随着人民生活水平的提高,环境保护越来越得到人们的关注,生产满足环保要求的清洁燃料是全球炼油工业生产发展的总趋势,汽油中的含硫化合物燃烧生成的SOx是环境污染的重要因素之一,生产低硫汽油是改善环境质量所必须的。目前石油炼制行业应用最多的脱硫方法为催化加氢,但加氢技术对汽油的深度脱硫效果并不理想,且深度加氢脱硫易使烯烃饱和,消耗大量氢气的同时,还降低了产品的辛烷值。氧化脱硫(ODS)是近年来发展起来的生产超低硫燃料的新技术,可在常温常压下进行,不耗费氢气,设备投资较少,对催化加氢难以脱除的苯并噻吩类化合物有较高的脱硫效率,是一项很有前途的脱硫技术。国内外在轻质油品的氧化脱硫方面已做了大量的研究,特别对苯并噻吩类化合物的模型研究工作非常充分。Otsuki从电子密度的角度研究了氧化反应的机理,认为含硫化合物脱硫的难易程度与S原子上的电子密度有关,50℃时电子密度为5.696~5.716的噻吩和甲基取代的噻吩类化合物不能被氧化,而电子密度为5.739的苯基噻吩和电子密度更高的二苯基噻吩可被氧化。噻吩和甲基取代的噻吩类化合物在催化裂化(FCC)汽油中的含量占含硫化合物总量的80%以上,可见噻吩和甲基取代的噻吩类化合物的氧化脱硫工作值得深入研究。本文以FCC汽油中电子密度最低的硫化物噻吩的正庚烷溶液和二甲苯溶液为研究对象,对其氧化过程中的影响因素、氧化机理进行了初步研究。
Thiophene (C4H4S) is a typical sulfur-containing compound in fluid catalytic cracking (FCC) gasoline. Oxidative desulfurization of C4 H4S in n-heptane solution was conducted with hydrogen peroxide (H2O2) and formic acid over a catalyst of 5A molecular sieve loaded with ceria. The effects of oxidative agent, solvent, reaction temperature as well as the addition of phase transfer catalyst were investigated in detail. The reaction course of oxidative desulfurization of C4 H4 S was preliminarily studied. The oxidation of C4H4S was achieved under mild reaction conditions and it was easy to raise the reaction temperature or increase the reaction time to achieve high oxidation conversions. The results showed that the conversion of C4 H4S in n-heptane solution was 78.2% under the condition of reaction temperature of 50℃, nH2O2 : ns= 10:1, VH2O2 : VHCOOH=1 : 1. The conversion of C4H4S was 94.5% when an emulsifier OP was added to this system. However, with the addition of tetrabutylammonium bromide (TBAB), a bromine substitution product appeared in the oxidation of C4 H4 S.