Benzene-Based Processes

Process Technology Evolution, Growth in the worldwide maleic anhydride industry is exclusively in the buianc-lo-inaleic anhydride route, often at the expense of benzene-based production. Table 2 shows I 995 and estimated 1996. 1997. and 2000 worldwide maleic production capacity broken down in categories of benzene, butane and phlhalie anhydride coproduct. As can be seen from this table butane routes are expected to grow at the expense of benzene-based processes. 

In spite of the potential advantages of a fluid bed, all benzene-based processes still rely heavily on the fixed-bed, tubular reactors.It is also believed to be the case with the Amoco butane process. The main reason for this overwhelming preference is the difficulty in producing catalysts with low attrition rates. 

Since the temperature and by-products are different for processes starting with benzene and C4 hydrocarbons, the construction materials of various plant equipment may vary. For the benzene-based process carbon steel is considered adequate. On the other hand, in C4-based processes, lower acids (acetic, acrylic, crotonic, etc.) are coproduced and hence suitable acid-resistant reactor tubes may be needed. /t-Butane oxidation is run at higher temperature, and so steel suitable for higher temperature is necessary. It has been sug-gested that a butane-based MA reactor can be easily converted to a benzene-based process but not vice-versa. 

In MA from the C4-hydrocarbon process, the nature of by-products is quite different. Among these are the lower monoacids (e.g., acetic, acrylic, crotonic), the corresponding aldehydes,etc. Some of these are produced in amounts too small to make an economic recovery possible. In either situation (benzene or C4), nitrogen, water, and the oxides of carbon are vented to the air after the recovery of products and hydrocarbons. If a significant amount of hydrocarbon is unreacted, it may be recycled if practical. If this is not possible, any of the available emission control technologies, especially for benzene-based processes, may be considered. ... 

Benzene SuIfona.tion. In the benzene sulfonation process, benzene reacts with concentrated sulfuric acid to form benzenesulfonic acid at about 150°C. The benzenesulfonic acid is neutralized with sodium sulfate to produce sodium benzenesulfonate, which is then fused with caustic soda to yield sodium phenate. The sodium phenate is acidified with sulfur dioxide and a small amount of sulfuric acid to release the phenol from the sodium salt. The phenol yield by this process can be as high as 88 mol % to that of the theoretical value based on benzene. Plants employing this technology have been shut down for environmental and economic reasons. 

U.S. consumption pattern 1999, 3 619t U.S. producers, 3 610t vapor-phase nitration of, 17 257 vinyl chloride reactions with, 25 632 world production by country, 3 611-612t Benzene-based catalyst technology, 15 500 Benzene-based fixed-bed process technology, 15 505-506 Benzene chlorination process, of phenol manufacture, 18 751 m-Benzenedisulfonic acid, 3 602 p-Benzenedisulfonic acid, 3 602 Benzene feedstock, 23 329 Benzene hexachloride, 3 602 Benzene manufacture, toluene in, 25 180-181... 

Fixed bed photoreactors, 19 99 Fixed-bed process technology benzene-based, 15 505—506 butane-based, 15 501-502 Fixed-bed reactors, in vinyl chloride manufacture by oxychlorination, 25 640... 

With full recycle of the benzene and processing of the PEB, the EB yield (yield being the percent of feed that ends up as the targeted product) is about 99%, based on the ethylene and benzene feed. (For a discussion of the difference between yield and conversion, see Appendix A.)... 

The heat requirements of the reactive distillation-based process are ca. 50% lower than in the conventional technology. In the alkylation of benzene to cumene reactive distillation effectively eliminated the hot spots and reduced the oligomerization of propylene (6). 

Is the current separation the most suitable or should other methods of separation be considered For example, distillation is commonly the workhorse in the chemical industry and is often the immediate choice. Other separation methods, such as pervaporation, can be sometimes more effective especially if the volatility differences are small. Pervaporation is a membrane-based process with the difference that the permeate appears as a vapor, thus permitting solute recovery and recycle. For example, benzene can be recovered from hydrocarbon streams using this method in fairly high concentrations and in a usable form ready for recycle. Many alternative separation methods must be considered, and one should not simply bank on past experience or expertise. 

Alkylation. In the field of alkylation of benzene with ethene zeolite-based catalysts are used for the past 20 years, replacing the conventional A1C13- and BF3-on-alumina based processes. Here the question in case of a new plant is not whether a zeolite-based process will be selected but rather which one to choose. The Mobil-Badger process uses ZSM-5 as the catalyst and is the most widely applied though recently other zeolites (Y, Beta and MCM-22) have come to the fore. 

Cumene capacity topped 9.5 million metric tons in 1998 and is projected to reach 10.4 million metric tons by the end of 2003 (19). Like ethylbenzene, cumene is used almost exclusively as a chemical intermediate. Its primary use is in the coproduction of phenol and acetone through cumene peroxidation. Phenolic resins and bisphenol A are the main end uses for phenol. Bisphenol A, which is produced from phenol and acetone, has been the main driver behind increased phenol demand. Its end use applications are in polycarbonate and epoxy resins. The growth rate of cumene is closely related to that of phenol and is expected to be approximately 5.1% per year worldwide over the next five years. Process technologies for both chemicals have been moving away from conventional aluminum chloride and phosphoric acid catalyzed Friedel-Crafts alkylation of benzene, toward zeolite-based processes. 

Another opportunity for advancement in ethylbenzene synthesis is in the development of liquid phase processes that can handle low cost feedstocks, including dilute ethylene such as ethane/ethylene mixtures. The use of dilute ethylene has become increasingly attractive since it has the potential to debottleneck ethylene crackers. Currently higher temperature, vapor phase technologies can tolerate contaminants that enter with the dilute ethylene feed from FCC units. However, these same contaminants can accelerate catalyst aging in lower temperature, liquid phase operations because they are more strongly adsorbed at the lower temperatures. Acid catalysts that tolerate elevated levels of contaminants would facilitate the development of dilute ethylene-based processes. These same catalysts could be useful in applications where lower cost or lower quality benzene feeds are all that are available. 

ExxonMobil Chemical Co. Xylene, mixed Toluene, benzene, C9+ aromatics Transalkylation/disproportionation-based process using benzene, toluene and C9+ to produce high yield mixed xylenes 1 1997... 

Friedel-Crafts technology and zeolite- or other solid catalyst-based processes are currently used for other aromatic alkylations, in particular for the manufacture of linear alkylbenzenes (LABs) made from C10-C14 olefins (Equation 8), or from the corresponding chloroparaffins and benzene, and also to make m- and p-cymene (isopropyltoluene Equation 9). LABs are used for the production of sulfonate detergents, while cymenes lead to m- and p-cresols through a procedure analogous to that used for the cumene-to-phenol process. 

AH of the processes described above require more benzene recycle than the aluminum chloride-based processes. Retrofitting an existing aluminum chloride-based plant to a zeoHte-based plant requires not only replacement of the reaction section but also additional investment in the distiHation train. Several producers have chosen to replace their old plants during the 1980s and early 1990s with new ones based on the Mobil-Badger process, at expanded capacities. 

Production of cresols based on alkylation of toluene, oxidation of cymenes, or isopropyl toluenes and cleavage into cresols and acetone is a direct extension of phenol process from benzene. The process is, however, more complex since three isomeric cymenes and cresols are involved. The chemistry of the process is as follows ... 

This was the world s first commercial benzene hydrogenation process on the industrial scale. It uses a fixed bed of platinum-based catalyst promoted by a lithhun salt, which can tolerate sulfur contents up to 300 ppm in the benzene, and whose LHSV in relation to liquid benzene is about 1.5. 

According to Arkenbout (1978), the first compound to be purified was naphthalene. This was achieved after successful results with laboratory scale in the purification of p-xylene from an eutectic system and benzene-based system as a solid solution system. There is no published data on industrial experience for this process. 

Most polymeric packings for size-exdusion diromatography in aqueous mobile phases are based on crosslinked glyddoxymethacrylate that is further hydrophilized and contains (—CH]—CHOH—CH2O— ) as the surface moiety. The exact composition, the nature of the crosslinker, the initiator, and the method of rendering the packings hydrophilic are all proprietary information that is not commonly disclosed by the manufacturers. But on the basis of studies available in die academic literature, one can surmise that the basic particle formation process is similar to the one described for styrene-divinyl-benzene-based packings. 

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