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Packed-bed pyrolysis is carried out of beech wood preliminarily impregnated with potassium compounds (KOH, KCl, KC2H3O2, and K2CO3) for ion percentages corresponding to 0-1.8 wt %. The study is mainly aimed at examining the influence of the chemical state of potassium on the global thermicity of packed-bed conversion never examined before. The lowering of primary decomposition temperatures and the enhancement of secondary decomposition of tarry vapors is associated with a remarkable increase in the global exothermicity of the process which highly modifies the conversion conditions and product distribution. Maximum temperature overshoots over a large part of the bed, with respect to the programmed value of 605 K, reach 100-150 K and correspond to minima in the char yields. The quantitative effects are dependent on the content and chemical state of potassium which exerts its action via first the alkaline pretreatment and then catalysis. Moreover, thermogravimetric curves show that the diminution in the primary decomposition temperature is directly related to the K content and the basicity of the additive.

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 ...

The combustion behavior of a honeycomb material used for the core in sandwich panels, consisting of aramid fiber sheets (Nomex) dipped in a phenolic resin, is studied. Char, produced from pyrolysis of thick samples at 950 K, preserves the honeycomb structure, but the total volume is highly reduced in spite of an increase in the wall thickness. Following softening, the more internal fibers lose their shape, giving rise to a highly porous swelled char. Instead, the more external ones, trapped by the resin char, still show their original shape but with evident shrinkage. Thermogravimetric curves in air are used to formulate a combustion mechanism. It consists of three reactions for the stage of oxidative decomposition of the honeycomb material and one reaction for combustion of the resulting char. Activation energies for the various steps vary in a narrow range of high values (190-256 kJ/mol), testifying low reactivity.

Fir wood pyrolysis is carried out for extracted, KOH and KCl impregnated, and impregnated-extracted samples. For Kþ concentrations in wood of 0.14% (dry mass basis), the effects of KOH are quantitatively higher, but both additives produce a significant diminution in the yields of hydroxyacetaldehyde, furfural, and sugars, the decomposition temperature, and the conversion time. Water extraction of KCl impregnated samples is apt to reproduce again the characteristics of extracted wood pyrolysis. Instead, water extraction of KOH impregnated samples only reports the yields of hydroxyacetaldehyde, acetic acid, and hydroxypropanone to the original values whereas differences in the other variables, especially characteristic times and temperatures and levoglucosan yields, remain very large. Therefore, the action of the impregnated Kþ compounds during wood pyrolysis can be attributed to both irreversible modifications in the wood structure during impregnation, whose entity depends on the basicity of the aqueous solution, and intrinsic action of the Kþ ion on the activity of the decomposition reactions.

Packed-bed pyrolysis (heating temperature 800 K) is studied of beech and fir wood, several agro-industrial residues (corn cobs and stalks, olive husks, wheat straw, hazelnut and almond shells, orange peels, grape residues, artichoke stems, brewer's spent grain, and pruning cuts from cherry, olive, vine, and poplar trees) and cellulose, aimed at determining the potentially most promising feedstock for the production of furfural. Parameters associated with conversion dynamics are mainly affected by the packed-bed density (0.1-1.1 g/cm3) whereas products mainly depend upon the feedstock chemical composition. In particular, the yields of condensable organic products increase with the holocellulose content (10-85%) up to 25-40% (dry sample mass basis). The higher yields of furfural (dry organics mass basis), in the range 2-0.8%, are obtained from feedstocks with significant contents of cellulose/ pentoses (corn cobs, almond shells, hardwoods such as beech, cherry, olive, and poplar woods, orange peels, corn stalks, and hazelnut shells), while interesting quantities (approximately 1-0.4%) of 2(5H)-furanone are observed in all cases. As expected, the highest yields of hydroxyacetaldehyde and levoglucosan (about 8 and 3%) are produced from fir wood. On the other hand, some agro-industrial residues (hazelnut and almond shells and olive husks), apart from acetic acid, also produce high yields of phenolic compounds.

Motivated by the production of compounds of good industrial value, pyrolysis of fir wood catalyzed by alkaline compounds (NaOH, KOH, Na2CO3, K2CO3, KC2H3O2, and NaCl) has been investigated. Catalysts have been impregnated in wood (preliminarily extracted with water) by means of aqueous solutions resulting in concentrations of the K or Na ion in wood of about 0.37−0.41%. Pyrolysis experiments have been done with a fixed-bed reactor preheated at 800 K.The decomposition process is anticipated at lower temperatures with conversion times from 2.5 (NaOH) to 1.7 (NaCl) times shorter. Formation of char, carbon dioxide, and water is favored with total yields between 70 and 61% versus 48% of extracted wood (dry sample mass basis). The yields of carbon monoxide are increased approximately from 4% to 6% while the yields of organic compounds are lowered to 19−29% (versus 43%) with the disappearance of sugar compounds and a strong diminution in other typical products of uncatalyzed wood pyrolysis but hydroxypropanone. ...

Weight loss curves of wood fast pyrolysis oils in air have been measured, under controlled thermal conditions, carrying out two separate sets of experiments. The first, which has a final temperature of 600 K, concerns evaporation/cracking of the oil and secondary char formation, processes associated with sample swelling and solidification. After collection and milling, in the second set of experiments, heterogeneous combustion of the secondary char is carried out to temperatures of 873 K. Although the details of the rate curves appear to be dependent on the commercial process (BTG, Dynamotive, Ensyn, Pyrovac) applied to produce the oil, the same qualitative features are observed in all cases. Secondary char formation and sample modification begin for temperatures of about 460-490 K. Moreover, a conceptual reaction mechanism, consisting of six main zones, can always explain the low-temperature (e600 K) devolatilization characteristics. Similar to primary char produced from wood pyrolysis, secondary char exhibits weight loss curves that present a devolatilization stage and a combustion stage, but with a significantly lower reactivity, as a consequence of a physical structure completely lacking micropore networks.

The coupled effects of particle size and external heating conditions (reactor heating rate and final temperature) on cellulose pyrolysis are investigated by means of a computer model accounting for all main transport phenomena, variable thermophysical properties and primary, and secondary reaction processes. The dynamics of particle conversion are predicted, and final product distributions are favorably compared with experimental measurements. A map is constructed, in terms of particle size as a function of the reactor temperature, to identify the transition from a kinetically controlled conversion to a heat transfer controlled conversion (thermally thin and thermally thick regimes) and from flash to slow-conventional pyrolysis. Conditions for maximizing oil, gas, or char yields are also discussed.

A laboratory-scale countercurrent fixed-bed gasification plant has been designed and constructed to produce data for process modeling and to compare the gasification characteristics of several biomasses (beechwood, nutshells, olive husks, and grape residues). The composition of producer gas and spatial temperature profiles have been measured for biomass gasification at different air flow rates. The gas-heating value always attains a maximum as a function of this operating variable, associated with a decrease of the air-to-fuel ratio. Optimal gasification conditions of wood and agricultural residues give rise to comparable gas-heating values, comprised in the range 5−5.5 MJ/Nm3 with 28−30% CO, 5−7% CO2, 6−8% H2, 1−2% CH4, and small amounts of C2− hydrocarbons (apart from nitrogen). However, gasification of agricultural residues is more difficult because of bed transport, partial ash sintering, nonuniform flow distribution, and the presence of a muddy phase in the effluents, so that proper pretreatments are...

A new experimental system is presented to investigate the fast pyrolysis of solid fuels, in the absence of heat- and mass-transfer limitations. It consists of an electrically heated furnace, where a thin layer of powdered solid is exposed, on both sides, to radiative heating. A PID temperature controller is programmed for two different working conditions: the usual constant furnace temperature (A) and a constant sample temperature (B). Cellulose pyrolysis is investigated in the temperature range 523−699 K. It is shown that significant heat-transfer limitations cannot be avoided with the modality A, unless very slow heating rates, as in the classical TGA systems, are applied. In the modality B (global heating rates 19−56 K/s), the independence of the char yields from the sample thickness, for values of this below a critical value, indicates negligible spatial temperature gradients and activity of intraparticle secondary reactions of primary vapors. External heat-transfer limitations, due mainly to endothe...