High Olefin Selectivity Research Articles

Role of p-benzoquinone for dispersion of silver nanoparticles in silver-polymer nanocomposite membranes

Solid state facilitated transport membranes with higher olefin selectivity were prepared using silver nanoparticles activated by electron acceptors, such as p-benzoquinone (pBQ) as olefin carriers and inert poly(ethylene co-propylene) (EPR) polymer matrix. Here, the effect of pBQ in silver-polymer nanocomposite membranes on the dispersion of silver nanoparticles on the polymer matrix and the structural properties of the membranes were investigated and correlated with the facilitated olefin transport. Transmission electron microscopy (TEM) and photographs clearly showed that pBQ plays an effective role as a stabilizing agent, resulting in a good dispersion of the silver nanoparticles in the EPR matrix. The good dispersion by pBQ was attributed to the strong interaction between pBQ and silver nanoparticles, as confirmed by x-ray photoelectron spectroscopy (XPS). Differential scanning calorimetry (DSC) also showed that the increased propylene permeance by pBQ was not caused by the increased chain flexibility of the membranes but facilitated olefin transport due to a reversible interaction between the olefin and silver nanoparticles.

Novel extruded fixed-bed MTO catalysts with high olefin selectivity and high resistance against coke deactivation

This report describes the catalytic performances of AlPO 4/ZSM-5 extrudates in comparison to conventional alumina- and silica-bound extrudates in the fixed-bed MTO (methanol to olefins) conversion. The novel AlPO 4/ZSM-5 extrudates are produced with an aluminium phosphate binder which undergoes a phase transition into an AlPO 4-tridymite phase upon calcination of the greenbodies. The finished AlPO 4/ZSM-5 extrudates are macroporous and mechanically very stable. In contrast to alumina, this novel matrix does not exhibit catalytic self-activity, and it does not release aluminium which is incorporated in the zeolite lattice. At temperatures above 400 °C, AlPO 4/ZSM-5 extrudates show superior activity, propylene selectivity and stability. The coke deactivation of AlPO 4/ZSM-5 extrudates can further be reduced dramatically, if a pre-reactor is installed upstream, where an equilibrium mixture of dimethyl ether (DME), methanol and water ( X MeOH = 87.7% at 275 °C) is produced. In contrast, the insertion of the DME pre-reactor has no significant effect on the coke resistance when extrudates with alumina- or silica-matrices are used.

Cooperative Effects in Ternary Cu−Ni−Fe Catalysts Lead to Enhanced Alkene Selectivity in Alkyne Hydrogenation

A new generation of heterogeneous Cu-Ni-Fe catalysts with appropriate metal ratios displayed outstanding alkene selectivity in the gas-phase hydrogenation of propyne (S(C(3)H(6)) up to 100%) and ethyne (S(C(2)H(4)) up to 80%). The design was accomplished by orchestrating key functions in the catalyst: copper is the base hydrogenation metal, nickel increases the hydrogen coverage to minimize oligomerization, and iron acts as structural promoter. In addition to the largely improved alkene selectivity compared to that of the commonly applied Pd catalysts, the ternary Cu-Ni-Fe catalysts promise substantial process advantages, since they do not require CO feeding as selectivity enhancer and they yield high alkene selectivity in a broad window of H(2)/alkyne ratios. The ternary system requires higher operating temperatures compared to those for palladium.

Effect of Si/Al ratio on performance of Pt–Sn-based catalyst supported on ZSM-5 zeolite for n-butane conversion to light olefins

The performance of Pt–Sn-based catalyst, supported on ZSM-5 of different Si/Al ratios were investigated for simultaneous dehydrogenation and cracking of n-butane to produce light olefins. The catalysts were characterized by number of physio-chemical techniques including XRF, TEM, IR spectra, NH 3-TPD and O 2-pulse analysis. Increase in Si/Al ratio of zeolite support ZSM-5 significantly increased light olefin's selectivity, while feed conversion decreases due to lower acidity of support. The results indicated that both the n-butane cracking and dehydrogenation activity to light olefin's over Pt–Sn/ZSM-5 samples with increasing Si/Al ratios greatly enhanced catalytic performance. The catalysts were deactivated with time-on-stream due to the formation of carbon-containing deposits. A coke deposition was significantly related to catalyst activity, while at higher Si/Al ratio catalyst the coke precursors were depressed. These results suggested that the Pt–Sn/ZSM-5 catalyst of Si/Al ratio 300 is superior in achieving high total olefins selectivity (above 90 wt.%). The Pt–Sn/ZSM-5 also demonstrates resistance towards hydrothermal treatment, as analyzed through the three successive reaction-regeneration cycles.

Partial hydrogenation of propyne over copper-based catalysts and comparison with nickel-based analogues

The partial hydrogenation of propyne was studied over copper-based catalysts derived from Cu–Al hydrotalcite and malachite precursors and compared with supported systems (Cu/Al 2O 3 and Cu/SiO 2). The as-synthesized samples and the materials derived from calcination and reduction were characterized by XRF, XRD, TGA, TEM, N 2 adsorption, H 2-TPR, XPS, and N 2O pulse chemisorption. Catalytic tests were carried out in a continuous flow-reactor at ambient pressure and 423–523 K using H 2:C 3H 4 ratios of 1–12 and were complemented by operando DRIFTS experiments. The propyne conversion and propene selectivity correlated with the copper dispersion, which varied with the type of precursor or support and the calcination and reduction temperatures. The highest exposed copper surface was attained on hydrotalcite-derived catalysts, which displayed C 3H 6 selectivity up to 80% at full C 3H 4 conversion and stable performance in long-run tests at T ⩾ 473 K. Both activated Cu–Al hydrotalcites (this work) and Ni–Al hydrotalcites [S. Abelló, D. Verboekend, B. Bridier, J. Pérez-Ramírez, J. Catal. 259 (2008) 85] exhibited a relatively high alkene selectivity under optimal operation conditions, but they present a markedly distinctive catalytic behavior with respect to temperature and hydrogen-to-alkyne ratio. The product distribution was assigned through Density Functional Theory (DFT) simulations to the different stability of subsurface phases (carbides, hydrides) and the energies and barriers for the competing reaction mechanisms. The behavior of Cu in partial alkyne hydrogenation resembles that of Au nanoparticles, while Ni is closer to Pd.

Carbon dispersed iron-manganese catalyst for light olefin synthesis from CO hydrogenation

High performance iron-manganese catalysts dispersed with carbon to produce light olefins from CO hydrogenation were prepared by sol-gel method using citric acid as precursor. The effects of carbon content on the bulk structure, the water gas shift reaction, the chain propagation ability and the activity and selectivity of the catalysts were investigated. The results showed that the catalysts were gradually reduced during the decomposition of the precursor when calcined under pure N2. The formation of iron-manganese mixed crystallites was favored and stabilized because of the enhanced interaction of iron and manganese with increasing carbon content. During the subsequent CO hydrogenation reaction, all the catalysts showed high activity and olefin selectivity. With increasing carbon content, the water gas shift (WGS) reaction was restrained and the chain propagation ability was inhibited. Catalysts with higher carbon content showed much lighter hydrocarbon products; however, the selectivity of CH4 was almost unchanged.

Effect of Preparation Method of Fe–based Fischer–Tropsch Catalyst on their Light Olefin Production

Fischer–Tropsch synthesis (FTS) for the production of light olefin from syngas was investigated on K–Fe–Cu–Al catalysts. The catalysts were prepared by different methods, such as K impregnated over co-precipitated Fe–Cu–Al, K impregnated over sol–gel (pechini) synthesized Fe–Cu–Al, Fe–Cu–K impregnated on alumina and K impregnated over co-precipitated Fe–Cu in a slurry phase of Al2O3. Among four catalysts, K impregnated over Fe–Cu–Al prepared by sol–gel method has shown the best activity. A favorable pore size distribution and pore volume, manifested in a facile reducibility of the iron oxide, is found to be responsible for high activity. The catalyst also exhibits high olefin selectivity compared with the others, due to the presence of moderate number of acid sites.

Control of Acid-Site Location of MFI Zeolite by Catalytic Cracking of Silane and Its Application to Olefin Synthesis from Acetone

Selective de-activation of acid sites located near the outer surface of zeolite was examined using the catalytic cracking of silane (CCS) method. From FT-IR analysis, adsorption species of silane compounds on the acid sites of zeolite during calcination were investigated. Moreover, the effects of types of silane compounds on the changes in zeolite properties, including the amounts of adsorbed ammonia and benzene within zeolite, prior to and after CCS treatment, were examined. The CCS method using diphenylmethylsilane (DPM-silane) was effective in de-activating the acid sites located near the outer surface of ZSM-5 zeolite. Olefin synthesis from acetone was carried out using ZSM-5 zeolite catalysts. The ZSM-5 zeolite after the CCS treatment using DPMsilane exhibited high olefin selectivity as well as low aromatic selectivity.

Fischer–Tropsch Synthesis Using Zeolite-supported Iron Catalysts for the Production of Light Hydrocarbons

Fischer–Tropsch synthesis (FTS) for the production of olefins from syngas was investigated on FeCuK impregnated on zeolite catalysts such as ZSM-5, Mordenite and Beta-zeolite. ZSM-5 supported catalyst showed the best activity among the three catalysts due to the high reducibility of iron oxides. It also exhibited high olefin selectivity compared to a catalyst prepared by physical mixing of the two components, due to the presence of moderate number of acid sites.

Synthesis, characterization and catalytic properties of SAPO-34 synthesized using diethylamine as a template

SAPO-34 molecular sieve was successfully synthesized using diethylamine (DEA) as a template. The influence of template concentration and silica concentration on the synthesis were investigated. Pure SAPO-34 could be obtained when n(DEA)/ n(Al 2O 3) ⩾ 1.5 and n(SiO 2)/ n(Al 2O 3) > 0.1 in the synthesis gel. Further increase of DEA concentration in the starting gel [ n(DEA)/ n(Al 2O 3) > 3] has a negative effect on both crystallinity and crystal yield. The products were characterized by XRD, XRF, SEM, NMR, FT-IR, TG-DTA and nitrogen adsorption techniques. It was found that SAPO-34 synthesized with DEA as a template has the characteristic of high silicon incorporation and exhibits good thermal and hydrothermal stability. The catalytic performance of SAPO-34 was tested by methanol-to-olefin (MTO) reaction and high olefins (C 2H 4 + C 3H 6) selectivity was obtained.

CO hydrogenation over cobalt and iron catalysts supported over multiwall carbon nanotubes: Effect of preparation

CO hydrogenation was investigated over Co or Fe catalysts supported on multiwall carbon nanotubes (MWNTs). Two types of catalysts were prepared. For the simple impregnation method, metal acetate precursors were deposited onto the surface of MWNTs. These catalysts were denoted as “I-samples.” The second family of catalysts was prepared by deposition of preprepared metal oxide nanoparticles onto the MWNT support. These samples were labeled “P-samples.” All of the samples were characterized by TPR and TEM measurements and tested in CO hydrogenation. TPR measurements showed easy reducibility of the metal ions in the I-Co and I-Fe samples. TEM images generally pointed to a rather uniform particle size both before and after the reaction. The highest catalytic activity and high selectivity toward C 2–C 4 and C 5+ fractions, as well as for olefin formation, were found for I-Fe. Catalytic activity was lower for P-Co and P-Fe. It can be established that these novel catalyst systems have high activity with high olefin selectivity and high fractions of larger hydrocarbons.

Characterization of Fischer?Tropsch Cobalt-Based Catalytic Systems (Co/SiO2 and Co/Al2O3) by X-ray Diffraction and Magnetic Measurements

Results of the characterization of six Co-based Fischer–Tropsch (FT) catalysts, with 15% Co loading and supported on SiO2 and Al2O3, are presented. Room temperature X-ray diffraction (XRD), temperature and magnetic field (H) variation of the magnetization (M), and low-temperature (5 K) electron magnetic resonance (EMR) are used for determining the electronic states (Co0, CoO, Co3O4, Co2+) of cobalt. Performance of these catalysts for FT synthesis is tested at reaction temperature of 240 °C and pressure of 20 bars. Under these conditions, 15% Co/SiO2 catalysts yield higher CO and syngas conversions with higher methane selectivity than 15% Co/Al2O3 catalysts. Conversely the Al2O3 supported catalysts gave much higher selectivity towards olefins than Co/SiO2. These results yield the correlation that the presence of Co3O4 yield higher methane selectivity whereas the presence of Co2+ species yields lower methane selectivity but higher olefin selectivity. The activities and selectivities are found to be stable for 55 h on-stream.

Propylene from butanes

In the chemical industry C2–C4 olefins are critical building blocks for high value commodity products. One of the key challenges in Fischer Tropsch Synthesis (FTS) technology development is to manipulate process conditions and/or catalytic systems in order to suppress methane selectivity while still producing mainly C2–C4 products with maximum olefin content. Sasol developed an iron catalyst promoted with sodium and sulphur that yielded a fairly high proportion of C2–C4 products with lower than expected methane selectivity. Due to the unexpected low methane selectivity in combination with high olefin selectivity necessitated the evaluation of other promoters similar to sulphur in combination with alkali promoters (i.e. sodium and potassium) in order to understand whether the combination of sulphur and sodium is unique or whether other alkali and non-metal promoters will yield similar results or even improve the selectivity further. By employing high throughput experimentation, a total of 306 catalysts were synthesised and tested in order to identify whether other possible non-metal FTS promoters could either match or improve the selectivities observed for sodium and sulphur and to also identify potential optimum promoter levels for maximum C2–C4 olefin selectivity and minimum methane formation. The results showed that from the series of catalysts evaluated sulphur and sodium yielded the highest olefin selectivity in combination with low methane selectivity and that a mole ratio of at least 2:1 Na:S is required for optimum C2–C4 selectivity. Apart from the statistical analysis of data and subsequent comparison of catalyst selectivity, the catalysts were also evaluated based on the expected Schulz Flory selectivity correlation. For unique catalyst selectivity a significant shift should be observed. In this paper the results of high throughput experimentation are presented and discussed using the direct relations of C2–C4 selectivity and methane selectivity in order to distinguish unique catalyst systems that are selective towards C2–C4 olefin production.

Oxidative dehydrogenation of isobutane on MCM-41 mesoporous molecular sieves

MCM-41 mesoporous molecular sieves containing silicon and vanadium have been prepared by a direct hydrothermal route. Aluminium-containing [Si,Al]-MCM-41 and purely siliceous [Si]-MCM-41 solids were synthesised for comparison purposes. 51V static and magic-angle-spinning NMR studies of [Si,V]-MCM-41 showed one type of VO 4 in the as-prepared samples (site I) and two types of monodispersed and distorted to various extent VO 4 tetrahedra, chemically bound to the walls of MCM-41 (sites IVa and IVb), in the calcined and rehydrated samples. NMR parameters of vanadium units are given. The catalytic performance of MCM-41 materials was probed in the oxidative dehydrogenation (ODH) of isobutane. The highest selectivities to isobutene (48–59%) were observed for the [Si,V]-MCM-41 materials with Si/V=85 and 30, respectively. On the contrary, a sample containing V 2O 5 bulk-like species exhibited much lower selectivity to isobutene, especially at the isobutane conversion higher than 5%. The presence of isolated vanadium species, as found by 51V NMR, was responsible for the high olefin selectivity in the ODH of isobutane.

Effect of precipitating agent on the catalytic behaviour of precipitated iron catalysts

Iron precipitated catalysts have been prepared using different precipitating agents (NH4OH, K2CO3) at different pH values. In situ Mossbauer (MES) study of the reduced catalyst prepared using NH4OH revealed the presence of superparamagnetic Fe2+, Fe3+ and magnetically split α-Fe only, whereas the catalyst prepared with K2CO3 also showed an extra magnetic sextuplet of Fe3O4. For both catalyst systems, in situ MES revealed that during Fischer–Tropsch synthesis α-Fe was converted into ɛ'-Fe2,2C and finally into χ-Fe2,5C when the synthesis time was increased. The rate of formation of hydrocarbons was observed to increase with the increase in the degree of carburisation with the NH4OH catalyst showing a higher rate of reaction. The K2CO3 catalyst exhibited higher olefin selectivity than the NH4OH catalyst under similar pH conditions.

97/03723 Synthetic diesel fuel and process for its production

Catalytic reaction performances of home-made mesoporous MnO2-supported Fe-based catalyst with copper promoter for Fischer–Tropsch synthesis (FTS) are investigated in a slurry-phase reactor at 533 K–573 K and 1.0 MPa. The present catalyst system exhibits high olefin selectivity, however, the selectivity to ethylene is lower than the extrapolation based on the C3+. Simultaneously, the catalyst gives high oxygenates productivity except for the C1 oxygenates. Comprehensive product distributions including hydrocarbon and oxygenates at different temperatures are presented. Particular attention is paid to the new overall distribution of product based on the carbon numbers when the hydrocarbon is combined with oxygenates. The new distributions at different temperatures show similar trends, displaying low C1 product selectivity and almost accordant C2 product selectivity with the extrapolation from Anderson–Schulz–Flory (ASF) law. An attempt is made to elucidate the deviation behavior of C1 and C2 hydrocarbon.

Microcalorimetric Studies of Surface Acid/Base Properties of Magnesium Iron Catalysts Prepared from Hydrotalcite-Type Precursors

Magnesium–iron mixed oxides with Mg/Fe molar ratios 1,3, and 6 were prepared from hydrotalcite-type precursors. Microcalorimetric adsorption of NH3and CO2showed that the surface acidity and basicity of the mixed oxides after calcination at 673 K are similar despite the different Mg/Fe ratios. Increasing calcination temperature from 673 to 773 K significantly decreased the surface area of the 3 Mg/Fe oxide, but the densities of both the acid and base sites were not changed. Mössbauer spectroscopy revealed that the reduction of the 3 Mg/Fe oxide (Fe2O3/MgO) in H2at 673 K converted all Fe3+to Fe2+. The resulted FeO/MgO exhibited the same acidity as that of the Fe2O3/MgO, but the basicity of the FeO/MgO was greatly enhanced. Reduction at 773 K resulted in the formation of 76% Fe2+and 24% Fe0as detected by Mössbauer spectroscopy. The Fe/FeO/MgO sample formed exhibited very low heat for the adsorption of NH3(40 kJ/mol) indicating that all iron atoms on the surface are Fe0. However, a substantial basicity remained on the surface of this sample that may account for its high olefin selectivity compared with pure iron catalyst in the Fischer–Tropsch synthesis.

Selective synthesis of ?-olefins on Fe-Zn Fischer-Tropsch catalysts

Fe/Zn oxides promoted with K and Cu selectively produce α-olefins at typical Fischer-Tropsch synthesis conditions (2/1 H2/CO, 1 MPa, and 270°C). The simultaneous presence of K and Cu introduces a synergistic activity enhancement while maintaining the high olefin selectivity obtained by alkali promotion. Structural and morphological differences in Fe-Zn oxides prepared from ammonium glycolate complexes or precipitated from nitrate solutions have only a small influence on catalytic properties. Catalyst behavior is strongly influenced by synergistic promoter effects (Cu, K) and by the controlled in situ conversion of iron oxide precursors to carbides.

Methanol to olefins—prediction of the performance of a circulating fluidized-bed reactor on the basis of kinetic experiments in a fixed-bed reactor

The conversion of methanol to olefins (MTO) over a zeolite catalyst is used as an example for the investigation of a circulating fluidized bed (CFB) reactor/regenerator system. A lumped-species reaction scheme has been developed which accounts for the most relevant components. Kinetic experiments were carried out in a standard fixed-bed Berty reactor over the 400°C to 500°C range at atmospheric pressure. The MTO process was performed in a circulating fluidized bed (riser dimensions: internal diameter 0.03 m, height 11 m) that is coupled with a regenerator for continuously burning off the coke deposits. Conversion of more than 98% and a very high olefin selectivity have been achieved. Based on the estimated kinetic parameters and on a CFB reactor model, methanol conversion and product distribution is predicted and compared with experimental data. The agreement is satisfactory for the whole temperature range examined.

Hydrogenation of carbon monoxide on unsupported Fe-Mn-K catalysts for the synthesis of lower alkenes: promoter effect of manganese

Unsupported Fe-Mn-K catalysts prepared earlier by incorporating potassium in-situ during coprecipitation of iron- and manganese oxides have been found to exhibit good catalytic activity and high alkene selectivity in the C 2-C 4 range, during syngas conversion. The effect of manganese on the alkali promoted iron catalysts towards hydrocarbon synthesis was studied here. Manganese in moderate amount promotes catalytic activity as well as selectivity of lower alkenes. Using a catalyst containing about 20 mol-% Mn and 0.5% K, at 673 K, 3 kg/cm 2 pressure, WHS V = 800 h −1 and H 2/CO = 1, it was possible to obtain good carbon monoxide coversion with 70–80% lower alkenes without formation of excess methane and carbon dioxide.