Oxidative Desulphurization Research Articles

Catalysis for Society: Towards Improved Process Efficiency in Catalytic Selective Oxidations

This short review documents some examples of the recent innovations in the field of catalytic selective oxidation aimed at improving process performance and process sustainability in general. Some strategies adopted in order to increase selectivity to the desired product are illustrated, including unconventional procedures for the oxidation reaction—the cyclic mode as compared to the co-feed mode—and special arrangements of the catalytic bed, as in the case of the oxidation of o-xylene to phthalic anhydride. The choice of which oxidant to use is also discussed, in relation to the process of oxidative desulphurization of gasoil.

Oxidative desulphurization of light cycle oil: Monitoring by FTIR spectroscopy

Oxidative desulphurization received attention as an alternative or an additional technology for deep fuel desulphurization. We studied oxidative desulphurization as an approach to remove sulphur organic compounds in light cycle oil. By FTIR spectroscopy appropriate conditions for oxidation have been experimentally identified as up to 90% of the sulfur compounds in LCO were removed. This spectroscopic technique allowed sulphones quantification by 1302 cm − 1 band interpretation. Inasmuch sulphones have higher polarity than the parent sulphide molecules they are preferentially extracted from the feedstock. FTIR analysis permits to estimate degree of the sulphur compounds oxidation, degree of desulphurization by extraction method and to register micro quantity of oxidized products.

Investigation of straight-run diesel oil fractions with sulfur high content oxidative desulphurization

The article deals with desulphurization of straight-run diesel fractions by selective oxidation of sulphuric compounds with their further separation. The possibility of commercial diesel fuels production with sulphur content up to 0.2 mas % from straight-run fractions with sulphur content of 0.25–0.67 mas % has been shown.

In situ synthesis of Au/Ti-HMS and its catalytic performance in oxidation of bulky sulfur compounds using in situ generated H 2O 2 in the presence of H 2/O 2

Gold particles are supported on Ti-containing mesoporous silica (Ti-HMS) through an in situ process. The obtained samples were characterized by a series of techniques including ICP, powder X-ray diffraction, N 2 sorption, UV-visible spectroscopy and transmission electron microscopy. The performance of the catalyst in direct synthesis of H 2O 2 from H 2/O 2 in methanol solvent and oxidative desulphurization using the in situ generated H 2O 2 have been systematically investigated. The results show that in situ synthesized Au/Ti-HMS, the organic template of which is eliminated via extraction with ethanol, successfully maintains the typical wormhole structure of HMS and possesses uniform mesopores, which is confirmed by N 2 sorption and TEM. UV-visible spectroscopy result confirms the simultaneous existence of Au and Ti active centers in this bifunctional catalyst. Gold particles supported on Ti-HMS show high activity in the direct synthesis of H 2O 2 from H 2 and O 2 in methanol solvent. Furthermore, high removal rate of bulky sulfur compounds can be obtained using the in situ generated H 2O 2 over Au/Ti-HMS. Final conversion rate of the substrates confirms the dominant role of the in situ H 2O 2 oxidation in deep desulphurization. In addition, this bifunctional catalyst can avoid the insufficiency of H 2O 2 caused by the decomposition comparing with the Ti-HMS/commercial H 2O 2 system.

The effect of N-containing compounds on oxidative desulphurization of liquid fuel

The oxidative removal of organic sulfur compounds from model fuel with H 2O 2 over Ti-containing molecular sieves in the presence of N-containing compounds had been studied. The effect of the types and amounts of nitrides on oxidative desulphurization were investigated. It has been shown that pyridine and pyrrole have adverse impact on the oxidation of thiophene and lead to the decrease of corresponding removal rate. The pyridine has stronger influence than pyrrole. Quinoline and indole have no impact on the final removal rate of thiophene. However, the two kinds of nitrides, as well as carbazole, have obvious impact on the oxidation removal of benzothiophene and 4,6-dimethyl dibenzothiophene. The effect of nitrides on oxidative desulphurization can be attributed to the strong adsorption of nitrides and their oxidized products on the active sites of catalysts. For pyridine and quinoline, which are basic nitrides, their adsorptions on catalysts are even stronger than that of sulfides.

Oxidative Desulphurization of 4,6-Dimethyldibenzothiophene with Hydrogen Peroxide over Ti-HMS

Oxidative desulphurization of 4,6-dimethyldibenzothiophene (DMDBT) in octane has been investigated with hydrogen peroxide (H2O2) over Ti-HMS under mild conditions. Among the several Ti-containing catalysts, Ti-HMS exhibits high catalytic activity for the oxidation of DMDBT. The effects of the amount of the Ti-HMS catalyst, the mole ratio of H2O2 and the S-containing molecule (H2O2/S), the concentration of DMDBT, and the temperature on the reaction rate were investigated. The reaction rate of the oxidative desulphurization was promoted with the increase of the amount of the catalyst, the H2O2/S mole ratio, the concentration of DMDBT, as well as the temperature. The Arrhenius apparent activity energy of the oxidative reaction of DMDBT with H2O2 over Ti-HMS was determined as 38.54 kJ mol-1. The reaction system H2O2/Ti-HMS shows a high intrinsic catalytic activity for sulfur-containing compounds present in diesel in the following order: DMDBT < benzothiophene (BT) < dibenzothiophene (DBT). BT and DBT can be completely converted into their corresponding sulfoxides and sulfones in 3 h. The removal of DMDBT can be achieved by nearly 90%, and as a result, the sulfur level of a model fuel can be lowered from 226.1 to 22.9 ppm with a H2O2/S mole ratio of 4:1 at 333 K.

Deep desulphurization of gasoline and diesel fuels using non-hydrogen consuming techniques

Desulphurization of FCC gasoline and diesel fuels has been investigated by chemical oxidation of sulphur containing compounds with hydrogen peroxide in the presence of an acid catalyst such as formic acid and acetic acid, followed by extraction of the oxidized compounds using acetonitrile. Oxidative desulphurization (ODS) of diesel fuel was found to be very promising approach for the reduction of up to 92% of sulphur at low temperature (50 °C) and atmospheric pressure. The direct extraction of diesel oil without any oxidation has resulted in about 45% sulphur removal, however such direct extraction also removed other aromatic hydrocarbons and affected the yield. The ODS is not successful with FCC gasoline due to the high olefinic content that tends to react with hydrogen peroxide to form epoxides. GC–MS technique was used to identify the sulphones during the oxidation of thiophenes. This study recommends that the oxidation extraction technique be used as an additional process to the hydrodesulphurization to enable the refiners to meet the future environmental sulphur regulations. The conventional hydrodesulphurization can be used to lower the sulphur content to few hundreds ppm. Then, the oxidation/extraction approach needs to be used to go for ultra-deep desulphurization as it may provide better mean and cost effective way in order to meet the future sulphur environmental requirements.

Electron transfer process. Part 2. Desulphurization of organic sulphur from feed and mercury-treated coals oxidized in air at 50, 100 and 150°C

In this paper, experiments have been undertaken to understand the nature of organic sulphur compounds retained after oxidation at 50,100 and 150°C for both feed and Hg-treated coals as well as the extent of desulphurization by the electron transfer process. It has been observed that oxidation of coal in air resulted in the predominant formation of disulphide compounds. Besides these compounds, aliphatic thiol compounds seem to have been leached out by the electron transfer process. Maximum desulphurization achieved by the electron transfer process carried out in absence of naphthalene is 19.17wt% in feed coal and 17.78wt% in Hg-treated coal of the total organic sulphur for the samples oxidized at 100°C. The desulphurization reaction has been found to follow pseudo-first-order kinetics and their rate constants have been calculated. The activation energies and frequency factors calculated for these coal samples are found to be in the range 21.28–25.53kJmol−1 and 5.01×10−4–28.18×10−4min−1, respectively. Kinetic studies reveal that the desulphurization reaction is non-spontaneous in nature which is further supported by the negative value of ΔS and positive value of ΔG. Low frequency factors and negative values of ΔS suggest that desulphurization by electron transfer process is an associated reaction. Although the positive value of ΔH attributes the endothermicity of the desulphurization reaction which requires input of energy for effective desulphurization, but the energy liberated during the formation of ion-radicals is utilized for rupture of bonds in those organic sulphur compounds which contain relatively weak C–S as well as S–S bonds. Total desulphurization (summation of oxidative desulphurization and desulphurization by electron transfer process, in absence of naphthalene) of organic sulphur is found to be 27.38wt% in feed coal and 28.45wt% in Hg-treated coals. This suggests that the presence of Hg2+ ion and naphthalene has no significant influence on desulphurization. The results of this work have considerable technological interest.

Redox and coordinative properties of N,N′-dithiobisamines: Oxidative desulphurization by copper(II) ions and Cr(CO) 5[S 2(NR 2) 2] complexes

N,N′-dithiobisamines, R 2N—S—S—NR 2, NR2N(CH 3) 2, N(CH 2CH 3) 2, ▪, ▪ or N(CH 2—C 6H 5) 2, are oxidized to SO 2 by copper(II) salts with formation of copper(I) complexes, while from the reaction with pentacarbonyl (tetrahydrofuran)chromium the novel complexes Cr(CO) 5[S 2(NR 2) 2] were isolated. They have been characterized by elemental analysis as well as by spectroscopic methods. The π-acceptor abilities of the sulphur-containing ligands in the Cr(CO 5)L complexes are discussed and compared with those found for their analogous monothio derivatives. Reactivity of the coordinated sulphur compounds towards acids and copper(II) salts is less than that of the free ligands.

Enhanced hydrodesulphurization of cokes deposited on iron ore by air gasification

The influence on air-gasification of cokes deposited on iron ores were studied in under successive desulphurization at 750 °C under atmospheric hydrogen. Gasification promoted by steam (water: 40 μl min −1) at 350 °C for 125 min gasified 21% of the coke and allowed 25% oxidative desulphurization (based on sulphur in the coke) during the gasification and enhanced the successive hydrodesulphurization level up to 63% giving a total desulphurization of 88%. This level is comparable with that achieved after grinding. Gasification at higher temperatures, which burned more coke, was less effective in enhancing hydrosedulphurization. Gasification increases the access of hydrogen molecules to sulphur atoms in the coke. Gasification, which increases the surface area of the coke and removes the sulphur preferentially, is discussed in terms of reactivity.

Nickel peroxide as a selective oxidant in the pyrimidine series. The synthesis of N1-substituted orotic and 2-thioorotic acids

A versatile route to the synthesis of iV1-substituted orotic or 2-thioorotic acids is described. The method involves three st&gt;eps: (i) Preparation of 6-hydroxy- methyl-2-thio-1,3-thiazine (24); (ii) conversion of the 1,3-thiazine into the 1- substituted 2-thiouracil by reaction with a primary amine (see Scheme 8); (iii) oxidation of the 6-hydroxymethyl group to a carboxyl group. 3,4-Dihydro-6-hydroxymethyl-4-oxo-2-thio-2H-1,3-thiazine was prepared directly from the reaction of dithiocarbamio acid with ethyl γ-hydroxytetrolate (an improved synthesis of this ester is described). Reaction of the thiazine with primary Bmines was straightforward and produced the related 6-hydroxymethyl-2-thio- uracils in high yield (see Table 2). Similar reactions with O-benzylhydroxylamine formed the 0-benzyl derivative of the Nl-hydroxy-2-thiopyrimidine (40). Nickel peroxide has served as a very selective oxidant in the pyrimidine series. Smoot'h oxidation of the hydroxymethyl group to carboxyl is demonstrated by the conversion of the 6-hyclroxymethyluracils into the corresponding orotic acids. The same products result from the 2-thiouracils on treatment with excess reagent because additional oxidative desulphurization of the 2-thione group occurs. More interestingly, seleotive oxidation of the 6-hydroxymethyl group can be achieved in the presence of the 2-thione group using two equivalents of nickel peroxide, to form a 1-substituted 2-thioorotic acid (Scheme 9). Application of this method to the preparation of I-hydroxyorotic acid mas successful, but only in the presence of excess nickel peroxide reagent. Under other conditions rapid decarboxylation occurred to form either 1-benzyloxyuracil or 1-benzyloxy-2-thiouracil and this has been developed into a useful synthetic route to these products. The role of nickel complexes in this deoarboxylation is discussed in terms of the hard/soft, acid/base theory. P.m.r. data on all compounds are reported.