Process for the purification of paraxylene
The proposed process uses crystallization technology to purify paraxylene simultaneously of large concentrations of C8 aromatics and also small concentrations of oxygenated species.
1. A process for the production of Para-xylene comprising:
(i) reacting toluene with methanol under alkylation conditions in the presence of a catalyst suitable for the production of a product comprising para-xylene and oxygenates as impurities, and having a BI of more than 200;
(ii) recovering said product comprising para-xylene and oxygenates from step (i);
(iii) subjecting said product from step (ii) to purification by crystallization;
(iv) recovering a paraxylene fraction from step (iii), said fraction characterized by a BI of 30 or less and having a lower amount of oxygenate impurities than said product recovered from step (ii); wherein there is no clay treating step between steps (i) and (iii).
2. The process of claim 1 , wherein said catalyst comprises a porous crystalline material having a Diffusion Parameter for 2,2 dimethylbutane of about 0.1-15 sec −1 when measured at a temperature of 120° C. and a 2,2 dimethylbutane pressure of 60 torr (8 kPa) wherein said porous crystalline material has undergone prior treatment with steam at a temperature of at least 950° C. to adjust the Diffusion Parameter of said material to about 0.1-15 sec −1 .
3. The process of claim 2 , wherein said Diffusion Parameter of said porous crystalline material is about 0.5-10 sec −1 .
4. The process of claim 1 , wherein said porous crystalline material has undergone prior treatment with steam at a temperature of at least 1000° C. for between about 10 minutes and about 100 hours.
5. The process of claim 4 , wherein said treatment with steam reduces the pore volume of the catalyst to not less than 50% of that of the pore volume of the catalyst before said treatment with steam.
6. The process of claim 1 , wherein the catalyst contains at least one oxide modifier selected from the group consisting of oxides of elements of Groups IIA, IIIA, IIIB, IVA, IVB, VA and VIA of the Periodic Table.
7. The process of claim 1 , wherein the catalyst contains at least one oxide modifier selected from the group consisting of oxides of boron, magnesium, calcium, lanthanum and phosphorus.
8. The process of claim 7 , wherein the catalyst contains about 0.1 to about 10 wt % of the oxide modifier based on the elemental modifier.
9. The process of claim 1 , wherein the catalyst has an average particle size of about 20 to 200 microns.