We recently received a spent H2S scavenger sample for laboratory analysis. Over the years, we’ve seen many samples like that shown in the figure above: red or yellow in color with two distinct layers. After hundreds of samples, we’ve been experts at spent scavenger anaylsis.
For analysis, we first shook the sample to make sure it was well-mixed. This sample mixed quickly, turned cloudy and opaque, and remained mixed for a few minutes. Using Quantitative Raman Spectroscopy, we measured the dithiazine (DTZ) content at 11%. The triazine content was zero — there is no signature peak from the triazine ring visible in the spectrum.
After the sample sat for a couple hours, it separated back into two layers. We measured each layer separately. The top layer measured at 5% DTZ. The bottom layer is too concentrated to be measured directly, but after a 1/4 dilution, it measured as 52% DTZ. As a fun side experiment, if we measure the height (i.e. , volume) of the two layers, these numbers correspond to…11% total DTZ. It’s always a good day when the math checks out. 😄
In the spectrum above, we show the Raman data for the diluted bottom layer (blue), the top layer (black), the mixed sample (green), and a DTZ analytical standard (purple). The top and bottom layers contain MEA and TDZ. This data exemplifies why Raman spectroscopy is ideal for spent scavenger analysis.
We know this scavenger solution started at about 30% triazine. If we assume the system is closed — that H2S is introduced but no water or other liquid is removed — then we can deduce more about the results. The 30% triazine was completely consumed into thiadiazine (TDZ) and 11% DTZ, which means the sample should contain 12% TDZ. And if there is 12% TDZ and 11% DTZ, there should be 12% monoethanolamine by weight. Using our low-percent monoethanolamine measurement technique, we confirm the amine concentration in the mixture is as-expected.