HYTHANE

Hythane is a gaseous blend of 10%–30% hydrogen and 70%–90% methane which is currently produced from petroleum and natural gas.

The hydrogen addition to natural gas improves engine combustion, and reduces carbon dioxide and nitrous oxide emission, as hydrogen is a clean fuel. It is referred to as biohythane when organic material is converted via the fermentative processes that generate biomethane and biohydrogen.

Biohythane reactor systems typically comprise two-stage processes where the raw biomass influent is converted to biohydrogen in the first stage and the liquid effluent from the first stage continues to the second stage to be converted to biomethane by the methanogenesis step.

The combined output of the two-stage systems normally comprises between 10% and 15% hydrogen, 50% and 55% methane, and 30% and 40% carbon dioxide.

Hydrogen is by far the most abundant element in the universe, making up 75% of the mass of all visible matter in stars and galaxies and the most simplest of all the elements. On Earth, hydrogen mostly exists in molecules such as those of water, minerals in the earth and organic compounds, but at very low quantities in the atmosphere.

HYDROGEN ATOMIC STRUCTURE

Elementary hydrogen contains a single electron and a nucleus that consists of a single proton, although in a rare form (or “isotope”) of hydrogen contains both a proton and a neutron and is called Deuterium or Heavy Hydrogen. Other isotopes, such as tritium with two neutrons and one Proton are unstable.

Most of the mass of a hydrogen atom is concentrated in its nucleus. The radius of the electron’s orbit, which defines the size of the atom, is approximately 100000 times larger than the radius of the nucleus. Therefore hydrogen atoms consist largely of empty space as is the case in atoms of all elements, although all others are heavier and have more electrons.

Chemically, the atomic arrangement of a single electron orbiting a nucleus is highly reactive. For this reason, hydrogen atoms naturally combine into molecular pairs (H2 instead of H). Molecular mass of Hydrogen (H2): 2.016 x 10-3 kg/Kmol).

All substances exist on earth as either a gas, liquid or solid. Most substances will change from one of these states to another depending on the temperature and pressure.

Hydrogen has the second lowest boiling point and melting points of all substances, just after helium. Hydrogen is a liquid below its boiling point of 20 K (–253 ºC) and a solid below its melting point of 14 K (–259 ºC) and atmospheric pressure. Temperatures below 200 K (–73 ºC) are known as cryogenic temperatures, and liquids at these temperatures are known as cryogenic liquids.

Hydrogen is odorless, colorless and tasteless. Compounds such as mercaptans and thiophanes that are used to odorize natural gas may not be added to hydrogen for fuel cell use as they contain sulfur that would poison the fuel cells.

Hydrogen is non-toxic but can act as a simple asphyxiant by displacing the oxygen in the air. Oxygen levels below 19.5% are biologically inactive for humans and at concentrations below 12%, immediate unconsciousness may occur with no prior warning symptoms. The potential for asphyxiation in unconfined areas is almost negligible due to the high buoyancy and diffusivity of hydrogen.

Gases that accompany hydrogen when reforming from fossil fuels, such as nitrogen, carbon dioxide, carbon monoxide and other trace gases, can also act as asphyxiants. In addition, carbon monoxide is a poisonous gas that is a severe health hazard.

The affinity of hemoglobin (in the blood) for carbon monoxide is 200–300 times greater than its affinity for oxygen. As a result, inhalation of carbon monoxide quickly restricts the amount of oxygen in the bloodstream and asphyxiation ensues. Asphyxiation can continue for some time after a victim is moved to fresh air.

Carbon monoxide is flammable over a very wide range of concentrations in air (12.5 – 74%). The autoignition temperature of carbon monoxide is 609 °C. Carbon monoxide has almost the same density as air and will therefore not diffuse by rising.

A mixture of carbon monoxide and air is potentially flammable and explosive, and can be ignited by a spark or hot surface.

H2 DENSITY

Density is measured as the amount of mass contained per unit volume at a given pressure and temperature. Hydrogen has the lowest atomic weight of any substance and therefore has very low density both as a gas and a liquid.

Substance	Vapor Density (20 ºC/1 atm)	Liquid Density ( normal boilling, 1 atm)
​Hydrogen	0.08376 kg/m3	70.8 kg/m3
Methane	0.65 kg/m3	422.8 kg/m3
Gasoline	4.4 kg/m3	700 kg/m3

A common way of expressing relative density is as specific gravity. Specific gravity is the ratio of the density of one substance to that of a reference substance, both at the same temperature and pressure. The reference substance for vapors is air (1.203 kg/m3) and water for liquids (1000 kg/m3). Gaseous hydrogen, has a specific gravity of 0.0696, approximately 7% the density of air. Liquid hydrogen, has a specific gravity of 0.0708, and is thus approximately (and coincidentally) 7% the density of water.

The ideal gas equation can be used accurately to describe the behavior of real gases at pressures up to approximately 100 barg at normal ambient temperatures. At higher pressures, the results become increasingly inaccurate. Therefore, the ideal gas relationship cannot be used accurately at gas storage pressures.

HYDROGEN CONTENT

Even as a liquid, hydrogen is not very dense. Ironically, every cubic meter of water (made up of hydrogen and oxygen) contains 111 kg of hydrogen whereas a cubic meter of liquid hydrogen contains only 71 kg of hydrogen. Thus, water packs more mass of hydrogen per unit volume, because of its tight molecular structure, than hydrogen itself. The sema is true for Methanol, where 1 m3 of methanol contains 100 kg of hydrogen an cubic meter of heptane contains 113 kg, or amonia.

The same happens with liquid hydrogen containing organic compounds as well, hydrocarbons are compact hydrogen carriers.

LEAKAGE of H2

The molecules of hydrogen gas are smaller than all other gases, and it can diffuse through many materials considered airtight or impermeable to other gases. This property makes hydrogen more difficult to contain than other gases.

Leaks of liquid hydrogen evaporate very quickly since the boiling point of liquid hydrogen is so extremely low.

The small molecule size that increases the likelihood of a leak also results in very high buoyancy and diffusivity, so leaked hydrogen rises and becomes diluted quickly, especially outdoors.

In contrast, leaking gasoline or diesel spreads and evaporates slowly resulting in a widespread fire hazard. Propane gas is denser than air so it accumulates in low spots and disperses slowly, resulting in a fire or explosion hazard. Methane gas is lighter than air, so it disperses rapidly, but not as rapidly as hydrogen. When used as vehicle fuel requires the use of a leak detection equipment because the potential fire hazard.