Agricultural HDPE pyrolysis for environmental management: Feedstock complexity, reaction dynamics, and circular resource recovery.

The role of polymeric structures and the presence of a catalyst in the pyrolysis of polyolefin mixtures and used tires was studied in a fixed bed reactor at 450 degrees C. Our results showed that while thermal pyrolysis of high density polyethylene (HDPE) produced 23.3%wt of condensable products, a mixture of polyolefins (HDPE, LDPE, and PP) showed an increase of more than 23%wt in this fraction. In both cases, a wide carbon number distribution was obtained for the condensable products, confirming that there was not any selectivity. By using HZSM-5 zeolites, the pyrolysis of pure HDPE was dramatically changed with both more gaseous products and a major selectivity toward C10-C16 hydrocarbons in the condensable fraction. It is noteworthy that, although the PP present in the mixture increases the production of lighter hydrocarbons as compared with pure HDPE, no major differences in product distribution were observed between HDPE and polyolefin mixture in catalytic pyrolysis. However, the zeolites used improved the quality of condensable products that can be used as potential fuels or feedstocks. When used tires were thermally pyrolyzed, a decrease of 33.5%wt in the solid product fraction (char and unreacted polymer) compared with pure HDPE was observed. In the case of catalytic pyrolysis of used tires, the increase of gaseous products is not as pronounced as in pure HDPE. Moreover, the carbon number distribution under catalytic pyrolysis was significantly different compared to that obtained for polyolefins. These results give evidence about the strong effect of both polymer microstructure and mixture on the pyrolysis processes

The increasing amount of plastic waste (PW) generation has become an important concern due to the leveled-off recycling rates. Therefore, governmental agencies around the world, including state governments in the United States, have proposed initiatives to minimize the amount of PW that is landfilled and encourage recycling or energy recovery. Circular economy is a strategy that attempts on reusing PW to produce new polymers while avoiding its disposal and the use of virgin material. Chemical recycling raises an interesting technology prospect due to the potential reduction of pollutant emissions and the establishment of a circular economy through the production of monomers and fuels. This dissertation initially presents a resource assessment for available MSW in Mexico and concludes that when the organic and polyolefin plastic components are converted to liquid hydrocarbon transportation biofuels through a pyrolysis-based pathway, up to 7% of Mexico’s transportation-fuel consumption could be met. A preliminary carbon footprint analysis (CFA) shows that liquid transportation biofuels from the organic portion of MSW (paper, packaging, wood, yard trimmings) sequesters 9.5 g CO2 eq. per MJ biofuel, with significant pathway credits due to avoiding landfill CH4 emissions. The greenhouse gas (GHG) emissions from the conversion of the polyolefin plastic in the MSW are positive (88 g CO2 eq. per MJ), though still lower than current fossil transportation fuels in Mexico (95.5 g CO2 eq. per MJ). In this Ph.D. research, pyrolysis vapors from waste high density polyethylene (HDPE) were subjected to secondary degradation by varying the temperature and vapor residence time (VRT) in the reaction zone of a newly-designed two-stage micropyrolysis reactor (TSMR). Temperature and VRT variations showed a strong effect on the product distribution, with low temperature (625 ºC) and short VRT (1.4 s) producing a wide range of gases and liquid products and with high temperature (675 ºC) and long VRT (5.6 s) producing mostly hydrocarbon gases (monomers) and mono- and poly-aromatics. The last two chapters of the dissertation present a novel multiproduct/multiprocessing pyrolysis-based refinery design for the conversion of 500 tonnes/day of high-density polyethylene (HDPE) waste. The products obtained from the refinery are chemical grade ethylene and propylene, an aromatics mixture, and low- and high-molecular weight hydrocarbon mixtures (MWHCs). The energy efficiency was 72 and 77% for the base case and the heat integrated (HI) refinery, respectively. The net present values (NPVs) were 367 and 383 million U.S. dollars (MM USD), for the base case and the heat

The inert and oxidative flash pyrolysis of High Density Poly-Ethylene (HDPE) is studied up to 20 000 K.s-1, under pressure up to 3.0 MPa and at temperature ranging from 1000 K to 1500 K. These conditions are considered to represent those waited onboard a hybrid rocket engine using HDPE as solid fuel. Recycling applications may also find some interest. The pyrolysis products are analysed by Gas Chromatograph, Flame Ionisation Detector and Mass Spectrometer to quantify the effects of each physical parameter on the HDPE decomposition. The classical products distribution diene-alkene-alkane for each carbon atoms number is shown to be modified at such high temperature because of the pyrolysis of primary products. The pressure effect, which is generally neglected in HDPE pyrolysis studies found in open literature, is proved to be a major factor (up to one order of magnitude on the ethylene mass fraction). The heating rate presents noticeable consequences on the pyrolysis products distribution with a larger formation of light species while heavier ones are favoured under oxidative pyrolysis conditions. The experimental data should serve in the future to improve the accuracy of kinetic mechanisms for later use in numerical computing.

HDPE pyrolysis-steam reforming in a tandem spouted bed-fixed bed reactor for H2 production

Experimental flash pyrolysis of high density polyethylene under hybrid propulsion conditions

ABSTRACTIn this work, the synergistic effect of the γ-ray irradiation and catalyst on the pyrolysis of High-Density Polyethylene (HDPE) waste was investigated in a batch reactor. Two catalysts, Zeolite Socony Mobil–5 (ZSM-5) and Ferric oxide, were used, and their loading was optimized. The results revealed that the degradation temperature significantly reduced with increasing dosage of irradiation. The complete pyrolysis of HDPE waste occurs at a temperature of 400°C and reaction time of 240 min (4 h), while in a case of irradiation-induced pyrolysis, there is higher yield and decrease in the residence time of pyrolysis. Irradiation with a higher dosage (2,000 kGy) increases the rate of thermo-catalytic pyrolysis for HDPE waste and gives maximum conversion.

Effect of carbon nanotubes on thermal pyrolysis of high density polyethylene and polypropylene

Production of light hydrocarbons from pyrolysis of heavy gas oil and high density polyethylene using pillared clays as catalysts

Modelling pyrolysis process for PP and HDPE inside thermogravimetric analyzer coupled with differential scanning calorimeter

An experimental investigation was carried out to study two process parameters of thermocatalytic pyrolysis of high density polyethylene (HDPE) plastic waste, and the liquid yield of pyrolysis (plastic oil) was analyzed over its working characteristics in a direct injection compression ignition (DICI) engine. A series of pyrolysis experiments with four different heating rates (5, 10, 15, and 20 °C/min) were performed in identical environments with the objective of analyzing the heating rate and residence time on end products. It was found that the liquid yield was maximum at the heating rate of 10 °C/min and the residence time decreases with an increase in the heating rate due to variation of reaction kinetics at different heating rates. The characterization of the plastic oil revealed that the major constituents belong to alkene, alkane, and alcohol functional groups; totally 90 six fuel range hydrocarbons were present ranging from C5 to C28, and the other thermophysical properties were comparable with th...

Pyrolysis of high density polyethylene (HDPE) in the open system was studied. A plastic bag for food packing was used as a source of HDPE. Pyrolysis was performed at temperatures of 400, 450 and 500?C, which were chosen based on thermogravimetric analysis. The HDPE pyrolysis yielded liquid, gaseous and solid products. Temperature rise resulted in the increase of conversion of HDPE into liquid and gaseous products. The main constituents of liquid pyrolysates are 1-n-alkenes, n-alkanes and terminal n-dienes. The composition of liquid products indicates that the performed pyrolysis of HDPE could not serve as a standalone operation for the production of gasoline or diesel, but preferably as a pre-treatment to yield a product to be blended into a refinery or petrochemical feed stream. The advantage of a liquid pyrolysate in comparison to crude oil is the extremely low content of aromatic hydrocarbons and the absence of polar compounds. The gaseous products have desirable composition and consist mainly of methane and ethene. The solid residues do not produce ash by combustion and have high calorific values. Co-pyrolysis of HDPE with mineral-rich lignite indicated positive synergetic effect at 450 and 500?C, which is reflected through the increased experimental yields of liquid and gaseous products in comparison to theoretical ones.

Liquid-fed waste plastic pyrolysis pilot plant: Effect of reactor volume on product yields

The study of catalyst type and dispersion on pyrolysis of high density polyethylene (HDPE) was investigated in batch and semi-batch reactor system. The separation system in semi-batch was rapidly separated between oil and gas products while in batch system was separated after cooling down process. The obtained oil products in semi-batch system had higher in short-chain hydrocarbon. Because the increased pressure and the high severity in batch system led to occur side reactions. Two types of catalyst were studied, Cat A was acid catalyst with 200 m2/g surface area and 20 A average pore diameter and HZSM-5 zeolite was stronger acid catalyst with 550 m2/g surface area and 7 A average pore diameter. The catalytic pyrolysis of HZSM-5 zeolite had lower reaction temperature around 400 ?C and produced higher gas yield. These lower temperatures come from high consumed heat for cracking HDPE to gas products. Cat A catalyst was obtained naphtha as main product. The thermal pyrolysis of HDPE was obtained higher in heavy hydrocarbon products such as wax and diesel from lower rate of cracking reaction. The thermal pyrolysis and catalytic pyrolysis of Cat A had the reaction temperature around 430 ?C because lower rate of cracking reaction. The higher acidity of HZSM-5 led to higher rate of cracking reaction and produce higher gas yield products than Cat A. For dispersion of catalyst in HDPE, the extruded plastic with catalyst shows the highest activity of catalyst than mixing with impeller because waxy state before oil formation in pyrolysis of HDPE was difficult to make the dispersion. The increased dispersion of catalyst was higher rate of cracking reaction. This result was obtained in both Cat A and HZSM-5 zeolite.

Investigation of high-density polyethylene pyrolyzed wax for asphalt binder modification: Mechanism, thermal properties, and ageing performance

Coprocessing behavior of mixtures of high density polyethylene (HDPE) and deoiled cakes of Jatropha and Karanja was studied by thermogravimetric analyses under dynamic conditions in the presence of nitrogen atmosphere and compared with those of individual materials. Experiments were carried out in the temperature range of ambient temperature to 900 °C at two heating rates (5 and 20 °C/min). Kinetic studies indicated activation energies for HDPE decomposition to be 235 and 258 kJ/mol at heating rates of 5 and 20 °C/min, respectively. Values of activation energy for pyrolysis of cakes of Jatropha and Karanj and those for cake-HDPE mixtures varied with the rate of heating as well as with the three temperature ranges. This variation has been explained based on the materials’ decomposition behavior. Reduction in activation energy for decomposition of the mixtures implies synergetic effects to be existing when two materials are coprocessed together.