Polymer pyrolysis and oxidation studies in a continuous feed and flow reactor : cellulose, polystyrene, and polyethylene
Department of Chemical Engineering, Chemistry and Environmental Science
Doctor of Philosophy
Bozzelli, Joseph W.
Trattner, Richard B.
Kebbekus, Barbara B.
Grow, James M.
Booty, Michael R.
A dual zone, continuous feed tubular reactor is developed to assess the potential for formation of products from incomplete combustion in thermal oxidation of common polymers. Solid polymer powder (cellulose, polystyrene, or polyethylene) is fed continuously into a volatilization oven where it fragments and vaporizes under continuous steady state conditions. The gas phase polymer fragments flow directly into a second, main flow reactor oven and undergo further pyrolysis and oxidation reaction. Temperatures in the main flow reactor are varied independently of the volatilization zone to observe conditions needed to convert the initial polymer fragments to CO2 and H2O. Combustion products are monitored at main reactor temperatures from 400°C to 750°C and at 2 seconds residence time with four, on-line GC/FID's; polymer reaction products and intermediates are further identified by GC/MS.
Forty one species are positively identified in the volatilization of cellulose. Increases in temperature at constant fragment reaction time shift the molecular weight distribution of gas products toward lower mass and increase extent of conversion. Complete conversion (mineralization) of identified cellulose fragments is observed at 2 seconds reaction time and 750°C under fuel lean conditions. Major volatilization products at 400°C are carbonyl compounds, hydrocarbons, furans, pyrans, and anhydrosugars. Cellulose in the presence of NaCl (5% of Cl) shows higher decomposition of levoglucosan and more rapid conversion of major initial products to CO and CO2. Formation of major initial products, C6 oxygenated species, hydrocarbons (C5-C7), furan derivatives (C4 and C5), and light species (C1 - C4) are somewhat inhibited by NaCl at fuel equivalence ratios Φ = ~0.25 and Φ = ~ 0.8, but increase higher at Φ= ~0.8 except for light species at low temperatures.
Fifty two initial fragments from combustion of polystyrene are positively. Major initial products are monomer, dimer, and trimer styrene. Increases in temperature of the main reactor increase production of polynuclear aromatic hydrocarbons (PAHs) and the extent of conversion. Complete conversion of identified initial fragments is observed at 2 seconds residence time and 750°C under both Φ = ~0.1 and Φ =~0.8. There are no observed NaCl effects on combustion of polystyrene: The product distribution versus temperature is changed for high yield species and complete decomposition of initial products is increased by about 50°C at Φ =~0.8 relative to Φ = ~0.1.
The pyrolysis and oxidation of medium density polyethylene (MDPE) with branch chains is conducted in the main reactor temperature range of 400°C to 650°C. Fuel equivalence ratios are between Φ = 0.24 and 0.32 at 2 seconds residence time. Ninety species are positively identified. Major products are alkanes, alkenes, aldehydes, ketones, and alcohols in the range of C1 to C22. Most prominent products over 1% (by mass) are CO, CO2, methane, ethene, formaldehyde, propene, propane, butene, 2-pentanone, and pentanal. Complete combustion is achieved at relatively low temperature of the main reactor, 650°C.
njit-etd2000-065 (375 pages ~ 14,670 KB pdf)
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Created January 25, 2007