Polyethylene catalytic reactions

Abstract. This paper presents results from quantum molecular dynamics Simula tions applied to catalytic reactions, focusing on ethylene polymerization by metallocene catalysts. The entire reaction path could be monitored, showing the full molecular dynamics of the reaction. Detailed information on, e.g., the importance of the so-called agostic interaction could be obtained. Also presented are results of static simulations of the Car-Parrinello type, applied to orthorhombic crystalline polyethylene. These simulations for the first time led to a first principles value for the ultimate Young s modulus of a synthetic polymer with demonstrated basis set convergence, taking into account the full three-dimensional structure of the crystal. 

It was noted early by Smid and his coworkers that open-chained polyethylene glycol type compounds bind alkali metals much as the crowns do, but with considerably lower binding constants. This suggested that such materials could be substituted for crown ethers in phase transfer catalytic reactions where a larger amount of the more economical material could effect the transformation just as effectively as more expensive cyclic ethers. Knbchel and coworkers demonstrated the application of open-chained crown ether equivalents in 1975 . Recently, a number of applications have been published in which simple polyethylene glycols are substituted for crowns . These include nucleophilic substitution reactions, as well as solubilization of arenediazonium cations . Glymes have also been bound into polymer backbones for use as catalysts " " . 

Polymerization on heterogeneous catalysts differs from other catalytic reactions in the sense that the product remains on the catalyst. Several techniques can be used to study the polymer product after reaction. Figures 9.29 and 9.30 show several examples of polymer that was formed at 160 °C (i.e., above its melting point), and subsequently cooled to room temperature. During cooling, polyethylene crystallizes and is expected to develop its well-known spherulite morphology [101]. 

In most cases the catalytically active metal complex moiety is attached to a polymer carrying tertiary phosphine units. Such phosphinated polymers can be prepared from well-known water soluble polymers such as poly(ethyleneimine), poly(acrylic acid) [90,91] or polyethers [92] (see also Chapter 2). The solubility of these catalysts is often pH-dependent [90,91,93] so they can be separated from the reaction mixture by proper manipulation of the pH. Some polymers, such as the polyethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers, have inverse temperature dependent solubility in water and retain this property after functionalization with PPh2 and subsequent complexation with rhodium(I). The effect of temperature was demonstrated in the hydrogenation of aqueous allyl alcohol, which proceeded rapidly at 0 °C but stopped completely at 40 °C at which temperature the catalyst precipitated hydrogenation resumed by cooling the solution to 0 °C [92], Such smart catalysts may have special value in regulating the rate of strongly exothermic catalytic reactions. 

The distribution of the products obtained from this reaction depends upon the reaction temperature (Fig. 5.2-2) and differs from other polyethylene recycling reactions in that aromatics and alkenes are not formed in significant concentrations. Another significant difference is that this ionic liquid reaction occurs at temperatures as low as 90 °C, whereas conventional catalytic reactions require much higher temperatures, typically 300-1000 °C [90j. A patent filed under the Secretary of State for Defence (UK) has reported a similar cracking reaction for lower molecular weight hydrocarbons in chloroaluminate(iii) ionic liquids [91]. An example is the cracking of hexane to products like propene and isobutene (Scheme 5.2-40). The reaction was... 

Hyde, J. Licence, P. Carter, D. Poliakoff, M. (2001) Continuous Catalytic Reactions in Supercritical Fluids. Appl. Catal., A. Vol.222, No.1-2, pp.119-131 Jin, S. Kang, C Yoon, K Bang, D. Park, Y. (2009) Elect of compatibilizer on morphology, thermal, and rheological properties of polypropylene/functionalized multi-walled carbon nanotubes composite. /. Ayyl. Polym. Set. Vol.lll, No.2, pp.1028-1033 Joen, H Jung, H Lee, S. Hudson, S. (1998) Morphology of polymer/Silicate Nanocomposites Hieh Density Polyethylene and a Nitrile Copolymer. Polym. Bull. Vol.41, No.l, pp.107-111... 

Alkene polymerization is one of the most important catalytic reactions in commercial use. The Ziegler-Natta catalysts, for which Ziegler and Natta won the Nobel Prize in 1963, account for some 15 million tonnes of polyethylene and polypropylene annually. These catalysts are rather similar to the metathesis catalysts in that mixtures of alkylaluminum reagents and high-valent early metal complexes are used. The best known is TiCl3/Et2AlCl, which is active at 25°C and 1 atm this contrasts with the severe conditions required for thermal polymerization (200 C, 1000 atm). Not only are the conditions milder, but the product shows much less branching than in the... 

The catalytic reaction takes place in an essentially anhydrous liquid medium that acts as a common solvent for the H2S, the SO2, and the catalyst. The process is operated at temperatures above the melting point of sulfur, but below the sulfur dew point of the gas mixture to be treated. The solvent first proposed (Renault, 1969) was tributyl orthophosphate containing an alkaline substance as the catalyst. However, polyethylene glycol soon became the solvent of choice because of its good thermal and chemical stability, low vapor pressure, low cost, and availability. Additional advantages are the low solubility of sulfur in the solvent and of the solvent in sulfur. 

ThermoFuel (1) A process for making diesel fuel from waste plastic. Preferred plastics are polyethylene and polystyrene. The plastic is first melted in an extruder and then pyrolyzed continuously in a cylindrical chamber at 370°C-420°C, giving a Cg to C g hydrocarbon mixture having a peak at C,g. An important feature is the incorporation of a catalytic reaction tower after the main pyrolysis reactor, which incorporates metal plates made from a proprietary catalytic metal alloy. Distillation yields an average of 930 L of diesel per ton of waste plastic. Developed by Ozmotech, Australia, and now offered by EnviroSmart Technologies of Roosendaal, the Netherlands. In 2006, there were plans for 31 installations in Europe to be made over the next 4 years. 

The feed to a steam cracker is a mixture of steam with either LPG (liquefied petroleum gas a mixture of primarily ethane, propane, and butane) or a heavier petroleum fraction, such as naphtha or gas oil. A large number of individual reactions take place. The feed hydrocarbons are cracked to smaller molecules and are dehydrogenated to produce olefins. The reactor operates at about 850 °C and the residence time typically is less than 1 s. Steam cracking is a homogeneous (non-catalytic) reaction. Steam crackers produce monomers that form the building blocks for important, high volume polymers such as polyethylene and polypropylene. 

Aguado, J., et al., 2007. Feedstock recycling of polyethylene in a two-step thermo-catalytic reaction system. Journal of Analytical and Applied Pyrolysis 79 (1—2), 415—423. 

Polyethylene (PE) is a genetic name for a large family of semicrystalline polymers used mostiy as commodity plastics. PE resins are linear polymers with ethylene molecules as the main building block they are produced either in radical polymerization reactions at high pressures or in catalytic polymerization reactions. Most PE molecules contain branches in thek chains. In very general terms, PE stmcture can be represented by the following formula ... 

The chemical iadustry manufactures a large variety of semicrystalline ethylene copolymers containing small amounts of a-olefins. These copolymers are produced ia catalytic polymerisation reactions and have densities lower than those of ethylene homopolymers known as high density polyethylene (HDPE). Ethylene copolymers produced ia catalytic polymerisation reactions are usually described as linear ethylene polymers, to distiaguish them from ethylene polymers containing long branches which are produced ia radical polymerisation reactions at high pressures (see Olefin POLYMERS, LOWDENSITY polyethylene). 

The three isomers constituting n-hutenes are 1-hutene, cis-2-hutene, and trans-2-hutene. This gas mixture is usually obtained from the olefinic C4 fraction of catalytic cracking and steam cracking processes after separation of isobutene (Chapter 2). The mixture of isomers may be used directly for reactions that are common for the three isomers and produce the same intermediates and hence the same products. Alternatively, the mixture may be separated into two streams, one constituted of 1-butene and the other of cis-and trans-2-butene mixture. Each stream produces specific chemicals. Approximately 70% of 1-butene is used as a comonomer with ethylene to produce linear low-density polyethylene (LLDPE). Another use of 1-butene is for the synthesis of butylene oxide. The rest is used with the 2-butenes to produce other chemicals. n-Butene could also be isomerized to isobutene. ... 

The living nature of ethylene oxide polymerization was anticipated by Flory 3) who conceived its potential for preparation of polymers of uniform size. Unfortunately, this reaction was performed in those days in the presence of alcohols needed for solubilization of the initiators, and their presence led to proton-transfer that deprives this process of its living character. These shortcomings of oxirane polymerization were eliminated later when new soluble initiating systems were discovered. For example, a catalytic system developed by Inoue 4), allowed him to produce truly living poly-oxiranes of narrow molecular weight distribution and to prepare di- and tri-block polymers composed of uniform polyoxirane blocks (e.g. of polyethylene oxide and polypropylene oxide). 

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