Effect of Antifreeze Agents on the Formation of Hydrogen Sulphide Hydrate

Abstract

Abstract The effects of various antifreeze agents on the formation of hydrogensulphide hydrate have been studied. On a molar basis the relative lowering ofTM (the maximum temperature at which solid hydrogen sulphide hydrate can existin equilibrium with the given solution) for the various agents is: sodiumchloride 1.00, calcium chloride 1.71, methyl alcohol 0.57, ethyl alcohol 0.68, ethylene glycol 0.73, diethylene glycol 0.73, sucrose 0.87, dextrose 0.71. On aweight basis the relative lowering of TM is: sodium chloride 1.00, calciumchloride 0.91, methyl alcohol 1.08, ethyl alcohol 0.89, ethylene glycol 0.69, diethylene glycol 0.41, dextrose 0.23, and sucrose 0.15. Introduction The solid hydrate of hydrogen sulphide, H2S?6H2O1, is in equilibrium withwater and liquid hydrogen sulphide at 85?F at a partial pressure of hydrogensulphide approximately equal to the vapor pressure of hydrogen sulphide at thattemperature. At temperatures below 85?F, in the presence of excess hydrogensulphide (greater than the amount required to react with the water present) thehydrate is in equilibrium with liquid hydrogen sulphide at approximately thevapor pressure of hydrogen sulphide. In the presence of excess water, the solid hydrate is in equilibrium withliquid water, containing dissolved hydrogen sulphide, at a pressure lower thanthe vapor pressure of liquid hydrogen sulphide at the same temperature. Thelower the temperature, the greater the difference between the decompositionpressure of the hydrate and the vapor pressure of liquid hydrogen sulphide atthat temperature. Conditions conducive to the formation of solid hydrogen sulphide hydrate mayexist in wells producing a gas containing a high percentage of hydrogensulphide under high pressure, or in the lead lines from such wells. This papergives the results of tests made with various antifreeze agents which might beuseful in decomposing the hydrate or in preventing the formation of the hydrateof hydrogen sulphide. Apparatus Fig I shows a diagram of the apparatus used. The sample under observationwas contained in a glass tube 34 cm long, having a 6 mm id and a wall thicknessof 2.5 mm. The lower end of this tube was closed with a plug of butyl rubber.The upper end of the tube was connected to a diaphragm gauge, with a stainlesssteel diaphragm, a manometer, a vacuum pump, and a cylinder of hydrogensulphide. The tube was held nearly horizontal, with the liquid resting along the lowerside of the tube. It was found that when the tube was held in a verticalposition, it broke with explosive violence as soon as it became filled withsolid hydrate. Presumably this was caused by the expansion which occurred onsolidification of the hydrate. The difficulty disappeared when the tube washeld in an inclined position during the tests. T.P. 2450