Alkyl Aromatics Research Articles

Study on low-temperature pyrolysis of large-size printed circuit boards

An energy-saving pyrolysis process of FR4-type printed circuit board (PCB) was designed with lower pyrolysis temperature (500°C) and large-size PCB sample (16–20cm2). The pyrolysis experiment of the PCB was carried out based on the process. The properties of pyrolytic gas and tar were compared to the pyrolysis results of previous process with high temperature (800°C) and small-size PCB (1.5–2cm2 or powder). Endothermic heat of PCB pyrolysis reaction was calculated based on the experiment data collected. The results showed that: (1) PCB pyrolysis produced 10.17wt% of gas, 18.23wt% of tar and 71.60wt% of solid particle. Similar to previous studies, CO, CO2, 2-methyl propene was the main components in pyrolysis gas and the pyrolysis tar consisted of phenol and alkyl aromatics. However, the content of propylene, bromomethane, and bromine were significantly different in the pyrolysis gas of this study. (2) Metals and fiberglass were easier to be separated compared to the case of regular pyrolysis with 800°C pyrolysis final temperature and small-size sample. Copper sheets and fiberglass which adhere to a plenty of carbon were collected manually; a little amount of gold and nickel stayed in the residue. (3) Endothermic heat of PCB pyrolysis reaction is about 19.692MJ/kg. The calorific capacity is about 2.386MJ for pyrolytic gas and 4.502MJ for tar from each kilogram PCB pyrolysis. The overall calorific capacity of pyrolytic gas and tar accounts for 35% of required pyrolysis heat.

Determination of Hydrogen Solubility in Heavy Fractions of Crude Oils by a Modified Direct Method

The solubility of hydrogen in Venezuelan heavy coking gas oil (HCGO), Karamay atmospheric residue (KRAR), Liaohe atmospheric residue (LHAR), and Venezuelan atmospheric residue (VNAR) was measured at temperatures in the range 150 °C to 350 °C at pressures up to 11 MPa by a modified direct method. The measurement accuracy and reliability were examined by determining hydrogen solubility in toluene and n-heptane at temperatures of 25 °C, 50 °C and 100 °C, and results are in a good agreement with the data reported. The order of hydrogen solubility in the four feedstocks at the same experimental condition is VNAR < LHAR < KRAR < HCGO. The impact of oil properties, such as aromatic ring number and alkyl chain length, on hydrogen solubility was discussed. The results indicate that the condensed aromatics play a key role in the fractions of high boiling points. The hydrogen dissolving capacity in different derived oils with the same boiling range can be tentatively determined via analyzing the H/C atomic ratio of the oils.

ChemInform Abstract: Palladium‐Catalyzed Oxidative Aminocarbonylation: A New Entry to Amides via C—H Activation.

A novel palladium-catalyzed oxidative aminocarbonylation reaction via C(sp3)–H activation was established, which provides a convenient and general method for the construction of arylacetamides via the carbonylation reaction of alkyl aromatics and amines. By using this protocol, the marketed drug ibuprofen could be easily obtained.

Preparative microfluidic electrosynthesis of drug metabolites.

In vivo, a drug molecule undergoes its first chemical transformation within the liver via CYP450-catalyzed oxidation. The chemical outcome of the first pass hepatic oxidation is key information to any drug development process. Electrochemistry can be used to simulate CYP450 oxidation, yet it is often confined to the analytical scale, hampering product isolation and full characterization. In an effort to replicate hepatic oxidations, while retaining high throughput at the preparative scale, microfluidic technology and electrochemistry are combined in this study by using a microfluidic electrochemical cell. Several commercial drugs were subjected to continuous-flow electrolysis. They were chosen for their various chemical reactivity: their metabolites in vivo are generated via aromatic hydroxylation, alkyl oxidation, glutathione conjugation, or sulfoxidation. It is demonstrated that such metabolites can be synthesized by flow electrolysis at the 10 to 100 mg scale, and the purified products are fully characterized.

Highly Selective Aromatic Alkylation of Phenol and Anisole by Using Recyclable Brønsted Acidic Ionic Liquid Systems

AbstractA highly efficient ionic liquid catalyst system for selective alkylation of phenol and anisole with alkenes is described. By using Brønsted acidic triflate ionic liquids containing the SO3H group attached to the cation, it was possible to recycle the catalyst and reuse it after a simple workup procedure. Moreover, selectivity towards the monoalkylated products was improved to 93 % by using a biphasic system.

Synthesis of indole analogues of the natural schweinfurthins.

An interest in the schweinfurthins, natural stilbenes with significant antiproliferative activity, has prompted efforts to prepare a set of indole analogues. To approach the desired compounds through a Horner-Wadsworth-Emmons condensation, new indole derivatives bearing a phosphonomethyl substituent in the B-ring were required. The parent indole system with the necessary substitution pattern was obtained through Stobbe condensation and cyclization. A prenyl substituent was incorporated at the C3 position of a 4,6-disubstituted indole through a highly regioselective electrophilic aromatic substitution reaction, while metalation and alkylation provided the C2-prenylated indole. After introduction of the phosphonate group through classical reactions, the new indole phosphonates were found to undergo the desired condensation with nonracemic aldehydes representing the schweinfurthin left half. This approach provides facile access to new heteroaromatic analogues of the natural schweinfurthins and should be applicable to many other natural stilbenes as well.

An insight into effect of methanol on catalytic behavior of Amberlyst 35 resins for alkylation desulfurization of fluid catalytic cracking gasoline

Alkylation desulfurization of fluid catalytic cracking (FCC) gasoline over solid acid catalysts is considered to be a viable path to meet environmental regulations of sulfur emissions. However, side reactions in the process such as alkenes oligomerization and aromatic alkylation lead to the formation of significant amounts of coke, which will greatly reduce the catalyst lifetime and require keeping high catalyst selectivity for thiophenic compounds alkylation. In this paper, both the experimental and theoretical investigations were carried out to further explain the effect of methanol on the catalytic behavior of macroporous sulfonic resins Amberlyst 35 (A35) in the alkylation desulfurization process of FCC gasoline. The results indicated that adding suitable amount of methanol (about 1.0wt% of the feed gasoline) was beneficial to improve the catalytic behavior of A35 in this process. The competition adsorption of suitable amount of methanol and its ether product with isoalkenes could greatly reduce the activated alkenes on the acid sites of A35 and have little impact on the alkylation of thiophenic sulfurs. They could also decrease the alkenes conversion for side reactions of alkenes oligomerization, which was favorable for improving the catalytic selectivity for thiophenic compounds alkylation and prolonging the catalytic lifetime of A35.

Tailoring zeolite morphology by Charge Density Mismatch for aromatics processing

Nano-crystalline zeolites UZM-5 and UZM-14 were synthesized via the Charge Density Mismatch (CDM) approach and were shown to have distinct morphologies that significantly impact aromatic alkylation and transalkylation reactions. UZM-5 has surface structure features and thin plate morphologies favorable for catalyzing the alkylation of benzene with ethene. The alkylation activity depends on the crystallinity and morphology, which affect acidity and access to surface cups and internal pores. Nano-crystalline mordenite, UZM-14, was characterized in terms of crystallite length in the direction of the 12-MR channels, mesoporosity, and accessibility of acid sites. Aromatics transalkylation performance was shown to correlate with mesoporosity and crystallite length along the pore direction. This was rationalized in terms of decreased diffusion path length in the micropores and improved accessibility of feed molecules to acid sites in the interior of the zeolite crystals.

Investigation on Asphaltene Structures during Venezuela Heavy Oil Hydrocracking under Various Hydrogen Pressures

Venezuela heavy oil under various hydrogen pressures has been hydrocracked to investigate the variation of asphaltene components during reaction. Asphaltenes have been isolated from the product and analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR). The experimental data revealed that the interlamellar spacing and interchain spacing of the asphaltenes increased while the layer diameter decreased with the hydrogen pressure increasing. At the same time, the amount of aromatic carbon and alkyl carbon of the asphaltenes decreased gradually and the amount of naphthenic carbon increased. As the hydrogen pressure increased, the substitution ratio and the condensation degree parameter (HAU/CA) of the aromatic system in the periphery increased gradually and the replacement index and peri-position condensation index of asphaltenes decreased obviously.

Revisiting Smectic E Structure through Swollen Smectic E Phase in Binary System of 4-Nonyl-4′-isothiocyanatobiphenyl (9TCB) and n-Nonane

Thermodynamic and diffraction analyses were performed to establish the phase diagram for a binary system between 4-n-nonyl-4'-isothiocyanatobiphenyl (9TCB) and n-nonane. The swollen SmE structure is identified in the binary system. Upon swelling, a characteristic two-dimensional herringbone array is maintained whereas the layer spacing of SmE structure increases with the content of n-nonane. Considering the difficulties in explaining the experimental findings based on the traditional model of SmE structure, a new model, lamellar with two types of sublayers consisting of aromatic core and alkyl chain moieties, is proposed.

Palladium-Catalyzed Oxidative Aminocarbonylation: A New Entry to Amides via C–H Activation

A novel palladium-catalyzed oxidative aminocarbonylation reaction via C(sp(3))-H activation was established, which provides a convenient and general method for the construction of arylacetamides via the carbonylation reaction of alkyl aromatics and amines. By using this protocol, the marketed drug ibuprofen could be easily obtained.

NMR investigations on products from thermal decomposition of Kuwaiti vacuum residues

Three vacuum residues (VR) obtained from Ratawi Burgan (RB), Lower Fars (LF) and Eocene (EOC) crude oils were thermally cracked at three different temperatures (T: 400°C, 415°C, 430°C) and reaction times (t: 30, 50, 60min). The chemical compositions of the non-gaseous products (i.e. cracked oil and pitch) were investigated in terms of changes in operating conditions and nature of feedstock. The findings show that under severe operating conditions, the type of feed affects the VR’s thermal stability (RB–VR<LF–VR≈EOC–VR). The sulfur content of the cracked oils (CO) varies between 3.6 and 4.4wt%, depending on the feedstock (RB–CO<EOC–CO<LF–CO). The pitch contains between 7.1wt% and 9.6wt% sulfur. SARA-separation of the VRs shows that the VRs consist mainly of aromatic hydrocarbons (95%). 1H and 13C NMR were used to obtain quantitative data (average structural parameters) about the structural composition of the VRs and the non-gaseous products. The VRs are mainly made of alkyl aromatics with more than three cata-condensed aromatic rings that decompose under heat into saturated hydrocarbons and aromatics with less aliphatic carbon. Under the chosen reaction conditions, the effect of feedstock and cracking severity on the chemical composition of the cracked oil is only minor. Throughout all experiments, the cracked oil contains three times more aliphatic carbon (≈62%) than aromatic carbon (≈21%). The aromatic moiety is mono- or di-aromatic. The pitch, on the other hand, shows a steady increase in aromatic carbon with increasing reaction severity (41–71wt%). Under the most severe cracking conditions, about 30% of the aromatic carbon is found in bridge head position of peri-condensed polyaromatic hydrocarbons (PAHs) (PAHRB<PAHLF≈PAHEOC).

A silica gel supported cobalt(II) Schiff base complex as efficient and recyclable heterogeneous catalyst for the selective aerobic oxidation of alkyl aromatics

Abstract A silica gel supported cobalt(II) Schiff base complex was synthesized and used for the oxidation of alkyl aromatics using molecular oxygen as an oxidant under atmosphere pressure. The catalyst shows a high conversion of alkyl aromatics and selectivity to benzylic ketones, and could be reused at least 5 times without significant loss of catalytic activity.

Fast and Efficient Bromination of Aromatic Compounds with Ammonium Bromide and Oxone

A highly efficient, rapid and regioselective protocol was developed for the ring bromination of aromatic compounds under mild conditions with ammonium bromide as a source of bromine source and Oxone^® (potassium peroxysulfate) as an oxidant. No metal catalyst or acidic additive is required. A variety of aromatic compounds, including methoxy, hydroxy, amino, and alkyl arenes, reacted smoothly to give the corresponding monobrominated products in good to excellent yields in very short reaction times. Moreover, dibromination of deactivated anilines to give the corresponding dibromides proceeded in high yields. Interestingly, 1-(2-naphthyl)ethanone provided a ring-brominated product.

Methane Activation and Transformation on Ag/H-ZSM-5 Zeolite Studied with Solid-State NMR

With regard to a general interest in methane utilization in a rational way the activation and transformation of methane on Ag-modified zeolite ZSM-5 (Ag/H-ZSM-5) have been studied with solid-state NMR. The activation of methane occurs by dissociation of the C–H bond on silver cations via the “carbenium” pathway: methane C–H bond cleavage results in the methoxy groups (O–CH3) and possibly silver-hydride species (Ag–H). The formation of surface methoxy groups on Ag/H-ZSM-5 has been detected experimentally with 13C CP/MAS NMR at 508–623 K for the first time. A comparative analysis of the kinetics of the H/D exchange between methane and acid hydroxyl groups for H-ZSM-5 and Ag/H-ZSM-5 zeolites reveals a significant promoting effect of silver cations on the H/D exchange reaction and therefore on methane activation. This effect has been rationalized in terms of reversible methane dissociation on the surface of Ag/H-ZSM-5 zeolite and further involvement in the exchange of the methoxy groups and the silver-hydride species. Ethane represents the first intermediate product of methoxy group transformation. It is formed by the reaction of a methoxy group with methane. Further, dehydrogenation of ethane offers ethene, producing immediately π-complexes with Ag+ cations, which are stable at temperature as high as 673 K. At 823 K π-complexes decompose and ethene undergoes oligomerization, cyclization, dehydrogenation, and aromatization to give benzene. In the presence of methane, ethene π-complexes decompose and become involved in oligomerization and aromatization reaction at lower temperature, already at 673 K. Methane is also involved in the reaction of coaromatization with ethene. This involvement occurs by the alkylation of aromatics, formed from ethene, with methane. Further demethanation of methylbenzenes in the presence of dihydrogen evolved at the stages of ethene transformation to aromatics produces benzene as the main reaction product.

Oxidation of Alkyl Aromatics Over SBA-15 Supported Cobalt Oxide

SBA-15 supported Co3O4 with different weight percentage have been prepared by wet impregnation method. The prepared catalysts were characterised by XRD, DRUV-vis, FT-IR, N2 adsorption-desorption, TPR, XPS, SEM and TEM. The TPR profile revealed good dispersion of active sites and interaction of Co3O4 on SBA-15 support. The catalytic activity of SBA-15 supported Co3O4 was evolved in liquid phase benzylic oxidation under mild condition using H2O2 as the oxidant. The benzylic oxidation was ascribed by hydrogen abstraction of the C-H bond. The various reaction parameters such as Co3O4 loading, solvent, temperature and reaction time on the catalytic activity were also investigated. The 5 wt% of Co3O4/SBA-15 catalyst was found to exhibit high conversion (-75%) with product selectivity of -87%.

Mechanisms of the Deactivation of SAPO-34 Materials with Different Crystal Sizes Applied as MTO Catalysts

SAPO-34 materials with comparable Brønsted acid site density but different crystal sizes were applied as methanol-to-olefin (MTO) catalysts to elucidate the effect of the crystal size on their deactivation behaviors. 13C HPDEC MAS NMR, FTIR, and UV/vis spectroscopy were employed to monitor the formation and nature of organic deposits, and the densities of accessible Brønsted acid sites and active hydrocarbon-pool species were studied as a function of time-on-stream (TOS) by 1H MAS NMR spectroscopy. The above-mentioned spectroscopic methods gave a very complex picture of the deactivation mechanism consisting of a number of different steps. The most important of these steps is the formation of alkyl aromatics with large alkyl chains improving at first the olefin selectivity, but hindering the reactant diffusion after longer TOS. The hindered reactant diffusion leads to a surplus of retarded olefinic reaction products in the SAPO-34 pores accompanied by their oligomerization and the formation of polycyclic aromatics. Finally, these polycyclic aromatics are responsible for a total blocking of the SAPO-34 pores, making all catalytically active sites inside the pores nonaccessible for further reactants.

Effects of crystallinity of ZSM-5 zeolite on para-selective tert-butylation of ethylbenzene

Highly crystalline ZSM-5 zeolites are important for para-selective alkylation of alkyl aromatics, because they carry few external acid sites for isomerization of p-dialkyl products. Such zeolites (Si/Al = 25, 50, and 75) were synthesized in a fluoride medium between pH 4 and 6. Their crystallinities, crystal sizes, and surface areas were higher than those of a commercial ZSM-5 zeolite. Their para selectivities in alkylation were tested for vapor-phase tert-butylation of ethylbenzene between 200 and 400 °C. As expected, all the catalysts showed more than 90% para selectivity. At 300 °C, ethylbenzene conversion decreased in the order ZSM-5(25, commercial) > ZSM-5(25) > ZSM-5(50) > ZSM-5(75). The catalysts had weak, medium, and strong acid sites, but all the acid sites of ZSM-5(75) were weaker than those of ZSM-5(25) and ZSM-5(50). The high activity of commercial ZSM-5 was caused by its strong acid sites being stronger than those of the synthesized zeolites. Although the activity of the commercial catalyst was higher than those of the present catalysts, the selectivity for 4-t-butylethylbenzene (4-t-BEB) was low. The optimum feed ratio (ethylbenzene:t-butyl alcohol) was 2:1 and the feed rate was 1.65 h−1 for high ethylbenzene conversion and 4-t-BEB selectivity. Time-on-stream studies showed slow catalyst deactivation. Highly crystalline ZSM-5 zeolites are therefore better than a commercial zeolite for para-selective alkylation of alkyl aromatics. They do not require much post-modification for high para selectivity. A fluoride medium is therefore better than an alkaline medium for obtaining highly crystalline para-selective ZSM-5 zeolites.

ChemInform Abstract: Aerobic Oxidative Esterification of Benzyl Alcohols with Catalytic Tetrabromomethane under Visible Light Irradiation.

AbstractA new photooxidative method allows the synthesis of aromatic alkyl esters under metal‐free conditions.

Synthesis and characterization of room temperature columnar mesogens of cyclotriphosphazene with Schiff base units

New supermolecular liquid crystals have been synthesized by attaching polycatenar aromatic units with three terminal alkyl chains through imine linking groups to a central cyclotriphosphazene ring, and these were investigated by polarizing microscopy, DSC and XRD. Compounds with several different linear terminal alkyl chains can form liquid crystals with columnar phases, and most of these are room temperature columnar phases. A model is proposed for the organization of the molecules in the columns, which is based on the nanosegregation of the aromatic cores and alkyl chains and a staggered organization of the star-shaped molecules in columns. Branching of the peripheral alkyl chains leads to an amorphous material.