Ethylbenzene processes

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. 

Two catalysts have emerged as commercially viable. The Mobil—Badger ethylbenzene process, which has been in commercial use since 1980, employs a ZeoHte catalyst and operates in the gas phase. A Hquid-phase ethylbenzene process joindy Hcensed by Lummus and UOP uses a Y-type ZeoHte catalyst developed by Unocal. This Hquid-phase process was commercialized in 1990. The same Y-type ZeoHte catalyst used for the production of ethylbenzene is being offered for the production of cumene but has not yet been commercialized. 

Fig. 1. Mobil-Badger vapor-phase ethylbenzene process where PEB = polyethylbenzene.

Eig. 3. Monsanto ethylbenzene process. Courtesy of i dwcarbon Processing. 

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). 

Alkar [Alkylation of aromatics] Also (incorrectly) spelled Alcar. A catalytic process for making ethylbenzene by reacting ethylene with benzene. The ethylene stream can be of ary concentration down to 3 percent. The catalyst is boron trifluoride on alumina. Introduced by UOP in 1958 but no longer licensed by them. Replaced by the Ethylbenzene process. 

Zeolite-Based Alkylation. Zeolites have the advantage of being noncot-rosive and environmentally benign. The Mobil-Badger vapor-phase ethylbenzene process was ihe lirsl zeolite-based process to achieve commercial success. It is based on a synthetic zeolite catalyst. ZSM-5. and has the desirable characteristics of high activity, low oligomerization, and low coke formation. See also Molecular Sieves. 

EBMax is a liquid phase ethylbenzene process that uses Mobil s proprietary MCM-22 zeolite as the catalyst. This process was first commercialized at the Chiba Styrene Monomer Co. in Chiba, Japan in 1995 (16-18). The MCM-22-based catalyst is very stable. Cycle lengths in excess of three years have been achieved commercially. The MCM-22 zeolite catalyst is more monoalkylate selective than large pore zeolites including zeolites beta and Y. This allows the process to use low feed ratios of benzene to ethylene. Typical benzene to ethylene ratios are in the range of 3 to 5. The lower benzene to ethylene ratios reduce the benzene circulation rate which, in turn, improves the efficiency and reduces the throughput of the benzene recovery column. Because the process operates with a reduced benzene circulation rate, plant capacity can be improved without adding distillation capacity. This is an important consideration, since distillation column capacity is a bottleneck in most ethylbenzene process units. The EBMax process operates at low temperatures, and therefore the level of xylenes in the ethylbenzene product is very low, typically less than 10 ppm. 

In the early 1980s Monsanto introduced an A1C13 process based on the same chemistry used in the ethylbenzene process. This process can be operated at lower benzene/propylene ratios than the SPA process because AICI3 can transalkylate the polyalkylated benzenes back to cumene. The process also operates at temperatures lower than the SPA process because the more highly acidic anhydrous AICI3 tends to produce significantly more undesired n-propylbenzene at equivalent temperatures. This technology is currently used in five plants. 

Current zeolite catalysts already operate at process temperatures that require minimal external heat addition. Heat integration and heat management will be of increasing concern at the lower benzene to propylene ratios because the cumene synthesis reaction is highly exothermic (AHf= -98 kJ/mole). Recycle, particularly in the alkylation reactor, is likely to become increasingly important as a heat management strategy. The key will be how to limit the build-up of byproducts and feed impurities in these recycle loops, particularly as manufacturers seek cheaper and consequently lower quality feedstocks. As in the case of ethylbenzene, process and catalyst innovations will have to develop concurrently. 

In the ethylbenzene process the 1-methylbenzyl alcohol (MBA) co-product is dehydrated to monomeric styrene (SM). The theoretical SM/PO ratio is 1.8 1 and commercial plants operate in the range 2.2-2.7 l, indicating that the selectivity of ethylbenzene hydroperoxide (EBHP) formation is much higher than that of... 

Styrene (SM) can be synthesized in a single step via alkylation of toluene with methanol which offers significant advantages in raw material costs and energy consumption as compared to the benzene to styrene via ethylbenzene process. This single-step process is carried out at a temperature of 400°C and uses a cesium-boron type X zeolite catalyst. The reaction is [31] ... 

D. Gandi and T. Mortimer, Direct Ethylbenzene Process, 1994 Sud-Chemie International Styrene Symposium, Louisville, Ky., Nov. 2—4,1994. 

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