Protecting stainless steel surfaces using ppm levels of sulfur compounds during ethylene production

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With well over 100 million tonnes produced annually in the world, ethylene is one of the largest chemical feedstocks produced by the petrochemical industry. In North America, a primary product obtained from ethylene is the widely used polyethylene, and NOVA Chemicals Corporation operates the largest ethylene and polyethylene complexes in the world in Alberta, Canada. Ethylene is produced by high temperature steam cracking of a variety of hydrocarbons, with ethane being preferred. Unfortunately, coke (solid forms of carbon) is produced as a bi-product, which decreases production efficiency, increases production costs through higher energy use, and inevitably leads to plant down-time to remove coke and replace high temperature corrosion damaged metal infrastructure. In particular, metal dusting of stainless steel tubing can lead to catastrophic failure of high pressure gas lines. It is known in the industry that low levels of a variety of sulfur species in the hydrocarbon feed can reduce the severity of coke build-up and metal dusting over time, but the level of protection is highly dependent on the amount and type of sulfur species, as well as the composition of the hydrocarbon feed and the length of time it remains in the hot zone of the furnace. In collaboration with NOVA, we will develop a significantly better understanding of the relationship between these factors by performing a series of novel studies that approximates the hot zone exposure of the steel to ethane, steam, and sulfur species with varied residence times at 500-1000oC. In the course of training students in a field where qualified people in Canada are scarce, this information will be used to generate solutions through precise selection of the right sulfur species and optimum concentration/conditions such that coking and steel corrosion is minimized. This research will have significant ramifications in a wide variety of Canadian industries that rely on metals such as steel that are exposed to high temperature hydrocarbon reactions, both in terms of developing preventative measures, as well as technical training in a variety of areas including gaseous hydrocarbon kinetics, surface reactions, metal corrosion and surface and material characterization.