Direct synthesis of isoparaffin from synthesis gas under supercritical conditions

To produce isoparaffins from synthesis gas directly, modified Fischer–Tropsch (FT) synthesis was carried out under supercritical conditions using n-butane as a medium. One-step FT synthesis using a hybrid catalyst consisting of Co/SiO₂, HZSM-5 and Pd/SiO₂ was carried out. Introduction of supercritical-phase n-butane increased light isoparaffins significantly and suppressed the formation of the by-product, methane. Under supercritical-phase butane, hydrogenolysis and isomerization reactions were promoted. Due to the fact that the optimum temperatures for FT and HZSM-5 catalysts are different, 513 K and over 573 K, respectively, two-step FT synthesis was also carried out to optimize the reaction temperatures. The first-step reaction used Co/SiO₂ catalyst containing small amount of HZSM-5 for FT synthesis at 513 K, and the second-step reaction used a hybrid catalyst containing Pd/SiO₂ and zeolite for hydrogenolysis and isomerization of hydrocarbons at 573 K. Introduction of supercritical n-butane increased the isoparaffin selectivity, and decreased the methane selectivity significantly. The production of heavy hydrocarbons C₉+ was inhibited in both gas and supercritical phase. The isoparaffin selectivity in the gas phase decreased with time-on-stream, but very stable for the supercritical-phase reaction. Because water and heavy hydrocarbons were removed from active sites on zeolite and the zeolite acidity was promoted in the supercritical medium, the selectivity of isoparaffin was considered stable. Among zeolites added to the hybrid catalyst in the second-step reactor, HZSM-5 and H-beta zeolite were suitable for producing light isoparaffins. These results indicated that two-step FT synthesis under supercritical n-butane was superior for producing light isoparaffins from synthesis gas directly.     

Fischer–Tropsch synthesis over a Co/SiO2 catalyst modified with Mn- and Zr under practical conditions

Fischer–Tropsch (FT) synthesis activity and the stability of a Co/SiO₂ catalyst modified with Mn- and Zr were examined under various practical conditions. Dependence of FT synthesis on reaction pressure and bench-scale FT synthesis were investigated. Evaluating catalyst lifetime during continuous FT reactions was conducted. The Co + Mn + Zr/SiO₂ catalyst exhibited relatively greater activity and stable reactivity for 168 h. Sulfur resistance of catalysts were investigated and results showed that the presence of 4 ppm H₂S drastically affected catalytic activity. The Co + Mn + Zr/SiO₂ catalyst exhibited greater activity even with H₂ presence and the sulfur poisoning rate was almost similar on both Co + Mn + Zr/SiO₂ and Co/SiO₂ catalysts.     

Fischer–Tröpsch synthesis over Co/TiO2: Effect of ethanol addition

The effect of the addition of ethanol (2% and 6%) during Fischer–Tröpsch (FT) synthesis has been investigated using a 10% Co/TiO₂ catalyst in a stirred basket reactor (T = 220 °C, P = 8 bar, H₂/CO = 2). The transformation of ethanol vapour (2% and 6% in nitrogen) over the Co/TiO₂ catalyst was also studied in the absence of the synthesis gas under FT reaction conditions. Ethanol was observed to be incorporated in the growing chain and was found to (i) increase the selectivity to light products, (ii) increase the olefin to paraffin ratio and (iii) significantly decrease the catalyst activity. These effects were almost completely reversed when the ethanol in the feed was removed. Thermodynamic predictions, TPR and XRD analysis have shown that cobalt metal particles were oxidised to CoO by ethanol but that re-reduction to Co metal was possible when ethanol was removed from the feed stream allowing the catalyst to recover most of its initial performance, in particular when high flow rates were used.     

Middle distillates from hydrocracking of FT waxes: Composition,characteristics and emission properties

A light cobalt catalyzed Fischer–Tropsch (FT) wax was subjected to hydrocracking in the range of temperature 319–351 °C and hydrogen pressure between 3.5 and 6.0 MPa. The catalyst used was platinum on amorphous silica–alumina. Hydrocracking reaction led to an increase of middle distillate yield up to 85% with a contemporary increase of iso-paraffins concentration which resulted in a remarkable improvement of cold flow properties of the products. The freezing point of C₁₀–C₁₄ fraction passed from ?23 to ?45 °C while the pour point of C₁₅–C₂₂ fraction decreased from 13 to ?23 °C. The latter fraction displayed high cetane numbers ranging between 75 and 80. Changes in carbon distribution and molecular structure of products during hydrocracking have been rationalized in the light of the accepted hydrocracking mechanism where n-paraffins undergo to consecutive isomerization reactions leading to isomers with progressively higher branching degree and concomitant cracking reaction. Experimental evidences support the view that apparent reactivity of n-paraffins is chain length dependent, increasing with the molecular weight. Detailed characterization by NMR and GC showed that branching groups abundance in the middle distillate products was the following: methyl ? ethyl > propyl.Emission tests carried out with FT diesel and commercial ultra low sulfur diesel showed that FT diesel has excellent combustion properties and leads to a reduction of emissions.     

On-line GC and GC–MS analyses of the Fischer–Tropsch products synthesized using ferrihydrite catalyst

Fischer–Tropsch (FT) synthesis reaction was performed using ferrihydrite catalyst. During 100 h of FT synthesis reaction, composition changes of the reaction product were studied according to the reaction time using an on-line GC, and the final FT products collected in traps were analyzed by GC–MS. Also, an effect of gas feed ratio of H₂/CO on the selectivity of the synthetic products was studied. As a H₂/CO feed ratio increased, not only CO conversion and activity of catalyst improved two times, but also CO₂ conversion was reduced by approximately 40% thereby improving the efficiency of catalyst significantly.     

Ionic liquid as an efficient promoting medium for synthesis of dimethyl carbonate by oxidative carbonylation of methanol

The synthesis of dimethyl carbonate by oxidative carbonylation of methanol using Cu salt catalysts in the presence of various room temperature ionic liquids (RTILs) was reported. Among the ionic liquids used, N-butylpyridinium tetrafluoroborate was the most effective promoter in terms of the conversion of methanol and the selectivity to dimethyl carbonate (DMC). The influences of reaction temperature, pressure, time, molar ratio of CO/O₂, and amount of the ionic liquid on the oxidative carbonylation of methanol were investigated. The results indicated that under the reaction conditions of 120 °C and 2.4 MPa of a 2:1 mixture of CO and O₂, 17.2% conversion of methanol, 97.8% selectivity of DMC and a DMC productivity of 4.6 g g⁻¹ cat h⁻¹ were achieved. The N-butylpyridinium tetrafluoroborate-meditated CuCl catalyst system could be reused at least five recycles with the same selectivity and a slight loss of catalytic activity due to loss of the catalyst during handling and transferring the reaction mixture.     

Effect of the hybrid catalysts preparation method upon direct synthesis of dimethyl ether from synthesis gas

Direct synthesis of DME from synthesis gas attains more attention recently due to higher conversion and lower cost in comparison to dehydration of the methanol. In this work Synthesis gas To Dimethylether (STD) conversion was examined on various hybrid catalysts prepared by seven different methods. These catalysts had the same general form as CuO/ZnO/Al₂O₃ with theoretical weight ratio 31/16/53, respectively. A novel preparation method for hybrid catalyst namely sol–gel impregnation has also been developed which showed better performance in comparison with the other methods. Also, in order to find out the effect of various alumina contents at a fixed CuO/ZnO ratio on the performance of the hybrid catalyst, a series of catalysts with different contents of alumina have been prepared by sol–gel impregnation method. The optimum weight ratio for CuO/ZnO/Al₂O₃ catalyst has been found to be about 2:1:5, respectively. These catalysts characterized by TPR, XRD, XRF, BET, TGA, N₂O absorption. The catalysts performance were tested at 240 °C, 40 bar and space velocity 1000 ml/g_cat.h, with the inlet gas composition H₂/CO/N₂ = 64/32/4 in a micro slurry reactor.     

Hydroformylation of 1-octene using rhodium–phosphite catalyst in a thermomorphic solvent system

The use of a liquid–liquid biphasic thermomorphic or temperature-dependent multicomponent solvent (TMS) system, in which the catalyst accumulates in one of the liquid phases and the product goes preferably to the other liquid phase, can be an enabling strategy of commercial hydroformylation processes with high selectivity, efficiency and ease of product separation and catalyst recovery. This paper describes the synthesis of n-nonanal, a commercially important fine chemical, by the hydroformylation reaction of 1-octene using a homogeneous catalyst consisting of HRh(PPh₃)₃(CO) and P(OPh)₃ in a TMS-system consisting of propylene carbonate (PC), dodecane and 1,4-dioxane. At a reaction temperature of 363 K, syngas pressure of 1.5 MPa and 0.68 mM concentration of the catalyst, HRh(CO)(PPh₃)₃, the conversion of 1-octene and the yield of total aldehyde were 97% and 95%, respectively. With a reaction time of 2 h and a selectivity of 89.3%, this catalytic system can be considered as highly reactive and selective compared to conventional ones. The resulting total turnover number was 600, while the turnover frequency was 400 h^?1. The effects of increasing the concentration of 1-octene, catalyst loading, partial pressure of CO and H₂ and temperature on the rate of reaction have been studied at 353, 363 and 373 K. The rate was found to be first order with respect to concentrations of the catalyst and 1-octene, and the partial pressure of H₂. The dependence of the reaction rate on the partial pressure of CO showed typical substrate inhibited kinetics. The kinetic behavior differs significantly from the kinetics of conventional systems employing HRh(CO)(PPh₃)₃ in organic solvents. Most notable are the lack of olefin inhibition and the absence of a critical catalyst concentration. A mechanistic rate equation has been proposed and the kinetic parameters evaluated with an average error of 5.5%. The activation energy was found to be 69.8 kJ/mol.     

A novel low-temperature methanol synthesis method from CO/H2/CO2 based on the synergistic effect between solid catalyst and homogeneous catalyst

The activity of a binary catalyst in alcoholic solvents for methanol synthesis from CO/H₂/CO₂ at low temperature was investigated in a concurrent synthesis course. Experiment results showed that the combination of homogeneous potassium formate catalyst and solid copper–magnesia catalyst enhanced the conversion of CO₂-containing syngas to methanol at temperature of 423–443 K and pressure of 3–5 MPa. Under a contact time of 100 g h/mol, the maximum conversion of total carbon approached the reaction equilibrium and the selectivity of methanol was 99%. A reaction pathway involving esterification and hydrogenolysis of esters was postulated based on the integrative and separate activity tests, along with the structural characterization of the catalysts. Both potassium formate for the esterification as well as Cu/MgO for the hydrogenolysis were found to be crucial to this homogeneous and heterogeneous synergistically catalytic system. CO and H₂ were involved in the recycling of potassium formate.     

Effect of component interaction on the activity of Co/CuZnO for CO hydrogenation

Co/CuZnO is known as a base metal catalyst active for C₂₊ oxygenate synthesis. This study probed the interactions of the different components of Co/CuZnO catalysts on CO hydrogenation using Fischer–Tropsch synthesis (250 °C, H₂/CO = 2) and SSITKA. Only combination of all three metal components produced a catalyst with relatively high C₂₊ oxygenate selectivity, but with much lower activity compared to that for Co/Al₂O₃. In situ reaction characterizations, albeit at somewhat different conditions than alcohol synthesis, helped explain interaction of the components. SSITKA, under methanation conditions, indicated that the most striking feature for the combination of Co with ZnO and/or Cu was a much decreased amount of reaction intermediates. Ethane hydrogenolysis results suggested that the different components for these catalysts were in close contact and few or no large ensembles (n ? 12) of Co atoms existed, confirming that ZnO and/or Cu covered/blocked a substantial number of active sites on Co for CO hydrogenation.     

Polyoxometalate as co-catalyst of tetrabutylammonium bromide in polyethylene glycol (PEG) for coupling reaction of CO2 and propylene oxide or ethylene oxide

The coupling reaction of CO₂ and propylene oxide or ethylene oxide to produce corresponding cyclic carbonate in the presence of a catalytic system composed of n-Bu₄NBr, α₂-(n-Bu₄N)₉P₂W₁₇O₆₁(Co²⁺ · Br) (abbreviated as P₂W₁₇Co) and PEG (MW 400) has been investigated. The experimental results indicated that the synthesis of propylene carbonate (PC) or ethylene carbonate (EC) achieved with over 98% yield and 100% selectivity within 1 h at 120 °C by using the above catalyst system. When the catalyst system was recycled, the catalytic activity slowly diminished. Moreover, a plausible mechanism was proposed.     

Solvent free synthesis of chalcone and flavanone over zinc oxide supported metal oxide catalysts

Liquid phase Claisen–Schmidt condensation between 2′-hydroxyacetophenone and benzaldehyde to form 2′-hydroxychalcone, followed by intramolecular cyclisation to form flavanone was carried out over zinc oxide supported metal oxide catalysts under solvent free condition. The reaction was carried out over ZnO supported MgO, BaO, K₂O and Na₂O catalysts with 0.2 g of each catalyst at 140 °C for 3 h. Magnesium oxide impregnated zinc oxide was observed to offer higher conversion of 2′-hydroxyacetophenone than other catalysts. Further MgO impregnated with various other supports such as HZSM-5, Al₂O₃ and SiO₂ were also used for the reaction to assess the suitability of the support. The order of activity of the support is ZnO > SiO₂ > Al₂O₃ > HZSM-5. Various weight percentage of MgO was loaded on ZnO to optimize maximum efficiency of the catalyst system. The impregnation of MgO (wt%) in ZnO was optimized for better conversion of 2′-hydroxyacetophenone. The effect of temperature and catalyst loading was studied for the reaction.     

Hydrogenation of carbon monoxide to methane over mesoporous nickel-M-alumina (M = Fe,Ni, Co,Ce, and La) xerogel catalysts

Mesoporous nickel(30 wt%)-M(10 wt%)-alumina xerogel (30Ni10MAX) catalysts with different second metal (M = Fe, Ni, Co, Ce, and La) were prepared by a single-step sol–gel method for use in the methane production from carbon monoxide and hydrogen. In the methanation reaction, yield for CH₄ decreased in the order of 30Ni10FeAX > 30Ni10NiAX > 30Ni10CoAX > 30Ni10CeAX > 30Ni10LaAX. Experimental results revealed that CO dissociation energy of the catalyst and H₂ adsorption ability of the catalyst played a key role in determining the catalytic performance of 30Ni10MAX catalyst in the methanation reaction. Optimal CO dissociation energy of the catalyst and large H₂ adsorption ability of the catalyst were favorable for methane production. Among the catalysts tested, 30Ni10FeAX catalyst with the most optimal CO dissociation energy and the largest H₂ adsorption ability exhibited the best catalytic performance in terms of conversion of CO and yield for CH₄ in the methanation reaction. The enhanced catalytic performance of 30Ni10FeAX was also due to a formation of nickel–iron alloy and a facile reduction.     

Improvement of promoters on the Fischer–Tropsch activity of mechanically mixed Fe catalysts

The precipitated Fe₂O₃ was promoted with K, Cu, Zn and Al by impregnation and mechanical mixing. Their activity for Fischer–Tropsch (FT) synthesis was tested in fixed bed reactor under the conditions of 503 K and 1.6 MPa syngas (H₂/CO = 2). The Fe catalysts co-promoted by K, Cu, Zn and Al showed increasing CO conversion with time on stream. At present, the improvement is ascribed to the increased resistance to water oxidation on active sites and the further formation of active sites during FT synthesis with the addition of K, Cu, Zn and Al to Fe catalysts. The carbon deposition is not responsible for the variety of catalytic activity in this study.     

Fischer–Tropsch synthesis: effect of small amounts of boron,ruthenium and rhenium on Co/TiO2 catalysts

The effect of the addition of small amounts of boron, ruthenium and rhenium on the Fischer–Tropsch (F–T) catalyst activity and selectivity of a 10 wt.% Co/TiO₂ catalyst has been investigated in a continuously stirred tank reactor (CSTR). A wide range of synthesis gas conversions has been obtained by varying space velocities over the catalysts. The addition of a small amount of boron (0.05 wt.%) onto Co/TiO₂ does not change the activity of the catalyst at lower space times and slightly increases synthesis gas conversion at higher space times. The product selectivity is not significantly influenced by boron addition for all space velocities investigated. Ruthenium addition (0.20 wt.%) onto Co/TiO₂ and CoB/TiO₂ catalysts improves the catalyst activity and selectivity. At a space time of 0.5 h-g cat./NL, synthesis gas conversion increases from 50–54 to 68–71% range and methane selectivity decreases from 9.5 to 5.5% (molar carbon basis) for the promoted catalyst. Among the five promoted and non-promoted catalysts, the rhenium promoted Co/TiO₂ catalyst (0.34 wt.% Re) exhibited the highest synthesis gas conversion, and at a space time of 0.5 h-g cat./NL, synthesis gas conversion was 73.4%. In comparison with the results obtained in a fixed bed reactor, the catalysts displayed a higher F–T catalytic activity in the CSTR.     

Palladium carboxylate/boron trifluoride etherate catalyst system for the selective dimerization of styrene

The selective dimerization of styrene to 1,3-diphenyl-1-butene with Pd(carboxylate)₂ + BF₃OEt₂ catalyst system in both “phosphine-free” and “phosphine-modified” fashions has been investigated. For the Pd(OAc)₂ + 2PR₃ + 7BF₃OEt₂ catalyst system, a TON of 145 000 and 90% selectivity to dimers have been achieved at 80 °C for 5 h. This TON is twice as large as compared to that achieved with the Pd(β-diketonate)₂-based systems. Styrene dimers up to 95% consist of trans-1,3-diphenyl-1-butene. The simplicity of this catalyst system composition might be of industrial importance.     

Sodium borohydride as the hydrogen supplier for proton exchange membrane fuel cell systems

This paper introduces and discusses the latest research on the use of H₂ generated via the NaBH₄ hydrolysis reaction for proton exchange membrane fuel cells (PEMFCs). To realize the NaBH₄–PEMFC system, many hydrolysis catalysts such as Ru/anion-exchange resins, Pt/LiCoO₂, Co powder/Ni foam, PtRu/LiCoO₂ and Ru/carbon have been proposed. Through these efforts, the hydrolysis reaction conversion approached 100%. In addition, the average H₂ generation rate based on most of the reports generally ranged from 0.1 to 2.8 H₂ l min^− 1 g^− 1 (catalyst), which produced a level of PEMFC performance equivalent to 0.1–0.3 kW g^− 1 (catalyst). However, it was also reported that the H₂ generation rate was 28 H₂ l min^− 1 g^− 1 (catalyst) with the catalyst of Pt/carbon (acetylene black).Considering these reports and the advantageous features of NaBH₄ hydrolysis, the NaBH₄–PEMFC system seems to be technologically feasible and would constitute an alternative system of supplying H₂ in fuel cells.However, some challenges remain, such as the deactivation of the catalyst, the treatment of the by-products, and the proper control of the reaction rate. In addition, if the price of NaBH₄ were to be further reduced, this system could become the most powerful competitor in portable application fields of PEMFC.     

Phosphotungstic heteropoly acid as efficient heterogeneous catalyst for solvent-free isomerization of α-pinene and longifolene

Silica-supported H₃PW₁₂O₄₀ (PW), the strongest heteropoly acid in the Keggin series, is an efficient, environmentally friendly heterogeneous catalyst for the liquid-phase isomerization of α-pinene and longifolene into their more valuable isomers – camphene and isolongifolene, respectively, which are intermediates in the synthesis of expensive fragrances. The reactions occur under solvent-free conditions in the temperature range of 80–100 °C, with low catalyst loadings (0.15–5 wt%) and high turnover numbers (up to 6000 per proton). The catalyst can be easily recovered and reused. No PW leaching is observed in the reaction system.     

Enzymatic conversion of corn oil into biodiesel in a batch supercritical carbon dioxide reactor and kinetic modeling

Synthesis of fatty acid methyl esters (FAME) as biodiesel from corn oil was studied in a batch supercritical carbon dioxide (SC-CO₂) bioreactor using immobilized lipase (Novozym 435) as catalyst. Effects of reaction conditions on the contents of FAME, monoacylglycerols (MAG), diacylglycerols (DAG), and triacyglycerols (TAG) were investigated at various enzyme loads (5–15%), temperatures (40–60 °C), substrate mole ratios (corn oil:methanol; 1:3–1:9), pressures (10–30 MPa), and times (1–8 h). The highest FAME content (81.3%) was obtained at 15% enzyme load, 60 °C, 1:6 substrate mole ratio, and 10 MPa in 4 h. A reaction kinetic model was used to describe the system, and the activation energy of the system was calculated as 72.9 kJ/mol. Elimination of the use of organic solvents, chemical catalysts and wastewater as well as reasonably high yields make the enzymatic synthesis of biodiesel in SC-CO₂ a promising green alternative to conventional biodiesel process.     

Ammonia decomposition on tungsten carbide

Decomposition of NH₃ is an important reaction in the cleaning of syngas obtained from the gasification of biomass as well as for the production of hydrogen for fuel cells from easily condensed NH₃. To the best of our knowledge, this paper reports for the first time a detailed study of NH₃ decomposition on tungsten carbide (WC). Results for a commercially available Fe ammonia synthesis catalyst (Amomax-10) are also reported for comparison.The WC catalyst was characterized by BET, XRD, SEM, EDX and temperature programmed reaction (TPRx). The catalytic behavior of WC strongly depended on pretreatment conditions. The highest activity was obtained with WC samples pretreated in an 80/20 mixture of H₂–CO. Complete decomposition of NH₃ was observed at 550 °C for 4000 ppm of NH₃ at a space velocity of 1,884,000 h⁻¹. At lower temperatures, the activity of the WC catalyst reached steady-state after an induction period that decreased in time with increasing temperature. Reconstruction of the surface during pretreatment and during decomposition of NH₃ is suggested to be responsible for the behavior of the catalyst observed during TPRx and time-on-stream (TOS) isothermal reaction. The commercial Fe NH₃ synthesis catalyst, although active for NH₃ decomposition, showed rapid partial deactivation following an induction period with a steady-state conversion of only 35% at 650 °C and the space velocity used. Thus, WC appears to be an excellent catalyst for use in ammonia decomposition.