An Alternative to the Cymenes Production from Scrap Tire Rubber Using Heteropolyacid Catalysts

Abstract

The catalytic reforming of pyrolytic oil comes from scrap tires rubber (STR) was studied using as catalyst three different heteropolyacids (HPA) supported on commercial silica (CARiACT Q-10); H3PW12O40 (HPW), H3PMo12O40 (HPMo) and H4PMo11VO40 (HPMoV). A specify attention was given to influence of acidity of catalysts (i.e. strength and acid site types i.e. Lewis and/or Bronsted) on the concentration of cymenes in the pyrolytic oil. The catalytic performance was evaluated in a fixed bed reactor at laboratory-scale equipped with two independent thermal zones; in the first, the STR pyrolysis takes place to produce volatile compounds which, consequently, were transformed in a catalytic zone. The resulting pyrolysis oil in each test was collected in two cooling traps and characterized by GC-MS and GC-FID for the identification and quantification of all aromatic compounds. The results showed a decrease on the pyrolytic oil yield when HPA based catalysts were used, which seems to be promoted by an higher number of Bronsted sites. It has reached an increase in the aromatic concentration, compared to the test without catalyst, of up to 140% for the Molybdenum-based catalysts and close to 89% for the Tungsten-based catalyst. The major compounds obtained were cymenes and its production was closely associated to the type and strength of acid sites. Thus, the highest amount of cymenes (mainly p-cymene) was obtained with the highest number of Lewis sites and the highest ratio of Lewis/Bronsted acid sites, i.e. Molybdenum-based catalysts. On the contrary, the lowest yields were obtained when the Tungsten-based catalyst was used associated to its higher number of Bronsted acid sites and its strong acidity that promote the cracking reactions.