HYDROGEN ENERGY Hydrogen storage Hydrogen Uses of hydrogen

HYDROGEN ENERGY Hydrogen storage: Hydrogen Uses of hydrogen: production: Advantages of hydrogen: Solar. Hydroge n energy system The Chemical Technology Metallur gy and refining Effluents Water Transportation Direct Thermal Process Thermochmical process Electrolysis The steamcatalytic Photocatalytic of water Process reforming process

OBJECTIVES OF CHAPTER 5 (HYDROGEN ENERGY) By the end of the chapter students should be able to: 1. 2. 3. 4. 5. 6. 7. 8. Gain an understanding of how hydrogen can be used as a source of energy Introducing the advantages of hydrogen when used as a source of energy Presenting the methods used for hydrogen storage and transport Presenting the uses of hydrogen in fields other than energy Understanding the processes of producing hydrogen using solar energy Describing the solar/ hydrogen energy system Determine methods of hydrogen production Explain advantages of hydrogen

INTRODUCTION Producing hydrogen for storing and transmitting solar energy seems the proper solution to recent difficulties of energy shortage and environmental pollution. The availability and the economic advantages of using hydrocarbons directly as heat, leaves no chance for the utilization of hydrogen as energy source. However, hydrogen is potentially a more flexible energy carrier and energy storage medium. It can be converted to other forms of energy needed by the users such as mechanical, electrical, and thermal with high efficiency. Hydrogen has good combustion characteristics and is non polluting because upon combustion, the only products are heat and water vapor. It can be used to fire boilers, run gas turbines of power fuel cells. It could also be used for ground air transportation.

Equations of Chapter 5 Hydrogen Energy The thermochemical process (two steps cycle) for producing hydrogen is expressed by: H 2 O + CH 4 → CO + 3 H 2 CO + 2 H 2 → CH 4 + ½ O 2 And the sum of the 2 equations will be: H 2 O → H 2+ ½ O 2 An example for a three steps process is given by: H 2 O +Cl 2 → 2 HCl + ½ O 2 2 HCl + 2 Cr. Cl 2 → 2 Cr. Cl 3 + H 2 2 Cr. Cl 3 → 2 Cr. Cl 2 + Cl 2 Another example is: 6 Fe. Cl + 8 H 2 O → 2 Fe 3 O 4 + HCl + 2 H 2 2 Fe 3 O 4 + 3 Cl 2 + 12 HCl → 6 Fe. Cl 3 + 6 H 2 + O 2 6 Fe. Cl 3 → 6 Fe. Cl 2 + 3 Cl 2 And in both cases hydrogen is produced.

Using a photo- catalyst, hydrogen could be produced through a photocatalytic process as follows: H 2 O +2 X + photoenergy → 2(reduced X) + 2 H+ + ½ O 2 2 (reduced X) + 2 H+ → 2 X + H 2 and the sum will be: H 2 O → 2 H 2 + ½ O 2

Water could be electrically electrolyized to produce hydrogen (which is liberated at the cathode according to the equation: 4 H 2 O + 4 e- → 2 H 2 + 4 OH- At the anode, the following pocess takes place: 4 OH- → 2 H 2 O + O 2 + 4 e- Thus, the overall process is as follows: 2 H 2 O + electrical energy → 2 H 2 + O 2

Using a photo- catalyst, hydrogen could be produced through a photocatalytic process as follows: H 2 O +2 X + photoenergy → 2(reduced X) + 2 H+ + ½ O 2 2 (reduced X) + 2 H+ → 2 X + H 2 and the sum will be: H 2 O → 2 H 2 + ½ O 2

The steam catalytic reforming process for producing hydrogen takes place by reacting steam with a light hydrocarbon at 1500 OC in the presence of a catalyst, as follows: CH 4+ H 2 O (g) + heat →catalyst 1 CO+3 H 2 CO+ H 2 O (g) + heat →catalyst 2 CO 2+H 2 And the sum is: CH 4 + 2 H 2 O(g) + heat →catalyst CO 2 + 4 H 2

Activities The following activities could be performed on different chapters of the course: Chapter 5 (Hydrogen energy): Reporting: • Students are asked to write a report on hydrogen storage and transfer. • A report could be written on the techniques used for solar production of hydrogen. Net search: • Student can search on the different chemical materials that could be used as catalysts in thermo chemical process of hydrogen production. • Students can search to determine the types of photo catalysts used in the photo catalytic process for hydrogen production.

Chatting: • Students can chat on the uses of hydrogen in different fields. • Chatting on the advantages of hydrogen as an energy source. • Chatting to discuss the different types of light hydrocarbons that can be used in the steam catalytic reforming process for hydrogen production.

Summary Hydrogen energy This chapter presents the importance o hydrogen as an energy source. The advantages of hydrogen when used as a fuel are given. It is also illustrated the means of hydrogen storage and transfer. Other uses of hydrogen are given. Such uses are: in chemical technology, in metallurgy and refining, in effluent and water treatment and in transportation. The different means of producing hydrogen using solar energy are illustrated. These means are: direct thermal process, thermochemical process, electrolysis of water, the photocatalytic process and the steam catalytic reforming process. Advantages of hydrogen as an energy source are also illustrated in the present chapter.