Ethane from absorption plants

Adsorption. Adsorption processes have been used to recover hydrocarbons that are heavier than ethane from natural gas. Although the adsorption process has appHcations for the recovery of pentane and heavier hydrocarbons from lean gas, the percentage recovery of LPG components in these plants usually is low compared to the normal recovery of LPG in modem turboexpander or oil-absorption plants. 

In a sensitive and specific colorimetric method 1,1,1-trichloro-2,2-bis(p-methoxyphenyl)-ethane is extracted from plant or animal tissue, using benzene or petroleum ether as the solvent. The solvent is evaporated at room temperature by a current of air and the residue dehydroha log ena ted with 2% alcoholic potassium hydroxide. By petroleum ether extraction the resulting 1,1-dichloro-2,2-bis(p-methoxyphenyl)-ethylene is removed from the reaction mixture. After the solvent is removed by air evaporation the dehydroha log ena ted methoxychlor is isolated from the nonsaponifiable portion of the fats and waxes by dissolving the residue in hot acetone, chilling, and filtering. After the acetone is removed by air evaporation, the residue is treated with 85% sulfuric acid. This produces a red solution with an absorption maximum at 555 m/z, the intensity of which can be read on a colorimeter and is a function of the methoxychlor concentration. Beer s law is obeyed over the range of 1 to 50 micrograms. 

Before the advent of turbo-expander plants in the early 1970s, the preferred method for removal of LPG materials from the gas stream was by absorption in a suitable solvent. To increase the absorption efficiencies, especially for the recovery of ethane, this technology was developed by applying refrigerated solvent to the gas stream. 

Within the Esso gas facility, there was a unit dedicated to removing ethane, propane, and other light hydrocarbons from natural gas via absorption into lean oil. This oil, now made rich by the addition of these hydrocarbons, was later distilled to remove the hydrocarbons and recycled back into the system. This distillation process involved the use of a reboiler and a fractionation column. The cold (tube) side of the reboiler contained the rich oil and the warm (shell) side contained lean oil. On September 25, 1998, a process upset caused the lean oil pump to stop, disrupting circulation of the warm lean oil through the reboiler for several hours. As a result, the overall temperature of the reboiler dropped to the temperature of the rich oil, which was -54 °F (-47.8 °C). Ice formed on the outside of the reboiler while plant personnel worked to bring the upset back to normal operating conditions. 

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