Production of para-xylene
The invention is a process for producing paraxylene, benzene and/or toluene is alkylated with methanol in the presence of a catalyst under conditions effective to convert said benzene and/or toluene to xylene and produce a product stream containing water, xylene and one or more phenolic impurities. The said product stream is separated into a water-rich stream and a xylene-rich stream containing one or more phenolic impurities and at least a portion of the xylene-rich stream is contacted with an aqueous solution of a base under conditions to remove at least some of the phenolic impurities from the xylene-rich stream portion.
1. A process for producing paraxylene, the process comprising:
(a) alkylating benzene and/or toluene with methanol in the presence of a catalyst under conditions effective to convert said benzene and/or toluene to xylene and produce a product stream containing water, xylene and one or more phenolic impurities, 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. for between about 10 minutes and about 100 hours to adjust the Diffusion Parameter of said material to about 0.1-15 sec −1 ;
(b) separating said product stream into a water-rich stream and a xylene-rich stream containing one or more phenolic impurities; and
(c) contacting at least a portion of said xylene-rich stream with an aqueous solution of a base in a plurality of stages under conditions to reduce the level of phenolic impurities in said xylene-rich stream to less than 0.1 ppmw, wherein said xylene-rich stream is in a liquid phase; then
(d) washing said xylene-rich stream with water to remove any phenate salts and any residual aqueous solution of base; then
(e) a step of separation of paraxylene from said xylene-rich stream by adsorptive separation to leave a paraxylene-depleted stream.
2. The process of claim 1 , wherein the phenolic impurities are selected from phenol, methyl phenol and dimethyl phenol.
3. The process of claim 2 , wherein the xylene-rich stream portion contacted with said aqueous solution of a base in (c) comprises phenolic impurities in an amount up to about 1000 ppmw.
4. The process of claim 1 , wherein the base comprises an alkali metal compound.
5. The process of claim 1 , wherein the base is sodium hydroxide.
6. The process of claim 1 , wherein said aqueous solution comprises a 0.01 N to 10 N sodium hydroxide solution.
7. The process of claim 1 , wherein said contacting (c) is conducted for a time from about 0.5 to about 60 minutes.
8. The process of claim 1 , further comprising:
(f) recovering said water after said washing (d) as a recycle water stream;
(g) purifying said recycle water stream to remove said phenate salts and residual aqueous solution of base to produce a purified water stream; and
(h) introducing said purified water stream as said water in said washing (d).
9. The process of claim 1 , further comprising isomerizing said paraxylene-depleted steam in a xylene isomerization unit.
10. The process of claim 1 , further comprising transalkylating said paraxylene-depleted stream in a transalkylation unit.