有机-无机型杂多酸相转移催化氧化脱硫性能研究

Study on Oxidative Desulfurization Catalyzed by Organic-inorganic Heteropolyacids as Phase Transfer Catalyst

合成了四种有机-无机型杂多酸催化剂,包括[π-C5H5NC16H33]3[PW4O16],[π-C5H5NC16H33]3[PMo4O16],[π-C5H5NC12H25]3[PW4O16]和[π-C5H5NC12H25]3[PMo4O16].以有机硫的正辛烷溶液为模拟油品,H2O2为氧化剂,乙腈为萃取剂,在两相体系中,考察了上述四种催化剂对模拟油品中二苯并噻吩(DBT)氧化脱硫的催化活性.结果表明,[π-C5H5NC16H33]3[PW4O16]具有最佳的催化活性.采用[π-C5H5NC16H33]3[PW4O16]进行后续研究发现,反应完毕,[π-C5H5NC16H33]3[PW4O16]以沉淀的形式析出,可以重复利用且脱硫效果很好.研究表明,上述有机-无机型杂多酸属于相转移催化剂,氧化脱硫反应体系属于反应控制相转移催化体系.在相同实验条件下,由于电子云密度和空间位阻效应共同的作用,DBT、噻吩(TH)、苯并噻吩(BT)和4,6-二甲基二苯并噻吩(4,6-DMDBT)脱硫由易到难的顺序为DBT>4,6-DMDBT>BT>TH,并分别通过GC-MS分析确定它们的氧化产物.将[π-C5H5NC16H33]3[PW4O16]进一步应用于柴油氧化脱硫,其中硫含量由355 mg/kg(mg/kg等同于ppmw)降至26 mg/kg,去除率达92.7%.利用上述四种有机-无机型杂多酸作催化剂,研究DBT氧化反应过程动力学,确定DBT的表观反应级数均为一级,表观活化能为47.9~55.4kJ/mol.

In this paper, organic-inorganic heteropolyacids were prepared, including [π-CsH5NC16H3313[PW4O16], [π-CsHsNC16H3313[PM04O16], [rr-CsHsNC12H2513[PW4O16] and [π-CsHsNC12H2513[PM04O16]. The efficiency of oxidative desulfurization was investigated on the four kinds of catalysts under the same conditions using the simulated oil prepared by dissolving organo-sulfur in normal octane. The results show that the catalytic activity of [π-CsHsNC16 H3313[PW4016] is the best. The catalytic activity of these heteropolyacids was following the order of [π-C5HsNC16H3313[PW4016] ~ [n-CsHsNC12H2513[PW4016]〉[^-CsHsNCI6H3313[PMo4OI6]〉[π-CsHsNC12H2513[PM04OI6]. Under the optimal experimental conditions, pre-reaction time between H202 and the catalyst being 10 min, reaction temperature being 60 C, O/S molar ratio being 10, the amount of catalyst being 1 wt% of n-octane, and the catalyst being [n-CsHsNC16H3313[PW4O16], the diben- zothiophene （DBT） conversion was nearly 100% after 60 rain. The catalyst [π-C5HsNCI6H3313[PW4016] can be reclaimed by auto precipitation due to the exhausting of 1-1202. The results show that organic-inorganic heteropolyacids are phase transfer catalyst and oxidative desulfurization system belongs to the phase transfer catalysis system controlled by reaction. The cata- lytic activity of the recycled [π-CsHsNC16H3313[PW4016] is almost the same as the fresh. Then, the efficiency of oxidative desulfurization was investigated with different simulated oils using DBT, thiophene （TH）, benzothiophene （BT） and 4,6-dimethyldibenzothiophene （4,6-DMDBT）, respectively. Under the same conditions, the efficieneies of oxidative desulfu- rization decrease in the order of DBT〉4,6-DMDBT〉BT〉TH, the result was influenced by electron density on the sulfur atoms and the sterie hindrance. It showed that the final desulfurization product of TH, BT, DBT and 4,6-DMDBT was SO]-, SO42-, DBT sulphone and 4,6-DMDBT sulphone, respectively. [π-CsH5NC16H3313[PW4016] used in desulfurization of the real diesel and the sulfur removal rate was 92.7%. The sulfur content was reduced from 355 mg/kg to 26 mg/kg. Fur- thermore, by studying the kinetics of DBT oxidation by H202, the reaction order was foUnd to be 1 st to DBT. The activation energy ranged from 47.9 kJ/mol to 55.4 kJ/mol by different organic-inorganic heteropolyacids. It indicates the reaction proc- ess is quite fast in ODS. The new type of catalysts has a broad development prospect in oil desulfurization.