Dehydration of liquid-phase solvents

Dehydration of solvents using molecular sieves: 1. Molecular sieves can be used for the deep dehydration of most solvents, and are generally suitable for applications where the water content is below 3%. Depending on the properties of the solvent, different molecular sieves can be chosen; the degree of dehydration achievable is in the range of several hundred to dozens of PPM. 2. In cases where the raw material has a high water content, the molecular sieve unit can be used in combination after distillation or membrane dehydration. 3. For different operating conditions, either a single-tower adsorption process or a multi-tower adsorption process can be selected. 4. The regeneration gas source for the regeneration system can be nitrogen or air; it is important to select the appropriate gas source and regeneration method depending on the solvent used, as this has a significant impact on operational safety, nitrogen consumption, and energy savings during regeneration.

There are two questions: 1. Can molecular sieve dehydration achieve a good dehydrating effect on solvents with a high water content? 2. What is the lifespan of molecular sieves? Can it be regenerated? Will dehydration introduce impurities that affect product quality?

1. Molecular sieves are used to dehydrate the liquid solvent; the water content in the solvent should preferably be no more than 3%. If the water content is too high, a large amount of molecular sieve is required, which leads to rapid saturation, frequent regeneration, high energy consumption for regeneration, and substantial consumption of nitrogen gas for regeneration – all of which make it uneconomical. 2. The service life of liquid-phase adsorption molecular sieves is 2–5 years; the more frequently they are regenerated, the shorter their lifespan becomes. Therefore, a lower moisture content in the feed water is beneficial for extending their service life. 3. During the dehydration process, only molecular sieves develop a trace amount of powder after long-term use; therefore, a precision filter is installed at the equipment outlet.

I have the following questions: 1. Is it appropriate to use molecular sieves for solvent liquid-phase dehydration nowadays, and what is their service life under such conditions? 2. During the dehydration process, what proportion of the molecular sieve’s weight is occupied by the solvent adsorbed by it?

Are there structural differences required for molecular sieves used in liquid-phase dehydration versus those used in gas-phase dehydration? How long is the typical lifespan of molecular sieves used for gas-phase dehydration?

1. Molecular sieve liquid-phase dehydration is particularly suitable for deep dehydration when the solvent has a low water content, and its service life is generally 2-3 years. 2. If dehydration is the only requirement for the logistics process, it is necessary to choose an appropriate molecular sieve that absorbs only water and not the solvent of the main material.

Liquid-phase and gas-phase dehydration differ mainly in their adsorption processes; the service life of molecular sieves used in gas-phase dehydration is 3–5 years.

Using molecular sieves for dehydration is a last resort; try to use other methods instead whenever possible. Theoretically, molecular sieves do not operate in a steady state, and their dehydration efficiency varies depending on the time of use； 2: Switching back and forth is troublesome ； 3: Molecular sieve regeneration may cause secondary pollution ； 4: Molecular sieve operation costs have no advantage.

Well, molecular sieves are particularly suitable for applications where the water content of the incoming medium is low (e.g., a few thousand PPM) and further deep dehydration to levels of a few dozen PPM is required. In such situations, the need to switch the molecular sieves isn’t frequent; regeneration can take place once every few days or even dozens of days. Secondary pollution occurs when trace amounts of powder appear after the molecular sieve has been in use for a long time; a precision filter can be installed to address this issue. In conditions where the moisture content of the inlet medium is low, regeneration occurs only once every few days, resulting in extremely low operating costs and energy consumption.

For operations where the water content of the feed medium is reduced from a few thousand PPM to several dozen PPM through deep dehydration, what are appropriate values for the contact time between the material and the molecular sieve (or the material flow rate), as well as the saturated adsorption capacity of the molecular sieve (under both dynamic and static conditions), when making an initial estimate of the amount of molecular sieve required?