Recycling of polystyrene

Pyrolysis for the Recycling of Polystyrene Plastic (PSP) Wastes in a Swirling Fluidized-Bed Reactor... 

J. M. Arandes, J. Erena, M. J. Azkoiti, M. Olazar, and J. Bilbao, Thermal recycling of polystyrene and polystyrene - butadiene dissolved in a light cycle oil,. 1. Anal Appl Pyrol, 70, 747 (2003). 

In 1993, over 41 million pounds of polystyrene was recycled into new plastics products in the U.S. (77). Eor commingled plastics, gasification comes closest to competing with low cost landfilling (57). 

Addition of rubber particles of 30% to 100% by weight to cement with a grain size of approximately 40 to 60 mesh (0.4 to 0.25 mm) will produce a lightweight cement. The addition of rubber particles also creates a low permeability. The compositions are advantageous for cementing zones subjected to extreme dynamic stresses such as perforation zones and the junctions of branches in a multi-sidetrack well. Recycled, expanded polystyrene lowers the density of a hydraulic cement formulation and is an environmentally friendly solution for downcycling waste materials. 

The key to the successful production of polystyrene is the reaction. The ratio of materials to be used is a compromise of the literature values, as was discussed in the section on the scope. All the authors discussing suspension polymerization say the reaction should be allowed to go to completion. (Removing and recycling the unreacted styrene would be more expensive.) It will be assumed that this means 99.8% of the styrene is reacted, and that this can be accomplished by using an average of the temperatures and cycle times given in Table 2E-2. 

Methylrheniumtrioxide (MTO) can straightforwardly be immobilized using copolymers consisting of polystyrene and polyvinyl pyridine. The authors proposed two possible structures 18 shown in Scheme 4.10. In the presence of H2O2 these catalysts are efficient and selective heterogeneous catalysts for the epoxidation of alkenes. It was shown that their activity is maintained for at least five recycling experiments [23 dj. In analogy to this work, bipyridyl-functionalized mesoporous silica can be employed for the immobilization of MTO [75]. 

Copolymeriziation of polystyrene-bound dicyanoketene acetal (DCKA) and ethylene glycol dimethacrylate (EGDMA) yielded a polymer (41) with high n -acidity. It was found to be an effective and completely recyclable catalyst in the high yielding carbon-carbon bond-forming reaction of dimethylacetals with silylated nucleophiles (Scheme 4.26) [118]. 

In 2000, Benaglia and coworkers reported preparation of MeO-PEG supported quaternary ammonium salt (10) and examined the catalytic efficiency in a series of phase-transfer reactions (Fig. 5.3) [69]. The reactions occurred at lower temperatures and with shorter reaction times than with comparable insoluble 2% cross-linked polystyrene-supported quaternary ammonium salts, although yields varied with respect to classical solution phase quaternary ammonium salt catalyzed reactions. It was observed that yields dropped with a shorter linker, and that PEG alone was not responsible for the extent of phase-transfer catalysis. While the catalyst was recovered in good yield by precipitation, it contained an undetermined amount of sodium hydroxide, although the presence of this byproduct was found to have no effect on the recyclability of the catalyst... 

Genpak, a plastic products manufacturer, and Mobil are in the process of opening and operating one of the first plants to recycle polystyrene foam items such as food containers, cups, and cutlery. The materials are being collected from Massachusetts schools and institutions by New England CRInc, a major reclamation firm and recycled materials end-use manufacturer. The plant has a capacity to recycle 3 million lb per year of polystyrene resin, which will be reused by the companies or sold to producers of insulation, fence posts, and flower pots. The new company is expecting a profit by 1992. 

There are reports of numerous examples of dendritic transition metal catalysts incorporating various dendritic backbones functionalized at various locations. Dendritic effects in catalysis include increased or decreased activity, selectivity, and stability. It is clear from the contributions of many research groups that dendrimers are suitable supports for recyclable transition metal catalysts. Separation and/or recycle of the catalysts are possible with these functionalized dendrimers for example, separation results from precipitation of the dendrimer from the product liquid two-phase catalysis allows separation and recycle of the catalyst when the products and catalyst are concentrated in two immiscible liquid phases and immobilization of the dendrimer in an insoluble support (such as crosslinked polystyrene or silica) allows use of a fixed-bed reactor holding the catalyst and excluding it from the product stream. Furthermore, the large size and the globular structure of the dendrimers enable efficient separation by nanofiltration techniques. Nanofiltration can be performed either batch wise or in a continuous-flow membrane reactor (CFMR). 

Over the years it has been shown that complexes prepared from organophosphorous ligands in combination with peroxotungstic acid or its quaternary ammonium salts exhibit efficient catalytic properties. In order to make an efficient recycling of the catalyst possible and get tungsten-free products and effluents, some of these catalysts were immobilized onto polystyrene, poly benzimidazole and polymethacrylate copolymers modified by the introduction of the phosphorous(V)-containing ligands. 

The immobilization of the sensitizer and catalyst is especially effective, because contamination of the materials (NBD and QC) with a sensitizer or catalyst markedly lower the efficiency of this system. 4-(N,N-dimethylamino)benzophenone was immobilized on poly(styrene) (30) and silica gel to use it as insoluble sensitizer 101 The polymer pendant sensitizer (30) was much more active than the monomeric compound when used in acetonitrile. Usually, the sensitizing activity of the sensitizer remained almost unchanged through immobilization, but sometimes decreased depending on their structure. As a catalyst of back reaction to release heat, Co(II)-tetraphenylporphyrine was anchored on polystyrene) beads (31), and showed good activity in its immobilized form10Z>. Activity decrease was observed- after several times recyclings of the catalyst. 

Z. Zhang, T. Hirose, S. Nishio, Y. Morioka, N. Azuma, A. Ueno, H. Ohkita, and M. Okada, Chemical recycling of waste polystyrene into styrene over solid acids and bases, Ind. Eng. Chem. Res. 34, 4514 (1995). 

H. Ukei, T. Hirose, S. Horikawa, Y. Takai, M. Taka, N. Azuma and A. Ueno, Catalytic degradation of polystyrene into styrene and a design of recyclable polystyrene, with dispersed catalysts. Catalysis Today 62, 67-75 (2000). 

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