Enhancing p -xylene selectivity during m -xylene transformation using mildly pre-coked ZSM-5 catalyst

Abstract

In the present work, the transformation of m-xylene was studied over fresh and pre-coked H-ZSM-5 catalyst in a riser simulator over the temperature range of 350-500 o C.Significant differences were observed in both the activity and product selectivity pattern for the two forms of the catalyst.While, the fresh catalyst generally gave higher m-xylene conversion, the pre-coked catalyst produced higher Isomerization/Disproportionation (I/D) and Para/ Ortho xylene (P/O) ratios .For both forms of the catalyst, m-xylene conversion was found to increase with both reaction temperature and reaction time (0-15 s). A maximum conversion of 30.8% was achieved at 500 o C for a reaction time of 15 s using the fresh catalyst. The corresponding value for the pre-coked catalyst was 24.6%. P/O and I/D ratios as high as 2.5 and 10 respectively were observed with the pre-coked catalyst. It was also observed that the P/O and I/D ratios decreased with increasing temperature for both catalyst and that the difference between these ratios for the two catalysts is more pronounced between 400 and 450 o C than at higher temperatures. Kinetic modeling of the m-xylene transformation over the pre-coked catalyst yielded a lower activation energy for p-xylene formation compared to the fresh catalyst. And an activation energy of 17.5 kcal/mol for the of m-xylene dispropotionation was obtained for the precoked catalyst compared to 7.82 kcal/mol for the fresh catalyst. These values are indicative of the restriction posed on disproportionation by the pre-coked catalyst as reflected by higher I/D ratios.

Production of p‐Xylene from Biomass by Catalytic Fast Pyrolysis Using ZSM‐5 Catalysts with Reduced Pore Openings

“…Researchers have used ZSM‐5 catalysts with finely tuned pore‐opening sizes that imposed greater space confinement to increase the selectivity for p ‐xylene over the other isomers ( para selectivity) in the toluene alkylation and toluene disproportionation reactions beginning in the late 1970s with the work of Kaeding et al 9b. 10 Impregnating phosphorus on ZSM‐5 was found to provide superior para selectivity of the xylenes by supposedly narrowing the pore opening of the zeolites 10b,c.…”

Xylene isomerization kinetic over acid-functionalized silicalite-1 catalytic membranes: Experimental and modeling studies

“…The solution routine start with an initial guess of k 1 , k 2 , k 3 , k −1 , k −2 , k −3 and˛. The initial guess of these parameters was made by referring to the data reported in the literature [1,2,7]. The best fit was verified by evaluating the simulated and experimental C m , C p and C o which should be in close agreement with the convergence less than ±0.05.…”

“…With increasing demand of p-xylene, selective production of p-xylene by m-xylene isomerization using zeolite catalyst has gained considerable interest over the years and much attention has been focused on ZSM-5 zeolite as catalyst due to its high activity and shape selectivity [1,2]. Recently, the application of zeolite membrane as catalytic membrane has been reported by number of researchers [3][4][5][6][7][8] to improve p-xylene yield by selective removal of the product from the reactor.…”

Quantitative conversion of triglycerides to hydrocarbons over hierarchical ZSM-5 catalyst

“…As the increase of NH 4 + concentration, the heavy aromatics appeared and the amount increased with the acid strength. The p-xylene dominated the organic liquid products could be assigned to the shape selectivity of hierarchical ZSM-5 and the isomerization of m-xylene [40,59].…”