Dehydrocyclization Reaction Research Articles

Green hydrocarbons and fuels from municipal polymer waste co-fed with natural gas using a batch catalytic slurry process

Landfilled solid waste polymers were converted into high octane green fuels and hydrocarbons by a catalytic depolymerization process. Experiments were conducted in a batch catalytic reactor pressurized with methane as a co-feed. Design of Experiments (DOE) methodology was used for process optimization and parametric study. The operating conditions that maximize the liquids aromatic hydrocarbons were found using response optimizer tool. The reaction temperature and polymer to catalyst ratio (PCR) were found to have significant effects on the responses and methane pressure was not significant for yields of solids, liquids and gaseous products. However, pressurized methane facilitated dehydrocyclization reactions resulting in increased monoaromatic hydrocarbons in the final liquid products. Experiments conducted with methane feed at optimized reaction conditions resulted in 89% aromatic hydrocarbons, 8% paraffins and about 3% other hydrocarbons in liquid products. Aromatic products included benzene (6.5%), toluene (25%), xylenes (27%), ethylbenzene (4.5%), other monoaromatics (22%) and polyaromatic hydrocarbons (4%). Gaseous products contained propylene (47%) and hydrogen (23.9%). The utilization of waste polymers as feedstock materials, flare gas (methane) as a co-feed, and zeolite catalysts makes this batch zeolitic slurry process greener, resulting in green hydrocarbons and green fuels.

Effect of Hydroxyl-Containing Fragments on the Structure and Properties of Membrane-Forming Polyamide-Imides.

The structural features and thermophysical and transport properties of dense nonporous membranes of the casting type from (co)polyamide-imides synthesized by the polycondensation of the diacid chloride of 2-(4-carboxyphenyl)-1,3-dioxoisoindoline-5-carboxylic acid and diamines 5,5'-methylene-bis (2-aminophenol) (DADHyDPhM) and 4,4'-methylenebis(benzeneamine) (DADPhM), taken in molar ratios of 7:3, 1:1, and 3:7, have been studied. The effect of hydroxyl-containing modifying fragments of dihydroxy diphenylmethane introduced in various amounts into the main polymer chain on the pervaporation properties of the formed films is discussed. It has been shown that the presence of the residual solvent N-methyl-2-pyrrolidone in the films not only has a plasticizing effect on the characteristics of film membranes but also promotes the preferential transmembrane transport of polar liquids, primarily methanol (permeation rate over 2 kg for a copolymer with a ratio of DADHyDPhM:DADPhM = 7:3). The removal of the residual solvent from the polymer film, both thermally (heating to 200 °C) and by displacement with another solvent as a result of sequential pervaporation, led to a significant decrease in the rate of transfer of polar liquids and a decrease in the selectivity of the membrane. However, the dehydrocyclization reaction resulted in more brittle films with low permeability to penetrants of different polarities. The results of our comprehensive study made it possible to assume the decisive influence of structural changes in membranes occurring in connection with the competitive formation of intra- and intermolecular hydrogen bonds.

Methanol-to-olefins catalysis on window-cage type zeolites/zeotypes with syngas co-feeds: Understanding syngas-to-olefins chemistry

Catalyst lifetime and product selectivity of methanol-to-olefins (MTO) catalysis on window-cage type zeolites and zeotypes are examined and interpreted to elucidate the critical role of high-pressure H2 and CO in MTO catalysis at conditions relevant for syngas-to-olefins (STO) conversion (H2/CH3OH >100, CO/CH3OH >100). Propylene co-feed experiments elucidate that acid-catalyzed hydrogenation reactions transpire and enhance olefins-cycle propagation by intercepting formaldehyde-mediated condensation and dehydrocyclization reaction cascades to result in an increase in catalyst lifetime (>7×) and decrease ethylene-to-propylene (∼1.5×) and ethylene-to-butenes ratios (∼1.6×) during MTO with high-pressure H2 co-feeds. CO is mechanistically relevant in increasing ethylene-to-propylene (∼1.5–3.0×) and ethylene-to-butenes ratio (∼1.7×) during MTO catalysis only at high CO (3–8 bar) and syngas pressures (24 bar, H2/CO∼2–16); at these high pressures, CO participates in carbonylation reactions to enhance aromatics-cycle propagation and enable a pathway for ethylene production via methyl acetate formation. These results suggest that high-pressure syngas introduces new catalytic pathways to distinguish MTO catalysis from STO catalysis and MTO catalysis in the presence of high-pressure syngas reagents.

Vapour Phase Synthesis of 2-Methylpyridine and 4-Methylpyridine Over Potassium Salts of 12-Tungstophosphoric Acid

Vapor phase dehydrocyclization reaction of acetaldehyde and ammonia was investigated over K salts of 12-tungstophosphoric acid as catalysts in a continuous flow fixed bed reactor at 350–450℃. The yield of 2-methylpyridine and 4-methylpyridine were found to be in the range of 38.0–64.5%. The 2-methylpyridine and 4-methylpyridine are used for the preparation of insecticides, poultry drugs, cattle drugs and anti-tuberculosis drugs, veterinary analgesics etc. respectively. The reaction conditions such as temperature, contact time, and molar ratio for achieving optimal yield with respect to 2-methylpyridine and 4-methylpyridine were discussed. Catalysts were characterized through BET surface area, FT-IR, XRD and TGA. NH3-TPD studies exhibit the moderate acidity. The morphology of the catalysts was also studied by FESEM.

A single-step catalytic process for the production of high-octane molecules from normal paraffins using zeolite supported bi-functional catalysts

Stringent fuel specifications qualify no single refinery stream to work alone as gasoline fuel and reformulated gasoline blends various refinery streams appropriately to meet the desired fuel specifications. Branched paraffins, generally called isomerate, along with toluene and xylenes belonging to aromatics, are the desired components in gasoline. Benzene minimization is desired due to carcinogenicity considerations. Through existing conventional processes, the formation of these various components is thermodynamically favored under different sets of reaction conditions (lower reaction temperature favors branched paraffin while higher reaction temperature favors aromatics). Here we report a single-step process that works on a single catalyst system to produce low-benzene, toluene-and-xylene-rich, branched paraffin (isomerate)-rich and high-octane gasoline product from n-heptane. Several ZSM-5 zeolites varying in framework Si/Al ratio have been studied to select the proper acidity, followed by metal functionalization with Pt and, or Co to facilitate the branching and dehydrocyclization reactions of n-heptane in a vapor-phase continuous-flow operation in the presence of N2 as carrier gas. Detailed reaction studies indicated exciting findings related to co-formation of iso-heptanes and aromatics through a common cyclic intermediate in a single step process; thus, provides a path from linear alkanes to a promising gasoline stock for fuel applications.

A fan-shaped synthetic chiral nanographene

We report the synthesis and characterization of a fan-shaped chiral nanographene 1, which is composed of 6 hexabenzocoronene subunits with 216 conjugated carbon atoms. In the dehydrocyclization reaction, 38 CC bonds are formed simultaneously. 1 exhibits strong panchromatic absorption from the ultraviolet to the near-infrared, with an absorption coefficient of 209,000 L mol−1 cm−1 at 564 nm. Optically pure samples, obtained via chiral HPLC, show distinct ECD signals (|Δε| = 704 L mol−1 cm−1 at 405 nm). Upon excitation, 1 emits near-infrared fluorescence at 820 nm with a quantum yield of 5.5%. These photophysical properties of 1 were analyzed with the assistance of DFT calculations.

MECHANISM OF HEXANE DEHYDROCYCLIZATION TO BENZENE USING BI-FUNCTIONAL REFORMING CATALYST

The Mechanism of n. hexane dehydrocyclization reaction to benzene has beenstudied with pure hydrocarbons and synthetic naphtha feedstock at the operating conditions: T = 400° - 520°C PT = 10 – 30 kg/cm2 and H2/HC = 4-10 mole/mole using a Catatest Unit operated in a continuous system. The results show that n, hexadiene has been formed as a mayor source of the intermediate molecule of the methylcycloamil ion, an optimum metal site activity was observed for a given acid-site of bi-functional reforming catalyst and – 1 (minus one) of the total reaction order of n. hexane dehydrocyclization to benzene.

Modeling, Kinetic and Experimental optimization of Reforming Unit for ‎Al- Doura Heavy Naphtha over bi and Tri-metallic Catalysts

In the present work mathematical representation (simulation studies) and experimental work in order to describe the Iraqi heavy naphtha ‎(feed stock) for catalytic reforming process ‎reaction kinetics. Tri and bi-metal catalysts were prepared by adding of tin and iridium (Ir) ‎to classical catalyst using in catalytic reforming unit in Al –Doura refinery to enhance ‎th reaction selectivity. Catalysts performance (activity and selectivity) for the three main catalytic reforming reactions were investigated such as dehydrogenation, hydrocracking, and dehydrocyclization reaction. Catalysts performances were investigated under the following operating condition: constant reaction pressure equal to 6 atm‎, the reaction temperature range of (480, 490, 500, and 510 ˚C), constant hydrogen to hydrocarbon ratio of 4:1, and WHSV (weight hour space velocity) range of (1, 1.5, and 2 hr-1) The results show that as reaction temperatures increase‎ higher conversion of Paraffins and Naphthenes components ‎in Iraqi heavy naphtha while negative impact on conversion as‎ weight hourly space velocity increase (i.e., higher WHSV shows lower conversion). Generally tri and bi-metal catalysts the aromatics and light components ‎yields will be increased under the same operating conditions reforming process.

Nitrogen-doped carbon supported nanocobalt for the synthesis of functionalized triazines via oxidative cleavage of biomass derived vicinal diols as carbon synthons

The efficient conversion of renewable biomass resources into value-added nitrogen-containing chemicals has become the focus of recent research. Herein, we report the preparation of nitrogen-doped carbon supported cobalt catalysts comprising a unique core−shell structure, and the regulation of their catalytic behavior in the dehydrocyclization reaction. Abundant biomass-derived diols were employed as carbon synthons to react with amidines, and they furnished structurally diverse 1,3,5-triazines, a class of compounds found in numerous natural and biomedical products. The synthetic protocol has the advantages of a broad substrate scope, good functional group tolerance, a reusable metal catalyst, and easily available reactants. The method is convenient and practical for the synthesis of versatile triazines with advantageous biological and physical properties.

Noble Metal Substrate Identity Effects on the Self-Assembly, Dynamics, and Dehydrocyclization Reaction of Octaethylporphyrin Molecules

Noble Metal Substrate Identity Effects on the Self-Assembly, Dynamics, and Dehydrocyclization Reaction of Octaethylporphyrin Molecules

Effect of modifiers on Fe-Pt/Al2O3 catalysts for alkanes hydrotreatment

Zeolite-containing polyfunctional catalysts Fe-Pt/Al2O3 (КТ-17, КТ-18), modified with additives of molyb-denum, phosphorus and cerium, were synthesized. The developed catalytic systems were studied in treatment of C14 alkane obtaining a gasoline fraction. Reaction products contain C4-C9 iso-alkanes, C10-C14 iso-alkanes, C4-C10 alkanes, aromatic hydrocarbons and C1-C3 alkanes. In addition, 0.2–0.6 % of heavy hydro-carbons was found in reaction products. The yield of C4-C9 iso-alkanes at 380 °C reached 37.9 %. By means of physical and chemical methods it has been found that the zeolite containing catalysts Fe-Pt /Al2O3 modi-fied by various additives are complex systems. Micro-diffraction and Mossbauer spectroscopy methods al-lowed detecting nanosized hetero clusters of Fe-Pt, Fe-Mo, Pt-Mo in catalysts structure. Depending on chem-ical composition of clusters, particle size varies between 20 and 80 Ǻ. KT-18 catalyst demonstrates high ac-tivity in the process of heavy alkanes treatment; sizes of platinum (d = 200 Å) and iron (d = 30–50 Å) parti-cles were determined by electron microscopy. Activity of KT-18 catalyst is higher than that of highly dis-persed KT-17. The main feature of KT catalysts is their polyfunctionality. During alkanes processing simul-taneous and consecutive reactions of hydrocracking, dehydrogenation, isomerization, dehydro-cyclization and hydro-desulfurization take place.

Effects of Cerium Doping on Pt–Sn/Al2O3 Catalysts for n-Heptane Reforming

A series of trimetallic Pt–Sn–Ce catalysts supported on chloride Al2O3 was prepared by a sequential impregnation method and applied for n-heptane reforming and characterized by several techniques, including N2 physiosorption, transmission electron microscopy, X-ray diffraction, hydrogen temperature-programmed reduction, CO chemisorption, ammonia temperature-programmed desorption, pyridine desorption Fourier-transform infrared spectroscopy, and in situ diffuse reflectance infrared Fourier transform spectroscopy. We have demonstrated that the introduction of Ce can promote isomerization reactions by suppressing undesirable hydrogenolysis reactions, whereas it does not significantly influence the dehydrocyclization reactions. The characterization results show that CeOx can enhance the reducibility of Pt species via enhancing the Pt dispersion. In addition, Ce increases the proportion of medium-strength acid sites, which does not only promote isomerization activity, but also suppresses the undesirable reactions such as hydrogenolysis and cracking.

Ethylene Conversion into Propylene and Aromatics on HZSM-5: Insights on Reaction Routes and Water Influence

Ethanol is an alternative for producing petrochemicals, especially propylene and aromatics (benzene, toluene, and xylenes). To understand ethanol processing routes into olefins and aromatics, it is interesting to use ethylene that is the major primary product of ethanol reaction into hydrocarbons and the intermediate for the formation of olefins and aromatics. In this work, the influence of the operating conditions (ethylene partial pressure, reaction temperature and contact time) in the ethylene conversion into propylene and aromatics, and in the product yield was investigated using HZSM-5 zeolite as catalyst. Lower contact time and ethylene partial pressure, and higher reaction temperature favored propylene yield. Olefin production was based on the formation of carbene species from ethylene that reacts with ethylene to produce propylene and on ethylene dimerization to form butenes. On the other hand, intermediate reaction temperatures and contact times, and higher ethylene partial pressure promote the formation of aromatics, where the dehydrocyclization reaction is favored over hydrogen transfer. The presence of water vapor in long-term reactions deactivated the catalyst. For propylene production, the decrease of ethylene conversion was due to zeolite framework dealumination, while for aromatic formation the reaction mechanism was changed.

1-4-4 Ga-ZSM-5 ゼオライト-アルミナ複合担体触媒によるn-pentaneの接触改質

1-4-4 Ga-ZSM-5 ゼオライト-アルミナ複合担体触媒によるn-pentaneの接触改質

Hexapole [9]Helicene

Herein we present the first hexapole [9]helicene (H9H). Co-catalyzed [2+2+2] cyclotrimerization of a dinaphthopyrene (DNP) functionalized alkyne provides the hexaaryl benzene precursor 2, which is transformed into H9H via a dehydrocyclization reaction. Formation of each embedded [9]helicene involves forging of a new C-C bond, which stitches together two [4]helicene subunits of the neighboring DNP blades, reminiscent of the initial method Martin developed for the preparation of [9]helicene in the 1960s. Single-crystal X-ray analysis of both 2 and H9H discloses their extremely distorted and crowded structural features. Chiral resolution, optical and electronic properties of H9H are also presented.

Effects of diffusional constraints on lifetime and selectivity in methanol-to-olefins catalysis on HSAPO-34

Reaction-transport formalisms show that the effects of crystallite size, H+ density, and Si speciation of HSAPO-34 on catalyst lifetime and selectivity in methanol-to-olefins catalysis are all manifestations of diffusional constraints. Both structural catalyst properties—i.e., crystallite size and H+ density—and intrinsic kinetic constants (per H+)—regulated, in silicoaluminophosphates, by Si speciation—affect the severity of these diffusional restrictions. Methanol-to-olefins catalysis on HSAPO-34 occurs by a complex network of autocatalytic reactions in which temporal gradients persist along with spatial gradients inherent to continuous-flow, fixed-bed reactors. Invocation of reaction rates in the interpretation of lifetime and selectivity trends in such systems requires defined quantities averaged in both time and space because measured observables conflate instantaneous reaction rates with spatial and temporal gradients. Quantities defined herein, i.e., total turnovers and cumulative selectivity, provide such rigorous assessments of lifetime and selectivity that permit causative correlation between rates of reactions within the complex network of autocatalytic reactions and material properties of HSAPO-34. Total turnovers decreases with increasing diffusional constraints because dehydrocyclization reactions experience stronger diffusional constraints than olefins methylation, aromatics dealkylation, and methanol transfer hydrogenation. Cumulative selectivity to paraffins increases with increasing diffusional constraints because transfer hydrogenation reactions of methanol, ethylene, and propylene experience stronger diffusional constraints than all other reactions within the complex reaction network. The approaches detailed herein codify the chemical and physical origins of trends in process outcomes with system variables for reaction systems characterized by complex reaction networks and prevailing spatial and temporal concentration gradients.

Production of Gasoline Fuel from Alga‐Derived Botryococcene by Hydrogenolysis over Ceria‐Supported Ruthenium Catalyst

AbstractHydrogenolysis of hydrogenated botryococcene (Hy‐Bot) was conducted over various supported Ru catalysts, Ir/SiO2, and Pt/SiO2–Al2O3. Ru/CeO2 with very high dispersion showed the highest yield (70 %) of gasoline‐range (C5–C12) alkanes at 513 K. The main gasoline‐range products were dimethylalkanes. This yield is comparable to or higher than the gasoline yields from botryococcene in the literature, which were obtained at much higher temperature. Ir/SiO2 also showed a high fuel yield, but the activity was much lower than that with the Ru catalysts. The reaction over Pt/SiO2–Al2O3 slowed down before total conversion of Hy‐Bot was achieved. Ru/CeO2 was stable in the hydrogenolysis of Hy‐Bot without loss of activity and selectivity during reuses. The carbon balance was low for the hydrogenolysis of Hy‐Bot over all catalysts if the main products are heavy hydrocarbons, whereas for the hydrogenolysis of squalane the carbon balance was kept near 100 %. 1H NMR spectra of the product mixture and thermogravimetric analyses of the product mixture and the recovered catalyst revealed that the formation of aromatic compounds, polymeric products, and coke was negligible for the carbon balance. In a model reaction using substrate compounds with a substructure of Hy‐Bot, only 2,5‐dimethylhexane, which has a C6 chain with two Cprimary−Ctertiary bonds, produced a cyclic product, 1,4‐dimethylcyclohexane, which has a higher boiling point than the substrate. This dehydrocyclization reaction makes the product distribution in the hydrogenolysis of Hy‐Bot more complex.

Steering On‐Surface Reactions by a Self‐Assembly Approach

Abstract4,4′‐Bis(2,6‐difluoropyridin‐4‐yl)‐1,1′:4′,1′′‐terphenyl (BDFPTP) molecules underwent dehydrocyclization and covalent coupling reactions on Au(111) according to scanning tunneling microscopy (STM) measurements and density functional theory (DFT) calculations. Self‐assembly of the reactants in well‐defined molecular domains prior to reaction could greatly enhance the regioselectivity of the dehydrocyclization reaction and suppress defluorinated coupling, demonstrating that self‐assembly can efficiently steer on‐surface reactions. Such a strategy could be of great importance in surface chemistry and widely applied to control on‐surface reactions.

Steering On-Surface Reactions by a Self-Assembly Approach.

4,4'-Bis(2,6-difluoropyridin-4-yl)-1,1':4',1''-terphenyl (BDFPTP) molecules underwent dehydrocyclization and covalent coupling reactions on Au(111) according to scanning tunneling microscopy (STM) measurements and density functional theory (DFT) calculations. Self-assembly of the reactants in well-defined molecular domains prior to reaction could greatly enhance the regioselectivity of the dehydrocyclization reaction and suppress defluorinated coupling, demonstrating that self-assembly can efficiently steer on-surface reactions. Such a strategy could be of great importance in surface chemistry and widely applied to control on-surface reactions.

The role of sulfur in modification of active sites of reforming catalysts

The features of the interaction of hydrogen sulfide with the surface of supports (alumina and silica) and catalysts (Pt/SiO2, Pt/Al2O3, Re/Al2O3, and Pt–Re/Al2O3) have been studied. It has been found that the adsorption of sulfur on the supports is completely reversible. The amount of irreversibly adsorbed sulfur (Sirrev) and Sirrev/metal ratios in the catalysts after treatment in a hydrogen atmosphere at 500°C have been determined. Sulfurization reduces the dispersion of platinum to 5% and increases the amount of ionic platinum on the catalyst surface. Regarding the dehydrocyclization reaction of n-heptane, the optimal amount of sulfur required for sulfurization of the catalyst with the composition 0.25% Pt 0.3% Re/γ-Al2O3 (0.3% Zr) is 0.072 wt %.