Hydrogenation Of Dibenzyltoluene Catalyzed By Composite Magnesium-based Hydrides

The safe storage and transportation of hydrogen is one of the main constraints for the promotion and application of hydrogen energy.Finding materials with high hydrogen storage capacity is one of the effective ways to solve this problem.Hydrogen slurry is prepared by mechanically mixing hydrogen storage alloys and Liquid Organic Hydrogen Carriers.The existing hydrogen slurry systems mostly consist of rare earths and hydrides,benzene and toluene.However,rare earths and their hydrides have low hydrogen storage capacity,benzene,toluene,and other materials have poor hydrogen absorption and desorption kinetics,low boiling points,biological toxicity.To increase the hydrogen storage capacity of hydrogen slurry,improve the kinetic performance of hydrogen absorption and desorption of LOHCs,expand the applicable range of hydrogen slurry.First,this paper selects dibenzyltoluene(DBT,6.2 wt%)with high boiling point(?390?),non-biotoxicity,high hydrogen storage capacity and composite magnesium-based hydrogen storage material(16 wt%LaNis-Mg hydride,6.6 wt%,replaced by LM below)constitute a two-phase composite system to increase the hydrogen storage capacity of hydrogen slurry and expand the applicable range of hydrogen slurry;secondly,by introducing LM into the hydrogen slurry system,optimize the DBT Hydrogenation kinetic performance,screen out the main catalytic phase in LM,reduce the optimal hydrogenation temperature of the hydrogen slurry system;finally,comprehensive use of scanning electron microscopy,differential scanning calorimetry analysis,X-ray diffraction,hydrogen nuclear magnetic resonance spectroscopy to study the changes of microscopic morphology,initial hydrogen release temperature,phase composition,spatial structure.By testing the hydrogenation kinetic performance of the hydrogen slurry,the mechanism of improving the hydrogenation kinetic performance of the hydrogen slurry is explored.The composite magnesium-based hydrogen storage material was prepared by mechanical ball milling in a hydrogen atmosphere.By analyzing its phase composition,the results showed that under the preparation process conditions of a ball-to-material ratio of 100:1,a rotation speed of 400 rpm,a ball milling time of 8 h,the phase composition of LM is MgH2,MgzNiH4,LaH3.Under the condition of not adding other components,the hydrogenation kinetics experiment was carried out on DBT to study the effect of reaction temperature on its hydrogenation performance.The results show that the increase of the reaction temperature can increase the hydrogenation rate of DBT,but the effect is not obvious.When the reaction temperature is 240? and the initial hydrogen pressure is 6 MPa,the 10 h hydrogenation amount of DBT is 0.1 wt%,when the reaction temperature was raised to 330? and the initial hydrogen pressure was 6 MPa,the 10 h hydrogenation amount of DBT is 1.3 wt%.The thesis studies the hydrogenation performance of the two-phase composite hydrogen storage system composed of LM and DBT.The results show that LM has a significant catalytic effect on the hydrogenation performance of DBT,the catalytic performance is affected by the reaction temperature of the hydrogen slurry system and the solid-to-liquid ratio(the mass ratio of LM to DBT).The hydrogenation performance of the hydrogen slurry system shows a trend of first rising and then decreasing with the continuous increase of the reaction temperature.When the solid-liquid ratio is 1:50 and the initial hydrogen pressure is 6 MPa,compare the effect of the reaction temperature on the hydrogenation performance of the hydrogen slurry When the reaction temperature is 300?,the hydrogenation amount of hydrogen slurry for 20 h is 0.4 wt%;when the reaction temperature is 300?,the hydrogenation amount of hydrogen slurry for 20 h is 4.4 wt%;when the reaction temperature is 330?,the hydrogenation amount of hydrogen slurry for 20 h is 4.1 wt%.The hydrogenation performance of the hydrogen slurry system increases first and then decreases with the continuous increase of the solid-liquid ratio.When the reaction temperature is 300? and the initial hydrogen pressure is 6 MPa,compare the effect of the solid-liquid ratio,when the solid-liquid ratio is 1:50,the hydrogenation amount of hydrogen slurry for 20 h is 4.4 wt%;when the solid-liquid ratio is 1:15,the hydrogenation amount of hydrogen slurry for 20 h is 5.1 wt%;when the solid-liquid ratio is 1:10,The hydrogenation amount of hydrogen slurry for 20 h is 4.4 wt%.Based on the above research,to further confirm the catalytic phase and mechanism of LM,MgH2,Mg2NiH4,LaH3 were prepared with a solid-to-liquid ratio of 1:15,a reaction temperature of 300? and an initial hydrogen pressure of 6 MPa Under the conditions of,the same hydrogenation experiment was carried out on hydrogen slurries of different compositions.The hydrogenation amount of hydrogen slurry of LM and DBT for 10 h is 4.3 wt%;the hydrogenation amount of hydrogen slurry of MgH2 and DBT for 10 h is 0.4 wt%;the hydrogenation amount of hydrogen slurry composed of Mg2NiH4 and DBT in 10 h is 4.2 wt%;the hydrogen slurry composed of LaH3 and DBT is 0.2 wt%in 10 h.The results show that Mg2NiH4 is the main catalytic hydrogenation phase of LM.DBT has three unsaturated benzene rings.The three benzene rings are connected by methyl groups.They are the side ring,middle ring,and side ring.To further confirm the hydrogenation process of DBT in hydrogen slurry,the hydrogenation products of different degrees were carried under the test of hydrogen nuclear magnetic resonance spectrum analysis.The result of the analysis is that the hydrogenation sequence of DBT is always that one end side ring is hydrogenated first,the other end side ring is then hydrogenated,the middle ring is hydrogenated last.