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.

No abstract

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.

New mesoionic 4-(2-dialkylamino-1,3-dithiol-2-ylium-4-yl)phenolates have been obtained from the corresponding 1,3-dithiolium salts under weak basic conditions. The 1,3-dithiolium salts have been synthesized by the cyclocondensation of 1-(4-hydroxyphenyl)-1-oxaethan-2-yl dithiocarbamates. The latter compounds have been obtained from the reaction of the 2-bromo-1-(4-hydroxyphenyl)ethan-1-one with various salts of dithiocarbamic acids. UV-Vis investigations proved the intramolecular charge transfer for the mesoionic 1,3-dithiolium phenolates.