Isomerism butylenes

Skeletal isomerization requires higher temperature and stronger acid catalysts than do double-bond migration and cis-trans isomerization. Butylenes, for example, are transformed to isobutylene over supported phosphoric acid catalysts.98 The equilibrium mixture at 300°C contains approximately equal amounts of straight-chain and branched butenes. Similar studies were carried out with pentene isomers.99 Side reactions, however, may become dominant under more severe conditions.100... 

O 22.19%. Several isomers are known. A liq mixt of isomeric butylene oxides has the props bp 62-5°, Hash p 5°F, pour p -150°, d 0.826 at 25°, vap d 2.49 highly toxic liq dangerous when exposed to heat or flame expl range 1.5 to 18.3%(Ref 2). Other props methods of prepn are given in the Refs. The 1,4-isomer (tetrahydrofuran or tetramethylene oxide) is described in detail in the Refs. Butylene oxides are used as solvs as org intermediates Refs l)Beil 17, 10, (5) [l5l 2)Sax(l957), 405 1166 3)CondChemDict(196l), 186 1122... 

Low temperatures in the alkylation reaction zone favor the isomerization of butylene-1 to butylene-2 during the alkylation reaction. Where low temperatures are not used for economic reasons, however, as is the case with many HF alkylation units, this isomerization is sometimes carried out in a separate unit and the isomerized product then charged to the alkylation unit. Catalysts for this isomerization reaction are phosphoric acid and silica-alumina. Some polymer is usually made when isomerizing with these catalysts, but when the polymer production is limited to diisobutylene, it will be alkylated to produce the trimethylpentanes. Any polymer made from normal butylenes, however, is an inferior feed for alkylation units. When this type of polymer is made, it is usually removed by fractionation before charging the isomerized butylene feed to the alkylation unit. 

Trimethylacetic Acid (Pivalic acid)—the third of the valeric acids—has also been investigated by Petersen. It yields irimethylcarbinol and probably hexamethylethane, besides an isomeric body, and also two isomeric butylenes, isobutylene predominating with perhaps also / -butylene. Aldehyde is not formed neither is an ester formed. 

Isovaleric acid gives diisobutane, triniethylmothyl isovalerate, and triinethylcarbinol, also a little isobutyl isoval-erate, isobutyl alcohol, and isobutyrie aldehyde, and, finally, two isomeric butylenes, isobutylene and / -butylene. 

Butylene Glycol Dinitrate Of the four isomeric butylene glycols, the 1,3-compound appears to be the only one which has attracted any interest as a... 

How do the facts agree with the prediction of three isomeric butylenes Experiment has shown that not three but four alkenes of the formula C4H8 exist they have the physical properties shown in Table 5.1. 

Ethers, such as MTBE and methyl / fZ-amyl ether (TAME) are made by a catalytic process from methanol (qv) and the corresponding isomeric olefin. These ethers have excellent octane values and compete on an economic basis with alkylation for inclusion in gasoline. Another ether, ethyl tert-huty ether (ETBE) is made from ethanol (qv) and isobutylene (see Butylenes). The cost and economic driving forces to use ETBE vs MTBE or TAME ate a function of the raw material costs and any tax incentives that may be provided because of the ethanol that is used to produce it. 

Isomerization. Isomerization of any of the butylene isomers to increase supply of another isomer is not practiced commercially. However, their isomerization has been studied extensively because formation and isomerization accompany many refinery processes maximization of 2-butene content maximizes octane number when isobutane is alkylated with butene streams using HF as catalyst and isomerization of high concentrations of 1-butene to 2-butene in mixtures with isobutylene could simplify subsequent separations (22). One plant (Phillips) is now being operated for this latter purpose (23,24). The general topic of isomerization has been covered in detail (25—27). Isomer distribution at thermodynamic equiUbrium in the range 300—1000 Kis summarized in Table 4 (25). 

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. ... 

L. Ploense, M. Salazar, B. Gurau, and E.S. Smotkin, Proton Spillover Promoted Isomerization of n-Butylenes on Pt-black Cathodes/Nafion 117, JACS119, 11550-11551(1997). 

BLISS [Butylene isomerization system] A process for isomerizing / -butenes to isobutene. Piloted by Texas Olefins Company in Houston, TX, 1990 to 1992. 

Isomerization, 12.T63, 404 of n-butane, 13 697 butylenes, 4 409-410, 410t carbohydrate hydroxyl groups, 4 712 carboxylic acids, 5 44 catalytic aerogels for, J 763t of cyclohexane, 13 706 facilitation of, 20 100 maleic, 20 99-100 maleic anhydride 492, 15 493 paraffin, 16 844... 

The process calls for feeding ethylene and mixed butylenes to the bottom of a reactor. The mixed butylenes consist of both butene-1 and butene-2. (Refer to Figure 1—10 to refresh your memory about the difference.) A slurry of rhenium-based catalyst is introduced at the top. As the ethylene and butylenes bubble past the catalyst, the ethylene and butene-2 will react to form propylene (the carbon count is right). Simultaneously, as the butene-2 is consumed, butene-1 isomerizes to create more. 

Figure 13.38 Mechanism for unimolecular skeletal isomerization of n-butylene.

Every chemical process of practical interest, such as the isomerization of butylenes written previously, forms several products (some undesired) and involves multiple reactions. Consider next the reaction system... 

Butenes or butylenes are hydrocarbon alkenes that exist as four different isomers. Each isomer is a flammable gas at normal room temperature and one atmosphere pressure, but their boiling points indicate that butenes can be condensed at low ambient temperatures and/or increase pressure similar to propane and butane. The 2 designation in the names indicates the position of the double bond. The cis and trans labels indicate geometric isomerism. Geometric isomers are molecules that have similar atoms and bonds but different spatial arrangement of atoms. The structures indicate that three of the butenes are normal butenes, n-butenes, but that methylpropene is branched. Methylpropene is also called isobutene or isobutylene. Isobutenes are more reactive than n-butenes, and reaction mechanisms involving isobutenes differ from those of normal butenes. 

Hydration of Olefins. The earliest and still the largest production of chemicals from petroleum hydrocarbons was based on the hydration of olefins to produce alcohols by the employment of sulfuric acid. The addition of olefins to sulfuric acid to form alkyl sulfates and dialkyl sulfates takes place on simple contact of the hydrocarbons with the acid. To keep down polymerization and isomerization of the hydrocarbons, the temperature is kept relatively low, usually below 40° C. and commonly considerably lower than that (18). The strength of the sulfuric acid used depends on the olefin to be absorbed. Absorption of ethylene requires an acid concentration higher than 90%, whereas propylene and butylenes are readily absorbed in 85% acid or less. The alkyl and dialkyl sulfate solutions, on dilution and heating, are hydrolyzed to the alcohols plus small amounts of by-product ethers. After distilling off the organic products, the dilute sulfuric acid is reconcentrated and re-used. 

Although not a separate process, isomerization plays an important role in pretreatment of the alkene feed in isoalkane-alkene alkylation to improve performance and alkylate quality.269-273 The FCC C4 alkene cut (used in alkylation with isobutane) is usually hydrogenated to transform 1,3-butadiene to butylenes since it causes increased acid consumption. An additional benefit is brought about by concurrent 1-butene to 2-butene hydroisomerization. Since 2-butenes are the ideal feedstock in HF alkylation, an optimum isomerization conversion of 70-80% is recommended.273... 

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