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Hydrogen, a colorless and odorless gas, can be produced in a variety of ways, depending on the energy used in the production process and the environmental impact it produces. Many people who are new to hydrogen energy may not be able to distinguish between different types of hydrogen energy, such as gray hydrogen, blue hydrogen, and green hydrogen. The purpose of this article is to analyze the production process and potential impact of each type of hydrogen energy to help readers better understand the production and manufacturing of hydrogen energy.
Classification of hydrogen production
01. Black hydrogen and brown hydrogen
Black and brown hydrogen are hydrogen produced from fossil fuels and are considered one of the least environmentally friendly types of hydrogen due to the way they are produced in a way that ranks among the best in terms of environmental impact. Black hydrogen is manufactured by reshaping coal with steam, while brown hydrogen is based on lignite. Both methods release large amounts of carbon monoxide and carbon dioxide during production, greenhouse gases that not only pose a threat to the climate, but are far from being sustainable.
02. Gray hydrogen
Grey hydrogen is produced by remodeling the steam of natural gas. Although it is produced in a relatively efficient way, hydrogen is produced in a way that results in the release of around 10 tonnes of carbon dioxide, which has a significant impact on climate change. At a time when the world's largest amount of hydrogen is produced, CO2 emissions from grey hydrogen have become a major contributor to the climate.
Fig.1 The production process of grey hydrogen
03. Blue hydrogen
Blue hydrogen is hydrogen produced from natural gas using the SMR (Steam methane reforming) process, where natural gas is mixed with hot steam and catalysts. A chemical reaction occurs to produce hydrogen and carbon monoxide. Water is added to the mixture to convert carbon monoxide into carbon dioxide and more hydrogen. If CO2 emissions are captured and stored underground, the process is considered carbon neutral or zero-carbon, and the hydrogen produced is called "blue hydrogen".
Fig.2 The production process of blue hydrogen
04. Blue-green hydrogen
Blue-green hydrogen is produced by pyrolysis of methane or the splitting of methane into hydrogen and solid carbon using a reactor or blast furnace. Blue-green hydrogen is still in the early stages of commercialization, and the value of green consciousness relies on the clean energy required by pyrolysis and the storage of carbon substances.
Fig.3 The production process of blue-green hydrogen
05. White hydrogen
White hydrogen is a by-product of industrial chemical processes or hydrogen present in nature. Although considered zero-carbon and sustainable, its actual contribution is limited due to the low production volumes.
06. Orange hydrogen
Orange hydrogen is naturally produced hydrogen in the earth's crust and can be extracted by hydraulic fracturing. However, this extraction process is not yet mature and it is unclear whether it can be implemented on a large scale, while also involving environmental interventions.
Fig.4 The production process of orange hydrogen
07. Green hydrogen
Green hydrogen is an environmentally friendly hydrogen energy source that is produced through the electrolysis of renewable energy. Since the energy comes from renewable sources, green hydrogen is considered an important energy source in the fight against climate change. Green hydrogen is green hydrogen when the energy used for power electrolysis comes from renewable energy sources such as wind, water, or solar.
Fig.5 The production process of green hydrogen
08. Red hydrogen
Red hydrogen, similar to green hydrogen, is also produced through electrolysis, but the energy comes from nuclear power plants. Although radioactive waste is generated, this waste can be recycled, making red hydrogen environmentally friendly.
09. Yellow hydrogen
Yellow hydrogen is also produced by electrolysis, but its energy comes from the public grid. However, if the grid relies heavily on fossil fuels, the environmental impact of yellow hydrogen will be limited.