Phenolic wastewater treatment with ethers for removal and recovery of phenolics

Liquid-liquid extraction is used for the removal of phenolics from wastewater streams using an ether extractant which has a high partition coefficient and a low solubility in water such as methyl tertiary-butyl ether. The resulting phenolics-ether mixture may be separated by distillation or by the use of an aqueous solution of an alkali metal hydroxide to form a phenate in an aqueous phase and the ether in an organic phase followed by phase separation. Any ether dissolved in the wastewater is removed by distillation or the solubility of the ether in the wastewater is retarded by adding an aqueous alkali salt solution. In the distillation embodiment, an environmentally acceptable wastewater is readily obtained. In the salt treatment embodiment, the wastewater is suitable for treatment in the overall plant complex associated with the phenol/acetone plant.

BACKGROUND OF THE INVENTION 
The present invention relates to a process for treating wastewater streams 
containing phenolics and more specifically to the extraction of the 
phenolics with ethers and then the recovery of the phenolics and the 
recycle of the ethers. 
Various methods have been used in the past to remove phenolics (phenol and 
cresol) from wastewater streams including chemical reaction, adsorption 
with resins, absorption with macromolecular an substances and 
liquid-liquid extraction. An example of a chemical reaction method is U.S. 
Pat. No. 3,843,643, dated Oct. 22, 1974, where a chemical such as 
hexamethylene tetramine is added to phenolic wastewater so as to react 
with phenol to form a phenol-hexamethylene tetramine adduct and the adduct 
is separated from the wastewater with subsequent decomposition of the 
adduct and further separation of the phenol from the hexamethylene 
tetramine in which the amine can be recycled either as a solid or 
concentrated slurry. Other chemical treatment methods for phenolic 
wastewater involve the use of hydroxides or carbonates of alkali metals in 
conjunction with chlorine gas (Japanese Patent Application 48-104,352, 
dated Dec. 27, 1973) or the use of monopersulfuric acid (U.S. Pat. No. 
3,711,402, dated April, 1973). However, these chemical reaction methods 
involve cumbersome recovery and the recycle of solid chemical treating 
agents or slurries. Also, there may be the costly consumption of the 
chemical treating agents. 
A process where adsorption with resins is used is Japanese Patent 
Application 4-346,954, dated Dec. 2, 1992, which relates to a process 
wherein phenols are removed from phenolic wastewater by adsorption onto 
styrene--divinylbenzene resins, after which the phenols are deadsorbed 
with a deadsorption agent and recovered. This involves the use of costly 
adsorption resins and the problem of disposing of them when they are 
spent. 
The absorption technique is illustrated in German Patent Application 
2,531,101, dated Jan. 22, 1976, in which phenols are removed from phenolic 
wastewater by absorption into macromolecular substances, namely 
poly-alpha-halo-ketones. Once again, this involves the use of costly 
substances and the attendant disposal problem. Also, with the adsorption 
and absorption there can be complex regeneration procedures. 
Japanese Patent Application 49-080,029, dated Aug. 2,1974, relates to a 
process wherein phenols are removed from phenolic wastewater using either 
benzene or toluene as extracting agents with a subsequent distillation to 
recover either the benzene or toluene and the phenols. It is also known 
that cumene (isopropylbenzene) can be used commercially for the removal of 
phenols from phenolic wastewater. However, the extracting agents which 
have been used have low partition or distribution coefficients making the 
extraction inefficient. 
SUMMARY OF THE INVENTION 
A liquid-liquid extraction process is used for the removal of phenolics 
from wastewater streams and involves the use of extractants composed of 
ethers which have a high partition coefficient for the phenolics. The 
process further involves the separation and recovery of the phenolics and 
the ethers and the recycle of the ethers. The separation and recovery may 
involve a distillation and stripping arrangement or it may involve the use 
of an aqueous alkali salt solution to retard the solubility of the ether 
extractant in the dephenolated wastewater in conjunction with the use of 
an aqueous solution of an alkali metal hydroxide to convert the phenolics 
in the ether extractant to an alkali metal phenate solution from which the 
phenolics are recovered. The separation process using distillation and 
stripping produces an environmentally acceptable wastewater. The alternate 
process produces a suitable salt solution which may be subsequently 
crystallized, such as to a Na.sub.2 SO.sub.4 hydrate, for sale to the 
paper industry with the equilibrium water suitable for discharge into a 
river or ocean.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The invention relates to the treatment of a wastewater stream which 
contains phenolic contaminants. Included would be wastewater streams 
containing phenol, cresols or mixtures of both. Just as an example, such 
wastewater streams might be from bisphenol A plants or phenol/acetone 
plants. As one specific example, the wastewater stream from a bisphenol A 
plant might contain on the order of 0.7% by weight (7,000 ppmw) phenolics 
whereas the level of phenolics in wastewater for disposal should be 10.0 
ppmw or less by weight and preferably less than 1.0 ppmw. All references 
to percentages and parts will be by weight. 
In the present invention, the wastewater stream containing the phenolics is 
contacted with the ether extractant. This contact can take place in any 
suitable equipment providing contact between the liquids and may be single 
stage, such as in a drum equipped for phase separation, or multistage, 
such as in a liquid-liquid extraction column. The invention will be 
described with reference to the liquid-liquid extraction column but is not 
limited to such a process and equipment. 
As depicted in FIG. 1, the wastewater stream 10 containing the phenolics is 
introduced into the top of the liquid-liquid extraction column 12. 
Introduced into the bottom of the column 12 is the ether extractant 14 
from the ether drum 16. The ethers which can be used in the extraction 
column 12 are those which have a high partition coefficient for the 
phenolics, are not very soluble in water, and are readily available and 
inexpensive. Examples are ethyl tertiary-amyl ether, diisopropyl ether, 
ethyl tertiary-butyl ether and methyl tertiary-butyl ether (MTBE). All of 
the examples which follow use MTBE as the preferred ether. 
The ether and the wastewater flow countercurrently in the column 12 in 
which the ether extracts the phenolics from the wastewater. The ether 
which now contains the phenolics is withdrawn at 18 from the top of the 
column 12 whereas the wastewater now depleted in phenolics is withdrawn at 
20 from the bottom of the extraction column. The extraction column 12 
contains, for example, eight perforated trays and operates at a 
temperature of about 25.degree. C. at atmospheric pressure. As an example, 
the wastewater 20 may contain about 5.2 % ether and 44 ppb phenolics and 
94.8 % water. The wastewater 20 flows to the wastewater drum 22 for mixing 
with other streams and for treatment as will be explained hereinafter. The 
overhead 18 from the extraction column 12 may now contain, as an example, 
95.52 % ether, 3.36 % water and 1.12 % phenolics. 
The overhead 18 from the extraction column 12 flows to the extract drum 24 
and is then pumped to the phenol-ether recovery column 26 which includes a 
reboiler 28. As an example, this column 26 may have 24 trays and have a 
bottoms temperature of 108.degree. C. and an overhead temperature of 
59.degree. C. when using MTBE as the extractant. The bottoms 30 from the 
column 26 contains about 55.7 % water, 44.2 % phenolics and about 188 ppm 
MTBE. This water-phenolics stream 30 may be processed in any way desired 
such as recycling to the source plant such as the bisphenol A plant. In 
this example, the overhead 32 from the column 26 is basically an MTBE 
stream and has a composition of about 2 % water and 98 % MTBE with only 
negligible phenolics. The overhead 32 is condensed at 34 and passed to the 
reflux drum 36. From the reflux drum 36, the MTBE stream is pumped at 38 
with a portion, perhaps 67% returning to the column 26 as reflux in line 
40 and the remainder being recycled in line 42 to the ether drum 16. 
The wastewater 44 from the wastewater drum 22 is pumped to the ether 
stripper 46 which has a reboiler 48, an overhead condenser 50, a reflux 
drum 52 and a reflux pump 54. As previously indicated, the wastewater feed 
44 to the column 46 contains about 94.8 % water, 5.2 % MTBE and perhaps 
about 44 ppb phenolics. The column 46 has 20 trays, an overhead 
temperature of 63.degree. C., a bottoms temperature of 1 05.degree. C. and 
operates at essentially atmospheric pressure. The composition of the 
overhead 56 is about 94.8% MTBE and 5.2% water while the composition of 
the bottoms 58 is essentially 100% water with perhaps 13.8 ppm MTBE and 
0.05 ppm phenolics. About 67% of the overhead is reflux at 60 with the 
remainder being recycled in line 62 to the ether drum 16. Any make-up MTBE 
which is required is added at 64. 
Another embodiment of the invention is shown in the process flow diagram of 
FIG. 2, wherein all equipment and streams are at ambient temperature and 
essentially atmospheric pressure. In this embodiment, a liquid-liquid 
extraction column 12 is still used with the same ether extraction method 
including the ether feed line 14, the ether drum 16 and the make-up of 
ether feed 64. However, since there is a significant amount of ether that 
is soluble in the wastewater in the FIG. 1 embodiment, on the order of 
5.2% ether as cited earlier, this FIG. 2 embodiment uses a procedure to 
retard the solubility of the ether extractant in the dephenolated 
wastewater. This is done by adding an aqueous alkali salt solution 66 to 
the phenolic wastewater feed 10 to form stream 67. The addition of salt or 
salt solution also enhances the ease of the liquid-liquid extraction step 
by increasing the density difference between the extract and raffinate 
phases. The salt or salt solution 66 may be any alkali salt which will 
retard the solubility of the ether in water thereby significantly reducing 
downstream recovery equipment, chemical consumption and concomitant costs. 
The salt lowers the solubility of the ether because the salt is a third 
component whose solubility is greater than the solubility of the ether in 
water. Examples are sodium sulfate and sodium carbonate and the amount 
that is added is in the range of 10-18 wt., based on the phenolic 
wastewater feed. This technique will lower the concentration of the ether 
in the dephenolated wastewater 68 to between 0.1 to 0.01%. The amount of 
ether is down to a level such that an ether stripper such as 46 of the 
FIG. 1 embodiment is unnecessary to purify the dephenolated wastewater 68 
and to recover the ether. The salt can be crystallized to a Na.sub.2 
SO.sub.4 hydrate for sale to the paper industry leaving equilibrium water 
suitable for discharge into a river or ocean. 
The addition of the salt discussed above may be unnecessary for certain 
phenolic wastewaters such as from a phenol/acetone plant where sufficient 
alkali salt may already be present in the wastewater. 
The overhead 70 from the column 12 of FIG. 2 containing approximately the 
same quantities and components as in the FIG. 1 embodiment is treated with 
an aqueous solution of a hydroxide of an alkali metal 72, such as NaOH or 
KOH, which reacts with the phenolics to form an aqueous alkali metal 
phenate solution such as an aqueous sodium phenate solution. These 
reactants are mixed at 74 to promote the reaction which forms two phases, 
an aqueous phase containing the phenate and an organic phase containing 
the ether. These two phases are separated in the phase separator 76. The 
organic phase 78 containing the nearly pure ether is recycled to the ether 
drum 16. The aqueous phase 80 containing the phenate is processed as 
desired to recover the phenol or may be directly recycled to a phenol 
plant. Stream 80 can be sent to the neutralizer in the phenol plant. Any 
residual MTBE would ultimately be distilled in the existing phenol 
purification columns. 
The embodiment shown in FIG. 2 can be practiced in a number of different 
ways as regards the salt addition. For example, for sodium sulfate added 
to the phenolic wastewater so as to achieve a salt content in the phenolic 
wastewater feed to the liquid-liquid extractor ranging from about 10-18%, 
dry sodium sulfate or a prepared aqueous solution of sodium sulfate having 
a concentration of 18-19% at about 10-25.degree. C. Also, a typical 
aqueous sodium sulfate purge from the neutralization section of a phenol 
plant having a sodium sulfate concentration of about 20-22% at about 
40-50.degree. C. can be used. 
A typical material balance, employing the stream numbers given in FIG. 2, 
while using ethyl tertiary-amyl ether, dry sodium sulfate and 5000 kg/hr 
of a phenolic water containing 10,000 ppm phenol, is given below. In this 
example, 600 kg/hr of dry sodium sulfate are added to the 5000 kg/hr 
phenolic water, so as to form a 14.0% ratio, based on the phenolic water 
itself. 
__________________________________________________________________________ 
Material Balance for Embodiment No. 2, Kg/h.sup.1.2 
Stream No. 
-- 10 66 67 70 68 72 80 78 64 14 
Description 
Purified 
Phenolic (Dephenol- 
Sodium Make- 
Total 
Mol. 
Waste Extractor 
Extractor 
ated) 20% Phenate 
Recycle 
up Ether to 
Component 
Wt. Water 
Dry Salt 
Feed Overhead 
Wastewater 
NaOH 
Solution 
Ether 
Ether 
Extractor 
__________________________________________________________________________ 
Phenol 94.11 
50.00 50.00 
50.00 
(0.02) 
Water 18.02 
4950.00 4950.00 
.sup.3 
4950.00 
97.88 
107.45 
.sup.3 .sup.3 
Sodium Sulfate 
142.04 700.00 
700.00 
.sup.3 
700.00 .sup.3 .sup.3 
Ethyl tertiary-amyl 
116.23 2496.05 
(700) 2496.05 
3.95 
2500.00 
Ether 3.95 
Sodium Hydroxide 
40.00 24.47.sup.4 
3.19 
Sodium Phenate 
116.08 61.74 
TOTAL -- 5000.00 
700.00 
5700.00 
2546.05 
5653.95 
122.35 
172.38 
2496.05 
3.95 
2500.00 
__________________________________________________________________________ 
.sup.1 Numbers in parentheses () are concentrations in ppm. 
.sup.2 All streams can be assumed to be at 20-25.degree. C. 
.sup.3 The solubility of water in ethyl tertiaryamyl ether is 0.2% at 
20.degree. C., but has not been taken into account for stream numbers 70, 
78 and 14, for simplicity. The same is applicable for any sodium sulfate 
contained in this dissolved water. 
.sup.4 NaOH added in 15% excess of theoretical (stoichiometric) to insure 
conversion of phenol to sodium phenate.