Acid-Catalyzed Reactions in Carbon Dioxide-Enriched High-Temperature Liquid Water

Hunter, Shawn E.; Savage, Phillip E.

doi:10.1021/ie020565z

Cited by 85 publications

(74 citation statements)

References 18 publications

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“…Table 1 shows that the amount of Pd on the Pd particles and weakens π back-donation from Pd to adsorbate species, which prevents the phenol from adsorption and reaction. The rapid catalyst deactivation observed in the presence of both CO 2 and water may be ascribed to the acidic nature of the aqueous phase [29][30][31]. This causes the leaching of Pd in a larger amount and a more significant structural change in the surface of Pd particles.…”

Section: Catalyst Characterizationmentioning

confidence: 99%

Multiphase reaction media including dense phase carbon dioxide and/or water: A case study for hydrogenation of phenol with a Pd/Al2O3 catalyst

Yoshida

Narisawa

Fujita

et al. 2013

Journal of Molecular Catalysis A: Chemical

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Multiphase reaction media including dense phase CO 2 and/or water were applied for a test reaction of hydrogenation of phenol with a Pd/Al 2 O 3 catalyst. The features of these reaction media were clarified and the actions of dense phase CO 2 and water were discussed. Different characterization methods (XPS, in situ high pressure FTIR, ICP) were used to study (i) the surface of supported Pd particles that varied during the reaction, (ii) the competitive adsorption of phenol, water, and CO that was formed from H 2 and CO 2 under pressurized conditions, and (iii) the leaching of active Pd species. Dense phase CO 2 caused the deactivation of catalyst and it 2 occurred more rapidly in the presence of both dense phase CO 2 and water. In the system including water alone, the catalyst deactivation also happened but gradually. At the latter stage of reaction in this system, phenol was not consumed but cyclohexanone did transform to cyclohexanol. Those results may be explained by the leaching of Pd species and a structural change of supported Pd particles, resulting in a change in their adsorption behavior. The Pd leaching is more significant in acidic aqueous phase dissolving CO 2 at high pressure.

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Section: Catalyst Characterizationmentioning

confidence: 99%

Multiphase reaction media including dense phase carbon dioxide and/or water: A case study for hydrogenation of phenol with a Pd/Al2O3 catalyst

Yoshida

Narisawa

Fujita

et al. 2013

Journal of Molecular Catalysis A: Chemical

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“…Recently, Hunter and Savage reported, for the first time, the acceleration of simple acid-catalyzed organic reactions in high-temperature liquid water by adding carbon dioxide; carbonic acid generated in situ from water and carbon dioxide lowers the pH of the solution (20). The addition of carbon dioxide as an environmentally benign acid catalyst also should be effective for polysaccharide hydrolyses under hydrothermal conditions.…”

Section: Introductionmentioning

confidence: 99%

Polysaccharide Hydrolysis Accelerated by Adding Carbon Dioxide under Hydrothermal Conditions

Miyazawa

Funazukuri

2005

Biotechnology Progress

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Polysaccharides such as agar, guar gum, starch, and xylan were hydrolyzed to produce mono- and oligosaccharides under hydrothermal conditions with and without carbon dioxide in a small batch reactor. The molecular weight distributions of the polysaccharide hydrolyzates shifted to lower molecular weights by increasing the carbon dioxide load, corresponding to higher pressures of carbon dioxide. For example, the yield of glucose produced from the hydrolysis of starch at 200 degrees C was increased significantly from 3.7% to 53.0% (on a carbon weight basis) of the initial polysaccharide by increasing carbon dioxide load in a reaction time of 15 min. Carbonic acid generated from water and carbon dioxide appeared to lower the pH of high-temperature and high-pressure water. Polysaccharide hydrolysis under hydrothermal conditions in the presence of carbon dioxide is an environmentally benign method to produce mono- and oligosaccharides because the process does not require the use of conventional acids and bases followed by neutralization and separation.

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“…[75][76][77][78][79][80][81][82] Notably, the formation of carbonic acid can enhance the rate of acid-catalyzed reactions, which include hydrolysis and dehydration, without the drawback of neutralization and/or solvent recovery. 75,76,[82][83][84][85][86] The use of CO 2 -H 2 O mixtures during biomass pre-treatment has also been shown to reduce the crystallinity of the cellulose-rich fraction allowing a reduction in enzyme loading of 33% during subsequent saccharification. 86 Relvas et al modelled the kinetics of the hemicellulose, xylan and arabinan hydrolysis in the presence of CO 2 added during hydrothermal processes and demonstrated that the formation of carbonic acid led to an increase in the kinetic reaction constants for both intermediates and final products.…”

Section: Catalytic Processesmentioning

confidence: 99%

Introduction to High Pressure CO2 and H2O Technologies in Sustainable Biomass Processing

Questell‐Santiago

Luterbacher

2017

High Pressure Technologies in Biomass Conversion

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Biomass is an attractive source of renewable carbon-based fuels and chemicals and their production is envisaged within the framework of integrated biorefineries. Multiple research efforts to make biorefineries more economically competitive and sustainable are ongoing. In this context the use of high-pressure CO2 and CO2/H2O mixtures for biomass conversion is especially attractive. These mixtures are cheap, renewable, environmentally benign and allow tuning of various processing parameters by varying temperature, pressure and CO2 loading. This chapter presents a broad introduction of the principal processes and conversion routes being considered within biorefineries, and how high-pressure CO2 and CO2/H2O mixtures could help address certain challenges associated with biomass conversion. Some of the principle advantages associated with high-pressure CO2 and CO2/H2O mixtures that we highlight here are their abilities to act as green substitutes for unsustainable solvents, to enhance acid-catalysed reaction rates by in situ carbonic acid formation, to reduce mass transfer-limitations, and to increase access to substrates and catalysts. We discuss these advantages in the context of the trade-offs associated with implementing large-scale high-pressure systems including safety concerns and increased capital costs. With this introduction, we highlight both the principal benefits and challenges associated with the use of high-pressure CO2 and CO2/H2O mixtures, which are further detailed in subsequent chapters.

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Acid-Catalyzed Reactions in Carbon Dioxide-Enriched High-Temperature Liquid Water

Cited by 85 publications

References 18 publications

Multiphase reaction media including dense phase carbon dioxide and/or water: A case study for hydrogenation of phenol with a Pd/Al2O3 catalyst

Multiphase reaction media including dense phase carbon dioxide and/or water: A case study for hydrogenation of phenol with a Pd/Al2O3 catalyst

Polysaccharide Hydrolysis Accelerated by Adding Carbon Dioxide under Hydrothermal Conditions

Introduction to High Pressure CO2 and H2O Technologies in Sustainable Biomass Processing

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