Projected Trends in U.S. Liquid Fuels Demand

1. Projected Trends in U.S. Liquid Fuels Demand • With world oil prices in the range of 15-25 USD/bbl, liquid fuel chemistry is the single most valuable catalytic technology in practice. • Within the gasoline fraction, fuel blend quality is especially • important, with acid catalyzed processes playing the central • role. J.S. Parent

2. Gasoline Blend Formulations J.S. Parent

3. Performance Value of Gasoline Components J.S. Parent

4. Refinery Processes - Applications of Acid Catalysis J.S. Parent

5. Acid Catalysis vs. Metal/Organometallic Catalysis • Where selectivity is concerned, using acid catalysis is akin to performing surgery with farm implements. • wide range of products accessible from carbenium ion intermediates • selectivity for given compounds is very often quite poor • Why acid catalysis for fuel production? • Relatively cheap initiators compared to organometallic compounds • Solid “superacids” allow for heterogeneous, gas-phase chemistry • Fuel performance is insensitive to structure in comparison with drug action, polymer performance. J.S. Parent

6. Estimated Refining Catalysts/Usage in 1987 J.S. Parent

7. General Kinetics of Acid Catalyzed Processes • The acid catalyzed processes utilized for fuel production can be classified as truly catalytic (closed sequences without loss of active species) or as chain reactions (closed sequences requiring initiation and experiencing large-scale deactivation). • Processes generally involve: • 1. Carbenium ion generation • 2. Transformation • olefin isomerization • rearrangement • alkylation • fragmentation (cracking) • hydride abstraction • 3. Chain processes terminate by • hydride abstraction • collapse of ion pair J.S. Parent

8. Carbenium Ion Generation • 1. Protonation of an unsaturated hydrocarbon • If the olefin is not strongly basic, a strong acid is required to generate the carbocation • 2. Protonation of a saturated hydrocarbon • predominant mechanism in the cracking of alkanes • carbonium ion • 3. Electron removal from a neutral molecule J.S. Parent

9. Basicity of Unsaturated Hydrocarbons • The ease of substrate protonation, while easily measured for relatively good bases (ketones, amines, etc), is difficult to estimate for hydrocarbons. • Theoretical estimates of proton affinity for various olefins point to increasing basicity with increased carbenium ion substitution. • Direct measurements of these equilibria are not possible, because several catalytic reactions (polymerization, isomerization, hydride transfer) take place as soon as the carbenium ion is formed in strongly acidic media. J.S. Parent

10. Superacids • Combinations of Lewis and Bronsted acids can create extremely acidic conditions that are needed for hydrocarbon conversions. • Acid Ho • HSO3F -12.8 • BF3 / H2O -11.4 • H2SO4 (98%) -9.36 • HF -10.2 • BF3 / HF -16.8 • TaF5 (10mol%) / HF -18.9 • SbF5 (10mol%) / HF -18.9 • SbF5 / HSO3F -18.9 • The term Friedel-Crafts Acids is often used. These are metal halides, organometal halides or organometals that coordinatively stabilize conjugate bases (anions, conjugate bases of Bronsted acids, halogens) by complexation. AlCl3 activated by HCl is the best known example. J.S. Parent

11. Relative Stability of Alkyl Cations • The stability of alkyl cations is influenced by: • inductive effects (substituents) • hyperconjugation J.S. Parent

12. Hammond’s Postulate • The transition state for alkene protonation closely resembles the carbocation. Therefore, the factors that contribute to the relatively high energy of the carbocation contribute to the instability of the transition state. • Hammond’s Postulate is the assumption that the transition state for the formation of reactive intermediates resembles the intermediates themselves. • Protonation of isobutylene to • give the tertiary carbocation • has the more stable transition • state, and is therefore the • kinetically preferred reaction • pathway. J.S. Parent