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The pyrolysis of wastes from the production of cereals (rice husks, wheat and barley straw, spelt husk and straw, corn cobs, hulls and stalks) and protein and oil-protein crops (chickling vetch, lentil, chickpea and soybean straw and pods, sunflower stalks and husks) is investigated for the conditions of thermal analysis and packed-bed conversion. The differences in the thermogravimetric curves (heating rate 5 K/min) can be summarized by about 40–50 K for the peak temperature and 50–60 K for the temperature range where devolatilization occurs and by factors of about 2 and 1.6 for the peak rate and the char yield. They reduce when the comparison is limited to the same part of the plants, such as pods/husks and straws. Hot water washing emphasizes the qualitative similarity in the shape of the rate curves, which becomes the same as for hardwoods, and quantitatively reduces the differences in the peak rate. The different chemical properties of the feedstock also affect the magnitude of the reaction-induced overheating in the packed bed and consequently the yields of products though pyrolytic runaway never occurs. [ABSTRACT FROM AUTHOR]

The pyrolytic conversion of industrial hemp ( Cannabis sativa ), subjected to various pretreatments, and its parts (woody core and fibers) has been investigated. For the conditions of thermal analysis, dominated by primary decomposition, the qualitative features of hemp and woody core devolatilization are practically coincident with those of wheat straw and beech wood, respectively. Retting and decortication significantly affect the magnitude and position of the peak rate and the char yield. Fiber decomposition, though reflecting the qualitative behavior of the majoritarian component cellulose, is deeply affected by hemicellulose/lignin/ash contamination. Packed-bed pyrolysis reproduces the qualitative similarities between hemp and wheat straw, on one side, and woody core and beech wood, on the other, mainly in relation to the thermal field (magnitude of reaction-induced overheating) with differences in the yields/composition of the lumped classes of products. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM AUTHOR]

The gaseous and liquid products of the fixed-bed pyrolysis of agricultural residues (hazelnut shells, olive pomace, straw pellets) and wood (beech wood and softwood pellets) are chemically characterized and compared. The heating temperature is varied in the range 473-800 K but the process occurs in the presence of large thermal overshoots. These reach their maxima for heating temperatures below (residues, overshoots up to about 225 K) or above (wood, overshoots up to about 85 K) approximately 650 K. Though mainly originated from secondary decomposition, overheating also highly enhances the primary decomposition rates, globally leading to short volatile residence times. As a consequence, the product distribution is modified. In particular, at low heating temperatures, also following pyrolytic runaway, the residues produce the largest amounts of volatiles and the yields of several condensable organic compounds (acetic acid, propionic acid, formic acid, hydroxypropanone, levoglucosan, guiacols and syringols) reach their maxima, with even qualitative deviations from the usual trends observed in pyrolysis. [ABSTRACT FROM AUTHOR]

The influence of the loaded zinc chloride content (0-11 wt %, dry sample basis) on the pyrolysis of beechwood particles packed in a bench-scale bed was studied. Given an external heating temperature of 655 K, the temporal profiles of the thermal field showed maximum values progressively increasing from 683 to 790 K as the catalyst content was increased from 0 to about 5 wt %. Based on cumulative char and water yields increasing from about 51 to 70 wt % and yields of condensable organics decreasing from about 35 to 15 wt %, the enhancement in the global exothermicity of the conversion process can be attributed to the successive predominance of dehydration with cross-linking reactions over depolymerization reactions. The exothermic effects were found to be qualitatively similar to but quantitatively lower than those associated with a sulfuric acid treatment. For higher acid contents and both additives, the noncatalytic effects associated with their loading were also found to contribute significantly to the characteristics of the thermal field. Specifically, for zinc chloride, the successively higher effective thermal conductivities of the bed caused a progressive reduction in the spatial gradients and maximum temperatures. [ABSTRACT FROM AUTHOR]

Thepyrolysis of particles of glucomannan, the main component ofsoftwood hemicelluloses, is investigated in a fluidized-bed reactor.A first set of experiments is carried out for temperatures in therange 530–690 K to determine yields and composition of products.The most abundant are char, water, and carbon dioxide. The condensableorganic fraction mainly consists of acetic acid, formic acid, hydroxypropanone,hydroxyacetaldehyde, and furfuryl alcohol. The second set of experimentsis made to determine the weight loss characteristics of small samplesexposed in the expanded bed at temperatures of 503–593 K thatare then used to develop one- or two-stage pyrolysis mechanisms. [ABSTRACT FROM AUTHOR]

A detailed two-dimensional mathematical model is studied for the unsteady heat-and mass-transfer equations coupled with a quasi-steady formulation of the electromagnetic field for the microwave-induced pyrolysis of a wood block. The aspects examined include the description of the flow field based on either the assumption of constant pressure and one-dimensional flow velocity directed along the wood fibers or the linked two-dimensional variation of pressure and velocity in accordance with the Darcy law and deviations from the assumptions of local thermal equilibrium between the solid and gas/vapor phase. © 2011 American Institute of Chemical Engineers AIChE J, 52: 610-624, 2012 [ABSTRACT FROM AUTHOR]

Abstract: A comprehensive mathematical model is applied to simulate the effects of the input power and tar cracking on the pyrolysis of wood blocks for both microwave-induced and conventional heating. Despite of the highly different process dynamics for the two cases, the yields of the primary product classes (char, tar, gas) are comparable. Instead, while in the case of conventional heating the presence of secondary reactions leads to very low yields of the condensable products, these are always produced in high quantities in the other heating modality (50–56% for the typical kinetics of wood tar cracking). Also, the conversion times increase by a factor of about three (input power between 1500 and 500W) and up to factors of 6–7 (input power 250W) (versus factors of 3–16 for conventional heating). [Copyright &y& Elsevier]