Selectivity improvement in xylene isomerization

Transformation of ethylbenzene-m-xylene feed over MCM-22 zeolites with different acidities

“…The much higher than one molar ratio between toluene and trimethylbenzene (TMB) for all catalysts is an indication that not only direct xylene disproportionation to those two products takes place, but also secondary reactions of toluene formation by transmethylation of benzene or ethylbenzene with xylenes have proceeded in accordance to Silva et al [5] and Benazzi et al [4] respectively. Analogous effect of selective improvement in xylene isomerization and significant reduction in xylene loss by effective elimination of the strong acid sites of zeolite ZSM-5 is observed by Bauer et al [28]. The authors also introduce hydroisomerisation function by loading Pt to the modified support.…”

“…The spectra in the hydroxyl stretching region show ( The band at 3727 cm -1 is also registered by Meloni at al. [26] in MCM-22 materials with higher Si/Al ratio and corresponds to the "hydroxyl nests" detected on steamed [27], acidleached [28] or steam and acid-treated [23] zeolites of the MCM-22 type. In our case the intensity of the band at 3727 cm -1 is the highest for the more severely steam-treated D500/Ox.…”

A solid-state NMR, FT-IR and TPD study on acid properties of sulfated and metal-promoted zirconia: Influence of promoter and sulfation treatment

“…0.55 nm) or tributylphosphine oxide (TBPO; size ca. 0.82 nm), additional qualitative and quantitative information, such as the amount and location (internal versus external) of acid sites can also be inferred by the 31 P MAS NMR spectroscopy [27], as illustrated previously for various solid acid catalysts [45][46][47].…”

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

“…Silylation usually leads to narrowing of the pore opening and high p-xylene selectivity results due to the higher p-xylene diffusivity compared to that o-or mxylene [46]. Bauer et al (28) reported that k 1 /k 2 for the pre-coked catalyst is almost double that the fresh catalyst.…”

“…It was reported that for toluene disproportionation reaction over HZSM-5, a coke content of around 2 wt% is needed for para-selectivity enhancement [21,28]. Bauer et al [7] argued that an additional thermal treatment of the pre-coked HZSM-5 by hydrogen or alkanes is effective in enhancing p-xylene selectivity and only a small amount of coke is needed for the treatment (around 0.3 wt%).…”