Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1056'731~
This invention relates to purification of waste water obtained
during the production of an ester plasticizer through esterification of a
polybasic carboxylic acid with an aliphatic alcohol. More particularly,
this invention is directed to removing organic components from waste water
and returning them to an esterification process in order to leave behind
water which can be readily purified so that it meets environmental standards
and can be discharged. The presnnt invention is particularly concerned with
decreasing the biological oxygen demand of a waste water effluent from an
ester plasticizer production process.
Esters of aromatic or aliphatic polycarboxylic acids such as
phthalic acid, trimellitic acid, adipic acid, sebacic acid, and azelaic acid,
with aliphatic alcohols such as 2-ethyl hexanol, isooctanol, isononanol or
decanol are used in large amounts for plasticizing plastic materials, espec-
ially polyvinyl chloride. Of particular importance are the esters of
phthalic acid with 2-ethyl hexanol (dioctylphthalate-DOP), isononyl alcohol
(diisononyl phthalate-DINP), isodecyl alcohol (diisodecyl phthalate-DIDP)
and butyl alcohol (dibutyl phthalate-DPB).
The reaction of the starting compounds, i.e., alcohol and acid or
acid anhydride, can be accelerated by addition of catalysts, especially
protonating compounds such as ~ulfuric acid, to an extent such that it is
possible to operate under mild conditions of temperature. Apart from the
addition of catalysts, it is usual in many cases to remove the water formed
in the reaction from the equilibrium by means of an entraining agent.
When using sulfuric acid as the protonating catalyst, alkyl sul-
furic acid and, in a very minor amount, dialkyl sulfates are generally form-
ed from the starting alcohols in side reactions. Therefore, the raw esters
also contain alkyl sulfuric acid in addition to residual amounts of unreact-
ed carboxylic acids and alcohols as well as sulfuric acid.
In general, the raw esters are first neutralized with alkaline
solutions such as sodium hydroxide or potassium hydroxide solution or with
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aIkali metal carbonates, e.g., aqueous sodium carbonate solution. The result-
ant aIkali metal salt9 of the organic acids including those of alkyl sulfuric
acid are water-soluble and are separated wi~h the aqueous phase. Sodium salts
of alkyl sulfuric acids, partially esterified polycarboxylic acids and carboxy-
lic acids are, as is known, surface-active at the corresponding molecular wei-
ght of the organic residue. Examples thereof include semi-esters of phthalic
acid with monoalcohols having four or more carbon atoms and alkyl sulfates
of octyl alcohol or alcohols of higher molecular weight. Due to the surface-
activity of these compounds, larger amounts of otherwise sparingly soluble
organic compounds, viz. the esters themselves and their starting compounds,
are dissolved in the waste waters of the ester plasticizer production in ad-
dition to these compounds.
The content of organic materials in wa3te waters is usually charact-
erized by the oxygen necessary for the reaction to form CO and water. This
value is known as the COD (chemical oxygen demand). For the waste water from
the plasticizer ester production, COD values of 350 to 400 G oxygen per liter
waste water are not unusual. Waste waters of this kind cannot be treated
without a pretreatment in biological treatment means. In general, it is
necessary either to subject them to a prepurification by specific measures
or at least to dilute them with large amounts of unloaded or uncontaminated
water.
The waste waters from the ester synthesis also undesirably aggravate
the separation of oils from other waste waters when passed jointly with the
latter through oil removal basins. Therefore, problems in connection with
environment protection have been encountered to an increased extent. In
addition economic disadvantages through losses of valuable products have been
experienced.
Broadly, this invention relates to a process for removing organic
components from the waste water effluent obtained in the production of an
ester plasticizer through esterification of a polybasic aliphatic or aromatic
carboxylic acid with an aliphatic alcohol in the presence of sulfuric acid
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catalyst, which waste water contains an aIkyl sulfuric acid 6r dialkyl sulfate,
ester plasticizer reactants and products, which process comprises:
A. Heating said waste water to a temperature above 200 C under a pres-
sure below 45 kgs/sq. cm. g.; and
B. Thereafter mechanically removing by centri~uging or decanting an
organic phase, leaving behind an aqueous phase.
Surprisingly, in accordance with its invention, it has been dis-
covered that if the effluent waste water is heated to a temperature above
200C under the particular prevailing pressure, there is formed an organic
phase and aqueous phase. The organic phase can be removed by mechanical or
thermal methods.
Generally speaking, the process of the present invention is carried
out by heating the effluent waste water containing the alkyl sulfuric acid
or dialkyl sulfate, esterification reactants and products at a temperature
of at least 200 C, preferably between 210 and 250C. Generally speaking,
the heating can be carried out at a pressure between atmospheric and 40 kg/
9q. cm. g. pressure. A convenient pressure is an autogenous pressure develop-
ed employing a closed vessel such as an autoclave. The effluent waste
water is generally treated for a period of at least 15 minutes and generally
up to 5 hours, depending upon the temperature employed. Preferably, the
duration of the heat treatment is between 60 and 300 minutes. For example,
at 220C the desired reactions can be completed by heating the effluent
waste water for a period of about 2 ~ours.
Effluent waste waters resulting from neutralization with an aqueous
soda solution generally contain minor residual amounts of sodium carbonate
in addition to larger amounts of sodium hydrogen carbonate. In accordance
with this invention not only the sodium carbonate but also a portion of the
sodium hydrogen carbonate is reacted to effect evolution of carbon dioxide.
Accordingly, the reaction can also take place in the absence of chemicals
having an alkaline reaction, e.g., in the presence of sodium hydrogen car-
1056738
bonate which has a neutral reaction. Thus, the reactions can differ by the
fact of saponification of the esters in the presence of strong bases.
In carrying out the present invention under certain circumstances
it is desirable from the standpoint of process engineering to suppress the
C2 evolution, especially when purifying waste waters containing sodium
carbonate. This is done to prevent the waste gases from being formed or
to avoid an excessive increase in pressure during the reaction. In such
cases, the C02 evoluti~ncan be prevented, and the C02 which would nonmally
evolve can be bound within the reaction mixture by adding a stoichiometric
amount of an alkaline solution such as a sodium or potassium hydroxide
solution, thereby forming in the material being treated an alkalicarbonate.
After the process is completed, the reaction mixture i9 cooled,
preferably employing untreated effluent water flowing in countercurrent
therewith. The resultant organic phase separates within a few minutes. Up
to 150 kg of organic products are obtained per cubic meter of effluent water.
Surprisingly, the ester plasticizers dissolved in the effluent water are
hardly attacked. On the other hand, the alcohols present therein are split
off almost quantitatively from the aIkyl sulfates and from the semi-esters
of the dicarboxylic acids and are separated with the organic phase. A small
amount of olefins having partially been fonmed during the ester synthesis
and being dissolved in the untreated effluent water can be obtained as by-
product.
Where the waste water has a high alkali-hydrogen carbonate content
it i9 generally desired to pretreat the waste water by the addition thereto
of an alkali metal hydroxide in at least a stoichiometric amount.
The process can also be conducted by adding to the effluent water,
such as after the separation of the organic phase, a mineral acid to adjust
the pH of the aqueous phase to 3 to 3.5. Such process removes from the
aqueous phase alkali metal salts of dicarboxylic acids. These materials
were present in the effluent waste water in the form of the dicarboxylic
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acid prior to treatment with the mineral acid.
It has been found that after the separation of the organic phase,
the effluent water still contains, among other things, the salts of the
carboxylic acids, e.g., the disodium salt of phthalic acid. These dicarbox-
ylic acids are sparingly soluble in water and can be readily separated from
the aqueous phase by the aforesaid addition of mineral acid such as sulfuric
acid, hydrochloric acid or phosphoric acid. The phthalic acid is largely
separated at a pH of as low as 3.0 to 3.5. It can then be recovered by
known methods, e.g., by filtration, centrifuging, decanting or the like.
Without considering the dicarboxylic acids, 85 % of the organic
materials are removed from the effluent water in the process according to
the invention. A more than 98 % separation of the organic materials is
achieved when effecting the separation described above of the carboxylic
acids with subsequent filtration. The organic materials still remaining
in the water may be separated without any difficulty by partial distillation.
There are several means for effecting the removal of the developing
organic phase from the aqueous phase. These are generally mechanical methods.
Mechanical methods for removing the organic phase include decantation and
centrifugation.
It will be realized that the heart of the present invention is
the fornation of an organic phase and an aqueous phase by heating the efflu-
en~ waste water to a temperature of at least 200C under the prevailing
pressure. By whatever means the organic materials are removed, they can be
reused in the ester plasticizer production, since the organic materials
which are removed are almost exclusively starting materials, intermediate
products and finished products of the ester plasticizer process. As such,
they can readily be returned into the synthesis. The return of the materials
recovered from the effluent water does not disadvantageously affect the ester
plasticizer production and does not detract from the quality of the esters
produced.
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The production of the esters is usually carried out with an
amount of alcoho] in excess of the stoichiometric amount, generally a
stoichiometric excess of 10 to 50~0. Therefore, the separation of the excess
alcohol from the ester produced is a measure which is necessary for proces-
ses of this kind. The separated alcohol is returned into the esterification
stage either directly or after processing, e.g., by distillation. The
alcohol recovered in the treatment of the effluent water may be separated
without special measures and further used in known manner. Thus, in addition
to ~he improvement of the quality of the waste water, the present invention
leads to an extensive recovery of valuable products and, therefore, to an
improvement of the yield based on the starting materials charged for the
production of esters.
In order to more fully illustrate the nature of the invention and
the manner of practicing the same, the following examples are presented:
~XAMPLES
The untreated process effluent water had the following character-
istics on an average:
Flow rate 400-500 liters/hr.
pH 9.5
Sodlum carbonate37.6 g/liter
Sodium hydrogen carbonate 29.0 g/liter
COD 360-380 g/liter
The experiments described hereafter were carried out with this
effluent water. The composition of the waste water is typical of phthalic
acid esters and other esters of aliphatic dicarboxylic acids and aliphatic
alcohols.
Example 1
Into a 5 liter autoclave with stirrer were introduced 3.3 liters
of effluent water having the composition mentioned above. Then the auto-
clave was rapidly heated to the temperature given in the following table
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and maintained at this temperature for 2 to 5 hours. The pressure in the
autoclave increased as the rate ofconversio~ progressed. The increase in
pressure could be reduced by adding 45% sodium hydroxide solution (see column
2 of the Table). After Termination of the reaction time. the reaction mix-
ture was cooled to room temperature, depressurized and drained from the aut-
oclave. The upper organic phase was separated, weighed and analyzed by gas
chromatopgraphy. The aqueous phase was examined for residual contaminations.
The results are given in the following Table.
Table
Experiment 1 2 3 4 5
Quantity of waste water (liters 3.3 3.3 3.3 3.3 3.3
Temperature (C.) 210 210 210 200 220
Duration (hours) 5 5 5 5 2
Maximum pressure (kgs./sq.cm.g.)33 25 36 28 41
Stirring no yes yes yes yes
45% NaOH added (g. per batch) - 150
Quantit2 of organic products (g.) 355 362 364 204 360
Experiment 1 2 3 4 5
Composition of the or~anic
Product
Hydrocarbons 4.7 4.8 4.3 5.3 4.6
Olefin 33.7 27.8 29.625.6 31.0
Alcohol 57.3 66.1 60.564.5 58.8
Esters 3.9 1.0 5.4 4.2 5.4
Other organic compounds 0.4 0.3 0.2 0.4 0.4
Characteristics of the aqueous phase
pH 7.9 8.1 7.5 8.5 8.1
Na2CO content (g./liter) 1.1 4.0 0.4 3.0 1.7
NaHC03 content (g./liter) 36.5 53.2 29.139.3 34.8
COD (g.~liter) 63 51 52 99 52
The aqueous phase of experiment 3 was acidified with sulfuric acid
1(~56738
to pH 3Ø The phthalic acid was immediately precipitated in crystalline
form. After filtration, the water had a COD of 6.0 g/liter. In part of the
further experiments, COD values of 2.5 to 3.0 g/liter were even found.
Example 2
3.3 liters of the effluent water were mixed with 60 g of concentrat-
ed sulfuric acid, i.e., with the amount which converts the sodium carbonate
present in waste water into sodium hydrogen carbonate. The solution was
then treated in the manner described in Example 1 for 3 hours at 220C. The
yield of organic materials was 356 g. The organic product had the following
composition:
Hydrocarbon4.5%
Olefin 28.6%
hlcohol 61.9%
Ester 4.8%
By-productsO.2%
Example 3
Into a 1 cu.m. pressure reactor filled with a tower packing of
stainless steel were pumped 500 liters of the waste water having the compos-
ition mentioned above. The water was previously preheated under pressure to
230C. No further heat was supplied to the reactor.
Upon completion of the reaction, the reaction mixture was cooled
with untreated waste water and thereafter with cooling water in countercurrent
flow relation and depressurized to atmospheric pressure. In a phase separator
arranged down-stream of the reactor, the organic phase was separated from the
aqueous phase and returned into the esterification process. Organic product
having the following composition was recovered at a rate of 56.1 kg/hr:
Hydrocarbon 4.3%
Olefin 29.5%
Alcohol 60.6%
Ester 5.5%
Non-specified by-products 0.1%
