柴油深度脱硫中的反应工程问题及对策

Chemical reaction engineering problems in deep hydrodesulfurization of diesel fuel and corresponding solution

柴油深度脱硫受到3个反应工程问题的限制:一是反应速率级数对总硫浓度呈二级,因此在硫浓度很低时加氢脱硫速率极慢;二是4,6-二甲基二苯并噻吩(4,6-DMDBT)的甲基取代基有空间位阻,需采取先加氢、后氢解的途径;三是脱硫反应受到硫化氢的抑制作用,特别在硫浓度很低时,硫化氢的抑制作用更加明显。为了获得超低硫柴油(<50μg/g),根据反应工程原理,气液逆流加氢操作是一种有效的方式。

Deep desulfurization of diesel fuel is subjected to three reaction engineering problems:the first one is due to the second order dependence on the total sulfur concentration in the reaction rate expression,which means the hydrodesulfurization rate is extremely slow when the sulfur concentration is very low in meeting the required sulfur level standard;the second one comes from the stereo-resistance arising from the methyl substitutions in 4,6-dimethyldibenzothiophene(4,6-DMDBT) molecule;and the third one is from the inhibiting effect of H_2S which is produced during hydrogenation,and its influence is critical especially when the sulfur concentration is very low.In obtaining ultra low sulfur of less than 50 μg/g in diesel,gas-liquid countercurrent flow is an effective way in view of the chemical reaction engineering principle,and it was verified by the current work.