Isobutane ethylene alkylation

Use of Catalysts Containing Transition Metal Cations. Ethyl -ene being alkylated over certain zeolite catalysts reacts specifically. Ethylene can not, however, be alkylated with Isobutane In the presence of H2SO., because of the formation of stable ethylsulphates. We examined the Isobutane - ethylene alkylation over crystalline aluminosilicates and found that those catalysts containing RE and/or Ca In combination with transition metal cations were most active. The alkylation has resulted In not hexanes as would be expected, but an alkylate containing octane Isomers as the major product (about 80%). Moreover, the product composition was similar to that obtained from n-butene over CaREY. The TMP-to-DMH ratios were 7.8 and 7.1 respectively. 

Aliphatic alkylation is widely used to produce high-octane gasolines and other hydrocarbon products. Conventional paraffin (alkane)-olefin (alkene) alkylation is an acid-catalyzed reaction it involves the addition of a tertiary alkyl cation, generated from an isoalkane (via hydride abstraction) to an olefin. An example of such a reaction is the isobutane-ethylene alkylation, yielding 2,3-dimethylbutane. 

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... 

Ethalk [Ethylene alkylation] A catalytic process for combining ethylene with isobutane, to make a gasoline blending component, using a dilute ethylene stream. Developed by Technip Benelux (formerly KTI) from 1995, but not piloted by mid-1999. 

In the present paper, catalytic activity of a number of zeolltic catalysts In alkylation of Isobutane with various olefins have been Investigated and some considerations of ethylene alkylation have been made. 

Mechanistically, as elucidated by Schmerling (19) and as illustrated for isobutane-ethylene (alkane-alkene) alkylation (Scheme 1), the reaction is initiated by protonation of the alkene (ethylene) to form a very acidic primary ethyl cation (step 1) which rapidly abstracts a hydride ion from an isobutane molecule to generate the chain carrying t-butyl cation (step 2). This can then alkylate another molecule of ethylene to form the secondary-2-methyl-t-butyl carbenium ion (step 3). This cation rapidly undergoes a... 

In similar rocking autoclave experiments, isobutane was alkylated by ethylene at 40-150° using REX catalyst (154. The products at low temperatures were chiefly hexanes, with 2,3-dimethylbutane predominating. At higher temperatures, large amounts of pentanes and moderate amounts of heptanes and octanes were also formed. 

On the other hand, ethylene cannot be used in isobutane/olefin alkylation on sulphuric acid, because of the formation of stable ethylsulfates. However, when using a R,Ca-Y catalysts in combination with transition-metal cations (especially Ni) (Minachev et al. 1977) an alkylate containing octane isomers as the major product (about 80%), without the formation of hexanes has been obtained. They observed a strong influence of the chemical composition on the catalytic behaviour of R,Ca-Y zeolites, showing a maximum on a R,Ca-Y (16.6% Ca and 64.2% R) zeolite. 

Svlfuric Add Alkylation. Despite some disadvantages, such as acid-reGOLYery expense and refrigeration to minimize oxidation, about four fifths of the alkylate produced for motor fuels is based on sulfuric acid as a catalyst. As with HF alkylation, isobutane is alkylated with olefins (other than ethylene), and a flow diagram for such a process is ven in Fig. 14-5. 

Isobutane is alkylated with a mixture of ethylene and propylene, the ratio of the lighter to the heavier olefin being about 4 1. In commercial production, 70-90 lb of alkylate is produced per pound of aluminum... 

When usiag HF TaF ia a flow system for alkylation of excess ethane with ethylene (ia a 9 1 molar ratio), only / -butane was obtained isobutane was not detectable even by gas chromatography (72). Only direct O -alkylation can account for these results. If the ethyl cation alkylated ethylene, the reaction would proceed through butyl cations, inevitably lea ding also to the formation of isobutane (through /-butyl cation). 

The catalysts used in the industrial alkylation processes are strong Hquid acids, either sulfuric acid [7664-93-9] (H2SO or hydrofluoric acid [7664-39-3] (HE). Other strong acids have been shown to be capable of alkylation in the laboratory but have not been used commercially. Aluminum chloride [7446-70-0] (AlCl ) is suitable for the alkylation of isobutane with ethylene (12). Super acids, such as trifluoromethanesulfonic acid [1493-13-6] also produce alkylate (13). SoHd strong acid catalysts, such as Y-type zeoHte or BE -promoted acidic ion-exchange resin, have also been investigated (14—16). 

The value of butylenes ia the United States is determined by their value ia alkylation of isobutane to high octane gasoline. Table 11 shows how the chemical use of ethylene, propylene, butylenes, and butanes varied between 1983 and 1988 and their corresponding price swiags. 

Alkylation of isobutane and ethylene with a complex of hquid hydrocarbon -1- AICI3 -1- HCl. 

Table 5.3-4 Alkylation of ethylene and 2-butene with isobutane. Semicontinuous pilot-plant results...

Alkylation in the petroleum industry, a process by which an olefin (e.g., ethylene) is combined with a branched-chain hydrocarbon (e.g., isobutane) alkylation may be accomplished as a thermal or a catalytic reaction. 

The ability of zeolites to catalyze paraffin-olefin alkylation has been known since 1968. Garwood and Venuto of Mobil described the use of rare-earth hydrogen X faujasite for the alkylation of isobutane with ethylene to give branched Cg-Cg... 

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. 

Problem 6.60 Ethylene is alkylated with isobutane in the presence of acid (HF) to give chiefly (CH,),CHCH(CH,)2, not (CHiljCCHjCH,. Account for the product. 

The use of thermal and catalytic cracking processes for the production of high-octane motor gasolines is accompanied by the production of quantities of light hydrocarbons such as ethylene, propylene, butene, and isobutane. These materials are satisfactory gasoline components octane-wise, but their vapor pressures are so high that only a portion of butanes can actually be blended into gasoline. Alkylation is one of several processes available for the utilization of these excess hydrocarbons. 

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. 

Successful catalytic alkylation of isobutane with ethylene has been accomplished in one commercial installation using aluminum chloride catalyst (I). The chief product of the reaction is 2,3-dime thy lbutane, a hydrocarbon having very high aviation octane ratings. Ethylene has also been alkylated with isobutane in a thermal process to give 2,2-dimethylbutane as the chief product component (6). When sulfuric or hydrofluoric acid alkylation with ethylene is attempted, the ethylene forms a strong bond with the acid, and fails to react with isobutane. The net result is the formation of little or no product, accompanied by excessive catalyst deterioration. 

The main products formed by the catalytic alkylation of isobutane with ethylene (HC1—AICI3, 25-35°C) are 2,3-dimethylbutane and 2-methylpentane with smaller amounts of ethane and trimethylpentanes.13 Alkylation of isobutane with propylene (HC1—AICI3, — 30°C) yields 2,3- and 2,4-dimethylpentane as the main products and propane and trimethylpentanes as byproducts.14 This is in sharp contrast with product distributions of thermal alkylation that gives mainly 2,2-dimethylbutane (alkylation with ethylene)15 and 2,2-dimethylpentane (alkylation with propylene).16... 

In the ethane-ethylene reaction in a flow system with short contact time, exclusive formation of n-butane takes place (longer exposure to the acid could result in isomerization). This indicates that a mechanism involving a trivalent butyl cation depicted in Eqs. (5.1)—(5.5) for conventional acid-catalyzed alkylations cannot be operative here. If a trivalent butyl cation were involved, the product would have included, if not exclusively, isobutane, since the 1- and 2-butyl cations would preferentially isomerize to the rm-butyl cation and thus yield isobutane [Eq. (5.9)]. It also follows that the mechanism cannot involve addition of ethyl cation to ethylene. Ethylene gives the ethyl cation on protonation, but because it is depleted in the excess superacid, no excess ethylene is available and the ethyl cation will consequently attack ethane via a pentacoordinated (three-center, two-electron) carbocation [Eq. (5.10)] ... 

More information is available about orientation, when a second alkyl group is introduced into the aromatic ring, and about relative rates. As might be expected, propene reacts more easily than ethylene [342,346] and isobutene more easily than propene [342]. Normal butenes are sometimes isomerised in the process practically the same product composition, consisting mainly of 2,2,4-trimethylpentane, is obtained in the alkylation of isobutane whether the olefin component is isobutene or 2-butene [339]. In the alkylation of aromatic hydrocarbons, this side reaction is negligible. 

Thermal alkylation was never a totally successful commercial process because of the severe operating conditions required. The reaction was carried out in a heater coil with temperatures of 900°-975°F, pressures in the range of 3000-5000 psig, and contact times of 2-7 seconds (16). Polymerization of the olefins occurred readily under these conditions, and low olefin concentrations had to be used to minimize undesirable side reactions. Ethylene could be alkylated more readily than the higher molecular weight olefins, and either normal butane or isobutane could react with the olefin. In general, the yields and quality of the product were not equal to those obtained with catalytic alkylation. 

Typical heterogeneous Ziegler catalysts operate at temperatures of 70 100°C and pressures of 0.1 2 MPa (15 300 psi). The polymerization reactions are carried out in an inert liquid medium (e.g, hexane, isobutane) or in the gas phase. Molecular weights of LLDPE resins are controlled by using hydrogen as a chain-transfer agent. Reactivities of a-olefins in copolymerization with ethylene depend on two factors the size of the alkyl groups attached to their double bonds and the type of catalyst,... 

Propane as a degradation product of polyethylene (a byproduct in the reaction) was ruled out because ethylene alone under the same conditions does not give any propane. Under similar conditions but under hydrogen pressure, polyethylene reacts quantitatively to form C3 to C6 alkanes, 85% of which are isobutane and isopentane. These results further substantiate the direct alkane alkylation reaction and the intermediacy of the pentacoordinate carbonium ion. Siskin also found that when ethylene was allowed to react with ethane in a flow system, n-butane was obtained as the sole product, indicating that the ethyl cation is alkylating the primary C—H bond through a five-coordinate carbonium ion [Eq. (5.66)]. 

Feed stock for the first sulfuric acid alkylation units consisted mainly of butylenes and isobutane obtained originally from thermal cracking and later from catalytic cracking processes. Isobutane was derived from refinery sources and from natural gasoline processing. Isomerization of normal butane to make isobutane was also quite prevalent. Later the olefinic part of the feed stock was expanded to include propylene and amylenes in some cases. When ethylene was required in large quantities for the production of ethylbenzene, propane and butanes were cracked, and later naphtha and gas oils were cracked. This was especially practiced in European countries where the cracking of propane has not been economic. 

Diisopropyl has been used to raise octanes of both aviation and motor gasolines but has not been made in large quantities. It is produced by the alkylation of isobutane with ethylene over aluminum chloride catalyst. 

HF is intimately contacted with isobutane and mixed with light olefins (ethylenes, propenes, etc.) under pressure at 40-45°C to produce branch chain fuel which has very high octane value. HF, being only slightly soluble in hydrocarbons, is easily separated, recycled and regenerated. The alkylate is water washed and dried. The consumption of hydrofluoric acid per barrel of alkylate varies from 0.09 to 0.23 kg. 

The explanation of the experimental results is that the alkylation proceeds In two steps - first ethylene dimerization takes place (7) and then n-butene (or its precursor) formed alkylated with Isobutane as follows ... 

Dimerization presumably takes place on the transition metal-containing sites, and alkylation on the acidic sites of zeolltic surface. The sodium form of zeolite exchanged with transition metal cations Is capable of dimerization (and further polymerization), but does not practically exhibit alkylating capacity. This explains the composition of the product obtained from ethylene and Isobutane over this catalyst (Table V, column 3). 

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