Solvent recovery equipment for the shoe materials industry
I. Commonly Used Solvents in the Shoe Materials Industry and the Necessity of Recycling
Commonly used solvents: acetone, methyl ethyl ketone (MEK), toluene, xylene, N,N-dimethylformamide (DMF), ethyl acetate, cyclohexanone, etc. These solvents are typically used for diluting polyurethane (PU) pastes, cleaning equipment, and adhesives, etc.
Necessity of Recycling:
Economy: The solvent accounts for a relatively high proportion of the raw material cost. Recovery and recycling can be carried out, directly reducing the procurement cost.
Environmental compliance: The emission standards for VOCs (volatile organic compounds) are becoming increasingly strict in various countries. Recovery is one of the most effective means to achieve compliance with emission standards (even near-zero emissions), and it can prevent hefty fines.
Workplace safety: Reduce solvent vapor concentration in the workplace to lower the risks of fire, explosion and occupational health hazards.
Social Responsibility: Implementing sustainable development and enhancing corporate image.
II. Mainstream Solvent Recovery Technologies and Equipment
The core principle is to enrich, separate and purify the gas containing solvents to obtain reusable liquid solvents.
1. Adsorption recovery method (the most commonly used)
Technical principle: Utilizing porous materials such as activated carbon or zeolite molecular sieves to selectively adsorb solvent molecules in the waste gas. Once the adsorption capacity is saturated, the solvent is desorbed by steam (for water-soluble solvents) or hot nitrogen (for non-water-soluble and easily hydrolyzed solvents), and the gas rich in solvents is then condensed and recovered.
Applicable solvents: It has the widest application range, especially suitable for medium and low concentration, large air volume waste gas, such as exhaust from coating and drying lines.
Equipment features:
Activated carbon adsorption + steam desorption: A classic process, it has a good recovery effect on ketones, esters, benzene, etc. The equipment investment is relatively low.
Zeolite rotor/zeolite fixed bed + hot air desorption: More suitable for treating complex and mixed solvent waste gas, with good water resistance and stable operation, but with higher investment.
Process flow: Pretreatment (filtration, cooling) → Adsorption → Desorption → Condensation → Oil-water separation → Distillation purification (if necessary) → Solvent storage tank.
2. Condensation recovery method
Technical principle: Through deep cooling (down to -70℃ or even lower), the solvent vapor in the waste gas is directly liquefied and recovered.
Applicable solvents: It is suitable for high-concentration and low-flow-rate waste gas, such as the breathing gas of solvent storage tanks and the waste gas from the mixing room.
Equipment features:
The recovered solvent has a high purity and requires no further separation.
It is often used as a pre- or post-unit of adsorption method to form a "condensation + adsorption" combined process, improving the overall recovery efficiency and economy.
The operating energy consumption is relatively high (especially in deep cryogenic conditions).
3. Membrane separation recovery method
Technical principle: By taking advantage of the selective permeability of special high-molecular membranes to solvent vapor and air, the solvent is enriched on one side of the membrane and then condensed and recovered.
Applicable solvents: Suitable for treating high-concentration waste gas, usually used in combination with condensation or adsorption methods.
Equipment features:
The equipment is compact, easy to operate and causes no secondary pollution.
High requirements for the quality of the incoming gas (pre-treatment is needed to remove particulate matter and oil mist).
Membrane modules are relatively expensive and are suitable for specific scenarios.
