Highly selective absorption separation of H2S and CO2 from CH4 by novel azole-based protic ionic liquids

Recently, the selective removal of H₂S and CO₂ has been highly desired in natural gas sweetening. Herein, four novel azole-based protic ionic liquids (PILs) were designed and prepared through one-step neutralization reaction. The solubility of H₂S (0–1.0 bar), CO₂ (0–1.0 bar), and CH₄ (0–5.0 bar) was systematically measured at temperatures from 298.2 to 333.2 K. NMR and theoretical calculation were used to investigate the reaction mechanism between these PILs and H₂S. Reaction equilibrium thermodynamic model (RETM) was screened to correlate the H₂S solubility. Impressively, 1,5-diazabicyclo[4,3,0] non-5-ene 1,2,4-1H-imidazolide ([DBNH][1,2,4-triaz]) shows the highest H₂S solubility (1.4 mol/mol or 7.3 mol/kg at 298.2 K and 1.0 bar) and superior H₂S/CH₄ (831) and CO₂/CH₄ (199) selectivities compared with literature results. Considering the excellent absorption capacity of H₂S, high H₂S/CH₄, and CO₂/CH₄ selectivity, acceptable reversibility, as well as facile preparation process, it is believed that azole-based PILs provide an attractive alternative in natural gas upgrading process.     

ON THE ANALYSIS OF NONCATALYTIC GAS-SOLID KINETICS DATA HAVING WEAK TEMPERATURE DEPENDENCE

Noncatalytic gas-solid reactions should exhibit strong temperature dependence when the rate is controlled by surface kinetics. However, there are a number of examples in the literature where apparent activation energies less than 10 kcal/mol have been reported as being representative of intrinsic kinetics. This conclusion is often based on electrobalance data in which large gas Row rates were used to eliminate mass transfer resistance and the fact that fractional conversion-time results are consistent with the surface kinetics control version of a gas-solid reaction model.

The oxidation of FeS was studied in an electrobalance reactor as a function of O₂ mol fraction, temperature, and gas flow rate. The global rate was first-order in O₂ and weakly dependent on temperature and flow rate. Data analysis used the approximate solution to the grain model. The single-resistance surface kinetics variation of the model provided good match with the conversion-time data, but the apparent activation energy was only about 7 kcal/mol. A two-resistance mass transfer-product layer diffusion variation provided equally good match with the data, and the dependence of reaction coefficients on reaction variables was in general agreement with theory.     

Effects of Pretreatments of Cu/ZnO-Based Catalysts on Their Activities for the Water–Gas Shift Reaction

The effects of the pretreatments of Cu/ZnO-based catalysts prepared by a coprecipitation method on their activities for the water–gas shift reaction at 523K were investigated. The activity of a Cu/ZnO/ZrO₂/Al₂O₃ catalyst for the water–gas shift reaction was less affected by calcination at temperatures ranging from 673-973K and by H₂ treatment at 573 or 723K than that of a Cu/ZnO/Al₂O₃ catalyst. The catalyst activity could be correlated mainly to the Cu surface area of the catalyst.     

A LaNi5-Hydride Thermal Absorption Compressor for a Hydrogen Refrigerator

The compound LaNi₅ absorbs nearly 6 atoms of hydrogen per formula unit at an equilibrium pressure of 2.5 at and room temperature. LaNi₅ exhibits a high rate of absorption and desorption of hydrogen and the heat of reaction is about 7.4 kcal/mol H₂. The dependence of the equilibrium pressure in the two-phase region on temperature is utilized to compress hydrogen from 4 to 45 at, which are suitable working pressures for a hydrogen refrigerator. Three vessels containing LaNi₅ are heated and cooled between 410 K and 290 K in cyclic operation. A system of selfoperating valves establishes a steady flow of hydrogen gas through a Joule-Thomson system. In the present design, employing precooling with liquid nitrogen at 78 K, 1 W of cold is produced at 26 K. Hydrogen-sorption properties of LaNi₅ are given and the problems encountered in practical use of the material discussed.     

Low-temperature H2S removal from gas streams with SBA-15 supported ZnO nanoparticles

Mesoporous silica SBA-15 with zinc oxide (ZnO) nanoparticles was prepared via incipient wetness impregnation and ultrasonic method, followed by in situ activation at 523 K. The mesoporous materials obtained were characterized by ICP, XRD, FTIR, nitrogen adsorption, TEM and XPS. The prepared materials showed a superior ability to remove H₂S down to parts per billion (ppb) from gas stream at lower temperature (298 K), and the highest H₂S breakthrough capacity, 436 mg S/g adsorbent, was observed for SBA-15 with 3.04 wt% zinc loading. The enhancement of H₂S removal capacity was attributed to the integration of the high surface area of the mesoporous material and the promising desulphurization properties of ZnO nanoparticles. It was believed that ZnO-modified SBA-15 is a promising adsorbent for H₂S cleaning at ambient conditions, which will extend the application of the mesoporous materials to the environmental protection area.     

Low-temperature catalytic decomposition of hydrogen sulfide on metal catalysts under layer of solvent

When hydrogen sulfide decomposition {2 H₂S ? 2 H₂?+?S₂^(gas)} is carried out in the flow regime at room temperature on metal catalysts placed in a liquid capable of dissolving H₂S and sulfur, the reaction equilibrium can be significantly (up to 100%) shifted to the right yielding the desired product – hydrogen. The process efficiency was demonstrated using aqueous solutions of monoethanolamine (MEA), sodium carbonate, which is widely used in industry for H₂S absorption from tail gases, and aqueous hydrazine as examples. IR and Raman spectroscopy data demonstrated that sulfur obtained in the solutions is in the form of diatomic molecules. DFT calculations showed that diatomic sulfur forms weakly bound coordinative complexes with solvent molecules. Some problems related to sulfur accumulation and recovery from the solvents are discussed.     

Kinetics of heptane reforming on Pt/L zeolite

The kinetics of heptane reforming over 0.64% Pt/KBaL have been measured over a wide range of conditions from 390 to 475 ° C, 0.05 to 1.00 atm heptane, and 0.2 to 25.0 atm hydrogen. Below about 6 atm H₂, the catalyst deactivates due to carbon fouling of the platinum particles. The reaction rate increases with hydrogen pressure under these conditions, presumably because this accelerates the rate of carbon hydrogenation off the metal surface. Above 6 atm H₂, no deactivation occurs. The activation energies and reaction orders in heptane and hydrogen at high H₂ pressure are: 39 kcal/mol, 0.7 and –1.9 for hydrogenolysis; 60 kcal/mol, 0.6 and –2.8 for isomerization; and 58 kcal/mol, 0.4 and –2.7 for dehydrocyclization. These kinetics are the same as those observed over platinum on nonacidic supports, and indicate that the reaction mechanism on Pt/KBaL is no different from that on monofunctional Pt catalysts.     

Generation of alkyl fragments on Rh/SiO2 and VO x -promoted Rh/SiO2

The adsorption of ethylene on Rh/SiO₂ and Rh-VO _x /SiO₂ has been studied by transmission FTIR spectroscopy. For C₂H₄ chemisorption at 298 K on Rh/SiO₂ molecularly adsorbed C₂H₄ and ethylidyne species are identified. It has been found that ethylidyne can be hydrogenated toward surface ethyl species in a reversible reaction at room temperature. On Rh-VO _x /SiO₂ the fragmentation of C₂H₄ into methylene species has been observed during C₂H₄ adsorption at 298 K.On leave from Zentralinstitut für Physikalische Chemie, Rudower Chaussee 5, O-1199 Berlin, Germany.     

Effect of non-steam component of steam-hydrogasifier product gas upon sulfidation of zinc oxide sorbent

Sulfidation of zinc oxide sorbent by desulfurization of steam-hydrogasifier product gas was affected by non-steam components of the reactant gas in a complicated manner. Relative abundance of each component appeared to shift the reaction equilibrium toward ZnO sulfidation, thereby enhancing the extent of sorbent utilization for sulfur removal, while their respective contributions were not simply additive toward the overall increase of sulfur capture capacity of the sorbent. This subtle outcome will have to be further investigated by varying, respectively, the individual abundance of each non-steam component as well as H₂S content of the reactant gas to be desulfurized.     

Characteristics and gas sensor applications of ZnO-Perovskite heterostructure

In this study, zinc oxide (ZnO) nanofibers were prepared using the electrospinning method, and the effects of different spinning voltages and annealing temperatures on the fiber structure were tested. La_0.8Sr_0.2FeO₃ (LSFO) perovskite film was prepared by a sol-gel method. Then we dip LSFO on ZnO nanofiber and grow it on the interdigital gold electrode substrate for gas sensors. The results show that the ZnO/LSFO heterostructure gas sensor has a good sensing response to H₂S gas and exhibits good gas selectivity. The best gas response is 52.17% under 4 ppm H₂S and work temperature 200°C, which has good recovery and reproducibility.     

Thermal dissociation of compressed ZnO and SnO2 powders in a moving‐front solar thermochemical reactor

The high‐temperature thermal dissociation reaction of ZnO and SnO₂ was investigated, as part of a two‐step thermochemical water‐splitting cycle for H₂ production. A lab‐scale solar reactor (1 kW) was designed, built, and operated for continuous dissociation of volatile oxides under reduced pressure. In this reactor, compressed oxide powders placed in a vertical ceramic cavity are irradiated by highly concentrated solar energy. The reactor design allows moving the reaction front for achieving continuous reactant feeding. ZnO and SnO₂ thermal dissociations were successfully performed at about 1900 K, with the recovery of up to 50% of products as nanopowders with high specific surface area (in the range 20–60 m²/g) and with mass fractions of reduced species up to 48 wt % for Zn and 72 wt % for SnO. The performed O₂ measurements confirmed the kinetics of ZnO dissociation and gave an activation energy of 380 ± 16 kJ/mol, based on an ablation regime of the ZnO surface. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

State Parameters and Phase Transformations in Carbonized Periclase Refractories

The effect of temperature and formulation (relative volumes of the gas phase) on phase and chemical transformations in the MgO – C – H₂O – air system at 298 – 2400 K is considered using methods of thermodynamic and physicochemical simulation with a view to using carbonized periclase refractories under industrial conditions. Temperature ranges for stable existence of refractory phases and formulation ranges (for the gas phase) with allowance for different chemical homo- and heterophase interactions are determined. Effects of temperature, concentration, and pressure of pore gases (CO₂, CO, CH₄, H₂O, H₂, etc.) on the bulk material and effects of the carbon component, porosity, intrinsic and atmospheric moisture on gasification processes are considered in terms of a theoretical simulation model.     

Effects of zirconia promotion on the activity of Cu/SiO2 for methanol synthesis from CO/H2 and CO2/H2

The effect of zirconia promotion on Cu/SiO₂ for the hydrogenation of CO and CO₂ at 0.65 MPa has been investigated at temperatures between 473 and 573 K. With increasing zirconia loading, the rate of methanol synthesis is greatly enhanced for both CO and CO₂ hydrogenation, but more significantly for CO hydrogenation. For example, at 533 K the methanol synthesis activity of 30.5 wt% zirconia-promoted Cu/SiO₂ is 84 and 25 times that of unpromoted Cu/SiO₂ for CO and CO₂ hydrogenation, respectively. For all catalysts, the rate of methanol synthesis from CO₂/H₂ is higher than that from CO/H₂. The apparent activation energy for methanol synthesis from CO decreases from 22.5 to 17.5 kcal/mol with zirconia addition, suggesting that zirconia alters the reaction pathway. For CO₂ hydrogenation, the apparent activation energies (~12 kcal/mol) for methanol synthesis and the reverse water-gas shift (RWGS) reaction are not significantly affected by zirconia addition. While zirconia addition greatly increases the methanol synthesis rate for CO₂ hydrogenation, the effect on the RWGS reaction activity is comparatively small. The observed effects of zirconia are interpreted in terms of a mechanism which zirconia serves to adsorb either CO or CO₂, whereas Cu serves to adsorb H₂. It is proposed that methanol is formed by the hydrogenation of the species adsorbed on zirconia.     

Gasification characteristics of combustible wastes in a 5 ton/day fixed bed gasifier

The gasification characteristics of combustible wastes were determined in a 5 ton/day fixed bed gasifier (1.2 m I.D. and 2.8m high). The fixed bed gasifier consisted of air compressor, oxygen tank, MFC, fixed bed gasifier, cyclone, heat exchanger, solid/gas separator, water fluidized bed reactor and blower. To capture soot or unburned carbon from the gasification reaction, solid/gas separator and water fluidized bed were used. The experiments with 10–50 hours of operation were carried out to determine the effects of bed temperature, solid/oxygen ratio and oxidant on the gas composition, calorific value and carbon conversion. The calorific values of the produced gas decreased with an increase of bed temperature because combustion reaction happened more actively. The gas composition of partial oxidation of woodchip is CO: 34.4%, H₂: 10.7%, CH₄: 6.0%, CO₂: 48.9% and that of RPF is CO: 33.9%, H₂: 26.1%, CH₄: 10.7%, CO₂: 29.2%. The average calorific values of produced gas were about 1,933 kcal/Nm³, 2,863 kcal/Nm³, respectively. The maximum calorific values were 3,100 kcal/Nm³ at RPF/oxygen ratio: 7     

The promoting effect of alcohols in a new process of low-temperature synthesis of methanol from CO/CO2/H2

The catalytic promoting effects of eleven different alcohols, as reaction medium, on the synthesis of methanol from feed gas of CO/CO₂/H₂ on Cu/ZnO solid catalyst were investigated. Added alcohol altered the reaction route to realize a low-temperature synthesis method where formate was an intermediate. Many alcohols showed catalytic promoting effect for methanol formation at temperature as low as 443 K, remarkably lower than that in the present industrial ICI process.     

Quantitative studies by differential scanning calorimetry of the reaction between hydrogen peroxide and lignocellulose

Heat of reaction and kinetic parameters were determined by differential scanning calorimetry for decomposition of hydrogen peroxide, reaction of hydrogen peroxide with lignocellulosic materials, glucose and pinitol, and for the reaction of the same materials with produced or introduced oxygen. The heat of decomposition of hydrogen peroxide obtained in N₂ (720 cal/g H₂O₂) was in fair agreement with literature data, considering the different temperature and pressure conditions. The heats of reaction of hydrogen peroxide and lignocelluloses were higher when determined in N₂ (1670–2500 cal/g H₂O₂) than in O₂ (1450–2020 cal/g H₂O₂) atmosphere. The activation energy for decomposition of hydrogen peroxide amounted to 20.3 kcal/mol in N₂ and 15.9 kcal/mol in O₂ with frequency factors of 5.7 × 10⁹ and 3.7 × 10⁷ min^?1, respectively. The activation energies for the reaction of hydrogen peroxide and lignocellulosic materials tested were similar and not influenced by the atmospheric composition, ranging overall between 19.7 and 22.4 kcal/mol. The corresponding frequency factors ranged between 2.77 × 10⁹ and 2.23 × 10¹¹.     

Fuel processor integrated H2S catalytic partial oxidation technology for sulfur removal in fuel cell power plants

H₂S catalytic partial oxidation technology with an activated carbon catalyst was found to be a promising method for the removal of hydrogen sulfide from fuel cell hydrocarbon feedstocks. Three different fuel cell feedstocks were considered for analysis: sour natural gas, sour effluent from a liquid middle distillate fuel processor and a Texaco O₂-blown coal-derived synthesis gas. The H₂S catalytic partial oxidation reaction, its integratability into fuel cell power plants with different hydrocarbon feedstocks and its salient features are discussed. Experimental results indicate that H₂S concentration can be removed down to the part-per-million level in these plants. Additionally, a power law rate expression was developed and reaction kinetics compared to prior literature. The activation energy for this reaction was determined to be 34.4 kJ/g mol with the reaction being first order in H₂S and 0.3 order in O₂.     

Experimental study on ZnO-TiO<Subscript>2</Subscript> sorbents for the removal of elemental mercury

ZnO-TiO₂ sorbents synthesized by an impregnation method were characterized through XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy) and EDS (Energy dispersive spectrometer) analyses. An experiment concerning the adsorption of Hg⁰ by ZnO-TiO₂ under a simulated fuel gas atmosphere was then conducted in a bench-scale fixed-bed reactor. The effects of ZnO loading amounts and reaction temperatures on Hg⁰ removal performance were analyzed. The results showed that ZnO-TiO₂ sorbents exhibited excellent Hg⁰ removal capacity in the presence of H₂S at 150 °C and 200 °C; 95.2% and 91.2% of Hg⁰ was removed, respectively, under the experimental conditions. There are two possible causes for the H₂S reacting on the surface of ZnO-TiO₂: (1) H₂S directly reacted with ZnO to form ZnS, (2) H₂S was oxidized to elemental sulfur (S _ad ) by means of active oxygen on the sorbent surface, and then S _ad provided active absorption sites for Hg⁰ to form HgS. This study identifies three reasons why higher temperatures limit mercury removal. First, the reaction between Hg⁰ and H₂S is inhibited at high temperatures. Second, HgS, as the resulting product in the reaction of mercury removal, becomes unstable at high temperatures. Third, the desulfurization reaction strengthens at higher temperatures, and it is likely that H₂S directly reacts with ZnO, thus decreasing the S _ad on the sorbent surfaces.     

Elaboration and characterization of PVP-assisted NiO thin films for enhanced sensitivity toward H2 and NO2 gases

It is widely demonstrated that the synthesis conditions of sol-gel films have a great impact on their gas sensing properties. In this work, transparent PVP-assisted nickel oxide thin films with an average grain size of ~5?nm were synthesized using two distinctive deposition procedures combining the sol-gel method with the spin-coating technique then tested as optical gas sensors for the detection of hazardous pollutant gases. The first method is ascribed to a typical spin-coating deposition followed by a thermal annealing, and the second method consisted on a multistep coating annealing process. Structural and morphological studies showed enhanced crystallization rate and homogeneous surface morphology using a multistep deposition. The as prepared films exhibit a clear and reversible response toward H₂, CO and NO₂ gases and the multistep deposition process enhanced the sensitivity of about 113% and 194% toward 1% of H₂ and 0.1% of NO₂ respectively. The shrinkage of the band gap from 4.07 to 3.91?eV and the increased PL intensity indicate the presence of higher rate of charge density and intrinsic defect states that promoted the sensitivity of the film. Furthermore, improved response intensity was detected in the near UV region and higher stability with fast response was obtained for hydrogen gas.     

Adsorptive Entfernung von Schwefelverbindungen aus Erdgas

Prior to the technical use of natural gas, toxic and corrosive components need to be removed. This work provides results from dynamic fixed‐bed experiments for the adsorption of sulfurous compounds, CO₂ and H₂O from carrier gas (CH₄ or N₂) on two adsorbents (zeolite 5A, silica‐alumina‐gel) used in industrial applications. The breakthrough curves were measured at ambient conditions (298 K, 1.3 bar) in a trace level concentration range up to 2000 mol‐ppm. Adsorption isotherms were derived using mass balances and a simple linear driving force model was fitted to the curves. Good agreement of experimental data and model calculation was obtained.