Improvement of coke-induced selectivation of H-ZSM-5 during xylene isomerization

Bauer, Frank; Chen, Wenhua; Zhao, Qi; Freyer, A.; Liu, Shang-Bin

doi:10.1016/s1387-1811(01)00318-3

Cited by 48 publications

(32 citation statements)

References 19 publications

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“…However, in that study the possible catalytic action of the coke was not considered. Increasing the selectivity of zeolite catalysts through carbon deposition is a strategy employed industrially in xylene isomerisation [58,59]. Furthermore, the activity of CNTs in the oxidative dehydrogenation of n-butane has recently been demonstrated [25].…”

Section: Activity Of Coke Deposits On Vo X /Al 2 Omentioning

confidence: 99%

Active coke: Carbonaceous materials as catalysts for alkane dehydrogenation

McGregor

Huang

Parrott

et al. 2010

Journal of Catalysis

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The catalytic dehydrogenation (DH) and oxidative dehydrogenation (ODH) of light alkanes are of significant industrial importance. In this work both carbonaceous material deposited on VOx/Al2O3 catalysts during reaction and unsupported carbon nanofibres (CNFs) are shown to be active for the dehydrogenation of butane in the absence of gas-phase oxygen. Their activity in these reactions is shown to be dependent upon their structure, with different reaction temperatures yielding structurally different coke deposits. Terahertz time-domain spectroscopy (THz-TDS), among other techniques, has been applied to the characterisation of these deposits -the first time this technique has been employed in coke studies. TEM and other techniques show that coke encapsulates the catalyst, preventing access to VOx sites, without a loss of activity. Studies on CNFs confirm that carbonaceous materials act as catalysts in this reaction. Carbon-based catalysts represent an important new class of potential catalysts for DH and ODH reactions.

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Section: Activity Of Coke Deposits On Vo X /Al 2 Omentioning

confidence: 99%

Active coke: Carbonaceous materials as catalysts for alkane dehydrogenation

McGregor

Huang

Parrott

et al. 2010

Journal of Catalysis

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“…The shape selective conversion of xylenes over ZSM-5 has been investigated in detail by several workers [1][2][3][4][5][6][7][8][9][10][11][12]. Modifications of ZSM-5 by various compounds have been employed to enhance p-xylene selectivity from xylene transformation process [13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

“…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%).…”

Section: Introductionmentioning

confidence: 99%

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

Al-Khattaf

2007

Chemical Engineering and Processing - Process Intensification

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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.

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“…Since xylene isomerization plays an important role in the petrochemical industry, mainly for phthalic and terephthalic acid production, research in this area is of great interest. Recent achievements in this¯eld are presented in a number of articles [6][7][8][9]. The best results for xylene isomerization in these publications provide product mixtures close to the xylene thermodynamic equilibrium [8], but the temperature required was rather high: from º 300ºC to º 400ºC.…”

Section: Introductionmentioning

confidence: 99%

Transformations of xylenes in trimethylammonium hydrochloride—Aluminum chloride ionic liquid

Ксенофонтов

Кustov

2003

Open Chemistry

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Isomerization of m-, o-and p-xylenes in the presence of trimethylammonium hydrochloride { AlCl 3 ionic liquid with di¬erent composition was studied. Ionic liquids with the following ammonium salt : AlCl 3 molar ratios were used: 1 : 2, 1 : 1.5 and 1 : 1.25. It was shown that isomerization of xylenes proceeds under mild conditions at temperatures from 60¸C to 110¸C. It was found that the activity and selectivity of the ionic liquids depends on their composition. The most e¬ective catalyst was the ionic liquid with the ammonium salt : AlCl 3 molar ratio equal to 1 : 2.

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Improvement of coke-induced selectivation of H-ZSM-5 during xylene isomerization

Cited by 48 publications

References 19 publications

Active coke: Carbonaceous materials as catalysts for alkane dehydrogenation

Active coke: Carbonaceous materials as catalysts for alkane dehydrogenation

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

Transformations of xylenes in trimethylammonium hydrochloride—Aluminum chloride ionic liquid

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