Caprolactam Isolation via Vacuum Distillation and Noble Metal Hydro-refining
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Solution Overview
Problem
Conventional methods for isolating ε-caprolactam from the upper lactam phase after Beckmann cyclohexyl oxime rearrangement fail to achieve the required quality due to residual minor substances, despite high yield, as they rely on extraction steps using toxic solvents and are inefficient in removing impurities.
Innovation Solution
A method involving distillation under reduced pressure to remove water and non-volatile components, followed by hydro-refining with noble metal catalysts and rectification in high-efficiency columns to achieve high ε-caprolactam concentration and quality, eliminating the need for extraction with organic solvents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional extraction methods using organic solvents are used to isolate ε-caprolactam from the upper lactam phase, then the isolation process can be performed, but the required quality cannot be achieved due to residual minor substances
Solution Approach 1:
The patent applies parameter changes by conducting distillation under reduced pressure (0.1-4 kPa) instead of atmospheric pressure, which enables effective separation of ε-caprolactam from minor substances at lower temperatures. This parameter change prevents thermal decomposition and achieves the required quality (absorbance <0.05, permanganate index <4.4) by optimizing the distillation conditions to selectively vaporize ε-caprolactam while leaving heavier impurities behind
Solution Approach 2:
The patent extracts ε-caprolactam from the upper lactam phase through selective distillation, separating it from water, ammonium sulfate, and non-volatile organic substances. The process takes out ε-caprolactam in pure form by exploiting its specific volatility characteristics, achieving complete separation from minor substances that conventional extraction methods cannot remove
2Ease of manufacture
If extraction steps using toxic solvents like trichlorethylene and benzene are used, then ε-caprolactam can be isolated, but toxic and volatile solvents must be handled and disposed of
Solution Approach 1:
The patent replaces the chemical extraction method (using organic solvents) with a physical separation method (distillation under reduced pressure). This substitution eliminates the need for toxic solvents like trichlorethylene and benzene, achieving the same isolation purpose through physical property differences (volatility) rather than chemical solubility, thereby removing all associated toxicity and disposal issues
Solution Approach 2:
The patent creates an inert environment by operating under reduced pressure (vacuum conditions of 0.1-4 kPa), which prevents oxidation and thermal decomposition of ε-caprolactam during the isolation process. This inert atmosphere approach replaces the need for protective chemical agents and ensures pure product recovery without contamination
3Quantity of substance
If conventional extraction and rectification methods are used, then ε-caprolactam can be recovered, but investment and operating costs are high
Solution Approach 1:
The patent changes the operating pressure parameter to reduced pressure (0.1-4 kPa), which dramatically reduces the energy required for distillation compared to atmospheric pressure operations. This parameter optimization allows ε-caprolactam to be vaporized and condensed at lower temperatures, reducing thermal energy consumption and operating costs while maintaining high recovery efficiency
Solution Approach 2:
The distillation process under reduced pressure serves multiple functions simultaneously: it separates ε-caprolactam from water and inorganic salts, removes volatile and non-volatile organic impurities, concentrates the product, and prevents thermal decomposition. This multi-functionality eliminates the need for separate extraction, filtration, and concentration steps, reducing both investment and operating costs
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 produces ε-caprolactam of higher quality with lower investment and operating costs, without using volatile or toxic solvents, effectively removing impurities and improving quality parameters such as absorbance and volatile base content.
Implementation Method 1
distillation under reduced pressure to remove water and non-volatile components
Implementation Method 2
distillation under reduced pressure to remove water and non-volatile components
Implementation Method 3
hydro-refining with noble metal catalysts
Implementation Method 4
hydro-refining with noble metal catalysts
Implementation Method 5
rectification in high-efficiency columns to achieve high ε-caprolactam concentration and quality
Data Source
AI summary
The invention relates to a method for the isolation of ε-caprolactam from the upper lactam phase obtained by separation from the sulfate phase after neutralization of the reaction mixture obtained from the Beckmann cyclohexyl oxime rearrangement with ammonia, in which the upper lactam phase is first distilled at a reduced or atmospheric pressure, by which means the water content in it is reduced to 5 to 10 % by weight, whereupon the solid phase formed by distillation is mechanically removed therefrom and the concentrated mixture thus obtained is distilled at a pressure of 0.1 to 4 kPa, whereby non-volatile components are removed therefrom. Subsequently, in the distillate thus obtained the ε-caprolactam concentration is adjusted to 30 to 70% by weight by adding at least one solvent selected from the group consisting of water, methanol, ethanol, propanol, iso-propyl alcohol, or a mixture of at least two of them and the mixture thus formed is refined by nitrogen at a temperature of 100 to 150 °C and a hydrogen pressure of 1 to 10 MPa in the presence of a supported heterogeneous catalyst which comprises at least one noble metal selected from the group consisting of Pd, Pt, Ru, whereby the multiple bonds of the impurities present are reduced. Afterwards, the raffinate thus obtained is rectified in a series of at least two rectification columns operating at a pressure of 0.05 to 4 kPa with a cumulative minimum column system efficiency of 10 theoretical plates, whereby light fractions and heavy residues are separated from the raffinate by rectification, thereby isolating ε-caprolactam therefrom.