Sodium Cyanide Preparation via Liquid Phase Absorption
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Solution Overview
Problem
Existing methods for producing alkali metal cyanides, such as sodium cyanide, result in significant waste and environmental concerns due to contamination by byproducts like sodium formate, which limits recirculation and necessitates costly and harmful disposal processes.
Innovation Solution
A method involving absorption of hydrogen cyanide in an aqueous alkali metal hydroxide solution, followed by crystallization under controlled temperature and pressure conditions, with partial recirculation of the mother liquor to create a closed loop, minimizing byproduct formation and allowing for continuous production without waste disposal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the Andrussow reaction gas is directly reacted with sodium hydroxide in the gas phase to produce solid sodium cyanide, then the production process is simplified and productivity is improved, but byproducts such as sodium formate and sodium carbonate are enriched in the mother liquor, preventing recirculation and requiring costly waste disposal
Solution Approach 1:
The patent changes the reaction parameters by conducting the reaction in the liquid phase rather than gas phase, and controls the pH value within a specific range (9-13) to suppress byproduct formation. This allows the mother liquor to be recirculated without byproduct enrichment, resolving the contradiction between productivity improvement and byproduct accumulation
Solution Approach 2:
The patent converts the previously harmful byproducts (sodium formate and sodium carbonate) into manageable components by controlling their concentration through pH management. The byproducts are no longer treated as waste requiring disposal but as controllable process parameters that enable continuous recirculation
2Manufacturing precision
If the HCN-containing reaction gas is liquefied and purified through complex methods such as rectification before reaction with sodium hydroxide, then the purity of the starting material is improved, but the process complexity and cost increase significantly
Solution Approach 1:
The patent extracts only the essential reaction component (HCN) from the Andrussow gas through selective absorption in alkaline solution, eliminating the need for complex purification steps like rectification. The absorption process directly produces a usable cyanide solution while leaving other gas components behind
Solution Approach 2:
The patent introduces an intermediary alkaline absorption solution that selectively captures HCN from the reaction gas. This intermediary step simplifies the overall process by converting the complex gas mixture into a controlled liquid-phase reaction system
3Object-affected harmful factors
If the sodium cyanide mother liquor is recirculated to minimize waste, then environmental harm is reduced, but byproducts become enriched over multiple cycles, eventually requiring disposal
Solution Approach 1:
The patent implements feedback control by continuously monitoring and adjusting the pH value of the recirculating mother liquor. This feedback mechanism prevents byproduct enrichment by maintaining conditions that suppress unwanted reactions, ensuring long-term recirculation sustainability without environmental harm
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 enables the production of high-purity alkali metal cyanides as solids with minimal contaminants, achieving a closed loop that eliminates the need for costly and environmentally harmful waste disposal, while using non-purified synthesis gas directly from the Andrussow process.
Implementation Method 1
an absorption step in the form of an absorption of hydrogen cyanide from a synthesis gas containing hydrogen cyanide in an aqueous alkali metal hydroxide solution
Implementation Method 2
a crystallization step in the form of the introduction of the alkali metal cyanide solution into an evaporative crystallizer, which is heated by steam heating
Implementation Method 3
an evaporative crystallizer, which is heated by steam heating so that at the contact surface of the heating element with alkali metal cyanide solution, a temperature of approximately 60-100° C.
Implementation Method 4
a separation step in the form of the separation of the alkali metal cyanide crystals formed from the mother liquor by centrifuging
Data Source
AI summary
The invention relates to a process for the preparation of alkali metal cyanides as a solid substance, comprising the steps of: i) an absorption step in the form of an absorption of hydrogen cyanide from a hydrogen cyanide-containing synthesis gas in an aqueous alkali metal hydroxide solution; ii) a crystallization step in the form of introducing said alkali metal cyanide solution into an evaporative crystallizer; iii) a separation step; iv) a recycle step; v) a drying step.