HYDROGENATION

1. HYDROGENATION

2. Hydrogenation Mechanism Factors Affecting Hydrogenation Hydrogen sources From Hydrocarbons Steam-Methane Reforming for the production of hydrogen objectives

3. Alkene Reactions A reaction where bonds are broken while hydrogen is added is called hydrogenolysis.

4. Hydrogenation is the addition of hydrogen to a chemical compound. Generally, the process involves elevated temperature and relatively high pressure in the presence of a catalyst. Hydrogenation yields many useful chemicals, and its use has increased phenomenally, particularly in the petroleum refining industry. Besides saturating double bonds, hydrogenation can be used to eliminate other elements from a molecule. These elements include oxygen, nitrogen, halogens, and particularly sulfur.

5. Nickel, copper, and various metal oxide combinations are the common catalysts The catalyst binds both the H2 and the unsaturated substrate and facilitates their union.

6. Alkene Reactions

7. H H B Y H H C C A X Mechanism of Catalytic Hydrogenation:

8. H H H H Mechanism of Catalytic Hydrogenation: B Y C C A X

9. B Y X A H H H C C H Mechanism of Catalytic Hydrogenation:

10. H H H H Mechanism of Catalytic Hydrogenation: Figure 6.1 B Y X A C C

11. B Y X A H H C C H H Mechanism of Catalytic Hydrogenation:

12. Factors Affecting Hydrogenation The Relationship between Process Conditions and their Effects on the Rates of Reaction Reaction Rate Temperature Pressure Agitation Catalyst

13. FOUR PROCESSES: Thermal Decomposition Steam Reforming Partial Oxidation By Product From Catalytic Reforming Hydrogen From Hydrocarbons

15. The bulk of direct hydrogen manufacturing in a petroleum refinery is still accomplished via either steam-methane reforming or steam-naphtha reforming. Partial oxidation of heavier hydrocarbons is also used to a limited extent. Steam-Methane Reforming

17. In the overall steam methane reforming (SMR) reaction, methane reacts with steam at high temperatures and moderate pressures in catalyst-filled tubes to generate synthesis gas, a mixture of hydrogen, carbon monoxide and some carbon dioxide.

19. Both are endothermic, as shown by the positive heat of reaction.

20. The temperature exiting the reformer furnace tubes is usually about 760oC (1,400oF), a level that provides maximum hydrogen production within the temperature limitation of the reformer tube metallurgy.

21. Additional hydrogen can be generated from the carbon monoxide byproduct following the reforming reaction. First, the reformer effluent gas is cooled in two steps to favor the equilibrium toward the right side of the reaction. Water-shift gas reactions

22. The first cooling step is followed by the high-temperature shift reactor, and the second cooling step is followed by a low-temperature shift reactor. Shift reactions are promoted as effluent gas flows down through the fixed catalyst reactor containing a ferric oxide catalyst in accordance with the reaction in Equation 5.

23. Hydrogen purification is generally carried out using one of two approaches — solvent-based systems or pressure-swing adsorption (PSA) processes. Hydrogen purification

24. solvent-based systems

25. The newer PSA process produces a hydrogen stream of four-nines (99.99%) purity. It separates carbon monoxide, carbon dioxide and unconverted hydrocarbons. A bank of adsorbers operates in a cycle where the adsorbers are rotated through a higher-pressure adsorption portion, followed by a pressure reduction, which allows the contaminants to be released from the adsorber. The hydrogen gas passes through the adsorber as almost-pure hydrogen PRESSURE SWING ADSORPTION

26. PSA