Butylene alkylate

BEA (Si/Al2 = 30), FAU (Si/Al2 = 8.6) and EMT (Si/Afi = 8.6) framework types were compared for i-butane/2-butylene alkylation. During the lifetime of the catalyst the butylene turnover number (TON) was approximately the same for each of the three zeolites and the acid sites were equivalent from the standpoint of stability in each case. With EMT the lowered selectivity to consecutive reaction products 2,2,4-TMP -I- 2,3,4-TMP relative to 2,2,3-TMP -i- 2,3,3-TMP and the lowered selectivity to heavies relative to BEA was interpreted as higher hydride transfer activity. 

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... 

As mentioned previously, the use of aluminum chloride alkylation has been very limited in the petroleum refining industry. The aluminum chloride catalyst, being somewhat more difficult to handle and regenerate, could not compete economically with H2S04 and HF catalysts for propylene and butylene alkylation. However, aluminum chloride will catalyze ethylene alkylation whereas H2S04 and HF will not. In the past, ethylene alkylation has not been used much because of the higher olefin feed cost (15). 

As shown in Table II, the alkylation of propylene and pentylenes results in higher acid consumptions and lower product octanes than butylene alkylation. Because of these penalties, only butylenes were alkylated for many years. However, the rapidly increasing demand for alkylate as a motor gasoline component has forced refiners to include propylene and, to a lesser extent, pentylenes in their alkylation feeds. 

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. 

One patented process (40) was introduced in the mid- 60s to reduce the amount of sulfuric acid required by alkylation it was called the Sulfuric Acid Recovery Process (SARP) and was jointly licensed by Texaco Development Corporation and Stratford Engineering Corporation. Chemically, SARP proved all claims made for it. Utilized only with propylene/butylene alkylation the acid requirement was reduced as much as 70% actual acid dilution rates were lower than 0. 2 acid/gallon alkylate. However, the spent acid from SARP was different and could not be regenerated at the same rate as regular spent alkylation acid. This caused the chemical companies to increase the charges for regenerating the SARP spent acid to a point where there was no economic incentive to operate SARP. The two commercial SARP installations are not in use at the present time although new possibilities for SARP have arisen just in the past few months. 

Olah et al. reported the triflic acid-catalyzed isobutene-iso-butylene alkylation, modified with trifluoroacetic acid (TFA) or water. They found that the best alkylation conditions were at an acid strength of about//q = —10.7, giving a calculated research octane number (RON) of 89.1 (TfOH/TFA) and91.3 (TfOH/HaO). Triflic acid-modified zeohtes can be used for the gas phase synthesis of methyl tert-butyl ether (MTBE), and the mechanism of activity enhancement by triflic acid modification appears to be related to the formation of extra-lattice Al rather than the direct presence of triflic acid. A thermally stable solid catalyst prepared from amorphous silica gel and triflic acid has also been reported. The obtained material was found to be an active catalyst in the alkylation of isobutylene with n-butenes to yield high-octane gasoline components. A similar study has been carried out with triflic acid-functionalized mesoporous Zr-TMS catalysts. Triflic acid-catalyzed carbonylation, direct coupling reactions, and formylation of toluene have also been reported. Tritlic acid also promotes transalkylation and adaman-tylation of arenes in ionic liquids. Triflic acid-mediated reactions of methylenecyclopropanes with nitriles have also been investigated to provide [3 + 2] cycloaddition products as well as Ritter products. Tritlic acid also catalyzes cyclization of unsaturated alcohols to cyclic ethers. ... 

Aluminas may be used for the dehydrofluorination of alkylfluorides, which are byproducts of the HF-catalyzed isobutane—butylene alkylation process. Fluoroalkanes are converted to olefins on alumina at temperatures of 170—220 °C. FIF is adsorbed on the alumina and aluminum fluoride is formed as a consequence, regeneration is needed every 6 months (596). 

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. 

Butylenes. Butylenes are the primary olefin feedstock to alkylation and produce a product high in trimethylpentanes. The research octane number, which is typically in the range of 94—98, depends on isomer distribution, catalyst, and operating conditions. 

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). 

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. 

The Cy and Cg paraffias comprise about 90% of the alkylate Cg accounts for over 60%. Over 70% of the commercial alkylation processes employ sulfuric acid as the catalyst. Among the butylenes, 2-butene is superior to 1-butene. The C —fraction from the catalytic crackers is considered to be a superior feedstock to the alkylation unit. 

Polymer Gasoline. Refinery trends tend to favor alkylation over polymerisation. Unlike the alkylation process, polymerisation does not require isobutane. The catalyst is usually phosphoric acid impregnated on kieselghur pellets. Polymerisation of butylenes is not an attractive alternative to alkylation unless isobutane is unavailable. The motor octane number of polymer gasoline is also low, and there is considerable shrinkage ia product volume. The only commercial unit to be built ia recent years is at Sasol ia South Africa. The commercial process was developed by UOP ia the 1940s (104). 

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. 

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. 

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. 

Seasonal chances in gasoline sales and heating oil sales compel some modifications to be made in conversion level. Therefore, the conversion pattern of a given catalytic cracking unit can vary from season to season. In summer operations, for instance, higher yields of motor gasoline are desired, both from direct production of 5/430° FVT catalytic naphtha and also from conversion of butylenes and isobutane to alkylate. 

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... 

Propylene and butylenes Feed to alkylation or polymerization units... 

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