Akbari Azam, Omidkhah Mohammadreza, Towfighi Darian Jafar
Chemical Engineering Department, Tarbiat Modares University, P.O. Box 14115-143, Tehran, Iran.
Chemical Engineering Department, Tarbiat Modares University, P.O. Box 14115-143, Tehran, Iran.
Ultrason Sonochem. 2015 Mar;23:231-7. doi: 10.1016/j.ultsonch.2014.09.002. Epub 2014 Sep 10.
Oxidative desulfurization of thiophenic sulfur compounds of benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyl dibenzothiophene (4,6-DMDBT) with MoOx/Al₂O₃ catalyst and H₂O₂ oxidant has been facilitated and more selective under ultrasonic irradiation. The catalyst with the optimum 10% of Mo loading consisted of isolated tetrahedral molybdenum oxide species based on FTIR analysis. The increase of Mo loading to 15% and 20% caused to generation of polymolybdate and MoO₃ crystals which decreased desulfurization activity. Sonication enhanced the apparent reaction rate constants in oxidation of all three sulfur compounds. An increase in the Arrhenius factor (A0), which is the total number of collisions per second, could explain the acceleration in the rate constants by sonication. The apparent activated energy (Ea) of BT oxidation was reduced from 96.6 to 75.3 kJ/mol by using ultrasound. This indicated that ultrasound had also a chemical effect, like a catalytic influence, in the acceleration of BT removal. DBT oxidation was reduced when investigated in the presence of tetralin, naphthalene and 2-methyl naphthalene as the model aromatic compounds of actual light oils. A higher selectivity toward DBT elimination in the presence of aromatics was obtained by sonication when compared with the silent treatment. Ultrasound cleaned the catalyst surface from adsorbed aromatics. On the basis of the obtained results, a mechanistic proposal for this desulfurization was explained. Oxidation was performed by nucleophilic attack of sulfur atom to the molybdenum peroxide species of tetrahedral molybdates, which was more advanced by sonication.
在超声辐照下，使用MoOx/Al₂O₃催化剂和H₂O₂氧化剂对苯并噻吩（BT）、二苯并噻吩（DBT）和4,6-二甲基二苯并噻吩（4,6-DMDBT）中的噻吩类硫化合物进行氧化脱硫变得更加容易且具有更高的选择性。基于傅里叶变换红外光谱（FTIR）分析，负载量为10%的最佳催化剂由孤立的四面体氧化钼物种组成。将Mo负载量增加到15%和20%会导致多钼酸盐和MoO₃晶体的生成，从而降低脱硫活性。超声处理提高了所有三种硫化合物氧化反应的表观反应速率常数。阿仑尼乌斯因子（A0）的增加，即每秒的总碰撞次数，可以解释超声处理对速率常数的加速作用。通过超声处理，BT氧化的表观活化能（Ea）从96.6 kJ/mol降至75.3 kJ/mol。这表明超声在加速BT去除方面也具有化学效应，类似于催化作用。当以四氢萘、萘和2-甲基萘作为实际轻质油的模型芳香化合物进行研究时，DBT的氧化作用减弱。与无超声处理相比，超声处理在存在芳烃的情况下对DBT的去除具有更高的选择性。超声去除了吸附在催化剂表面的芳烃。基于所得结果，对这种脱硫过程提出了一个机理建议。氧化反应是通过硫原子对四面体钼酸盐的过氧化钼物种的亲核攻击进行的，超声处理能使这一过程更顺利地进行。
