Solid acid catalysts commercial

Our thanks go to Engelhard (USA), Mel-Chemicals (UK) Sasol (D), Tolsa (E) and Sud-Chemie (D) for providing the commercial solid acid catalysts. The financial support by Endura and the Ministero dell Istruzione, dell Universita e della Ricerca (MIUR, Roma) is gratefully acknowledged. 

Another recent new application of a microporous materials in oil refining is the use of zeolite beta as a solid acid system for paraffin alkylation [3]. This zeolite based catalyst, which is operated in a slurry phase reactor, also contains small amounts of Pt or Pd to facilitate catalyst regeneration. Although promising, this novel solid acid catalyst system, has not as yet been applied commercially. 

Traditionally, the production of LABs has been practiced commercially using either Lewis acid catalysts, or liquid hydrofluoric acid (HF).2 The HF catalysis typically gives 2-phenylalkane selectivities of only 17-18%. More recently, UOP/CEPSA have announced the DetalR process for LAB production that is reported to employ a solid acid catalyst.3 Within the same time frame, a number of papers and patents have been published describing LAB synthesis using a range of solid acid (sterically constrained) catalysts, including acidic clays,4 sulfated oxides,5 plus a variety of acidic zeolite structures.6"9 Many of these solid acids provide improved 2-phenylalkane selectivities. 

HETACAT An alkylation process using a solid acid catalyst. Not commercialized as of 1997. 

Zeolite catalysts play a vital role in modern industrial catalysis. The varied acidity and microporosity properties of this class of inorganic oxides allow them to be applied to a wide variety of commercially important industrial processes. The acid sites of zeolites and other acidic molecular sieves are easier to manipulate than those of other solid acid catalysts by controlling material properties, such as the framework Si/Al ratio or level of cation exchange. The uniform pore size of the crystalline framework provides a consistent environment that improves the selectivity of the acid-catalyzed transformations that form C-C bonds. The zeoHte structure can also inhibit the formation of heavy coke molecules (such as medium-pore MFl in the Cyclar process or MTG process) or the desorption of undesired large by-products (such as small-pore SAPO-34 in MTO). While faujasite, morden-ite, beta and MFl remain the most widely used zeolite structures for industrial applications, the past decade has seen new structures, such as SAPO-34 and MWW, provide improved performance in specific applications. It is clear that the continued search for more active, selective and stable catalysts for industrially important chemical reactions will include the synthesis and application of new zeolite materials. 

Concentrated sulfuric acid and hydrogen fluoride are still mainly used in commercial isoalkane-alkene alkylation processes.353 Because of the difficulties associated with these liquid acid catalysts (see Section 5.1.1), considerable research efforts are still devoted to find suitable solid acid catalysts for replacement.354-356 Various large-pore zeolites, mainly X and Y, and more recently zeolite Beta were studied in this reaction. Considering the reaction scheme [(Eqs (5.3)—(5.5) and Scheme 5.1)] it is obvious that the large-pore zeolitic structure is a prerequisite, since many of the reaction steps involve bimolecular bulky intermediates. In addition, the fast and easy desorption of highly branched bulky products, such as trimethylpentanes, also requires sufficient and adequate pore size. Experiments showed that even with large-pore zeolite Y, alkylation is severely diffusion limited under liquid-phase conditions.357... 

Solid Acid Catalysts. There have been commercial alkylation processes in operation that apply solid acids (viz., zeolites) in the manufacture of ethylbenzene... 

Acid-Catalyzed Synthesis. The acid-catalyzed reaction of alkenes with hydrogen sulfide to prepare thiols can be accomplished using a strong acid (sulfuric or phosphoric acid) catalyst. Thiols can also be prepared continuously over a variety of solid acid catalysts, such as zeolites, sulfonic acid-containing resin catalysts, or aluminas (22). The continuous process is utilized commercially to manufacture the more important thiols (23,24). The acid-catalyzed reaction is commonly classed as a Markownikoff addition. Examples of two important industrial processes are 2-methyl-2-propanethiol and 2-propanethiol, given in equations 1 and 2, respectively. 

Sulfated zirconia is a good example of a structural Lewis acid which has been chemically treated to enhance acidity. It has been extensively studied as a solid acid catalyst for vapour phase reactions and we1112 and others14 have found that a mesoporous version of this material is a particularly effective catalyst for liquid phase Friedel-Crafts alkylation reactions and to a lesser extent Friedel-Crafts benzoylations. The commercial (MEL Chemicals Ltd) material SZ999/1 shows a nitrogen isotherm characteristic of a mesoporous solid (surface area 162 m2g, pore volume 0.22 cm3g )- Whereas microporous and mesoporous materials are capable of rapidly catalysing the alkylation of benzene with various alkenes (Table 1), on reuse only the mesoporous... 

Aromatic ketones are important intermediates in the production of fine chemicals and pharmaceuticals1,2. Thus, the anti-rheumatic Naproxen is produced by the Friedel-Crafts acetylation of 2-methoxynaphthalene into 2-acetyl-6-methoxynaphthalene and subsequent Willgerodt-Kindler reaction. Commercial acylation processes involve over-stoechiometric amounts of metal chlorides (e g. AICI3) as catalysts and acid chlorides as acylating agents, which results in a substantial formation of by-products and in corrosion problems. This is why the substitution of these corrosive catalysts by solid acid catalysts and of acid chlorides by anhydrides or acids is particularly desirable. 

HETACAT An alkylation process using a solid acid catalyst. Not commercialized as of 1997. Lerner, B.A., Chem. Ind. (London), 1996, (1), 16. 

OATS [Olefinic Alkylation of Thiophenic Sulfur] A gasoline desulfurization process. Thiophenes and mercaptans are catalytically reacted with olefins to produce higher-boiling compounds that can more easily be removed by distillation prior to hydrodesulfurization. This minimizes hydrogen usage. The process uses a solid acid catalyst in a liquid-phase, fixed bed reactor. Developed by BPAmoco in 2000 and tested in Bavaria and Texas. First used commercially at the Bayernoil refinery, Neustadt, in 2001. The process won a European Environment Award in 2002. 

Various kinds of oxide materials, including single oxides, mixed oxides, molybdates, heteropoly-ions, clays, and zeolites, are used in catalysis they can be amorphous or crystalline, acid or basic. Furthermore the oxides can be the actual catalysts or they can act as supports on which the active catalysts have been deposited. Silica and alumina are commonly used to support both metals and other metal oxide species. Amorphous silica/alumina is a solid acid catalyst, it is also used as a support for metals, when bifunctional (acid and metal) catalysis is required, e.g., in the cracking of hydrocarbons. Other acid catalysts are those obtained by the deposition of a soluble acid on an inert support, such as phosphoric acid on silica (SPA, used in the alkylation of benzene to cumene. Section 5.2.3). They show similar properties to those of the soluble parent acids, while allowing easier handling and fixed bed operation in commercial units. 

In the following the characteristics of product distribntion over various microporous solid acidic catalysts are discussed. The catalysts tested were zeolites, commercial cracking catalysts, clays and their pillared analogues. 

Acid catalysts are used to promote the alkylation of ethylene to benzene. Acid catalysts suitable for benzene alkylation include protonic acids (i.e., H2SO4, HF, and H3PO4), Friedel-Crafts catalysts (i.e., AICI3 and BF3), and more recently, solid acid catalysts. Solid acid catalysts used for the commercial manufacture of EB are typically zeolitic molecular sieves and materials such as ZSM-5, faujasite, MCM-22, and zeolite beta. Zeolites physical and chemical properties can be modified to optimize the activity, selectivity, and stability of the catalysts. This flexibility of zeolites has made them the preferred catalyst of choice. 

Figure 2.31 Synthesis of methylenedianiline (MDA). Comparison of the commercial process (a) with a new one based on the use of solid acid catalysts (b). Source adapted from de Angelis et at. [237],...

Using grants from the US Department of Energy and the National Science Foundation, Exelus started developing a viable solid-acid catalyst alternative for isoparaffin alkylation. In order to produce a commercially viable process, the goal was to develop a catalyst that was useable in a simple fixed-bed reactor process using a benign solid-acid catalyst. Our desire to use a fixed-bed reactor... 

Isoparaffin alkylation reactions are very fast and they suffer from severe pore diffusion limitations. As a result, when catalyst particle size is increased from 100 pm (for slurry reactors) to 1.6 mm for fixed-bed reactors, the catalyst activity reduces by 10-fold according to basic mass transfer models using experimental values of the intrinsic rate constant, as shown in figure 4. To match the catalyst productivity of a slurry reactor, one would need to build a fixed-bed reactor with ten times the volume - not practical for a commercial scale system. In addition to using a fixed-bed reactor, we wanted to ensure that the solid-acid catalyst was both robust as well as benign (i.e. environmentally fiiendly). 

By integrating optimized acid sites with superior mass transport characteristics and a pore architecture that reduces pore-mouth plugging, a catalyst with enhanced performance can be created. Figure 5 demonstrates that both the catalyst selectivity and lifetime are significantly improved. As shown in figure 6, which compares the performance of Exelus solid-acid catalyst with other commercially available systems, the new catalyst system is easily able to achieve a step-change in performance over other solid-acid catalysts. 

Although many solid-acid catalysts have been reported for the vapor-phase Beckmann rearrangement [2], their performance has been less than satisfactory from an industrial standpoint and the heterogeneously catalyzed Beckmann rearrangement has not yet been commercialized. In this chapter heterogeneous catalysis of the Beckmann rearrangement, its mechanism, and acid properties and reaction conditions suitable for the reaction will be reviewed. 

By far the greatest amount of work in this area has been eentered on the commercially important transformation of a-pinene (1) into, primarily, eamphene (2) and limonene (3) (Scheme 1). The first use of a heterogeneous catalyst for the isomerization of a-pinene was reported by Gurvieh in 1915 [2] and many forms of solid-acid catalyst have subsequently been studied in relation to this reaction. We shall study just a few of these. 

The preparation of campholenic aldehyde (12) from a-pinene oxide (13) is currently a commercial process in which zinc bromide is used as the catalyst. Ravasio et al. [20] have investigated replacing the zinc bromide with a commercial mixed co-gel solid-acid catalyst. They found that by use of Si02-Al203 (1.2 %) or Si02-Zr02 (4.7 %) they could readily achieve a 72 % yield of 12 under relatively mild conditions (25-60 °C, toluene) although small quantities of several side-products were also still formed (Scheme 2). 

The study of heterocyclic compounds constitutes a major endeavor in the fields of organic chemistry and the life sciences. Although numerous texts on the synthesis, structure, and reactivity of heterocyclic compounds have been written [1,2], the application of solid-acid catalysts to the synthesis of heterocyclic compounds is rarely emphasized in the literature. The authors of this section of the book have chosen not to pursue an exhaustive literature review-type approach to this topic but rather to cover selected areas of this subject from the viewpoint of an industrial chemist. More specifically, an account of the synthesis of pyridines is given which relies heavily on patent literature. Pyridine bases constitute a sizable semicommodity industry that provides a platform into the pyridine derivatives that are precursors to numerous fine chemicals. In addition, this section includes selected examples of the synthesis of non-pyridine heterocycles which might be of commercial importance. 

The synthesis of pyridine bases with solid-acid catalysts is of considerable commercial importance. In the future, zeolites and related catalysts can be expected to have an impact on other areas of heterocyclic chemistry, because they bring the combined benefits of high yields and environmentally clean processes. The use of these catalysts to introduce new functions into pre-formed heterocycles or to manipulate their side chains-a topic not addressed here-is an area worthy of more research activity. Hopefully, this brief review provides some insight into heterocyclic chemistry and encourages readers to pursue their own catalysis research in this fascinating and fruitful area. 

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