Hydrogen Production

Hydrogen Production

Representation of the Hydrogen Colors
Representation of the Hydrogen Colors

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.

MSR process schematic representation
MSR process schematic representation

Coal Gasification

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

Coal gasification process diagram
Coal gasification process diagram

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.

POX flow diagram

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:
  • Water electrolysis reaction: 2H2O + 2e- → H+ + 2HO-
  • The water is enriched with an extra ingredient to make the water more conductive to electricity (usually Sodium Choride (NaCl))
  • The NaCl, up-on into contact with water, breaks down into sodium cations and chlorine anions
  • The external circuit through which the electrodes are connected is then excited by a DC source.
  • The chlorine anions are oxidized on the anode, thus forming diatomic Chlorine gas that subsequently escapes from the mixture, the protons obtained as a result of Electrolysis deposit their positive charge on the cathode, thus forming diatomic hydrogen gas that also escapes from the mixture and is collected. Remaining in the mixture are hydroxyl anions and sodium cations which can be converted into caustic sodium in crystalline form by simply dehydrating the mixture.
PEM Electrolysis

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:
  • The waste volume is introduced into the anode chamber
  • DC voltage is applied to the system
  • Organic matter is oxidized by the bacteria In the anode chamber with the products being carbon dioxide and protons, among other impurities
  • The protons penetrate the semipermeable membrane and when they eventually reach the cathode chamber, they are reduced and form hydrogen gas
Commonly used materials for electrodes are the following:
  • Stainless steel
  • Carbon-based composite
  • Graphite
  • Carbon cloth

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.

Schematic representation of a Microbial Electrolysis Cell
Schematic representation of a Microbial Electrolysis Cell

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.

Direct conversion of Plastic waste to Hydrogen and MWCNT
Direct conversion of Plastic waste to Hydrogen and MWCNT

Other methodologies, currently in R&D stage

  • Methane Pyrolysis
  • Plasma Electrolysis (Conventional AWE with extremely high voltage connected to the electrode circuit)
    • Essentially an Electrolysis process taking place under extremely high Voltage as compared to conventional AWE, THE or PEM Electrolysis
    • Produces Hydrogen on a much more efficient rate due to overall high temperature
    • Can be further enhanced by enrichment of the electrolyte solution (acetic acid ex.)
    • Great potential in Future Hydrogen Production
  • Artificial Photosynthesis


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