Water Gas Shift Reaction

Research Developments and Applications

Panagiotis Smirniotis, Krishna Gunugunuri

• Publisher: Elsevier
• Year: 2015
• Print ISBN:
  9780124201545
• eBook ISBN:
  9780444633538
• Topic: Technology & Engineering
• Subtopic: Chemical & Biochemical Engineering
• Index: Technology & Engineering

Water Gas Shift Reaction: Research Developments and Applications outlines the importance of hydrogen as a future fuel, along with the various hydrogen production methods. The book explains the development of catalysts for Water Gas Shift (WGS) reaction at different temperatures and steam/CO ratios, and also discussing the effect of different dopants on the WGS activity of iron oxide and the promotion and inhibition roles of the dopants on the WGS activity of iron oxide are explained. In addition, the book describes extensive characterization of modified ferrite catalysts, especially with Mossbauer spectroscopy and its advantage in understanding properties of metal doped ferrite catalysts, the exact dopant location, and its effect on electron hopping capability and WGS activity of Fe redox couple. - Outlines the importance of the Water Gas Shift Reaction and its application for hydrogen production - Provides detailed information on potential catalysts, their development, and their pros and cons, giving the reader insights on how modified ferrite catalysts work at different temperatures and different steam to CO ratios - Reviews hydrogen technology, its current importance, and production methods - Presents a clear presentation of the topics with many graphics and tables - Offers basic and advanced knowledge of catalysts characterization instrumental techniques

Chapter 1

Introduction About WGS Reaction

Abstract

This chapter mainly explains history and background of the WGS reaction. This chapter gives brief description about thermodynamic, kinetic and mechanistic aspects of the WGS reaction. This chapter also explains various ways to conduct WGS reaction, i.e., homogeneous, heterogeneous, membrane and photo-assisted WGS reactions. This chapter also gives brief introduction about various types of catalysts such as high temperature (HT), low temperature, sulphur tolerant and ultra HT catalysts used for the WGS reaction. Various metals and metal oxides investigated for the WGS reaction were also presented in this chapter.

Keywords

Water-gas shift reaction (WGSR)

Thermodynamics

Membrane reactors

Photo-catalysis

Homogeneous catalysis

Noble metals

Modified ferrites

Cu-based catalysts

1.1 History and Background

1.1.1 Water Gas

Water gas is an equimolar mixture of carbon monoxide and hydrogen. It can be synthesized by passing steam through coke. During late nineteenth century town gas developed the manufacturing process for the water gas.

$\mathrm{C}+{\mathrm{H}}_2\mathrm{O}\to \mathrm{C}\mathrm{O}+{\mathrm{H}}_2\mathrm{\Delta }\mathrm{H}=131.2\mathrm{kJ}/\mathrm{mol}$

(1.1)

The reaction is endothermic, so the fuel must be continually re-heated to keep the reaction going. In order to do this, an air stream, which alternates with the vapour stream, is introduced for the combustion of carbon.

$2\mathrm{C}+{\mathrm{O}}_2\to 2\mathrm{C}\mathrm{O}\mathrm{\Delta }\mathrm{H}=-220.8\mathrm{kJ}/\mathrm{mol}$

(1.2)

These two reactions take place in cycle basis, as the temperature of the second reaction reaches sufficiently high the steam cycle restarts. Because of the wide temperature range in reality a small amount of carbon dioxide is always present in the water gas. Because of contamination in the air blow cycle a small amount of nitrogen is also present in the water gas.

In the early 1990s, production of water gas using steam reforming of methane received tremendous importance if the ultimate objective is generation of pure hydrogen since it provides highest molar ratio of H₂/CO of Equation (1.3).

${\mathrm{C}\mathrm{H}}_4+{\mathrm{H}}_2\mathrm{O}\to \mathrm{C}\mathrm{O}+3{\mathrm{H}}_2\mathrm{\Delta }\mathrm{H}=206.3\mathrm{kJ}/\mathrm{mol}$

(1.3)

Partial oxidation of methane is another way to produce water gas (Equation 1.3). This process is mainly used when we need lesser H₂/CO ratio and if there are difficulties in external heat supply, internal heat generation is needed as in the case of fuel processors for fuel cell applications. Partial oxidation of methane produces H₂/CO in a ratio of 2. If we need H₂/CO in a ratio of 1, dry reforming of methane can be done (Equation 1.4).

${\mathrm{C}\mathrm{H}}_4+0:5{\mathrm{O}}_2\to {\mathrm{C}\mathrm{O}}_2+2{\mathrm{H}}_2\mathrm{\Delta }\mathrm{H}=35.6\mathrm{kJ}/\mathrm{mol}$

(1.4)

${\mathrm{C}\mathrm{H}}_4+{\mathrm{C}\mathrm{O}}_2\to 2{\mathrm{C}\mathrm{O}}_2+2{\mathrm{H}}_2\mathrm{\Delta }\mathrm{H}=247.4\mathrm{kJ}/\mathrm{mol}$

(1.5)

Water gas is used extensively in the industry for the manufacture of ammonia, methanol, hydrogen (for hydrotreating, hydrocracking of petroleum fractions and other hydrogenations in the petroleum refining and petrochemical industry), hydrocarbons (by the Fischer-Tropsch process) and metals (by the reduction of the oxide ore).

1.1.1.1 Types of Water Gas

1.1.1.1.1 Carburetted Water Gas

Water gas had a lower calorific value than coal gas, so the calorific value was often boosted by passing the gas through a heated retort into which oil was sprayed. The resulting mixed gas was called carburetted water gas.

1.1.1.1.2 Semi-Water Gas

Semi-water gas is a mixture of water gas and producer gas made by passing a mixture of air and steam through heated coke. The heat generated when producer gas is formed keeps the temperature of the coke high enough to allow water gas to be formed.

1.1.2 Water-Gas Shift Reaction

The water-gas shift reaction (WGSR) was discovered by Italian physicist Felice Fontana in 1780 [1,2]. However, the reaction was first patented by the British scientists Ludwig Mond and Langer C in 1888 for fuel cell application in coal gasification [3]. Ludwig Mond, one of the greatest chemist-industrialists of all time, focused part of his industrial chemical technology developments on the synthesis of ammonia from coal. Mond developed the process for producing the so-called Mond gas (the product of the reaction of air and steam passed through coal/coke – CO₂, CO, H₂, N₂, etc.), which became the basis for future coal gasification processes [4]. Mond and his assistant Carl Langer were the first to use the term ‘fuel cells’ while performing experiments with the world’s first working fuel cell using coal-derived Mond gas [4]. One of the hardest tasks was to feed pure hydrogen to the ‘Mond battery’ due to the large quantities of carbon monoxide present in Mond gas, which poisoned the Pt electrode. Therefore, Mond solved this problem by passing the Mond gas mixture and steam over finely divided nickel at 400 °C, reacting the carbon monoxide and steam to give carbon dioxide and more hydrogen. This reaction is termed as ‘Water-Gas Shift Reaction’. After CO₂ removal by a simple alkaline wash, the H₂-rich stream obtained could be successfully fed to the hydrogen cell [5].

The WGSR is a reversible chemical reaction between carbon monoxide and steam to form carbon dioxide and hydrogen.

${\mathrm{C}\mathrm{O}}_{\left(\mathrm{g}\right)}+{\mathrm{H}}_2\mathrm{O}\leftrightarrow {{\mathrm{C}\mathrm{O}}_2}_{\left(\mathrm{g}\right)}+{{\mathrm{H}}_2}_{\left(\mathrm{g}\right)}\mathrm{\Delta }{\mathrm{H}}_{298\mathrm{K}}=-41.16\mathrm{kJ}/\mathrm{mol}$

(1.6)

In the past, ammonia synthesis plants used water-gas process to produce hydrogen since it provides an economical way to produce hydrogen in the quantity required by the Haber ammonia synthesis process [6,7]. In the ammonia synthesis plant, first CO was removed from water gas by liquefication and scrubbing with hot caustic soda solution. Very soon they realized that the carbon monoxide liquefication process was unsuitable for large-scale plants. Then they used WGSR to convert CO into CO₂ by pass...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• Chapter 1: Introduction About WGS Reaction
• Chapter 2: High-Temperature WGS Reaction
• Chapter 3: Low-Temperature WGS Reaction
• Chapter 4: WGS Reaction over Co-Mo Sulphided Catalysts
• Chapter 5: Ultra High Temperature WGS Reaction
• Chapter 6: WGS Reaction in Membrane Reactors
• Chapter 7: Homogeneous WGS Reaction
• Chapter 8: Photo-Catalytic Water-Gas Shift Reaction
• Chapter 9: Mechanism and Kinetics of the WGS Reaction
• Index