Waste Acid Stripping Column for Nitric and Sulfuric Recovery
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Solution Overview
Problem
Current processes for concentrating waste acid from nitration processes are inefficient in recovering and recycling sulfuric and nitric acids, leading to energy consumption issues and contamination of waste streams, with challenges posed by nitrogen-oxygen compounds like nitroorganics and nitrous components.
Innovation Solution
A process involving a stripping column where waste acid is separated into a vapor phase containing nitric acid, with additional concentrated sulfuric acid used to concentrate nitric acid in the stripping steam, achieving high concentrations of both sulfuric and nitric acids, and subsequent stages for purification and recycling, reducing waste water pollutants and energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If waste acid is concentrated using conventional evaporators, then sulfuric acid concentration is improved, but energy consumption increases and nitrogen-oxygen compounds cause contamination and deposition problems
Solution Approach 1:
The invention changes the operating parameters by conducting concentration at reduced pressure (vacuum conditions) instead of atmospheric pressure, lowering the boiling point and energy requirements. Additionally, the two-stage process with intermediate cooling changes the thermal parameters to prevent deposition while maintaining concentration efficiency
Solution Approach 2:
The concentration process is divided into two distinct stages: first stage concentrates sulfuric acid to 85-95% while removing water, and the second stage further concentrates to 96-98% after intermediate cooling. This segmentation allows optimization of energy usage at each stage and prevents nitrogen-oxygen compound deposition by interrupting the heating process
2Quantity of substance
If waste acid is concentrated to high sulfuric acid levels, then acid recovery is improved, but nitrogen-oxygen compounds deposit on equipment and contaminate waste streams
Solution Approach 1:
The invention performs preliminary cooling of the concentrated sulfuric acid between the first and second concentration stages. This intermediate cooling action prevents nitrogen-oxygen compounds from reaching their deposition temperature range during subsequent concentration, thereby avoiding equipment fouling while still achieving high final concentration
Solution Approach 2:
The two-stage concentration process with intermediate cooling maintains continuous operation without stopping, but introduces a cooling step that prevents deposition. The continuous removal of water and controlled temperature management ensure that nitrogen-oxygen compounds remain in solution throughout the process rather than precipitating
3Quantity of substance
If conventional stripping and concentration processes are used, then sulfuric acid is recovered, but nitric acid and nitroorganics are lost in waste streams
Solution Approach 1:
The invention extracts and separates nitric acid and nitroorganics from the waste acid stream before the concentration process begins. The stripping column selectively removes these components, which are then condensed and collected separately, preventing their loss in waste streams while allowing sulfuric acid to be concentrated and reused
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 method allows for the recovery of sulfuric and nitric acids in highly concentrated forms, reducing waste water pollutants and energy consumption, with nitric acid concentration reaching up to 99.99% and sulfuric acid concentration optimized for reuse, minimizing organic load in waste water.
Implementation Method 1
separated in a stripping column in countercurrent to steam from the bottom of the stripping column into at least one vapor phase, which contains nitric acid
Implementation Method 2
the nitric acid vapors obtained from the top of the column of the first stage are condensed and a nitric acid is obtained directly in a highly concentrated form
Implementation Method 3
at least one evaporator (V3) for highly concentrating the purified sulfuric acid
Data Source
Figure 1
Figure 2
AI summary
Processing waste acid obtained from nitroaromatics production, preferably dinitrotoluene- or trinitrotoluene production, comprises: adding a pre-heated waste acid comprising sulfuric acid, water, nitric acid, nitrosylsulfuric acid and nitro-organics, into a stripping column in a counter-flow to the steam obtained from the bottom of the stripping column by heating a pre-concentrated sulfuric acid; separating nitric acid, optionally nitro-organics and the pre-concentrated sulfuric acid into at least one vapor phase; and processing the obtained nitric acid and the nitro-organics. Processing waste acid obtained from nitroaromatics production, preferably dinitrotoluene- or trinitrotoluene production, under recovery of concentrated and purified sulfuric acid and nitric acid, comprises: (i) adding a pre-heated waste acid comprising sulfuric acid and water (up to 80 wt.%), nitric acid, nitrosylsulfuric acid and nitro-organics, preferably dinitrotoluene and mononitrotoluene, into a stripping column in a counter-flow to the steam, which is obtained from the bottom of the stripping column by heating a pre-concentrated sulfuric acid in a first phase; (ii) separating nitric acid, optionally nitro-organics and the pre-concentrated sulfuric acid into at least one vapor phase; and (iii) supplying the obtained pre-concentrated sulfuric acid from the bottom of the stripping column for further purification to separate the highly concentrated nitro-organics in a first downstream stage, and processing nitric acid obtained from the nitric acid vapor phase, and the nitro-organics including the nitro-organics obtained during the further purification and concentration of the pre-concentrated sulfuric acid, and returning back to the nitration process in a second downstream stage. The step (i) comprises: adding the pre-heated waste acid into the stripping column for stripping in the counter-flow to the steam obtained from the pre-concentrated sulfuric acid in concentrating the stripping steam containing nitric acid in the counter-flow to the purified and optionally fresh concentrated sulfuric acid (75-97 wt.%, preferably 80-96 wt.%); and condensing the nitric acid vapors obtained from the top of the column of the first stage, and thus directly obtaining a highly concentrated form of nitric acid for returning back to the nitration process. An independent claim is also included for a device for performing the above method comprising: a first stripping column (K1) with a feeding line for the processed waste acid, an associated evaporator for obtaining the pre-concentrated sulfuric acid and a discharging for the nitric acid containing vapor phase; an additional stripping column (K2) with an associated evaporator for producing a purified sulfuric acid and at least one additional evaporator for highly concentrating the purified sulfuric acid; heat exchanger condensers for vapor phases, which are obtained as top products from the stripping columns and the evaporators; optionally a washing column for washing of nitrogen-containing gases; required piping for feeding the starting materials, transporting, distributing and discharging vapor phase, liquid phase, processing products and waste gases obtained as processing streams; and required heating-, cooling- and pressure control equipments. The first stripping column is provided with a feeding line for a highly concentrated purified sulfuric acid, which is produced during the processing of the waste acid.