Removal of hydrocarbons and recovery of hydrogen from hydrogenation tail gas via hydrates formation using reverse thinking: Cast a small fish for a big one

摘要

We conducted the removal of hydrocarbons and concentrating of H-2 from the tail gas of diesel hydrogenation (tail gas for short) using hydrate separation method. Based on the preliminary separation results, it is necessary to apply hydrate thermodynamic promoter to further improve the separation efficiency. In order to avoid the introduction of new impurity, we added propane (C3H8), one component of tail gas, in the feed gas as the hydrate promoter by reverse thinking, because it runs counter to the hydrocarbons removal from tail gas. The formation equilibrium conditions of tail gas hydrates were measured, and the enthalpy of hydrates equilibrium dissociation was calculated by the Clausius Clapeyron equation. The results show that the addition of C3H8 significantly decreases the formation equilibrium pressure of tail gas hydrates at the same temperature. It indicates that C3H8 indeed performs as a thermodynamic promoter for tail gas hydrates. Consequently, the driving force for hydrates formation increases, and more hydrates form at the equilibrium state. As a result, the total removal rate of hydrocarbons and the recovery rate of H-2 are both increased, while the concentration of H-2 in equilibrium gas almost keeps unchanged. The results demonstrate that the addition of C3H8 behaves as an inducer to enclose relatively more hydrocarbons into hydrate phase, and it also accelerates the hydrates formation rate at the same time. This work presents a new research idea, i.e., cast a small fish for a big one, for the flexible and optimum application of hydrate separation technology. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.