Chemical Technology H2 Industries IIT Notes

1. Hydrogen Production
Dr. Raveendra Gundlapalli
Assistant Professor
Department of Chemical Engineering
IIT (BHU) Varanasi

2. Hydrogen
• Hydrogen is a colorless and odorless gas as well as being non-toxic. It is easily ignited and it burns with a pale blue and almost invisible
flame. The hydrogen vapor is lighter than air. It is flammable over a wide range of vapor-air concentrations. It does not exist in nature
in its pure form. It can be produced from chemical compounds and by electrolysis from water
• Its atomic weight is 1.008 (H) and molecular weight is 2.016 (H2)
➢ Hydrogen is a fascinating energy carrier. Its conversion to heat or power is simple and clean. When combusted with Oxygen, Hydrogen
forms water. No pollutants are generated or emitted. The water is returned to nature where it originally came from.
➢ A "Hydrogen Economy" is projected as the ultimate solution for energy and environment.

3. ➢ Why Hydrogen is important for Energy industry
• It is the smallest of all atoms. Consequently, hydrogen is the lightest gas, about 8 times lighter than methane
(representing natural gas).
• The gravimetric higher heating value "HHV“ of a fuel gas are of little Therefore, for most practical assessments it is more
meaningful to refer the energy content of fuel gases to a reference volume relevance for practical applications.
• The following are the values for hydrogen and methane at 1 bar and 25°C
➢ Energy density of different energy sources (all values are approximate)
• Diesel or Gasoline : 43 MJ /kg (12 kWh/kg in electrical units) (1 Wh is 3600 J)
• Natural gas: 55 MJ / kg (15 kWh/kg in electrical units)
• Hydrogen: 130 MJ /kg (36 kWh/kg in electrical units)
• Lithium ion Battery : 200 Wh/kg
• Sodium-ion Battery : 150 Wh /kg
• Lead acid battery : 35 Wh /kg
• Vanadium redox flow battery : 25 Wh /kg
• Hydrogen has highest energy per unit and therefore utilization of it lead to modern green economy

4. ➢Production of Hydrogen
• Reforming of hydrocarbons
• Electrolysis of water
• Gasification of coal / biomass
➢Storage of Hydrogen
• It can be stored as gas at high pressures (200 – 800 atm) at ambient temperatures through isothermal compression
• It can be stored as cryogenic liquid at -250 oC at ambient atmosphere through liquefaction
• It can be stored on surface of solid (like Metal Hydrides) through adsorption at ambient Temperature and Pressure
➢Use of Hydrogen
• Used to produce power through combusting it with oxygen – for heat and electricity applications
H2 (g) + 0.5 O2 (g) → H2O (g); △H=−231 kJ and can produce temperature os about 2500 0C
• Used to produce power through fuel cell device – for automobile applications
➢Challenges in Hydrogen Economy
• Stability and reliability of fuel cells
• Cost of system integration (balance of plant) with renewables
• Supply-chain for large-scale Hydrogen
• Technical standards and regulations

5. • Based on the method of production of Hydrogen, a colour code has been given to it
• Green – Produced through electrolysis of water by using clean electricity from renewables (like solar and wind), no
carbon is produced in this process
• Pink - Produced through electrolysis of water by using clean electricity from nuclear energy
• Yellow - Produced through electrolysis of water by using solar energy directly
• Blue – Produced through natural gas with added carbon capture and storage (CCS)
• Grey – It is produced as same way as blue hydrogen but without CCS
• Black / Brown – Produced through coal and petrochemicals with more damage to environment

6. ➢Utility scale energy storage systems that are
in application compared to hydrogen systems
➢ India's Mission on Hydrogen economy is 1-1-1 (bringing the cost of hydrogen to 1$ -per 1kg – in 1 decade).
➢ Present cost of Hydrogen is around 10 $ per kg.
• Super-Capacitors : Range of 10 kW to 1 MW
• Fly-Wheels : Range of 10 kW – 10 MW
• Batteries : Range of 1 kW to 100 MW
• Compressed-Air : Range of 10 MW to 100 MW
• Pumped-Hydro : Range of 100 MW to 1 GW
• Hydrogen : Range of 1 MW to 1 GW
SMES – Superconducting Magnetic Energy Storage

7. Production of Hydrogen
➢ There are basically three main processes
to produce although aadditional methods
for production of hydrogen exist
a) Reforming of Natural Gas
b) Gasification of Biomass / Coal / Wood
c) Electrolysis of Water

8. Steam reforming of natural gas
• Steam reforming is a strongly endothermic conversion of hydrocarbons which react with water steam
• The steam reforming reaction is for an arbitrary hydrocarbon written as:
• There will be a water gas (CO + H2) shift reaction to convert Carbon monoxide to hydrogen. Catalyst used for this reaction is Iron oxide
(FeO) promoted by Chromium. Catalyst can also be named as Iron Chromate
• The heat needed for the strongly endothermic steam reforming process may come from burners. At atmospheric pressure and a ratio
of (H2O / CxHy = 1), complete conversion at equilibrium conditions is achieved at 900 0C. In practice higher pressures are used and
then a catalyst based on Nickel is needed to enhance the reaction. Solid carbon is formed in the furnace as complete conversion is
hard to achieve at high pressures.
• The high temperature may also result in thermal cracking of the hydrocarbons. Then poisoning of the catalyst may occur and the
reaction can be hindered which causes an increase of the temperature. By operating at a high H2O/C ratio and light hydrocarbons, the
formation of solid carbon can be avoided.
• If H2O and O2 both are introduced in the steam reforming process, so-called auto-reforming occurs, but it requires pure oxygen (which
has high production cost) but results in high energy efficiency
• Reformer gas from the reaction of steam reforming of methane with Nickel catalyst is quenched with steam to give 350 0C input gas
to another catalytic converter (this is so called shift in water gas (CO+H2) reaction to reduce CO and increase H2 production).
Otherwise, water gas at reformer temperature can form back to methane and water with the following reaction

9. ➢ Following is the typical process flow sheet for the production of Hydrogen through steam reforming of hydrocarbons.
This is also a process for production of synthesis gas using hydrocarbons
➢ Following is the simple flow sheet for the production of Hydrogen through steam reforming of hydrocarbons.
PSA is Pressure Swing Adsorption

10. ➢ The PSA process
• The effluent water gas is quenched and scrubbed with potassium carbonate to remove CO2. this
unit typically consists of Pressure Swing Adsorption (PSA) process where water gas is adsorbed and
CO2 is scrubbed off as an effluent form the PSA unit.
• PSA is the technology used to separate and purify components of a gas mixture under pressure
according to each component’s molecular characteristics and affinity for a specific adsorbent
material. Specific adsorptive materials preferentially adsorb a target gas at pressure. The pressure
is then swung low to desorb the adsorbed material, leaving a purer gas.
• The PSA process works basically at constant temperature and uses the effect of alternating
pressure and partial pressure to perform adsorption and desorption.
• Since heating or cooling is not required, short cycles within the range of minutes are achieved.
• The pressure swing adsorption process has four basic process steps:
• Adsorption
• Depressurization
• Regeneration
• Repressurization
Figure: Typical PSA unit
➢ For high purity of Hydrogen, additional stages in shift converter and additional stages in PSA (more than 2 beds) unit is recommended
➢ After Scrubbing, the traces of CO are removed by Methanation reaction

11. Gasification Process to produce Hydrogen
➢ Gasification is a technological process that can convert any
carbonaceous (carbon-based) raw material such as coal into fuel
gas, also known as synthesis gas (syngas for short). Gasification
occurs in a gasifier, generally a high temperature/pressure vessel
where oxygen (or air, if we use air, most of the energy may lose in
heating Nitrogen)) and steam are directly contacted with the coal
or other feed material causing a series of chemical reactions to
occur that convert the feed to syngas and ash/slag residues.
➢ Gasification offers an alternative to more established ways of
converting feedstocks like coal, biomass and some waste streams
into electricity and other useful products
➢ For complete conversion of coal, high temperature and proper
ratios of O2/C and H2O/C are required as otherwise methane CH4
appears in the produced syngas. As most of the reactions are
heterogeneous, chemical reaction kinetics and thermodynamics
affect the process and the transfer speed of the reactants to the
solid surfaces has significant role as well.
➢ Gasifiers are configured as fixed, moving or fluidized beds or as
entrained flow. The bed configurations have high residence times
for the reactants and may operate at low temperature. The
efficiency is high but the content of methane and other
hydrocarbons might be high in the syngas.
Figure: Typical gasification process depicting its usefulness

12. Differences between Gasification – Combustion - Pyrolysis

13. Electrolysis of water to produce Hydrogen
➢ Electrolysis is a process in which electrical energy is transformed to chemical energy. In electrolysis of water, redox reactions of water
occur by using a direct electric current. The overall reaction means decomposition of water into hydrogen and oxygen as:
➢ The unit being used to split water into hydrogen and oxygen is called an electrolyzer. Typical voltage of the reaction is about 2 V
➢ The reaction proceeds in dissociation of water into ions. Water is mainly composed of non-dissociated molecules of water while only
one molecule out of 550 million is dissociated into H3O+ and OH- ions. The concentration of these ions, as a result of auto-ionization
of water, is too low to establish a charge in the water.
➢ Accordingly, it is necessary to use an electrolyte dissolved in the water. Such an electrolyte could be an acid or a dissociate salt.
Typical substances are NaSO4, NaOH or H2SO4 which enable water to be conductive.
➢ Two porous electrodes immersed in an electrolytic solution are used and these are connected to an external electric power source.
The electrodes might be plated with some precious metal operating as a catalyst.
➢ Electrolyzers consist of an anode and a cathode separated by an electrolyte. Different electrolyzers function in different ways, mainly
due to the different type of electrolyte material involved and the ionic species it conducts.
➢ The half reactions occurring at the electrodes depend on the electrolyte. If NaSO4 is used, bipolar molecules of H2O; Na+ and SO4
-
ions exist in the solution before any reaction occurs. As the reaction starts migration of charge appears.
➢ The cathode is charged negatively and the positive Na+ ions migrate to this electrode and water is reduced. The anode is charged
positively and here negative SO4
- ions are found and water is oxidized. The half reactions are:
➢ When H2SO4 is used, it is dissociated to H3O+ ions, which are migrating to the cathode while SO4
- ions migrate to the anode. The half
reactions then are:

14. ➢ There are three types of electrolyzers
a) PEM (polymer electrolyte membrane) Electrolyzers (H+)
b) AEM (alkaline exchange membrane) Electrolyzers (OH-)
c) Solid Oxide Electrolyzers (O2-)
➢ Polymer Electrolyte Membrane (PEM) Electrolyzers
In a PEM electrolyzer, the electrolyte is a solid specialty plastic material.
• Water reacts at the anode to form oxygen and positively charged hydrogen ions (protons).
• The electrons flow through an external circuit and the hydrogen ions selectively move across the PEM to the cathode.
• At the cathode, hydrogen ions combine with electrons from the external circuit to form hydrogen gas.
➢ Alkaline Electrolyzers
• Alkaline electrolyzers operate via transport of hydroxide ions (OH-) through the electrolyte from the cathode to the anode with hydrogen being generated
on the cathode side.
• Electrolyzers using a liquid alkaline solution of sodium or potassium hydroxide as the electrolyte have been commercially available for many years.
➢ Solid Oxide Electrolyzers
• Solid oxide electrolyzers, which use a solid ceramic material as the electrolyte that selectively conducts negatively charged oxygen ions (O2-) at elevated
temperatures, generate hydrogen in a slightly different way.
• Steam at the cathode combines with electrons from the external circuit to form hydrogen gas and negatively charged oxygen ions.
• The oxygen ions pass through the solid ceramic membrane and react at the anode to form oxygen gas and generate electrons for the external circuit.

15. • Combustible gases : H2, CO, Natural gas (CH4), Butane and Propane
• Non-combustible gases: N2, CO2, O2 (but it is a combustion supporting gas)
• Synthes gases (or) Syngas: the gases which are synthesized through a chemical process
• Hydrogen (H2) can be named as a syngas
• Water gas (CO + H2) can also be named as a syngas
• Producer gas (CO + H2 + N2) can also be named as a syngas
• Coke oven gas (CO + H2 + CH4) can also be named as a syngas
• Natural gas (CH4) can’t be named as a syngas, because it exists mostly naturally
• LPG – mainly consists of mixture of propane and butane with other gases in small composition.
• It can be observed that Hydrogen must be there in any syngas