Isomerization isobutane

The relative rate of isobutane isomerization has been shown by Anderson and Avery 24) to be markedly increased by using a (111) platinum film surface. On the other hand, this did not occur with n-butane, nor did it occur with either iso- or n-butane over a (100) platinum surface (cf. Table II). A triangular array of adjacent sites on a (111) platinum surface can be readily fitted by an adsorbed isohydrocarbon, and this structure also fits to allow the carbon orbitals to be directed normally to the surface. On simple geometric grounds, this adsorbed structure is specific to the (111)/... 

Supplemental processes which can be operated in conjunction with alkylation and/or sulfuric acid production can influence the overall economics. Examples are (1) the integration of normal butane-to-isobutane isomerization with alkylation, utilizing common fractionation equipment and (2), utilizing 65% sulfuric acid extraction of isobutylene or isoamylene from olefins fed to alkylation, justified by monetary return on sale of the high purity iso-olefin as a petrochemical feedstock, which reduces quantity of alkylate produced and reduces isobutane required while producing still higher quality alkylate with sulfuric acid catalyst. 

Fig. 5. Isobutane isomerization. % conversion to n-butane as a function of Sn/Pt atomic ratio. Catalysts prepared by coimpregnation SI Pt/Al203 blank X SI without H2.

TABLE 7.30. Kinetic Parameters for Isobutane Isomerization Over Metal Catalysts... 

We cite isomerization of Cs-Ce paraffinic cuts, aliphatic alkylation making isoparaffinic gasoline from C3-C5 olefins and isobutane, and etherification of C4-C5 olefins with the C1-C2 alcohols. This type of refinery can need more hydrogen than is available from naphtha reforming. Flexibility is greatly improved over the simple conventional refinery. Nonetheless some products are not eliminated, for example, the heavy fuel of marginal quality, and the conversion product qualities may not be adequate, even after severe treatment, to meet certain specifications such as the gasoline octane number, diesel cetane number, and allowable levels of certain components. 

Two constitutionally isomeric alkanes have the molecular formula C4H10 One has an unbranched chain (CH3CH2CH2CH3) and is called n butane, the other has a branched chain [(CH3)3CH] and is called isobutane Both n butane and isobutane are common names... 

Methyl /-Butyl Ether. MTBE is produced by reaction of isobutene and methanol on acid ion-exchange resins. The supply of isobutene, obtained from hydrocarbon cracking units or by dehydration of tert-huty alcohol, is limited relative to that of methanol. The cost to produce MTBE from by-product isobutene has been estimated to be between 0.13 to 0.16/L ( 0.50—0.60/gal) (90). Direct production of isobutene by dehydrogenation of isobutane or isomerization of mixed butenes are expensive processes that have seen less commercial use in the United States. 

Reactions of /l-Butane. The most important industrial reactions of / -butane are vapor-phase oxidation to form maleic anhydride (qv), thermal cracking to produce ethylene (qv), Hquid-phase oxidation to produce acetic acid (qv) and oxygenated by-products, and isomerization to form isobutane. 

Isomerization. Stmctural isomerization of / -butane to isobutane is commercially useful when additional isobutane feedstock is needed for alkylation (qv). The catalysts permit low reaction temperatures which favor high proportions of isobutane in the product. The Butamer process also is well known for isomerization of / -butane. 

Production of maleic anhydride by oxidation of / -butane represents one of butane s largest markets. Butane and LPG are also used as feedstocks for ethylene production by thermal cracking. A relatively new use for butane of growing importance is isomerization to isobutane, followed by dehydrogenation to isobutylene for use in MTBE synthesis. Smaller chemical uses include production of acetic acid and by-products. Methyl ethyl ketone (MEK) is the principal by-product, though small amounts of formic, propionic, and butyric acid are also produced. / -Butane is also used as a solvent in Hquid—Hquid extraction of heavy oils in a deasphalting process. 

The hydrocarbon cracking operations that generate feed olefins generally do not produce sufficient isobutane to satisfy the reaction requirements. Additional isobutane must be recovered from cmde oil or natural gas Hquids or generated by other refinery operations. A growing quantity of isobutane is produced by the isomerization of / -butane [106-97-8]. 

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). 

After reaction at 200 - 250 F and 350 psig the reactor effluent is stripped to remove recycle HCl. The stripper bottoms is cooled and caustic washed to remove remaining traces of HCl. The product can then be sent to the alkylation plant for fractionation or a tower provided in the isomerization plant for fractionation of isobutane and recycle of unconverted normal butane back to isomerization. 

The demand for aviation gasoline during World War II was so great that isobutanc from alkylation feedstock was insufficient. This deficiency was remedied by isomerization of abundant normal butane into isobutane using the isomerization catalyst aluminum chloride on alumina promoted by hydrogen chloride gas. 

Like propane, n-hutane is mainly obtained from natural gas liquids. It is also a hy-product from different refinery operations. Currently, the major use of n-hutane is to control the vapor pressure of product gasoline. Due to new regulations restricting the vapor pressure of gasolines, this use is expected to he substantially reduced. Surplus n-butane could be isomerized to isobutane, which is currently in high demand for producing isobutene. Isobutene is a precursor for methyl and ethyl tertiary butyl ethers, which are important octane number boosters. Another alternative outlet for surplus n-butane is its oxidation to maleic anhydride. Almost all new maleic anhydride processes are based on butane oxidation. 

Constitutional isomerism is not limited to alkanes—it occurs widely throughout organic chemistry. Constitutional isomers may have different carbon skeletons (as in isobutane and butane), different functional groups (as in ethanol and dimethyl ether), or different locations of a functional group along the chain (as in isopropylamine and propylamine). Regardless of the reason for the isomerism, constitutional isomers are always different compounds with different properties, but with the same formula. 

The activity and decay behaviour of the different porous heteropolycompounds were compared in two reactions requiring strong acid sites the n-butane isomerization and the isobutane/2-butene alkylation. Although these two reactions are important in the petroleum refining industry, n-butane isomerization is often used as a "test reaction" since it is known that this reaction requires very strong acid sites and only a limited number of oxides are active in this reaction, under mild conditions (T = 473 K). 

Other types of non-micro-channel, non-micro-flow micro reactors were used for catalyst development and testing [51, 52]. A computer-based micro-reactor system was described for investigating heterogeneously catalyzed gas-phase reactions [52]. The micro reactor is a Pyrex glass tube of 8 mm inner diameter and can be operated up to 500 °C and 1 bar. The reactor inner volume is 5-10 ml, the loop cycle is 0.9 ml, and the pump volume adds a further 9 ml. The reactor was used for isomerization of neopentane and n-pentane and the hydrogenolysis of isobutane, n-butane, propane, ethane, and methane at Pt with a catalyst. 

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