Hydrogenation Of Polystyrene Research Articles

Mechanism and Kinetics of Polystyrene Hydrogenation Catalyzed by a Monolithic Pd-NCNTs@FN Catalyst

Mechanism and Kinetics of Polystyrene Hydrogenation Catalyzed by a Monolithic Pd-NCNTs@FN Catalyst

New advances in catalysts for polystyrene hydrogenation

Polystyrene is one of the most widely used plastics, and could be catalytic hydrogenated to polycyclohexylethylene with improved physical properties. The research progress in the efficiency palladium catalyst for polystyrene hydrogenation was illustrated and reviewed, further development was discussed.

Carbon Nanotube Modified Ceramic Foams as Structured Palladium Supports for Polystyrene Hydrogenation

Fe doped ceramic foams (CFs) were synthesized by organic template replication and consequently modified by carbon nanotubes (CNTs) via facile chemical vapor deposition (CVD). CNTs were in situ anch...

Tunable growth of carbon nanotubes forests on nickel foam as structured support for palladium catalyst toward polystyrene hydrogenation

Heterogeneous catalytic hydrogenation of polystyrene (PS) over classical porous catalysts to polycyclohexylethylene (PCHE) with added commercial values is severely limited by pore diffusion of polymer coils due to the large molecule size and high solution viscosity. To improve accessibility of PS to active sites and eliminate catalyst separation, a structured catalyst, Pd supported on CNTs decorated nickel foam (Pd/[email protected]) was prepared and displayed an excellent hydrogenation activity. The high performance could be contributed to the non-porous and wide-open structure of CNTs layer and strong π–π interaction between CNTs surface and PS molecules which facilitates the diffusion and adsorption of PS coils respectively. The average diameter and graphitization degree of CNTs could be tuned by adjusting the chemical vapor deposition (CVD) temperature and consequently its surface area and interaction with PS molecules. CVD temperature was optimized to obtain Pd/[email protected] with highly dispersed Pd nanoparticles and enhanced adsorption capacity of PS. It shows great industrial potential for structured Pd/[email protected] catalyst with outstanding catalytic activity and stability.

Palladium supported on carbon nanotube modified nickel foam as a structured catalyst for polystyrene hydrogenation

A structured support of carbon nanotubes modified nickel foam (CNTs@NF) was synthesized through a facile method of chemical vapor deposition. The entangled CNTs layer with open pores and the dense carbon layer beneath covered around the skeleton of nickel foam establishes a hybrid hierarchical structure with large effective surface area which dramatically promotes the internal diffusion of large polystyrene (PS) coils. Palladium was chosen as the catalyst for PS hydrogenation and deposited on the CNTs@NF support in the form of nanoparticles. Characterization analysis including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermo gravimetric analysis (TGA), Raman spectrum and N2 physisorption were conducted to investigate the morphology and structure of the resulting Pd supported on CNTs@NF catalysts (Pd/CNTs@NF). The macroscopic structured Pd/CNTs@NF catalyst was applied to PS hydrogenation and displayed a quite excellent hydrogenation activity with a final hydrogenation degree (HD) of 73.6%, almost 8 times higher than nickel foam supported Pd catalyst (Pd/NF) and remarkably similar to powdered CNTs supported Pd catalyst (Pd/CNTs) under the identical condition. Moreover, the turn-over-frequency (TOF) of Pd/CNTs@NF (0.041 s−1) was also comparable to Pd/CNTs (0.056 s−1), which confirmed a similar intrinsic catalytic activity of Pd on both supports. Inspiringly, the performance of Pd/CNTs@NF catalyst was comparable to powdered Pd/CNTs catalyst with the merit of eliminating filtration operation. It has revealed the structured Pd/CNTs@NF catalyst with outstanding recyclability could be an attractive alternative to the powdered Pd/CNTs catalyst for heterogeneously catalyzed polymers hydrogenation reactions.

Palladium Supported on Carbon Nanotubes Decorated Nickel Foam as the Catalytic Stirrer in Heterogeneous Hydrogenation of Polystyrene

Carbon nanotubes supported palladium (Pd/CNTs) catalyst displayed excellent activity toward hydrogenation of polystyrene (PS) to produce polycyclohexylethylene (PCHE) with added commercial values. However, its application is limited by the costly catalyst filtration process and energy-consuming elevated agitation speed. Herein, a dense, homogeneous and strongly attached layer of CNTs was decorated on nickel foams and employed as the catalyst support for palladium nanoparticles. Structured catalyst (Pd/CNTs@NF) was directly used as the catalyst stirrer in a rotating foam stirrer reactor (RFSR) for PS hydrogenation. Owing to the enhanced mass-transfer process, the hydrogenation degree reached 68.8%, which was 45.1% higher than that obtained in a slurry reactor using powdered Pd/CNTs catalyst under identical reaction conditions. Outstanding attachment strength of CNTs on the foam and catalytic stability in eight runs of recycling were also demonstrated. This work elucidates the promising feasibility of struc...

The mesopore-elimination treatment and silanol-groups recovery for macroporous silica microspheres and its application as an efficient support for polystyrene hydrogenation

Supported Pd catalyst with an enhanced catalytic performance for polystyrene hydrogenation was successfully prepared by using macroporous silica microspheres (MSM) as the support. In order to eliminate the macromolecular diffusion limitation and improve the metal utilization, MSM was treated with steam at 800 °C first to remove mesopores and then refluxed with aqueous solutions to increase SiOH groups on the surface for Pd immobilization. The optimum support was obtained after the steam treatment for 2 h and using ammonia solution as reflux liquors, and the corresponding catalyst showed superior hydrogenation activity with a high conversion of 95%.

Hydrogenation of polystyrene-b -polybutadiene-b -polystyrene mediated by group (IV) metal metallocene complexes

Various group (IV) metal complexes, namely bis(cyclopentadienyl) titanium dichloride, bis(pentamethylcyclopentadienyl) titanium dichloride, cyclopentadienyl titanium trichloride, pentamethylcyclopentadienyl titanium trichloride, bis(cyclopentadienyl) zirconium dichloride, and bis(cyclopentadienyl) hafnium dichloride, were used as the catalysts for mediating styrene–butadiene–styrene hydrogenation. The catalytic efficiency of these catalysts was examined. The results show that catalyst activity strongly depends on the chemical structure of the metallocene complex. We also found that trialkylaluminum has a significant influence on the hydrogenation activity and thermal stability of metallocene catalysts. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2141–2149

Adsorption and Reaction Kinetic Studies of the Heterogeneous Catalytic Hydrogenation for Polystyrene

We applied silica hollow microspheres with through holes in the shell as supports to prepare Pd-based supported catalyst (Pd/SHMs) for heterogeneous catalytic hydrogenation of polystyrene (PS) and also systematically studied the adsorp- tion and reaction behavior of PS molecules over Pd/SHMs. The dynamic adsorption and reaction models of PS molecules under different temperatures have been established and the partially hydrogenated products were also comprehensively ana- lyzed. The result shows that both the adsorption capacity and saturation time are increased as the temperature increasing and this hydrogenation reaction is confirmed to be a first-order reaction and the activation energy is calculated to be 58.3 kJmol -1 . After separating and purifying three samples with different hydrogenation degrees, we further analyzed the partially hydrogenated products and the results show that they are all actually comprised of two kinds of substances with different properties, one with high hydrogenation conversion rate (ca. 85%) and the other with low hydrogenation ratio (ca. 25%). It is proved that PS heterogeneous hydrogenation process exists secondary adsorption and competitive adsorption phenomenon, and obeys the Blocky mechanism. This work lays the foundation for PS adsorption and hydrogenation reaction and is also favorable for the understanding of the adsorption and catalytic process for other unsaturated polymers over heterogeneous catalysts.

New understanding and controllable synthesis of silica hollow microspheres with size-tunable penetrating macroporous shells as a superior support for polystyrene hydrogenation catalysts

Download options Please wait... Supplementary files Supplementary information PDF (871K) Article information DOI https://doi.org/10.1039/C3TA11824J Article type Communication Submitted 08 May 2013 Accepted 24 Jun 2013 First published 24 Jun 2013 Download Citation J. Mater. Chem. A, 2013,1, 9597-9602 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions New understanding and controllable synthesis of silica hollow microspheres with size-tunable penetrating macroporous shells as a superior support for polystyrene hydrogenation catalysts D. Pan, G. Shi, T. Zhang, P. Yuan, Y. Fan and X. Bao, J. Mater. Chem. A, 2013, 1, 9597 DOI: 10.1039/C3TA11824J To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Deng Pan Gang Shi Teng Zhang Pei Yuan Yu Fan Xiaojun Bao

Effect of Supports on the Catalytic Hydrogenation of Polystyrene

The heterogeneous catalytic hydrogenation of polystyrene dissolved in cyclohexane over Pd-containing catalysts have been investigated in a batch reactor. Ultraviolet technique was employed to monitor the hydrogenation extent. The catalyst properties were modified by sol–gel methods. The effects of temperature and catalyst support were investigated over the ranges 500–1,500 psig and 138 to 190 °C. In each case, fully saturated materials were obtained with no chain scission (i.e., degradation). The rate of hydrogenation showed strong dependence on the catalyst support.

Effect of Polymer Size on Heterogeneous Catalytic Polystyrene Hydrogenation

The effect of polymer coil size on the rate of polystyrene (PS) hydrogenation was studied in a slurry reactor with mixtures of decahydronaphthalene (DHN) and carbon dioxide (CO2) as the solvent for the polymer. The PS coil size was changed by varying the polymer molecular weight from 9300 g/mol to 357 000 g/mol and by varying the CO2 concentration. Using a 5% Pd/5% Ru/SiO2 catalyst, the rate of aromatic ring hydrogenation at 150 °C was found to be strongly dependent on the size of a polymer coil relative to the average pore diameter of the catalyst. Significant pore diffusion limitations, as indicated by values of the Weisz modulus, were observed with increasing polymer molecular weight. Increasing the concentration of CO2 resulted in increased reaction rates, with an improvement of nearly 2 orders of magnitude at the highest PS molecular weight.

Hydrogenation of polystyrene in CO 2-expanded liquids: The effect of catalyst composition on deactivation

The effect of catalyst composition on the hydrogenation of the aromatic rings of polystyrene dissolved in carbon dioxide-expanded decahydronaphthalene (CO 2-DHN) was studied using a slurry reactor at 150 °C. Catalyst deactivation occurred within 15 min of the addition of CO 2 to the reactor when 5% Pd/SiO 2 or 5% Pd/Al 2O 3 was used as the catalyst. The deactivation is believed to be a consequence of CO formation via the reverse water-gas shift reaction, as CO was observed at the end of each hydrogenation reaction. In an effort to convert CO to CH 4 before the poisoning of Pd sites occurred, a methanation catalyst such as 5% Ru/Al 2O 3 or 65% Ni/SiO 2–Al 2O 3 was physically mixed with 5% Pd/SiO 2 or 5% Pd/Al 2O 3 and used to hydrogenate PS. Carbon monoxide concentrations decreased, but no significant improvements in aromatic ring hydrogenation were observed. When a catalyst containing both a hydrogenation and methanation function in a single catalyst particle (1.6% Ru/4.2% Pd/SiO 2) was used, the degrees of hydrogenation in CO 2-DHN matched those obtained when neat DHN was the solvent. Furthermore, no CO was detected when the reaction was catalyzed by the bimetallic catalyst. These results suggest that the methanation function must be proximate to the hydrogenation (reverse water-gas shift) function in order for aromatic ring hydrogenation to proceed as rapidly in a CO 2-expanded solvent as in the unexpanded solvent.

Hydrogenation of Polystyrene in CO2-Expanded Solvents: Catalyst Poisoning

Organic solvents expanded with supercritical carbon dioxide can be excellent media for hydrogenation reactions. However, catalyst poisoning by CO formed via the reverse water-gas-shift reaction occurs during many hydrogenations in the presence of CO2. In this research, the hydrogenation of polystyrene in CO2-expanded decahydronaphthalene was studied in a batch reactor using two hydrogenation catalysts, 5%Pd/BaSO4 and 65%Ni/Al2O3/SiO2. The 5%Pd/BaSO4 catalyst deactivated at 150 °C and CO2 pressures of 250−2250 psig (1.8−15.6 MPa). Approximately 50 ppm CO was present in the CO2-rich light phase after about 10 h at 150 °C, 750 psig H2 pressure, and 2250 psig CO2 pressure. A model that incorporates CO poisoning was developed to describe deactivation of the Pd/BaSO4 catalyst. The 65%Ni/Al2O3/SiO2 catalyst was more active for ring hydrogenation than 5%Pd/BaSO4, and very little CO was formed in the presence of CO2. The Ni catalyst deactivated in the presence of CO2 at 180 °C, possibly due to H2O formed in a meth...

Phase equilibrium for the hydrogenation of polystyrene in CO 2–swollen solvents

Polystyrene (PS) can be hydrogenated using a heterogeneous catalyst suspended in a solvent swollen by supercritical carbon dioxide (scCO 2). Various phase equilibria are involved in this system. First, the application of scCO 2 to a solution of PS can cause the polymer to precipitate. Therefore, the effect of CO 2 pressure and temperature on the phase behavior of various solvents containing dissolved PS was investigated, leading to the selection of decahydronaphthalene (DHN) for in-depth study. It was found that the CO 2 pressure required to precipitate PS from DHN increased with the temperature. The volume of solutions containing various concentrations of PS in DHN increased considerably as the CO 2 pressure was increased. Volume expansions of 35–40% were obtained between 40 and 150 °C and between 3 and 9 wt.% PS. Moreover, calculations using the Peng–Robinson equation of state showed that the H 2 concentration in the liquid phase was higher in CO 2–swollen DHN than in the pure solvent, at a constant H 2 partial pressure. The rate constant for PS hydrogenation was found to be higher in CO 2–swollen DHN than in the pure solvent.

Kinetic and Transport Processes in the Heterogeneous Catalytic Hydrogenation of Polystyrene

The heterogeneous catalytic hydrogenation of polystyrene (PS) dissolved in decahydronaphthalene was studied in a batch reactor using 5% Pd/BaSO4 as the catalyst. The effects of temperature and H2 partial pressure were investigated over the ranges from 90 to 180 °C and 1.72 to 6.89 MPa. The PS concentration ranged from 1 to 9 wt %. The rate of ring hydrogenation was approximately first-order with respect to PS, with an apparent activation energy of 59.6 kJ/mol. The hydrogenation rate depended on the agitation rate up to a threshold value, which increased with the concentration of PS in the solution. The possible influence of three mass-transfer steps (H2 transport from the gas into the polystyrene solution, PS transport to the surface of the catalyst particles, and PS diffusion in the pores of the catalyst) is analyzed. The last two steps do not appear to be kinetically important at the conditions of this study.

Catalytic Hydrogenation of Polystyrene

The use of ultra wide pore silica as a catalyst for the hydrogenation of polystyrene to give poly(cyclohexylethylene) (PCHE) has facilitated the development of a dramatically improved process with much milder conditions. The large pores allow rapid diffusion into and out of the catalyst, so that the interior surfaces are also available for reaction. The mild conditions give rise to high-quality PCHE, whose structure is shown in the Figure.

Hydrogenation of polystyrene- b-polybutadiene- b-polystyrene block copolymers using a metallocene/ n-butyllithium catalyst – the role of n-butyllithium

A metallocene catalyst system, primarily the bis( η 5-cyclopentadienyl)cobalt (Cp 2Co) combined with n-butyllithium ( n-BuLi), was found to be active for the hydrogenation of polystyrene- b-polybutadiene- b-polystyrene (SBS) block copolymer. Data from the UV spectroscopy of the catalyst system indicated that one of the Cp ligand in the original Cp 2Co was substituted by the butyl group forming a CpCoBu as the major catalytic species. The kinetics of the hydrogenation reaction were studied by monitoring the extent of saturation of double bonds on the polybutadiene segment of the copolymer using FTIR spectroscopy. The temperature dependence of the hydrogenation rate was analyzed and the activation energy was determined as 14.11 kcal/mol of the double bond.

Heterogeneous catalytic hydrogenation of polystyrene: thermodynamics of poly(vinylcyclohexane)-containing diblock copolymers

Heterogeneous catalytic hydrogenation of 1,4-poly(isoprene) (PI), atactic poly(styrene) (PS), and two poly(styrene)-poly(isoprene) (PS-PI) diblock copolymers was performed using two palladium supported catalysts. In each case fully saturated materials were obtained with no chain degradation. The dynamic and thermodynamic properties of these materials were investigated using DSC and dynamic mechanical spectroscopy. Saturated poly(styrene), denoted poly(vinylcycloherane) (PVCH), exhibited a T that is 40 deg higher than that of poly(styrene)