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.     

Degradation of polystyrene using montmorillonite clay catalysts

Summary The performance of acid-treated montmorillonite catalysts in the degradation of polystyrene (PS) was investigated in this study. The degradation was carried out in a semi-batch reactor with a mixture of PS and catalyst at 400-450^oC. The commercial Süd Chemie acid-treated montmorillonite clays (K-series) showed good catalytic activity for the degradation of PS. The styrene monomer and ethylbenzene were major liquid products. The increase of surface acidity enhanced further cracking of styrene dimer and trimer to produce styrene monomer. Higher production of ethylbenzene for K30 may be related to its bigger pore volume and surface area compared to those of K5. High degradation temperature favored styrene monomer production.     

Selective dimerization of styrene to 1,3-diphenyl-1-butene by acetyl perchlorate

The linear unsaturated dimer of styrene, 1,3-diphenyl-1-butene, was obtained exclusively in the oligomerization of styrene by acetyl perchlorate in various solvents. In benzene, the linear dimer was produced in more than 90% yield at 50°C. In n-hexane and cyclohexane, the yield of the linear dimer was lower. The yield of the linear dimer was strongly dependent on the nature of solvent. When an increasing amount of 1,2-dichloroethane was added to benzene, the yield of the linear dimer gradually decreased. On the other hand, when a small amount of 1,2-dichloroethane was added to n-hexane or cyclohexane, the yield of the linear dimer increased. The yield of the linear dimer was almost independent of the reaction temperature and the initiator concentration. For comparison, the dimerization of α-methylstyrene was carried out, and the effects of the initiator and the solvent on the structure of dimers were investigated. On the basis of these results, the mechanism of the dimerization of styrene initiated by acetyl perchlorate is discussed.     

Stopped-flow investigation of the cationic oligomerization of trans-1,3-diphenyl-1-butene initiated by trifluoromethanesulfonic acid in dichloromethane

Reaction of trans 1,3-diphenyl-1-butene (D), the trans ethylenic dimer of styrene, with trifluoromethanesulfonic acid in dichloromethane has been performed at temperatures lower than room temperature using a stopped-flow technique with real time UV-visible spectroscopic detection. The main product of the reaction was the indanic dimer of D. A transient absorption at 340 nm has een assigned to 1,3-diphenylbutylium, a model for the polystyryl cation. Other absorptions at 349 nm and 505 nm have also been observed and were assigned to an allylic cation, 1,3-diphenyl-1-buten-3-ylium, resulting from hydride abstraction from D. This species was very stable at temperatures lower than −30°C. A general mechanism was proposed based on a kinetic study of the involved reactions.     

Synthesis of functionalized linear poly(divinylbenzene). III. Synthesis of polymeric delocalized carbanion of poly(divinylbenzene) and its reactions

A polymeric delocalized carbanion of poly(divinylbenzene) [poly(DVB)] (2) was obtained by the proton abstraction with alkyllithium from the acidic methine moieties (H_A) of linear poly(DVB) (1) , which was prepared by the polymerization of DVB initiated by acetyl perchlorate. The formation of polyanion 2 was confirmed by UV–visible spectroscopy (λ_max = 630 nm) and the reaction with methyl iodide to give methylated poly(DVB). Delocalized polyanion 2 reacted with various electrophilic reagents in THF at 60°C, to yield poly(DVB) derivatives having pendant trimethylsilyl, vinyl, vinyloxyl, hydroxyl, and carboxyl groups. Proton abstraction with base and subsequent reactions with electrophiles were also studied with the linear unsaturated dimer of styrene (1,3-diphenyl-1-butene), as a model for poly(DVB) 1 .     

Investigation of thermal and catalytic degradation of polystyrene waste into styrene monomer over natural volcanic tuff and Florisil catalysts

Thermal and catalytic degradation of polystyrene waste over two different samples of natural volcanic tuff catalyst comparative with Florisil catalyst has been carried out in order to establish the conversion degree into styrene monomer. The polystyrene waste (PS) was subjected to a thermal degradation process in the range of 380–500°C in presence of studied catalysts in a ratio of 1/10 in mass, catalyst/PS. The catalysts were characterized by N₂ adsorption-desorption isotherms (BET), Scanning Electron Microscopy (SEM) and Fourier-transform infrared spectrometry (FTIR). Influences of temperature and type of catalysts on the yields and on the distribution of end-products obtained by thermal and catalytic degradation of polystyrene waste have been studied. The maximum yields of liquid products were obtained at 460°C degradation temperature and were calculated between 83.45% and 90.11%. The liquid products were characterized by gas chromatography mass spectrometry (GC-MS) and FTIR analytical techniques. The GC-MS results showed that the liquid products contained styrene monomer up to 55.62%. The FTIR spectra of liquid products indicated the specific vibration bands of the functional groups of compounds of liquid products. The amounts of styrene monomer obtained were influenced by structural and textural properties of studied catalyst and the contribution on product distribution is discussed.      

Synthesis of the block copolymer of styrene and 1-butene with a novel supported Ti-catalyst

The present investigation deals with sequential block copolymerization of styrene and 1-butene with a novel MgCl₂-supported TiCl₄ catalyst modified with a rare earth compound NdCl_x(OR)_y (SN-1 catalyst), which was developed in our laboratory. The catalytic activities are 1300–2500 g/g·Ti·h. Analyses of copolymers with solvent extraction, ¹³C-NMR, WAXD, GPC, and DSC was performed. The results indicate that the SN-1 catalyst selectively gave crystalline diblock copolymers of isotactic polystyrene and isotactic poly(1-butene), with the styrene unit content of 30–60 mol %. © 1996 John Wiley & Sons, Inc.     

Cu(I)-catalyzed α-alkylation of ketones with styrene derivatives

α-Alkylation of ketones with styrene derivatives was developed using a mesitylcopper-dppp complex as a soft Brønsted base catalyst. No waste derived from the alkylating reagent was produced in this catalytic alkylation reaction. The bisphosphine ligand structure, as well as the reaction solvent, had profound effects on catalyst activity. The reaction proceeded under mild conditions from a range of ketones and styrene derivatives. The present catalysis is especially useful for the selective mono-alkylation of ketones.     

聚苯乙烯热降解机理的理论研究

采用密度泛函理论B3LYP/6-311G（d）方法,对聚苯乙烯（PS）热降解反应机理进行了研究。PS热降解的主要产物是苯乙烯,其次是甲苯、α-甲基苯乙烯、乙苯和二聚体等芳烃化合物。PS热降解反应主要包括主链C-C键均裂、β-断裂、氢转移和自由基终止等反应。针对以上各类反应进行了路径设计和理论计算分析,对参与反应的分子的几何结构进行了优化和频率计算,获得了各热降解路径的标准动力学和热力学参数。计算结果表明,苯乙烯主要由自由基的链端β-断裂反应形成;二聚体主要由分子内1,3氢转移的反应形成;α-甲基苯乙烯由分子内的1,2氢转移后进行β-断裂形成;甲苯由苯甲基自由基夺取主链上的氢原子形成;乙苯由苯乙基自由基夺取氢原子形成。动力学分析表明,苯乙烯形成所需要的能垒低于其他产物形成所需要的能垒,故苯乙烯为主要的热降解产物;这与相关实验结果基本一致。     

Examination of catalyst for α-metylstyrene oligomerization “Phosphoric Acid on Sibunit” under conditions of laboratory and industrial application

A catalyst obtained by impregnation of a mesoporous carbon carrier sibunit with orthophosphoric acid is examined under conditions of pilot plant manufacturing for producing α-methylstyrene dimer. The produced catalyzate (the product obtained with catalysis, 300 ton) containing ca. 70% of targeted 2,4-diphenyl-4-methyl-1-penetene at 95% conversion was after filtration used for control of molecular mass at producing polystyrene of different sorts. Consumption of the catalyst under optimal conditions of exploitation of the installation was ca. 1.5 kg per 1 ton of dimer at temperature ca. 50°C and volume rate ～ 0.5 h^?1. Content of 2,4-diphenyl-4-methyl-1-pentene in the dimer can be elevated to 80% by significant decreasing conversion (～50%) and by application of solvents.     

Synthesis of fully substituted pyrazolo[3,4-b]pyridine-5-carboxamide derivatives via a one-pot four-component reaction

A one-pot four-component reaction of an aliphatic or aromatic amine, diketene, an aromatic aldehyde and 1,3-diphenyl-1H-pyrazol-5-amine in the presence of p-toluenesulfonic acid as a catalyst has been developed. In this reaction, a new class of fully substituted pyrazolo[3,4-b]pyridine-5-carboxamide derivatives is produced under mild reaction conditions and in good yields at ambient temperature.     

Thermal degradation of polyethylene and polystyrene from the packaging industry over different catalysts into fuel-like feed stocks

Thermal degradation of waste polymers was carried out as a suitable technique for converting plastic polymers into liquid hydrocarbons, which could be used as feed stock materials. The catalytic degradation of waste plastics (polyethylene and polystyrene) was investigated in a batch reactor over different catalysts (FCC, ZSM-5 and clinoptillolite). The effects of catalysts and their average grain size on the properties of main degradation products (gases, gasoline, diesel oil) are discussed. The temperature range of 410-450 °C was used in the process. Both equilibrium FCC catalyst and natural clinoptilolite zeolite catalyst had good catalytic activity to produce light hydrocarbon liquids, and ZSM-5 catalyst produced the highest amount of gaseous products. Gases and liquids formed in cracking reactions were analyzed by gas chromatography. The liquid products consisted of a wide spectrum of hydrocarbons distributed within the C₅-C₂₈ carbon number range depending on the cracking parameters. The composition of hydrocarbons had linear non-branched structure in case of polyethylene, while from polystyrene more aromatics (ethyl-benzene, styrene, toluene, and benzene) were produced. The yields of volatile products increased with increasing degradation temperature. The olefin content of liquids was measured with an infrared technique and an olefin concentration of 50-60% was observed. The concentration of unsaturated compounds increased with decreasing temperature, and in the presence of catalysts. The activation energies were calculated on the basis of the composition of volatile products. The apparent activation energies were decreased by catalysts and catalyst caused both carbon-chain and double bond isomerisation.     

Production of 1,3-Butadiene From C4 Raffinate-3 Through Oxidative Dehydrogenation of n-Butene Over Bismuth Molybdate Catalysts

Recent progress on the bismuth molybdate catalysts for oxidative dehydrogenation of n-butene to 1,3-butadiene was reported in this review. A number of bismuth molybdate catalysts, including pure bismuth molybdates (α-Bi₂Mo₃O₁₂, β-Bi₂Mo₂O₉, and γ-Bi₂MoO₆) and multicomponent bismuth molybdates, were prepared by a co-precipitation method for use in the production of 1,3-butadiene from C₄ raffinate-3 through oxidative dehydrogenation of n-butene. It was observed that multicomponent bismuth molybdate catalyst was more efficient than pure bismuth molybdate catalyst in the oxidative dehydrogenation of n-butene. Various experimental measurements such as temperature-programmed reoxidation, X-ray photoelectron spectroscopy, and O₂-temperature-programmed desorption analyses were carried out to elucidate the different catalytic activity of bismuth molybdate catalysts. It was revealed that a bismuth molybdate catalyst with a higher oxygen mobility showed a better catalytic performance in terms of conversion of n-butene and yield for 1,3-butadiene. We have successfully demonstrated from experimental findings that oxygen mobility of bismuth molybdate catalyst played a key role in determining the catalytic performance in the oxidative dehydrogenation of n-butene to 1,3-butadiene.     

Effect of the Brush Structure on the Degradation Mechanism of Polystyrene–Clay Nanocomposites

Summary: Pyrolysis‐GC‐MS and TGA‐FT‐IR methods have been used to perform a comparative degradation study of polystyrene and a polystyrene–clay composite. An abnormally high yield of α‐methylstyrene has been detected for the composite. This and other differences in degradation products have been explained by enhanced intermolecular interaction of the grafted PS chains, forming a brush structure. A conceptual model of the process has been suggested.

GC pyrograms of virgin PS (A) and PS–clay composite (B) pyrolyzed at 500 °C (1: styrene; 2: 2,4‐diphenylbut‐1‐ene; 2′: dimer derivatives; 3: 2,4,6‐triphenylhex‐1‐ene; 3′: trimer derivatives; 4: α‐methylstyrene).     

Polymerization and reaction of tetraoxane with various olefins catalyzed by BF3O·(C2H5)2

The copolymerization of tetraoxane with various olefins by BF₃·O(C₂H₅)₂ in ethylene dichloride at 30°C has been studied. The gas chromatographic technique was employed for the determination of concentration of each compound. The rate of tetraoxane consumption was decreased by the addition of olefins in the order of; no addition > trans-stilbene > styrene > 1,1-diphenylethylene > 2-chloroethyl vinyl ether > cyclohexene ≥ indene ≥ α-methylstyrene. The formation of the methanol-insoluble copolymer of tetraoxane and olefin was not confirmed. However, 4-methyl-4-phenyl-1,3-dioxane and 4,4-diphenyl-1,3-dioxane were formed in the reaction of tetraoxane with α-methylstyrene and 1,1-diphenylethylene, respectively. 4,4-Diphenyl-1,3-dioxane was identified on the basis of the molecular weight measurement, elemental analysis and NMR and infrared spectroscopy. On the other hand, 1,3-dioxane derivatives were not formed in the reaction of tetraoxane with α,β-disubstituted olefins. Monomer composition dependence of the copolymerization of tetraoxane with 1,1-diphenylethylene or α-methylstyrene has been studied. The amount of 4,4-diphenyl-1,3-dioxane formed reached a maximum at a monomer composition of 1:1 in the reaction of tetraoxane with 1,1-diphenylethylene. The formation of cyclic dimer of α-methylstyrene was suppressed by tetraoxane.     

Reaction between isocyanides and dialkyl acetylenedicarboxylates in the presence of 4,5-diphenyl-1,3-dihydro-2H-imidazol-2-one. One-pot synthesis of 5H-imidazo[2,1-b][1,3]oxazine derivatives

The reactive 1:1 intermediate produced in the reaction between alkyl or aryl isocyanides and dialkyl acetylenedicarboxylates was trapped by 4,5-diphenyl-1,3-dihydro-2H-imidazol-2-one to yield highly functionalized 2,3-diphenyl-5H-imidazo[2,1-b][1,3]oxazine derivatives in fairly good yields.     

A comparative study on thermal and catalytic degradation of polybutylene terephthalate

A comparative study on the thermal and catalytic degradation of polybutylene terephthalate (PBT) at atmospheric pressure was conducted. The weight loss of PBT under thermal degradation was significantly influenced by the temperature between 360 °C and 380 °C, but little affected by the PBT particle size. Four groups of catalysts include metal chloride, metal oxide, metal acetate, and metal copper powder were used to test PBT degradation activity. Copper (II) chloride is the most active one for increasing the percentage PBT weight loss more than 100% in comparison with the result of thermal degradation at a temperature of 360 °C for 30 min. PBT and catalyst mixtures can be prepared by impregnation and physical method, the former resulted in a better PBT degradation. The percentage PBT weight loss in the presence of CuCl₂ increased steadily between 320 °C and 380 °C which was different from the results of thermal degradation. The time for obtaining a same percentage PBT weight loss reduced effectively when compared to the catalytic to thermal degradation. The weight ratio of CuCl₂/PBT was tested between 0 and 0.2 and the optimal ratio was 0.1. The gaseous product distribution analyzed by GC/MS for PBT thermal and catalytic degradation revealed almost the same and the major products were ethane, carbon monoxide, carbon dioxide, 1-butene, 2-butene, 1,3-butadiene, and butadiene dimmer. But the relative abundance of major products was changed, especially for 1,3-butadiene increased dramatically, and a new chlorocompound was produced in catalytic degradation. In condensed liquid product, both the number and the molar mass of components were more and greater than that of in gaseous product and 4-heptylacetophenone was the most abundance product. In PBT catalytic degradation, 4-heptylacetophenone and some products were decreased and some even disappeared completely while the abundance of benzoic acid increased and three new products were generated.     

Highly selective hydroarylation of propiolic acid derivatives using a PtCl2/AgOTf catalytic system

Hydroarylation of propiolic acid derivatives with arenes in trifluoroacetic acid efficiently proceeded in the presence of PtCl₂/AgOTf catalyst to give cis-cinnamic acid derivatives in good to high yields. This PtCl₂/AgOTf-catalyzed reaction did not afford any 4-arylbuta-1,3-diene-1,3-dicarboxylic acid derivatives formed by Pd(OAc)₂-catalyzed hydroarylation. The specific optimization of the catalytic hydroarylation and application to electron-rich arenes are reported.     

Silica-supported perchloric acid (HClO4–SiO2): a mild, reusable and highly efficient heterogeneous catalyst for multicomponent synthesis of 1,4-dihydropyridines via unsymmetrical Hantzsch reaction

Facile synthesis of some 1,4-dihydropyridine derivatives via Hantzsch reaction of 5,5-dimethyl-1,3-cyclohexanedione (dimedone), 1,3-diphenyl-2-propen-1-one derivatives and ammonium acetate under solvent-free condition in the presence of silica-supported perchloric acid (HClO₄–SiO₂) is described. The catalyst is easily prepared, stable, reusable and efficient under the reaction conditions.     

Liquid-phase catalytic oxidation of organic substrates by a recyclable polymer-supported copper(II) complex

Chloromethylated polystyrene beads cross-linked with 6.5 % divinylbenzene were functionalized with 2-(2′-pyridyl) benzimidazole (PBIMH) and on subsequent treatment with Cu(OAc)₂ in methanol gave a polymer-supported diacetatobis(2-pyridylbenzimidazole)copper(II) complex [PS-(PBIM)₂Cu(II)], which was characterized by physicochemical techniques. The supported complex showed excellent catalytic activity toward the oxidation of industrially important organic compounds such as phenol, benzyl alcohol, cyclohexanol, styrene, and ethylbenzene. An effective catalytic protocol was developed by varying reaction parameters such as the catalyst and substrate concentrations, reaction time, temperature, and substrate-to-oxidant ratio to obtain maximum selectivity with high yields of products. Possible reaction mechanisms were worked out. The catalyst could be recycled five times without any metal leaching or much loss in activity. This catalyst is truly heterogeneous and allows for easy work up, as well as recyclability and excellent product yields under mild conditions.