Development of Bulk Organic Chemical Processes—History, Status, and Opportunities for Academic Research

Abstract

Open AccessCCS ChemistryMINI REVIEW1 Mar 2021Development of Bulk Organic Chemical Processes—History, Status, and Opportunities for Academic Research Carolin Schneider, Thomas Leischner, Pavel Ryabchuk, Ralf Jackstell, Kathrin Junge and Matthias Beller Carolin Schneider Leibniz-Institut für Katalyse e.V., 18059 Rostock , Thomas Leischner Leibniz-Institut für Katalyse e.V., 18059 Rostock , Pavel Ryabchuk Leibniz-Institut für Katalyse e.V., 18059 Rostock Galapagos NV, 2800 Mechelen , Ralf Jackstell Leibniz-Institut für Katalyse e.V., 18059 Rostock , Kathrin Junge Leibniz-Institut für Katalyse e.V., 18059 Rostock and Matthias Beller *Corresponding author: E-mail Address: [email protected] Leibniz-Institut für Katalyse e.V., 18059 Rostock https://doi.org/10.31635/ccschem.021.202000680 SectionsAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail The production of bulk organic chemicals has a strong impact on our daily life. In this review, an overview of important industrial processes using homogeneous catalysts is given. Using specific carbonylation and hydrogenation case studies, we want to show how basic research can contribute to the development of such processes and what challenges exist in this area of academic research. Download figure Download PowerPoint Introduction Industrial organic chemicals continue to have a questionable reputation in our society and are considered to be involved in many environmental and health problems. However, if properly produced and applied, they provide efficient solutions to many long-term problems. In fact, over the past 150 years, the development of the chemical industry, its products, and underlying processes have resulted in key contributions not only improving the quality of all aspects of human living standards but also significantly increasing our life expectancy.1 At present, chemicals are used for a plethora of consumer goods as well as other industrial sectors, including agricultural manufacturing, construction, rubber and plastic products, textiles, petroleum refining, pulp and paper, and primary metals. Since the beginning, the production of synthetic organic chemical products has relied to a large extent on the valorization of available and inexpensive feedstocks, which were subsequently transformed into more valuable and complex products.2 Originally, side-products of the coal industry, such as coal tar, were used and technically applicable processes for synthetic dyes, pharmaceuticals, and polymers were developed. Following this general concept, until today, the production of most organic chemicals depends on fossil-based feedstocks—coal, oil, and gas (Figure 1). However, due to current efforts towards a more sustainable world and circular economy, an increasing number of chemical products are likely to be produced from renewables over the next few years. Figure 1 | Valorization of basic feedstocks. Download figure Download PowerPoint Typically, the final products of the chemical industry are subdivided into basic chemicals, fine and specialty chemicals, and consumer products. Bulk or so-called commodity chemicals are manufactured on a large scale to cover global demand, while fine chemicals are produced in small and limited quantities (<1000 tons/year).3 Consequently, the valorization of the applied raw materials has improved and the corresponding processes have been highly optimized. Due to the high volumes, most bulk chemicals are produced in dedicated continuous process plants. In contrast, fine chemicals are typically manufactured in batch reactors and multipurpose plants. For bulk processes, cost-efficiency is a focal point and the revenue per unit is relatively low; however, the financials are based on volume and the overall profit is satisfactory. On the other hand, fine chemicals are more expensive and their cost is correlated with their performance. Usually, they are highly useful building blocks, influencing our everyday life through combinations with other chemicals or substrates to generate, for example, specific materials, drugs, fragrances, or food additives. In this review, we are going to provide the reader with an overview of important bulk chemical processes featuring homogeneous catalysts. Moreover, we are going to demonstrate based on two specific case studies: (1) How academic research can contribute to the development of related processes? (2) What challenges exist in this area? The Importance of Bulk Chemicals In general, in this review, the term bulk chemicals is used for products manufactured on a large scale (>100,000 tons/annum) from primary feedstocks (oil, gas, coal, and biowaste) that take only a few steps. Other characteristics are their less complex chemical structures and a relatively low cost (<1–2€/kg). In Scheme 1, a typical selection of bulk chemicals is shown.3,4 For such products, the manufacturing processes are generally known and often commercially available from engineering companies. Although the necessary technologies are accessible, an important barrier to entry bulk chemical manufacturing is the considerable investment in a new plant. Thus, the implementation of new technologies is not simply a question of innovation or the efficiency of the respective process. Scheme 1 | Selected examples of bulk chemicals and their average prices from January 2010 to February 2014 with standard deviations for northwestern Europe (price in €/kg).4 Download figure Download PowerPoint Most bulk chemical production sites operate continuously utilizing heterogeneous catalysts. However, in several specific cases, for example, carbonylation and oxidation, homogeneous catalysts are also used. An important parameter when evaluating the efficacy of such a process is the space time yield of the catalyst system. Although the direct costs for the catalyst system are typically extremely low (<1 cent/kg product), it has a strong influence on the overall process costs, due to its control of substrate conversion and product selectivity. Industrial Processes with Homogeneous Catalysts: From Past to Present The term catalysis was coined by Berzelius in 1836, even though biocatalysts (enzymes) had already been used since ancient times to produce alcoholic beverages (on large scale). The first examples of "modern" industrial catalytic processes, such as the Deacon process (oxidation of HCl into chlorine) and the production of sulfuric acid, were developed without an in-depth understanding of the underlying chemical reactions. Since the beginning of the 20th century, catalysis has had a tremendous impact on the chemical industry and the development of its processes. A timeline of selected milestones of industrial discoveries and realizations is shown in Scheme 2. An industrial landmark innovation was the realization of the Haber–Bosch process in 1913, allowing the production of ammonia from dinitrogen and H2. This process laid the foundation for the development of many high-pressure reactions on an industrial scale. Today's most important example of bulk chemicals being produced in the presence of a homogeneous catalyst was discovered by Otto Roelen at Ruhrchemie, Germany, in 1938. Specifically, he observed the formation of aldehydes from olefins and CO in the presence of a cobalt catalyst. The underlying principles and chemical reactions were investigated in-depth in the decades after and resulted in significantly more efficient Rh-based catalyst systems. In the 1950s and 60s, processes including the Wacker oxidation of ethylene and the carbonylation of methanol to acetic acid (Monsanto process), were invented and marked the beginning of the prevailing role of noble metals in industrial catalysis. Scheme 2 | Selected milestones of industrial chemistry. (Company names are given when a process was established, while concepts with later launched processes are given without company names.) Download figure Download PowerPoint Xylene Oxidation (AMOCO Process) Based on the low costs and availability of feedstocks with only C–C and C–H bonds (alkanes, alkenes, and arenes), oxidation reactions to introduce oxygen atoms or hydroxyl groups are of fundamental industrial importance for a fossil-based chemical industry. In this respect, one of the most prominent examples is the oxidation of para-xylene to yield terephthalic acid (TPA). As one of the main components in the polyester industry, it is mainly used to produce polyester terephthalate (PET) and polyester fibers. Scheme 3 | Xylene oxidation under the conditions of the AMOCO process and its reaction pathway. Download figure Download PowerPoint Initial experiments to prepare TPA can be traced back to photochemical investigations performed by Ciamician and Silber in 1912.5 They investigated the effect of light on the oxidation of certain benzene derivatives. After a continuous reaction of 1 year (!), they obtained TPA and p-toluic acid.6 Later, further efforts in this direction were conducted by Stephens7; however, these studies were similarly not applicable on an industrial scale, based on the long reaction time. Today, 70% of TPA for PET production is obtained from the oxidation of para-xylene.8,9 Notably, for TPA applications, a highly selective process is necessary (impurities <25 ppm), which avoids costly purification steps.10,11 To design an easier and better purification process, esterification with methanol was introduced, resulting in the formation of dimethyl terephthalate (DMT). Initially, the oxidation reaction to produce p-toluic acid was performed with no solvent at a temperature of 180 °C and an air pressure of 0.8 MPa in the presence of a cobalt catalyst. DMT was eventually formed after esterification, a second oxidation step, and another esterification reaction.12 Obviously, this process is complicated and resulted in increased costs. However, in 1955, a cobalt-catalyzed air oxidation in the presence of bromide ions provided a solution to this problem. This so-called AMOCO process was subsequently commercialized in the late 1970s (Scheme 3).13,14 Since then, several attempts have been made to further improve this process by means of, for example, reaction in sub- or supercritical water,15,16 catalyst heterogenization,17–20 using carbon dioxide as a co-oxidant, or alternative promoters.21–23 However, each of these efforts have not replaced the original AMOCO process. Under optimal conditions, more than 98% of para-xylene reacts to the desired product with selectivities around 95% within 8–24 h. Although the high yield and selectivity are remarkable, there are interests toward an improved process due to environmental problems. This is especially true for the replacement of bromide, which forms highly toxic side products.24 The largest commercial production plants are run by British Petroleum (BP), BP Zhuhai Chemical Co., Ltd., and JBF Petrochemicals Ltd. (JBF) and produce more than 10 MT TPA per annum.25 In addition, the license for production is also owned by DuPont, Dow Chemical, Mitsubishi Chemical, Eastman Chemical, Hitachi, Mitsui Chemicals, Interquisa, and Grupo Petromex.26 Oxo-Synthesis A serendipitous discovery led to the largest application of homogeneous catalysis in industry. Initially working on Fischer–Tropsch reactions with heterogenous cobalt catalysts, Otto Roelen observed the formation of aldehydes and ketones in the reaction of alkenes and synthesis gas (syngas).25,,28 Typically, in this reaction, a mixture of linear and branched aldehydes (n-aldehydes and iso-aldehydes, respectively) is formed as major products (Scheme 4). Scheme 4 | General reaction scheme for a hydroformylation reaction. Download figure Download PowerPoint Remarkably, the first industrial unit was built only 4 years later after the discovery of the reaction at IG Farben Leuna/Merseburg in Germany. In 2008, nearly 10.4 million metric tons of oxo chemicals had been produced,29 while each plant is producing several hundred thousand metric tons per year. Due to the versatility of the formed aldehydes, it is possible to produce aliphatic alcohols, esters, and amines with follow-up reactions. Literature analysis demonstrates that there has been a steady increase of scientific publications on various aspects of hydroformylations, while the number of patent applications is stagnating.30 Over the years, several companies have performed oxo reactions and applied this methodology on an industrial scale. For instance, BASF, Exxon, Sasol, and Shell have used cobalt catalyst systems with less syngas at temperatures from 120 to 190 °C and pressures of 4–30 MPa. Furthermore, Shell have applied cobalt-derived systems for the preparation of high-boiling aldehydes or alcohols.31 For nearly 30 years, cobalt-based catalysts have overwhelmingly been used in hydroformylation reactions. However, in the 1970s, phosphine-modified Rh-complexes were introduced. Despite the much higher cost of rhodium, these systems have proved to be superior for short-chain olefins, due to the possibility to work at low pressures (1.8–6.0 MPa) and medium temperatures (85–130 °C).32 Especially, "low-pressure oxo processes" (LPOs) of ethylene, propene, and butenes are now commonly applied in industry and cover 70% of the hydroformylation capacity (e.g., Dow Chemical, BASF, and Mitsubishi).30 With respect to reactivity of [HM(CO)xLy]-type metal complexes in hydroformylations, the following order of activity is observed33: Rh ≫ Co > Ir , Ru > Os > Pt > Pd ≫ Fe > Ni Consequently, it is unsurprising that today only rhodium- and cobalt-based catalysts are applied in industry. Due to the necessity of harsh reaction conditions using cobalt, rhodium is mainly used in modern developments. Interestingly, in 1980, only 10% of the industrial hydroformylation capacities were rhodium-based, while only 15 years later, roughly 80% feature rhodium as the catalyst metal.34 In a few cases, bimetallic systems have been applied, whereby Co-salts were added in low concentrations to prevent catalyst deactivation via impurities (e.g., sulfur compounds or butadiene).35 In hydroformylation processes, the active catalyst determines the overall economics to a substantial extent.30 Thus, there is high demand for tailor-made ligands in these reactions. Their cost and long-term stability are also crucial points for the overall cost of the industrial process. As a result, numerous ligands have been developed for diverse industrial applications (Scheme 5).30 Scheme 5 | Selection of industrial relevant ligands. Download figure Download PowerPoint Shell Higher Olefin Process The Shell higher olefin process (SHOP) allows the production of linear alpha olefins from simple ethylene (Schemes 6 and 7). The key step of the process is a homogeneous nickel-catalyzed oligomerization followed by isomerization and metathesis reactions.36 In the first step, a mixture of linear olefins ranging from C4 to C30+ is produced. Via distillation, it is possible to separate a C6–C18 mixture, which is further fractionated to yield starting materials for synthetic lubricants, plasticizer alcohols, detergent alcohols, or synthetic fatty acids. Lighter (<C6) and heavier (>C18) alkenes undergo double-bond isomerization in the presence of potassium metal catalysts. In the final and third step, metathesis of this isomerized mixture with ethylene is performed using an alumina-supported molybdate catalyst. The main products of interest are higher olefins, which are further used in industry to give so-called fatty alcohols, which are precursors for plasticizers and detergents.37 The annual global production of alpha olefins through this method is over 1 million tons per annum.38 Shell is selling their linear alpha and internal olefins under the Neodene label.39,40 Scheme 6 | Reaction scheme for the Shell higher olefin process. Conditions are depenent on the reaction step. Download figure Download PowerPoint Originally, this process was developed by chemists at Shell Development in Emeryville, CA (USA) in a collaboration with the Royal Shell Laboratories at Amsterdam in the Netherlands.41–49 Interestingly, this process constituted the first industrial realization of a two-phase liquid/liquid technology, whereby in the ethene oligomerization step, a nickel-phosphine catalyst (80–120 °C, 7–14 MPa) was dissolved in 1,4-butanediol, while the olefinic products form a second phase, allowing an easy product/catalyst separation.50 Scheme 7 | Comparison of electrolysis pathway and direct hydrocyanation to give adiponitrile. Download figure Download PowerPoint Evidently, the development of the active nickel catalyst was inspired to a large extent by the basic work of Ziegler and Wilke at MPI Mülheim, Germany.51,52 Based on their studies, Keim at Shell introduced P–O chelate ligands for this process (Scheme 6)53–61 and performed detailed mechanistic studies.62–69 Although this process was very innovative from the viewpoint of basic science too (the first applied technology for biphasic catalysis), it did not inspire many scientists, simply because it was not known at the time to academic research groups. Hydrocyanation Another example of the application of molecular catalysts for bulk chemical production in industry is the hydrocyanation reaction of 1,3-butadiene. To date, this transformation is the basis for the production of Nylon (polyamide 6,6), one of the most important synthetic fibers. During the 1930s, researchers at DuPont, the developer of Nylon 6,6, looked for economic ways of a direct addition of hydrogen cyanide (HCN) to 1,3-butadiene. Initially, however, an indirect hydrocyanation was used by DuPont (Scheme 7).70 In this stoichiometric process, 1,3-butadiene was treated with chlorine to give 1,4-dichlorobut-2-ene, which was reacted with sodium cyanide to give adiponitrile. Obvious disadvantages of this scheme were the use of chlorine,71 and the number of steps. Hence, a more efficient process was highly desired. At the time, the direct addition of HCN to unsaturated carbon–carbon bonds was known on a small scale, but none of these routes proved to be industrially feasible.72,73 Even though first experiments with homogeneous catalysts were not delivering adiponitrile,74 the work of Drinkard, who introduced tetrakis(triethyl-phosphite)nickel(0) for hydrocyanation of 1-hexene,75 and further studies,75–77 finally resulted in a commercial process at DuPont. The current path for adiponitrile synthesis can be divided into two steps. First, 1,3-butadiene and HCN react in the presence of a tailored Ni[(ArO)3P]4 catalyst system to yield linear 3-pentenenitrile and branched 2-methyl-3-butenenitrile (approximate ratio 2:1) (Scheme 8). The branched product can be isomerized to the linear isomer in the presence of a Lewis acid promoter. Finally, kinetically controlled isomerization of the double bond with a hydridonickelcomplex and selective HCN addition leads to the desired adiponitrile with >90% yield.71,78 The first plant to produce adiponitrile using this technology began operation in 1971. It should be mentioned that aside from this process, adiponitrile is also manufactured by electrosynthesis using acrylonitrile as the raw material. This technology is used by BASF and Monsanto.79 Scheme 8 | Adiponitrile from 1,3-butadiene. Download figure Download PowerPoint Development of New Processes It is well known that our civilization faces severe challenges and problems in the coming decades, which will likely not be solved based on today's technologies. Indeed, we must establish a renewable energy system, produce enough food and clean water for a and at the time use less and improved ways to the carbon of our products, and of these will also on the chemical industry to new and improved processes. At the time, the of new should not be As an example, is one of the most in and In this the use of fossil-based raw materials in the chemical industry is Furthermore, there is the carbon dioxide to be in the coming years, which will provide a strong toward more a sustainable and production of chemicals as well as a toward renewable feedstocks. Obviously, technologies for a typical plant scale of tons per is not an easy due to the large investment of the Hence, of technologies are much more likely than process For example, it is more that carbonylation reactions in the will be run with carbon by carbon dioxide which is from renewable than new reactions. At this it must be that most organic bulk chemicals are in strong global the costs of the products be higher even if the new process is more What is the role of in this To be without industrial for at it is very to the challenges of a new process and often solutions for are developed and in highly scientific Hence, we is a for basic science can processes, but such time. The typical industry and academic research groups with a of years is simply too are that industry and from In the following two case studies will be our in this The following two case studies will give our on which can be when academic and industrial researchers work in on the development of new processes. The first case is based on a long-term with a company in the of carbonylation while in the second example, a with a our work on methanol In cases, the importance of improved catalyst systems will be for carbonylation reactions an important to produce aldehydes and a of acid derivatives. Hence, using starting materials such as and or the corresponding esters, aldehydes, and are available on the of carbonylation reaction. the most relevant of carbonylation is based on olefins, which have been by industrial Otto Roelen and and after the original the first oxo the underlying In addition to olefins, carbonylation of methanol to produce acetic acid one of the largest homogeneous carbonylation process. methanol reacts in with hydrogen to which is by a rhodium (Monsanto or For olefin carbonylation processes and methanol the of the respective catalyst system over the years have for major economic and as well as the of new As an example, discovered a highly efficient reaction using to yield in the presence of a specific complex (Scheme Scheme | Reaction pathway using to produce by Download figure Download PowerPoint problems with the a final commercial Due to interest in the carbonylation of ethylene was further investigated by After this reaction the basis of the so-called process (Scheme which was first commercialized in and is producing tons of per for its implementation was the use of the tailored in the presence of an To be without this no process have been to catalyst produce metric tons of the be produced with a selectivity under conditions From the there is a cost of with or other C4 Scheme 10 | Reaction scheme for the process for Download figure Download PowerPoint at the process, it is researchers around the world continue to be active in the of ligands for molecular catalysts in carbonylation and related processes. In this respect, our has a of producing new ligands and evaluating the corresponding metal complexes in various catalytic reactions. we first in the process within the of a long-term industrial with In several with industrial the question was if this reaction can be used for other less olefins than Especially, we were to if it was possible to also of olefins a major of which is an important industrial Hence, we a catalyst for the of as a system for highly After a selection of commercially available including structures and catalysts, we did not Obviously, to the of olefins, the development of a new catalyst system is To we on the of key reactions of the known catalytic that to be to improve to the the formation of a metal complex is for a catalytic A major for olefins are the isomerization to a more as well as the of the final Based on mechanistic studies, we that the of the had to be which can be by a On the other hand, a strong acid is to form the active Obviously, this a that must be that the use of an within the to this problem. Hence, inspired by the work of a of the was (Scheme Indeed, with this in it possible to a of highly olefins in to With respect to this catalyst known carbonylation catalysts by Specifically, in the presence of the olefins such as ethylene and were in at °C and temperature within 10 and 30 Notably, the no conversion in the In

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