Dissolution Behavior Of Hydrogen In The Recycle Solvent Of Mild Coal Direct Liquefaction

Coal stockpile in our country is very large.Direct coal liquefaction(DCL)can convert coal to oil and high value-added chemical products,which has important economic value.At the same time,it can guarantee the energy security of our country.However,there are still some problems in the process of DCL,which are high reaction temperatures about 450℃,and high hydrogen pressures up to 19 MPa.These increase the costs of DCL process operation and reaction equipment.In order to reduce the costs of DCL production,therefore,it is necessary to develop new DCL process,which has mild reaction conditions(temperatures about 420℃,pressures lower than 10 MPa).Pre-hydrogenation of recycle solvent is an important step in the process of DCL,and the study of hydrogen transfer in the reaction of DCL is a hot topic.In this work,first,the solubility of physical-interacted hydrogen in a recycle solvent was studied.Then,the chemical equilibrium of hydrogen in the recycle solvent was investigated.Finally,through the solubility of physical-interacted hydrogen and chemical-interacted hydrogen,the hydrogen transfer in the recycle solvent was analyzed.Hydrogen must be dissolved firstly in recycle solvents in the process of pre-hydrogenation.Hence,the solubility of hydrogen in model compounds,naphthalene and tetralin,was investigated.The results indicate that the solubility of physical-interacted hydrogen in model compounds conforms to Henry’s law in the experimental measurement range.The solubility of hydrogen in tetralin is approximately equal to that of hydrogen in naphthalene.The solubility of hydrogen increases with the increase of temperature and pressure.In addition,the presence of iron catalyst did not affect the solubility of physical-interacted hydrogen in the model compounds.The solubility data of hydrogen were correlated using the equation of Henry’s law.It is found that the equation can well express the solubility of hydrogen in tetralin and naphthalene in the range of temperatures and pressures studied.The heat of dissolution and enthalpy of dissolution were calculated,which showed that the dissolution of hydrogen is an endothermic process,which indicates that the increase of temperature is beneficial to the solubility of physical-interacted hydrogen.In addition,in the presence of different catalysts,the chemical equilibria of the system of hydrogen,naphthalene and tetralin were studied.Different catalysts take different times to reach the reaction equilibrium.The reaction rate of Pd catalyst is the fastest,followed by Co-Mo catalyst and Fe catalyst.The effect of temperature and pressure on the reaction equilibrium was investigated by using Pd-C catalyst.The equilibrium constants and Gibbs free energy at different temperatures were determined by thermodynamic calculation.Then the effects of different reaction components and n-dodecane on the reaction equilibrium were investigated.It is found that the initial components of the reaction and the addition of 50 wt%n-dodecane do not change the equilibrium constant of the reaction.At last,the solubility of physical-interacted hydrogen in the recycle solvents was calculated by the correlation equation between 360～420℃,and the solubility of chemical-interacted hydrogen(hydrogen stored in the form of tetralin)at different temperatures was determined according to the calculation of the equilibrium constant.It is found that the chemical-interacted hydrogen is dominant in the hydrogenation process.When the temperature is increased,the solubility of chemical-interacted hydrogen decreases,the solubility of physical-interacted increases,and the total solubility of hydrogen decreases.During the increase of temperature,chemical-interacted hydrogen is transferred to physical-interacted hydrogen.