Formation Of Aromatic Compounds Research Articles

Glycation modification of protein hydrolysate from channel catfish (Ictalurus Punetaus) viscera to mitigate undesirable flavor: Unraveling structure and flavor characteristics

To investigate the impacts of glycation modification on the structure and flavor of fish viscera-derived protein hydrolysates, channel catfish viscera was utilized and hydrolyzed by Flavourzyme, followed by glycation with glucosamine, xylose, ribose and glucose, respectively. The structural characteristics, taste and odor of glycated products were evaluated. The results revealed that glycation led to an increase in peptides (<1 kDa) and a decrease in peptide fraction (>5 kDa). UV and fluorescence spectra indicated a gradual rise in absorbance and fluorescence intensity. Glucosamine-induced glycation significantly mitigated bitterness, while enhancing saltiness and umami. GC–MS/MS analysis revealed that glycation led to reduced undesirable odor, and formation of aromatic compounds. LC-MS/MS identified Arg and Lys as the main modification sites. Interestingly, aldehydes were found to modify peptides via carbonyl-amine reaction, leading to decreased fishy odor. The present study contributes to flavor improvement of fish viscera-derived peptides through glycation and high-value utilization of fish viscera.

Catalytic co-pyrolysis of yellow poplar and HDPE using MOF-incorporated HY zeolite catalysts

Catalytic co-pyrolysis of yellow poplar and high-density polypropylene (HDPE) was conducted using metal oxide on hydrogen y-type (HY) zeolite to selectively produce monoaromatic hydrocarbons. The reaction was investigated using a tandem micro-reactor connected to a gas chromatography–mass spectrometry (GC–MS) system, encompassing both in-situ and ex-situ studies. Fe oxide/HY and Cu oxide/HY catalysts, prepared via a metal–organic framework (MOF)-incorporated technique, demonstrated excellent metal dispersion and enhanced electron density. The Cu oxide/HY catalyst showed significant production of benzene, toluene, ethylbenzene, and xylene, reaching up to 28% in in-situ studies. Owing to its strong acid sites, this catalyst facilitated the formation of aromatic compounds. In ex-situ studies, furan and acetaldehyde were consumed through the Diels–Alder reaction. The increase in aromatic compounds was highlighted by a synergistic effect percentage as high as 175%. The mechanism of aromatic formation was elucidated through dealkylation, Diels–Alder, and aromatization reactions. The Cu oxide/HY catalyst, combined with the MOF-incorporated preparation technique presents a promising system for catalytic co-pyrolysis of biomass and HDPE. This approach will facilitate efficient and sustainable aromatic hydrocarbon production from renewable and plastic waste sources.

Relationship between flavor characteristics and lipid oxidation in air-dried beef at different roasting stages

Lipid oxidation plays a key role in the formation of flavor during hot processing. The purpose of this study was to investigate the lipid oxidation, lipid molecular changes and their effects on flavor of air-dried beef at different roasting stages. The results revealed that the degree of lipid oxidation increased and the unsaturation of fatty acids decreased from 47.30% to 30.77%. A total of 48 volatile compounds were identified by headspace-solid phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS). Notably, the types and contents of volatile compounds in S3 group exceeded those in S1 and S2, showing significant differences in the degree of separation among all groups. The aroma differences among the groups were associated with aromatic compounds formed by the oxidation of lipids. Moreover, a total of 59 lipids with significant differences were identified through liquid chromatography-tandem mass spectrometry (LC-MS/MS). These lipids may have major roles in the formation of aromatic compounds, particularly triglyceride, phosphatidylcholine, and lysophosphatidylcholine. This investigation elucidated the mechanisms for the flavor developments of air-dried beef during roasting stages.

Unveiling the synthesis of aromatic compounds in sauce-flavor Daqu from the functional microorganisms to enzymes

Aromatic compounds serve as the primary source of floral and fruity aromas in sauce-flavor (Maotai flavor) baijiu, constituting the skeleton components of its flavor profile. Nevertheless, the formation mechanism of these compounds and key aroma-producing enzymes in sauce-flavor Daqu (fermentation agent, SFD) remain elusive. Here, we combined metagenomics, metaproteomics, metabolomics, and key enzyme activity to verify the biosynthesis pathway of aromatic compounds and to identify key enzymes, genes, and characteristic microorganisms in SFD. The results showed that the later period of fermentation was critical for the generation of aromatic compounds in SFD. In-situ verification was conducted on the potential key enzymes and profiles in various metabolites, providing comprehensive evidence for the main synthetic pathways of aromatic compounds in SFD. Notably, our results showed that primary amine oxidase (PrAO) and aldehyde dehydrogenase (ALDH) emerged as two key enzymes promoting aromatic compound synthesis. Additionally, two potential key functional genes regulating aromatics generation were identified during SFD fermentation through correlation analysis between proteins and relevant metabolites, coupled with in vitro amplification test. Furthermore, original functional strains (Aspergillus flavus-C10 and Aspergillus niger-IN2) exhibiting high PrAO and ALDH production were successfully isolated from SFD, thus validating the results of metagenomics and metaproteomics analyses. This study comprehensively elucidates the pathway of aromatic compound formation in SFD at the genetic, proteomic, enzymatic, and metabolomic levels, providing new ideas for the investigation of key flavor substances in baijiu. Additionally, these findings offer valuable insights into the regulatory mechanisms of aromatic compounds generation.

Correlation between the bacterial flora and sensory quality of Bayannur sour porridge

In this study, the bacterial flora structure, sensory quality and culturable lactic acid bacteria resources of sour porridge in Bayannur area were analyzed. Furthermore, these bacterial sequencing data were combined with the high-throughput sequencing data of Ordos sour porridge to analyze the microbiota differences. MiSeq results showed that Lactiplantibacillus, Acetobacter, Lacticaseibacillus, Lactobacillus, and Limosilactobacillus were the main bacterial genera in sour porridge. Further comparative analysis showed that the average relative abundance of 7 dominant bacteria genera was significantly higher in sour porridge from Bayannur area (P < 0.05). Electronic nose and electronic tongue demonstrated that the primary volatile flavor substances in sour porridge were terpene compounds, and the change in taste characteristics was mainly reflected in the sour taste index. Correlation showed that most of LAB genera and Acetobacter were positively correlated with the formation of aromatic compounds. Pure culture showed that Lacticaseibacillus paracasei and Lactiplantibacillus plantarum were the dominant LAB in sour porridge. Overall, certain differences in the bacterial flora of sour porridge from different regions were identified, with Lactiplantibacillus, Acetobacter, Lacticaseibacillus, Lactobacillus, and Limosilactobacillus being characteristic of sour porridge in Bayannur area. Moreover, some LAB genera and Acetobacter were found to have a positive effect on flavor formation in sour porridge.

A Short Review: Changes in the Physical-Chemical Properties of Cacao Beans During the Fermentation Process

Fermentation is one of the main processes influencing cacao beans’ quality. Proper post-harvest cacao processing can affect the quality of cacao beans. Spontaneous fermentation of cacao beans is carried out carefully for 5 d to 7 d, characterized by a series of activities of certain microorganisms from three groups of microorganisms: yeasts, lactic acid, and acetic acid. Yeast aims to liquefy the pulp, while lactic acid and acetic acid bacteria play a role in raising and lowering the pH of cacao beans during fermentation. The activity of microorganisms affects the formation of aromatic compounds in fermented cacao beans. During the fermentation process, there is a change in pH and an increase in temperature in the seed heap; this creates conditions that cause changes in the seed’s structure at the cellular level and the metabolites present in the seeds. Leucine, alanine, phenylalanine, and tyrosine are precursors contributing to cacao and chocolate aroma formation. The post-harvest processes affect the yield of cacao beans that will be used in the chocolate industry. Each process must be considered to produce high-quality fermented cacao beans.

Proposal for Enhancing the Taste and Nutritional Value of Braised Fish

Braised fish, a highly popular Chinese dish known for its delectable taste and rich nutritional content, is prone to being affected by factors such as its inherent fishy taste. To elevate the dish's flavor profile and impart a delightful aroma, it becomes essential to mask the fishy taste effectively. This study compared the salt solution method, sensory masking method, biological method, and acid-base method to comprehensively analyze and address the underlying causes of the fishy taste. It was observed that both the salt solution method and sensory masking method proved successful in concealing the fishy smell. While the biological method effectively mitigated the production of fishy substances, it fell short in completely eliminating the fishy smell. On the other hand, the acid-base method demonstrated promising results in significantly reducing the fishy odor. Furthermore, manipulating the Maillard reaction's efficiency by controlling water activity and temperature through the use of the control variable method was studied. The highest Maillard reaction rate was achieved when the water activity was set at 0.7, and a neutral or weak base pH was maintained. Optimizing temperature and processing time led to the successful formation of aromatic compounds while minimizing damage to human cells. In addition to enhancing the taste, incorporating vegetables such as tofu, broad beans, or celery into braised fish recipes can offer additional health benefits, such as preventing obesity and reducing the presence of carcinogens.

Chemical upcycling of PVC-containing plastic wastes by thermal degradation and catalysis in a chlorine-rich environment

Chlorine (Cl)-containing chemicals, including hydrogen chloride, generated during thermal degradation of polyvinyl chloride (PVC) and corresponding mixture impede the chemical recycling of PVC-containing plastic wastes. While upgrading plastic-derived vapors, the presence of Cl-containing chemicals may deactivate the catalysts. Accordingly, herein, catalytic upgrading of pyrolysis vapor prepared from a mixture of PVC and polyolefins is performed using a fixed-bed reactor comprising zeolites. Among the H-forms of zeolites (namely, ZSM-5, Y, β, and chabazite) used in this study, a higher yield of gas products composed of hydrocarbons with lower carbon numbers is obtained using H-ZSM-5, thus indicating further decomposition of the pyrolysis vapor to C1–C4 hydrocarbons on it. Although the formation of aromatic compounds is better on H-ZSM-5, product distributions can be adjusted by further modifying the acidic properties via the alteration of the Si/Al molar ratio, and maximum yields of C1–C4 compounds (60.8%) and olefins (64.7%) are achieved using a Si/Al molar ratio of 50. Additionally, metal ion exchange on H-ZSM-5 is conducted, and upgrading of PVC-containing waste-derived vapor to aromatic chemicals and small hydrocarbon molecules was successfully performed using Co-substituted H-ZSM-5. It reveals that the highest yield of gas products on 1.74 wt% cobalt (Co)-substituted H-ZSM-5 is acquired via the selection of an appropriate metal and metal ion concentration adjustment. Nevertheless, introduction of excess Co into the H-ZSM-5 surface decreases the cracking activity, thereby implying that highly distributed Co is required to achieve excellent cracking activity. The addition of Co also adjusted the acid types of H-ZSM-5, and more Lewis acid sites compared to Brønsted acid sites selectively produced olefins and naphthenes over paraffins and aromatics. The proposed approach can be a feasible process to produce valuable petroleum-replacing chemicals from Cl-containing mixed plastic wastes, contributing to the closed loops for upcycling plastic wastes.

A novel solar disk chamber reactor for agricultural waste recycling and biochar production

The quality and properties of biochar are generally influenced by the nature of the raw materials and pyrolysis techniques. To assess the quality of sesame biochar production, a disc chamber reactor set on a solar parabolic dish concentrator was proposed as a modified slow pyrolysis technique. To evaluate the physicochemical characterizations of the produced biochar, two pyrolysis settings were used: 470 °C for 1 h (T1) and 440 °C for 2 h (T2) to produce biochar from sesame stalk feedstock (SS) using the proposed solar disk chamber reactor. Ash content, mass fraction of elements (C, H, and O%), pH, surface area, zeta potential, Fourier transform infrared (FTIR), and scanning electron microscope (SEM) were investigated. The results showed that the mass of T1 biochar decreased by 5% when compared to T2, while ash content, pH, fixed carbon, and volatile gases for both biochars were relatively close. The H/C and O/C molar ratios were below 1.00 and 0.4, respectively, indicating a loss of degradable polar contents and the formation of aromatic compounds. The surface area of T2 biochar was three times the surface area of T1, with the opposite trend in mean pore diameter. Two biochars showed the same FTIR peaks and SEM data, with small differences in their characteristics, demonstrating that pyrolysis time and temperature had a tight relationship. Both biochars showed approximately similar properties. The reactor’s efficiency is mainly affected by solar energy and atmospheric conditions during operation, which influence the average surface temperature. In Egypt, climatic conditions would be more favorable in the summer to improve the efficiency of parabolic solar dish concentrators for producing high-quality biochar.Graphical abstract

The impact of H-ZSM-5 catalyst on the mechanism of fuel-N conversion during glutamic acid pyrolysis

During the pyrolysis of biomass, Fuel-bound Nitrogen (Fuel-N) is converted into N-containing compounds present in bio-oil and biochar. These compounds are easily oxidized into NOx during subsequent utilization, causing ecological damage. Catalytic fast pyrolysis has emerged as a promising method for denitrogenation in recent years, but the underlying catalyst mechanism still needs to be determined. This study analyzed the impact of catalyst H-ZSM-5 on the mechanism of Fuel-N conversion during the pyrolysis of glutamic acid, a model compound for nitrogenous biomass, through experimental studies and theoretical calculations. According to literature data, the pyrolysis of glutamic acid predominantly yielded the N-containing products pyrrole, glutarimide, and pyrrolidone. The H-ZSM-5 catalyst showed optimum denitrification at 600 ℃, resulting in a 49.62% reduction in the proportion of N-containing compounds. In the catalytic pyrolysis products, the generation of toluene and naphthalene increased. In-situ DRIFTS experiments were consistent with the results of Py-GC-MS experiments, with catalytic pyrolysis promoting deaminations and decarboxylations, decreased imines and nitriles, and increased aromatic hydrocarbons. Additionally, the energy barrier changes of each pyrolysis pathway were calculated based on Density Functional Theory (DFT). The results showed that the H-ZSM-5 catalyst primarily promoted the deamination reaction, followed by the decarboxylation and dehydration condensation reactions, while inhibiting the dehydrogenation reaction. Moreover, the energy barrier for unsaturated hydrocarbon addition reactions was reduced, facilitating the formation of aromatic compounds. The acid sites inside the H-ZSM-5 catalyst weakly interacted with the reactants, making it easier to detach the amino group during catalytic pyrolysis. This study provides a reference for the denitrification of bio-oil and biochar. Subsequent work can realize the regulation of nitrogen conversion by changing the acidity and concentration of catalyst acid sites.

Brewer´s spent yeasts for oenology: from characterisation to must fermentation

In order to follow the principles of the circular economy, the spent brewer´s yeasts were in this work evaluated to be considered as a raw material for production of yeast derivatives for oenology. They provide natural source of organic nutrition, improve organoleptic properties and physico-chemical stability of wines. In this work, the spent yeasts from different beer styles were evaluated for their primary characteristics. Three types of yeast derivatives were prepared, inactive yeasts used for active dry yeast rehydration, lysates for organic nitrogen supply during fermentation and yeast hulls for adsorption of fermentation inhibitors. The chemical properties, fermentation kinetics and aromatic compounds formation of spent yeast derivatives were comparable to the well-recognized commercial products. However, the sensory analysis of final wines revealed bread-like and yeast autolysis off-flavors.

Hydrocarbon selectivity enhancement through catalytic fast co-pyrolysis of almond shell and plastic blends

BackgroundThe aim of this article is to explore possible pathways for the synergistic optimization of bio-oil by the catalytic fast co-pyrolysis of almond shell (AS) and plastic residues (polyethylene, PE, and polystyrene, PS). Pyrolysis was carried out at 650 °C at a heating rate of 20 °C/ms at a residence time of 20 s. Hydrogen from the plastic promoted the decarboxylation of acids and decarbonylation of carbonyls and sugars from biomass waste.ResultsCo-pyrolysis results showed a fall in oxygen in the AS/plastics blends, whereas carbon yields increased as did the calorific value of the oil. As expected, AS/PE blends enhanced production of hydrocarbon fractions, especially olefins, with yields reaching 81.1%, whereas AS/PS blends enhanced formation of aromatic compounds. HZSM-5 assisted the increase of monocyclic aromatics content in AS/PE blends. AS/PS blends favoured the increased of aromatics (45% of total hydrocarbons for 1:2 AS/PE-HZ). For AS/PS-HZ blends toluene was enhanced as was the production of 1,3,5-cycloheptatriene.ConclusionsThese findings helped to gain a great insight into how catalytic co-fast pyrolysis of feedstocks can enhance the formation of value-added products, promoting their economic potential for agricultural exploitations.Graphical

Mechanisms and Kinetics of the Dehydrogenation of C6–C8 Cycloalkanes, Cycloalkenes, and Cyclodienes to Aromatics in H-MFI Zeolite Framework

This work employs periodic density functional theory to elucidate dehydrogenation mechanisms of C6–C8 cycloalkanes, cycloalkenes, and cyclodienes into aromatics during methanol-to-olefin (MTO) chemistries in H-MFI zeolites. Aromatic compounds act as co-catalysts that predominantly form ethylene over propylene products and lead to site-blocking polyaromatic compounds; thus, understanding the formation of aromatic compounds during MTO is critical to understanding its selectivity and catalyst stability. Ring dehydrogenation reactions occur via sequential hydride transfer followed by deprotonation. The rate-controlling hydride transfer reactions were investigated with surface-bound protons (Z–H) and alkyls (Z–CnH2n+1) as hydride-accepting species. Hydride transfers via proton-mediated routes occur with intrinsic free energy barriers (623 K) of 215 kJ mol–1 for C6H12, 164 kJ mol–1 for C6H10, and 141 kJ mol–1 for C6H8, whereas methyl-mediated counterparts occur with intrinsic free barriers of 101, 95, and 81 kJ mol–1, respectively. Transition states for hydride transfer reactions prefer channel intersections within MFI networks, and their activation barriers suggest that methyl-mediated routes are favored over proton-mediated counterparts during MTO. Methyl substituents on hydrocarbon rings generally increase activation barriers for hydride transfers that occur proximal to the −CH3, partly because of steric hindrances between the hydride acceptor and ring-bound −CH3. Rapid double-bond isomerization within cyclohexenes and cyclohexadienes allows hydride transfer reactions to occur away from sterically hindering methyl substituents in methylated and dimethylated C6 ring hydrocarbons. The impact of carbocation substitution in hydride-accepting species was explored by contrasting barriers of methyl (Z–CH3), ethyl (Z–C2H5), 2-propyl (Z–C3H7), and tert-butyl (Z–C4H9) surface-bound alkyls. Intrinsic activation barriers decrease with increasing substitution of the alkyl hydride acceptor, consistent with those alkyls forming more stable carbocations. However, when accounting for steric hindrances associated with the co-adsorption of hydrocarbon rings near surface-bound alkyls, apparent free barriers are larger for more-substituted alkyls. Taking these apparent barriers into account, we predict that methyl-mediated hydride transfer reactions are responsible for the aromatization of hydrocarbon rings during MTO, leading to the CH4 formed during MTO reactions as the aromatic pool is enriched.

Изотопия углерода индивидуальных ароматических соединений нефти для понимания их геохимии

The article analyzes published and original data related to the carbon isotopic composition of individual aromatic compounds of fossil organic matter and oil. It has been shown that there is reliable evidence of the intramolecular isotopic heterogeneity of a number of molecules. For example the isotopically depleted carbon of the methyl group of alkylnaphthalenes and the terminal methyl of n-alkanes. The 13C inheritance from the biochemical precursor during the aromatization is also well documented in the example of diterpenes in the series abietic acid — dehydroabietane — simonellite — retene, as well as in the other terpene and steroid series. At the same time, there is evidence of carbon isotopic fractionation during the formation of several aromatic compounds from a single precursor. The increasing aromatization of the prebuild polycyclic structure does not change the 13C value of the molecule, and the formation of aromatic compounds with different numbers of aromatic rings in competing reactions leads to isotope differentiation in accordance with the thermodynamically determined distribution of carbon isotopes. If the suggestion is correct, it is the key to the understanding of specific petroleum aromatic hydrocarbons formation mechanism. It is possible that a comparison of 13C values for pairs of compounds formed during the transformation of one precursor will also provide information on the temperature conditions for the occurrence of the corresponding reactions.

Significant influence of different sulfur forms on Sulfur-containing polycyclic aromatic compound formation in high-sulfur coals

Sulfur-containing polycyclic aromatic compounds (SPACs) are important compounds found in coal. Previous research suggests that sulfur content is the most important controlling factor for SPAC formation. However, different forms of sulfur occur in coal. To study the influences of different sulfur forms on SPAC-formation mechanisms, six samples collected from the No. 14 coal seam of the Yuzhou Coalfield were identified to be high-pyrite sulfur coal (HPSC). Ten samples collected from the No. 11 coal seam from the Yuzhou Coalfield were identified to be high organic-sulfur coal (HOSC). Four samples collected from the No. 15 coal seamof the Dengfeng Coalfield were identified to be high sulfate-sulfur coal (HSSC). The study of the influences of different sulfur forms on SPAC-formation may better understand SPAC-formation mechanism.The collected samples were investigated using a microscope and organic geochemical methods. The microscopic findings revealed that the three coals have similar random vitrinite reflectance (Rr) values and have undergone similar geothermal processes. The geochemical results showed that the SPAC species and their contents in the HPSC, HSSC, and HOSC samples are very different. The HOSC samples of the No. 11 coal seam contained 65 SPACs; however, the HPSC samples of the No. 14 coal seam contained only 25 SPACs, and the HSSC samples of the No. 15 coal seam contained 44 SPACs. The average ratio of total-SPAC/total-PAC (T-SPAC/T-PAC) reaches 55.0 wt% in the HOSC samples, whereas the ratio is only 19.3 wt% in the HPSC samples, and 22.6 wt% in the HSSC samples. Coal maturity should not be a factor in the SPAC discrepancy because the three coal seams herein underwent similar geothermal processes. The sulfur forms may explain the apparent discrepancy of SPACs. Compared to the other two types of coal, the contents of pyrite, sulfur, and iron (Fe) are much higher in HPSC, and sulfur prefers to react with Fe to form pyrite, resulting in a lower SPAC content in HPSC and HSSC.The sulfur forms were influenced by the peat/coal-forming environments, which were affected by storm events. Finally, possible comprehensive formation pathways for major SPAC species have been proposed.

N-heterocyclic carbene-catalyzed arene formation reactions

N-heterocyclic carbene-catalyzed reactions for the formation of aromatic compounds are reviewed. The reactions are subdivided into 4 types based on their activation modes. A brief summary on the achievements and the challenges remaining in N-heterocyclic carbene (NHC)-catalyzed arene construction processes is provided at the end of this review. An outlook into the future research direction within this field is also given based on our own opinion and knowledge on the trends of the development of NHC organocatalysis.

Investigation on effect of coal fly ash on properties of corn straw pyrolysis products

The impact of coal fly ash (FA) is often ignored in the co-utilization of biomass and coal. Therefore, the influence of FA on the properties of pyrolysis products made from corn straw (CS) was investigated in this study. First, the distribution of co-pyrolysis bio-oil was investigated using pyrolysis-gas chromatography and mass spectrometry at 500°C-800 °C. Then, in a free-falling fixed-bed reactor, FA and CS were co-pyrolyzed, gaseous product yields were computed, and solid product composition and morphology were determined using X-ray diffraction, scanning electron microscopy, and the N2 adsorption–desorption isotherm, respectively. According to the findings, FA greatly promoted the degradation of oxygen-containing components in bio-oil and the formation of aromatic compounds at higher temperatures. The CS5-FA1 was the most favorable ratio for bio-oil production at 800 °C. Furthermore, the addition of FA had the highest stimulating effect on CO2 at 500 °C and 800 °C, and the yield of the other pyrolysis gases (CH4, CO, and H2) was also increased at 800 °C.

Fast pyrolysis of agroindustrial wastes blends: Hydrocarbon production enhancement

Fast pyrolysis of waste from agroindustry may be an alternative choice for sustainable use of enhanced biofuels. Plastics are one option for improving the hydrogen to carbon efficiency ratio (H/Ceff) of biomass feedstock. Waste from agroindustry in blends with biomass could modify the reaction mechanism for removing oxygen by substituting decarbonylation and decarboxylation with dehydration. Firstly, fast pyrolysis was performed to find the optimal mass blending ratio for olive pomace (OP) and agroindustrial polymers (polyethylene (PE), polystyrenes (PS) and polyvinyl chloride (PVC)) according to hydrocarbon production. Experimental results for the 1.5:1 OP/PE, 1:1.5 OP/PS and 1:1.5 OP/PVC mass blending ratios at 500 °C, showed synergistic enhancement of hydrocarbon yields. Alkenes yield were enhanced for 1.5:1 OP/PE, where the light hydrocarbons fraction (C6-C10) first increased and then decreased with temperature, reaching a maximum at 650 °C. For 1:1.5 OP/PS and 1:1.5 OP/PVC, it was improved the aromatic compounds formation, being 500 °C and 650 °C the optimal reaction temperature for the former and the later, respectively. Benzene, toluene and xylene were in large quantities obtained for PS and PVC blends with OP. Additionally, the synergistic effect on pyrolysis of the blends did not show any clear trend for pyrolytic gas emissions. In general, as reaction temperature increased, CO and CO2 emissions fell and CH4 was enhanced. Finally, olefin and aromatic yields were promoted for blends with a higher H/Ceff.

Validation of the Application of the Pyrolysis Process for the Treatment and Transformation of Municipal Plastic Wastes

Only around 30 % of the 27.1 million tonnes of plastic waste recovered annually in Europe is being recycled efficiently into new products. The most common way to recycle plastics nowadays is through mechanical recycling methods that involve sorting plastics by type, melting them and reprocessing into recycled products. Mechanical recycling requires clean, high-purity mono-material streams, that must be obtained by separation at source (by the citizen or industry) or by manual or automated sorting of mixed waste streams. However, this degree of separation is very difficult or even impossible due to composition or contamination of the plastic waste, such is the case for example of complex materials like composites, made of more than one material that in most cases cannot be separated, and of highly contaminated plastic residues (e.g. food packaging). In economic terms, plastic recycling is not always cost-efficient since many times recycling costs are not covered by the prices of the recycled plastics. As a result, approximately 70 % of European plastic waste is not recycled due to technical or economic reasons, so, they are sent to landfill or to incineration. One of the possible solutions to deal with this type of plastic wastes is the pyrolysis process which allows taking profit of plastics organic matter and tolerates a certain degree of contamination. Pyrolysis products have good quality. Gases have high calorific value and liquids have high energetic content and stability characteristics, including well-defined distillation point, stability of physical properties, low acidity, and high miscibility with conventional fuels. However, products obtained by plastic waste pyrolysis depend on the operational conditions and are strongly affected by the type of plastic waste used. The main purpose of this study is to validate the application of the pyrolysis process for treatment and transformation of plastic mix (essentially derived from MSW and from end-of-life composites) into mainly profitable liquids, together with gases and solid by using thermal (or catalytic) pyrolysis. The raw materials studied were waste streams from municipal solid waste (MSW), containing mainly plastic (i.e. PE, PP, PS, and small amounts of PET and PVC) separated from organic waste pool, as well as end-of-life composites (i.e. packages, electrical wastes, vehicles, etc.). After sorting of these waste materials, plastic fractions of different composition were processed in the pyrolysis reactor. The pyrolysis experiments were carried out in batch 5.5 L reactor using different mixtures, operational conditions and catalysts. All gaseous hydrocarbons produced were measured and collected for direct analysis by gas chromatography (GC), whilst liquid hydrocarbons were distilled and solids were extracted with hexane. Liquid fractions were analysed using a GC-MS (gas chromatography-mass spectrometry) to identify their main compounds, which were quantified by GC. The experimental results obtained showed that, for instance, the use of polystyrene favoured highly the formation of aromatic compounds, mainly toluene, ethylbenzene and xylene, while in presence of polyethylene the hydrocarbons produced are mainly paraffins. Also, the presence of PS, PET and PVC increases the solid content, decreasing the liquid yield.

The effect of introducing Ga on the ZSM-5-catalyzed methanol to aromatics reaction: taking methylcyclopentane to benzene as an example.

Naphthenes are key intermediates in the formation of aromatic compounds during the methanol to aromatics (MTA) reaction, and the dehydrogenation process is more important than the hydrogen transfer process. Theoretical studies were performed to investigate the methylcyclopentane, which represents a naphthene, to benzene MTA process catalyzed by ZSM-5 before and after introducing Ga, showing that Ga-ZSM-5 was more favorable for carrying out the reaction than two H-type ZSM-5 (H-Z1 and H-Z2) models. H-Z1 and H-Z2 are favorable for the transfer of H during ring expansion reactions and the reformation of Brønsted acids, but the dehydrogenation reactions involving H-Z1 and H-Z2 require high free-energy barriers to be overcome. Although introducing Ga to ZSM-5 is not conducive to the transfer of H after dehydrogenation, it can reduce the extremely high dehydrogenation free-energy barrier compared with H-Z1 and H-Z2; this is mainly because Ga at dehydrogenation active centers, [GaH]2+, can accept electrons and donate them to the H atoms of [GaH]2+, giving H negative charge and making it easy to combine with positive B-acid H atoms that come from methylcyclopentane, cyclohexene, and cyclohexadiene to produce H2. Also, analysis of the transition state structures of all DH processes shows that Ga-ZSM-5 is more favorable for promoting the combination of H to produce H2 than H-Z1 and H-Z2.