Non-conventional Technologies For Fuel Desulphurization Available to Purchase

Refinery distillates, especially gas oil fractions contain considerable amounts of alkylated benzo-thiophene components which are most recalcitrant to desulphurization via classical hydrodesulfurisation. Fuel regulations continue to tighten worldwide in response to the need for cleaner air and refiners meet these regulations at a very significant cost. In fact, most refiners will need a major revamp of existing HOS medium pressure units or even install new grass root units. The need to cut the operational and capital costs has necessitated a renewed look into non-hydrogen consuming, low temperature and pressure processes for producing ultra low sulphur fuels. Non-conventional approaches for ultra low sulphur fuels (ULSF) belong either to oxidative or to selective adsorption routes. In oxidative routes, biodesulfurization (BOS) involving specialized bacteria and oxidation catalysed by chemical oxidants have been thoroughly investigated. BOS by genetically engineered strains has capability to produce ULSO having <10 ppm sulphur. However, to be commercially viable, conversion rates, biocatalyst cost, its stability and overall process economics must out-perform competing techniques. Attempts are being made to derive advantages of nano-technology to enhance BOS efficiency. Biocatalysts e.g. have been assembled on the surface of nano alumina so that benzo-thiophenes can be quickly transferred to the cells. Oxidative desulfurization (ODS) can be attractive alternate to HOS when the hydrogen costs are prohibitive. Globally more than 10 companies have been engaged in researching ODS process technology, issuing about 20 patents in last 5 years. Several conversion extraction desulfurization (CEO) processes, comprising oxidation and extraction have been developed. However, oxidation selectivity, catalyst costs and requirement of multiple separation process steps are few areas which need further improvements. Recent years have also witnessed a lot of interest in desulphurization of fuels by selective adsorption process for removing sulfur (SARS). Such SARS systems are being developed, not only for refinery but also for small stationary/mobile applications e.g. ultra clean gasoline for fuel cell applications. New active large pore size adsorbents, impregnated with transition metals can clean > 20 volumes of fuel before needing regeneration to restore their activity. Small SARS systems are especially attractive at gas stations for fuel cell vehicles. This presentation will review the recent advancements in oxidative and adsorption technologies for fuel desulfurization. Some results obtained in the author's labs for process improvement in biodesulfurization of diesel fractions will also be discussed.