Nitric Acid Production via Integrated Reactor-Absorber
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The Ostwald process for producing nitric acid requires large absorption towers and is inefficient due to the diluteness of nitrous gases and temperature-dependent reaction rates, necessitating refrigerated cooling and subsequent bleaching to remove nitrogen dioxide impurities.
Innovation Solution
A process utilizing a gaseous oxidizer feed of ammonia, steam, and oxygen, where the reaction mixture is cooled in a heat exchanger to condense water vapor and oxidize nitrogen monoxide, achieving high conversion of nitrogen monoxide to nitric acid without the need for an absorption tower, producing dilute nitric acid that avoids bleaching requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a large absorption tower is used to facilitate reaction and absorption of nitrous gases, then conversion of nitrogen monoxide to nitric acid is improved, but device complexity and space requirements increase
Solution Approach 1:
The patent combines the reaction and absorption processes into a single integrated reactor-absorber vessel, eliminating the need for separate absorption towers. The reactor-absorber performs both the oxidation of nitrogen monoxide and the absorption of produced nitric acid simultaneously, reducing device complexity while maintaining high conversion efficiency
Solution Approach 2:
The patent changes the operating parameters by using elevated pressures (typically 5-20 atm) and optimized temperature profiles within the reactor-absorber. These parameter changes enhance the reaction rate and absorption efficiency, allowing high conversion without requiring large tower structures
2Reliability
If refrigerated cooling is provided within the absorption tower to prevent nitrogen oxide escape, then nitrogen oxide retention is improved, but energy consumption and device complexity increase
Solution Approach 1:
The reactor-absorber system uses the exothermic heat of reaction from the oxidation of nitrogen monoxide to maintain the temperature profile needed for efficient absorption. The system essentially uses its own reaction heat to drive the process, eliminating the need for external refrigeration while maintaining nitrogen oxide retention
Solution Approach 2:
The patent operates at elevated pressures which shift the equilibrium and enhance absorption efficiency at higher temperatures. By changing the pressure parameter, the system achieves effective nitrogen oxide retention without requiring refrigerated cooling
3Ease of manufacture
If water ballast is admitted prior to ammonia oxidation and retained throughout the process, then nitric acid concentration is improved (avoiding bleaching), but product concentration is limited to dilute ranges
Solution Approach 1:
The patent uses water ballast to control the concentration of nitric acid in the reaction mixture, maintaining it in the 20-40% range. This parameter control prevents the formation of nitrogen dioxide impurities that would require bleaching, simplifying the manufacturing process while producing dilute nitric acid suitable for many applications
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
This process intensifies the reaction/absorption process, achieving over 95% conversion of nitrogen monoxide to nitric acid with concentrations between 20% to 40% HNO3, reducing the need for bleaching and tower infrastructure, while maintaining efficient heat and mass transfer.
Implementation Method 1
the reaction mixture is then cooled to below the dew point of the reaction mixture in a heat exchanger whereby: a) the nitrogen monoxide is oxidised and the water vapour is caused to condense
Implementation Method 2
the reaction mixture is then cooled to below the dew point of the reaction mixture in a heat exchanger
Implementation Method 3
the nitrogen monoxide is oxidised
Implementation Method 4
the products of the nitrogen monoxide oxidation react with and are absorbed by the condensed water to produce the nitric acid
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A process for producing nitric acid is disclosed in which a gaseous oxidiser feed composed at least substantially of ammonia, steam and an oxidising gas is exposed to conditions whereby the ammonia is oxidised to produce a reaction mixture including nitrogen monoxide and water vapour. The reaction mixture is then cooled in a heat exchanger whereby: a) the nitrogen monoxide is oxidised and the water vapour is caused to condense, b) the products of the nitrogen monoxide oxidation react with and are absorbed by the condensed water, and c) substantially all of the nitrogen monoxide in the reaction mixture is converted to nitric acid. Also disclosed is a nitric acid solution when produced by the disclosed process.