Troublesome triazine titrations

Titrations are a classic method for the measurement of amine concentration in solution. Amines are basic compounds—they will accept at H+ to become protonated. If we slowly add acid to an amine containing solution, the amine will grab the added hydrogen ions and the concentration of free H+—in other words, pH—will change very slowly. Once the amine is fully protonated, the pH will change rapidly will the addition of very little additional acid.

A classic high school experiment starts by adding a pH indicator to a mixture—let’s say an amine solution—and then dispensing hydrochloric acid drop-by-drop from a buret. The amount of acid added can be mapped to the concentration of amine by observing the color change. This process is fraught with inaccuracies, most notably the human factor involved in watching for a color change. The process can be greatly improved with automation; not only automated acid dispensing, but also the use of a pH meter or conductivity probe.

The simplicity and low-cost have resulted in the frequent use of titrations for the measurement of triazine concentration. This approach is challenging, if not impossible, to perform accurately in a wide variety of solutions because MEA-Triazine is not an amine. Under acidic conditions, triazine hydrolyzes to monoethanolamine and formaldehyde. The titration is more complex, as the added acid first hydrolyzes the triazine and then protonates the amine before reaching an endpoint. If a triazine solution contains nothing but triazine, this method can work for triazine determination.

MEA-triazine hydrolyzes into monoethanolamine and formaldehyde

But how do you know your triazine solution is just triazine? What if there is some excess monoethanolamine? When there is excess amine, the triazine will hydrolyze and then the free amine plus the released amine will protonate, resulting in a different endpoint. There is no way to differentiate the endpoint as being only triazine or being triazine plus amine. The resulting calculation will incorrect report a much higher triazine concentration. 

As an example of a troublesome triazine titration, a chemical manufacturer started with formalin and monoethanolamine. The theoretical maximum triazine concentration is 51% by weight. However, due to some unknowns in their process, the triazine they produced measured at 37% by weight via titration. Assuming that they had excess formaldehyde, they added additional monoethanolamine. The resulting batch measured 60% triazine. Although beyond the theoretical limit for the maximum possible, they were pleased with the results and prepared to ship a 60% blend to their customer.

With Raman spectroscopy, we are able to determine more in-depth information. We measured the sample for triazine and excess amine. It showed 37% triazine by weight—and more than 10% excess monoethanolamine. In other words, the initial batch had no free amine or formaldehyde. By adding amine, the manufacturer was able to increase the predicted triazine concentration as measured due to the titration, but in all reality, they were just adding free amine. We added formaldehyde to this solution, it immediately became warm as the excess amine reacted, and the triazine concentration increased by a few percent while the free amine decreased.

If you are the customer or end user of this triazine, what would happen? Two things: first, you would expect the triazine to have a certain scavenging capacity and operating efficiency. Breakthrough will more occur quickly and dithiazine solids will form sooner than expected. Best case scenario, you find poor performance and change your scavenger early. Worse case, you take a jackhammer to the scale in your tower. In either case, you have lost tens of thousands of dollars.

Second, monoethanolamine is also an H2S scavenger, but a reversible one. It will scavenge some H2S, possibly convincing you that the triazine batch is good. But when the spent scavenger gets warm, the amine will release the H2S, creating a serious hazard where one is not expected. This release may occur down a well where it is not an issue—or maybe in a tote sitting in the hot sun.

With an OndaVia OPAL-103 Triazine Analyzer, you can quantify the triazine concentration separately from any excess amine. A mistake costs thousands of dollars, testing costs a handful.

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