Catalytic hydration

Although catalytic hydration of ethylene oxide to maximize ethylene glycol production has been studied by a number of companies with numerous materials patented as catalysts, there has been no reported industrial manufacture of ethylene glycol via catalytic ethylene oxide hydrolysis. Studied catalysts include sulfonic acids, carboxyUc acids and salts, cation-exchange resins, acidic zeoHtes, haUdes, anion-exchange resins, metals, metal oxides, and metal salts (21—26). Carbon dioxide as a cocatalyst with many of the same materials has also received extensive study. 

Isopropyl Alcohol. Propylene may be easily hydrolyzed to isopropyl alcohol. Eady commercial processes involved the use of sulfuric acid in an indirect process (100). The disadvantage was the need to reconcentrate the sulfuric acid after hydrolysis. Direct catalytic hydration of propylene to 2-propanol followed commercialization of the sulfuric acid process and eliniinated the need for acid reconcentration, thus reducing corrosion problems, energy use, and air pollution by SO2 and organic sulfur compounds. Gas-phase hydration takes place over supported oxides of tungsten at 540 K and 25... 

Direct Hydration of Ethylene. Hydration of ethylene to ethanol via a Hquid-phase process cataly2ed by dilute sulfuric acid was first demonstrated more than a hundred years ago (82). In 1923, the passage of an ethylene-steam mixture over alumina at 300°C was found to give a small yield of acetaldehyde, and it was inferred that this was produced via ethanol (83). Since the late 1920s, several industrial concerns have expressed interest in producing ethanol synthetically from ethylene over soHd catalysts. However, not until 1947 was the first commercial plant for the manufacture of ethanol by catalytic hydration started in the United States by Shell the same process was commerciali2ed in the United Kingdom in 1951. 

Hydration. Ethanol [64-17-5] is manufactured from ethylene by direct catalytic hydration over a H PO —Si02 catalyst at process conditions of 300°C and 7.0 MPa (1015 psi). Diethyl ether is also formed as a by-product. 

Zabor et al. (Zl) have described studies of the catalytic hydration of propylene under such conditions (temperature 279°C, pressure 3675 psig) that both liquid and vapor phases are present in the packed catalyst bed. Conversions are reported for cocurrent upflow and cocurrent downflow, it being assumed in that paper that the former mode corresponds to bubble flow and the latter to trickle-flow conditions. Trickle flow resulted in the higher conversions, and conversion was influenced by changes in bed height (for unchanged space velocity), in contrast to the case for bubble-flow operation. The differences are assumed to be effects of mass transfer or liquid distribution. 

Catalytic hydration and alcoholation of unsaturated compounds such as alkenes or alkynes would be a high value-adding step in the synthesis of compounds of complicated structure as well as in the large-scale production of industrially useful simple compounds. The activation of the O-H bond of water, alcohol, or carboxylic acid by transihon metals is relevant to a variety of such catalytic processes. 

K. Tani and Y. Kataoka, begin their discussion with an overview about the synthesis and isolation of such species. Many of them contain Ru, Os, Rh, Ir, Pd, or Pt and complexes with these metals appear also to be the most active catalysts. Their stoichiometric reactions, as well as the progress made in catalytic hydrations, hydroal-coxylations, and hydrocarboxylations of triple bond systems, i.e. nitriles and alkynes, is reviewed. However, as in catalytic hydroaminations the holy grail", the addition of O-H bonds across non-activated C=C double bonds under mild conditions has not been achieved yet. 

Table 1 Selected results on catalytic hydration of terminal alkynes RCCH.a...

Gupta and Douglas [AIChE J., 13 (883), 1967] have studied the catalytic hydration of isobutylene to f-butanol, using a cation exchange resin catalyst in a stirred tank reactor. 

Direct catalytic hydration of ethylene in the vapor phase at 136 atm was studied by Mace Bonilla (Chem Eng Prog 50 385, 1954) who concluded that... 

An interesting feature of pseudocationic polymerisations is that they are relatively insensitive to water which may be without effect on the kinetics even in concentrations up to ten times greater than that of the catalyst. This is of great diagnostic value since the carbonium ions derived from polymerisable olefins are instantly destroyed by water if the ionogenic catalyst is a conventional acid. If it is a metal halide, water may form a catalytic hydrate and its effect on rate and degree of polymerisation (DP) will depend on its concentration relative to the catalyst, and other factors. 

The general reaction for the catalytic hydration of an alkene to produce an alcohol is shown in Figure 3-6, and the mechanism is in Figure 3 7. This process is an excimple of a Markovnikov addition (as seen in Organic Chemistry 1). 

Oxymercuration-demercuration is a useful laboratory method for the synthesis of small quantities of alcohol. Like the catalytic hydration reaction, this process is an example of Markovnikov addition. It s a useful procedure because it tends to result in high yields and rearrangements rarely occur. 

Ethanol can be readily produced by industrial processes such as the sulfonation-hydrolysis process and the direct catalytic hydration process as outlined by the following equations ... 

Ethanol, Etbylol, Ethyl Alcohol or Alcohol (Alcool in Fr, Alkohol in Ger and Alkogol in Rus), CH.gCHaOH mw 46.07, colorless liq, sp gr 0.879 at 20°/4, fr p —114.5°, bp 78.4°, fl p of 95% ale 14°C(57°F), heat of combustion 327.6kcal/mole and heat of formation —66.4kcal/nole, miscible with w, eth, methanol 8c chlf sol in many other org solvents. It is a good solvent for many expls and its mixture with eth dissolves NC of 12%N. Alcohol can be derived from ethylene either by direct catalytic hydration or by means of ethyl sulfate as an intermediate. 

A unique aspect of the catalytic activity of CA is the fact that the hydroxo form of the enzyme catalyzes the hydration of CO2 through the direct binding of CO2 to the hydroxo ligand, whereas the aqua form of the enzyme catalyzes the dehydration of hydrogen carbonate through a ligand substitution process. This difference in mechanism is nicely demonstrated by the overall volume profile shown in Figure 23, which was constructed on the basis of the effect of pressure on the catalytic hydration and dehydration processes. Both these catalytic processes show characteristic pH dependencies that center around the pXa value of the coordinated water molecule. Many model Zn(II) and... 

Uses and Reactions. Dihydromyrcene is used primarily for manufacture of dihydromyrcenol (25), but there are no known uses for the pseudocitronellene. Dihydromyrcene can be catalytically hydrated to dihydromyrcenol by a variety of methods (103). Reaction takes place at the more reactive tri-substituted double bond. Reaction of dihydromyrcene with formic acid gives a mixture of the alcohol and the formate ester and hydrolysis of the mixture with base yields dihydromyrcenol (104). The mixture of the alcohol and its formate ester is also a commercially available product known as Dimyrcetol. Sulfuric acid is reported to have advantages over formic acid and hydrogen chloride in that it is less complicated and gives a higher yield of dihydromyrcenol (105). 

One of the newer developments in the production of alcohols is the direct catalytic hydration of ethylene to ethyl alcohol. Temperature and pressure must be higher than in the conventional process, but the use and reconcentration of large amounts of sulfuric acid are avoided. 

The catalytic hydration of olefins can also be performed in a three-phase system solid catalyst, liquid water (with the alcohol formed dissolved in it) and gaseous olefin [258,279,280]. The olefin conversion is raised, in comparison with the vapour phase processes, by the increase in solubility of the product alcohol in the excess of water [258]. For these systems with liquid and vapour phases simultaneously present, the equilibrium composition of both phases can be estimated together with vapour-liquid equilibrium data [281]. For the three-phase systems, ion exchangers, especially, have proved to be very efficient catalysts [260,280]. With higher olefins (2-methylpropene), the reaction was also performed in a two-phase liquid system with an ion exchanger as catalyst [282]. It is evident that the kinetic characteristics differ according to the arrangement (phase conditions), i.e. whether the vapour system, liquid vapour system or two-phase liquid system is used. However, most kinetic and mechanistic studies of olefin hydration were carried out in vapour phase systems. 

Traditionally, ethanol has been made from ethylene by sulfation followed by hydrolysis of the ethyl sulfate so produced. This type of process has the disadvantages of severe corrosion problems, the requirement for sulfuric acid reconcentration, and loss of yield caused by ethyl ether formation. Recently a successful direct catalytic hydration of ethylene has been accomplished on a commercial scale. This process, developed by Veba-Chemie in Germany, uses a fixed bed catalytic reaction system. Although direct hydration plants have been operated by Shell Chemical and Texas Eastman, Veba claims technical and economic superiority because of new catalyst developments. Because of its economic superiority, it is now replacing the sulfuric acid based process and has been licensed to British Petroleum in the United Kingdom, Publicker Industries in the United States, and others. By including ethanol dehydrogenation facilities, Veba claims that acetaldehyde can be produced indirectly from ethylene by this combined process at costs competitive with the catalytic oxidation of ethylene. 

A variety of methods exist for the hydration of nitriles to amides or to acids (ref. 8). While acidic and basic catalysts have long been employed, the importance of catalytic hydration, especially under neutral conditions, is... 

Ethylene is catalytically hydrated to ethyl alcohol by steam at 100°— 300°, the catalysts being salts of phosphoric acid. (E.P., 423877.)... 

Nitriles can be catalytically hydrated, principally by palladium complexes (equation 185). In an initial study, [Rh(OH)(CO)(PPh3)2] (140) was found to be the best catalyst.642 Other complexes exhibiting catalytic activity were the iridium analogue of complex (140), [Pt(CsHa)(diphos)] (141) and [Pt(C6H8)(PPh3)2] (142). 

The catalytic oxidation of cyclohexane is performed in the liquid phase with air as reactant and in the presence of a catalyst. The resulting product is a mixture of alcohol and ketone (Table 1, entry 12) [19]. To limit formation of side-products (adipic, glutaric, and succinic acids) conversion is limited to 10-12 %. In a process developed by To ray a gas mixture containing HC1 and nitrosyl chloride is reacted with cyclohexane, with initiation by light, forming the oxime directly (Table 1, entry 12). The corrosiveness of the nitrosyl chloride causes massive problems, however [20]. The nitration of alkanes (Table 1, entry 13) became important in a liquid-phase reaction producing nitrocyclohexane which was further catalytically hydrated forming the oxime. 

Propan-2-ol (2-propanol, isopropyl alcohol) is made by the catalytic hydration of propylene. Isopropyl alcohol is commonly used as rubbing alcohol (rather than ethanol) because it has less of a drying effect on the skin, and it is not regulated and... 

Some simple compounds are made both from oil and from plants. The ethanol used as a starting material to make other compounds in industry is largely made by the catalytic hydration of ethylene from oil. But ethanol is also used as a fuel, particularly in Brazil where it is made by fermentation of sugar cane wastes. This fuel uses a waste product, saves on oil imports, and has improved the quality of the air in the very large Brazilian cities, Rio dc Janeiro and Sao Paulo. 

In the World War II era, 72 percent of U.S. ethanol was derived from molasses fermentation. By 1978 the balance was 90 percent from direct catalytic hydration and the rest from fermentation. In 1998 the balance had returned to the dominance of fermentation, with 83 percent of the 10 billion lb of U.S. ethanol made in this way. The recent swing toward fermentation is due to the use of 90 percent of the fermentation ethanol as motor fuel, as a result of post-oil-embargo U.S. government policy. 

Acetaldehyde. Acetaldehyde has been made from ethanol by dehydrogenation and by catalytic hydration of acetylene. Today direct oxidation of ethylene in the liquid phase catalyzed by palladium and copper has replaced these earlier methods. Figure 10.14 shows an ethylene-to-acetaldehyde unit based on this last route. 

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