Catalysts solid acid

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

A new process for the manufacture of p-diethylbenzene developed by Indian Petrochemicals Corporation was commercialized.376 p-Diethylbenzene is produced by alkylating ethylbenzene with ethanol over a highly shape-selective, pore-size-regulated, high-silica zeolite. The catalyst exhibits a steady activity of 6-8% conversion with 97-98% selectivity. 

New studies with zeolites were reported the main concern was selectivity 

Highly regioselective dialkylation of naphthalene was performed with 2-propanol380 and tert-butyl alcohol381 over dealuminated H-mordenite, and with tert-butyl alcohol over HY and Beta zeolites.382 Selectivities are within 60-84%. Computational modeling showed that the kinetic diameter of the 2,6-disubstituted isomer is smaller than that of the 2,7 isomer, which may explain the selective formation of the former within the appropriate zeolitic framework.382 

Since the development of clayzic, other montmorillonite-supported catalysts were also prepared and studied. New examples are montmorillonites modified with FeCl3 or SbCl3 from acetonitrile solution that show good characteristics in 

To avoid the production of waste acid, it is attractive to perform acid-catalyzed reactions with solid acids, and sulfonic acid-type polymeric ion-exchangers are often employed in the industry. Transport through the liquid phase in the narrow pores of the beads proceeds slowly, with the result that transport limitation is often encountered. Although several technical processes are performed with ion-exchangers as solid-acid catalysts, little literature is available other than the patent literature. For hybrid materials see Sections 3.3 and 3.5. 

Other solid catalysts are zeolites (cf. Section 3.2) and clay minerals (Section 

Many reactions in the fine-chemical industry are performed with organic liquids or in organic solvents. When the surface of a solid-acid catalyst is hydrophilic, the presence of small amounts of water can completely block the surface of the catalyst. Carefully dried catalysts and reagents must then be employed. It may be noted that zeolites with a high silica-to-alumina ratio are hydrophobic. The (internal) surface of the zeolite is, therefore, not readily poisoned by accumulation of (traces of) water. With zeolites, moreover, use can be made of the uniform size of the pores to perform shape-selective reactions after passivation of the catalytic sites on the external surface of the zeolite crystallites. In the bulk-chemical industry several interesting reactions have been developed with zeolite catalysts [27] (cf. the review of Tanabe and Hdlderich [28]). 

The narrow pores within zeolite crystallites do not promote the transport of liquids. Although small zeolite erystallites are attractive for liquid phase reactions, the size of solid crystallite particles required for separation from the liquid remains ca 3 pm. Small zeolite crystallites are therefore taken up in binders to provide larger particles. The binders are supposed to have wide pores through which transport is rapid. 

The development of clay minerals as solid-acid catalysts has been impeded by the general use of natural clay minerals often contaminated with impurities which are difficult to remove. Clay minerals are often used as supports for homogeneous catalysts, such as zinc chloride. 

Selective carbon-carbon bond formation is one of the most important reactions in both industrial and academic fields. Clean carbon-carbon bond formation depends on the development of heterogeneous acid and base catalysts, as described in this part. Mechanistic considerations can also identify new carbon-carbon bond formations. Section 6.2.2.1 focuses on catalysis by montmorilonite clays because various types of such solid acid catalysts have been simply prepared. The following section reviews recent developments in solid base catalysts for such chemistry and the final section of this chapter describes solid acid-base bifunctional catalysts, which are important concepts for one-pot sequential reactions. 

In a reaction with cycloxexane, toluene, and strong bases, the methoxy groups are regarded as methylation reagents that behave as methyl cations [90, 92]. 

P-position of the Si atom affords the allylsihlated product. Alkene (soft base) activation, which leads to an undesired alkene oligomerization, might be inhibited by use of a protonic acid as a hard acid. 

The Ti +.mont also acted as a reusable heterogeneous acid catalyst for esterification of carboxylic acids vdth alcohols [101], deprotection of acetals [102], and the condensation of glycerol with ketones or aldehydes into cycHc acetals under mild reaction conditions [103]. 

When sodium cations in the mont interlayer are exchanged with Sc + using an aqueous solution of Sc(OTf)j, a monomeric aqua complex, [Sc(H20)g] +, was formed in the interlayer space [104]. The Sc -mont could efHdently catalyze the Michael reaction of 1,3-dicarbonyl compounds with enones in water solvent. The Michael addition reaction of 1,3-dicarbonyl compounds with enones provides access to 1,5-dioxo synthons, which can be transformed easily into cyclohexanone derivatives for use as important intermediates in steroid and terpenoid syntheses. Initially, both the 1,3-dicarbonyl compound and the enone coordinate with the Sc + center, which acts as a Lewis add site. Subsequently, successive carbon-carbon bond formation produces an intermediate Sc-alcoholate, followed by protolysis to afford the Michael adduct and regenerate the initial Sc species, [Sc(H20)g] +. The importance of coordination of both the substrates is evidenced by IR spectrometry. 

According to this mechanism, acetone undergoes the sequential activation, first by the protonation and then by the thiol attack. Thus, the highly electrophilic propylidene sulphonium intermediate is created, which successively reacts with phenol molecules. The functional groups are distributed on the catalyst surface near each other, and, they are also located close to the pore walls. Such location of the functional groups significantly increases the catalytic activity of the silica material SBA-15 and provides the steric driving force that favors the formation of the p,p isomer of Bisphenol-A. 

In the search for better understanding of the catalyst porosity and acidity, various amorphous aluminosilicates with controlled porosity in the micro-region (ERS-8), meso-region (MCM-41, HMS) 

Original inorganic catalysts, prepared simply by mixing of concentrated phosphoric, boric and sulphuric acids of an appropriate molar ratio, followed by drying at 100°C for 24 hours in vacuo, were also found to be effective. They showed high conversion of acetone (91.8%) and high BPA selectivity (93.4%) [48], Moreover, ionic liquids consisted of triethylamine hydrochloride and anhydrous aluminium chloride (EtjNHCl-AlCy were tested and the reaction selectivity of 94.7% and the BPA yield of 85.1% were reached [49]. 

For the time being, the maximum BPA yields on the solid inorganic acids and the organic functionalized solid acids are still lower than those on the conventional ion-exchange resins that can provide BPA yields more than 90%. 

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Acids are not limited to liquid (or gaseous) systems. Solid acids also play a significant role. Acidic oxides such as silica, silica-alumina, etc. are used extensively as solid acid catalysts. New solid acid systems that are stronger than those used conventionally are frequently called solid superacids. 

Many superacid-catalyzed reactions were found to be carried out advantageously not only using liquid superacids but also over solid superacids, including Nafion-H or certain zeolites. We extensively studied the catalytic activity of Nafion-H and related solid acid catalysts (including supported perfluorooctanesulfonic acid and its higher ho-... 

Solid acid catalyst Solid bridges Solid carbon dioxide... 

Slotted plate for catalyst support designed with openings for vapor flow Ion exchanger fibers (reinforced ion exchange polymer) used as solid-acid catalyst None specified Hydrolysis of methyl acetate Evans and Stark, Eiir. Pat. Appl. EP 571,163 (1993) Hirata et al., Jap. Patent 05,212,290 (1993)... 

The reaction occurs in the liquid phase at relatively low temperatures (about 50°C) in the presence of a solid acid catalyst. Few side reactions occur such as the hydration of isohutene to tertiary hutyl alcohol, and methanol dehydration and formation of dimethyl ether and water. However, only small amounts of these compounds are produced. Figure 5-8 is a simplified flow diagram of the BP Etherol process. 

The center of the line is located at 126 ppm. The shape and position of the lines are comparable to those observed in the spectra of pyrogenic deposits (sp -hybridized carbon), for example, in coked catalysts where carbon is produced during the deactivation of solid acid catalysts [30, 31]. 

Zeolites are used in various applications such as household detergents, desiccants and as catalysts. In the mid-1960s, Rabo and coworkers at Union Carbide and Plank and coworkers at Mobil demonstrated that faujasitic zeolites were very interesting solid acid catalysts. Since then, a wealth of zeolite-catalyzed reactions of hydrocarbons has been discovered. Eor fundamental catalysis they offer the advantage that the crystal structure is known, and that the catalytically active sites are thus well defined. The fact that zeolites posses well-defined pore systems in which the catalytically active sites are embedded in a defined way gives them some similarity to enzymes. 

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. 

It has been revealed that the formation of protonic acid sites from molecular hydrogen is observable for the catalysts other than Pt/S042--Zr02, and the protonic acid sites thus formed act as catalytically active sites for acid-catalyzed reaction. We propose the concept "molecular hydrogen-originated protonic acid site" as a widely applicable active sites for solid acid catalysts. 

Acid-catalysed rearrangement of epoxides is another widely used reaction in the fine chemicals industry. Here again the use of solid acid catalysts such as zeolites is proving advantageous. Two examples are shown in Fig. 2.25 the isomerization of rsophorone oxide (Elings et al., 1997) and the conversion of a-pinene oxide to campholenic aldehyde (Holderich et al., 1997 Kunkeler etal., 1998). Both products are fragrance intermediates. 

Apart from a few reports" on solid acid catalyzed esterification of model compounds, to our knowledge utilization of solid catalysts for biodiesel production from low quality real feedstocks have been explored only recently. 12-Tungstophosphoric acid (TPA) impregnated on hydrous zirconia was evaluated as a solid acid catalyst for biodiesel production from canola oil containing up to 20 wt % free fatty acids and was found to give ester yield of 90% at 200°C. Propylsulfonic acid-functionalized mesoporous silica catalyst for esterification of FFA in flotation beef tallow showed a superior initial catalytic activity (90% yield) relative to a... 

During the last decade many industrial processes shifted towards using solid acid catalysts (6). In contrast to liquid acids that possess well-defined acid properties, solid acids contain a variety of acid sites (7). Sohd acids are easily separated from the biodiesel product they need less equipment maintenance and form no polluting by-products. Therefore, to solve the problems associated with liquid catalysts, we propose their replacement with solid acids and develop a sustainable esterification process based on catalytic reactive distillation (8). The alternative of using solid acid catalysts in a reactive distillation process reduces the energy consumption and manufacturing pollution (i.e., less separation steps, no waste/salt streams). 

The following experimental results are presented on the use of solid acid catalysts in esterification of dodecanoic acid with 2-ethylhexanol and methanol. In the next figures, conversion is defined as X [%] = 100-(1 - [Acid]fi ai / [Acid]Muai), and the amount of catalyst used is normahzed cat [%] - 100-A/cat / (A/acid + Milcohol)-Several alcohols were used to show the range of apphcability. The selectivity was assessed by testing the formation of side products in a suspension of catalyst in alcohol. Under the reaction conditions, no products were detected by GC analysis. 

Sulfur-free fuel, since solid acid catalysts do not leach into the biodiesel product. 

The experimental results are presented for the esterification of dodecanoic acid (C12H24O2) with 2-ethylhexanol (CgHigO) and methanol (CH4O), in presence of solid acid catalysts (SAC). Reactions were performed using a system of six parallel reactors (Omni-Reacto Station 6100). In a typical reaction 1 eq of dodecanoic acid and 1 eq of 2-ethylhexanol were reacted at 160°C in the presence of 1 wt% SAC. Reaction progress was monitored by gas chromatography (GC). GC analysis was performed using an InterScience GC-8000 with a DB-1 capillary colunm (30 m x 0.21 mm). GC conditions isotherm at 40°C (2 ntin), ramp at 20°C min to 200°C, isotherm at 200°C (4 min). Injector and detector temperatures were set at 240°C. 

Friedel-Crafts alkylations are among the most important reactions in organic synthesis. Solid acid catalysts have advantages in ease of product recovery, reduced waste streams, and reduction in corrosion and toxicity. In the past, people have used (pillared) clays (18), heteropolyacids (19) and zeohtes (20) for Friedel-Craft alkylations, with mixed success. Problems included poor catalyst stabihty and low activity. Benzylation of benzene using benzyl chloride is interesting for the preparation of substitutes of polychlorobenzene in the apphcation of dielectrics. The performance of Si-TUD-1 with different heteroatoms (Fe, Ga, Sn and Ti) was evaluated, and different levels of Fe inside Si-TUD-1 (denoted Fei, Fe2, Fes and Feio) were evaluated (21). The synthesis procedure of these materials was described in detail elsewhere (22). 

Reactivity of a number of solid acid catalysts that include zeolites, resin, nafion and HP As was determined for the direct reaction of ethylene with acetic acid to produce ethyl acetate (Table 1). It was established that the Keggin HSiW supported on silica is very active for the vapom phase reaction of acetic acid with ethylene at about 180°C, 145 psig with a high molar ratio of ethylene to... 

Table 1 Solid acid catalysts for the reaction of ethylene with acetic acid to produce ethyl acetate (6).

In summary, the Avada process is an excellent example of process intensification to achieve higher energy efficiency and reduction of waste streams due to the use of a solid acid catalyst. The successful application of supported HP As for the production of ethyl acetate paves the way for future applications of supported HP As in new green processes for the production of other chemicals, fuels and lubricants. Our results also show that application of characterization techniques enables a better understanding of the effects of process parameters on reactivity and the eventual rational design of more active catalysts. 

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. 

Figure 2 also includes a comparative experiment, where the solid acid catalyst is a sample of non-fluorided (but calcined), acidic mordenite. Here we see a) a significant loss of alkylation activity with time on stream and b) a measurably lower... 

Hoefnagel AJ, Gunnewegh EA, Downing RS, van Bekkum H (1995) Synthesis of 7-hydro-xycoumarins catalysed by solid acid catalysts. J Chem Soc Chem Commun 1995 225-226... 

Beckmann rearrangement of oxime is an acid catalysed reaction. The environmental problems associated with the use of sulphuric acid instigated interest to use number of solid acid catalysts [1], There are only scanty references about Lewis acid ion-exchanged MeAlPOs. Beyer et al. [2], Mihalyi et al. [3] and Mavrodinova et al. [4] already suggested the presence of Lewis acid metal ions as MO+ species in zeolites. The present study focussed the synthesis and characterisation of Fe3+, La3+ and Ce3+ ion-exchanged MAPO-36. The catalytic results of Beckmann rearrangement of cyclohexanone oxime over ion-exchanged catalysts are delineated in this article. 

A. Onda, T. Ochi, and K. Yanagisawa, Selective hydrolysis of cellulose into glucose over solid acid catalysts, Green Chem., 10 (2008) 1033-1037. 

C. Moreau, R. Durand, D. Peyron, J. Duhamet, and P. Rivalier, Selective preparation of furfural from xylose over microporous solid acid catalysts, Ind. Crops Prod., 7 (1998) 95-99. 

Addition of a solid acid catalyst such as Montmorillonite K10 increased the yield significantly under the action of either thermal heating (64%) or MW irradiation (66%) [52 c]. Under the latter conditions the reaction time was reduced. Comparable results were obtained for the synthesis of aminocoumarins 39-42 (Tab. 7.3) [53]. 

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

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