Oxidative Desulfurization Of Sulfide Over Titanium Silicalite

Facing the increasing seriously environmental problems, the world has seen a more andmore stringent level for sulfur content in liquid fuels proposed in many countries. Thetraditional hydrodesulphurization process (HDS) becomes economically insufficient with thedecreasing sulfur in fuels. Currently, oxidative desulphurization (ODS) become the hotspotwhich is investigated extensively for its mild reaction condition, simple equipment, andhighly efficiency.In this paper, titanium containing molecular sieves and H₂O₂ were used as the catalystsand the oxidant, respectively, for the oxidative desulphurization of model fuel withmulti-types sulfur compounds including thiophene (Th), benzothiophene (BT),dibenzothiophene (DBT) and 4, 6-dimethyldibenzothiophene(4, 6-DMDBT). The effect of thereaction temperature and the pore size and kinds of the catalysts on oxidative desulphurizationwas investigated. It has been shown that with the increase of the reaction temperature, theremoval rates of sulfur compounds have been improved. In addition, the reaction speed evenfast and reached the balance in a short time under higher temperature. The removal efficiencyof 4, 6-DMDBT was enhanced when the Ti-HMS with larger pore size was used as catalyst.Ti-HMS exhibited high activity in the oxidative desulphurization of model fuel, in which thelarge molecular sulfur compounds are in the majority. However, the meso-microporouscomposite Ti-WMS and mixture of Ti-HMS and TS-1 were preferable for oxidativedesulphurization of the model fuel containing more small molecular sulfides.The micron-scale TS-1 was modified by tetrapropylammonium hydroxide (TPAOH).The modified TS-1 was used as the catalyst in oxidative desulphurization of2-methylthiophene from model fuel and exhibited high activity. The samples before and aftermodification were characterized by XRD, UV-Vis, N₂ physical adsorption/desorption andTEM techniques. The modification conditions were investigated, including the concentrationof TPAOH, the modification temperature and the modification time. It has been shown thatthe modified sample possessed the typical MFI structure. After modification, the content offramework titanium as well as the extra-framework titanium in TS-1 decreased. However, themodified sample has larger surface area and pore volume than the original sample. In addition,some larger pores of about 1.4 nm and 40-60 nm have been found in the modified TS-1sample, which may be responsible for the improvement of catalytic behavior of TS-1. The modified sample exhibits excellent activity in oxidative removal of 2-Methylthiophene, withthe removal rate of 93.9ï¼…, much higher than that of original sample (70.5ï¼…). The optimalmodification conditions are as follows: the concentration of TPAOH is 0.4mol/l; thetemperature is 413K; the time is 24 h.