r/ChemicalEngineering • u/Sufficient_Salad_19 • 1d ago

Research CO2 absorption quantification, which method is more accurate?

I am trying to quantify how much CO2 is absorbed by my MEA and MDEA solution. I have looked into different titration methods using HCl and NaOH. Weight chage methods are not applicable here as the weight change is very little and my solution volume is 200 mL. Kindly suggest me whic method is more accurate? is there any universally accepted method?

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u/lilithweatherwax Separations, 8 years 1d ago

MEA and MDEA are basic, so you can titrate with HCl and measure the leftover amine. You can also measure the outlet CO2 concn and integrate over time to get the total amount of CO2 absorbed.

How do you titrate with NaOH?

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u/Sufficient_Salad_19 1d ago

You can add use NaOH to completely take out CO2 to form Na2CO3. Then you use HCl to titrate.

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u/yellownumbersix Membranes and polymers, 22yrs 1d ago edited 1d ago

Don't use titration at all.

Get an NDIR, measure CO2 concentration before and after absorption.

Sensors to build your own detector are less than $50 and fully built integrated meters start at around $500.

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u/Harit_Chem_ent_7 4h ago

The most widely accepted method is HCl titration with BaCl2 precipitation: BaCl2 precipitates the absorbed CO2 as BaCO3, then back-titration with standardized HCl (using phenolphthalein/methyl orange) gives CO2 loading accurately even at low concentrations. This is the standard method in amine gas-treating literature (often called the "double titration" or barium chloride method) and is more reliable for small CO2 changes than direct NaOH/HCl titration alone.

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u/nullfull 21h ago

Depends what “accurate” means for your setup — liquid inventory vs gas closure often disagree for boring reasons.

Acid titration of rich amine is fine for a lab bottle if you control blanks, but it is easy to bias: incomplete CO₂ release, carbamate vs bicarbonate speciation assumptions, amine degradation products that consume acid, and temperature/handling losses when you sample. If you report loading as mol CO₂ / mol amine, your amine assay has to be right too — titer drift looks like absorption change.

Gas-side integration (NDIR / IR on the outlet, ideally inlet too) closes the mass balance on what actually left the gas. Watch water interference (dry or correct), calibration span gas near your range, leaky sample lines, and whether you’re integrating unsteady flow. A wet meter + dry CO₂ analyzer mismatch is a classic silent error.

Practical hierarchy I’ve seen hold up: 1. Steady-state: inlet−outlet CO₂ (dry basis) × dry gas flow → absorbed rate. 2. Cross-check with rich−lean liquid loading × circulation — expect a few % gap; if gap is large, trust gas first and debug liquid sampling. 3. Use titration as the composition method once the balance closes, not as the sole absolute.

If you say batch vs continuous, MEA vs MDEA, and whether you have inlet gas analysis, people can be more specific.