The effect of synthesis gas composition on the Fischer–Tropsch synthesis over Co/γ-Al2O3 and Co–Re/γ-Al2O3 catalysts

The Fischer–Tropsch synthesis over Co/γ-Al₂O₃ and Co–Re/γ-Al₂O₃ was investigated in a fixed-bed reactor at 20 bar and 483 K using feed gases with molar H₂/CO ratios of 2.1, 1.5 and 1.0 simulating synthesis gas derived from biomass. With lower H₂/CO ratios in the feed, the CO conversion and the CH₄ selectivity decreased, while the C₅₊ selectivity and olefin/paraffin ratio for C₂–C₄ increased slightly. The water–gas shift activity was low for both catalysts, resulting in high molar usage ratios of H₂/CO (close to 2.0), even at the lower inlet ratios (i.e. 1.5 and 1.0). For both catalysts, the drop in the production rate of hydrocarbons when shifting from an inlet ratio of 2.1 to 1.5 was significant mainly because the H₂/CO usage ratio did not follow the change in the inlet ratio. The hydrocarbon selectivities were rather similar for inlet H₂/CO ratios of 2.1 and 1.5, while significantly deviating from those for an inlet ratio of 1.0. With the studied catalysts, it is possible to utilize the advantages of an inlet ratio of 1.0 (higher selectivity to C₅₊, lower selectivity to CH₄, no water–gas shifting of the bio-syngas needed prior to the FT reactor) if a low syngas conversion is accepted.     

Screening ionic liquids as candidates for separation of acid gases: Solubility of hydrogen sulfide,methane, and ethane

The solubility of the major constituents of natural gas in ionic liquids (ILs) can be used to identify their potential for acid gas removal from a producing gas stream. We have developed models for the solubility of H₂S, CH₄, and C₂H₆ in ILs at typical conditions encountered in natural gas treatment. In this work, a conductor‐like screening model for realistic solvation was used to predict the activity coefficients for solutes in ILs and a cubic EOS was used for vapor‐phase corrections from ideality. Empirical correlations were developed to extrapolate solubilities where experimental data are not available at desired conditions; targeted in this study at 298.15 K and 2000 kPa. Over 400 possible ILs were ranked based on the higher selectivity of absorption of CO₂ and H₂S over CH₄ and C₂H₆. The best 15% (58) of promising ILs for sour gas treatment predominantly contain the anions BF₄, NO₃, and CH₃SO₄ and the cations N₄₁₁₁, pmg, and tmg. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2993–3005, 2013     

A new analytical modeling for the determination of thermodynamic quantities of refrigerants

A new analytical fundamental equation of state (EOS) is presented for fluids. The equation is explicit in the effective molecular potentials and allows calculation of all thermodynamic properties over the whole fluid surface (gas, liquid, supercritical and gas–liquid phase transition). Outside the critical area (± 0.05T_c), it is valid in a vast range of temperature and pressure (0.8T_c to 7.5T_c and up to 120P_c,). The EOS is applicable for a variety of refrigerants such as C₃H₂F₄ (HFO-1234ze (E)), hydrofluorocarbons (HFCs) including C₃F₈ (R218), C₃H₂F₆ (R236ea), C₃H₂F₆ (R236fa), C₃H₃F₅ (R245ca), C₃HF₇, C₄F₈ (RC318), C₄F₁₀, C₅F₁₂, natural refrigerants including NH₃, CO₂, hydrocarbons, monatomic gases and some other fluids. Calculations of second derivatives properties of fluids are sensitive tests of EOS behavior. Therefore, estimation of the thermodynamic properties including Joule-Thomson coefficient, μ_JT, and speed of sound, w, has been considered.     

Alkali-thermal gasification and hydrogen generation potential of biomass

Generating hydrogen gas from biomass is one approach to lowering dependencies on fossil fuels for energy and chemical feedstock, as well as reducing greenhouse gas emissions. Using both equilibrium simulations and batch experiments with NaOH as a model alkaline, this study established the technical feasibility of converting various biomasses (e.g., glucose, cellulose, xylan and lignin) into H₂-rich gas via catalyst-free, alkalithermal gasification at moderate temperatures (as low as 300 °C). This process could produce more H₂ with less carbon-containing gases in the product than other comparable methods. It was shown that alkali-thermal gasification follows C _x H _y O _z + 2xNaOH + (x–z)H₂O = (2x + y/2–z)H₂ + xNa₂CO₃, with carbonate being the solid product which is different from the one suggested in the literature. Moreover, the concept of hydrogen generation potential (H₂-GP)—the maximum amount of H₂ that a biomass can yield, was introduced. For a given biomass C _x H _y O _z , the H₂-GP would be (2x + y/2–z) moles of H₂. It was demonstrated experimentally that the H2-GP was achievable by adjusting the amounts of H₂O and NaOH, temperature and pressure.

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Properties of cold lake bitumen saturated with pure gases and gas mixtures

This paper presents new data for the viscosity, density and gas solubility of Cold Lake bitumen saturated with light gases and gas mixtures over a temperature range of 15 to 103°C at up to 10 MPa pressure. Specifically, the gases whose effects on the bitumen properties were measured are N₂, CH₄, CO₂ and C₂H₆, and two mixtures of CO₂ and CH₄. With CO₂ and C₂H₆, experiments were also performed in the liquid-liquid region, and the results of these experiments generally agree with the previously published predictions. The viscosity of the gas-free Cold Lake bitumen is comparable to that of a Marguerite Lake bitumen that was tested previously. Due to the large solubilities of C0₂ and C₂H₆, the reduction in gas-saturated bitumen viscosity is quite dramatic. The density of the gas-saturated bitumen decreases with increased amounts of the dissolved CH₄ and C₂H₆ gases, but no such trends are evident for the N₂ and CO₂ gases. The results of the experiments with two binary gas mixtures (i.e., CO₂ and CH₄) indicate that the bitumen properties are affected largely by the major gas constituent.     

Pressure dependence of gas permeability in a rubbery polymer

The effect of pressure on gas permeability of a rubbery polymer, 1,2-polybutadiene, is investigated for 15 gases with various molecular sizes and solubilities in the ranges of pressure up to 110 atm at 25°C. The permeability for slightly soluble gases (He, Ne, H₂, N₂, O₂, and Ar) decreases with increasing pressure, and that for soluble gases (CH₄, Kr, CO₂, N₂O, C₂H₄, Xe, C₂H₆, C₃H₆, and C₃H₈) increases with increasing pressure. Logarithms of permeability coefficient versus feed-gas pressure for the slightly soluble gases, CH₄ and Kr, is linear within each pressure range, whereas such plots become convex toward the pressure axis for more soluble gases, such as CO₂, N₂O, C₂H₄, Xe, C₂H₆, C₃H₆, and C₃H₈. By analyzing the pressure dependence of permeability using sorption data of the gases, contributions of concentration and hydrostatic pressure to the gas diffusivity are estimated. © 1996 John Wiley & Sons, Inc.     

Heat capacity of polymer melts from the polymer chain-of-rotators equation of state

Recently, the chain-of-rotators equation of state derived from the rotational partition function was extended to polymers. Values of the three equation of state (EOS) parameters were obtained from fitting with experimental pressure–volume–temperature data and the parameters were correlated with the structure of the polymer repeat unit. In this article, the residual molar heat capacity derived from an EOS is added to the ideal gas heat capacity from Benson's group contribution method to obtain the polymer molar heat capacity at constant pressure, C_p. Predictions from the polymer chain-of-rotators (PCOR) using correlated parameters are compared with those obtained from PCOR, Sanchez–Lacombe, Flory–Orwoll–Vrij, and the perturbed-hard-sphere chain equations of state using parameters fitted from experimental data. Deviations of calculated C_p from the formula of van Krevelen for liquid polymers are likewise presented. With the correlations developed for its parameters, the PCOR offers the advantage of predicting the C_p for polymer melts from just the knowledge of the polymer's structure. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:841–848, 1998     

Selective transport of CO2, CH4, and N2 in coals: insights from modeling of experimental gas adsorption data

Selective adsorption and transport of gases in coal are important for natural gas recovery and carbon sequestration in depleted coal seams for environmental remediation. Gases are stored in coal mainly in the adsorbed state. In this study, the interaction energies of adsorbates (CO₂, CH₄, and N₂) and micropores with various widths are investigated using a slit-shape pore model. The experimental adsorption rate data of the three gases conducted on the same coal sample are numerically simulated using a bidisperse model and apparent diffusivities of each adsorbate in the macropore and micropore are determined. The results indicate that the relative adsorbate molecule size and pore structure play an important role in selective gas adsorption and diffusion in micropores. Generally, the microporous coals diffusion is activated and the apparent micropore diffusivities of gases in coal decrease strongly with increase in gas kinetic diameters. Apparent micropore diffusivity of CO₂ is generally one or two order of magnitude higher than those of CH₄ and N₂ because their kinetic diameters have the relation: CO₂ (0.33 nm)<N₂ (0.36 nm)<CH₄ (0.38 nm). In contrast to theoretical values, apparent macropore diffusivity of CO₂ is also larger than those of CH₄ and N₂, suggesting that coal has an interconnected pore network but highly constricted by ultra micropores with width <∼0.6 nm. It is also found that the apparent diffusivity strongly decreases with an increase in gas pressure, which may be attributed to coal matrix swelling caused by gas adsorption. Therefore, rigorous modeling of gas recovery and production requires consideration of specific interaction of gas and coal matrix.     

Preparation and C3H8/Gas Separation Properties of a Synthesized Single Layer PDMS Membrane

In this paper, a new polydimethylsiloxane (PDMS) membrane was synthesized and its ability for separation of heavier gases from lighter ones was examined. Sorption, diffusion, and permeation of H₂, N₂, O₂, CH₄, CO_2, and C₃H₈ in the synthesized membrane were investigated as a function of pressure at 35°C. PDMS was confirmed to be more permeable to more condensable gases such as C₃H₈. This result was attributed to very high solubility of larger gas molecules in hydrocarbon?based PDMS in spite of their low diffusion coefficients relative to small molecules. The synthesized membrane showed much better gas permeation performance than others reported in the literature. Increasing upstream pressure increased solubility, permeability and diffusion coefficients of C₃H₈, while these values decreased slightly or stayed constant for other gases. Local effective diffusion coefficient of C₃H₈ and CO₂ increased with increasing penetrant concentration which indicated plasticization effect of these gases over the range of penetrant concentration studied. C₃H₈/gas solubility, diffusivity and overall selectivities also increased with increasing feed pressure. Ideal selectivity values of 4, 13, 18, 20, and 36 for C₃H₈ over CO₂, CH₄, H₂, O_2, and N₂, respectively, at upstream pressure of 7 atm, confirmed the outstanding separation performance of the synthesized mebrane.     

Synthesis and gas permeation properties of a single layer PDMS membrane

In this work, a new polydimethylsiloxane (PDMS) membrane was synthesized and its sorption, diffusion, and permeation properties were investigated using H₂, N₂, O₂, CH₄, CO₂, and C₃H₈ as a function of pressure at 35°C. PDMS, as a rubbery membrane, was confirmed to be more permeable to more condensable gases such as C₃H₈. The synthesized PDMS membrane showed much better gas permeation performance than others reported in the literature. Based on the sorption data of this study and other researchers' works, some valuable parameters such as Flory‐Huggins (FH) interaction parameters, χ, etc., were calculated and discussed. The concentration‐averaged FH interaction parameters of H₂, N₂, O₂, CH₄, CO₂, and C₃H₈ in the synthesized PDMS membrane were estimated to be 2.196, 0.678, 0.165, 0.139, 0.418, and 0.247, respectively. Chemical similarity of O₂, CH₄, and C₃H₈ with backbone structure of PDMS led to lower χ values or more favorable interactions with polymer matrix, particularly for CH₄. Regular solution theory was applied to verify correctness of evaluated interaction parameters. Local effective diffusion coefficient of C₃H₈ and CO₂ increased with increasing penetrant concentration, which indicated the plasticization effect of these gases over the range of penetrant concentration studied. According to high C₃H₈/gas ideal selectivity values, the synthesized PDMS membrane is recommended as an efficient membrane for the separation of organic vapors from noncondensable gases. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Investigation of gas properties, design, and operational parameters on hydrodynamic characteristics, mass transfer, and biomass production from natural gas in an external airlift loop bioreactor

An external airlift loop bioreactor (EALB) was used for production of biomass from natural gas. The effect of riser to downcomer cross sectional area ratio (A_r/A_d), volume of gas-liquid separator, superficial gas velocity (U_sgr), and physical properties of gases and their mixtures [υ_g (μ/ρ) and D_g] were investigated on mixing time, gas hold-up, and volumetric gas liquid mass transfer coefficients (k_La). It was found that A_r/A_d has remarkable effects on gas hold-up and k_La due to its influence on mixing time. Kinematic viscosity (υ_g) showed its significant role on mixing time, gas hold-up and k_La when different gases used (mixing time changes directly whereas gas hold-up and k_La change indirectly). Moreover, it was found that diffusion coefficient of gas in water (D_g) has remarkable effect on k_La. The volumetric mass transfer coefficients for methane and its mixtures with oxygen (three different mixtures) were determined at different geometrical and operational factors. In average, the rate of oxygen utilization is approximately 1.8 times higher than that of methane. A gas mixture of 25 vol% methane and 75 vol% oxygen was the best gas mixture for biomass production in the EALB. The correlations developed for predicting the mixing time, gas hold-up, and k_La in terms of U_sgr, A_r/A_d, volume of gas-liquid separator, and gas phase properties have been found to be encouraging.     

Mathematical modelling on rapid decompression in base natural gas mixtures under rupturing

The paper presents a one-dimensional mathematical model of transient compressible thermal multi-component gas mixture flows in pipes. The set of the mass, momentum and enthalpy conservation equations is solved for gas phase in the model. Thermo-physical properties of multi-component gas mixture are calculated by solving the Equation of State (EOS) model. The Soave–Redlich–Kwong (SRK–EOS) model is chosen. Gas mixture viscosity is calculated on the basis of the Lee–Gonzales–Eakin (LGE) correlation. Numerical analysis on rapid decompression process in a shock tube having base natural gases is performed by using the proposed mathematical model. The model is successfully validated on the experimental measurements of the decompression wave speed in base natural gas mixtures. The proposed mathematical model shows a very good agreement with the experiments in a wide range of pressure values and predicts the decompression in base natural gases much better than analytical and mathematical models, which are available from the open source literature.     

Investigation into a gas–solid–solid three-phase fluidized-bed carbonator to capture CO2 from combustion flue gas

A two-dimensional (2D) transient model was developed to simulate the local hydrodynamics of a gas (flue gas)–solid (CaO)–solid (CaCO₃) three-phase fluidized-bed carbonator using the computational fluid dynamic method, where the chemical reaction model was adopted to determine the molar fraction of CO₂ at the exit of carbonator and the partial pressure of CO₂ in the carbonator. This investigation was intended to improve an understanding of the chemical reaction effects of CaO with CO₂ on the CO₂ capture efficiency of combustion flue gases. For this purpose, we had utilized Fluent 6.2 to predict the CO₂ capture efficiency for different operation conditions. The adopted model concerning the reaction rate of CaO with CO₂ is joined into the CFD software. Model simulation results, such as the local time-averaged CO₂ molar fraction and conversion of CaO, were validated by experimental measurements under varied operating conditions, e.g., the fraction of active CaO, chemical reaction temperature, particle size, and cycle number at different locations in a gas–solid–solid three-phase fluidized bed carbonator. Furthermore, the local transient hydrodynamic characteristics, such as gas molar fraction and partial pressure were predicted reasonably by the chemical reaction model adopted for the dynamic behaviors of the gas–solid–solid three-phase fluidized bed carbonator. On the basis of this analysis, capture CO₂ strategies to reduce CO₂ molar fraction in exit of carbonator reactor can be developed in the future. It is concluded that a fluidized bed of CaO can be a suitable reactor to achieve very effective CO₂ capture from combustion flue gases.     

Evaluation of pure‐component adsorption properties of silicalite based on the Langmuir and Sips models

The Langmuir and Sips models parameters were estimated for the adsorption of several light gases and hydrocarbons (H₂, CH₄, CO₂, CO, N₂, C₂H₆, C₃H₈, n‐C₄H₁₀) in silicalite along with their functionality with temperature. This is a scientific attempt to resume and reconcile the number of available experimental data and supply scientists and other operators with the adsorption properties of silicalite within a wider range of temperature and pressure. Furthermore, to provide readers with more detailed information on where each of the two models work better, the analysis is divided into three temperature ranges: low‐temperature, high‐temperature, and whole temperature range. As a result, it is found that the Langmuir model works well in the whole temperature range for the light gases considered but not for the other hydrocarbons, for which it is better to use the Sips model by splitting calculation over low‐ and high‐temperature range. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3911–3922, 2015     

Pure and mixed gas permeation study of silica incorporated polyurethane-urea membrane modified by MOCA chain extender

Polyurethane-urea (PUU) nanocomposite membranes have been prepared using various loadings of silica (SiO₂) nanoparticles. A Novel PU was fabricated by a two-step bulk polymerization technique based on polycaprolactone (PCL), hexamethylene diisocyanate (HDI), and diamine chain extender, 4,4-methylenebis(2-chloroaniline) (MOCA). The FTIR spectra indicated that the extent of phase separation reduces with increasing SiO₂ content. The presence of crystal regions in the soft and hard segments was confirmed by DSC and XRD analyses. The obtained results illustrated a decrement in the gases' permeation in the presence of SiO₂ particles. By increasing the filler content up to 15 wt% and pressure of 8 bar, the gas permeation value of the CO₂, O₂, and N₂ decreased 36%, 54%, and 59%, respectively. However, the permselectivity of the CO₂/N₂ and O₂/N₂ increased considerably, 55% and 13% respectively. On the contrary, by raising the temperature, a dramatic augmentation in the permeability of all gases with a simultaneous reduction in the selectivity values of both gas pairs was revealed. Increasing the pressure led to a decrease in the permeability values of all membranes for O₂ and N₂, whereas the permeability for CO₂ increased with the pressure. Nevertheless, the selectivity values for the pair of gases increased (at a pressure of 10 bar, 1.66 and 1.17 times the neat PU for CO₂/N₂ and O₂/N₂, respectively). Furthermore, the permeability of the CO₂, O₂, and N₂ for the mixed gases was smaller than for pure ones at the same gas upstream pressure. Nonetheless, like the pure gas, the selectivity of both pair gases increased.     

Correlation and prediction of gas solubility in cold lake bitumen

The solubility data for pure light gases, namely N₂, CH₄, CO₂ and C₂H₆, in Cold Lake bitumen are correlated by use of the Peng-Robinson equation of state. Modeling Cold Lake bitumen as a mixture of three pseudocomponents adequately matched two sets of the gas-solubility data. The critical properties and acentric factor for the bitumen pseudocomponents were estimated using the Kesler-Lee correlations. For each gas-bitumen pair, a single constant value of the binary interaction parameter is shown to predict the gas-solubility data with average deviations ranging from 2 to 8%. Subsequently, these calculations were extended to predict the solubility of CO₂+CH₄ gas-mixtures in Cold Lake bitumen. It is shown that the solubility predictions for the gas mixtures data are higher by approximately 6 to 9%.     

Experimental and theoretical study of the adsorption of pure molecules and binary systems containing methane, carbon monoxide, carbon dioxide and nitrogen. Application to the syngas generation

This study takes place in the context of the use of a Synthesis Gas in Gas To Liquid process, liquid hydrocarbon production by conversion based on Fischer–Tropsch synthesis. Our aim is the process improvement by a selective recycling of the tail gas. So, we measure pure component isotherms for four gases (CO₂, CH₄, CO, N₂) of the tail gas until 2000 kPa and binary mixture (CO₂–CH₄; CO₂–N₂; CH₄–N₂) equilibria at 303.15 K and 400 and 950 kPa onto a ZSM-5 zeolite. We also predict the binary mixture equilibria by the Ideal Adsorbed Solution Theory (IAST) and the Vacancy Solution Model (VSM, Flory–Huggins and Wilson forms) and we obtain very good results. So not only binary mixture equilibria but also ternary and quaternary mixture adsorption can be predicted. With these data (experimental and simulated), we can conclude that the CO₂ is the most adsorbed component while N₂ is the least one. These two components can be separated from CH₄ and CO which are sent in the Synthesis Gas production step.     

Effect of water on the solubilities and mass transfer coefficients of gases in a heavy fraction of fischer-tropsch products

The effects of water on the solubilities, C^*, and volumetric mass transfer coefficients, k_La, for CO, H₂, CH₄ and CO₂ in a heavy fraction of Fischer-Tropsch liquid were examined at elevated pressures and temperatures at different mixing power inputs. For these gases, higher solubilities were measured in the hydrocarbon mixture saturated with water than those obtained in the hydrocarbon free of water. The k_La values for the four gases were slightly affected by the presence of dissolved water in the hydrocarbon mixture; and they were strongly dependent on the power input per unit liquid volume. Two empirical correlations for k_La as a function of turbine speed and pressure are proposed.     

Characterization of Epoxytrienes Derived from (3Z,6Z,9Z)-1,3,6,9-Tetraenes, Sex Pheromone Components of Arctiid Moths and Related Compounds

Cis-9,10-epoxy-(3Z,6Z)-1,3,6-henicosatriene has been identified from a pheromone gland of arctiid species, such as Hyphantria cunea. Since the diversity of lepidopteran species suggests that structurally related compounds of the 9,10-epoxide are also utilized as a sex pheromone components, epoxytrienes derived from (3Z,6Z,9Z)-1,3,6,9-tetraenes with a C₁₉–C₂₁ chain were systematically synthesized and characterized. While 1,2-epoxy-3,6,9-triene was not obtained, peracid oxidation of each tetraene produced a mixture of three cis-epoxides (3,4-epoxy-1,6,9-triene, 6,7-epoxy-1,3,9-triene, and 9,10-epoxy-1,3,6-triene), which were separable by LC as well as GC. Detailed inspection of the mass spectra of the C₁₉–C₂₁ epoxides indicated the following diagnostic ions for determining the chemical structures: m/z 79, M-70, and M-41 for the 3,4-epoxytrienes; m/z 79, 95, 109, and 149 for the 6,7-epoxytrienes; and m/z 79, 106, 120, M-121, and M-107 for the 9,10-epoxytrienes. Resolution of two enantiomers of each C₂₁ epoxytriene was accomplished by HPLC equipped with a chiral column, and analysis of the pheromone extracted from virgin females of H. cunea revealed the 9S,10R configuration of the natural epoxytriene as the same configuration of C₂₁ 9,10-epoxydiene, a main pheromone component of this species. GC-EAD analysis of the optically pure epoxides showed that the antennae of male H. cunea were stimulated more strongly (>100 times) by the (9S,10R)-isomers than the antipodes.