Explanations of the Formation of Branched Hydrocarbons During Fischer–Tropsch Synthesis by Alkylidene Mechanism

After completely hydrogenation of Fischer–Tropsch synthesis (FTS) products on Pt/C catalyst, the branched C₈, C₁₀, C₁₁, and C₁₂ alkanes were identified using authentic samples to be methyl branched alkanes in both Co and Fe catalyzed reactions. No detectable ethyl branched and dimethyl branched alkanes were observed. The total amount of branched hydrocarbons in Co catalyzed FTS is about 5 % while the amount of branched hydrocarbons in Fe catalyzed FTS is about 25 %. The branched hydrocarbon distribution of Co catalyzed FTS does not obey the Anderson–Schulz–Flory (ASF) kinetics and the branched hydrocarbon distribution of Fe catalyzed FTS shows larger α value than that of straight chain alkanes. These results were explained by the formation of 2-alkylidene through readsorbed 1-alkenes, which can grow to form methyl branched hydrocarbons. Since the rate of propagation of 2-alkylidene is much slower than that of ethylidene and 1-alkylidenes, a “kink” will result in C₂ in the FT product distribution plot.     

CO/CO2加氢高选择性合成化学品和液体燃料

一氧化碳/二氧化碳（CO/CO₂）转化利用是碳一化学与CO₂捕集利用中的重要环节,也是当今碳资源的非石油路线利用最具挑战性的方向之一。CO₂的高效活化与定向转化是CO₂利用过程中的关键问题,而CO加氢转化最大的瓶颈问题为如何有效控制C-O键的活化、C—C键的形成、碳链增长及终止。本文主要综述 CO/CO₂加氢高选择性合成重要化工原料低碳烯烃（C₂ ⁼～C₄ ⁼）以及一步高效合成汽油馏分（C₅～C₁₁）等方面取得的突破性进展。目前,CO/CO₂加氢主要经过费托合成与氧化物/分子筛双功能两条路线合成低碳烯烃与汽油燃料。针对费托合成C₂ ⁼～C₄ ⁼,分析表明棱柱状碳化钴得到的烃类产物分布可以显著突破Anderson-Schulz-Flory（ASF）分布的限制,而分子筛已被广泛用于构建双功能费托催化剂,由于酸性分子筛具有加氢裂化、低聚与异构化等功能,使得CO/CO₂还可以直接高选择性地转化为C₅～C₁₁烃类。另一方面,将可以活化CO或CO₂到甲醇的可还原型氧化物与具有C—C偶联功能的SAPO-34或HZSM-5分子筛进行耦合,也可以实现CO/CO₂加氢一步合成低碳烯烃或汽油且具有非常优异的选择性和高转化率。今后,借鉴纳米合成领域新方法,使产物分布打破经典ASF限制,最大限度地提高目标烃类化合物的选择性并显著减少甲烷的生成是研究关键。     

A comprehensive mathematical model for the Fischer-Tropsch synthesis in well-mixed slurry reactors

A new product distribution quasi-steady-state model was proposed for the Fischer-Tropsch (FT) synthesis in slurry reactors, being applicable to their transient simulation. It may consider two chain propagation mechanisms or sites and the possibility of 1-olefin readsorption with secondary reactions, recovering the Anderson-Schulz-Flory (ASF) model, the two superimposed ASF model and the 1-olefin readsorption model as particular cases. The hydrocarbon compounds were lumped according to the number of carbon atoms in their molecules for the paraffin and 1-olefin families. The phases were assumed to be well mixed in the reactor and transient mass balances were performed for each component, allowing simulation of operation in constant liquid level and no liquid withdrawal conditions. A rigorous calculation of the vapor-liquid equilibrium (VLE) through cubic equations of state was used to describe the phase behavior. Rate expressions for the FT and the water gas shift reactions are taken from the literature and expressed in terms of fugacities. Simulation results showed that the inclusion of both the olefin readsorption and the two chain propagation mechanisms may explain the anomalies present in experimental hydrocarbon product distribution. Moreover, the effect of phase-equilibrium modeling on product distribution simulation was shown to be slightly important in the conditions analyzed. Compositional lumping schemes for the hydrocarbons were investigated to speed up the simulations. Results showed that lumping can speed up computations up to 250 times with negligible loss of accuracy.     

Predicting Separation of Lower Hydrocarbon from Natural Gas by a Nano‐Porous Membrane using Capillary Condensation

In the present work, the potential of a nano‐porous membrane for predicting the separation of lower hydrocarbons from natural gas by capillary condensation was explored. While a gas permeates through a capillary at a suitable pressure, the adsorbed layer may attain a thickness enough to fill the entire membrane pore. Poiseuille flow of the condensed phase follows. Our computed results have established that for a passage through a nano‐porous membrane, gas having lower condensation pressure condenses in the pores at a pressure which is about an order of magnitude lower than its vapor pressure at the concerned temperature. In the case of propane/methane and butane/methane binary mixtures, propane and butane are preferentially condensed and permeation rates up to 700 g mol/m² s bar for propane and 600 g mol/m² s bar for butane have been achieved at a temperature lower than the critical temperature of the permeating species and higher than the critical temperature of the non‐permeating species. Since methane has a much lower critical temperature than both propane and butane, it gets physically dissolved in the condensed phase of propane, butane in the case of propane/methane and butane/methane binary mixtures, respectively. An equation of state (EOS) approach has been adopted to calculate the fugacity of methane in the gas, as well as in the condensed phase, in order to estimate its solubility. The Peng‐Robinson equation of state was used. Computation of the separation factor for methane/propane and methane/butane was performed over a wide range of temperature, pressure, and gas composition. The separation factor which is expectedly a function of these variables ranged from 0.3–75 for methane/propane and 0.7–140 for methane/butane binary mixtures. It has been established that an acceptable degree of separation is achievable at moderate pressure and at low temperature for the removal of propane and butane from natural gas. The results have the potential to be used for further refinement and optimization of the process conditions so that this strategy can be exploited for large‐scale removal of lower hydrocarbon from natural gas at a low cost.     

Preparation of Porous Scaffolds from Silk Fibroin Extracted from the Silk Gland of Bombyx mori (B. mori)

In order to use a simple and ecofriendly method to prepare porous silk scaffolds, aqueous silk fibroin solution (ASF) was extracted from silk gland of 7-day-old fifth instar larvae of Bombyx mori (B. mori). SDS-page analysis indicated that the obtained fibroin had a molecular weight higher than 200 kDa. The fabrication of porous scaffolds from ASF was achieved by using the freeze-drying method. The pore of porous scaffolds is homogenous and tends to become smaller with an increase in the concentration of ASF. Conversely, the porosity is decreased. The porous scaffolds show impressive compressive strength which can be as high as 6.9 ± 0.4 MPa. Furthermore, ASF has high cell adhesion and growth activity. It also exhibits high ALP activity. This implies that porous scaffolds prepared from ASF have biocompatibility. Therefore, the porous scaffolds prepared in this study have potential application in tissue engineering due to the impressive compressive strength and biocompatibility.     

Recombination products from the radiolysis of tricaproin

A low molecular weight triglyceride, tricaproin, has been selected to study the higher molecular weight products produced by irradiation. In a previous publication the identification of the primary radiolytic products in tricaproin was reported. In the present work, 28 compounds considered to have been produced by the combination of free radicals have been identified. Among these are hydrocarbons, ketones, esters, alkanediol diesters and glyceryl ether diesters. Reaction mechanisms for the production of these compounds are discussed.     

Catalytic hydrothermal treatment of pine wood biomass: effect of RbOH and CsOH on product distribution

Low‐temperature hydrothermal treatment of pine wood biomass was performed in the presence of RbOH and CsOH catalysts (280 °C for 15 min). The effect of the catalysts on the distribution of products and the volatility distribution of oxygenated hydrocarbons was studied in detail. Oxygenated hydrocarbons were extracted from the liquid and solid portions and analysed individually by gas chromatography/mass spectrometry. Catalytic (RbOH and CsOH) hydrothermal treatment of wood biomass produced mainly phenolic compounds and benzenediol derivatives. The use of RbOH and CsOH catalysts hindered the formation of char and favoured the formation of oil products, as observed previously for various other base catalysts. The volatility distribution of hydrocarbons (ether extract) was characterised by carbon‐normal paraffin (C‐NP) gram and it was found that the oxygenated hydrocarbons from all runs, including thermal, were distributed in the boiling point region of n‐C₆ to n‐C₁₇. Copyright © 2005 Society of Chemical Industry     

The conversion of methane with silica-supported platinum catalysts: the effect of catalyst preparation method and platinum particle size

The particle size distribution of platinum in silica prepared by the complexing agent-assisted sol–gel method and impregnation method and also in MCM-41 has been compared and its influence on the product distribution in the non-oxidative dehydrogenation of methane has been investigated. The sol–gel method gives a narrow range of platinum particle size distribution compared to the impregnation method. It was found that as the particle size increases, the selectivity for the higher hydrocarbons increases though the yield decreases.     

Transformation of C1C4 Alcohols into Hydrocarbons on an Amorphous Silica–Alumina Catalyst

The transformation of ethanol, 2-propanol and 2-butanol into hydrocarbons has been studied on an amorphous silica—alumina and the results compared with those obtained earlier for methanol. Experiments were carried out at temperatures ranging from 310 to 450°C, contact times from 1 to 14 h, and atmospheric pressure. Ethanol produced only ethene, while the other alcohols produced hydrocarbons containing up to twelve carbon atoms. The highest liquid yield was obtained from methanol. According to the product distribution ethene did not appear as the precursor in the hydrocarbon chain growth.     

Measurements of particle-size distribution during suspension polymerization

The particle-size distribution is one of the main characteristics of polymers produced by suspension polymerization which determines the final properties of the product. Since the on-line measurement of particle-size distribution during the course of polymerization is not a straightforward task, a technique has been developed to accomplish such a measurement for a predefined polymerization process. In this paper the experimental procedure is described in detail and the experimental data are shown for the batch suspension polymerization of methyl methacrylate using benzoyl peroxide as initiator, water as suspending phase and agarose as suspending agent. The particle-size distributions have been measured both for a base case and also when varying some operating conditions including stirring speed, water-to-monomer weight ratio, and suspending agent concentration. Average values and variances of the surface distribution and of the volume distribution are also computed and shown for comparison. © 1999 Society of Chemical Industry     

Deactivated iron catalyst in the fischer-tropsch synthesis

The selectivity for higher hydrocarbons (C₁₁–C₁₇) has been studied in the Fischer-Tropsch synthesis using fresh and used fused iron catalysts under different reaction conditions. On increasing the temperature higher hydrocarbon products were formed in the C₁₁–C₁₇ range. The deactivated fused iron catalyst is less active but selective to heavier hydrocarbon chain molecules. The product distribution is shifted towards heavier hydrocarbons due to the effects of the pore volume, presence of potassium and site densities at the surface.     

Notes on the issues of equilibrium in the Fischer–Tropsch synthesis

The product distribution for the Fischer–Tropsch synthesis is normally described using the kinetically derived (Anderson–Schultz–Flory) ASF model. Variations of the kinetic model have been proposed to explain deviations from the ASF distribution. The Fischer–Tropsch system can be equally well described using a pseudo‐element (CH₂, H₂, O) equilibrium approach. A one‐parameter equilibrium model is derived for the product distributions for alkenes, alkanes and alcohols. The Fischer–Tropsch system should be considered as three separate partial equilibria systems: the product homologous series; the water gas shift system, and the redox behaviour of the catalyst with the H₂/O ratio of the gas. This approach correctly predicts the impacts of changes in a variety of parameters (temperature pressure, feed composition) on the ASF product distribution. In addition, the catalyst phase changes with gas composition and pressure, indicative of an equilibrium response. Equilibrium is of much greater importance to the Fischer–Tropsch system than previously thought, and the decision to use a complex kinetics‐based model rather than a simpler equilibrium based model should be taken with care.     

Production of gasoline range hydrocarbons from catalytic reaction of methane in the presence of ethylene over W/HZSM-5

The catalytic conversion of a methane and ethylene mixture to gasoline range hydrocarbons has been studied over W/HZSM-5 catalyst. The effect of process variables, such as temperature, percentage of volume of ethylene in the methane stream and catalyst loading on the distribution of hydrocarbons was studied. The reaction was conducted in a fixed-bed quartz-micro reactor in the temperature range of 300–500 °C using percentage of volume of ethylene in methane stream between 25 and 75% and catalyst loading of 0.2–0.4 g. The catalyst showed good catalytic performance yielding hydrocarbons consisting of gaseous products along with gasoline range liquid products. The mixed feed stream can be converted to higher hydrocarbons containing a high-liquid gasoline product selectivity (>42%). Non-aromatics C₅–C₁₀ hydrocarbons selectivity in the range of 12–53% was observed at the operating conditions studied. Design of experiment was employed to determine the optimum conditions for maximum liquid hydrocarbon products. The distribution of the gasoline range hydrocarbons (C₅–C₁₀ non-aromatics and aromatics hydrocarbons) was also determined for the optimum conditions.     

Acrolein formation in the oxidation of ethane over silica catalysts supporting iron and cesium

A significant yield of aldehydes was obtained by the partial oxidation of ethane over alkali‐modified Fe/SiO₂ catalysts at 475°C (<2% in the case of Cs–Fe/SiO₂). Not only acetaldehyde and formaldehyde but also acrolein were produced in the present system. There are no reports regarding the catalysts for the direct acrolein formation from partial oxidation of ethane. Such significant promoting effect of alkali‐modified Fe/SiO₂ catalysts in the partial oxidation of hydrocarbons has never been observed. Aldol‐type condensation for formation of acrolein could occur in the partial oxidation of ethane over alkali‐modified Fe/SiO₂ catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Antheraea pernyi Silk Fibroin-Coated PEI/DNA Complexes for Targeted Gene Delivery in HEK 293 and HCT 116 Cells

Polyethylenimine (PEI) has attracted much attention as a DNA condenser, but its toxicity and non-specific targeting limit its potential. To overcome these limitations, Antheraea pernyi silk fibroin (ASF), a natural protein rich in arginyl-glycyl-aspartic acid (RGD) peptides that contains negative surface charges in a neutral aqueous solution, was used to coat PEI/DNA complexes to form ASF/PEI/DNA ternary complexes. Coating these complexes with ASF caused fewer surface charges and greater size compared with the PEI/DNA complexes alone. In vitro transfection studies revealed that incorporation of ASF led to greater transfection efficiencies in both HEK (human embryonic kidney) 293 and HCT (human colorectal carcinoma) 116 cells, albeit with less electrostatic binding affinity for the cells. Moreover, the transfection efficiency in the HCT 116 cells was higher than that in the HEK 293 cells under the same conditions, which may be due to the target bonding affinity of the RGD peptides in ASF for integrins on the HCT 116 cell surface. This result indicated that the RGD binding affinity in ASF for integrins can enhance the specific targeting affinity to compensate for the reduction in electrostatic binding between ASF-coated PEI carriers and cells. Cell viability measurements showed higher cell viability after transfection of ASF/PEI/DNA ternary complexes than after transfection of PEI/DNA binary complexes alone. Lactate dehydrogenase (LDH) release studies further confirmed the improvement in the targeting effect of ASF/PEI/DNA ternary complexes to cells. These results suggest that ASF-coated PEI is a preferred transfection reagent and useful for improving both the transfection efficiency and cell viability of PEI-based nonviral vectors.     

Hydrothermal upgrading of wood biomass: Influence of the addition of K2CO3 and cellulose/lignin ratio

The hydrothermal treatment of two different wood biomass samples such as cherry (hard wood) and cypress (soft wood), whose composition is different i.e. lignin, cellulose and hemicellulose were performed at 280 °C for 15 min with aq. K₂CO₃ with different concentrations (0–1 M). The soft wood biomass contains higher lignin content than hard wood biomass. The cellulose rich cherry wood biomass produced higher proportion of acetic acid than cypress. The lignin rich cypress produced the hydrocarbons with major portion of phenolic hydrocarbons and derivatives than cherry. The total oil yields from both cherry and cypress wood biomass produced 50 wt% of liquid hydrocarbons at 280 °C for 15 min with 0.5 M K₂CO₃ solution. The volatility distribution of liquid hydrocarbons showed the characteristic features of soft and hard wood biomasses.     

Equilibrium distribution data for salicylic acid + water + solvent systems

Equilibrium distribution data have been presented at 30 °C for the distribution of salicylic acid between water and each of the solvents benzene, toluene, xylene and kerosene. The equilibrium distribution plots reveal that except in the case of kerosene, the acid favours the solvent layer more than the aqueous phase at higher concentrations, i.e., above 0.04 wt- % acid content. At lower concentrations the acid prefers more the aqueous phase. In the case of kerosene, the acid favours only the aqueous phase uniformly at all concentrations. The lower hydrocarbons seem to be better suited for the extraction of salicylic acid from the aqueous phase.     

Hydrogenation of Carbon Oxides over Perovskite-Type Oxides

Transition metals, metal oxides and metal-containing mixed oxides have been extensively used for Fischer-Tropsch hydrocarbon synthesis (1-9) and their ability to yield oxygenated compounds. During the last two decades, an extensive search has been carried out in examining the mechanism of catalytic hydrogenation of co and CO, which produced hydrocarbons and oxygenate compounds. The catalytic models for hydrocarbon synthesis have already been reviewed by Vannice (lo), which gives detailed information and discusses the data which were obtained during their development. As a broad product distribution is obtained during the FT synthesis, the mechanisms are extremely complicated and not clearly understood: therefore this topic is beyond the objective of this chapter and hence no further attention will be paid.     

Hydrogenation of Carbon Oxides over Perovskite-Type Oxides

Transition metals, metal oxides and metal-containing mixed oxides have been extensively used for Fischer-Tropsch hydrocarbon synthesis (1–9) and their ability to yield oxygenated compounds. During the last two decades, an extensive search has been carried out in examining the mechanism of catalytic hydrogenation of co and CO, which produced hydrocarbons and oxygenate compounds. The catalytic models for hydrocarbon synthesis have already been reviewed by Vannice (lo), which gives detailed information and discusses the data which were obtained during their development. As a broad product distribution is obtained during the FT synthesis, the mechanisms are extremely complicated and not clearly understood: therefore this topic is beyond the objective of this chapter and hence no further attention will be paid.     

Decomposition of CH4 over supported Ir catalysts

The decomposition of methane and its conversion into higher hydrocarbons have been investigated on supported Ir catalysts. The effects of temperature, flow rate and support materials have been examined. The interaction of CH₄ with iridium has been observed at as low a temperature as 473 K. As a result, hydrogen, a small amount of ethane and surface carbonaceous species were produced. With increase of the temperature, the extent of the decomposition significantly increased. At 773 K, the initial conversion varied between 2.0–5.0%, which decreased to low values in a short reaction time. Taking into account the dispersion of Ir, the most effective sample in the decomposition of CH₄ was Ir/MgO. By means of Fourier transform infrared spectroscopy adsorbed CH₃ was identified as a reaction intermediate of methane decomposition. Temperature programmed reactions revealed that the reactivity of surface carbon produced in the decomposition of CH₄ depends on the nature of the support. Hydrogenation of the most reactive carbonaceous species led to the production of aliphatic hydrocarbons up to six carbon atoms.