Two-Step Scrubbing Process for Dinitrotoluene Purification
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Solution Overview
Problem
Current processes for scrubbing crude dinitrotoluene (DNT) mixtures from toluene nitration produce wastewater that requires complex and costly treatment to meet regulatory standards, with incomplete removal of toxic nitrocresols and nitrobenzoic acids, leading to significant environmental and operational challenges.
Innovation Solution
A two-step scrubbing process involving a first step with a scrubbing acid containing nitric acid and sulfuric acid, followed by a second step with a low-acid scrubbing acid at a pH of 4 or less, effectively separates DNT from mineral acids and toxic compounds, allowing the wastewater to be directly treated biologically without intermediate steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional three-step scrubbing process (acid scrub, alkali scrub, neutral scrub) is used to remove impurities from crude DNT, then the product purity is improved, but the wastewater requires complex and costly treatment to meet regulatory standards
Solution Approach 1:
The invention extracts and removes nitrobenzoic acids from the wastewater stream using an extraction process. The nitrobenzoic acids are selectively separated from the scrubbing water through liquid-liquid extraction, allowing the wastewater to be discharged without complex treatment while maintaining product purity requirements
Solution Approach 2:
The invention changes the pH parameter of the scrubbing process to optimize the separation of nitrobenzoic acids. By controlling the pH during extraction, the nitrobenzoic acids are converted to their ionized form which remains in the aqueous phase, while other impurities are removed in the organic phase, simplifying wastewater treatment
2Reliability
If an alkali scrub is used to remove weakly acidic impurities like nitrocresols and nitrobenzoic acids, then the removal efficiency of these impurities is improved, but the wastewater contains high levels of sulfate and nitrate requiring extensive treatment
Solution Approach 1:
The invention converts the harmful effect of nitrobenzoic acids in wastewater into a beneficial separation process. By using extraction with an organic solvent, the nitrobenzoic acids are selectively transferred from the aqueous phase to the organic phase, where they can be easily separated and the cleaned wastewater discharged
Solution Approach 2:
The invention introduces an organic extracting solvent as an intermediary substance between the wastewater and the nitrobenzoic acids. This intermediary facilitates the selective transfer of nitrobenzoic acids from the aqueous phase to the organic phase, enabling effective removal without complex treatment processes
3Reliability
If multiple scrubbing steps are performed to reduce impurities to trace levels, then the wastewater quality is improved, but the process time and operational complexity increase significantly
Solution Approach 1:
The invention segments the impurity removal process into two distinct functional stages: (1) removal of most impurities during the main scrubbing process, and (2) selective extraction of nitrobenzoic acids from the wastewater. This segmentation allows each stage to be optimized independently, reducing overall process time while achieving the required wastewater quality
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 wastewater pollution with sulfate and nitrate, minimizes the presence of nitrobenzoic acids in the wastewater, and enables direct biological treatment, adhering to regulatory standards, thus simplifying and cost-reducing the wastewater management process.
Implementation Method 1
a first scrubbing step (SS-I), the crude mixture is extracted with a scrubbing acid I comprising nitric acid, nitrogen oxides and sulfuric acid in a scrub comprising at least one extraction stage
Implementation Method 2
in a second scrubbing step (SS-II), the prescrubbed crude mixture is extracted with a scrubbing acid II in a scrub comprising at least one extraction stage
Data Source
AI summary
The invention relates to a process for scrubbing a crude mixture comprising dinitrotoluene, nitric acid, nitrogen oxides and sulfuric acid obtained in the nitration of toluene after the nitrating acid has been separated off, which comprises two scrubbing steps (SS-I) and (SS-II), whereini) in a first scrubbing step (SS-I), the crude mixture is extracted with a scrubbing acid I comprising nitric acid, nitrogen oxides and sulfuric acid in a scrub comprising at least one extraction stage, where the scrubbing acid discharged from the first extraction stage (SS-I-1) of the first scrubbing step (SS-I) has a total acid content of from 20 to 40% by weight and a prescrubbed crude mixture is obtained,ii) in a second scrubbing step (SS-II), the prescrubbed crude mixture comprising dinitrotoluene is extracted with a scrubbing acid II in a scrub comprising at least one extraction stage, where the scrubbing acid discharged from the first extraction stage (SS-II-1) of the second scrubbing step (SS-II) has a pH of less than or equal to 4 and a mixture comprising dinitrotoluene which is essentially free of nitric acid, sulfuric acid and nitrogen oxides is obtained.