Note: Descriptions are shown in the official language in which they were submitted.
11~5738
The present invention ~elates to a process for
the recovery of an oxidation catalyst heavy-metal component
from a high-boiling distillation residue obtained from the
esterified oxidation product resulting from the oxidation
of an alkyl aromatic compound in the liquid phase with oxygen
or an oxygen containing gas in the presence of a dissolved
oxidation catalyst having a heavy-metal component, the heavy-
metal component being a member of the group consisting of
cobalt, manganese, nickel and mixtures thereof wherein an
aqueous acidic extract containing said heavy-metal component
is obtained as a result of extracting said heavy-metal component
from said high-boiling distillation residue or from the ash
obtained on combustion of said high-boiling distillation residue,
said aqueous extract containing as acid, for example, a member
of the group consisting of mineral acids and aliphatic mono-
carboxylic acids, the latter containing for example 1 to 4
carbon atoms.
In particular, the invention concerns a process for
the recovery and reuse of heavy-metal oxidation catalyst from
the Witten DMT process, starting with high-boiling distillation
residues having a cobalt content of 1 to 10 g/kg residue and in
some cases a manganese content of 0.1 to 5 g/kg residue and/or
a nickel content of 0.1 to 5 g/kg residue, obtained in the.
oxidation of mixtures containing p-xylene (PX) and/or methyl
p-toluate (PTE) in the liquid phase with (preferably 4 to 8 bar)
an oxygen-containing gas under elevated pressure for example
a pressure of 4 to 10 bar preferably 4 to 8 bar and at an
elevated temperature, for example 140 to 200C, preferably a
temperature of 140 to 170C in the ~resence of dlssolved heavy-
metal oxidation catalyst, subsequent esterificatlon of the
: oxidation product with methanol under elevated pressure, for
example a pressure of 20 to 30 bar and at elevated temperature,
for example a temperature of 230 to 280C, and separation of
-1-
~45~31!3
the esterification product by distillation into a fraction
rich in methyl p-toluate (PTE), a fraction rich in dimethyl
terephthalate (DMT), and a high-boiling distillation residue,
by extraction of the heavy-metal oxidation catalyst with water,
dilute aqueous mineral acids, aqueous, low-molecular weight
aliphatic monocarboxylic acids, or alcohols, under heating,
optionally after combustion of the high-boiling distillation
residues and dissolving the heavy-metal oxidation catalyst
in the combustion residue (ash) with mineral acids.
DMT is required as raw material for the production
of polyester by reaction with ethylene glycol or tetramethyl-
ene glycol for fibers, filaments, films, or molded components.
DMT is manufactured in numerous large-scale technical plants
in accordance with the method which has become known as the
Witten process or also the Witten-Hercules process.
Technically, the process is conducted by reacting
the PX- and PTE-containing mixture, in the absence of solvents
and halogen compounds, in the presence of cobalt compounds and
manganese compounds dissolved in the reaction mixture, to an
oxidized product consisting predominantly of p-toluic acid
(PTA), monomethyl terephthalate (MMT), and terephthalic acid
(TPA), and esterifying the oxidized product at 230 to 280C
and 20 to 30 bar with methanol. The heavy-metal oxidation
catalyst system is preferably employed in amounts, based on
the quantity of oxidized product and converted to the metal
content, of about 70 to 200 ppm cobalt and 2 to 100 (for example
7 to 100) ppm manganese. The esterification product is separated
in a so-called raw ester distillation into a fraction rich in
PTE, a fraction rich in DMT, as well as into a high-boiling
distillation residue, by means of a distillation step. The
fraction rich in PTE is introduced into the oxidation stage,
the fraction rich in DMT is passed on to subsequent purification
--2--
738
and working-up stages. The high-boiling residue contains, in
addition to the organic components, compounds of the heavy-metal
oxidation catalyst system, e.g. cobalt and manganese.
It is technical feasible to feed high-boiling
distillation residues of the oxidation of alkyl aromatics,
from which no further useful products can be recovered any
longer, be it by means of isolation or by means of conversion,
to a combustion stage, optionally while utilizing the heat of
combustion, and to separate the heavy-metal-containing ashes
present in the flue gases of the combustion process by means
of cyclones or electrostatic filters (see United States Patent
3,341,470).
The heavy metal content of ashes of the aforementioned
type is composed of the catalyst components still existing
in the high-boiling distillation residues insofar as they have
not been removed previously, for example by an extraction,
furthermore of the materials of the production plant, due to
corrosion, as well as of the components of the added fuels of
the residue combustion. e.g. mazut or heavy fuel oil.
Ashes of the above-mentioned type can be treated
with mineral acids, and the heavy metals can be precipitated
as carbonates or hydroxides from the solutions (see DOS ~German
Unexamined Laid-Open Application~ 2,260,498). In ~-OS
22 60 498 (German Unexamined Laid-Open Application) a process
is disclosed for the recovery of cobalt and manganese compounds
out of residues of the production of aromatic carbonic acids,
which residues are still containing iron and copper compounds,
by, among other measures, extraction with dilute sulfuric acid
and precipitating and separating, after stepwise raising the
pH, iron hydroxide and the carbonates of cobalt and manganese.
However, technical difficulties are encountered in the separation
of such precipitates by filtration or centrifuging, as well as
--3--
5738
in the removal of the adhering, corresponding mineral acid by
washing out of the filter cake. The complete removal of the
inorganic mineral acid residues is one of the prerequisites
for reusing the heavy metals stemming from the high-boiling
distillation residues as oxidation catalysts in the oxidation
of alkyl aromatics in the liquid phase with atmospheric oxy-
gen.
The invention furthermore presupposes that heavy-
metal components, such as, for example, iron, chromium,
vanadium, molybdenum, copper, and titanium are enriched in
such ashes from the combustion of high-boiling distillation
residues of the manufacturing process for alkyl aromatics by
oxidation in the liquid phase in the presence of heavy-metal
oxidation catalysts, which components for example stem from
the materials of the manufacturing plant and from the fuels for
the residue combustion, and which considerably reduce and/or
inhibit the activity of the cobalt, manganese, or nickel
catalyst and/or mixtures thereof when recycled into the oxi-
dation reaction (of the Witten Process).
It would be extraordinarily advantageous to be
able to recover oxidation catalyst components e.g., a mixture
of cobalt and manganese and/or nickel components from the
high-boiling residue, optionally after combustion of the
residue, and reuse these catalyst components for the oxidation
of, for example, PX and PTE.
It would be advantageous to be able to recover from the
distillation residues of the raw ester distillation, catalyst
components and to make available directly aqueous solutions
suitable for use in the oxidation or for some other utilization
of the valuable catalyst components from the extract, without
evaporation or any additional measures necessary due to the
presence for example of TMA and TMME.
5738
The present invention thus relates to a p~ocess to
obtaining, from the acidic extracts or fxom.the mineral acidic
solutions a catalyst regenerate extensively free of interfering
organic components, especially TMA and TMME, furthermore extensi-
vely free of metal compounds from the materials of the manufactu-
ring plant e.g. ensuing from corrosion.
According to the present invention there is in general
provided a process for the recovery of a heavy-metal oxidati.on
catalyst component from a high-boiling distillation residue ,
said heavy-metal component being selected from the group consis-
ting of
cobalt,
cobalt and manganese,
cobalt and nickel,
and cobalt, manganese and nickel,
said residue being obtained from the esterified oxidation product
resulting from the oxidation of an alkyl aromatic compound in the
liquid phase with oxygen or an oxygen containing gas in the
presence of a dissolved oxidation catalyst having a heavy-metal
component as defined above,which comprises providing a suitable
aqueous acidic extract containing said heavy-metal component,
said extract being obtained as a result of extracting said heavy-
metal component from said high-boiling distillation. residue or
- from the ash obtained on combustion of said high-boiling distil-
lation residue, said extract containing as acid one or more
aliphatic monocarboxylic acids containing 1 to 4 carbon atoms
and
~ A) trcati.ng thc aqucous acidi.c cxtract with a
strongly acidic cation exchange resin in the alkali metal ion
form, optionally at an elevated temperature, until the exchange
capacity has been reached and
(b) subsequently washing the cation exchange resin
~, .
~l~S738
with a suitable washing liquid, optiona~lly a-t an elevated
t.emperature , and regenerati~g the cation exchange resin, e.y.
at room.temperature, with an aqueous solution containing at
least one salt selected from the group consisting of alkali
metal salts of low-molecular aliphatic monocarboxylic acids
having 1 to 4 carbon atoms (e.g. Na+ or K acetate and mixtures
thereof) to displace said heavy-metal component and recover as
product an aqueous solution containing said heavy-metal compo-
nent. If desired, the aqueous regenerating solution may also
contain one or more acids selected from the group consisting
of low-molecular aliphatic monocarboxylic acids having 1 to 4
carbon ~toms (e.g. acetic or formic acid).
In accordance with the present invention, the acidic
extract treated in step (a) may be obtained by extraction of the
heavy-metal component from said high-boiling distillation
residue with an aqueous acid, said acid being a low-molecular
aliphatic monocarboxylic acid of 1 to 4 carbon atoms or a mixture
thereof, under heating.
~ lso, in accordance with the present invention, the
acidic extract treated in step (a) may be obtained by extracting
the ashes obtained after combustion of said high-boiling distil-
lation residue with an aqueous acid, said acid being a mineral
acid or a mixture of mineral acids, with the addition of an
oxidizing agent under heating, subsequently diluting with water,
increasing the pH of the diluted extract by adding a suitable
alkali metal hydroxide to precipitate any iron and chromium
as the hydroxides, filtering to effect the combined removal of
the hydroxides as well as any insoluble ash components, effecting
dilution with water, then effecting acidification of the filtrate
with an acid, said acid being a low-molecular aliphatic mono-
carboxylic acid of 1 to 4 carbon atoms or a mixture thereof,
and removal of the alkali metal ions contained in the filtrate
45738
with the aid of a strongly acidic cation exchange resin loaded
with Co2 , Mn2 and/or Ni2 io~s.
In accordance with a particular embodiment of the
present invention, the aqueous acidic extract treated in step
(a) is obtained by extracting the ashes obtained after combustion
of said high-boiling distillation residue with aqueous hydro-
chloric acid with the addition of aqueous H2O2 at about 95C
for a duration of 0.1 to 4 hours, subsequently diluting with
water, increasing the pH of the diluted extract to a value of
at least 6 by adding NaOH and heating at about 95C for 0.1 to
2 hours to precipitate any iron and chromium as hydroxides, filte-
ring to effect the combined removal of the hydroxides as well
as any insoluble ash components, effecting dilution with water,
then effecting acidification of the filtrate to pH 5 or
below with acetic acid, and removal of the Na ions contained
in the filtrate with the aid of a strongly acidic cation exchange
resin loaded with Co2 , Mn2 and/or Ni2 ions. F
German Patent Application P 29 23 681 suggests a
process for the recovery of oxidation catalyst from the catalyst-
containing distillation residue obtained in DMT production, and
for the reuse of the thus-recovered catalyst in the oxidation,
with the objective of maintaining the selectivity of the oxida-
tion at the same high level as in case of using fresh catalyst.
It has been demonstrated therein that, in the extraction of the
catalyst-containing distillation residue from the raw ester
distillation, trimellitic acid (TMA) and the monomethyl ester of r
trimellitic acid (TMME) are dissolved together with the catalyst,
and that TMA and TMME can considerably impair the course of the
oxidation reaction when recycled into the oxidation with the
catalyst. For this reason, in the aforementioned process, the r
quantitative ratio of TMA + TMME to the heavy-metal oxidation
catalyst in the extract is set at a value of at most 1.8: 1.
5738
According to the in~entio~, the content of T~A and
TMME in the extract frcm the distillation residue can be higher
by a multiple, for example fivefold, than the content of cobalt-
manganese, and thus can amount to almost three times the ratio
of TMA + TMME to the heavy-metal oxidation catalyst admitted
in Patent Application P 29 23 681.
The content of TMA and TMME in the extract is
dependent on the type of raw ester processing and thus on the
chemical composition of the high-boiling distillation residue.
With an increasing concentration of TMA and TMME in the extract,
a raised consumption of heavy-metal oxidation catalyst is
required to ensure a flawless progression of the oxidation
reaction upon a recycling of the extracted catalyst.
Furthermore, the invention permits the recovery and
reuse of cobaIt compounds or cobalt and manganese compounds
in conjunction with nickel compounds.
According to the present invention a process of the
above-indicated type, can be characterized in more particular ~ -
embodiments by i,
(a) treating an aqueous,acidic extract, which
contains the heavy-metal component and has a cobalt content of
0.2 to 20 g/l, also in some cases a manganese content of 0.05 to
lO g/l, and/or also in some cases a nickel content of 0.05 to
lO g/l, with a strongly acidic cation exchange resin in the
alkali metal form, e.g. Na or K form, optionally at an
elevated temperature until the exchange capacity has been
reached, and subsequently
(b) washing thc cation cxchanc3c rcsin, for cx~mpl~
with water, optionally, at an elevated temperature and regenere-
ting the cation exchange resin at room temperature with an
aqueous acetic acid solution containing Na or K acetate, thus
displacing the heavy metal component and obtaining an aqueous
- 8 -
~D
5738
acetic acid solution containing said heav~-~etal component.
Thus, the present inventio~ provides a process for
the recovery of a heavy-metal oxidation catalyst solution
containing a heavy-metal component as defined above, from
a high-boiling distillation residue having a cobalt content
of 1 to 10 g/kg and in some cases a mangenese content of 0.1
to 5g/kg of residue and/or a nickel content of 0.1 to 5 g/kg
of residue, which is obtained in the production of dimethyl
terephthalate by the oxidation of mixtures containing p-xylene
and/or methyl p-toluate in the liquid phase with oxygen or
an oxygen-containing gas under a pressure of 4 to 10 bar and
at a temperature of 140 to 200C in the presence of dissolved
heavy-metal oxidation catalyst having a heavy-metal component
as defined above, subsequent esterification of the oxidation
product with methanol under a pressure of 20 to 30 bar and at
a temperature of 230 to 280C, and distillatory separation of
the esterification product into a fraction rich in methyl
p-toluate, a fraction rich in dimethyl terephthalate, and the
high-boiling distillation residue; which comprises providing
a suitable aqueous acidic extract containing said heavy-metal
component, said extract being obtained as a result of extracting
said heavy-metal component from said high-boiling distillation
residue or from the ash obtained on combustion of said high-
boiling distillation residue, said extract containing as acid,
one or more aliphatic monocarboxylic acids containing 1 to 4
carbon atoms, and is characterized by
(a) treating the aqueous, acidic extract, which
contains the heavy-metal component and which can have a cobalt
content of 0.2 to 20 g/l, in some cases a manganese content of ~
0.05 to 10 g/l, and/or in some cases a nickel content of 0.05 to r
10 g/l, with a strongly acidic cation exchange resin in the
alkali metal form, e.g. Na or K form, optionally at an elevated
~ ) -- g _
~.~
- ~145738
temperature until the exchange capacity has been reached, and
subsequently
(b) washing the cation exchange resin, for example
with water, optionally at an elevated temperature and regenera-
ting *he cation exchange resin at room temperature with an
aqueous acetic acid solution containing Na or K acetate, thus
displacing the heavy-metal component and obtaining an aqueous
acetic acid catalyst solution containing said heavy-metal
component.
In accordance with the present invention, the aqueous
acidic extract can be provided as lndicated above by extracting
the heavy-metal component from the residue with a suitable
monocarboxylic acid. Alternatively, the aqueous acidic extract
can be obtained by extracting the ashes obtained after combustion
of said high-boiling distillation residue with an aqueous acid,
said acid being a mineral acid or a mixture of mineral acids,
with the addition of an oxidizing agent under heating, subsequently ~ -
diluting with water , increasing the pH of the diluted extract
by adding NaOH to precipitate any iron and chromium as the t
hydroxides, filtering to effect the combined removal of the
hydroxides as well as any insoluble components, effecting
dilution with water, then effecting acidification of the filtrate
with acetic acid, removal of the Na ions contained in the filtrate
with the aid of a strongly acidic cation exchange resin loaded
with Co2 , Mn2 and/or Ni2+ ions. F
The type of ion-exchanger used for the invention r
can be based on polystyrene copolymerized with divinylbenzene
and crosslinked. Thc activc groups arc bound sulfonic acid-
(HSO3-) groups. Suitable acidic cation exchange resins for
use in the in~ention are Lewatit* S 100, Amberlite* IR 120, r
Dowex * 50.
* Trade marks
- 9a -
~ . - .
..
1~5738
The temperatures used during the eXchange tre~tment
and the washing step preferably are between 10C and 90C.
By means of the working up of the combustion products
stemming from the high-boiling distillation residues, in
accordance with this invention, it is possible in a simple
way to obtain an aqueous organic catalyst solution which is
free of mineral acid residues and free of impurities e.g.
TMA and TMME, inhibiting the activity of the catalyst components.
The thus obtained aqueous catalyst solutions can
contain cobalt acetate and manganese acetate with a content of
about 5 to 70 g/l of cobalt, 1 to 35 g/l of manganese, and
in some cases nickel acetate with a content of about 1 to 35 g/l
of nickel. These aqueous solutions, containing the catalyst
components for example as the acetates, are advantegeously
recycled directly into the oxidation of the mixtures containing
p-xylene and/or methyl p-toluate.
The ion exchanger for absorbing the heavy-metal
component is in the alkali metal form and preferably in the sodium
or potassium form.
Preferably, the exchanger, loaded with catalyst metal
ions, is regenerated with dilute aqueous sodium acetate solu-
tions, because with the strongly acidic ion exchangers used
according to the invention the egeneration equilibrium
i
R-(Co ) + 2 Na < ~ R-(Na )2 + Co
as compared to the regeneration equilibrium
R-(Co ) + 2 H ~ _ > R-(H )2 + Co
wherein R means the stationary ion exchange matrix,is oriented
more into the direction of the right-hand side of the reaction
equation.
By means of the treatment o~ the obtained extracts
on solutions according to this invention with strongly acidic cation exchangers
- 9b -
ll~S~38
especially resins an upward concentration of the catalyst metal content in the
extract to values up to about 20 times the initial concentration
i5 made possible in a surprisingly simple way, and in the case
of extracting the distillation residue high contents of TMA
and TMME are not interfering, by complex formation, in the
exchange of the catalyst metal ions by the counter ion, e.g.
the sodium ion on the cation exchanger (e.g. exchange resin).
. According to the invention, there is no need for
concentrating the extract by evaporation which, with increased
TMA and TMME concentrations, would lead to losses of catalyst
metal by precipitations and sedimentations. Rather, a quan-
titative separation of TMA and TMME, as well as other ac-
companying organic compounds, is attained in a simple manner.
In view of the disturbances caused by considerable contents
of TMA and TMME in the oxidation of mixtures containing PX
and/or PTE, this result is of special value.
The process of this invention can be conducted
technically either by extraction of the distillation residue
or by combustion of the distillation residue and subsequent
processing with aqueous mineral acids and subjecting the
solutions so obtained to the further processing as described
herein.
In the case of extracting the distillation residue
relative amounts by weight of the extracting agent can be
in the range of 0.3 : 1 to 5 : 1.
The percentage recovery of the cobalt, manganese and/or
nickel present in the high boiling distillation residue depends
on the percentage recovery of the extraction step, optionally
after combustion of the high-boiling distillation residues.
The percentage recovery of the cobalt, manganese and/or
nickel in the combined steps a) and b) according to the inven-
~ .
--10--
S738
tion is almost 100 %, typically 98 ~ and is ranging betweeen
about 95 and 99.9 %.
The total percentage recovery of the cobalt r manganese
and/or nickel in the overall process covered by the invention
is about 85 to 99 ~.
The process of this invention is conducted technical-
ly in a preferred embodiment by cooling the acidic, aqueous
extracts from a temperature of about 95C to approximately
room temperature, and separating the thus-precipitated organic
components. This is followed by reheating to about 70C
to avoid subsequent precipitations. During the following
loading of the strongly acidic cation exchanger in the Na
form at about 70C, any amounts of organic components, es-
pecially TMA, TMME, TPA, MMT, and the like, still present in
the extract, are not absorbed on the exchanger but rather
remain in the aqueous phase and pass unhindered through the
exchanger. In case this wastewater, loaded primarily with
alkali metal ions and organic compounds, cannot be passed on
to biological processing but rather must be treated thermally,
the alkali metal ions can be exchanged by treatment with a
strongly acidic cation exchanger in the H+ ion form, and
removed by elution with a strong acid, preferably hydrochloric
acid, in the form of a neutral salt, e.g. NaCl, in an aqueous
solution. Upon reaching the exchange capacity with Co2+
and Mn2+, the loaded exchanger is treated with fully deminer-
alized water, likewise heated to about 70C, as the washing
liquid. This treatment serves for removing the organic com-
ponents absorbed on the exchange resin, which settle as a
smeary film on the exchange resin matrix and would considerably
reduce the exchange capacity if they were not removed with
each cycle. The thus-produced washing water is suitably
recycled into the extraction stage.
--11--
`-- 1145738
During the subsequent regeneration, conducted at
room temperature, about two bed volumes of an aqueous sodium
acetate solution collected during the preceding regeneration
cycle as the last runnings and having been combined with the
forerunnings of the preceding regenerating cycle are introduced
to the exchanger, loaded with Co2+ and Mn2+, the bed volume
of which is initially filled with fully demineralized washing
water. About 50~ of the bed volume is withdrawn as a solution
free of Co2+/mn2+. Subsequently, about 15% of the bed volume
is collected as forerunnings with a low Co2+/Mn2 content.
The next fractions withdrawn is about 135% of the bed volume
as a Co2 /Mn2 acetate solution (called concentrate herein-
below). For a complete displacement of the catalyst metal
components from the exchanger, about 80% of the bed volume
of
/
.. /
:, /
/
-12-
,
- '
~S738
an approximately 15~ aqueous sodium acetate solution containing
about 10 to 15 g/l of free acetic acid is introduced onto the
exchanger, and thereafter about 80% of the bed volume of fully
demineralized water is fed onto the exchanger, in order to
remove the sodium acetate solution which contains Co and ~n
ions. The thus-obtained solutions, amounting in total to
about 160% of the bed volume, are withdrawn, until a pronounced
reduction in the Co2+/Mn2+ concentration, in an amount of about
5-10% of the bed volume, and combined with the concentrate,
and the subsequent fractions in an amount of about 150 to 155%
of the bed volume are discharged as the last runnings, combined
with the previously obtained forerunnings, and reserved for
use in the following regenerating cycle.
In the case of processing the residues from the
combustion of the high-boiling distillation residues, which
contain heavy metal components including the metals of the
oxidation catalyts they are dissolved in mineral acids, e.g.
hydrochloric acid or sulfuric acid with the addition of
oxidizing agents, for example a hydrogen peroxide solution or
nitric acid to oxidize, inter alia, Fe2 ions . The impurities
which have accumulated in the solution and stem from the
materials of the plant and the fuels, such as, for instance,
iron, chromium, vanadium, molybdenum, copper, and titanium,
are then precipitated, by adjusting the solution to a pH of
about 6 or thereabove, with a suitable base for example, an
alkali metal base (i.e. an aqueous sodium hydroxide solution),
in the form of the hydroxides and the precipitates are filtered
off together with the insoluble proportions of the residue
(ash). The thus-purified solution is adjusted to a pH of 5
or therebelow by adding at least one linear, low-molecular
aliphatic monocarboxylic acid of 1 to 4 carbon atoms, for
example acetic acid. The ions such as Na contained in
- 13 -
~:~4~738
the solution are removed by treatment wi~h a strongly acidic
cation exchange resin loaded with Co , Mn2 and/or Ni2 ions~
The resulting (acetic)-acid- containing heavy metal solution
is then treated with a strongly acidic cation exchange resin,
e.g. in the Na or K form,until the exchange capacity has been
reached, and the cation exchange resin is subsequently washed
optionally at an elevated temperature e.g. 50 to 90C and
regenerated at room temperature with alkali metal (e.g. Na or
K ) acetate-containing solutions, thus displacing the metal
ions of the catalyst components and obtaining an aqueous,
(e.g. acetic) acid solution which contains the metal ions of
the catalyst components.
The following examples serve for a further explana-
tion of the invention.
The combustion residue utilized in Examples 3 and 4
was obtained by burning a high-boiling distillation residue
from the Witten DMT process at 800-1200C and separation
from the flue gases in an electrostatic filter. In this con-
nection, 95% by weight of such a residue was combusted with
the addition of 5% by weight of heavy fuel oil. The high-
boiling distillation residue fed to the combustion contained
about 0.1 - 1.0 ~ by weight of ash-forming heavy-metal
components.
Example 1
100 kg of distillation residue from the raw ester
distillation was extracted with 60 1 of reaction water of the
DMT production with an acid content of about 3~, calculated as
acetic acid, at about 95C, to a residual Co2 content of
20 ppm; this di~tillation residue was obtained in an industrial
plant for DMT production by the combined continuous oxidation
of PX- and PTE-containing mixtures in the liquid phase with
atmospheric oxygen under 8 bar pressure and at temperatures of
- 14 -
1145~3~3
150 to 170 C with the use of a solution of cobalt acetate and
manganese acetate in aqueous acetic acid, a stationary concen-
tration of about 90 ppm cobalt and lO ppm manganese being set
in the oxidation product; subsequent continuous esterifica-
tion of the oxidation product at temperatures of about 250 C
and under 25 bar pressure with methanol; and continuous separa-
tion of the esterification product by vacuum distillation,
wherein, in a first distillation colunm, a fraction rich in
PTE is withdrawn overhead and recycled into the oxidation, and
the sump product of this column is separated in a second, subse-
quent column into a fraction in DMT, withdrawn overhead, and
into a high-boiling distillation residue having a cobalt
content of 2.3 g/kg and a manganese content of 0.2 g/kg of
residue.
After decanting, 56 l of a Co /Mn -containing
extract was obtained having a Co2 content of 3O8 g/l and a
Mn2 content of 0.3 g/l. The hot extract was cooled to 20 C
and thus-precipitated organic compounds were separated by
filtration.
The filtered solution was heated to 70 C to prevent
subsequent precipitation and passed from below through a tube
charged with a strongly acidic cation exchanger loaded with
Na ions commercially available under the name of "Lewatit S
100." The resin volume was 1.1 1. The loading was continued
until theincipient exhaustion of the ion exchange capacity.
From the produced 56 l Co-Mn extract, l9 l,corre-
sponding to a total content of 78.4 g Co + Mn + or 2.66 eq.
Co2 , was conducted at 70 C over the cation exchanger.
Subsequently, the cation exchanger was washed with fully demi-
neralized water introduced from the top at 70 C. Thereupon,
the cation exchanger was eluted from the top with 2.2 l of a
10~ aqueous acetic-acid sodium acetate solution, corresponding
- 15 -
5~3~3
to 1.3 eq. Na ~1, and then a subsequent washing step was
conducted with 1 1 of fully demineralized water at room tempera-
ture, thus obtaining 0.4 1 of forerunnin~s, 2.0 1 of con-
centrate, and 0.8 1 of last runnings.
The forerunnings contained 4.8 g/l Co2 , 0.4 g/l Mn2
and 0.8 g/l CH3COOH.
The last runnings contained 11.2 g/l Co2+, 0.9 g/l
Mn2+, 9.5 g/l Na and 6.3 g/l CH3COOH.
The aqueous concentrate contained the following
10 components :
Co2+ = 30~1 g/l
Mn2+ = 2.6 g/l
Na = 1.0 g/l
CH3COOH = 12.0 g/l
Organic cannot be detected
Impurities (polarographically)
; The thus-obtained Co , Mn containing and the Na
containing forerunnings and last runnings, respectively, were
combined and utilized again as the eluting solution to avoid
Co + and Mn losses.
Example 2
In a continuously operating extraction plant, 300
kg/h of the high-boiling distillation residue of the raw
ester distillation obtained as in Example 1 was extracted
under agitation at about 95C with 150 kg/h of acidic reac-
tion water from the DMT production, the origin and acid content
of which were in correspondence with Example 1.
The aqueous solution obtained after separation of
the organic phase contained 4.6 g/l of Co2+ and 0.4 g/l of
Mn2 . This solution was cooled to about 20C and separated
by filtration from the precipitated organic products, which
were recycled into the process, and was then collected in a
- 16 -
i73~3
container. After heating to about 70 C to avoid subsequent
precipitation of organic compounds, 650 l/hOf this solution
was conducted at a temperature of 70 C over a column charged
with 180 l of a resin loaded with Na+ ions under the commercial
name of "Lewatit S 100". The loading of the exchanger was
completed after about 3 hours.
Thereafter a flushing step was conducted with 400 1
of hot, demineralized water in order to remove organic
compounds. Subsequently, the catalyst ions were eluted at ap-
proximately room temperature with a solution containing sodium
acetate and with a content of 10 ta 15 g/l of free acetic acid
consisting, in part, of the forerunnings and last runnings of
the preceding elution as well as a 15% sodium acetate solution.
In total, 515 l of solution was used for eluting pruposes.
After elution, the exchanger was washed with 170 1 of fully
demineralized water.
Four fractions were collected: 90 l Co - and Mn -free
solution, 35 1 of forerunnings, 240 1 of concentrate, and
320 l of last runnings.
The forerunnings contained 5.8 g/l Co , 0.4 g/l Mn
and 1.0 g/l CH3COOH.
The last runnings contained 16.6 g/l Co2 , 1.3 g/l
Mn2 , 19.4 g/l Na and 10.8 g/l CH3COOH.
The concentrate contained
37.0 g/l Co and
3.1 g/l Mn
No organic components except for acetic acid could be
detected by polarography. The forerunnings and last runnings
were combined and reused for the subsequent cycle. The con-
centrate was recycled directly into the oxidation described in
Example l. ~he activity of this concentrate was identical to
that of a fresh catalyst solution having the same cobalt and
- 17 -
:
1145738
manganese acetate concentration. _ _
Example 3
By combustion of 25 kg of a distillation residue,
obtained analogously as in Example 1, having a cobalt content
of 0.23 weight %, a manganese content of 0.025 weight % and
traces of iron, nickel, chromium, molybdenum, copper and tita-
nium, with heavy fuel oil, 113.3 g of a combustion residue
were obatined.
50.5 g of a combustion residue from the DMT process
was processed under agitation with 300 ml of dilute HCl solu-
tion (- 12% HCl) and 2 ml of 30% H2O2 solution for two hours
at 95 C.
The specimen employed contained :
50. 7 % cobalt
5.4 % manganese
0.37 ~ iron
0.13 ~ nickel
100 ppm chromium
1,000 ppm molybdenum
100 ppm vanadium
100 ppm copper
100 ppm titanium
The solution was then diluted with 1 liter of fully
demineralized water and combined with about 40 % strength sodium
hydroxide solution to pH 7. The amount of sodium hydroxide
solution consumed was 9 ml. The solution was then heated for
one hour to 95 C and filtered through a folded filter.
The filtrate, after dilution with fully demineralized
water, was adjusted to a volume of 8 liters and to pH 4 with
5 ml of concentrated acetic acid.
The solution contained :
2.9 g cobalt/l
- 18 -
4~38
0.2 g manganese/l
6 ppm nickel
<5 ppm iron
~5 ppm chromium, molybdenum, vanadium, copper,
titanium.
The thus-obtained solution was conducted, to extensive-
ly remove the Na ions, through a column with 25 ml of a strongly
acidic cation exchange resin located with Co2+ and Mn2+ ions.
. A column with 250 ml of strongly acidic cation ex-
change resin "Lewatit S 100" in the Na+ form was charged with
the solution.
The wastewater obtained at the discharge end
contained :
30 ppm cobalt
2 ppm manganese.
The exchanger was loaded with 3.5 1 of the above
solution until incipient exhaustion (limit value = 30C ppm
cobalt in the effluent).
The exchanger was then washed with 250 ml of fully
demineralized water.
The cobalt and manganese ions were eluted with the
following solution :
400 ml of combined forerunnings and last runnings
fraction from the preceding experiment
200 ml of an 18% strength sodium acetate solution
with 15 g of free acetic acid per liter
200 ml of fully demineralized water.
The forerunnings contained 4.2 g/l Co2 , 0.3 g/l Mn2 and
0.6 g/l CH3COOH (free acid).
The last runnings contained 20.5 g/l Co2 , 1.4 g/l Mn
18.7 g/l Na and 8.7 g/l CH3COOH (free acid).
The elution yielded :
-- 19 --
il4S738
60 ml of a forerunnings fraction
400 ml of a main fraction depleted of Na
340 ml of a last runnings fraction rich in Na+.
The forerunnings and last runnings were combined
and utilized for elution purposes during the subsequent ex-
periment.
The main fraction contained :
30.9 g cobalt/l
. 2.1 g manganese/l
75 ppm nickel
< 5 ppm chromiumi molybdenum, vanadium,
copper, titanium
175 ppm sodium.
The thus-obtained main fraction can be utilized as
the catalyst solution in the DMT process.
ExamPle 4
By combustion of 25 kg of a distillation residue,
obtained analogously as in Example 1, having a cobalt content
of 0.20 weight ~, a manganese content of 0.020 weight %, a ;
nickel content of 0.10 weight % and traces of iron, chromium,
molybdenum, copper and titanium, with heavy fuel oil, 120.2 g
of a combustion residue were obtained.
50.1 g of a combustion residue was made into a
solution with 350 ml of 12% hydrochloric acid and 2 ml of 30%
H O solution for 2 hours at 95 C.
2 2
The ash residue utilized contained :
40.6 % Co
4.3 % Mn
19.8 % Ni
- 30 2,970 ppm Fe
< 100 ppm Cr
800 ppm Mo
- 20 -
,
,
5738
lo o ppm v
ppm Cu
< 100 ppm Ti
1,280 ppm Na.
The thus-processed extract was adjusted to pH 6.2
with 7 ml of an approximately 40% strength sodium hydroxide
solution. After one hour, the solution, heated to 95 C,
was filtered through a folded filter. The filtrate was diluted
to 10 1 with fully demineralized water and adjusted to pH 3.9
with 10 ml of concentrated acetic acid.
The solution contained :
1.84 g Co/l
0.16 g Mn/l
0.87 9 Ni/l
< 5 ppm Fe
< 5 ppm Cr
< 5 ppm Mo
< 5 ppm V
< 5 ppm Cu
< 5 ppm Ti.
The thus-obtained solution was treated, to extensively
remove the Na ions, with 250 ml of a strongly acidic cation
exchange resin loaded with Co2+, Mn2+, and Ni2 ions.
` A column with 250 ml of a strongly acidic cation
exchange resin "Lewatit S 100" in the Na form was charged with
the solution.
The wastewater obtained at the discharge end con-
tained:
25 ppm Co
2 ppm Mn
10 ppm Ni.
To load the exchanger until incipient exhaustion,
- 21 -
73t3
4.7 1 of the solution was consumed.
The exchanger was then washed with 250 ml of fully deminaralized
water.
For eluting the Co , Mn , and Ni ions, the
following solutions were employed :
390 ml of combined forerunnings and last runnings
fraction of the preceding experiment
200 ml of 18% sodium acetate solution containing
15 g of free acetic acid per liter
210 ml of fully demineralized water.
The forerunnings contained 3.6 g/l Co , 0.3 g/l Mn
1.8 g/l Ni and 0.5 g/l CH3COOH (free acid).
The last runnings con~ained 13.4 g/l Co2 , 1.3 g/l
Mn2 , 7.2 g/l Ni 8.9 g/l CH3COOH (free acid) and 15.8 g/l Na .
The following solutions were obtained during
elution :
80 ml of a forerunnings fraction
400 ml of a main fraction depleted of Na ions
320 ml of a last runnings fraction rich in Na .
The main fraction contained :
21.5 g Co/1
1.9 g Mn/1
10.2 g Ni/l
< 5 ppm Fe
< 5 ppm Cr
< 5 ppm Mo
< 5 ppm V
< 5 ppm Cu
< 5 ppm Ti
240 ppm Na.
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