Alkaline Spin Bath Recycling via Vacuum Crystallization
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Solution Overview
Problem
There is a need for an efficient method to recycle alkaline spin baths used in cellulose spinning, particularly for cellulose carbamate spinning dope, to minimize waste and maintain high-quality fiber production while avoiding the use of harmful chemicals and reducing environmental impact.
Innovation Solution
A method involving the recycling of an aqueous alkaline spin bath through vacuum crystallization steps to recover coagulation salts and sodium hydroxide, maintaining their purity and preventing zinc ion accumulation, while also recovering nitrogenous compounds and ammonia, thereby optimizing chemical recycling and maintaining spin bath composition for continuous spinning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an acidic spin bath containing sulphuric acid is used to coagulate cellulose carbamate spinning dope, then coagulation efficiency is improved, but vast amounts of sulphuric acid are consumed and unnecessary waste streams of sodium sulphate are produced
Solution Approach 1:
The invention changes the pH parameter of the spin bath from acidic to alkaline by using sodium carbonate instead of sulphuric acid. This parameter change allows the coagulation process to proceed efficiently while avoiding the consumption of large amounts of acid and the generation of salt waste streams, thus resolving the contradiction between coagulation efficiency and chemical consumption.
Solution Approach 2:
The invention implements a recycling system where the alkaline spin bath is continuously circulated and the sodium carbonate is recovered and reused. This discards the conventional approach of continuous chemical consumption and replaces it with a closed-loop system that recovers and reuses the coagulation agent, significantly reducing chemical consumption and waste generation.
2Loss of substance
If an alkaline spin bath with coagulation salt is used for coagulation, then chemical waste is reduced, but the spin bath requires recycling to maintain composition and prevent zinc ion accumulation
Solution Approach 1:
The invention implements a continuous recycling system where the alkaline spin bath is continuously circulated between the spin bath and a recycling system. This continuous action maintains the chemical composition by continuously removing zinc ions through hydroxide precipitation and regenerating the coagulation salt, thus preventing zinc accumulation while maintaining coagulation efficiency without requiring complex batch-wise intervention.
Solution Approach 2:
The recycling system uses the inherent chemical properties of the spin bath components to achieve self-cleaning and self-regeneration. Sodium hydroxide in the spin bath automatically precipitates zinc ions as zinc hydroxide, which is then filtered out, and the sodium carbonate is regenerated and reused. This self-service mechanism reduces the need for external chemical additions and complex control systems.
3Manufacturing precision
If vacuum crystallization is used to recover coagulation salt, then salt purity is improved, but energy consumption increases due to evaporation and crystallization steps
Solution Approach 1:
The invention utilizes phase transitions of water (evaporation from liquid to vapor) and sodium carbonate (from dissolved state to crystalline solid) to separate and purify the coagulation salt. By controlling the evaporation and crystallization process under vacuum conditions, high-purity sodium carbonate is recovered while minimizing energy consumption through efficient heat transfer and vacuum operation.
Solution Approach 2:
The invention changes physical parameters (temperature, pressure, concentration) to control the crystallization process. By gradually concentrating the spin bath through controlled evaporation and then applying vacuum to induce crystallization at lower temperatures, the system achieves high-purity salt recovery with reduced energy input compared to high-temperature evaporation methods.
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 method achieves high-quality cellulose carbamate filaments or fibers with minimal waste, efficient chemical recycling, and reduced environmental emissions, ensuring sodium hydroxide and sodium carbonate contents are maintained within optimal ranges for continuous spinning.
Implementation Method 1
subjecting the concentrated aqueous spin bath to a first vacuum crystallization to recover a first part of the coagulation salt
Implementation Method 2
evaporating at least part of water and/or free ammonia present in the withdrawn portion of the aqueous spin bath to obtain a concentrated aqueous spin bath
Data Source
Figure 1
AI summary
According to an example aspect of the present invention, there is provided a method of recycling an aqueous alkaline spin bath used in manufacture of cellulose carbamate textile fibre. The method comprising feeding a cellulose carbamate spinning dope into an aqueous alkaline spin bath, withdrawing a portion of the aqueous alkaline spin bath and subjecting the withdrawn portion to evaporation, first vacuum crystallization, further evaporation and second vacuum crystallization, and finally, returning the recovered coagulation salt back to the spin bath.