Waste Sulphuric Acid Concentration via Extractive Rectification
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Solution Overview
Problem
The concentration of waste acid from nitration processes is hindered by foreign constituents like nitric acid, nitro-organic compounds, and nitrous constituents, leading to energy-intensive methods, environmental pollution, and inefficient recycling, particularly due to the volatility and low solubility of these substances, which result in losses and contamination of waste streams.
Innovation Solution
A method involving partial purification of waste acid in a stripping column followed by reduced-pressure evaporation, using extractive rectification with concentrated sulphuric acid as an extracting medium to recover and concentrate nitric acid, while minimizing energy consumption and waste production, by integrating two stripping columns and coordinating with the nitration process to recycle sulphuric acid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional concentration methods are used to concentrate waste acid from nitration processes, then sulphuric acid concentration can be increased, but energy consumption increases and environmental pollution worsens due to volatile and insoluble foreign constituents
Solution Approach 1:
The concentration process is divided into multiple stages: first stripping column for preliminary purification, second stripping column for further purification, and evaporator for final concentration. Each stage targets specific contaminants, allowing progressive concentration with reduced energy input at each step rather than attempting single-stage concentration.
Solution Approach 2:
Foreign constituents (nitric acid, nitro-organic compounds, nitrous constituents) are extracted and removed from the waste acid stream through stripping columns before final concentration. This extraction step separates contaminants from the sulphuric acid, enabling more efficient concentration of the acid component with lower energy requirements.
2Quantity of substance
If conventional concentration methods are used to concentrate waste acid from nitration processes, then sulphuric acid concentration can be increased, but environmental pollution increases due to formation of contaminated waste streams
Solution Approach 1:
The stripping columns selectively extract and remove harmful foreign constituents (nitric acid, nitro-organic compounds, nitrous constituents) from the waste acid stream before the evaporation stage. This extraction prevents these contaminants from being concentrated in the final waste streams, reducing environmental pollution while achieving sulphuric acid concentration.
Solution Approach 2:
The process converts the harmful presence of volatile and insoluble contaminants into a beneficial separation opportunity. By utilizing the different physical properties (volatility, solubility) of contaminants versus sulphuric acid, the system automatically separates and removes harmful substances during the concentration process, turning a pollution problem into a purification advantage.
3Power
If direct steam is used in the concentration process, then heating efficiency is improved, but the process complexity and waste production increase
Solution Approach 1:
A heat exchange system acts as an intermediary between the steam source and the waste acid. Instead of direct steam injection, the system uses heat exchange surfaces to transfer thermal energy from steam to the acid stream. This intermediary approach maintains heating efficiency while avoiding the complexity and waste generation associated with direct steam contact.
4Productivity
If foreign constituents are present in the waste acid, then the concentration process can proceed, but losses and contamination occur due to volatility and low solubility of these substances
Solution Approach 1:
The stripping columns perform preliminary removal of foreign constituents before the main concentration process in the evaporator. By addressing the contamination issue early in the process sequence, the system prevents losses and contamination during the final concentration stage, maintaining productivity while reducing substance losses.
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 reduces direct steam use, minimizes liquid waste, and simplifies the process, making it more economical and environmentally friendly by effectively recovering and concentrating sulphuric acid while reducing the presence of contaminants in waste streams.
Implementation Method 1
subjected to at least partial purification in a stripping column to remove said further constituents
Implementation Method 2
fed to a further concentration stage in one or more downstream evaporators operating at reduced pressure
Implementation Method 3
the production of a highly concentrated nitric acid required in the nitration process from a more dilute nitric acid by extractive rectification with the use of concentrated sulphuric acid as an extracting medium
Data Source
AI summary
A method for recovering diluted waste sulfuric acid by extractive rectification with concentrated sulfuric acid which is re-concentrated for reutilization. Waste sulfuric acid from the nitration process is fed into a first column, optionally together with another waste sulfuric acid in a DNT washing acid, and divided into an overhead product containing nitric acid and nitro-organic compounds and a prepurified sulfuric acid in the bottom product. The prepurified sulfuric acid withdrawn from the bottom of the first column is fed to the top of a second column, into the bottom zone of which another waste sulfuric acid is fed in the form of a diluted sulfuric acid recovered from the nitric acid concentration system so the prepurified sulfuric acid from the first column is further purified in the second column and is preconcentrated along with the diluted sulfuric acid recovered from the extractive rectification of nitric acid.