Aromatic Formation Research Articles

Synergistic effect on thermal behavior and product characteristics during co-pyrolysis of biomass and waste tire: Influence of biomass species and waste blending ratios

The work aims to get a full understanding of the co-pyrolysis synergy between different biomass and waste tire for high value utilization of both biomass and waste tire. Rice husk (RH), wheat straw (WS) and moso bamboo (MB) were chosen to co-pyrolyze with waste tire (WT). Influence of biomass species and blending ratios on co-pyrolysis synergistic effect was studied by analyzing thermal behavior, product yields and character. Thermogravimetry analysis proved the existence of synergistic effect and measured positive decomposition synergy for MB/WT. Char production showed little synergy for all biomass during co-pyrolysis while positive synergistic effect in liquid production was weakened with WT blending. Co-pyrolysis char integrated both biomass char and WT char characteristic. The pore structure was corresponding to that of biomass char and improved by synergy for all biomass, especially WS and MB. Co-pyrolysis oil mainly consisted of the typical components of bio-oil and WT oil, showing lower oxygenated compounds percentage than bio-oil. Aromatic hydrocarbons formation was inhibited while alicyclic hydrocarbons formation was intensified by co-pyrolysis interaction and MB/WT co-pyrolysis showed significant synergy in ethers and furans production. Co-pyrolysis showed positive synergistic effect on CO and CO2 generation and negative synergistic effect on H2 and CH4 content.

The Exploitation of a Hempseed Byproduct to Produce Flavorings and Healthy Food Ingredients by a Fermentation Process.

Following the One Health principles in food science, the challenge to valorize byproducts from the industrial sector is open. Hemp (Cannabis sativa subsp. sativa) is considered an important icon of sustainability and as an alternative food source. Hemp seed bran, in particular, is a byproduct of industrial hemp seed processing, which is not yet valorized. The success, and a wider market diffusion of hemp seed for food applications, is hindered by its unpleasant taste, which is produced by certain compounds that generally overwhelm the pleasant bouquet of the fresh product. This research concerns the exploration of hemp seed bran through fermentation using beneficial lactobacilli, focusing on the sensorial and bioactive traits of the products when they are subjected to bacterial transformation. By studying of the aromatic profile formation during the fermentation process the aim was to modulate it in order to reduce off-odors without affecting the presence of healthy volatile organic compounds (VOCs). Applying multivariate analyses, it was possible to target the contribution of processing parameters to the generation of flavoring and bioactive compounds. To conclude, the fermentation process proposed was able to reduce unpleasant VOCs, whilst at the same time keeping the healthy ones, and it also improved nutritional quality, depending on time and bacterial starters. The fermentation proposed was a sustainable biotechnological approach that fitted perfectly with the valorization of hemp byproducts from the perspective of a green-oriented industrial process that avoids synthetic masking agents.

Effects of the Deacetylation Degree of Chitosan on 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) Formation in Chemical Models and Beef Patties

The effects of the deacetylation degree (DD) of chitosan on heterocyclic aromatic amine formation were investigated in chemical models and beef patties. The results in model systems showed that at lower addition levels (10 mg), chitosan with 85% DD showed the strongest inhibitory effect against 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) formation, while chitosan with a higher DD (95%) or a lower DD (72 and 50%) did not show any significantly inhibitory effect. Further mechanism study showed that chitosan addition reduced the content of Maillard reaction intermediates including phenylacetaldehyde and the aldol condensation product but increased the PhIP precursor creatinine residue in the chemical model, indicating that chitosan at least partially competed with creatinine to react with phenylacetaldehyde to inhibit PhIP formation. In roast beef patties, 0.15% (w/w) chitosan (85% DD) significantly reduced the formation of PhIP, MeIQx, 4,8-DiMeIQx, Harman, and Norharman by 56.21, 33.32, 31.35, 25.14, and 28.12%, respectively. Moreover, chitosan significantly inhibited the formation of aldehydes in roast beef patties, further confirming the above-mentioned inhibition mechanism. However, the addition of chitosan might promote fatty acid oxidation. In addition, chitosan addition below 0.15% (w/w) had no significant effect on the textural properties of the roast samples.

The roles of low molecular compounds on the light aromatics formation during different rank coal pyrolysis

Light aromatic hydrocarbons are an important by-product of the coal chemical industry. The structure and properties of low molecular compounds (LMCs) embedded in coal are different from those of coal macromolecular skeleton structure, they have important effects on the coal pyrolysis. In this paper, the roles of LMCs on the formation of light aromatics during coal pyrolysis are investigated. The results show that LMCs have little effect on the thermal weight loss behavior of the three coals, but they can influence the carbon structure distribution of coals. The main source of light aromatics from coal pyrolysis is derived from thermal cracking of the coal macromolecular framework. And also the LMCs will be pyrolyzed to generate light aromatics. The total amount of BTEXN from extracts of Shengli coal (SL), Pingshuo coal (PS) and Hexi coal (HX) pyrolysis was 15%, 91%, and 12% of that of raw coal. The alkylbenzenes, naphthalene series, and PAHs can be cracked to form light aromatics. The long chain and cyclic aliphatic compounds can not only provide hydrogen for the free radical fragment of aromatics but also generate light aromatics. And the content of these compounds in the extracts of PS is higher than that of the other two coals. Due to the complexity of the combination between LMCs and coal structure, the extracts are easier to generate light aromatics than LMCs embedded in coal during pyrolysis. Because the composition and content of low molecules in coal with different metamorphic degrees are different, the effects of LMCs on the pyrolysis of low rank coal are more obvious compared with high rank coal.

Role of hypobromous acid in the transformation of polycyclic aromatic hydrocarbons during chlorination

Hypobromous acid (HOBr), a highly reactive active species, can be formed and impact reaction processes with organic pollutants in source water during chlorination disinfection of the water containing bromide (Brˉ). In this study, we investigated the transformation kinetics of 10 parent polycyclic aromatic hydrocarbons (PAHs) and formation mechanisms of transformation products in the presence of Brˉ during chlorination. The results indicated that HOBr can accelerate the processes of electrophilic substitution (ES) and single electron transfer (ET) reactions in PAHs, and the second-order rate constants of HOBr are 102–103 times higher than those of hypochlorous acid (HOCl) with PAHs. HOBr was more conductive to induce ES reactions than HOCl. In water containing Brˉ, HOBr and HOCl dominate the reaction processes with PAHs, although other active bromine species may still affect reaction processes. In terms of transformation products, higher reactivity of HOBr results from faster formation of oxygenated PAHs (OPAHs) and halogenated PAHs (HPAHs) than HOCl. As an example of 3 model PAHs, anthracene transforms faster to its oxygenated products at a higher concentration, while pyrene and fluorene transform faster to halogenated products. These fundamental results were essential to understanding the transformation kinetics of PAHs and the formation of toxic disinfection by-products in the presence of Brˉ.

Inference of reaction kinetics for supercritical water heavy oil upgrading with a two‐phase stirred reactor model

AbstractWe present the development and application of a two‐phase stirred reactor model for heavy oil upgrading in the presence of supercritical water (SCW), with coupled phase‐specific thermolysis reaction kinetics and multicomponent hydrocarbon–water phase equilibrium. We demonstrate the inference of oil and water phase kinetics parameters for a compact lumped reaction kinetics scheme through the application of this model to two different sets of batch reactor experiments reported in the literature. We infer that, although SCW can suppress the formation of newer polynuclear aromatics (PNA) from distillate range species, it is broadly ineffective in deterring the combination of pre‐existing PNA fragments in the oil feed. Quantification of the conversion to distillate liquids before the onset of coke formation helps arrive at a clear conclusion on whether the use of SCW in the batch reactor leads to better product outcomes for different oil feeds and operating conditions.

Catalytic Depolymerization of Waste Polyolefins by Induction Heating: Selective Alkane/Alkene Production.

Low- and high-density polyethylene (LDPE/HDPE) have been selectively depolymerized, without added H2, to C2–C20 + alkanes/alkenes via energy-efficient radio frequency induction heating, coupled with dual-functional heterogeneous Fe3O4 and Ni- or Pt-based catalysts. Fe3O4 was used to locally generate heat when exposed to magnetic fields. Initial results indicate that zeolite-based Ni catalysts are more selective to light olefins, while Ni supported on ceria catalysts are more selective to C7–C14 alkanes/alkenes. LDPE conversions up to 94% were obtained with minimal aromatic, coke, or methane formation which are typically observed with thermal heating. Two depolymerization mechanisms, a reverse Cossee–Arlman mechanism or a random cleavage process, were proposed to account for the different selectivities. The depolymerization process was also tested on commercial LDPE (grocery bags), polystyrene, and virgin HDPE using the Ni on Fe3O4 catalyst, with the LDPE resulting in similar product conversion (∼48%) and selectivity as for virgin LDPE.

Unraveling Hydrocarbon Pool Boosted Propane Aromatization on Gallium/ZSM‐5 Zeolite by Solid‐State Nuclear Magnetic Resonance Spectroscopy

AbstractPropane aromatization on metal‐modified zeolites provides a promising route to produce valuable chemicals such as benzene, toluene and xylene via non‐petroleum feedstocks. The mechanistic understanding of propane conversion to aromatics is still challenging due to the complexity of the aromatization process. Herein, by using solid‐state NMR spectroscopy and GC‐MS, it is shown that cyclopentenyl cations are formed as active intermediates during propane aromatization on Ga/ZSM‐5 zeolite. Autocatalysis of propane to aromatics is identified in the induction period. The cyclopentenyl cations serve as key hydrocarbon pool species to co‐catalyze propane conversion and promote aromatics formation, revealing a dominant hydrocarbon pool process in propane aromatization.

Unraveling Hydrocarbon Pool Boosted Propane Aromatization on Gallium/ZSM-5 Zeolite by Solid-State Nuclear Magnetic Resonance Spectroscopy.

Propane aromatization on metal-modified zeolites provides a promising route to produce valuable chemicals such as benzene, toluene and xylene via non-petroleum feedstocks. The mechanistic understanding of propane conversion to aromatics is still challenging due to the complexity of the aromatization process. Herein, by using solid-state NMR spectroscopy and GC-MS, it is shown that cyclopentenyl cations are formed as active intermediates during propane aromatization on Ga/ZSM-5 zeolite. Autocatalysis of propane to aromatics is identified in the induction period. The cyclopentenyl cations serve as key hydrocarbon pool species to co-catalyze propane conversion and promote aromatics formation, revealing a dominant hydrocarbon pool process in propane aromatization.

Effects of interactions between organic solid waste components on the formation of heavy components in oil during pyrolysis

This study focused on the interaction between organic solid waste (OSW) components on the formation and chemical composition of heavy components (>150 m/z) in OSW-oil. Rice husk (RH) and polypropylene (PP) as typical biomass and plastic fractions in OSW, were co-pyrolyzed at different blend ratios and different temperatures. The heavy components were characterized by FT-ICR MS, UV-F and GC MS. The results indicated that the yield of heavy components in PP-oil was higher than in RH-oil under the same temperature. Heavy hydrocarbons were found in PP-oil, while heavy phenols and heavy lipids existed in RH-oil. Significant interactions occurred at high temperatures (>600 °C). The interactions promoted the heavy components in all the blend-oils, corresponding to an increase of 20–35% compared to the calculated value of the content in PP-oil and RH-oil. At low PP ratio (25PP + 75RH), PP provided hydrogen to the reactive O-containing species in RH, leading to promoted heavy phenols and heavy lipids. At high PP ratio (50PP + 50RH and 75PP + 25RH), large aromatics (>3 rings) increased of 48–111% with respect to the calculated values. Plenty of PP‑hydrogen and a rich oxygen environment provided by RH radicals enhanced the formation of heavy aromatics and heavy PAH.

Direct Evidence on the Mechanism of Methane Conversion under Non‐oxidative Conditions over Iron‐modified Silica: The Role of Propargyl Radicals Unveiled

AbstractRadical‐mediated gas‐phase reactions play an important role in the conversion of methane under non‐oxidative conditions into olefins and aromatics over iron‐modified silica catalysts. Herein, we use operando photoelectron photoion coincidence spectroscopy to disentangle the elusive C2+ radical intermediates participating in the complex gas‐phase reaction network. Our experiments pinpoint different C2‐C5 radical species that allow for a stepwise growth of the hydrocarbon chains. Propargyl radicals (H2C−C≡C−H) are identified as essential precursors for the formation of aromatics, which then contribute to the formation of heavier hydrocarbon products via hydrogen abstraction–acetylene addition routes (HACA mechanism). These results provide comprehensive mechanistic insights that are relevant for the development of methane valorization processes.

Direct Evidence on the Mechanism of Methane Conversion under Non-oxidative Conditions over Iron-modified Silica: The Role of Propargyl Radicals Unveiled.

Radical‐mediated gas‐phase reactions play an important role in the conversion of methane under non‐oxidative conditions into olefins and aromatics over iron‐modified silica catalysts. Herein, we use operando photoelectron photoion coincidence spectroscopy to disentangle the elusive C2+ radical intermediates participating in the complex gas‐phase reaction network. Our experiments pinpoint different C2‐C5 radical species that allow for a stepwise growth of the hydrocarbon chains. Propargyl radicals (H2C−C≡C−H) are identified as essential precursors for the formation of aromatics, which then contribute to the formation of heavier hydrocarbon products via hydrogen abstraction–acetylene addition routes (HACA mechanism). These results provide comprehensive mechanistic insights that are relevant for the development of methane valorization processes.

Aromatization mechanism of coupling reaction of light alkanes with CO over acidic zeolites: Cyclopentenones as key intermediates

The aromatization of light alkanes (C4-C6) is an important value-added reaction. However, the yield of aromatics is always limited by the simultaneous generation of small alkanes (CH4 and C2H6) due to H/C balance. Herein, we demonstrate that the introduction of CO into light alkanes over zeolites significantly enhanced aromatic selectivity and an aromatics selectivity of 85% was achieved in the case of cyclopentane and CO coupling reaction over H-ZSM-5. Methyl-substituted cyclopentenones were observed and considered as the most important intermediates for aromatics formation. Multiple characterizations revealed the coupling mechanism: (1) CO inserts into carbenium ions to form acylium cations, (2) acylium cations react with olefins to generate unsaturated ketones, (3) unsaturated ketones cyclize to methyl-substituted cyclopentenones, (4) methyl-substituted cyclopentenones convert to monocytic aromatics. Methyl-substituted indanones were also discovered causing the generation of binuclear aromatics, such as naphthalene. Nano-sized ZSM-5 and TEOS modifications were applied to enhance the BTX selectivity.

Isobutane Transformation to Aromatics on Zn-Modified Zeolites: Intermediates and the Effect of Zn2+ and ZnO Species on the Reaction Occurrence Revealed by 13 C MAS NMR.

To clarify the effects of different Zn species, zeolite topology and acidity (quantity of Brønsted acid sites, BAS) on alkane aromatization, isobutane transformation on Zn2+ /H-ZSM-5, Zn2+ /H-BEA, and ZnO/H-BEA zeolites has been monitored with 13 C MAS NMR. The alkane transformation has been established to occur by aromatization and hydrogenolysis pathways. Zn2+ species is more efficient for the aromatization reaction because aromatic products are formed at lower temperatures on Zn2+ /H-BEA and Zn2+ /H-ZSM-5 than on ZnO/H-BEA. The larger quantity of BAS in ZnO/H-BEA seems to provide a higher degree of the hydrogenolysis pathway on this catalyst. The mechanism of the alkane aromatization is similar for the zeolites of different topology and containing different Zn species, with the main reaction steps being the following: (i) isobutane dehydrogenation to isobutene via isobutylzinc; (ii) isobutene stabilization as a π-complex on Zn sites; (iii) isobutene oligomerization via the alkene insertion into Zn-C bond of methyl-σ-allylzinc formed from the π-complex; (iv) oligomer dehydrogenation with intermediate formation of polyene carbanionic structures; (v) aromatics formation via further polyene dehydrogenation, protonation, cyclization, deprotonation steps with BAS involvement.

Aromatics formation by cracking and dehydrocyclization of n-hexane using Zn ion-exchanged ZSM-5–Al2O3 hierarchical composite catalysts

Aromatics formation by cracking and dehydrocyclization of n-hexane using Zn ion-exchanged ZSM-5–Al2O3 hierarchical composite catalysts

Insight into the effects of regulating denitrification on composting: Strategies to simultaneously reduce environmental pollution risk and promote aromatic humic substance formation

Denitrification during composting is a hidden danger that causes environmental pollution risk and aromatic humic substance damage, which needs to be better regulate urgently. In this study, two denitrification regulation methods, moisture and biochar amendment, were conducted during chicken manure composting. Denitrification performance data showed two regulation methods obviously reduced NO3−-N, NO2−-N and N2 contents. Humic substance increased by 25.3 % and 29.1 % under two regulations. Microbiological analysis indicated that two regulation methods could decreasing denitrifying functional microbes with aroma degradation capability. Subsequently, denitrification gene narG, nirS, nosZ were significantly inhibited (p < 0.05) and the aromatic degradation metabolism pathways were down-regulated. Correlation analysis further revealed the important influence of interspecific interactions and non-biological characteristics on functional microbes. These results provided important scientific basis to denitrification regulation in the practice of composting, which achieved the purpose of simultaneously controlling environmental pollution risk and conducing end-product formation.

Multifunctional Catalyst Combination for the Direct Conversion of CO2 to Propane.

The production of carbon-rich hydrocarbons via CO2 valorization is essential for the transition to renewable, non-fossil-fuel-based energy sources. However, most of the recent works in the state of the art are devoted to the formation of olefins and aromatics, ignoring the rest of the hydrocarbon commodities that, like propane, are essential to our economy. Hence, in this work, we have developed a highly active and selective PdZn/ZrO2+SAPO-34 multifunctional catalyst for the direct conversion of CO2 to propane. Our multifunctional system displays a total selectivity to propane higher than 50% (with 20% CO, 6% C1, 13% C2, 10% C4, and 1% C5) and a CO2 conversion close to 40% at 350 °C, 50 bar, and 1500 mL g–1 h–1. We attribute these results to the synergy between the intimately mixed PdZn/ZrO2 and SAPO-34 components that shifts the overall reaction equilibrium, boosting CO2 conversion and minimizing CO selectivity. Comparison to a PdZn/ZrO2+ZSM-5 system showed that propane selectivity is further boosted by the topology of SAPO-34. The presence of Pd in the catalyst drives paraffin production via hydrogenation, with more than 99.9% of the products being saturated hydrocarbons, offering very important advantages for the purification of the products.

Effect of O2/CH4 atmosphere on tar production during coal pyrolysis

In this paper, coal pyrolysis in O2/CH4 atmosphere was studied by an atmospheric fixed-bed reactor. The effect of reaction temperature on yield, fraction distribution and composition of tar was explored to understand formation of tar during coal pyrolysis. The results show that the addition of O2 to CH4 can enhance tar formation and tar yield reaches 18.15 wt.% at the O2/CH4 ratio of 15:85 and temperature of 650 °C, which is about 1.24 and 1.7 times as those in CH4 and N2 atmosphere, respectively. The fraction distributions of tar were obtained with simulated distillation, which indicates the addition of O2 to methane can improve the content of asphalt at 550 °C and the contents of anthracene oil and asphalt at 600 °C. The contents of naphthalene oil, wash oil, anthracene oil and asphalt from coal pyrolysis at 650 °C are improved by using O2/CH4 as pyrolysis atmosphere. The results of gas chromatography – mass spectrometry / flame ionization detector show that the addition of O2 to CH4 is conducive to formation of aliphatics, aromatics and alcohols, but unbeneficial to formation of phenols compared with that in pure CH4 atmosphere. Lower aromaticity and longer alkyl-substituents of tar from O2/CH4 atmosphere than that from N2 atmosphere indicate that CH3 from methane-oxygen reaction directly combine with coal radicals to increase tar yield and affect the fraction distribution and composition of tar.

A thermodynamic study for the stability of some aromatic complexes formation derived from the reaction of 4-dimethyl amino benzaldehyde with diazotized dinitro aniline reagents.

Abstract The basis of this research includes the preparation of aromatic azoimine complexes resulting from the coupling reaction (4) of Schiff bases with diazotized dinitroaniline reagent. Ultraviolet spectra, infrared spectra, and melting points are among the most important physical methods used to identification the right compounds prepared in this study. After that, the stoichiometric ratios of the components of the complex were determined using the molar ratio method, and we got a ratio of (1:1) for all the studied complexes. Finally, the factors that affect the stability constant values were studied, namely: A-Effect of acidity function: These stability constants were studied for each of the prepared complexes at each acidic function (pH) and different temperatures, and we obtained values for the stability constants, which are evidence of the preparation of stable azo complexes. B-The effect of temperature: These stability constants were calculated at a range of temperature (313–273oK) which allowed us to know that the reactions of formation of azo dyes are spontaneous and exothermic from the negative values of (∆G and ∆H) respectively, as well as the negative (∆S) value that supports what was mentioned previously. C-Effect of Structure: The location and the type of function group also has an effect on the values of the stability constants of the prepared complexes, and this was proved by the variation in the values of the stability constants.

Formation of Light Aromatics and Coke during Catalytic Reforming of Biopolymer-Derived Volatiles over HZSM-5

Formation of Light Aromatics and Coke during Catalytic Reforming of Biopolymer-Derived Volatiles over HZSM-5