Most hydrogen produced today in the world is made via steam methane reforming (SMR). It is a mature hydrogen production process in which high-temperature steam (700°C–1,000°C) is used to produce hydrogen from methane-based feed such as Natural Gas. In the SMR, methane reacts with steam under 3–25 bar pressure in the presence of a nickel-based catalyst to produce hydrogen, carbon monoxide, and a relatively small amount of carbon dioxide. SMR is the endothermic process therefore, heat must be supplied to the process for the reaction to proceed.
Following reaction majorly occurs in the SMR process:
Reaction (3) is called “water gas shift (WGS) reaction”. In this reaction carbon monoxide and steam are reacted using a catalyst to produce carbon dioxide and more hydrogen. This process occurs in two stages, consisting of a high-temperature shift (HTS) at 350oC and a low-temperature shift (LTS) at 190-210oC.
Hydrogen produced from the SMR process includes small quantities of carbon monoxide, carbon dioxide, and hydrogen sulfide as impurities and, depending on use, may require further purification. The primary steps for purification include:
- Feedstock purification – This process removes poisons, including sulfur (S) and chloride (Cl), to increase the life of the downstream steam reforming and other catalysts.
- Product purification – In this final process step carbon dioxide and other impurities are removed from the gas stream either by pressure-swing adsorption (PSA) or using chemical absorption process such as amine sweetening.
High to ultra-high purity hydrogen may be needed for the durable and efficient operation of fuel cells. Impurities are believed to cause various problems in the current state-of-the-art fuel cell designs, including catalyst poisoning and membrane failure. As such, additional process steps may be required to purify the hydrogen to meet industry quality standards. Additional steps could also be needed if carbon capture and sequestration technologies are developed and utilized as a part of this method of hydrogen production.
Steam reforming can also be used to produce hydrogen from other fuels, such as ethanol, propane, or even gasoline.