Evaluation of heteropoly acids as catalysts in the production of gasoline additive oxygenates

In the present study vapor phase ETBE synthesis was conducted in the presence of acidic ion-exchange resins and heteropoly acid catalysts. Highest ETBE conversion was obtained with Amberlyst 15 among ion-exchange resins. Reaction experiments in the presence of Amberlyst 15 was repeated by altering feed composition via water addition, ETBE conversions in the presence of water in the feed was found to be lower than ETBE conversions with pure ethanol, in the presence of Amberlyst 15. Nevertheless ETBE conversions obtained in the presence of Amberlyst 15 with water in the feed was higher than the conversions obtained in the presence of Amberlyst 16 and Amberlyst 35 with pure ethanol in the feed composition. Reaction experiments conducted in the presence of silicotuntsic acid (STA), tungstophosphoric acid-Keggin (TPA-K) and tungstophosphoric acid-Dawson (TPA-D) revealed that STA had exhibited highest activity. Experiments conducted in the presence of heat treated STA and TPA-K showed a detoriation in proton structure of STA starting from 673K. The temperature of proton loss was found as 473K in the case of TPA-K.Heteropoly acid salts and supported heteropoly acid catalysts were synthesized in the course of study to increase their activity and stability. Investigations on catalyst activity revealed some decrease due to cation exchange with STA. This result was also supported with characterization studies. ETBE conversions obtained in the presence of AC-STA at 373K was found to be 20% higher than STA. PH-STA catalysts containing 8% STA in molecular structure revealed higher activity than pure STA based on catalyst (STA) amount. These results revealed an increase in catalyst activity when impregnated onto a support material. Stability of the catalysts were tested by washing with ethanol for three successive runs (8 hours in each run). Results indicated that activity of the supported catalysts had been preserved for the first 8 hours.Reaction results conducted in the presence of STA with varying isobuten concentrations and temperatures were compared with reaction rate expressions written for different mechanisms. It was found that best fit had been obtained for modified Langmuir-Hinshelwood kinetic model.