Cellulose pyrolysis has been the subject of a large number of papers. However, the origin and nature of many products are still not well understood. This chapter begins by noting the difficulties connected to experimental and conceptual definitions and characterizations of slow and fast pyrolysis. The most representative results published during the long history of pyrolysis are summarized. The chapter points out the main controversies, unresolved questions and well established facts of cellulose pyrolysis. Special emphasis is placed on the primary steps of cellulose deconstruction and also on the formation and properties of intermediate species. The chapter concludes with suggestions for future research topics.

This poster gives an overview of current research developed at CNRS Nancy (France) on the thermochemical conversion of lignocellulosic biomass. The main studied processes are pyrolysis and gasification to produce electricity, biofuels intermediates or value-added chemicals such as aromatics. A multiscale approach is developed ranging from molecular to process scales. The studies at molecular and mesoscopic levels give insight into the mechanisms of biomass pyrolysis and are used to design reactors. Conversely, the detailed mass and energy balances of processes point out process units with low energy efficiency and/or high environmental impact and stress the improvement of reactors and the need of more fundamental knowledge. The methodology will be highlighted by examples at: 1. the molecular scale: advanced NMR studies are used for understanding primary pyrolysis of biomass. Tar are analysed by photo-ionisation mass spectrometry and tar cracking kinetics are studied. 2. the mesoscopic and particle scales: the mechanism of biomass pyrolysis are studied by in-situ rheology and H NMR. Heat and mass transfers inside biomass particles are studied by specific devices with an imposed heat flux density (W/m2) [1]. 3. the reactor scale: Fluidised bed or cyclone are designed and home built in the lab. Advanced reactor models are developed and handled hydrodynamic, transfers and chemical kinetics. 4. the process scale: Bioenergy chains are modelled under Aspen Plus [2] to provide advanced life cycle inventory: from forest growth to end products. [1] JAAP 103, 255-260, 2013. [2] Energy & Fuels 27 (12), 7398-7412, 2013.

The use of biomass as an alternative energy resource requires its prior processing. Many options are possible. The present paper focuses on thermochemical routes and more specifically on fast pyrolysis carried out for the preparation of so called bio-oils. The optimization and scaling up of fast pyrolysis processes for improving bio oils yields and properties come up against several difficulties. The aim of the paper is to show that some of them are related to the lack of several basic scientific knowledges, more specifically at the level of the high temperature fast pyrolysis reactor. The analysis of these challenges (biomass sample thermal decomposition, biomass-reactor interactions, secondary reactions) suggests the development of several research topics. L’utilisation de la biomasse en tant que ressource énergétique de substitution nécessite sa transformation préalable. De nombreuses options sont possibles. Cet article s’intéresse aux voies thermochimiques et plus spécifiquement à la pyrolyse rapide mise en oeuvre pour la préparation d’huiles de pyrolyse. L’optimisation et l’extrapolation des procédés de pyrolyse rapide pour améliorer les rendements et propriétés des huiles de pyrolyse se heurtent à plusieurs difficultés. Le but de cet article est de montrer que certaines sont liées au manque de certaines connaissances scientifiques de base, plus précisément au niveau du réacteur haute température. L’analyse de ces verrous (décomposition thermique d’un grain de biomasse, interactions biomasse-réacteur, réactions secondaires) suggère le développement de plusieurs axes de recherche.

The use of biomass as an alternative energy resource requires its prior processing. Many options are possible. The present paper focuses on thermochemical routes and more specifically on fast pyrolysis carried out for the preparation of so called bio-oils. The optimization and scaling up of fast pyrolysis processes for improving bio oils yields and properties come up against several difficulties. The aim of the paper is to show that some of them are related to the lack of several basic scientific knowledges, more specifically at the level of the high temperature fast pyrolysis reactor. The analysis of these challenges (biomass sample thermal decomposition, biomass-reactor interactions, secondary reactions) suggests the development of several research topics.

Fast pyrolysis of biomass is a promising process for the preparation of bio-oil dedicated to energy production. Inorganic species originally present in biomass are known to induce problems such as bio-oil instability or deposits and fouling. However the mechanisms of inorganic species release during biomass pyrolysis into the raw bio-oils still remain unclear. The present work focuses on the determination of inorganic distribution in the products from wheat straw and beech wood fast pyrolysis performed in a fluidized bed. More specifically, the bio-oils are fractionated by using a series of condensers. The results show that more than 60wt.% of the inorganic content of the overall bio-oil is contained in the aerosols. Several possible interpretations for this observation are discussed. It is likely that the inorganics are transported within the aerosols droplets and solid particles which are recovered in the bio-oils, either by mechano-chemical processes, or by entrainment of submicron intermediate liquid compound formed in the first steps of biomass fast pyrolysis.

Fast pyrolysis is a promising process for the preparation of bio-oil dedicated to energy valorization. The effects of inorganic species (K, Na, Ca, and Mg) on bio-oil stability are known, such as deposits, fouling or slagging issues. This study focuses on determination of the repartition of inorganic species in all pyrolysis products. Then we established an inorganic balance on liquid products in order to characterize the mass transfer of inorganic species from the insoluble residue to the bio-oil. Our data suggest that Na behavior is typically different from Ca, K and Mg. (Resume d'auteur)

The continuous self stirred tank reactor is a well known suitable device for studying the kinetics of high-temperature gas phase reactions. Temperature and composition are uniform at any point of the reactor, and for a given residence time, it is easy to calculate the values of kinetic constants from a very simple mathematical model. The aim of the present paper is to report the first experimental results obtained on the thermal cracking of vapours produced by the pyrolysis of biomass. The experiments are carried out between 836 and 1303K and under mean residence times ranging from 0.3 to 0.5 s. The calculated activation energy (59kJmol-1) and preexponential factor (1930s-1) are in good agreement with those obtained by other authors operating in more usual devices, but needing the solving of more sophisticated models.

The present paper shows that it is possible to carry out the thermal decomposition of solid particles followed, by the partial cracking of the evolved vapours, inside a cyclone rector heated at its walls. The results obtained with isocyanuric acid and with biomass particles are reported. From a mathematical model, it is possible to derive the kinetic constants of the gas phase cracking reactions. The results obtained with both solids are very similar. It is concluded that the thermal reaction of isocyanuric acid can be used as a model reaction for simulating the thermal cracking of the vapours formed during the fast pyrolysis of biomass.

Ablation characterizes the phenomena occurring when a solid, submitted to a high external heat flux density, gives rise to solids, liquids and/or gases that can be rapidly and continuously eliminated. Ablation can be exploited for carrying out the fast pyrolysis of materials such as biomass. This paper describes and compares, on a fundamental point of view, two methods of biomass ablative pyrolysis. In the first one, biomass is pressed against a hot surface (contact ablative pyrolysis). In the second one, biomass intercepts a concentrated radiation (radiant ablative pyrolysis). The comparison is made on the basis of the values of ablation thickness and velocity (derived from experiments and modelling), and of product fractions and compositions. The results can be very different in spite of the fact that biomass may be subjected to similar heat flux densities in both cases. The paper shows the advantages, drawbacks and complementarities of each technology.

The image furnace technology has been applied to the study of the first steps of biomass flash pyrolysis. The experiments performed with small pellets of cellulose show that the reaction primarily passes through the intermediate of short lifetime liquid species (ILC). The quantitative study of the variations of the sample mass loss and of the mass of ILC reveals the existence of a transient period followed by a steady-state regime resulting from an equilibrium between cellulose decomposition into ILC and ILC vaporization. A mathematical model has been solved in parallel. The results agree very well with the experimental measurements and yield additional information on the temperatures of cellulose pyrolysis and of ILC vaporization.

This chapter contains section titled: Introduction Experimental, Methods Nature and Conditions of Formation of the Products Overall Interpretations Application of These Results to the Comparison of Pyrolysis Reactors on the Basis of Heat Transfer Mechanisms Conclusions Notation References

The present paper reports first experimental results showing that it is possible to produce zinc from the thermal reduction of zinc oxide in the presence of cellulose. The experiments are performed in a solar simulator where small pellets of ZnO+cellulose mixtures are submitted to a brief controlled concentrated radiation. The reaction is very fast and occurs at temperatures that are more than 1000 K lower than those corresponding to the direct ZnO splitting. Several possible reaction mechanisms are discussed and it is concluded that the ZnO reduction seems to involve interactions with the liquid species formed during cellulose thermal depolymerization. Side experiments performed in less severe conditions with an electric furnace confirm the low temperatures of reaction. In order to errand the results to the more practical case of biomass, it is suggested to continue similar experiments with other components such as lignin.

It is possible to use concentrated solar energy for producing zinc by direct high temperature dissociation of ZnO. The purpose of the present paper is to show that the overall efficiency of such a process as well as the quality of the products may be controlled by several chemical and physical factors such as heat and mass transfer efficiencies, hydrodynamics and reactor design. The results of three complementary experimental approaches are reported. They are interpreted in connection with simplified models in order to describe the controlling processes occurring in the high temperature and quench sections of the reactor. One of the conclusions is that zinc can be recovered by condensation on the cold walls of a heat exchanger and/or under the form of small dispersed particles. Finally, it is shown that the reactor design must be optimized inside the perspective of a given future use of zinc.

This paper reports the experimental results of the fast pyroysis of wood sawdust performed in two different cyclone reactors. The mass balances are close to 100% and the char fractions always smaller than 3%. The flexibility of the cyclone reactor is such that, according to the operating conditions, it can be used either for the fast gasification or for the fast liquefaction of biomass. Side experiments reveal that a fraction of the gaseous products can be used as the carrier gas (recycling process) without noticeable changes of the gas composition and with fast gasification yields close to 100%. It is shown that the vapor-phase cracking reactions mainly occur inside a very thin and hot boundary layer close to the heated surface of the cyclone. The results of the modeling of these phenomena are used to derive kinetic constants that prove to be in very good agreement with those of the literature. The conclusion is that the cyclone appears as a very efficient multifunctional reactor making it possible to perform in less than a second heating and pyrolysis of the reactants as well as the quenching and separation of the products.

It is possible to dissociate samples of zinc oxide at high temperature by using a concentrated radiation as a best source. However, the reoxidation radiation between the products is very fast and it is hence necessary to cool down very rapidly (quench) the gases. The present paper describes two experimental methods of analysis owned at measuring the quench efficiency (i.e. the fraction of zinc recovered). The accuracy of both methods is first presented. Then, preliminary results obtained in an image furnace are given. It is concluded that it is necessary to optimize the quench reactor in order to enhance to efficiency of zinc production.

This paper reports some results of experiments made to determine optical properties of the components of biomass, mainly cellulose. Indeed, cellulose is a highly reflecting and weakly absorbing (semi transparent) material and in some experiments, a concentrated radiation is used (from solar furnaces for instance). The reflectivity is determined with a commercial reflectometer. About 85% of the incident flux is reflected by a pure cellulose pressed pellet. The subduing factor is determined with a specific experimental apparatus using optical fibers. For cellulose, about 80% of the flux which is not reflected by the surface of the pellet is absorbed after 10(-3) m. This subduing factor can be well represented by an exponential law.