Published: July 28, 2011 r2011 American Chemical Society 3950 dx.doi.org/10.1021/ef200712h | Energy Fuels 2011, 25, 3950–3960 ARTICLE pubs.acs.org/EF Effect of Vacuum on Lignocellulosic Biomass Flash Pyrolysis in a Conical Spouted Bed Reactor Maider Amutio, Gartzen Lopez, Roberto Aguado, Maite Artetxe, Javier Bilbao, and Martin Olazar* Department of Chemical Engineering, University of the Basque Country, Post Office Box 644, E48080 Bilbao, Spain ABSTRACT: The continuous flash pyrolysis of lignocellulosic biomass under atmospheric and vacuum conditions (0.25 atm) has been studied in a bench-scale plant provided with a conical spouted bed reactor. A previous kinetic study has been carried out in thermobalance, and the kinetic data have been fitted to a three parallel and independent reaction model by deconvolution of the differential thermogravimetry (DTG) curve. The influence of vacuum on product yields, compositions, and properties has been carried in a bench-scale plant at 400 and 500 °C. Vacuum operation in a conical spouted bed is advantageous for biomass pyrolysis because of the reduction in the N 2 mass flow rate required for the spouted bed regime. Consequently, the energy requirements for heating N 2 and the problems related to the condensation of the outlet stream are significantly reduced. The yields obtained and the composition of the bio-oil provide evidence that the vacuum operation does not affect the good gassolid contact and the excellent performance of the conical spouted bed reactor for lignocellulosic biomass flash pyrolysis. High bio-oil yields are obtained, 77% at 500 °C and under 0.25 atm. Vacuum leads to a slightly heavier and less oxygenated bio-oil and a char fraction with improved surface characteristics. 1. INTRODUCTION There is an urgent need to find alternative raw materials to fossil fuels because of falling oil reserves and a rising demand for energy, automotive fuels, raw materials for the current petro- chemical industry, and H 2 . Accordingly, lignocellulosic biomass is the only renewable source of fixed carbon that can be converted into liquid, solid, and gaseous fuels, apart from heat and power, with no contribution to the net emission of CO 2 . Pyrolysis is one of the technologies with the best industrial perspectives for this valorization, because the process conditions can be optimized to maximize the yields of gases, liquids, or chars. 1,2 The production of a liquid fraction or bio-oil by means of lignocellulosic biomass flash pyrolysis has received growing interest because of the perspectives of bio-oil as a feed for refinery units (biorefinery). 3 Thus, it is possible to decouple bio-oil production in rural areas and on a moderate scale from its upgrading in either refinery units to obtain transportation fuels and valuable chemicals or large power plants to convert it into heat and power. 46 The refinery units attracting more attention for bio-oil co-feeding are fluidized catalytic cracking (FCC) units 79 and the methanol to olefin (MTO) process. 10 Flash pyrolysis maximizes the bio-oil yield and is carried out at moderate temperatures (around 500 °C) with short vapor resi- dence times (typically below 1 s) and high heating rates, 10 3 10 4 °Cs 1 . These characteristics maximize the bio-oil yield, given that secondary cracking reactions are minimized. 11,12 Furthermore, char must be rapidly withdrawn from the reaction environment, because hot char is catalytically active for cracking organic vapors. 13 The flash pyrolysis of biomass produces bio-oil yields typically in the 6080 wt % range, a gas yield of 1020 wt %, and a char yield in the 1525 wt % range. 1113 Gas is mainly composed of CO 2 and CO; therefore, its heating value is relatively low, but it can be used to supply energy to the pyrolysis plant. Char can be used as fuel, owing to its high heating value, can be subjected to activation processes to obtain active carbon for purification processes, and can also be used as a support for metallic or acid catalysts. 1419 In addition, biomass pyrolysis char has the potential for soil amendment because of long-term carbon sequestration in the soil. 20 A wide range of reactor configurations has been used to perform biomass flash pyrolysis, such as fluidized-bed reactors, 2123 transport and circulating fluidized-bed reactors, 24,25 ablative reactors (rotating and cyclonic), 26 auger reactors, 27 and vacuum reactors. 28 The conical spouted bed reactor (CSBR), which is an alternative to fluidized beds, is of proven suitability for biomass flash pyrolysis. 29,30 Particle cyclic movement allows for the handling of particles of irregular texture, fine particles, sticky solids, and those with a wide size distribution, with no segrega- tion and agglomeration problems. 31,32 Furthermore, the great versatility concerning the gas flow rate allows for operation with short gas residence times (as low as milliseconds) in the dilute spouted bed regime. 33 The vigorous particle cyclic movement and the high inert gas flow rate contribute to a high heating rate and high heat- and mass-transfer rates between phases. 34 Calo- naci et al. 35 have confirmed that the bio-oil yield obtained in the CSBR is close to the maximum obtainable yield predicted by their macrokinetic model. In addition, the CSBR is appropriate for continuous operation, which is especially relevant for the implementation of large-scale biomass flash pyrolysis with the additional advantage of a simple design. Biomass flash pyrolysis under vacuum improves the opera- tional capacity of this technology by enhancing certain require- ments: (i) it decreases the mass flow rate of inert gas, and consequently, less energy is required to heat the inert gas to the Received: May 13, 2011 Revised: July 27, 2011