Heterogeneous solid acid catalysts

Joseph JK, Jain SL, Sain B (2006) Ion exchange resins as recyclable and heterogeneous solid acid catalysts for the Biginelli condensation an improved protocol for the synthesis of 3,4-dihydropyrimidin-2-ones. J Mol Catal A Chem 247 99-102... 

Scheme 1 Sucrose is hydrolyzed into a mixture of glucose and fructose when exposed to an acid catalyst. Sulfuric acid has been used for this, but also heterogeneous solid acid catalysts have found use, especially acidic ion exchange resins.

Styrene. Styrene is the largest benzene derivative with annual consumption about 11.5 billion lb in the United States. It is produced mainly by catalytic dehydrogenation of high-purity ethylbenzene (EB) in the vapor phase. The manufacture process for EB is based on ethylene alkylation with excess benzene. This can be done in a homogeneous system with aluminum chloride catalyst or a heterogeneous solid acid catalyst in either gas or liquid-phase reaction. In the past decade, the liquid-phase alkylation with zeolite catalyst has won acceptance. Those processes have advantages of easier product separation, reducing waste stream, and less corrosion. In addition, it produces less xylene due to lower... 

Most of the units built prior to the 1990s employ a homogenous HF acid catalyst system and the units built post-1990 employ heterogenous solid acid catalyst systems. As such, detailed discussion in this entry will be focused on these two manufacturing routes with particular emphasis on the heterogenous catalyst system. 

ZSM-5, a heterogeneous solid acid catalyst with MFI cages connected by 10-ring micropores, has been widely used in the fields of oil refining and petrochemical industries [32]. 

Sabitha, G., Srinivas, C., Raghavendar, A., Yadav, J.S. 2010. Phosphomolyhdic acid (PMA)-S iOj as a heterogeneous solid acid catalyst for the one-pot synthesis of 2Ff-indazolo [ 1,2-fc] phthalazine-triones. Helvetica ChimicaActa 93(7) 1375-1380. 

Tungstate Sulfuric Acid as a New Heterogeneous Solid Acid Catalyst..69... 

TUNGSTATE SULFURIC ACID AS A NEW HETEROGENEOUS SOLID ACID CATALYST... 

To conclude, in this study, we presented a simple and clean method for the synthesis of several heterogeneous solid acid catalysts that are capable of efficiently catalyzing synthesis of various heterocyclic biological compounds. We believe that these eco-friendly, inexpensive, recyclable catalysts can be used for simple experimental procedures with solvent-free reaction conditions, low catalyst loading, short reaction... 

Table 6.6 Recent heterogeneous solid acid catalysts for biodiesel production... 

A more recent development in ethylbenzene technology is the Mobil-Badger process,161,314-316 which employs a solid acid catalyst in the heterogeneous vapor-phase reaction (400-45O C, 15-30 atm). A modified H-ZSM-5 catalyst that is regenerable greatly eliminates the common problems associated with... 

Since solid acid catalysts are used extensively in chemical industry, particularly in the petroleum field, a reliable method for measuring the acidity of solids would be extremely useful. The main difficulty to start with is that the activity coefficients for solid species are unknown and thus no thermodynamic acidity function can be properly defined. On the other hand, because the solid by definition is heterogeneous, acidic and basic sites can coexist with variable strength. The surface area available for colorimetric determinations may have widely different acidic properties from the bulk material this is especially true for well-structured solids like zeolites. It is also not possible to establish a true acid-base equilibrium. 

Solid acid catalysts such as mixed oxides (chalcides) have been used extensively for many years in the petroleum industry and organic synthesis. Their main advantage compared with liquid acid catalysts is the ease of separation from the reaction mixture, which allows continuous operation, as well as regeneration and reutilization of the catalyst. Furthermore, the heterogeneous solid catalysts can lead to high selectivity or specific activity. Due to the heterogeneity of solid superacids, accurate acidity measurements are difficult to carry out and to interpret. Up until now, the most useful way to estimate the acidity of a solid catalyst is to test its catalytic activity in well-known acid-catalyzed reactions. 

Whereas solid acid catalysts (zeolites) have been intensively studied, only recently has the use of basic solid catalysts received substantial interest for production of intermediate and fine chemicals [1], Heterogeneous catalytic transformations are environmentally friendly compared with processes requiring neutralization and... 

Mochida, I. and Y. Yoneda, Linear Free Energy Relationships in Heterogeneous Catalysis II. Dealkylation and Isomerization Reactions on Various Solid Acid Catalysts., J. of Catal., 7,393-396,1967. 

Obviously, it is very desirable to substitute these modes of benzylic ether preparation by an heterogeneous catalysis process. Clays (50) and resins (51, 52) which were the first solid acid catalysts used have given low or moderate yields. The first experiments with zeolites were carried out by Rhodia (53, 54) on the etherification of vanillic alcohol (A) in a batch reactor over a HBEA zeolite with a Si/Al ratio of 12.5 ... 

Whereas superacid (HF-BF3, HF-SbFs, HF-TaFs, HSOiF-Sbf s, etc.)-cata-lyzed hydrocarbon transformations were first explored in the liquid phase, subsequently solid acid catalyst systems, such as those based on Nafion-H, longer-chain perfluorinated alkanesulfonic acids, fluorinated graphite intercalates, and so on, were also developed and utilized for heterogeneous reactions. The strong acidic nature of zeolites was also explored. 

An impressive number of papers and books has been published and numerous patents have been registered on the aq lation of aromatic compounds over solid catalysts. Recently Sartori and Maggi [1] have written an excellent review with 267 references on the use of solid catalysts in Friedel-Crafts acylation. In one section of this review, namely acylation of aromatic ethers or thioethers, the authors report work on acylation by solid catalysts such as zeolites, clays, metal oxides, acid-treated metal oxides, heteropolyacids or Nafion. When examining in details these results, it appeared very difficult for us to build upon these experimental results as the reaction conditions differ drastically from one paper to the next. This prompted us to reinvestigate the scope and limitations of the Friedel-Crafts acylation using heterogeneous solids as catalysts, trying as much as we could to rationalize the observed effects. 

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