ZSM-5, its preparation and use in ethylbenzene dealkylation
A new configuration of ZSM-5 is provided whereby the crystals have a higher average silica to alumina ratio at the edges of each crystallite than in the centre as determined from a narrow slit line scan profile obtained from SEM/EDX or TEM/EDX elemental analysis. Such ZSM-5 crystals are obtained by a preparation process using L-tartaric acid. The new configuration ZSM-5 provides significantly reduced xylene losses in ethylbenzene dealkylation, especially when combined with silica as binder, and one or more hydrogenation metals selected from platinum, tin, lead, silver, copper, and nickel.
1. ZSM-5 crystals, prepared using L-tartaric acid and comprising a ZSM-5 crystallite having an average SAR at the edge of the crystallite and an average SAR at the centre of the crystallite, as determined using element maps produced from SEM/EDX or TEM/EDX elemental analysis, wherein a distribution profile is obtained from the elemental maps, and wherein the distribution profile displays structural variations in SAR distribution at the edge of the crystallite to SAR distribution at a centre of the crystallite, wherein the average SAR at the edge of the crystallite is higher than the average SAR at the centre of the crystallite, and wherein the average SAR at the edge of the crystallite is determined by (1) calculating an average of an SAR at three outermost points at each end of the distribution profile, and then (2) calculating an average of the values obtained at each end.
2. ZSM-5 crystals as claimed in claim 1 , wherein the ZSM-5 crystallite has a ratio of the average SAR at the edge of the crystallite to the average SAR at the centre of the crystallite that is at least 1.15.
3. ZSM-5 crystals as claimed in claim 2 , wherein the ratio is at most 3.
4. ZSM-5 crystals as claimed in claim 1 , wherein a slope of a second order polynomial fitted to SAR values between two edge SAR maxima, expressed as −y′ 0 , is at least 2.
5. ZSM-5 crystals as claimed in claim 1 , wherein a slope of a second order polynomial fitted to SAR values between two edge SAR maxima, expressed as −y′ 0 , is at most 6.
6. ZSM-5 crystals as claimed in claim 1 , wherein a lateral resolution of the distribution profile is about 50 nanometers (nm).
7. A catalyst composition, comprising: ZSM-5 crystals, prepared using L-tartaric acid and comprising a ZSM-5 crystallite having an average SAR at the edge of the crystallite and an average SAR at the centre of the crystallite, as determined using element maps produced from SEM/EDX or TEM/EDX elemental analysis, wherein a distribution profile is obtained from the elemental maps, and wherein the distribution profile displays structural variations in SAR distribution at the edge of the crystallite to SAR distribution at a centre of the crystallite, wherein the average SAR at the edge of the crystallite is determined by (1) calculating an average of an SAR at three outermost points at each end of the distribution profile, and then (2) calculating an average of the values obtained at each end; and a silica binder in an amount in the range of from 30 to 80 wt %, based on the total of ZSM-5 crystals.
8. A catalyst composition as claimed in claim 7 , which also contains a hydrogenation metal selected from the group consisting of platinum, tin, lead, silver, copper, and nickel.
9. A catalyst composition as claimed in claim 8 , wherein the total amount of ZSM-5 crystals present in the catalyst composition is in the range of from 20 to 50 based on a total carrier.
10. A catalyst composition as claimed in claim 9 , wherein the total carrier has been subjected to a dealumination treatment with ammonium hexafluorosilicate.
11. A catalyst composition as claimed in claim 7 , wherein a lateral resolution of the distribution profile is about 50 nanometers (nm).