Recovery and reuse of heavy-metal oxidation catalyst from the Witten DMT process

A process for the recovery and reuse of a heavy-metal oxidation catalyst solution from a high-boiling distillation residue having a cobalt content of 1-10 g/kg of residue is disclosed. The distillation residue 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 an elevated pressure and at an elevated temperature in the presence of dissolved heavy-metal oxidation catalyst, by subsequent esterification of the oxidation product with methanol and by a 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. The process involves the steps of effecting extraction of the heavy-metal oxidation catalyst from the high-boiling distillation residue with aqueous low-molecular aliphatic monocarboxylic acids under heating; treating the aqueous, acidic extract, which contains the heavy-metal oxidation catalyst and has a cobalt content with a strongly acidic cation exchange resin in the alkali metal form at an elevated temperature until the exchange capacity has been reached, and washing the cation exchange resin at an elevated temperature with water and regenerating the cation exchange resin at room temperature with a solution containing Na.sup.+ or K.sup.+ acetate to displace the catalyst components and to obtain an aqueous acetic acid catalyst solution containing the catalyst components.

This invention relates to a process for the recovery and reuse of 
heavy-metal oxidation catalyst solution from the Witten process for 
producing dimethyl terephthalate (DMT), starting with high-boiling 
distillation residues having a cobalt content of 1-10 g/kg residue and in 
some cases a manganese content of 0.1-5 g/kg residue and/or a nickel 
content of 0.1-5 g/kg residue, obtained in the oxidation of reaction 
mixtures containing p-xylene (PX) and/or methyl p-toluate (PTE) in the 
liquid phase with oxygen-containing gases under elevated pressure, 
preferentially 4-10 bar and at elevated temperature, preferentially 
140.degree.-200.degree. C. in the presence of dissolved heavy-metal 
oxidation catalyst, subsequent esterification of the oxidation product 
with methanol under elevated pressure, preferentially 20-30 bar, and at 
elevated temperature, preferentially 230.degree.-280.degree. C., and 
separation of 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 dilute aqueous mineral acids or 
aqueous, low-molecular aliphatic monocarboxylic acids, 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 tetramethylene glycol for fibers, filaments, 
films, or molded components. DMT is manufactured in numerous largescale 
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- und/or 
PTE-containing reaction mixture, in the absence of solvents and halogen 
compounds, in the presence of cobalt compounds and manganese compounds 
dissolved in the reaction mixture, to provide an oxidized product 
consisting predominantly of p-toluic acid (PTA), monomethyl terephthalate 
(MMT), and terephthalic acid (TPA), and esterifying the oxidized product 
at 230.degree.-280.degree. C. and 20-30 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 
70-200 ppm cobalt and 2-100 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 and working-up stages. The high-boiling residue 
contains, in addition to the organic components, the compounds of the 
heavy-metal oxidation catalyst system, e.g. cobalt and manganese. 
It is technically 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 U.S. Pat. No. 3,341,470). 
In DE-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 centrifugation, as well 
as 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 oxygen. 
It is of extraordinary advantage for the DMT process to recover the 
oxidation catalyst, i.e. a mixture of cobalt compounds and manganese 
compounds and/or nickel compounds, from this high-boiling distillation 
residue by extraction, optionally after combustion of the residue, and 
reuse this catalyst for the oxidation of PX and/or PTE. 
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 stem from the materials of the manufacturing 
plant and from the fuels of 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 oxidation reaction 
of the "Witten process". 
It is an object of the present invention to recover, from the distillation 
residues of the raw ester distillation, the catalyst components, and to 
make available directly, without evaporation, the aqueous solutions 
suitable for use in the oxidation or for some other utilization of the 
valuable catalyst components either from the extract or from the 
dissolving of the combustion residue of said distillation residue with 
mineral acids. 
The invention has the purpose of obtaining, from the acidic extracts or 
from the mineral acidic solutions a catalyst regenerate extensively free 
of interfering organic components and, furthermore, extensively free of 
metal compounds resulting from the materials of the manufacturing plant. 
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 thusrecovered 
catalyst in the oxidation, with the objective of maintaining the 
selectivity of the oxidation 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 
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 stage with the catalyst. For this reason, 
in the aforementioned process, the 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. 
According to this invention, the content of TMA and TMME in the extract 
from the distillation residue can be higher by a multiple, for example, 
fivefold, than the content of cobalt-manganese catalyst, and thus can 
amount to almost three times the ratio of TMA+TMME to the heavy-metal 
oxidation catalyst admitted in the process of the German 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 cobalt 
compounds or cobalt and manganese compounds in conjunction with nickel 
compounds. 
These objects have been attained by the invention. The object is attained, 
in a process of the above type, by the following steps: 
(a) treating an aqueous, acidic extract, which contains the heavy-metal 
oxidation catalyst and has a cobalt content of 0.2-20 g/l also in some 
cases a manganese content of 0.05-10 g/l, and also in some cases a nickel 
content of 0.05-10 g/l, with a strongly acidic cation exchange resin in 
the alkali metal from, e.g. Na.sup.+ or K.sup.+ form, optionally at an 
elevated temperature until the exchange capacity has been reached; and 
(b) washing the cation exchange resin subsequently, optionally at an 
elavated temperature, and regenerating the cation exchange resin at room 
temperature with solutions containing Na.sup.+ or K.sup.+ acetate, thus 
displacing the catalyst components and obtaining an aqueous acetic acid 
solution containing the catalyst components. 
The type of ion-exchanger used for the invention is based on polystyrene 
copolymerized with divinylbenzene and crosslinked. The active groups are 
bound sulfonic acid- (HSO.sub.3 -) groups. Suitable acidic cation exchange 
resins for use in the invention are Lewatit S 100, Amberlite IR 120, Dowex 
50. 
The temperatures used during the exchange treatment and the washing step 
preferably are between 10.degree. C. and 90.degree. C. 
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, as 
TMA and TMME, inhibiting the activity of the oxidation metal catalyst 
components. 
The thus-obtained aqueous catalyst solutions contain cobalt acetate and 
manganese acetate with a content of about 5-70 g/l of cobalt, 1-35 g/l of 
manganese, and in some cases nickel acetate with a content of about 1-35 
g/l nickel. These aqueous solutions, containing the catalyst components as 
the acetates, are advantageously recycled directly into the oxidation of 
the mixtures containing p-xylene and/or methyl p-toluate. 
Besides the cations of the alkali metal group, preferably sodium or 
potassium, the ion exchanger for adsorbing the catalyst metal components 
can also be used in the H.sup.+ ion form. 
Preferably, the cation exchange resin, loaded with the catalyst metal ions, 
is regenerated with dilute aqueous sodium acetate solution because with 
the strongly acidic cation exchange resins used according to the invention 
the regeneration equilibrium 
EQU R--(Co.sup.2+)+2 Na.sup.30 .revreaction.R--(Na.sup.+).sub.2 +Co.sup.2+ 
as compared to the regeneration equilibrium 
EQU R--(Co.sup.2+)+2 H.sup.+ .revreaction.R--(H.sup.+).sub.2 +Co.sup.2+ 
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 of the obtained extracts or solutions according 
to this invention with strongly acidic cation exchangers especially 
resins, an upward concentration of the catalyst metal content in the 
extract to values up to about 20 times the initial concentration is 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 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 quantitative separation of TMA and TMME, as well as other 
accompanying 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 is 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 are 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 invention is almost 100%, 
typically 98% and is ranging between about 95 and 99.9%. 
The total percentage recovery of the cobalt, manganese and/or nickel in the 
overall process covered by the invention is about 85 to 99%. In a 
preferred embodiment the acidic, aqueous extracts are cooled from a 
temperature of about 95.degree. C. to approximately room temperature, and 
the thus-precipitated organic components are separated. This is followed 
by reheating to about 70.degree. C. to avoid subsequent precipitations. 
During the following loading of the strongly acidic cation exchanger in 
the Na.sup.+ form at about 70.degree. C., any amounts of organic 
components, especially TMA, TMME, TPA, MMT and the like, still present in 
the extract, are not bound on the exchanger but rather in the aqueous 
phase and pass unhindered through the exchanger. In case this waste water, 
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.sup.+ ion form, and removed by elution with a 
strong acid, preferably hydrochloric acid, in the form of the neutral 
salt, e.g. NaCl, in an aqueous solution. Upon reaching the exchange 
capacity with Co.sup.2+ and Mn.sup.2+, the loaded exchanger is treated 
with fully demineralized water, likewise heated to about 70.degree. C., as 
the washing liquid. This treatment serves for removing of those organic 
components adsorbed 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. 
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 Co.sup.2+ and Mn.sup.2+, 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 Co.sup.2+ 
/Mn.sup.2+. Subsequently, about 15% of the bed volume is collected as 
forerunnings with a low Co.sup.2+ /Mn.sup.2+ content. The next fraction 
withdrawn is about 135% of the bed volume as a Co.sup.2+ /Mn.sup.2+ 
acetate solution (called concentrate hereinbelow). For a complete 
displacement of the catalyst metal components from the exchanger, about 
80% of the bed volume of an approximately 15% aqueous sodium acetate 
solution containing about 10-15 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.sup.+ and Mn.sup.+ ions. The 
thus-obtained solutions, amounting in total to about 160% of the bed 
volume, are withdrawn, until a pronounced reduction in the Co.sup.2+ 
/Mn.sup.2+ 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 150-155% of the bed volume are discharged as the last 
runnings, combined with the previously obtained forerunnings, and reserved 
for use in the next regenerating cycle. 
In case of processing the residues obtained from the combustion of the 
high-boiling distillation residues, which contain the heavy metal 
components including the metals of the oxidation catalyst, 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, Fe.sup.2+ 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, for example, aqueous sodium hydroxide solution, in the form of the 
hydroxides and the precipitates are filtered off together with the 
insoluble proportions of the combustion 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 1-4 carbon atoms; 
for example, acetic acid. The Na.sup.30 ions contained in the solution 
are removed by treatment with a strongly acidic cation exchange resin 
loaded with Co.sup.2+, Mn.sup.2+ and/or Ni.sub.2+ ions. The resulting 
acetic-acid-containing heavy metal solution is then treated with a 
strongly acidic cation exchange resin in the Na.sup.+ or K.sup.+ form 
until the exchange capacity has been reached, and the cation exchange 
resin is subsequently washed, optionally at an elevated temperature, e.g. 
50.degree. to 90.degree. C. and regenerated at room temperature with 
Na.sup.+ or K.sup.+ acetate-containing solutions, thus displacing the 
metal ions of the catalyst components and obtaining an aqueous, acetic 
acid solution which contains the metal ions of the catalyst components. 
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.degree.-1200.degree. C. and separation from the flue gases in an 
electrostatic filter. In this connection, 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 heavy-metal components. The following examples serve 
for a further illustration of the invention.

EXAMPLE 1 
100 kg of a distillation residue from the raw ester distillation was 
extracted with 60 l of reaction water of the DMT production with an acid 
content of about 3%, calculated as acetic acid, at about 95.degree. C., to 
a residual Co.sup.2+ content of 20 ppm; this distillation residue was 
obtained in an industrial plant for DMT production by the combined 
continuous oxidaton of PX- and PTE-containing mixtures in the liquid phase 
with atmospheric oxygen under 8 bar pressure and at temperatures of 
150.degree.-170.degree. C. with the use of a solution of cobalt acetate 
and manganese acetate in aqueous acetic acid, a stationary concentration 
of about 90 ppm cobalt and 10 ppm manganese being set in the oxidation 
product; subsequent continuous esterification of the oxidation product at 
temperatures of about 250.degree. C. and under 25 bar pressure with 
methanol; and continuous separation of the esterification product by 
vacuum distillation, wherein, in a first distillation column, 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, subsequent column in 
to a fraction rich 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.sup.2+ /Mn.sup.2+ -containing extract was 
obtained having a Co.sub.2+ content of 3.8 g/l and a MN.sup.2+ content of 
0.3 g/l. The hot extract was cooled to 20.degree. C. and thus-precipitated 
organic compounds were separated by filtration. 
The filtered solution was heated to 70.degree. C. to prevent subsequent 
precipitation and passed from below through a tube charged with a strongly 
acidic cation exchanger loaded with Na.sup.+ ions commercially available 
under the name of "Lewatit S 100". The resin volume was 1.1 l. The loading 
was continued until the incipient exhaustion of the ion exchange capacity. 
From the resulting 56 l of Co-Mn extract, 19 l, corresponding to a total 
content of 78.4 g Co.sup.2+ +Mn.sup.2+ or 2.66 eq. Co.sup.2+, was 
conducted at 70.degree. C. over the cation exchanger. Subsequently, the 
cation exchanger was washed with fully demineralized water introduced from 
the top at 70.degree. C. Thereupon, the cation exchanger was eluted from 
the top with 2.2 l of a 10% aqueous acetic-acid sodium acetate solution, 
corresponding to 1.3 eq. Na.sup.+ /l, and then a subsequent washing step 
was conducted with 1 l of fully demineralized water at room temperature, 
thus obtaining 0.4 l of forerunnings, 2.0 l of aqueous concentrate, and 
0.8 l of last runnings. 
The forerunnings contained 4.8 g/l Co.sup.2+, 0.4 g/l Mn.sup.2+ and 0.8 g/l 
CH.sub.3 COOH. 
The last runnings contained 11.2 g/l Co.sup.2+, 0.9 g/l MN.sup.2+, 9.5 g/l 
Na.sup.+ and 6.3 g/l CH.sub.3 COOH. 
The aqueous concentrate contained the following components: 
______________________________________ 
Co.sup.2+ = 30.1 g/l 
Mn.sup.2+ = 2.6 g/l 
Na.sup.+ = 1.0 g/l 
CH.sub.3 COOH = 12.0 g/l 
Organic cannot be detected 
Impurities (polarographically) 
______________________________________ 
The thus-obtained Co.sup.++, Mn++ containing and the Na.sup.+ containing 
forerunnings and last runnings, respectively, were combined and 
utilizedagain as the eluting solution to avoid Co.sup.++ and Mn.sup.++ 
losses. 
EXAMPLE 2 
In a continuously operating extraction plant, 300 kg/h of the highboiling 
distillation residue of the raw ester distillation obtained as in Example 
1 was extracted under agitation at about 95.degree. C. with 150 kg/h of 
acidic reaction 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 Co.sup.2+ and 0.4 g/l of Mn.sup.2+. This solution was 
cooled to about 20.degree. C. and separated by filtration from the 
precipitated organic products, which were recycled into the process, and 
was then collected in a container. After heating to about 70.degree. C. to 
avoid subsequent precipitation of organic compounds, 650 l/h of this 
solution was conducted at a temperature of 70.degree. C. over a column 
charged with 180 l of a resin loaded with Na.sup.+ 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 l of hot, demineralized 
water in order to remove organic compounds. Subsequently, the catalyst 
ions were eluted at approximately room temperature with a solution 
containing sodium acetate and with a content of 10-15 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 purposes. After elution, the exchanger 
was washed with 170 l of fully dimineralized water. 
Four fractions were collected: 90 l Co.sup.++ - and Mn.sup.++ -free 
solution, 35 l of forerunnings,. 240 l of concentrate, and 320 l of last 
runnings. 
The forerunnings contained 5.8 g/l Co.sup.2+, 0.4 g/l Mn.sup.2+ and 1.0 g/l 
CH.sub.3 COOH. 
The last runnings contained 16.6 g/l Co.sup.2+, 1.3 g/l Mn.sup.2+, 19.4 g/l 
Na.sup.+ and 10.8 g/l CH.sub.3 COOH. 
The concentrate contained 
37.0 g/l Co.sup.++ and 
3.1 g/l Mn.sup.++. 
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 concentrate was recycled directly into the 
oxidation described in Example 1. The activity of this concentrate was 
identical to that of a fresh catalyst solution having the same cobalt and 
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 titanium, with heavy fuel oil, 113.3 g of a 
combustion residue were obtained. 
50.5 g of said combustion residue from the DMT process was processed under 
agitation with 300 ml of dilute HCl solution (=12% HCl) and 2 ml of 30% 
H.sub.2 O.sub.2 solution for two hours at 95.degree. C. 
The combustion residue employed contained: 
______________________________________ 
50.7% by weight cobalt 
5.4% by weight manganese 
0.37% by weight iron 
0.13% by weight 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.degree. 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 
0.2 g manganese/l 
6 ppm nickel 
&lt;5 ppm iron 
&lt;5 ppm chromium, molybdenum, vanadium, copper, titanium 
______________________________________ 
The thus-obtained solution was conducted, to extensively remove the 
Na.sup.+ ions, through a column with 250 ml of a strongly acidic cation 
exchange resin loaded with Co.sup.2+ and Mn.sup.2+ ions. 
A column with 250 ml of strongly acidic cation exchange resin "Lewatit S 
100" in the Na.sup.+ form was charged with the solution. 
The waste water obtained at the discharge end contained: 
30 ppm cobalt 
2 ppm manganese. 
The exchanger was loaded with 3.5 l of the above solution until incipient 
exhaustion (limit value - 300 ppm cobalt in the effluent). 
The exchanger was then washed with 250 ml of fully dimineralized water. 
The cobalt and manganese ions were eluted with the following solutions: 
400 ml of combined forerunnings and last runnings fractions 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 Co.sup.2+, 0.3 g/l Mn.sup.2+ and 0.6 g/l 
CH.sub.3 COOH (free acid). 
The last runnings contained 20.5 g/l Co.sup.2+, 1.4 g/l Mn.sup.2+, 18.7 g/l 
Na.sup.+ and 8.7 g/l CH.sub.3 COOH (free acid). 
The elution yielded: 
60 ml of a forerunnings fraction 
400 ml of a main fraction depleted of Na.sup.+ 
340 ml of a last runnings fraction rich in Na.sup.+. 
The forerunnings and last runnings were combined and utilized for elution 
purposes during the subsequent experiment. 
The main fraction contained: 
______________________________________ 
30.9 g cobalt/liter 
2.1 g manganese/liter 
75 ppm nickel 
&lt;5 ppm chromium, 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 said combustion residue was made into a solution with 350 ml of 
12% hydrochloric acid and 2 ml of 30% H.sub.2 O.sub.2 solution for 2 hours 
at 95.degree. C. 
The combustion residue utilized contained: 
______________________________________ 
40.6% by weight Co 
4.3% by weight Mn 
19.8% by weight Ni 
2,970 ppm Fe 
&lt;100 ppm Cr 
800 ppm Mo 
&lt;100 ppm V 
80 ppm Cu 
&lt;100 ppm Ti 
1,280 ppm Na. 
______________________________________ 
The resulting solution 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.degree. C., was filtered through a folded filter. The 
filtrate was diluted to 10 l with fully demineralized water and adjusted 
to pH 3.9 with 10 ml of concentrated acetic acid. 
The solution contained: 
______________________________________ 
1.84 grams Co/liter 
0.16 grams Mn/liter 
0.87 grams Ni/liter 
&lt;5 ppm Fe 
&lt;5 ppm Cr 
&lt;5 ppm Mo 
&lt;5 ppm V 
&lt;5 ppm Cu 
&lt;5 ppm Ti. 
______________________________________ 
The thus-obtained solution was treated, to extensively remove the Na.sup.+ 
ions, with 250 ml of a strongly acidic cation exchange resin loaded with 
Co.sup.2+, Mn.sup.2+, and Ni.sup.2+ ions, 
A column with 250 ml of a strongly acidic cation exchange resin "Lewatit S 
100" in the Na.sup.+ form was charged with the resulting solution. 
The waste water obtained at the discharge end contained: 
25 ppm Co 
2 ppm Mn 
10 ppm Ni, 
To load the exchanger until incipient exhaustion, 4.7 liters of the 
solution was consumed. The exchanger was then washed with 250 ml of fully 
demineralized water. 
For eluting the Co.sup.2+, Mn.sup.2+, and Ni.sup.2+ ions, the following 
solutions were employed: 
390 ml of combined forerunnings and last runnings fraction of the preceding 
experiment 
200 ml of an 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.sup.2+, 0.3 g/l Mn.sup.2+, 1.8 g/l 
Ni.sup.2+ and 0.5 g/l CH.sub.3 COOH (free acid). The last runnings 
contained 13.4 g/l Co.sup.2+, 1.3 g/l Mn.sup.2+, 7.2 g/l Ni.sup.2+ 8.9 g/l 
CH.sub.3 COOH (free acid) and 15.8 g/l Na.sup.+. 
The following solutions were obtained during elution: 
80 ml of a forerunnings fraction 
400 ml of a main fraction depleted of Na.sup.+ ions 
320 ml of a last runnings fraction rich in Na.sup.+ 
The main fraction contained: 
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21.5 grams Co/liter 
1.9 grams Mn/liter 
10.2 grams Ni/liter 
&lt;5 ppm Fe 
&lt;5 ppm Cr 
&lt;5 ppm Mo 
&lt;5 ppm V 
&lt;5 ppm Cu 
&lt;5 ppm Ti 
240 ppm Na. 
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