Note: Descriptions are shown in the official language in which they were submitted.
Method for Processina waste waters containing ~
, .,~
oraanic phosphorus com~ounds in particular
sulfonated arylphosphines
Tne invention rela~es IO the processin~ of waste waters
containing water-soluble organic phosphorus compounds, in
particular sulfonated arylphosphines, and possibly
further organic contaminants, as well as water-soluble
sulfates. The object of the novel method is to free the
waste waters from unwanted impurities to the extent that
they may be passed to conventional purification
installations or may be recycled to chemical reactions as
process water.
Triarylphosphines sulfonated in the aryl groups have
found widespread use, particularly when dissolved in
water together with rhodium compounds, as catalysts in
chemical industry. Inter alia, they are used successfully
in hydroformyla~ion of olefins (cf. DE 26 27 354 B1);
cyclic amines are added to conjugated dienes in their
presence (cf. EP 01 76 398 A1); or they are used as
catalysts for hydrogenation of organic compounds.
The preparation of sulfonated triarylphosphines according
to a proven method (DE 32 35 030 Al) uses triarylphos-
phines as starting materials which are reacted with
oleum. The sulfonation mixture is hydrolyzed and extrac-
ted with a wa~er-insoluble amine dissolved in a water-
insoluble organic solvent. From the organic phase the
sulfonated triarylphosphine is isolated by treatment with
the aqueous solution of basic reagents. Suitable bases
for the transfer of the arylphosphinesulfonic acid into
the aqueous phase and, at the same time, for conversion
into the salt required as the end product are the hydr-
oxides of the alkali and alkaline earth metals, in
particular an alkali metal hydroxide, ammonia, and also
the alkali metal carbonates. However, water-soluble
amines may also be used, such as methylamine, ethylamine,
propylamine, butylamine or ethanolamine. In order to
obtain compounds as uniform as possible, i.e. compounds
-- 2 --
sulfonated to the same degree, the reaction with the base
is preferably carried out at different discrete pH
values. The useful products are obtained in a pH range of
about 4.5 to 7. Below a pH of 4.5 and above a pH of 7 to
pH 12, it is predominantly by-products and secondary
products of sulfone reaction that are extracted; the
aqueous solutions produced in these pH ranges constitute
the waste water.
Depending on the water-soluble basic extractant used, the
waste water contains between 1 and 8~ by weight of alkali
metal salts, alkaline earth metal salts, ammonium salts
or alkylammonium salts. It is loaded with water-soluble
phosphorus compounds, in particular sulfonated
arylphosphines, and further organic substances, which
account for the COD value (about 5 to 25 g/l).
The COD value - the abbreviation COD stands for chemical
oxygen demand - is a characteristic value for the loading
of waters by organic substances. It is the amount of
potassium dichromate, expressed as the oxygen equivalent,
which is consumed by the oxidizable substances contained
in a liter of water. The determination of the COD value
is carried out accord~ng to a standardized procedure. I~
is described, for example, in Ullmanns Encyclopadie der
Technischen Chemie (Encyclopedia of Industrial
Chemistry), 4th Edition (1981), Volume 6, pp. 376 et seq.
As used herein, water-soluble organic phosphorus
compounds are in particular sulfonated triarylphosphines,
the term phosphines in the present instance being used in
an extended sense including phosphine oxides and
phosphine sulfides. If the sulfonated triarylphosphine
is, for example, the sulfonation product of
triphenylphosphine, then the waste water contains (the
abbreviations used hereinafter of the compounds are shown
in parentheses) inter alia the phosphines
-- 3 --
tris(m-sulfophenyl)phosphine (TPPTS)
bis(~-sulfophenyl)phenylphosphine (TPPDS)
~?h-~-Y'(~.-s 'f^~henyl)phosphine (~
in addition the phosphine oxides formed by oxidation
tris(m-sulfophenyl)phosphine oxide (TPPOTS)
bis(m-sulfophenyl)phenylphosphine oxide (TPPODS)
and in small amounts the phosphine sulfides produced by
reduction processes
tris(m-sulfophenyl)phosphine sulfide (TPPSTS)
bis(m-sulfophenyl)phenylphosphine sulfide (TPPSDS)
EP 41 134 A2 discloses the separation of water-soluble
salts of aromatic sulfonic acids from sulfonation mix-
tures with the help of water-insoluble amines. To this
end, the sulfonation mixture is diluted with water and
subsequently mixed with an amount of a solvent-free amine
equivalent to the sulfonic acid. The sulfonic acid forms
a lipophilic ammonium salt which separates spontaneously
from the aqueous phase. This preparative method pre-
supposes that the sulfonation mixture is essentially free
of unsulfonated starting material and other neutral
substances. Waste products of chemical processes do not
~enerally meet this requirement, as the formation of
neutral substances as contaminants, albeit only in small
amounts, by side reactions and secondary reac~ions can
never be excluded. Furthermore, purification operations
are not based on preparative methods; rather should khey
be described as analytical processes which must detect
and separate off even those substances which are only
present in trace amounts.
It is an object of the invention to provide a method
which allows the reliable removal of water-soluble
organic phosphorus compounds and other contaminants from
;~r~
-- 4 --
waste waters. This method shall not be sub~ect to any
constraints and shall be economical. It is to produce
w~ ' e- C r such pl_ity ~2' ' he W~ _e- -.ay be p2ssed o
conventional purification installations or outfalls or,
in order to eliminate waste waters wholly or partly, may
be recycled into chemical reactions.
According to the invention this object is achieved by a
method for processing waste waters which contain, in
addition to water-soluble inorganic salts, water-soluble
organic phosphorus compounds, in particular sulfonated
arylphosphines, and possibly further organic
contaminants, which comprises the addition of an
inorganic acid to the waste waters in such an amount that
per mole of sulfonate groups ( -S03- ) present in solution
at least 1.1 mole of hydrogen ions are present, the
subsequent extraction using at least one mole of an amine
sparingly soluble or insoluble in water per mole of
dissolved sulfonate groups, the mutual separation of the
organic and the aqueous phase, and further processing of
the organic phase.
The method according to the invention ensures that
organic phosphorus compounds dissolved in the waste
water, in particular sulfonated arylphosphines and
further organic contaminants, which in total are measured
as the COD value, are substantially removed. The purified
waste waters do not pollute the environment and may be
used as process water for chemical reactions.
The method according to the invention is applied to waste
waters produced in the preparation of sulfonated aryl-
phosphines. Which specific process variants are appliedin an individual case is immaterial in this context. The
method cited in the context of the description of the
prior art is only mentioned as an example; other prepara-
tion methods are possible. An important characteristic of
the waste waters employed according to the invention,
~r~
-- 5 --
because of their impact on the environment, is the
concentration of the phosphorus compounds dissolved in
'hem. In typical waste wate_s said concent.a~ion is
400 to 1500 ppm by weight, in particular 600 to 1200 ppm
by weight, and results, for example in the case of the
TPPTS synthesis, from the content of TPPTS, TPPDS,
TPPOTS, TPPODS. TPPSTS and TPPSDS. Including said
phosphorus compounds, the waste waters contain in total
1 to 30 g/l, in particular 5 to 25 g/l, of compounds
which are measured as the COD value.
The waste waters to be reprocessed according to the novel
method are first acidified. To this end they are treated,
according to the invention, with an amount of an
inorganic acid such that per mole of sulfonate groups
present in solution at least 1.1 mol, in particular 1.5
to 3.0 mol of hydrogen ions are present. A higher excess
of acid does no harm but is unnecessary, for example for
economic reasons, but in particular also to avoid
unnecessary pollution of the waste water. If free base is
still present in the waste waters in addition to the
sulfonate, the amount of hydrogen ions required for its
neutralization shall be added to the amount of hydrogen
ions to be used according to the invention.
The hydrogen ions are added to the waste waters in the
form of strong inorganic acids such as hydrochloric acid,
sulfuric acid, nitric acid and phosphoric acid. Particu-
larly suitable are sulfuric acid and phosphoric acid. If
polybasic acids such as sulfuric or phosphoric acid are
used, the amount of hydrogen ion added to the waste water
depends on the acidity constant of the individual
dissociation steps. It can be assumed that up to an
acidity constant of about 0.7 x I 0 -2 complete dissociation
of the hydrogen ions takes place, and that therefore
one mole of acid produces one mole of hydrogen ions.
Accordingly, one mole of sulfuric acid as a dibasic acid
with an acidity constant in the second dissociation step
- 6 - ~ 4
of 1.2 x 10-2 produces two moles of hydrogen ions, while
the tribasic phosphoric acid, in accordance with the
acidlty cor.stant in the -_st dissociation step of
0.75 x 10-Z, only produces one mole of hydrogen ions.
After acidification, in a second step the contaminants
contained in the waste waters are extracted using an
amine which is sparingly soluble or insoluble in water.
The required amount of amine also depends on the amount
of sulfonate groups contained in the waste water. Per
mole of sulfonate groups present in solution at least one
mole of amine and preferably 1 to 4 mol of amine are
added to the waste water.
Instead of first adding acid to the waste waters and
subsequently extracting the contaminants with an amine,
it is a particular embodiment of the method according to
the invention that the required amount of acid and amine
be added in the form of an amine salt. It is evident that
in this case the molar quantities of acid and amine are
equal. ~s the acid is always used in excess, based on
dissolved sulfonate, there will then equally always be an
excess of amine.
Conveniently, the amine used for the extraction is liquid
under the conditions of the extraction. Its effect is,
inter alia, due to the fact that it reacts with the
acidic components of the waste water to form salts. The
amine salts must also be sparingly soluble in water, but
readily soluble in organic solvents. Another mode of
action of the amine is based on the purely physical
solution of contaminants contained in the waste wat0rs.
Possible amines forming, with acids, salts which are
sparingly soluble in water but which are lipophilic are
acyclic or cyclic aliphatic, aromatic, araliphatic and
heterocyclic primary, secondary or tertiary, preferably
secondary or tertiary amines. Preferred are acyclic,
~'r`~3~ k ~
-- 7
branched or nonbranched aliphatic amines having, in
total, 10 to 60, in particular 13 to 36 carbon atoms.
Exa~ples of such compounds are tri-n-hexylamine, tri-
n-octylamine, triisooctylamine, bis(2-ethylhexyl)amine,
S triisononylamine (in the form of the isomer mixture),
isotridecylamine (in the form of the isomer mixture),
diisononyl(2-phenylpropyl)amine, isononylbis(2-phenyl-
propyl)aminel triisotridecylamine (in the form of the
isomer mixture), N,N-dimethylhexadecylamine,
N,N-dimethyloctadecylamine. The extractants that were
found particularly useful are isotridecylamine, tri-
n-octylamine and triisooctylamine.
In principle, the amines may be used undiluted for the
purpose of extraction. More advantageously, however, they
are used as a solution in an organic solvent which is
immiscible or only sparingly miscible with water. The
concentration of the amine in the solution can extend
over a wide range. It is mainly limited by the solubility
of the amine salts in the solvent and by the viscosity of
the salt solution produced. Accordingly, the solutions
usually contain 10 to 50, preferably 15 to 35~ by weight
of amine. In the selection of the solvent, predominant
consideration is given to its physical properties.
Desirable characteristics are sparing solubility in
water, low volatility and little or no tendency to form
emulsions. In addition, the solvent should be inert, non-
toxic and inexpensive, have good hydrodynamic properties
and should also be effective in extractinq other con-
taminants dissolved in the waste waters. Suitable sol-
vents are kerosine-like fractions, i.e. hydrocarbons with
boiling points between 175 and 325C, aromatic fractions,
C4-C20-alcohols, C~-C20-ethers. Preferred are kerosine-like
fractions and toluene. Amine salts are always used in the
form of solutions, the same solutions being used as for
the amines. The concentration of the salts in the solu-
tion is normally also 10 to 50, preferably 15 to 35% by
weight.
- 8 -
The extraction is, as a rule, carried out at normal
temperature and normal pressure, without however
excluding conditions different from these, for example
superatmospheric pressure.
Further processing of the organic phase in a third step,
for the purpose of transferring the contaminants into a
concentrated aqueous solution and regenerating the amine,
can be carried out in several ways. It has been found
useful, for example, to re-extract the amine phase with
the aqueous solution of an inorganic base. Suitable
compounds are the hydroxides of the alkali and alkaline
earth metals, in particular sodium hydroxide, as well as
the alkali metal carbonates. The base is employed as a 5
to 30% by weight solution and, relative to the amine, is
used preferably in a stoichiometric amount or, where
appropriate, in an excess of up to 20~. A greater excess
of the base adds a further unwanted solution component to
the aqueous solution which contains the contaminants in
concentrated form, and should therefore be avoided.
Another successfully applied method for further
reprocessing of the amine phase is its treatment with
steam. To this end, steam of at least 1.8 MPa is passed
into the amine solution. The contaminants then pass into
the aqueous phase which is separated from the amine
phase, for example by decanting.
The amine recovered after treatment with a base or with
steam may, together with the solvent used where required,
be reused for extractive treatment of waste waters
according to the me~hod according to the invention. From
time to time, like the solvent, it may be purified, for
example by distillation.
The method according to the invention is carried out
discontinuously and, preferably, continuously, the
apparatus generally employed for extractive separation of
materials, such as extraction columns and mixer-settlers,
- 9 -
being used. Single-step or multi-s~ep operation is
possible.
The following examples describe the invention, but do not
limit it to these particular embodiments.
Examples l to 7
In the following examples, waste waters are used whose
phosphorus content and COD value are shown in the follow-
ing table.
Waste water, sulfuric acid (29.9% by weight, based on the
aqueous solution) and a solution of triisooctylamine in
toluene (approxima~ely 20~ by weight, based on the
solution) as the extractant are successively introduced
into a stirred reactor. The mixture is stirred for 30
minutes at room temperature, and the water phase, i.e.
the purified waste water, is separated from the amine
phase. The amine phase is re-extracted by stirring for 30
minutes with aqueous NaOH solution. The aqueous phase
obtained after phase separation contains in concentrated
form nearly all the contaminants of the waste water,
while the amine phase can be reused as the extractant.
The reaction conditions and the results of the waste
water processing are also summarized in the table.
Examples 1 to 4 describe the novel method; the opera-
tional conditions of Examples 5 to 7 do not correspond to
those of the invention.
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