Hydrodesulfurisation catalysts

Characterisation of Coke on Deactivated Hydrodesulfurisation Catalysts and a Novel Approach to Catalyst Regeneration... 

In the case of palladium particles supported on magnesium oxide, Heiz and his colleagues have shown,29 in an elegant study, a correlation between the number of palladium atoms in a cluster and the selectivity for the conversion of acetylene to benzene, butadiene and butane, whereas in the industrially significant area of catalytic hydrodesulfurisation, the Aarhus group,33 with support from theory, have pinpointed by STM metallic edge states as the active sites in the MoS2 catalysts. 

A catalytic example of C-S bond breakage in benzothiophene has been reported by Bianchini [47], A catalytic desulfurisation was not yet achieved at the time as this is thermodynamically not feasible at such mild temperatures because of the relative stability of metal sulfides formed. Bianchini used a water-soluble catalyst in a two-phase system of heptane-methanol/water mixtures in which the product 2-ethylthiophenol is extracted into the basic aqueous layer containing NaOH. Figure 2.43 gives the reaction scheme and the catalyst. The 16-electron species Na(sulfos)RhH is suggested to be the catalyst. Note that a hydrodesulfurisation has not yet been achieved in this reaction because a thiol is the product. Under more forcing conditions the formation of H2S has been observed for various systems. 

Hydrotreating and Hydrogenation. - Nitride and oxynitride catalysts have been extensively investigated as catalysts for hydrotreating (in particular hydronitrogenation and hydrodesulfurisation) and hydrogenation (for CO, aromatics, crotonaldehyde and alkenes ° the reduction of NO with H2 has been covered in the previous section). 

Leglise, J. Van Gestel, J. Duchet, J.C. Promotion and inhibition by hydrogen sulfide of thiophene hydrodesulfurisation over a sulfide catalyst. 

H.R. Reinhoudt, The development of novel catalysts for deep hydrodesulfurisation of diesel fuel, Ph.D. Thesis, 1999, Delft University of Technology, The Netherlands. 

Molybdenum disulfide catalysts, promoted by cobalt or nickel, are used to remove organosulfur compoimds from crude petroleum by hydrogenolysis— hydrodesulfurisation or HDS [124,125,126], These compounds are imdesirable because they poison motor vehicle autoexhaust catalysts and bum to sulfur dioxide, an environmental pollutant. The most difficult compounds to desulfurise are sulfur heterocyclics thiophene, benzothiophene, dibenzothiophene and their methyl substituted derivatives. A typical reaction is the removal of sulfiir from thiophene ... 

P.C.H. Mitchell (1981). In Catalysis. A Specialist Periodical Report, (Ed.) C. Kimball D.A. Dowden, pp. 175-184. Vol. 4. The Royal Society of Chemistry, London. Sulfide catalysts characterization and reactions including hydrodesulfurisation. 

The soft (chloroform-extractable) and hard coke fractions fi om a suite of deactivated Co/Mo hydrodesulfurisation (HDS) catalysts with carbon contents ranging from 5 to 18% have been characterised. The hard coke accounted for between 50 and 70% of the total carbon, but was responsible for much less of a reduction in BET surface area as the carbon content increased. Indeed, significant variations in hard coke structure were revealed by solid state C NMR with the aromaticity ranging from 0.6 to over 0.9 with increasing carbon content and time on stream. The relatively high aliphatic contents and atomic H/C ratios for the hard cokes obtained at low levels of carbon deposition (5-7%) suggested that much of the carbon should be removed under reductive conditions. Indeed, hydropyrolysis, in which the deactivated catalysts were heated from ambient to 500°C under a hydrogen pressure of 15 MPa, removed over 90% of the carbon and recovered 70% of the BET surface that had been lost. 

Exchange of radioactive sulfur and the hydrodesulfurisation mechanism has been studied intensively for the last two decades by the Moscow Zelinsky Institute Group. The first studies appeared in the 80s,P l and an increasing research activity has been apparent in the last few years.The method of their exchange studies is based on the preparation of S-labelled catalyst samples, followed by testing in the thiophene HDS reaction and... 

On the Role of Catalyst Sulfur in Catalytic Hydrodesulfurisation Some Conclusions from Tracer Studies... 

Figure 8.11 Refinery flow scheme showing the processes for treatment of the different fractions of crude oil. The main processes that use zeolite catalysts are indicated by shading. (HDS-hydrodesulfurisation, HDT-hydrotreating, FCC-fluidised catalytic cracking) [Adapted from reference 89 with permission. Copyright 1997 Wiley-VCH Verlag GmbH Co. KGaA.]...

Basically two strategies exist for the removal of sulfur compounds from hydrocarbons. They may be removed upstream or downstream of the reformer. For a higher sulfur content, as is present in mixtures of higher hydrocarbons such as heavy diesel or aviation fuel, the desulfurisation must be performed upstream of the reformer, otherwise the reforming catalyst suffers from sulfur poisoning. The operating temperature of the adsorption materials applied is usually around ambient or in a temperature range below 300 °C. Hydrodesulfurisation, which is applied on an industrial scale, is not suited to small mobile fuel processors, but could be used in stationary applications on the smaller scale. 

In this type of reactors, the gas and the liquid phase flow over a fixed bed of catalysts. The fixed bed reactors can be mainly classified into three types, (i) co-current down-flow of both gas and liquid phases (ii) downward flow of liquid with gas in the countercurrent upward direction and (iii) co-current up-flow of both gas and liquid. Reactors with co-current down-flow of gas and liquid is called as trickle bed reactors (TBR) and the co-current up-flow reactors are also referred to as packed bubble column reactors. Trickle bed reactors, wherein, the liquid reactant trickles down concurrently along with the gaseous reactant, over a fixed bed of catalyst pellets finds its application in wide variety of chemical, petrochemical and biochemical processes along with its application in waste water treatment. The examples of application of trickle bed reactors are given in detail in several monographs. (Satterfield (1975), Shah (1979), Al-Dahhan (1997) and Saroha (1996)). These include oxidation, hydrogenation, isomerisation, hydrodesulfurisation, hydroprocessing. These types of reactors are also applicable for esterification reactions (Hanika (2003)). 

Metal phosphides have been extensively studied for many applications, for example, corrosion-resistant materials [94], catalysts for hydrodesulfurisation and hydrodenitrogenation of petroleum fuels [95-100] and oxygen barriers in capacitors [101]. In addition, applications associated with the magnetic properties of these compounds have been also studied in depth [102-105]. 

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