GB1560132A

GB1560132A - Process for the production of ferrocyanide blue

Info

Publication number: GB1560132A
Application number: GB3450777A
Authority: GB
Original assignee: Degussa GmbH; Deutsche Gold und Silber Scheideanstalt
Current assignee: Evonik Operations GmbH
Priority date: 1976-08-25
Filing date: 1977-08-17
Publication date: 1980-01-30
Also published as: JPS5326800A; ES460529A1; DE2638228A1; NL183408B; NL183408C; NL7707439A; JPS5747128B2; FR2362903B2; FR2362903A2; DE2638228C2; BE858075A

Description

(54) A PROCESS FOR THE PRODUCTION OF FERROCYANIDE BLUE (71) We, DEUTSCHE GOLD-UND SILBER-SCHEIDEANSTALT VORMALS ROESSLER a body corporate organised under the laws of Germany of 9 Weissfrauenstrasse, 6 Frankfurt Main 1, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to a process for the production of ferrocyanide blue.

Our prior patent application No. 53320/74 (Serial No. 1,491,697), referred to herein as the parent patent, relates to a process for the production of ferrocyanide blue which comprises simultaneously introducing into water an aqueous solution containing ferrocyanide ions and an aqueous ferrous salt solution, provision being made for optimum mixing (as defined in the parent patent) during precipitation, after which the precipitate formed (white paste) is aged in the reaction medium itself at elevated temperature in the presence of salts produced during the reaction and is subsequently converted into ferrocyanide blue by oxidation in acid medium. The ferrocyanide blue is produced in the form of extremely uniform, substantially spherical and substantially non-agglomerated particles.

Further development of this process has now shown that the quantity of potassium salts added during or after precipitation of the white paste can amount to less than 1 mole down to 0.2 mole or to more than 3 moles up to 5 moles, based on 1 mole of ferrocyanide.

These quantities of potassium salts are used for the calcium and sodium ferrocyanides mentioned in the parent patent.

Accordingly, the present application relates to a process for the production of ferrocyanide blue which comprises simultaneously introducing into water an aqueous solution of calcium and/or sodium ferrocyanide and an aqueous ferrous salt solution, provision being made for optimum mixing (as hereinbefore defined) during precipitation, adding at least one potassium salt after the precipitation, the quantity of potassium salt amounting to less than 1 mol down to 0.2 mol or to more than 3 moles up to 5 moles based on 1 mol of the ferrocyanide, aging the precipitate formed (white paste) in the reaction medium itself at elevated temperature in the presence of the salts produced during the reaction and subsequently converting the aged precipitate into ferrocyanide blue by oxidation in acid medium.

As used herein, the term "optimum mixing" means that the reactants are stirred with an intensity which. is not high enough to damage the precipitated product.

All the disclosures made in the parent patent relating to the way in which the process is carried out, including testing of the tinting strength, also apply to the present further development.

On the one hand, it was not foreseeable that, by using very small quantities of potassium, there would no longer be any need to use ammonium ions in order to provide the ferrocyanide blue with equally high tinting strength (105%), see Example 1, and this under conditions that are very favourable to the environment because no ammonium ions are added. On the other hand, the larger quantities of potassium salts, i.e. the quantities amounting to more than 3 moles, impart a very high tinting strength (135%), see Example 2, without any change in the other pigment properties, such as dispersibility, reactivity and flow behaviour. Instead of a tinting strength of 120%, a tinting strength of 135% is obtained, see Example 2 in comparison with Example 4 of the parent application.

The invention is illustrated by the following Examples: EXAMPLE I The following solutions are simultaneously introduced with stirring through ring pipes provided with bores into 2000 cc of water at 20"C over a precipitation time of 1 hour: 3500 cc of potassium-sodium-hexacyanoferrate-II- solution containing: 435 g of Na4[Fe(CN)6] . 10 H2O 380 g of K4[Fe(CN)6] . 3 HzO pH-value 4.5 (adjusted by the addition of dilute H2SO4) temperature 20"C 5000 cc of ferrous sulphate solution containing: 670 g of FeSO4 .7 7 H20 pH-value 2.5 temperature 20"C.

The same excess of ferrous sulphate, namely 3 g of FeSO4 7H2O per litre of alkali metal ferro-ferrocyanide, is present throughout the entire duration of the precipitation process.

The excess of ferrous sulphate is determined by titrating a filtrate sample with N/ 10 KMnO.

The alkali metal ferro-ferrocyanide is then aged in an autoclave for 1.5 hours at 1 100C/0.5 atm gauge in the presence of 50 g of K2SO4 (salt or solution).

Oxidation into alkali metal ferri-ferrocyanide (ferrocyanide blue) is obtained by adding 860 cc of hydrochloric acid (concentration 110 g/ 1 of HC1) and 44 g of sodium chlorate at a temperature of 65"C. The relative tinting strength amounts to 105%.

EXAMPLE 2 The following solutions are simultaneously introduced with stirring through ring pipes provided with bores into 2000 cc of water at 20"C over a precipitation time of 1 hour: 3240 cc of calcium hexacyanoferrate-II-solution containing: 890 g of Ca2[Fe(CN)6] 12 H2O+275 g of Cay12 pH-value 10 temperature 20 C 5000 cc of ferrous chloride solution containing: 730 g ofFeCI2 .4 4 H20 pH-value 1.5 temperature "C.

The same excess of ferrous chloride, namely 2.5 g of FeCI2 .4 4 H2O per litre of ferro- ferrocyanide, is present throughout the entire duration of the precipitation process. The excess of ferrous chloride is determined by titrating a filtrate sample with N/10 KMnO4.

The ferro-ferrocyanide is then aged for 1 hour at 960C in the presence of 650 g of KCl (salt or solution) and is thus converted into alkali metal ferro-ferrocyanide.

Oxidation into alkali metal ferri-ferrocyanide (ferrocyanide blue) is obtained by adding 1140 cc of hydrochloric acid (concentration 110 g/ 1) and 70 g of NaC 103 at a temperature of 65"C. The relative tinting strength amounts to 135%.

WHAT WE CLAIM IS: 1. A process for the production of ferrocyanide blue which comprises simultaneously introducing into water an aqueous solution of calcium and/or sodium ferrocyanide and an aqueous ferrous salt solution, provision being made for optimum mixing (as hereinbefore defined) during precipitation, adding at least one potassium salt after the precipitation, the quantity of potassium salt amounting to less than 1 mol down to 0.2 mol or to more than 3 moles up to 5 moles based on 1 mol of the ferrocyanide, aging the precipitate formed (white paste) in the reaction medium itself at elevated temperature in the presence of the salts produced during the reaction and subsequently converting the aged precipitate into ferrocyanide blue by oxidation in acid medium.

2. A process for the production of ferrocyanide blue substantially as herein described with particular reference to either of the Examples.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

EXAMPLE I The following solutions are simultaneously introduced with stirring through ring pipes provided with bores into 2000 cc of water at 20"C over a precipitation time of 1 hour: 3500 cc of potassium-sodium-hexacyanoferrate-II- solution containing:

435 g of Na4[Fe(CN)6] . 10 H2O

380 g of K4[Fe(CN)6] . 3 HzO pH-value 4.5 (adjusted by the addition of dilute H2SO4) temperature 20"C 5000 cc of ferrous sulphate solution containing: 670 g of FeSO4 .7 7 H20 pH-value 2.5 temperature 20"C.

The same excess of ferrous sulphate, namely 3 g of FeSO4 7H2O per litre of alkali metal ferro-ferrocyanide, is present throughout the entire duration of the precipitation process.

The excess of ferrous sulphate is determined by titrating a filtrate sample with N/ 10 KMnO.

The alkali metal ferro-ferrocyanide is then aged in an autoclave for 1.5 hours at 1 100C/0.5 atm gauge in the presence of 50 g of K2SO4 (salt or solution).

Oxidation into alkali metal ferri-ferrocyanide (ferrocyanide blue) is obtained by adding 860 cc of hydrochloric acid (concentration 110 g/ 1 of HC1) and 44 g of sodium chlorate at a temperature of 65"C. The relative tinting strength amounts to 105%.

EXAMPLE 2 The following solutions are simultaneously introduced with stirring through ring pipes provided with bores into 2000 cc of water at 20"C over a precipitation time of 1 hour: 3240 cc of calcium hexacyanoferrate-II-solution containing:

890 g of Ca2[Fe(CN)6] 12 H2O+275 g of Cay12 pH-value 10 temperature 20 C 5000 cc of ferrous chloride solution containing: 730 g ofFeCI2 .4 4 H20 pH-value 1.5 temperature "C.

The same excess of ferrous chloride, namely 2.5 g of FeCI2 .4 4 H2O per litre of ferro- ferrocyanide, is present throughout the entire duration of the precipitation process. The excess of ferrous chloride is determined by titrating a filtrate sample with N/10 KMnO4.

The ferro-ferrocyanide is then aged for 1 hour at 960C in the presence of 650 g of KCl (salt or solution) and is thus converted into alkali metal ferro-ferrocyanide.

Oxidation into alkali metal ferri-ferrocyanide (ferrocyanide blue) is obtained by adding 1140 cc of hydrochloric acid (concentration 110 g/ 1) and 70 g of NaC 103 at a temperature of 65"C. The relative tinting strength amounts to 135%.

WHAT WE CLAIM IS: 1. A process for the production of ferrocyanide blue which comprises simultaneously introducing into water an aqueous solution of calcium and/or sodium ferrocyanide and an aqueous ferrous salt solution, provision being made for optimum mixing (as hereinbefore defined) during precipitation, adding at least one potassium salt after the precipitation, the quantity of potassium salt amounting to less than 1 mol down to 0.2 mol or to more than 3 moles up to 5 moles based on 1 mol of the ferrocyanide, aging the precipitate formed (white paste) in the reaction medium itself at elevated temperature in the presence of the salts produced during the reaction and subsequently converting the aged precipitate into ferrocyanide blue by oxidation in acid medium.
2. A process for the production of ferrocyanide blue substantially as herein described with particular reference to either of the Examples.