Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Process for workiny up waste waters comprising rhodium
compounds, derivatives of orqanic phos~hines and other
impurities in dis~olved form
The invention relates to a proces~ for working up wa~te
waters which comprise rhodium compounds, water-soluble
derivatives of organic phosphines, furthermore aryl-
sulfonates and/or carboxylates and, if appropriate, other
organic impurities in dissolved form. Its aim is to
separate off the rhodium almost completely and to remove
- lQ the dissolved phosphorus compounds and the other organic
impurities to the extent that, where possible, the waste
water can be introduced into conventional purification
plants, in to river cGurses or other receiving waters or
can b~ recycled into chemical reactions as proce~s water.
Wa~te waters which comprise, inter alia, rhodium com-
pounds and organic pho6phorus compounds in dissolved form
occur in various processes carried out industrially.
Thus, rhodium complex compounds which contain organic
phosphines as ligands, together with excess complexing
ligands, form a water-soluble catalyst system, the
solubility of which is based on the presence of sulfon-
ated or also carboxylated aryl radicals in the organic
phosphines. According to the process described in
DE 26 27 354 B1, the system is employed successfully for
hydroformylation of olefins. The active catalyst system
is formed under the reaction conditions from rhodium or
a rhodium compound, the triarylphosphines used in the
form of the alkali metal, ammonium or alkaline earth
metal sulfonates, and synthesis gas. It is known from
3Q EP 0 176 398 A to add cyclic amines onto con~ugated
dienes in the presence of the catalyst system mentioned,
and furthermore the system is employed successfully for
hydrogenation of organic compounds.
During longer use, the activity and selectivity of such
catalyst systems decrease. In the case of the hydro-
formylation reaction, for example, this reduction in
quality is due to catalyst poisons, such as iron
2~3 ~2~
-- 2
carbonyl, which can be formed by the action of synthesis
gas on the transportation lines and the reactor material,
and to higher-boiling condensation product of the
aldehydes. The reduction in the concentration of the
sulfonatPd phosphine employed in excess by oxidation to
phosphine oxide , by degradation to aromatic sulfonic
acids or by reduction of sulfo groups, or reaction with
sulfur-containing impurities of the synthesis gas to give
phosphine sulfides leads to a decrease in the activity of
the catalysts. It is therefore necessary for the spent
catalyst solution to be replaced by fresh catalyst
solution from time to time, and for the rhodium to be
separated off and recovered from the spent solution. The
noble metal should be separated off here as completely as
possible and in a form which allows its reuse as a
catalyst component, since the profitability of the
proces4 greatly depends on keeping the rhodium losses as
low as possible.
A process for the recovery of rhodium from aqueous
solutions comprising rhodium complex compounds and, if
appropriate, excess complexing ligands i8 known from
DE 36 26 536 Al. It comprises adding as water-soluble
salt of a carboxylic acid having 7 to 22 carbon atoms in
excess, based on the rhodium, to the solution, subse~
quently treating the solution with an oxidizing agent at
50 to 200C, and separating off the rhodium precipitated
as a compound which i8 sparingly soluble in water. About
90 to 95~ of the rhodium present in the solution can be
recovered in this manner. Oxygen, air or hydrogen per-
oxide i3 used as the oxidizing agent.
A further development of the procedure outlined above isdescribed in DE 37 44 214 A1. The oxidative treatment of
the solutions is carried out in two stages, in each case
in the presence of a water-soluble salt of a carboxylic
acid having 7 to 22 carbon atom~. In the first stage, the
solutions are reacted with oxygen or an oxygen-containing
O f~
-- 3 --
ga8 at 80 to 140C, and in the second stage they are
reacted with hypochlorite at 50 to 140C. The proce~s
allows about 95~ of the rhodium present in the sol-ltions
to be recovered.
DE 38 33 427 A1 also relate~ to a process for the
recovery of rhodium from aqueous solutions comprising
rhodium complex compounds and, if appropriate, complexing
ligands by a one-stage or two-stage treatment of the
solutions with oxidizing agents in the presence of a
water-soluble salt of a carboxylic acid having 7 to 22
carbon atoms in exce~s, based on the rhodium. The aqueou~
solutions are treatedl simultaneously or in succession,
with hydrogen peroxide or a substance which forms hydro-
gen peroxide and with oxygen or an oxygen-containing gas.
g4 to 98~ of the rhodium originally present is separated
off from the aqueous solutions by this route.
In the processe~ de~cribed above, the rhodium is obtained
a~ a compound which i~ sparingly soluble in water and
which can be extracted with an organic solvent. Residual
amount~ of rhodium, a~ well as water-soluble organic
phosphorus compounds, the main proportion of which are
sulfonated arylphosphine oxides, sulfonated arylphosphine
sulfide~ and sulfonated arylphosphinic acids, and
furthermora aryl~ulfonic acids and carboxylic acids
essentially still remain in the water. The above list of
impurities contained in the waste water is given merely
by way of example and i8 in no way complete. Other water-
soluble substances may he formed, depending on the
reactants and the reaction conditions.
The ob~ect of the invention is to recover further rhodium
from the aqueous phase which remains after the rhodium
has been separated off, and at the same time to reduce
the content of phosphorus compounds and other organic
impurities to the extent that, where possible, the water
3S can be introduced into conventional purification plants
20~J~f~r
-- 4 --
or receiving waters or, for partial or complete avoidance
of wa~te waters, can be recycled into chemical reactions.
According to the invention, the ob~ect i8 achieved by a
procef~s for working up waste waters which comprise
rhodium compounds, water-soluble derivatives of organic
phosphine~, furthermore arylsulfonates and/or carboxy-
lates and, if appropriate, other organic impurities. It
comprises adding to the waste waters an inorganic acid in
an amount such that at least 1.1 mol of hydrogen ions are
present per mol of sulfonate radicals (-SO3-) and/or
carboxylate radicals (-C00~) present in solution, subse-
quently extracting the mixture with at least one mol of
an amine which is sparingly soluble or insoluble in water
per mol of dissolved sulfonate radicals and~or carboxy-
late radicals, separating the organic and aqueous phasefrom one another and further processing the organic
phase.
The process according to the invention ensures that the
rhodium compounds, organic phosphorus compounds, further-
more salts of aromatic sulfonic acids and~or salts ofcarboxylic acids and other organic impurities dissolved
in the waste water, which overall result in the COD
value, are largely removed. The purified waste waters do
not pollute the environment and can be used as process
water for chemical reactionY.
The process according to the invention starts from waste
waters which are obtained when rhodium and water-soluble
organic phosphine derivatives are separated off from
aqueous solutions used as a catalyst phase. It is of no
importance which separation process is used in an indivi-
dual case. The processes mentioned in the context of
outlining the prior art are given merely as examples, and
other separation and working up processes are possible.
An e~sential featura of the waste waters employed
according to the invention is the nature and
2 ~ 2 r ~
concentration of the ~ubstances dissolved in them.
Because of their economic value or their influence on the
environment, substances which are important are, in
particular, rhodium, the concentration of which in
typical waste waters is between 1 and 50 ppm by weight,
in particular 3 and 30 ppm by weight, water-soluble
phosphorus compounds, which are present in a concentra-
tion of O.S to 1.5% by weight, in particular 0.7 to 1.2~
by weight of phosphorus, ~ulfonic acids, which are
present in a concentration of 1.0 to 2.5% by weight, in
particular 1.4 to 2.0% by weight, and carboxylic acids,
which are present in a concentration of 2.0 to 4.0~ by
weight, in particular 2.5 to 3.5% by weight. In terms of
the ~ubstances, the rhodium dissolved in the waste water
i~ in the form of rhodium salts; the phosphorus compounds
are mainly sulfonated or carboxylated arylphosphine
oxides and arylphosphine sulfides; the sulfonic acids are
chiefly obtained by cleavage of sulfonated arylphosphines
and are accordingly arylsulfonates; and the content of
carboxylic acids is essentially based on the addition of
carboxylates during the prior recovery of rhodium.
Including the abovementioned substances, the waste water~
comprise in total 200 to 350 g/l, in particular 230 to
290 g/l, of compounds which result in the COD value. The
COD value, the abbreviation COD represents chemical
oxygen demand, i~ a parameter for the degree of con-
tamination of waste waters. It is the amount of potassium
dichromate, expressed as oxygen equivalents, consumed by
the oxidizing contents of one liter of water. The COD
value is determined by a standsrdized procedure~ The
determination i~ described, for example, in Ullmanns
Encyclopadie der Technischen Chemie (Ullmann's Encyclo-
pedia of Industrial Chemistry), 4th edition (1981),
volume 6, page 376 et seq.
The waste waters to be worked up by the novel process are
first acidified. For this purpose, according to the
invention, an inorganic acid is added in an amount such
2 ~ ,C,,~ ,~
-- 6 --
that at least 1.1 mol, in particular 1.2 to 3.5 mol, of
hydrogen ions are present per mol of sulfonate radicals
and/or carboxylate radicals present in the solution. A
higher exces of acid does no harm, but it is not
necessary, for example, for economic reasons, but in
particular also to avoid unnecessary pollution of the
wa~te water. If free ba3e is still present in the waste
waters, in addition to sulfonates and/or carboxylates,
- the amount of hydrogen ions required to neutralize it i~
to be added to the amount of hydrogen ions to be used
according to the invention.
The ~ulfonate radicals can be determined, for example, by
high pre~sure liquid chromatography (HPLC). Carboxylates
can be determined, for example, potentiometrically with
mineral acids, or, after conversion into the free acid~
and extraction, by gas chromatography.
The hydrogen ion3 are added to the waste waters in the
form of strong inorganic acids, such as hydrochloric
acid, sulfuric acid, nitric acid and phosphoric acid.
Sulfuric acid and phosphoric acid are particularly
suitable. If polyba~ic acids, such as sulfuric acid or
phosphoric acid, are used, the amount of hydrogen ions
introduced into the waste water depends on the acid
constant of the individual dissociation stage~. It can be
as3u~ed that up to an acid constant of about 0.7 x 10-2,
complete dis~ociation of the hydrogen ions takes place,
that is to say one mol of acid produces one mol of
hydrogen ions. Accordingly, one mol of sulfuric acid, a6
a dibasic acid and with an acid constant in the second
dissociatio~ stage of 1.2 x 10-2, gives two mol of hydro-
gen ions, while the tribasic phosphoric acid, correspond-
ing to the a~ d constant in the first dissociation stage
of 0.75 x 10-2, produces only one mol of hydrogen ions.
After the acidification, rhodium and the impurities
contained in the waste waters are extracted in a second
2 ~
-- 7 --
operating step with the aid of an amine which i8
sparingly ~oluble or insoluble in water. The amount of
amine required also depends on the amount of sulfonate
radicals and/or carboxylate radicals contained in the
waste water. At least one mol of amine is added to the
waste water per mol of sulfonate radicals and/or
carboxylate radicals present in the solution. It is
possible to use excess amine, but this results in no
advantageR .
Instead of first adding acid to the waste waters and then
extracting the impurities with an amina, in a particular
embodiment of the process according to the invention the
amount of acid and amine required can be added in the
form of an amine salt. In this ca3e, the molar substance
amounts of acid and amine used are of course the same.
Since the acid is always used in excess, based on dis-
solved sulfonate and/or carboxylate, an amine excess is
then also always present.
The amine used for the extraction is advantageously
liquid under the conditions of the extractionr Its action
is based, inter alia, on the fact that it reacts with the
acid content of the waste water to form salts. The amine
salt~ must al80 be ~paringly soluble in water, but on the
other hand readily soluble in organic solvent~. Another
mode of action of the amine is based on the purely
phy~ical solution of impurities contained in the waste
waters.
Possible amines which form, with acids, salts which are
sparingly soluble in water but lipophilic are acyclic or
cyclic aliphatic, aromatic, araliphatic and heterocyclic
primary, secondary or tertiary, preferably secondary or
tertiary, amines. Preferred amines are acyclic, branched
or unbranched aliphatic amines having a total of 10 to
60, in particular 13 to 36, carbon atoms. Examples of
such compounds are tri-n-hexylamine, tri-n-octylamine,
~0~'3~
-- 8
tri-i~ooctylamine, di-2-ethylhexylamine, tri-i~ononyl-
amine (in the form of the isomer mixture), isotridecyl-
amine (in the form of the i30mer mixture), di-isononyl-
2-phenylpropylamine, isononyl-di-2-phenylpropylamine,
S tri-isotridecylamine (in the form of the i~omer mixture),
N,N-dimethyl-hexadecylamine and N,N-dimethyl-octadecyl-
amine. Isotridecylamine, tri-n-octylamine and tri-iso-
octylamine have proved to be particularly suitable
extraction agents.
The amines can in principle be employed in undiluted form
for the extraction. However, it i8 more advantageous to
use them as a ~olution in an organic solvent which i8
immiscible or only slightly miscible with water. The
concentration of the amine in the solution can extend
over a wide range. It is essentially limited by the
solubility of the amine salts in the solvent and by the
viscosity of the salt solution obtained. The solution~
accordingly usually contain 10 to 50, preferably 15 to
35% by weight of amine. For selection of the solvent, its
physical properties are chiefly decisive. A low solubil-
ity in water, low evaporation and little or no tendency
to form emulsions are desirable. The solvent moreover
should be inert, non-toxic and inexpensive, display good
hydrodynamic properties and also have a good extraction
capacity for other impurities dissolved in the waste
water~. Suitable solvents are kerosine-like fractions,
aromatic fractions, C4-C20-alcohols and Ca-C20-ether~.
Rerosine-like f-ractions, i.e. hydrocarbons having boiling
points of between 175 and 325C, and toluene are pre-
ferred. The amine salts are always employed in the formof solution~, the same solvents as for the amines being
used. The concentration of the salts in the solution is
likewise usually 10 to 50, preferably 15 to 35% by
weight.
The extraction is as a rule carried out at normal
temperature and under normal pressure, but condition~
~ O ~ rJ
_ 9 _
which deviate from these, for example increa~ed pressure,
are not excluded.
Further processing of the organic phase in a third
operating step for recovery of the rhodium, conversion of
the impurities into a concentrated aqueous solution and
regeneration of the amine can be carried out in various
ways. It has thus proved appropriate to reextract the
amine phase with the aqueous ~olution of an inorganic
base. Suitable compounds are the hydroxides of the alkali
metals and alkaline earth metals, in particular ~odium
hydroxide, and in addition also the alkali metal car-
bonates. The base is employed as a 5 to 30~ strength by
weight solution and is preferably used in the stoichio-
metric amount, based on the amine, and if appropriate in
an excess of up to 20%. A larger excess of base adds
another undesirable solution constituent to the aqueous
solution comprising the impurities in concentrated form,
and should therefore be avoided. Another process success-
fully used for working up the amine phase i8 its treat-
ment with steam. For this purpose, steam of at least1.8 MPa is passed into the amine solution. Rhodium and
the impurities pas~ into the aqueous phase here, which i8
separ~ted from the amine phase, for example, by
decanting.
The amine recovered after treatment with a base or with
steam can be employed again, together with the solvent
employed if appropriate, for extractive treatment of
waste waters by the process according to the invention.
It can b0 purified from time to time, for example by
di~tillation, as can the solvent.
The rhodium is separated off from the aqueous ~olution by
known processes, for example as a sparingly soluble
carboxylic acid ~alt, and the aqueou~ solution comprising
the impurities in concentrated form is disposed of.
20~40s."j
-- 10 --
The proce~s according to the in~ention iB carried out
discontinuou~ly or, pre~erably, continuously, the appar-
atuses customary for extractive substance separations,
such as extraction columns and mixer-settlers, being
used. It can be carried out in one or more stages.
The following examples de~cribe the invention, but do not
limit it to these specific embodiments.
Examples 1 to 7
Waste waters A, B, C and D, the contents of which are
summarized in Table 1, are employed in the following
examples.
The waste water, 3ulfuric acid (29.9% by weight, based on
the aqueous solution) and a solution of tri-isooctylamine
in toluene ~about 20% by weight, based on the solution),
as the extraction agent, are introduced in succesæion
into a stirred reactor. The mixture is stirred at room
temperature for 30 minutes, and the aqueous phase, i.e.
the purified waste water, is then separated from the
amine phase. The amine phase is reextracted by stirring
with aqueous NaOH solution for 30 minutes. The aqueous
phase obtained after the phase separation comprise~
virtually all the impurities of the waste water in
concentrated form, and the amine phase can be used again
as ths extraction agent. The reaction conditions and the
results of the working up of the waste water are
summarized in Table 2.
Examples 1 to 5 de~cribe the novel process, and Examples
6 and 7 were carried out under conditions which do not
correspond to those of the invention.
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Example~ 8 to 10
Exampl~s 8 to 10 were carried out in the same manner as
Examples 1 to 7, but u~ing ~alts of tri-isooctylamine
(Example 8: ~ulfate; Example 9: hydrogen sulfate; Example
S 10: dihydrogen phosphate) instead of acid and amine. They
were used a~ a solution in toluene (about 20% by weight
of salt, based on the solution).
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