Ethylene direct catalytic hydration

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. 

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... 

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. 

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. 

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. 

Derivation (1) From ethylene by direct catalytic hydration or with ethyl sulfate as intermediate (2) fermentation of biomass, especially agricultural wastes (3) enzymatic hydrolysis of cellulose... 

This process is ordinarily operated in close conjunction with a petroleum refinery as a source for ethylene. Propylene is converted to isopropanol by essentially the same process, but under milder conditions. The corrosive nature of this process and the difficulty of acid recovery have led to successful development of commercial procedures for the direct catalytic hydration of ethylene under nonacidic conditions. 

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. 

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. 

Ethanol is manufactured from a variety of biomass feedstocks by anaerobic fermentation and from ethylene by direct vapor-phase catalytic hydration and sulfation-hydrolysis. The stoichiometries that represent the major processes are as follows ... 

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. 

The current process of choice involves the direct hydration of ethylene with a catalytic amount of phosphoric acid (Fig. 1). Temperatures average 300 to 400°C with 1000 psi. 

The difficulties attending the catalytic vapor phase hydration of olefins, while not apparent from the claims made in the patents which have been obtained for such processes, are serious and numerous. Aside from those already mentioned, the difficulties of separating the alcohol from the dilute liquid condensate by distillation and of purifying the alcohols from hydrocarbon polymers by a process of chlorination or selective absorption must be overcome. In view of the success that has attended the hydration of olefins, particularly those higher than ethylene, by means of absorption in sulfuric acid followed by dilution and distillation, it is probable that direct hydration processes at the present stage of the art will be unable to compete as long as cheap sulfuric acid is available. 

Effect of Operating Variables. The direct hydration of ethylene is an equilibrium i eaction (see Sec. V) which is favored by low temperatures, high pressures, and high steam. ethylene ratios. He catalytic activity of the phosphoric acid catalyst increases with increasing temperature, decreases with increasing pressure because of lower concentration, and decreases with high steam ethylene ratios at hi pressures because of moisture absorption. Thus, the process conditions that favor ethanol production adversely affect the catalyst activity. For this reason, operating conditions must necessarily be chosen on the basis of economic considerations. 

The hydration of oleflns is important for the direct synthesis of alcohols from olefins in the pietroleum industry and has been extensively studied over various solid acid catalysts. In the case of ethanol synthesis from ethylene and water, silicotungstic acids, silicophosphoric acids, solid phosphoric acids, metal sulfates, " and metal oxides have been studied as solid acid catalysts. In its industrial process, a solid phosphoric acid catalyst (Shell patent) is widely used throughout the world. The nature of the active (acidic) sites which exhibit high catalytic activity and selectivity is discussed below together with the hydration mechanism involving the catalytic behavior. 

Direct hydration of propylene in a vapor-phase, catalytic process also is commercially practiced. This is similar to hydration of ethylene to make ethanol. Relative to the sulfuric acid-mediated process, it offers the advantage of decreased corrosion. However, it suffers from a requirement for a pure propylene feed, whereas the former process can be used with a dilute, refinery stream. 

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