Ethylbenzene, alkylation

Figure 41.7 Ethylbenzene alkylation activity vs. catalyst particle diameter.

The alkylation product of benzene (W) and ferf-butylbenzene (S4) with ethylene yields predominantly sec-butyl alkylates. This is the case because the ethylbenzene alkylate formed reacts very rapidly in the normal side-chain alkylation reaction. The sec-butyl aromatic alkylates much less readily. The much greater ease of side-chain alkylation over nuclear alkylation also accounts for the exclusive formation of side-chain alkylates from compounds, such as cumene, that are predominantly metalated on the ring by alkylalkali metal compounds. 

Since aprotio sites in the zeolites under study were generated via ion exchange of protons inside crystal volume, the aprotio sites formed are also situated inside crystals. In connection with this, a position selectivity of primary alkylation must be influenced by structural restrictions which are put on the ti nsition state by ZSM-5 type zeolite. Hence, as follows from refs.[6,7], para-isomer must be a primary product of alkylation. Taking into account these ideas,the schemes of the main routes of investigated reactions are accepted (Jigs. 1,2). As seen from the schemes, the pathways of both reactions are practically the same. The only difference is that in the case of ethylbenzene alkylation proceeds... 

Future ethylbenzene alkylation catalyst development efforts will also undoubtedly focus on systems that convert less conventional feedstocks including ethane and ethanol. The two-step Dow ethane based process for ethylbenzene production is believed to be uneconomical because of its high capital investment requirement (26). However, it is a very attractive concept, and could be implemented if more efficient catalysts or improved process designs could be developed. 

Schmidt, R. Zarchy, A. Petersen, G. New developments in cumene and ethylbenzene alkylation—Paper 124b. In 1st Annual Aromatic Producers Conference—AIChE Spring Meeting, New Orleans, LA, Mar 10-14, 2002. 

Alkylbenzenes are also obtained (but in somewhat lower yield) from phenyl-sodium and alkyl bromides. Thus ethylbenzene is produced from phenyl-sodium and ethyl bromide ... 

Friedel-Crafts alkylation using alkenes has important industrial appHcations. The ethylation of benzene with ethylene to ethylbenzene used in the manufacture of styrene, is one of the largest scale industrial processes. The reaction is done under the catalysis of AlCl in the presence of a proton source, ie, H2O, HCl, etc, although other catalysts have also gained significance. 

For example, ia the iadustriaHy important alkylation of benzene with ethylene to ethylbenzene, polyethylbenzenes are also produced. The overall formation of polysubstituted products is minimized by recycling the higher ethylation products for the ethylation of fresh benzene (14). By adding the calculated equiUbrium amount of polyethylbenzene to the benzene feed, a high conversion of ethylene to monoethylbenzene can be achieved (15) (see also... 

Propylene oxide [75-56-9] is manufactured by either the chlorohydrin process or the peroxidation (coproduct) process. In the chlorohydrin process, chlorine, propylene, and water are combined to make propylene chlorohydrin, which then reacts with inorganic base to yield the oxide. The peroxidation process converts either isobutane or ethylbenzene direcdy to an alkyl hydroperoxide which then reacts with propylene to make propylene oxide, and /-butyl alcohol or methylbenzyl alcohol, respectively. Table 1 Hsts producers of propylene glycols in the United States. 

Alkylated aromatics have excellent low temperature fluidity and low pour points. The viscosity indexes are lower than most mineral oils. These materials are less volatile than comparably viscous mineral oils, and more stable to high temperatures, hydrolysis, and nuclear radiation. Oxidation stabihty depends strongly on the stmcture of the alkyl groups (10). However it is difficult to incorporate inhibitors and the lubrication properties of specific stmctures maybe poor. The alkylated aromatics also are compatible with mineral oils and systems designed for mineral oils (see Benzene Toulene Xylenes and ethylbenzene). ... 

Ethjlben ne Synthesis. The synthesis of ethylbenzene for styrene production is another process in which ZSM-5 catalysts are employed. Although some ethylbenzene is obtained direcdy from petroleum, about 90% is synthetic. In earlier processes, benzene was alkylated with high purity ethylene in liquid-phase slurry reactors with promoted AlCl catalysts or the vapor-phase reaction of benzene with a dilute ethylene-containing feedstock with a BF catalyst supported on alumina. Both of these catalysts are corrosive and their handling presents problems. 

These operations have been gradually replaced by the Mobd-Badger process (28), which employs an acidic ZSM-5 catalyst and produces ethylbenzene using both pure and dilute ethylene sources. In both cases, the alkylation is accomplished under vapor-phase conditions of about 425°C,... 

There are two main subclasses ofhydroperoxid.es organic (alkyl) hydroperoxides, ie, ROOH, and organomineral hydroperoxides, ie, Q(OOH), where Q is sihcon (43), germanium, tin, or antimony. The alkyl group in ROOH can be primary, secondary, or tertiary. Except for ethylbenzene hydroperoxide, only alkyl hydroperoxides are commercially important. 

Most of the industrially important alkyl aromatics used for petrochemical intermediates are produced by alkylating benzene [71-43-2] with monoolefins. The most important monoolefins for the production of ethylbenzene, cumene, and detergent alkylate are ethylene, propylene, and olefins with 10—18 carbons, respectively. This section focuses primarily on these alkylation technologies. 

Fig. 3. Unocal—Lummus—UOP ethylbenzene process AR = alkylation reactor TR = transalkylation reactor BC = benzene column ...

Vapor-Phase Processes. Although vapor-phase alkylation has been practiced since the early 1940s, it could not compete with Hquid-phase processes until the 1970s when the Mobil—Badger vapor-phase ethylbenzene process was introduced (Eig. 4). The process is based on Mobil s ZSM-5 zeohte catalyst (38,52,53). The nonpoUuting and noncorrosive nature of the process is one of its major advantages over the AlCl hquid-phase system. 

Catalysts. Nearly aU. of the industrially significant aromatic alkylation processes of the past have been carried out in the Hquid phase with unsupported acid catalysts. For example, AlCl HF have been used commercially for at least one of the benzene alkylation processes to produce ethylbenzene (104), cumene (105), and detergent alkylates (80). Exceptions to this historical trend have been the use of a supported boron trifluoride for the production of ethylbenzene and of a soHd phosphoric acid (SPA) catalyst for the production of cumene (59,106). 

Styrene is manufactured from ethylbenzene. Ethylbenzene [100-41-4] is produced by alkylation of benzene with ethylene, except for a very small fraction that is recovered from mixed Cg aromatics by superfractionation. Ethylbenzene and styrene units are almost always installed together with matching capacities because nearly all of the ethylbenzene produced commercially is converted to styrene. Alkylation is exothermic and dehydrogenation is endothermic. In a typical ethylbenzene—styrene complex, energy economy is realized by advantageously integrating the energy flows of the two units. A plant intended to produce ethylbenzene exclusively or mostly for the merchant market is also not considered viable because the merchant market is small and sporadic. 

The transalkylation reaction is essentiaHyisothermal and is reversible. A high ratio of benzene to polyethylbenzene favors the transalkylation reaction to the right and retards the disproportionation reaction to the left. Although alkylation and transalkylation can be carried out in the same reactor, as has been practiced in some processes, higher ethylbenzene yield and purity are achieved with a separate alkylator and transalkylator, operating under different conditions optimized for the respective reactions. 

A small fraction of the hydrocarbons decompose and deposit on the catalyst as carbon. Although the effect is minute ia terms of yield losses, this carbon can stiU significantly reduce the activity of the catalyst. The carbon is formed from cracking of alkyl groups on the aromatic ring and of nonaromatics present ia certain ethylbenzene feedstocks. It can be removed by the water gas reaction, which is catalyzed by potassium compounds ia the catalyst. Steam, which is... 

The advance (ca 1996) in alkylation technology enables the production of ultrahigh purity ethylbenzene at a low cost. With this ethylbenzene as the intermediate, a dehydrogenation unit of the present design will be able to produce styrene of 99.95% purity routinely. It may prompt a new standard in the styrene industry. 

Ethyltoluene is manufactured by aluminum chloride-cataly2ed alkylation similar to that used for ethylbenzene production. All three isomers are formed. A typical analysis of the reactor effluent is shown in Table 9. After the unconverted toluene and light by-products are removed, the mixture of ethyltoluene isomers and polyethyltoluenes is fractionated to recover the meta and para isomers (bp 161.3 and 162.0°C, respectively) as the overhead product, which typically contains 0.2% or less ortho isomer (bp 165.1°C). This isomer separation is difficult but essential because (9-ethyltoluene undergoes ring closure to form indan and indene in the subsequent dehydrogenation process. These compounds are even more difficult to remove from vinyltoluene, and their presence in the monomer results in inferior polymers. The o-ethyltoluene and polyethyltoluenes are recovered and recycled to the reactor for isomerization and transalkylation to produce more ethyltoluenes. Fina uses a zeoHte-catalyzed vapor-phase alkylation process to produce ethyltoluenes. 

Styrene. Commercial manufacture of this commodity monomer depends on ethylbenzene, which is converted by several means to a low purity styrene, subsequendy distilled to the pure form. A small percentage of styrene is made from the oxidative process, whereby ethylbenzene is oxidized to a hydroperoxide or alcohol and then dehydrated to styrene. A popular commercial route has been the alkylation of benzene to ethylbenzene, with ethylene, after which the cmde ethylbenzene is distilled to give high purity ethylbenzene. The ethylbenzene is direcdy dehydrogenated to styrene monomer in the vapor phase with steam and appropriate catalysts. Most styrene is manufactured by variations of this process. A variety of catalyst systems are used, based on ferric oxide with other components, including potassium salts, which improve the catalytic activity (10). 

All lation. Friedel-Crafts alkylation (qv) of benzene with ethylene or propjiene to produce ethylbenzene [100-41 -4] CgH Q, or isopropylbenzene [98-82-8] (cumene) is readily accompHshed ia the Hquid or vapor phase with various catalysts such as BF (22), aluminum chloride,... 

In recent years alkylations have been accompHshed with acidic zeoHte catalysts, most nobably ZSM-5. A ZSM-5 ethylbenzene process was commercialized joiatiy by Mobil Co. and Badger America ia 1976 (24). The vapor-phase reaction occurs at temperatures above 370°C over a fixed bed of catalyst at 1.4—2.8 MPa (200—400 psi) with high ethylene space velocities. A typical molar ethylene to benzene ratio is about 1—1.2. The conversion to ethylbenzene is quantitative. The principal advantages of zeoHte-based routes are easy recovery of products, elimination of corrosive or environmentally unacceptable by-products, high product yields and selectivities, and high process heat recovery (25,26). 

ABB Lummus Crest Inc. and Unocal Corp. have Hcensed a benzene alkylation process usiag a proprietary zeoHte catalyst. Unlike the Mobil-Badger process, the Unocal-Lummus process is suitable for either ethylbenzene or cumene manufacture (27,28). 

Benzene is alkylated with ethylene to produce ethylbenzene, which is then dehydrogenated to styrene, the most important chemical iatermediate derived from benzene. Styrene is a raw material for the production of polystyrene and styrene copolymers such as ABS and SAN. Ethylbenzene accounted for nearly 52% of benzene consumption ia 1988. 

All lation. An exceUent example of alkylation is the Mobil-Badger process, which uses ZSM-5-type zeoHte to produce ethylbenzene by alkylation of benzene with ethylene (12,40) ... 

---