Details

Autor(en) / Beteiligte

• Shabtai, Joseph
• Xiao, Xin
• Zmierczak, W

Titel

Depolymerization−Liquefaction of Plastics and Rubbers. 1. Polyethylene, Polypropylene, and Polybutadiene

Ist Teil von

• Energy & fuels, 1997-01, Vol.11 (1), p.76-87

Ort / Verlag

Washington, DC: American Chemical Society

Erscheinungsjahr

1997

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• The solid superacid-catalyzed depolymerization−liquefaction (DL) reactions of high-density polyethylene (HDPE), isotactic polypropylene (PPR), and cis-polybutadiene (PB) samples were systematically investigated as a function of processing conditions, i.e., temperature (350−450 °C), time (0.5−3.0 h), H2 pressure (500−2000 psig), catalyst type and concentration, and the presence of solvents. Catalysts used included SO4 2-/Fe2O3, SO4 2-/ZrO2, and a Pt-modified SO4 2-/ZrO2. At temperatures >400 °C, with 1−2 wt % of SO4 2-/Fe2O3 or SO4 2-/ZrO2 as catalyst, there is an overlap of catalytic and noncatalytic, viz. thermal DL, reactions. Under such conditions HDPE yields a liquid product consisting of C5−C30 (mostly C5−C12) normal and branched paraffins, accompanied by small amounts of cycloparaffins and olefins. Selective catalytic DL of HDPE was achieved at lower temperature (350 °C) in the presence of 17−33 wt % of SO4 2-/ZrO2 or the more active Pt/SO4 2-/ZrO2 catalyst, preferably in the presence of a chemically compatible solvent, i.e., n-octadecane. Under such conditions the high-yield (>90 wt %) product predominantly consists of branched paraffins in the gasoline boiling range. PPR, which shows high DL reactivity due to its multiply branched polymeric chain structure, yields a similar gasoline-like mixture of C5−C12 branched paraffins as main product. The change in product composition from HDPE and PPR as a function of temperature and reaction time allows for elucidation of mechanistic aspects of the stepwise DL reactions of these polymers. For HDPE results are rationalized in terms of a carbonium ion mechanism involving extensive skeletal isomerization and attendant β-cleavage reactions leading to low branched paraffins as final products. Results obtained demonstrate that at mild temperatures, under properly designed catalytic conditions, waste HDPE and PRR feeds could be effectively converted into desirable multibranched paraffins which represent potential blending components for reformulated, nonaromatic gasolines.