Desulfurization application

Thus, several improvements have been made in the Rhodococcus strains to make desulfurization application possible or attractive however, the sulfur removal rate still remains the biggest bottleneck and no biocatalysts capable of rates needed for commercialization exist as of yet. 

These two strains, B. sphaericus strain ATCC 53969 and R. rhodochrous strain ATCC 53968 discovered by Kilbane as being capable of dibenzothiophene desulfurization were patented as two separate (European) patents [67,91], respectively. These two patents issued by 1991 also described the use of the enzymes derived from these organisms and their cell-free extracts for desulfurization applications. Both strains were reported to carry out selective cleavage of C—S bonds in organic carbonaceous materials. The organism, Bacillus sphaericus strain ATCC 53969, was, however, reported in Exxon patents, to be capable of C—C bond cleavage as well and therefore its ability to perform desulfurization without loss of fuel value is questionable. 

Polyurethane pump liners and pump parts are selected for fine slurries with an average particle diameter of (minus 230 (m, minus 65 mesh). Impellers may operate up to a tip speed of 31 m/s (6100 ft/sec). Polyurethane lined pumps are used for flue gas desulfurization applications as well as for pumping fairly fine tailings from copper and gold plants and for moly and flotation circuits where oils are used as reagents. The upper limit for use of polyurethane is 82°C. Nominal hardness is 80 Shore A. 

The higher alloyed grades 1.4529, 1.4562, 1.4565, all with PRE values >40, are denoted superaustenite. They were developed to improve general corrosion resistance and to prevent pitting and crevice corrosion in a high chloride-containing environment such as sea water, flue gas desulfurization applications, or chemical processes (Kearns, 1987 Gillesen, 1991 Olsson, 1997). 

Anon., 1977, J. of the Air Pollution Control Assoc. 27 (October) pp. 948-961, condensed from The Status of Flue Gas Desulfurization Applications in the United States, A Technological Assessment, Federal Power Commission (Historical Research by J. C. Marten). 

Hydrogen Hydrogen recovery was the first large commercial membrane gas separation. Polysulfone fiber membranes became available in 1980 at a time when H9 needs were rising, and these novel membranes qiiickly came to dominate the market. Applications include recovery of H9 from ammonia purge gas, and extraction of H9 from petroleum crackiug streams. Hydrogen once diverted to low-quahty fuel use is now recovered to become ammonia, or is used to desulfurize fuel, etc. H9 is the fast gas. 

The rotational operation of a CFB leads to a vortex motion in the freeboard which tends to inhibit particle loss by elutriation. Because of the relatively compact nature of the CFB and the operating flexibility provided by the rotational motion, the CFB has been proposed for a variety of applications including coal combustion, flue gas desulfurization, gas combustion, coal liquefaction and food drying. 

Hydrofining usually involves only minor molecular changes of the feed with hydrogen consumption in the range of about 100 to 1,000 cu.ft./bbl. Typical applications include desulfurization of a wide range of feeds (naphtha, light and heavy distillates, and certain residua) and occasional pretreatment of cat cracker feeds. 

Desorption The removal of adsorbed materials from a solid sorbent by the use of a solvent or the application of heat. Desulfurization The removal of sulfur from flue or other sulfur-containing gases. 

Two techniques, electrochemical reduction (section IIl-C) and Clem-mensen reduction (section ITI-D), have previously been recommended for the direct reduction of isolated ketones to hydrocarbons. Since the applicability of these methods is limited to compounds which can withstand strongly acidic reaction conditions or to cases where isotope scrambling is not a problem, it is desirable to provide milder alternative procedures. Two of the methods discussed in this section, desulfurization of mercaptal derivatives with deuterated Raney nickel (section IV-A) and metal deuteride reduction of tosylhydrazone derivatives (section IV-B), permit the replacement of a carbonyl oxygen by deuterium under neutral or alkaline conditions. 

Sulfenamides, R2NSR, prepared from an amine and a sulfenyl halide, are readily cleaved by acid hydrolysis and have been used in syntheses of peptides, penicillins, and nucleosides. They are also cleaved by nucleophiles and by Raney nickel desulfurization." The synthesis and application of sulfenamides have been reviewed. ... 

Through the work of especially Goldfarb et al. but also of Buu-Hoi et al., Badger et al., and Wynberg et al., the Raney nickel desulfurization of thiophenes has been developed to an important tool for the synthesis of aliphatic compounds. During the last 5 years over fifty papers have appeared describing applications of this method. 

Glaser and Litt (G4) have proposed, in an extension of the above study, a model for gas-liquid flow through a b d of porous particles. The bed is assumed to consist of two basic structures which influence the fluid flow patterns (1) Void channels external to the packing, with which are associated dead-ended pockets that can hold stagnant pools of liquid and (2) pore channels and pockets, i.e., continuous and dead-ended pockets in the interior of the particles. On this basis, a theoretical model of liquid-phase dispersion in mixed-phase flow is developed. The model uses three bed parameters for the description of axial dispersion (1) Dispersion due to the mixing of streams from various channels of different residence times (2) dispersion from axial diffusion in the void channels and (3) dispersion from diffusion into the pores. The model is not applicable to turbulent flow nor to such low flow rates that molecular diffusion is comparable to Taylor diffusion. The latter region is unlikely to be of practical interest. The model predicts that the reciprocal Peclet number should be directly proportional to nominal liquid velocity, a prediction that has been confirmed by a few determinations of residence-time distribution for a wax desulfurization pilot reactor of 1-in. diameter packed with 10-14 mesh particles. 

Neither Ca, Sr nor Ba metal has any structural integrity. The principal application of metallic Ca is as a reducing agent in the preparation of metals, such as Th and Zr. Like Mg, it can be used in the deoxidation and desulfurization of steels. Small quantities are used for alloying with Al and for the removal of Bi from Pb. Neither Sr nor Ba have any significant commercial uses. Barium is used to a limited extent as a getter to remove reactive gases from vacuum tubes. 

Metal polysulfido complexes have attracted much interest not only from the viewpoint of fundamental chemistry but also because of their potential for applications. Various types of metal polysulfido complexes have been reported as shown in Fig. 1. The diversity of the structures results from the nature of sulfur atoms which can adopt a variety of coordination environments (mainly two- and three-coordination) and form catenated structures with various chain lengths. On the other hand, transition metal polysulfides have attracted interest as catalysts and intermediates in enzymatic processes and in catalytic reactions of industrial importance such as the desulfurization of oil and coal. In addition, there has been much interest in the use of metal polysulfido complexes as precursors for metal-sulfur clusters. The chemistry of metal polysulfido complexes has been studied extensively, and many reviews have been published [1-10]. 

NiMo and NiW formulations have succeeded in desulfurizing the sterically hindered compounds, by fully hydrogenating at least one of the lateral rings, facilitating their elimination. From this point of view, the need for a high hydrogenation activity when producing ultra-low sulfur fuel is explained. Consequently, the preferential application of a Ni-Mo(W) for the manufacture of ULS fuels can be easily understood, as well. 

From the conventional view of oil refining, a sulfur removal processes that yields H2S is preferred, as it is supposed to retain the maximum heating value of the desulfurized product. Notwithstanding, the application of anaerobic bacteria has rarely found opportunities in refining operations and only for the treatment of exhaust gas streams, containing sulfur species in the form of H2S, and usually by a biological combination with chemical treatments. Some of these examples will be discussed in Section 2.4 where bioprocesses for gas streams treatment are considered. 

Other Rhodococcus strains similar to those described above in terms of the desulfurization ability have also been isolated [83], The purpose of identifying such Rhodococcus strains, in several cases, appears to be the development of in-house biocatalysts for BDS application. The specificity of the desulfurizing strains of organosulfur compounds in addition to DBT has also been studied (Table 3). 

In this section, we will consider the methodologies used for genetic engineering of biocatalysts for desulfurization and the biocatalysts developed so far via various technologies. The application of genomic techniques as reported in patent literature associated with BDS is described first. 

Recent work at Diversa [219] investigated use of alternate Rhodococcus strains as hosts for desulfurization genes. It was reported that R. opacus was the most suitable for the application. This was due to its ability to grow fast and use triglycerides as carbon source for production of reduced co-factors during the desulfurization process. 

---