Solving a mystery of high impurity concentrations

matric_196-pick-16x9Early in 2014, one of our customers was experiencing high impurity concentrations in their product. High levels of both the typical impurities and unexpected oxidized contaminations were present in their product overhead. This was problematic because a high-value stream was failing specifications and the only solution was to sell it as a lower-value commodity. Using our uncommon expertise in chemical, engineering and environmental technologies, MATRIC conducted a thorough study which included thoughtful analysis of data, discussion amongst experienced scientists, and experiments in the laboratory to understand the reasons for the high levels in order to control and prevent them.

We began by analyzing the feed to the problematic column. Data obtained here revealed that it contained no precursor to the impurity, suggesting that it was being formed in the distillation process. We surmised that the most likely origin of the observed impurity was from the product itself. There are at least two possible avenues for this decomposition: thermal and acid-catalyzed.

Our customer’s desired product is thermally stable at the recorded base temperature of the column in question. We supposed that for thermal decomposition to occur, there would have to be a spot source of high temperature, perhaps due to exposure to steam from dry or plugged tubes in the column reboiler. Our experts were able to determine a relationship between pH and impurity formation. Further GC-MS analysis of the suspect material showed that side-product was present along with the precursor to the known impurity.

The samples in question also contained small amounts of two unknowns. By using our experience and knowledge of the process, we were able to apply thoughtful gas chromatography-mass spectrometry techniques to elucidate the impurities in question. Interestingly, both of these compounds were of a composition such that they reacted during the client’s routine analysis methods and skewed the results—hence why their identity was so difficult to ascertain.

We were also able to determine from plant data that a large increase of one of the impurities was also associated with a two-fold increase in the amount of water present.  This observation suggests that there was an air leak present, bringing oxygen and humidity into the column.  We deduced an influx of air and the presence of water caused iron in the system to rust which further increased the concentration of impurities present.

Ultimately, we were able to surmise the impurities’ identity and origin. Based on discussions and lab results at MATRIC, we were able to supply our client with a series of very specific recommendations and operating conditions for their plant so that they could alleviate the formation of their impurities.  We were also able to assist in recommending analytical techniques to verify these impurities if ever again encountered and distinguish them from more common and misleading interferences so their product can retain its high value.

— For more information on MATRIC’s GC-MS capabilities, contact Eric King.