1. A process for separating meta-xylene from a hydrocarbon feed comprising isomers containing 8 carbon atoms, comprising:
a step for bringing said feed into contact with a metaselective adsorbant comprising a faujasite type zeolite, the percentage of water in said zeolite being in the range 0 to 8% by weight and the adsorption temperature being from 25\xb0 C. to 250\xb0 C.;
a desorption step employing a desorbant; and
a step for separating meta-xylene from said desorbant;
said process being characterized in that said desorbant is selected from the group consisting of tetraline methyl tetraline, ethyl tetraline, propyl tetraline, isopropyl tetraline, methylethyl tetraline, dimethyl tetraline and diethyl tetraline.
2. A meta-xylene separation process according to claim 1, in which the faujasite type zeolite is selected from:
X faujasites in which the (SiAl) ratio is from 1.0 to 1.5;
Y faujasites in which the (SiAl) ratio is more than 1.5.
3. A meta-xylene separation process according to claim 1, in which the faujasite type zeolite is a Y faujasite.
4. A meta-xylene separation process according to claim 3, in which the Y faujasite has exchangeable sites which are at least 70% occupied by sodium atoms.
5. A meta-xylene separation process according to claim 3, in which the faujasite has a (SiAl) ratio of 2.5 to 3.
6. A meta-xylene separation process according to claim 1, in which the adsorbant is in the form of an agglomerate comprising faujasite type zeolite crystals dispersed in an inorganic binder.
7. A meta-xylene separation process according to claim 6, in which the faujasite is included in the agglomerate in an amount of 75% to 98% by weight with respect to the total agglomerate weight.
8. A meta-xylene separation process according to claim 1, in which the adsorbant has a water content of 0 to 1% by weight.
9. A meta-xylene separation process according to claim 8 comprising, prior to the contact step, an adsorbant pre-treatment step comprising:
at least one drying stage at a constant temperature of 60\xb0 C. to 120\xb0 C. for a period of 0.5 hours to 3 hours; and
at least one activation stage at a constant temperature of at least 235\xb0 C. for a period of 0.5 hours to 3 hours.
10. A meta-xylene separation process according to claim 9 in which, between the drying stage and the activation stage, the observed temperature rise is from 1 to 50\xb0 C.min.
11. A meta-xylene separation process according to claim 1, in which the adsorption temperature is from 100\xb0 C. to 200\xb0 C.
12. A meta-xylene separation process according to claim 11, in which the adsorption temperature is from 120\xb0 C. to 180\xb0 C.
13. A meta-xylene separation process according to claim 1, in which the desorbant has a volume ratio with respect to the feed of 0.5 to 2.5 by volume.
14. A meta-xylene separation process according to claim 13, in which the desorbant has a volume ratio with respect to the feed of 1 to 2 by volume.
15. A meta-xylene separation process according to claim 1, in which the operating pressure is from atmospheric pressure to 20 bars.
16. A meta-xylene separation process according to claim 1, in which the adsorbant is in the form of one or more fixed beds.
17. A meta-xylene separation process according to claim 1, in which contact with the adsorbant is carried out using a simulated moving bed technique.
18. A meta-xylene separation process according to claim 1, wherein the desorbant is tetraline.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1) An apparatus for flossing teeth, the apparatus comprising a powered flossing device, a means for detecting the orientation of said flossing device, and a means for activating and deactivating said powered flossing device as a function of the detected orientation of the flossing device.
2) A powered flossing device having a housing, a power source, a length of floss on a spool, and a powered means for rotating said spool, comprising:
means for detecting the orientation of said flossing device and activating said powered means for rotating said spool as a function of the detected orientation of said flossing device.
3) The powered flossing device of claim 2 further comprising a means for illuminating the user’s teeth and means for activating said means for illuminating as a function of the detected orientation of said flossing device.