OXIDATIVE DESULFURIZATION OF DIESEL USING HYDROGEN PEROXIDE AND TERT-BUTYL HYDROPEROXIDE AS OXIDANTS

Oxidative desulfurization of hydrodesulfurized (HDS) diesel, HDS diesel doped with dibenzothiophene (DBT) and isooctane doped with DBT was studied by using hydrogen peroxide, tert-butyl hydroperoxide as oxidants, metal acetylacetonates like vanadyl acetylacetonate, manganese acetylacetonate, molybdenum acetylacetonate, iron acetylacetonate and, sodium tungstate as catalysts for oxidation of sulfur compounds to sulfones/sulfoxides followed solvent extraction with acetonitrile or N-methyl pyrrolidinone (NMP). Among the various catalysts studied vanadyl acetylacetonate was found to be the most effective with both hydrogen peroxide and tert-butyl hydroperoxide oxidants and yielded maximum 77.65% oxidative desulfurization of the HDS diesel with 540 ppmw initial sulfur content. The oxidative desulfurization of HDS diesel (initial sulfur content 300ppmw) doped with DBT and isooctane doped with DBT to bring their sulfur contents to 2800 ppmw, using hydrogen peroxide, vanadyl acetylacetonate oxidant system and acetonitrile as solvent for extraction yielded diesel with 262ppmw and isooctane with 40 ppmw sulfur contents. These results indicated that while it is easier to oxidize and remove DBT sulfur, it is relatively difficult to oxidize and remove sulfur compounds like 4,6-dimethyl dibenzothiophene and other similar hindered alkyl dibenzothiophene derivatives present in diesel using this oxidative desulfurization system

Ultra low sulfur diesel by oxidative desulfuriztion of HDS diesel

Due to increasing environmental concerns developed countries have put stringent limits on sulfur levels in fuel and now these limits are being implemented in the developing countries also. The US EPA released new regulation limiting sulfur in diesel to 15ppm by 2006. In India diesel fuel with 50 ppm sulfur is to be used in 11 major cities and 350 ppm in rest of the country by 2010. The pressing needs to reduce sulfur levels to ultra low in diesel have aggressively accelerated the research and development activities in the area of diesel desulfurization. The most targeted deep hydrodesulfurization processes have inherent problems like high capital and operational costs, high energy requirements difficult to justify it for small refiners on one hand and limitations of the catalyst to desulfurize sulfur species like 4,6-dimethyl dibenzothiophene (4,6-DMDBT) on the other hand. Owing to these difficulties, alternative methods like oxidative desulfurization, biodesulfurization, liquid-liquid extraction, and selective adsorption are being investigated worldwide for desulfurization of diesel fuel. Among the alternative approaches oxidative desulfurization, which involves oxidation of sulfur compounds present in diesel to more polar sulphones/ sulphoxides followed by their removal by solvent extraction/ adsorption has attracted worldwide attention. Oxidation of sulfur compounds present in HDS diesel containing about 500ppm sulfur was extensively studied first in mixer settler and then in a continuous counter current oxidation reactor with a oxidizing solution consisting of carboxylic P-16 XII RTM, 14th – 16th NOVEMBER, 2005 HYDERABAD 540 acid (CA) and active oxygen containing species to achieve their quantitative oxidation to sulphones/ sulfoxides. This was followed by counter current extraction of sulphones/ sulphoxides from oxidized diesel with N-methyl pyrolidinone - antisolvent mixture and final finishing by passing through a bed of silica/ alumina to obtain ultra low sulfur diesel (ULSD). Oxidation of sulfur compounds present in HDS diesel was also studied in a continuous down flow fixed bed laboratory reactor with organic hydroperoxide in presence of transition metal containing heterogeneous catalyst to achieve their quantitative oxidation to sulphones/ sulphoxides. The sulphones/sulphoxides thus formed could be removed from oxidized diesel by adsorption on solid alumina / silica to obtain ultra low sulfur diesel (ULSD). Both these approaches for oxidative desulfurization (ODS) of HDS diesel were found to be efficient to obtain ultra low sulfur diesel (ULSD) with less than 10 ppm sulfur content and are discussed in detail in this article

Higher order Moreau's sweeping process: Mathematical formulation and numerical simulation

International audienceIn this paper we present an extension of Moreau's sweeping process for higher order systems. The dynamical framework is carefully introduced, qualitative, dissipativity, stability, existence, regularity and uniqueness results are given. The time-discretization of these nonsmooth systems with a time-stepping algorithm is also presented. This differential inclusion can be seen as a mathematical formulation of complementarity dynamical systems with arbitrary dimension and arbitrary relative degree between the complementary-slackness variables. Applications of such high-order sweeping processes can be found in dynamic optimization under state constraints and electrical circuits with ideal diodes

Thermodynamics of the rupture in a Morse lattice

The rupture of a Morse lattice is considered in the present paper. The critical rupture force Fcr is found to decrease with the number of particles N as Fcr ~ 1/$\sqrt{N}$. The partition function is obtained for two states of the lattice – with all equal bond lengths and one broken bond. In the first case an accurate expressions for thermodynamic parameters are obtained, and thermodynamic expressions are derived in the harmonic approximation in the latter case. The analytical predictions are confirmed by extensive MD simulations. Cis-trans isomerization is considered as an example. Volume fractions of trans- and cis-isomers versus number of monomer units N are found depending on the torsion stiffnesses