Continuous mode calculations

[niema]

Hi,

I do not know how to calculate the number of moles of gas that is absorbed due to chemical reaction in the reactor.

I have an open system. A gas mixture (absorbed gas A and a dilluting (neutral with respect to the liquid phase) gas B) is fed to the reactor through the sparger located in the bottom part (liquid phase). Flow rates of these gases are controlled using the mass flow controlles. Gas mixture leaves the reactor in the top part of the reactor and it goes directly to the gas detector which is used to determine the concetration of the gas A in the gas gmixture (in units like percent by volume, mg/m3). The pressure in the reactor is equal to atmospheric pressure.

I would like to calculate the number of moles of reacting gas A in the liquid phase. How can I do that?

Thank you.

Best regards,

 

[sshep]

Hello Niema,

It would be best to clarify again because language like "absorbed in the chemical reaction" and "moles of reacting gas in the liquid phase" are misleading. The concentration of reacting gas A in the liquid and consumption A by the reaction are two different quantities. Perhaps this can help:

The concentration of A in the liquid can be estimated from Henry's Law as a vapor-liquid equilibrium, but the accuracy of this assumption depends heavily on several factors especially the speed of the reaction. For example, a fast reaction may be limited by the diffusion of reactants into the liquid so that the actual concentration of A in the liquid is quite low. In such a case the mass transfer rates required to solve for xA could be quite difficult to calculate. If you have a local rate expression for the reaction then your best hope is to back calculate the local reactant concentration from assumptions on the other reactant concentrations, etc.

On the otherhand if you want to calculate the consumption of A (absorbed in the chemical reaction) it is easy. If you have a recycle then it is simply the make-up rate of A less purged A. If there is no recycle of offgas then you can calculate A consummed directly by a material balance on the product rate from reaction stochiometry. You can also check by calculating gas side feed and outlet rates of A which is done by using your analysis and assuming that the inert gas flow in equals out.

Please better clarify what you know and what you need to know again. If you provide the details of the actual reaction then perhaps we can help you with the assumptions needed to formulate a reasonable engineering model.

best wishes always,
sshep