TITLE Coal/Polymer Coprocessing with Efficient Use of Hydrogen

University Coal Research Contractors Review Conference

AUTHORS Linda J. Broadbelt* ; Matthew J. De Witt ; phone: [phone]

Others  :  http://www.netl.doe.gov/publications/proceedings/97/97ucr/broadbel.pdf
PID  :  6029

来源: CEUR

【 摘 要 】

OBJECTIVE: Environmental and economical concerns over diminishing landfill space and the growing abundance of mixed plastic waste mandate development of viable strategies for recovering high-valued resources from waste polymers.Coprocessing of waste polymer mixtures with coal allows for the simultaneous conversion of coal and plastics into high-valued fuels.However, there is limited information about the underlying reaction pathways, kinetics, and mechanisms controlling coal liquefaction in the presence of polymeric materials. A series of model compound experiments has been conducted, providing a starting point for unraveling the complex, underlying chemistry.Thermolysis studies of model compounds of polyethylene and coal were conducted in batch reactors.Tetradecane (C14H30) was used as a polyethylene mimic, and 4-(naphthylmethyl)bibenzyl (NBBM) was used as a coal model compound.Reaction temperatures were 420 and 500˚C, and batch reaction times ranged from 5-150 minutes. Detailed product analysis using gas chromatography and mass spectrometry enabled the reactant conversion and product selectivities to be determined.Reaction of single components and binary mixtures allowed the kinetic coupling between feedstocks to be examined. RESULTS TO D ATE: The major products observed from the pyrolysis of tetradecane were a -olefins, with minor selectivity to n-alkanes.The highest selectivity, 0.13, was obtained for 1-heptene, and a -olefins with carbon numbers of 6 to 11 were also observed in significantly quantities.The product distribution was rationalized in terms of typical free radical Rice-Herzfeld and Rice-Kossiakoff mechanisms [1-2]. The mechanism is initiated by carbon-carbon bond fission to form two primary radicals.These primary radicals form secondary radicals through hydrogen abstraction from a secondary carbon or through an intramolecular hydrogen rearrangement.These secondary radicals then undergo b -scission to form a - olefins and primary radicals.Termination occurs by recombination or disproportionation of radicals. Two of the major products formed during pyrolysis of NBBM, which are afforded by carbon-carbon bond fission and subsequent hydrogen abstraction, were toluene and 1-methyl-4-(naphthylmethyl) benzene, each observed with a selectivity greater than 0.28 at all reaction times studied.The other major product was 1-(2-phenylethenyl)-4-(naphthylmethyl) benzene, with an initial selectivity of approximately 0.35 which decreased linearly with reaction time to 0.11 at 150 minutes.Minor selectivities were observed for a number of products from NBBM pyrolysis, including methyl bibenzyl and phenyl methyl naphthalene. Mechanistic interpretation using the ideas put forth by Walter et al. [3] successfully accounted for the majority of the products observed in significant yield.The formation of high yields of toluene and 1- methyl-4-(naphthylmethyl) benzene was consistent with a