Commingled Waste Research Articles

97/00915 Liquefaction of commingled waste plastics containing PVC

Direct liquefaction studies were conducted on a washed, commingled waste plastic (CWP), as received from the American Plastics Council and after addition of 5 wt.% of polyvinyl chloride (PVC). Both non-catalytic and catalytic experiments were performed the catalytic experiments utilized 1 wt.% of HZSM-5. The experiments on the CWP-PVC mixture were conducted with and without the addition of 5 wt.% of calcium hydroxide. The effect of PVC on product yields was evaluated. Oil quality was examined by GC simulated distillation. The forms of occurrence of chlorine in the liquefaction products were determined by x-ray absorption fine structure (XAFS) spectroscopy utilizing the X-ray absorption near edge structure (XANES).

Thermal and catalytic coprocessing of Illinois No. 6. coal with model and commingled waste plastics

Coprocessing of waste plastics with coal was investigated at reaction conditions typical of direct liquefaction using slurry phase Mo and Fe hydrogenation catalysts. Reactions were performed with individual model polymers including polyisoprene, polystyrene, and high and low density polyethylene (HDPE, LDPE), and with coal alone in the presence and absence of a hydrogen donor solvent and catalysts at 400 °C and of an initial H 2 pressure of 5.6 MPa. Polyisoprene and polystyrene liquefied readily at these conditions; however, neither HDPE nor LDPE liquefied much with these catalysts or conditions. The conversion to THF solubles and product distributions from coprocessing reactions with coal and each polymer performed at the same reaction conditions were compared to those obtained with individual polymers. The coprocessing reactions with polyisoprene and polystyrene yielded thermal and catalytic conversions in the range of 62.3 to 95.5% while the coprocessing reactions with HDPE or LDPE yielded low conversion in the range of 20.2 to 43.2%. Catalytic reactions using carbon black, minerals, and fluid catalytic cracking catalysts were performed with HDPE and LDPE to evaluate their effect on conversion. After pretreatment, the fluid catalytic cracking catalysts showed activity for converting LDPE at 440 °C with an initial H 2 pressure of 5.6 MPa. Subsequent coprocessing reactions of LDPE and coal and commingled plastics and coal were performed with four fluid catalytic cracking catalysts and a zeolite HZSM-5. HZSM-5 was the most effective catalyst for converting both coprocessing systems although more gaseous products were produced than with the fluid catalytic cracking catalysts. The coprocessing reactions with commingled plastics, which consisted primarily of HDPE with some polypropylene, and coal yielded less conversion and less hexane-soluble materials than the LDPE coprocessing system.

Direct liquefaction of waste plastics and coliquefaction of coal-plastic mixtures

We have conducted further investigations of the direct liquefaction reactions of waste plastics, medium and high density polyethylene (PE), polypropylene (PPE) and coal-plastic mixtures, varying the catalyst, temperature, gas, pressure, time and solvent. The experiments used four types of catalysts: a commercial HZSM-5 zeolite catalyst, and three catalysts synthesized in our laboratory, ferrihydrite treated with citric acid, coprecipitated Al 2O 3SiO 2, and a ternary ferrihydrite-Al 2O 3SiO 2. For direct liquefaction of plastics alone, a solid acid catalyst such as HZSM-5 or Al 2O 3SiO 2 markedly improves oil and total liquid yields, as determined by pentane and THF solubility, respectively. Yields are higher when using either a waste oil solvent or no solvent than using tetralin as the solvent. For PE, temperatures of 430 °C or higher are required for good yields, while PPE gives excellent yields at 420 °C. A commingled plastic provided by the American Plastics Council (APC) exhibited peak oil and total liquid yields at 445–460 °C. The oil yields and total liquid from PE (HZSM-5, 430 °C) and the APC commingled waste plastic decreased only slightly with decreasing hydrogen pressure (from 800 to 100 psig H 2 (cold)). Furthermore, yields were as high under nitrogen (200–600 psig, cold) as under hydrogen. Coliquefaction experiments were conducted on 50-50 mixtures of PE, PPE and the APC plastic with Black Thunder coal. For these experiments, the best results were obtained when the solvent was tetralin or a mixture of tetralin and waste oil. Lower yields were observed with only waste oil or with no solvent. Either HZSM-5 or Al 2O 3SiO 2-ferrihydrite increased oil and total yields by approximately 10% at 460 °C. Under the same conditions, yields from a PPE-coal mixture were substantially higher than those from a PE-coal mixture.

Catalytic reactions in waste plastics, HDPE and coal studied by high-pressure thermogravimetry with on-line GC/MS

High-pressure thermogravimetry (TG) with rapid on-line gas chromatography/mass spectrometry (GC/MS) has been used to investigate the effects of different catalysts on decomposition reactions of commingled waste plastics (predominantly PE), high-density polyethylene (HDPE) and mixtures of DECS-6 coal with waste plastics in H 2 at 900 psig. This permits direct evaluation of relative decomposition and residual char amounts as well as yield and composition of the evolved products. Catalysts evaluated for the conversion of waste plastics include solid superacids such as Fe 2O 3 SO 4 2− , Al 2O 3 SO 4 2− , Al 2O 3 SO 4 2− promoted by 0.5% Pt, and ZrO 2 SO 4 2− (all added at 10 wt%), as well as a conventional cracking catalyst of SiO 2Al 2O 3 in a 4:1 ratio, a hydrocracking catalyst of NiMo Al 2O 3 mixed with SiO 2 Al 2O 3 (both added at 50%), and an HZSM-5 zeolite catalyst (added at 10%). Under these conditions cracking activity for waste plastics reveals the following order: SiO 2 Al 2O 3 , HZSM-5 > NiMo Al 2O 3 mixed with SiO 2Al 2O 3 > solid superacids. Of the solid superacids studied, the ZrO 2 SO 4 2− catalyst possesses the highest cracking activity and the approximate order of cracking activity is ZrO 2 SO 4 2− > Al 2O 3 SO 4 2− > Pt/Al 2O 3/SO 4 2− > Fe 2O 3 SO 4 2− no catalyst. The stronger the cracking catalyst, the lighter the aliphatic products and the more abundant the isomeric constituents. Similar results are found for HDPE with these catalysts. For co-processing of coal with commingled waste plastic the HZSM-5 zeolite catalyst shows the most promising results by increasing the rate of the decomposition reactions at 420°C nearly tenfold. Hydrocracking catalysts, such as NiMo Al 2O 3 mixed with SiO 2 Al 2O 3 , show potential promise for co-processing of coal with commingled waste plastic due to their combined hydrogenation and cracking ability. By contrast, a superacid such as ZrO 2 SO 4 2− or a cracking catalyst such as SiO 2 Al 2O 3 appears to have little effect on the decomposition rate of the mixture. To what extent these findings are influenced by transport limitations (e.g. due to incomplete mixing or degree of crystallinity) and/or catalyst pretreatments is being studied further.

Blend structure of commingled plastic from recycled polyethylene and polystyrene

AbstractThe hierarchical morphology of commingled plastic waste in the form of thick beams prepared by the ET‐1 process has been examined. Blends of recycled high‐density polyethylene (RHDPE, New Jersey Curbside Tailings) with 25 and 35 wt % expanded polystyrene (EPS) were compared with blends of a virgin high‐denisty polyethylene resin (VHDPE). At the macroscale, observed with the optical microscope, the beams consisted of a solid skin that extended about one‐third of the distance to the center of the beam and a voided core with about half the density of the skin. The phase morphology of the skin at the microscale was characterized by examining etched cryogenic fracture surfaces in a scanning electron microscope. The blends of RHDPE and VHDPE exhibited a gradient morphology with highly elongated EPS domains near the edge and spherical or co‐continuous EPS domains closer to the core. The morphology gradient was created by the competition between the relaxation rate of the melt‐flow morphology and the cooling rate in the mod. In addition to high‐density polyethylene, a variety of other components were identified in RHDPE by photoacoustic infrared and thermal analysis. These included polypropylene, polystyrene, poly(ethylene terephthalate), and chunks of nonpolymeric material. As a result of the heterogeneous composition, the crystallinity of RHDPE was significantly lower than that of VHDPE. © 1994 John Wiley & Sons, Inc.