Process and plant for removing dyes from waste textiles
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Solution Overview
Problem
Existing methods for recycling polyester and cotton fabrics suffer from partial degradation and incomplete dye removal, which affects the quality and usability of recycled materials, particularly when elastane and other contaminants are present.
Innovation Solution
A process involving the use of solvents like DMF or DMAC, with optional alkali water, at controlled temperatures (80-140°C) and centrifugation, to extract dyes from textiles, followed by solvent recovery and reuse, minimizing material degradation and ensuring complete dye removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If existing methods (dichloromethane pre-treatment, glycol ether decolorizing agents, magnetic activated carbon) are used to remove dyes from waste textiles, then some dye removal is achieved, but the removal is incomplete and polyester/cotton degradation occurs
Solution Approach 1:
The invention changes the chemical parameters of the extraction system by using dimethylformamide (DMF) or dimethylacetamide (DMAC) as solvents, which have different chemical properties compared to existing methods. These solvents operate at specific temperature ranges (80-140°C) and pH conditions (pH 12-14 with alkali water) that optimize dye removal while preserving fiber integrity. The parameter changes in solvent type, temperature, and pH collectively resolve the contradiction between complete dye removal and fiber degradation prevention.
Solution Approach 2:
The invention introduces alkali water as an intermediary substance that facilitates the extraction process. The alkali water works in combination with DMF or DMAC to enhance dye removal efficiency while the centrifugation process acts as a mediator to separate the extracted dye from the textile material. This intermediary approach allows complete dye removal without direct harsh chemical action on the fibers, thus preventing degradation.
2Productivity
If higher temperatures or stronger chemicals are used to remove dyes more completely, then dye removal efficiency improves, but polyester and cotton fibers degrade
Solution Approach 1:
The invention optimizes the temperature parameter within a specific range (80-140°C) that is sufficient to break dye-fiber bonds and enable complete dye extraction, yet not high enough to cause fiber degradation. The chemical parameters are controlled through pH adjustment (12-14) using alkali water, which facilitates dye removal through controlled chemical environment without harsh conditions that would damage fibers. This parameter optimization resolves the contradiction between removal efficiency and fiber strength preservation.
3Manufacturing precision
If solvents are used to extract dyes from textiles, then dye removal is achieved, but solvent recovery and environmental safety become concerns
Solution Approach 1:
The invention implements a solvent recovery system that captures and recycles DMF or DMAC after the extraction process. The centrifugation step separates the solvent from the extracted dye and textile material, allowing the solvent to be recovered and reused. This recovery approach eliminates the need to discard solvents, reducing environmental impact and operational costs while maintaining effective dye extraction.
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 effectively removes dyes from polyester and cotton fibers with minimal degradation, allowing for efficient recycling of polyester and cotton materials, including elastane, with solvent recovery rates up to 99.9% and reduced energy consumption.
Implementation Method 1
extracting the textile material with the solvent to provide a solution comprising solvent and extracted material, said extracted material including at least said dye
Implementation Method 2
removing said solution of solvent and extracted material from said textile material by centrifuging
Data Source
AI summary
In a process for removing dyes from a textile material, comprising or consisting of polyester fibers, or comprising or consisting of cotton fibers, a batch of said textile material is reduced to clippings having small size, treated with a solvent under stirring in an extraction chamber and centrifugated to remove the solvent, the solution comprising solvent and extracted material is used as a solvent to extract dye from another batch of textile material.