Ethylbenzene production

The alkylation process is the addition of an alkene to benzene, usually over an acidic catalyst to give the alkyl benzene. The reaction is non-selective, and polyalkyl benzenes are regular impurities in the cmde product stream. The degree of poly substitution is usually Umited by controlling the ratio of reactants. 

Dry benzene was alkylated with ethylene in either the liquid or gas phases using acidic catalysts  

Although the use of dehydrogenation processes to supply butadiene declined as the more economical supplies from steam cracking of naphtha were introduced, the production of styrene from ethylbenzene dehydrogenation has been continuously developed, since styrene is not available in sufficient quantities as a byproduct. 

From about 1950, Shell 205 and similar catalysts based on alkalized iron and chromium oxides were used exclusively for styrene productioa As plant capacities were rapidly expanded, efforts were increased to improve the performance of the catalyst. Higher potash levels were introduced and cement binders were used to increase strength and selectivity. Ethylbenzene conversion, which was still about 30-50% in the 1950 s, was increased to at least 60% by 1960. Better plant designs were developed and reactors with up to three beds were introduced. One of the first higher selectivity catalysts included vanadium pentoxide with the conventional chromium oxide and potash. Improvements often led to different catalysts being used in a single reactor to optimize operation. 

Steam mole ratio as low as 3 1, while catalysts containing mixed chromium, ceria, and molybdenum promoters, togetlier with potash, were more selective but had to be operated at steam ratios of about 7 1  

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Eig. 4. Mobil—Badger process for ethylbenzene production H = heater Rx = reactor P = prefractionator BC = benzene recovery column ... 

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. 

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. 

No commercial process is offered at this time for side chain alkylation of toluene with methanol for styrene and ethylbenzene production. In the literature the reaction is typically carried out at toluene to methanol molar ratios from 1.0 7.5 to 5 1 from 350 to 450 °C at atmospheric pressures. In some cases inert gas is introduced to assist vaporizing the liquid feed. In other cases H2 is co-fed to improve activity, selectivity and stability. Exelus recently claimed 80% yields in their ExSyM process at full methanol conversion using a 9 4 toluene methanol feed ratio at 400-425 °C and latm (101 kPa) in a bench-scale operation. This performance appears to be... 

The catalyst consists of basic and acid sites in a microporous structure provided by zeolite and microporous materials [58-62]. Basic sites are provided by framework oxygen and/or occluded CsO. Acid sites are provided by the Cs cation and, possibly, additives such as boric and phosphoric acids. The addition of Cu and Ag increased the activity [63, 64]. Incorporation of li, Ce, Cr and Ag also has been shown to increase the styrene to ethylbenzene product ratio [65]. The reactivity of catalysts is sensitive to the presence of occluded CsO, which is in turn influenced by the preparative technique as shown by Lacroix and co-authors [64] and pointed out by Lercher [61]. 

In a long-term study ( 20 years) of about 200 ethylbenzene production workers exposed to an undefined concentration of this compound, none of the workers showed changes in haematological parameters or serum enzyme levels as a measure of liver function (Bardodej Cirek, 1988). 

In the Mohil-Badger vapor-phase process, fresh and recycled benzene are vaporized and preheated to the desired temperature and fed to a multistage fixed-bed reactor. Ethylene is distributed to the individual stages. Alkylation takes place in tile vapor phase. Separately, file polyethylbenzene stream from the distillation section is mixed with benzene, vaporized and heated, and fed to the transalkylator, where polyethylbenzenes react with benzene to form additional ethylbenzene. The combined reactor effluent is distilled in the benzene column. Benzene is condensed in the overhead for recycle to the reactors. The bottoms from the benzene column are distilled in the ethylbenzene column to recover the ethylbenzene product in the overhead. The bottoms stream from the ethylbenzene column is further distilled in the polyefitylbenzene column to remove a small quantity of residue. The overhead polyethylbenzene stream is recycled to the reactor section for transalkylation to ethylbenzene. 

Divinylbenzene. This is a specialty monomer used primarily to make cross-linked polystyrene resins. The largest use of divinylbenzene (DVB) is in ion-exchange resins for domestic and industrial water softening, Ion-exchange resins are also used as solid acid catalysts for certain reactions, such as esterification. Divinylbenzene is manufactured by dehydrogenation of diethylbenzene, which is an internal product in the alkylation plant for ethylbenzene production,... 

The enhanced diffusivity of polynuclear compounds in sc C02 has been utilized to enhance catalyst lifetimes in both 1-butene/isoparaffin alkylations (Clark and Subramaniam, 1998 Gao et al., 1996). The former may be catalyzed using a number of solid acid catalysts (zeolites, sulfated zeolites, etc.), and the use of sc C02 as a solvent/diluent permits the alkylations to be carried out at relatively mild temperatures, leading to the increased production of valuable trimethylpentanes (which are used as high-octane gasoline blending components). The enhancement of product selectivity in the latter process is believed to result from rapid diffusion of ethylbenzene product away from the Y-type zeolite catalysts, thus preventing product isomerization to xylenes. 

UOP introduced the Alkar process for ethylbenzene production in 1966. The Alkar process operates in the vapor-phase with boron trifluoride on an alumina support as the catalyst. By the 1980s, about 15% of the world s ethylbenzene was... 

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 EBMax process, benzene is fed to the bottom of the liquid-filled multibed reactor. Ethylene is co-fed with the benzene and also between the catalyst beds. Polyethylbenzenes, which are almost exclusively diethylbenzenes, undergo transalkylation with benzene in a second reactor. Mobil-Badger offers both liquid phase and vapor phase transalkylation processes. The vapor phase process removes benzene feed coboilers such as cyclohexane and methylcyclopentane as well as propyl and butylbenzenes. Because the EBMax process produces very low levels of propyl and butylbenzenes, for most applications, the more energy efficient liquid phase process is preferred. Worldwide, there are currently ten licensed EBMax units with a cumulative ethylbenzene production capacity of five million metric tons per year. 

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. 

Product quality The ethylbenzene product contains less than 100 ppm of C8 plus C9 impurities. Product purities of 99.95% to 99.99% are expected. 

These processes account for over S5 per cent of world ethylbenzene production capacity. 

It is concluded that elimination of the separate catalyst complex phase in the AICI3 alkylation process adds significantly to its attractiveness. In addition to the ease with which a liquid phase catalyst can overcome any poisoning and get back on stream, the new homogeneous process can operate at higher temperatures and recover the heat of reaction to generate steam. It can also operate in a less corrosive environment while producing an ethylbenzene product of exceptional purity and can reduce the amount of aluminum chloride required several fold. 

Silica S1O2-AI2O3 Alkylation for ethylbenzene production... 

For the propylene oxide process, the economics of ethylbenzene production are the same as above. Propylene is a co-product of the ethylene process described in detail in cluqiter 3, and is economically frivorable as shown there. The propylene oxide process itself is economically promising as shown in Problem 4-3. 

Ethylbenzene production has a smaller demand for the ethylene stream than the products already described and currently stands 19th in volume of production. It is made by both liquid phase processes under moderate conditions employing aluminum chloride catalysis and by vapor phase processes at 150-250°C and 30-50 atm in the presence of a supported boron trifluoride catalyst (Eq. 19.26). 

Woodle, G.B. Zarchy, A.S. Morita, M. Shinohara, K. Leading-edge ethylbenzene production, Lummus/ UOP liquid phase EB process. 1998 International Styrene Symposium Sappora, Japan, Jun 14-18,1998. 

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