The thermodynamics of benzene adsorption on carbon obtained by the pyrolysis of hypercrosslinked polystyrene

The Glukauf chromatography method was used to study the adsorption of benzene on a microporous carbon material prepared by the pyrolysis of hypercrosslinked polystyrene. The thermodynamic characteristics of adsorption were determined as functions of the degree of pore filling. Over the range of relative pressures studied (<0.005), adsorption was shown to occur in ultramicropores by the mechanism of primary filling without condensed phase formation. Original Russian Text ? L.D. Asnin, V.A. Davankov, A.V. Pastukhov, K. Kaczmarski, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 7, pp. 1356–1359.     

Characterization of the liquid product recovered through pyrolysis of PMMA-ABS waste

Thermal decomposition of waste polymethylmethacrylate-acrylonitrile-butadiene-styrene (PMMA-ABS) blend has been carried out using analytical and lab-scale pyrolysis methods in order to identify the substantial components appearing in the liquid product. Additionally decomposition characteristics of the blend have been investigated regarding the possible interrelation between the two components during the pyrolysis. The interactions between PMMA and ABS seem to modify the decomposition characteristics of the ABS, resulting in a lower degradation temperature than that of pure ABS. Moreover the simultaneous decomposition results in recombination of the products yielding new volatile compounds. During batch pyrolysis relatively high amount of gas production was observed, that is in contradiction with the results obtained by analytical pyrolysis and the data found in the literature where pyrolysis of the PMMA as well as the ABS was reported to yield low amount of gas products. The liquid product retrieved from thermal decomposition has been analyzed with respect to the possible utilization as a propellant. Hence aside from the investigation of contained elements and compounds, determination of density, viscosity, research octane number (RON), calorific value, and gaseous emissions has been carried out as well. The relatively high yield (65 wt%), and outstanding compression tolerance (RON = 110.2) observed at the pyrolysis oil make it a feasible fuel admixture.     

Model-free kinetics analysis of ZSM-5 catalyzed pyrolysis of waste LDPE

Both thermal and catalytic decomposition of waste LDPE sample is studied to understand the effect of catalyst (ZSM-5) on the decomposition behaviour. The nonlinear Vyazovkin model-free technique is applied to evaluate the quantitative information on variation of E_α with α for waste LDPE sample under both catalytic and noncatalytic nonisothermal conditions. The literature reported data on such variation under noncatalytic condition and effects of different catalysts on the LDPE sample are compared with the results of the present study.Results show that the optimum catalyst composition is around 20 wt.%, where the reduction in maximum decomposition temperature is around 70 °C. Presence of ZSM-5 shows similar reduction in maximum decomposition temperature as reported for Al-MCM-41 and MCM-41. Similar trend to literature reported data is observed for variation of E_α with α for LDPE under nonisothermal noncatalytic condition. ZSM-5 catalyzed decomposition of the LDPE sample in the present study indicates that E_α is strong and increasing function of α and consists of four steps. Cracking of large polymer fragments on the external surface of the catalyst, oligomerization, cyclization, and hydrogen transfer reactions inside the catalyst pores might be the possible reaction mechanisms involved during catalytic decomposition.     

Detailed mechanistic modeling of high-density polyethylene pyrolysis: Low molecular weight product evolution

A detailed, mechanistic model for high-density polyethylene pyrolysis was created based on the modeling framework developed in our previous work and was used to study the time evolution of low molecular weight products formed. Specifically, the role that unzipping, backbiting, and random scission reaction pathways play in the evolution of low molecular weight species was probed. The model tracked 151 species and included over 11,000 reactions. Rate parameters were adapted from our previous work, literature values, and regression against experimental data. The model results were found to be in excellent agreement with experimental data for the evolution of condensable low molecular weight products. The time evolution curves of specific low molecular weight products indicated that the random scission pathway was important for all species, while the backbiting pathway played a complementary role. Net rate analysis was used to further elucidate the competition between the pathways. Net rate analysis of end-chain radicals showed that the unzipping pathway was not competitive with the other pathways, as expected based on experimental yields of ethylene. The random scission pathway was found to be controlling, with the backbiting pathway playing a more minor role for product formation. By comparing the net rates for formation of specific mid-chain radicals via intramolecular hydrogen shift reactions, the contribution of the backbiting pathway was shown to vary, with radicals formed via the most facile x,x + 4-intramolecular hydrogen transfer reactions being favored.     

Adsorption of methylene blue dye from aqueous solution by agricultural waste: Equilibrium,thermodynamics, kinetics,mechanism and process design

The adsorption of methylene blue (MB) dye from aqueous solution onto a cashew nut shell (CNS) was investigated as a function of parameters such as solution pH, CNS dose, contact time, initial MB dye concentration and temperature. The CNS was shown to be effective for the quantitative removal of MB dye, and the equilibrium was reached in 60 min. The experimental data were analysed by two-parameter isotherms (Langmuir, Freundlich, Temkin and Dubinin-Radushkevich models) using nonlinear regression analysis. The characteristic parameters for each isotherm and the related correlation coefficients were determined. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were also evaluated, the sorption process was found to be spontaneous and exothermic. Pseudo-first-order, pseudo-second-order and Elovich kinetic models were used to analyze the adsorption process. The results of the kinetic study suggest that the adsorption of MB dye matches the pseudo-second-order equation, suggesting that the adsorption process is presumably chemisorption. The adsorption process was found to be controlled by both surface and pore diffusion. Analysis of adsorption data using a Boyd kinetic plot confirmed that the external mass transfer is a rate determining step in the sorption process. A single-stage batch adsorber was designed for different CNS doses to effluent volume ratios using the Freundlich equation. The results indicated that the CNS could be used effectively to adsorb MB dye from aqueous solutions.     

Non-isothermal thermogravimetric pyrolysis kinetics of waste petroleum refinery sludge by isoconversional approach

Pyrolysis of petroleum refinery sludge has received global acclamation as a clean conversion technique for providing solution of sludge disposal as well as efficient resource utilization. This communication reports the kinetics study of pyrolysis of petroleum refinery sludge. Experiments were carried out by means of thermogravimetric analysis at different heating rates of 5, 10 and 20°C min⁻¹. The pyrolytic reaction is significant in the temperature range of 200–350°C and analysis and evaluation of kinetic parameters is done in the 100–500°C region of non-isothermal TG curves obtained in nitrogen atmosphere. The activation energy is calculated by iso-conversional method, then other kinetic parameters are determined by considering single reaction and two reaction global kinetic model. Two-reaction model is found to fit satisfactorily the experimental results.     

矿物质对桦甸油页岩热解产物影响特性

对桦甸油页岩进行逐级酸洗并对原样及各级酸洗样品的热解产物进行了碳平衡计算以及气相色谱和傅里叶红外光谱实验,得到了矿物质对油页岩热解不凝性气体、半焦以及页岩油的影响特性。结果表明,碳酸盐可以促进有机碳和氢向页岩油中转化,而硅酸盐对有机碳和氢向页岩油中转化具有抑制作用,碳酸盐和硅酸盐均可以使得页岩油中氢碳原子比降低。碳酸盐促进了油页岩热解产油并抑制了干酪根向不凝气分解转化,而硅酸盐抑制了油页岩热解产油但对干酪根向不凝气的分解转化具有促进作用。碳酸盐和硅酸盐均可以促进热解不凝气中CO_2和H_2的生成,而对CO的生成具有抑制作用,碳酸盐可以抑制热解不凝气中碳氢化合物的生成,而硅酸盐对其生成具有促进作用。碳酸盐和硅酸盐均可以使得页岩油中脂肪链长度变短及异构化程度变大,并能够提高干酪根热解产物的芳构化程度。     

The pyrolysis of dimethyl sulfide,kinetics and mechanism

The kinetics of the gas phase pyrolysis of dimethyl sulfide (DMS) was studied in a static system at 681–723 K by monitoring total pressure-time behavior. Analysis showed the pressure increase to follow DMS loss. The reaction follows two concurrent paths: with a slow, minor, secondary reaction: In a seasoned reactor the reaction follows a 3/2 order rate law with rate coefficient given by with θ = 2.303 RT in kcal/mol. A free radical mechanism is proposed to account for the data and a theoretical rate coefficient is derived from independent data: which agrees well with the experimental one over the range studied. The reaction is initiated by Me₂S → Me + MeS? and propagated by metathetical radical attack on Me₂S. C₂H₄ is formed by an isomerization reaction which may in part be due to a hot radical: Thermochemical data are listed, many from estimations, for both molecular and radical species of interest in the present system.     

Mechanistic analysis and thermochemical kinetic simulation of the pathways for volatile product formation from pyrolysis of polystyrene, especially for the dimer

Simulations of the initial distribution of volatiles from pyrolysis of polystyrene were based on propagation rate constants estimated by thermochemical kinetic procedures. The voluminous database exhibits a disturbing lack of consistency with respect to effects of conversion level, temperature, and reactor type. It therefore remains difficult to assign the true primary distribution of the major products, styrene, 2,4-diphenyl-1-butene (“dimer”), 2,4,6-triphenyl-1-hexene (“trimer”), 1,3-diphenylpropane, and toluene, and its dependence on conditions. Probable perturbations by secondary reactions and selective evaporation are considered. The rate constant for 1,3-hydrogen shift appears much too small to accommodate the commonly proposed “back-biting” mechanism for dimer formation. Dimer more likely arises by addition of benzyl radical to olefinic chain-ends, followed by β-scission, although ambiguities remain in assigning rate constants for the addition and β-scission steps. With this modification, the major products can be successfully associated with decay of the sec-benzylic chain-end radical. In contrast, the minimal formation of allylbenzene, 2,4-diphenyl-1-pentene, and 2,4,6-triphenyl-1-heptene suggests a minimal chain-propagating role for the prim chain-end radical. Compared with polyethylene, the much enhanced “unzipping” to form monomer from polystyrene and the more limited depth of “back-biting” into the chain arise from an enthalpy-driven acceleration of β-scission coupled with a kinetically driven deceleration of intramolecular hydrogen transfer. In contrast, the greater “unzipping” of poly(isobutylene) compared with polyethylene is proposed to result from relief of steric strain.     

Tautomerism of pyrimidyl-2-methane derivatives: medium effects,thermodynamics, kinetics and mechanism

The Investigation of tautomeric equilibria among pyrimidyl-2-methanes has been undertaken. Pyrimidyl-pyrimidyledene equilibrium has been found in the case of 5-substituted 2-pyrimidyl-cyanoacetic esters. Unsymmetrically substituted pyrimidyl-2-methanes form two types (1-NH and 3-NH) of ylidene tautomers, which differ in ring proton spin coupling constants. The effect of substituents in the pyrimidine ring and of the solvent on tautomeric equilibrium are discussed. A drastic effect is produced by acids (CF₃ COOH) which shift the equilibrium toward the ylidene tautomer of higher basicity. The thermodynamic and kinetic characteristics and the mechanism of the tautomeric equilibrium were examined.     

Retention, kinetics and thermodynamics profile of cadmium adsorption from iodide medium onto polyurethane foam and its separation from zinc bulk

The sorption behaviour of 2.5 × 10⁻⁵ M solution of Cd(II) on polyurethane foam (PUF) from iodide medium have been investigated. The conditions were optimized from aqueous solutions of different pH (1-10) and of acids of varied concentration (0.01-1.0 M). The maximum concentration of KI was found to be 0.24 M and equilibration time was established to be 20 min. The data successfully followed the Freundlich and Dubinin-Radushkevich (D-R) isotherms at low metal ion concentration while Langmuir isotherm followed at higher metal ion concentration. The Freundlich parameter 1/n = 0.66 ± 0.02 have been evaluated whereas D-R isotherm yields the sorption free energy E = 10.5 ± 0.1 kJ mol⁻¹ indicating ion exchange type chemisorption. The monolayer coverage (XL) constant of Langmuir isotherm was found to be 23.7 ± 0.4 mg g⁻¹. The numerical values of thermodynamics parameters enthalpy (ΔH), entropy (ΔS) and Gibbs free energy (ΔG) indicated the endothermic and spontaneous nature of sorption. The Scatchard plot analysis was tested to evaluate the binding sites of the PUF and stability constants of sorption were determined. On the basis of these parameters, the sorption mechanism was discussed. Among the foreign ions tested, Pb(II), Hg(II), cyanide and nitrite should be absent. The clean separation of Cd(II) from Zn(II) ions in the ratio 1:250, respectively, was achieved by column chromatography.     

Removal of nickel ions by adsorption on nano-bentonite: Equilibrium,kinetics, and thermodynamics

Nano-bentonite was used as an adsorbent to remove nickel ions from aqueous solutions. Experimental investigation was carried out to identify the effect of pH, contact time, initial concentration, and adsorbent dose of Ni(II). Equilibrium data were described by and fitted to Langmuir, Freundlich, and Dubinin–Radushkevich models. Results showed that the optimum conditions for the removal of the Ni(II) are initial concentration 100 mg/L, adsorbent dose 0.5 g, and pH 6. Surface morphology and functionality of nano-bentonite were characterized by SEM and FTIR. The kinetics data were more accurately described by pseudo-second-order model. The intra-particle diffusion model gave multi-linear curves, so more than one step controlled the adsorption process. Nano-bentonite removed nickel with maximum adsorption capacity of 39.06 mg/g (30°C, pH) and thermodynamic data indicated that adsorption reaction is spontaneous and of an endothermic nature.     

Organoactinides promote the dimerization of aldehydes: scope, kinetics, thermodynamics, and calculation studies

Surprising catalytic activities have been found for the actinide complexes Cp*(2)ThMe(2) (1), Th(NEtMe)(4) (2), and Me(2)SiCp'(2)Th(C(4)H(9))(2) (3) toward oxygenated substrates. During the catalytic dimerization of benzaldehydes to their corresponding esters, complexes 1 and 2 gave 65 and 85% yield in 48 h, respectively, while the geometry-constrained complex 3 gave 96% yield in 24 h. Exploring the effect of substituents on benzaldehyde, it has been found that, in general, electron-withdrawing groups facilitate the reaction. Kinetic study with complexes 1 and 3 reveals that the rate of the reaction is first order in catalyst and substrate, which suggests the rate equation "rate = k[catalyst](1)[aldehyde](1)". The activation energy of the reaction was found to be 7.16 ± 0.40 and 3.47 ± 0.40 kcal/mol for complexes 1 and 3 respectively, which clearly indicates the advantage of the geometry-constrained complex. Astonishing are the reactivity of the organoactinide complexes with oxygen-containing substrates, and especially the reactivity of complex 3, toward the dimerization of substrates like p-methoxybenzaldehyde, m/p-nitrobenzaldehyde, and furanaldehyde and the reactivity toward the polymerization of terephthalaldehyde. Density functional theory mechanistic study reveals that the catalytic cycle proceeds via an initially four-centered transition state (+6 kcal/mol), followed by the rate-determining six-centered transition state (+13.5 kcal/mol), to yield thermodynamically stable products.     

Crystallization kinetics of isotactic polystyrene from isotactic-atactic polystyrene blends

In an attempt to facilitate a better understanding of the role of noncrystallizable components on the crystallization kinetics, spherulitic growth rates as well as the morphology and melting behavior of isotactic polystyrene in blends with various molecular weight atactic polystyrenes (900 to 1,800,000) over a wide range of concentrations have been studied. The growth rates are uniformly depressed with increasing amounts of atactic diluent. In addition, they are dependent on the molecular weight of the added polystyrene, generally decreasing in the molecular weight ranges between 4800 and 19,800 and between 51,000 and 1,800,000. However, between these two ranges, anomalous growth rates showing a sudden increase are observed, which may be explained by an increase in the entrapment of the noncrystallizable diluent. An explanation based on morphological observations, which showed an increase in coarseness of the spherulites with increasing molecular weight of the added atactic polystyrene, is offered.     

Valorization of two waste streams into activated carbon and studying its adsorption kinetics,equilibrium isotherms and thermodynamics for methylene blue removal

Wastes must be managed properly to avoid negative impacts that may result. Open burning of waste causes air pollution which is particularly hazardous. Flies, mosquitoes and rats are major problems in poorly managed surroundings. Uncollected wastes often cause unsanitary conditions and hinder the efforts to keep streets and open spaces in a clean and attractive condition. During final disposal methane is generated, it is much more effective than carbon dioxide as a greenhouse gas, leading to climate change. Therefore, this study describes the possible valorization of two waste streams into activated carbon (AC) with added value due to copyrolysis. High efficiency activated carbon was prepared by the copyrolysis of palm stem waste and lubricating oil waste. The effects of the lubricating oil waste to palm stem ratio and the carbonization temperature on the yield and adsorption capacity of the activated carbon were investigated. The results indicated that the carbon yield depended strongly on both the carbonization temperature and the lubricating oil to palm stem ratio. The efficiency of the adsorption of methylene blue (MB) onto the prepared carbons increased when the lubricating oil to palm stem ratio increased due to synergistic effect. The effects of pH, contact time, and the initial adsorbate concentration on the adsorption of methylene blue were investigated. The maximum adsorption capacity (128.89 mg/g) of MB occurred at pH 8.0. The MB adsorption kinetics were analyzed using pseudo-first order, pseudo-second order and intraparticle diffusion kinetic models. The results indicated that the adsorption of MB onto activated carbon is best described using a second order kinetic model. Adsorption data are well fitted with Langmuir and Freundlich isotherms. The thermodynamic parameters; ΔG°, ΔH° and ΔS° indicate that the adsorption is spontaneous and endothermic.     

Iridium-catalyzed dehydrogenation of substituted amine boranes: kinetics, thermodynamics, and implications for hydrogen storage

Dehydrogenation of amine boranes is catalyzed efficiently by the iridium pincer complex (kappa (3)-1,3-(OP ( t )Bu 2) 2C 6H 3)Ir(H) 2 ( 1). With CH 3NH 2BH 3 (MeAB) and with AB/MeAB mixtures (AB = NH 3BH 3), the rapid release of 1 equiv of H 2 is observed to yield soluble oligomeric products at rates similar to those previously reported for the dehydrogenation of AB catalyzed by 1. Delta H for the dehydrogenation of AB, MeAB, and AB/MeAB mixtures has been determined by calorimetry. The experimental heats of reaction are compared to results from computational studies.     

Mechanisms of thermal degradation of polystyrene,polymethacrylonitrile, and their copolymers on flash pyrolysis

The mechanism of thermal degradation of homopolymers of styrene (St) and methacrylonitrile (MAN) and their copolymers was investigated theoretically and experimentally by the pyrolysis gas chromatography using a Curie-point pyrolyzer. Poly(St-co-MAN)s generate dimers and trimers as well as monomers by flash pyrolysis. Parameter α was proposed to account for the competition between the back-biting reaction and depolymerization. The back-biting parameter α is defined as the ratio of rate constants, α = k_bb/k_dp, where k_bb is the rate constant for the back-biting reaction and k_dp is that for depolymerization. The back-biting process is followed by β-scission, where dimer and trimer are generated, and directly correlated with the C—H bond dissociation energies in the polymer chain. Using the back-biting parameter α, where 1/α is equal to the zip length n in depolymerization, the boundary effect for the difference of monomer yields from the homopolymers of St and MAN and their copolymers is well explained. The calculated values of boundary effect parameters, β_St and β_MAN, agreed well with the experimental results. It was found that thermal degradation mechanisms of homo- and copolymers of vinyl compounds can be analyzed comprehensively using the back-biting parameter α and the boundary effect parameter β. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2315–2330, 1998     

Aluminum hydride for solid-state hydrogen storage:Structure,synthesis, thermodynamics,kinetics, and regeneration

Aluminum hydride(AlH3) is a binary metal hydride that contains more than 10.1 wt% of hydrogen and possesses a high volumetric hydrogen density of 148 kg H2 m^-3.Pristine AlH3 can readily release hydrogen at a moderate temperature below 200℃.Such high hydrogen density and low desorption temperature make AlH3 one of most promising hydrogen storage media for mobile application.This review covers the research activity on the structures,synthesis,decomposition thermodynamics and kinetics,regeneration and application validation of AlH3 over the past decades.Finally,the future research directions of AlH3 as a hydrogen storage material will be revealed.