HCN Removal from Crude Dinitrotoluene via Stripping
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current processes for producing dinitrotoluene (DNT) generate hazardous side products like HCN, leading to complex and costly wastewater treatment requirements, especially with stringent regulations, and pose risks to hydrogenation catalysts due to cyanide presence.
Innovation Solution
A process involving the distillation and/or stripping of crude DNT mixtures to remove HCN before washing, using a flash evaporator or distillation column with a stripping gas, allowing for the recovery of nitric and sulfuric acids and recycling, while keeping HCN in the gaseous phase for easy removal, thereby reducing wastewater contamination and treatment needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a multistage scrub is used to remove impurities from crude DNT, then the purity of the product is improved, but the amount of wastewater generated increases and treatment costs increase
Solution Approach 1:
The invention extracts and removes HCN from the crude DNT stream before the washing process using a stripping column. By separating HCN in the gas phase through stripping with inert gas or vacuum, the harmful substance is removed prior to liquid-liquid extraction, reducing the contamination load on subsequent washing stages and minimizing wastewater generation while maintaining product purity
Solution Approach 2:
The stripping process is performed as a preliminary step before the multistage washing/scrubbing process. By removing HCN beforehand, the subsequent washing stages deal with reduced impurity loads, allowing for more efficient operation with less water consumption and reduced wastewater treatment requirements
2Productivity
If HCN is present in the DNT stream, then the nitration process can proceed, but hydrogenation catalysts are damaged and safety risks increase
Solution Approach 1:
HCN is extracted from the crude DNT stream using a stripping column where it is removed in the gas phase through contact with inert gas or vacuum application. This separation allows the nitration process to continue producing DNT while the harmful HCN is continuously removed, protecting downstream hydrogenation catalysts from cyanide poisoning and eliminating safety hazards
Solution Approach 2:
An inert gas (such as nitrogen) or vacuum acts as an intermediary medium in the stripping column to remove HCN from the crude DNT stream. The inert gas bubbles through or contacts the liquid stream, selectively absorbing HCN while leaving DNT and other process components unchanged, thereby protecting downstream catalysts without interfering with the nitration process
3Object-affected harmful factors
If distillation and stripping are used to remove HCN before washing, then HCN levels are reduced to below 25 ppm and treatment requirements are minimized, but additional process equipment is required
Solution Approach 1:
A stripping column is introduced as a dedicated unit operation to extract HCN from the crude DNT stream before washing. This single piece of equipment performs the critical function of reducing HCN to below 25 ppm, protecting downstream processes and minimizing wastewater treatment requirements, while adding only one essential unit to the process flow
Solution Approach 2:
The stripping process operates by changing physical parameters (temperature, pressure, gas flow rate) to favor HCN removal. By optimizing these parameters, the system achieves effective HCN reduction to below 25 ppm using a relatively simple stripping column, avoiding the need for multiple complex treatment units while meeting the harmful factor reduction target
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 effectively reduces HCN levels in DNT streams to below 25 ppm, minimizing wastewater treatment requirements and protecting hydrogenation catalysts by removing HCN from the organic phase before washing, thus simplifying and cost-reducing the overall process.
Implementation Method 1
before the first washing step is carried out, the crude mixture is distilled and/or stripped to remove HCN therefrom
Implementation Method 2
The gaseous phase obtained from the top of the flash evaporator, stripping or distillation column is partially condensed
Implementation Method 3
using a flash evaporator or distillation column with a stripping gas, allowing for the recovery of nitric and sulfuric acids and recycling, while keeping HCN in the gaseous phase for easy removal
Implementation Method 4
The gaseous phase obtained from the top of the flash evaporator, stripping or distillation column is partially condensed in order to recover a condensate containing nitric acid, sulfuric acid and dinitrotoluene while keeping at least 50 % of the HCN in the gaseous phase
Data Source
AI summary
A process for the preparation of dintrotoluene which comprises (a) nitrating toluene with a nitrating acid, wherein said nitrating acid is a mixture of nitric acid and sulfuric acid, in one or more nitration steps, and separating the nitrating acid from the process stream thus formed, wherein a crude mixture comprising dinitrotoluene and a fraction of said nitrating acid dissolved therein is obtained, said crude mixture further comprising at least 50 ppm of HCN, and (b) washing the crude dinitrotoluene containing mixture in one or more washing steps, wherein, before the first washing step is carried out, the crude mixture is distilled and/or stripped to remove HCN there-from, wherein a crude dinitrotoluene containing mixture which is essentially free of HCN is obtained.