Transalkylation catalysts

The solvent is 28 CC-olefins recycled from the fractionation section. Effluent from the reactors includes product a-olefins, unreacted ethylene, aluminum alkyls of the same carbon number distribution as the product olefins, and polymer. The effluent is flashed to remove ethylene, filtered to remove polyethylene, and treated to reduce the aluminum alkyls in the stream. In the original plant operation, these aluminum alkyls were not removed, resulting in the formation of paraffins (- 1.4%) when the reactor effluent was treated with caustic to kill the catalyst. In the new plant, however, it is likely that these aluminum alkyls are transalkylated with ethylene by adding a catalyst such as 60 ppm of a nickel compound, eg, nickel octanoate (6). The new plant contains a caustic wash section and the product olefins still contain some paraffins ( 0.5%). After treatment with caustic, cmde olefins are sent to a water wash to remove sodium and aluminum salts. 

Propylene feed, fresh benzene feed, and recycle benzene are charged to the upflow reactor, which operates at 3—4 MPa (400—600 psig) and at 200—260°C. The SPA catalyst provides an essentially complete conversion of propylene [115-07-1] on a one-pass basis. A typical reactor effluent yield contains 94.8 wt % cumene and 3.1 wt % diisopropylbenzene [25321-09-9] (DIPB). The remaining 2.1% is primarily heavy aromatics. This high yield of cumene is achieved without transalkylation of DIPB and is unique to the SPA catalyst process. 

Zeolite Catalysts. Uaocal has iatroduced a fixed-bed fiquid-phase reactor system based oa a Y-type zeofite catalyst (62). The selectivity to cumene is geaeraHy betweea 70 and 90 wt %. The remaining components are primarily polyisopropylbenzenes, which are transalkylated to cumene ia a separate reactioa zoae to give an overall yield of cumene of about 99 wt %. The distillation requirements iavolve the separation of propane for LPG use, the recycle of excess benzene to the reaction zones, the separation of polyisopropylbenzene for transalkylation to cumene, and the production of a purified cumene product. 

The Tatoray process, which was developed by Toray Industries, Inc., and is available for Hcense through UOP, can be appHed to the production of xylenes and benzene from feedstock that consists typically of toluene [108-88-3] either alone or blended with aromatics (particularly trimethylbenzenes and ethyl-toluenes). The main reactions are transalkylation (or disproportionation) of toluene to xylene and benzene or of toluene and trimethylbenzenes to xylenes in the vapor phase over a highly selective fixed-bed catalyst in a hydrogen atmosphere at 350—500°C and 1—5 MPa (10—50 atm). Ethyl groups are... 

The Xylene Plus process of ARGO Technology, Inc. (95,96) and the FINA T2BX process (97) also use a fixed-bed catalyst in the vapor phase for transalkylation of toluene to produce xylenes and benzene. The Mobil low temperature disproportionation (LTD) process employs a zeoHte catalyst for transalkylation of toluene in the Hquid phase at 260—315°C in the absence of hydrogen (98). 

Another example of catalytic isomerization is the Mobil Vapor-Phase Isomerization process, in which -xylene is separated from an equiHbrium mixture of Cg aromatics obtained by isomerization of mixed xylenes and ethylbenzene. To keep xylene losses low, this process uses a ZSM-5-supported noble metal catalyst over which the rate of transalkylation of ethylbenzene is two orders of magnitude larger than that of xylene disproportionation (12). 

In experiments with [2- 4C] propene in the presence of a Re207-Al2C>8 catalyst, the ethene formed showed no radioactivity, while the butene showed a specific radioactivity twice as high as that of the starting material. This result is completely consistent with a transalkylidenation scheme, and excludes a transalkylation reaction. Similar results were obtained by Clark and Cook (62) in experiments with radioactive propene on a M0O3-C0O-AI2O3 catalyst. 

Tetralin, hydrogenation of, 12 Titanium compounds as catalysts, 188 Titanium dichloride, 192, 193 number of propagation centers, 198-200 Titanium trichloride, 193, 194 Toluene in exhaust gases, 67 Transalkylation, 141, 142 Transalkylidenation, 142 Transition metal compounds as catalysts, 174... 

Alkylation/transalkylation pro- Process using a solid catalyst containing 107... 

In this section, the reactivities of organosilicon compounds for the Friedel-Crafts alkylation of aromatic compounds in the presence of aluminum chloride catalyst and the mechanism of the alkylation reactions will be discus.sed, along with the orientation and isomer distribution in the products and associated problems such as the decomposition of chloroalkylsilanes to chlorosilanes.. Side reactions such as transalkylation and reorientation of alkylated products will also be mentioned, and the insertion reaction of allylsilylation and other related reactions will be explained. 

Failure of hexylpyrene as the liquefaction solvent may be due to the easy dealkylation (13) or high carbonization reactivity probably catalyzed by coals. Transalkylation for coal-liquefaction may require the acid-catalyst (14) or high pressure (15). 

Experiments carried out by feeding TBPE only over H-MWW, showed that the O-alkylated product do not rearrange to C-alkylated phenol derivatives in our conditions, but it is hydrolysed to phenol. So, TBPE is not a reaction intermediate and perforce O-and C-alkylation are parallel reactions. Also o-TBP and p-TBP were fed each of them alone over our catalysts. As it could be observed in Fig. lb, o-TBP convert to p-TBP (by transalkylation) and in minor extent 2,4-DTBP (by disproportionation), while p-TBP (results not shown here) convert to 2,4-DTBP (by disproportionation). Because the transalkylation and disproportionation are bimolecular reactions and need large spaces, it is plausible to suppose that the alkylation could not take place in the pores, but on the external surface of H-MWW zeolites. 

The synergism of a dual-catalyst system comprising of Pt/ZSM-12 and H-Beta aiming to improve the benzene product purity during transalkylation of aromatics has been studied. Catalyst compositions of the dual-catalyst system were optimized at various reaction temperatures in terms of benzene product purity and premium product yields. Accordingly, a notable improvement in benzene purity at 683 K that meets the industrial specification was achieved using the cascade dual-bed catalyst. 

The catalytic performances obtained during transalkylation of toluene and 1,2,4-trimethylbenzene at 50 50 wt/wt composition over a single catalyst Pt/Z12 and a dualbed catalyst Pt/Z 121 HB are shown in Table 1. As expected, the presence of Pt tends to catalyze hydrogenation of coke precursors and aromatic species to yield undesirable naphthenes (N6 and N7) side products, such as cyclohexane (CH), methylcyclopentane (MCP), methylcyclohexane (MCH), and dimethylcyclopentane (DMCP), which deteriorates the benzene product purity. The product purity of benzene separated in typical benzene distillation towers, commonly termed as simulated benzene purity , can be estimated from the compositions of reactor effluent, such that [3] ... 

Table 1. Product yields of transalkylation reaction of toluene and 1,2,4-trimethylbenzene (at 623 K) over Pt-supported single- and dual-bed catalysts.

Figure 1. Effects of H-Beta ratio (y) in the dual-bed catalyst Pt/Z12(x) HB(y) on (a) benzene purity and (b) product yields during transalkylation reaction (see text) at 623 K.

A dual-bed catalyst system has been developed to tackle the key problems in benzene product impurity during heavy aromatics transalkylation processing over metal-supported zeolite catalysts. It was found that by introducing zeolite H-Beta as a complementary component to the conventional single-bed Pt/ZSM-12 catalyst, the cascaded dual-bed catalyst shows synergistic effect not only in catalytic stability but also in adjustments of benzene product purity and product yields and hence should represent a versatile catalyst system for heavy aromatics transalkylation. 

Kureha A process for making di-isopropyl naphthalene mixtures from naphthalene and propylene by transalkylation. It operates at 200°C, using a silica/alumina catalyst. Operated in 1988 at the Rutgerswerke plant in Duisberg-Meiderich, Germany. The name has also been used for a process for making acetylene from petroleum. 

Tatoray [Transalkylation aromatics Toray] A process for transalkylating toluene, and/or trimethylbenzenes, into a mixture of benzene and xylenes. Operated in the vapor phase, with hydrogen, in a fixed bed containing a zeolite catalyst. Developed jointly by Toray Industries and UOP and now licensed by UOP. First operated commercially in Japan in 1969 as of 1992, 23 units were operating and 6 more were in design and construction. 

Karge and Ladebeck (90) studied the alkylation of benzene with olefins over aluminum-deficient, beryllium exchanged mordenite and found a considerable extension of the lifetime of the catalyst, as compared to H-mordenite. The authors were able to carry out quite efficiently the alkylation reaction as well as the transalkylation of ethylbenzene at relatively low temperatures. 

Production of p-xylene via p-xylene removal, i.e., by crystallization or adsorption, and re-equilibration of the para-depleted stream requires recycle operation. Ethylbenzene in the feed must therefore be converted to lower or higher boiling products during the xylene isomerization step, otherwise it would build up in the recycle stream. With dual-functional catalysts, ethylbenzene is converted partly to xylenes and is partly hydrocracked. With mono-functional acid ZSM-5, ethylbenzene is converted at low temperature via transalkylation, and at higher temperature via transalkylation and dealkylation. In both cases, benzene of nitration grade purity is produced as a valuable by-product. 

The data are summarized in Table II. They have been normalized to kx x s i for each zeolite catalyst. In general it is seen that the7transfer of an ethyl group (E,E E,X) occurs faster than that of a methyl group (X,E X,X). This is in agreement with the indicated mechanism for transalkylation (Figure 4) which involves a benzylic carbenium ion intermediate. In the case of methyl transfer, this is a primary cation,... 

Table II. Transalkylation Kinetics Over Various Zeolite Catalysts...

We have shown that the high selectivity of ZSM-5 in xylene isomerization relative to larger pore acid catalysts is a result of its pore size. It is large enough to admit the three xylenes and to allow their interconversion to an equilibrium mixture it also catalyzes the transalkylation and dealkylation of ethylbenzene (EB), a necessary requirement for commercial feed but it selectively retards transalkylation of xylenes, an undesired side reaction. 

There are several means to maximize the yield in the desired monoalkylation product high aromatic/alkylation agent ratio, association of a transalkylation unit to the alkylation unit, and use of a shape selective zeolite as catalyst. 

In the chapter on benzene and in Figure 2—7, you saw that toluene disproportionation yielded both benzene and mixed xylenes. When the catalyst-prompted methyl group removes itself from the toluene, it usually attaches itself to another toluene molecule in a way that it forms xylene. That s transalkylation. The freed methyl group might attach itself momentarily to another free benzene molecule, or it might attach itself to the methyl group of another toluene, forming ethylbenzene. However, the creation of benzene and xylenes predominates, and the combined yields of the two are 92-97%. 

Serra, J.M., Corma, A., and Guillon, E. (2008) Catalyst comprising a lOMR zeolite and a 12MR zeolite, and its use in transalkylation of aromatic hydrocarbons. US Patent 7419931. 

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