How to recycle tetrahydrofuran waste gas? Recovery route and key points of configuration for water-soluble ether solvents

Tetrahydrofuran is used a lot in the process of pharmaceutical synthesis, polyurethane and some electronic materials. Its recovery difficulties are completely different from those of conventional aromatic hydrocarbon solvents: miscible with water, low boiling point, and easy to generate peroxides. These three characteristics determine that its recovery route cannot simply copy the practice of condensation and re-stratification, and the condensate treatment and storage links should be considered separately.

What are the effects of the three properties of tetrahydrofuran

One is miscible with water. The condensate cannot be separated by static stratification, and the recovered mixture is often an aqueous mixture, which needs to be purified by distillation according to the subsequent process or directly enter the corresponding process for reuse. Second, the boiling point is low and the volatilization at normal temperature is fast. If the collection link is not sealed properly, the gas source concentration will be diluted by ambient air, and the scale of the device will be forced to enlarge. Third, the storage link should pay attention to the problem of peroxide, long-term storage or exposure to air after the risk, storage and treatment methods should be implemented according to the process requirements of the user.

Configuration steps

1. First sort out the air source point and exhaust time, and do a good job of airtight collection to reduce the unorganized emission of diluted air source.
2. The condensation temperature is determined according to the composition and concentration, the boiling point of tetrahydrofuran is low, and the conventional refrigerant can usually meet most of the liquefaction.
3. Condensate shall be provided with intermediate tank and sampling port, and purification or reuse path shall be determined according to the water content.
4. After condensation, the residual low-concentration exhaust gas can be concentrated again to reduce the external displacement.
5. Recycled and reutilized amounts are included in the material ledger, and the balance is checked regularly.

How to deal with condensate is more appropriate

Differences from conventional solvent recovery

Comparison item	Tetrahydrofuran	Common solvents (such as toluene, ethyl acetate)
water-soluble	mutual solubility with water	Most are insoluble in water or have limited solubility
Condensate separation	Cannot be stratified by standing still.	Allow it to stand until the layers separate.
Boiling Point Level	Low, fast volatilization	Moderate or low
Storage Concerns	Storage conditions shall be controlled according to process requirements	Routine Closed Storage

The treatment of the water-containing condensate is directly related to the reuse target. If the return process is not sensitive to moisture content, it can be reused after simple treatment. If the process requirements are high, it is necessary to complete distillation purification. The scale is determined according to the amount of recovered liquid and the target purity, and is matched with the capacity of the condensation section to avoid backlog caused by large front-end recovery and back-end purification. The by-product water phase and kettle residue shall be disposed according to the environmental protection management requirements of the user, and the responsibility interface shall be clarified in the scheme stage.

Concerns in operation

The degree of containment of the collection system is more worthy of investment than the condensation temperature level, because the scale of the equipment will be significantly enlarged after the gas source is diluted, and the unit recovery income will decrease. Condensate outlet temperature and condensate volume to keep continuous records, used to determine the state of the heat transfer surface. The storage time of the intermediate tank shall be controlled according to the process requirements to avoid long-term accumulation. The sampling analysis suggests a fixed frequency, and the change of water content will affect the choice of reuse mode.

Pre-configuration checklist

Confirm the gas source composition, concentration fluctuation range, exhaust temperature, water content and the quality requirements of the reuse process, and then determine the recovery route and condensate treatment method. These data are clear, the scheme is not prone to the problem of disconnection between front-end recycling and back-end recycling.