Dialkylation of Benzene and Polynuclear Aromatics

Preparation of the starting material DIPB is typically achieved by isopropylation of benzene or cumene by use of conventional Friedel-Crafts catalysts [8] although solid acids [9], resins [10] and, more recently, zeolites [11,12] have also been mentioned as catalysts. Likewise, alkylation of polynuclear aromatics, e. g. biphenyl or naphthalene, gives rise to valuable intermediates. 4,4 -DialkyIbiphenyl can be converted into 4,4 -biphenyldicarboxylic acid, a monomer for a variety of 

Selective alkylation is therefore highly desired. Zeolites have proven to have excellent properties in this respect, and shape-selective reactions on these materials are well known [14]. Dow Chemical pioneered the shape-selective alkylation of polynuclear aromatics with olefins such as propylene, using as catalysts modified mordenite zeolites, which were not considered at the time to behave strictly as shape-selective catalysts [15,16]. Mordenite zeolites were not the catalyst of choice for such reactions because the alkylation of aromatics, and in particular of polynuclear aromatics, was recognized already as a first step in the reactions leading to coke formation and catalyst deactivation [17]. How was it possible to convert these unsuitable zeolites into stable and highly shape-selective catalysts for industrial applications The answer to this question will be used to illustrate the criteria and methods used to develop the so-called 3-DDM catalysts, or 3-dimensional dealuminated mordenites. 

Mordenite is known in both natural and synthetic crystalline forms with a guest-free unit cell (uc) composition Na8AlgSi4o096. This requires eight Al/uc and an Si/ 

A1 ratio of 5 = Si02/Al203 = 10 (molar). Mordenite is the most siliceous of 

The dealumination of mordenite by different treatments has been the subject of numerous studies [21-24]. Many of these dealumination studies observed marked differences from sample to sample [25]. Alteration of the lattice symmetry and reduced thermal stability has been observed in acid-dealuminated mordenite heated above 650 K [26]. The variety of changes involved in the dealumination of mordenite, and the problems associated with reproducibility, crystallographic symmetry changes, and the lack of specific knowledge relating to sample source and treatment conditions make interpretation of the literature on this subject a challenge. The introduction of SI is an attempt to help clarify differences between data on mordenite and mordenite catalysts. 

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