Pyrolysis of hydrocarbon mixtures characteristic of coal: Application to dibenzyl mixture

Thermal cracking of dibenzyl dissolved in two solvents, tetralin and decalin, has been studied in a flow reactor, in the presence of steam, under atmospheric pressure and at temperatures between 600 and 750 °C. The nature of the products obtained depends upon the structure of the hydrogen-donor agent, but is independent of the structure of dibenzyl. Valuable products such as ethylene and a benzene, toluene and xylene (BTX) mixture, obtained by a β-scission reaction with a monomolecular mechanism, are predominant when decalin is used as solvent. The dehydrogenation of tetralin to naphthalene precedes cracking reactions of the bimolecular type, which lead to significant production of hydroaromatics such as indene. Cracking of dibenzyl, followed by hydrogen transfer from the solvent to the radicals formed, leads to toluene irrespective of the chemical nature of the hydrogen donor.     

Anionic ring‐opening polymerization of adipic anhydride initiated by potassium poly(ethylene glycol)ate

Poly(adipic anhydride) (PAA) was prepared by the ring‐opening polymerization of adipic anhydride (AA) initiated by potassium poly(ethylene glycol)ate. The effects of various factors, such as the amount of initiator, concentration of the monomer, reaction time and temperature, and polarity of the solvent on the polymerization were investigated. The crude polymerized product was a mixture of PAA homopolymer and poly(ethylene glycol)–poly(adipic anhydride) block copolymer, as confirmed by ¹H‐NMR and gel permeation chromatography. Chain‐transfer reactions occurred intensively for the AA polymerization in both the nonpolar solvent toluene and the polar solvents CHCl₃ and tetrahydrofuran, which predominantly determined the molecular weight and the monomer conversion for the polymerized product. The lower monomer conversion in toluene was ascribed to a lower livingness for the initiator in the nonpolar solvent when compared with other two, polar solvents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2194–2201, 2003     

Grafting of low density poly(ethylene) with butyl acrylate: Synthesis and characterisation

Low density poly(ethylene) was grafted with butyl acrylate using benzoyl peroxide as free radical initiator in an inert atmosphere and toluene as solvent. Various parameters such as reaction time, temperature, initiator concentration and ratio of monomer to polymer were varied to study their effects on percentage of grafting and grafting efficiency of butyl acrylate on to low density poly(ethylene). The graft copolymers were characterised by IR spectroscopy. The change in the solubility behaviour of low density poly(ethylene) due to grafting was studied by turbidometric titration. Thermal stability of graft copolymers was found to be higher than that of LDPE. Intrinsic viscosity data showed an increase in viscosity with increasing grafting percentage.     

Solvent and oxidant effects on the Au/TiO2-catalyzed aerobic epoxidation of stilbene

Molecular oxygen can be used as the main oxidant to selectively epoxidize trans-stilbene over Au/TiO₂ catalysts, in a free-radical process. However, the nature of the radical initiator has a critical influence on the reaction selectivity. tert-Butylhydroperoxide (TBHP, catalytic amount) leads to high yields of epoxide; on the other hand, hydrogen peroxide and di-tert-butylperoxide merely cause degradation of trans-stilbene. The choice of the solvent is also critical. Amongst the selected solvents, only alkyl-substituted cyclohexanes lead to high yields of epoxide, despite the poor dispersion of the catalytic powder. Other solvents, including the more polar ones and cyclohexane, are significantly less efficient, both in terms of total activity and epoxide production. The latter does not go beyond the yield expected from the potential stoichiometric reaction between TBHP and trans-stilbene (5%). On the basis of these results, an aerobic epoxidation mechanism is proposed in which molecular oxygen is activated by a substituted cyclohexyl radical produced by abstraction of a tertiary hydrogen atom from the solvent molecule by a tert-butylperoxy radical.     

GC/MS and PGC/MS analyses of plasma polymerization for benzaldehyde

Gas chromatography/mass spectrometry studies of gas condensates in plasma and pyrolysis products of plasma polymer for benzaldehyde were made. Both products' analyses indicate the significant presence of benzyl and carbonyl groups in plasma polymer samples. Infrared measurements were also used to correlate the structures suggested by GC/MS results. A radical mechanism, which involved hydrogen abstraction, aldehyde group abstraction, and benzyl fragmentation under plasma activation, was proposed. The highly crosslinked and branched structures of the plasma polymer were attributed to the subsequent reactivity of free radicals, formed as a result of the scission of the chemical bonds in the benzaldehyde molecules.     

Electrochemical oxidation of aliphatic hydrocarbons promoted by inorganic radicals. II. NO3 radicals

The anodic electrolysis of linear alkanes in tert-butanol/H₂O solutions containing HNO₃ and saturated with oxygen at P_{O 2}=1 atm results in the partial oxidation of the hydrocarbons to the corresponding isomeric ketones. The experimental data are in support of a mechanism in which the first steps are: (1) one-electron transfer from the nitrate ion to the anode to give a nitrate radical; (2) hydrogen abstraction by the nitrate radical on the aliphatic substrate to give an alkyl radical; (3) molecular oxygen addition by the alkyl radical and formation of peroxy radicals. These species decay by bimolecular reactions and a carbonyl function is formed. The isomer distribution is in excellent accord with a statistical H abstraction from the secondary C–H bonds.     

The thermal degradation of polystyrene nanocomposite

Nanocomposite formation brings about an enhancement of many properties for a polymer, including enhanced fire retardancy. This study was carried out to determine if the presence of clay causes changes in the degradation pathway of polystyrene. In the case of virgin PS, the degradation pathway is chain scission followed by β-scission (depolymerization), producing styrene monomer, dimer and trimer, through an intra-chain reaction. As the clay loading is increased, the evolved products produced through inter-chain reactions become significant. Due to the barrier effect of the clay layers, the radicals have more opportunity to undergo radical transfer, producing tertiary radicals, and then radical recombination reactions, producing head-to-head structures, and hydrogen abstraction from the condensed phase also occurs. In the presence of clay, the color of solid residues darkens as the clay content increases. It is thought that this color change is caused by the formation of conjugated double bonds in the presence of clay.     

Synthesis and reactions of a polyfunctional macroinitiator based on manganese carbonyl: uses in graft copolymerization

The rapid reaction between polytetrafluoroethylene radicals and the benzene ring has been utilized in synthesizing a polyfunctional macroinitiator. For this purpose a copolymer of styrene and methyl methacrylate in acetic acid solution was allowed to react with polytetrafluoroethylene radicals generated photochemically from the monomer and manganese carbonyl. Analogy with the reactions of benzene, which have now been further studied, suggests that the radicals undergo both addition and substitution reactions with aromatic nuclei in the copolymer, so that the final copolymer carries grafts of short polytetrafluoroethylene chains with Mn(CO)₅ end-groups. At 100°C scission of CF₂Mn(CO)₅ bonds occurs with formation of active radicals, so that the copolymer behaves as a polyfunctional macroinitiator. A study of the initiation mechanism is reported which shows that elimination of carbon monoxide precedes rupture of the CF₂Mn(CO)₅ bond. Applications of the macroinitiators are exemplified by network formation on heating in styrene and graft polymerization with poly(N-vinyl-2-pyrrolidone). Reaction between poly(methyl methacrylate) and polytetrafluoroethylene radicals proceeds through hydrogen abstraction and radical recombination. It occurs less readily than interaction of the radicals with the copolymer, so that, for comparable conditions, the polytetrafluoroethylene grafts are longer and the product is less soluble.     

Experimental and kinetic modeling study of the oxidation of n-propylbenzene

The oxidation of n-propylbenzene was studied experimentally in a jet-stirred reactor at atmospheric pressure over the high temperature range 900-1250 K, and for variable equivalence ratio (0.5≤φ≤1.5). Concentration profiles of 23 species (reactants, stable intermediates and final products) were measured by probe sampling followed by on-line and off-line GC analyses. For the first time, the oxidation of n-propylbenzene was modeled using a detailed chemical kinetic reaction mechanism (124 species and 985 reactions, most of them reversible) also validated for the oxidation of benzene and toluene. Sensitivity analyses and reaction path analyses, based on species rates of reaction, were used to interpret the results. The routes involved in n-propylbenzene oxidation have been delineated: n-propylbenzene oxidation proceeds via thermal decomposition yielding benzyl and 2-phenyl-1-ethyl, and by H-atom abstraction yielding phenylpropyl radicals. Recombination reactions of benzyl with methyl and H yield ethybenzene and toluene, respectively, whereas the oxidation of these radicals yields benzaldehyde. Phenylpropyl radicals react by β-scission yielding ethylene, styrene and propene. The isomerization of 1-phenyl-2-propyl to 2-phenyl-1-propyl reduces the importance of propene formation and increases that of styrene.     

Electrochemical production of OH. radicals and their reaction with toluene

The reaction between electrochemically generated Fenton's reagent and toluene was studied. The products arising from this reaction system were consistent with a primary hydrogen atom abstraction from the methyl group of toluene to give benzyl radicals.Benzaldehyde was obtained with a current yield higher than 60%; benzyl alcohol was also produced in smaller quantities in some experiments. The dependence of the yields on reagent concentrations, temperature and coulombs passed was examined. On the basis of the experimental results a mechanism is proposed involving peroxy and alkoxy radicals as intermediates.     

Investigation of organic solvent/oil sorption capabilities of phenylene-bridged cross-linked poly(alkoxysilane)s

Phenylene-bridged cross-linked poly(alkoxysilane)s produced by the condensation of 1,4-bis(triethoxysilyl) benzene (BTEB) with different lengths of aliphatic diols in proper stoichiometric ratios were successfully prepared. The synthesized phenylene-bridged poly(alkoxysilane)s were characterized by Fourier transform infrared spectroscopy (FTIR), solid-state ¹³C and ²⁹Si cross polarization magic angle spinning nuclear magnetic resonance (CP-MAS NMR), and thermal gravimetric analysis (TGA). The oil and organic solvent uptake capacity, reusability, absorption and desorption kinetics of cross-linked polymers were examined. The effect of chain length of the linear diol monomers on the polymer-solvent interaction was also investigated. The swelling experiments were conducted in oils such as gasoline, euro diesel and organic solvents such as dichloromethane, tetrahydrofuran, benzene and toluene. All the synthesized polymers have high and fast swelling properties in oils and organic solvents. The reutilize properties of polymer in organic solvents were also investigated.     

Synthetic hydrogels. 1. Effects of solvent on poly(acrylamide) networks

Acrylamide hydrogels were synthesized in a series of hydro-organic solvents to examine how solvent affects the network structure by influencing properties of the first formed polymer in the reaction mixture. The looser and more heterogeneous network structure of gels formed in aqueous solutions of ethylene glycol or propylene glycol was found to be largely due to the reduced chain lengths of the primary polymer molecules. Results from NMR analysis of the monomer, and intrinsic viscosity measurements of the polymer in various solvents indicate that solvent effects on the reactivity of the monomer and the propagating radical impose an overriding control over properties of the resultant networks.     

NUMERICAL SOLUTION OF UNSTEADY CONVECTIVE DIFFUSION WITH CHEMICAL REACTION IN TIME DEPENDENT FLOWS

An earlier computer model for tubular high pressure polyethylene reactors is extended to take into account two radical generating sources, in addition to an injected initiator: a long-lived intermediate, possibly generated from the interaction of ethylene with trace amounts of oxygen, and the ethylene itself undergoing thermal polymerization. The first of these reactions can account for the smoothing of the temperature profile near the peak temperature, attributed by Lee to initiator and radical carryover; the second, whose inclusion is justified by experiments recently performed by Buback, can account for the explosive decomposition of ethylene known to occur in LDPE reactors if the temperature is allowed to exceed about 350°C, and it also can contribute significantly to polymer production at very high temperatures. The contribution of both reactions must be evaluated quantitatively, if reliable heat transfer coefficients are to be obtained from experiment.     

AN IMPROVED MODEL FOR TEMPERATURE AND CONVERSION PROFILES IN TUBULAR HIGH PRESSURE POLYETHYLENE REACTORS

An earlier computer model for tubular high pressure polyethylene reactors is extended to take into account two radical generating sources, in addition to an injected initiator: a long-lived intermediate, possibly generated from the interaction of ethylene with trace amounts of oxygen, and the ethylene itself undergoing thermal polymerization. The first of these reactions can account for the smoothing of the temperature profile near the peak temperature, attributed by Lee to initiator and radical carryover; the second, whose inclusion is justified by experiments recently performed by Buback, can account for the explosive decomposition of ethylene known to occur in LDPE reactors if the temperature is allowed to exceed about 350°C, and it also can contribute significantly to polymer production at very high temperatures. The contribution of both reactions must be evaluated quantitatively, if reliable heat transfer coefficients are to be obtained from experiment.     

Detailed mechanistic modeling of poly(styrene peroxide) pyrolysis using kinetic Monte Carlo simulation

Conventional continuum mechanistic models for polymer degradation typically involve thousands of coupled differential-algebraic equations, requiring an efficient solver to solve the complex set of stiff model equations. This can be overcome by formulating the problem in terms of a stochastic simulation procedure, requiring only iterative operations to solve the model. The present work describes the detailed mechanistic modeling of pyrolysis of poly(styrene peroxide) (PSP) using kinetic Monte Carlo (KMC) simulation to predict the product yields and gain a better understanding of the product evolution pathways. The traditionally accepted mechanism of PSP pyrolysis proposed by Mayo and Miller, which involves the key reaction steps of peroxide bond fission, alkoxy radical recombination and disproportionation, and end chain β-scission, was initially tested using the KMC model to predict the peroxide concentration profile and the product yields. This model was only qualitatively able to predict the major products, benzaldehyde and formaldehyde, while the formation of minor products like α-hydroxy acetophenone, phenyl glycol, and phenyl glyoxal was not captured at all. Hence, a new mechanism that also incorporated hydrogen abstraction and β-scission was proposed and implemented in KMC. The final model tracked 949 reactions of 83 species. The rate coefficients for all the reaction steps were based on the existing literature reports, and hence no parameter estimation was done to fit the model against the experimental data. The revised model was quantitatively able to predict all the products of PSP pyrolysis, which was attributed to the stabilization of the alkoxy radicals by hydrogen abstraction, and the subsequent generation of additional alkoxy radicals by β-scission. KMC allowed the dominant pathways for the formation of minor products and dimers to be identified explicitly. Finally, the implications of this study in understanding the effect of trace peroxide bonds on poly(styrene) pyrolysis are outlined.     

α-呋喃甲酸烷基酯类香料的合成

以０．０１ｍｏｌ对甲苯磺酸和５ｍｌ３０％过氧化氢作催化剂，在苯或甲苯中０１ｍｏｌα 呋喃甲酸和０５～０１２ｍｏｌ脂肪醇回流反应３ｈ，以８０％～９５６％的收率合成了７个糠酸烷基酯。结果表明酯的收率普遍提高。     

Surface modification of poly(ethylene terephthalate) fibers via controlled radical graft polymerization

Functional chemical modifications on poly(ethylene terephthalate) (PET) fibers via radical graft polymerization could be controlled by managing mutual interactions and affinities between different components in the grafting reaction system. Hansen solubility parameters was used as a tool to quantify affinities of related agents and the polymer, and provided reliable results. The latest results proved the practicality of using Hansen solubility parameters in controlling radical graft polymerizations on surface modifications of PET fibers. Four different monomers with different hydrophilic properties in different solvent and initiator systems were examined, and results confirmed that interactions of initiator‐PET, initiator‐solvent, monomer‐PET, monomer‐solvent, and monomer‐initiator play important roles in determining the grafting reaction efficiency. Results revealed that for the selected grafting systems studied, hydrophilic monomers presented overall favoring affinities toward PET leading to higher grafting yields compared to hydrophobic monomers. The results have instructive impact to commercial applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45990.     

Reinforcing of expanded polymer morphology using peroxy radical initiator

There was investigated the possibility of increasing the apparent specific surface area of polystyrene sorbents by radical-induced post-polymerization reaction using di-tert-butyl peroxide as free radical initiator. It is known that in addition to the activation of vinyl groups, tert-butyl peroxide is also able of abstraction of hydrogen atoms from aliphatic carbons and this way produces active centers for creation of post-polymerization crosslinking. Radical-induced post-polymerization morphology changes were confirmed by detailed morphological examinations of both dry and swollen materials showing distinct reinforcing of the expanded polymer morphology. However, due to the specific character of the post-polymerization reaction, the achieved additional crosslinking was not extensive and only moderate increase to the apparent BET surface area was achieved.     

Depth-gradient and photoinitiator-free photocrosslinking of poly(ethylene oxide)

Poly(ethylene oxide) (PEO) films are photocrosslinked by continuous UV irradiation without photoinitiators. Maximum gel fraction and swelling of the photocrosslinked PEO films reach up to about 38.8% and 2824%, respectively. From NMR analysis, the photocrosslinking mechanism of PEO can be attributed to recombination between methine radicals, which are generated from the polymer chain by hydrogen abstraction. However, the relatively low degree of crosslinking is attributed to more facile photooxidation of the generated radicals and concomitant photo-scission of the crosslinks. Depth-gradient crosslinked structure can be formed by inherent UV absorption and successive photoscission of the crosslinked polymer surface, which can be made uniform by adjusting UV energy. The photocrosslinked PEO shows the higher glass transition temperature as much as 7.3°C coupled with significantly enhanced storage modulus and thermal stability. The lower crystallinity causes by the reduced recrystallizability of the crosslinked polymer chains in melt. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Grafting of Maleic Anhydride onto Acrylonitrile-Butadiene-Styrene Terpolymer: Synthesis and Characterization

The graft copolymerization of maleic anhydride (MAH) onto a acryloni-trile-butadiene-styrene (ABS) terpolymer was carried out using benzoyl peroxide (BPO) as an initiator and toluene as a solvent. The effects of various parameters such as monomer concentration, initiator concentration, reaction time, and temperature on graft yield were studied. Addition occurs in the butadiene region of the polymer, either by the loss of vinylic hydrogen and subsequent radical formation and addition of monomer or by addition to the double bond. The graft copolymers were characterized by infrared, thermogravirnetric analysis, and differential scanning calorimetry. Thermal stability was improved and T _g was increased.