Electrochemical HCl Recycling for Isocyanate Production
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Solution Overview
Problem
Current recycling processes for hydrogen chloride in isocyanate production, such as catalytic oxidation and gas phase electrolysis, face challenges including sensitivity to load changes, catalyst deactivation, and increased operational complexity, leading to reduced cost-effectiveness and efficiency.
Innovation Solution
An integrated process involving electrochemical oxidation of hydrogen chloride to produce chlorine, which is then recycled for phosgene production, allowing for simpler operation and easier adjustment to varying load states, while minimizing the impact of impurities and improving catalyst longevity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If catalytic oxidation of hydrogen chloride is used for recycling, then chlorine can be regenerated, but the process becomes sensitive to load changes and catalyst deactivation occurs
Solution Approach 1:
The patent replaces the catalytic oxidation system (chemical mechanism) with an electrolysis system (electrical mechanism). The electrolytic cell uses electrical current to directly convert hydrogen chloride to chlorine and hydrogen according to the reaction: 2HCl → H2 + Cl2. This substitution eliminates catalyst sensitivity to load changes while maintaining reliable chlorine regeneration, as the electrical process can be easily adjusted by varying current intensity.
2Productivity
If gas phase electrolysis of hydrogen chloride is implemented, then chlorine production is achieved, but technical demands on plant components increase and safety costs rise
Solution Approach 1:
The patent changes the physical state parameter of the electrolysis process from gas phase to liquid phase. By conducting electrolysis in the liquid phase (using hydrochloric acid solution instead of gaseous HCl), the process reduces technical demands on plant components. Liquid phase electrolysis allows for lower pressure operation, simpler reactor design, and reduced safety requirements while maintaining high chlorine production efficiency through controlled electrical current.
3Quantity of substance
If hydrogen chloride is not completely converted in gas phase electrolysis, then additional process steps are required for separation, but conversion efficiency is reduced
Solution Approach 1:
The patent implements a continuous electrolysis process where hydrochloric acid solution is continuously fed into the electrolytic cell, and the products (chlorine gas and hydrogen gas) are continuously removed. This continuous operation ensures high conversion rates of hydrogen chloride to chlorine while simplifying the overall process. The continuous flow regime prevents accumulation of unconverted material and eliminates the need for additional separation steps, as the gaseous products naturally separate from the liquid electrolyte.
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
The process enhances the reliability and cost-effectiveness of isocyanate production by enabling rapid startup and shutdown, easy capacity adjustment, and maintaining high conversion rates with reduced catalyst degradation and operational complexity.
Implementation Method 1
electrochemical oxidation of the hydrogen chloride produced in the course of the phosgenation process
Implementation Method 2
the electrolysis of an aqueous solution of hydrogen chloride (hydrochloric acid)
Data Source
AI summary
An isocyanate is produced by:(a) reacting chlorine with carbon monoxide to form phosgene,(b) reacting the phosgene with an organic amine to form an isocyanate and hydrogen chloride,(c) separating the isocyanate and hydrogen chloride,(d) optionally, purifying the hydrogen chloride,(e) preparing an aqueous solution of the hydrogen chloride,(f) optionally, purifying the aqueous solution of hydrogen chloride,(g) subjecting the aqueous hydrogen chloride solution to electrochemical oxidation to form chlorine, and(h) returning at least a portion of the chlorine produced in (g) to (a).