Process for producing benzene carboxylic acid salts from aromatic materials

This invention relates to a method of producing an aqueous solution which comprises soluble benzene carboxylic acid salts which is substantially free of soluble humic acid salts. A first aqueous solution (22) which comprises soluble humic acid salts and soluble benzene carboxylic acid salts is reacted with carbon dioxide (32) and an inorganic chemical (34) selected from the group consisting of magnesium bicarbonate, magnesium carbonate, a double salt of magnesium carbonate, and mixtures thereof in a mixing zone (30) under conditions operable for converting the soluble humic acid salts to precipitated magnesium humic acid salts while maintaining the soluble benzene carboxylic acid salts in solution. The reacted first aqueous solution (36) is then separated in a separation zone (40) into (i) a second aqueous solution (44) which comprises the soluble benzene carboxylic acid salts and which is at least substantially free of soluble humic acid salts, and (ii) a mixture (42) which comprises precipitated magnesium humic acid salts.

TECHNICAL FIELD 
The technical field of the invention relates to the production of benzene 
carboxylic acid salts from aromatic materials. Suitable non-limiting 
aromatic materials are coal, coal char, coke, chars produced from lignite, 
pitch, tar, petroleum residium, petroleum, shale oil, and tar sands. The 
invention is useful for the separation of benzene carboxylic acid salts 
from an aqueous solution which comprises a mixture of dissolved aromatic 
carboxylic acid salts. 
BACKGROUND ART 
U.S. Pat. No. 3,629,328 discloses a method of purifying organic acids such 
as terephthalic acid by forming a solution of the acid in an aqueous 
solution of a weak acid salt of magnesium, treating the solution to reduce 
impurities upon recrystallization of the acid, cooling the solution to 
recrystallize the acid in a free acid form, and separating the acid from 
the mother liquor. 
U.S. Pat. No. 3,115,521 discloses a process for purifying aromatic acids by 
treating an aqueous solution of an alkaline salt of an aromatic carboxylic 
acid with carbon monoxide under pressure. The impurities precipitate, and 
the solution can be further treated with activated carbon to remove the 
remaining colored impurities. 
U.S. Pat. No. 2,745,872 discloses a method for separating mixtures of salts 
of terephthalic acid and isophthalic acid by forming a mixture of the 
salts with a concentrated aqueous solution of an inorganic alkali metal 
salt, the aqueous solution being insufficient to dissolve all of the mixed 
alkali phthalic acid salts, and separating a solid phase and a liquid 
phase from the mixture. 
U.S. Pat. No. 3,206,504 discloses a method for separating isophthalic acid 
from other aromatic carboxylic acids by treating the mixture of acids with 
reagents to preferentially solubilize the terephthalic acid and 
monocarboxylic acids present without solubilizing too much of the 
isophthalic acid, and then separating a solution of the solubilized 
impurities from the solid bulk of the mass. 
Canadian Pat. No. 718,043, discloses a method for separating impurities 
from naphthalene dicarboxylic acid prepared by the oxidation of 
dimethylnaphthalene. Impure dinaphthalene carboxylic acid is dissolved in 
aqueous sodium hydroxide, acidifying the solution to precipitate 
impurities, separating the impurities, further acidifying the solution to 
precipitate purer naphthalene dicarboxylic acid and separating the acid. 
Canadian Pat. No. 498,786 discloses a process for oxidizing coal at 
elevated temperature and pressure with an oxygen-containing gas in the 
presence of an aqueous alkaline solution to produce a solution of alkaline 
salts of organic acids such as sodium salts. The alkaline solution is then 
discharged from the reaction vessel and is filtered to remove ash. The 
alkaline solution is then treated with a mineral acid to free the organic 
acids from their salts. The organic acids in solution are extracted from 
the acidified aqueous solution by a solvent such as methyl ethyl ketone. 
British Pat. No. 815,835 discloses a process for producing aromatic 
carboxylic acids, their esters and salts, by reacting an aromatic 
halogenated hydrocarbon with the formate of an alkali or alkaline earth 
metal at an elevated temperature or pressure. Instead of using formate 
directly, the formate may be formed in situ using a compound such as 
magnesium hydroxide. The reaction may then be extracted with benzene, and 
the residue treated with water and acidified. The precipitate is the free 
acid desired. 
U.S. Pat. No. 2,785,198 discloses a process for producing polycarboxylic 
acids from bituminous coal, lignites, peat and the like or their 
carbonization products such as coal, tar, or pitch by thermal treatment 
with oxidizing agents such as nitric acid, chromic acid, permanganate, or 
oxygen or air under super-atmospheric pressure in an alkaline medium. The 
alkaline medium disclosed is sodium hydroxide. Also disclosed is a process 
for extracting low molecular weight polycarboxylic acids from the crude 
oxidation product produced by the thermal oxidation of carbonaceous 
matter. The oxidation produced is extracted with at least one polar 
organic solvent for both the monocyclic aromatic and the high molecular 
weight polycarboxylic acids so as to cause dissolution of the 
polycarboxylic acids. The solution is treated with water to dissolve the 
monocyclic acids in the water. The aqueous solution of monocyclic aromatic 
polycarboxylic acids is separated from the remainder of the mixture, and 
the monocyclic aromatic polycarboxylic acids are recovered. 
The crude oxidation product is subject to an extraction treatment with a 
polar organic solvent for both the monocyclic aromatic and high molecular 
weight polycarboxylic acids, and treating the thusly formed solution with 
water to extract the monocyclic aromatic polycarboxylic acids from the 
remainder of the mixture. 
U.S. Pat. No. 2,193,337 discloses a process for producing organic acids by 
heating carbonaceous material such as sawdust, wood chips, peat, or coal 
with oxygen-containing gases at elevated pressures and temperatures in the 
presence of at least 10 times the weight of the carbonaceous material of 
water and preferably an oxide or hydroxide of an alkali or alkaline earth 
metal. Oxalic acid and other organic acids which are formed, such as 
mellitic and benzoic acid or acetic acid, may be isolated from the 
resulting reaction mixture as salts of the alkali or alkaline earth 
metals. The caustic material disclosed is an oxide or hydroxide of an 
alkali metal or an alkaline earth metal and specifically lime, quick-lime, 
and caustic soda. 
U.S. Pat. No. 2,786,074 discloses a process for making organic acids by 
oxidizing carbonaceous materials at elevated temperatures and pressures 
with gaseous oxygen in the presence of an alkaline solution. Alkalis which 
are suitable for use in a high pressure reactor are specified as sodium 
hydroxide, potassium hydroxide, and mixtures thereof. 
U.S. Pat. No. 2,461,740 discloses a process for oxidizing carbonaceous 
material to aromatic acids using a two-stage oxidation process. 
In the first stage, the carbonaceous material is oxidized to a state where 
it is soluble in aqueous alkali such, for example, as a solution of sodium 
hydroxide, potassium hydroxide, sodium carbonate, or potassium carbonate, 
especially at elevated temperatures. 
Any acid or acid anhydride with suitable oxidizing properties which can be 
regenerated by air and recycled in the process can be employed, for 
example, sulfur trioxide, oxides of nitrogen, or the acids formed by 
reaction of these compounds with water. Specifically disclosed are sulfur 
trioxide, N.sub.2 O.sub.3, and N.sub.2 O.sub.5. 
In the second stage, U.S. Pat. No. 2,461,740 discloses the use of a high 
pressure elevated temperature reaction of oxygen gas in aqueous alkali. 
The aqueous alkali employed is a solution of sodium hydroxide, potassium 
hydroxide, sodium carbonate, or potassium carbonate. 
U.S. Pat. No. 3,023,217 discloses a process for introducing carboxyl groups 
into aromatic compounds free from carboxyl groups, such as aromatic 
carbocyclic hydrocarbons and aromatic heterocyclic hydrocarbons. The 
patent discloses a process for introducing into aromatic carbocyclic or 
aromatic heterocyclic compounds free from carboxyl groups by reacting such 
materials in the absence of substantial amounts of oxygen, such as a 
non-oxidative atmosphere and under anhydrous conditions, with alkali metal 
salts of aliphatic carboxylic acids at elevated temperatures and pressures 
in the presence of catalysts. As disclosed in the process, it is necessary 
to exclude the presence of substantial quantities of oxygen. Examples of 
aliphatic carboxylic acids which are used in the form of their alkali 
metal salts, especially their potassium salts, are oxalic acid, malonic 
acid, maleic acid, and trichloroacetic acid. 
Examples of suitable compounds free from carboxyl groups which may be used 
as starting materials for the process are aromatic carbocyclic compounds 
free from carboxyl groups such as monocyclic aromatic hydrocarbons such as 
benzene or its derivatives having saturated alkyl or cycloalkyl 
substitutes attached thereto, and dicyclic aromatic hydrocarbons such as 
naphthalenes, diphenyl, and other polycyclic aromatic hydrocarbon 
compounds. Similarly, aromatic heterocyclic compounds free from carboxyl 
groups which may be used as starting materials are heterocyclic compounds 
which contain one or more heteroatoms in the ring and which are designated 
as having an aromatic character because of their chemical behavior. 
U.S. Pat. No. 2,948,750 discloses a process for carboxylating aromatic 
hydrocarbons by direct introduction of carbon dioxide to produce 
polycarboxylic acids. 
Suitable starting materials which are disclosed are aromatic hydrocarbons, 
especially benzene but also toluene, xylene, cumene and diisopropyl 
benzene and other benzenes substituted with saturated or unsaturated alkyl 
or cycloalkyl radicals, naphthalene, diphenyl, diphenylmethane and other 
aromatic compounds which may also be substituted with hydrocarbon 
radicals. 
Selective carboxylation is accomplished by heating the starting materials 
in the presence of an acid-binding agent, and carbon dioxide under 
anhydrous conditions. Examples of the acid-binding agent are carbonates of 
alkali metals, especially potassium carbonate, the salts of other weak 
acids such as bicarbonates, formates, or oxalates. Similarly, the 
corresponding compounds of other metals are suitable; for example, the 
carbonates of the alkali earth metals. 
U.S. Pat. No. 3,023,216 discloses a method of introducing carboxyl groups 
into aromatic carbocyclic compounds free from carboxyl groups by reacting 
these compounds in a non-oxidative atmosphere with alkali metal salts of 
aromatic carbocyclic or aromatic heterocyclic carboxylic acids. 
Suitable compounds which are free from carboxyl groups which may be used as 
starting compounds in this patent are similar to the starting compounds in 
U.S. Pat. No. 2,948,750. 
U.S. Pat. No. 3,023,216 discloses reacting aromatic carboxylic compounds 
free from carboxyl groups with aromatic carboxylic acids in the form of 
their alkali metal salts. 
Both U.S. Pat. Nos. 3,023,216 and 2,948,750 require specific chemical 
compounds as starting materials. 
U.S. Pat. No. 2,833,816 discloses a process for oxidizing aromatic 
compounds using a catalyst comprising a lower aliphatic carboxylate salt 
of a heavy metal and bromine. Examples of a heavy metal are manganese, 
cobalt, nickel, chromium, vanadium, molybdenum, tungsten, tin, and cerium. 
The metals may be supplied in the form of metal salts; for example such as 
manganese acetate. The bromine may be supplied as ionic bromine, or other 
bromine compounds soluble in the reaction medium such as potassium 
bromate. 
Thus, the process requires the conjoint presence of bromine and a heavy 
metal oxidation catalyst. 
The starting material required is an aromatic compound containing one or 
more aliphatic substituents to produce corresponding aromatic carboxylic 
acids. 
U.S. Pat. No. 3,064,043 discloses a process for oxidizing para-toluic acid 
or para-formyl toluene to produce terephthalic acid. 
U.S. Pat. No. 3,064,046 discloses a process for oxidizing toluic acid or 
formyl toluene to produce orthophthalic acid or isophthalic acid. 
Both U.S. Pat. Nos. 3,064,043 and 3,064,046 require specific starting 
materials to be oxidized. 
U.S. Pat. No. 3,558,458 discloses a process for preparing aromatic acids by 
treating an alkyl aryl ketone with water at an elevated temperature in the 
presence of a reaction promoting agent. The reaction promoting agent may 
comprise an alkaline catalyst, a transition metal salt, or actinic light. 
Examples of an alkaline catalyst include potassium acetate, lithium 
acetate, rubidium acetate, and cesium acetate. The process is conducted in 
water at a temperature of about 200.degree. to 400.degree. C. 
The art discloses processes for the alkaline oxidation of coal employing 
large amounts of chemicals relative to the amount of water soluble coal 
acid produced, see U.S. Pat. No. 2,786,074 and a report entitled 
"Production of Chemicals by Oxidation of Coal", Battelle Laboratory, 
Columbus, Ohio of Mar. 31, 1975. 
Recovery of caustic soda and sodium carbonate was disclosed by Industrial 
and Engineering Chemistry, Volume 44 (1952), at page 2791 in an article 
entitled "Water-Soluble Polycarboxylic Acids by Oxidation of Coal" 
beginning at page 2784. 
Japanese patent disclosure 18,365 discloses the reclamation of alkali by 
recrystallization and requires the consumption of one part by weight of 
the alkali and 1.5 parts of sulfuric acid for each two parts of coal 
consumed. 
Non-alkaline oxidation of coal generally yields about 10 parts by weight of 
water soluble coal acids based on 100 parts of coal carbon consumed. 
Alkaline oxidation yields have been about 30 to about 42 parts per 100 
parts of coal carbon consumed. Therefore, alkaline oxidation processes are 
favored because of the higher yield possible. 
In systems like HCl/KCl, H.sub.2 SO.sub.4 /K.sub.2 SO.sub.4, and HNO.sub.3 
/KNO.sub.3, the salts do not produce an alkali solution by hydrolysis 
because the acids involved are too strong. These systems over oxidize the 
coal and therefore result in much lower yield of coal acids. 
Another disadvantage of treatment of coals with strong acids is the 
production of unwanted by-products by chlorination, sulfation, or 
nitration of the aromatic nuclei of the coal. 
Coal acids have been prepared by nitric acid oxidation, U.S. Pat. Nos. 
3,468,943; 3,709,931; 2,555,410; in the presence of nitrogen catalyst, 
U.S. Pat. No. 3,702,340; and oxidation in a non-alkaline aqueous medium, 
U.S. Pat. No. 3,259,650. 
The caustic-oxygen treatment of coal has been described in U.S. Bureau of 
Mines Information Circular No. 8234 at pages 74 to 98. 
In another process, U.S. Pat. No. 3,259,650 discloses the use of a 
non-alkaline medium and produces lower yields of water soluble coal acids. 
U.S. Pat. No. 2,927,130 discloses a process for the recovery of alkalis and 
terephthalic acid from aqueous solutions containing alkali salts of 
terephthalic acid. Alkalis of interest are sodium, potassium and ammonium. 
The patent discloses that dialkali salts of terephthalic acid in aqueous 
solution can easily be divided into difficulty soluble monoalkali salts 
and alkali bicarbonate by introducing carbon dioxide into the solution, 
and that the difficulty soluble monoalkali salts of terephthalic acid can 
be hydrolyzed with water into free terephthalic acid and dialkali salts of 
terephthalic acid. The free terephthalic acid separates out as a solid, 
while the dialkali terephthalate remains in solution. 
U.S. Pat. No. 2,819,300 discloses a process for oxidizing carbonaceous 
material with nitric acid, and then oxidizing the oxidation products 
produced from the nitric acid-carbonaceous material reaction with sulfuric 
acid to complete the oxidation to benzene carboxylic acids. 
Although oxidation can be carried out in reclaimable acidic media, these 
processes are not as desirable because of lower yields and unwanted 
by-products due to chlorination, sulfation, and nitration. 
The art discloses a process for preparing terephthalic acid by heating pure 
potassium phthalate, or pure potassium isophthalate, or pure potassium 
benzoate in the presence of catalyst such as cadmium, zinc and other 
metals, as reported in the Journal of American Chemical Society, Volume 
79, pages 6005 to 6008. 
The art discloses a catalytic process for preparing terephthalic acid from 
toluene by oxidizing toluene to benzoic acid, reacting the thusly formed 
benzoic acid with potassium terephthalate in a methathesis reaction to 
produce terephthalic acid and potassium benzoate, and heating the thusly 
formed potassium benzoate in the presence of a catalyst to produce 
potassium terephthalate and benzene by a disproportionation reaction. 
Terephthalic acid and benzene are recovered and the thus formed potassium 
terephthalate is recycled to the methathesis reaction. The process is 
reviewed in Stanford Research Institute Report No. PEP'76-2-3 of February, 
1977. 
U.S. Pat. No. 3,215,735 discloses a process for treating a solution 
containing dialkali terephthalate and non-terephthalic acid as impurities 
with a reagent to adjust the pH of the solution so that terephthalic acid 
is in a soluble form while essentially all of the non-terephthalic acid is 
in an insoluble filterable form. 
U.S. Pat. No. 3,579,572 discloses a process for the production of 
terephthalic acid which comprises treating an aqueous lithium or magnesium 
terephthalate solution with carbon dioxide under pressure, at a 
temperature between its solidification temperature and 80.degree. C., and 
separating the terephthalic acid which precipitates. 
U.S. Pat. No. 3,766,258 discloses a process for the catalytic carboxylation 
of an alkali metal aromatic carboxylate to an acid containing at least one 
more carboxyl group. 
U.S. Pat. No. 2,171,871 discloses that alkali metal derivatives of organic 
acid salts may be reacted with various reagents reactive with alkali metal 
organic compounds, e.g. carbon dioxide, sulfur dioxide or organic halides, 
to produce valuable products. 
U.S. Pat. No. 2,176,348 discloses a process for preparing mellitic acid by 
a two-step oxidation of coal. The coal is first treated with a suitable 
oxidizing acid with or without the presence of a catalyst, followed by 
oxidation with an oxidizing salt such as alkaline permanganate. 
U.S. Pat. No. 2,762,840 discloses that polycarboxy aromatic acids can be 
prepared by controlled oxidation with oxygen gas of an aqueous, alkaline 
suspension of bituminous coal. 
U.S. Pat. No. 2,981,751 is directed toward a process for the oxidation of 
substituted aromatic compounds having at least one aliphatic, 
cycloaliphatic or partially oxidized aliphatic or cycloaliphatic 
substituent attached to the aromatic nucleus in the presence of an 
oxygen-containing gas and a calcined solid oxidation catalyst. 
The substituted aromatic feed materials disclosed are toluene, 
butylbenzene, xylene, cumene, durene, dibutylbenzene, acetophenone, 
propiophenone, benzaldehyde, tolualdehyde, Tetralin, para-xylene, 
acetophenone, and cumene hydroperoxide. The oxidation is in the presence 
of a calcined solid oxidation catalyst which is derived by calcining an 
inorganic base having deposited thereon catalytic amounts of a promoting 
metal component. 
U.S. Pat. No. 3,529,020 discloses a process for oxidizing an organic 
material in the presence of a heavy metal crystalline aluminosilicate 
having uniform pores sufficiently large to permit entry of at least a 
portion of the organic material, and an oxidation initiator which is 
present in the pores. The heavy metal crystalline aluminosilicate acts as 
a catalyst. 
One embodiment of this invention is a process for producing benzene 
carboxylic acid salts comprising treating a mixture of an aromatic 
material, water, a water soluble reagent comprising a Group Ia or IIa 
metal, the reagent producing an alkaline solution by hydrolysis, and a 
promoter agent, with oxygen under conditions sufficient to convert at 
least a portion of the aromatic material to a benzene carboxylic acid salt 
of the reagent. The promoter having the formula R--X--CH.sub.2 --R', 
wherein: 
R comprises a radical selected from the group consisting of alkoxy, 
phenoxy, substituted phenoxy, hydroxyl, carboxyl, aldo, keto, phenyl, 
substituted phenyl, alkyl, substituted alkyl, and hydrogen; 
X comprises a radical, with at least two points of substitution, selected 
from the group consisting of benzene ring, substituted benzene ring, 
multi-ring system, substituted multi-ring system, saturated ring, 
substituted saturated ring, and (CH.sub.2).sub.n, where n is an integer of 
at least one; and 
R' comprises a radical selected from the group consisting of hydrogen, 
alkyl, substituted alkyl, phenyl, substituted phenyl, hydroxyl, carboxyl, 
aldo, keto, alkoxy, phenoxy, and substituted phenoxy. 
The promoter also comprises at least one easily extractable hydrogen, and 
has the property of increasing the yield of benzene carboxylic acid salt 
thusly produced from said aromatic material by an amount higher than the 
conversion of the aromatic material to benzene carboxylic acid in the 
absence of said promoter. 
In another embodiment the promoter agent has the property of increasing the 
yield of benzene carboxylic acid salts by an amount substantially higher 
than an amount equivalent to a stoichiometric conversion of the promoter 
agent to benzene carboxylic acid salt. The thusly formed benzene 
carboxylic acid salt is then recovered from the mixture or further 
processed into more valuable products such as by isomerization to 
terephthalic acid. 
SUMMARY AND DISCLOSURE OF THE INVENTION 
This invention separates an aqueous solution which comprises soluble 
benzene carboxylic acid salts, hereinafter referred to as soluble "BCA" 
salts, from an aqueous solution which comprises soluble humic acid salts 
and soluble BCA salts. By benzene carboxylic acid or "BCA" we mean herein 
any one of or any mixture of benzoic; 1,2 benzene dicarboxylic; 1,3 
benzene dicarboxylic; 1,4 benzene dicarboxylic; 1,2,3 benzene 
tricarboxylic; 1,2,4 benzene tricarboxylic; 1,3,5 benzene tricarboxylic; 
1,2,3,4 benzene tetracarboxylic; 1,2,3,5 benzene tetracarboxylic; 1,2,4,5 
benzene tetracarboxylic; benzene pentacarboxylic; or benzene 
hexacarboxylic acid. In other words, by benzene carboxylic acid or BCA as 
used herein and claimed we mean a benzene ring with one or more carboxyl 
groups attached directly to a ring carbon and containing no other 
substituted group or groups. 
The aromatic material can be coal of any grade such as bituminous, 
subbituminous or anthracite, peat, lignite, coke, char, petroleum, 
petroleum fractions such as petroleum residium, tar, pitch, oil shale, oil 
from oil shale, chars and cokes from lignite, mixtures thereof, and any 
other material containing or capable of evolving or producing aromatic 
material, either liquid or solid. Coals, coal char, coke, chars produced 
from lignite, petroleum residium, tar, pitch and mixtures thereof are 
preferred aromatic feed material because such material will produce a good 
yield of BCA salts by this invention. 
Bituminous coal is especially preferred because of the very high yield of 
BCA salts produced by this process. Whereas, anthracitic coals because of 
their high aromaticity produce a high percentage of polynuclear aromatic 
acid salts. Similarly, yields from lignites are low because the oxidation 
of lignite produces little aromatic material, and therefore the yield of 
BCA salts is low. 
In general, the water soluble reagent is such that it produces an alkaline 
solution by hydrolysis. In general its chemical formula comprises a cation 
selected from the group consisting of alkali metals, ammonium, and 
mixtures thereof. Thus, hydrogen is excluded from the group comprising 
alkali metals. Water soluble reagents which comprise potassium or sodium 
alkali metals are preferred members of the group because they are more 
reactive, have a higher rate of reaction in this invention, produce a high 
yield of BCA salts, and/or are relatively less expensive. 
A water soluble reagent such as potassium carbonate, potassium bicarbonate, 
a double salt of potassium bicarbonate, or mixtures thereof is especially 
preferred because it gives a high yield of BCA salts in this invention, it 
is economical and may be regenerated as set forth in the preferred 
embodiment below. Other examples of water soluble reagents which may be 
used are potassium carbonate, sodium carbonate, lithium carbonate, 
potassium acetate, potassium formate, potassium propionate, sodium 
acetate, sodium formate, sodium propionate, lithium acetate, lithium 
formate, lithium propionate, etc. 
Pure water in the mixture to be oxidized is not required and in fact 
process water may be used over and over at least in part. 
If desired, the addition of a promoter agent to the mixture can be used to 
increase the yield of BCA salts. 
Promoters having the formula R--X--CH.sub.2 --R', are especially useful 
wherein: 
R comprises a radical selected from the group consisting of alkoxy, 
phenoxy, substituted phenoxy, hydroxyl, carboxyl, aldo, keto, phenyl, 
substituted phenyl, alkyl, substituted alkyl, and hydrogen; 
X comprises a radical, with at least two points of substitution, selected 
from the group consisting of benzene ring, substituted benzene ring, 
multi-ring system, substituted multi-ring system, saturated ring, 
substituted saturated ring, and (CH.sub.2).sub.n, where n is an integer of 
at least one; and 
R' comprises a radical selected from the group consisting of hydrogen, 
alkyl, substituted alkyl, phenyl, substituted phenyl, hydroxyl, carboxyl, 
aldo, keto, alkoxy, phenoxy, and substituted phenoxy. 
Preferably, the promoter also comprises at least one easily extractable 
hydrogen, and has the property of increasing the yield of benzene 
carboxylic acid salt thusly produced from said aromatic material by an 
amount higher than the conversion of the aromatic material to benzene 
carboxylic acid in the absence of said promoter. 
While we do not wish to be bound by theory, it is believed that the 
promoter agent controls the oxidation of the feed aromatic material by 
providing a free radical which serves as a chain transfer agent for the 
oxidation reaction, thereby speeding up the rate of oxidation and 
simultaneously controlling the oxidation process so as to increase the 
yield of BCA salts while reducing the conversion of the feed aromatic 
material to carbon dioxide. 
It is preferable that the promoter agent be soluble in the alkaline 
solution used in the oxidation zone. It is especially preferable that the 
promoter agent be completely soluble in the quantity in which it is used 
in the oxidation zone. It is also preferred that the promoter agent have a 
boiling point of about 300.degree. C. or higher in order to prevent 
appreciable vaporization of the promoter agent in the oxidation zone. It 
is also preferred that the promoter agent have a plurality of reactive 
sites, that is, aliphatic groups, alicyclic groups, hydroxyl groups and/or 
substituted groups such as ether groups, ringed ether groups or aromatic 
groups in its chemical structure. 
It is also preferred that the promoter agent have surfactant properties, be 
stable in that it has a good shelf life, and be non-toxic for industrial 
hygiene purposes. 
Preferably about 1 to about 10 parts by weight of water per part by weight 
of feed aromatic material, about 1 to about 10 parts by weight of a water 
soluble reagent per part by weight of feed aromatic material, and about 
0.0001 to about 2 parts by weight of a promoter agent per part by weight 
of feed aromatic material are used in preparing the slurry. In general, 
the water soluble reagent comprises a cation selected from the group 
consisting of alkali metals, ammonium, and mixtures thereof. More than 10 
parts promoter can in some embodiments be used if desired but usually such 
large quantities of promoter are uneconomical. Preferably enough water is 
used to enable the slurry to be pumped. Preferably enough water soluble 
reagent is used to supply the stoichiometric requirements of the reaction. 
The mixture can be formed in any manner in a mixing zone using mixers 
suitable for handling slurries containing solids if a solid or solid-like 
carbonaceous material is used to produce the aromatic carboxylic acid 
salts and BCA salts, or mixers suitable for handling liquids if liquid 
aromatic materials are to be used to produce the carboxylic acid salts. 
The mixture is removed from the mixing zone and fed to a reaction zone 
wherein the mixture is reacted with oxygen, or an oxygen-containing gas 
such as air. The reaction zone and the mixing zone can be, if desired, in 
the same vessel as in some batch-type processes, or they may be separate 
vessels as in some continuous processes. However, a continuous process for 
the oxidation of the aromatic feed material is preferred over a batch 
system not only because of process efficiency but also because yields 
appear to be higher. 
The mixture is treated with oxygen under conditions sufficient to convert 
at least a portion of the aromatic material into BCA salts of the reagent. 
In general, a temperature of about 200.degree. to about 350.degree. C. is 
required. The pressure in the reaction zone should be sufficient to 
maintain a liquid state in the reaction zone. Generally this requires a 
pressure of from about 250 to about 2000 psia and a period of time from 
about 2 minutes to about 4 hours. Preferred conditions of oxidation are a 
temperature from about 250.degree. to about 300.degree. C., a pressure 
from about 1000 to about 1600 psia, and a period of time from about 0.5 to 
about 2 hours. 
Reaction times in the reaction zone depend upon the temperature, degree of 
agitation, the proportion of feed aromatic material, water, and water 
soluble reagent, the solid-to-liquid ratio, and the particle size of the 
solid material. 
During oxidation aromatic carboxylic acids are formed which react with the 
water soluble reagent which comprises a cation selected from the group 
consisting of alkali metals, ammonium, and mixtures thereof to form 
aromatic carboxylic acid salts of the cation of the water soluble reagent. 
The aromatic carboxylic acid salts comprise soluble BCA salts of the 
cation, soluble humic acid salts of the cation, and soluble non-BCA salts 
of the cation. By soluble non-BCA salts as used herein is meant those 
soluble aromatic carboxylic acid salts of the cation which have a lower 
molecular weight than the soluble humic acid salts excluding the soluble 
BCA salts. 
The oxidation products are separated into (1) an aqueous solution which is 
substantially free of undissolved solids and which comprises the soluble 
aromatic carboxylic acid salts of the cation of the reagent, and (2) a 
mixture which comprises mainly solids which comprise the undissolved 
solids in the oxidized product mixture. It is the object of this invention 
to separate the soluble benzene carboxylic acid salts of the cation of the 
reagent from the soluble humic acid salts of the cation of the reagent. 
This invention separates from the aqueous solution of soluble aromatic 
carboxylic acid salts which is substantially free of undissolved solids, 
an aqueous solution which comprises soluble benzene carboxylic acid salts 
which is at least substantially free of soluble humic acid salts and 
undissolved solids. This is accomplished by treating the aqueous solution 
of soluble aromatic carboxylic acid salts with carbon dioxide and an 
inorganic chemical selected from the group consisting of magnesium 
bicarbonate, magnesium carbonate, a double salt of magnesium carbonate, 
and mixtures thereof under conditions operative for converting at least a 
major part, and preferably at least substantially all, of the soluble 
humic acid salts to precipitated magnesium humic acid salts while 
maintaining at least the major part, and preferably at least substantially 
all, of the soluble benzene carboxylic acid salts in solution. The treated 
solution is then separated into a liquid part which comprises at least a 
major part of the soluble benzene carboxylic acid salts and which is at 
least substantially free of the soluble humic acid salts and undissolved 
solids, and a mixture which comprises mainly solids which comprise at 
least a major part, and preferably at least substantially all, of the 
precipitated magnesium humic acid salts, and any other undissolved solids 
in the treated product. This invention, therefore, is useful to separate 
soluble benzene carboxylic acid salts from an aqueous solution which 
comprises other soluble aromatic carboxylic acid salts such as soluble 
humic acid salts. Such a solution containing such mixtures of soluble 
aromatic carboxylic acid salts can be produced from processes other than 
solely the aqueous alkaline oxidation of an aromatic material, as 
described above. Such soluble aromatic carboxylic acid salts can be made 
to comprise a cation selected from the group consisting of alkali metals, 
ammonium, and mixtures thereof. In one embodiment of this invention, such 
soluble aromatic carboxylic acid salts comprise principally soluble 
potassium benzene carboxylic acid salts. In one embodiment of this 
invention when such soluble aromatic carboxylic acid salts are produced by 
the aqueous alkaline oxidation of an aromatic material, the water soluble 
reagent is a water soluble potassium reagent, and in a preferred 
embodiment the potassium reagent is selected from the group consisting of 
potassium carbonate, potassium bicarbonate, and mixtures thereof. 
In general, then, this invention is a process for separating an aqueous 
solution which comprises soluble benzene carboxylic acid salts from an 
aqueous solution which comprises soluble humic acid salts as well as 
soluble benzene carboxylic acid salts. The process comprises treating the 
aqueous solution with carbon dioxide and an inorganic chemical selected 
from the group consisting of magnesium bicarbonate, magnesium carbonate, a 
double salt of magnesium carbonate, and mixtures thereof under conditions 
operative for converting at least a major part of the soluble humic acid 
salts to precipitated magnesium humic acid salts while maintaining at 
least the major part of the soluble benzene carboxylic acid salts in 
solution. The treated aqueous solution is then separated into: (1) a 
second aqueous solution which comprises at least a major part of the 
soluble benzene carboxylic acid salts and which is at least substantially 
free of the soluble humic acid salts and undissolved solids, and (2) a 
mixture which comprises mainly solids which comprise at least a major part 
of the precipitated magnesium humic acid salts. Conditions operative for 
treating the aqueous solution with carbon dioxide and the magnesium 
inorganic chemical are a temperature from slightly above the melting 
temperature of the aqueous solution to be treated to about 100.degree. 
C., a carbon dioxide partial pressure of at least about 1 psi, an amount 
of magnesium inorganic chemical from about 1 to about 10 percent by weight 
of the aqueous solution to be treated, and a period of time of treating 
from about 5 minutes to about 5 hours. Temperatures just above the melting 
point of the solution to be treated are necessary because the reaction 
forming the magnesium humates occurs in the liquid state. Temperatures 
greater than about 100.degree. C., although they can be used, are not 
desirable because the solubility of the carbon dioxide in the aqueous 
solution becomes relatively low, and hence lowers the concentration of 
magnesium bicarbonate formed by its absorption into the solution which in 
turn slows up the precipitation of magnesium humates. Of course, if the 
magnesium inorganic chemical is totally magnesium bicarbonate, then little 
if any carbon dioxide is required since magnesium bicarbonate is readily 
soluble in the aqueous solutions under the conditions operable for 
precipitating magnesium humates. In one preferred embodiment, the 
temperature is from about 10.degree. to about 35.degree. C. Temperatures 
below about 10.degree. C. are not desirable because the cooling costs for 
maintaining the lower temperature become expensive. Similarly, 
temperatures above 35.degree. C. are not desirable because heating costs 
become more expensive, and also the solubility of carbon dioxide decreases 
as the temperature increases. Broadly speaking, carbon dioxide partial 
pressure less than 1 psi are not preferred because the carbon dioxide 
solubility into the aqueous solution becomes very slow. Thus, higher 
carbon dioxide partial pressure are preferred. Carbon dioxide partial 
pressure over about 2,000 psi are not desirable, however, because the 
capital cost of providing high pressure equipment to effect the process is 
substantially more expensive than low pressure equipment. However, high 
carbon dioxide partial pressure does increase the solubility rate of 
carbon dioxide in the aqueous solution, and hence the rate of formation 
and precipitation of magnesium humates. Because of these factors, it is 
preferred to conduct the formation and precipitation of magnesium humates 
at a carbon dioxide partial pressure from about 50 to about 150 psi. 
Carbon dioxide partial pressure below about 50 psi result in decreased 
solubility of the carbon dioxide into the aqueous solution, and hence a 
slowing up of the formation and precipitation of magnesium humates, while 
carbon dioxide partial pressures greater than about 150 psi result in 
higher equipment cost for the process. The period of time of treating with 
the magnesium reagent and carbon dioxide will vary depending on the 
temperature, the selection of magnesium reagent, and/or the partial 
pressure of carbon dioxide. Generally, the period of time for treating is 
from about 5 minutes to about 5 hours. Treating times less than about 5 
minutes probably will not precipitate all the humates unless extremely low 
temperatures and extremely high carbon dioxide partial pressures are used. 
Similarly, treating times greater than about 5 hours usually do not 
improve the precipitation of magnesium humates unless extremely high 
temperatures and extremely low carbon dioxide partial pressures are used. 
Therefore, in this invention it is preferred to use a period of time for 
treating from about 0.5 to about 2 hours. Times less than about 0.5 hours 
may not precipitate all the humates unless low temperatures and high 
carbon dioxide partial pressures are used. While treating times greater 
than about 2 hours usually produce little improvement in magnesium humate 
formation and precipitation unless high temperatures and low carbon 
dioxide partial pressures are used. 
The ratio of magnesium chemical to soluble humate is from about 0.5 to 
about 10 when calculated on a magnesium carbonate and average carboxyl 
group per humate basis. In other words, at least one bicarbonate ion 
should be provided per humate carboxyl group in order to precipitate all 
humates. Ratios greater than about 10 are not desirable merely because the 
cost of the magnesium chemical becomes too expensive. Preferably this 
ratio is from about 1 to about 4, which provides a stoichiometric amount 
of bicarbonate to humate carboxyl group of from 2 times to 8 times 
stoichiometric amount required to precipitate all humates. When the 
aromatic material is selected from the group consisting of coal, coal 
char, coke, chars produced from lignite, pitch, tar, petroleum residium, 
and mixtures thereof, the amount of magnesium inorganic chemical usually 
required is from about 1 to about 10 percent by weight of the solution of 
soluble aromatic carboxylic acid salts based on a magnesium carbonate 
basis for a solution which does not contain undissolved solids. It has 
been found that such solutions produced by the aqueous alkaline oxidation 
of coal usually have between about 1 to about 2 percent humates by weight 
for a solution which does not contain undissolved solids. 
In the preferred embodiment of this invention, the BCA's formed during the 
aqueous alkaline oxidation react with the water reagent to form BCA salts, 
and carbon dioxide or the volatile acid of the reagent, all of which can 
be reclaimed by recycling directly or venting the vapor from the reactor 
and condensing. After treatment with the magnesium inorganic chemical as 
described above the soluble BCA salts can be separated from the mixture by 
evaporation and drying or by other means. The separated BCA salts can be 
recovered or further treated, for example, as by isomerizing to produce 
terephthalic acid salt which can be further treated for production and 
recovery of terephthalic acid. 
Alternatively, the BCA salts while in solution can be converted to BCA's by 
treatment of the soluble BCA salt solution with an acid. The BCA's are 
caused to precipitate at least in part by the aforementioned treatment. 
The precipitate BCA's can then be recovered from the aqueous slurry. 
For example, in one embodiment of this invention, after separating an 
aqueous solution which comprises at least a major part of the soluble BCA 
salts and which is at least substantially free of soluble humates, water 
is removed from the solution in a dewatering zone. In the dewatering zone, 
an amount of water is removed which is sufficient that upon the addition 
of "an acid of said reagent" that at least a portion of the BCA salt will 
be converted to an aromatic carboxylic acid precipitate. The solution will 
contain the regenerated reagent which can be recycled for further use. 
As used above and hereinafter, the expression "an acid of the reagent" 
means an acid which is formed by the replacement of the Group Ia or IIa 
metal atom of the water soluble reagent with hydrogen. For example, if the 
water soluble reagent is potassium acetate then the "acid of the reagent" 
is acetic acid. 
The dewatering zone can be in the same vessel as the reaction zone as in 
some batch processes, or it can be in a separate vessel as in some 
continuous processes. 
The water from the dewatering zone can be used in the mixing zone to supply 
at least part of the water requirements for the mixing zone. 
The dewatered mixture, i.e., the mixture from the dewatering zone, is then 
treated in an acidification zone with an acid of the reagent to convert 
the BCA salt to an aromatic carboxylic acid precipitate and the reagent. 
For example, potassium terephthalate treated with carbonic acid or with 
carbon dioxide is converted to potassium hydrogen terephthalic and 
potassium bicarbonate. 
The acidification zone may be in the same vessel as the dewatering zone as 
in some batch processes, or it can be in a separate acidification vessel 
as in some continuous processes. Sufficient acid is added in this 
embodiment to the mixture to effect the conversion of the BCA salts to 
BCA's and to cause precipitation. 
After forming the BCA precipitate, the precipitate is separated from the 
mixture in a separation zone. Any apparatus capable of separating solids 
from liquids may be used such as a filter. The separated solid comprises 
the BCA precipitate. 
In one embodiment of the invention, the separated liquid from the 
separation zone is treated in a regeneration zone to recover the reagent 
from the liquid. The liquid stream from the acidification zone contains 
both the reagent and an acid of the reagent. The reagent and the acid of 
the reagent are separated in a separation zone. The separated reagent can 
be used for additional treatment of fresh aromatic material in the mixing 
zone whether the process is batch or continuous. The separated acid of the 
reagent can be used to acidify additional material in the acidification 
zone whether the process is batch or continuous. 
In another embodiment of this invention, terephthalic acid is produced by 
drying the BCA salts produced from the feed aromatic material and heating 
the dry BCA's under isomerization conditions of elevated temperature and 
pressure to produce terephthalic acid salt. In one embodiment, 
isomerization is performed without converting the BCA salts to BCA salts 
of a different alkali metal or ammonium prior to isomerizing the BCA 
salts. Thus, for example, in this particular embodiment, sodium salts of 
BCA's are not converted to potassium salts of BCA's prior to 
isomerization, thereby saving the step of converting sodium BCA salts to 
potassium BCA salts prior to isomerization and associated cost. 
The terephthalic acid salt thusly produced is then converted to a 
terephthalic acid, and the water soluble reagent comprising said alkali 
metal or ammonium is regenerated. Terephthalic acid is recovered and the 
water soluble reagent thusly regenerated is recycled to the oxidation zone 
to supply a portion of the water soluble reagent required for producing 
the BCA salts. 
The process is especially preferred where the feed aromatic material is 
coal, the reagent is a potassium carbonate, the promoter agent if used is 
toluic acid, xylene, trimethylbenzene, tetramethylbenzene, 
pentamethylbenzene, hexamethylbenzene, 1,2,3,4-tetrahydronaphthalene, an 
ethoxylated secondary alcohol, or mixtures thereof, and the magnesium 
inorganic chemical is magnesium carbonate.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring to FIG. 1, which is a block diagram of a process for producing 
aromatic carboxylic acid salts, which comprise BCA salts, from coal and 
the isomerization of the BCA salts to terephthalate, a finely divided 
coal, preferably bituminous coal, water, potassium reagent, and, if 
desired, a promoter agent, are introduced into mixing zone 5 through 
conduit 6. The potassium reagent is selected from the group consisting of 
potassium carbonate, potassium bicarbonate, or mixtures thereof. About 2 
to about 10 parts by weight of water, about 1 to about 10 parts by weight 
of potassium reagent based on a K.sub.2 CO.sub.3 basis, and, if desired, 
about 0.0001 to about 2 parts by weight of a promoter agent per part by 
weight of coal are introduced into mixing zone 5. Preferably about 4 to 
about 8 parts by weight of water, about 2 to about 4 parts by weight of 
potassium reagent, and about 0.05 to about 0.15 parts by weight of an 
aromatic organic acid promoter agent per part by weight of coal are used 
in preparing the slurry. In an especially preferred embodiment, about 6 
parts by weight of water, about 3 parts by weight of potassium carbonate, 
and about 0.1 parts of an aromatic organic acid promoter agent, such as 
toluic acid, are added to mixing zone 5 per part by weight of feed coal 
introduced into mixing zone 5. Any type of mixer may be used, although a 
mixer for mixing slurries containing solids is preferred. 
After mixing, the mixture is removed from mixer 5 and introduced into 
oxidizing zone 10, which can comprise an autoclave, through stream 8, 
along with a recycle stream of soluble potassium humates and soluble 
potassium non-BCA salts through conduit 14. An oxygen-containing gas such 
as air or a stream of oxygen is introduced into oxidizing zone 10 through 
conduit 12. From about 1 parts to about 2.4 parts by weight of oxygen per 
part by weight of coal is charged to oxidizing zone 10. Preferably about 2 
parts by weight of oxygen per part by weight of feed coal is charged to 
the oxidizing zone. The coal in the alkaline aqueous slurry is oxidized to 
produce soluble potassium aromatic carboxylic acid salts which comprise 
soluble potassium BCA salts, soluble potassium non-BCA salts, and soluble 
potassium humic acid salts. Carbon dioxide and water are also 
simultaneously produced during the oxidation reaction. 
Oxidizing zone 10 is operated at a temperature of about 200.degree. to 
about 350.degree. C., preferably about 270.degree. C., and at a pressure 
of about 250 to about 2000 psig, preferably about 1000 to about 1600 psig. 
Temperatures below about 200.degree. C. are not desirable because the rate 
of reaction is very slow and temperatures above about 350.degree. C. are 
not desirable because the formation of carbon dioxide is favored over the 
formation of BCA salts. Pressures outside this range can be used; however, 
lower pressures are not desirable because kinetic rates are lower, and 
higher pressures are not desirable because of the cost of high pressure 
equipment and compression costs. Of course, the pressure must be equal to 
or greater than the water vapor pressure in the oxidizer at the oxidation 
temperature. Preferably the contents of oxidation zone 10 are agitated to 
increase product yield and to lower reaction time. 
Gases comprising carbon dioxide and water vapor are removed from oxidation 
zone 10 through line 15 and fed into a condenser (not shown) wherein water 
vapor is condensed and carbonic acid is formed. The condensate and 
remaining uncondensed gas are removed from the condenser and fed to a 
separator where the condensate is separated from the remaining gas 
comprising carbon dioxide in the separator. The gas is removed from the 
separator through one stream, and the condensate through another stream. 
Both the gas and the condensate can be used in subsequent steps in the 
process, if desired. 
The aromatic carboxylic acid salts, including the potassium BCA salts, are 
removed from oxidation zone 10 in stream 16 and fed to separation zone 20 
to separate liquids from solids. Separation zone 20 can comprise a filter, 
such as a precoated revolving drum filter or a vacuum filter. The liquid 
product containing the dissolved newly formed potassium BCA salts is 
removed from separator 20 in stream 22. The solids which contain unreacted 
coal and ash are removed from separation zone 20 in stream 24 and, if 
desired, recycled, preferably after ash removal, to oxidation zone 10 to 
undergo further oxidation for the production of additional aromatic 
carboxylic acid salts including BCA salts. 
Separation step 20 is optional and is not needed if the solids in stream 16 
will not interfere with a subsequent isomerization step, as described 
later. With aromatic feed materials such as coals, however, separation 
step 20 is usually required. 
Liquid stream 22 from separator 20 is fed to mixing zone 30 wherein it is 
mixed with carbon dioxide supplied through conduit 32 and stream 34 which 
comprises a magnesium inorganic chemical selected from the group 
consisting of magnesium bicarbonate, magnesium carbonate, a double salt of 
magnesium carbonate, and mixtures thereof. 
In mixing zone 30 the magnesium inorganic chemical either already comprises 
magnesium bicarbonate or forms magnesium bicarbonate under the conditions 
of temperature, carbon dioxide partial pressure, and residence time 
present in the mixing zone. Should the magnesium inorganic chemical be 
magnesium bicarbonate, then the carbon dioxide partial pressure is of less 
importance. In any event, magnesium bicarbonate, which is soluble, reacts 
with the soluble potassium humates and at least a part of the soluble 
potassium non-BCA salts to produce a magnesium precipitate which comprises 
magnesium humates and magnesium non-BCA salts. In general, at least a 
major part, and preferably substantially all of the soluble potassium 
humates are converted to insoluble magnesium humates, and at least about 
15 percent of the soluble potassium non-BCA salts are converted to 
insoluble magnesium non-BCA salts. Preferably at least about 25 percent of 
the soluble potassium non-BCA salts are converted to insoluble magnesium 
non-BCA salts. It is preferred to operate mixing zone 30 at a temperature 
from about 10.degree. to about 35.degree. C., a carbon dioxide partial 
pressure from about 50 psi to about 150 psi, while agitating over a period 
of time from about 0.5 to about 2 hours. Preferably about 1 to about 10 
parts by weight of magnesium inorganic chemical is mixed with 100 parts by 
weight of solution containing the soluble potassium aromatic carboxylic 
acid salts fed to mixing zone 30 in stream 22, based on a magnesium 
carbonate basis and a solution which is substantially free of undissolved 
solids. 
After the formation and precipitation of magnesium humates and magnesium 
non-BCA salts, the mixture is removed from mixing zone 30 in stream 36 and 
introduced into separation zone 40 wherein the liquids and solids are 
separated. Separation zone 40 can comprise, for example, a filter. 
A mixture which comprises mainly solids which comprise at least a major 
part, and preferably substantially all, of the precipitated magnesium 
carboxylic acid salts is removed from separation zone 40 in stream 42 and 
introduced into mixing zone 50 along with a potassium reagent and water to 
produce a mixture which comprises soluble potassium humic acid salts and a 
magnesium precipitate selected from the group consisting of magnesium 
carbonate, a double salt of magnesium carbonate, and mixtures thereof. The 
potassium reagent is selected from the group consisting of potassium 
carbonate, potassium bicarbonate, and mixtures thereof. The mixture in 
mixing zone 50 is heated under conditions operable for converting 
insoluble magnesium aromatic carboxylic acid salts contained therein to 
soluble potassium humates and soluble potassium non-BCA salts. Also formed 
in mixing zone 50 are potassium carbonate and a magnesium precipitate 
selected from the group consisting of magnesium carbonate, a double salt 
of magnesium carbonate, and mixtures thereof. Conditions operable for 
effecting the formation of soluble potassium humates and soluble potassium 
non-BCA salts in mixing zone 50 are at a temperature from about 25.degree. 
to about 150.degree. C., an amount of potassium reagent from about 0.5 
parts to about 6 parts by weight per part by weight of magnesium salts fed 
to mixing zone 50, and an amount of water from about 5 parts to about 50 
parts by weight per part by weight of magnesium salts fed to mixing zone 
50 in stream 42. 
The mixture is removed from mixing zone 50 in stream 54 and introduced into 
separation zone 60, which can comprise a filter, to separate the solids 
from the liquids. A stream which comprises mainly solids which comprise 
the magnesium inorganic precipitate is recycled to mixing zone 30 by way 
of stream 82 and 34. The liquids removed in stream 14 from separation zone 
60 comprise at least a major part of the soluble potassium humic acid 
salts produced in mixing zone 50. Stream 14 is at least substantially free 
of undissolved solids and dissolved magnesium aromatic carboxylic acid 
salts. 
Liquid stream 44 from separation zone 40 contains at least a major part of 
the soluble potassium BCA salts, and no more than about 85 percent of the 
soluble potassium non-BCA salts produced in oxidation zone 10. Preferably, 
stream 44 contains no more than about 75 percent of the soluble potassium 
non-BCA salts produced in oxidation zone 10. Stream 44 also comprises 
potassium and magnesium bicarbonates. 
Stream 44 is fed to heating zone 70 wherein the liquid is heated to convert 
potassium and magnesium bicarbonates to potassium and magnesium 
carbonates. Preferably, this conversion is achieved by heating the mixture 
with steam. However, an inert gas such as nitrogen could be used to speed 
the removal of carbon dioxide produced in the conversion of the 
bicarbonates to carbonates. Heating zone 70 is heated to a temperature 
from about 80.degree. to about 150.degree. C., for a period of time from 
about 0.1 to about 2 hours. The soluble potassium carbonate and the 
precipitated magnesium carbonate formed in the heating zone are removed in 
stream 72 and fed to separating zone 80 which can comprise a filter, to 
separate liquids and solids. Solids are removed from separating zone 80 in 
stream 82 which comprises the magnesium carbonate and recycled to mixing 
zone 30. Liquid stream 84 comprises a solution of potassium BCA salts, 
potassium non-BCA salts which were not precipitated in separating zone 40, 
and potassium carbonate. 
Stream 84, comprising the soluble potassium BCA salts, is further treated 
so that the potassium BCA salts can be ultimately isomerized to 
dipotassium terephthalate. Preferably, stream 84 is fed to mixing zone 90 
where it is mixed with an isomerization catalyst. The mixture of soluble 
BCA salts and isomerization catalyst is removed from mixing zone 90 in 
stream 92 where it is fed to drying zone 100 which can comprise, for 
example, a spray dryer. A dried mixture suitable for isomerization is 
removed from drying zone 100 in stream 102 and fed to isomerization zone 
110 where it is isomerized. 
In isomerization zone 180, the dry potassium aromatic carboxylic acid salts 
which comprise potassium BCA salts, are catalytically isomerized at a 
temperature of from about 400.degree. to about 440.degree. C., at a 
pressure of from about 5 to about 30 atmospheres, for a period of time of 
from about 10 to about 100 minutes, to cause isomerization of the 
dipotassium benzene dicarboxylic acid salts to dipotassium terephthalate. 
Transcarboxylation reactions can also occur which will contribute to the 
formation of dipotassium terephthalate. 
Preferably, a carbon dioxide atmosphere is maintained in isomerization zone 
110. In an especially preferred embodiment, a portion of the carbon 
dioxide that is produced in oxidation zone 10 is used to create the carbon 
dioxide atmosphere in isomerization zone 110. If desired, gases other than 
carbon dioxide can be removed from the gas from oxidation zone 10 before 
the gas is introduced into isomerization zone 110. In any event, stream 
114, which preferably comprises carbon dioxide, must be substantially free 
of free oxygen and H.sub.2 O. If desired, any inert atmosphere such as 
nitrogen may be introduced into the isomerization zone in stream 114 
rather than the preferred carbon dioxide. 
Examples of catalysts useful for promoting the isomerization are the 
oxides, carbonates, or halides of zinc or cadmium. Organic salts, 
particularly carboxylates such as cadmium benzoate, are particularly good 
catalysts. Cadmium iodide is a preferred catalyst, in concentrations 
varying from 1 to 15 parts by weight per 100 parts by weight of aromatic 
carboxylic acid salts. The preferred concentration of cadmium iodide is 
about 5 parts by weight per 100 parts by weight of the aromatic carboxylic 
acid salt mixture. 
In FIG. 2 and FIG. 3, the steps and streams which have the same element 
number as in FIG. 1 represent identical steps and streams as described 
above with reference to FIG. 1. FIG. 2 also is a schematic block diagram 
of an alternative process for producing terephthalic acid from coal which 
involves a secondary and separate oxidation of humates, rather than the 
recycle of humates as exemplified in FIG. 1 by stream 14. In the 
embodiment of this invention as shown by FIG. 2, the solids separated in 
separating zone 40 which are removed in stream 42, are introduced into 
second oxidizing zone 120 along with water, a potassium reagent selected 
from the group consisting of potassium carbonate, potassium bicarbonate, 
or mixtures thereof, and an oxygen-containing gas such as air, or a stream 
of oxygen, as shown collectively as stream 122. The precipitated magnesium 
aromatic carboxylic acid salts which comprise precipitated magnesium humic 
acid salts, are oxidized under conditions operative to convert the 
precipitated magnesium aromatic carboxylic acid salts to soluble potassium 
aromatic carboxylic acid salts which comprise soluble potassium BCA salts. 
Conditions operative for effecting this oxidation are similar to the 
conditions in oxidizing zone 10. In particular, the operable conditions 
are from about 2 to about 10 parts by weight of water, about 1 to about 10 
parts by weight of potassium reagent based on a K.sub.2 CO.sub.3 basis, 
from about 1 parts to about 2.4 parts by weight of oxygen, and, if 
desired, about 0.0001 to about 2 parts by weight of a promoter agent per 
part by weight of precipitated magnesium aromatic carboxylic acid salts 
fed to oxidizing zone 120. The temperature, pressure, and residence time 
for oxidizing zone 120 are similar to that of oxidizing zone 10. 
The embodiment of this invention in FIG. 2 has the advantage of oxidizing 
the magnesium aromatic carboxylic acid salts without converting all of the 
magnesium humates to soluble potassium humates. Stream 124, containing the 
newly formed soluble potassium aromatic carboxylic acid salts and any 
remaining precipitated magnesium humic acid salts, is removed from 
oxidizing zone 120 and fed to separating zone 130, which can comprise a 
filter, wherein liquids are separated from solids. Liquid stream 132, 
removed from separating zone 130, can be introduced into mixing zone 90 
for further processing along with the soluble potassium BCA salts 
contained in stream 84. Stream 134, which comprises mainly solids which 
comprise precipitated magnesium aromatic carboxylic acid salts, can be 
recycled to secondary mixing zone 30 for further processing until such 
magnesium aromatic carboxylic acid salts are converted ultimately to 
soluble potassium aromatic carboxylic acid salts which comprise potassium 
BCA salts, or carbon dioxide. As in oxidizing zone 10, carbon dioxide is 
produced in oxidizing zone 120 and removed in gaseous vent stream 126. 
Stream 126 can be used as a source of carbon dioxide to be introduced into 
isomerizing zone 110, if desired. The advantage of the FIG. 2 embodiment 
of this invention over the FIG. 1 embodiment is that all of the 
precipitated magnesium aromatic carboxylic acid salts do not have to be 
converted to soluble potassium aromatic carboxylic acid salts before they 
are subjected to additional oxidation. In FIG. 1, where the recycled 
aromatic carboxylic acid salts such as humates are recycled to the same 
oxidation zone as the coal, if magnesium humates rather than potassium 
humates were recycled, a substantial loss of magnesium from the system 
would occur as it is removed with the ash and unreacted coal in stream 24. 
Of course, the magnesium compound could be recovered from the ash but to 
do so is an additional incurred process expense which it is desirable to 
avoid. Thus, if the humates are to be directly oxidized in their magnesium 
form, it is desirable to do so in a zone which is separate from the coal 
oxidation zone to avoid loss of magnesium from the system or alternatively 
an expense recovery step. 
FIG. 3 represents an alternative embodiment of this invention, shown in 
block diagram format, for a process for producing terephthalic acid from 
coal which comprises during the oxidation step the in situ precipitation 
of magnesium humates. In this embodiment, formation and precipitation of 
the magnesium humates and magnesium non-BCA salts occur in situ in 
oxidizing zone 10. A magnesium inorganic chemical is fed to oxidizing zone 
10 in stream 18. At least the major part, and preferably at least 
substantially all of the magnesium inorganic chemical is supplied by way 
of recycle stream 166. Make-up magnesium inorganic chemical selected from 
the group consisting of magnesium bicarbonate, magnesium carbonate, a 
double salt of magnesium carbonate, and mixtures thereof, can be added as 
required to the process in stream 35. Stream 35 is employed to replenish 
magnesium losses which occur in the several embodiments of the process. 
Separating zone 40 in FIG. 3 not only separates the precipitated magnesium 
aromatic carboxylic acid salts which comprise magnesium humates and 
magnesium non-BCA salts, but also ash, any unreacted coal, and any other 
solids in stream 16. New separating zone 140, mixing zone 150, and 
separating zone 160 are required in order to remove ash from the system 
and recover and recycle the magnesium inorganic chemical. In particular, 
mixing zone 50, which can comprise a stripper in all embodiments, converts 
the magnesium aromatic carboxylic acid salts to soluble potassium aromatic 
carboxylic acid salts in the manner similar to that described in FIG. 1 
embodiment. Solids and liquids are removed from mixing zone 50 in stream 
54 and introduced into separating zone 140, which can comprise a filter, 
where liquids are separated from solids. Liquid stream 14, which comprises 
soluble potassium aromatic carboxylic acid salts which comprise potassium 
humates, no more than about 85 percent of the non-BCA salts and preferably 
no more than about 75 percent of the non-BCA salts which were produced in 
oxidizing zone 10, and recycle potassium reagent in the form of potassium 
carbonate, potassium bicarbonate, or mixtures thereof, is recycled to 
oxidizing zone 10 in stream 14. Solids are removed from separating zone 
140 in stream 144 and fed to mixing zone 150, along with water and carbon 
dioxide. Stream 144 comprises coal ash, unreacted coal, and a precipitated 
magnesium inorganic chemical selected from the group consisting of 
magnesium carbonate, a double salt of magnesium carbonate, and mixtures 
thereof. In mixing zone 150, the precipitated magnesium inorganic chemical 
is converted to soluble magnesium bicarbonate which is separated from the 
remaining solids in the stream in separating zone 160 which can comprise a 
filter. A magnesium bicarbonate solution is removed from separating zone 
160 by way of stream 162 which is then recycled to oxidation zone 10 
through means streams 166 and 18. Ash and other solids in stream 154 are 
removed from the separating zone in stream 164. FIG. 3 embodiment of this 
invention has the advantage that the coal or other aromatic carbonaceous 
material is treated with the magnesium inorganic chemical during oxidation 
of the fed aromatic material to precipitate magnesium humates and 
magnesium non-BCA salts in situ without the necessity of separation of the 
ash and unreacted coal immediately after the oxidizing step as provided in 
oxidizing zone 10. 
In general, it is to be understood that streams such as streams 6, 52, 122 
and 152, although showing the various reactants entering the various zones 
in one stream, can be fed to the various zones in separate streams. For 
example, the oxygen schematically shown entering oxidizing zone 120 of 
FIG. 2, along with water and the potassium reagent, usually will be fed 
separately to the oxidizing zone. This and other minor variations through 
the process can be readily adapted to fit the needs of specific aromatic 
feed materials to be oxidized, as will be apparent to one skilled in the 
art. Furthermore, although these embodiments are preferred, it is to be 
understood that the use of coal as the aromatic feed material and the use 
of a potassium reagent selected from the group consisting of potassium 
carbonate, potassium bicarbonate, and mixtures thereof, many other 
aromatic feed materials can be oxidized by this invention and any alkaline 
reagent which produces an alkaline solution by hydrolysis and which 
comprises a cation selected from the group consisting of alkali metals, 
ammonium, and mixtures thereof, can be used as the water soluble reagent. 
EXAMPLE 1 
MAGNESIUM TREATMENT ON A TYPICAL COAL OXIDATION PRODUCT 
50 ml of an aqueous solution of oxidation product from the caustic 
oxidation of coal was treated at 25.degree. C., with 2.000 gram of 
magnesium carbonate and pressurized to 200 psig with CO.sub.2. The slurry 
was stirred for 1 hour, depressurized, and immediately filtered. The 
precipitate was black due to the magnesium salts of humic acids, and the 
solution was orange in color, homogeneous, and clear. The amount of 
soluble solids in the filtrate and the amount of precipitated solids were 
determined and are reported in Table 1. A second experiment was conducted 
identical to the first but in which the magnesium carbonate treatment was 
carried out at 40.degree. C. instead of room temperature. The results of 
these experiments are also shown in Table 1. 
These data show that the procedure precipitates about 30% of the non-BCA 
coal acids and all of the humic acids as magnesium salts in the coal 
oxidation product. These precipitated aromatic acids, as their magnesium 
salts, can be liberated by treating with potassium carbonate, which will 
precipitate the magnesium as the extremely insoluble carbonate and convert 
the precipitated magnesium aromatic acid salts into soluble potassium 
salts. 
EXAMPLE 2 
OXIDATION USING THE MAGNESIUM PRECIPITATE-RECYCLE 
An oxidation experiment using the recycle embodiment of this invention was 
carried out using a batch coal oxidation unit (BCOU). The heart of the 
BCOU is a 300 ml Autoclave Engineer Magnadive autoclave. The BCOU is set 
up so that air can be continuously purged through the batch reactor 
without water loss from the system. CO.sub.2 produced during the oxidation 
is collected from the off-gas from the reactor and quantitatively 
determined by weighing. 
TABLE 1 
______________________________________ 
Magnesium Carbonate Treatment of Coal Oxidation Product 
BCA Content Humic Acids 
Non-BCA 
(Wt. % of (Wt. % of (Wt. % of 
Sample Solids).sup.(1) 
Solids).sup.(1) 
Solids).sup.(1) 
______________________________________ 
Oxidation Product; 
Sample No. A-92 
4.02 .+-. 0.4.sup.(2) 
6.1 11.3 
First 
Experiment 
at 25.degree. C. 
Filtrate 3.71 nil 8.12 
Precipitate nil 6.6 3.5 
Second 
Experiment 
at 40.degree. C. 
Filtrate 4.2 nil 9.9 
Precipitate nil 6.7 2.7 
______________________________________ 
.sup.(1) Percentages are based on the weight of soluble solids, calculate 
as acids, in Sample No. A92 (first entry). 
.sup.(2) Average of several analyses. 
For this recycle experiment the following feeds were prepared: 
Slurry I 15 gram air weathered Pocahontas coal, 45 gram K.sub.2 CO.sub.3, 
1.5 gram toluic acid, 0.73 gram 85% by weight KOH pellets diluted to 500 
gram total weight with di-ionized water (D.I.H.sub.2 O). This slurry was 
then ball milled for 16 hours prior to use. 
Slurry II 45 gram air weathered Pocahontas coal, 45 gram K.sub.2 CO.sub.3, 
4.5 gram m-toluic acid, 2.2 gram 85% by weight KOH pellets diluted to 600 
gram total weight with D.I.H.sub.2 O. This slurry was then ball milled for 
16 hours prior to use. 
Solution A 93.75 gram of K.sub.2 CO.sub.3 in 500 gram of D.I.H.sub.2 O. 
Oxidation Cycle 1 
150 grams of Slurry I were placed in the BCOU. The BCOU was then heated to 
280.degree. C. at a nitrogen pressure of 1300 psig, introduced to the BCOU 
at a rate of 750 ml/min (STP). Once the BCOU reached equilibrium the 
N.sub.2 flow was switched to an air flow of 750 ml/min. The air flow was 
continued for 30 minutes after which time the N.sub.2 flow was 
re-established and all the CO.sub.2 produced was swept into an ascarite 
trap for measurement. The reactor was then cooled and the entire reactor 
product was treated with 4 grams MgCO.sub.3 and gaseous CO.sub.2. After pH 
of the solution reached 8 the CO.sub.2 treatment was continued for another 
45 minutes. The slurry was then filtered, the solid washed with 
D.I.H.sub.2 O and the entire liquid product was freeze-dried and submitted 
for BCA analysis. The filtered solid thusly produced was treated with 60 
grams of Solution A and the mixture heated to boiling for 5 minutes. The 
resulting slurry was then filtered, the solid washed with water (this 
solid was acidified, dried and analyzed for carbon hydrogen) and the 
entire liquid product (filtrate plus washing) was added to 30 grams of 
Slurry II, diluted to 150 grams, and charged to the BCOU. 
Multiple Cycle 
In this experiment, the procedure as described above for "Oxidation Cycle 
1", was repeated until samples from five cycles were collected. The 
results are given in Table 2. These results clearly show the recycle 
embodiment of this invention results in effective separation of humic acid 
salts. These salts are then recycled for further oxidation. The 
selectivity of the conversion of coal to BCA salts for this multiple 
recycle run is significantly improved over a run without recycle of 
humates. Based on this selectivity the calculated BCA yield for this 
multiple recycle embodiment was 37 mole %. This improvement is even more 
pronounced when it is appreciated that the above conditions in the recycle 
embodiment were not optimized. Considerably better yields can be expected 
after optimization. 
A yield of 32 mole percent was obtained using optimized conditions on a 
single pass experiment without recycle. 
TABLE 2 
______________________________________ 
RESULTS OF 5 CYCLE RECYCLE OXIDATION RUN 
Carbon Distribution in Product 
Grams Grams Grams of 
Coal Grams of Carbon 
Carbon Carbon Grams Carbon 
as Humic 
Cycle Feed to to Unreacted 
to & Non-BCA 
No. Reactor CO.sub.2 
Carbon BCA Acids 
______________________________________ 
1 3.91 .32 .98 .14 .4 
2 1.95 .23 .53 .22 .7 
3 1.95 .30 .92 .18 .6 
4 1.95 .31 .19 .38 1.1 
5 1.95 .30 .16 .12 .4 
Final 
Residue 
N/A N/A N/A N/A 3.9.sup.(3) 
TOTAL 11.71 1.76 2.78 1.04 7.1 
______________________________________ 
##STR1## 
- - 
##STR2## 
- - 
##STR3## 
- - 
-Calculated BCA yield based on BCA/CO.sub.2 selectivity = 37 mole % 
.sup.(3) by difference 
N/A = not applicable 
Industrial Applicability 
Benzene carboxylic acids can be used as precursors for producing more 
valuable chemicals such as terephthalic acid. As previously described, dry 
potassium benzene carboxylic acids can be isomerized to produce 
terephthalic acid. Terephthalic acid is useful as a precursor for 
producing polyesters which are useful for producing fibers for the garment 
industry and plastic containers for liquids and other materials in the 
bottle or container industry. Benzoic acid is useful as a precursor to 
valuable chemicals such as phenol. 1,3,5-benzenetricarboxylic acid is 
useful as a crosslinking agent in the polymer industry. 1,3-benzene 
dicarboxylic acid has been used as a monomer for polyester. Furthermore, 
the octyl esters of the latter two acids are useful as plasticisers.