Dissolution behavior of hydrogen in the model recycle solvent of mild direct coal liquefaction

Abstract

Direct coal liquefaction (DCL) at mild conditions (about 693 K and less than 10 MPa) is an important and efficient way for the conversion of coal to high value-added chemicals and fuel oil. In the process of DCL, the pre‑hydrogenation of a recycle solvent is an important step and the recycle solvent is always heated from low temperatures to high temperatures. So, it important to study the dissolution behavior and the migration of hydrogen in the recycle solvent for DCL processes, especially for mild DCL processes. First, physical solubility of hydrogen in a model recycle solvent of naphthalene and 1,2,3,4-tetrahydronaphthalene was measured, and the Henry's constants at different temperatures were obtained. Then, the chemical solubility of hydrogen (chemical bonded hydrogen via hydrogenation of naphthalene to 1,2,3,4-tetrahydronaphthalene) in the recycle solvent was measured simultaneously. The equilibrium constants of the hydrogenation reaction at different temperatures were obtained. Finally, through the physical solubility of hydrogen and chemical solubility of hydrogen, the dissolution and migration of hydrogen in the recycle solvent were analyzed. When the temperature is increased, the physical solubility of hydrogen increases, the chemical solubility of hydrogen decreases, the total solubility of hydrogen decreases due to the dominant contribution of chemical solubility of hydrogen, and interestingly a small part of hydrogen released from 1,2,3,4-tetrahydronaphthalene is transferred to physical solubility. When the pressure is increased, the chemical solubility of hydrogen, the physical solubility of hydrogen and the total solubility of hydrogen all increase