Pressurised pyrolysis of Miscanthus using a fixed bed reactor F. Melligan a , R. Auccaise b , E.H. Novotny b , J.J. Leahy a , M.H.B. Hayes a , W. Kwapinski a,⇑ a Department of Chemical and Environmental Sciences, Carbolea Group, University of Limerick, Limerick, Ireland b Embrapa Solos, Rua Jardim Botânico 1024, Brazil article info Article history: Received 1 August 2010 Received in revised form 23 October 2010 Accepted 27 October 2010 Available online 3 November 2010 Keywords: Pyrolysis Pyrolytic-oil Bio-oil Char Miscanthus abstract Miscanthus x giganteus was pyrolysed, in a fixed bed reactor in a constant flow of dinitrogen gas, at a rate of 13 °C/min from ambient to 550 °C, then held for 25 min at this temperature. The pressures employed ranged from atmospheric to 26 bar. The major compounds identified in the bio-oil were water, phenol, and phenol derivatives. The water contents impact on the usefulness of the bio-oil as a fuel. However, the phenols could provide useful platform chemicals and products. The properties of the char were determined using elemental analyses, surface area measurements using the Brunauer–Emmett–Teller equation, a calorimetric bomb, Scanning Electron Microscopy, and solid state 13 C NMR spectroscopy. The chars were highly carbonised, especially at the higher pressures, and provided thermally stable materials. Pressure impacted greatly on the surface area. Char formed at atmospheric pressure had a surface area of 162 m 2 /g, whereas that from the highest pressure applied was only 0.137 m 2 /g. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Much interest has focused in recent years on the utilisations of biomass as alternative sources of fuel largely because biomass can be regarded as a carbon neutral source of energy (Muradov and Veziroglu, 2008). It also contains very low levels of nitrogen and sulphur. Pyrolysis, in which biomass feedstock is heated to between 350 and 600 °C or higher in the absence of oxygen (typically in an N 2 atmosphere) provides a facile procedure for the conversion of bio- mass into pyrolytic-oil (bio-oil), a char (biochar), and gas (syn-gas). This technique can utilise abundant lignocellulosic feedstocks, which include biomass crops (such as Miscanthus and coppiced willows), agricultural residues, biorefinery wastes, etc. Typically pyrolysis is divided into three modes: fast, intermediate, and slow (Bridgwater, 2006). The mode and conditions used can influence the relative proportions of the three products obtained. Slow pyro- lysis uses a low heating rate and a long vapour residence time, and it is used to maximise char yields (Kwapinski et al., 2010). Fast pyrolysis, with a very high heating rate and a short vapour resi- dence time, maximises liquid yields. Although pyrolysis of biomass has achieved commercial status, there still are many aspects of the process that require further study. Some studies have looked investigated the ways that different process conditions influence the products of biomass pyrolysis and also the various methods used to identify the products formed (Briens et al., 2008, Cao et al., 2010, Stolarek and Ledakowicz, 2005; Wongsiriamnuay and Tippayawong, 2010). Heo et al. (2010) con- sidered Miscanthus as a feedstock taking account of varying parameters such as temperature, particle size, feed rate and gas flow rate. They concluded that temperature was the only factor that had a dramatic influence on product yields. The influence of pressure on the products of the pyrolysis of biomass has been largely overlooked. A study of the pressurised pyrolysis of wheat straw by Mahinpey et al. (2009) has indicated that reactor pressure has a significant influence on both the yields and the quality of the products obtained. However, that work looked at a narrow range of reaction pressures, 0.689 (10 psi) to 2.758 bar (40 psi). It was concluded that 1.379 bar (20 psi) is the optimum pressure with respect to the product yields for the pyro- lysis of wheat straw in a tubular reactor. Fjellerup et al. (1996) worked with pulverized wheat straw in a pressurised entrained flow reactor at pressures of 10 and 20 bar and temperatures of 700–1000 °C. They concluded that the final product yield under the two pressures was very similar. The focus on char in the study of Whitty et al. (2008a) suggested that pressurised pyrolysis of kraft liquors resulted in a reduction of the char particle size as the pressure was increased. However, the opposite was observed by Mahinpey et al. (2009) for a wheat straw feedstock. There are data to indicate large differences in the yields and properties of the products from the pyrolysis of different feed- stocks. This statement is based on a study by Özçimen and Ersoy-Meriçboyu (2010). That study looked at several different feedstocks, such as apricot stones, hazelnut shells, chestnut and grape seeds. The results showed that pyrolysis of these materials under the same conditions gave products that were significantly different. The major differences were in the surface areas of the 0960-8524/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2010.10.129 ⇑ Corresponding author. Tel.: +353 61202641. E-mail address: witold.kwapinski@ul.ie (W. Kwapinski). Bioresource Technology 102 (2011) 3466–3470 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech