Adiabatic Nitration Sulfuric Acid Oxidation
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Solution Overview
Problem
The continuous adiabatic nitration process for producing nitrobenzene faces issues with disruptive precipitation, leading to operational disruptions and equipment fouling, particularly in heat exchangers, due to the formation of metal sulfates and black carbon-containing precipitates, which can result in process shutdowns for cleaning.
Innovation Solution
Incorporating an oxidizing agent, such as nitric acid, nitrous acid, or nitrosylsulfonic acid, into the concentrated sulfuric acid stream before its reuse in the nitration reaction, maintaining a concentration of 10 ppm to 5,000 ppm, ensures that the sulfuric acid comes into contact with the oxidizing agent for at least 1 minute to prevent the formation of precipitates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If sulfuric acid is recycled in the adiabatic nitration process, then productivity is improved through continuous operation, but metal sulfates precipitate and accumulate causing equipment fouling and operational disruptions
Solution Approach 1:
The patent extracts and removes metal ions from the recycled sulfuric acid stream before the acid enters the nitration reactor. This is achieved through a metal removal unit that separates metal contaminants from the sulfuric acid, preventing metal sulfate precipitation in downstream equipment while maintaining the benefits of sulfuric acid recycling for continuous operation
Solution Approach 2:
The patent applies preliminary action by treating the sulfuric acid with an oxidizing agent before recycling it to the nitration process. This oxidation treatment modifies the chemical environment to prevent metal sulfate precipitation, addressing the fouling issue before it occurs in the heat exchangers and equipment
2Manufacturing precision
If sulfuric acid is concentrated after phase separation, then manufacturing precision is improved by restoring acid concentration, but black carbon-containing precipitates form causing heat exchanger fouling
Solution Approach 1:
The patent introduces an oxidizing agent as an intermediary substance that acts on the sulfuric acid during concentration and recycling. This oxidizing agent prevents the formation of black carbon-containing precipitates by oxidizing potential precursors, thereby protecting heat exchangers from fouling while allowing the concentration step to proceed effectively
3Loss of substance
If metal sulfates precipitate in sulfuric acid, then loss of substance occurs through solid accumulation, but cleaning operations require process shutdowns reducing productivity
Solution Approach 1:
The patent removes metal ions from the sulfuric acid recycling stream through a dedicated metal removal unit, preventing metal sulfate precipitation and accumulation. This continuous removal approach eliminates the need for periodic cleaning shutdowns while minimizing loss of metal-containing substances
Solution Approach 2:
The patent maintains continuous operation by implementing online metal removal and oxidizing treatment in the sulfuric acid recycling loop. This continuous prevention strategy eliminates the need for intermittent cleaning shutdowns, ensuring uninterrupted nitration production while preventing metal sulfate accumulation
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 approach significantly reduces the formation of black precipitates, enhances system availability, minimizes maintenance costs, and eliminates incineration costs for residue disposal, ensuring smooth continuous operation and improved heat transfer efficiency.
Implementation Method 1
an oxidizing agent is added so that a concentration of the oxidizing agent of 10 ppm to 5,000 ppm, based on the total mass of the concentrated sulfuric acid to be returned to the nitration, is achieved
Implementation Method 2
The starting materials benzene and nitric acid are reacted in a large excess of sulfuric acid, which absorbs the heat of reaction released
Implementation Method 3
the essentially nitric acid-free reaction mixture obtained after the reaction zone is fed to a phase separation apparatus in which two phases are formed... introduced into an apparatus for flash evaporation of the water, in which water is extracted from the by applying a negative pressure and using the high temperature of the circulating acid
Data Source
AI summary
The invention relates to a continuously operated adiabatic process for producing nitrobenzene by the nitration of benzene with nitric acid and sulfuric acid. According to said method, the diluted sulfuric acid obtained after successful nitration of the untreated nitrobenzene and separation of the latter from the aqueous phase, is concentrated in order to be re-used in the nitration process, and once concentrated is supplied with an oxidant for at least one minute, before being brought into contact again with fresh nitric acid, such that the concentration of the oxidant achieves between 10 ppm and 5,000 ppm in relation to the total mass of the concentrated sulfuric acid that is to be re-used in the nitration process.