Polyethylene hydrogen production

With large single crystals of polyethylene, the gelation dose is some 10 times greater than for the same polymer grown under conventional conditions (14). This is not caused by any inherent difference in the effect of radiation since both the radical concentration (deduced from ESR measurements) and hydrogen production are similar. We must therefore assume that most of the links produced in the single crystal are internal links which do not influence solubility. This is understandable in a crystal where each molecule folds backward on itself. 

Fig. 5. Hydrogen production from irradiated polyethylene of low additives content.

CHANG, Z., LA VERNE J.A., Hydrogen production in y-ray and helium ion radiolysis of polyethylene, polypropylene, poly(methyl-methacrylate) and polystyrene J. Polym.Sci. A 38 (2000) 1656-1661. 

Iridium complexes with triphenylphosphine modified with poly(ethylene oxide)s 14 at one of the phosphine groups were active in two-phase hydrogenation of allylbenzene, although the catalyst activity and selectivity with respect to the hydrogenation product, propylbenzene, was substantially lower than in the case of its low molecular analogue and one of the main products was propenylbenzene. Similar results were obtained for an iridium complex with polyethylene oxide modified with pyridyl groups [53],... 

The properties of the end product also depend on the structure of the initial polymer. Thus high vinyl polybutadienes which will have ethyl side groups after hydrogenation cannot crystallize and so remain rubbery. As the vinyl content decreases so the hydrogenated product becomes more like low density polyethylene whilst linear... 

Electron beam crosslinking takes place when very high energy radiation is used to initiate molecular crosslinking in high-density polyethylene. This product is extruded like normal HDPE then taken to an E-beam facility and routed under a beam or ray in the accelerator where it is dosed with a specific amount of radiation to release the hydrogen atoms and cause polymer chains to bond or link to the open carbon sites. 

Studies on thermal degradation of PE have reported hydrogen production in the fluidised-bed pyrolysis of a low-density polyethylene (LDPE) [a.54]. Hydrogen may be produced from the polymer melt and/or from thermal dehydrogenation of volatile products in the gas phase as a secondary reaction at the reactor temperature. From the results, it seems more possible that hydrogen is formed in the polymer melt, because, if more hydrogen were produced from thermal dehydrogenation of volatile products in the gas phase, increased... 

Masson, J.P., Mofina, R., Roth, E., Gaussens, G., and Lemaire, F. Obtention and evaluation of polyethylene-based solid polymer electrolyte membranes for hydrogen-production. International Journal of Hydrogen Energy, 7(2), 167-171, 1982. 

Chang, Z. and LaVeme, J.A., Hydrogen production in the heavy ion radiolysis of polymers. 1. Polyethylene, propylene, poly(methyhnethacrylate) and polystyrene, /. Phys. Chem. B, 104,10557,2000. 

Anhydrous hydrogen fluoride is also available in cylinders, and aqueous hydrogen fluoride, either 50% or 70%, is also shipped in polyethylene bottles and carboys. Typical product specifications and analysis methods are given in Table 4. 

The quaHty of the feedstock is important since it affects not only the product quaHty but the rate of hydrogenation. Some of the impurities that affect the rate are sulfur, phosphoms, haHdes, polyethylene, and moisture. Impurities are usually removed by clay treatment or by distillation (30). 

Triacetin resistance is especially critical when filter tips are made in one location, stored, and then shipped to another location. For these operations, polyethylene-based adhesives are used because of their low polarity and therefore excellent resistance to triacetin. Where filter plugs are attached at the same location shortly after production, EVA-based adhesives are suitable and preferred. Both types of adhesives use low odor, clean tackifiers such as hydrogenated hydrocarbons or pure monomer resins (typically a-methylstyrene based). Rosin, rosin esters, and phenol-containing tackifiers are not acceptable. EVA-based adhesives use a higher level of wax (about 1 /3 of the formula) than polyethylene-based adhesives (5-20% wax) due to the lower crystallinity and slower set of EVA vs. PE. Application viscosities are 2000-5000 cP. 

An example of the way in which process competition works in the manufacture of plastics is the story of acrylonitrile. The first process for the production of this plastic was based upon the reaction between hydrogen cyanide and acetylene, both hard to handle, poisonous, and explosive chemicals. The raw material costs were relatively low as compared to materials for other monomers, but the plant investment and manufacturing costs were too high. As a result, originally acrylonitrile monomer (1950s) sold for about 30 cents per pound and the future of the material looked dim as other plastics such as polyethylene became available at much lower prices due to their lower production costs. 

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