Aromatization isomerization

Many reactions occur in the reactor under reforming conditions. These are aromatization reactions, which produce aromatics isomerization reactions, which produce branched paraffins and other reactions. 

Historically, the earliest C8 aromatic isomerization catalysts tended to use amorphous supports with a halogen such as chloride or fluoride. Due to water sensitivity and corrosion issues, these were replaced by large-pore zeolites such as mordenite. The larger pore size was more favorable toward bimolecular transalkylation, whereas the chlorided alumina support tended to promote cracking. In both... 

There are two distinct types of catalysts used for Cg aromatics isomerization. These differ in the manner that EB is converted. The catalysts that are used to isomerize EB tend to have higher metal activity and larger-pore molecular sieve components capable of accommodating naphthenic species without cracking them. EB isomerization type catalysts tend to require more regular regenerations than EB dealkyla-... 

Harmer et al.29 have applied the sol-gel technique to prepare 1,1,2,2-tetrafluor-oethanesulfonic acid supported on silica, which proved to be an excellent catalyst for several processes such as alkylation and acylation of aromatics, isomerization, oligomerization, and Fries rearrangement. This material has activity similar to that of triflic acid but is much easier to handle. 

For PtSn supported on a nonacidic alumina the addition of Sn causes an increase in activity up to Sn/Pt = 4, and then a decline in activity for low pressure operation (42). The increase in activity is much less at 400 psig operation than the two-fold increase observed at atmospheric pressure. However, there is a change in the selectivity of aromatic isomers produced from n-octane at both 15 and 400 psig as Sn is incorporated into the catalyst. Thus, both Pt and Pt/Sn catalysts produce only (> 90-95%) ethylbenzene and o-xylene as the dehydrocyclization products from n-octane. However, Pt produces ethylbenzene o-xylene = 1 1 whereas a catalyst with Sn/Pt = 4 produces ethylbenzene o-xylene = 1 2. This change in aromatic isomerization leads to two postulates ... 

The catalytic reactions occurring in C8 aromatics isomerization and toluene disproportionation or transalkylation with heavy aromatics are given in the following paragraphs. The catalysts used for these reactions and the processes are also described. 

Aris [Aromatics isomerization] A process for the hydrocatalytic isomerization of C8 fractions. Developed by Leuna-Werk and Petrolchemische Kombinate Schwedt in 1976. The catalyst is platinum deposited in a mixture of alumina and natural mordenite. 

Reference Rault, J., P. Renard, and F. Alario, Maximizing Paraxylene Production with ParamaX, IFP March 2000. Dupraz, C., F. Alario, J. Magne-Drisch., E. Merlen, and J. Rault,., Aromatics Isomerization, WRA 2000, Amsterdam, March 2000. 

In this part, we will summarize some of our results on the investigation of the toluene intramolecular isomerization pathways." " Both cluster approach and periodic approach methods have been employed which allow giving an illustration of the consequence of the simplistic model in the cluster approach. H-Mordenite (H-MOR) zeolite is used for the periodic calculations. The toluene molecule does not have a problem to fit within the large 12-membered ring channels of this zeolite. Furthermore, the intramolecular transition states do not suffer from steric constraints. It is known that intramolecular aromatics isomerization can proceed via two different reaction pathways (see Figure 7). The first route proceeds through a methyl shift isomerization, whereas the second route involves a dealkylation or disproportionation reaction which results in the formation of a methoxy species and benzene as intermediate. 

In aromatic isomeric bicyclic compounds, those with bridge rings have lower b.ps. than those with two isolated or condensed rings. 

The dihalocyclopropane route is the method of choice for the synthesis of benzocyclopropenes and linearly fused cyclopropanaphthalenes, but is unsuccessful for angular cyclopropa[u]naph-thalene. Treatment of l,l-dichloro-la,2,3,7b-tetrahydro-l/f-cyclopropa[a]naphthalene(5) with potassium /ert-butoxide gave a mixture of 1-chloromethylnaphthalene, 1-terr-butoxymethyl-naphthalene and 2-terf-butoxy-l-chloromethylene-l,2,3,4-tetrahydronaphthalene, but none of the expected cyclopropa[n]naphthalene. The failure of the reaction has been attributed to difficulties in the aromatization. Isomerization of the initially produced cyclopropenyl double bond into the cyclohexane ring would require disruption of the aromatic character of the adjacent benzene nngT t-r>> 62 Similarly, attempted aromatization of l-chloro-l,2,3,7b-tetra-hydro-l//-cyclopropa[a]naphthalene (6) with 2,3-dichloro-5,6-dicyanobenzoquinone or via N-bromosuccinimide bromination followed by reaction with base afforded 4,5-benzotropone instead of cyclopropa[fl]naphthalenc. ... 

Unsupported and SiC/Al203-supported W2C catalysts are multifimctional. n-Alcanes are transformed by aromatization, isomerization, and hydrogenolysis. Aromatization can be increased by the addition of O2 traces. 

Catalyst Evaluation. The powdered molecular sieves were evaluated following the treatment described above, without further activation. The 1-hexene isomerization and Cg aromatic isomerization tests were conducted in tubular, fixed bed, continuous flow microreactors. The catalyst bed contained one gram molecular sieve powder and one to three grams of similarly sized quartz chips used as diluent. The reactor was heated to the chosen reaction temperatures in a fluidized sand bath, and the reaction temperature was monitored by a thermocouple located m the catalyst bed. Typical runs lasted 3 to 5 hours during which samples were collected every 30 minutes. 

The production of para-xylene is of interest to the petrochemical industry because of its use as monomer in polyester production. In addition to Cg aromatic isomerization, there are a number of important routes to para-xylene including the alkylation of toluene with methanol and the disproportionation of toluene. The catalytic properties of the SAPO molecular sieves for toluene methylation reactions have been described(11). While both large and medium pore SAPO s were active for the alkylation reaction, the medium pore materials were distinguished by remarkably high selectivity for methylation reactions, with disproportionation of the toluene feed representing less than 2% of the total conversion. By comparison, large pore SAPO-5 had nearly 60% disproportionation selectivity and the zeolite reference LZ-105 had nearly 80% disproportionation selectivity. The very low disproportionation activity of the medium pore SAPO s, attributed to their mild acid character, resulted in reduced losses of toluene to benzene and increased xylene yields relative to LZ-105 and SAPO-5. 

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