Process biodesulfurization

The application of biocatalytic technologies in the refining industry will be possible only if it can improve product yields and produce cleaner fuels economically. The hurdle to commercialization of the biodesulfurization process is still the activity of the biocatalyst. The reasons for this will be evident from the discussion in Chapter 3. 

Biodesulfurization (BDS) is the excision (liberation or removal) of sulfur from organosul-fur compounds, including sulfur-bearing heterocycles, as a result of the selective cleavage of carbon-sulfur bonds in those compounds by the action of a biocatalyst. Biocatalysts capable of selective sulfur removal, without significant conversion of other components in the fuel are desirable. BDS can either be an oxidative or a reductive process, resulting in conversion of sulfur to sulfate in an oxidative process and conversion to hydrogen sulfide in a reductive process. However, the reductive processes have been rare and mostly remained elusive to development due to lack of reproducibility of the results. Moderate reaction conditions are employed, in both processes, such as ambient temperature (about 30°C) and pressure. 

Apart from biocatalyst activity, several other parameters are important in development of a biodesulfurization process. These parameters include oil/water ratio, composition of aqueous phase used for biocatalyst suspension during desulfurization, biocatalyst loading, oil/water separation following completion of desulfurization, potential for biocatalyst recycle, recycle of aqueous phase to reduce fresh water usage and wastewater minimization, as well as secondary oil separation and purification operations. 

The process steps have not received as much attention, except the third step. As of now, a commercial process has not been developed although one pilot scale study has been conducted. This section will describe the research efforts conducted to date and report on the process options considered for biodesulfurization. 

The possibility of producing certain value-added compounds such as surfactants, which can be derived from intermediates produced in petroleum biodesulfurization processes, has been evaluated. HPBS is a molecule with amphiphilic characteristics desirable for surfactant applications [243], Several oxidation reactions, from the 4S pathway are considered before reaching the final product. The compounds of the invention include acyloxybiphenylsulfinates, acyloxybiphenylsulfonates, alkyl sulfinatobiphenyl ethers, and alkyl sulfonatobiphenyl ethers. The invention also provides methods of producing these compounds. 

In a biodesulfurization process, there are actually three phases. For a liquid mixture containing the three phases - liquid fossil fuel, water, and the biocatalyst, more than one filter would be required. One filter will preferentially collect either the liquid fossil fuel or aqueous phase as the filtrate. The retentate will then flow to the second filter, which will collect the component not removed before. The remaining retentate, containing the biocatalyst, can then, preferably, be recycled. The process can be used to resolve an emulsion or microemulsion of the liquid fossil fuel and aqueous phase resulting from a... 

Recently, several thermophilic organisms have been reported to be capable of sulfur-specific biodesulfurization. These include the Paenibacillus [87,151], Mycobacterium [30,31,85,94,294,295], etc. The ability to desulfurize sulfur compounds other than DBT derivatives, including benzothiophene, naphthothiophene, and benzonaphthothio-phene derivatives has also been demonstrated, thus widening the substrate specificity of the biodesulfurization process. Second, the thermophilic ability of the organisms offers temperature and operational advantages to further improve the commercialization potential of the BDS process. 

Borole, A. P., and Kaufman, E. N., Process considerations in crude oil biodesulfurization. Abstracts of Papers of the American, Chemical Society, 1999. 217 p. U798-U798. 

W09617940 [45] desulfurization of fossil fuel with flavoprotein. biodesulfurization of a fossil fuel by adding an amount of a flavoprotein to the biocatalytic reaction mixture. Incubation and separation complete the process scheme. 

The second development for which IGT is known world-wide is their work on biodesulfurization. The IGT intellectual property package, developed by Kilbane s group, includes two microorganisms, R. rhodochrous strain ATCC 53968 (IGTS8) and B. sphaericus strain ATCC 53969 as well as the enzymes derived from them and cell-free extracts. The biocatalysts and their use were protected in a series of eight patents (plus one US equivalent) and though in some patents a process is claimed, the main emphasis is on biocatalyst. A summary of these patents and the comparison with the early patents of EBC was given in Chapter 3. The patents were entitled ... 

Plummer invented a process for the biodesulfurization of hydrocarbons [157], in which organic sulfur compounds contained in liquid hydrocarbons are converted to elemental sulfur. The reaction is carried out in the presence of a biocatalyst and hydrogen, by dissolving completely the liquid hydrocarbons in an organic solvent, such as a nucleophilic and/or electrophilic solvent(s). The nucleophilic solvent should have a pKa greater than 2, and the electrophilic solvent more negative than -2. Recommended nucleophilic solvents include -butylamine, diethylamine, butanediamine, ethylenimine, toluene, pyridine, aniline, and acetophenone. The electrophilic solvents could be methylethylketone, pyrrole, or benzaldehyde. 

In an in depth comparison of the cumulative knowledge discussed in Chapter 3, with what one could extract from the technological results reported in this Chapter, perhaps the first observation that one can make is the difference between the content of the biocatalyst development vs. process development results. The results on biocatalyst improvements constitute the majority of the open literature reports. The most important bottleneck holding advancement of the biodesulfurization technology is the ability to break the second C-S bond, releasing the sulfur from the organosulfur molecules. The IP portfolio does not provide a real solution for that problem. 

Some of the first studies on the biodegradation of sulfur compounds focused on their fate and removal from oil-contaminated environments. Another major area of study is the microbial process of "biodesulfurization" which has been suggested as a means of selectively removing sulfur compounds from petroleum prior to refining. Information gathered from these two areas of research provide the basis of the present knowledge of metabolism of organosulfur compounds in petroleum. This information is reviewed with emphasis on the metabolism of dibenzothiophenes and n-alkyl tetrahydrothiophenes (n-alkyl thiolanes). 

The ultradeep desulfurization of the current infrastructure fuels has become a bottleneck in the production of H2 for fuel cell applications. It is urgent to develop a more efficient and environmentally friendly process and technology for the ultradeep desulfurization of the hydrocarbon fuels. Consequently, many approaches have been conducted in order to improve the conventional HDS process and to develop new alternative processes. These approaches include catalytic HDS with improved and new catalysts, reactor and/or process, adsorptive desulfurization,27 oxidative desulfurization (ODS), extractive desulfurization (EDS), and biodesulfurization (BDS) by using special bacteria and others. Some of these works were reviewed recently by Topsoe et al.,15 Whitehurst et al.,28 Kabe et al.,29 Cicero et al.,30 Babich and Moulijn,31 Dhar et al.,32 Song,33 Song and Ma,16,34 Bej et al.,35 Mochida and Choi,36 Hemandez-Maldonado and Yang,37,38 Hemandez-Maldonado et al.,39 Topsoe,40 Brunet et al.,41 Gupta et al.,42 and Ito and van Veen.43... 

Other work (Malik et al., 2004) has focused on the various factors (which are suspected to limit the coal biodesulfurization process rate) on bacterial oxidation of ferrous iron. An attempt has been made to find whether this reaction is inhibited due to the presence of solid particles and/or the release of inorganic components from solids during coal biodesulfurization. The data showed that silicon was responsible for retarding the central step of iron oxidation during coal biodesulfurization. Consequently, operational strategies, which tend to minimize the concentration of toxic inorganic components in the leachate, would be a better option than conventional batch process for enhanced biodesulfurization. 

Malik, A., Dastidar, M.G., and Roychoudhury, P.K. 2004. Factors limiting bacterial iron oxidation in biodesulfurization system. International Journal of Mineral Processing, 73(1) 13-21. 

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