Analysis of the Catalytic Effects Induced by Alkali and Alkaline Earth Metals (AAEMs) on the Pyrolysis of Beech Wood and Corncob

The catalytic pyrolysis of beech wood and corncob was experimentally investigated considering six additives containing alkali and alkaline earth metals (Na2CO3, NaOH, NaCl, KCl, CaCl2 and MgCl2). Thermogravimetric analyses (TGA) were carried out with raw feedstocks and samples impregnated with different concentrations of catalysts. In a bid to better interpret observed trends, measured data were analyzed using an integral kinetic modeling approach considering 14 different reaction models. As highlights, this work showed that cations (Na+, K+, Ca2+, and Mg2+) as well as anions (i.e., CO32−, OH−, and Cl−) influence pyrolysis in selective ways. Alkaline earth metals were proven to be more effective than alkali metals in fostering biomass decomposition, as evidenced by decreases in the characteristic pyrolysis temperatures and activation energies. Furthermore, the results obtained showed that the higher the basicity of the catalyst, the higher its efficiency as well. Increasing the quantities of calcium- and magnesium-based additives finally led to an enhancement of the decomposition process at low temperatures, although a saturation phenomenon was seen for high catalyst concentrations

Thermogravimetric Analysis and Kinetic Modeling of the AAEM-Catalyzed Pyrolysis of Woody Biomass

This work analyzes the catalytic effects induced by alkali and alkaline earth metals (AAEMs) on pyrolysis kinetics. To this end, thermogravimetric analyses (TGA) were carried out with raw beech wood and samples impregnated with NaCl, KCl and MgCl2 at four heating rates (5, 10, 15 and 30 °C/min). Obtained results showed that AAEM compounds promote the decomposition of biomass by reducing the initial and peak pyrolysis temperatures. More specifically, the catalytic effect of the alkaline earth metal was shown to be stronger than that of alkali metals. To further interpret the obtained trends, a kinetic modeling of measured data was realized using two isoconversional methods (the Ozawa–Flynn–Wall (OFW) and Kissinger–Akahira–Sunose (KAS) models). With a view to identifying a suitable reaction model, model fitting and master plot methods were considered to be coupled with the isoconversional modeling approaches. The 3-D diffusion reaction model has been identified as being well suited to properly simulate the evolution of the conversion degree of each sample as a function of the temperature. Furthermore, the kinetic parameters derived from the present modeling work highlighted significant decreases of the activation energies when impregnating wood with AAEM chlorides, thus corroborating the existence of catalytic effects shifting the decomposition process to lower temperatures. A survey of the speculated pathways allowing to account for the impact of AAEMs on the thermal degradation of woody biomass is eventually proposed to better interpret the trends identified in this work

Analysis of the Catalytic Effects Induced by Alkali and Alkaline Earth Metals (AAEMs) on the Pyrolysis of Beech Wood and Corncob

The catalytic pyrolysis of beech wood and corncob was experimentally investigated considering six additives containing alkali and alkaline earth metals (Na2CO3, NaOH, NaCl, KCl, CaCl2 and MgCl2). Thermogravimetric analyses (TGA) were carried out with raw feedstocks and samples impregnated with different concentrations of catalysts. In a bid to better interpret observed trends, measured data were analyzed using an integral kinetic modeling approach considering 14 different reaction models. As highlights, this work showed that cations (Na+, K+, Ca2+, and Mg2+) as well as anions (i.e., CO32−, OH−, and Cl−) influence pyrolysis in selective ways. Alkaline earth metals were proven to be more effective than alkali metals in fostering biomass decomposition, as evidenced by decreases in the characteristic pyrolysis temperatures and activation energies. Furthermore, the results obtained showed that the higher the basicity of the catalyst, the higher its efficiency as well. Increasing the quantities of calcium- and magnesium-based additives finally led to an enhancement of the decomposition process at low temperatures, although a saturation phenomenon was seen for high catalyst concentrations

A new and original microwave continuous reactor under high pressure for future chemistry

International audienceA new and original high pressure reactor has been designed and developed for continuous flow chemistry under micro-waves at industrial scale. The reactor originality is that the microwave applicator is the reactor itself. It allows then theuse of metallic and thick walls for the reactor adapted to a use at high pressures and high temperatures. Wave propaga-tion coupled to heat transfer was simulated using COMSOL MultiphysicsVRand the design was optimized to minimizewave reflections and maximize energy transfers in the reacting medium. This leads to extremely good energy yields.Experiments confirm that the microwave energy is fully absorbed by the reacting medium. The reactor allows continuouschemical reactions at a kg/h scale, under microwave heating, up to 7 MPa and 2008C. The double dehydration of hexy-lene glycol has been performed under various operating conditions demonstrating then the operability of this new reac-tor.V

Kinetic analysis of reduction of 4-Nitrophenol by (water soluble) PalladiumNanoparticles Studied by a Langmuir-Hinshelwood mechanism. Does we compareapples and oranges ?

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The prediction multi-phase, multi reactant equilibria by minimizing the Gibbs energy of the system : Review of available techniques and proposal of a new method based on a Monte Carlo technique

International audienceSince already a few decades, researchers developed tools to predict chemical reactions in the context of the chemical industry. Numerical tools are now available to predict final chemical equilibriums using the principle of minimizing the Gibbs free energy of the reactions. In this paper, after recalling some basis on thermochemical equilibria, a brief review of the most renown techniques available to find the minimum of the Gibbs energy is presented. From this, limitations are discussed. Mathematically, the equations are always strongly non-linear, and the standard step by step resolution techniques may fail to find the global minimum. When non-mixed phases are present (solids, for instance), the calculations often fail. An example is given with biphenyl-CO2 mixtures. Especially when many phases are postulated. An alternative resolution method is proposed based on a Monte Carlo method which does not require nor a linearization of the Gibbs equation neither a step by step resolution. The method can solve any multi-phase and any multi-reactant equilibrium but is much more computer resource demanding than the traditional methods. It was implemented in a home-made code (CIRCE) briefly described in Appendix A

Improving the Predictability of Chemical Equilibrium Software

Over the past few decades, researchers have been developing tools to predict chemical reactions to aid the growing field of industrial chemistry. Currently, a large variety of numerical tools are used to predict the final chemical equilibrium based on the minimization of the Gibbs free energy. Because of the mathematical complexity of the problem, numerical methods were developed to solve this problem. These methods were reviewed in another study (submitted for publication in Comput. Chem. Eng., Predicting multi-phase chemical equilibria using a Monte Carlo technique, 2018) exhibiting their limitations and proposing an alternative. In this study, the sensitivity of the prediction as a function of the thermochemical (input) parameters is discussed showing that significant deviations are possible when the relative uncertainty between the enthalpies of formation is larger than a few kJ/mol. Often the scatter between various data sources is much larger than this. To solve this difficulty, it was attempted to derive all the required thermodynamical parameters from a base of molecular descriptors common to the chemistry targeted in this work (organic). The group contribution theory is implemented and in particular the UNIFAC descriptors and is shown to give very satisfactory results

Applied numerical chemistry in process engineering R&D

Numerical modeling can be a great help in research and development activities to guide technical choice and/or to better interpret the experimental data. Significant developments are underway about the numerical simulation of complex chemical reaction as those investigated in laboratories. The resources of quantum chemistry are often used. About the industrial process in which chemical reaction occurs, numerical resources are available to describe flows, heat transfer and mechanical aspects. In between, there is a need to be able to foresee the evolution of the chemical reaction (yield, heat releases,...) as function of the process conditions (temperature, pressure,...). Since the reality of the reaction may be rather complex including not only the reaction with multiple components but phase changes, the modeling may prove difficult. Softwares were developed for this but for limited ranges of applications. In combustion processes for instance, NASA developed in the seventies the code CEA which was reproduced elsewhere. The basic principle is to minimize the Gibbs free energy of a given chemical reaction for which a series of potential final products is prescribed. The equation is completed by the usual conservation laws (mass in any case and depending on the reaction the energy and or pressure/temperature). In practice the method is particularly appealing and known to provide a number of very valuable and practical results. Unfortunately, the Gibbs free equation is "stiff" and to solve the mathematical problem drastic assumption are made to "linearise" the Gibbs free energy equation. This results in very strong limitations among which the quais impossibility to account for multiphase chemical equilibriums. In CIRCE, a software developed by the Technological University of Compiegne we tried to solve this problem replacing the traditional method by a Monte-Carlo technique. In this paper, this method is presented and typical results are given including distillations of multi-components mixtures and pyrogasifications

Sensitivity of the predictability of chemical equilibrium software to the choice of the products

Over the past few decades, researchers have been developing tools to predict chemical reactions to aid the growing field of industrial chemistry. Currently, a large variety of numerical tools are used to predict the final chemical equilibrium based on the minimization of the Gibbs free energy. Due to the mathematical complexity of this problem, numerical methods were developed to solve this problem. These methods were reviewed in another study (CIRCE, A New Software to Predict the Steady State Equilibrium of Chemical Reactions. Comput. Chem. Eng 2018, submitted for publication) exhibiting their limitations and proposing an alternative. In this study, the sensitivity of the prediction to the choice of the most likely products is investigated. In this work, the impact of an improper choice of the final product is investigated showing a first order influence when a product is missing. A method is devised to generate automatically an exhaustive list of final products. Another method is proposed to select in this list those products likely to appear depending on the temperature of the reaction. The method is illustrated on the example of the pyrolysis of ethanol