Rev. Chim. ♦ 71 ♦ no. 2 ♦ 2020 ♦ http://revistadechimie.ro 403 https://doi.org/10.37358/RC.20.2.7943 Oligo-Aromatization of Light Hydrocarbons from Petroleum Refining Processes Over ZnO/MFI Microporous Material IULIEAN V. ASAFTEI 1 , ION SANDU 2 *, NICOLAE BILBA 1 *, NECULAI CATALIN LUNGU 1 , MARIA IGNAT 1 *, ELVIRA MAHU 1 1 Al. I. Cuza University, Faculty of Chemistry, 11 Carol I Blvd, 700506, Iasi, Romania 2 Al. I. Cuza University, ARHEOINVEST Interdisciplinary Platform, 22 Carol I Blvd, 700506 Iasi, Romania 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. Keywords: light hydrocarbons, aromatization, ZnO/HZSM-5, solid-state ion exchange Light alkanes C2 – C5 are contained in non-associated natural gas (as compressed natural gas) and in associated gas (as petroleum casing-head gas). A considerable amount of C2 – C4 hydrocarbons (alkanes and alkenes) result from petroleum refining processes, especially from destructive technological processes such as catalytic cracking (FCC). The consumption of light gaseous hydrocarbons as feed materials in petrochemical and other syntheses does not exceed 30% of the overall quantity produced [1]. The most important way to get chemicals with great importance is the direct conversion of lower hydrocarbons (less expensive and abundant) into hydrogen-deficient hydrocarbons (aromatics or alkenes) by catalytic aromatization and oligomerization [2]. The selective transformation of light hydrocarbons C2 – C4 (alkanes and alkenes) into more valuable aromatic – rich liquid hydrocarbons by direct catalytic route is an area of great industrial relevance and also of academic interest for the production of benzene, toluene and xylenes (BTX). The main reason for the production of aromatics is the application of aromatics as high octane blending components for gasoline (utilization that will grow less and less due to antipollution legislation and because of carcinogenic nature of benzene, especially) [3], as an excellent solvent and a base chemical in a number of petrochemical (as feedstock for rubbers and fibres) and chemical (as commodity chemicals) processes. The aromatic hydrocarbons are produced from coal by coking (under pyrolitic conditions) and from crude oil by catalytic reforming or hydroforming of heavy naphtha (reformates up to 60 – 70 vol. %), by naphtha pyrolisis (5 – 60 vol. % BTX) and by catalytic cracking FCC of naphtha gasoline (with about 25 - 35 vol. % BTX) [4-6]. The yield of BTX from catalytic processes controlled by thermodynamics (B: T: X = 32: 36: 32, respectively) does not match the marked demand (55: 11: 43) [7]. However, it is well-known that the alkanes have a low reactivity evidenced by theirs standard Gibbs free energy of formation (ΔGf 0 , 298K) and the energy (strength) of its C-H bonds. The bond energy of C-C bond in alkanes is lower than of C-H bond, so the C-C bond cleavage is more facile compared to C-H bond cleavage. On increasing of the carbon number of the alkanes, ΔGf 0 (kJ mol -1 ) becomes less negative (for n-heptane is yet positive) and the C-H bond energy decreases indicating decreasing stability (440, 423, 413 and 404 kJ mol -1 for methane, ethane, propane and n-butane) [8, 9]. The corresponding alkenes are much more reactive and easy to activate (i.e. ΔGf 0 , 298K for propylene is +63 kJ mol -1 and -23.5 kJ mol -1 for propane). The overall alkane’s aromatization reaction is endothermic as large amounts of molecular hydrogen must be removed. If the feedstock is a mixture of small alkanes and alkenes in a well-defined proportion it is possible that the reaction system to be almost isothermal. *email: sandu_i03@yahoo.com; n.bilba@yahoo.com; maria.ignat@uaic.ro