Industrial Processes

Monsanto/Cativa Acetic Acid Process

In 2023, 17.88 million tons of acetic acid were produced. Acetic acid is primarily used to make vinyl acetate, which is a vital component in adhesives, paints, chewing gum, and many other common products. In the 1960’s, Monsanto revolutionized the production of acetic acid, utilizing a rhodium-based catalyst to yield a selectivity >99%.

SK. Monsanto Process for Acetic Acid Synthesis. Chem-Station Int. Ed. May 11, 2017. https://en.chem-station.com/reactions-2/2017/05/monsanto-process-for-acetic-acid-synthesis.html Chem-Station Int. Ed. +1

The Monsanto process was eventually replaced by the Cativa process, developed by BP, utilizing an Iridium catalyst instead. The iridium catalyzed reaction was found to be 150 times faster than the reaction with a rhodium catalyst and yields fewer side products. Due to the vast decrease in impurities, the Cativa process takes less energy to purify the acetic acid, making it a greener process, producing roughly 30% less CO2 emissions.

SK. Cativa Process for Acetic Acid Synthesis. Chem-Station Int. Ed. May 11, 2017. https://en.chem-station.com/reactions-2/2017/05/cativa-process-for-acetic-acid-synthesis.html

Ziegler-Natta Polymerization

Ziegler-Natta polymerization is fundamental to the function of society today, being used and built upon to develop polymers such as polyethylene, which is produced in excess of 10 million tons annually to make plastic packaging, bottles, containers, and many other items. Karl Ziegler’s and Giulio Natta’s discovery won them the 1963 Nobel Prize in Chemistry. Ziegler-Natta polymerization relies on predominantly titanium catalysts and are activated by organoaluminum compounds.

Simplified mechanism for Zr-catalyzed ethylene polymerization.

Hydroformylation

Hydroformylation was an accidental discovery made by Otto Roelen in 1938, calling it the ‘oxo process’. This process forms aldehydes from alkenes. Aldehydes are widely used throughout many industries, reaching a production of 10.4 million tons of chemicals made from the oxo process in 2008. this processed is used in the manufacturing of detergents, pharmaceuticals, and organic synthesis. Currently, rhodium or cobalt based catalysts are used in this process due to other transition metals being not reactive enough and the catalyst has a general chemical formula of [HM(CO)xLy]. Rhodium, despite its high cost; is highly preferred to cobalt due to its much less demanding reaction environment.

Haynes, A.; Maitlis, P. M.; Morris, G. E.; Sunley, G. J.; Adams, H.; Badger, P. W.; Bowers, C. M.; Cook, D. B.; Elliott, P. I. P.; Ghaffar, T.; Green, H.; Griffin, T. R.; Payne, M.; Pearson, J. M.; Taylor, M. J.; Vickers, P. W.; Watt, R. J. Promotion of Iridium-Catalyzed Methanol Carbonylation: Mechanistic Studies of the Cativa Process. Catal. Today 2000, 58, 19–32. https://doi.org/10.1016/S0920-5861(00)00263-7:contentReference[oaicite:22]{index=22}

Hydrogenation

Hydrogenation is the process by which hydrogen atoms are added to unsaturated organic molecules, targeting carbon–carbon double or triple bonds. This reaction increases the degree of saturation of a molecule, making it an important reaction that could be used in many different industries, ranging from pharmaceuticals to food processing. Hydrogenation was first studied in the gas phase by French chemist Paul Sabatier in 1897. Sabatier discovered that some metal complexes, in his case, nickel, could speed up the addition of hydrogen to organic compounds, which was a huge advancement in the field of chemistry. This research also influenced German scientist Wilhelm Normann, because in 1903, he patented his liquid-phase hydrogenation in Europe, which was later bought and used by American companies. However, in 1912, Sabatier was awarded the Nobel Prize in Chemistry for his work, and his findings later revolutionized industrial processes, such as the hydrogenation of oils and the production of margarine.

Later researchers found that some of the most efficient metal centers to use in homogeneous hydrogenation include but are not limited to, ruthenium(II), rhodium(I), and iridium(I). One of the most widely used catalysts that was discussed in earlier sections, is Wilkinson's catalyst, [RhCl(PPh₃)₃]. This catalyst is very useful due to its selectivity, since it has the power to reduce alkenes to alkanes and alkyenes to either cis-alkenes or alkanes, and its mild reaction conditions.

Olefin Metathesis 

Olefin metathesis is the process by which two olefins (alkenes) swap substituents when reacted with a metal complex, forming new carbon–carbon double bonds. This reaction is unique because it goes through a four-membered ring intermediate between the two olefins reacting and  "cuts-and-pastes" a carbon and its substituents onto the opposite reactant, forming a new product. This transformation was first observed in the 1950s by chemists at DuPont, although the mechanism wasn’t understood until 20 years later. While Robert H. Grubbs made early contributions to understanding the process, it wasn’t until the early 1970s that French chemists Yves Chauvin and Jean-Louis Hérisson proposed the mechanism we now know, involving a the four-membered ring, or metallacyclobutane, intermediate. Their findings helped pave the way for chemists and the future olefin metathesis research. An example of this being Grubbs and Richard R. Schrock, who both developed highly efficient and versatile catalysts, ruthenium and molybdenum-based, respectively, that had very desirable characteristics, like producing high yields and having high functional group tolerance. Because of the discoveries made in the field, Chauvin, Grubbs, and Schrock were given the Nobel Prize in Chemistry in 2005.