Kinetic Analysis of Digestate Slow Pyrolysis with the Application of the Master-Plots Method and Independent Parallel Reactions Scheme.

Pietro Bartocci,Roman Tschentscher,Ruth Elisabeth Stensrød,Francesco Fantozzi,Marco Barbanera

doi:10.3390/molecules24091657

Pietro Bartocci, Roman Tschentscher + Show 3 more

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https://doi.org/10.3390/molecules24091657

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Abstract

The solid fraction obtained by mechanical separation of digestate from anaerobic digestion plants is an attractive feedstock for the pyrolysis process. Especially in the case of digestate obtained from biogas plants fed with energy crops, this can be considered a lignin rich residue. The aim of this study is to investigate the pyrolytic kinetic characteristics of solid digestate. The Starink model-free method has been used for the kinetic analysis of the pyrolysis process. The average Activation Energy value is about 204.1 kJ/mol, with a standard deviation of 25 kJ/mol, which corresponds to the 12% of the average value. The activation energy decreased along with the conversion degree. The variation range of the activation energy is about 99 kJ/mol, this means that the average value cannot be used to statistically represent the whole reaction. The Master-plots method was used for the determination of the kinetic model, obtaining that n-order was the most probable one. On the other hand, the process cannot be modeled with a single-step reaction. For this reason it has been used an independent parallel reactions scheme to model the complete process.

Highlights

The Importance of Digestate Slow-Pyrolysis ProcessCoupling of anaerobic digestion and pyrolysis in integrated processes has become more and more interesting [1]
The thermal degradation profile of solid digestate can be divided into three stages, influenced by its chemical and physical composition in terms of hemicellulose, cellulose, and lignin
The solid fraction of biogas digestate was studied as a potential feedstock for pyrolysis, by analyzing its decomposition kinetics

Summary

Introduction

Coupling of anaerobic digestion and pyrolysis in integrated processes has become more and more interesting [1]. Anaerobic digestion is a very promising technology to be adopted for biomasses with important moisture content (at least more than 50%). The residue of the anaerobic digestion process is called digestate and contains ashes and components that cannot be decomposed efficiently by the microbia, which are present in the anaerobic digestor (mainly belonging to the following species: Clostridium, Peptococcus, Bifidobacterium, Desulfovibrio, Corynebacterium, Lactobacillus, Actinomyces, Staphylococcus, Streptococcus, Micrococcus, Bacillus, Pseudomonas, Selemonas, Veillonella, Sarcina, Desulfobacter, Desulfomonas, and Escherichia coli) [2]. Digestate can be used to produce energy through the subsequent steps of solid liquid separation and pyrolysis.

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