Isopropylation of benzene with 2-propanol over AFI aluminophosphate molecular sieves substituted with alkaline earth metal

Aluminophosphate (AlPO4-5) molecular sieves partly substituted with alkaline earth metal in the framework (MAPO-5; M = Mg, Ca, Sr, and Ba) have been employed as catalysts for the isopropylation of benzene with 2-propanol. The incorporation of alkaline earth metal ions gives rise to Brønsted acidity of different acidic strengths. The influence of type of alkaline earth metals, MO/Al2O3 ratio, reaction parameters such as reaction temperature, molar ratio of benzene and 2-propanol (B/IP), space velocity, and time on stream were studied. The selectivity of cumene (IPB) and benzene conversion was in the order Mg ≫ Ca > Sr > BaAPO-5. This order is correlated with acidity of the molecular sieves. The selectivity of IPB for MgAPO-5 was maximized at MgO/Al2O3 = 0.1. It increased with reaction temperature, low WHSV, high B/IP ratio, whereas it decreased with time on stream. The major by-products were 1,3- and 1,4-diisopropylbenzenes (1,3- and 1,4-DIPBs): among them, 1,3-DIPB was predominant over 1,4-DIPB at higher temperatures. The dealkylation of 1,3- and 1,4-DIPBs gives IPB as a major product. Molecular modeling studies reveal that 1,3-DIPB is the most stable and bulkier among DIPB isomers.