The conversion of n-heptanes into aromatic hydrocarbons benzene, toluene and xylenes (BTX), by the chromatographic pulse method in the temperature range of 673 - 823K was performed over the HZSM-5 and Ag-HZSM-5 zeolites modified by ion exchange with AgNO3 aqueous solutions. The catalysts, HZSM-5 (SiO2/Al2O3 = 33.9), and Ag-HZSM-5 (Ag1-HZSM-5 wt. % Ag1.02, Ag2-HZSM-5 wt. % Ag 1.62; and Ag3-HZSM-5 wt. % Ag 2.05 having different acid strength distribution exhibit a conversion and a yield of aromatics depending on temperature and metal content. The yield of aromatic hydrocarbons BTX appreciably increased by incorporating silver cations Ag+ into HZSM-5.
The conversion of light hydrocarbons resulted as by-product of petroleum refining (mixtures of (n + i) butanes, 52.28 � 63.20 vol.%, (1-, cis-, trans-, 2-) butenes, 28.64 � 36.43 vol.% and propane � propylene, 4.79 � 14.64 vol.%) over bifunctional 5% ZnO/HZSM-5 co-catalyst in a fixed-bed stainless-steel reactor (Twin Reactor System Naky) at 450�C, 4 atm. total pressure and at a space velocity (WHSV) of 1 h-1 have been investigated. The results indicate that the selectivity to light aromatics � benzene, toluene and xylenes (BTX) � and to both the gaseous C1, C2 - C4 hydrocarbons and liquid (i + n) C5 � C10 aliphatic hydrocarbons depends on the time on stream of the process. This is a result of coke deposition (polyunsaturated compounds) and catalyst deactivation. The aromatics BTX represent 59-60 wt% in the liquid product during the first 24-36 hours time-on-stream and only 20-30 wt% after 40 hours of reaction when the aliphatic hydrocarbon C5 � C10 (mostly iso) and ]C10 (denoted �oligo�) reach to 70 � 80 wt%. The aromatic products were principally toluene, xylenes and benzene, theirs concentration varying with the time on stream of the process. The initial aromatization process described as dehydrocyclodimerization of alkanes and alkenes, principally to aromatics BTX and molecular hydrogen is accompanied by an oligomerization, isomerisation, cracking and alkylation process to form finally in the liquid product an excessively mixture of iso- and normal- C5 � C10 aliphatic hydrocarbons and ] C10.
The conversion of n-heptanes by the chromatographic pulse method in the temperature range of 673 - 823K on the MFI zeolites modified by ion exchange with Ni(NO3)2 aqueous solutions was studied. The catalysts, HZSM-5 (SiO2/Al2O3 = 33.9), and Ni-HZSM-5 (wt. % Ni, 0.57, 1.09, 1.34,) having different acid strength distribution exhibit a conversion and a yield of aromatics depending on temperature and metal content. The highest selectivity for n-heptanes aromatization was obtained on the catalyst Ni3-HZSM-5 (wt. % Ni 1.34) at 823K. The metal actions and the acidic properties of zeolites have an important effect on the aromatization of n-heptanes.
Three synthons: methylene, nitrene and carbon monoxide form aziridinone in the presence of molecular nitrogen at low temperatures. This one, in contact with the same three synthons could form the precursors of the first proteinogenic amino acids. This paper is a theoretical, thermodynamically and reactivity study concerning the formation of the three previously named amino acids at low temperature conditions. The key intermediates are identified in the formation of the three amino acids: aziridinone, aziridinonil and methyl-aziridinonil radicals. The quantitative results, enthalpies of formation, reaction enthalpies and free energies were taken from quantum mechanical calculations acquired by density functional method (DFT): B88-LYP.
The synthesis of 1,3‐[bis‐N‐6A‐deoxy‐β‐cyclodextrin‐6A‐yl‐aminocabonyl]‐7‐pyridin‐4‐yl indolizine is reported. The reaction proceeds by an amidation between 6‐amino‐β‐cyclodextrin and 1,3‐[bis‐(‐4‐nitrophenoxycarbonyl)‐7‐[pyridine‐4‐yl)] and yields the first sensor having in its structure the fluorescent indolizine and two β‐cyclodextrin fragments. The sensing ability towards phenol, p‐cresol and adamantan‐1‐ol has been evaluated by fluorescence spectroscopy. The molecular modelling study realised by MM3 and AM1 methods shows that non cooperative conformations are favoured, thus explaining that inclusion ability is not increased by such dimer, and that sensitivity is not enhanced as compared to corresponding monomeric sensors.
Paraffin�s and olefins in the cracked naphtha can be transformed into aromatics and iso-paraffins to reduce the olefins content as well to improve the octane number of the gasoline commercial fraction. In this work Ni-HZSM-5 bifunctional catalyst was prepared by ion exchange with Ni(NO3)2 aqueous solution. The activity of Ni-HZSM-5 (wt.% 1.34% Ni) catalyst prepared by ion exchange method was investigated in the conversion of light hydrocarbons resulted as by-products of petroleum refining process (mixtures of butenes and (normal + iso) butanes as main components). The obtained Ni-based catalyst has been compare with HZSM-catalyst. The conversion experiments have been performed in a fixed-bed stainless-steel reactor (Twin Reactor System Naky) at 450oC, under 4 atm. (over Ni-HZSM-5) and 8 atm. pressure (over HZSM-5), respectively and at a space velocity (WHSV) of 1h-1. The catalytic activity of (Ni-HZSM-5 catalyst) monitored over 10 catalytic tests (with regeneration of catalyst after each test) using a mixtures butanes-butylenes. The catalytic activity and selectivity towards liquid products - BTX aromatic hydrocarbons and oligo(iC5-iC10, nC5-nC10, ] C10) - depends on time streaming, composition of butanes-butylenes mixture and pressure. In the first hours of each test the aromatic BTX are the main component of the liquid product (connected with butylenes consume) and after that, the oligo fraction become predominant. The initial aromatization process described as dehydrocyclodimerization of alkanes and alkenes, principally to aromatics BTX and molecular hydrogen, is accompanied by oligomerization, isomerization, cracking and alkylation processes to form finally in the liquid phase product an excessively mixture of iso- and normal - C5 -C10 and ] C10 aliphatic hydrocarbons.
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