Fe-Anderson型多金属氧酸盐和苯磺酸基低共熔溶剂仿生体系的构建及其柴油绿色氧化脱硫

在过去的几十年里,人们越来越关注环境污染问题.柴油中的硫化物燃烧后可转化为SOx,对环境造成严重污染.因此,为了满足严格的国家标准要求,生产硫化物含量极低的燃料油是一个巨大挑战.氧化脱硫(ODS)体系是用于深度脱硫的加氢脱硫(HDS)体系的替代或补充,包括硫化物的氧化和氧化产物的分离.它是处理芳香硫化合物及其衍生物最有效的方法之一,引起了人们的极大关注.在我们之前的工作中报道了Co聚阴离子催化剂和对甲苯磺酸基低共熔剂(DESs)通过仿生方法将柴油中的硫化物氧化为相应的硫化物.尽管已经取得了很大的进展, DESs仿生体系仍然有很大的发展空间.例如,多金属氧酸盐(POMs)在生物模拟体系中的作用没有得到明确阐述.更困难的是构建DES的物理化学性质与仿生体系氧化脱硫效率之间的关系.因此,解决上述问题是催化氧化脱硫(AODS)仿生过程中最关键的挑战之一,迫切需要进一步研究.本文采用仿生方法研究了一种新型高效的AODS体系,该体系能显著提高ODS的效率.采用重结晶法制备了安德森型催化剂Na3Fe(OH)6Mo6O18,并将其应用于柴油AODS体系.通过分析紫外-可见光谱(UV-Vis)、红外光谱(FT-IR)以及气质联用光谱(GC-MS),我们推测了通过多步电子转移AODS体系的仿生机理.首先, POM和氧气形成过氧聚阴离子,然后与苯磺酸形成苯基过氧磺酸.由于过氧磺酸盐对富电子的硫原子具有很高的选择性,所以它优先攻击硫原子.因此,二苯并噻吩被氧化成二苯并噻吩砜.还原后的苯磺酸和POM被氧气氧化,形成新的催化循环.这些结果表明,耦合氧化还原体系和ETMs通过低能量途径将电子从苯磺酸基DES转移到氧化剂,从而促进了反应过程.最终,二苯并噻吩易被氧化为二苯并噻吩砜.DES的物理性质表明,在60℃时, n(PEG2000)/n(BSA)=2.5体系中DES粘度最大,推测可能是氢键较强所致.此外,PEG2000/2.5BSA体系脱硫效果也是最好的.这一结果表明,脱硫体系的活性与氢键的强度有关.将该仿生策略应用于模型柴油的AODS中,在60 min内二苯并噻吩脱除率达到95%,表现出前所未有的性能,并且该仿生体系也可以成功应用于真实柴油的氧化脱硫.该催化剂可重复使用五次,且反应活性无明显降低,表明该催化体系具有商业应用潜力.

Green aerobic oxidative desulfurization of diesel by constructing an Fe-Anderson type polyoxometalate and benzene sulfonic acid-based deep eutectic solvent biomimetic cycle

A unique redox-coupled biomimetic system was developed, in which Fe-Anderson type polyoxometalates(POMs) were employed as electron transfer mediators(ETMs) and benzenesulfonic acid(BSA)-based deep eutectic solvents(DESs) were used as electron-donors for aerobic oxidative desulfurization(AODS) of diesel fuel. Different compositions of DESs were used and the polyethylene glycol 2000(PEG2000)/2.5 BSA system showed the highest desulfurization activity, with the removal of dibenzothiophene(DBT) at 60 ℃ reaching 95% in 60 min. The excellent desulfurization activity of the system is due to the in situ formation of peroxysulfonate via a biomimetic process. By constructing a coupled redox system, Fe-Anderson type POMs as ETMs reduce the activation energy of oxygen-activated sulfonate. The physical characteristics of four different DESs were tested. The results show that the conductivity of DESs is correlated with the composition of BSA-based DESs. However, there is no similar trend in viscosity testing at the same temperature, and the maximum viscosity value is obtained for the PEG2000/2.5 BSA system at 60 ℃, which may be associated with the stronger hydrogen bonds. It is worth noting that the PEG2000/2.5 BSA system also possesses the best desulfurization activity, which suggests that the activity of the desulfurization system is related to the strength of the hydrogen bond in DESs. Finally, the biomimetic desulfurization system exhibits excellent performance and good stability under mild reaction conditions(60 ℃, atmospheric pressure, oxygen as the oxidant).