Name: Mohamed Ismail Abd Alhafiz ID: 5310059Name: Rafat Hamdy ID:308235Name: Mohamed Yacoub ID:Name: Basma ID:

Pharos University in AlexandriaFaculty of Engineering

Dept of Petrochemical Engineering

Carbon Dioxide Conversion By Water-Gas Shift Reaction

Chemical Engineering Reaction and Industrial Catalysis

Contents

Introduction Applications High Temperature Shift Catalysts Low Temperature Shift Catalysts Fuel cells Reaction Conditions Reverse Water Gas Shift References

Introduction The water-gas shift (WGS) reaction is used to convert carbon monoxide (CO)

to carbon dioxide (CO2) and hydrogen (H2) through a reaction with water (H2O) (the mixture of carbon monoxide and hydrogen is known as water gas):

   The water gas shift reaction was discovered by Italian physicist Felice

Fontana in 1780. It wasn’t until much later when the industrial value of this reaction was better realized. Prior to early 20th century, hydrogen was obtained by reacting steam under high pressure with iron to produce iron, iron oxide and hydrogen.

At present, the Hydrogen economy ideal is gaining popularity and is becoming an important concept in both the political and research realms. Focus on hydrogen as a replacement fuel source for hydrocarbons is increasing. With this increasing interest, the WGSR has been receiving much attention over recent years.

Applications The WGSR is an important industrial reaction that is used in the

manufacture of ammonia, hydrocarbons, methanol, and hydrogen. It is also often used in conjunction with steam reformation of methane and other hydrocarbons. It provides a source of hydrogen at the expense of carbon monoxide, which is important for the production of high purity hydrogen for use in ammonia synthesis. The water-gas shift reaction may be an undesired side reaction in processes involving water and carbon monoxide.

The equilibrium of this reaction shows a significant temperature dependence and the equilibrium constant decreases with an increase in temperature, that is, higher carbon monoxide conversion is observed at lower temperatures. In order to take advantage of both the thermodynamics and kinetics of the reaction, the industrial scale water gas shift reaction is conducted in multiple adiabatic stages consisting of a high temperature shift (HTS) followed by a low temperature shift (LTS) with intersystem cooling.

High Temperature Shift CatalystsThe typical composition of commercial HTS catalyst has been reported as 74.2% Fe2O3, 10.0% Cr2O3, 0.2% MgO (remaining percentage attributed to volatile components). The chromium acts to stabilize the iron oxide and prevents sintering. The operation of HTS catalysts occurs within the temperature range of 310 oC to 450 oC. The temperature increases along the length of the reactor due to the exothermic nature of the reaction.

Low Temperature Shift CatalystsThe typical composition of commercial LTS catalyst has been reported as 32-33% CuO, 34-53% ZnO, 15-33% Al2O3. The active catalytic species is CuO. The LTS shift reactor operates at a range of 200 oC to 250 oC.

Fuel cellsThe WGSR can aid in the efficiency of fuel cells by increasing hydrogen production. The WGSR is considered a critical component in the reduction of carbon monoxide concentrations in cells that are susceptible to carbon monoxide poisoning such as the proton exchange membrane (PEM) fuel cell. The benefits of this application are two-fold: not only would the water gas shift reaction effectively reduce the concentration of carbon monoxide, but it would also increase the efficiency of the fuel cells by increasing hydrogen production.

Reaction Conditions

The WGSR is an exothermic, equilibrium-limited reaction that exhibits decreasing conversion with increasing temperature. Reviews of the catalyzed WGSR at temperatures below 600oC are available in the open literature. A catalyst is required under these conditions because of the lower reaction rate at low temperature. A universal rate expression and mechanistic understanding have proven to be unattainabled due to the numerous amount of variables involved such as catalyst composition, active surface and structure of the catalyst, age of the catalyst, operating pressure and temperature, and gas composition.

Reverse Water Gas Shift

Depending on the reaction conditions, the equilibrium for the water gas shift can be pushed in either the forward or reverse direction. The reversibility of the WGSR is important in the production of ammonium, methanol, and Fischer-Tropsch synthesis where the ratio of H2/CO is critical. Many other industrial companies exploit the reverse water gas shift reaction (RWGS) reaction as a source of the synthetically valuable CO from cheap CO2. Typically, It is done using a copper on aluminium catalyst.

References Lamm, editors, Wolf Vielstich, Hubert Gasteiger, Arnold (2003). Handbook

of fuel cells : fundamentals, technology, applications  Jacobs, G.; B. H. Davis (2007). "Low temperature water-gas shift

catalysts".  Callaghan, Caitlin (2006). Kinetics and Catalysis of the Water-Gas-Shift

Reaction.  Newsome, David S. (1980). "The Water-Gas Shift Reaction". Catalysis

Reviews: Science and Engineering

Whitlow, Jonathan E.; Parish (2003). Operation, Modeling and Analysis of the Reverse Water Gas Shift Process.