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Thermogravimetric curves are measured, at heating rates of 5, 10 and 20 K/min under a nitrogen flow, of industrial hemp and shives, a by-product of bast fiber production, after water retting and mechanical decortication of the plant stalk. To understand the influences of the pretreatments, measurements are also made for water-retted and water-washed hemp, and shives obtained from manual decortication. Beech wood is used for comparison. It is found that a five-component degradation scheme (in number of two, one and two, for the pseudo- hemicellulose, cellulose and lignin, in the order) provides an excellent description in all cases. The kinetic parameters are affected more by pretreatments (retting and decortication) than chemical composition (hemp stalks or shives). Moreover, in addition to the quantitative similarities between shives and beech wood, the differences between hemp and shives can be taken into account by slightly higher activation energies of the latter for the second and third component (177 and 195 kJ/mol versus 160 and 177 kJ/mol), thus describing its higher thermal stability. The performances of a standard three-component scheme are also evaluated.

Kinetic models of beech wood decomposition, based on the three main pseudo-components, hemicellulose (one or two steps), cellulose (one step) and lignin (one or two steps), are applied for the first time to predict differential thermogravimetric (DTG) and differential scanning calorimeter (DSC) curves available from the literature. For the conditions that minimize the activity of secondary reactions, it is found that while the DTG curves are already well predicted by the extensively used three-step model, at least an additional step is required for the pseudo-lignin decomposition for a good prediction of the DSC data. The pseudo-cellulose decomposition is a globally endothermic process with the corresponding heat varying from about 601–528 J/g (of volatile evolved), as the number of reaction steps is increased from three to five. Pseudo-hemicellulose decomposition also takes place endothermally with reaction heats of 245 J/g (one step) or 321 and 226 J/g (two steps). Instead pseudo-lignin decomposition occurs with remarkable exothermicity corresponding to −923 J/g (one step) or −728 and −635 J/g (two steps).

Thermogravimetric data on the devolatilization rate of beech wood are re-examined with the aim of incorporating the effects of high heating rates (up to 108 K min −1 ) in the global kinetics. The mechanism consisting of three independent parallel reactions, first-order in the amount of volatiles released from pseudo-components with chief contributions from hemicellulose, cellulose and lignin, is considered first. It is found that the set of activation energies estimated by Gronli et al. [M.G. Gronli, G. Varhegyi, C. Di Blasi, Ind. Eng. Chem. Res. 41 (2002) 4201–4208] (100, 236 and 46 kJ mol −1 , respectively) for one slow heating rate results in very high deviations between predicted and measured rate curves. The agreement is significantly improved by a new set of data consisting of activation energies of 147, 193 and 181 kJ mol −1 , respectively. In this case, the overlap is reduced between the reaction rates of the three pseudo-components whose chemical composition is also modified. In particular, instead of a slow decomposition rate over a broad range of temperatures, the activity of the third reaction is mainly explicated along the high-temperature (tail) region of the weight loss curves. The performances of more simplified mechanisms are also evaluated. One-step mechanisms, using literature values for the kinetic constants, produce large errors on either the conversion time (activation energy of 103 kJ mol −1 ) or the maximum devolatilization rate (activation energy of 149 kJ mol −1 ). On the other hand, these parameters are well predicted by two parallel reactions, with activation energies of 147 and 149 kJ mol −1 .

Product distribution from straw and washed straw pyrolysis shows the usual temperature (660–990 K) dependence, but the pretreatment makes the initial degradation temperature slightly higher and gives rise to larger yields of condensable products (mainly at the expenses of char). Water washing also affects decomposition of straw in air. Devolatilization again takes place at higher temperatures and with a higher peak rate, but char combustion reactivities are always lower. Hot water washing of large (0.5–1 mm) straw char particles is less effective for ash removal than straw washing, independently of the temperature and the atmosphere where chars were formed. In particular, for low temperature (520 K) and air, the ash removed decreases as successively higher conversion levels are examined.