Hydrogen can be produced through various processes, most of today’s hydrogen production comes from fossil fuel processing, namely Coal Gasification, Methane Steam Reforming and Petroleum fraction partial Oxidation. Hydrogen produced by these processes is classified as ‘Grey’ due to the gaseous pollutant emissions although it is important to note that if Carbon Capture and Storage technology were to be implemented, then the produced Hydrogen would be classified as ‘Blue’. ‘Green’ Hydrogen can only come through a process that, in all aspects, is zero-emission, the most well known system that can produce it is an R.E.S. powered Electrolysis module.
Methane (CH4) Steam Reforming
M.S.R. is a thermochemical process, during which methane molecules react with water in the form of steam at temperatures, often above 1073,3 K in order to produce hydrogen gas, followed by another stage at which the produced carbon monoxide reacts with water in the form of steam to produce carbon dioxide and hydrogen gas (again). This process accounts for 48% of the total amount of hydrogen produced per year, but given hydrocarbon deposits are declining it is imperative to limit this percentage as, given the technological evolution of electrolysis units, it would be counterproductive to consume an existing fuel (CH4, LNG as a compressed gas Fuel for internal combustion engines) while producing Carbon Dioxide in the process. Clean hydrogen production is essential if at any point we strive for a Carbon-free industry.
Coal gasification is a practice, through which 18% of the world's hydrogen production is achieved and shares basically the same principle as P.OX, in particular Coal reacts with pure oxygen in the presence of water vapor, from the reaction arises carbon monoxide, carbon dioxide, diatomic hydrogen and impurities. Subsequently, and after the impurities have been separated, carbon monoxide, through the Catalytic Shift Reaction, produces hydrogen and carbon dioxide. The Hydrogen is then separated.
Coal Gasification reaction: CH0.8 + O2 + H2O → CO + CO2 + H2 + Coal Residue
Petroleum fraction partial oxidation
POX is a hydrogen production method based on the oxidation of a particular type of hydrocarbon in the presence a controlled amount of oxidizing agent in the form of pure oxygen, so as to produce carbon monoxide and hydrogen, as opposed to complete oxidation that would correspondingly produce CO2 + H2O. The reaction takes place under very high pressure (typically between 1300-1800 psi). Hydrogen is produced by the catalytic shift reaction of CO while any residual amount of Carbon Dioxide is absorbed via a basic solvent. This practice is responsible for producing 30% of the world's hydrogen production.
Alkaline Water Electrolysis
Electrolysis of water is a well-known hydrogen production technology through the breakdown of water molecules into individual synthetics (hydrogen and oxygen). The devices that separate water by means of an electrical charge are electrochemical and consist of two electrodes(anode, cathode) and an external electrical circuit, connected the electrodes. The Water requires the addition of some chemical compound so that it becomes more electrically conductive and receptive to the process.
The principle of operation of the device in question can be summarized as follows:
Microbial Electrolysis Cells
Organic waste is another source from which Hydrogen production can occur combined with the fact that waste management is a vital area of industrial activity. The recovery of energy from wastewater is not a new technology, the scientific community has invested in the subject and there is power generating electrochemical technology based on the degradation of the organic fraction within the wastewater volume by specific microorganisms under anaerobic conditions, these devices are called Microbial Fuel Cells (MFC), however, a similar technology has also been developed for the production of hydrogen or methane (Microbial Electrolysis Cells).
The device in question functions as follows:
Commonly used materials for electrodes are the following:
Such technology cannot not be characterized as zero-emission as the production process involves carbon in the form of organic compounds, therefore although hydrogen, which can be a pure form of energy, is produced and while it is advantageous to apply renewable energy technologies, as a small amount of electrical power is required by the device, carbon dioxide emissions remain, in this context Carbon Capture and Storage systems can be implemented so that the environmental footprint of this technology is reduced to a minimum.
Polymer waste treatment
Plastics can be directly converted to Hydrogen and Carbon Nanotubes through a process where polymer waste is shredded and mixed with various metal-oxides(Fe, Al) that catalyze the –to be initiated- reaction, the mixture then is exposed to microwave radiation that results in carbon nanotubes and a gaseous fraction composed of 97% pure Hydrogen. The reasoning behind this process’ success is the fact that polystyrene(often related to human cancer), polyethylene, polypropylene are not at all affected by the radiation which means that the catalysts are excited to the required degree.