Biomass decomposition in near critical water

doi:10.1016/j.enconman.2009.11.009

Energy Conversion and Management

Volume 51, Issue 3, March 2010, Pages 612-620

https://doi.org/10.1016/j.enconman.2009.11.009 Get rights and content

Abstract

Conversion of baby food (taken as model biomass for protein and carbohydrate containing biomass) to the valuable chemicals in near critical water (648 K and 24 MPa) in an autoclave is presented in this work. K₂CO₃, Nickel on silica and Zeolith (HZSM-5) are selected as catalysts. A detailed characterization of the aqueous phases is performed by High Pressure Liquid Chromatography, UV–Vis Spectroscopy, Total Organic Carbon Analyser. Solid particles recovered by the experiments are also subjected to Scanning Electron Microscopy analysis. This study determines the effect of reaction conditions on the reactivity of the major biomass component. Acetic, formic and glycolic acid, aldehydes (acetaldehyde, formaldehyde), phenol and phenol derivatives, furfural, methyl furfural, hydroxymethyl furfural are the intermediates found in the aqueous phase. Baby food contains mostly carbohydrates, proteins, a variety of salts and minerals, etc. Thus, the results show the effect of these ingredients on the hydrothermal conversion of biomass. It is found that the formation and degradation pathways of the intermediates are influenced by the biomass structure.

Introduction

Degradation of biomass in sub- and supercritical water cannot be easily described by the well-defined single reaction steps due to the complex formation and degradation pathways of the products. Effect of various ingredients of biomass, e.g. cellulose, lignin, hemicellulose proteins, fats, different kinds of carbohydrates, minerals on the complexity of the product types should also be considered. Conversion of biomass model compounds under these conditions is a useful method since it gives some hints about the chemistry of the biomass conversion in these media by the help of the key compounds. Supercritical water treatment is one of the progressive technologies for biomass conversion [1], [2], [3]. Water in supercritical conditions has lower dielectric constant than water. According to this difference, supercritical water can dissolve and destructive variety of organic compounds [4], [5]. Water under these conditions is not only reaction media, but also reactant. Thus, water as a reactant leads to hydrolysis reactions, leading the rapid degradation of complex biomass structure such as hydrolysis of cellulose to sugars.

An important reason why the hydrothermal conversion of biomass in sub- and supercritical water is developed is that the major part of the up to now unused biomass is wet biomass with water content often of 80% or more. For the dry processes, this biomass has to be dried, for the hydrothermal gasification not, which saves drying cost.

At incomplete gasification or liquefaction, in the aqueous phase, phenols, furfurals, organic acids, aldehydes, etc. are found. Determining of these products enables us to compare results of a model compound reaction with that of real biomass in order to better understand the nature of biomass conversion in supercritical water.

Baby food includes proteins, fats, and different kinds of carbohydrates and can be taken as model biomass of very reproducible composition. Baby food has a composition similar to potential feedstocks like residues from the food industry, and it is a very fine and homogenous sludge to be handled in lab-scale plants. Degradation of baby food under supercritical water conditions leads to formation of sugars, acids, aldehydes, furfurals, phenols [6], [7].

In this study, degradation of the baby food in a batch reactor (Parr – Model no: 4571) at 648 K and at 24 MPa is performed. The experiments are also conducted in the presence of K₂CO₃, Nickel on silica and HZSM-5 at 648 K. Carbon balance for the aqueous phase is calculated via total organic carbon content of the aqueous phase. The structure of the solid particles found in the vessel at the end of the experiments is also analysed by the SEM analysis.

Section snippets

Experimental

In the experiments, baby food (ÜLKER Bebelac – TÜRKİYE) in powder form taken as the representative of protein and carbohydrate containing materials is the feedstock. 0.5% (w/w) K₂CO₃ (MERCK), 0.5% (w/w) HZSM-5 (ACROS ORGANICS CAS: 1318-02-1) and 0.5% (w/w) Nickel on silica catalyst (ACROS ORGANICS – 70 wt.% 30–40 M2 Ni surface/G) are used in the experiments.

Table 1 shows the physical properties of the catalysts. Zeolites are a class of micro porous materials that have a well-defined

Results and discussion

Fig. 3 shows thermal behaviour of baby food. It is clear from the figure that weight loss of baby food occurred mainly between 473 K and 673 K. Water releases from the structure at first accordingly. Then degradation of constituents found in the baby food such as carbohydrates, proteins, fatty acids, vitamins occurred at the temperatures between 523 K and 623 K. This is the reason why the experimental temperature in this work is 648 K. Baby food contains minerals, proteins, fats and different kinds

Conclusions

A simplified reaction scheme for the conclusions of this work is given in Fig. 12.

This study is suggested that the near and sub-critical water application could become a useful method to transform baby food to the valuable chemicals effectively. We observed that baby food decomposition in near critical water enhanced in the presence of catalysts. The catalysts especially Ni on SiO₂ play an important role for degradation or formation of intermediates. The reduced amounts of phenols for baby food

Acknowledgements

We thank TUBITAK (The Scientific and Technological Research Council of Turkey) for providing financial support for this work through the Project “106M412”. Our special thanks are to Dr. Andrea Kruse and Sonja Habicht (Forsungszentrum Karlsruhe—ITC—CPV) for the analysis of the aqueous phase. The SEM analysis is done by Wilhelm Habicht, who is gratefully acknowledged.

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Biomass decomposition in near critical water

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

Acknowledgements

Energy Convers Manage

Energy Convers Manage

Energy Convers Manage

Biomass Bioenergy

Carbohydr Res

Carbohydr Res

Carbohydr Res

Carbohydr Res

Int J Hydrogen Energy

Mater Lett