Water Gas Shift Equilibrium Constant

Mastering the Water-Gas Shift Equilibrium Constant: A Comprehensive Guide

The efficient production of hydrogen, a crucial element in various industries from ammonia synthesis to fuel cells, often relies on the water-gas shift (WGS) reaction. This crucial chemical process elegantly balances the supply and demand of hydrogen and carbon monoxide, converting one into the other depending on the desired outcome. Understanding the equilibrium constant of this reaction, Keq, is paramount for optimizing reactor design, predicting product yields, and ensuring efficient operation. This article delves into the intricacies of the water-gas shift equilibrium constant, providing a comprehensive understanding for those seeking guidance or in-depth information.

1. The Water-Gas Shift Reaction: A Foundation

The WGS reaction itself is a reversible reaction involving the reaction of carbon monoxide (CO) and water (H₂O) to produce carbon dioxide (CO₂) and hydrogen (H₂):

CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g)

The equilibrium constant, Keq, describes the ratio of products to reactants at equilibrium. For the WGS reaction, it's expressed as:

Keq = ([CO₂][H₂]) / ([CO][H₂O])

where the bracketed terms represent the partial pressures or molar concentrations of each gas at equilibrium. The value of Keq is temperature-dependent, significantly influencing the reaction's direction and the ultimate hydrogen yield. A high Keq favors product formation (CO₂ and H₂), while a low Keq favors reactant formation (CO and H₂O).

2. Temperature Dependence: A Crucial Factor

The WGS reaction is exothermic, meaning it releases heat. According to Le Chatelier's principle, increasing the temperature shifts the equilibrium to the left, favoring the reactants and reducing Keq. Conversely, lowering the temperature shifts the equilibrium to the right, favoring the products and increasing Keq. However, lowering the temperature also slows down the reaction rate. Therefore, finding the optimal temperature involves a careful balance between achieving a high Keq and maintaining a reasonable reaction rate. Industrial WGS reactors often operate at temperatures between 350°C and 550°C to achieve this balance, utilizing catalysts to speed up the reaction.

3. Pressure Dependence: A Secondary Consideration

Unlike temperature, the pressure dependence of the WGS reaction is less pronounced. Since the number of moles of gas on the reactant side is equal to the number of moles on the product side, changes in pressure have a minimal impact on the equilibrium position. This contrasts with reactions where the number of moles changes, where pressure significantly affects the equilibrium constant.

4. Catalyst Selection: The Key to Efficiency

The WGS reaction, while thermodynamically favorable at lower temperatures, is kinetically slow without a catalyst. Various catalysts are employed, with iron-chromium oxide being historically significant and copper-based catalysts becoming increasingly prevalent for their higher activity and selectivity at lower temperatures. The catalyst's choice directly affects the reaction rate and, consequently, the time required to reach equilibrium. The optimization of catalyst properties, such as surface area, active site density, and resistance to poisoning, is crucial for industrial applications.

5. Real-World Applications and Implications

The WGS reaction is fundamental to several crucial industrial processes:

Ammonia Production: The Haber-Bosch process for ammonia synthesis requires a substantial amount of hydrogen. The WGS reaction is used to purify and increase the hydrogen content in the synthesis gas (a mixture of CO and H₂).
Fuel Cell Technology: Fuel cells utilize hydrogen as fuel. The WGS reaction plays a vital role in purifying the hydrogen stream from sources like natural gas reforming.
Petroleum Refining: The WGS reaction is incorporated in various refining processes, impacting the production of different fuels and chemicals.
Carbon Monoxide Removal: The reaction can be used to remove toxic carbon monoxide from gas streams, crucial for safety and environmental protection.

6. Conclusion

The water-gas shift equilibrium constant is a critical parameter influencing the efficiency and product yield of the WGS reaction. Understanding its temperature dependence and the role of catalysts is vital for optimizing this crucial chemical process across diverse industrial applications. Careful consideration of thermodynamic and kinetic factors is essential for designing efficient reactors and achieving desired hydrogen production levels.

Frequently Asked Questions (FAQs)

1. How does the presence of impurities affect the equilibrium constant? Impurities can act as poisons, reducing the catalyst's activity and slowing down the reaction, indirectly affecting the time taken to reach equilibrium. However, they don't directly change the value of Keq itself, which is solely a function of temperature.

2. Can Keq be determined experimentally? Yes, Keq can be determined experimentally by measuring the partial pressures or concentrations of all reactants and products at equilibrium at a specific temperature.

3. What is the typical range of Keq for the WGS reaction? The value of Keq varies significantly with temperature. At typical industrial operating temperatures (350-550°C), it ranges from several to several tens.

4. How does the choice of catalyst affect the reaction rate without changing Keq? Catalysts provide an alternative reaction pathway with lower activation energy, thereby accelerating the rate at which equilibrium is achieved without affecting the equilibrium position itself.

5. Beyond temperature, what other factors can influence the kinetics of the WGS reaction? Factors like catalyst surface area, particle size, and the presence of promoters or inhibitors can significantly impact the reaction rate. The concentration of reactants also plays a crucial role in the kinetics, influencing the rate at which equilibrium is approached.

Search Results:

The water gas shift reaction: Catalysts and reaction mechanism 15 Mar 2021 · Conventionally, the equilibrium constant (K p) for WGSR is described based on Eq. (2), where p i stands for the partial pressure of each reactant and product [21], [24]. The equilibrium constant based on thermodynamic properties can be derived as shown in Eq.

Water–gas shift reaction - Wikipedia The water–gas shift reaction (WGSR) describes the reaction of carbon monoxide and water vapor to form carbon dioxide and hydrogen: CO + H 2 O ⇌ CO 2 + H 2 The water gas shift reaction was discovered by Italian physicist Felice Fontana in 1780.

How is the equilibrium constant for the water-gas shift reaction ... 24 Jul 2021 · Consider the following equilibrium process at $\pu {686 ^\circ C}$: $$\ce {CO2 (g) + H2 (g) <=> CO (g) + H2O (g)}$$ The equilibrium concentrations of the reacting species are $ [\ce {CO}] = \pu {0.050...

Equilibrium constants for WGSR (Twigg, 1989) | Download Table In the carbon based hydrogen production, Water gas shift reaction is the intermediate step used for hydrogen enrichment and CO reduction in the synthesis gas. This paper makes a critical...

Expressions for Equilibrium Constant Water-gas shift reaction: … The results show that CO and CH4 concentrations increase in the product gas when the biomass is fed at the location near to the bottom of the bed, while CO2 and H2 increase in the case of on-bed...

Finding the equilibrium constant of the water gas-shift reaction by ... Finding the equilibrium constant of the water gas-shift reaction by direct minimization of Gibbs free energy. The water–gas shift reaction is a gas-phase reaction, widely used in industry, between carbon monoxide and water to form carbon dioxide and hydrogen:

Thermodynamic Modeling of Water N. Azcan - International … Abstract— Water gas shift reaction (WGSR) is one of the fundamental reactions which occurs during supercritical water gasification. A stoichiometric thermodynamic model is developed to estimate equilibrium composition of WGSR with reaction temperature, equilibrium constant and Gibbs free energy of reaction. The algorithm

7.7: Equilibrium Equations and Equilibrium Constants 21 Jan 2025 · Only partial pressures for gas-phase substances or concentrations in solutions are included in the expressions of equilibrium constants. As such, the equilibrium constant expression for this reaction would simply be \[K_{P}=P_{CO_{2}}\nonumber \] because the two solids and one liquid would not appear in the expression.

A Review of the Water Gas Shift Reaction Kinetics - ResearchGate 30 Jan 2010 · This paper makes a critical review of the developments in the modeling approaches of the reaction for use in designing and simulating the water gas shift reactor.

Chemical Equilibria in Methanol Synthesis Including the Water–Gas Shift ... 28 Apr 2016 · A novel formulation representation of the equilibrium constant for water gas shift reaction. International Journal of Hydrogen Energy 2022 , 47 (65) , 27821-27838.

Thermodynamic equilibrium analysis of water-gas shift reaction … 15 Dec 2017 · Thermodynamic equilibrium of water-gas shift reaction (WGSR) under various temperatures, pressures and steam-to-CO (S/C) ratios was analyzed by Gibbs free energy minimization method. Coal-derived syngases with various CO2 and …

Water-Gas Shift - an overview | ScienceDirect Topics 6 Feb 2010 · Variation of the equilibrium constant for the water gas shift (WGS) reaction with temperature, calculated from Eqn (1.3). However, this reaction proceeds from the reactants to the products without variation of moles; therefore, a pressure increase does not …

(154b) Comparison of Equilibrium Constant of the Reaction Water Gas ... The reaction water-gas-shift is a secondary reaction that produce hydrogen and carbon dioxide from the reaction carbon monoxide with water, this reaction occurs in the synthesis of Fischer-Tropsch, in the synthesis methanol, conversion of hydrocarbons by reform among others.

DOI:10.1002/apj.364 Special Theme Research Article The water-gas shift ... 19 Aug 2009 · The WGS reaction is an equilibrium-limited reaction, and CO conversion is favored at lower temperatures due to its exothermicity (Eqn (1)). Equation (2) is widely seen in the literature to describe the equilibrium constant (K p) as a function of temperature[11]: K p = exp 4577.8 T −4.33 (2) As the temperature increases, the equilibrium con-

14.4.2: Water-Gas Shift Reaction - Chemistry LibreTexts The turn-over-frequency for the WGSR is proportional to the equilibrium constant of hydroxyl formation, which rationalizes why reducible oxide supports (e.g. CeO 2) are more active than irreducible supports (e.g. SiO 2) and extended metal surfaces (e.g. Pt).

Modeling the Water-Gas Shift Reaction | Industrial & Engineering ... A novel formulation representation of the equilibrium constant for water gas shift reaction. International Journal of Hydrogen Energy 2022, 47 (65) , 27821-27838. https://doi.org/10.1016/j.ijhydene.2022.06.105

Thermodynamic Modeling of the Water-Gas Shift Reaction in In this study, stoichiometric and non-stoichiomet-ric thermodynamic models for WGSR are formulated using Gibbs free energy minimization to predict the equilibrium composition of each species. Activity coefficients of each species are determined using PR-EoS assuming constant pressure conditions.

On the basic effects on the gas composition governed by the water-gas ... 15 Aug 2020 · Simple correlations for the water-gas shift (WGS) equilibrium constant over wide temperature ranges. Analytical solutions for product ratios in WGS equilibrium. Graphical representation of key equations illustrating the basic effects of stoichiometry and thermodynamics.

A novel formulation representation of the equilibrium constant for ... 30 Jul 2022 · The water gas shift reaction (WGSR) is regarded as an important stage commonly encountered in carbon monoxide (CO) removal and hydrogen generation and purification from the product stream to obtain a high energy density fuel.

Water gas shift equilibria via the NIST Webbook 1 Feb 2013 · We will examine the water gas shift enthalpy, free energy and equilibrium constant from 500K to 1000K, and finally compute the equilibrium composition of a gas feed containing 5 atm of CO and H_2 at 1000K.