Ethylbenzene, catalytic cracking

The ethylene feedstock used in most plants is of high purity and contains 200—2000 ppm of ethane as the only significant impurity. Ethane is inert in the reactor and is rejected from the plant in the vent gas for use as fuel. Dilute gas streams, such as treated fluid-catalytic cracking (FCC) off-gas from refineries with ethylene concentrations as low as 10%, have also been used as the ethylene feedstock. The refinery FCC off-gas, which is otherwise used as fuel, can be an attractive source of ethylene even with the added costs of the treatments needed to remove undesirable impurities such as acetylene and higher olefins. Its use for ethylbenzene production, however, is limited by the quantity available. Only large refineries are capable of deUvering sufficient FCC off-gas to support an ethylbenzene—styrene plant of an economical scale. 

Feed stock for the first sulfuric acid alkylation units consisted mainly of butylenes and isobutane obtained originally from thermal cracking and later from catalytic cracking processes. Isobutane was derived from refinery sources and from natural gasoline processing. Isomerization of normal butane to make isobutane was also quite prevalent. Later the olefinic part of the feed stock was expanded to include propylene and amylenes in some cases. When ethylene was required in large quantities for the production of ethylbenzene, propane and butanes were cracked, and later naphtha and gas oils were cracked. This was especially practiced in European countries where the cracking of propane has not been economic. 

Newer catalysts of the fluoride type promise to be much more versatile. Essentially all ethylene from catalytic cracking was once burned as fuel but can now be utilized for the production of ethylbenzene using newer catalysts. 

Desulfurization of petroleum feedstock (FBR), catalytic cracking (MBR or FI BR), hydrodewaxing (FBR), steam reforming of methane or naphtha (FBR), water-gas shift (CO conversion) reaction (FBR-A), ammonia synthesis (FBR-A), methanol from synthesis gas (FBR), oxidation of sulfur dioxide (FBR-A), isomerization of xylenes (FBR-A), catalytic reforming of naphtha (FBR-A), reduction of nitrobenzene to aniline (FBR), butadiene from n-butanes (FBR-A), ethylbenzene by alkylation of benzene (FBR), dehydrogenation of ethylbenzene to styrene (FBR), methyl ethyl ketone from sec-butyl alcohol (by dehydrogenation) (FBR), formaldehyde from methanol (FBR), disproportionation of toluene (FBR-A), dehydration of ethanol (FBR-A), dimethylaniline from aniline and methanol (FBR), vinyl chloride from acetone (FBR), vinyl acetate from acetylene and acetic acid (FBR), phosgene from carbon monoxide (FBR), dichloroethane by oxichlorination of ethylene (FBR), oxidation of ethylene to ethylene oxide (FBR), oxidation of benzene to maleic anhydride (FBR), oxidation of toluene to benzaldehyde (FBR), phthalic anhydride from o-xylene (FBR), furane from butadiene (FBR), acrylonitrile by ammoxidation of propylene (FI BR)... 

However, other authors have proposed that the primary product of the PS catalytic cracking is styrene, as in thermal cracking, which is further converted into ethylbenzene, toluene, benzene, etc. on the acid sites of the catalyst. De la... 

An inspection of the industrial use of zeolites as catalysts shows, however, that only a rather limited number of zeolite topologies are currently used in major industrial processes. Among the more important ones are ultrastable Y (USY) (FAU), rare-earth-exchanged faujasite-type (X, Y) (FAU) andZSM-5-type (MFI) zeolites in fluid catalytic cracking (FCC) of oil fractions [4] noble-metal-loaded U SY for hydroisomerization and hydrocracking of naphtha feedstocks [5] mordenite (MOR) and zeolite Omega (MAZ) -based catalysts for C4-C6 alkane isomerization [6] zeolites ZSM-23 (MTT), ZSM-35 (FER), ZSM-5 for selective oil dewaxing [7] ZSM-5, silicalite (MFI), MCM-22 (MWW), Beta-type (BEA) zeolites for aromatics alkylation to yield ethylbenzene, p-xylene. 

Improvements in chemical processes are very often based on the discovery or development of new catalysts or adsorbents. One particularly exciting example in the field of zeolite catalysis is the replacement of the formerly used amorphous silica-aliunina catalysts in fluid catalytic cracking (FCC) of vacuiun gas oil by rare earth exchanged X-type zeoUtes [1]. This resulted in considerably improved yields of the desired gasoUne and, hence, a much more efficient utilization of the crude oil. Fiuther examples are the introduction of zeolite HZSM-5 as catalyst in the synthesis of ethylbenzene from benzene and ethylene [2], for xylene isomerization [3] and for the conversion of methanol to high-... 

Styrene. All commercial processes use the catalytic dehydrogenation of ethylbenzene for the manufacture of styrene.189 A mixture of steam and ethylbenzene is reacted on a catalyst at about 600°C and usually below atmospheric pressure. These operating conditions are chosen to prevent cracking processes. Side reactions are further suppressed by running the reaction at relatively low conversion levels (50-70%) to obtain styrene yields about 90%. The preferred catalyst is iron oxide and chromia promoted with KzO, the so-called Shell 015 catalyst.190... 

Tphe excellent catalytic activity of lanthanum exchanged faujasite zeo-A lites in reactions involving carbonium ions has been reported previously (1—10). Studies deal with isomerization (o-xylene (1), 1-methy 1-2-ethylbenzene (2)), alkylation (ethylene-benzene (3) propylene-benzene (4), propylene-toluene (5)), and cracking reactions (n-butane (5), n-hexane, n-heptane, ethylbenzene (6), cumene (7, 8, 10)). The catalytic activity of LaY zeolites is equivalent to that of HY zeolites (5 7). The stability of activity for LaY was studied after thermal treatment up to 750° C. However, discrepancies arise in the determination of the optimal temperatures of pretreatment. For the same kind of reaction (alkylation), the activity increases (4), remains constant (5), or decreases (3) with increasing temperatures. These results may be attributed to experimental conditions (5) and to differences in the nature of the active sites involved. Other factors, such as the introduction of cations (11) and rehydration treatments (6), may influence the catalytic activity. Water vapor effects are easily... 

It is noted that Mo/DM is the best performing catalyst with the highest steady state activity and lowest deactivation rate. The deactivation rate is the lowest even under the influence of intense acid-catalyzed side reactions known to produce coke, i.e. oligomerization of styrene and cracking of ethylbenzene. Obviously, the high surface area and high connectivity of the support have played a determining role in the catalytic reaction. The effects they exert can be looked at in two ways ... 

Fig. 20. Effect of activation temperature on catalytic activity. O, ethylene-benzene alkylation (160) , toluene disproportionation (157) A, n-hexane cracking (161) O, 1-methyl-2-ethylbenzene isomerization (158).

Sudi a Catalytic system has also been developed by Mobil with its MHTT process (MobO High Temperature IsomcrizationX It uses platinum deposited over a low add ZSM5 zeolite and is well adapted to feedstock having a high paraffins and ethylbenzene content. Paraffins are cracked and ethylbenzene hydrodealkylated. 

Various reactions have been studied on mixed rare earth and the La and Ce forms. These include ethylation of benzene 18), propylation of toluene 14), o-xylene isomerization 21), butane cracking 14), cracking of n-hexane, n-heptane, and ethylbenzene (8), and isomerization and disproportionation of 1-methy 1-2-ethylbenzene (7). Other reactions are summarized by Venuto and Landis 18). In several reports, an optimum calcination temperature for best catalytic performance has been demonstrated (7, 8, 14, 18, 21). 

The transformation of n-butane over the Ga and Zn modified ZSM-5 catalysts produced similar aromatic hydrocarbons and gaseous products as over H-ZSM-5. Ethyl benzene was the only aromatic which was not formed with the proton form catalyst. Ga-H-ZSM-5 and Zn-H-ZSM-5 exhibited higher catalytic activity and selectivity to aromatics than the H-ZSM-5 catalyst The amount of cracking products formed for Ga- and Zn- modified catalysts were smaller than for ZSM-5 in its proton form. Toluene constituted almost 50 % of the aromatics formed while benzene, xylenes and ethylbenzene formed the rest The conversion of n-butane and selectivity to aromatic hydrocarbons increased with increasing temperature. The effect of temperature on n-butane conversion and aromatic selectivity over the catalysts is given in Figures 4 and 5. The product selectivity obtained from the transformation of n-butane over the H-ZSM-5, Ga-H-ZSM-5 and Zn-H-ZSM-5 catalysts at 803 K is given in Table 1. 

Typical test reactions often used for the characterization of zeolites are the cracking of n-hexane - and disproportionation of ethylbenzene. The catalytic activity of a zeolite is determined by the concentration of protons and the acid strength. 

Figure 5.15 Selectivities of benzene (O), toluene ( ), ethylbenzene (A), and cracking products (V) as a function of conversion at 550 °C in the catalytic treatment of PS (dashed line and open symbols) and styrene (filled line and closed symbols) over a commercial FCC catalystP...

Feedstocks processed commercially include C8 aromatic extracts from catalytic reformates and pyrolysis liquids resulting from ethylene cracking plants. Composition of these stocks vary widely, the major differences being their ethylbenzene content. Fresh feeds from which ethylbenzenes have been removed typically contain 2-4 wt % ethylbenzene. Inclusion of C8 aromatic extracts from pyrolysis liquids can increase ethylbenzene content to 30 wt % or higher. Fresh feeds with this range of ethylbenzene contents have been processed successfully over octafining catalyst. 

It was shown that solid-state ion exchange is also a suitable route to preparation of active acidic or bifunctional catalysts. Introduction of Ca or Mg into mordenite [21] or La " into Y-type zeolite, mordenite or ZSM-5 [22] by solid-state reaction yielded, after brief contact with small amounts of water, acidic zeolite catalysts which were, for instance, active in disproportionation and/or dealkylation of ethylbenzene or in cracking of n-decane [43]. The contact with water was essential to generate, after solid-state ion exchange, acidic Brpnsted centres (compare, for instance. Figure 2). In the case of solid-state exchange between LaClj and NH -Y an almost 100% exchange was achieved in a one-step procedure, and the hydrated La-Y reaction product exhibited a catalytic performance (selectivity in ethylbenzene disporportionation, time-onstream behaviour) comparable to or even better than that of a conventionally produced La-Y (96) catalyst [22,23]. In fact, compared to the case of NH -Y the introduction of La " " by solid-state reaction proceeded less easily and was frequently lower than 100% with H-ZSM-5 or H-MOR. 

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