Alkylation with butylenes

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... 

Alkylation of isobutylene and isobutane in the presence of an acidic catalyst yields isooctane. This reaction proceeds through the same mechanism as dimerization except that during the last step, a proton is transferred from a surrounding alkane instead of one being abstracted by a base. The cation thus formed bonds with the base. Alkylation of aromatics with butylenes is another addition reaction and follows the same general rules with regard to relative rates and product stmcture. Thus 1- and 2-butenes yield j -butyl derivatives and isobutylene yields tert-huty derivatives. 

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). 

Figure 13.42 Mechanism for/-butane alkylation with 2-butylene and 1-butylene.

Table 13.5 Steps for i-butane alkylation with 2-butylene to make TMP.

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. 

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... 

Considerable effort has been put into minimizing the adverse effects of these olefins. It was found that alkylating propylene and pentylenes in a mixture with butylenes promoted the desired reactions and reduced the octane and acid consumption penalties. Furthermore, by optimizing temperature, isobutane-to-olefin ratio, acid strength, and other variables, the deleterious effects of propylene and pentylenes in the feed can be minimized (4, 8, 21). The decision as to how much of these olefins to include in the alkylation unit feed depends on many different factors, such as their value relative to alkylate, butylene and isobutane avails, alkylate volume and octane requirements, acid costs, etc. 

In the petroleum industry, catalytic cracking units provide the major source of olefinic fuels for alkylation. A feedstock from a catalytic cracking units is typified by a Ci/C 4 charge with an approximate composition of propane, 12.7% propylene, 23.6% isobmaiie, 25.0% n-bulane, 6.9% isobutylene, 8.8% 1-butylene, 6.9% and 2-butylene, 16.1%. The butylenes will produce alkylates with octane numbers approximately three units higher than those from propylene. 

In the production of aviation and motor alkylates, both propylene and amylenes are inferior feed stocks when compared with the butylenes. These feeds produce lighter and heavier alkylates, respectively, than the butylenes, both alkylates having a lower octane than the trimethylpentane produced from butylenes. Also, acid consumption when sulfuric acid catalyst is used is two or more times as great with propylene or amylenes than with butylenes. Hydrofluoric acid catalyst, on the other hand, is not consumed at a higher rate on propylene and amylene feeds but does make a higher percentage of tar. 

One possible advantage of the HF process in propylene/ butylene alkylation is the production of isobutylene from isobutane effected by the hydride-ion transfer to propylene. Isobutylene is the C4 olefinic isomer which produces a significantly higher octane alkylate with HF. This shift, however, converts as much as 22% of the propylene to propane and is a debit. 

Some normal butane is also produced from butylenes but this is estimated at only 4-6%. The higher octane isobutylene alkylate and a claimed yield increase must be contrasted with normal paraffin production from olefins and a higher isobutane requirement. The typical mixed 03 = 704= feed can be made to produce a high octane alkylate with either acid catalyst by the optimization of other variables. The highest alkylate octane numbers reported are produced with sulfuric acid catalyst, alkylating with a typical cat cracker butylene olefin. 

TrimethyIpentane and other isooctanes. Isononanes, isodecanes, and isoundecanes... Alkylation of isobutane with butylenes ... 

Typical yields of alkylate obtained in plants operated during World War II were in the order of 1-2 gallons per pound of catalyst in the alkylation of isobutane with butylenes and only about 0.5 gallon per pound for alkylation with propene or amylenes (Anonymous, 39). The octane numbers of the alkylates (175° end point) obtained with butylenes, propene, and amylenes were about 92-94, 88-89, and 89-90, respectively. 

Alkylated phenol. The most commonly used alkylated phenol ethoxylates (APE) have included octyl phenol ethoxylate and nonylphenol ethoxylates with 3-11 moles of EO, which were produced by alkylation of butylene dimer or propylene trimer onto phenol and subsequent ethoxylation. They had been used extensively in laundry and hard surfacecleaning applications in the nonionic form, and as the sulfated and phosphated derivatives of the low-mole ethoxylates in a variety of industrial applications. Concerns over the environmental impact of the partial metabolites generated during the waste treatment of these surfactants has prompted their elimination from European consumer product formulations, and their deformulation from most consumer products in North America and elsewhere in the world. 

In many instances, BAB has been produced at the same locations that also produce LAB. However, the principal raw material is different. To produce BAB, propylene tetramer (tetrapropylene) is used as the principal olefinic raw material to alkylate with benzene. Propylene tetramer is produced at two types of plants those dedicated to propylene oligomerization and those plants which have flexible oligomerization capability for mixtures of propylenes, butylenes, and amylenes. Propylene tetramer is a highly branched material and has many structures, some of which are shown in Figure 2.3. The alkylation catalyst used to produce BAB has exclusively been hydrofluoric (HF) acid. 

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. 

Butene. Commercial production of 1-butene, as well as the manufacture of other linear a-olefins with even carbon atom numbers, is based on the ethylene oligomerization reaction. The reaction can be catalyzed by triethyl aluminum at 180—280°C and 15—30 MPa ( 150 300 atm) pressure (6) or by nickel-based catalysts at 80—120°C and 7—15 MPa pressure (7—9). Another commercially developed method includes ethylene dimerization with the Ziegler dimerization catalysts, (OR) —AIR, where R represents small alkyl groups (10). In addition, several processes are used to manufacture 1-butene from mixed butylene streams in refineries (11) (see BuTYLENEs). 

All lation. The combination of olefins with paraffins to form higher isoparaffins is termed alkylation (qv). Alkylate is a desirable blendstock because it has a relatively high octane number and serves to dilute the total aromatics content. Reduction of the olefins ia gasoline blendstocks by alkylation also reduces tail pipe emissions. In refinery practice, butylenes are routinely alkylated by reaction with isobutane to produce isobutane—octane (26). In some plants, propylene and/or pentylenes (amylenes) are also alkylated (27). 

Alkylate is composed of a mixture of isoparaffins whose octane numbers vary with the olefins from which they were made. Butylenes produce the highest octane numbers, propylene the lowest, and amylenes (pentylenes) the iatermediate values. AH alkylates, however, have high (>87) octane numbers that make them particularly valuable. 

Alkylate. Alkylation means the chemical combination of isobutane with any one or a combination of propylene, butylenes, and amylenes to produce a mixture of highly branched paraffins that have high antiknock properties with good stabiUty. These reactions are cataly2ed by strong acids such as sulfuric or hydrofluoric acid and have been studied extensively (98—103). In the United States mostly butylenes and propylene are used as the olefins. 

Siace the heating values are similar to LPG, butylenes may be blended with LPG for bottie gas (105,106). In Europe, because LPG is unavailable, it is common to use butylenes as fuel. In the United States, butylenes have a higher value as an alkylate feed. LPG, which is readily available, is used as fuel iastead. 

MethylceUulose is made by reaction of alkaU ceUulose with methyl chloride until the DS reaches 1.1—2.2. HydroxypropyhnethylceUulose [9004-65-3], the most common of this family of products, is made by using propylene oxide in addition to methyl chloride in the reaction MS values of the hydroxypropyl group in commercial products are 0.02—0.3. Use of 1,2-butylene oxide in the alkylation reaction mixture gives hydroxybutyhnethylceUulose [9041-56-9, 37228-15-2] (MS 0.04—0.11). HydroxyethyhnethylceUulose [903242-2] is made with ethylene oxide in the reaction mixture. 

To obtain light ends conversion, alkylation and polymerization are used to increase the relative amounts of liquid fuel products manufactured. Alkylation converts olefins, (propylene, butylenes, amylenes, etc.), into high octane gasoline by reacting them with isobutane. Polymerization involves reaction of propylene and/or butylenes to produce an unsamrated hydrocarbon mixture in the motor gasoline boiling range. 

Figure 11.4-2 shows process flows for an HF alkylation unit. The three sections are 1) reaction, 2). settling and 3) fractionation. In the reaction section isobutane feed is mixed with the olefin feed (usually propylene and butylene) in approximately a 10 or 15 to 1 ratio. In the presence of the HF acid catalyst the olefins react to form alkylate for gasoline blending. The exothermic reaction requires water cooling. The hydrocarbon/HF mixture goes to the settling... 

Alkylation (Figure 4.11) combines low-molecular-weight olefins (primarily a mixture of propylene and butylene) with isobutene in the presence of a catalyst, either sulfuric acid or hydrofluoric acid. The product, called alkylate, consists of... 

Alkylation is used in mariy petroleum refineries to react unsaturated butylenes with isobutane to form high octane iso-octane (alkylate). The reaction is carried out in a two hquid-phase system sutfuric acid/tiydrocarbon. 

The first serious notice of C4 hydrocarbons came with the development of refinery cracking processes. When catalytic cracking became popular, refiners were faced with disposing of a couple of thousand barrels per day of a stream containing butane, butylenes, and small amounts of butadiene. Their first thought was to burn it all as refinery fuel, but then they developed the alkylation process. With that, they could undo some of the molecule shatter that took place in the crackers and reassemble some of the smaller pieces as alkylate, a high-octane gasolinerblending component. 

Isobutylene is the most chemically reactive of the butylene isopiers. If the objective is just to get the isobutylene out of the C4 stream, it can be removed by reaction with methanol (CH3OH) to make MTBE (methyl tertiary butyl ether), by reaction with water to make TBA (tertiary butyl alcohol), by polymerization, or by solvent extraction. After that, butene-1 can be removed by selective adsorption or by distillation. That leaves the butene-2 components, together with iso- and normal butane, which are generally used as feed to an alkylation plant. 

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