H2S Scavenger Development During the Oil and Gas Industry Search for an MEA Triazine Replacement in Hydrogen Sulfide Mitigation and Enhanced Monitoring Techniques Employed During Their Evaluation

Abstract

Hexahydro-1,3,5-tris(2-hydroxyethyl)-s-triazine (MEA-triazine) is by far the most ubiquitous H2S scavenger used globally and occupies at least 80% of the available oilfield market. While almost the perfect scavenger in terms of kinetics and H2S uptake, this product does suffer from a number of undesirable effects which are usually tolerated or managed by various engineering modifications. For example, pH elevation causes scaling issues, deposition of intractable polymeric solids and increased ethanolamine load in crudes entering a refinery are some of the most prominent. A new scavenging technology has been developed that offers an alternative to triazine. The guiding principles in the design of this technology were to achieve, equal or better scavenger efficiency compared to triazine, equal or better reaction kinetics compared to triazine, "best in class" solids control, minimal pH impact, cost competitive with triazine, no impact on fluid separation and minimal refinery impact. A family of products have been developed which are multicomponent systems, each having a designated function. The active scavenger is based upon a "latent" or hidden form of a small molecule scavenger (SMS), similar to a protecting group strategy in organic synthesis. The steady state active SMS concentration remains very low in the initial product, but it is released upon demand when it encounters hydrogen sulfide in its operational environment. The SMS release can be greatly enhanced using a suitable catalyst or synergist, over the base scavenger/carrier system, which enables a more efficient use of the base molecule. The quality and exact nature of the spent fluid is critically important to H2S scavengers and much effort has gone into the control and handling of the byproduct. High sulfur scavenger byproducts are almost always solid in nature and can cause numerous operational issues. MEA triazine has such a problem and polymerization of the initially formed monomeric dithiazine to amorphous dithiazine is one of the drivers to develop an alternative as is presented here. This new suite of products has undergone successful field trials in both gas contact towers and direct injection applications. Some challenges have also arisen, as expected with any innovation, in other application areas and environments where unexpected issues have been encountered. An honest and informative account of the design, development, properties, field trial results and future direction for this exciting new technology are discussed as well as a critical evaluation against the aforementioned triazine industry benchmark.