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•Microwave-assisted fixed bed pyrolyzer with ex-situ catalytic bed was adopted.•A co-melting feeding process of polyethylene and waste edible oil was proposed.•This process enhances ...the synergistic production of monocyclic aromatics.•The mixing ratio of feedstocks has an important effect on product distribution.•The catalytic co-pyrolysis mechanism was speculated.
In this study, a new delayed feeding process for blending waste edible oil (WEO) as cosolvent with molten low-density polyethylene (LDPE) applied in microwave-assisted fixed bed pyrolysis was proposed. The experiment was carried out at the melting temperature of 250 ℃, the pyrolysis temperature of 550 ℃, and the catalytic temperature of 450 ℃. The co-feeding of the WEO and molten LDPE effectively promoted the formation of light aromatics, with the content of monocyclic aromatic hydrocarbons as high as 82.69 % (LDPE/WEO = 1:3) and the relative content of BTEX (benzene, toluene, ethylbenzene, xylenes) as high as 65.96 %. The proportion of feedstocks affects the distribution of pyrolysis products by adjusting the content of hydrogen radicals in the pyrolysis system. Hydrogen radicals derived from LDPE can combine with oxygen-containing intermediate from triglycerides, to promote the removal of oxygen in the form of H2O, and inhibit the decarboxylation and decarbonylation reactions. Compared with the pre-feeding process, the relative content of BTEX increased by 14.43 % and the relative content of PAHs decreased by 10.86 %. The application of downdraft reactors further improved the relative content of BTEX in pyrolysis oil. When the mass of SiC was 500 g, the peak relative content of BTEX was 69.79 %. This study provides a new process for the effective production of light aromatic hydrocarbons.
•Ex-situ catalytic technology was used to co-pyrolysis C. odorata and soapstock.•The optimal catalytic parameters and C. odorata and soapstock ratio were determined.•Soapstock proved to be a good ...hydrogen supplier to increase the quality of bio-oil.
Fast microwave-assisted catalytic co-pyrolysis of Chromolaena odorata (C. odorata) and soybean soapstock with HZSM-5 as an ex-situ catalyst was investigated. Effects of catalytic temperature, feedstock: catalyst ratio and C. odorata: soybean soapstock ratio on the yield and composition of the bio-oil were discussed. Results showed that catalytic temperature greatly influenced the bio-oil yield. Co-pyrolysis of C. odorata and soybean soapstock improved the bio-oil yield, and the maximum bio-oil yield of 55.14% was obtained at 250 °C. However, the addition of HZSM-5 decreased bio-oil yield but improved the quality of bio-oil. Moreover, the proportion of oxygen-containing compounds decreased dramatically with the addition of soybean soapstock. The C. odorata: soybean soapstock ratio of 1:2 and feedstock: catalyst ratio of 2:1 were the optimal condition to upgrade the bio-oil. In addition, the resulted biochar contained various essential elements and could be used as soil repair agent.
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•The pyrolysis products of different types of waste cooking oil were compared.•The decomposition rate of the ester bond is faster than the fatty acid carbon chain.•Fatty acid ...composition affects the generation of pyrolysis products.•The degree of deoxidation is related to the raw material H/Ceff.•The presence of methoxy is conducive to the formation of benzene and alkyl benzene.
In this study, aromatics were prepared by continuous microwave pyrolysis experiment in the presence and absence of HZSM-5 using different types of waste cooking oil (corn oil, rice oil, rapeseed oil, sunflower seed oil, soybean oil, blending oil, peanut oil, palm oil), and the effects of raw material characteristics on pyrolysis products were compared. The results showed that the fatty acid composition of waste cooking oil affects the composition of pyrolysis products. For example, linoleic acid promotes naphthene and inhibits olefin formation; oleic acid is easy to form C9 and C10 compounds; compared with oleic acid and linoleic acid, palmitic acid is not conducive to deoxidation. In addition, the deoxidation degree of waste cooking oil is related to the raw material H/Ceff, and the order from high to low is corn oil > rapeseed oil > sunflower seed oil > peanut oil > soybean oil. The yield of the oxygen-containing compounds is inversely proportional to it. With the use of HZSM-5 catalyst, the content of toluene and xylene in liquid products is significantly increases, especially the content of xylene. The catalytic effect of rice oil is the most significant, with xylene content increased by 19.2% compared with the non-catalytic pyrolysis. This provides a reference for the efficient treatment of waste oil and the production of aromatics in the future.
To address the challenging issues of waste plastic pollution and petroleum shortage, we report herein a pulse pressurized catalytic pyrolysis process where polyethylene is continuously converted into ...aromatics using HZSM-5 catalyst incorporated with hydrated SiO2. Pressurization improves the activity of single-pulse pyrolysis of polyethylene by 14.42%. In contrast to the linear decrease of BTEXS relative yield with a K value of − 0.23 under non-pressurized conditions, pressurization results in a notable stability in the latter stage, characterized by a K value of only − 0.063. Comprehensive catalyst characterization demonstrates that pressurization promotes the release of water from hydrated SiO2, enabling HZSM-5 to effectively undergo dealumination and obtain suitable acidity and pore structure, and ultimately enhancing the resistance to carbon deposition. In summary, pressurization improves both pyrolysis activity and catalysis stability, offering a promising strategy for the high-value utilization of waste plastics.
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•Pulse pressurized catalytic pyrolysis process for plastic upcycling is proposed.•Pressurization improves single pulse pyrolysis activity of polyethylene by 14.42%.•Pressurization improves overall catalytic stability of HZSM-5.•Pressurization promotes dealumination of HZSM-5 with synergism of hydrated SiO2.
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•Microwave pyrolysis treated polyethylene terephthalate and low-density polypropylene simultaneously.•Coconut husk carbon showed favorable process features and product features as ...microwave absorbent.•This process enhances the synergistic production of monocyclic aromatics.•High yields of oil (42.50 wt%) were obtained with a high content of monocyclic aromatics (77.11 %).
The application of biochar as microwave absorbers in microwave-assisted catalytic fast pyrolysis (MACFP) has been widely studied. It has been reported that coconut husk carbon (CHC) showed good process characteristics and product distribution as microwave absorbers. However, the existing studies did not pay much attention to the reusability of CHC absorbers. In this study, the CHC absorbers prepared from agricultural and forestry wastes were reused in multiple cycles in the MACFP of polyethylene terephthalate (PET) and low-density polyethylene (LDPE). Compared with typical microwave absorbers such as spherical silicon carbide (SiC) and granular activated carbon (GAC), CHC demonstrated favorable process characteristics with relatively high heating rate (29 °C/min) and short heating time (within 12 min). In terms of product properties, the highest liquid yield of 51.67 wt% and the highest content of monocyclic aromatic hydrocarbons (MAHs) of 82.82 % were obtained at the appropriate pyrolysis temperature (550 °C). After five consecutive uses, the CHC bed still produced comparable heating profiles and product distributions, compared to that of SiC. At the same time, a positive synergistic effect between PET and LDPE was observed. The co-feeding of PET and LDPE (50L50P) appropriately increased the liquid yield (42.50 wt% vs 38.75 wt%) and the relative content of MAHs (77.11 % vs 72.96 %) in comparison to their theoretical value. Finally, this study supplies a new strategy for utilizing recycled CHC as a microwave absorber for the treatment of hydrogen-rich and hydrogen-deficient mixed plastic wastes to produce MAHs products, which also reduces waste and realizes energy conversion.
The current high volume of plastic waste, but low recycling rate, has led to environmental pollution and wasted energy. Greenhouse gas CO2 can facilitate thermal cracking to dehydrogenate waste ...plastics, and has potential value for producing olefins. In this work, the pyrolysis properties of low-density polyethylene (LDPE) were studied by thermogravimetric analysis and Py-GC/MS. The effect of the pyrolysis atmosphere, using N2 or CO2, with various MCM-41 catalyst ratios on pyrolysis product distribution, were investigated. The experimental results show that the olefin selectivity under a N2 atmosphere was from 30.32 % to 44.66 % which increased as the MCM-41 catalyst was increased. Under a CO2 atmosphere, the olefin selectivity reached a maximum of 60.39 %. The Boudouard reaction was also enhanced by the introduction of CO2. The carbon content of the subdivided olefins showed that in CO2, the promotion of C5-C12 olefins was relatively weak when non-catalyzed or at low catalytic ratios, but increased significantly at higher MCM-41 catalyst ratios. With a ratio of LDPE: MCM-41 = 5:4, the CO2 atmosphere showed the greatest promotion of C5-C12 olefins over N2, with an increase of 14.66 % compared to N2, representing a 48.54 % yield of the liquid product. Producing C5-C12 olefins under these conditions maximized energy efficiency. These results show that catalytic pyrolysis of LDPE under a CO2 atmosphere has great potential to produce C5-C12 olefins, which can be used to produce high-value chemicals such as naphtha and gasoline. This opens new opportunities for the chemical recycling of plastic waste.
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•The effects of atmosphere and catalyst ratio on the product were investigated.•Olefin selectivity in N2 increased from 33.07 % to 44.66 % with the addition of MCM-41.•In the CO2 atmosphere, C5-C12 olefins are 14.66 % more selective compared to N2.•The introduction of CO2 promotes the Boudouard reaction.•The C5-C12 olefins produced can be applied to make naphtha, gasoline, and others.
The single-use of polyolefins-based individual protective equipment has led to the rapid generation of substantial plastic waste. This study aimed at cleaner disposal of the polyolefin waste, and ...carried out the continuous microwave pyrolysis (CMP) of low-density polyethylene (LDPE) over dual-catalyst beds of MCM-41 and HY. The dual-catalyzed trial was able to produce more condensate fractions with higher selectivity of monocyclic aromatic hydrocarbons (MAHs), compared with using only MCM-41 or HY zeolite. It was because the larger pore size of the MCM-41 catalyst (4.00 nm) could crack long-chain polyolefin intermediates into shorter chains. This alleviates steric and diffusional resistance while entering and exiting the micropores of the HY zeolite (0.74 × 0.74 nm). The maximum liquid yield (63.75 wt%) and MAHs selectivity (78.21%) were achieved at a catalysis temperature of 450 °C, feedstock to catalyst ratio of 8:3, and HY to MCM-41 ratio of 2:1. In addition, the performance of the CMP reactor was also compared favorably with the batch microwave pyrolysis (BMP) reactor under the same conditions. It has been found that the CMP reactor generated more MAHs products, whereas the BMP reactor was more selective for the generation of polycyclic aromatic hydrocarbons (PAHs) and gas products. The combination of CMP and the co-catalysis process offers new insight into sustainable management and value-added recovery of medical plastic waste.
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•A dual-catalyst bed of MCM-41 and HY was developed in a continuous microwave pyrolysis system.•High yields of oil (63.75 wt%) were obtained with high aromatic content.•The comparisons between continuous and batch microwave pyrolysis were analyzed.•Effective conversion of waste plastics to gasoline-range hydrocarbons was achieved.
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•Microwave-assisted catalytic fast co-pyrolysis technology was used in a downdraft system.•Using microwave hydrothermal synthesis synthesized the ZSM-5/SiC composite catalyst.•The ...composite catalyst was SiC ceramic foam as support to form a film of ZSM-5 on the surface.
A ZSM-5/SiC composite catalyst was synthesized and characterized by Brunauer–Emmett–Teller analysis, X-ray diffraction, and scanning electron microscopy in this study. The composite catalyst had the characteristics of ZSM-5 and SiC, and the surface of SiC grew evenly with a layer of ZSM-5. The effect of the composite catalyst on the product distribution and chemical composition in a co-pyrolysis downdraft system was investigated. In a down system with a catalytic temperature of 450 °C, a feed-to-catalyst ratio of 2:1, and a soybean-soapstock-to-straw ratio of 1:1, the proportions of alkanes, olefins, aromatics, and phenoxy compounds were 6.82%, 4.5%, 73.56% and 11.11%, respectively. The composite catalyst combined the catalytic performance of ZSM-5 and SiC, increasing the proportion of aromatics and decreasing the proportion of oxygen-containing compound in the bio-oil. Moreover, the composite catalyst maintained its activity after reusing several times.
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•Microwave-assisted catalytic pyrolysis reaction occurred in a dual microwave system.•Composite catalyst was prepared by shaping SiC powder with ZSM-5.•Composite catalyst displayed ...better catalysis under microwave irradiation.
The composite catalysts were synthesized with SiC powder and ZSM-5 and were characterized by Brunauer-Emmett-Teller, X-ray diffraction, thermogravimetric analysis, pyridine-infrared spectroscopy, and scanning electron microscopy. The catalysts showed a high heating rate and excellent catalytic performance for pyrolysis vapors, and the product fractional distribution and chemical compositions of bio-oil in a tandem system (microwave pyrolysis and microwave ex-situ catalytic reforming) was examined. Experimental results confirmed the quality of bio-oil produced by the microwave-induced catalytic reforming was better than that product through electric heating. Additionally, 36.94 wt% of bio-oil was obtained using the catalyst with 20%ZSM-5/SiC under the following conditions: feed-to-catalyst ratio, 2:1; pyrolysis temperature, 550 °C; and catalytic temperature, 350 °C. The selectivities of hydrocarbons reached up to 75.88%. After five cycles, the activity of the regenerated composite catalyst was retained at 95% of the original catalyst.
