Nitrobenzene Continuous Process Redispersing Emulsion
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Solution Overview
Problem
Current processes for nitrobenzene production in adiabatic nitration of benzene with sulfuric and nitric acids face limitations in achieving high space-time yields while maintaining product quality and process control, particularly due to constraints in start temperature and dispersion frequency.
Innovation Solution
The process involves using nitrating acid with at least 3.0 wt.% nitric acid and 67.0 wt.% sulfuric acid, a start temperature between 100.0° C. and 102.0° C., and redispersing the emulsion of nitrating acid and benzene at least 4 times within the first 13 vol.% of the reaction space, with at least 60% nitric acid conversion occurring in this zone, and optionally incorporating external cooling to manage the reaction end temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the start temperature is increased to achieve higher reaction rates and space-time yields, then productivity improves, but the risk of runaway reaction and loss of process control increases
Solution Approach 1:
The reaction space is divided into a start zone (first 13 vol.%) and an end zone, with different functional requirements. The start zone is designed to achieve rapid nitric acid conversion (at least 60%) through intense dispersion and controlled temperature, while the end zone completes the reaction. This segmentation allows high productivity in the start zone without compromising overall process safety and control.
Solution Approach 2:
The benzene and nitrating acid are pre-dispersed to form an emulsion before entering the reaction space, and redispersed at least 4 times within the start zone. This preliminary and repeated dispersion action ensures intimate mixing and uniform heat distribution before and during the main reaction, enabling high reaction rates while preventing hot spots and maintaining process control.
2Productivity
If the reaction proceeds rapidly with high nitric acid conversion in the start zone, then space-time yield improves, but the temperature control becomes more difficult
Solution Approach 1:
The process employs temperature monitoring and control mechanisms that respond to the exothermic reaction progress. The heat of reaction is utilized to heat the waste acid in the flash evaporator, creating a feedback loop where reaction heat is recovered and reused. This feedback mechanism enables rapid conversion in the start zone while maintaining overall temperature control through heat recovery and reuse.
Solution Approach 2:
The exothermic heat of reaction is utilized to heat the waste acid in the flash evaporator to the required concentration and temperature. This self-service approach uses the reaction's own heat to maintain process temperatures, enabling high conversion rates without external heating and simplifying temperature control while achieving space-time yields of at least 5 tons/m³h.
3Manufacturing precision
If intensive dispersion and redispersion are applied to achieve high conversion in the start zone, then manufacturing precision improves, but device complexity increases
Solution Approach 1:
The dispersion and redispersion operations are integrated into the continuous flow process, occurring automatically as the reaction mixture flows through the reaction space. The emulsion is formed continuously and redispersed at least 4 times within the start zone without interrupting the continuous flow. This continuous action achieves precise nitric acid conversion control (at least 60% in the start zone) while avoiding the complexity of batch-wise or periodically activated dispersion systems.
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 enables a space-time yield of at least 5 tons of nitrobenzene per cubic meter of reaction space per hour with maintained product quality and controlled process parameters, as demonstrated by achieving yields up to 6 tons/m3h without compromising the quality of the nitrobenzene.
Implementation Method 1
benzene is metered into this nitrating acid and reacts with the nitric acid to form substantially water and nitrobenzene
Implementation Method 2
The sulfuric acid then takes up the evolved heat of reaction and the water formed in the reaction
Implementation Method 3
the reaction mixture is generally fed into a phase separation apparatus, where two phases are formed; the first phase being crude nitrobenzene and the second phase waste acid
Implementation Method 4
the waste acid obtained in the phase separation apparatus is conventionally fed into a flash evaporator, where water is evaporated as the waste acid is expanded into the vacuum
Data Source
AI summary
The invention relates to a continuous process for the manufacture of nitrobenzene. This process comprises the nitration of benzene with nitrating acid that contains at least 3.0 wt. % of nitric acid and at least 67.0 wt. % of sulfuric acid, in a reaction space in which the start temperature of the reaction is above 100.0° C. but below 102.0° C. In addition, this process requires that the benzene and the nitrating acid are dispersed in one another several times.