3. Properties of hydrogen

Hydrogen is an element that possesses one proton and one electron. It is greatly plentiful and owns chemical properties that are exclusive and significant. Hydrogen is among the most available element in the world, which is chemically tied to the earth in great quantities and has to be free from an extensive assortment of feedstock. Other than water, the feed includes all hydrocarbon origin, namely natural gas, oil, biomass, and coal [25]. Currently, capital and maintenance costs, hazard and safety risk control, conversion performance, operation and design process flexibility are the key norms for the generating hydrogen. The selection of the feedstock and the minimization of the waste production play important role in setting criteria for maximizing hydrogen production.

can react with more electropositive elements like alkali metals and assume a partial negative charge. In addition, there is an intermolecular bonding known as hydrogen bonding that exists between hydrogen and elements like oxygen, fluorine, or nitrogen. This type of bonding is vital for the stability of many biological units. Hydrogen compounds with metals and metalloids are known as hydrides. H+ ion is formed when hydrogen is oxidized its electron is removed. Frequently, the H+ in aqueous solutions is termed as the hydronium ion, which is crucial in the chemistry of acid–base. There are three hydrogen isotopes in the universe:

H, <sup>2</sup>

hydrides are characterized by the participation of one or more hydrogen anions that possess reducing, nucleophilic, or basic properties. The bonding of hydrogen to a more electropositive element or group generates hydrides. While hydrides compounds usually react as reducing agent or Lewis bases by giving electrons, other metal hydrides react as hydrogen- atom donors

a) Saline or ionic, these hydrides are formed by the bond between a very electropositive metal, mostly an alkaline earth or an alkali metal and hydrogen atom. Reducing reagents and hetero-

b) Covalent hydrides, often seen in the complex metal hydride, transition metal hydrides, are

c) Interstitial hydrides usually occur in metals or alloys. They are often characterized by metallic bonding. Interstitial binary hydrides are formed when hydrogen gets in contact with

A major hurdle in the hydrogen economy lies in its transport and storage. Though H2 is characterized by very low volumetric energy density, but it possesses high energy density based on mass. At ambient conditions molecular hydrogen is present as a gas, which is difficult. Liquefied or pressurized hydrogen gas is required to get sufficient fuel energy. When the gas pressure increased definitely the volumetric energy density will improve, however this entails a larger amount of energy be used to pressurize the gas. Otherwise, slush or liquid hydrogen can be employed [30–32]. An extensive amount of energy must be used to liquefy the hydrogen, which is cryogenic and hence boils at 20 K. Hydrogen is not suitable to be stored in tanks since hydrogen diffuses through any liner material arranged to preserve it, which eventually leads to the wearying of the container. Hydrogen is often kept in compound form like chemical hydride. The compounds can be shifted from place to place fairly easily and then decomposed into hydrogen gas. The requirements of compound to form at high pressure and temperatures and for the hydrogen to be desorbed lead the current barriers to practical storage. The surface of solid storage material adsorbs hydrogen and then be desorbed when needed. This technology is yet to be improved. Hydrogen has one of the widest explosive/

geneous bases are good examples of the uses of ionic hydrides in organic synthesis.

hydrogen centers that form hydrides, or those that are nucleophilic.

and acids and. For example, the common drying reaction of calcium hydride:

H, and <sup>1</sup>

CaH<sup>2</sup> þ 2H2O ! 2H<sup>2</sup> þ Ca OH ð Þ<sup>2</sup> (2)

H respectively. Compounds of

Hydrogen Production from Light Hydrocarbons http://dx.doi.org/10.5772/intechopen.76813 43

tritium, deuterium, and protium denoted as <sup>3</sup>

Categories of hydrides are as follows:

transition metals.

3.3. Barriers fuel hydrogen

#### 3.1. Physical properties of hydrogen

Hydrogen is the simplest element chemically present. Hydrogen possesses only one proton, atomic number of unity, and average atomic weight of about 1 amu. H is the hydrogen symbol. Hydrogen is the most abundant chemical substance in the universe, particularly in planets and stars. Nevertheless, it is rare to find monoatomic hydrogen on Earth since it combines with other elements by covalent bonds. Hydrogen as such is not poisonous. It is nonmetal, tasteless, colorless, odorless, and highly flammable gas. The molecular formula is H2. On the Earth, hydrogen compounds exist as hydrocarbons and water. The most familiar isotope of hydrogen is protium, (1H). It has a single proton and a single electron with no neutron. Hydrogen is characterized by melting point of �259.14�C, a boiling point of �252.87�C, and density of 0.08988 g/L. Hydrogen is lighter than air. It has two separate oxidation states, (+1, �1), that facilitate it to react as both a reducing agent and an oxidizing agent. There are two separate spin isomers of hydrogen diatomic molecules, viz. orthohydrogen and parahydrogen. In the room temperature, the orthohydrogen constitutes 3/4 of hydrogen gas while the parahydrogen forms 1/4. Hydrogen is obtainable in different states, like compressed gas, liquid, slush, and solid and metallic forms [26, 27].

#### 3.2. Chemical properties of hydrogen

Hydrogen is extremely combustible gas and burns in the air starting from low concentration of 4–75%. The enthalpy for the combustion reaction for hydrogen is -286 kJ/mol., and is defined by the equation:

$$2\text{H}\_2(\text{g}) + \text{O}\_2(\text{g}) \leftrightarrow 2\text{H}\_2\text{O}(l) \quad \Delta H = -572 \text{ kJ} \tag{1}$$

Moreover, a mixture of chlorine and hydrogen from 5 to 95% can cause an explosion. The explosion of these mixtures can be easily triggered by sunlight, heat and spark [28, 29]. The temperature at which the hydrogen autoignition happens is at 500�C. Invisible ultraviolet light to bare eyes are radiated by flames of pure hydrogen-oxygen. Therefore, a flame detector is essential to monitor the leak of burning. Because hydrogen floats in air, its flames cause less harm than hydrocarbon fires, and rises rapidly. H2 reacts with oxidizing elements, like chlorine and fluorine to form the corresponding hydrogen halides. Since hydrogen is an effective reducing agent, compounds of hydrogen halides are easily formed from the reaction of hydrogen and chlorine and fluorine. H2 commonly forms compounds with a lot of elements in spite of its stability. In the case of reaction, hydrogen can react with more electronegative elements like oxygen or halogens and therefore can have a partial positive charge. On the other hand, it can react with more electropositive elements like alkali metals and assume a partial negative charge. In addition, there is an intermolecular bonding known as hydrogen bonding that exists between hydrogen and elements like oxygen, fluorine, or nitrogen. This type of bonding is vital for the stability of many biological units. Hydrogen compounds with metals and metalloids are known as hydrides. H+ ion is formed when hydrogen is oxidized its electron is removed. Frequently, the H<sup>+</sup> in aqueous solutions is termed as the hydronium ion, which is crucial in the chemistry of acid–base. There are three hydrogen isotopes in the universe: tritium, deuterium, and protium denoted as <sup>3</sup> H, <sup>2</sup> H, and <sup>1</sup> H respectively. Compounds of hydrides are characterized by the participation of one or more hydrogen anions that possess reducing, nucleophilic, or basic properties. The bonding of hydrogen to a more electropositive element or group generates hydrides. While hydrides compounds usually react as reducing agent or Lewis bases by giving electrons, other metal hydrides react as hydrogen- atom donors and acids and. For example, the common drying reaction of calcium hydride:

$$\text{CaH}\_2 + 2\text{H}\_2\text{O} \to 2\text{H}\_2 + \text{Ca(OH)}\_2\tag{2}$$

Categories of hydrides are as follows:

has to be free from an extensive assortment of feedstock. Other than water, the feed includes all hydrocarbon origin, namely natural gas, oil, biomass, and coal [25]. Currently, capital and maintenance costs, hazard and safety risk control, conversion performance, operation and design process flexibility are the key norms for the generating hydrogen. The selection of the feedstock and the minimization of the waste production play important role in setting criteria

Hydrogen is the simplest element chemically present. Hydrogen possesses only one proton, atomic number of unity, and average atomic weight of about 1 amu. H is the hydrogen symbol. Hydrogen is the most abundant chemical substance in the universe, particularly in planets and stars. Nevertheless, it is rare to find monoatomic hydrogen on Earth since it combines with other elements by covalent bonds. Hydrogen as such is not poisonous. It is nonmetal, tasteless, colorless, odorless, and highly flammable gas. The molecular formula is H2. On the Earth, hydrogen compounds exist as hydrocarbons and water. The most familiar isotope of hydrogen is protium, (1H). It has a single proton and a single electron with no neutron. Hydrogen is characterized by melting point of �259.14�C, a boiling point of �252.87�C, and density of 0.08988 g/L. Hydrogen is lighter than air. It has two separate oxidation states, (+1, �1), that facilitate it to react as both a reducing agent and an oxidizing agent. There are two separate spin isomers of hydrogen diatomic molecules, viz. orthohydrogen and parahydrogen. In the room temperature, the orthohydrogen constitutes 3/4 of hydrogen gas while the parahydrogen forms 1/4. Hydrogen is obtainable in different states, like compressed gas, liquid, slush, and

Hydrogen is extremely combustible gas and burns in the air starting from low concentration of 4–75%. The enthalpy for the combustion reaction for hydrogen is -286 kJ/mol., and is defined

Moreover, a mixture of chlorine and hydrogen from 5 to 95% can cause an explosion. The explosion of these mixtures can be easily triggered by sunlight, heat and spark [28, 29]. The temperature at which the hydrogen autoignition happens is at 500�C. Invisible ultraviolet light to bare eyes are radiated by flames of pure hydrogen-oxygen. Therefore, a flame detector is essential to monitor the leak of burning. Because hydrogen floats in air, its flames cause less harm than hydrocarbon fires, and rises rapidly. H2 reacts with oxidizing elements, like chlorine and fluorine to form the corresponding hydrogen halides. Since hydrogen is an effective reducing agent, compounds of hydrogen halides are easily formed from the reaction of hydrogen and chlorine and fluorine. H2 commonly forms compounds with a lot of elements in spite of its stability. In the case of reaction, hydrogen can react with more electronegative elements like oxygen or halogens and therefore can have a partial positive charge. On the other hand, it

2H2ð Þþ g O2ð Þ\$g 2H2O lð Þ ΔH ¼ �572 kJ (1)

for maximizing hydrogen production.

42 Advances In Hydrogen Generation Technologies

3.1. Physical properties of hydrogen

solid and metallic forms [26, 27].

by the equation:

3.2. Chemical properties of hydrogen

a) Saline or ionic, these hydrides are formed by the bond between a very electropositive metal, mostly an alkaline earth or an alkali metal and hydrogen atom. Reducing reagents and heterogeneous bases are good examples of the uses of ionic hydrides in organic synthesis.

b) Covalent hydrides, often seen in the complex metal hydride, transition metal hydrides, are hydrogen centers that form hydrides, or those that are nucleophilic.

c) Interstitial hydrides usually occur in metals or alloys. They are often characterized by metallic bonding. Interstitial binary hydrides are formed when hydrogen gets in contact with transition metals.

#### 3.3. Barriers fuel hydrogen

A major hurdle in the hydrogen economy lies in its transport and storage. Though H2 is characterized by very low volumetric energy density, but it possesses high energy density based on mass. At ambient conditions molecular hydrogen is present as a gas, which is difficult. Liquefied or pressurized hydrogen gas is required to get sufficient fuel energy. When the gas pressure increased definitely the volumetric energy density will improve, however this entails a larger amount of energy be used to pressurize the gas. Otherwise, slush or liquid hydrogen can be employed [30–32]. An extensive amount of energy must be used to liquefy the hydrogen, which is cryogenic and hence boils at 20 K. Hydrogen is not suitable to be stored in tanks since hydrogen diffuses through any liner material arranged to preserve it, which eventually leads to the wearying of the container. Hydrogen is often kept in compound form like chemical hydride. The compounds can be shifted from place to place fairly easily and then decomposed into hydrogen gas. The requirements of compound to form at high pressure and temperatures and for the hydrogen to be desorbed lead the current barriers to practical storage. The surface of solid storage material adsorbs hydrogen and then be desorbed when needed. This technology is yet to be improved. Hydrogen has one of the widest explosive/ ignition mixes ranges with air. The leak of hydrogen from its mixture with air will most probable cause an explosion, since the mixture of air and hydrogen form a broad explosive/ ignition when it gets contact with flame or spark. The utilization of hydrogen as a fuel is confined by this issue, particularly in non-open areas like underground parking or tunnels. The burning flames of pure hydrogen in the UV range are unseen; therefore flame detector is essential to sense the hydrogen leakage. Moreover, hydrogen can be detected by smelling since it is odorless. While the hydrogen economy is expected to make a smaller carbon footprint, there are lots complexities regarding the ecological matters of hydrogen manufacturing. Fossil fuel reforming represents the main source of hydrogen; nonetheless this technique eventually leads to larger carbon dioxide emissions when compared to fossil fuel used in an internal combustion engine. Other problems comprise hydrogen production through electrolysis entails a larger energy input than straight using renewable energy and the likelihood of other lateral outputs [33].

5. Hydrogen production from fossil fuels

5.1. Methods for hydrocarbon reforming

autothermal reforming [40].

5.1.1. Method of steam reforming

during the steam reforming is:

Hydrogen is generated from fossil fuels using numerous technologies, the principal of which are pyrolysis and hydrocarbon reforming. These techniques are the most advanced and normally employed, recovering virtually the whole hydrogen needs. About 48% of hydrogen is obtained from natural gas, 18% from coal, and 30% from naphtha and heavy oils [37–39]. Currently, the fuels from the fossil possess the principal role in the world hydrogen resource. Membrane reactors are used in the chemical and biochemical industries, to produce H2 from traditional fuels. A membrane frame permits mass transfer by the influence of driving forces of pressure, concentration, electric potential, temperature, and other driving forces. Membranes are classified into biological and synthetic based on their nature. A high selectivity and permeability, excellent chemical and stability are the required characteristics of the efficient H2-production membrane. Consequently, for a composite membrane, indispensable parts include a permeable support permitting the gases

Hydrogen Production from Light Hydrocarbons http://dx.doi.org/10.5772/intechopen.76813 45

crossing, blended with a barrier restrictive to the inter-diffusion in the metallic support.

The process by which the hydrocarbon fuel is changed to produce hydrogen via reforming systems is termed hydrocarbon reforming. During the hydrocarbon reforming other components are employed along with the hydrocarbon. These include carbon dioxide and the system is termed as CO2 reforming or dry reforming. Moreover steam may include as reactants in the reforming system of the hydrocarbon. This system is branded as steam reforming. Both dry and steam reforming reactions are endothermic, Therefore, it necessary to furnish energy. Reforming the hydrocarbon with oxygen is known as partial oxidation, and the reaction is exothermic. When the steam and partial oxidation reactions are combined the system is called

In the steam reforming process, the catalytic conversion of hydrocarbon into hydrogen and carbon monoxide is carried out in the presence of steam in the feed. The reforming procedure comprises gas purification, methanation, water-gas shift and synthesis gas production. Most feedstock contains natural gas, methane, and a mixture of light hydrocarbons, which include propane, butane, ethane, pentane, and both light and heavy naphtha. When the feed is contaminated with organic sulfur compounds, a desulphurization stage should precede the reforming step to circumvent the deactivation of the reforming catalyst which CO2 is seized and put in the ocean or geological reservoirs [41]. The primary chemical reaction that occurs

Depending on the values n and m dictate the hydrocarbon type. For instance, methane reforming n and m are equal to 1 and 4 respectively. The methane steam reforming is the best and well- advanced method employed for extensive hydrogen output. The conversion performance amounts to 74–85%. When natural gas and steam are reacted over a nickel-based catalyst

CnHm þ nH2O ! fn þ 1=2mÞH<sup>2</sup> þ nCO (3)

## 4. Hydrogen technology

Climate variation and fossil fuel exhaustion are the chief reasons leading to hydrogen technology. Various technologies are available for the production of hydrogen: These include electrical, thermal, hybrid and biological methods. Thermal conversion processes are the most utilized processes, with steam reforming becoming the best [34, 35]. Several reforming technologies are performed in industry. Hydrogen is also obtained from splitting water by electrolysis. Nevertheless, because of the strong bonds in water molecules, a 39.3 kWh of electrical energy is theoretically required to split 1 kg of water. Moreover, for hydrocarbon feedstock solar energy accomplishes most of the thermal conversion processes. Currently, in the refinery hydrogen is used as a raw material, rather than as an energy carrier. Often, hydrogen is transported via pipelines when it generated on-site. On the other hand, the procurement of an efficient, safe, and compact storage technology is vital for the transition from the fossil fuelbased energy carriers toward hydrogen. In recent days fuel cell applications are operated with liquefied hydrogen, kept in cryogenic tanks. Enormous research investigations are currently carried out in the arena of hydrogen solid-state storage. Nevertheless, the appropriate materials regarding the hydrogen storage capacity, cost, and thermodynamics are not yet enough. Lifetime, high storage density, prolonged cycle ability, satisfactory sorption kinetics and thermodynamics are the essential parameters for a hands-on storage material. No doubt hydrogen is a future energy carrier needed to have the proper the infrastructural technologies and logistics. Fossil fuel has the potential to balance between hydrogen as energy carrier of the future and the famous fossil fuel energy carriers. Hydrogen production processes are categorized as conventional and alternative energy resources like solar and wind, natural gas, coal, nuclear, biomass. There are several techniques for hydrogen generation from diverse raw materials and energy input selections. Having environmentally friendly properties, hydrogen became an eminent choice for an alternative fuel. The combustion techniques of fossil fuel destroy the environment and these days, less than 15% of total energy consumption of the world is not based on these techniques [36]. Consequently, hydrogen utilization as an alternative fuel is ideal since it is not an unsafe, poisonous or uncertain mode of production.
