Phosphoric acid on silica catalysts

The phosphoric acid on silica catalyst is also an important catalyst for the production of petrochemical intermediates like nonene and alkylated aromates. 

Cumene is an important intermediate in the industrial production of phenol, acetone and a-methylstyrene. The large-scale production of cumene is based on the alkylation of benzene with propene over Friedel-Crafts [1] or phosphoric acid on silica catalysts [2]. Zeolites, namely ZSM-5 and ZSM-11, have also been shown to be potential catalysts for this process [3, 4]. However, the formation of cumene (isopropylbenzene. IPB) on this catalysts is accompanied by its isomerization to n-propylbenzene (NPB). The latter is considered as an undesired by-product with respect to further processing of cumene to phenol and acetone. Therefore, preventing the formation of NPB would enable the substitution of the current catalysts used in the industrial process by ZSM-5 or ZSM-11 type solid acids which have major advantages in terms of environmental protection, safety, and avoidance of corrosion. 

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. 

Oligomerization of iso-butene was used as a model reaction for testing of improved catalysts based on phosphoric acid on silica. The catalysts were produced by impregnation of silica spheres (2-3 mm diameter) with ortho-phosphoric acid, drying and calcining under various conditions. 

The Shell process, now in commercial operation (see process description) uses a phosphoric acid-on Celite catalyst to effect a 4.2 per cent once-through conversion. Mace and Bonilla showed that a tungsten oxfde-on silica gel catalyst was the most effective of several types investigated. Yields of 4.6 mole per cent were obtained at optimum conditions of 580 F (300 C), 2,000 psi pressure, steam ethylene mole ratio of 1, and a space velocity of 1,500 reciprocal hours. 

Ethene and water are mixed and passed over a catalyst (phosphoric acid on silica) at a temperature of 300°C and a pressure of 70 atm ... 

Conversion of ethylene to ethanol was observed over zirconium or aluminum phosphate catalysts impregnated with phosphoric acid, and the activities are slightly better than that of phosphoric acid on silica, the industrial catalyst for ethylene hydration. The active species for this transformation was identified to be liquid phosphoric acid present on the catalyst (150). 

Dehydration of ethanol has been effected over a variety of catalysts, among them synthetic and naturally occurring aluminas, silica-aluminas, and activated alumina (315—322), hafnium and zirconium oxides (321), and phosphoric acid on coke (323). Operating space velocity is chosen to ensure that the two consecutive reactions,... 

The reactor is a vessel with beds of solid catalyst. Most commercial processes use a catalyst called kieselguhr, which is phosphoric acid deposited on a silica/alumina pellet. Because of the weight of the pellets, supported beds at multiple levels in the vessel are used so the bottom layers wont be crushed.-... 

As the loading of STA on the catalyst support is decreased, incomplete anhydride conversion is observed and significant hydrolysis of the anhydride to form iso-butyric acid is observed (Table 2). Use of silica supported phosphoric acid results in lower ketone yields and significant hydrolysis of the iso-butyric anhydride. Blank reactions (catalyst and anhydride, 90°C, 30 min) indicates that hydrolysis of anhydride is observed in the presence of these catalysts and may result from either dehydroxylation of the silica support or residual water in the catalyst, ffowever this reaction is slow (42%STA/silica, 44% conversion and 70%P[3PO4/silica, 86% conversion respectively). 

Ethylamines. Mono-, di-, and triethyl amines, produced by catalytic reaction of ethanol with ammonia (330), are a significant oudet for ethanol. The vapor-phase continuous process takes place at 1.38 MPa (13.6 atm) and 150—220°C over a nickel catalyst supported on alumina, silica, or silica—alumina.. In this reductive amination under a hydrogen atmosphere, the ratio of the mono-, di-, and triethyl amine product can be controlled by recycling the unwanted products. Other catalysts used include phosphoric acid and derivatives, copper and iron chlorides, sulfates, and oxides in the presence of acids or alkaline salts (331). Piperidine can be ethylated with ethanol in the presence of Raney nickel catalyst at 200°C and 10.3 MPa (102 atm), to give IV-ethylpiperidine [766-09-6] (332). 

Another important addition reaction is the one used in the manufacture of ethanol. Ethanol has important uses as a solvent and a fuel (p. 94). It is formed when water (as steam) is added across the double bond in ethene. For this reaction to take place, the reactants have to be passed over a catalyst of phosphoric(v) acid (absorbed on silica pellets) at a temperature of 300 °C and pressure of 60 atmospheres (1 atmosphere =... 

For commercial processes, formed supports are more useful. Compared with other supports, fumed oxide supports showed new catalytic effects [41]. Some intensively investigated applications for these supports are abstracted in the following. SiC>2 pellets have been successfully introduced in a new generation of precious metal supports in vinylacetate monomer production [42]. This resulted in better selcctivities and an up to 50% higher space-time yield compared with supports based on natural alumo-silicates. In alkene hydration fumed silica pellets serve as a support for phosphoric acid. In this case, an increased catalyst lifetime and a higher space-time yield were observed [43]. Pyrogenic TiC>2 powder can be used as a starting material for the manufacture of monolithic catalysts [44] for the selective reduction of NOv with ammonia. 

Other workers also report studies on alkylation of aromatics over silica-alumina (63). Ivanov el al. alkylated coal-tar aromatics with olefins in the presence of aluminum chloride-hydrogen chloride and obtained a product suitable for use as a lubricating oil (143). Topchiev and Paushkin have reported high yields in the alkylation of isopentene with propylene in the presence of a catalyst containing phosphoric acid and boron trifluoride (395). 

In the case of cumene, UOP introduced a liquid-phase process in the 1940s to compete with aluminum chloride technology. The catalyst is SPA, a solid phosphoric acid catalyst in which the phosphoric acid is supported on silica. Many improvements were made to the SPA catalyst and process over the years, leading to 70% of the world s cumene being produced with SPA by the 1990s. In 1996, UOP introduced the Q-Max process, featuring a zeolitic catalyst and operating in the liquid phase (21). A new Q-Max catalyst, QZ-2001 , was introduced in 2001. 

Work has been reported on the conversion of aldehyde 81, the Diels-Alder cycloadduct of acrolein and cyclopentadiene, to its fully saturated primary alcohol and thereafter to bicyclo[3.3.0]octyl hydrocarbons.133 A silica/alumina catalyst system provides cu-bicyclo[3.3.0]octane, while phosphoric acid and Kieselguhr gives the A2-olefin. Since this cyclic alkene reacts under Koch-Haaf conditions to produce the... 

Friedel-Crafts alkylation processes were traditionally operated at 65-70°C with AICI3 and at 40-60°C with HF. A variety of solid acid catalysts have been developed at the laboratory level, mainly based on zeolites, heteropolyacids or sulfated zirconia (zirconia treated with sulfuric acid). The most recent industrial achievement is the Detal process (UOP-CEPSA) which is based on silica-alumina impregnated with HF. The selectivity towards linear alkylbenzenes exceeds 95%. The cymene processes use AICI3 in the liquid phase or supported phosphoric acid as catalysts. 

In a continuation of their work, however, Heilmann and Maier found that their imprinted silica gels exhibited selective transesterification and lactonisation that was no better than control materials containing phosphoric acid [55]. In fact, the catalytic activity could be removed by rinsing the gel in water. The TSA apparently turns into phosphoric acid during the high temperature treatment and then remains on the gel as a Bronsted acid catalyst (Fig. 8.15). The enhancement of selectivity... 

Hydration and Dehydration Reactions. Hydration and dehydration catalysts have a strong affinity for water. One such catalyst is AI2O3, which is used in the dehydration of alcohols to form olefins. In addition to aliunina, silica-alumina gels, clays, phosphoric acid, and phosphoric acid salts on inert carriers have also been used for hydration-dehydration reactions. An example of cm industrial catalytic hydration reaction is the synthesis of ethanol from ethylene ... 

Cumene is produced by alkylating benzene with propene. The reaction needs a catalyst in recent years, zeolite-based catalysts have become almost universally used in cumene plants [2], although older plants using aluminum chloride (AICI3) or phosphoric acid supported on silica are still operating. 

The addition of phosphate to the catalyst had a dramatic influence on the polymer product. It produced a strong enhancement of the low-MW side of the MW distribution, like that resulting from other catalyst modifications that increase surface acidity. An example is given in Figure 142. Three GPC curves are shown, representing the polymer produced with three different catalysts. One was obtained for polymer made with Cr/ silica activated at 500 °C. The other two represent polymer made with the same catalyst, but first impregnated with 0.5 or 1.0 mmol of phosphoric acid g 1 of catalyst, and then also calcined in air at 500 °C. 

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