Support And Hydrogen Spillover Effects In Liquid-Phase Dearomatization Over Zeolite Supported Catalyst

Nowadays, Solvent-oils are widely used in daily life and industrial field, however, All of solvent-oils in the country contain certain amount of aromatics, and this has seriously limited their application fields. Therefore, dearomatization of solvent-oils is very necessary for oil refining. There are many dearomatization methods, and among them, catalytic hydrogenation method including gas- and liquid-phase hydrogenation is a method widely used. Gas-phase hydrogenation is popular in most factories, but it asks for high reaction temperature and pressure, this would cost more energy resources. So, in this research, liquid-phase hydrogenation with low reaction pressure and temperature was used to dearomatize the trace amount of aromatics in 6^# solvent-oil. In our previous study, it was found that zeolite support obtaining proper surface acidity can improve the hydrogenation activity and sulfur tolerance of noble metal catalysts. Thereby, zeolite HBeta and HUSY with proper acidity were chose as the support and additional agent of Ru supported catalyst, and their acidity was further improved by modification and ion-exchanging method. It was hoped that Ru catalyst supported on modified HBeta and Ru/HUSY mixed with additional agent HUSY could exhibit better hydrogenation activity and sulfur tolerance.Firstly, Under the condition of 85℃and 1:60g/mL (HBeta/mother liquor of NaAlO₂), HBeta was modified by NaAlO₂ solution with different concentration (0.03mol/L, 0.06mol/L, 0.15mol/L, 0.30mol/L) in a given time (4h) and by 0.03mol/L NaAlO₂ solution in different modifying time(4h, 6h, 8h, 12h), respectively. The effect of time and concentration of NaAlO₂ on acidity of HBeta were studied by IR, Pyridine-IR and NH₃-TPD techniques. Then, Ru catalyst supported on modified HBeta was prepared by impregnation and characterd by Pyridine-IR. Further, its hydrogenation activity was studied in 0.06wt% benzene/hexane model reactant. The result showed that the acid amount of HBeta modified by 0.03mol/L NaAlO₂ solution increased with the increase of modifying time and reached highest at 8h. This was mainly resulted from realumination and silicon-soluting effect of NaAlO₂ solution before and after 8 hour. The realumination effect increased the acid amount of HBeta, while the silicon-soluting effect caused part loss of Al in the structure of HBeta. It was also showed that the acid strength of HBeta modified by 12h was only stronger than HBeta. Under the given time (4h), with the concentration of NaAlO₂ solution increasing from 0.03 to 0.06mol/L, the acid amount of modified HBeta increased, while the acid strength of modified HBeta was firstly weaker and then became stronger than HBeta. NaAlO₂ with concentration no more than 0.06mol/L is favor for realumination of HBeta, while the acid strength of HBeta modified by 0.06mol/L NaAlO₂ improved remarkablely. When modified with liquor concentration between 0.06-0.15mol/L, B acid and L acid sites of HBeta decreased and increased, respectively. The structure and acid amount of HBeta were destroyed and decreased sharply with concentration above 0.3mol/L, This may be due to the solving of Si atoms from zeolite framework into liquor. The hydrogenation activity of Ru catalyst supported on HBeta modified by different time improved and the activity of Ru/HBeta-0.03-6h is the highest among them, this may be resulted from the co-effect of acid amount and diffusion effect of the support. The same result was found in metal catalysts supported on HBetas realuminated with various concentration of mother liquor and their hydrogenation follows: Ru/HBeta-0.06-4h > Ru/HBeta-0.03-4h > Ru/HBeta-0.30-4h>Ru/HBeta-0.15-4h>Ru/HBeta, and the reason for this is still needed to find.Secondly, Mixed catalysts were prepared by mixing additional molecule sieves agents (NaY, USY, Si-MCM-41 HY, HUSY, HBeta) with Ru/HUSY (Ru%=1.0 or 2.5wt. %). The influence of additional agents and their additional proportion on the hydrogenation activity of Ru/HUSY with/without sulfur were studied. The result showed that the addition of H-zeolite, especially HUSY, can improve effectively the hydrogenation, this was due to hydrogen spillover phenomenon between active metal sites and acid sites of the support. Also, the addition of H-zeolite improved sulfur tolerance of catalyst, this may be due to sulfur adsorption of additional agent which could decrease the sulfur poisoning of the catalyst. Similarly, the improvement of sulfur-tolerant of Ru catalysts supported on Na-zeolite was because the Na-zeolite can adsorb part amount of sulfur in solvent-oil. With amount of additional zeolite agents increasing, the hydrogenation activity and sulfur tolerance of mixed catalyst increased and reaches the highest when the proportion of HUSY: Ru/HUSY is 5. After the hydrogenation, Benzene and sulfur containing in solvent-oil can be reduced below 5 and 1ppm, respectively.