Purification of acetic acid produced by the low water carbonylation of methanol by treatment with ozone

Acetic acid produced by the low water carbonylation of methanol and containing iodide, unsaturates and carbonyl impurities is purified by treatment with ozone.

Application Ser. No. 936,188, filed Dec. 1, 1986 (now abandoned), discloses 
purification of acetic acid by treatment with a compound such as hydrazine 
or derivatives thereof. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the purification of acetic acid and relates more 
particularly to the purification of acetic acid resulting from the low 
water catalytic , carbonylation of methanol. 
2. Description of the Prior Art 
Various methods have been employed for producing acetic acid including, for 
example, the oxidation of acetaldehyde, the oxidation of petroleum 
naphtha, butane or the like, or the direct synthesis of methanol and 
carbon monoxide. One of the more useful commercial methods for the 
production of acetic acid is the carbonylation of methanol as disclosed in 
U.S. Pat. No. 3,769,329. The carbonylation catalyst comprises rhodium, 
either dissolved or otherwise dispersed in a liquid reaction medium or 
else supported on an inert solid, along with a halogen-containing catalyst 
promoter as exemplified by methyl iodide. The rhodium can be introduced 
into the reaction system in any of many forms, and it is not relevant, if 
indeed it is possible, to identify the exact nature of the rhodium moiety 
within the active catalyst complex. Likewise, the nature of the halide 
promoter is not critical. A large number of suitable promoters are 
disclosed, most of which are organic iodides. Typically, the reaction is 
conducted with the catalyst being dissolved in a liquid reaction medium 
through which carbon monoxide gas is continuously bubbled. 
An improvement in the prior art process for the carbonylation of an alcohol 
to produce the carboxylic acid having one carbon atom more than the 
alcohol in the presence of a rhodium catalyst is disclosed in copending, 
commonly assigned application U.S. Ser. No. 699,525, filed Feb. 8, 1985; 
European Patent Application No. 161,874, published Nov. 21, 1985; and U.S. 
Ser. No. 870,267, filed Jun. 3, 1986. As disclosed therein, acetic acid 
(HAc) is produced from methanol (MeOH) in a reaction medium comprising 
methyl acetate (MeOAc), methyl halide, especially methyl iodide (MeI), and 
rhodium present in a catalytically-effective concentration. The invention 
therein resides primarily in the discovery that catalyst stability and the 
productivity of the carbonylation reactor can be maintained at 
surprisingly high levels, even at very low water concentrations, i.e., 4 
wt. % or less, in the reaction medium (despite the general industrial 
practice of maintaining approximately 14 wt. % or 15 wt. % water) by 
maintaining in the reaction medium, along with a catalytically-effective 
amount of rhodium, at least a finite concentration of water, methyl 
acetate and methyl iodide, a specified concentration of iodide ions over 
and above the iodide content which is present as methyl iodide or other 
organic iodide. The iodide ion is present as a simple salt, with lithium 
iodide being preferred. The applications teach that the concentration of 
methyl acetate and iodide salts are significant parameters in affecting 
the rate of carbonylation of methanol to produce acetic acid especially at 
low reactor water concentrations By using relatively high concentrationsof 
the methyl acetate and iodide salt, one obtains a surprising degree of 
catalyst stability and reactor productivity even when the liquid reaction 
medium contains water in concentrations as low as about 0.1 wt. %, so low 
that it can broadly be defined simply as "a finite concentration" of 
water. Furthermore, the reaction medium employed improves the stability of 
the rhodium catalyst, i.e., resistance to catalyst precipitation, 
especially during the product-recovery steps of the process wherein 
distillation for the purpose of recovering the acetic acid product tends 
to remove from the catalyst the carbon monoxide which in the environment 
maintained in the reaction vessel, is a ligand with stabilizing effect on 
the rhodium. U.S. Ser. No. 699,525 and U.S. Ser. No. 870,267 are herein 
incorporated by reference. 
The acetic acid which is formed by the carbonylation of methanol is 
converted to a high purity product by conventional means such as by a 
series of distillations. While it is possible in this manner to obtain 
acetic acid of relatively high purity, the acetic acid product contains a 
considerable amount of by-product impurities, determinable on the basis of 
their reducing action on permanganate. The amount of such reducing 
impurities is referred to as the permanganate time. Since the permanganate 
time is an important commercial test which the acid product must meet for 
many uses, the presence therein of such impurities is highly 
objectionable. Apparently, the removal of minute quantities of these 
impurities by conventional rectification alone is difficult since the 
impurities distill over with the acetic acid. 
Among the residual impurities which have been found to degrade the 
permanganate time are alkyl iodide impurities which are most likely 
carried over into the product stream from the catalyst solution in the 
reactor. Also found in the acetic acid product are various unsaturated and 
carbonyl impurities including crotonaldehyde, ethyl crotonaldehyde and the 
2-methyl-2-pentanal isomer thereof. As has been previously stated, it is 
both difficult and costly to remove the iodides, unsaturates and carbonyl 
impurities from the acetic acid product by physical methods since such 
impurities are present in such minute amounts. Accordingly, an economical 
process for removing such impurities is needed. 
Various methods have been suggested to purify or remove nonacidic 
components from carboxylic acids. For example, U.S. Pat. No. 4,576,683 
discloses a method of separating C.sub.1 -C.sub.10 aliphatic and C.sub.3 
-C.sub.10 olefinic carboxylic acids from mixtures with nonacids by 
extractive distillation using an amide as an extractant to recover an 
extractant-acid mixture by rectification. The method disclosed in the 
patent is described as being particularly suitably applied on aqueous 
mixtures of formic, acetic and/or propionic acid which mixtures contain 
unconverted hydrocarbons and other oxygenated compounds such as mixtures 
with alcohols, aldehydes and/or ketones and which may also contain further 
contaminants such as effluents from the tent are selected from lactams 
having 5 or 6 membered rings Pyrrolidone and derivatives thereof are 
specifically disclosed. 
U.S. Pat. No. 4,268,362 is concerned with providing a method of removing 
formaldehyde from raw acetic acid which has been formed by synthetic 
reactions such as oxidation of acetaldehyde, gas phase or liquid phase 
oxidation of butane, oxidation of petroleum naphtha or paraffins, as well 
as the reaction of methanol with carbon monoxide. The separation process 
involves treating the acetic acid in a heating zone at a temperature at 
about the boiling point of the acetic acid or higher, removing the heated 
product and delivering it to a distillation zone and operating the 
distillation zone so as to obtain a lower boiling fraction, a higher 
boiling fraction and an intermediate acetic acid fraction which will have 
a formaldehyde content of 300 ppm or lower. 
U.S. Pat. No. 3,725,208 is concerned with a process for the removal of 
small amounts of aldehyde impurities from acrylic acids which comprises 
adding to the acrylic acid minor amounts of a compound selected from the 
group consisting of sulfuric acid, hydrazine, phenyl hydrazine, aniline, 
monoethanolamine, ethylene diamine and gylcine and subjecting the acrylic 
acid mixture to distillation. Although hydrazine usually reacts 
exothermically with acrylic acid to form pyrrazolidone, and amines such as 
monoethanolamine and ethylene diamine have the properties of forming salts 
and aminocarboxylic acids with these compounds react predominantly with 
aldehydes contained in acrylic acid and can remove them from the acrylic 
acid. 
Japanese Patent Application 60-222439 discloses purification of acetic 
anhydride produced by the ketene process in which acetic acid is thermally 
cracked to ketene which then combines with acetic acid through an 
absorption reaction to produce acetic anhydride. The impurities contained 
in acetic anhydride produced in this manner are many low and high boiling 
compounds present at the time when acetic acid is thermally cracked and 
when acetic acid and ketene are reacted. However, the exact nature of the 
impurities contained in the acetic anhydride are not disclosed. Treatment 
with ozone gas in the absence of an oxidation catalyst was found to 
provide a quality product equal to or greater than that produced in 
purification by distillation. 
Japanese Patent Publication 55(1980)-64545, published May 15, 1980, 
discloses purification of acetic acid in which an ozone-containing gas is 
introduced to the acetic acid in the absence of an oxidation catalyst to 
obtain acetic acid of a higher quality as measured by a potassium 
permanganate test and sulfuric acid colon test. The identities of the 
impurities contained in acetic acid are not identified. 
U.S. Pat. No. 3,928,434 to Saunby discloses reducing the content of 
oxidizable impurities in acetic acid produced by hydrocarbon oxidation by 
treating the acetic acid with oxygen in the presence of a transition metal 
compound to oxidize unsaturated ketones. Saunby, in col. 1, lines 45-60, 
points out that, heretofore, oxidizable impurities can be destroyed by 
reaction with ozone, but that such treatment suffers the drawback of the 
risk involved in handling ozone at elevated temperatures in organic 
liquid. The Saunby disclosure is directed to removal of alpha, 
beta-unsaturated ketone impurities in acetic acid produced by hydrocarbon 
oxidation. 
SUMMARY OF THE INVENTION 
The present invention is directed to the purification of acetic acid and 
the improvement of permanganate time by subjecting the acid to treatment 
with ozone or an ozone containing gas. Thus acetic acid, as formed and 
recovered from the low water catalytic carbonylation of methanol, can be 
purified of minute amounts of unsaturates, iodides and carbonyl compounds 
by treatment with ozone which reacts with such impurities. The 
ozone-derived impurities are subsequently separated from the acetic acid 
by adsorption on an absorbent such as activated carbon, or an ion-exchange 
resin which is at least partially converted to the silver or mercury form. 
DETAILED DESCRIPTION OF THE INVENTION 
The ozonolysis treatment of the present invention is applicable to the 
purification of acetic acid which has been produced by the low water 
carbonylation of methanol in the presence of a metal catalyst such as 
rhodium. The purification process of the present invention is particularly 
useful when the carbonylation reaction is catalyzed by a metal such as 
rhodium and a halide promoter such as an organic halide disclosed in U.S. 
Pat. No. 3,769,329 to Paulik et al. The process of purifying acetic acid 
in the present invention is more particularly useful when the acetic acid 
is formed by the carbonylation of methanol under low water conditions such 
as set out in U.S. Ser. No. 699,525 wherein the catalyst solution not only 
contains the rhodium catalyst and organic halide promoter, but also 
contains an additional iodide salt. It has been found that organic iodide 
impurities as well as unsaturated and carbonyl impurities degrade the 
commercial value of the acetic acid product. 
In the low water carbonylation of methanol to acetic acid as exemplified in 
U.S. Ser. No. 699,525 and U.S. Ser. No. 870,267, the catalyst which is 
employed includes a rhodium component and a halogen promoter in which the 
halogen is either bromine or iodine. Generally, the rhodium component of 
the catalyst system is believed to be present in the form of a 
coordination compound of rhodium with a halogen component providing at 
least one of the ligands of such coordination compound. In addition to the 
coordination of rhodium and halogen, it is also believed that carbon 
monoxide ligands form coordination compounds or complexes with rhodium. 
The rhodium component of the catalyst system may be provided by 
introducing into the reaction zone rhodium in the form of rhodium metal, 
rhodium salts and oxides, organic rhodium compounds, coordination 
compounds of rhodium, and the like. 
The halogen promoting component of the catalyst system consists of a 
halogen compound comprising an organic halide. Thus, alkyl, aryl, and 
substituted alkyl or aryl halides can be used. Preferably, the halide 
promoter is present in the form of an alkyl halide in which the alkyl 
radical corresponds to the alkyl radical of the feed alcohol which is 
carbonylated. For example, in the carbonylation of methanol to acetic 
acid, the halide promoter will comprise methyl halide, and more preferably 
methyl iodide. 
The liquid reaction medium employed may include any solvent compatible with 
the catalyst system and may include pure alcohols, or mixtures of the 
alcohol feedstock and/or the desired carboxylic acid and/or esters of 
these two compounds. The preferred solvent and liquid reaction medium for 
the low water carbonylation process comprises the carboxylic acid product. 
Thus, in the carbonylation of methanol to acetic acid, the preferred 
solvent is acetic acid. 
Water is also added to the reaction medium but at concentrations well below 
what has heretofore been thought practical for achieving sufficient 
reaction rates. It is known that in rhodium-catalyzed carbonylation 
reactions of the type set forth in this invention, the addition of water 
exerts a beneficial effect upon the reaction rate, U.S. Pat. No. 3,769,329 
to Paulik. Thus, commercial operations run at water concentrations of at 
least 14 wt. %. Accordingly, it is quite unexpected that reaction rates 
substantially equal to and above reaction rates obtained with such high 
levels of water concentration can be achieved with water concentrations 
below 14 wt. % and as low as 4.0 wt. % to 0.1 wt. %. 
In accordance with the carbonylation process most useful in the present 
invention, the desired reaction rates are obtained even at low water 
concentrations by including in the reaction medium an ester which 
corresponds to the alcohol being carbonylated and the acid product of the 
carbonylation reaction and an additional iodide ion which is over and 
above the iodide which is present as a catalyst promoter such as methyl 
iodide or other organic iodide. Thus, in the carbonylation of methanol to 
acetic acid, the ester is methyl acetate and the additional iodide 
promoter is an iodide salt, with lithium iodide being preferred. It has 
been found that under low water concentrations, methyl acetate and lithium 
iodide act as rate promoters and catalyst stabilizers only when relatively 
high concentrations of 5 wt. % to 20 wt. % of each of these components are 
present and that the promotion is higher when both of these components are 
present simultaneously. This has not been recognized in the prior art 
previous to disclosure of commonly assigned U.S. Ser. No. 699,525 and U.S. 
Ser. No. 870,267. The concentration of lithium iodide used in the 
reaction medium of the preferred carbonylation reaction system is believed 
to be quite high as compared with what little prior art there is dealing 
with the use of halide salts in reaction systems of this sort. 
The carbonylation reaction may be carried out by intimately contacting the 
feed alcohol, which is in the liquid phase, with gaseous carbon monoxide 
bubbled through a liquid reaction medium containing the rhodium catalyst, 
halogen-containing promoting component, alkyl ester, and additional 
soluble iodide salt promoter, at conditions of temperature and pressure 
suitable to form the carbonylation product. Thus, when the feed is 
methanol, the halogen-containing promoting component will comprise methyl 
iodide and the alkyl ester will comprise methyl acetate. It will be 
generally recognized that it is the concentration of iodide ion in the 
catalyst system that is important and not the cation associated with the 
iodide, and that at a given molar concentration of iodide, the nature of 
the cation is not as significant as the effect of the iodide 
concentration. Any metal iodide salt, or any iodide salt of any organic 
cation, can be used provided that the salt is sufficiently soluble in the 
reaction medium to provide the desired level of the iodide. The iodide 
salt can be a quaternary salt of an organic cation or the iodide salt of 
an inorganic cation. Preferably, it is an iodide salt of a member of the 
group consisting of the metals of Group Ia and Group IIa of the Periodic 
Table as set forth in the "Handbook of Chemistry and Physics" published by 
CRC Press, Cleveland, Ohio, 1975-76 (56th Edition). In particular, alkali 
metal iodides are useful, with lithium iodide being preferred. In the low 
water carbonylation most useful in this invention, the additional iodide 
over and above the organic iodide promoter is present in the catalyst 
solution in amounts of from 2-20, preferably 10-20 wt. %, the methyl 
acetate is present in amounts of from 0.5-30, preferably 2-5 wt. %, and 
the methyl iodide is present in amounts of from 5-20 and 14-16 wt. %. The 
rhodium catalyst is present in amounts of from 200-1,000 and preferably 
300-600 ppm. 
Typical reaction temperatures for carbonylation will be approximately 
150.degree.-250.degree. C., with the temperature range of about 
180.degree.-220.degree. C. being the preferred range. The carbon monoxide 
partial pressure in the reactor can vary widely but is typically about 
2-30 atmospheres and preferably about 4-15 atmospheres. Because of the 
partial pressure of by-products and the vapor pressure of the contained 
liquids, the total reactor pressure will range from about 15-40 
atmospheres. 
A reaction and acetic acid recovery system which can be employed, within 
which the present improvement is used, comprises (a) a liquid-phase 
carbonylation reactor, (b) a so-called "flasher", and (c) a "methyl 
iodide-acetic acid splitter column". The carbonylation reactor is 
typically a stirred autoclave within which the reacting liquid contents 
are maintained automatically at a constant level. Into this reactor there 
are continuously introduced fresh methanol, sufficient water to maintain 
at least a finite concentration of water in the reaction medium, recycled 
catalyst solution from the flasher base, and recycled methyl iodide and 
methyl acetate from the overhead of the methyl iodide-acetic acid splitter 
column. Alternate distillation systems can be employed so long as they 
provide means for recovering the crude acetic acid and recycling to the 
reactor catalyst solution, methyl iodide, and methyl acetate. In the 
preferred process, carbon monoxide is continuously introduced into the 
carbonylation reactor just below the agitator which is used to stir the 
contents. The gaseous feed is, of course, thoroughly dispersed through the 
reacting liquid by this means. A gaseous purge stream is vented from the 
reactor to prevent buildup of gaseous by-products and to maintain a set 
carbon monoxide partial pressure at a given total reactor pressure. The 
temperature of the reactor is controlled automatically, and the carbon 
monoxide feed is introduced at a rate sufficient to maintain the desired 
total reactor pressure. 
Liquid product is drawn off from the carbonylation reactor at a rate 
sufficient to maintain a constant level therein and is introduced to the 
flasher at a point intermediate between the top and bottom thereof. In the 
flasher, the catalyst solution is withdrawn as a base stream 
(predominantly acetic acid containing the rhodium and the iodide salt 
along with lesser quantities of methyl acetate, methyl iodide and water), 
while the overhead of the flasher comprises largely the product acetic 
acid along with methyl iodide, methyl acetate and water. A portion of the 
carbon monoxide along with gaseous by-products such as methane, hydrogen 
and carbon dioxide exits the top of the flasher. 
The product acetic acid drawn from the base of the methyl iodide-acetic 
acid splitter column (it can also be withdrawn as a side stream near the 
base) is then drawn off for final purification such as to remove water as 
desired by methods which are obvious to those skilled in the art 
including, most preferably, distillation. The overhead from the methyl 
iodide-acetic acid splitter, comprising mainly methyl iodide and methyl 
acetate, is recycled to the carbonylation reactor along with fresh methyl 
iodide, the fresh methyl iodide being introduced at a rate sufficient to 
maintain in the carbonylation reactor the desired concentration of methyl 
iodide in the liquid reaction medium. The fresh methyl iodide is needed to 
compensate for losses of methyl iodide in the flasher and carbonylation 
reactor vent streams. 
The crude dry acetic acid product is not adequately purified since it 
contains residual by-products such as organic and metal iodides, 
unsaturates, and carbonyl impurities of which crotonaldehyde, ethyl 
crotonaldehyde and 2-methyl-2-pentanal are the most prominent. In the high 
water carbonylation of methanol of Paulik et al (U.S. Pat. No. 3,769,329), 
which generally teaches that a substantial quantity of water helps in 
obtaining adequately high reaction rates, and in European Patent 
Application 0055618, which teaches that typically 14-15 wt. % water is in 
the reaction medium of a typical acetic acid plant using this technology, 
impurities such as 2-methyl-2-pentanal, crotonaldehyde and 
ethyl-crotonaldehyde are not present but become a problem as the water 
content is lowered below 14 wt. % in the low water carbonylation of 
methanol. Small amounts of these impurities degrade the commercial 
usefulness of the acetic acid product and, accordingly, it has been 
discovered that by treating the acetic acid with ozone, it becomes 
possible to obtain a desired degree of purification as evidenced by the 
permanganate test. 
According to the invention, the crude acetic acid is subject to ozonolysis 
by generating the ozone gas and bringing the gas into physical contact 
with the acetic acid product in the presence of a catalytically effective 
amount of an oxidation catalyst. 
Ozone (O.sub.3) is a gaseous allotropic form of oxygen in which three atoms 
form the molecule rather than the normal two. Although ozone is a strong 
oxidizing agent, it is not a specific oxidant and, hence, will oxidize any 
material it contacts which has a lower oxidation potential. As such, when 
it contacts the aforesaid impurities in acetic acid, it will oxidize the 
carbon to carbon double bond linkages of unsaturates, for example, which 
apparently contribute to short permanganate times in the acetic acid 
product. This theory of operation, however, is not to be regarded as 
essential to an understanding of the invention. Available data, as shown 
hereinafter, indicate that the benefit of the ozone contacting is due to 
the ability of the ozone to render iodides, unsaturates and carbonyl 
compounds inactive, thus preventing their influence on acetic acid either 
during storage or subsequent use. 
Ozonolysis may be carried out by generating the ozone from any suitable 
source such as a quartz lamp, a silent electric discharge or spark 
discharge commonly called corona discharge, but it is preferable to obtain 
the ozone from a source of radiation in the range between about 1000 and 
2950 angstrom units in wave length, applied in air or oxygen. For 
commercial production of ozone, it is preferable to use corona discharge 
technology on either air or oxygen. UV radiation type generators are 
usually only used on a small scale system. The maximum weight ratio of 
ozone in the liquid acetic acid is governed by the flammability limits of 
acetic acid--O.sub.2 vapor phase compositions. In the examples hereinafter 
set forth, ozone was introduced into the mid point of a cylindrical vessel 
and contacted with a downwardly flowing stream of acetic acid at a 
temperature of about 95.degree. F. (35.degree. C.). Sufficient pressure 
was employed to keep the acetic acid below the flammability limit of 2.5 
volume percent in oxygen or 3.8 volume percent in air (.about.10 psig in 
air or 25 psig in O.sub.2). 
The ozone exposure time will vary, but it has been found that the effect is 
substantially instantaneous, while on the other hand, over exposure is not 
harmful. Good results are obtained when the exposure time is less than 
one-half hour, usually about 1 to 15 minutes. The preferred quantity of 
ozone will range from about 3 ppm to 5000 ppm based on the weight of the 
acetic acid treated. High levels of ozone are not detrimental except for 
associated costs. 
The ozonolysis may be carried out at temperatures of 70.degree. F. 
(21.degree. C.) to 115.degree. F. (52.degree. C.) in a continuous or 
batchwise fashion. Temperature and pressure considerations are not 
critical so long as flammability limits are not exceeded. 
The iodides, unsaturates and carbonyl impurities in acetic acid apparently 
react with ozone to form a reactive oxygenated species or complex which 
may be separated from the acetic acid. Such separation can be accomplished 
by passing the solution through a carbonaceous material or a 
macroreticulated strong-acid cation exchange resin which is stable in the 
organic medium and has at least one percent of its active sites converted 
to the silver or mercury ion-exchange form. 
As indicated, the ion exchange resin has been at least partially converted 
to the silver or mercury form. It is important in practice to use an ion 
exchange resin with suitable properties. The ion exchange resin should not 
be of the gel-type. As is known, gel-type polymers are characterized by 
the fact that their porosity essentially depends on the volume increase 
which they exhibit upon exposure to a given solvent system. Ion exchange 
resins which depend essentially upon swelling for their porosity are not 
suitable for the practice of the present invention. 
The ion exchange resins used in the present invention may thus be termed 
"non-gel-type" ion exchange resins. Such useful resins are typically 
considered to be macroreticular ion exchange resins and usually have pores 
considerably larger than those of the gel-type. However, the present 
invention is not limited to any specific pore-size of the ion-exchange 
resin. Usually the ion exchange resins used in the present invention have 
an average pore size from about 50 to 1,000 angstroms. Preferably, the 
average pore size is from about 200 to 700 angstroms. 
The ion-exchange resin should also be of the type typically classified as a 
"strong acid" cation exchange resin. Preferably the resin of the 
"RSO.sub.3 H type." It is beyond the scope of the present invention to 
teach how to manufacture or otherwise characterize ion exchange resins, as 
such knowledge is already well known in that art. For the purposes of the 
present invention it is sufficient to characterise an ion exchange resin 
useful therein as being a strongly-acidic cation exchange resin of the 
non-gel type, and thus macroreticulated. 
A preferred ion exchange resin for use in the practice of the present 
invention is a macroreticulated resin comprised a sulfonated copolymer of 
styrene and divinyl benzene. The most preferred resin such as that 
available from Rohm and Haas under the trademark Amberlyst.RTM. 15, has 
the following properties: 
______________________________________ 
Hard, dry 
spherical 
Appearance particles 
______________________________________ 
Typical particle size distribution 
percent retained on 
16 mesh U.S. Standard Screens 
2-5 
-16 + 20 mesh U.S. Standard Screens 
20-30 
-20 + 30 mesh U.S. Standard Screens 
45-55 
-30 + 40 mesh U.S. Standard Screens 
15-25 
-40 + 50 mesh U.S. Standard Screens 
5-10 
Through 50 mesh, percent 
1.0 
Bulk density, lbs./cu. ft. 
38 (608 g/L) 
Moisture, by weight less than 1% 
Percentage swelling from dry state 
to solvent-saturated state 
hexene 10-15 
toluene 10-15 
ethylene dichloride 15-20 
ethyl acetate 30-40 
ethyl alcohol (95%) 60-70 
water 60-70 
Hydrogen ion concentration 
4.7 
meq./g. dry 
Surface Area, m.sup.2 /g. 
50 
Porosity, ml. pore/ml. bead 
0.36 
Average Pore Diameter, Angstroms 
240 
______________________________________ 
A final characteristic of the resin when used to remove iodide compounds 
from non-aqueous, organic media, and one that is inherent in most ion 
exchange resins meeting the foregoing requirements, especially when the 
resin is specifically indicated to be designated for non-aqueous 
applications, is that the resin is stable in the organic medium from which 
the iodide compounds are to be removed. By the term "stable," it is meant 
that the resin will not chemically decompose, or change more than about 50 
percent of its dry physical dimension upon being exposed to the organic 
medium containing the iodide compounds. 
The ion exchange resin as indicated above, should be at least partially 
converted to the silver or mercury form. Conversion to the silver form is 
preferred. 
The method of converting the ion exchange resin to the silver or mercury 
form is not critical. Any mercury or silver salt which has reasonable 
solubility in water or a suitable non-aqueous organic medium can be used. 
Silver acetate and silver nitrate are typical salts. The organic medium 
which may be used to load silver ions on the exchange resin may be, for 
example, acetic acid. When mercury is desired, rather than silver, a 
suitable salt is mercuric acetate. 
The ion exchange resin is converted, to the desired degree, to the silver 
or mercury form, by simply contacting the resin with a solution of the 
desired silver or mercury salt for a sufficient length of time to allow 
for association of the metal ions with the resin. 
The amount of silver or mercury associated with the resin is not critical 
and may be from as low as about 1 percent of the active acid sites to as 
high as 100 percent, converted to the silver or mercury form. Preferably 
about 25 percent to about 75 percent are converted to the silver or 
mercury form, and most preferably about 50 percent. As stated previously, 
the preferred metal is silver. 
As some silver may be leached from the silver-treated ion exchange resin 
during conditions of actual use, it may be useful to have a bed of 
ion-exchange resin which has not been bed of silver-treated ion exchange 
resin. With respect to the processing steps, the non-aqueous organic 
medium which contains the iodide impurities is simply placed in contact 
with the silver-loaded ion exchange resin described above, using any 
suitable means. For example, the resin may be packed into a column by 
pouring slurries thereof into a column. The organic medium is then simply 
allowed to flow therethrough. Any other suitable means of placing the 
resin in contact with the organic medium may be employed. 
When a packed column is used, the organic medium is usually allowed to flow 
therethrough at a predetermined rate. The particular rate used in any 
given instance will vary depending upon the properties of the organic 
medium, the particular resin, the degree and nature of the iodide 
compounds to be removed, and the percent of iodide compounds to be 
removed. 
A typical flow rate, such as is used when acetic acid is to be purified, is 
from about 0.5 to about 20 bed volumes per hour ("BV/hr"). A bed volume is 
simply the volume of the resin bed. A flow rate of 1 BV/hr then means that 
a quantity of organic medium equal to the volume occupied by the resin bed 
passes through the resin bed in a one hour time period. Preferred flow 
rates are usually about 6 to about 10 BV/hr and the most preferred flow 
rate is usually about 8 BV/hr. 
The temperature at which the iodide compound removal takes place is also 
not critical. Broadly, the method may be performed at any temperature from 
about the freezing point of the organic liquid to the decomposition 
temperature of the resin. As a practical matter, the temperature employed 
is usually from about 17.degree. C. to about 100.degree. C., typically 
from about 18.degree. C. to about 50.degree. C., and preferably under 
ambient conditions of about 20.degree. C. to about 45.degree. C. 
In one embodiment of the present invention the non-aqueous organic medium 
is contacted with a carbonaceous material in addition to contacting the 
aforementioned ion exchange resin. Preferably, the carbonaceous material 
is used in a contacting step prior to the step of contacting the ion 
exchange resin. Although the aforementioned ion exchange resin is useful 
in removing iodide compounds, it is not very effective in removing iodine 
itself. 
As discussed in U.S Pat. No. 1,843,354, carbonaceous materials have been 
found to be effective absorbers of iodine. Carbonaceous materials listed 
therein include activated carbons, wood charcoals, bone char, lignite and 
the like. Preferably, activated carbon is used. It appears that activated 
carbons of the type usually identified as gas-phase carbons work best in 
removing iodine from such organics. Gas-phase activated carbons typically 
have surface areas on the order of 1,000 to 2,000 m.sup.2 /g. The most 
preferred activated carbon is one derived from coconut shells, such as is 
available under the designation Pittsburgh PCB 12X30 carbon. 
Usually the non-aqueous organic medium is placed in contact with the 
carbonaceous material in the same manner as with the ion exchange resin, 
under the same or comparable conditions. 
The present invention can be more fully understood by referring to the 
following examples which illustrate the best mode now contemplated for 
carrying out of the invention. In the examples the "permanganate time" is 
determined as follows: 
One ml of an aqueous 0.1N potassium permanganate solution is added to 50 ml 
of acetic acid in a graduated cylinder at room temperature. The cylinder 
is stoppered and shaken, and a timer is immediately started to measure the 
time required for the purple color to change to a yellow-amber end point 
which is compared to a standard reference color indicating the content of 
unsaturate, iodide and carbonyl impurities.