Direct hydration

Figure 10.3a shows a simplified fiowsheet for the production of isopropyl alcohol by the direct hydration of propylene. Different reactor technologies are available for the process, and separation and recycle systems vary, but Fig. 10.3a is representative. Propylene... 

Figure 10.3 Outline flowsheet for the production of isopropyl alcohol by direct hydration of propylene. (From Smith and Petela, Chem. Eng., 513 24, 1991 reproduced by permission of the Institution of Chemical Engineers.)...

Commercial Synthesis ofR,S-Mahc Acid. The commercial synthesis of R%-mahc acid involves hydration of maleic acid [110-16-7] or fumaric acid [110-17-8] at elevated temperature and pressure. A Japanese patent (33) describing a manufacturing procedure for malic acid claims the direct hydration of maleic acid at 180°C and 1.03—1.21 MPa (150—175 psi). 

E. Matsunaga and R. G. Muller, Secondary Butyl Mlcohol via Direct Hydration, Process Economics Program, Review No. 84-2-2, SRI International, Menlo Park, Calif., Aug. 1985. 

The indirect hydration, also called the sulfuric acid process, practiced by the three U.S. domestic producers, was the only process used worldwide until ICI started up the first commercial direct hydration process in 1951. Both processes use propylene and water as raw materials. Early problems of high corrosion, high energy costs, and air pollution using the indirect process led to the development of the direct hydration process in Europe. However, a high purity propylene feedstock is required. In the indirect hydration process, C -feedstock streams from refinery off-gases containing only 40—60 wt % propylene are often used in the United States. 

Direct Hydration. The acid-catalyzed direct hydration of propylene is exothermic and resembles the preparation of ethyl alcohol from ethylene (qv). 

A typical process scheme for the direct hydration of propylene is shown ia Figure 2. Turnkey plants based on this technology are available (71,81). The principal difference between the direct and iadirect processes is the much higher pressures needed to react propylene direcdy with water. Products and by-products are also similar, and refining systems are essentially the same. Under some conditions, the high pressures of the direct process can increase the production of propylene polymers. 

Fig. 2. Direct hydration process for the manufacture of isopropyl alcohol. The steps within the dashed box differentiate the direct from the indirect...

A Hquid-phase variation of the direct hydration was developed by Tokuyama Soda (78). The disadvantages of the gas-phase processes are largely avoided by employing a weakly acidic aqueous catalyst solution of a siHcotungstate (82). Preheated propylene, water, and recycled aqueous catalyst solution are pressurized and fed into a reaction chamber where they react in the Hquid state at 270°C and 20.3 MPa (200 atm) and form aqueous isopropyl alcohol. Propylene conversions of 60—70% per pass are obtained, and selectivity to isopropyl alcohol is 98—99 mol % of converted propylene. The catalyst is recycled and requites Htde replenishment compared to other processes. Corrosion and environmental problems are also minimized because the catalyst is a weak acid and because the system is completely closed. On account of the low gas recycle ratio, regular commercial propylene of 95% purity can be used as feedstock. 

Fig. 3. Direct hydration process where the product is isolated as diisopropyl ether.

Butanol is produced commercially by the indirect hydration of / -butenes. However, current trends are towards the employment of inexpensive Raffinate 11 type feedstocks, ie, C-4 refinery streams containing predominandy / -butenes and saturated C-4s after removal of butadiene and isobutylene. In the traditional indirect hydration process, / -butenes are esterified with Hquid sulfuric acid and the intermediate butyl sulfate esters hydroly2ed. DEA Mineraloel (formerly Deutsche Texaco) currentiy operates a 2-butanol plant employing a direct hydration of / -butenes route (18) with their own proprietary catalyst. 

There are two main processes for the synthesis of ethyl alcohol from ethylene. The eadiest to be developed (in 1930 by Union Carbide Corp.) was the indirect hydration process, variously called the strong sulfuric acid—ethylene process, the ethyl sulfate process, the esterification—hydrolysis process, or the sulfation—hydrolysis process. This process is stiU in use in Russia. The other synthesis process, designed to eliminate the use of sulfuric acid and which, since the early 1970s, has completely supplanted the old sulfuric acid process in the United States, is the direct hydration process. This process, the catalytic vapor-phase hydration of ethylene, is now practiced by only three U.S. companies Union Carbide Corp. (UCC), Quantum Chemical Corp., and Eastman Chemical Co. (a Division of Eastman Kodak Co.). UCC imports cmde industrial ethanol, CIE, from SADAF (the joint venture of SABIC and Pecten [Shell]) in Saudi Arabia, and refines it to industrial grade. 

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. 

Other Methods of Preparation. In addition to the direct hydration process, the sulfuric acid process, and fermentation routes to manufacture ethanol, several other processes have been suggested. These include the hydration of ethylene by dilute acids, the hydrolysis of ethyl esters other than sulfates, the hydrogenation of acetaldehyde, and the use of synthesis gas. None of these methods has been successfilUy implemented on a commercial scale, but the route from synthesis gas has received a great deal of attention since the 1974 oil embargo. 

Aluminum oxide has been the most widely used catalyst (151). At 320°C and 1.01—1.42 MPa, 50—66% conversion to alcohol based on the ether was obtained. Ethanol produced by the direct hydration of ether generally has a foul odor owing to the presence of polymeric hydrocarbon material, which can be removed by washing the aqueous alcohol with ether (152). 

Ethyl Ether. Most ethyl ether is obtained as a by-product of ethanol synthesis via the direct hydration of ethylene. The procedure used for production of diethyl ether [60-29-7] from ethanol and sulfuric acid is essentially the same as that first described in 1809 (340). The chemical reactions involved in the production of ethyl ether by the indirect ethanol-from-ethylene process are like those for the production of ether from ethanol using sulfuric acid. 

Fig. 12 shows the atom density profiles as a function of the coordinate z along the pore axis. Oxygen atom positions correlate with positive and negative surface charges as a result of direct hydration and through hydrogen bonds, respectively. In a similar manner the maxima of the and CP density... 

The direct hydration of ethylene with water is the process currently used ... 

The production of isopropanol from propylene occurs by either a direct hydration reaction (the newer method) or by the older sulfation reaction followed by hydrolysis. 

In the direct hydration method, the reaction could be effected either in a liquid or in a vapor-phase process. The slightly exothermic reaction evolves 51.5 KJ/mol. 

The hydroboration/oxidation sequence is complementary to the direct, mercury(ll)-catalyzed hydration reaction of a terminal alkyne because different products result. Direct hydration with aqueous acid and mercury(IJ) sulfate leads to a methyl ketone, whereas hydroboration/oxidation of the same terminal alkyne leads to an aldehyde. 

Alcohols can be prepared by hydration of alkenes. Because the direct hydration of alkenes with aqueous acid is generally a poor reaction in the laboratory, two indirect methods are commonly used. Hydroboration/oxiclation yields the product of syn, non-Markovnikov hydration (Section 7.5), whereas... 

The stereochemical outcome is replacement of the C—B bond by a C—O bond with retention of configuration. In combination with stereospecific syn hydroboration, this allows the structure and stereochemistry of the alcohols to be predicted with confidence. The preference for hydroboration at the least-substituted carbon of a double bond results in the alcohol being formed with regiochemistry that is complementary to that observed by direct hydration or oxymercuration, that is, anti-Markovnikov. 

Direct hydration, of ethylene, 10 538 Direct hydrogenation, 6 827 Direct immunosensors, 14 154 Direct ingot (dingot) method, 25 409 Direct initiation, 14 270 Direct injection (DI) diesel engines, 12 421 Direct inlet injection, gas chromatography, 6 383, 415-416 Directional couplers, 17 446 Directional drilling techniques, in sulfur extraction, 23 572 Directive 89/107/EEC (EU), 12 36 Direct liquefaction, 6 827 Direct marketing, technical service personnel and, 24 343 Direct metal nitridation, 17 211-213 aerosol flow reactor, 17 211-212 Direct methanol fuel cells (DMFC),... 

The reactions are accompanied by a considerable volume change, and a dilatometric method was employed by Bell and Higginson (1949), who added acetaldehyde-water mixtures (containing about equal quantities of MeCHO and MeCH(OH)2) to an excess of acetone, and thus measured kj, in presence of a large number of acid catalysts. The direct hydration of acetaldehyde in aqueous buffer solutions is inconveniently fast at room temperatures, but ( (j + A ) was measured dilatometrically at 0°C by Bell and Darwent (1950), who established the existence of general acid-base catalysis. 

I PA could always be made by direct hydration, but the severe operating conditions (high pressures and temperatures) and puny yields had always limited the economic enthusiasm for the process. Then catalysis research paid off with the development of a sulfonated polystyrene cationic exchange resin catalyst, a mouthful in itself. The breakthrough permitted reduced pressures and temperatures without loss of yield. The catalyst works in the vapor phase, the liquid phase, and the mixed phase. 

Unfortunately, secondary and tertiary butyl alcohols (SBA and TBA) cannot be made by the Oxo process. Instead they are produced either by indirect or direct hydration of the corresponding olefin. Normal butylene gives SBA and isobutylene gives TBA. The processes are similar to the corresponding routes to IPA. 

Which alcohols are made commercially by direct hydration and which ones can only be made by indirect hydration or more complicated processes Which ones can go either way ... 

Direct hydration Indirect hydration Other process... 

See Section 8.2 for direct hydration and for net hydration through formation of vinylboranes by hydroboration. 

There is also an apparent trend in manufacturing operations toward simplification by direct processing. Examples of this include the oxidation of ethylene for direct manufacture of ethylene oxide the direct hydration of ethylene to produce ethyl alcohol production of chlorinated derivatives by direct halogenation in place of round-about syntheses and the manufacture of acrolein by olefin oxidation. The evolution of alternate sources, varying process routes, and competing end products has given the United States aliphatic chemical industry much of its vitality and ability to adjust to varying market conditions. 

Isopropanol is manufactured in the United States by the indirect hydration of propylene in processes which may involve the use of concentrated or dilute sulfuric acid, whereas, in European countries and Japan, a direct hydration process is used in which propylene reacts with water in the presence of a catalyst. It is used mainly for the production of acetone, but also as a solvent and in the manufacture of other chemicals and in pharmaceutical and cosmetic formulations (lARC, 1977). 

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