Research ArticleMATERIALS SCIENCE

Efficient and selective degradation of polyethylenes into liquid fuels and waxes under mild conditions

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Science Advances  17 Jun 2016:
Vol. 2, no. 6, e1501591
DOI: 10.1126/sciadv.1501591
  • Fig. 1 Degradation of PE through CAM with light alkanes (for example, n-hexane).

    (A) Proposed PE degradation pathway through catalytic CAM. Dehydrogenation of both PE and light alkane (n-hexane used as an example) creates unsaturated olefins. Subsequently, cross olefin metathesis followed by hydrogenation causes breakdown of PE chain into shorter chains. Repeating the tandem reaction in multiple cycles results in degradation of PE into short alkanes appropriate for use as transportation oil. (B) Structures of the dehydrogenation and olefin metathesis catalysts used in this study.

  • Fig. 2 Degradation of various grades of PEs with n-octane (2.5 ml for HDPE-1 and LLDPE and 4 ml for all other PEs) by 2 (4.2 μmol Ir) and Re2O7/γ-Al2O3 (57 μmol Re2O7): The distribution of degradation products after 4 days at 175°C.

    More detailed degradation product distributions are summarized in table S1.

  • Fig. 3 Degradation of postconsumer PE plastic bottle (HDPE), food packaging film (HDPE), and grocery shopping bag (a blend of HDPE and LLDPE) into oils.

    (A) Degradation of PE plastic wastes (0.3 g) with petroleum ether (8 ml) by 2 (10 μmol Ir) and Re2O7/γ-Al2O3 (86 μmol Re2O7) at 175°C after 4 days. (B) PE plastic wastes used in the degradation (left), CAM degradation reaction mixture (middle), and oil products isolated from the degradation mixture (right). (C) GC trace for the oil products from the degradation of the PE plastic bottle.

  • Fig. 4 Degradation of HDPE-2 (120 to 135 mg) with n-octane (4 ml) by 2 (4.2 μmol Ir) and Re2O7/γ-Al2O3 (57.0 μmol Re2O7) at 175 °C after 2, 4, 6, 8, 24, 48, and 96 hours.

    (A) Distributions (wt %) of oil and wax products. (B) Mw of the isolated PE wax products. (C) Molecular weight distributions (PDI) of the isolated PE wax products.

  • Table 1 Cross metathesis of HDPE-1 (120 mg) with n-hexane (7.7 M, 3 ml) using various γ-Al2O3– supported Ir catalysts (20.1 μmol Ir) and Re2O7/γ-Al2O3 (57 μmol Re2O7): The conversion of PE to oil and wax products and the distribution of soluble n-alkane products after heating the mixture for 3 days at 150°C.

    The amounts of soluble products were determined by GC analysis with mesitylene as an internal standard. The amounts of n-hexane after the degradation reactions were not included. As the starting material, the intensity of the n-hexane signal was too strong (relative to other n-alkane products) to be precisely measured by GC analysis. Wax products are the isolated solid hydrocarbon products. Aside from wax products, the major products from PE degradation are liquid oil hydrocarbons. Thus, weight percentages (wt %) of oils from PE degradation were estimated with the mass of the starting PE minus the wax products. N/A, not applicable.

    EntryIr catalystHDPE-1(mg)Mass (mg) and concentration (mM) of
    soluble products
    Mass (g) and concentration
    (M) of total soluble products
    Wax products (mg)Wt % of oils
    C3-C5C7-C12C13-C21C22-C30≥C31
    11120304/
    1553
    671/
    1932
    74/
    115
    12/
    10
    10/
    7
    1.07/
    3.62
    5356%
    210374/
    1926
    788/
    2248
    57/
    90
    0.7/
    0.6
    N/A1.22/
    4.27
    N/AN/A
    32120202/
    1073
    416/
    1171
    93/
    138
    20/
    18
    12/
    8
    0.74/
    2.41
    298%
    420245/
    1290
    597/
    1662
    69/
    114
    2/
    2
    N/A0.91/
    3.07
    N/AN/A
    53120225/
    1180
    523/
    1461
    116/
    174
    29/
    24
    23/
    14
    0.92/
    2.85
    695%

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/6/e1501591/DC1

    Supplementary Materials and Methods

    fig. S1. GC traces for the reactions of HDPE-1 with Ir complex 1 or 2, and the control experiments without HDPE-1.

    fig. S2. GC trace for the reaction of 1-octene with recycled Re2O7/Al2O3.

    fig. S3. GC traces for the control experiments in the absence of one of the dual catalysts or in the absence of both catalysts.

    fig. S4. GPC traces for the wax products.

    fig. S5. GC traces for the oil products from the degradation of the PE plastic bottle, film, and bag.

    fig. S6. GPC traces for the wax products obtained from the reaction with HDPE-2 after 2, 4, 6, 8, 24, 48, and 96 hours.

    table S1. Degradation of various grades of PE with n-octane (2.5 or 4.0 ml) by [Ir] (4.2 μmol) and Re2O7/Al2O3 (57 μmol Re2O7): The distribution of n-alkane products and conversion of PE to oil products after 4 days at 175°C.

    table S2. Degradation of HDPE-2 at different time intervals: The distribution of n-alkane products and conversion of PE to oil products.

    References (3538)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Materials and Methods
    • fig. S1. GC traces for the reactions of HDPE-1 with Ir complex 1 or 2, and the control experiments without HDPE-1.
    • fig. S2. GC trace for the reaction of 1-octene with recycled Re2O7/Al2O3 in toluene after 12 hours at 175°C.
    • fig. S3. GC traces for the control experiments in the absence of one of the dual catalysts or in the absence of both catalysts.
    • fig. S4. GPC traces for the wax products.
    • fig. S5. GC traces for the oil products from the degradation of the PE plastic bottle, film, and bag.
    • fig. S6. GPC traces for the wax products obtained from the reaction with HDPE-2 after 2, 4, 6, 8, 24, 48, and 96 hours.
    • table S1. Degradation of various grades of PE with n-octane (2.5 or 4.0 ml) by Ir (4.2 μmol) and Re2O7/Al2O3 (57 μmol Re2O7): The distribution of n-alkane products and conversion of PE to oil products after 4 days at 175°C.
    • table S2. Degradation of HDPE-2 at different time intervals: The distribution of n-alkane products and conversion of PE to oil products.
    • References (35–38)

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