Search

Petrochemistry is a branch of chemistry and chemical engineering that studies reactions and processes of the transformation of petroleum derivatives and natural gas into useful petrochemicals. In its beginning, petrochemistry, or rather the organic chemical industry, was based on the acetylene and Reppe chemistry. The main raw materials of the petrochemical industry nowadays are olefins and aromatic hydrocarbons, with a pronounced tendency toward development of new processes and higher usage of syngas, methane and other alkanes. Here, the reactions and new processes of direct conversion of methane into more valuable petrochemicals are reviewed. Reactions of partial oxidation of methane, dehydroaromatization of methane, oxidative and non-oxidative coupling of methane to higher hydrocarbons are also described and discussed.

In this paper, lubricants based on lauric acid and different polyols -- neopentyl glycol (NPG), trimethylolpropane (TMP) and pentaerythritol (PE) -- were synthesized. After purification, their purity of > 97 mol% was confirmed by infrared spectroscopy and proton nuclear magnetic resonance. Synthesized lubricants 100 to 5000 ppm formulations with diesel showed similar density, kinematic viscosity, and low-temperature behavior to diesel according to standard tests, meaning that they can be used in current diesel engines. They have improved the lubricity of the formulations, as confirmed by a lower coefficient of friction, and an almost 50 % improvement in wear scar diameter (according to EN 12156-1). [ABSTRACT FROM AUTHOR]

In recent decades, conventional biodiesel synthesis from methanol or ethanol and sunflower and rapeseed oil as feedstock has also introduced the use of higher and branched alcohols and the use of waste sources of triglycerides. This study examined the influence of reactant molar ratio (5:1-12:1), mass fraction of the potassium hydroxide catalyst (1-3 wt%), time (30-120 min), type of feedstock and alcohol on the conversion of fatty acid alkyl esters. The results showed that the presence of structural branching had a negative influence on the reaction conversion. Regarding the feedstocks, the highest conversions were obtained when using coconut oil rich in short-chain saturated fatty acids, while the conversions of biodiesel obtained from animal fat and unsaturated oils were lower. Molar ratio of the reactants and the mass fraction of the catalyst had the highest influence on the reaction conversion. [ABSTRACT FROM AUTHOR]

The composite materials based on poly(methyl methacrylate) and poly(methyl methacrylate-co-dimethylaminoethyl methacrylate) with nanocellulose in the proportion of 1, 2.5, and 5 wt% were prepared. The homogeneous distribution of nanofillers in the polymer matrix was obtained from the solution by the ex situ method. Exclusion size chromatography showed that the strong shear force applied during homogenization caused the largest polymer molecules to crack and thus slightly reduce the average molecular weight of the polymer matrix. Higher glass transition temperatures of composites compared to pure polymer matrices and their increase with increasing filler content, confirm the homogeneity of distribution and compatibility of nanocellulose with the investigated methacrylate matrices. The addition of nanocellulose increases the hydrophilicity of materials, which facilitates printing and may favor their use as packaging materials. [ABSTRACT FROM AUTHOR]

Nanofluids have attracted the attention of the scientific community during last twenty years and the number of papers on nanofluids has increased significantly as a result. The increased thermal conductivity of the fluid due to the addition of nanoparticles is a basic feature that has raised intensive research on nanofluids. Considering a permanent urge in the industry to improve efficiency of production processes, including the cooling streams of processes, the increased thermal conductivity of cooling fluids opens the possibility of achieving that goal. This paper provides an overview of nanofluid preparation methods and a description of parameters that affect the thermal conductivity of nanofluids. Also, the overviews of few models that describe the thermal conductivity of nanofluids as well as of possible mechanisms that contribute to the increase in thermal conductivity of nanofluids are given. [ABSTRACT FROM AUTHOR]

Copyright of Kemija u Industriji is the property of Croatian Society of Chemical Engineers and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper describes the results obtained in the study of the photobehaviour of heteroanalogs of stilbene bearing oxazole and pyridine rings at the opposite sides of the ethene moiety. The effect of the positional isomerism of the n -pyridyl group ( n = 2, 3 and 4) on the competitive relaxation processes of the excited states (fluorescence, isomerization and cyclization) was investigated and compared with the behaviour previously reported for the 5-styryloxazole analogue. The group in Zagreb prepared the compounds and followed their photochemistry in preparative conditions while the group in Perugia studied the spectral properties of the trans/cis isomers and the cyclization products and measured the quantum yields of the competitive processes in mild conditions with the main aim to clarify the mechanism of the primary stages after excitation. The photobehaviour revealed an important deactivation effect of the n,π* states introduced by the nitrogen atom. This effect reflects the one reported for styrylpyridines, the analogous compounds with a phenyl instead of an oxazolyl ring. Quantum-mechanical Hyperchem calculations proved to be useful to describe the conformational equilibria and the role of conformers on photoreactivity while more refined DFT calculations on the Z isomers allowed the structure dependent competition between their isomerization/cyclization processes and the possible role of intramolecular H-bonds on the deactivation pathways to be explained. For the compound with n = 4, side processes of hydrogen shift in the primary dihydrophenanthrene-like intermediate and of solvent addition accompanying the photocyclization process were evidenced. [ABSTRACT FROM AUTHOR]

MoS 2 monolayer samples were synthesized on a SiO 2 /Si wafer and transferred to Ir(111) for nano-scale characterization. The samples were extensively characterized during every step of the transfer process, and MoS 2 on the final substrate was examined down to the atomic level by scanning tunneling microscopy (STM). The procedures conducted yielded high-quality monolayer MoS 2 of milimeter-scale size with an average defect density of 2 × 10 13 cm -2 . The lift-off from the growth substrate was followed by a release of the tensile strain, visible in a widening of the optical band gap measured by photoluminescence. Subsequent transfer to the Ir(111) surface led to a strong drop of this optical signal but without further shifts of characteristic peaks. The electronic band gap was measured by scanning tunneling spectroscopy (STS), revealing n-doping and lateral nano-scale variations. The combined use of STM imaging and density functional theory (DFT) calculations allows us to identify the most recurring point-like defects as S vacancies.

Alkyl chains of different length were added onto surface of multiwall carbon nanotubes (MWCNT). Oxidized multiwall carbon nanotubes (MWCNT-COOH) were reacted with thionyl chloride (SOCl2) and further in esterification reaction with given alcohols gave corresponding methyl ester (MWCNT- COOCH3), n-butyl ester (MWCNT-COOC4H9) and n-dodecyl ester (MWCNT-COOC12H25) modified carbon nanotubes. Functionalization of MWCNTs was confirmed by FTIR, Raman and X-ray photoelectron spectroscopy as well as by thermogravimetric analysis. n-Butyl ester and n-dodecyl ester modified carbon nanotubes showed contact angle for water of about 142 and 150 degrees, while the oxidized and methyl ester modified carbon nanotubes showed seepage. Dispersibility of oxidized and alkyl ester modified carbon nanotubes in methanol and toluene was quantified by UV-Vis spectroscopy and differs significantly in both solvents for all systems.

A new synthetic approach is presented for the synthesis of naphthoxazoles and fused heterobenzoxazoles. The starting 5-(aryl/furyl/thienyl/pyridyl ethenyl)oxazoles are prepared from the corresponding α,β-unsaturated aldehydes using Van Leusen reagent in very good yields and are transformed into naphthoxazoles and fused heterobenzoxazoles on irradiation under aerobic conditions and in the presence of iodine.