Operating conditions to maximize clean liquid fuels yield by oligomerization of 1-butene on HZSM-5 zeolite catalysts Marta Díaz , Eva Epelde * , Zuria Tabernilla , Ainara Ateka , Andr  es T. Aguayo , Javier Bilbao Department of Chemical Engineering, University of the Basque Country (UPV/EHU), P. O. Box 644, 48080, Bilbao, Spain article info Article history: Received 11 April 2020 Received in revised form 4 June 2020 Accepted 4 July 2020 Available online 9 July 2020 Keywords: Oligomerization 1-butene HZSM-5 zeolite Liquid fuels Catalyst stability abstract The effect of operating conditions has been extensively studied for the selective oligomerization of 1- butene to clean synthetic liquid fuels. HZSM-5 zeolite (SiO 2 /Al 2 O 3 ratio ¼ 30e280) based catalysts provided with a hierarchical porous structure have been tested in a fixed bed reactor under the following conditions: 175e325  C; 1.5e40 bar; space time, 0.5e6g catalyst $h mol C 1 . Special attention has been paid to individual and lumped gaseous and liquid product distribution (which have been characterized by gas chromatography, GC  GC/MS and simulated distillation), as well as to catalyst stability, by performing long duration experiments (20 h). An optimum region to maximize both naphtha (C 5-11 , >40%), and diesel (C 12-20 , >20%) yields has been established at 250e275  C and 30 bar for space time values of 2e4g catalyst h mol C 1 . Furthermore, the catalysts have tended to a pseudo-stationary deactivation state after 5 h on stream, where the coke deposited on the spent catalysts is mainly composed of adsorbed bulky oligo- mers (determined by TPD-N 2 ), with low coke contents ~1.0e1.5 wt% (determined by TPO). © 2020 Elsevier Ltd. All rights reserved. 1. Introduction The availability of transportation fuels is facing several chal- lenges related to crude oil depletion, rise in price, demand fluctu- ations, and more restrictive legislations on greenhouse gas emissions [1 ,2]. The oligomerization of lower olefins (ethylene, propylene and butenes), especially those obtained from sources alternative to oil, is becoming an attractive route to produce envi- ronmentally friendly synthetic fuels (gasoline, jet fuel and diesel) [3e7]. The hydrocarbons produced by oligomerization (after a hy- drogenation step) are almost exclusively composed of a mixture of alkanes and isoalkanes, free of heteroatoms, aromatics and sulphur, with low concentration of naphthenes [8,9]. Light olefin oligomerization also gives an opportunity to valorize low-value refinery streams, such as naphthas coming from FCC units, or Fischer-Tropsch tail gas, among others [8, 10e13]. In addition, in some geographical areas a surplus of ethylene is ex- pected, as steam crackers will boost the use of shale gas ethane as feedstock [14]; and also of butenes, since MTBE octane booster has been banned [15]. Particularly, the oligomerization of butenes is gaining special attention, as these butenes can be produced from biomass derived syngas [16], from decarboxylation of g-valer- olactone [9, 17], from fermentation [18, 19] and/or from fast pyrolysis (bio-oil) of biomass [20e22], contributing to a sustainable pro- duction of bio-fuels [22,23]. Furthermore, this fluctuating olefin demand/supply makes oligomerization an interesting alternative over other valorization routes, such as isobutane/butene alkylation [24,25] or olefin interconversion (in order to intensify propylene production) [26]. Various catalysts including solid phosphoric acid (SPA), metal- organic framework, zeolites (HZSM-5, H-Beta, H-Ferrierite, HeY, etc.), aluminum-silicates, amorphous silica-alumina (ASA), meso- structured aluminosilicates (Al-MTS, Al-MCM-41, Al-SBA-15, BEA, TUD-1, etc.), activated carbons, ion-exchange resins (Amberlyst, Purolite, Nafion, etc.) and ionic liquids have been studied in the literature for olefin oligomerization [17 ,27e29]. Among them, ze- olites are the most promising ones to replace the commercial SPA catalyst, due to their lower environmental impact, ease of regen- eration, and product versatility (gasoline, jet fuel and diesel) by adjusting the oligomerization conditions [27 ,30,31]. Particularly, HZSM-5 yields in products with lower branching degree (methyl mono-branched olefinic chains) [8,32], compared with larger pore zeolites [10,33]. The product distribution towards hydrocarbons in the gasoline (C 5 eC 11 ) and diesel (C 12 eC 20 ) range is driven by the * Corresponding author. Department of Chemical Engineering, P.O. BOX 644, 48080, Bilbao, Spain. E-mail address: eva.epelde@ehu.eus (E. Epelde). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy https://doi.org/10.1016/j.energy.2020.118317 0360-5442/© 2020 Elsevier Ltd. All rights reserved. Energy 207 (2020) 118317