Hydrodealkylation Catalytic

Primary steam reforming Secondary steam reforming Carbon monoxide conversion Carbon monoxide methanation Ammonia synthesis Sulfuric acid synthesis Methanol synthesis Oxo synthesis Ethylene oxide Ethylene dichloride Vinylacetate Butadiene Maleic anhydride Phthalic anhydride Cyclohexane Styrene Hydrodealkylation Catalytic reforming Isomerization Polymerization (Hydro)desulfurization Hydrocracking... 

Properties. Table 4 contains typical gasoline quaUty data from the New Zealand plant (67). MTG gasoline typically contains 60 vol % saturates, ie, paraffins and naphthenes 10 vol % olefins and 30 vol % aromatics. Sulfur and nitrogen levels in the gasoline are virtually lul. The MTG process produces ca 3—7 wt % durene [95-93-2] (1,2,4,5-tetra-methylbenzene) but the level is reduced to ca 2 wt % in the finished gasoline product by hydrodealkylation of the durene in a separate catalytic reactor. 

Table 9 is a summary of world toluene supply and demand for 1996. North America, Asia, and Western Europe dominated the world s toluene business ia 1996. The three regions together accounted for over 85% of world production, imports, exports, and actual consumption, respectively. North America led ia production and consumption, while Asia led ia imports and exports. Table 10 presents the world toluene supply and demand. The worldwide demand for toluene increased by 7% from 1993 to 1994 and from 1994 to 1995, consecutively, because of higher hydrodealkylation (HDA) and disproportionation (TDP) operations, plus strong demand for all other derivatives. Over 70% of toluene is derived from a single source, catalytic reformate. 

Toluene Hydrodeall lation. Benzene is produced from the hydrodemethylation of toluene under catalytic or thermal conditions. The main catalytic hydrodealkylation processes are Hydeal (UOP) and DETOL (Houdry) (49). Two widely used thermal processes are HD A (Arco and Hydrocarbon Research Institute) and THD (Gulf). These processes contribute 25—30% of the world s total benzene supply. 

In catalytic toluene hydrodealkylation, toluene is mixed with a hydrogen stream and passed through a vessel packed with a catalyst, usually supported chromium or molybdenum oxides, platinum or platinum oxides, on siHca or alumina (50). The operating temperatures range from 500—595°C... 

A typical catalytic hydrodealkylation scheme is shown ia Figure 3 (49). The most common feedstock is toluene, but xylenes can also be used. Recent studies have demonstrated that and heavier monoaromatics produce benzene ia a conventional hydrodealkylation unit ia yields comparable to that of toluene (51). The use of feeds containing up to 100% of C —aromatics iacreases the flexibiUty of the hydrodealkylation procedure which is sensitive to the price differential of benzene and toluene. When toluene is ia demand, benzene suppHes can be maintained from dealkylation of heavy feedstocks. 

The main producers of benzene in Canada are the Nova Corp. of Alberta, Petro-Canada, Inc., and Shell Canada Ltd. These three companies have an armual capacity of 567,000 t. Most Canadian benzene is obtained from catalytic reformate, pyrolysis gasoline, and hydrodealkylation. Coal is not an important source of benzene in Canada. 

Some of the principal Japanese producers of benzene are Mitsubishi Petrochemical Co., Ltd., Nippon Steel Chemical Co., Ltd., Sanyo Petrochemical Ltd., and Idemitsu Kosan Ltd. Until 1967, the main source of Japanese benzene was coal-based. Today, approximately 40—45% of benzene production in Japan is based on pyrolysis gasoline (74), about 40% catalytic reformate, and the remainder coke oven light oil and thermal hydrodealkylation. 

After the cmde BTX is formed, by reforming in this case, a heart cut is sent to extraction. Actually, the xylenes and heavier components are often sent to downstream processes without extraction. The toluene produced is converted to ben2ene, a more valuable petrochemical, by mnning it through a hydrodealkylation unit. This catalytic unit operates at 540—810°C with an excess of hydrogen. Another option is to disproportionate toluene or toluene plus aromatics to a mixture of ben2ene and xylenes using a process such as UOP s Tatoray or Mobil s Selective Toluene Disproportionation Process (STDP) (36). 

Toluene is recovered as a high purity product by fractionating the mixed aromatics obtained from the extraction of catalytic reformate or powerformate. About 70 fractionation trays are required to produce toluene having a purity of 99.7 percent. Toluene is consumed principally as a feedstock for hydrodealkylation plants. Toluene is used in a number of solvent applications. 

Catalytic conversion processes include naphtha catalytic reforming, catalytic cracking, hydrocracking, hydrodealkylation, isomerization, alkylation, and polymerization. In these processes, one or more catalyst is used. A common factor among these processes is that most of the reactions are initiated hy an acid-type catalyst that promotes carhonium ion formation. 

Manufacture Benzene used to be made from coal, but it is now made from petroleum by two different routes catalytic reforming of naptha and hydrodealkylation of toluene. The first route provides toluene as a byproduct for the second route. 

Bextol A catalytic hydrodealkylation process using an oxide catalyst. 

For many years benzene was made from coal tar even as late as 1949, when all of it was made by this old process. New processes began to take over in the 1950s, which were used for 50% of the benzene in 1959, 94% in 1972, 96% in 1980, and near 100% in the 1990s. These new processes consist of catalytic reforming of naphtha and hydrodealkylation of toluene in a 70 30 capacity ratio. 

More toluene is formed than is needed in the catalytic reforming of naphtha. Benzene is always in tight supply. Table 8.7 shows the catalytic reformate production percentages of benzene, toluene, and xylene vs. the U.S. chemical demand. When the price is right it is economical to hydrodealkylate (add hydrogen, lose the methyl) toluene to benzene. This is best done on pure toluene, where the yield can be as high as 98.5%. The reaction can be promoted thermally or catalytically. As much as 30-50% of all benzene is made this way. 

The use of computers has made it possible to characterise models with large numbers of individual steps. Andersson and Lamb [25] used an analogue computer to estimate parameters in a model with 15 reactions which described naphthalene production by hydrodealkylation. Also, they were able to predict temperature distributions and effluent concentrations for a commercial reactor. Kurtz [26] took 200 simultaneous reactions into account in an experimental study of the gas-phase chlorination of methyl chloride. Model discrimination and parameter estimation for catalytic processes are discussed in a comprehensive review by Froment [27]. 

Fig. 1. Process for convening toluene or Cg aromatic hydrocarbons (catalytic hydrodealkylation) to high-purity benzene. (OOP, Inc)...

In the synthetic processes, mixtures of products are often obtained. Variation in the supply/demand balance of the alkyl pyridine isomers has led to much research on processes which may alleviate such imbalances, including development of the catalytic hydrodealkylation of alkyl pyridines to pyridine as well as the alkylation of pyndine. 

For many years benzene (benzol) was made from coal tar, but new processes that consist of catalytic reforming of naphtha and hydrodealkylation of toluene are more appropriate. Benzene is a natural component of petroleum, but it cannot be separated from crude oil by simple distillation because of azeotrope formation with various other hydrocarbons. Recovery is more economical if the petroleum fraction is subjected to a thermal or catalytic process that increases the concentration of benzene. 

Toluene is converted into benzene by a catalytic hydrodealkylation (HDA) process at elevated temperature and pressure. The importance of this process is influenced by the relative value and demand for benzene, as benzene from this source is normally more costly than that isolated directly from refinery reformate streams. Benzene (along with xylenes) can also be obtained by the catalytic TDP. It has became favorable in recent years. Toluene consumption for toluene disproportionation versus HDA has changed from about 1/5 in 1990 to 2/1 in 2000. The volume of toluene that finds use as a solvent is expected to show a continued decline because of regulations controlling the emission of VOCs. 

These diffusion limitations are particularly pronounced with HMORIO (Si/Al ratio of 10) catalysts, which can be explained by the quasi absence of mesopores (26, 27). With the other samples and especially with HMOR90, mesopores created by dealumination allow a quasi tridimensional diffusion of organic molecules in the pore system, decreasing or suppressing diffusion limitations. These diffusion limitations are also responsible for the abnormally low value of TOF per protonic site found with HMORIO catalysts for hydrodealkylation and for disproportionation, i.e. for the other primary reactions involving acid catalytic sites. 

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. 

Toluene is the most abundant and lowest cost aromatic material. This is a reason to be the valuable raw material for the production of various chemical products. The main chemical use for toluene Is, in fact, production of benzene by dealkylation. The reaction can be carried out either thermally or catalytically using variety of catalysts including supported metals or metal oxides [1-6], amorphous silica-alumina [7] and zeolites [8-19]. The simplest toluene hydrodealkylation reaction is the reaction in which the methyl group is removed in the presence of the forming mainly methane CeHsCHs + H2 —> CeH0 + CH4... 

This study was undertaken with the objective of closely following the relationships of silica/alumina ratio with catalytic properties of ZSM-5 zeolite in toluene transformation under hydrodealkylation process conditions. It was hoped that the data would reveal the reaction pathway of the dealkylation and subsequently shed light on the mechanism of H-ZSM-5 catalyzed transformation of toluene. 

Very good linear dependence for hydrodealkylation was found except for zeolite samples with high Si/AI ratio. The higher values of the initial reaction rates obsen/ed on these samples are presumably due to another type of catalytic centers (for example one-electron acceptor centers) on very high siliceous zeolites (Si/AI >1000). The dependence of turnover number (TON) for the particular toluene transformation reactions as a function of the strong acid sites concentration has shown [24] that hydrodealkylation occured on strong acid sites and didn t depend on the concentration of these sites. However, TON dependence for hydrocracking and condensation reactions was non-linear and influenced by the concentration of active sites. 

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