ANS:A - natural gas as a source of hydrogen.

Natural gas, primarily composed of methane (CH4), is used as a source of hydrogen in gas-based fertilizer plants through a process called steam methane reforming (SMR) or steam reforming. Here's how it works:

1. Steam Methane Reforming (SMR): In the SMR process, natural gas (mainly methane) is reacted with steam (H2O) at high temperatures (typically between 700°C to 1000°C) in the presence of a catalyst, usually nickel. The chemical reaction is as follows:

𝐶𝐻4+𝐻2𝑂→𝐶𝑂+3𝐻2CH4​+H2​O→CO+3H2​ This reaction converts methane and water into carbon monoxide (CO) and hydrogen gas (H2). Carbon monoxide is a byproduct in this process and can be further reacted to produce additional hydrogen through the water-gas shift reaction: 𝐶𝑂+𝐻2𝑂→𝐶𝑂2+𝐻2CO+H2​O→CO2​+H2​

2. Hydrogen Separation: After the reforming reaction, the resulting gas mixture contains hydrogen, carbon monoxide, carbon dioxide, and residual methane. The hydrogen is then separated from the other gases using various methods such as pressure swing adsorption (PSA) or membrane separation.
3. Utilization in Fertilizer Production: The separated hydrogen gas is a key raw material used in the production of ammonia (NH3), a primary component of nitrogen-based fertilizers. In the Haber-Bosch process, hydrogen is reacted with nitrogen (usually obtained from air) at high pressure and temperature in the presence of an iron catalyst to produce ammonia:

𝑁2+3𝐻2→2𝑁𝐻3N2​+3H2​→2NH3​ This ammonia can then be further processed to produce various nitrogen-based fertilizers such as urea, ammonium nitrate, and ammonium sulfate. Using natural gas as a source of hydrogen in gas-based fertilizer plants offers several advantages, including high hydrogen content in natural gas, relatively low cost compared to other hydrogen sources, and efficient conversion through steam methane reforming. Additionally, natural gas is readily available in many regions with established infrastructure for extraction, transportation, and distribution.