Hydration of propylene

Isopropanol (2-propanol) is an important alcohol of great synthetic utility. It is the second-largest volume alcohol after methanol (1998 U.S. production was approximately 1.5 billion pounds) and it was the 49th ranked chemical. Isopropanol under the name isopropyl alcohol was the first industrial chemical synthesized from a petroleum-derived olefin (1920). 

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. 

Gas phase hydration, on the other hand, is carried out at temperatures above 200°C and approximately 25 atmospheres. The ICI process employs WO3 on a silica carrier as catalyst. 

Older processes still use the sulfation route. The process is similar to that used for ethylene in the presence of H2SO4, hut the selectivity is a little lower than the modern vapor-phase processes. The reaction conditions are milder than those used for ethylene. This manifests the greater ease with which an isopropyl carhocation (a secondary carhonium ion) is formed than a primary ethyl carhonium ion  

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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.)...

Worldwide, approximately 85% of acetone is produced as a coproduct with phenol. The remaining 17% is produced by on-purpose acetone processes such as the hydration of propylene to 2-propanol and the dehydrogenation of 2-propanol to acetone. The cost of production of 2-propanol sets the floor price of acetone as long as the acetone demand exceeds the coproduct acetone supply. However, there is a disparity in the growth rates of phenol and acetone, with phenol demand projected at 3.0%/yr and acetone demand at 2.0%/yr. If this continues, the coproduct supply of acetone will exceed the total acetone demand and on-purpose production of acetone will be forced to shut down the price of acetone is expected to fall below the floor price set by the on-purpose cost production. Projections indicate that such a situation might occur in the world market by 2010. To forestall such a situation, companies such as Mitsui Petrochemical and Shinnippon (Nippon Steel) have built plants without the coproduction of acetone. 

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. 

The effects of pressure and temperature on the equihbrium concentration of alcohol ia both phases of hydration of propylene when both Hquid and vapor phases are present have been calculated and are presented ia Table 3. Low temperature reduces by-product diisopropyl ether. 

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... 

Propylene glycol (1,2-propanediol) is produced by the hydration of propylene oxide in a manner similar to that used for ethylene oxide ... 

Figure 8-4. A flow diagram for the hydration of propylene to isopropanol (1) propylene recovery column, (2) reactor, (3) residual gas separation column, (4) aqueous - isopropanol azeotropic distillation column, (5) drying column, (6) isopropyl ether separator, (7) isopropyl ether extraction.

Propanediol (1,2-Propylene glycol, 1,2-Dihydroxy propane, Methyl glycol). CH3.CHOH.CH2OH mw 76.09 colorl, viscous, stable, hygr liq bp 187.3°, d 1.0381g/cc at 20/20° RI 1.4293 at 27° fl pt (open cup) 210°F autoignition temp 780°F. Misc with w, ales, and many org solvents in all proportions. Can be prepd by hydration of propylene oxide. On nitration it yields the exp] 1,2-Propanediol Dinitrate (see below)... 

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. 

The only data on chemical conversion in fixed-bed bubble-flow operation that have come to the author s attention are the few results referred to in Section V,A,6 obtained by Zabor et al. (Zl) for catalytic mixed-phase hydration of propylene. 

The hydration of propylene with sulfuric acid catalyst in high-temperature water was investigated using a flow reaction system.31 The major product is isopropanol. A biopolymer-metal complex, wool-supported palladium-iron complex (wool-Pd-Fe), has been found to be a highly active catalyst for the hydration of some alkenes to the corresponding alcohols. The yield is greatly affected by the Pd/Fe molar ratio in the wool-Pd-Fe complex catalyst and the catalyst can be reused several times without remarkable change in the catalytic activity.32... 

Synthesis gas is also the precursor to MTBE via methanol. The process requires isobutylene as well. Ethyl alcohol is made by direct, catalyzed hydration of ethylene. The route to isopropyl alcohol historically used to be solely indirect hydration of propylene, which occurs at much lower pressures and temperatures than the direct method, but advances in catalysis now make the direct route competitive. 

Propylene glycol is produced by hydration of propylene oxide in a process similar to that for the production of ethylene glycol by hydration of ethylene oxide. 

Propene is used as a starting material for numerous other compounds. Chief among these are isopropyl alcohol, acrylonitrile, and propylene oxide. Isopropyl alcohol results from the hydration of propylene during cracking and is the primary chemical derived from propylene. Isopropyl alcohol is used as a solvent, antifreeze, and as rubbing alcohol, but its major use is for the production of acetone. Acrylonitrile is used primarily as a monomer in the production of acrylic fibers. Polymerized acrylonitrile fibers are produced under the trade names such as Orion (DuPont) and Acrilan (Monsanto). Acrylonitrile is also a reactant in the synthesis of dyes, pharmaceuticals, synthetic rubber, and resins. Acrylonitrile production occurs primarily through ammoxidation of propylene CH3- CH = CH2 + NH3 + 1.5 02—> CH2 = CH - C = N + 3 H20. 

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). 

Ion exchange resins are used widely as heterogeneous catalysts of processes that require acid or base catalysis, for example, hydration of propylene to isopropanol, reaction of isobutylene with acetonitrile, and many others. The same kind of equipment is suitable as for ion exchange, but usually regeneration is not necessary, although some degradation of the resin naturally occurs over a period of time. 

Pritchard and Long1416-141 studied the distribution of lsO in products obtained on hydration of propylene oxide and isobutylene oxide in Hs180, both in alkaline and in acid solutions (Eqs. 611 and 612). Their results are consistent with the premise that attack by water occurs predominantly on the terminal epoxide carbon atom, unless an... 

Early attempts to use heteropoly compounds as catalysts are summarized in reviews published in 1952 (//) and 1978 (7). The first industrial process using a heteropoly catalyst was started up in 1972 for the hydration of propylene in the liquid phase. The essential role of the Keggin structure in a solid heteropoly catalyst was explicitly shown in 1975 in a patent concerning catalytic oxidation of methacrolein. Systematic research in heterogeneous catalysis with these materials started in the mid-1970s and led to the recognition of quantitative relationships between the acid or redox properties and catalytic performance... 

There are two main process categories for the direct hydration of ethylene to ethanol. Vapor-phase processes contact a solid or liquid catalyst with gaseous reactants. Mixed-phase processes contact a solid or liquid catalyst with liquid and gaseous reactants. Generally, ethanol is produced by a vapor-phase process mixed-phase processes are used for the analogous hydration of propylene to 2-propanol. Important exceptions to these two generalizations exist, but the discussion that follows emphasizes technology associated with the commercially important vapor-phase direct hydration of ethylene. 

The very remarkable formation of isopropyl alcohol can only be explained by assuming the hydration of propylene or the molecular rearrangement of the group CH3CH2CH2 —. 

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... 

F autoignition temp 780°F. Misc with w, ales, and many org solvents in aU proportions. Can be prepd by hydration of propylene oxide. On nitration it yields the expl 1,2-Propanediol Dinitrate (see below)... 

A cooling coil has been located for use in the hydration of propylene oxide discussed in Example 8-4. The cooling coil has 40 fF of cooling surface and the cooling water flow rate inside the coil Is sufficiently large that a constant coolant temperature of 85°F can be maintained. A typical overall heat-transfer coefficient for such a coil is 100 Btu/h-ft -°F. Will the reactor satisfy the previous constraint of 125°F maximum temperature if the cooling coil is used ... 

Most acetone is manufactured today in the United States by thermochemical cumene oxidation. It is a co-product with phenol. Acetone is also manufactured by dehydrogenation of 2-propanol, which is made by hydration of propylene. Most 1-butanol is manufactured today by hydrogenation of n-butyraldehyde, which is obtained by the hydroformylation of propylene (0x0 reaction). It is also manufactured by hydrogenation of crotonaldehyde, which is obtained by the... 

Isopropyl Alcohol, USP. I.sopropanol (2-propannl) is a colorless, volatile liquid with a characteristic odor and a slightly bitter taste. It is considered a suitable substitute for ethanol in most ea.ses but must not be ingested. Isopropyl alcohol is prepared commercially by (he sulfuric acid-cata-lyzcd hydration of propylene ... 

The indirect, sulfate ester-based process, used to introduce this chapter, was one of the first petrochemical processes (Section 19.3). This method still has a place since its capability of selective absorption of propylene enables it to be used with refinery gas streams to capture low concentrations of propylene, unlike the conditions for alternative processes. The direct hydration of propylene to isopropanol is also possible, but this requires a refinery stream containing a much higher concentration of propylene to be competitive. For this reason both petrochemical processes are still viable in their respective feedstock niches. 

Etherification of propylene and isopropyl alcohol to produce diisopropyl ether, an octane enhancer, has been patented as a two-stage process.The first step involves the hydration of propylene to isopropyl alcohol using acidic ion-exchange resins or acidic zeolites and an optional cosolvent and the second step involves the etherification of propylene and isopropyl alcohol using an acidic catalyst such as Amberlyst 36 in a CD column. 

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