Carbon Dioxide Utilisation

Closing the Carbon Cycle

Peter Styring, Elsje Alessandra Quadrelli, Katy Armstrong

• Publisher: Elsevier
• Year: 2014
• Print ISBN: 9780444627469
• eBook ISBN: 9780444627483
• Topic: Technology & Engineering
• Subtopic: Renewable Power Resources
• Index: Technology & Engineering

Carbon Dioxide Utilisation: Closing the Carbon Cycle explores areas of application such as conversion to fuels, mineralization, conversion to polymers, and artificial photosynthesis as well as assesses the potential industrial suitability of the various processes. After an introduction to the thermodynamics, basic reactions, and physical chemistry of carbon dioxide, the book proceeds to examine current commercial and industrial processes, and the potential for carbon dioxide as a green and sustainable resource. While carbon dioxide is generally portrayed as a "bad" gas, a waste product, and a major contributor to global warming, a new branch of science is developing to convert this "bad" gas into useful products. This book explores the science behind converting CO2 into fuels for our cars and planes, and for use in plastics and foams for our homes and cars, pharmaceuticals, building materials, and many more useful products. Carbon dioxide utilization is a rapidly expanding area of research that holds a potential key to sustainable, petrochemical-free chemical production and energy integration. - Accessible and balanced between chemistry, engineering, and industrial applications - Informed by blue-sky thinking and realistic possibilities for future technology and applications - Encompasses supply chain sustainability and economics, processes, and energy integration

Part 1

Introductory Concepts

Outline

Chapter 1. What is CO2? Thermodynamics, Basic Reactions and Physical Chemistry

Chapter 2. Carbon Dioxide Capture Agents and Processes

Chapter 3. CO2-Derived Fuels for Energy Storage

Chapter 4. Environmental Assessment of CO2 Capture and Utilisation

Chapter 1

What is CO₂? Thermodynamics, Basic Reactions and Physical Chemistry

Michael North Green Chemistry Centre of Excellence, Department of Chemistry, The University of York, Heslington, York, UK

Abstract

This introductory chapter introduces the structural, physical and spectroscopic properties of carbon dioxide and shows how these are linked to its role in global warming. The phase behaviour of carbon dioxide is introduced including the accessibility of a supercritical phase. The kinetics and thermodynamics of reactions involving carbon dioxide are introduced to provide a theoretical basis for understanding the reactions of carbon dioxide and the limitations as to what catalysis can achieve. Finally, the commercially important chemical reactions of carbon dioxide are surveyed within this kinetic and thermodynamic framework.

Keywords

kinetics; thermodynamics; reactivity; phase-behaviour; structure

Chapter Outline

1.1 Introduction 3

1.2 Spectroscopy and its role in climate change 5

1.3 Phase behaviour and solvent properties 6

1.4 Kinetics and thermodynamics 8

1.5 Commercially important reactions of carbon dioxide 12

References 15

1.1. Introduction

Carbon dioxide (CO₂) is a triatomic molecule with a molecular weight of 44 Da. It is a gas at room temperature and pressure. At atmospheric pressure it sublimes directly from a solid to a gas at −78 °C. Carbon dioxide is a relatively inert gas which is neither explosive nor flammable and which does not support combustion. Therefore, it is widely used in fire extinguishers and fire suppression systems, though some care is needed especially in confined spaces as it is an asphyxiant and has a density (1.98 kg/m³ at 0 °C) greater than that of air. Carbon dioxide occurs naturally in the Earth's atmosphere as a result of volcanic eruptions, forest fires and plant and animal respiration. It is essential to the growth of green plants which use photosynthesis to convert carbon dioxide and water into sugars. These are key parts of the natural carbon cycle which controls the level of carbon dioxide in the Earth's atmosphere and hence the surface temperature of the planet.¹ Prior to the start of the industrial revolution, atmospheric carbon dioxide levels were around 270 ppm by volume.²

The carbon dioxide molecule has a linear structure in which each carbon–oxygen bond has a length of 116.3 pm and is composed of a σ- and a π-bond. The two π-bonds are orthogonal to one another and like any carbon–oxygen bonds are polarised such that the carbon atom carries a partial positive charge (+0.592) and the oxygen atoms carry a partial negative charge (−0.296) due to the higher electronegativity of oxygen compared to carbon. Figure 1.1 shows various representations of carbon dioxide.

FIGURE 1.1 Representations of carbon dioxide.

The chemical reactivity of carbon dioxide is determined by the polarisation of the carbon oxygen bonds, and the chemistry is dominated by the reaction of carbon dioxide with nucleophiles which react at the central carbon atom (Scheme 1.1). The nucleophile may be a neutral species with a lone pair of electrons (e.g., an amine), may possess an electron-rich π-bond (e.g., a phenolate) or may possess a carbon-metal σ-bond (e.g., a Grignard reagent). The other key feature of the chemistry of carbon dioxide is its coordination to metals. This is an important area as the coordination of carbon dioxide to a metal can significantly change both the electron distribution and molecular geometry within the carbon dioxide molecule, thus dramatically changing its chemical reactivity.

This is the basis of many metal-induced and metal-catalysed reactions of carbon dioxide. The area is however complicated by the numerous ways in which carbon dioxide can coordinate to one or more metals due to its ability to coordinate through either carbon or oxygen and to bridge between metal atoms. As shown in Figure 1.2, there are at least 13 known coordination geometries in carbon dioxide metal complexes.^3a–3d,4 If just the monometallic complexes are considered, an electron deficient metal will coordinate to one of the oxygen atoms (ηO1)

and this does not change the geometry of the carbon dioxide, but will withdraw electron density from it, thus making the carbon atom more susceptible to attack by nucleophiles. In contrast, metals with loosely held electrons may coordinate to the carbon atom of carbon dioxide (ηC1)

which both makes the carbon atom less electron deficient and hence less susceptible to attack by nucleophiles: this also changes the overall geometry of the CO₂ unit from linear to bent.

SCHEME 1.1 Reaction of carbon dioxide with nucleophiles.

FIGURE 1.2 Carbon dioxide metal complex geometries.

1.2. Spectroscopy and its role in climate change

The carbon dioxide molecule has three vibrational modes: two stretches (symmetric and anti-symmetric) and a bend (Figure 1.3). For gaseous carbon dioxide, the symmetric stretch (1286–1388cm⁻¹) does not involve a change in the molecular dipole moment and hence it is infrared inactive, but Raman active. The anti-symmetric stretch (2349cm⁻¹) and bend (667cm⁻¹) do involve a change in the molecular dipole moment and hence are infrared active.⁴ The ¹³C NMR resonance of carbon dioxide in non-polar solvents occurs at 126 ppm.⁴

The infrared active vibrations of carbon dioxide are directly responsible for its role as a greenhouse gas. The Earth's atmosphere is transparent to visible light coming from the sun which strikes the Earth's surface and is reemitted as infrared radiation. The main components of the Earth's atmosphere (oxygen and nitrogen) are also transparent to infrared radiation. Howe...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• Preface
• Part 1. Introductory Concepts
• Part 2. Contribution to Materials
• Part 3. Energy and Fuels
• Part 4. Perspectives and Conclusions
• Index