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Catalyst developments: The past 90 years

07.01.2012  |  Heinen, R. ,  IHS Chemical, The Woodlands, Texas

While catalysis has made many advances in the last 90 years, the application of new technologies developed in other areas may offer great promise for future breakthroughs.

Keywords: [catalyst] [refining] [polymers] [hydrocracking] [petrochemicals] [alkylation] [Ziegler-Natta] [metallocenes]

Prior to 1922, the development of three important German catalytic processes had shown the potential impact that catalysis could have on the process industry. One was the so-called contact process for producing sulfuric acid catalytically from the sulfur dioxide generated by smelting operations. Another was the catalytic method for synthetic production of the valuable dyestuff indigo. The third was the catalytic combination of nitrogen and hydrogen for the production of ammonia—the Haber-Bosch process for nitrogen fixation.

Present day value

The impact of catalysis is substantial with over 90% of all industrial chemicals produced aided by catalysts. Annually speaking, process catalysts have become a $13 billion business worldwide. The value-added products dependent on process catalysts include petroleum-based products, chemicals, pharmaceuticals, synthetic rubber, plastics and many others. The annual value of catalyst-aid products is estimated at $500–600 billion.

The definition of a catalyst that was coined in the 19th century is still used today: a substance that alters the velocity of a chemical reaction without itself being consumed. Although that is theoretically true, in practice, catalysts decrease in activity with use and suffer losses in material handling, thus requiring periodic replacement. These factors, together with economic growth and discoveries of new applications contribute to the continued growth of the catalyst business.

The other side of the picture is the drive to find more-efficient, long service life, more active and selective catalyst systems. Economic and practical considerations provide incentives to develop new catalysts, along with a greater understanding of catalysis systems in general. Development is further driven by the need for new sources of energy and chemicals, concern over environmental pollution, desire and demand for new products, and the cost and potential restrictions on the availability of the noble metals used in many catalysts.

CATALYSTS TAKE OFF

The rapid growth of catalysis began around the time of World War II (WWII) with the development of catalytic cracking of crude oil. The process enabled the breaking of large hydrocarbon molecules into smaller compounds needed to process transportation fuels and petrochemicals. An important process breakthrough was the Houdry process that coupled the endothermic cracking reaction with the exothermic reaction (heat is released) of catalyst regeneration in a cyclic, continuous operation. The wartime need for toluene feedstock for trinitrotoluene (TNT) production supported the development of catalytic reforming processes—the dehydrogenation, cyclization and isomerization of aliphatic hydrocarbons obtained from crude oil to form aromatic compounds. Owing chiefly to this process, toluene production increased tenfold from 1940 to 1944, to 1 billion liters.

Significant developments since the 1940s have made catalytic processes even more important to the modern petroleum refining and petrochemical/chemical processing industries. These have included the emerging metallocene and other single-site catalysts (SSCs) for the polymerization of olefins, the Ziegler-Natta titanium (Ti) halide–aluminum alkyl catalysts, zeolite catalysts for petroleum refining and petrochemicals production, catalysts for the oxo reaction to convert olefins to aldehydes and catalysts for the reaction of diisocyanates with polyols to produce polyurethanes.

Refining industry

Petroleum refining, for example, is the source for the largest share of industrial products. Upgrading crude oil technology consists almost entirely of catalytic processes. In 2009, catalysts for the refining market were a $3.2 billion business worldwide. The largest catalyst segment in terms of value is catalytic cracking, while the largest-volume products are alkylation catalysts. Other major refinery catalyst market sectors, in terms of value, include hydrotreating, reforming and hydrocracking.

Worldwide environmental regulations now mandate the production of cleaner fuels. Consequently, refiners are experiencing severe pressures from market forces that demand a change in the product mix, aside from quality. On the regulatory side, stringent product specifications limit sulfur content along with changes in gasoline and diesel composition. Major technological challenges to refining operations include achieving “zero” or heavily reduced sulfur content in all fuel for almost all countries around the world. The phase-out of methyl tertiary butyl ether (MTBE) in reformulated gasoline in the US and other nations has forced operating changes for reformer operations to achieve the required high-octane number of gasoline-blending components. Environmental pressures have become the major driving forces in catalysis and process design, as modifications and/or new technologies are required to facilitate compliance with the regulations, while still allowing the hydrocarbon processing industry to economically provide hydrocarbon-based products without interruption and meet the increasing needs of the growing global population.

  Fig. 1. New UOP catalytic cracking unit installed
  at the Rock Island Refinery. Petroleum Refiner,
  October 1949.

Polymerization catalysts

Polymerization catalyst sales in 2009 were estimated at $4.3 billion. Major market segments include polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyvinyl chloride (PVC) and polystyrene (PS). Polyolefin catalysts are the largest single market sector, with about a 50%–60% market share of the total poly-merization market, equivalent to about $2.2–2.6 billion. Significant new technical developments that were introduced commercially since the 1990s are:

  • SSCs for polymerization offer tremendous opportunities for polyolefins development
  • Polymers with closely controlled molecular-weight distributions allow greater control over properties and facilitate new product applications.

Metallocenes, the initial class of SSCs developed, are very expensive. Less complicated ligands are used in metallocene catalysts for PE than for PP, facilitating PE catalyst development. Technical improvements have reduced the cost of metallocene-produced polymers to levels that are more competitive with those produced with conventional Ziegler-Natta polymerization catalysts. Polymers based on SSCs have unique properties and are creating new markets. Even in the existing market, some metallocene-based polymers can be competitive with conventional polymers, which has added a new dynamic to some applications.

Advanced Ziegler-Natta catalysts have been developed; these catalyst systems can produce polyolefins with properties similar to those produced by metallocenes. We expect that Ziegler-Natta catalysts will remain the dominating technology due to cost benefits.

We will summarize some of the major developments in catalysis that have occurred over the last 90 years. While the list of advances and the implications of these developments on the process industry are too numerous to list, they represent some of the most noteworthy.

  Fig. 2. The arrival of a 96-ton cat-cracker
  reactor is part of an expansion at the Anglo-
  Iranian Oil Co.’s Grangemouth, Scotland,
  refinery. On the left is the topping unit; the
  catalytic cracker is under construction, as
  shown on the right of the photo. Petroleum
  Refiner,
May 1952.

PETROLEUM REFINING CATALYSTS

The major processes involved in petroleum refining are distillation, catalytic hydrotreating, catalytic reforming, isomerization, catalytic cracking, catalytic hydrocracking, alkylation and thermal operations. Only distillation and thermal operations involve no catalysts. The utilization of each refining process depends on the quality of the crude oil and the demand for the various product streams and products. Many of the advances in refining process technology were possible due to catalyst developments. Much of this work was driven by the need to increase production of the refined products needed to support the war efforts in the mid-1900s. These developments provided the basis for many processes that are common processing practices in the present-day refining industry.


  Fig. 3. View of the new catalytic
  cracking and thermal refining unit for
  West Germany’s newest refinery
  constructed by Esso A.G., a German
  affiliate of Standard Oil Co. (New
  Jersey). The $12 million expansion is
  located in Hamburg, Germany, and
  replaces the older refinery destroyed
  during WWII; it is the most modern
  refinery in Europe. Petroleum Refiner,
  May 1954.

Catalytic cracking

The first full-scale commercial catalytic cracker for the selective conversion of crude petroleum to gasoline went on stream at the Marcus Hook refinery in 1937. Pioneered by Eugene Jules Houdry (1892–1962), the catalytic cracking of petroleum revolutionized the industry. The Houdry process conserved crude oil by doubling the amount of gasoline produced by other processes. It also greatly improved the gasoline octane rating, making possible today’s efficient, high-compression automobile engines. During WWII, the high-octane fuel shipped from Houdry plants played a critical role in the Allied victory.

The most dramatic benefit of the earliest Houdry units was in the production of 100-octane aviation gasoline, just before the outbreak of WWII. The Houdry plants provided a better gasoline for blending with scarce high-octane components, as well as byproducts that could be converted by other processes to make more high-octane fractions. The increased performance gave Allied planes some advantage over the Axis. In the first six months of 1940, at the time of the Battle of Britain, 1.1 million bbl/month of 100-octane aviation gasoline was shipped to the Allies. Houdry plants produced 90% of this catalytically cracked gasoline during the first two years of the war.

The original fixed-bed Houdry process units have been outmoded by engineering advances that transformed the fixed-bed to more economical fluidized-bed systems, and introduced the use of crystalline aluminosilicate catalysts to provide higher gasoline yields. Yet, it is remarkable that, 70 years after Houdry’s discovery, the same fundamental principles are still the primary platform for manufacturing gasoline worldwide.

Donald Campbell, Homer Martin, Eger Murphree and Charles Tyson were known for their development of a process still used today to produce more than half of the world’s gasoline. These “four horsemen” were part of the Exxon Research Co. They began thinking of a design that would allow for a moving catalyst to ensure a steady and continuous cracking operation. The four ultimately invented a fluidized-solids reactor bed and a pipe-transfer system between the reactor and regenerator unit in which the catalyst is processed for re-use. The fluid catalytic cracking (FCC) process revolutionized the petroleum industry by more efficiently transforming heavier oil fractions into lighter, usable products. Catalysts for this process have evolved significantly over the past 30 years from the original amorphous silica/alumina products. Essentially all commercial gasoline refining processes now use zeolite catalysts, and FCC is the largest market for zeolites.

Catalytic hydroprocessing

Reactions involving catalytic hydrogenation of organic substances were known prior to 1897. The property of finely divided nickel to catalyze the fixation of hydrogen on hydrocarbon (ethylene and benzene) double bonds was discovered by the French chemist Paul Sabatier who found that unsaturated hydrocarbons in the vapor phase could be converted into saturated hydrocarbons by using hydrogen and a catalytic metal. His work was the foundation of the modern catalytic hydrogenation process.

Soon after Sabatier’s work, a German chemist, Wilhelm Normann, found that catalytic hydrogenation could be used to convert unsaturated fatty acids or glycerides in the liquid phase into saturated ones. He was awarded a patent in Germany in 1902 and in Britain in 1903, which was the beginning of what is now a worldwide industry.

In the mid-1950s, the first noble metal catalytic reforming process (UOP’s Platformer Process) was commercialized. At the same time, the catalytic hydrodesulfurization (HDS) of the naphtha feed to such reformers was also commercialized. In the decades that followed, various proprietary catalytic HDS processes have been commercialized. Most refineries have one or more HDS units.

Catalytic hydrocracking

Hydrocracking was first developed in Germany as early as 1915 to provide coal-based liquid fuels from domestic coal deposits. The first plant that might be considered as a commercial hydrocracking unit began operation in Leuna, Germany, in 1927. Similar efforts to convert coal to liquid fuels took place in Great Britain, France and other countries. Between 1925 and 1930, Standard Oil of New Jersey collaborated with I.G. Farbenindustrie of Germany to develop a hydrocracking technology capable of converting heavy petroleum oils into fuels. Such processes required pressures of 200 bar—300 bar and temperatures of over 375°C, and they were very expensive.

In 1939, Imperial Chemical Industries (ICI) of Great Britain developed a two-stage hydrocracking process. During WWII, this two-stage hydrocracking process helped refiners in Germany, Great Britain and the US to supply the needed volumes of aviation gasoline. After WWII, hydrocracking technology became less important, as increased availability of petroleum crude oil from the Middle East removed the motivation and the economics to convert coal into liquid fuels. Newly developed FCC processes were more economical than hydrocracking to convert high-boiling petroleum oils to fuels.

In the early 1960s, hydrocracking become economical in part due to the introduction of zeolite-based catalysts, during the period from about 1964 to 1966. Zeolite-based catalysts performed much better than the earlier catalysts, and these catalysts permitted operation at lower pressures. The combination of higher performance and lower operating pressures significantly reduced the cost of building and operating hydrocrackers.

Alkylation

The alkylation process started with an observation that puzzled Herman Pines in 1930 when he was working in the lab of Universal Oil Products (UOP). While vigorously shaking petroleum fractions with concentrated sulfuric acid in a calibrated glass cylinder to determine how much of the oil dissolved in the aqueous acid phase, Pines observed that, after a few hours, the phase boundary between oil and acid had shifted again. Apparently, paraffins had formed from the olefins. Pines concluded that this process required the simultaneous formation of a highly unsaturated coproduct, which remained dissolved in the aqueous phase in a process called “conjunct polymerization”.

Alkylation was commercialized in 1938, and experienced tremendous growth during the 1940s stemming from demand for high-octane aviation fuel during WWII. After the war, refiners’ interests shifted from producing aviation fuels to using alkylate as a blending component in gasoline motor fuels. Alkylation capacity remained relatively flat through the 1960s due to the lower cost of other blending components. When the US Environmental Protection Agency’s lead phase-down program began in the 1970s and completed in the 1980s, alkylate demand sharply increased. Alkylate was sought as a blending component to compensate for lead removal from gasoline. As additional environmental regulations were imposed worldwide, the importance of alkylate as a blending component for motor fuel increased.

Catalytic reforming

In the 1940s, Vladimir Haensel, while working for UOP, developed a platinum-based catalytic reforming process for producing a high-octane gasoline from low-octane naphthas known as the UOP Platforming process. Haensel’s process was commercialized by UOP in 1949 when the first Platforming unit was built by the Old Dutch Refining Co. in Muskegon, Michigan.

Dr. Sinfelt, at Standard Oil Co., was researching alternate petroleum conversion chemistries and developed the application of novel, highly active and selective bimetallic-cluster catalyst systems to produce high-octane motor gasoline without lead additives. Earlier work on metal alloys had demonstrated the relation between catalytic performance of a metal and its electron band structure. However, the possibility of using this to catalytically influencing the selectivity of chemical transformations (product selectivities) had not been considered. Dr. Sinfelt, through in-depth studies on bimetallic catalysts, discovered how to influence chemical reaction selectivity. He discovered that it is possible to catalyze one type of chemical reaction in preference to others that are thermodynamically favorable. He showed that bimetallic catalysts could be used to effectively reduce undesirable competing reactions. This made possible the economic conversion of low-octane-number molecules to high-octane number molecules.

Many versions of this process have been developed by the major oil companies and other organizations. In 1971, UOP commercialized a fully regenerative reforming process called continuous catalysis regeneration (CCR). The Institut Français du Pétrol (IFP) also offers a CCR process. This process stacks the reactors so that the catalyst may be withdrawn from the bottom reactor, regenerated and fed back to the top reactor without interrupting operations. The process uses lower operating pressures, thereby increasing the yield of hydrogen and aromatics and improving the octane rating.

PETROCHEMICAL PROCESSING CATALYSTS

Ziegler-Natta catalysts

German Karl Ziegler, for his discovery of the first titanium-based catalysts, and Italian Giulio Natta, for using them to prepare stereo-regular polymers from propylene, were awarded the Nobel Prize in Chemistry in 1963. Ziegler discovered the basic catalyst systems for polymerizing ethylene to linear high polymers. Ziegler’s research had started with propylene but was unsuccessful, and he then shifted his focus to ethylene. Natta was a professor at the Institute of Industrial Chemistry at Milan Polytechnic and was a consultant for Montecatini. Natta learned of Ziegler’s success with ethylene polymerization and pursued propylene polymerization, thus determining the crystal structure in 1954 for which Ziegler and Natta were awarded the Nobel Prize in Chemistry.

In the early 1950s, workers at Phillips Petroleum discovered that chromium (Cr) catalysts are highly effective for the low-temperature polymerization of ethylene. A few years later, Ziegler discovered that a combination of TiCl4 and Al(C2H5)2Cl gave comparable activities for PE production. Natta used crystalline α-TiCl3 in combination with Al(C2H5)3 to first produce isotactic PP, which decreased the atacticity, and it was key to PP market development. Usually, Ziegler catalysts refer to Ti-based systems for conversions of ethylene, and Ziegler-Natta catalysts refer to systems for conversions of propylene. In the 1970s, magnesium chloride (MgCl2) was discovered to greatly enhance the activity of the Ti-based catalysts. These catalysts were so active that the small amount of residual Ti was no longer removed from the product. They enabled commercialization of linear-low-density PE (LLDPE) resins and it allowed the development of noncrystalline copolymers.

  Fig. 4. Catalytic cracking unit No. 3—the largest
  cat cracker in Amoco Oil’s Texas City refinery
  will be among the units modified to process
  high-sulfur crude oils. Hydrocarbon Processing,
  October 1973.

Ziegler-Natta catalysts have been used in the commercial manufacture of various polyolefins since 1956. In 2010, the total volume of plastics, elastomers and rubbers produced from alkenes with these and related catalysts worldwide exceeded 100 million metric tons. Together, these polymers represent the largest-volume commodity plastics, as well as the largest-volume commodity petrochemicals in the world.

Metallocenes

One of the most exciting developments in chemical-process catalysts is the new class of SSCs—metallocene and nometallocene. Polymers based on SSCs have unique properties and are creating new markets. Even in the current market, some metallocene-based polymers, especially LLDPE, are replacing conventional polymers.

Metallocene catalysts are just as old as the Ziegler-Natta systems, but the first systems using them were found to have low activity. It wasn’t until 1980, when metallocene catalysts were put together with a methyl aluminoxane cocatalyst, that their full potential was realized. Their big advantage over the Ziegler-Natta systems is that these systems catalyze the reaction of olefins through only one reactive site. Due to this “single-site” reaction, the polymerization continues in a far more controllable fashion, leading to polymers with narrow molecular weight ranges and, more importantly, predictable and desirable properties. Also, it has been found that changing the ligands (functional groups attached to the metal) within the metallocene molecule can controllably affect the properties of the polymer. This is very attractive to petrochemical companies trying to keep up with the demand for engineered plastics.

  Fig. 5. Qatofin’s Ras Laffan, Qatar, complex is
  one of the latest world scale olefins and
  polyethylene manufacturing sites. Hydrocarbon
  Processing,
April 2011.

Research and development

Following the lead of the pharmaceutical industry, oil, petrochemical and catalyst companies are turning to high-throughput screening (HTS), including combinatorial chemistry, to accelerate catalyst development as short as two years, and, therefore, shortening the time-to-market of new products. For example, UOP is developing HTS expertise to develop new catalysts and adsorbents, which it considers to be at the basis of its competitive advantage. Other companies developing their own HTS capabilities include BASF and Johnson Matthey. Research using these methods, as well as banks of microreactors, continues at the R&D centers of the major energy and chemical companies.

In the last two decades, catalyst development has been transitioning from an art form into a science based on advances in physical and chemical instrumentation plus computer-based modeling tools. New initiatives in catalytic processes are focused on reducing cycle time for catalyst discovery and process development from five to ten years down to three to five years. New approaches are designed to integrate and validate catalyst design methodologies along with HTS techniques and process modeling.

Combinatorial chemistry is speeding up innovation and accelerating availability of improved catalytic materials for the chemical industry. HTE refers to high-throughput experimentation. The term combinatorial catalysis is really a misnomer because, although this concept may be used to visualize libraries of catalysts to be tested, it is actually the HTE techniques that are the key to decreasing catalyst development time. The application of HTE to catalyst research requires developing new methods for catalyst preparation, reactors and instrumentation, along with new methods for rapid analysis and information systems capable of handling the large quantities of generated data.

THE FUTURE

The rapidly growing field of biotechnology brings with it opportunities in the field of enzyme-catalyzed reactions. The role of genetically engineered microorganisms in synthesizing rare and valuable peptides used in human therapeutics is now well established. The same techniques of molecular biology can also be used to enhance the properties of enzymes as catalysts for industrial processes.

This approach can potentially revolutionize the applications of biological systems in catalysis. Enzymes and other biological systems work well in dilute aqueous solutions at moderate temperature, pressure and pH. The reactions catalyzed by these systems are typically environmentally friendly in that few byproducts or waste products are generated. The reactions are typically selective with extremely high yields. Enzymes can be used to catalyze a whole sequence of reactions in a single reactor, resulting in vastly improved overall yields with high positional specificity and 100% chiral synthesis in most cases. The improved use of enzyme-based catalyst technology with whole-cell catalysis, reactions catalyzed by single enzymes, and mixed enzymatic and chemical syntheses are all important for fostering new catalyst technology.

Whole cells of various microorganisms are being used more frequently in the catalytic synthesis of complex molecules from simple starting materials. The use of whole microbial cells as biosynthetic catalysts takes advantage of one of the unique properties of enzymes: They were designed by nature to function together in complex synthetic or degradative pathways. Because of this property, whole cells and microorganisms can be used as catalytic entities that carry out multiple reactions for the complete synthesis of complex chiral molecules. A number of specialty chemicals with complex synthetic schemes can be produced most efficiently by intact microorganisms utilizing a series of enzyme-catalyzed reactions designed by nature to work together.

The biotechnology field has a growing number of examples of reactions of industrial significance catalyzed by isolated enzymes. The enzymatic conversion of acrylonitrile to acrylamide was recently commercialized in Japan. Japanese companies and researchers have been very diligent in developing enzymatic processes for the synthesis of fine chemicals. The stereospecificity of enzyme-catalyzed reactions has been used to advantage in polymer synthesis, as well. Workers at ICI have developed a combined enzymatic and chemical process for the synthesis of polyphenylene from benzene. These are only a few of the developments that demonstrate the potential for the process industry to utilize breakthroughs in other areas to improve the range of products that can be produced economically. While catalysis has made great advances over the last 90 years, the application of new technologies developed in other areas offers great promise for future breakthroughs. HP

The author

Russell Heinen is the director of technology services for IHS Chemical and manages the Process Economics Program (PEP), and the Carbon Footprint Initiative. He has 30 years of experience in energy and chemical consulting. He joined IHS in 2010 when SRI Consulting (SRIC) whom he had been with for more than 13 years was aquired by IHS. Based in The Woodlands, Texas, his specific expertise covers natural gas, refining, and chemicals market analysis and technology evaluations. This experience has recently been focused on helping clients to identify new opportunities in the downstream chemical markets and assisting companies with technology evaluations and selections. In addition to these studies, he also is responsible for the Carbon Footprint Initiative, which helps companies understand and manage their strategy related to carbon emissions. Mr. Heinen holds a BS degree in engineering from Rice University in Houston, and received an MBA from the Jesse H. Jones Graduate School of Administration at Rice University in 1982. He is a registered engineer in the state of Texas, and is a member of the American Institute of Chemical Engineers.



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