Upgrading of Bio-Oil in a Continuous Process with Dolomite Catalyst Beatriz Valle,* ,† Borja Aramburu, † Claudia Santiviago, ‡ Javier Bilbao, † and Ana G. Gayubo † † Department of Chemical Engineering, University of the Basque Country, P.O. Box 644, 48080, Bilbao, Spain ‡ Industrial Applications Department, National University of Asuncion, Asuncion, Paraguay ABSTRACT: Catalytic upgrading was applied to the liquid product obtained from biomass fast pyrolysis (raw bio-oil) in a continuous reaction system by using dolomite as a low-cost catalyst. The upgrading reactor operates at atmospheric pressure without external H 2 supply and consists of a thermal treatment section, where pyrolytic lignin is deposited, and a catalytic upgrading section, where the thermally treated oil is valorized in-line. The reaction products, i.e., solid (pyrolytic lignin), gases, and upgraded oil, are collected separately after each reaction. The effect that temperature (400-700 °C) and time on stream (up to 4 h) have on the yield and composition of the products obtained was analyzed for a space-time of 2.4 g dolomite h/g feed . The dolomite effectively reduced the O/C ratio and removed the carboxylic acids and sugars (mainly levoglucosan) contained in the bio-oil. A gaseous product interesting as a fuel and as raw material for syngas production was obtained below 600 °C, provided that dolomite is not saturated (efficient CO 2 capture). Thus, for reaction times of ≈2 h the concentration values in the 400-500 °C range are H 2 (5-12%), CO (48-38%), CO 2 (2.2-3.2%), and CH 4 (23-31%). A good deoxygenation level (≈70%) was achieved after 0.5 h reaction at 600 °C, yielding oil with the O/C ratio ≈ 0.25 and composed of acetone (22%), phenol (51%), and alkyl-substituted phenols (22%). Upgraded oil with low O/C ratio (≈0.21) and high contents of phenol (86.4%) and alkyl- phenols (5.3%) was obtained after 4 h of reaction at 700 °C. This oil has a promising potential for use in phenolic resins formulation and diesel fuel blending. 1. INTRODUCTION The world energy consumption is continuously growing, and the global supply of fossil fuels is not likely to meet the future demand set by the developing countries, so that alternative and efficient energy sources are needed to mitigate this shortage. Biomass has attracted increasing interest as a renewable energy source, and its use as an alternative fuel resource represents one of the best means of reducing the dependence on petroleum energy. 1,2 The fast pyrolysis for producing bio-oil from lignocellulosic biomass is an economically advantageous process because it requires short reaction times and moderate reaction temperatures, 3,4 and the technology is already mature. 5-8 The raw bio-oil is a dark brown viscous liquid with a high content of water (15-30 wt %) and oxygen (30-40 wt %), low heating value, low volatility, thermal instability, and strong corrosiveness. It is a complex mixture containing several oxygenated chemical functionalities (e.g., carbonyl groups, acids, alcohols, aldehydes, esters, ketones, sugars, mono- phenols) and phenolic oligomers derived from biomass lignin. 9,10 The low pH of bio-oil (≈2.5) is due to the carboxylic acids content (mainly formic and acetic). The presence of phenolic oligomers causes the bio-oil tendency to polymerize over time, and the aldol reactions promoted by the acids also accelerate its aging. 11 These drawbacks make the raw bio-oil unsuitable for direct use as a fuel and problematic for long-term storage. Consequently, deoxygenation of raw bio-oil is necessary prior to its use as an engine fuel, since higher H/C ratio (low O/C) and very low acids content are required. Furthermore, for coprocessing the raw bio-oil in conventional refining units, the concentration of coke precursors (phenolic compounds) should be reduced. 12-14 Bio-oil conversion to products has been approached by three main routes: 9 (1) catalytic cracking, (2) hydrodeoxygenation (HDO), and (3) thermal aging. Applying zeolite based catalysts at 500-550 °C improves the bio-oil quality 13-17 and produces value-added compounds (e.g., olefins 18-20 and aromatics 21,22 ). This process can also be performed by in situ cracking of volatile compounds in the pyrolysis reactor (catalytic pyrolysis), 23,24 which results in partially deoxygenated bio-oils with higher aromatic and phenolic compounds. 25-27 HDO catalyzes bio-oil with supported metal catalysts at high pressures (>70 bar) and temperatures (≥350 °C), with H 2 consumption (490-710 L/L bio‑oil ). 28 Oxygen is removed as water, CO 2 and CO through dehydration, decarboxylation, and decarbonylation reactions, and a highly deoxygenated product (as low as 0.2 wt % of total oxygen 29 ) can be obtained. Thermal aging causes a 20-50 wt % decrease in phenols content (phenolic ethers to a greater extent) and a 50-65 wt % decrease in high molecular weight compounds. Consequently, the Conradson Carbon Residue index (CCR) diminishes from 4.8 wt % to about 1.5 wt %, and the effective hydrogen index increases by 30%. 12 This treatment has been used as a prior step to a subsequent in-line catalytic step for obtaining hydrocarbons (olefins 15,18 and aromatics 16,21 ) and hydro- gen. 30-32 In these papers, the phenolic compounds (derived from the lignin contained in biomass) were separated, as pyrolytic lignin, in the thermal aging step. A wide variety of catalysts has been tested for the HDO process, e.g., sulfide/oxide catalysts (Co-MoS 2 , Ni-MoS 2 ) and transition metals (Ru, Pt, and Pd) supported on Al 2 O 3 and Received: July 16, 2014 Revised: September 2, 2014 Published: September 3, 2014 Article pubs.acs.org/EF © 2014 American Chemical Society 6419 dx.doi.org/10.1021/ef501600f | Energy Fuels 2014, 28, 6419-6428