Bitumen desulfurization

In bitumen, sulfur is present primarily as thioethers, sulfides, and thiophene derivatives, with thiophene sulfur being particularly difficult to remove by hydrodesul-furization. Transition metal ion-exchanged natural zeolites could be used as economical and disposable materials for bitumen desulfurization. ... 

Flotation or froth flotation is a physicochemical property-based separation process. It is widely utilised in the area of mineral processing also known as ore dressing and mineral beneftciation for mineral concentration. In addition to the mining and metallurgical industries, flotation also finds appHcations in sewage treatment, water purification, bitumen recovery from tar sands, and coal desulfurization. Nearly one biUion tons of ore are treated by this process aimuaHy in the world. Phosphate rock, precious metals, lead, zinc, copper, molybdenum, and tin-containing ores as well as coal are treated routinely by this process some flotation plants treat 200,000 tons of ore per day (see Mineral recovery and processing). Various aspects of flotation theory and practice have been treated in books and reviews (1 9). 

Valentine [61] also disclosed the use of R. rhodococcus ATCC 53968 for a desulfurization process of emulsified bitumen. The variety of possible biocatalyst types include... 

A process innovation was introduced by Valentine [61], who added an SOx sorbent for mitigating the inhibiting effects of the formed oxysulfides. This process was developed for sulfur removal from extra heavy oils, bitumens, and its emulsions, such as the trade mark Orimulsion. Any active biocatalyst may be used in this process carried out at temperatures close to 50°C. The main features disclosed in patents protecting the use of R. rhodochrous-bas d biocatalysts, in desulfurization reactions are summarized in Table 12. 

Shell s microbiological desulfurization process is carried out by mixing coal with an aqueous biocatalyst solution [158], The coal considered in this invention concerns bituminous coal containing inorganic sulfur (pyritic).This process seems to be applicable to refinery pet-coke, which contains sulfur in the form of inorganic sulfides. Nowadays, when coke has become one of the major products of heavy oil and bitumens refining, such desulfurization processes might have potential uses. 

The two patents awarded to Valentine [26,27] concern with desulfurization and both are applicable to the biotreatment of bitumen fuels. The first one deals with desulfurization of Orimulsion , which is a bitumen derived fuel in an O/W emulsion form. Therefore, it seems than the inventor wanted to take the advantage of having the water already incorporated in the feedstock and alleviate the mass transfer limitations of the biotreatment. The second one deals with bitumens in general. 

The sulfur content of petroleum varies from less than 0.05 to more than 14 wt% but generally falls in the range 1 to 4 wt%. Petroleum with less than 1 wt% sulfur is referred to as low-sulfur, and that with more than 1 wt% sulfur is referred to as high-sulfur. The refining industry considers heavy oils, residua, and bitumen to be high-sulfur feedstocks. Hence they are the focus of many conversion and desulfurization scenarios. 

With all of the scenarios in place, there is no doubt that petroleum and its relatives residua, heavy oil, and extra heavy oil (bitumen) will be required to produce a considerable proportion of liquid fuels into the foreseeable future. Desulfurization processes will be necessary to remove sulfur in an environmentally acceptable manner to produce environmentally acceptable products. Refining strategies will focus on upgrading the heavy oils and residua and will emphasize the differences between the properties of the heavy crude feedstocks. This will dictate the choice of methods or combinations thereof for conversion of these materials to products (Schuetze and Hofmann, 1984). 

This process is suitable for the desulfurization of high-sulfur residua (atmospheric and vacuum) to produce low-sulfur fuel oils or catalytic cracking feedstocks. In addition, the process can be used, through alternate design types, to upgrade high-sulfur crude oils or bitumen that are not suitable for the more conventional refining techniques. 

The LC-Fining process has been applied to desulfurization of bitumen extracted from the Athabasca tar sands (Bishop, 1990). In one reported instance, a low-solids bitumen and a high-solids bitumen were employed as feedstocks whereupon good conversion of the bitumen to lower-sulfur products was noted... 

The LC-Fining process is a hydrocracking process capable of desulfurizing, demetallizing, and upgrading a wide spectrum of heavy feedstocks by means of an expanded bed reactor. Operating with the expanded bed allows the processing of heavy feedstocks, such as atmospheric residua, vacuum residua, and oil sand bitumen. 

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