Investigation of Fouling Formation during H2S Scavenging with 1,3,5-tri-(2-hydroxyethyl)-hexahydro-s-triazine
Author
Madsen, Henrik
Term
4. term
Education
Publication year
2011
Abstract
Dette projekt undersøger belægning (fouling) rigt på kulstof og svovl, som tilstopper vandbehandlingssystemet på Shells raffinaderi i Fredericia, og om belægningen hænger sammen med Maersk Oils brug af H2S‑scavengeren 1,3,5‑tri‑(2‑hydroxyethyl)‑hexahydro‑s‑triazine. Arbejdet kombinerer en massebalance baseret på procesdata fra Maersk, en kinetisk model fra litteraturen og elektrospray‑ionisations‑massespektrometri (ESI‑MS) af reaktionssystemer (HS–/triazine, H2S/triazine og H2S/brugt scavenger), samt undersøgelser af opvarmning og reaktionen mellem MEA og H2S. Belægningen er karakteriseret med infrarød spektroskopi (IR), røntgendiffraktion (XRD), TS/VS‑analyse og Hansen opløsningsparameteranalyse (HSP), og sammenlignes med ren trithiane. Resultaterne viser, at triazinen først omdannes til thiadiazin og derefter til dithiazin, hvor reaktionen standser; trithiane blev ikke detekteret. Overdosering af scavenger med H2S frembringer et udfældet materiale identisk med Shells belægning, som er semikrystallinsk, indeholder forskellige C–S‑bindinger med tegn på ringåbning, og er meget svær at opløse, om end opløsningsmidler med HSP‑værdier δH = 0–9 og δP = 5–11 påvirker den. Massebalancen indikerer, at størstedelen af den brugte scavenger udledes med produceret vand, men under vedligehold kan indholdet i olien stige kraftigt; den kinetiske model peger på, at selve scavengingen er hurtigere end triazinhydrolyse, hvilket begrænser formaldehyddannelse. I MEA/H2S‑forsøget blev en lille mængde disulfid påvist. Samlet set viser arbejdet, at belægningen hos Shell er en direkte følge af anvendelsen af H2S‑scavenger, og at dithiazin sandsynligvis polymeriserer til et kulstof‑svovl‑forbundet materiale.
This thesis investigates carbon‑ and sulfur‑rich fouling that clogs the water treatment system at Shell’s Fredericia refinery and whether it arises from Maersk Oil’s use of the H2S scavenger 1,3,5‑tri‑(2‑hydroxyethyl)‑hexahydro‑s‑triazine. The study combines a mass balance based on Maersk process data, a kinetic model from the literature, and electrospray ionization mass spectrometry (ESI‑MS) of reaction systems (HS–/triazine, H2S/triazine, and H2S/spent scavenger), along with tests of heating effects and the MEA/H2S reaction. The fouling is characterized by infrared spectroscopy (IR), X‑ray diffraction (XRD), TS/VS analysis, and Hansen solubility parameter (HSP) analysis, and compared with pure trithiane. Results show that the triazine first converts to thiadiazine and then to dithiazine, where the reaction stops; trithiane was not detected. Overspending the scavenger with H2S produces a precipitate identical to Shell’s fouling, which is semicrystalline, contains various C–S bonds with indications of ring opening, and is very difficult to dissolve, though solvents with HSP values δH = 0–9 and δP = 5–11 affect it. The mass balance indicates that most spent scavenger exits with produced water, but maintenance events can greatly increase its content in oil; the kinetic model suggests scavenging is faster than triazine hydrolysis, limiting formaldehyde formation. A small amount of disulfide was detected in the MEA/H2S test. Overall, the work shows that Shell’s fouling is a direct consequence of the scavenger use, with dithiazine likely polymerizing into a carbon–sulfur‑linked material.
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