Classifications

• • 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

Definitions

• the invention relates to a process for the preparation of blue iron hexacyanoferrate III pigments and the pigments obtained by the process.
• Blue iron hexacyanoferrate III pigments (C.I. Pigment Blue 27; C.I. No. 77510) are commercially available under various names such as Prussian Blue, Berlin Blue, Milori Blue or Iron Blue.
• These blue pigments are formed by oxidizing complex iron (II) hexacyanoferrate (II) compounds, also known as Berlin's white or white dough (II), with oxidizing agents in dilute acids such as chlorate / hydrochloric acid, dichromate or air in dilute sulfuric acid (pH ⁇ 0 , 5) received.
• II complex iron
• II hexacyanoferrate
• dilute acids such as chlorate / hydrochloric acid, dichromate or air in dilute sulfuric acid (pH ⁇ 0 , 5) received.
• the chemical composition of the white dough (II) and the blue iron hexacyanoferrate III pigments (I) is complex and, within certain limits, also depends on the manufacturing process.
• II becomes by the (simplified) formula and the blue pigments through reproduced, wherein Me is an alkali metal cation, preferably potassium or sodium ion, an ammonium, or a mixture of these cations.
• the iron (II) cyanoferrate (II) is prepared by precipitating iron (II) salts with complex alkali metal hexacyanoferrates (II) in aqueous solution.
• iron (II) salts with complex alkali metal hexacyanoferrates (II) in aqueous solution.
• alkali metal salts are obtained per part by weight of "white dough" (II), which are a considerable burden on the waste water.
• Another disadvantage of the prior art method is that before oxidation to I, the salts contained in (II) have to be washed out, which is very time consuming.
• the white dough is prepared by reacting freshly precipitated iron (II) hydroxide with hydrogen cyanide in an alkaline medium or by reacting iron (II) salts with hydrogen cyanide with the addition of alkali metal hydroxide or ammonia at pH) 4.
• the object of the present invention was to develop a technically inexpensive and environmentally friendly process for the production of blue iron hexacyanoferrate III pigments.
• blue iron hexacyanoferrate III pigments can be obtained by oxidation of complex iron II cyan compounds of the formula II if the complex iron II hexacyanoferrate II compound is obtained by anodic oxidation of metallic iron in hydrogen cyanide as the reaction medium or in a reaction medium containing hydrogen cyanide at pH ⁇ 7 and an anode potential - measured against the hydrogen normal electrode - of ⁇ 0.76V.
• the complex iron-II-cyan compound (II) is obtained in high yield and high purity by the process according to the present invention.
• the process according to the invention is very environmentally friendly since there are practically no by-products or by-products due to the reaction. It was surprising that the anodic oxidation, i.e. by electrochemical reaction of iron with hydrogen cyanide in an acidic reaction medium (electrolyte) the complex iron-II-cyano compound (II) is formed practically quantitatively. In contrast, the complexes (II) are obtained by the process of the prior art only in an alkaline medium at pH> 8.
• reaction medium - also referred to as an electrolyte - is introduced into an electrolysis cell with an iron anode and an iron or chromium-nickel-steel cathode and the electrolysis is measured at the desired temperature at an anode potential against the normal hydrogen electrode - performed by ⁇ 0.76 V.
• the process can be carried out batchwise or continuously.
• the electrolyte will be circulated in the cell.
• the filtrate can be used again as an electrolyte after the used parts have been added.
• the electrolyte in the cells will be circulated and continuously removed Separate the iron (II) cyano compound (II) formed from part of the electrolyte. After the used components have been added, the filtrate is continuously returned to the system.
• the isolated (II) can then be oxidized to MeFe [Fe (CN) 6 ] pigments (I) in a manner known per se.
• the iron-II complex can also be oxidized directly in the electrolyte, which offers advantages in terms of technical implementation.
• the reaction medium for the electrolysis are hydrogen cyanide and its mixtures with C 1 to C 4 alkanols with primary, secondary or tertiary hydroxyl group, C 2 to C 6 alkane diols, diethylene glycol, triethylene glycol, dipropylene glycol, C 3 to C 6 alkane polyols , Water or with mixtures of these liquids.
• the reaction medium is preferably a mixture of hydrogen cyanide and water.
• the hydrogen cyanide content in the electrolyte can be between 100 and 0.001% by weight.
• Conductive salts are advantageously added to the electrolyte in order to improve the conductivity and to dope the iron (II) cyano compounds (II).
• the conductive salts there are those of the prior art which are soluble in at least the required concentration in the electrolytes mentioned.
• the amount of the conductive salts is generally 0.1 to 10% by weight, based on the electrolyte.
• Possible conductive salts are, for example: salts of alkali metals, alkaline earth metals, earth metals and rare earths, such as salts of lithium, sodium, potassium, rubidium, magnesium, calcium, strontium, aluminum, cerium, and also salts of metals of the iron group and ammonium.
• Suitable anions are e.g. Chloride, sulfate, hydrogen sulfate, mono- and dihydrogen phosphate, hydrogen sulfite, cyanide, the hexacyanoferrates, hydrogen oxalate, oxalate, maleate and fumarate.
• Ammonium and potassium salts are preferred as conductive salts.
• Ammonium chloride, ammonium hydrogen oxalate, potassium chloride, potassium hydrogen sulfate, potassium hydrogen sulfite and potassium hydrogen oxalate are particularly preferred as conductive salts, since iron-II-cyano complexes (II) are obtained in the presence of these conductive salts, which give oxidation forms to (I) which are particularly strongly colored pigment forms with a reddish blue color give high gloss.
• the electrochemical reaction in which iron is anodically oxidized and hydrogen is deposited on the cathode, can be carried out at temperatures of from -20 ° C. to 150 ° C., if appropriate under pressure.
• the reaction is preferably carried out without pressure at temperatures from -5 to + 20 ° C. If you work at temperatures> 20 ° C, the reaction must be carried out under pressure because of the low boiling point of the hydrogen cyanide.
• the electrolysis will be carried out at normal pressure, in particular at temperatures from 10 to 20 ° C.
• the electrolysis is preferably carried out in the pH range from 1 to 6, in particular in the pH range from 2 to 5.
• the current density is usually 30 to 5000 A / m2. It is advantageous to work at current densities of 200 to 2000 A / m 2 in order to ensure current yields of approximately 95% and above. At current densities> 2000 A / m 2 , a very good mass transfer must be ensured so that there is no depletion of cyanide ions in the anode boundary layer and thus a decrease in the current efficiency. Current densities of ⁇ 30 Alm 2 require a higher concentration of hydrogen cyanide to ensure the complexation of the anodized iron.
• the anodes on which the reaction to (II) takes place are fluidized bed or fluidized bed anodes, e.g. from pieces of iron, iron granules or iron shavings on an electrically conductive base or compact iron anodes in the form of rods, blocks or sheets or iron oxide anodes.
• the anode material (iron) is separated from the cathode compartment by diaphragms or anodically resistant screens or nets made of metal or plastic.
• the electrical contacting of fluidized bed and fluidized bed anodes with the power source can take place when using metal sieves via the sieve or via anodic, stable metal or carbon rods inserted into the filling.
• the cathode for reducing the hydrogen overvoltage on the surface is e.g. with nickel-aluminum-zinc alloys, with nickel, cobalt, molybdenum, molybdenum-iron alloys, with tungsten, with tungsten-iron-nickel alloys or iron - cobalt alloys (iron content in each case 65 to 95% by weight; DE- OS 30 03 819 (P 30 03 819.8)). coated with vanadium, vanadium alloys or sulfides of molybdenum, tungsten, nickel or cobalt.
• the electrolysis cells are preferably cells with compact iron anodes in the form of rods or plates.
• the distance between the anode and cathode is preferably 2 to 10, in particular 3 to 6 mm.
• Process product (II) can be separated and isolated from the electrolytes by filtering, centrifuging or decanting.
• filter aids are advantageously added to the reaction mixture beforehand, as a result of which the filtration time can be shortened considerably. After the missing components have been added, the filtrate can be used again as an electrolyte.
• the oxidation of the complex iron (II) cyano compound (II) takes place in a manner known per se, e.g. in aqueous suspension at pH ⁇ 6 with chlorate, chlorine or hydrogen peroxide. 1
• the white dough II obtained by the process according to the invention is preferably oxidized in aqueous sulfuric acid suspension at pH 0 to 3 and at temperatures between 70 and 95 ° C. with air or oxygen. Under these conditions, very strong, grain-soft and reddish pigments I are obtained which are very easily dispersible and give very brilliant colors.
• the oxidation is preferably carried out at temperatures between 75 and 85 ° C.
• the air or oxygen is stirred into the suspension and finely distributed or injected via a jet nozzle.
• the oxidation can also take place in a column into which air or oxygen is injected in a fine distribution below.
• the redox potential of the suspension is advantageously checked during the oxidation from II to I in order to avoid overoxidation.
• the oxidation can be regarded as complete when 95 to 99% of the iron (II) cyano compound I have been oxidized.
• the filtrate from (I) can be reused as an electrolyte after the missing components have been added.
• Very fine-particle pigments I which are well dispersible in water, are obtained by oxidation of II with air or oxygen at pH> 8 and temperatures of 20 to 50 ° C. The oxidation can be monitored by measuring the redox potential will. After the oxidation has ended, the reaction mixture is acidified and the pigment is isolated. To improve the dispersibility in water, small amounts (ie 0.01 to 0.2% by weight, based on (I)) of polyols, such as diethylene glycol, triethylene glycol or glycerol, are added to the reaction mixture.
• polyols such as diethylene glycol, triethylene glycol or glycerol
• the iron-II complex (II) can be anodically oxidized both in the acidic and in the alkaline range.
• the invention is illustrated by the following examples.
• the percentages relate to the weight.
• the specified potentials were measured against the hydrogen standard electrode.
• the electrolyte is a solution of 97% water, 2% hydrogen cyanide and 1% potassium hydrogen sulfate.
• electrolysis is carried out until the hydrogen cyanide concentration in the electrolyte is 0.05%.
• the white dough suspension obtained is then adjusted to pH 1.5 with sulfuric acid and oxidized by gassing with atmospheric oxygen at 88 ° C. (duration: approx. 3 h).
• the MeFe [Fe (CN) 6 ] (Berlin blue) formed during the oxidation is filtered off and washed neutral with water.
• the filter cake is then dried at 120 ° C.
• the yield is ⁇ 97% pigment, based on the hydrogen cyanide used.
• the pigment gives purer, redder and improved shades than products which are obtained by the process of the prior art from iron (II) salt and sodium or potassium cyanoferrate (II).
• Example 1 In the electrolysis cell specified in Example 1, a solution of 93% water, 5% hydrogen cyanide and 2% potassium chloride is introduced as the electrolyte. At a current density of 1500 A / m 2 , a cell voltage of 2.0 V, a flow rate of 1.5 m / sec and an anode potential of ⁇ -0.2 V (measured against the hydrogen normal electrode), electrolysis is carried out until the Hydrogen cyanide concentration in the electrolyte is 0.04%.
• the white dough suspension obtained is then added 5 mg of Fe ++ in the form of FeSO 4 per liter of suspension and the pH is adjusted to 1.0 using sulfuric acid.
• the oxidation to the pigment and the work-up are carried out as in Example 1.
• a very granular pigment is obtained which, in comparison with the pigments of the prior art in the lacquer and in the printing ink, gives purer and redder colorations which are superior in gloss.
• the dyeings are approximately 19% stronger than the dyeings obtained with the strongest colored corresponding pigments on the market.
• Example 1 In the electrolysis cell specified in Example 1, a solution of 88% methanol ', 1.5% water, 10% hydrogen cyanide and 0.5% potassium chloride is introduced as the electrolyte. With a current density of 1200 A / m 2 , a cell voltage of 4.8 V, a flow rate of 1.8 m / sec and an anode potential of ⁇ -0.2 V (measured against the normal hydrogen electrode) is electrolyzed until the hydrogen cyanide concentration in the electrolyte is 0.02%. This suspension is separated off on a suction filter under nitrogen and the isolated white dough is introduced into so much water that an 8% suspension is formed.
• the aqueous suspension is adjusted to pH 1.0 with dilute sulfuric acid and, after addition of 0.15% potassium chlorate (based on the suspension), oxidized at 80 ° C. for 1 hour.
• the MeFe [Fe (CN) 6 ] pigment (Berlin blue) resulting from the oxidation is worked up as in Example 1.
• Example 2 It is electrolyzed as in Example 2, but the suspension obtained is filtered under nitrogen and the filter material is introduced into sufficient water to form a 5% suspension.
• the suspension is adjusted to pH 12 with aqueous 25% potassium hydroxide solution and oxidized with atmospheric oxygen at 30 ° C. (duration about 1 h). After the oxidation, the suspension is acidified to pH 1 with dilute sulfuric acid and the Berlin blue is worked up as in Example 1.
• a finely divided pigment is obtained which can be very easily dispersed in water after the addition of a little triethylene glycol.
• the electrolysis is stopped at a hydrogen cyanide content of 0.05%.
• the suspensions are oxidized at pH 1.5 and 80 ° C by gassing air (duration: approx. 3 h). After separation, washing and drying, pigments are obtained which give the paint good coverage. Depending on the alkaline earth or earth metal used, pigments are obtained which produce more or less greenish blue tints.

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• Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• Compounds Of Iron (AREA)
• Pigments, Carbon Blacks, Or Wood Stains (AREA)

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• 1981
  • 1981-04-04 DE DE19813113777 patent/DE3113777A1/de not_active Withdrawn
• 1982
  • 1982-03-24 US US06/361,431 patent/US4451339A/en not_active Expired - Fee Related
  • 1982-03-24 DE DE8282102445T patent/DE3261338D1/de not_active Expired
  • 1982-03-24 EP EP82102445A patent/EP0064154B1/fr not_active Expired
  • 1982-04-02 JP JP57053966A patent/JPS57179018A/ja active Pending

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