Tetrahydrofuran (THF), also known as oxacyclopentane, has extremely strong polarity and form azeotropes with water. The azeotropic point is 64℃ at normal pressure, and the mass fraction of tetrahydrofuran in its azeotropic composition is 93.3%. Under constant pressure and temperature, for an azeotropic system, it is impossible to achieve high-purity separation using ordinary distillation methods.
.png)
Waste THF Solution
Distillation technology is the earliest typical unit operation to achieve industrialization in the separation of liquid mixtures. It is widely used in environmental protection fields such as petroleum, chemical industry, and medicine. It generates a vapor-liquid two-phase system by heating, and uses the difference in volatility of each component in the mixture to achieve the purpose of component separation and purification. In the application process, it is often encountered that the relative volatility between the components to be separated is close to 1 or an azeotropic system is formed. If the conventional distillation method is used for separation, it is not feasible or uneconomical. At this time, special distillation methods such as azeotropic distillation, extractive distillation, and pressure swing distillation are often required. At present, the main methods for treating tetrahydrofuran wastewater are extractive distillation, pressure swing distillation, adsorption method, pervaporation membrane separation method, and biochemical method. Pervaporation easily removes components from water to below 1%. Higher concentrate purification levels are possible but require a relatively large membrane surface, because the encountered fluxes are relatively low (low driving force).
.png)
PV & VP
Flow Diagram of Zeolite Pervaporation Process
There is also an alternative process, referred to as vapor permeation. Vapor permeation involves the supply being introduced in vapor form before it comes into contact with the membrane. This alternative is particularly interesting if the supply comes from an earlier process step in vapor form. Pervaporation is not based on a liquid-vapor balance like distillation, but is based on differences in sorption and diffusion in the various components in the supply. This it is an interesting alternative for separating azeotropic mixes or mixes with similar boiling points. Further, it offers an energy advantage because only the permeating component must be converted in the gas phase.
.png)
Zeolite Pervaporation System for THF DehydrationIn the Grignard reaction process of petrochemical and pharmaceutical chemical industries, the water content in tetrahydrofuran solvent is strictly required (generally less than 500ppm). The solvent needs to be dehydrated and reused. The traditional pressure swing distillation method used for tetrahydrofuran dehydration consumes more than 1.5 tons of steam per ton of product. The tetrahydrofuran product recovery rate is low. The column is prone to produce peroxides, which brings safety hazards in operation. For this problem, pervaporation membranes are used for the purification of tetrahydrofuran (THF) solvents, shortening the separation process of THF and water, increasing the product recovery rate by 4~5%. It needs only 0.35 tons of steam per ton of product. At the same time, due to the operation at low temperature and low pressure, the system safety is better.
.png)
.png)
