characterized net, that as thioaldehydes compounds of aldehydes and Hydrogen sulfide used.   7. A process for the preparation of ammonia or alkali and Peroxodisulfates according to Claims 1 to 6, characterized net, that as thiocarboxylic acids, thiocarboxylic esters, Thioalkanols or thioketals aliphatic C₁ to C₄ Ver used. 8. A process for the preparation of ammonia or alkali solutions and Peroxodisulfates according to claim 1 to 7, characterized gekennzeich net, that as Dithioverbindungen thiocarbonic acids and / or Dimercaproalkanol used. 9. Process for the preparation of ammonia or alkali solutions and peroxodisulfates according to claims 1 to 8, characterized characterized in that as the nitrogen-containing heteroaromatic pyridine and / or derivatives of pyridine and / or quinoline and / or Derivatives of quinoline and / or fused ring systems of the pyridine and / or pyrimidine and / or pyrimidine derivatives and / or pyridazine and / or pyridazine derivatives and / or Pyrazon and / or pyrazone derivatives and / or pyrazine and / or Pyrazine derivatives used. 10. A process for the preparation of ammonia or alkali solutions and Peroxodisulfates according to Claims 1 to 9, characterized net, that the sulphate-containing solutions or wastewater in Presence of sodium and / or potassium and / or ammonium thiocyanate and / or rhodanilic acid and thiosemicarba zid and / or thioformamide and / or thiourea electroly Siert. 11. A process for the preparation of ammonia or alkali solutions and Peroxodisulfates according to claims 1 to 10, characterized net, that the concentration of thiocyanate and / or Rhodan Hydrogenic acid and / or Dirhodan in the sulfate-containing Solutions or wastewater 3 to 2000 ppm, preferably 100 to 800 ppm and continuous during the electrolysis is supplemented. 12. A process for the preparation of ammonia or alkali solutions and Peroxodisulfates according to claims 1 to 11, characterized net, that the proportion of in claims 1 and 5 to 10 bean additives have 10 to 1000 ppm, preferably 50 to 500 ppm, in addition to the content of thiocyanate and / or rhodan Hydrogenic acid and / or dirhodan is and during the Electrolysis is continuously supplemented.   13. A process for the preparation of ammonia or alkali and Peroxodisulfates according to claims 1 to 12, characterized records that the cathode compartment of the electrolytic cell or the electrolysis cell cascade aqueous 0.25 to 25gew .-% Ammonia solution or alkali solution supplied as a conducting electrolyte becomes. 14. A process for the preparation of ammonia or alkali solutions and Peroxodisulfates according to claims 1 to 13, characterized net, that the effluent concentration of the ammonia solution or the Alkali solution from the cathode compartment of the electrolysis cell or Electrolysis cell cascade 8 to 30 wt .-% is. 15. A process for the preparation of ammonia or alkali and Peroxodisulfates according to claims 1 to 14, characterized net, that the current density in the electrolysis 1 to 8 kA / m² is. 16. A process for the preparation of ammonia or alkali solutions and Peroxodisulfates according to Claims 1 to 15, characterized net, that the electrolysis cells are switched as a cascade, wherein in the last cell the additives for electrolysis the sulfate solution are eliminated by anodic oxidation. 17. A process for the preparation of ammonia or alkali solutions and Peroxodisulfates according to claims 1 to 16, characterized net, that in the anode space, the flow rate 1 to 8 m / s, preferably 2 to 4 m / s.