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), H 2 pressure (500-2000 psig), catalyst type and concentration, and the presence of solvents. Catalysts used included SO 4 2-/Fe 2 O 3 , SO 4 2-/ZrO 2 , and a Pt-modified SO 4 2-/ ZrO 2 . At temperatures >400 °C, with 1-2 wt % of SO 4 2-/Fe 2 O 3 or SO 4 2-/ZrO 2 as catalyst, there is an overlap of catalytic and noncatalytic, viz. thermal DL, reactions. Under such conditions HDPE yields a liquid product consisting of C 5 -C 30 (mostly C 5 -C 12 ) 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 SO 4 2-/ZrO 2 or the more active Pt/SO 4 2-/ZrO 2 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 C 5 -C 12 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.
Abstract--FTIR studies of six partially-deuterated montmorillonites (MS) reveal the presence of two O-D stretching bands, one between 2702-2728 cm ~ and another near 2680 cm -~ . For homoionic (Li, Na, Mg, Ca, or La) Wyoming-type MS, the position of the higher frequency band, designated as (O--O)h , is between 2714-2728 cm -t, whereas for homoionic Cheto-type MS it is between 2702-2706 cm -l. The lower frequency band, designated as (O-D)~, is in the narrow range of 2674-2684 cm ~. Resolution of two corresponding O-H bands, appearing near 3670 and 3635 cm -~, was observed only after partial dehydroxylation of the smectites. The changes in the relative intensities of the two O-D stretching bands as a function of the smectite type and of the Lewis acidity (charge density) of the exchangeable ion were determined. For Wyoming-type MS, the intensity of the (O-D)h band is much lower than that of the (O-D)t band, whereas for Cheto-type MS, the intensity of the (O-D)h band is about equal or slightly higher than that of the (O-D)z band. The observed resolution can be ascribed tentatively to the presence of (at least) two types of octahedral OH groups in the smectites, the (O-D)h band being assigned to A1MgOH and the (O-D)~ band to A1A1OH groups. Pillaring of Cheto-type MS with hydroxy-Al~3 oligocations resulted in products showing much higher thermal stability between 400-600~ compared to that of identically pillared Wyoming-type MS. Compositional and other factors, e.g., CEC values and mode of pillaring, may cause this difference in stability.
Abstract--Solutions containing hydroxy-SiA1 (HSA) oligocations were prepared by two procedures: (1) treatment of a mixture of orthosilicic acid and A1C13 with aqueous NaOH, followed by aging of the product; and (2) preliminary preparation and aging of hydroxy-Al~3 oligocations followed by reaction of the latter with orthosilicic acid. Ion exchange of Na,Ca-montmorillonite with HSA oligocations yielded pillared, crossqinked montmorillonites (designated as HSA-CLM) showing a maximum d(001) value of 19.5 ,~ for air-dried samples, and maximum surface areas of -500 m2/g after outgassing at 250~ -3 tort. Corresponding ion exchange of Li-fluorhectorite yielded HSA fluorhectorites (HSA-CLFH) showing a maximum d(001) value of 19.0/~ and a surface area of 355 mVg. Calculated structural formulae for the HSA-CLM and HSA-CLFH products, based on elemental analysis, showed a gradual increase in the Si/A1 ratio in the intercalated HSA oligocations with increasing Si/A1 ratio in the pillaring solution. Optimum d(001) values and surface areas of HSA-CLM and HSA-CLFH products were obtained using method 2 and applying a ratio of 1.6-2.5 mmole (Si)A1/g smectite.The thermal stabilities of HSA-CLM and HSA-CLFH products were determined by heat treatment between 250 ~ and 700~ and subsequent measurement of the d(001) values and surface areas. HSA-CLFH products showed the unusual behavior of increase of d (001) with increase in temperature from 400 ~ to 500~ and essential constancy of d(001) from 500 ~ to 600~ The HSA-CLM products showed a gradual decrease in surface area, whereas the HSA-CLFH products prepared with a Si/A1 ratio of 1.04-2.18 in the pillaring solution showed constant surface areas with increasing temperature from 250 ~ to 600~ HSA-CLM and HSA-CLFH show sharply higher acidities compared with those of reference A1-CLM and A1-CLFH samples obtained by pillaring with hydroxy-Al~3 oligocations. This increased acidity is probably due to the presence of acidic, surface silanol groups in the HSA oligocations.
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