Isobutene separation

J.P. Bran, G. Bulvestre, A. Kergreis, M. Guillou, Hydrocarbon separations with poly membranes. Part I. Butadiene-isobutene separation with nitrile rubber membranes, J. Appl. Polym. Sci. 18 (1974) 1663-1683. 

Present in the same order of magnitude as isobutene. Separation incomplete. 

C4 cuts from catalytic cracking contain little butadiene and acetylenic compounds. Hence they can be used directly for isobutene separation processes, but require prior hydrogenation to obtain 1-butene. By contrast, steam cracked effluents must systematically undergo hydrogenation pretreatmcnL This is necessary to eliminate the compounds liable to cause highly exothermic side-polymerizations, and to form gums that disturb the operation of the catalyst systems, solvents and adsorbents used in steps designed to produce the different C4 olefins. 

Membranes based on the above poly(phenylene oxide) binder and the hypercrosslinked particulate derived from finear polystyrene exhibit even higher selectivity, 540, in H2/isobutene separation, most likely due to size exclusion effect [396]. This experimental finding indicates that such type of heterogeneous membranes may successfully be used for effective separation... 

Yanglong G., Guanzhong L., Yunsong W., Ren W. 2003. Preparation and characterization of Pd-Ag/ceramic composite membrane and application to enhancement of catalytic dehydrogenation of isobutene. Separation and Purification Technology 32 271-279. 

Olefin Separation. Olefin-containing streams are separated either by the OlefinSiv process (Union Carbide Corp.) separating / -butenes from isobutenes in the vapor phase, or the Olex process (Universal Oil Product) a Hquid-phase process. 

In commercial extraction operations, the fractions that contain butadiene, isobutene, and 1- and 2-butenes usually first go through a butadiene extraction unit in which the butadiene is removed. This may be followed by isobutylene removal via reaction between isobutylene and methanol to form methyl /-butyl ether [1634-04-4] (MTBE). The butenes are then distilled from the MTBE. 1-Butene may then be separated from 2-butene by distillation. 

In the last few years, Idemitsu commercialized a 5000 metric ton/year integrated reaction and separation process in SCR isobutene, as shown in Rig. 22-24. The reaction of isobutene and water takes place in the water phase and is acid catalyzed. The product, sec-butanol, is extracted into the isobutene phase to drive the reversible reaction to the right. The. s c-butanol is then recovered from the isobutene by depressurizing the SCR phase, and the isobutene is recompressed and recycled. 

The industrial reactions involving cis- and trans-2-butene are the same and produce the same products. There are also addition reactions where both 1-butene and 2-butene give the same product. For this reason, it is economically feasible to isomerize 1-butene to 2-butene (cis and trans) and then separate the mixture. The isomerization reaction yields two streams, one of 2-butene and the other of isobutene, which are separated by fractional distillation, each with a purity of 80-90%. Table 2-3 shows the boiling points of the different butene isomers. 

An alternative method for separating the hutenes is hy extracting isobutene (due to its higher reactivity) in cold sulfuric acid, which polymerizes it to di- and triisohutylene. The dimer and trimer of isobutene have high octane ratings and are added to the gasoline pool. 

Figure 2-1 shows the two processes for the separation of n-butenes from isobutene. ... 

The reaction between isobutylene (separated from C4 fractions from cracking units or from cracking isobutane to isobutene) and formaldehyde produces a cyclic ether (dimethyl dioxane). Pyrolysis of dioxane gives isoprene and formaldehyde. The formaldehyde is recovered and recycled to the reactor. 

The three isomers constituting n-hutenes are 1-hutene, cis-2-hutene, and trans-2-hutene. This gas mixture is usually obtained from the olefinic C4 fraction of catalytic cracking and steam cracking processes after separation of isobutene (Chapter 2). The mixture of isomers may be used directly for reactions that are common for the three isomers and produce the same intermediates and hence the same products. Alternatively, the mixture may be separated into two streams, one constituted of 1-butene and the other of cis-and trans-2-butene mixture. Each stream produces specific chemicals. Approximately 70% of 1-butene is used as a comonomer with ethylene to produce linear low-density polyethylene (LLDPE). Another use of 1-butene is for the synthesis of butylene oxide. The rest is used with the 2-butenes to produce other chemicals. n-Butene could also be isomerized to isobutene. ... 

Additional adsorption sites are provided on open metal sites, when available. [Cu3(BTC)2] is performant in the selective adsorption and separation of olefinic compounds. The highly relevant separations of propene from propane and of isobutene from isobutane have been accomplished with separation factors of 2.0 and 2.1, respectively [101, 102]. [Cu3(BTC)2] also selectively takes up pentene isomers from aliphatic solvent in liquid phase, and even discriminates between a series of cis- and trans-olefin isomer mixtures with varying chain length, always preferring a double bond in cis-position. This behavior is ascribed to tt -complexation with the open Cu sites [100]. 

In a typical process, the conversion of isobutene in the reactor stage is 97 per cent. The product is separated from the unreacted methanol and any C4 s by distillation. The essentially pure, liquid, MTBE leaves the base of the distillation column and is sent to storage. The methanol and C4 s leave the top of the column as vapour and pass to a column where the methanol is separated by absorption in water. The C4 s leave the top of the absorption column, saturated with water, and are used as a fuel gas. The methanol is separated from the water solvent by distillation and recycled to the reactor stage. The water, which leaves the base of the column, is... 

This is, of course, the Hunter-Yohe mechanism, involving a zwitterion, but with this monomer it does not seem implausible in particular, the objection that it involves a large charge separation, which has some force in the case of a sterically hindered hydrocarbon such as isobutene, is probably not valid here, especially in view of the flexibility which... 

In the second scheme, the alkane is transformed to the olefin by oxidehydro-genation, and the outlet stream is sent to the second oxidation reactor without any intermediate separation." Isobutane and isobutene are recycled, together with oxygen, nitrogen, and carbon oxides. Finally, the third scheme differs from the first one in that hydrogen is separated from propane/propylene after the dehydrogenation step, and oxygen is preferably used instead of air in the oxidation reactor." ... 

Glycine <-butyl ester is a valuable intermediate for the preparation of peptides of glycine, since the labile /-butyl group can readily be removed by add under conditions which do not affect the blocked amino grouping. The present method using /-butyl chloroacetate is superior to that using the bromo derivative, since chloride is cheaper to prepare, less lachrymatory and more easily separated, by fractional distillation, from the /-butyl azidoacetate. The method is also less cumbersome than the procedure using isobutene. 

Besides ethylene and propylene, the steam cracking of naphtha and catalytic cracking in the refinery produce appreciable amounts of C4 compounds. This C4 stream includes butane, isobutane, 1-butene (butylene), cis- and trans-2-hutene, isobutene (isobutylene), and butadiene. The C4 hydrocarbons can be used to alkylate gasoline. Of these, only butadiene and isobutylene appear in the top 50 chemicals as separate pure chemicals. The other C4 hydrocarbons have specific uses but are not as important as butadiene and isobutylene. A typical composition of a C4 stream from steam cracking of naphtha is given in Table 8.3. 

These two ethers are used as blending agents (antiknock effect) in the petroleum industry. Especially, ethyl ferf-butyl ether is expected to become the most widely used octane booster on gasoline blending. Ethyl fcrf-butyl ether is mainly produced on an industrial scale by the reaction of isobutene with an excess of ethanol. Thus, the separation from ethanol is very important. 

Most butenes are produced in the cracking process in refineries along with other C-4 fractions such as the butanes. Butenes are separated from other compounds and each other by several methods. Isobutene is separated from normal butanes by absorption in a sulfuric acid solution. Normal butenes can be separated from butanes by fractionation. The close boiling points of butanes and butenes make straight fractional distillation an inadequate separation... 

In investigating the reaction of oxygen atoms with isobutene, analysis for propene was carried along with that for carbonyl compounds and CO. Propene was separated from isobutene at —112° to about — 115°C., which was possible due to the sufficient difference in vapor pressures (Table III). Experimental results have shown that the amounts of for-... 

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