Solvent recovery in the pharmaceutical industry

Principles of Chemical Engineering: lol:lol:lol:lol:lol

When a liquid substance is heated, its vapor pressure increases. When this vapor pressure equals the atmospheric pressure or some other given pressure, the liquid boils, reaching its boiling point. Distillation refers to the combined process of heating a liquid substance until it boils and turns into vapor, and then cooling that vapor back into a liquid. Fractionation: If a mixture of two volatile liquids is distilled, at the boiling temperature, an equilibrium is established between the gas phase and the liquid phase. The vapor produced contains a higher proportion of the more volatile components; when this vapor is condensed back into a liquid, its composition is similar to that of the gas phase (i.e., it contains more volatile components), while the residue contains a higher proportion of the high-boiling-point components (less volatile components). This constitutes a single instance of simple distillation. If the liquid obtained from vapor condensation is distilled again, another gas-liquid equilibrium occurs, and the vapor produced contains an even higher proportion of volatile components. Condensing this vapor again yields a liquid with an even higher concentration of volatile components. By carrying out a series of such systematic distillations, it is possible to obtain two liquids with components that are nearly pure. Although repeated simple distillations can yield liquids with nearly pure components, this method is time-consuming, involves significant losses during multiple distillations, and requires complex equipment. Therefore, fractionating columns are typically used to carry out multiple processes of vaporization and condensation—this is what fractionation entails. Inside a fractionating column, when the rising vapor comes into contact with the descending condensed liquid, part of the vapor condenses, releasing heat that causes part of the condensed liquid to vaporize. Heat exchange occurs between the two, resulting in an increase in the volatile components in the rising vapor and an increase in the high-boiling-point components (less volatile components) in the descending condensed liquid. Repeating this process multiple times is equivalent to carrying out multiple gas-liquid equilibria, thus achieving the effect of multiple distillations. As a result, near the top of the fractionating column, the proportion of volatile components is high, while in the flask, the proportion of high-boiling-point components (less volatile components) is high. As long as the fractionating column is tall enough, these components can be completely separated. Industrial distillation towers function in a similar manner to fractionating columns.

The principle is quite simple: it involves using the different boiling points of various solvents to control evaporation and condensation for recovery. The focus is on control

The same principle, different devices, various dissolution combinations, and constantly changing operational management.

I used to work at a pharmaceutical raw material company, where ethanol was recovered by taking advantage of its different boiling points

For principles of chemical engineering, just look at this one, haha~~~~~~~~~

There are currently four main methods for solvent recovery: 1. The most commonly used method is distillation + rectification; this is the oldest process, relying on the different boiling points of various components to achieve separation. 2. Organic membrane separation, which was quite popular in recent years. Separation is primarily achieved by taking advantage of the different dissolution and diffusion rates of various components in the membrane. 3. The molecular sieve adsorption method utilizes the selective adsorption of various components by molecular sieves for separation. 4. Inorganic molecular sieve pervaporation membranes utilize the regular pore sizes of the molecular sieve membrane, as well as the difference in size between solvent molecules and water molecules, to achieve separation based on the principle of size-based screening. These are the main separation methods at present. There is also a supergravity bed separation method, which is essentially distillation separation.