Applied Petrochemical Research (v.7, #1)
Catalytic upgrading of refinery cracked products by trans-hydrogenation: a review by Mustapha Danlami Garba; S. David Jackson (1-8).
The production of high premium fuel is an issue of priority to every refinery. The trans-hydrogenation process is devised to convert two low valued refinery cracked products to premium products; the conversion processes involve the combination of dehydrogenation and hydrogenation reaction as a single step process. The paper reviews the recent literature on the use of catalysts to convert low value refinery products (i.e. alkanes and alkynes or alkadienes) to alkenes (olefins) by trans-hydrogenation. Catalysts based on VO x , CrO x and Pt all supported on alumina have been used for the process. However, further studies are still required to ascertain the actual reaction mechanism, mitigating carbon deposition and catalyst deactivation, and the role of different catalysts to optimize the reaction desired products.
Keywords: Trans-hydrogenation; Catalysis; Hydrocarbon; Dehydrogenation; Hydrogenation
The genesis of supported cobalt catalysts by Fiona A. Wigzell; S. David Jackson (9-21).
The general objectives of this research were to investigate the effect of the support and the gas atmosphere on the decomposition and reduction of cobalt nitrate hexahydrate supported on silica and alumina to gain a greater understanding of the calcination and reduction procedures used in catalyst manufacturing processes. The decomposition was followed by TGA-DSC-MS. The observed breakdown on the unsupported complex is similar but not identical to previous reports with NO detected as an evolved gas. In an oxygen/argon atmosphere the decomposition is generally simplified for the supported samples with a fewer number of weight loss events. When supported on alumina, cobalt nitrate is stabilised with decomposition events shifting to higher temperatures, whereas when supported on silica, cobalt nitrate is destabilised with only one significant decomposition event, which occurs at a lower temperature than that of the unsupported complex. In a hydrogen/nitrogen atmosphere partial decomposition of cobalt nitrate occurs before reduction is initiated with both supported samples. When supported on alumina, cobalt nitrate reduction is catalysed with the two events that occur below 350 °C happening at lower temperatures, while reduction above 350 °C is moved to higher temperatures. The silica-supported complex in contrast exhibits reduction events that are all reduced in temperature relative to the unsupported salt. However, there is evidence of the formation of cobalt silicate with a high temperature reduction. The study has shown that the calcination and direct reduction of supported cobalt nitrate is significantly affected by the support and that different conditions are required to achieve the same state.
Keywords: Cobalt nitrate; Reduction; Oxidation; Silica; Alumina
Dehydrocyclization of n-octane over boron- and barium-doped V-Mg-O catalysts: influence of n-octane/oxygen ratios by Elwathig A. Elkhalifa; Holger B. Friedrich (23-32).
Boron- and barium-doped vanadium–magnesium oxide catalysts (BVMgO and BaVMgO) were synthesized by the wet impregnation method and were used for the oxidative dehydrogenation of n-octane at different n-octane/O2 molar ratios. The catalysts were characterized by ICP-OES, in situ XRD, 51V MAS NMR, SEM, EDX and TGA-DSC. The catalytic tests were carried out in a continuous flow fixed bed reactor. The incorporation of boron and barium as dopants into the VMgO system resulted in catalysts with some differences in properties, such as the details of phase transformations, porosity and degree of hydration. The catalytic performance was affected by the strength of the oxidative environment. Moreover, incorporation of barium enhanced the catalytic performance of VMgO, while the addition of boron adversely affected the performance of VMgO over all n-octane/O2 molar ratios with regard to both activity and oxidative dehydrogenation selectivity.
Keywords: Dehydrocyclization; Boron dopant; Barium dopant; VMgO; n-Octane
Effect of different precursor species on the metal dispersion of a Ni/γ-Al2O3 adsorbent for sulfur adsorption by Chi Zhang; Yong-Ming Chai; Chen-Guang Liu (33-40).
Nickel adsorbents supported on the γ-Al2O3 with different nickel precursor species were prepared by the incipient impregnation method to investigate the influence of different precursor species on the metal dispersion and the sulfur capacity of the adsorbents. The adsorbents were characterized by N2 adsorption–desorption, H2 temperature-programmed reduction (TPR), transmission electron microscopy (TEM), O2–H2 chemisorption, and FT-IR of adsorbed pyridine. The sulfur adsorption performance was investigated at ambient temperature and pressure. The results showed that adsorbent’s metal dispersion and sulfur capacity were influenced significantly by the metal precursor species. The adsorbents prepared by nickel nitrate exhibited higher sulfur capacity and metal dispersion compared to the adsorbents prepared by nickel formate and nickel acetate. The higher performance of adsorbent prepared by nickel nitrate can be mainly attributed to the relatively more uniform metal dispersion and the smaller particle size of the nickel particles. This study demonstrates that the precursor species is an important factor for affecting the adsorption performance and provides a novel design idea of high metal dispersed catalysts.
Keywords: Precursor species; Dry impregnation; Metal dispersion; Ni/γ-Al2O3 adsorbents
Carbonylation of glycerol with urea to glycerol carbonate over supported Zn catalysts by S. E. Kondawar; R. B. Mane; A. Vasishta; S. B. More; S. D. Dhengale; C. V. Rode (41-53).
Glycerol carbonylation with urea is a very feasible option to produce glycerol carbonate with a net result of CO2 fixation through urea synthesis. The prerequisite of an efficient catalyst for this reaction is to possess both acid and basic sites together. Several acidic supports were screened for ZnO catalyst in this work and Zn/MCM-41 was found to exhibit the best activity and almost complete selectivity to glycerol carbonate (GC). Although, non-catalytic glycerol carbonylation resulted in GC formation but glycerol conversion achieved was twice with Zn/MCM-41 as a catalyst. Further to that increase in Zn loading from 2 to 5% resulted in increase in glycerol conversion from 63 to 82%. The prepared catalysts were characterized by XRD, NH3 and CO2-TPD and effects of reaction parameters such as catalyst loading, glycerol to urea mole ratio and temperature on glycerol conversion and GC selectivity in batch mode of operation were also studied. Time on stream activity of 5% Zn/MCM-41 catalyst for continuous carbonylation of glycerol was also studied for ~100 h with an average conversion of ~55% and complete selectivity to GC. This indicated five times lower productivity of GC per h due to lower residence time than that in a batch operation as compared to that of a continuous operation. Activation energy estimated from the Arrhenius plot was found to be 39.82 kJ mol−1 suggesting that the reaction is kinetically controlled. A reaction pathway mediated by acid and basic sites of the Zn/MCM-41 catalyst is also proposed.
Keywords: Supported Zn; Glycerol-urea carbonylation; Glycerol carbonate; Zn loading; Acid–base ratio; Reaction pathway; Continuous process
A research into the thermodynamics of methanol to hydrocarbon (MTH): conflictions between simulated product distribution and experimental results by B. Liu; B. Yao; S. Gonzalez-Cortes; V. L. Kuznetsov; M. AlKinany; S. A. Aldrees; Tiancun Xiao; Peter P. Edwards (55-66).
Thermodynamic calculations and analysis were carried out for a rational understanding of the results from selected laboratory MTH reactions. Simulations without solid carbons (coke), CO, CO2 and light alkanes target on the yield of olefin and aromatic products, which has been found better referenced to the real experimental observations that occur in time-on-stream (TOS). The confliction between simulated data and real experimental results is presumably ascribed to the limited dwelling time of products in the reaction system. Hydrocarbon pool based reactions donate olefins and methyl-benzenes as primary products in a continuous-flow MTH reaction; when the dwelling time of product extends intra-conversions (H2 transfers) between products would further adjust the composition of MTH yield, in which case alkanes and aromatic products (cokes precursors) increase. In the case of intra-conversions are ignored due to limited product dwelling time, thermodynamic calculation on Gibbs free energy change of selected sub reactions shows fairly close results to the real experimental data, which well supports the above explanations. This work highlights the importance of proper choosing target products and/or sub reactions for a rational thermodynamic prediction of MTH product distribution obtained in time-on-stream.
Keywords: Methanol to hydrocarbon; Hydrocarbon pool mechanism; Thermodynamic; Intra-conversion; Dwelling time