Maximum possible MEA-triazine concentration

Once you build a tool to measure the triazine reaction, you develop a lot of expertise in the chemistry. We get a lot of questions about triazine production, both MEA- and MMA-. And we see a lot of strange math out there. One of those questions is: what is the maximum concentration triazine I can make? So we set about to do some MEA-triazine reaction calculations for you.

Let’s start with a couple assumptions. 1) Formaldehyde is your limiting reagent. You want to make the highest concentration triazine that you can given a certain formaldehyde concentration. 2) You are not distilling off any water. Everything you put into the reaction remains.

We do all of our triazine math as a percent weight (wt%). The wt% concentration of triazine (TRZ) is the ratio of the mass of the triazine to the total mass of the final product:

wt\%_{TRZ}=\frac{m_{TRZ}}{m_{final}} (1)

Remember conservation of mass? We start this process by mixing two reactants and we’ve assumed you aren’t losing any through another process. The mass of the final product must be the mass of the two reactants, the MEA solution and formaldehyde solution:

m_{final}=m_{FA-solution}+m_{MEA-solution} (2)

Note that I’m calling them the mass of the solutions, not the mass of the chemical. I do this because we usually work with solutions that are not 100% of the chemical, e.g. 37% formaldehyde where 100 g of 37% formaldehyde contains 37 g of formaldehyde and 63 g of water (and possibly some methanol).

In my opinion, there’s one reason there is so much confusion about this reaction: stoichiometry. The number of moles of each reactant that is important. One mole of something is just 6.022×1023 items. Why is the number of items important in a reaction? Because, for triazine, we take 3 MEA molecules and combine it with 3 formaldehyde molecules. The reaction is not 3 pounds of MEA plus 3 pounds of formaldehyde. Or gallons. Or liters. Or kilograms. Or truckloads. Or totes. It’s the number of molecules.

3\hspace{0.1cm}\textup{mol MEA} + 3\hspace{0.1cm}\textup{mol FA} \rightarrow 1 \hspace{0.1cm}\textup{mol triazine} + 3\hspace{0.1cm}\textup{mol water} (3)

So we have to convert from mass to moles. Monoethanolamine is 61 g/mol, formaldehyde is 30 g/mol, and triazine is 219 g/mol. (If you feel like you need more significant figures, go ahead. I’m not sure anyone is really making triazine with that level of precision.)

If we want no excess reactants, then we need to have C_{MEA}=C_{FA}. And we know that after the reaction, we will have C_{triazine}=3C_{FA}.

The concentration (in moles) for formaldehyde and monoethanolamine are given by:

C_{FA}=\frac{m_{FA-solution}\times wt\%_{FA}}{30 g/mol} (4)

C_{MEA}=\frac{m_{MEA-solution} \times wt\%_{MEA}}{61 g/mol} (5)

where the ratios are the %-weight of the starting solutions. For formaldehyde, this value is 35-37% (formalin), 50% (heated formalin), or 100% (paraformaldehyde). For MEA, this value should be >95%. If you are buying anything other than these values, stop. Go find a reputable supplier and get quality reactants.

Now let’s do some math! From equation 5:

m_{MEA-solution}=\frac{C_{MEA} \times 61}{wt\%_{MEA}}=\frac{C_{FA} \times 61}{wt\%_{MEA}} (6)

which is

m_{MEA-solution}=\frac{m_{FA-solution} \times wt\%_{FA}}{30}\frac{61}{wt\%_{MEA}} (7)

Now we substitute this equation into the final mass equation (2):

m_{final}=m_{FA-solution} \left[1+\frac{61}{30}\frac{wt\%_{FA}}{wt\%_{MEA}}\right] (8)

And now we can do some MEA-triazine reaction calculations:

wt\%_{triazine}=C_{triazine} \frac{219}{m_{final}}=\frac{C_{FA}}{3} \frac{219}{m_{final}} (9)

=\frac{219}{3}\frac{1}{m_{final}}\frac{m_{FA-solution} wt\%_{FA}}{30} (10)

And finally, we get:

wt\%_{triazine}=2.43 wt\%_{FA} \left[1+\frac{61}{30}\frac{wt\%_{FA}}{wt\%_{MEA}} \right]^{-1} (11)

This equation tells you the maximum concentration triazine solution you can produce starting from a formaldehyde concentration. Everything disappears except for the starting wt% of formaldehyde and monoethanolamine. And given that you should be using a quality monoethanolamine, for which we can set the MEA ratio to 1.00, then all that matters is your formaldehyde percentage.

So what does this equation tell us?

Formaldehyde concentration (wt%)Maximum triazine concentration (wt%)
MEA-triazine reaction calculations. Maximum possible MEA-triazine concentrations as a function of formaldehyde concentration
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