Aromatic Reactions Research Articles

An Improved Iodine-Catalyzed Aromatization Reaction and Its Application in the Synthesis of a Key Intermediate of Cannabidiol

In this study, the development of an improved process for the synthesis of a key cannabidiol intermediate, methyl olivetolate, is described. The process involves an improvement of the iodine-catalyzed aromatization of cyclohexanone using potassium persulfate as an oxidant. This approach enabled for the efficient synthesis of methyl olivetolate with a 90% yield and 99.84% HPLC purity on a 5 kg scale. Additionally, a total of 16 cyclohexanone substrates afforded higher yields (75-92%) of m-diphenol compounds compared to the established methods.

A Paternò-Büchi Reaction of Aromatics with Quinones under Visible Light Irradiation.

Reported herein is a Paternò-Büchi reaction of aromatic double bonds with quinones under visible light irradiation. The reactions of aromatics with quinones exposed to blue LED irradiation yielded oxetanes at -78 °C, which was attributed to both the activation of double bonds in aromatics and the stabilization of oxetanes by thiadiazole, oxadiazole, or selenadiazole groups. The addition of Cu(OTf)2 to the reaction system at room temperature resulted in the formation of diaryl ethers via the copper-catalyzed ring opening of oxetanes in situ. Notably, the substrate scope was extended to general aromatics.

The promoting and inhibitory mechanism of interaction between waste tires and Spirulina on their co-pyrolysis

Energy utilization of biomass and waste is an important thrust for carbon emission reduction. Co-pyrolysis is conductive to efficiently converting algae and waste tires, due to their complementary pyrolysis characteristics. However, the influence of the interaction between algae and waste tires on co-pyrolysis behavior is still controversial, due to the internal mechanism of interaction is unclear. Therefore, in this study, mechanism experiments and theoretical calculations were used to comprehensively investigate the interaction mechanism between Spirulina (SP) and waste tires (WT). The co-pyrolysis of SP and WT can be divided into two main steps: low-temperature SP decomposition and high-temperature WT decomposition. The activation energies of WT and mixture increase with the conversion rate, while those of SP change little at low conversion rates (<60 %). The pyrolysis activation energies of mixture are lower than the theoretical values, as the blending ratio of SP below 50 %. The interaction between SP and WT has both promoting and inhibiting effects on the pyrolysis of mixture. The attack of free radicals from SP pyrolysis and ash in WT promotes the pyrolysis of mixture, but the low-temperature polymerization reactions and high-temperature aromatization reactions inhibit the release of pyrolysis products. The formation of benzene compound is promoted due to the attack of free radicals and the polymerization between SP and WT.

Assessment of Performance and Deactivation Resistance of Catalysts in the Pyrolysis of Polyethylene and Post‐Consumer Polyolefin Waste

AbstractIn the present work, the catalyst performances of USY and REY zeolites and MgO, ZnO, and MgxAlOy oxides are investigated in the pyrolysis of virgin high‐density polyethylene (HDPE) and of post‐consumer polyolefin waste. The influence of operation parameters and catalyst deactivation resistance over four reaction cycles are evaluated. The results indicate that basic oxides do not show relevant cracking activity, so that the only identified effect for these catalysts is the production of liquid products with higher contents of paraffins when compared to thermal pyrolysis. Among the evaluated oxides, MgxAlOy is the most active and resistant to deactivation. The zeolites promote cracking and secondary reactions of isomerization, cyclization, and aromatization. Particularly, USY promotes the production of higher‐quality oils and shows higher deactivation resistance, when compared to REY. Additionally, a significant loss of catalyst activity is identified in reactions conducted with post‐consumer polyolefin wastes. However, increase in rates of coke formation and the presence of contaminants (such as halogens and metals) are not detected in the catalysts after the reactions.

Spaced‐confined capsule catalysts with tunable micro‐environments for efficient CO2 conversion

AbstractCO2 as a greenhouse gas causes a series of issues, and catalytic utilization of CO2 to fuels is a favorable strategy. Herein, we report the discovery in CO2 hydrogenation reaction where C5+ yield can be evidently improved by encapsulating ZnFe2O4 inside ZSM‐5, in which the micro‐environments of core‐shell components can be tuned. For the ZnFe2O4, the K promoter makes the FeC structure more electron deficient than the Na, which contributes to the formation of long‐chain olefins. ZSM‐5 with K or Ce modification presents enhanced adsorption ability of alkene, then promoting aromatization and isomerization reactions of alkenes. Compared with Ce, K‐ZSM‐5 contributes to isomerization rather than aromatization, forming more isoparaffins. In this work, regulating the microenvironment of capsule catalysts provides a new idea for the design of efficient tandem catalysts, and expands the ability of hybrid catalysts against other catalysts, thus presenting an excellent catalytic efficiency for CO2 upgrading.

Stereoselective Syntheses of Organophosphorus Compounds

The review is devoted to the theoretical and synthetic aspects of the stereochemistry of organophosphorus compounds. Organophosphorus compounds are not only widely exist in biologically active pharmaceuticals and agrochemicals, but also have widespread applications in material science and organic synthesis as ligands for transition metal complexes. One of the mainstreams for the development in this field is the creation of biologically active organophosphorus compounds that are searched and used as drugs or plant-protecting agents, which leads to the elaboration of advanced methods and monitoring, yielding up-to-date approaches to perform synthesis in an environmentally friendly manner. The review consists of two parts. The first part presents methods for the asymmetric synthesis of organophosphorus compounds using asymmetric organocatalysis and metal complex catalysis. In the review is described the nature of the chirality generation in the prebiotic period, the mechanisms of asymmetric induction, and double stereodifferentiation are discussed. The use of these methods for the preparation of chiral phosphorus analogs of natural compounds (phosphono-isonorstatin, phosphono-GABOB, phosphacarnitine, bis-phosphonates, and others) is described. Some data concerning of λ5-phosphanediones as metaphosphate anion analogues are also reported. The second part of the presented review shows examples of the use of these methods for the synthesis of phosphorus analogues of natural compounds—chiral phosphonoamino acids and hydroxyphosphonates: phosphonoaspartic acid, phosphonoglutamic acid, phosphonohomoproline, chiral bis-phosphonates. The reaction of dehydration aromatization with the formation of pho sphono isoindolinones, including isoindolinone bis-phosphonates, has been studied. Some of the synthesized compounds showed biological activity as protein tyrosine phosphatase inhibitors. A phosphonic analogue of iso-norstatine was synthesized. A stereoselective method for the synthesis of tetradecapentaenoic acid derivatives was developed.

Insights into pyrolysis process of coconut shell waste hydrochar: In-situ structural evolution and reaction kinetics

Coconut shell (CS) can be efficiently utilized by coupling hydrothermal carbonization (HTC) pretreatment with pyrolysis to meet the goal of global green development. In-situ Raman spectroscopy and thermogravimetric analyzer (TGA) were adopted to investigate the structural evolutions and reaction kinetics characteristics of hydrochar during the pyrolysis process. According to the results, the intensity of peak D and peak G in Raman spectrum decreased with increasing hydrothermal degree. Mild HTC treatment (≤200 °C) led to an increase in ID/IG, indicating the formation of large aromatic rings through small ring condensation. In contrast, severe HTC treatment (≥220 °C) reduced the ID/IG ratio, indicating an increased polycondensation of aromatic compounds and a higher degree of aromatization, resulting in larger molecules sizes. The spectral area below 400 °C reduced with increasing pyrolysis temperature due to the reduction of oxygen-containing functional groups and thermal radiation. Above 400 °C, the total area remains stable as the Raman spectrum scattering ability increases due to char formation and aromatization reactions. HTC-200 exhibited an increase in ID/IG from 0.54 to 0.72 and ID/I(Me + Ke + GL) from 0.58 to 0.68 with increasing pyrolysis temperatures. The activation energy during pyrolysis ranged from 194.50 to 238.34 kJ/mol for CS and 217.51–259.51 kJ/mol for HTC-200. Hydrothermal carbonization had a significant effect on pyrolysis behavior of hydrochar, as it was found that the mild HTC hydrochar followed D-type diffusion models when conversion rate was less than 0.65, and transitioned to higher reaction order in the late-stage of pyrolysis.

Methane dehydroaromatization (MDA) on VOx/HZSM-5 catalysts

In this study, the methane dehydroaromatization (MDA) on vanadium oxide (VOx)-based catalysts was investigated. Using various catalyst supports, VOx/HZSM-5 exhibited the highest MDA activity. In MDA using VOx/HZSM-5, an induction period was observed. Raman spectroscopy and XPS analysis indicated that V2O5 species result in the highly dispersed state by the contact with CH4. X-ray absorption fine structure analysis suggested the formation of VC species. Such structural changes lead to the induction period for the MDA reaction. Based on the effect of the catalyst support and the aromatization reaction of ethylene, we propose a mechanism in which methane forms ethylene on the vanadium catalyst, and ethylene is then aromatized with the aid of the acid sites and micropore structure of HZSM-5. Additionally, the effect of hydrogen co-feeding on the MDA reaction was investigated, which revealed that catalyst deactivation due to coke formation was suppressed in the presence of hydrogen.

Copper oxides supported sulfur-doped porous carbon material as a remarkable catalyst for reduction of aromatic nitro compounds

Synthesis and manufacturing of metal–organic framework derived carbon/metal oxide nanomaterials with an advisable porous structure and composition are essential as catalysts in various organic transformation processes for the preparation of environmentally friendly catalysts. In this work, we report a scalable synthesis of sulfur-doped porous carbon-containing copper oxide nanoparticles (marked CuxO@CS-400) via direct pyrolysis of a mixture of metal–organic framework precursor called HKUST-1 and diphenyl disulfide for aromatic nitro compounds reduction. X-ray diffraction, surface area analysis (BET), X-ray energy diffraction (EDX) spectroscopy, thermal gravimetric analysis, elemental mapping, infrared spectroscopy (FT-IR), transmission electron microscope, and scanning electron microscope (FE-SEM) analysis were accomplished to acknowledge and investigate the effect of S and CuxO as active sites in heterogeneous catalyst to perform the reduction-nitro aromatic compounds reaction in the presence of CuxO@CS-400 as an effective heterogeneous catalyst. The studies showed that doping sulfur in the resulting carbon/metal oxide substrate increased the catalytic activity compared to the material without sulfur doping.

On the reactivity and selectivity trends in the tandem Diels-Alder cycloaddition and dehydrative aromatization between dimethylfuran and ethene over solid acids

Tandem Diels-Alder (DA) cycloaddition and dehydration reactions between bio-derived furans and dienophiles offer a sustainable route potentially able to meet the growing demands of aromatic chemicals worldwide. In particular, efforts to maximize the production of p-xylene from dimethylfuran (DMF) and ethene have led to an expanding list of solid acids with, reportedly, outstanding catalytic performances. In this work, we have revisited the kinetic complexities of this reaction that are characterized by a distinct shift in the rate-limiting step depending sensitively on catalyst mass, and addressed the possible origins of reactivity and selectivity trends across a range of solid acids that hold promise for the target reaction, including aluminosilicates and a series of mesoporous metal phosphate catalysts (MOPOx; M = Sn, Ti, Zr, Hf, Nb and Ta), in both dehydration- and cycloaddition-limiting regimes. In contrast to initial p-xylene formation rates in the dehydration-limiting regime, which benefit from an increased acid strength of Brønsted acid sites, p-xylene formation rates within the cycloaddition-limiting regime are essentially unaffected by variations in acid site densities, Lewis and Brønsted acid strength, and pore confinement. Such weak dependences of DA reactivity on a multitude of acid properties provide strong hints that DA cycloaddition between DMF and ethene follows an inverse-electron-demand [4 + 2] route, most likely as a consequence of a more favorable adsorption of DMF than that of ethene on the acid sites enhancing so the electrophilicity of DMF, but not that of ethene as required by the normal-electron-demand cycloaddition. Product selectivities and carbon balances were tracked as functions of reaction time, conversion and reactant pressure or concentration to identify the side reactions and acid properties responsible for p-xylene selectivity losses and the ultimate formation of carbonaceous deposits. These findings deepen our understanding of the roles of Lewis acid sites and Brønsted acid sites for the chemical reactivities toward the DA cycloaddition, the consecutive cycloadduct dehydrative aromatization and undesired acid-catalyzed side reactions, and inform strategies to enhance DA reactivities and suppress deleterious side reactions from the standpoint of both materials and process design.

Synthesis of Hydrochars via Hydrothermal Carbonization of Zinc Chloride Activated Cotton Textile Waste

Anthropogenic pollution from fossil fuel combustion due to increasing global populations and emerging industries poses a serious threat to the environment. Therefore, it is vital to explore alternative green energy sources. Hence, this study synthesized renewable solid fuel hydrochars by utilizing biomass of cotton textile waste (CTW) as feedstock. ZnCl2 was selected as a catalyst due to its Lewis acid properties promoting hydrolysis and dehydration of raw materials towards hydrochar formation. The ZnCl2-activated cotton textile waste (ZnCl2-CTW) was prepared via the wet impregnation method at different ZnCl2 loading. The hydrochars were synthesized via hydrothermal carbonization of ZnCl2-CTW in a Parr batch reactor at the reaction temperature of 200 °C for 3 h. The hydrochars and CTW were characterized using a thermogravimetric analyser (TGA) to evaluate the proximate analysis, whereas an elemental analysis and determination of higher heating value (HHV) were conducted employing a CHNS analyser. The proximate analysis indicates the hydrochars volatile matter increases at higher catalyst loading, possibly due to the high content of bio-oil adsorbed on the hydrochars surface. The elemental analysis shows higher carbon and lower oxygen content for hydrochars compared to CTW, mainly due to the dehydration, decarboxylation, and aromatization reactions during HTC. Meanwhile, the HHV of hydrochars increases as catalyst loading increases to 1.5 g, which obtained the highest value of 18.41 MJ/kg, indicating good quality of solid fuel. This demonstrated that the ZnCl2 catalyst was useful in improving the energy density of hydrochars. Overall, ZnCl2 catalyst loading of 1.5 g has exhibited good performance in producing hydrochars via HTC of CTW. Thus, ZnCl2-CTW has the potential to produce hydrochar suitable as solid fuel, contributing to the conversion of waste into energy and the preservation of the environmental.

The Effect of Water Co-Feeding on the Catalytic Performance of Zn/HZSM-5 in Ethylene Aromatization Reactions.

During the methanol-to-aromatics (MTA) process, a large amount of water is generated, while the influence and mechanism of water on the activity and selectivity of the light olefin aromatization reaction are still unclear. Therefore, a study was conducted to systematically investigate the effects of water on the reactivity and the product distribution in ethylene aromatization using infrared spectroscopy (IR), intelligent gravitation analyzer (IGA), and X-ray absorption fine structure (XAFS) characterizations. The results demonstrated that the presence of water reduced ethylene conversion and aromatic selectivity while increasing hydrogen selectivity at the same contact time. This indicated that water had an effect on the reaction pathway by promoting the dehydrogenation reaction and suppressing the hydrogen transfer reaction. A detailed analysis using linear combination fitting (LCF) of Zn K-edge X-ray absorption near-edge spectroscopy (XANES) on Zn/HZSM-5 catalysts showed significant variations in the state of existence and the distribution of Zn species on the deactivated catalysts, depending on different reaction atmospheres and water contents. The presence of water strongly hindered the conversion of ZnOH+ species, which served as the active centers for the dehydrogenation reaction, to ZnO on the catalyst. As a result, the dehydrogenation activity remained high in the presence of water. This study using IR and IGA techniques revealed that water on the Zn/HZSM-5 catalyst inhibited the adsorption of ethylene on the zeolite, resulting in a noticeable decrease in ethylene conversion and a decrease in aromatic selectivity. These findings contribute to a deeper understanding of the aromatization reaction process and provide data support for the design of efficient aromatization catalysts.

Tunable Approach to Diverse Phenethylamines via Reduction of 5-Aryloxazolidines with Triethylsilane.

A rapid pathway for the synthesis of various β-phenethylamines from aromatic aldehydes has been developed. Initially, a wide range of 5-aryloxazolidines was prepared via the [3 + 2] cycloaddition reaction of N-methylazomethine ylide derived from sarcosine and paraformaldehyde. The subsequent reduction of 5-aryloxazolidines with triethylsilane in trifluoroacetic acid yields three types of products: N,N-dimethylphenylethanolamines, N,N-dimethylphenethylamines, and tetrahydroisoquinolines, depending on the substituents in the aromatic ring and reaction conditions. Moreover, an additional step of oxazolidine hydrolysis or ring-opening with hydrogen cyanide allowed us to synthesize N-methyl- or N-methyl-N-(cyanomethyl)phenethylamines.

Pyrrole βC-B-N Fused Porphyrins: Molecular Structures and Opto-Electrochemical Studies.

Herein, we report the design, synthesis, structure, and electrochemical study of doubly βC-B-N fused Ni(II) porphyrins (1-trans, 1-cis, 2-trans, and 2-cis). These compounds have been synthesized from A2B2 type dipyridyl Ni(II) porphyrins (Ar=Ph for 1 a; Ar=C6F5 for 2 a) via Lewis base-directed electrophilic aromatic borylation reactions. The solution state structures of these compounds have been established using 1H NMR, 11B NMR, 1H-1H COSY, 1H-13C HSQC, and 19F-13C HSQC NMR techniques. Single crystal X-ray analysis have revealed that 1-trans, 1-cis, and 2-trans adopt ruffled conformations, with alternate meso-carbons on the opposite sides of the mean porphyrin plane. The Soret bands in the absorption spectra of the B-N fused molecules are ~40 nm redshifted compared to unfused Ni(II) porphyrin precursors. The B-N fusion have diminished the redox potential of fused porphyrins. Although 1-trans and 1-cis, show four oxidation processes, 2-trans and 2-cis show only three oxidation processes. DFT studies have revealed that the tetrahedral geometry of the boron has induced a twist in the π-conjugation, which destabilizes the HOMO and stabilizes the LUMO in 1-trans, 1-cis, 2-trans, and 2-cis.

Molecular transformations of heteroatomic organic compounds in crude oils caused by biodegradation and subsequent thermal maturation: Insights from ESI FT-ICR MS

The Tarim and Junggar basins are major petroliferous sedimentary deposits in China. Some oil reservoirs in these basins experienced superimposed secondary alterations including early biodegradation followed by thermal maturation/alteration (SSA-B&M). Heteroatomic polar organic compounds in crude oil are significantly influenced by SSA-B&M, which play a vital role in understanding the evolutionary history of oil reservoir. However, research on such alterations is limited. The present study employed negative and positive ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) to investigate the molecular transformations of heteroatomic organic compounds in crude oils resulting from SSA-B&M. The findings indicate that biodegradation leads to an enrichment of naphthenic acids, while subsequent cyclization, aromatization and thermal cracking reactions enhances the aromaticity of the pyrolysis products of all the oil samples with varying degree of biodegradation. Notably, highest aromaticity was observed for the crude oil that has been most severely altered by biodegradation. During early and moderate stages of biodegradation, the abundances of O2 compounds (molecules contain two oxygen atoms) representing carboxylic acids were continuously increasing. However, at severe biodegradation levels, fatty acids with 1 double bond equivalents (DBE) underwent degradation, while the naphthenic acids were further enriched. Subsequently, during maturation, O2 compounds with 1 to 5 DBE experienced a steady decline in abundance. The naphthenic acids mainly experienced aromatization, while the fatty acids were partly decarboxylized and cracked thereby forming new n-alkanes. Biodegradation led to modification in neutral nitrogen compounds with 3 to 4 condensed rings (DBE = 9–12) and long alkyl side chains, while the impact on basic nitrogen compounds was relatively minimal. After subsequent thermal maturation, both neutral and basic nitrogen compounds with long alkyl side chains underwent cracking, while those with shorter alkyl side chains and higher degrees of condensation tended to remain relatively unchanged. Finally, two new indices were defined and tested to correctly evaluate the maturation and biodegradation level for crude oils that have experienced SSA-B&M.

Catalytic carbon–carbon bond cleavage in lignin via manganese–zirconium-mediated autoxidation

Efforts to produce aromatic monomers through catalytic lignin depolymerization have historically focused on aryl–ether bond cleavage. A large fraction of aromatic monomers in lignin, however, are linked by various carbon–carbon (C–C) bonds that are more challenging to cleave and limit the yields of aromatic monomers from lignin depolymerization. Here, we report a catalytic autoxidation method to cleave C–C bonds in lignin-derived dimers and oligomers from pine and poplar. The method uses manganese and zirconium salts as catalysts in acetic acid and produces aromatic carboxylic acids as primary products. The mixtures of the oxygenated monomers are efficiently converted to cis,cis-muconic acid in an engineered strain of Pseudomonas putida KT2440 that conducts aromatic O-demethylation reactions at the 4-position. This work demonstrates that autoxidation of lignin with Mn and Zr offers a catalytic strategy to increase the yield of valuable aromatic monomers from lignin.

Biodiesel-Derived Waste Glycerol as a Green Template for Creating Mesopores in the ZSM-5 Catalyst for Aromatics Production Applications.

The present study provides a novel sustainable approach for the synthesis of the ZSM-5 catalyst using biodiesel-derived waste glycerol as a green template as well as a mesopore creator, which is here reported for the first time, to the best of our knowledge. The use of bioglycerol in the preparation of ZSM-5 (Zn-Z-G and Zn-Z-T) materials exhibited a typical MFI zeolite structure, indicating glycerol played a similar role to that of a typical (TPA+) template in the formation of the ZSM-5 zeolite structure. The Zn-Z-G material also exhibited a large mesopore in the ZSM-5 pore structure, suggesting that glycerol played both template and mesopore creator roles. Interestingly, Zn-Z-GT prepared by the dual-template route using bioglycerol along with typical TPA+ showed a MFI zeolite structure with special catalytic features such as hierarchical micromesopores and well-balanced acid sites. These results reveal that the use of bioglycerol along with a typical TPA+ template had a promotional effect on creating such special properties in the Zn-Z-GT material. The Zn-Z-GT catalyst exhibited excellent catalytic performance in the naphtha aromatization reaction, resulting in achieving ∼58 wt % of the aromatic product and useful gas byproduct (14 wt %) with a minimum coke content (∼4 wt %) in a 12 h reaction period ascribed to its combined effect of hierarchical micromesopores and well-balanced acidity with optimum Lewis acid sites. The liquid product possessing high alkyl-aromatics with a high octane value (RON ∼ 109) produced in the present study can be used as an octane booster for liquid gasoline. The high alkyl-aromatics (>50 wt %) content of the liquid product also attracts various petrochemical applications. The effective utilization of waste bioglycerol as a green template and mesopore creator for the preparation of Zn-Z-GT can exhibit sustainability in the resultant material.

Dramatic Acceleration of the Hopf Cyclization on Gold(111): From Enediynes to Peri-Fused Diindenochrysene Graphene Nanoribbons.

Hopf et al. reported the high-temperature 6π-electrocyclization of cis-hexa-1,3-diene-5-yne to benzene in 1969. Subsequent studies using this cyclization have been limited by its very high reaction barrier. Here, we show that the reaction barrier for two model systems, (E)-1,3,4,6-tetraphenyl-3-hexene-1,5-diyne (1a) and (E)-3,4-bis(4-iodophenyl)-1,6-diphenyl-3-hexene-1,5-diyne (1b), is decreased by nearly half on a Au(111) surface. We have used scanning tunneling microscopy (STM) and noncontact atomic force microscopy (nc-AFM) to monitor the Hopf cyclization of enediynes 1a,b on Au(111). Enediyne 1a undergoes two sequential, quantitative Hopf cyclizations, first to naphthalene derivative 2, and finally to chrysene 3. Density functional theory (DFT) calculations reveal that a gold atom from the Au(111) surface is involved in all steps of this reaction and that it is crucial to lowering the reaction barrier. Our findings have important implications for the synthesis of novel graphene nanoribbons. Ullmann-like coupling of enediyne 1b at 20 °C on Au(111), followed by a series of Hopf cyclizations and aromatization reactions at higher temperatures, produces nanoribbons 12 and 13. These results show for the first time that graphene nanoribbons can be synthesized on a Au(111) surface using the Hopf cyclization mechanism.

Effects of production temperature on the molecular composition and seed-germination-promoting properties of sludge-based hydrochar-derived dissolved organic matter

Sludge hydrothermal carbonization demonstrates potential for converting sludge into multifunctional carbon materials for soil remediation. However, the influence of dissolved organic matter (DOM) with unclear molecular characteristics in sludge-based hydrothermal carbon on plant growth has not been sufficiently investigated. Herein, the effects of hydrothermal temperature on the molecular transformation pathways and plant-growth-promoting properties of DOM were investigated via FT-ICR MS–based molecular network analyses and seed germination experiments. Results indicated that the highest DOM yield was achieved at 220 °C. During low-temperature (180 °C) hydrothermal treatment, the hydrolysis of biopolymers, as well as the partial condensation and cyclization of small-molecule intermediates, occurred in the sludge. This process produced unsaturated CHNO compounds containing one or two N atoms, which promoted seed germination. Further, the toxicity of DOM to plants increased with rising hydrothermal temperature. This was accompanied by S doping and aromatization reactions, which mitigated the effects of plant growth hormones. This study provides theoretical support for the optimization of sludge hydrothermal treatment and production of plant growth hormones, enhancing the ecological value of sludge-based hydrochar.

Catalytic effect of metal salts on deoxygenation and aromatization reaction during pressurized pyrolysis of corncob waste at mild temperatures

Converting biomass to high quality bio-char with high carbon solidification at low energy consumption can greatly promote the application of biomass to alternative coal. Metal salts have been confirmed to enhance carbonization and dehydration during traditional pyrolysis and hydrothermal conversion, whereas the catalytic deoxygenation and aromatization mechanisms during dry mild pyrolysis in the presence of pressure are currently unclear. A mild gas-pressurized pyrolysis assisted by metal salts catalysts at 200–300 °C was proposed in this work. The effects of catalysts on three-phase products as well as synergistic catalytic reaction mechanism were studied. Results indicated that CaCl2, ZnCl2 promoted carbon fixation rates by 19.77 % and 26.89 %, and ZnCl2, KCl could remove oxygen content by 11.45 % and 6.56 % (wt.%, dry ash free basis). ZnCl2 exhibited the best deoxygenation and aromatization effect. With ZnCl2 catalysis at 280 °C, the volatile content reduced to 37.25 %, and O/C, H/C values decreased by 19.05 % and 11.25 %, achieving coking coal-like quality. FTIR and NMR results implied that oxygen-containing functional groups were removed even more rapidly under the catalysis of ZnCl2, facilitating the rearrangement of O-alkyl C and aliphatic C into aromatic C, exhibiting a higher aromatization degree in semi-char. Moreover, CH4 and H2 increased in gas products catalyzed by ZnCl2, while C2H4 and C2H6 decreased. Pressure inhibited the escape of small molecule gas volatiles, making them easily adsorbed on surfaces of molecular structures for secondary reactions. Under the action of the [ZnOZn]2+ acid sites, alkanes underwent dehydrogenation activation to yield H2, and demethylation activation to generate CH4, followed by cyclization reaction. The upgrading promotions of biomass were caused by the synergistic effect of pressure and ZnCl2 catalysis.