Refinery catalysts alkylation

Refinery alkylation processes utilize either sulfuric acid or hydrofluoric acid as reaction catalysts. The feedstock for both alkylation processes originates primarily from hydrocracking and catalytic cracking operations. Coker gas oils also serve as feedstock in some applications. The differences and similarities between sulfuric acid alkylation and hydrofluoric acid alkylation are shown in TABLE 2-5. Typical alkylation reactions are shown in FIGURE 2-9. A sulfuric acid alkylation unit is illustrated in FIGURE 2-10. 

The relative location of refinery and acid plant is one of the most important factors in the economic decision between sulfuric acid and anhydrous hydrogen fluoride as a catalyst for alkylation. Besides the distance, other factors such as regeneration of spent acid, energy costs, the nature of the feed and increasingly stringent regulatory constraints play an important role in the selection of alkylation catalyst. Sulfuric acid is selected for alkylation if feed is rich in pentenes or n-butene. HF is selected if the feed is rich in propenes or isobutane. 

So the competition will apparently continue, each refinery alkylation plant and catalyst selection being evaluated on an individual basis. 

Multiple supercritical isobutane regenerations of a partially deactivated USY solid acid catalyst also was tested utilizing a refinery alkylation feed blend Error Reference source not found,). The catalyst activity recovery was compared with the results of experiments that utilized a synthetic feed blend. 

A classic example of substitution concerns the use of hydrogen fluoride (HF) as an alkylation catalyst in oil refineries. The properties of HF that make it such an effective catalyst also make it a highly solvent and toxic chemical in the event of a release. An alternative alkylation catalyst is sulfuric acid. Although sulfuric acid is also a hazardous material, it cannot cause a catastrophic accident when released in the way that HF can. 

Alkylation fScheme 6.41 or refinery alkylation is the reaction of isobutane with short-chain olefins (C3—C5) in the presence of highly acidic catalysts. Alkylates are particularly suitable... 

Refinery alkylation takes place at high temperatures and pressures without catalysts. However, all industrially relevant processes proceed at low-temperatures in the presence of highly acidic catalysts. By appropriate choice of operating conditions, most of the alkylate can be made to fall within the gasoline boiling range with RONS of94-99 and MONs of 88-94. 

Isobutane is almost insoluble in the liquid acid catalysts used in refinery alkylation. Therefore, intense mixing is necessary to make sure that at least this low isobutene equilibrium concentration is maintained throughout the readion in the acid phase to allow the reaction to proceed properly. As the alkylation readion occurs at or near... 

Hydrogen fluoride (HF) has many industrial uses. In the process industries, it is used in many refineries as an alkylation catalyst (the alternative is sulfuric acid). The HF arrives either by tank car or truck. It is loaded into a storage tank, from where it is fed on a continuous basis. 

Isomerization. Isomerization is a catalytic process which converts normal paraffins to isoparaffins. The feed is usually light virgin naphtha and the catalyst platinum on an alumina or zeoflte base. Octanes may be increased by over 30 numbers when normal pentane and normal hexane are isomerized. Another beneficial reaction that occurs is that any benzene in the feed is converted to cyclohexane. Although isomerization produces high quahty blendstocks, it is also used to produce feeds for alkylation and etherification processes. Normal butane, which is generally in excess in the refinery slate because of RVP concerns, can be isomerized and then converted to alkylate or to methyl tert-huty ether (MTBE) with a small increase in octane and a large decrease in RVP. 

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). 

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). 

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). 

AH commercial processes for the manufacture of caprolactam ate based on either toluene or benzene, each of which occurs in refinery BTX-extract streams (see BTX processing). Alkylation of benzene with propylene yields cumene (qv), which is a source of phenol and acetone ca 10% of U.S. phenol is converted to caprolactam. Purified benzene can be hydrogenated over platinum catalyst to cyclohexane nearly aH of the latter is used in the manufacture of nylon-6 and nylon-6,6 chemical intermediates. A block diagram of the five main process routes to caprolactam from basic taw materials, eg, hydrogen (which is usuaHy prepared from natural gas) and sulfur, is given in Eigute 2. 

Washing light hydrocarbons with water is a common refinery practice. It finds application on the feed to catalytic polymerization plants. It is used to remove any entrained caustic from the mercaptan removal facilities as well as any other impurities such as amines which tend to poison the polymerization catalyst. Another use for water wash is in alkylation plants to remove salts from streams, where heating would tend to deposit them out and plug up heat exchanger surfaces. Water washing can be carried out in a mixer- settler, or in a tower if more intimate contacting is necessary. 

Alkad A process for improving the safety of alkylation processes using hydrofluoric acid as the catalyst. A proprietary additive curtails the emission of the acid aerosol that forms in the event of a leak. Based on observation of G. Olah in the early 1990s that liquid polyhydrogen fluoride complexes (of amines such as pyridine) depress the vapor pressure of HF above alkylation mixtures. Developed by UOP and Texaco and operated at Texaco s refinery at El Dorado, TX, since 1994. A competing process is ReVAP, developed by Phillips and Mobil. 

In the chapter on olefms plants, in the section on propylene, a route to making propylene involved butene-2. In this process, called metathesis, ethylene and butene-1 are passed over a catalyst, and the atoms do a musical chair routine. When the music stops, the result is propylene. The conversion of ethylene to propylene is an attraction when the growth rate of ethylene demand is not keeping up with propylene. Then the olefins plants produce an unbalanced product slate, and producers wish they had an on-purpose propylene scheme instead of just a coproduct process. The ethylene/butene-2 metathesis process is attractive as long as the supply of butylenes holds out. Refineries are big consumers of these olefins in their alkylation plants, and so metathesis process has, in effect, to buy butylene stream away from the gasoline blending pool. 

Alkylation A refinery process for producing high-octane components consisting mainly of branched chain paraffins. The process involves combining light olefins with isoparaffins, usually butene and isobutane, in the presence of a strong acid catalyst such as hydrofluoric or sulfuric acid. 

A gas-phase alkylation over an alumina-supported BF3 catalyst developed by UOP (Alkar process)312,313 reduces the corrosion problems associated with liquid-phase alkylation processes. An advantage of this technology is that it utilizes very dilute (8-10%) ethylene streams, such as refinery fuel gases (cracked gas streams). At the same time, to properly support BF3 is difficult. 

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