Oligo-Aromatization of Light Hydrocarbons from Petroleum Refining Processes Over ZnO/MFI Microporous Material

Abstract

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.

Transformation of Gaseous Technical Mixture of the Alkanes and Alkenes Into Liquid Fraction Over Ni-HZSM-5 Obtained by Ionic Exchange

“…The concentration of butenes (1-C 4 = , trans-2-C 4 = their production is connected to aromatic hydrocarbons formation. The molecular hydrogen was not detected in the gaseous phase [25].…”

“…Low temperature peak correspond to less acidic sites (terminal OH groups, cationic sites M z+ , AlO + ). The temperature and the amount of desorbed ammonia give information about strength and number of the acid sites [42,3,55,58,62,[83][84][85][86].…”

“…The operating conditions (temperature 450 o C, WHSV 1 h -1 and pressure 8 atm.) were in advance selected to obtain the high yield of liquid product during the catalytic tests [25].…”

“…HZSM-5 sample was involved in five catalytic tests, after each test; the catalyst being regenerated at 475 o C for 8h under nitrogen with 2% oxygen flow [25].…”

“…-Transformation of alkanes into alkenes; -Interconversion of alkenes into higher alkenes; -Aromatization of alkenes. Outstanding aromatization performance have been observed over the HZSM-5 zeolite with the incorporation of some metal species such Pt [8][9][10][11][12][13], Ga [1,2,12,[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30], Zn [2,3,5,[7][8][9][10][11][12][13][14][15][16][17]. Ni-HZSM-5 and Ag-HZSM-5 are also active in aromatization process of light hydrocarbons [20,56,[63][64][65][66][67].…”