Introduction: Catalysis in the Chemical Industry

PHILIP HOWARD, GEORGE MORRIS AND GLENN SUNLEY

1.1 Catalysis in the Chemical Industry

1.1.1 The Importance of Catalysis

In 1985 the National Academy of Sciences of the United States published a landmark study "Opportunities in Chemistry" which mapped out some of the important discoveries in the field over the preceding 20 years. The very first point made in the Pimentel Report (named after the chairman of the study group) was that the successful competitiveness of the chemical industry depends critically on the constant improvements of existing processes and the introduction of new ones. Thus advances in chemical catalysis and synthesis hold the key to a successful chemical industry. Indeed they estimated that a large proportion (ca.20%) of the entire US Gross National Product is generated through the use of catalytic processes.

More than 20 years have elapsed since the Pimentel Report and all mankind has benefitted enormously from the improvements to our lives that catalysis has brought. We now have access to cheaper and more effective fuels, to new drugs and medications, new polymers and other materials with useful properties, and new routes to a whole host of commodity and fine chemicals. Especially significant are the new, energy-saving, and environmentally more friendly ("greener") methodologies that chemists have devised to make the chemicals. These changes have largely been brought about by better catalysts. And metal catalysts, developed jointly by industrial and academic chemists, form one of the main classes of present-day industrial catalysts. We now understand how many catalysts work and are beginning to tune them to high degrees of selectivity and activity; in some cases such catalysts now begin to rival enzymes, the catalysts of Nature.

This book is primarily a textbook that aims to help students see chemistry from the perspective of the industrial or academic scientist who wants to find new processes for making compounds. To do this it examines and classifies the transformations that organic compounds undergo when catalyzed by metals. Many new and profitable processes based on metal catalyses have been developed by industry. The intellectual stimulus that the study of catalytic reactions has given to chemistry is also reflected in the award of Nobel Prizes to the many who have made significant contributions to the science of catalysis and the role of metal catalysts, for example, Ostwald (1909), Haber (1918), Bergius and Bosch (1931), Natta and Ziegler (1963), Fischer and Wilkinson (1973), Knowles, Noyori, and Sharpless (2001) and, most recently, Chauvin, Grubbs and Schrock (2005). Their contributions range from the development of basic kinetic principles, to high pressure processes, and to new catalysts for hydrogenation, stereospecific polymerization, enantioselective reactions and olefin metathesis.

Ostwald recognized that catalysis was about the interplay of reaction rates, i.e. the fundamental role played by a catalyst to accelerate one kinetic pathway against several other different thermodynamically feasible pathways. Since the catalyst does not appear in the reaction product, catalysis has been to some extent the Cinderella of chemistry: vital, hard-working, but unrecognized. Although in a few cases consumers buy a product that contains a catalyst: the enzymes in detergents, the cerium oxide coating on the walls of ovens, the car exhaust catalyst, or the yeast to make bread, wine or beer – even there the consumers are not buying a catalyst – they are buying cleaner clothes, washed with less electricity, a self-cleaning oven, a car that pollutes less, and the means to make food and drink. Generally, the value of catalysis lies not in the catalyst itself but in the products or effects they produce.

Catalysts and catalysis are fundamental to being able to produce the fuels, polymers, medicines, plant growth regulators and herbicides, paints, lubricants, fibres, adhesives and a vast array of other consumer products. As well as catalysis contributing some 20% to the Gross Domestic Product of the USA, it is also estimated that 80% of all chemicals processes, with a total value of more than US$1800 billion, involve a catalyst at some point.

In 2001 it was estimated that the world merchant market for catalysts was worth ca. US$25 billion, divided roughly equally between refining, petrochemicals, polymers, environmental (20–25% each) and with about 11% being used in fine chemicals. Refining is about the production of fuels (Chapter 3, Box 2), petrochemicals cover many of the basic commodity chemicals and the monomers required for the polymer industries; fine chemicals include pharmaceuticals and agrochemicals, as well as flavours and fragrances; and environmental is about exhaust gas and waste product clean-up. Vehicle catalytic converters use catalysts, as does the production of the main tonnage polymers: polyethylene, polypropylene, polystyrene, polyvinyl chloride and polyethylene terephthalate.

But these catalyst sales figures do not reflect the number of tonnes or the value added by the catalysts in each sector. For example even though the use of catalysts (by volume) are similar for refining and polymers, the annual world production of gasoline in 2004 was about 1 billion tonnes, that of polyethylene was around 50 million tonnes.

Catalysts add value in many ways, ranging from reducing the cost of manufacture to increasing the quality of a chemical product, to the production of novel chemical compounds and to the reduction in environmental emissions. To take one example, the catalytic cracking of crude oil was started by Houdry in 1936 using simple silica/alumina catalysts in a fixed bed; further development of refining technology has not only enabled huge increases in volumes of gasoline fuel obtained from a barrel of oil (now about 50%), but has also led to dramatic quality improvements by increasing the octane rating, while reducing sulfur and aromatics. Processes used to bring this about include fluid catalytic cracking (FCC), isomerization, catalytic reforming, hydrotreating, and hydro-cracking (see Section 3.2).

Catalytic converters (containing precious metal catalysts dispersed on ceramic honeycomb structures that oxidize carbon monoxide and unburnt hydrocarbons to carbon dioxide and water, and...