Design of catalysts for pour-point reduction of lube oil fractions

The discovery of new micro-porous materials has resulted in interesting applications in petroleum refining in recent times. An example is the use of molecular sieve based catalysts for pour-point (pp) reduction of petroleum oils used for lubricating oil production. Two different catalytic processes are available for the reduction of pp of petroleum oils. These are based on shape selective cracking of the n-paraffins and wax-isomerization. The requirements of the micro-porous materials for the two catalysts are different; these are discussed. The optimization of the catalyst parameters to design good catalysts for the two processes is described

Redox and catalytic chemistry of Ti in titanosilicate molecular sieves: an EPR investigation

An EPR study of Ti3+ in titanosilicate molecular sieves, TS-1, TiMCM-41, ETS-10 and ETS-4 is reported. Ti4+ is reduced to Ti3+ by dry hydrogen above 673 K. Ti ions in TS-1 and TiMCM-41 are located in tetragonally elongated Td and those of ETS-10 and ETS-4 in a tetragonally compressed Oh geometric positions. Reduction at 873 K revealed the presence of two non-equivalent Ti3+ sites in TS-1 and TiMCM-41. Ti4+ ions in a tetrahedral geometry are more difficult to reduce than in an octahedral symmetry. The effects of cation exchange and Pt impregnation, on the geometry and reducibility of titanium in ETS-10, are also examined. Interaction of a tetrahedrally coordinated Ti3+ with O2 or H2O2 results in a diamagnetic titanium(IV) hydroperoxo species. Under the same conditions, an octahedrally coordinated Ti3+ forms a paramagnetic titanium(IV) superoxo species. The higher catalytic activity of TS-1 and TiMCM-41 in selective oxidation reactions is probably a consequence of the formation of the hydroperoxy species on their surface during the catalytic reaction. The presence of Pt in the vicinity of Ti enables the use of H2 and O2 (instead of H2O2) to generate the active hydroperoxy site. The absence of formation of titanium hydroperoxy species in ETS-4 and ETS-10 is the cause of their inactivity in selective oxidation reactions

Hydrogenolysis of sorbitol over Ni, Pt and Ru supported on SBA-15

Hydrogenolysis of sorbitol (15% aqueous solution) has been carried out in a batch reactor over Ni (6 wt%), Pt (1 wt%) and Ru (1 wt%) supported on SBA-15 and carbon coated SBA-15 (SBA-15(C)). For comparison, the three metals have also been supported on activated carbon (AC). The catalysts are characterized by XRD, N2 and H2 adsorption measurements. Addition of Ca(OH)2 to the reaction mixture increases conversion and selectivity for the dihydroxy compounds, 1,2-propanediol (PD) and ethylene glycol (EG). Based on yield of dihydric alcohols (PD+EG), the performance of the catalysts at 220 °C and 60 bar in the presence of Ca(OH)2 is in the order: Ru-AC ~ Ru-SBA-15(C) > Ru-SBA-15 ~ Ni-SBA-15, the yields being 40, 39, 31 and 29 wt%, respectively

Where is the metal in metallosilicate molecular sieves ? An examination of some vanadosilicates

Metallosilicate molecular sieves result when the Al3+ ions in zeolitic materials (aluminosilicate) are replaced (isomorphous substitution) by other ions. A large number of metal ions have reportedly been incorporated in zeolite lattices. However, doubts arise regarding the location of these metal ions in the framework in many cases. Detailed characterization of the metallosilicates is necessary to identity the nature and location of the metal ions. As an example, the types of V-ions present in vanadosilicate molecular sieves of MEL, MFI and BEA structure types are discussed based on detailed physicochemical characterization of these materials. Also, the influence of preparation methods on the type and location of the V-ions are reported

Alkylation of m-cresol with methanol and 2-propanol over calcined magnesium-aluminium hydrotalcites

Magnesium-aluminium hydrotalcites (MgAl-HTs) with Mg/Al atomic ratio 2,3 and 4 were synthesized by the coprecipitation method. Vapour phase alkylation of m-cresol with methanol was carried out over these samples calcined at 723K in the temperature range 523-723K at atmospheric pressure. A mixture of O- and C- alkylated products, namely, 3-methyl anisole (3MA), 2,5- and 2,3-dimethylphenols (DMP) and 2,3,6-trimethylphenol (2,3,6-TMP) were obtained. The selectivity of these products depends on the m-cresol/methanol feed ratio, temperature and contact times. The catalytic activity of these catalysts are in the order MgAl 3.0-CHT > MgAl 2.0-CHT > MgAl 4.0-CHT. MgAl 3.0-CHT showed ~30% selectivity for 2,5-DMP and 40% selectivity for 2,3,6-TMP with ~40% conversion at 623K or ~70% conversion at 723K. The alkylation of m-cresol with 2-propanol over MgAl 3.0-CHT at 673K offered nearly 80% selectivity towards thymol with nearly 40% m-cresol conversion

Biomimetic oxidations using transition metal complexes encapsulated in zeolites

An account of biomimetic oxidations by metal phthalocyanines, tri- and tetra-aza macrocycles, Schiff bases (salen and saloph), dimeric Cu-acetate and Co-Mn-acetate complexes encapsulated in zeolite-Y and molecular sieves is reported. The selective oxidation reactions investigated include epoxidation of styrene, hydroxylation of phenol, oxidation of p-xylene to terephthalic acid, ethylbenzene to acetophenone and cyclohexane, cyclohexanol and cyclohexanone to adipic acid. In all these reactions, the encapsulated metal complexes exhibit enhanced activity or selectivity compared to the "neat" complexes. The reasons for the enhanced activity of metal complexes upon encapsulation in zeolites are reported

Structural chemistry of Co-Mo-alumnina catalysts

The structural chemistry of Co-Mo-alumina hydrodesulfurization catalysts has been critically reviewed in this article. The location and nature of cobalt in the sulfided catalysts has been discussed. Small MoS<SUB>2</SUB>, crystallites (10 to 30 Å) that occur on the surface of a sulfided sample are unstable due to the high, net negative charge on the sulfur ions on their edges. They incorporate cations like Co<SUP>2+</SUP> at the edges of the MoS<SUB>2</SUB> sheet (not intercalated between the sheets) and attain stability. It is shown that for the range of crystallito sizes of Mo<SUB>S</SUB>, in these systems, a maximum of one Co ion can be incorporated per two Mo ions in this manner. Cobalt thus lends structural stability to the MoS<SUB>2</SUB>, crystallites and suppresses the excessive formation of anion vacancies at crystallite edges. Molybdenum sulfide crystallites on sulfided Mo-A1<SUB>2</SUB>O<SUB>3</SUB>, lacking this stabilizing influence of cobalt, lose excess sulfur, leading to the creation of a larger concentration of multiple anion vacancies at their edges. The presence of these strongly acidic multiple vacancies, however, leads to a lower structural stability of these crystallites. Moreover, these strongly acidic sites are also deactivated faster in the presence of unsaturated molecules (like diolefins, olefins, etc.), accounting for the fact that the superiority of Co-Mo-Al<SUB>2</SUB>O<SUB>3</SUB> over Mo-Al<SUB>2</SUB>O<SUB>3</SUB> manifests itself mainly in the steady-state activity [61-63]. The advantages of this model over those currently in vogue are the following: (1) It offers an explanation for the rather high cobalt concentration [Co/(Co + Mo)=0.31 necessary for optimum catalytic activity, (2) it accounts for the established accessibility of cobalt in the Co-MoS<SUB>2</SUB> phase to probe moledules [40], and (3) the stabilization of the small MoS<SUB>2</SUB> crystallites in sulfided Co-Mo-Al<SUB>2</SUB>O<SUB>3</SUB> compared to Mo-Al<SUB>2</SUB>O<SUB>3</SUB> with the consequent lower loss of sulfur ions from the former in flowing hydrogen (Table 3 and Ref. 28). The migration and sintering of MoS<SUB>2</SUB> crystallites in sulfided Mo-<SUB>2</SUB>O<SUB>3</SUB> but not co-Mo-Al<SUB>2</SUB>O<SUB>3</SUB>, observed by Okamoto et al. [21], is also in accord with the above picture of stabilization of small MoS<SUB>2</SUB> crstallites by cobalt

Side chain methylation of toluene and ethylbenzene with dimethyl-carbonate over alkaline X-zeolite

Side chain methylation of toluene and ethylbenzene using dimethylcarbonate has been studied at atmospheric pressure in the temperature range 673K-773K in a fixed bed reactor over Na, K and Cs exchanged X-type zoelite. Methylation of toluene produces ethylbenzene and i-propylbenzene as the main products while n-and i-propylbenzenes are the major alkylated products from ethylbenzene. The Cs exchanged sample, is the most active, the catalyst prepared by exchanging with alkali hydroxide being more active than that prepared from the chloride. The influences of process parameters such as duration of run, temperature and contact time on conversion and product yields have been investigated. Tentative mechanisms for the formation of the various products are proposed