Benzene from toluene disproportionation

Disproportionation to Benzene and Xylenes. With acidic catalysts, toluene can transfer a methyl group to a second molecule of toluene to yield one molecule of benzene and one molecule of mixed isomers of xylene. This disproportionation is an equilibnum reaction. Disproportionation generates benzene from toluene and at the same time takes full advantage of the methyl group to generate a valuable product, i.e., xylene. Economic utility of the process is strongly dependent on the relative values of toluene, benzene, and the xylenes. 

Toluene disproportionation is a catalytic process in which 2 moles of toluene are converted to 1 mole of xylene and 1 mole of benzene. Although the mixed xylenes from toluene disproportionation are generally more costly to produce than those from catalytic reformate or pyrolysis gasoline,... 

An example of product selectivity is the ZSM-5 process, selective toluene disproportionation (Ref. 15), which is the second generation of our commercial toluene disproportionation process that produces xylenes and benzene from toluene. 

Toluene Disproportionation Process. A article by Stitt compares a conventional process to produce benzene from toluene wifli a reactive distillation process. Several steady-state economic indicators are used to show that the reactive distillation process does not prove to be a fruitful development opportunity. .. due to economic considerations. ... 

Xylenes Produetion Via Toluene Transalkylation and Disproportionation. The toluene that is produced from processes such as catalytic reforming can be converted into xylenes via transalkylation and disproportionation. Toluene disproportionation is defined as the reaction of 2 mol of toluene to produce 1 mol of xylene and 1 mol of benzene. Toluene transalkylation is defined as the reaction of toluene with or higher aromatics to produce xylenes ... 

Benzene, toluene, and a mixed xylene stream are subsequently recovered by extractive distillation using a solvent. Recovery ofA-xylene from a mixed xylene stream requires a further process step of either crystallization and filtration or adsorption on molecular sieves. o-Xylene can be recovered from the raffinate by fractionation. In A" xylene production it is common to isomerize the / -xylene in order to maximize the production of A xylene and o-xylene. Additional benzene is commonly produced by the hydrodealkylation of toluene to benzene to balance supply and demand. Less common is the hydrodealkylation of xylenes to produce benzene and the disproportionation of toluene to produce xylenes and benzene. 

Xylenes. The main appHcation of xylene isomers, primarily p- and 0-xylenes, is in the manufacture of plasticizers and polyester fibers and resins. Demands for xylene isomers and other aromatics such as benzene have steadily been increasing over the last two decades. The major source of xylenes is the catalytic reforming of naphtha and the pyrolysis of naphtha and gas oils. A significant amount of toluene and Cg aromatics, which have lower petrochemical value, is also produced by these processes. More valuable p- or 0-xylene isomers can be manufactured from these low value aromatics in a process complex consisting of transalkylation, eg, the Tatoray process and Mobil s toluene disproportionation (M lDP) and selective toluene disproportionation (MSTDP) processes isomerization, eg, the UOP Isomar process (88) and Mobil s high temperature isomerization (MHTI), low pressure isomerization (MLPI), and vapor-phase isomerization (MVPI) processes (89) and xylene isomer separation, eg, the UOP Parex process (90). 

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... 

Toluene alkylation with isopropyl alcohol was chosen as the test reaction as we can follow in a detail the effect of zeolite structural parameters on the toluene conversion, selectivity to cymenes, selectivity to para-cymene, and isopropyl/n-propyl ratio. It should be stressed that toluene/isopropyl alcohol molar ratio used in the feed was 9.6, which indicates the theoretical toluene conversion around 10.4 %. As you can see from Fig. 2 conversion of toluene over SSZ-33 after 15 min of T-O-S is 21 %, which is almost two times higher than the theoretical toluene conversion for alkylation reaction. The value of toluene conversion over SSZ-33 is influenced by a high rate of toluene disproportionation. About 50 % of toluene converted is transformed into benzene and xylenes. Toluene conversion over zeolites Beta and SSZ-35 is around 12 %, which is due to a much smaller contribution of toluene disproportionation to the overall toluene conversion. A slight increase in toluene conversion over ZSM-5 zeolite is connected with the fact that desorption and transport of products in toluene alkylation with isopropyl alcohol is the rate controlling step of this reaction [9]... 

In the last 15 years, as the demand for benzene and xylenes started to pull away from the demand of toluene, engineers and chemists scratched their heads and came up with a commercial process to increase the two at the expense of the one. Toluene disproportionation takes in toluene and turns out benzene and xylenes. 

The manufacture of the xylenes is a dejk vu story of benzene and toluene—cat reforming, olefin plants, a small amount naturally resident in crude oil, and coke making. A small but rapidly growing amount of xylene comes from catalytic disproportionation, the process described in the ben-... 

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%. 

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. 

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