By what means is carbon (IV) oxide produced along hydrogen removed from the mixture in the industrial preparation of hydrogen from natural gas?
Steam-methane reforming reaction
CH4 + H2O (+ heat) → CO + 3H2
Water-gas shift reaction
CO + H2O → CO2 + H2 (+ small amount of heat)
In the industrial preparation of hydrogen from natural gas, carbon (IV) oxide (carbon dioxide) is produced along with hydrogen. The removal of hydrogen and separation of carbon dioxide is achieved through a process called steam reforming. Here is a step-by-step explanation:
1. Natural gas, which mainly consists of methane (CH4), is the primary source for hydrogen production. It is combined with steam (H2O) in a steam reformer, also known as a steam methane reformer.
2. Inside the steam reformer, natural gas reacts with steam at high temperatures (typically around 700-1000°C) in the presence of a catalyst, usually nickel (Ni), to undergo a series of chemical reactions.
CH4 (methane) + H2O (steam) → CO (carbon monoxide) + 3H2 (hydrogen)
3. The methane in natural gas reacts with steam to produce carbon monoxide (CO) and hydrogen (H2). This is known as the primary reforming reaction.
4. However, the primary reforming reaction is not sufficient to completely remove carbon from the mixture. To further convert carbon monoxide to carbon dioxide, a secondary reaction called the water-gas shift reaction takes place.
CO (carbon monoxide) + H2O (steam) → CO2 (carbon dioxide) + H2 (hydrogen)
5. In the water-gas shift reaction, carbon monoxide reacts with steam to form carbon dioxide and more hydrogen. The hydrogen produced in this step is the desired product.
6. The resulting mixture after the water-gas shift reaction contains hydrogen, carbon monoxide, and carbon dioxide. To separate the hydrogen from the other gases, a purification process such as pressure swing adsorption (PSA) or membrane separation is employed.
7. These purification methods selectively remove carbon dioxide and other impurities, leaving behind purified hydrogen gas.
So, in summary, carbon (IV) oxide (carbon dioxide) is produced along with hydrogen in the industrial preparation of hydrogen from natural gas, but it is removed from the mixture through the secondary water-gas shift reaction and subsequent purification steps.
In the industrial preparation of hydrogen from natural gas, carbon dioxide (CO2) is produced along with hydrogen. To remove the carbon dioxide, a process called "carbon capture" is typically employed.
There are several methods for carbon capture, but one widely used technique in the industrial setting is called pressure swing adsorption (PSA). Here's an explanation of how this process works:
1. The first step is the removal of impurities such as sulfur compounds from the natural gas. This is done to prevent them from interfering with the subsequent steps.
2. The natural gas is then mixed with steam and undergoes a process called steam methane reforming (SMR). In this step, the natural gas reacts with steam at high temperatures (around 700-1000°C) and in the presence of a catalyst (usually nickel-based) to produce hydrogen gas (H2) and carbon monoxide (CO).
CH4 + H2O → CO + 3H2
3. The mixture of hydrogen and carbon monoxide is then subjected to a water-gas shift reaction. This reaction converts a portion of the carbon monoxide into additional hydrogen gas and carbon dioxide.
CO + H2O → CO2 + H2
4. To remove the carbon dioxide, the gas mixture is passed through a PSA unit. PSA operates based on the difference in adsorption capacity of gases on a solid material called an adsorbent.
5. An adsorbent material, such as activated carbon or zeolite, is used to selectively adsorb the carbon dioxide. The gas mixture is passed through a bed of adsorbent, and the carbon dioxide preferentially sticks to the adsorbent surface, while the hydrogen passes through.
6. Once the adsorbent bed is saturated with carbon dioxide, the process switches to a regeneration phase. This involves reducing the pressure in the adsorption vessel, which causes the carbon dioxide to desorb (detach) from the adsorbent. It is then collected for further processing or storage.
By utilizing pressure swing adsorption, carbon dioxide is effectively removed from the mixture, leaving behind primarily hydrogen gas.