Inﬂuence of Secondary Reactions on the Heat of Pyrolysis of Biomass Claudia Gomez, † Enric Velo, † Federica Barontini, ‡ and Valerio Cozzani* ,§ Centre d’Enginyeria de Processos i Medi Ambient (CEPIMA), UniVersitat Polite `cnica de Catalunya, AVenida Diagonal 647, 08028 Barcelona, Spain, Dipartimento di Ingegneria Chimica, Chimica Industriale e Scienza dei Materiali, UniVersita ` degli Studi di Pisa, Via DiotisalVi 2, 56126 Pisa, Italy, and Dipartimento di Ingegneria Chimica, Mineraria e delle Tecnologie Ambientali, Alma Mater Studiorum - UniVersita ` di Bologna, Via Terracini 28, 40131 Bologna, Italy The thermal behaviors during the pyrolysis of two different biomass samples, beech wood from carpentry residuals and artichoke thistle from energy-dedicated crops, were investigated. Thermogravimetry/differential scanning calorimetry (TG-DSC) and thermogravimetry coupled to Fourier transform infrared (TG-FTIR) analysis of evolving products were used to investigate the thermal effects of the pyrolysis process. The role of pretreatments (hot-water washing, ethanol extraction, and their combination) was also analyzed. High alterations in the heat demand were observed as a function of the initial sample mass and pyrolysis conditions. The role of vapor-solid secondary interactions was evidenced by the evolution proﬁles of the main pyrolysis products. 1. Introduction The need for sustainable energy sources is growing as the availability of fossil energy sources is diminishing. In the past few years, there has been a renewed interest in biomass as a potential supplier of useful energy and chemicals, with a reduced environmental impact compared to fossil fuels. 1-12 Pyrolysis and other thermochemical conversion processes represent an important option for energy recovery from biomass and waste. The upsurge of interest in the simulation and optimization of reactors for thermochemical processes requires appropriate models that integrate different operating conditions and different feedstocks, helping to achieve a better understanding of the reactions in the corresponding processes. 13-31 The heat of reaction has a signiﬁcant inﬂuence on thermal conversion routes, and understanding the effect of the reaction heat is important in the modeling of thermochemical processes. However, the thermal effects of pyrolysis reactions have been found to vary widely, ranging from exothermic to endothermic under different operating conditions. 32,33 Secondary reactions between volatiles and char, as well as autocatalytic effects due to impurities, are usually assumed to be the reasons for the wide variation of values reported in the literature for the heat requirements of the pyrolysis process. In fact, in several reactors proposed for slow pyrolysis and gasiﬁcation on an industrial scale, a relevant contact time is present among volatiles generated in the primary pyrolysis process and the primary char. 2,34,35 Under slow pyrolysis conditions, small particles of cellulose and wood show a global endothermic behavior, whereas samples with larger particle sizes exhibit exothermic behaviors. 36 This difference was explained in terms of the enhanced interaction of hot pyrolysis vapors with the decomposing solid, which involves an exothermic reaction that leads to the formation of char. Mok et al. 37 observed a linear relationship between reaction exothermicity and char yield. The yield of charcoal is also known to be favored by the presence of some mineral elements in biomass ash. 32 Inorganic ions are known to exert a great inﬂuence on the thermal degradation of the natural polymers (polysaccharides and lignin) that make up biomass materials. 38 The extractive content of samples is a further factor affecting the thermal and kinetic behavior of the pyrolysis process. 15,16,39,40 However, to the knowledge of the authors, no data have been reported in the literature concerning the impact of sample pretreatments on the thermal effects of the pyrolysis process. In previous studies, the pyrolysis of biomass feedstocks that represent a waste disposal problem and/or that have substantial energy and chemical potential was investigated. 41,42 In particular, previous investigations focused on the thermal behavior of woody samples coming from the carpentry industry and on raw material from energy crops (artichoke thistle) in Spain. The kinetic description of the primary decomposition process of these samples was provided, assuming a low heat demand coming from the thermal effects due to pyrolysis reactions. In the present study, the actual heat demand during the pyrolysis of these materials was investigated by differential scanning calorimetry (DSC). In the experimental runs, untreated, water-washed, and ethanol-extracted samples were used, as well as samples subjected to both water washing and ethanol extraction. Experimental runs involving thermogravimetry com- bined with DSC (TG-DSC) were also carried out, inﬂuencing the contact time available for vapor-solid secondary interac- tions. The proﬁles of volatile compounds formed during TG pyrolysis experimental runs, obtained by online FTIR analysis, were also analyzed, in an effort to better understand the effect of vapor-solid interactions on the composition of the evolved products. 2. Experimental Section 2.1. Materials. Artichoke thistle (Cynara cardunculus) from a specialized crop in the Spanish province of Soria was used as a reference material, representing a herbaceous biomass that is currently used for energy production in some European regions. The samples were milled to a ﬁne powder. A washing treatment was applied to obtain samples having a lower content of mineral matter. 41 Table 1 reports the ultimate and proximate analyses of untreated and washed samples. * To whom correspondence should be addressed. Tel.: (+39)-051- 2090240. Fax: (+39)-051-2090247. E-mail: valerio.cozzani@unibo.it. † Universitat Polite `cnica de Catalunya. ‡ Universita ` degli Studi di Pisa. § Alma Mater Studiorum - Universita ` di Bologna. Ind. Eng. Chem. Res. 2009, 48, 10222–10233 10222 10.1021/ie9007985 CCC: $40.75  2009 American Chemical Society Published on Web 10/26/2009