Microwave catalytic co-pyrolysis of waste cooking oil and low-density polyethylene to produce monocyclic aromatic hydrocarbons: Effect of different catalysts and pyrolysis parameters

Preparation, characterization and evaluation of microwave-assisted synthesized selenylation Codonopsis pilosula polysaccharides

In this work, the selenylation Codonopsis pilosula polysaccharide (Se-CPPS) were synthesized using an optimized microwave-assisted method. Then, physicochemical properties, including molecular weight, particle size, valence state of selenium, antioxidant capacity, release mechanism of selenium under gastrointestinal conditions, as well as their effects on HT-29 cell viability were comprehensively investigated. The results demonstrated that Se-CPPS with the highest selenium content (21.71 mg/g) was synthesized using 0.8% nitric acid concentration under microwave conditions of 90 min at 70 °C. FTIR and XPS analysis revealed that Se was bound to the polysaccharide chain in the form of O-Se-O and O-H···Se, with a valence state of either 0 or +4. In vitro investigations on antioxidant activity and selenium release capacity indicated that selenization not only enhanced the antioxidant activity of CPPS but also endowed Se-CPPS with robust selenium release capability in simulated gastric digestion. The effects of Se-CPPS on HT-29 cells was further investigated by CCK-8 method. The results showed that the selenide modification effectively reduced the toxicity of Na2SeO3 and enhanced the viability of CPPS. The findings of this study offer valuable methodological guidance for the synthesis of Se-polysaccharides with superior functional properties.

Production of C5-C12 olefins by catalytic pyrolysis of low-density polyethylene with MCM-41 in CO2/N2

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.

Breakdown of biomass for energy applications using microwave pyrolysis: A technological review

The agricultural industry faces a permanent increase in waste generation, which is associated with the fast-growing population. Due to the environmental hazards, there is a paramount demand for generating electricity and value-added products from renewable sources. The selection of the conversion method is crucial to develop an eco-friendly, efficient and economically viable energy application. This manuscript investigates the influencing factors that affect the quality and yield of the biochar, bio-oil and biogas during the microwave pyrolysis process, evaluating the biomass nature and diverse combinations of operating conditions. The by-product yield depends on the intrinsic physicochemical properties of biomass. Feedstock with high lignin content is favourable for biochar production, and the breakdown of cellulose and hemicellulose leads to higher syngas formation. Biomass with high volatile matter concentration promotes the generation of bio-oil and biogas. The pyrolysis system's conditions of input power, microwave heating suspector, vacuum, reaction temperature, and the processing chamber geometry were influence factors for optimising the energy recovery. Increased input power and microwave susceptor addition lead to high heating rates, which were beneficial for biogas production, but the excess pyrolysis temperature induce a reduction of bio-oil yield.

Green Aromatic Epoxidation with an Iron Porphyrin Catalyst for One-Pot Functionalization of Renewable Xylene, Quinoline, and Acridine

Sustainable functionalization of renewable aromatics is a key step to supply our present needs for specialty chemicals and pursuing the transition to a circular, fossil-free economy. In the present work, three typically stable aromatic compounds, representative of products abundantly obtainable from biomass or recycling processes, were functionalized in one-pot oxidation reactions at room temperature, using H₂O₂ as a green oxidant and ethanol as a green solvent in the presence of a highly electron withdrawing iron porphyrin catalyst. The results show unusual initial epoxidation of the aromatic ring by the green catalytic system. The epoxides were isolated or evolved through rearrangement, ring opening by nucleophiles, and oxidation. Acridine was oxidized to mono- and di-oxides in the peripheral ring: 1:2-epoxy-1,2-dihydroacridine and anti-1:2,3:4-diepoxy-1,2,3,4-tetrahydroacridine, with TON of 285. o-Xylene was oxidized to 4-hydroxy-3,4-dimethylcyclohexa-2,5-dienone, an attractive building block for synthesis, and 3,4-dimethylphenol as an intermediate, with TON of 237. Quinoline was directly functionalized to 4-quinolone or 3-substituted-4-quinolones (3-ethoxy-4-quinolone or 3-hydroxy-4-quinolone) and corresponding hydroxy-tautomers, with TON of 61.

Co-torrefaction of corncob and waste cooking oil coupled with fast co-pyrolysis for bio-oil production

Lignocellulosic biomass is a rich source of fixed renewable carbon and a promising alternative to fossil sources. However, low effective hydrogen to carbon ratio limits its applications. This work studied the influence of oil-bath co-torrefaction of corncob and waste cooking oil for co-pyrolysis. It was compared with dry torrefaction and hydrothermal wet torrefaction firstly. Residual of oil-bath co-torrefaction were the highest of 97.01 %. Oil-bath co-torrefaction could maximize hydrogen atoms retention in corncob, which has a positive significance for deoxygenation during pyrolysis. Oil-bath co-torrefaction could also reduce the average activation energy required for corncob decomposition, while it was increased with dry torrefaction. Oil-bath co-torrefaction coupled with co-pyrolysis was more suitable for hydrocarbon-rich bio-oil production. Oil-bath co-torrefaction temperature had the greatest influence on bio-oil composition. High pressure promoted formation of the CC double bond and degradation of lignin, which further promoted the formation of monocyclic aromatics in bio-oil.

Synthesis of CaO from waste shells for microwave-assisted catalytic pyrolysis of waste cooking oil to produce aromatic-rich bio-oil

Energy shortage and environmental pollution have attracted long-term attention. In this study, CaO were prepared from waste eggshell (EGC), preserved egg shell (PEC), clam shell (CLC) and crab shell (CRC), which were then compared with commercial CaO (CMC) to catalyze microwave-assisted pyrolysis of waste cooking oil (WCO) for enrichment of aromatics in bio-oil. The characterization results indicated that EGC and CLC contained 95.54% and 95.61% CaO respectively, which were higher than that of CMC (95.11%), and the pore properties of EGC were the best. In addition, the effects of CaO type and catalytic mode on pyrolysis were studied. In CaO catalytic pyrolysis, CMC and CLC in-situ catalysis produced more aromatics than ex-situ catalysis, and PEC and CRC were more conducive to aromatics formation in ex-situ condition. EGC was conducive to produce benzene, toluene and xylene (BTX) both in in-situ (19.04%) and ex-situ (20.76%) catalytic pyrolysis. In CaO/HZSM-5 catalysis, the optimal dual catalytic mode for generating monocyclic aromatic hydrocarbons (MAHs) was Mode A (CaO separated from HZSM-5 for ex-situ catalysis), and EGC/HZSM-5 performed well in benzene, toluene and xylene (BTX) production.

Microwave-Assisted Pyrolysis of Biomass with and without Use of Catalyst in a Fluidised Bed Reactor: A Review

Lignocellulosic biomass and waste, such as plastics, represent an abundant resource today, and they can be converted thermo-chemically into energy in a refinery. Existing research works on catalytic and non-catalytic pyrolysis performed in thermally-heated reactors have been reviewed in this text, along with those performed in microwave-heated ones. Thermally-heated reactors, albeit being the most commonly used, present various drawbacks such as superficial heating, high thermal inertia and slow response times. That is why microwave-assisted pyrolysis (MAP) appears to be a very promising technology, even if the process does present some technical drawbacks as well such as the formation of hot spots. The different types of catalysts used during the process and their impacts have also been examined in the text. More specifically, studies conducted in fluidised bed reactors (FBR) have been detailed and their advantages and drawbacks discussed. Finally, future prospects of MAP have been briefly presented.

Current Trends in Waste Plastics’ Liquefaction into Fuel Fraction: A Review

Polymers and plastics are crucial materials in many sectors of our economy, due to their numerous advantages. They also have some disadvantages, among the most important are problems with the recycling and disposal of used plastics. The recovery of waste plastics is increasing every year, but over 27% of plastics are landfilled. The rest is recycled, where, unfortunately, incineration is still the most common management method. From an economic perspective, waste management methods that lead to added-value products are most preferred—as in the case of material and chemical recycling. Since chemical recycling can be used for difficult wastes (poorly selected, contaminated), it seems to be the most effective way of managing these materials. Moreover, as a result this of kind of recycling, it is possible to obtain commercially valuable products, such as fractions for fuel composition and monomers for the reproduction of polymers. This review focuses on various liquefaction technologies as a prospective recycling method for three types of plastic waste: PE, PP and PS.

Investigation of product selectivity and kinetics of poplar sawdust catalytic pyrolysis over bi-metallic Iron-Nickel/ZSM-5 catalyst

Py-GC/MS and thermogravimetric analysis were carried out to systematically explore product selectivity and kinetics of poplar sawdust catalytic pyrolysis over bi-metallic Fe-Ni/ZSM-5. The results showed that the Fe-Ni/ZSM-5 exhibited an additive effect on the production of monocyclic aromatic hydrocarbons compared to mono-metallic catalysts (Fe/ZSM-5 or Ni/ZSM-5). Fe-Ni/ZSM-5 further increased the yield of toluene (17.28 mg g^-1), which was 41.4% and 80.9% higher than Fe/ZSM-5 and Ni/ZSM-5, respectively. According to the kinetic analysis, the average activation energy obtained from catalytic pyrolysis with Fe-Ni/ZSM-5 using the methods of Friedman, Starink, Flynn-Wall-Ozawa, and Kissinger-Akahira-Sunose was 156.19, 152.39, 154.30, and 152.11 kJ mol^-1, respectively. Fe-Ni/ZSM-5 addition lowered the activation energy compared to non-catalytic pyrolysis at the conversion rate of 0.15-0.75. The overall catalytic pyrolysis process of poplar sawdust follows the diffusion and nucleation models. The thermodynamic parameters (enthalpy and entropy) showed positive and negative values, respectively, indicating non-spontaneous reactions during the catalytic pyrolysis process.

Effect of Reaction Parameters on Catalytic Pyrolysis of Waste Cooking Oil for Production of Sustainable Biodiesel and Biojet by Functionalized Montmorillonite/Chitosan Nanocomposites

The use of waste oils as pyrolysis feedstocks to manufacture high-grade biofuels has prompted researchers to focus on developing renewable energy to overcome the depletion of fossil fuel supplies and the global warming phenomena. Because of their high hydrogen and volatile matter concentration, waste oils are ideal raw materials for the production of biofuels. It is challenging to attain satisfactory results with conventional methods, such as transesterification, gasification, solvent extraction, and hydrotreating due to flaws such as high energy demand, long time, and high operating costs. Catalytic pyrolysis of waste edible oils was employed as a resource for the generation of biodiesel. The application of the catalytic cracking process has the potential to alleviate the existing situation. In this study of catalytic cracking conversion of waste cooking oil to produce different biofuels, grades were investigated using two heterogeneous catalysts. The catalysts were activated montmorillonite (PAMMT) clay and its modified form using a chitosan biopolymer (PAMMT-CH) nanocomposite. The catalysts were identified using infrared spectroscopy, X-ray diffraction patterns, transmittance electron microscopy images, surface area, and thermal stability. The catalysts were tested for their performances using different amounts (0.1-1% by weight) at a temperature assortment of 200-400 °C during a time range of 60-300 min. The experimental studies were carried out in a batch reactor. GC mass spectra were used to investigate the catalytic cracking products. Fractional distillation is used to separate the final products from various reaction conditions. The physicochemical properties of resulting biofuels were profiled by quantifying their densities, viscosities, specific gravities, pour points, flash and fire points, cetane numbers, carbon and ash residues, and sulfur contents. The optimum conditions of the yield product were 300 and 400 °C, catalyst weights of 0.7 and 0.8% w/v, and reaction times of 120 and 180 min concerning the (PAMMT) and (PAMMT-CH) nanocomposite, respectively. The determined properties were located within the limits of the specific standards of ASTM specifications. As a result, the PAMMT nanocomposite produced biofuel comparable to biodiesel according to ASTM specifications, while the PAMMT-CH nanocomposite produced biofuel comparable to biojet.