Molecular sieve regeneration issue
Thread Content
The regeneration of molecular sieves refers to the state in which their static adsorption capacity for water and carbon dioxide is zero at the corresponding temperature and pressure, which is known as complete regeneration. As shown in the table: the static adsorption capacity of the adsorbents for water at different temperatures. Temperature (°C): 25, 50, 75, 100, 125, 150, 250. Molecular sieve: 22, 21, 18.5, 15, 9, 6, 3.5; Activated alumina: 10, 6, 2.5, <3, <1, 0. Note: The data in the table were obtained under a water vapor partial pressure of 0.1 KPa. This means that the water trapped in the molecular sieve can be completely desorbed only when the regeneration temperature is above 250 degrees; whereas in typical processes, the regeneration temperature is below 200 degrees, so about 5% of the water remains in the molecular sieve. Is this correct? So the question is: what about CO2? Does anyone have a table showing the static adsorption capacity of molecular sieves for CO2 at different temperatures? I would like to know about this data!
It can be considered that part of the capacity of the molecular sieve is occupied by water. However, during design, 1.5 to 2 times as much molecular sieve and alumina is typically used, so you need not worry about this issue.
Thank you. I mainly want to know at what temperature, for molecular sieves, CO2 can be completely desorbed!
Carbon dioxide is easier to desorb and in smaller quantities. The inlet temperature for the regeneration of molecular sieves in air separation units is generally around 180 degrees Celsius, while the peak temperature during cold blowing reaches around 100 degrees Celsius; at this point, regeneration is considered successful and meets the requirements for further adsorption~~
For Version A, my focus remains on the issue of the distribution heater. According to the table above, 6% of moisture remains at a heating temperature of 150 degrees; what about CO2? Can it be completely desorbed?
Complete desorption is possible; one reason is the low boiling point of carbon dioxide, and the other is the low amount of carbon dioxide adsorbed in the molecular sieve (in typical air separation designs, the carbon dioxide content in the inlet air is 500 ppm)~~
If complete desorption can occur at 150 degrees, then what is the purpose of high-temperature activation? Just for dehydration?
High-temperature regeneration of newly installed molecular sieves is carried out to prevent \"contamination\" (high water content) during transportation and installation. Of course, the water content of molecular sieves at the time of leaving the factory is generally low, and they are also sealed with nitrogen, which makes high-temperature regeneration unnecessary. As for high-temperature regeneration during operation, it is done mainly due to issues such as water entering the molecular sieves or a decrease in their adsorption capacity. The purpose of this regeneration is primarily to remove any residual water from the molecular sieves~~