Compositions – Solvents
Reexamination Certificate
2000-01-27
2001-09-18
Griffin, Walter D. (Department: 1764)
Compositions
Solvents
Reexamination Certificate
active
06290876
ABSTRACT:
FIELD OF THE INVENTION
The present invention provides for methods for improving the extraction of phenols in the propylene oxide styrene monomer process. More specifically, the present invention provides for methods for improving the removal of phenols from crude styrene with aqueous caustic.
BACKGROUND OF THE INVENTION
In the propylene oxide styrene monomer (POSM) process, methyl oxirane (propylene oxide) and ethenyl or vinyl benzene (styrene monomer) are co-produced. Molecular oxygen is reacted with ethylbenzene to form &agr;-hydroperoxy ethylbenzene which is then subsequently reacted with propene to form propylene oxide and &agr;-hydroxyethylbenzene, also known as methylbenzyl alcohol.
After removing the more volatile propylene oxide, the methylbenzyl alcohol is dehydrated to water and styrene monomer. These are co-distilled overhead and condensed into a water/oil separator, where the water forms a separate phase and is drained. The crude styrene phase is then extracted in a caustic wash drum with 5 to 10% of an aqueous caustic solution containing about 2 to 3% NaOH, sometimes with about an equal amount of a caustic solution recycled to remove phenolic byproducts of the above-described oxidation and epoxidation reactions.
The caustic extracted styrene is then rinsed in a water wash drum with 5 to 10% fresh water, also sometimes with about an equal amount recycled, to remove residual caustic and phenate salts from the crude styrene prior to distillation. Typically, the temperature of the extraction is about 100 to 110° F. The pH in the second stage is about 11.5 and in the first stage is about 14.
The present inventor has discovered a means to improve this extraction process while minimizing residual carryover of caustic and phenates to the styrene distillation towers. This method also helps eliminate the production and disposal as toxic waste of stable dispersion layers which otherwise accumulate in separation vessels.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention provides for an improved method for extracting phenols from crude styrene with aqueous caustic, the improvement comprising adding to the styrene an effective amount for the purpose of aiding extraction of an aromatic or alkylammonium tailed multi-polyether headed surfactant or a quaternary polyamine.
The aromatic or alkylammonium tailed multi-polyether headed surfactants (MPEHS) include those with hydrophobic “tails” comprising C
3
to C
18
alkylaryl diols to polyols and C
3
to C
22
alkyl or alkylaryl 1° or 2° amines. These are adducted with C
2
to C
3
alkylene oxides to form two or more hydrophilic heads per hydrophobe comprising separate polyether chains of degree of polymerization (dp) 3 to 30. The backbone and branches of the polymer contain only ether or amine linkages, and not, for example, esters or amides. Quaternary amines employ any convenient counterions, such as halides, sulfates, nitrates, phosphates, carboxylates, phenates, silicates, carbonates, or hydroxides.
Preferably, the multi-polyether headed surfactant comprises C
4
to C
9
alkylphenol-formaldehyde condensates of dp 4 to 8 adducted with ethylene oxide to form 4 to 8 polyether chains of dp 4 to 7 blended with the halide salt of linear C
12
to C
22
alkyl 2° amines adducted with ethylene oxide to form 2 polyether chains of dp 5 to 10.
The quaternary polyamines used in the present invention are those in which the backbone and branches of the polymer contain only ether or amine linkages and not, for example, esters or amides. The polyamine should have a degree of polymerization of about 60 to 6000 monomer units and an overall carbon to nitrogen or oxygen ratio of less than 10. These compounds are water soluble.
The quaternary polyamines include but are not limited to halides, sulfates, nitrates, phosphates, carboxylates, phenates, silicates, carbonates, or hydroxides of alkyl or alkylaryl quaternary amines. The preferred polyamines include but are not limited to poly(diallyldimethylammonium chloride), or poly(DADMAC), having the formula:
poly(N,N-dimethyl, 2-hydroxypropyleneammonium chloride), or poly(DMHPAC), having the formula:
and poly(N,N-dimethyl, 3-(2-hydroxypropyleneamine) propylammonium chloride) or poly[DM(HPA)PAC], having the formula:
The poly(DMHPAC) compound may be formed by reacting about equimolar amounts of 3-chloromethyl-1,2-oxirane (epichlorohydrin or EPI) with dimethylamine (DMA).
The poly[DM(HPA)PAC] may be formed by reacting about equimolar amounts of EPI and dimethylaminopropylamine (DMAPA).
The present inventor has discovered that these extraction aids assist in fluidizing, solubilizing and removing the surfactant barrier to improve extraction efficiency. This minimizes the caustic carryover to the crude styrene distillation section and eliminates the production and disposal of the dispersion layer.
The multi-polyether headed surfactants are preferably fed as solutions in aqueous or organic solvents that are compatible with both the MPEH's and the POSM process. The organic solvents include high boiling (i.e. greater than 400° F.) aromatic hydrocarbons, glycol ethers, such as 2-n-butoxy-2-ethoxyethanol (butyl carbitol), and native aromatic alcohols such as &agr;-hydroxyethylbenzene, which is most preferred.
Preferably the solutions are fed to the influent, unwashed styrene. The solutions may also be fed to the interstage, washed but not rinsed styrene. Preferably from about 3 to about 30 parts of MPEH per million parts of styrene are fed.
The quaternary polyamines are preferably fed as an aqueous solution to the influent caustic wash water or the fresh rinse water or most preferably both the caustic wash and rinse water, prior to mixing with the styrene.
The quaternary polyamines are fed in amounts ranging from about 1 part to about 100 parts polyamine per million parts of water with a range of about 3 to about 30 preferred, or about 0.1 part to about 10 parts per million parts of styrene with a range of about 0.2 parts to about 2.0 parts preferred.
The following examples are intended to show the efficacy of the present invention and should not be construed as limiting the scope of the invention.
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Patent Abstracts of Japan, vol. 005, No. 098 (C-060), Jun. 25, 1981.
BetzDearborn Inc.
Greenblum & Bernstein P.L.C.
Griffin Walter D.
Nguyen Tam M.
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