Chromium(III) Oxide Process via Ammonia Reduction
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Solution Overview
Problem
Current methods for producing chromium(III) oxide often result in high sulfur and alkali metal content, by-product formation, and complex purification processes, making them unsuitable for metallurgical applications and economically inefficient.
Innovation Solution
A process involving the reaction of sodium monochromate with gaseous ammonia at 200-800°C, followed by hydrolysis, pH reduction, isolation, and calcination at 700-1400°C to produce chromium(III) oxide with low sulfur and alkali metal content, minimizing by-product formation and simplifying purification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If reducing agents (carbon, organic compounds, hydrogen) are used to reduce alkali metal chromates, then chromium(III) oxide can be produced, but high carbon content and by-products are formed making the product unsuitable for metallurgical use
Solution Approach 1:
The patent extracts and eliminates the reducing agent step from the process. Instead of using carbon, organic compounds, or hydrogen to reduce chromates, the invention directly converts chromates to chromium(III) oxide through a specific chemical reaction with ammonium chloride, thereby removing the source of carbon contamination and by-products
Solution Approach 2:
The patent changes the chemical reaction parameters by using ammonium chloride as a reagent instead of traditional reducing agents. This parameter change in the chemical process allows for the formation of high-purity chromium(III) oxide without the carbon content and by-products associated with conventional reduction methods
2Manufacturing precision
If ammonium chloride is used in calcination to form chromium(III) oxide, then chromium(III) oxide can be produced, but ammonia and HCl sublime and enter exhaust air
Solution Approach 1:
The patent converts the potentially harmful sublimation of ammonium chloride into a beneficial process step. The sublimation and decomposition of ammonium chloride during calcination is harnessed to facilitate the formation of high-purity chromium(III) oxide, while the resulting gases are managed through controlled process conditions
3Manufacturing precision
If sodium dichromate is reacted with ammonium sulfate to form ammonium dichromate, then chromium(III) oxide can be produced, but sulfur is introduced making the product unsuitable for low-sulphur applications
Solution Approach 1:
The patent extracts and eliminates sulfur from the process by replacing ammonium sulfate with ammonium chloride as the reagent. This substitution removes the sulfur source that would otherwise be introduced into the chromium(III) oxide product, enabling production of low-sulphur grade material
4Manufacturing precision
If high temperatures above 700°C are used for calcination, then chromium(III) oxide content increases, but slag formation occurs in the furnace
Solution Approach 1:
The patent optimizes the calcination temperature parameter to a specific range (700-850°C) that balances chromium(III) oxide formation with prevention of slag formation. This parameter optimization allows high oxide content while avoiding the harmful effects of excessive temperature
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The process yields high-purity chromium(III) oxide with low sulfur and alkali metal content, suitable for metallurgical uses and pigment applications, improving yield and reducing operational complexities compared to prior art methods.
Implementation Method 1
reaction of sodium monochromate with gaseous ammonia
Implementation Method 2
followed by hydrolysis
Implementation Method 3
calcination of the hydrolysis product obtained in step c) at a temperature of from 700 to 1400° C.
Implementation Method 4
The thermal decomposition of pure ammonium dichromate, on the other hand, leads to no significant inevitable formation of a by-product
Data Source
AI summary
Process for preparing chromium(III) oxide, which comprises the steps:a) reaction of sodium monochromate with gaseous ammonia, in particular at a temperature of from 200 to 800° C.,b) hydrolysis of the reaction product obtained in step a) with the pH of the water for the hydrolysis being reduced before the hydrolysis or that of the alkaline mother liquor being reduced during or after the hydrolysis, to a value of from 4 to 11, preferably from 5 to 10, by means of an acid,c) isolation of the hydrolysis product which has precipitated in step b), preferably at a pH of from 4 to 11, in particular from 5 to 10, and optionally washing and optionally drying andd) calcination of the hydrolysis product obtained in step c) at a temperature of from 700 to 1400° C., in particular from 800 to 1300° C.