Hydrodemethylation of toluene

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. 

Benzene is also produced by the hydrodemethylation of toluene under catalytic or thermal conditions. 

We now propose a mechanism for the hydrodemethylation of toluene. We assume that toluene is adsorbed on the surface and then reacts with hydrogen in the gas phase to produce benzene adsorbed on the surface and methane in the gas phase. Benzene is then desorbed from the surface. Since approximately 75% of all heterogeneous reaction mechanisms are surface-reaction-limited rather than adsorption- or desorption-limited, we begin by assuming the reaction between adsorbed toluene and gaseous hydrogen to be reaction-rate-limited. Symbolically, this mechanism and associated rate laws for each elementary step are ... 

Example CD 10-3 Hydrodemethylation of Toluene in a PER without Pressure Drop [2nd Ed. Example 6-31... 

Heterogeneous Reactions. Historically, it has been the practice in many gas-solid catalyzed reactions to write the rale law in terms of partial pressures rather than concentrations. In heterogeneous catalysis it is the weight of catalyst that is important, rather than the reactor volume. Consequently, we use -rJI in order to write the rate law in terms of mol per kg of catalyst per time in order to design PBRs. An example of a heterogeneous reaction and corresponding rate law is the hydrodemethylation of toluene (T) to form benzene (B) and methane (M) carri out over a solid catalyst. 

We shall use the hydrodemethylation of toluene to illustrate these four operations. 

Styrene has enjoyed a special position among vinyl aromatic monomers because of its lack of isomers and consequent ease and simplicity of production Additional steps are normally required to make substituted styrene derivatives, and separation and purification of isomers are usually difficult Our discovery of novel technology to produce p-ethyltoluene is a unique departure from this situation A highly selective catalyst enables the manufacture of a substituted vinyl aromatic monomer without coproducing undesirable and dlfflcult-to-separate Isomers Furthermore, direct use of toluene eliminates the need for hydrodemethylation by which much of the benzene starting material for styrene is produced ... 

Proper choice of feedstocks and use of relatively severe operating conditions ia the reformers produce streams high enough ia toluene to be directiy usable for hydrodemethylation to benzene without the need for extraction. 

A further procedure will be described only for m-xylene, for which we obtained the following values of the constants fci = 173.7, fc2 = 84.2 mole hr-1 kg-1 atm-1 K — 20.6, Ko = 25.8 atm-1. The conclusions drawn from the study of consecutive hydrodemethylation were similar for all the three xylenes studied (100). The influencing of individual reactions by products and by the intermediate product was determined experimentally, by measuring their effect on the reaction of m-xylene and toluene. The adsorption coefficients, which express this effect, are listed in Table III. 

Toluene is convened 10 benzene by hydrodemethylation either under thermal or catalytic conditions. Benzene produced from this source generally supplies 25-30% of the total benzene demand. The feedstock is usually extracted toluene, but some reformers are operated under sufficiently severe conditions or with selected feedstocks to provide toluene pure enough to be fed directly to the dealkylation unit without extraction. 

These reactors were employed for coupling of isopentcnes dehydrogenation into isoprene with toluene hydrodemethylation. Hydrogen evolved during the first reaction in one compartment dissolved in palladium alloy plates and penetrated through them to the other compartment, where the second reaction took place. 

As examples, xylene isomerization, toluene hydrodemethylation, n-butene isomerization, dehydration of methanol to demethyl ether, hydration of acetylene to acetaldehyde [31], catalytic reduction of NO [86] have been described to be successful if applying different varieties of treated clinoptilolite (cation exchanged or activated ). For a rough estimate about the importance of clinoptilolite for catalytic applications a search in the Chemical Abstracts... 

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