Hydrogenation of 1,3-butadiene and the adsorbed hydrogens on a platinum electrode

Hydrogenation of 1,3-butadiene on a Pt electrode in M H₂So₄ was studied both on open circuit and under potentiostatic polarization to examine the reactivity of the adsorbed hydrogens. Results in region-H (P_H/P_B < 20 on open circuit, ø > 80 mV/rhe in the electroreduction) show that the most stable hydrogen is inactive and interchanges to the secondly stable hydrogen during the hydrogenation. The latter adsorbed hydrogen, H_qø, is always in equilibrium with H⁺ and e^? by Hø ? H⁺ + e^? and reacts with adsorbed diene, giving butenes and n-butane. The rate of the interchange is three orders of magnitude smaller than the hydrogenation rate. Among the surface elementary steps, the second addition of hydrogen atom seems to be slowest. Difference in hydrogen source, ie H₂ molecule or proton and electron, has no effect on the reaction mechanism.     

Steady-state methanation kinetics over a Ni/Al2O3 catalyst

Extensive kinetic data for the methanation reaction over a Ni/Al₂O₃ catalyst were obtained in a specially designed gradientless reactor operating at steady state. The reactor pressure was 101.3 kPa, and three temperatures were used, namely, 503, 513 and 523 K. The following three-parameter phenomenological model based on a proposed Langmuir-Hinshelwood mechanism adequately describes the data: r = L² K₃ K₄^0.5 k₅ P^0.5H₂ Pco/ [1 + K₃ (k₅ / k₆)Pco + K₄^0.5 P^0.5H₂ ]² With dissociative adsorption of hydrogen and hydrogen-assisted dissociation of adsorbed carbon monoxide, the postulated mari is the CH surface group, and the rds is the hydrogenation of the surface CH group.     

Kinetic study of the pyrolysis of tetrachloroethylene in a hydrogen rich environment

Experiments on pyrolysis of C₂Cl₄ with hydrogen in argon bath gas (C₂Cl₄: H₂: AR=0.5:7:92.5) were performed in a laboratory scale flow reactor, to determine reaction paths and kinetic parameters, plus to observe hydrogen as a source to convert chlorocarbons into hydrocarbons and HCl. The reaction was carried out at 1 atmosphere total pressure in the tubular flow reactor, over temperature ranges from 575 to 850 °C, with average residence times in the range of 0.3 to 1.2 s. The major reaction products were C₂HCl₃, CH₂CCl₂, C₂H₆, C₂H₄ and HCl. Trace intermediates including CH₄, C₂H₂, C₃H₆, C₃H₄, C₄H₈, C₄H₆, C₄H₄, C₂H₃Cl, C₂HCl, trans-CHClCHCl, cis-CHClCHCl C₂Cl₂ and aromatic compounds were found. The equation for overall loss of C₂Cl₄ (k (s⁻¹)) was 1.35×10⁶exp(−27055/RT). This study shows that C₂H₄ became the major product for reaction temperatures higher than 700 °C, and became one of the final products together with HCl.A detailed kinetic mechanism consisting of 202 elementary reactions with 59 species was developed to model the results obtained from the experiments. Sensitivity analyses were performed to rank the significance of each reaction in the mechanism. Modeling and sensitivity analysis revealed that C₂Cl₄+H→C₂HCl₃+Cl, C₂Cl₄+H→C₂Cl₃+Cl, and C₂Cl₄→C₂Cl₃+Cl are the primary reactions for the decomposition of C₂Cl₄.     

Heterocycles oligomerization in acidic zeolites: a UV-visible and IR study

FTIR spectroscopy shows that the first step of the interaction of pyrrole, furan and thiophene with H- $\beta $ and H-ZSM-5 zeolites is the formation of hydrogen bonded (precursor) species involving the Brønsted acid sites of the zeolite and the $\pi $ -electron system of the heterocyclic molecule. The precursors are then protonated to give monomeric BH⁺ (where B = C₄H₄NH, C₄H₄O or C₄H₄S) species which, in the presence of excess B, can further react to form entrapped coloured B_nH⁺ oligomeric species. Characterization by means of in situ UV-Vis reflectance spectroscopy shows that the oligomeric products contain up to six conjugated double bonds and that they have carbocationic nature. However, the precise structure of the responsible species (particularly those absorbing in the visible) cannot be completely elucidated. The carbocationic character of the oligomers is also documented by the changes induced in the electronic spectra by adsorption of NH₃, i.e., of a base capable of extracting H⁺ ions from B_nH⁺ to give NH ₄ ⁺ and B_n. The role of intermolecular hydrogen transfer in the intrazeolitic oligomerization process is also evidenced and discussed.     

Dehydrogenation of propane with selective hydrogen combustion: A mechanistic study by transient analysis of products

The role of lattice and adsorbed oxygen species in propane dehydrogenation in a perovskite hollow fiber membrane reactor containing a Pt–Sn dehydrogenation catalyst was elucidated by transient analysis of products with a sub-millisecond time resolution. Propane is mainly dehydrogenated non-oxidatively to propene and hydrogen over the catalyst, while lattice oxygen of the perovskite oxidizes preferentially hydrogen to water. For achieving high propene selectivity at high propane conversions, the formation of gas phase O₂ on the shell side of the membrane reactor should be avoided. Otherwise, oxygen species adsorbed over the Pt–Sn catalyst participate in non-selective C₃H₈/C₃H₆ transformations to C₂H₄ and CO_x.     

Optimization of Fischer‐Tropsch Process in a Fixed‐Bed Reactor Using Non‐uniform Catalysts

Optimization of Fischer‐Tropsch (FT) process in a fixed‐bed reactor is carried out using non‐uniform catalysts. The C₅⁺ yield of the reactions is maximized utilizing a combination of non‐uniform catalysts across the bed. A 1D heterogeneous model is developed to simulate the bed containing uniform and non‐uniform catalysts. It is found that the egg‐shell and surface‐layered catalysts result in higher C₅⁺ yield. Moreover, effects of cooling temperature are studied. Genetic Algorithm (GA) and Successive Quadratic Programming (SQP) methods are applied. Feed and cooling temperature are selected as decision variables together with distribution of non‐uniform catalysts along the bed. The optimization result shows 14.47 % increase in the C₅⁺ yield with respect to the base condition.     

Treatment of settled piggery waste by a down‐flow anaerobic fixed bed reactor

A study of the effect of organic volumetric loading rate (B_V) on the performance of a down‐flow anaerobic fixed bed reactor (DFAFBR) treating settled piggery waste was carried out at a range of between 1.1 and 6.8 g COD dm^?3 d^?1. The reactor operated at good removal efficiencies and stability under the operational conditions studied. Logarithmic empirical equations described adequately the removal efficiency for different parameters studied (COD, SCOD, BOD, TS, VS, TSS, VSS and phosphorous). Although process stability was affected by the increase of B_V, process failure was not observed. A logarithmic relationship was found to describe the influence of B_V on the TVFA/alkalinity ratio (p). A linear correlation was found between the effluent substrate concentration and the values of p and between p and the CO₂/CH₄ ratio in the biogas. The effect of the hydraulic volumetric loading rate (H_V) on the flow pattern of the reactor was evaluated. Dispersion number (D_n) was in the range of 0.17–0.37 for the maximum and minimum values of H_V studied, respectively. The ratio between the real and theoretical HRT increased as the H_V decreased. These results demonstrate that axial dispersion increased as the H_V and the Reynolds number decreased. Due to the hydraulic behaviour of the reactor, the kinetic model developed by Lawrence and McCarty was used for describing the experimental results obtained. Maximum specific substrate removal rate (K), specific organic loading rate constant (K_L), microbial decay coefficient (K_d), microbial yield coefficient (Y), maximum microbial growth rate (U_M) and saturation constant (K_S) were found to be: 3.1 (g COD g VSS^?1 d^?1), 3.0 (g COD g VSS^?1 d^?1), 0.062 (d^?1), 0.15 (g VSS g COD removed^?1), 0.39 (d^?1) and 2.6 (g SCOD dm^?3), respectively. Copyright © 2004 Society of Chemical Industry     

An ab initio electronic structure study of methyl adsorption and reaction on cluster models for the diamond surface

Electronic structure calculations were carried out for a series of hydrogen-terminated carbon clusters designed to model the 100- and 111-diamond surfaces, C_d(100) and C_d(111). The subjects of the calculations were: (1) methyl radical (CH_3^·) adsorption on an activated diamond surface; and (2) hydrogen abstraction from adsorbed methyl via reaction with gas-phase atomic hydrogen. The largest clusters were treated at the MP2/6-31G*//HF/6-31G* level of theory. The results of higher level calculations on smaller clusters were used to estimate corrections to the MP2/6-31G*//HF/6-31G* energies. It is concluded that methyl adsorption is 6.8 kcal mol⁻¹ more exothermic on C_d(100) than on C_d(111). Also, the barrier for hydrogen abstraction from methyl adsorbed on C_d(100) is 2.4 kcal mol⁻¹ lower than that for abstraction from methyl adsorbed on the C_d(111) surface. Finally, the abstraction reaction energy is 0.8 kcal mol⁻¹ lower for methyl adsorbed on C_d(100) compared to methyl adsorbed on C_d(111).     

The pyrolysis of benzonitrile

The pyrolysis of benzonitrile under nitrogen at atmospheric pressure has been studied at temperatures of 823–873 K in a flow reactor. The results demonstrate that conversion to hydrogen cyanide occurs directly by a free radical mechanism. The dominant products detected are hydrogen cyanide, monocyanodiphenyl, benzene, dicyanodiphenyl and dicyanobenzene. Reaction orders and activation energies have been determined for product formation. A reaction scheme involving three competing chain reactions in the gas phase with chain carriers H^., C₆H and ^.C₆H₄CN is proposed to explain the observed kinetics. A mechanism is advanced for the formation of significant quantities of polymer, consistent with infra-red spectra and elemental analysis.     

Ru-Mo/HZSM-5 Catalyzed Methane Aromatization in Membrane Reactors

Oxygen-free methane conversion into benzene was carried out in a catalytic membrane reactor over 0.5%Ru-3%Mo/HZSM-5 in the temperature range 873-973 K following three reaction protocols: (i) straight-run catalytic reactor without hydrogen permeation (OFF), (ii) cycled OFF/ON hydrogen permeation sequences, and (iii) cycled OFF/ON hydrogen permeation sequences intertwined with CH₄/H₂ regenerative steps. X-ray photoelectron spectroscopy analysis of fresh and spent catalysts identified, in all cases, three types of carbon species that formed during aromatization, including carbide formation. The presence of a permeating membrane did not give rise to different chemical states of carbon and molybdenum on the catalyst from those known to form in straight runs under no hydrogen permeation. The ON mode, i.e., during permeation, led to the accumulation of graphite-like and aromatic-aliphatic (coke) species on the catalyst. However, both types of carbon were reduced during the OFF step either by autogenous hydrogen or via an external source of hydrogen under CH₄/H₂ regenerative steps.     

Pyrolysis of wood at high temperature: The influence of experimental parameters on gaseous products

The pyrolysis of wood was carried out in an Entrained Flow Reactor at high temperature (650 to 950 °C) and under rapid heating conditions (> 10³ K s^− 1). The influence of the diameter and initial moisture of the particle, reactor temperature, residence time and the nature of the gaseous atmosphere on the composition of the gaseous products has been characterised. Particle size, between 80-125 and 160-200 μm, did not show any impact. Pyrolysis and tar cracking essentially happen in very short time period: less than 0.6 s; the products yields are only slightly modified after 0.6 s in the short residence times (several seconds) of our experiments. Higher temperatures improve hydrogen yield in the gaseous product while CO yield decreases. Under nitrogen atmosphere, after 2 s at 950 °C, 76% (daf) of the mass of wood is recovered as gases: CO, CO₂, H₂, CH₄, C₂H₂, C₂H₄ and H₂O. Tests performed under steam partial pressure showed that hydrogen production is slightly enhanced.     

Unusual Forms of Molecular Hydrogen Adsorption by Cu+1 Ions in the Copper-Modified ZSM-5 Zeolite

DRIFT and IR transmittance spectra of H₂ adsorbed at 77 K or at room temperature by the copper-modified ZSM-5 zeolite pre-evacuated or pre-reduced in CO at 873 K indicated several unusual forms of adsorbed hydrogen. H–H stretching frequencies of adsorbed species at 3075–3300 cm^–1 are by about 1000 cm<>^–1<> lower than in the free hydrogen molecules. This indicates unusually strong perturbation of adsorbed hydrogen by reduced Cu<>⁺¹<> ions that has been never before reported neither for hydrogen nor for adsorption of other molecules by any cationic form of zeolites or oxides.     

Expanding the chemistry of single‐ion conducting poly(ionic liquid)s with polyhedral boron anions

The synthesis of a new family of single‐ion conducting random copolymers bearing polyhedral boron anions is reported. For this purpose two novel ionic monomers, namely [B₁₂H₁₁(OCH₂CH₂)₂OC(?O)C(CH₃)?CH₂]^2?[(C₄H₉)₄N⁺]₂ and [8‐(OCH₂CH₂)₂OC(?O)C(CH₃)?CH₂‐3,3′‐Co(1,2‐C₂B₉H₁₀)(1′,2′‐C₂B₉H₁₁)]^?K⁺, having methacrylate function, diethylene glycol bridge and closo‐dodecaborate or cobalt bis(1,2‐dicarbollide) anions were designed. Such monomers differ from previously reported ones by (i) chemically attached highly delocalized boron anions, by (ii) valency of the anion (divalent anion and monovalent one) and by (iii) the presence of oxyethylene flexible spacer between the methacrylate group and bonded anion. Their free radical copolymerization with poly(ethylene glycol) methyl ether methacrylate and subsequent ion exchange provided lithium‐ion conducting polyelectrolytes showing low glass transition temperature (?53 to ?49 °C), ionic conductivity up to 9.1 × 10^?7 S cm^?1, lithium transference number up to 0.61 (70 °C) and electrochemical stability up to 4.1 V versus Li⁺/Li (70 °C). The incorporation of propylene carbonate (20–40 wt%) into the copolymers resulted in the enhancement of their ionic conductivity by one order of magnitude and significantly increased their electrochemical stability up to 4.7 V versus Li⁺/Li (70 °C). © 2019 Society of Chemical Industry     

Hydrogen mass transfer and mixing energy effects in SRC-II coal liquefaction reactors

This paper summarizes the experimental work performed on a bench-scale pre-pilot unit for investigating hydrogen mass transfer and mixing energy effects in SRC-II coal liquefaction reactors. Experiments were carried out with an Ireland Mine coal where the effects of mixing energy level (150–1000 rpm), method of hydrogen introduction (preheater flow and direct reactor sparging) and hydrogen treat rate (4 to 6 g of hydrogen/100 g of feed slurry) were investigated. Several runs using Powhatan No. 6 coal were also carried out where the effect of mixing energy level (200–1000 rpm) was investigated. Other run conditions were fixed to correspond to those likely to be used in commercial operation. The experimental results clearly indicated that below a mixing energy level corresponding to 400 rpm a significant cement-like solid deposition within the reactor (hydrogen mass transfer limitation) occurred. Below this mixing energy level the C₅+ liquid yield decreases, and the selectivity of the reaction changes, resulting in an increase in the C₁C₄ yield. This critical mechanical mixing level corresponds to a mixing energy per unit of reactor volume of ≈3500 ergs/cm³ s (350 watts m^?3). For the run conditions employed, increasing the preheater hydrogen flow from 4 to 6 g of $\text{H}{}_2\text{100 g}$ of slurry prevented the formation of solid deposits at a mechanical mixing energy level as low as that corresponding to 200 rpm. Furthermore, the highest C₅+ yield in the entire data set occurred when the preheater hydrogen flow was at the higher level.     

Effect of potassium ion on the stability and release rate of hydrogen peroxide encapsulated in silica hydrogels

Hydrogen peroxide (H₂O₂) is encapsulated in silica hydrogels using sol‐gel method and the effects of the K⁺ : Na⁺ ion ratio on gelation time, hydrogel structure, stability, and release rate of H₂O₂ were investigated. As the amount of K⁺ ions increased relative to the amount of Na⁺ ions at the same pH, the gel structure became less compact and the pore diameter increased. Hydrogen peroxide retention values up to 90 and 80% were observed at the end of 7 and 20 days, respectively, in the presence of K⁺ ions at low pH values when the initial H₂O₂ concentration was 19.9 wt %. Release rate of hydrogen peroxide decreased with decreasing pH for the two K⁺ : Na⁺ ion ratios studied. This work presents an environmentally friendly, low cost, and easy to scale up method to increase the stability of high initial concentrations of H₂O₂ at room temperature and customize the release rate. © 2016 American Institute of Chemical Engineers AIChE J, 63: 409–417, 2017     

Electro-oxidation of benzene in a fixed bed reactor

A fixed bed electrochemical reactor was used in the laboratory to oxidize benzene to quinone. The reactor consisted of a 3 mm thick bed of 1 mm lead shot, 0.5 m long by 0.05 m wide, sandwiched between a lead feeder plate and an asbestos diaphragm which was compressed against a stainless steel cathode plate. A dispersion of benzene in aqueous sulphuric acid was passed through the reactor and the rates of production of quinone, hydroquinone, carbon dioxide, oxygen and hydrogen, together with the cell voltage and pressure drop, were obtained for a range of operating conditions.Concentrations of quinone in the benzene product varied from 0.04 to 0.31 M and current efficiencies for quinone were in the range 22 to 55%. In a single pass of 1 M acid and benzene through the reactor at 25° C the quinone efficiency fell from 53% to 39% as the average superficial current density increased from 0.4 to 2.0 kA m^–2. At an average superficial current density of 2.0 kA m^–2 the quinone efficiency decreased with an increase in process temperature (25 to 50° C), but increased with increases in acid concentration (1 to 4 M), acid flow (0.5 to 1.0 cm³ s^–1), benzene flow (0.05 to 10 cm³ s^–1) and co-current nitrogen gas flow (0 to 32 cm³ s^–1 at STP). Recycling the 4 M sulphuric acid at 25° C raised the concentration of quinone in the product benzene but decreased the net current efficiency for quinone. Corresponding changes were observed in the cell voltage and in the current efficiencies for hydroquinone, carbon dioxide and oxygen. The results are discussed in terms of the process stoichiometry, electrode kinetics and mass transfer for three-phase flow in a fixed bed reactor.Nomenclature A Acid flow - a ₁ Liquid/liquid specific interfacial area - a _s Liquid/solid specific interfacial area - B Benzene flow - d ₃₂ Sauter mean drop diameter - d _P Particle diameter - E Current efficiency - F Faraday number - I Total current - i _l Superficial transfer-limited current density - K Liquid/liquid distribution coefficient - k _c Liquid/liquid mass transfer coefficient in continuous phase - k _s Liquid/solid mass transfer coefficient - L _c Superficial liquid load — continuous phase - L _d Superficial liquid load — disperse phase - Q _A Quinone concentration in aqueous phase - V ⁰ Standard electrode potential - z Number of electrons per equivalent     

Cyclopolymerization of Amino Acid-Based Diynes and Properties of the Obtained Polymers. Chiral Recognition and Metal Ion Extraction

Summary Cyclopolymerization of amino acid-derived novel dipropargyl ester and dipropargylamide was carried out using a rhodium catalyst. Polymers with cyclized structures were obtained under certain conditions. The dipropargylamide polymer exhibited a large specific rotation and an intense Cotton effect around 300 nm based on the chiral higher order structure. It adsorbed N-benzyloxycarbonyl-L-alanine more than the D-isomer, and extracted Li⁺, Na⁺, K⁺, and Cs⁺ from water phase into CH₂Cl₂ phase.     

An In Situ ESR Study of Pd/H-ZSM-5 Interaction with Different Adsorbents

In situ ESR at 120–473 K permits to monitor formation of transient paramagnetic ions/complexes (isolated Pd⁺ sites; Pd⁺/H₂O; Pd⁺/C₆H₆) upon interaction of isolated Pd²⁺ cations stabilized by the H-ZSM-5 matrix with different organic compounds and gas mixtures (NO, O₂, H₂O, H₂, propene, benzene). The in situ study provides insight into the elementary steps of redox processes on isolated Pd species in H-ZSM-5 zeolite under realistic conditions. Adsorbed water stabilizes the transient paramagnetic complex and decreases the rate of Pd²⁺ to Pd⁰ reduction by H₂. Strong bonding of NO _x ligands to Pd²⁺ species suppresses the reduction of Pd(II) ions. Sorption of benzene on preoxidized Pd²⁺/HZSM-5 is accompanied by an easy formation of organic cation-radicals and of a Pd⁺/benzene complex, the paramagnetic Pd⁺/benzene structure indicating a surprisingly high resistance to further reduction to Pd⁰. Illumination of the Pd/HZSM-5 by UV-visible light causes no measurable change in the redox properties of the catalyst.     

The electrochemical hydrogenation of edible oils in a solid polymer electrolyte reactor. I. Reactor design and operation

A new electrochemical method has been devised and tested for the moderate temperature/atmospheric pressure hydrogenation of edible oils, fatty acids, and fatty acid methyl esters. The method employed a solid polymer electrolyte (SPE) reactor, similar to that used in H₂/O₂ fuel cells, with water as the source of hydrogen. The key component of the reactor was a membrane-electrode-assembly, composed of a RuO₂ powder anode and either a Pt-black or Pd-black powder cathode that were hot-pressed as thin films onto the opposing surfaces of a Nafion cation-exchange membrane. During reactor operation at a constant applied current, water was back-fed to the RuO₂ anode, where it was oxidized electrochemically to O₂ and H⁺. Protons migrated through the Nafion membrane under the influence of the applied electric field and contacted the Pt or Pd cathode, where they were reduced to atomic and molecular hydrogen. Oil was circulated past the back side of the cathode and unsaturated triglycerides reacted with the electrogenerated hydrogen species. The SPE reactor was operated successfully at a constant applied current density of 0.10 A/cm² and a temperature between 50 and 80°C with soybean, canola, and cottonseed oils and with mixtures of fatty acids and fatty acid methyl esters. Reaction products with iodine values in the range of 60–105 were characterized by a higher stearic acid content and a lower percentage of trans isomers than those produced in a traditional hydrogenation process.     

The conductance of 1:1 electrolytes in sulfolane in the presence of proton donors at 30°C

The molar conductances of LiCl, LiNO₃, KCHCl₂COO and Na p-(NO₂)C₆H₄O in sulfolane, in the presence of HCl, CH₃COOH, CHCl₂COOH and p-(NO)₂C₆H₄OH have been determined. The data were analysed by the full Pitts equation and interpreted in terms of the ionic association constant (K_A) of the salts K⁺A^? and K⁺RHA^?, and the heteroconjugation constant (K_f) of RHA^?. Values of K_f have been calculated from the ratio of association constant K_A(K⁺A^?)/K_A(K⁺RHA^?).