PRODUCTION OF DIHYDROGEN

The Hydrogen element is a important raw materials for the chemical industry and increasingly, as a fuel. Although it's not present in significant of quantities in the Earth atmosphere or underground gas deposits, there is a biological turnover because various microorganisms is using H⁺ ion as a oxident or H₂ as a fuels. The most of the (H₂) Hydrogen molecule is produced from natural gas by using steam reforming, and Hydrogen molecule produced by other methods, notably coal gasification with CO₂ and thermally assisted electrolysis. The Hydrogen gas usually production synthesis by ammonia. The HEBER PROCESS, Hydrogenation of unsaturated fats and large scale manufacturing from organic chemicals. In the future H₂ may be produced from entirely renewable sources such as water and capturing the sunlight.

A SMALL-SCALE PREPARATION :

                                   In the laboratory, Hydrogen molecule (H₂) easy ways produced by the reaction of electropositive elements with aqueous alkali or acids, or hydrolysis of Saline hydrides. It's also produced by electrolysis.

There's many producers for preparing small quantities of pure H₂, but in the laboratory, H₂ molecules is produced by reaction to silicon or Aluminium with hot alkali solutions.

2Al(s) + 2OH⁻(aq) + 6H₂O (l) 2Al(OH)₄⁻(aq) +3H₂(ɡ)

Si(s) + 2OH⁻(aq) + H₂O(l)→ SiO²₃⁻(aq) +2H₂(ɡ)

And reaction of Zn with mineral acids :

Zn(s) +2H₃O⁺(aq) + H₂(ɡ)+ 2H₂O(l)

           This reaction of metal hydrides with water provides a convenient way to obtain little amount of H₂ outside the laboratory. Calcium hydride is particularly suited for this purpose as it is commercially available and expensive and it react with water at room temperature.

CaH(s) + 2H₂O(l) →Ca(OH)₂→ Ca(OH)₂(s) + 2H₂(ɡ)

Calcium hydride is used as a portable H₂ generator and has important applications in remote areas, such as filling meteorological balloons.

The pure H₂ is produced in little amounts of using a simple electrolysis cell, electrolysis of heavy water also a convenient way to prepare pure D₂.

(B) PRODUCTION FROM FOSSIL SOURCES:

                 Most hydrogen molecule for industry is produced by high - temperature reaction of H₂O with CH₄ or similar reaction with coke.

Hydrogen is produced in huge quantities to needs of industry, in fact production is often integrated directly into chemical processes that is required of hydrogen molecule as a feed stock. The main commercial processes for the production of H₂O and hydrocarbons at high temperature.

CH₄(ɡ)+ H₂O(ɡ) → CO(ɡ) + 3H₂(ɡ) ∆H= + 206.2 kj mol⁻¹

Increasingly, coke or coal is used. This reaction, which occurs at 1000⁰C, is

C(s) + H₂O(ɡ) → CO (ɡ) +H₂(ɡ)∆H =131.4 kj mol⁻¹

The mixture of CO and H₂ is known as water gas and further reaction with water produces more H₂.

CO(g) +H₂O(ɡ) → CO₂(ɡ) + H₂(g) ∆H = - 41.2 kj mol⁻¹

The overall coal gasification results in production of CO₂ and H₂

C(s) +2H₂O(ɡ) →CO₂(ɡ)+2H₂(ɡ)∆H= +90.2kj mol⁻¹

By implementing a system of capture CO₂ from the mixture and it's possible to use fossil fuels and minimize release of the greenhouse CO₂ into atmosphere. However this process is not a renewable ways for hydrogen molecule production and it's based on the use of fossil fuels. Dihdrogen consumption by on board fuel cells in vehicles is produced from methanol by using an automotive steam reformer.

(C) PRODUCTION FROM RENEWABLE SOURCES :

                        Production of H₂ molecule by electrolysis of water is costly and viable only in areas where electricity is cheap or if it's a byproduct of economically important process. Environmental pressure are driving technologies to produce of hydrogen molecule more efficiently from surplus or renewable energy including solar and biological sources.

Electrolysis is used to produce H₂ that's free from contaminated.

H₂O(l) → H₂(ɡ) +1/2 O₂(ɡ) Ecell = −1.23 V, ∆G= +237 kj mol⁻¹

This reaction, a large overpotential is required to offset the electrode kinetics, and particularly for the production of O₂. The best catalysis of are based on Pt, but it's too expensive to justify it's use large - scale plants. As a consequence, electrolysis of water is economically and environmentally only, if it's surplus to demand. These conditions are found in plenty of hydroelectric or nuclear energy. These also scope for off-shore wind farms and electricity grids and far from the population area's that are necessary for conventional power generation. Electrolysis is carried out using hundreds of cells arranged in series, each operating at 2 voltage nickel or Iron electrodes and aqueous NaOH as a electrolyte. The temperature of 80⁰C− 85⁰C are used to increase electrolytic current at low potential. The most important electrolytic H₂ production method is the "CHLOR - ALKALI PROCESS" which H₂ is produced the gaseous product is Cl₂, which requires a lower overpotential than O₂.

However, only about 0.1 percent of the global H₂ demand is produced by electrolysis. Including that produced in the chlor-alkali process. This percentage is improved by the development of cheap and efficient electrocatalysts to reduce the economically wasteful overpotential.

                       Hydrogen also can be produced by fermentation, using anaerobic bacteria that use cultivated biomass or biological waste their energy sources. Research is also under way to establish how best to produce hydrogen molecule by exploiting solar energy directly either through physical methods photoelectron - chemistry or thermolysis or biological process. The physical methods under investigation are outlined. The biological production could take place in "HYDROGEN FARMS" by nurturing photosynthetic microorganisms that have been modified to produce H₂ as well as organic molecules.