Middle distillates production via Fischer–Tropsch synthesis with integrated upgrading under supercritical conditions

A vertically aligned fixed‐bed reactor system with a cascade of three sequential catalyst beds has been used to incorporate Fischer–Tropsch synthesis (FTS) in the first bed, oligomerization (O) in the second bed, and hydrocracking/isomerization (HC or C) in the third bed (FTOC). Compared to gas phase FTS (GP‐FT) alone, gas phase FTS with the subsequent upgrading beds (GP‐FTOC) is demonstrated to result in a reduction in the olefin selectivity, a reduction in the C₂₆₊ selectivity, and a marked enhancement in the production of branched paraffins and aromatics. Utilization of supercritical hexane as the reaction medium in supercritical FTS (SC‐FT) and supercritical phase FTOC (SC‐FTOC) resulted in a significant reduction in both CH₄ selectivity and CO₂ selectivity. Interestingly, significant amounts of aldehydes and cyclo‐paraffins were collected in SC‐FT and in SC‐FTOC, respectively, while not being observed in traditional gas phase operation (both GP‐FT and GP‐FTOC). © 2014 American Institute of Chemical Engineers AIChE J, 60: 2573–2583, 2014     

Fischer‐Tropsch Synthesis Over Co‐Ru/γ‐Al2O3 Catalyst in Supercritical Media

The Fischer‐Tropsch synthesis (FTS) in gaseous and supercritical phases was examined in a continuous, high‐pressure fixed‐bed reactor by employing a cobalt catalyst (Co‐Ru/γ‐Al₂O₃). The kinetic modeling of the FTS was investigated in the reactor over a 60–80 mesh cobalt catalyst. The Langmuir‐Hinshelwood kinetic equation was used for both the Fisher‐Tropsch (FT) and water gas shift (WGS) reactions. The kinetic model was applied for simulation of the reactor with 16–20 mesh cobalt catalyst. The simulation results showed a good agreement with the experimental data. The experimental data showed that higher CO conversion and lower CH₄ and CO₂ selectivities were achieved in supercritical media compared to the gaseous phase. The BET surface area and pore volume enhancement results provided evidence of the higher in situ extraction and greater solubility of heavy hydrocarbons in supercritical media than in gaseous phases. Furthermore, the effects of supercritical solvent such as n‐pentane, n‐hexane, n‐heptane and their mixtures were studied. Moreover, the influence of reaction temperature, H₂/CO ratio, W/F_(CO+H2) and pressure tuning in the supercritical media FT synthesis were investigated, as well as the effect of the supercritical fluid on the heat transfer within the reactor. The product carbon distribution had a similar shape for all types of solvents and shifted to lighter molar mass compounds with increasing temperature, H₂/CO ratio, and W/F_(CO+H2). Finally, the product distribution shifted to higher molar mass hydrocarbons with increasing pressure. As a result, one may conclude that a mixture of hydrocarbon products of the FTS can be used as a solvent for supercritical media in Fischer‐Tropsch synthesis.     

Kinetic study of higher alcohol synthesis directly from syngas over CoCu/SiO2 catalysts

Higher alcohol synthesis (HAS) directly from syngas is one of the most promising approaches for utilizing nonoil resources cleanly and efficiently. A series of bimetallic CoCu catalysts with different Co/Cu ratios were prepared using a SiO₂ support. The structure of Cu modified Co catalysts was characterized using HRTEM, in/ex situ X‐ray diffraction, and temperature‐programmed reduction. It was evidenced that nanoscale metal particles were formed and the reduction of Co oxide at above 673 K. Meanwhile, the interaction between Co and Cu on the surface was assumed to be responsible for the enhanced selectivity to HAS. The intrinsic kinetics for this reaction was performed over a CoCu/SiO₂ catalyst under realistic conditions. The kinetic parameters, including apparent activation energies and reaction orders, were calculated through power‐law models. With the combination of chain growth probability and kinetics, the effect of temperatures on the reaction mechanism and the Cu promotional effects on Co catalysts were elaborated. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1797–1809, 2014     

Partial oxidation of methane in hollow‐fiber membrane reactors based on alkaline‐earth metal‐free CO2‐tolerant oxide

The U‐shaped alkaline‐earth metal‐free CO₂‐stable oxide hollow‐fiber membranes based on (Pr_0.9La_0.1)₂(Ni_0.74Cu_0.21Ga_0.05)O_4+δ (PLNCG) are prepared by a phase‐inversion spinning process and applied successfully in the partial oxidation of methane (POM) to syngas. The effects of temperature, CH₄ concentration and flow rate of the feed air on CH₄ conversion, CO selectivity, H₂/CO ratio, and oxygen permeation flux through the PLNCG hollow‐fiber membrane are investigated in detail. The oxygen permeation flux arrives at approximately 10.5 mL/min cm² and the CO selectivity is higher than 99.5% with a CH₄ conversion of 97.0% and a H₂/CO ratio of 1.8 during 140 h steady operation. The spent hollow‐fiber membrane still maintains a dense microstructure and the Ruddlesden‐Popper K₂NiF₄‐type structure, which indicates that the U‐shaped alkaline‐earth metal‐free CO₂‐tolerant PLNCG hollow‐fiber membrane reactor can be steadily operated for POM to syngas with good performance. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3587–3595, 2014     

Novel Co‐Mn‐O nanosheet catalyst for CO preferential oxidation toward hydrogen purification

Co‐Mn‐O composite oxide nanosheet catalyst was successfully prepared using a facile urea‐assisted one‐step hydrothermal method in the absence of organic or organic templating reagent. Co‐Mn‐O nanosheet catalyst was optimized by varying hydrothermal process parameters such as molar ratio of Co‐Mn to urea, hydrothermal temperature, and hydrothermal time. Various characterization techniques including scanning electron microscopy, X‐ray diffraction, nitrogen adsorption, X‐ray photoelectron spectroscopy, Raman spectroscopy, and H₂ temperature‐programmed reduction were used to reveal the relationship between catalyst nature and catalytic performance in CO preferential oxidation (CO PROX) in excess H₂. The developed Co‐Mn‐O nanosheet catalyst have demonstrated much superior catalytic performance to Co‐Mn‐O nanoparticle, particularly in the low temperature range, and 100% CO conversion over the developed Co‐Mn‐O nanosheet can be achieved in temperature range of 50 to 150°C at 10,000 mL g^?1 h^?1 of gas hourly space velocity in the standard feed. Furthermore, the almost complete CO removal over Co‐Mn‐O nanosheet at 125°C of low temperature with 94.9% selectivity can be achieved even in the simulated reformed gas. The excellent catalytic performance is ascribed to nanosheet morphology, more surface Co³⁺, smaller average crystallite size, higher reducibility, and strong Co‐Mn interaction. Catalytic stability investigation indicates the developed nanostructured catalyst exhibits high catalytic stability for CO PROX reaction in simulated gas. The developed Co‐Mn‐O nanosheet catalyst can be a potential candidate for catalytic elimination of trace CO from H₂‐rich gas for Proton exchange membrane fuel cell applications. © 2014 American Institute of Chemical Engineers AIChE J, 61: 239–252, 2015     

Energy efficient methane-to-syngas conversion with low H2/CO ratio by simultaneous catalytic reactions of methane with carbon dioxide and oxygen

By simultaneous reactions of methane with CO₂ and O₂ over NiO-CaO catalyst under certain reaction conditions, it is possible to convert methane into syngas with low H₂/CO ratio (1 2/CO <2) at above 95% conversion, with 100% CO selectivity and above 90% H₂ selectivity and also with very high CO productivity without catalyst deactivation due to coking for a long period, in a most energy efficient and safe manner, requiring little or no external energy.     

Equilibrium calculations for direct synthesis of dimethyl ether from syngas

Thermodynamic analysis of single‐step synthesis of dimethyl ether (DME) from syngas over a bi‐functional catalyst (BFC) in a slurry bed reactor has been investigated as a function of temperature (200–240°C), pressure (20–50 bar), and composition feed ratio (H₂/CO: 1–2). The BFC was prepared by physical mixing of CuO/ZnO/Al₂O₃ as a methanol synthesis catalyst and H‐ZSM‐5 as a methanol dehydration catalyst. The three reactions including methanol synthesis from CO and H₂, methanol dehydration to DME and water–gas shift reaction were chosen as the independent reactions. The equilibrium thermodynamic analysis includes a theoretical model predicting the behaviour and a comparison to experimental results. Theoretical model calculations of thermodynamic equilibrium constants of the reactions and equilibrium composition of all components at different reaction temperature, pressure, and H₂/CO ratio in feed are in good accordance with experimental values.     

Effects of H2S and process conditions in the synthesis of mixed alcohols from syngas over alkali promoted cobalt-molybdenum sulfide

The present work is an investigation of how the process conditions influence the synthesis of mixed alcohols from syngas over a K₂CO₃/Co/MoS₂/C catalyst. The emphasis in the investigations is upon the effects of H₂S in the syngas feed. However the effects of the temperature and of the partial pressures of H₂ and CO are also investigated. With or without H₂S in the feed the pre-sulfided catalyst requires an initiation period to reach a stabilized behavior, but the duration of this period depends upon the H₂S level. Operation with a feed containing more than 103 ppmv H₂S leads to a fairly rapid stabilization of the product distribution and ensures that higher alcohols are the dominant reaction products. With less than 57 ppmv H₂S in the feed the stabilization of the product distribution is much slower, and methanol is the dominant product. An investigation of the reaction kinetics indicates a high CO coverage and low hydrogen coverage. Hydrogen sulfide in the syngas feed generally promotes chain growth for both alcohols and hydrocarbons, but lowers the alcohol selectivity by enhancing the hydrocarbon formation. The highest alcohol productivity reached in these investigations was 0.276 g/g cat./h, and this was achieved at 350 °C, 100 bar, GHSV = 5244 h⁻¹, Feed: 49.9 vol% H₂, 50.1 vol% CO. Finally it is found that sulfur fed to the reactor as H₂S is incorporated into the condensed alcohol product, and the incorporation of sulfur species into the product continues for some time after H₂S has been removed from the feed. When the catalyst is operated with an S-free syngas feed, the amount of sulfur in the condensed liquid product decreases over time, but after 35 h of operation with an S-free syngas the alcohol product still contains 340 ppmw of sulfur. Thiols appear to be the dominant sulfur compounds in the product.     

Kinetics study on cnt‐supported RuKCo FTS catalyst in a fixed bed reactor

The rate of syngas (H₂/CO) consumption over a RuKCo/CNT Fischer–Tropsch synthesis (FTS) catalyst was measured in a fixed bed microreactor at 210–225°C, 2–3.5 MPa, H₂/CO feed molar ratios of 1–2.5, and gas hourly space velocity (GHSV) range of 2700–3600 h^?1. The data have been used to model the kinetics of the FTS reactions within the range of the studied conditions. One empirical power law model and four semi‐empirical kinetic models based on Langmuir–Hinshelwood‐type equation have been evaluated. The best fitting was obtained with the equation: similar to that proposed by Brötz et al. The estimated activation energy (E = 80–85 kJ/mol) is lower than that is reported in the literature. The validity of these results are restricted to fixed beds with the given catalyst in the tested conversion regime.     

Synthesis of higher alcohols from syngas over Zn–Cr–K catalyst in supercritical fluids

An investigation was carried out on the selective synthesis of higher alcohols from syngas in a supercritical fluid (a mixture of C₁₀–C₁₃ alkanes) by using a fixed bed reactor. Experiments were conducted over Zn–Cr–K catalyst in the temperature range of 360–400°C, a partial pressure of syngas of 7.5 MPa and a partial pressure of supercritical medium of 1.78 MPa. Comparison of results in the gas phase with those in the supercritical phase indicated that CO conversion was higher in the supercritical phase reaction. Alcohol selectivity decreased slowly with increasing temperature in the supercritical phase reaction but decreased rapidly in the gas phase reaction, due to the special properties of supercritical fluids (SCF). Product distributions were different in both reaction phases. The introduction of the supercritical medium promoted carbon chain growth and the content of C₂⁺OH was increased. The product distribution features with high methanol content of the gas phase synthesis were changed.     

完全液相法制CuZnAl合成二甲醚浆状催化剂的催化性能

利用完全液相法制备了CuZnAl浆状催化剂,考察了反应温度、反应压力、搅拌速度、原料气组成等工艺条件, 以及催化剂中各组分配比对浆态床合成气一步法合成二甲醚反应过程的影响。结果表明, 利用完全液相法制备的催化剂在升温段和降温段活性保持稳定,随着反应时间的延长,催化剂活性呈现增长趋势,且其水煤气变换反应速率很快。Cu/Zn/Al摩尔比为1∶1∶2.09时催化剂的CO转化率与DME 选择性最好。     

Review on Fischer–Tropsch synthesis in supercritical media

A detailed review of the recent works regarding applications of supercritical media in Fischer–Tropsch synthesis (FTS) is presented. Differences in activity, CH₄ and CO₂ selectivity, hydrocarbon and olefin distributions, catalyst stability and heat transfer between supercritical Fischer–Tropsch syntheses (SC-FTS) and conventional gas phase Fischer–Tropsch synthesis (GP-FTS) are compared. The effects of temperature, pressure, solvent type, supercritical media/syngas molar ratio on SC-FTS are discussed. Finally selective production of wax via SC-FTS is briefly presented. Experimental analyses reveal that unique properties of supercritical media can improve FTS catalyst activity and selectivity in SC-FTS due to higher heat and mass transfer rates in comparison to GP-FTS.     

Fischer‐Tropsch Synthesis: Modeling and Performance Study for Fe‐HZSM5 Bifunctional Catalyst

A water‐cooled fixed bed Fischer‐Tropsch reactor packed with Fe‐HZSM5 catalyst has been modeled in two dimensions (radial and axial) using the intrinsic reaction rates previously developed at RIPI. The reactor is used for production of high‐octane gasoline from synthesis gas. The Fischer‐Tropsch synthesis reactor was a shell and tube type with high pressure boiling water circulating on the shell side. By the use of a two‐dimensional model, the effects of some important operating parameters such as cooling temperature, H₂/CO ratio in syngas and reactor tube diameter on the performance capability of the reactor were investigated. Based on these results, the optimum operating conditions and the tube specification were determined. The model has been used to estimate the optimum operating conditions for the pilot plant to be operated in RIPI.     

Formation of poly‐vinyl‐alcohol structures by supercritical CO2

Poly‐vinyl‐alcohol (PVA) porous structures have been prepared using a supercritical phase inversion process in which supercritical carbon dioxide (SC‐CO₂) acts as the nonsolvent. First, we tested the versatility of the SC‐CO₂ phase inversion process, forming PVA/dimethylsulfoxide (DMSO) solutions with polymer concentrations ranging from 1 to 35% (w/w) and changing the process parameters. We worked at temperatures from 35 to 55°C and pressures from 100 to 200 bar obtaining different membranes morphologies: dense films, membranes with coexisting morphologies, and microparticles. However, we did not produce symmetric or asymmetric porous membranes. To obtain this result, we used casting solutions formed by adding acetone to DMSO with the aim of modifying the affinity between SC‐CO₂ and the liquid solvent. In this series of experiments, we obtained asymmetric membranes with skin layer thicknesses lower than 10 μm. The results obtained in this work have been explained considering that the membranes formation mechanism is related to the kinetics of the process; i.e. the affinity between the solvent (mixture of solvents) and SC‐CO₂. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Intrinsic and Effective Kinetics of Cobalt‐Catalyzed Fischer‐Tropsch Synthesis in View of a Power‐to‐Liquid Process Based on Renewable Energy

The production of liquid hydrocarbons based on CO₂ and renewable H₂ is a multi‐step process consisting of water electrolysis, reverse water‐gas shift, and Fischer‐Tropsch synthesis (FTS). The syngas will then also contain CO₂ and probably sometimes H₂O, too. Therefore, the kinetics of FTS on a commercial cobalt catalyst was studied with syngas containing CO, CO₂, H₂, and H₂O. The intrinsic kinetic parameters as well as the influence of pore diffusion (technical particles) were determined. CO₂ and H₂O showed only negligible or minor influence on the reaction rate. The intrinsic kinetic parameters of the rate of CO consumption were evaluated using a Langmuir‐Hinshelwood (LH) approach. The effectiveness factor describing diffusion limitations was calculated by two different Thiele moduli. The first one was derived by a simplified pseudo first‐order approach, the second one by the LH approach. Only the latter, more complex model is in good agreement with the experimental results.     

Polymerization of propylene using the high‐activity Ziegler–Natta catalyst system SiO2/MgCl2 (ethoxide type)/TiCl4/Di‐n‐butyl phthalate/triethylaluminum/dimethoxy methyl cyclohexyl silane

The bisupported Ziegler–Natta catalyst system SiO₂/MgCl₂ (ethoxide type)/TiCl₄/di‐n‐butyl phthalate/triethylaluminum (TEA)/dimethoxy methyl cyclohexyl silane (DMMCHS) was prepared. TEA and di‐n‐butyl phthalate were used as a cocatalyst and an internal donor, respectively. DMMCHS was used as an external donor. The slurry polymerization of propylene was studied with the catalyst system in n‐heptane from 45 to 70°C. The effects of the TEA and H₂ concentrations, temperature, and monomer pressure on the polymerization were investigated. The optimum productivity was obtained at [Al]/[DMMCHS]/[Ti] = 61.7:6.2:1 (mol/mol/mol). The highest activity of the catalyst was obtained at 60°C. Increasing the H₂ concentration to 100 mL/L increased the productivity of the catalyst, but a further increase in H₂ reduced the activity of the catalyst. Increasing the propylene pressure from 1 to 7 bar significantly increased the polymer yield. The isotacticity index (II) decreased with increasing TEA, but the H₂ concentration, temperature, and monomer pressure did not have a significant effect on the II value. The viscosity‐average molecular weight decreased with increasing temperature and with the addition of H₂. Three catalysts with different Mg/Si molar ratios were studied under the optimum conditions. The catalyst with a Mg/Si molar ratio of approximately 0.93 showed the highest activity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1177–1181, 2003     

Preparation and characterization of carbon nanotube-promoted Co–Cu catalyst for higher alcohol synthesis from syngas

A cobalt–copper catalyst promoted by “herringbone-type” multiwalled carbon nanotubes (CNTs) was developed. This catalyst displayed excellent performance for higher alcohol synthesis (HAS) from syngas, with the (C_2–8-alc. + DME)-STY reached 760 mg/(g·h) under the reaction conditions of 5.0 MPa and 573 K, which was 1.78 times that of the CNT-free host, Co₃Cu₁. The addition of a minor amount of the CNTs to the Co₃Cu₁ host did not cause a marked change in apparent activation energy for the HAS, but led to an increase at the surface of the catalyst of the concentration of catalytically active Co-species, CoO(OH), a kind of surface Co-species related closely to the selective formation of the higher alcohols. Excellent adsorption performance of this kind of CNTs for H₂ generated a surface micro-environment with a high concentration of H-adspecies on the functioning catalyst, thus increasing the rate of surface hydrogenation reactions in the HAS. Moreover, synergistic action of the high surface-concentration H-adspecies with CO₂ in the feed-gas led to a greater inhibition for the WGS side-reaction. All these factors contribute considerably to an increase in the yield of alcohols.     

Mass Transfer Characteristics of Syngas Components in Slurry System at Industrial Conditions

The gas‐liquid mass transfer behavior of syngas components, H₂ and CO, has been studied in a three‐phase bubble column reactor at industrial conditions. The influences of the main operating conditions, such as temperature, pressure, superficial gas velocity and solid concentration, have been studied systematically. The volumetric liquid‐side mass transfer coefficient k_La is obtained by measuring the dissolution rate of H₂ and CO. The gas holdup and the bubble size distribution in the reactor are measured by an optical fiber technique, the specific gas‐liquid interfacial area aand the liquid‐side mass transfer coefficient k_L are calculated based on the experimental measurements. Empirical correlations are proposed to predict k_L and a values for H₂ and CO in liquid paraffin/solid particles slurry bubble column reactors.     

CO oxidation from syngas (CO and H<Subscript>2</Subscript>) using nanoporous Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

The concept of “waste-to-wealth” is spreading awareness to prevent global warming and recycle the restrictive resources. To contribute towards sustainable development, hydrogen energy is obtained from syngas (CO and H₂) generated from waste gasification, followed by CO oxidation and CO₂ removal. In H₂ generation, it is key to produce more purified H₂ from syngas using heterogeneous catalysts. In this respect, we prepared Pt/Al₂O₃ catalyst with nanoporous structure using precipitation method, and compared its catalytic activity with commercial alumina (Degussa). Based on the results of XRD and TEM, it was found that metal particles did not aggregate on the alumina surface and showed high dispersion. Optimum condition for CO conversion was 1.5 wt% Pt loaded on Al₂O₃ support, and pure hydrogen was obtained after removal of CO₂ gas.     

Dechlorination of 1‐chlorohexadecane and 2‐chloronaphthalene in water under sub‐ and supercritical conditions

Reactions of 1‐chlorohexadecane and 2‐chloron‐aphthalene in water under sub‐ and supercritical conditions have been investigated so as to show the possible use of water for the dechlorinations of these organic chlorides. The reactions were carried out at 275°C to 430°C in a small SUS316 batch reactor under nitrogen atmosphere at the molar organic chloride/water ratio of 1/100. Under subcritical temperatures, hydrolysis reactions occurred catalyzed by H⁺ ions, whereas under supercritical conditions hydrodechlorinations occurred too, in which hydrogens evolved by the reaction of HCI with the metal wall of the reactor participated. The hydrogenation and hydrogenolysis of the primary reaction products also occurred for 1‐chlorohexadecane under supercritical conditions. The dechlorination selectivity was nearly 100% for these organic chlorides irrespective of the reaction conditions employed.