초록 ▼

The present invention relates to an improved process for producing red iron oxide pigments by the Penniman process with nitrate (also called nitrate process or direct red process) and to apparatus for implementing this process, and also to the use of the plant for producing red iron oxide pigments b

The present invention relates to an improved process for producing red iron oxide pigments by the Penniman process with nitrate (also called nitrate process or direct red process) and to apparatus for implementing this process, and also to the use of the plant for producing red iron oxide pigments by the Penniman process with nitrate.

대표청구항 ▼

1. A process for producing red iron oxide pigments, the process comprising: a) contacting iron and nitric acid to produce; an iron(II) nitrate solution comprising nitrogen-containing byproducts, anda first nitrogen oxide-containing stream comprising nitrous gases and dinitrogen monoxide,b) contactin

1. A process for producing red iron oxide pigments, the process comprising: a) contacting iron and nitric acid to produce; an iron(II) nitrate solution comprising nitrogen-containing byproducts, anda first nitrogen oxide-containing stream comprising nitrous gases and dinitrogen monoxide,b) contacting iron and nitric acid to produce; an aqueous haematite nucleus suspension comprising nitrogen-containing byproducts, anda second nitrogen oxide-containing stream comprising nitrous gases and dinitrogen monoxide,c) contacting the aqueous haematite nucleus suspension from step b) with the iron(l) nitrate solution from step a) in the presence of at least one of: I. at least one alkaline precipitant in the presence of at least one oxygen-containing gas, andII. in the presence of at least one oxygen-containing gas,to produce:a third nitrogen oxide-containing stream comprising nitrous gases and dinitrogen monoxide, andan aqueous suspension comprising red haematite pigment and nitrogen-containing byproducts comprising nitrate compounds, nitrite compounds, and ammonium compounds,d) separating the red haematite pigment from the aqueous suspension to leave an aqueous phase comprising the nitrogen containing components,e) oxidizing the second nitrogen oxide-containing stream from step b) to produce an oxidized second nitrogen oxide-containing stream,f) contacting the first nitrogen oxide-containing stream and/or the third nitrogen oxide-containing stream and/or the oxidized second nitrogen oxide-containing stream from step e) with an aqueous wash phase to produce: a prepurified gas stream comprising nitrous gases and dinitrogen monoxide, anda wash phase enriched with nitric acid, andg) heating the prepurified gas stream from step f) to a temperature of 200 to 1400° C., to remove dinitrogen monoxide and/or nitrous gases from the gas stream and produce a purified gas stream. 2. The process for producing red iron oxide pigments according to claim 1, further comprising: h) removing at least ammonium compounds and/or nitrite compounds and/or nitrate compounds from the aqueous phase from step d) to produce a purified wastewater. 3. The process for producing red iron oxide pigments according to claim 1, further comprising one or more of: i) returning the nitric acid-enriched wash phase formed in step f) to step a), b) and/or c), andj) utilizing the heated purified gas stream from step g) to preheat the prepurified gas stream from step f) to form a preheated, prepurified gas stream and a cooled, purified waste gas. 4. The process for producing red iron oxide pigments according to claim 1, wherein: step a) further comprises reacting 0.4 to 10 mol of the iron per mol of the nitric acid at a temperature of 60° C. or less to produce the iron(II) nitrate solution; andstep b) further comprises reacting the iron and nitric acid such that a reaction temperature on exposure of the iron to the nitric acid is at least 90° C. 5. The process for producing red iron oxide pigments according to claim 4, wherein: the temperature in step a) is 10 to 60° C., and step a) further comprises separating any unreacted iron from the prepared iron(II) nitrate solution; andthe reaction temperature on exposure of the iron to the nitric add in step b) is 90 to 99° C., and step b) further comprises separating any unreacted iron from the prepared aqueous haematite nucleus suspension. 6. The process for producing red iron oxide pigments according to claim 1, wherein step b) further comprises: adding the nitric acid to a mixture of the iron and water having a temperature from 60 to 120° C., where haematite nuclei present in the aqueous haematite nucleus suspension have a particle size of less than or equal to 100 nm and a specific BET surface area of 40 m2/g to 150 m2/g, measured according to DIN 66131. 7. The process for producing red iron oxide pigments according to claim 6, wherein: dilute nitric acid is added to the mixture of iron and water at a rate of addition sufficient to heat the reaction mixture by at least 15° C. within less than 120 minutes after the end of the addition of nitric acid, andthe process further comprises separating any unreacted iron from the aqueous haematite nucleus suspension. 8. The process for producing red iron oxide pigments according to claim 1, wherein: variant I. of step c) further comprises contacting the aqueous haematite nucleus suspension with the iron(II) nitrate solution and the alkaline precipitant in the presence of the at least one oxygen-containing gas at a temperature of 70 to 100° C., wherein the iron(II) nitrate solution from step a) and the at least one alkaline precipitant are metered in to the haematite nucleus suspension to form a reaction mixture, and the reaction mixture Is oxidized with the at least one oxygen-containing gas until the red haematite pigment achieves a desired color shade; andvariant II. of step c) further comprises contacting the haematite nucleus suspension with the iron and the iron(II) nitrate solution at a temperatures of 70 to 100° C. to produce a reaction mixture, and oxidizing the reaction mixture with the at least one oxygen-containing gas, until the red haematite pigment achieves the desired color shade. 9. The process for producing red iron oxide pigments according to claim 1, wherein: variant I. of step c) further comprises contacting the aqueous haematite nucleus suspension with the iron(II) nitrate solution and the alkaline precipitant in the presence of the at least one oxygen-containing gas at a temperature of 75 to 90° C., wherein the iron(II) nitrate solution from step a) and the at least one alkaline precipitant are metered in to the haematite nucleus suspension to form a reaction mixture, the at least one oxygen containing gas is air, and the reaction mixture is oxidized with the air, at a rate of 0.2 to 100 liters of the air, per hour and per liter of suspension, until the red haematite pigment achieves a desired color shade; andvariant II. of step c) further comprises contacting the haematite nucleus suspension with the iron and the iron(II) nitrate solution at a temperature of 75 to 90° C. to produce a reaction mixture, the at least one oxygen containing gas is air, and oxidizing the reaction mixture with 0.2 to 100 liters of the air, per hour and per liter of suspension, until the red haematite pigment achieves a desired color shade. 10. The process for producing red iron oxide pigments according to claim 1, wherein step d) further comprises: separation of the haematite pigment-from the suspension by at least one of filtration, sedimentation, and centrifugation to produce a filtercake,washing of the filtercake and subsequent drying of the filtercake, andone or more screening steps with different mesh sizes and with descending mesh sizes, carried out optionally before the red haematite pigment is isolated from the aqueous phase. 11. The process for producing red iron oxide pigments according to claim 10, wherein step d) further comprises adding at least one sulphate salt, and/or an alkali metal sulphate or alkaline earth metal sulphate to the haematite pigment suspension during or before the screening and/or during or before the separation. 12. The process for producing red iron oxide pigments according to claim 1, wherein step e) further comprises contacting the second nitrogen oxide-containing stream from step b) with at least one oxidizing agent, optionally in the presence of one or more catalysts and/or of high-energy radiation. 13. The process for producing red iron oxide pigments according to claim 1, wherein step e) further comprises contacting the second nitrogen oxide-containing stream from step b) with at least one oxidizing agent selected from the group consisting of air, oxygen, ozone and hydrogen peroxide in the presence of one or more catalysts and/or UV radiation. 14. The process for producing red iron oxide pigments according to claim 1, wherein: the second nitrogen oxide-containing stream from step b) contains from 1 to 2000 g/m3 of nitrous gases (calculated as g/m3 NO2) and/or from 0.5 to 2000 g/m3 of dinitrogen monoxide; andthe oxidized second nitrogen oxide-containing stream obtained after step f) contains not more than 50% of the original fraction of nitrogen monoxide present prior to step f). 15. The process for producing red iron oxide pigments according to claim 14, wherein the oxidized second nitrogen oxide-containing stream obtained after step f) contains less than 15% of the original fraction of nitrogen monoxide present prior to step f). 16. The process for producing red iron oxide pigments according to claim 1, wherein: step g) further comprises: Increasing the temperature of the prepurified gas stream obtained according to step f) first to 250 to 500° C. in the presence of a catalyst, and subsequently to 800 to 1400° C. in the absence of a catalyst; contacting the prepurified gas stream from step f) with ammonia or with a chemical compound that breaks down to give ammonia, in the presence of one or more catalysts, which may optionally be disposed on a support, andthe purified waste gas has a concentration of 0.001 to 0.3 g/m3 of nitrous gases (calculated as NO2), and/or 0.001 to 0.3 g/m3 dinitrogen monoxide. 17. The process for producing red iron oxide pigments according to claim 2, wherein step h) further comprises removing ammonium compounds, nitrate compounds, nitrite compounds, iron-containing compounds and/or sulphur-containing compounds from the aqueous phase from step d) by at least one of oxidative precipitation, denitrification, coagulation, flocculation, sedimentation, filtration, ultrafiltration, and reverse osmosis. 18. The process for producing red iron oxide pigments according to claim 11, wherein: step c) and/or step d) is carried out in the presence of sulphate salts,the process further comprises removing of at least ammonium compounds and/or nitrite compounds and/or nitrate compounds from the aqueous phase from step d to produce a salt-enriched wastewater, andthe salt-enriched wastewater is recycled back into step c) and/or step d). 19. Apparatus for producing the red iron oxide pigments according to the process of claim 1, the apparatus comprising: a first reactor configured for contacting the iron and the nitric acid to produce the iron(II) nitrate solution and first nitrogen oxide-containing stream of step a),a second reactor configured for contacting the iron and the nitric acid to produce aqueous haematite nucleus suspension and the second nitrogen oxide-containing stream of step b),a third reactor configured for receiving the aqueous haematite nucleus suspension from step b) and the iron(II) nitrate solution from step a) and contacting the aqueous haematite nucleus suspension and the iron(II) nitrate solution with at least one of: I. at least one alkaline precipitant in the presence of at least one oxygen-containing gas, andII. iron in the presence of at least one oxygen-containing gas,to produce the third nitrogen oxide-containing stream and the aqueous suspension of red haematite pigment of step c),at least one scrubber in communication with: (a) the first reactor via at least one first fluid line for receiving the first nitrogen oxide-containing stream of step a),(b) the third reactor via at least one third fluid line for receiving the third nitrogen oxide-containing stream of step c), and(c) the second reactor via at least one second fluid line in conjunction with at least one oxidizing unit, wherein the at least one oxidizing unit receives the second nitrogen oxide-containing stream of step b), and oxidizes the stream to produce the oxidized second nitrogen oxide-containing stream of step e), and the scrubber receives the oxidized second nitrogen oxide-containing stream,for washing the first, second and third streams with the aqueous wash phase to produce the prepurified gas stream and the wash phase enriched with nitric acid of step f), anda waste gas purifying unit in communication with the scrubber for receiving the prepurified gas stream from the scrubber, the waste gas purifying unit comprising a heater for heating the prepurified gas stream from step f) to the temperature of 200 to 1400° C., wherein the waste gas purifying unit removes the dinitrogen monoxide and/or nitrous gases from the gas stream to produce the purified gas stream. 20. The apparatus according to claim 19, further comprising: at least one separation device in communication with the third reactor for receiving the aqueous haematite pigment suspension and separating the red hematite pigment from the aqueous haematite pigment suspension;at least one wastewater purifying unit in communication with the third reactor and/or with the at least one separation device for receiving the aqueous phase of the suspension and removing at least ammonium compounds and/or nitrite compounds and/or nitrate compounds from the aqueous phase to produce purified wastewater; andat least one heat exchanger in communication with at least the scrubber and the waste gas purifying unit for exchanging heat from the heated purified gas stream exiting the waste gas purifying unit with the prepurified gas stream from the scrubber to preheat the prepurified gas stream and cool the purified gas stream.