Alkylation with 2-butene

Table III provides a comparison of alkylate compositions for both the liquid acid-catalyzed reactions with various feed alkenes. The data show that H2SO4 produces a better alkylate with 1-butene, whereas HF gives better results with propene or isobutylene. The products from 2-butene and also from pentenes (not shown in Table III) are nearly the same with either acid.

The BET surface area was determined for both fresh and spent catalysts, during the isobutane alkylation with 1-butene . LaY and Lap zeolites displayed a decrease in the BET area of 45 % approximately due to the coking, while the amorphous silica alumina a decrease of 33 %. This is the case where the pretreatment of the coked catalysts before the BET determination will eliminate some of the carbonaceous deposits, since the reaction temperature is typically below 100°C, and the pretreatment for BET determination with zeolite catalysts, is usually around 250°C. TPO studies clearly demonstrated that this treatment under vacuum eliminates a fraction of the coke, and therefore the real decrease in surface area due to coke deposition is larger than that measured by BET. 

It follows from the above discussion that the chain mechanism requires that markedly different products be obtained in the alkylation of isobutane with 1- and 2-butene, respectively. The former should yield dimethyl-hexanes and the latter, trimethylpentanea, as the major products. Such has been showm (Schmerling, 14d) to be the case when aluminum chloride (particulary when modified to diminish side reactions) was employed as catalyst. The product of the alkylation with 1-butene in the presence of aluminum chloride monomethanolate contained about 60% by w eight dimethylhexanes and 10% trimethylpentanes, whereas the 2-butene product contained 65% trimethylpentanes and only 4% dimethylhexanes. The difference in composition was apparent also in the A.S.T.M. octane numbers of the 125° end-point gasolines. That from 1-butene had an octane number of only 76.1 that from 2-butene, 94.1. 

Although the alkylation with 1-butene proceeded smoothly at 55°, relatively little alkylation occurred at 28°, a temperature which gave very satisfactory results with 2-butene. That the ease of alkylation with 1-butene at the higher temperature was not due to intermediate isomerization to 2-butene is evident from the composition of the products. 

The significance of the fact that the major product of the alkylation with 1-butene was dimethylhexanes while that with 2-butene was trimethylpentanes has been discussed in the section on the mechanism of the reaction. 

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 proposed mechanisms may also be used to explain the formation of paraffins having both lower and higher molecular weights than would be expected from simple addition of olefin molecules to isobutane molecules. A typical example is the formation of heptanes and nonanes when isobutane is alkylated with butene. The first step consists of... 

The products from butene-1 and n-butenes mixture containing mainly butene-2 were of comparable quality, probably because of Isomerization of the double bonds of the butenes, as In the case of H2SO4 alkylation. This was confirmed by a special experiment where butene-1 diluted with ten-fold n-butane was passed over the catalyst employed under the conditions of alkylation. In the product obtained both butene-1 and butene-2 Isomers were present In thermodynamic quantities. Moreover unexpectedly we have found that n-butane had been alkylated with butene-1 resulting In a liquid product composed mainly of D(W. 72% of the DMH fraction was 3,4 DMH - the product of the direct Interaction of n-butane and butene-1. This reaction In the presence of conventional mineral acids Is not known and Is very Interesting from a theoretical standpoint. 

Iso-butane is a highly demanded chemical in the refinery industry for the production of alkylates (by alkylation with butenes), and methyl tert-butyl ether (MTBE) (from isobutene and methanol), both important additives for reformulated gasolines. n-Butane isomerization is performed over platinum supported on chlorinated alumina. The chlorine compound which is continuously supplied to the feed in order to maintain the activity [1] is harmful to the environment. 

Zeolites catalyze alkylation of alkanes with olefins [76], The mechanism proposed for isobutane alkylation with butene is shown in Scheme III. 11 (the alkoxy species shown schematically are bound to the catalyst surface) [76a]. 

Scheme IILll. The classical mechanism of isobutene alkylation with butene.

An afterglow microwave plasma with stabilized pulse power was applied to the activation of zeolite catalysts for isobutane alkylation with butenes. It was found that the pretreatment of zeolite catalysts in a microwave plasma discharge affected their properties. The catalysts exhibited higher activity, stability in operation, and selectivity (the fraction of trimethylpentanes in the alkylate increased). The properties of catalysts after plasma activation depend on the treatment conditions such as plasma temperature and nonequilibrium character and depend only slightly on the initial activity of catalysts, which is primarily controlled by the catalyst preparation conditions. 

Isobutane alkylation with butenes is the process of producing high-octane products, such as trimethylpentanes (TMP) with 2,2,4-trimethylpentane being most desirable product with its 100% octane number. Up to now homogeneous catalysts were used on the industrial scale for this reaction with concentrated sulfuric acid or HF being the unprecedented catalysts. The disadvantages of these catalytic systems are well known and include, inter alia, corrosion problems, which are of environmental concern because of the necessity of utilization of sulfuric and fluoride wastes. 

The use of supercritical conditions is most perspective in the alkylation process where the lifetime of the catalyst is a burden. The comparison of the catalytic performances and stabilities of H-Beta and H-USY zeolites for isobutene alkylation with butenes in the supercritical isobutane phase [190] clearly shows that the zeolite structure strongly influences the performance and deactivation behavior of the zeohte in the alkylation process in supercritical (SC) conditions. H-Beta outperformed H-USY zeohte because of its lower deactivation and the stable quality of the alkylate, composed mainly of isoparaffins, whereas olefin di-/oligomerization was responsible for the H-USY deactivation. The stable activity of H-Beta was attributed to the effective extractive effect of the supercritical iC media to clean the acid sites located on the external surface of the small crystallites of H-Beta or located at the pore mouth. On the contrary, the deactivation observed for H-USY was caused by olefin oligomerization inside the zeolite supercages. The supercritical isobutane media cannot prevent the oligomers formation inside the zeolite supercages and extract these oligomers. 

Zhao, Z. Sun, W. Yang, X. Ye, X. Wu, Y. (2000). Study of the catalytic behaviors of concentrated heteropolyacid solution. I. A novel catalyst for isobutane alkylation with butenes. Catal. Lett., 65,115-121, ISSN1011-372X. 

Complex 169 is very susceptible to electrophilic attack, as shown in Scheme 32. The protonation of 169 with PyHCl gave back 166. In this reaction, the assistance of one of the oxygens as the primary site of the protonation cannot be excluded. The alkylation with MeOTf, unlike in the case of 161 (see Scheme 29),22 occurs at the alkylidene carbon as well, forming the 2,3-dimethyl-2-butene-W derivative 167, which was obtained also by the direct synthesis given in Scheme 31. 

With propene, n-butene, and n-pentene, the alkanes formed are propane, n-butane, and n-pentane (plus isopentane), respectively. The production of considerable amounts of light -alkanes is a disadvantage of this reaction route. Furthermore, the yield of the desired alkylate is reduced relative to isobutane and alkene consumption (8). For example, propene alkylation with HF can give more than 15 vol% yield of propane (21). Aluminum chloride-ether complexes also catalyze self-alkylation. However, when acidity is moderated with metal chlorides, the self-alkylation activity is drastically reduced. Intuitively, the formation of isobutylene via proton transfer from an isobutyl cation should be more pronounced at a weaker acidity, but the opposite has been found (92). Other properties besides acidity may contribute to the self-alkylation activity. Earlier publications concerned with zeolites claimed this mechanism to be a source of hydrogen for saturating cracking products or dimerization products (69,93). However, as shown in reaction (10), only the feed alkene will be saturated, and dehydrogenation does not take place. 

Cesium salts of 12-tungstophosphoric acid have been compared to the pure acid and to a sulfated zirconia sample for isobutane/1-butene alkylation at room temperature. The salt was found to be much more active than either the acid or sulfated zirconia (201). Heteropolyacids have also been supported on sulfated zirconia catalysts. The combination was found to be superior to heteropolyacid supported on pure zirconia and on zirconia and other supports that had been treated with a variety of mineral acids (202). Solutions of heteropolyacids (containing phosphorus or silicon) in acetic acid were tested as alkylation catalysts at 323 K by Zhao et al. (203). The system was sensitive to the heteropoly acid/acetic acid ratio and the amount of crystalline water. As observed in the alkylation with conventional liquid acids, a polymer was formed, which enhanced the catalytic activity. 

A clear example of the possible use of acid and/or superacid solids as catalysts is the alkylation of isobutane with butenes. Isobutane alkylation with low-molecular-weight olefins is one of the most important refining process for the production of high-octane number (RON and MON), low red vapor pressure (RVP) gasoline. Currently, the reaction is carried out using H2SO4 or HF (Table 13.1), although several catalytic systems have been studied in the last few years. 

It is important to note that, while the primary product Cg carbenium ions that are formed (after reaction with 2-butene or 1-butene) are secondary, they can undergo hydride shift or methyl shift and form a tertiary carbenium ion in each case. In that case the driving force is diminished for either of the two tertiary Cg carbenium ions to abstract a hydride ion from i-butane since this now becomes a transition from a large tertiary carbenium ion to a smaller tertiary carbenium ion. Nevertheless, this hydride transfer can still occur due to the high ratio of i-butane to tertiary Cg carbenium ion that exists in the reaction medium. At the same time the tertiary Cg carbenium ion may get alkylated with another butylene molecule to make the more stable C12 carbenium ion, which would then lead to heavies. 

Ir-catalyzed alkylation with a nitro compound was applied in a synthesis of flS,2R)-tra s-2-phenylcyclopentanamine, a compound with antidepressant activity (Scheme 9.41) [45]. The reaction of cinnamyl methyl carbonate with 4-nitro-l-butene gave the substitution product with 93% ee in 82% yield. A Grubbs I catalyst sufficed for the subsequent RCM. Further epimerization with NEts yielded a trans-cyclopentene in 83% yield via the two steps, while additional reduction steps proceeded in 90% yield. 

Good selectivity in alkene (ethylene or butene) alkylation with isoparaffins has been reported for acidic chloroaluminates 140). The ionic liquids have also been... 

The a./i-unsaturated cyclopentanecarboxylate 1 is alkylated with 4-bromo-l-butene with complete diastereoselectivity under deconjugation in 72% yield71. 

Butenes are used extensively in gasoline production to produce high-octane gasoline compounds. In alkylation reactions, butenes combine with isobutane to produce branched gasoline-range compounds (see Butane). Isooctane can be produced by dimerization of isobutene in the presence of sulfuric acid. Dimerization is the combination of a molecule with itself to produce a molecule called a dimer. The dimer has exactly twice the number of atoms in the original molecule. Therefore the dimerization of isobutene produces two dimers with the formula C H,... 

In the alkylation of isobutane with butenes, several variables have an important bearing on the quality of the alkylate produced. The most important is the concentration of isobutane in the reactor. Although theoretically only equimolecular ratios of isobutane and butene are required for the reaction, a large excess of isobutane in the reaction zone has been found necessary to suppress undesirable side reactions which result in loss of yield and octane number. Over-all isobutane-olefin ratios of 5 to 1 or higher are necessary for the production of high quality aviation alkylate. 

Temperature is an important variable in the alkylation process. When alkylating isobutane with butenes, a reaction temperature of 40° to 50° F. produces the highest quality alkylate with the lowest catalyst consumption. Commercial operation has been... 

The catalyst consumption for sulfuric acid alkylation is expressed in terms of pounds of fresh acid depleted per barrel of alkylate produced. When alkylating isobutane with butenes at 50° F. and maintaining an isobutane-olefin ratio of 5 to 1, the acid consumption will average 35 to 40 pounds per barrel when charging 98% acid and discarding 88% acid in a batchwise operation. 

Although the preceding discussion of the sulfuric and hydrofluoric acid processes has been confined to butene alkylation, isobutane has also been alkylated commercially with other olefins. Ethylene, propylene, pentenes, and dimers of butenes have been used for this purpose. It is also possible to use these olefins for the alkylation of isopentane. Such an operation, however, has not achieved commercial acceptance because it produces an inferior alkylate with a high catalyst consumption, and because isopentane is a satisfactory aviation gasoline component in its own right. 

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... 

Cycloalkanes possessing a tertiary carbon atom may be alkylated under conditions similar to those applied for the alkylation of isoalkanes. Methylcyclopentane and methylcyclohexane were studied most.5 Methylcyclopentane reacts with propylene and isobutylene in the presence of HF (23-25°C), and methylcyclohexane can also be reacted with isobutylene and 2-butene under the same conditions.20 Methylcyclopentane is alkylated with propylene in the presence of HBr—AlBr3 (—42°C) to produce l-ethyl-2-methylcyclohexane.21 C12H22 bicyclic compounds are also formed under alkylation conditions.21 22 Cyclohexane, in contrast, requires elevated temperature, and only strong catalysts are effective. HC1—AICI3 catalyzes the cyclohexane-ethylene reaction at 50-60°C to yield mainly dimethyl- and tetra-methylcyclohexanes (rather than mono- and diethylcyclohexanes). The relatively weak boron trifluoride, in turn, is not active in the alkylation of cyclohexane.23... 

Alkylation processes usually combine isobutane with an alkene or with mixed alkene streams (C3-C5 olefins from FCC units). The best octane ratings are attained when isobutane is alkylated with butylenes. Alkylation of higher-molecular-weight hydrocarbons (>C5) is less economic because of increased probability of side reactions. Phillips developed a technology that combines its triolefin process (metathesis of propylene to produce ethylene and 2-butenes) with alkylation since 2-butenes yield better alkylate than propylene.290 Since ethylene cannot be readily used in protic acid-catalyzed alkylations, a process employing AICI3 promoted by water was also developed.291... 

It is advantageous to pretreat butene feeds before alkylation.294-298 1,3-Butadiene is usually hydrogenated (to butenes or butane) since it causes increased acid consumption. The additional benefit of this process is that under hydrogenation conditions alkene isomerization (hydroisomerization) takes place, too. Isomerization, or the transformation of 1-butene to 2-butenes, is really attractive for HF alkylation since 2-butenes give better alkylate (higher octane number) in HF-cata-lyzed alkylation. Excessive 1,3-butadiene conversion, therefore, ensuring 70-80% isomerization, is carried out for HF alkylation. In contrast, approximately 20% isomerization is required at lower butadiene conversion for alkylation with H2SO4. 

Studies with sulfated zirconia also show similar fast catalyst deactivation in the alkylation of isobutane with butenes. It was found, however, that original activities were easily restored by thermal treatment under air without the loss of selectivity to trimethylpentanes. Promoting metals such as Fe, Mn, and Pt did not have a marked effect on the reaction.362,363 Heteropoly acids supported on various oxides have the same characteristics as sulfated zirconia.364 Wells-Dawson heteropoly acids supported on silica show high selectivity for the formation of trimethylpentanes and can be regenerated with 03 at low temperature (125°C).365... 

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