Problem 142 - A Complete Resource Book in Chemistry for JEE Main

Question

In context with the industrial preparation of hydrogen from water gas \(\left(\mathrm{CO}+\mathrm{H}_{2}\right)\), which of the following is the correct statement? (a) \(\mathrm{CO}\) and \(\mathrm{H}_{2}\) are fractionally separated using differences in their densities (b) \(\mathrm{CO}\) is removed by absorption in aqueous \(\mathrm{Cu}_{2} \mathrm{Cl}_{2}\) solution (c) \(\mathrm{H}_{2}\) is removed through occlusion with \(\mathrm{Pd}\) (d) \(\mathrm{CO}\) is oxidized to \(\mathrm{CO}_{2}\) with steam in the pres- ence of a catalyst followed by absorption of \(\mathrm{CO}_{2}\) in alkali.

Step-by-Step Solution

Answer

The correct statement is (d): CO is oxidized to CO2 with steam in the presence of a catalyst, followed by CO2 absorption in alkali.

Step 1: Understand the Problem

The problem involves selecting the correct statement about the industrial preparation of hydrogen from water gas (CO + H2). Water gas is a mixture, and these statements describe different methods for separating or converting the components into hydrogen.

Step 2: Analyze Each Option

Let's break down each option: (a) Fractional separation by density would not be efficient as CO and H2 densities are close. (b) CO can be removed by absorption with various chemicals, but Cu2Cl2 is not commonly used in this process. (c) Occlusion with Pd is possible for H2, but it's not a common industrial method for separating large quantities of hydrogen from CO. (d) This is a method where CO reacts with steam in the presence of a catalyst to form CO2 and H2, then CO2 is absorbed by alkali. This is known as the water-gas shift reaction.

Step 3: Identify the Correct Statement

In step 2, statement (d) describes the water-gas shift reaction, utilized in industries to convert CO in water gas into CO2 and H2. CO2 is then easily removed by absorption in an alkaline solution, leaving behind H2. This method is industrially preferred for producing hydrogen from water gas.

Key Concepts

Hydrogen Production

Hydrogen is a versatile and crucial element in various industries, frequently produced from a process called the water-gas shift reaction. This reaction transforms carbon monoxide (\(\text{CO}\)) into carbon dioxide (\(\text{CO}_2\)), simultaneously generating hydrogen gas (\(\text{H}_2\)). This process is a cornerstone for large-scale hydrogen production, crucial for applications such as fuel cell technology and ammonia synthesis.

The water-gas shift reaction proceeds as follows:\[\text{CO} + \text{H}_2\text{O} \rightarrow \text{CO}_2 + \text{H}_2\]This reaction occurs in two stages:

• A high-temperature shift (HTS) stage operating at around 350-400°C.
• A low-temperature shift (LTS) stage, occurring at 200-250°C.

Both stages typically use different catalysts to enhance the conversion efficiency. By maximizing hydrogen yield, industries ensure sufficient generation of hydrogen for subsequent separation and purification processes.

Industrial Chemistry

Industrial chemistry encompasses the vast landscape where chemical processes are optimized for the production and transformation of chemical products on a large scale. The water-gas shift reaction is a perfect example of a process designed with industrial efficiency in mind.

In an industrial setting, reactors are designed to ensure optimal reaction conditions such as temperature, pressure, and catalyst presence. These factors improve the reaction rate, maximize product yield, and ensure economic viability. The choice of catalysts is critical; for instance, iron oxide with chromium is used in high-temperature shifts, while copper-zinc oxide is preferred in low-temperature shifts.

This optimization plays a critical role in lowering costs and energy consumption. The process of hydrogen production from water gas through the water-gas shift reaction represents the practical implementation of chemical principles to meet industrial demand efficiently. Keeping such processes economically favorable is crucial for the sustainability of industrial chemistry practices.

Separation Techniques

Separation techniques are fundamental to the industrial production of hydrogen, particularly following the water-gas shift reaction. After \(\text{CO}\) has been converted to \(\text{CO}_2\) and \(\text{H}_2\), it is essential to effectively separate these components. This ensures a pure hydrogen stream for industrial use.

In practice, \(\text{CO}_2\) is typically absorbed by an alkaline solution, such as potassium carbonate, effectively removing most of the \(\text{CO}_2\) from the gas mix. Using chemical absorption leverages the solubility difference between \(\text{CO}_2\) and \(\text{H}_2\). Other advanced separation technologies include:

• Pressure Swing Adsorption (PSA): which utilizes pressurized gas to separate hydrogen from other gases based on molecular characteristics.
• Membrane Techniques: where selective permeable membranes allow the passage of hydrogen while blocking other gases.

These separation methods ensure the delivery of high-purity hydrogen necessary for industrial applications, fuel cells, and chemical synthesis. Efficient separation is key to the practicality of hydrogen production in industrial chemistry.