Sunggyu Lee

Kinetics and mechanisms of styrene monomer recovery from waste polystyrene by supercritical water partial oxidation

Waste polystyrene is becoming a major environmental concern, due to its large production quantities and non-biodegradable nature. Provided that the high molecular-weight material can be broken down into useful low molecular-weight hydrocarbons, waste polystyrene can be viewed as a highly valuable feedstock. This processing step can be accomplished by using supercritical water partial oxidation (SCWPO) technology. This technology uses the unique properties of supercritical water in an oxygen-deficient environment to partially oxidize the polymer. By using this technique, polystyrene has been successfully depolymerized into monomer, oligomer, and other useful hydrocarbons in a relatively short residence time with high efficiency. The kinetics and feasibility of the supercritical water partial oxidation process were experimentally investigated using four different oxygen-feed conditions. The styrene selectivity of the process, based on the product mass versus the feed mass, was determined to be as high as 71%, and was found to depend very strongly on the polymer/oxygen ratio. While the styrene selectivity was very high, the selectivity for benzene, toluene, and other hydrocarbons was substantially lower. The process was also compared with pyrolysis in supercritical water at the same temperature and pressure.

Graft copolymerization of acrylic acid onto polystyrene using the solid phase grafting technique

Graft copolymerization of acrylic acid (AAc) onto polystyrene (PS) by the solid phase graft copolymerization technique was studied. Benzoyl peroxide (BPO) was used as the free radical initiator. Acrylic acid was introduced into the reactor as an aqueous solution. Optimum reaction conditions to obtain maximum grafting were evaluated. The variables studied were temperature, initiator concentration, monomer concentration, acrylic acid-to-water ratio, and reaction time. The graft copolymer was characterized by infrared (IR) spectroscopy, and the graft level was quantified by the IR absorbance ratio technique and titration.

Alternative Source of Propylene

Synthesis gas derived from natural gas, coal, biomass or any other hydrocarbon source can be advantageously utilized to produce propylene. The approach adopted by the current investigation carries out the conversion of syngas in two stages: single-stage dimethyl ether (DME) synthesis followed by dimethyl ether conversion. Single-stage DME synthesis is carried out in the liquid phase utilizing the synergistic effect of dual catalysts, Cu/ZnO/Al 2 O 3 and γ-alumina. Dimethyl ether produced by this process is then converted to propylene using a shape-selective H-ZSM-5 catalyst. Very high selectivity towards propylene (as high as 68 wt%, the rest being ethylene and butenes) can be achieved by using this catalyst at appropriate reaction and feed conditions. In general, higher temperatures, low partial pressures of DME in the feed, and short contact times used over a H-ZSM-5 catalyst with low acidity increase the selectivity of DME conversion to propylene by inhibiting competing as well as successive reactions which would otherwise form other olefins, paraffins and aromatics. This article describes at length the second stage of the overall syngas-to-propylene process, focusing on the conversion of dimethyl ether to propylene over a wide range of reaction and feed conditions.

Use of Polymeric Compatibilizers in Polypropylene/Calcium Carbonate Composites

The effects of compatibilizing agents on the mechanical properties, viscoelastic properties, and morphology of polypropylene filled with calcium carbonate composites are investigated. It is found that the use of PP-g-MA and PP-g-AA significantly increases the tensile strength and improves particle dispersion and interfacial adhesion. The higher effect of compatibilization is obtained by using PP-g-MA as a compatibilizer. The results on the dynamic thermomechanical properties, viscoelastic properties, and SEM pictures also support the improved interfacial characteristics. It is also found that there exists a limiting amount of PP-g-MA at about 5% beyond which a further increase in the tensile strength is not obtained. The use of untreated calcium carbonate or SEBS-g-MA does not allow films to be drawn for the purpose of testing.

Performance of ZSM-5 Catalyst in the Dimethyl Ether to Olefins Process

ABSTRACT The conversion of dimethyl ether (DME) to hydrocarbons is the latter step in the conversion of syngas to hydrocarbons via DME. The shape-selective ZSM-5 zeolite catalyst plays an instrumental part in this reaction in limiting the higher end of the product spectrum. This process, being of an exothermic nature, results in a temperature rise across the catalyst bed causing some hydrocarbons to be deposited on the catalyst as coke. The presence of water as a byproduct in the catalyst environment also enhances the catalyst deactivation. Deactivation of the ZSM-5 catalyst is studied in detail in terms of catalyst performance and life over a period of time. The conversion of DME and the hydrocarbon product distribution are studied as a function of time-on-stream The SiO2/Al2O3molar ratio of the ZSM-5 catalyst is regarded to be important in determining the degree of coke formation as well as the product distribution of the final hydrocarbon product. Catalysts used in aging experiments were studied as to ...

Analysis of the Solid Phase Copolymerization Grafting Process

Solid phase grafting, which is an emerging process for the production of graft copolymers, was analyzed and reviewed as an environmentally friendly and inexpensive graft copolymerization process. The effect of the process variables; amount of initiator, catalyst, interfacial agent, monomer, reaction temperature and reaction time were examined. Two graft copolymers, produced by solid phase grafting, were used to show differences in graft percentage by changing the process conditions. The two graft copolymers used were maleic anhydride graft onto polypropylene and acrylic acid graft onto polystyrene. A proposed mechanism was given for each example and characteristic bonds proposed in the PP-g-MA mechanism was positively identified by NMR spectroscopy. Graft levels of 4 wt% PS-g-AAc and 9.6 wt% PP-g-MA were obtained providing comparable or superior graft levels to other grafting processes. Successful scale-up of the solid phase technique proved that this process is efficient and marketable.

Effect of plasma polymer treatment on aging of polyethylene films

Aging degradation of solid insulation is traditionally studied using various failure acceleration mechanisms alone or in combination. For example, multiple stress conditions, including electrical signals, elevated temperature, and/or a corrosive (saline) environment are often applied to molded insulation blocks that have been cut, scratched, or implanted with sharp metallic electrodes to provide a site for the onset of failure. The test configuration used in this study involves thin (50 /spl mu/m) commercially available polyethylene sheets lacking artificially induced defects. Periodic measurements are made on films while they are under soak in a saline solution with a sinusoidal voltage applied. Capacitance and dissipation results are presented which are indicative of the degradation induced by the stress conditions on untreated polymer films and on polymer films which have been coated with extremely thin (<100 nm) plasma polymerized films of two monomers.<<ETX>>