Octane System Research Articles

Intensification of polyethylene devolatilization in twin‐screw extruder with additives

AbstractAiming at the problem of difficult to remove high‐carbon α‐olefin in polyethylene, the influences of operation conditions and devolatilization additives on the devolatilization of LLDPE/1‐octene system in an exhaust twin‐screw extruder are studied by headspace gas chromatography. The results showed that the devolatilization efficiency increases with the devolatilization temperature and vacuum. With the screw rotational speed, the content of liquid additives and the gas velocity of gas additives increasing, the devolatilization efficiency first increases and then decreases. The devolatilization difficulty of different grades of polyethylene varies due to the difference of the viscosities. When the volatile content is high, the effect of devolatilization additives is anhydrous ethanol > surfactant > water > nitrogen. When the volatile content is low, the effect of nitrogen on devolatilization is obviously better than anhydrous ethanol and water. Finally, a novel devolatilization process is proposed, that is, an evacuation system (vacuum degree 0.08–0.1 MPa) is set up in each stage of the devolatilization section, the anhydrous ethanol is introduced in the first stage, and high‐purity nitrogen is introduced in the second, third, and fourth stages, which can ultimately reduce the VOC content of LLDPE products to less than the target value of 50 ppm.Highlights The devolatilization process is used to remove high carbon α‐olefins from LLDPE. Each additive has an optimal injection value. Ethanol is the most effective in the foam‐dominated devolatilization stage. Nitrogen is the most effective in the diffusion‐dominated devolatilization stage. A new additive‐enhanced twin‐screw extruder devolatilization process is proposed.

Fungal P450 Deconstructs the 2,5-Diazabicyclo[2.2.2]octane Ring En Route to the Complete Biosynthesis of 21R-Citrinadin A.

Prenylated indole alkaloids (PIAs) possess great structural diversity and show biological activities. Despite significant efforts in investigating the biosynthetic mechanism, the key step in the transformation of 2,5-diazabicyclo[2.2.2]octane-containing PIAs into a distinct class of pentacyclic compounds remains unknown. Here, using a combination of gene deletion, heterologous expression, and biochemical characterization, we show that a unique fungal P450 enzyme CtdY catalyzes the cleavage of the amide bond in the 2,5-diazabicyclo[2.2.2]octane system, followed by a decarboxylation step to form the 6/5/5/6/6 pentacyclic ring in 21R-citrinadin A. We also demonstrate the function of a subsequent cascade of stereospecific oxygenases to further modify the 6/5/5/6/6 pentacyclic intermediate en route to the complete 21R-citrinadin A biosynthesis. Our findings reveal a key enzyme CtdY for the pathway divergence in the biosynthesis of PIAs and uncover the complex late-stage post-translational modifications in 21R-citrinadin A biosynthesis.

Various synthetic approaches for [6,7,m]‐tricyclic compounds containing an oxygen‐bridged skeleton

AbstractWe report the synthesis of [6,7,5]‐tricyclic compounds containing an oxabicyclo [3.2.1] octane system from 1,6‐enyne carbonyl. We also synthesized [6,7,6]‐tricyclic compound from 1,7‐enyne carbonyl through Au‐catalyzed cyclization. The synthesis of oxacyclic compounds using iodine or oxygen is environmentally friendly cyclization methods. Oxacyclic compounds are useful for synthesizing various diterpene alkaloids.

Expanding the Diversity of Pyridines Through Annulation of Keto and Diketo Compounds

AbstractAn efficient gold [Au]‐catalyzed one‐pot synthesis has been developed for the construction of biologically interesting mono‐ and bipyridines by utilizing the commercially available cyclic ketones and propargylamine in a sealed tube. The formation of bipyridine derivative 21 a indicates that annulation followed by retro‐Diels–Alder reaction is occurring with norbornene system. However, keto‐derivatives containing bicyclo[2.2.2]octene system 25 indicate that retro‐Diels–Alder reaction is not facile. Compounds 32 a and 33 a were subjected to ring opening cross‐ metathesis to generate diversity and further functionalization of pyridine derivatives.

Carbon nanotube enhanced membrane filtration for trace level dewatering of hydrocarbons

A highly hydrophobic membrane prepared by immobilizing carbon nanotubes (CNTs) over PTFE microfiltration membrane is presented for the dewatering of organic-water mixtures containing trace amounts of water. The effects of different CNT concentrations on membrane morphology, wettability, hydrophobicity, porosity, and permeability were characterized. After immobilization of CNT into membranes, the contact angle increased by 9% and 16% compared to unmodified 0.1 μm and 0.22 μm pore sizes membranes respectively. The carbon nanotube immobilized membrane (CNIM) showed remarkable separation efficiency for octane and heptane water systems. The enhanced hydrophobicity of the CNIM helped nano/micro water droplets to coalesce on the CNT present on the membrane surface which led to their rejection. In general, the water rejection increased, and the solvent flux decreased with CNT incorporations. For the octane water system, CNIMs were fabricated with 0.1 and 0.22 μm pore sizes, at the optimized CNT loading of 3 and 6 wt%, the water rejection was 99.87% and 97.60% respectively while the fluxes were 44.947 kg/m2.hr and 54.66 kg/m2.hr for octane water system. Water rejection for CNIM with 0.1 μm pore size was 99.87% and 99.98% respectively for octane-water and heptane-water systems, which were 20.3% and 20.5% higher compared to one without the CNT coatings.

Molecular mechanism, liquid–liquid equilibrium and process design of separating octane-n-butanol system by ionic liquids

The development of clean and green separation technologies has become a key scientific issue in the chemical industry. Because of the wide applicability of ionic liquids (ILs) as green and recyclable extractants, their abilities to extract and separate n-butanol from octane were explored in this work. Based on quantum chemical methods and the COSMO-SAC model, the surface charge density distributions of 22 cations, 19 anions, octane, and n-butanol were calculated. Moreover, the infinite dilution activity coefficients of octane-n-butanol-IL systems were calculated. The distribution coefficients and separation coefficients were also determined. ILs with strong extraction effects (i.e., [Bmim][HSO4], [Bmim][NO3], and [Bmim][OTf]) were used to explore the separation mechanism at the molecular scale; this was conducted by analyzing charge density, bond energy, and bond length of intermolecular interactions. The liquid–liquid equilibrium data of octane-n-butanol-ILs systems were measured, and the distribution coefficients and separation coefficients of each system were calculated. The experimental data were regressed using the NRTL model to obtain the corresponding binary interaction parameters. A process for separating the azeotropic octane and n-butanol systems using ILs was proposed. This process was simulated and optimized using the Aspen Plus 11 software. In addition, the total annual cost was calculated. This work lays the foundation for the screening of green and clean separation solvents.

Protecting‐Group‐Free Total Synthesis of (–)‐Pallambins A—D

Main observation and conclusionA full account of the total synthesis of (–)‐pallambins A—D (1—6) is described. The strategy was devised by simulating their biosynthetic pathway. The left‐part bicyclo[3.2.1]octane system of pallambins C and D was efficiently constructed via a palladium‐ catalyzed oxidative cyclization. For construction of the right‐part tetrahydrofuran/γ‐lactone moiety (C/D rings), initial attempts to synthesize the allylic alcohol 15 for an one‐step Pd‐mediated alkoxycarbonylation have failed. However, during the course of this work, an unprecedented CH3Li‐mediated method for conversion of bromoisoxazoline to the corresponding β‐hydroxy nitrile has been discovered. Furthermore, a stepwise protocol was designed, namely an Eschenmoser‐Claisen rearrangement/Lactonization to generate the C ring, and a non‐classical Wittig reaction to form the D ring. During the course of this work, a palladium‐catalyzed method for dehydrobromination of bromide ketone was developed. Finally, an individual transformation of pallambins C (3) and D (4) generated pallambins A (5) and B (6) under mild UV irradiation. Thus, the first enantioselective total syntheses of (–)‐pallambins A—D have been achieved in 15 or 16 steps from the known chiral cyclohexenone 8. The described synthesis avoids protecting‐group manipulations by designing highly chemo‐ and stereoselective transformations.

Coarse-grained molecular dynamic simulations of interactions of poly(amidoamine) with sodium octadecyl sulfate at the water/octane interface

This study investigated the interactions of poly(amidoamine) (PAMAM) and sodium octadecyl sulfate (SOS) molecules at the water/octane interface by analyzing spatial structures and interfacial properties of water/PAMAM/SOS/octane (oil) systems. Coarse-grained molecular dynamic simulations were performed to examine the dependence of the systems on interfacial coverage (IC, corresponding to the concentration of SOS molecules) and PAMAM concentration (CPAMAM) in terms of density profiles, interaction energy, interfacial thickness, order parameters (SCD), interfacial tension (γ), and area compressibility modulus (KA). Simulation results showed that the presence of PAMAM molecules had a stronger effect on SOS head groups and pushed the head groups toward the oil phase. The interaction energy between PAMAM and SOS molecules increased with increments of CPAMAM in a fixed IC. Interfacial thickness and SCD increased with increased CPAMAM. The γ value in the presence of PAMAM was lower compared with pure SOS solutions and decreased with increased CPAMAM. The area compressibility modulus (KA) of SOS monolayer increased with increased CPAMAM.

Generation of 1-azabicyclo[3.2.1]octane and 5-azatricyclo[3.2.1.02,7]octane systems by carbenium ion rearrangements during production of the antihistamine drug Quifenadine

Dehydration of ethyl 3-hydroxyquinuclidine-3-carboxylate is one of the key steps during production of the antihistamine drug Quifenadine (Phencarol). The side products of this process were isolated and their structures proved using NMR spectroscopy. Carbenium ion rearrangements of quinuclidine-3-carboxylate gave rise to 1-azabicyclo[3.2.1]octane and 5-azatricyclo[3.2.1.02,7]octane systems, which serve as impurity standards for the manufacturing process of Quifenadine and are also interesting building blocks for medicinal chemistry.

Structure-Based Design and Synthesis of Apramycin-Paromomycin Analogues: Importance of the Configuration at the 6'-Position and Differences between the 6'-Amino and Hydroxy Series.

The preparation of a series of four analogues of the aminoglycoside antibiotics neomycin and paromomycin is described in which ring I, involved in critical binding interactions with the ribosomal target, is replaced by an apramycin-like dioxabicyclo[4.4.0]octane system. The effect of this modification is to lock the hydroxymethyl side chain of the neomycin or paromomycin ring I, as part of the dioxabicyclooctane ring, into either the gauche-gauche or the gauche-trans conformation (respectively, axial or equatorial to the bicyclic system). The antiribosomal activity of these compounds is investigated with cell-free translation assays using both bacterial ribosomes and recombinant hybrid ribosomes carrying eukaryotic decoding A site cassettes. Compounds substituted with an equatorial hydroxyl or amino group in the newly formed ring are considerably more active than their axial diastereomers, lending strong support to crystallographically derived models of aminoglycoside-ribosome interactions. One such bicyclic compound carrying an equatorial hydroxyl group has activity equal to that of the parent yet displays better ribosomal selectivity, predictive of an enhanced therapeutic index. A paromomycin analog lacking the hydroxymethyl ring I side chain is considerably less active than the parent. Antibacterial activity against model Gram negative and Gram positive bacteria is reported for selected compounds, as is activity against ESKAPE pathogens and recombinant bacteria carrying specific resistance determinants. Analogues with a bicyclic ring I carrying equatorial amino or hydroxyl groups mimicking the bound side chains of neomycin and paromomycin, respectively, show excellent activity and, by virtue of their novel structure, retain this activity in strains that are insensitive to the parent compounds.

Hydrate anti-agglomeration and synergy effect in normal octane at varying water cuts and salt concentrations

Abstract Anti-agglomeration is a promising approach to address hydrate risks in oil and gas flowlines from the deep sea. Salt concentration of the coproduced water with hydrocarbons is known to affect anti-agglomeration. Most studies report improvement in efficiency of anti-agglomeration but some authors report a decrease from salts. In this work, the effect of water cut (ratio of aqueous phase to total liquid) and NaCl concentration on the effectiveness of the cocamidopropyl dimethylamine anti-agglomerant (AA) are investigated in normal octane and methane systems. We also investigate the synergic effect of a cosurfactant (Span 80) in improving the performance of the AA at water cuts of 10%–30%. A likely mechanism of the synergism is suggested: the co-surfactant (Span 80) promotes the dispersion of water droplets in the oil phase and the AA prevents the agglomeration of the hydrate particles. We investigate emulsion formation and the phase behaviour of octane/brine/AA/Span 80 emulsion to shed light on the mechanisms at play. A solid-like fluid which hardly moves under gravity is observed when the normal octane and water/brine and the anti-agglomerant are mixed at a water cut of 95%. The solid-like behaviour which is attributed to flocculation can be remedied by the introduction of alcohols in the solution. There are similarities in emulsion formation and hydrate anti-agglomeration of normal octane and a condensate liquid which was investigated recently and there are also major differences.

Efforts Toward a Synthesis of Crotogoudin and Crotobarin

Two synthesis designs for the diterpenoid crotogoudin are discussed, and efforts to achieve each are described. First, a Cope rearrangement/intramolecular Diels–Alder cascade reaction was investigated. Second, a bioinspired sequence of cationic bicyclization and A-ring oxidative fragmentation set-up for a lactonization induced by a phenolic oxidation, ultimately providing a tricyclic intermediate that required only installation of the bridging ring of the salient bicyclo[2.2.2]octane system. This last endeavor was fraught with difficulty, but did lead to the development of conditions for cyclization of related keto-alkenes via manganese(III)-based radical chemistry.

THE RELATIONSHIP BETWEEN THE STRUCTURE OF PHASE EQUILIBRIUM DIAGRAM AND THE STRUCTURE OF FLOWSHEET DIAGRAMS OF MULTIPHASE QUATERNARY MIXTURES SEPARATION

In this work the structures of phase equilibrium diagrams of multiphase four-component systems n-hexane (n-heptane, n-octane) - cyclohexane - furfural - water were investigated. The systems are characterized by the existence of areas of three-phase separation. On the basis of the obtained data the synthesis of feasible variants of separation schemes was carried out, rational modes of functioning of each column were found, the energetically favorable variant was chosen. It was found that the use of preliminary phase separation in systems with n-hexane and n-octane is power-efficient, and the profit in case of the octane system (equimolar mixture) in comparison with the application of the first predetermined separation at the first stage is more than 25%. Certain difficulties (the high values of columns effectiveness: 60 and 40 theoretical plates) upon the separation of the hexane and heptane systems are due to the similar volatilities of n-hexane (n-heptane) and cyclohexane in the vicinity of the point of pure alkane.

Regioselective hydrocarbonylation of phenylacetylene to α,β-unsaturated esters and thioesters with Fe(CO)5 and Mo(CO)6

A highly regioselective hydrocarbonylation of phenylacetylene with thiols and alcohols was developed using metal carbonyls/diazabicyclo[2.2.2]octane (DABCO) system at 100 °C in DMF. The use of Mo(CO)6 and thiols in the presence of DABCO was applied as an efficient Pd-free method for hydrothiocarbonylation of phenylacetylene into trans-α,β-cinamyl thioesters in excellent yields (88–98%). Similar reaction using Fe(CO)5/ROH/DABCO system resulted into high yield synthesis of trans-α,β-cinamyl esters (87–98%). These reactions were conducted under mild reaction conditions without the need to use gaseous CO or any phosphine ligand and palladium catalyst.

Determination of critical properties for binary and ternary mixtures of short chain alcohols and alkanes using a flow apparatus

The critical temperatures and pressures of four binary systems and two ternary systems containing gasoline additives (ethanol+cyclohexane, ethanol+octane, 2-propanol+octane, 2-propanol+decane, ethanol+cyclohexane+octane and 2-propanol+octane+decane) were measured with a low-residence time flow apparatus. The critical properties were determined by observing critical opalescence and phase changes in a quartz glass tube. The expanded uncertainties of critical temperature and pressure were estimated to be less than ±0.4K and ±0.01MPa, respectively. The four binary systems show non-ideal behavior especially for ethanol+cyclohexane and ethanol+octane systems. The experimental data of all binary mixtures could be correlated to within 0.06% with the Redlich–Kister equations. Ternary mixtures are newly reported in this work and were correlated with Cibulka's and Singh's expressions.

Construction of a Bicyclo[3.2.1]octane System Carrying the (R)-Carvone Core under Oxidative Radical Conditions: Synthetic Access to (+)-Miroestrols

Bicyclo[3.2.1]octane systems carrying an ( R )-carvone core were successfully constructed by 5- exo -cyclization between a β-keto ester function and a 3,3-dimethylallyl group under oxidative radical conditions.

Computer simulations of material ejection during C60 and Arm bombardment of octane and β-carotene

Molecular dynamics (MD) computer simulations are used to investigate material ejection and fragment formation during keV C60 and Arm (m=60, 101, 205, 366, 872 and 2953) bombardment of organic solids composed from octane and β-carotene molecules at 0° and 45° impact angle. Both systems are found to sputter efficiently. For the octane system, material removal occurs predominantly by ejection of intact molecules, while fragment emission is a significant ejection channel for β-carotene. A difference in the molecular dimensions is proposed to explain this observation. It has been shown that the dependence of the sputtering yield Y on the primary kinetic energy E and the cluster size n can be expressed in a simplified form if represented in reduced units. A linear and nonlinear dependence of the Y/n on the E/n are identified and the position of the transition point from the linear to nonlinear regions depends on the size of the cluster projectile. The impact angle has a minor influence on the shape of the simplified representation.

ChemInform Abstract: Novel Design of 3,8‐Diazabicyclo[3.2.1]octane Framework in Oxidative Sulfonamidation of 1,5‐Hexadiene.

Abstract 1,5-Hexadiene reacts with trifluoromethanesulfonamide in the oxidative system (t-BuOCl+NaI) to give trans-2,5-bis(iodomethyl)-1-(trifluoromethylsulfonyl)pyrrolidine 5 and 3,8-bis(trifluoromethylsulfonyl)-3,8-diazabicyclo[3.2.1]octane 6. With arenesulfonamides ArSO2NH2 (Ar=Ph, Tol), the reaction stops at the formation of the trans and cis isomers of 2,5-bis(iodomethyl)-1-(arenesulfonyl)pyrrolidine 7 and 8 (1:1). The cis isomers of 7 and 8 do not undergo cyclization to the corresponding 3,8-disubstituted 3,8-diazabicyclo[3.2.1]octanes. The reaction with triflamide represents the first example of one-pot two-step route to 3,8-diazabicyclo[3.2.1]octane system.

Molecular dynamics simulation on volume swelling of CO2–alkane system

The microscopic mechanism of the volume swelling of CO2–alkane (decane, octane, hexane and cyclohexane) systems and the effects of temperature, pressure and alkane structure on the volume swelling of CO2–alkane systems are investigated by performing molecular dynamics simulation. It is shown that the increase in pressure, the reduction in temperature and the straight-chain structure of the alkane are of benefit to the volume swelling of CO2–alkane systems by calculating the volume swelling coefficient; CO2 in supercritical state plays a dominant role in the volume swelling of CO2–alkane systems. The microscopic process of the volume swelling of CO2–decane system shows that the increase in the average separation distance between decane molecules and the stretch of decane molecules result in the volume swelling of decane as CO2 dissolve into decane. The calculations of interaction energies in CO2–decane system indicate that the interaction between CO2 and decane molecules is responsible for the volume swelling of CO2–alkane system. Further study on the interaction between CO2 and decane molecules shows that the dispersion interaction, resulting in the different solubility of CO2 in alkanes, is the essence of the volume swelling for CO2–alkane system. This work is a good start on understanding the mechanism of alkane swelling influenced by CO2 at the molecular level and provides useful information for guiding CO2 enhancing oil recovery.

Cytisine-like alkaloids from Ormosia hosiei Hemsl. & E.H. Wilson

Four alkaloids named hosieines A–D were isolated from the root and stem of Ormosia hosiei. Their flat structures were established by mass spectrometry and by a combination of NMR experiments. These molecules probably share a common biosynthetic origin with the lupin alkaloids but they differ in the formation of the last ring, being here part of a rare 2-azabicyclo[3.2.1]octane system. Their absolute configuration was determined by X-ray crystallography using CuKα radiation. As has been described for cytisine, they display a remarkable affinity towards neuronal nicotinic acetylcholine α4β2 receptor.