Adipic Acid

Adipic Acid
Michael Tuttle Musser, E. I. DuPont de Nemours & Co., Sabine River Laboratory, Orange, Texas 77631,
United States

1.
2.
3.
4.
4.1.
4.2.
4.3.
5.
6.

Introduction . . . . . . . . . . . . . . . . .
Physical Properties . . . . . . . . . . . .
Chemical Properties . . . . . . . . . . .
Production . . . . . . . . . . . . . . . . . .
Nitric Acid Oxidation of Cyclohexanol
Butadiene-Based Routes . . . . . . . . .
Other Routes . . . . . . . . . . . . . . . .
Byproducts . . . . . . . . . . . . . . . . .
Quality Specications . . . . . . . . . . .

1
1
2
2
2
4
5
5
5

1. Introduction
Adipic acid, hexanedioic acid, 1,4-butanedicarboxylic acid, C6 H10 O4 , M r 146.14,
HOOCCH2 CH2 CH2 CH2 COOH [124-04-9], is
the most commercially important aliphatic dicarboxylic acid. It appears only sparingly in nature but is manufactured worldwide on a large
scale. Its primary application is in the production
of nylon 66 polyamide, discovered in the early
1930s by W. H. Carothers of DuPont. Manufacture of nylon 66 polyamide ber has grown
to become one of the dominant processes in the
synthetic ber industry. The historical development of adipic acid was reviewed in 1977 [5].

2. Physical Properties [6]

Adipic acid is isolated as colorless, odorless
crystals having an acidic taste. It is very soluble in methanol and ethanol, soluble in water
and acetone, and very slightly soluble in cyclohexane and benzene. Adipic acid crystallizes as
monoclinic prisms from water, ethyl acetate, or
acetone/petroleum ether. Some physical properties of adipic acid follow:

c 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

10.1002/14356007.a01 269

7.
8.
8.1.
8.2.
9.
10.
11.
12.

Storage and Transportation . . . . .

Derivatives . . . . . . . . . . . . . . . . .
Adiponitrile . . . . . . . . . . . . . . . .
Other Derivatives . . . . . . . . . . . .
Uses . . . . . . . . . . . . . . . . . . . . .
Economic Aspects . . . . . . . . . . . .
Toxicology and Occupational Health
References . . . . . . . . . . . . . . . . .

mp, C
bp, C
at 101.3 kPa
at 13.3 kPa
at 2.67 kPa
at 0.67 kPa
at 0.133 kPa
Relative density (170 C)
Bulk density, kg/m3
Solubility, g/100 g water
at 15 C
at 40 C
at 60 C
at 80 C
at 100 C
Dissociation constants
k1
k2
Specic heat of liquid (200 C),
kJ kg1 K1
Specic heat of vapor (300 C),
kJ kg1 K1
Heat of fusion, kJ/kg
Heat of vaporization, kJ/kg
Heat of solution in water, kJ/kg
10 20 C
90 100 C
Melt viscosity, mPa s
at 160 C
at 193 C

.
.
.
.
.
.
.
.

6
6
6
7
7
8
8
9

152.1
337.5
265
222
191
159.5
1.085
600 700
1.42
4.5
18.2
73
290
4.6 105
3.6 106
2.719
1.680
115
549
214
241
4.54
2.64

Flammability and explosion data are summarized in the following:

Closed cup ash point
Cleveland open cup ash point
Autoignition temperature
Dust cloud ignition temperature
Minimum explosive concentration
(dust in air)
Minimum cloud ignition energy
Maximum rate of pressure rise

196 C
210 C
420 C
550 C
0.035 kg/m3
600 J
18.6 MPa/s

Adipic Acid

3. Chemical Properties
Adipic acid is stable in air under most conditions, but heating of the molten acid above
230 250 C results in some decarboxylation to
give cyclopentanone [120-92-3], bp 131 C. The
reaction is markedly catalyzed by salts of metals,
including iron, calcium [7], and barium [8]. The
tendency of adipic acid to form a cyclic anhydride by loss of water is much less pronounced
compared to glutaric or succinic acids [9].
Adipic acid readily reacts at one or both carboxylic acid groups to form salts, esters, amides,
nitriles, etc. (Chap. 8). The acid is quite stable
to most oxidizing agents, as evidenced by its
production in nitric acid. However, nitric acid
will attack adipic acid autocatalytically above
180 C, producing carbon dioxide, water, and
nitrogen oxides.

4. Production
Early commercial processes for manufacturing adipic acid involved a two-step air oxidation of cyclohexane [110-82-7]. Oxidation of
cyclohexane to cyclohexanol cyclohexanone
at low conversion was followed by a highconversion process for air oxidation of the mixture to adipic acid. Currently (2000), however,
all large-scale production is via nitric acid oxidation of cyclohexanol [108-93-0], cyclohexanone [108-94-1], or a mixture of the two
[ketone alcohol (KA) oil].
Differences among commercial processes are
mainly in the manufacture of the KA oil. The
six carbon atoms of the adipic acid backbone
usually come from benzene, which is hydrogenated to cyclohexane, or phenol, which is hydrogenated to cyclohexanol. The cyclohexane is
then oxidized with air to KA oil. In the past 20
years, there has been a shift to the lower cost cyclohexane-based process [10]. (For KA production, see Cyclohexanol and Cyclohexanone).
Since the early 1980s, a great deal of research
has been carried out on the synthesis of adipic
acid from butadiene and carbon monoxide (Section 4.3). However, no commercial plant based
on this technology is currently in operation.

4.1. Nitric Acid Oxidation of

Cyclohexanol
Reaction Mechanism. The second step of
the conventional process, developed by DuPont
in the late 1940s, involves the oxidation of cyclohexanol, cyclohexanone, or a mixture of both
with nitric acid [11], [12]. Adipic acid is obtained in greater than 90 % yield. Major byproducts are carbon dioxide, nitrogen oxides, and
some lower molecular mass dicarboxylic acids.
Some byproducts arising from impurities in the
starting KA oil are also present.
The chemical mechanism was discussed originally in 1956 [13] and later in greater detail
[14], [15]. The latter reports include kinetic and
reactor design considerations. Results of related
studies, especially on the later stages of the reaction, were published at about the same time
[1618]. A summary of the ndings of these investigations is given in Figure 1.
Cyclohexanol (1) is oxidized to cyclohexanone (2), accompanied by generation of nitrous acid. The cyclohexanone then reacts by
one of three possible pathways leading to
the formation of adipic acid (8). The major fraction of the reaction occurs via nitrosation to produce 2-nitrosocyclohexanone (3),
then by further reaction with nitric acid to
form the 2-nitro-2-nitrosoketone (6). Hydrolytic
cleavage of this intermediate gives 6-nitro-6hydroximinohexanoic acid, also known as nitrolic acid (9). This breaks down further to give
adipic acid and nitrous oxide, the main unrecovered nitric acid reduction products. Typically
2.0 mol of nitric acid is converted to nitrous
oxide for each mole of adipic acid produced.
The second pathway occurs at higher temperature, where nitration predominates. At these
elevated temperatures, the pathway via the dinitroketone (4) becomes signicant.
The third path proposed by the early investigators involves the intermediate formation of the
1,2-diketone (5) or its dimer. Conversion of this
material to adipic acid in good yield requires the
use of a vanadium catalyst. The effect of vanadium on the overall yield suggests a signicant
contribution by this pathway.
The intermediate nitrosoketone (3) can undergo two important side reactions. Multiple nitrosation leads to the intermediate (10), which
loses carbon dioxide to produce glutaric acid

Adipic Acid

Figure 1. Reaction paths in nitric acid oxidation of cyclohexanol

(11) or succinic acid from subsequent reaction

with nitric acid. Copper metal is added to the nitric acid to inhibit these reactions. In systems
containing a relatively high steady-state concentration of the nitrosoketone (3) or the tautomeric oximinoketone, a Beckmann-type rearrangement leads to 5-cyanopentanoic acid (12)
in minor amounts. This material is slowly hydrolyzed to adipic acid.
Commercial Nitric Acid Oxidation Processes. The basic technology for carrying out
the nitric acid oxidation of cyclohexanol cyclohexanone (KA) remains similar to that described
in the early patent literature. Advances have centered on improvement in byproduct removal,
catalyst and nitric acid recovery, and suppression
of nitrous oxide, a greenhouse gas which was
traditionally vented to the atmosphere. Because
of the corrosive nature of nitric acid, plants are
constructed of stainless steel (type 304L or better), or of titanium in areas of most severe exposure. The block ow diagram in Figure 2 shows
a typical layout for a commercial nitric oxidation process [5], [19]. The reaction is carried out

in a continuously circulated loop of nitric acid

mother liquor (NML) that passes through the entire system, as shown by the bold line.

Figure 2. Flow diagram of a process for nitric acid oxidation of cyclohexanone cyclohexanol
a) Reactor; b) Cleanup reactor; c) NOx bleacher; d) Nitric
acid absorber; e) Concentrator; f) Crystallizer; g) Filter or
centrifuge; h) Dryer; i) Cooler

The reactor (a) is essentially a large

heat exchanger, controlled at 60 80 C and

Adipic Acid

0.1 0.4 MPa. To this is fed the recycled

NML, the KA feed material, the makeup
acid containing 50 60 % nitric acid and the
copper vanadium catalyst [20], [21]. Residence time in (a) is less than 5 min. In some facilities, the efuent is passed through a second reactor (b) at elevated temperature (110 120 C)
[22]. This high-temperature converter (b) can
be used to complete the reaction and reduce
the amount of impurities which need to be removed through crystallization. The reaction is
very exothermic (6280 kJ/kg) and normal heatexchanger surfaces tend to frost, leading to loss
of temperature control. Several different reactor
designs have been patented which aid in removing the heat of reaction and minimizing energy
usage in the process [2328]. An excess of recycled NML to KA feed stream of at least 3 : 1
and up to 1000 : 1 is maintained to control the
reaction and improve the yield [21].
The product stream is passed through a
bleacher (c), in which excess dissolved nitrogen oxides are removed with air and sent to
the absorber (d), where they are reabsorbed and
recovered as nitric acid. The off-gas from the
absorber can be used to initiate the oxidation
at lower temperatures by passing it through the
KA feed stream before it is fed to the oxidizer
[2931]. Removal of the NOx from the off-gas
by scrubbing with KA has also been described
[32]. The water produced in the process is then
removed in a concentrating still (e) that is usually operated under vacuum. The concentrated
product stream is either recycled to the reactor
with diversion of a portion to product recovery
or passed to product recovery prior to recycle of
the NML ltrate. Crude adipic acid is removed
from the NML loop by crystallization (f) followed by subsequent ltration or centrifugation
(g) [3335]. A portion of this efuent stream,
which contains high concentrations of glutaric
acid, succinic acid, and byproducts, is processed
to recover the vanadium and copper catalysts and
remove the byproduct acids. Metal recovery is
usually accomplished by ion exchange [36]. The
crude adipic acid from the rst crystallizer (g)
is dissolved and recrystallized at least one additional time before proceeding to a dryer (h) and
a cooler (i). If the adipic acid is not needed in
dry form, the crystals from the centrifuge/lter
(g) can be dissolved in water and added to a so-

lution of aqueous 1,6-hexanediamine to make

nylon salt.
Other improvements of the conventional process have been described [37], especially in connection with separation and recovery of the dibasic acid byproducts [3841]. The crude adipic
acid is rened to varying degrees, depending
upon the end use, but usually is recrystallized
from water. Destruction of impurities by reuxing in 60 % nitric acid containing dissolved
vanadium has been claimed to produce highquality product [42].

4.2. Butadiene-Based Routes

In the early 1970s, BASF began an extensive research program on producing dimethyl adipate,
a diester that could be hydrolyzed to adipic acid.
The process involved carbomethoxylation of butadiene with carbon monoxide and methanol to
give methyl 3-pentenoate using a cobalt catalyst
and pyridine at high-pressure [43]. The methyl
3-pentenoate was then separated from byproducts by distillation. The second carbomethoxylation to give dimethyl adipate occurs at lower
pressure but requires a lower pyridine to cobalt
ratio [44]. The hydrolysis of the diester to adipic
acid and methanol is a high-yield catalytic process [45]. The overall yield from butadiene appears to be about 70 %. It is believed this process
has been demonstrated on a pilot-plant scale, but
not yet commercialized.
In the mid-1980s, DuPont also began a major
program on a butadiene-based route. In contrast
to the BASF diester route, it involved the direct
dihydrocarboxylation of butadiene to adipic acid
(Fig. 3). The rst step [46], which can be catalyzed by palladium, rhodium, or iridium, leads
to largely 3-pentenoic acid (12). The second
step [47], catalyzed by rhodium or iridium gives
adipic acid (13), 2-methylglutaric acid (14), and
2-ethylsuccinic acid (15). The advantage of this
process was that the 2-methylglutaric and 2ethylsuccinic acids could be isomerized to adipic
acid by the same catalyst system [48]. The catalyst seems to require a halide promoter, such as
hydroiodic acid. The solvent for this process is
usually a saturated carboxylic acid, such as pentanoic acid, which is a byproduct of the process.
Since the late 1980s most major chemical com-

Adipic Acid
panies have issued numerous patents on variations of these butadiene based routes [4951].

acid to cyclohexene and subsequent oxidation

of the resulting ester with nitric acid [67]. Formation of adipic acid derivatives by electrolytic
coupling of acrylates has also been described
[68].

5. Byproducts

Figure 3. Hydrocarboxylation of butadiene to adipic acid

4.3. Other Routes

In addition to the commercial two-step air/nitric
acid oxidation of cyclohexane and the carboxylation/carbomethoxylation of butadiene, several other processes have been investigated.
Research at Monsanto on palladium halide
catalyzed dicarbonylation of 1,4-disubstituted
2-butenes was reported in early 1984 [52].
This process produces adipic acid from 1,4dimethoxy-2-butene, carbon monoxide, and palladium chloride at 100 C after the resulting unsaturated dimethyl ester has been hydrogenated
and hydrolyzed.
The one-step oxidation of cyclohexane with
nitric acid [53], [54], nitrogen dioxide [55], or
air has been described. The one-step all-air oxidation of cyclohexane is economically very attractive and has been heavily researched. Early
work was performed by Gulf Research and Development [5658], Asahi Chemical Industries
[59], [60], and others [61]. For example, cyclohexane is oxidized in one step to adipic acid in
70 75 % yield, in the presence of a cobalt acetate catalyst in acetic acid as solvent [59]. More
recently, there has been renewed interest in this
work, and several patents have been issued to
Redox Corporation and Bayer. [6265].
Adipic acid can be produced by ozonolysis of
cyclohexene [66] or by addition of a carboxylic

The major byproducts of nitric acid oxidation

of KA are glutaric acid [110-94-1] and succinic
acid [110-15-6], and minor amounts of pentanoic acid and hexanoic acid are also formed. In
commercial operations, the nitric acid reaction
medium (NML) contains high concentrations of
glutaric and succinic acids, resulting from the
recycling of the mother liquor after crystallization of the adipic acid. A portion of this stream is
diverted and processed separately to remove the
byproduct acids and recover nitric acid and the
copper and vanadium catalysts. Early commercial processes discarded these byproduct acids.
However, most companies now recover these
acids either as a mixture of dibasic acids (DBA)
or convert them to dibasic esters (DBE) for a
variety of uses.
Following the removal of the copper and
vanadium by ion exchange and distillation of
the nitric acid in water, methanol can be added
to convert the acids to their methyl esters. Then
the esters are distilled to give a mixture or the
individual esters [6971].
Sometimes the acids are removed by distillation to produce a mixture of acids and anhydrides, especially glutaric anhydride [108-55-4]
and succinic acid [108-30-5] [7276]. Separation of the individual acids by crystallization
and extraction with organic solvents has been
described [77], [78]. Other means of separating the byproduct acids include addition of inorganic salts [79], a C1 C6 primary alkylamine
[80], or urea [81], and extraction by a ketone
solvent [82].

6. Quality Specications
Commercial adipic acid is one of the purest
large-scale manufactured chemicals because of
the stringent requirements of its major consumer, the synthetic bers industry. The U.S.

Adipic Acid

FDA has approved adipic acid as a food additive.

Because essentially all adipic acid manufacturers use a nitric acid oxidation process, impurities
are similar. Purity is affected mostly by variations in the synthesis of the KA intermediate
and in the extent of adipic acid recrystallization
and purication. Some typical specications for
food-grade adipic acid are: color, APHA equivalence (Hazen) 10 max., water 0.2 % max., ash on
ignition 10 ppm max., iron 1.0 ppm max., adipic
acid content 99.6 % min. [83].
Procedures for analysis of food-grade adipic
acid are described in [84]. General methods for
water (Karl Fischer), color in methanol solutions
(APHA), iron, and other metallic impurities in
commercial acid have been summarized [85].
Resin-grade adipic acid frequently has limits for
succinic (ca. 50 ppm) and caproic (ca. 30 ppm)
acids, and for hydrocarbon oils (ca. 15 ppm).
Carboxylic acids can be determined by gas chromatography of their esters or by liquid chromatography of the free acids [86]. Total nitrogen can be determined by chemical reduction
and distillation of ammonia from an alkaline solution. Hydrocarbon oil may be determined by
IR analysis of a halocarbon extract of a solution
of the salt.

7. Storage and Transportation

Adipic acid is conveyed pneumatically or mechanically from the drying equipment to the storage or shipping container. These containers may
be aluminum or stainless steel railroad hopper
cars, trucks, plastic bags, or drums. Principal
hazards in handling adipic acid are the danger
of dust explosion and skin or mucus membrane
irritation on exposure to the dust. Particle size
control and ow characteristics are also important factors due to the tendency of adipic acid
that contains excessive nes to cake during storage.

8. Derivatives
8.1. Adiponitrile
The most important derivative of adipic
acid is adiponitrile, 1,6-hexanedinitrile, 1,4dicyanobutane, [111-69-3], M r 108.14, bp

298 300 C (at 101.3 kPa), 154 C (at 1.3 kPa),

25
fp 2.4 C, n25
D 1.4370, d 4 0.9599, an intermediate in the manufacture of the other major
nylon 66 component, 1,6-hexanediamine. The
original production process involved conversion
of the acid to the dinitrile by liquid- [87] or
vapor-phase dehydration [88] of the ammonium
salt in the presence of phosphoric acid or a
boron phosphorus catalyst. Although this was
the predominate technology used for adiponitrile production in the past, it is no longer used
by any major nylon 66 producers.
Other routes which have been used include a
process by Celanese, which in the 1960s and
1970s avoided manufacturing adiponitrile by
producing 1,6-hexanediamine from ammonolysis of 1,6-hexanediol, which in turn was made
by the hydrogenation of adipic acid [89]. This
adipic acid based route was shut down around
1980. In 1948, DuPont introduced, and for several years operated, a process based on furfural
[90]. From 1951 to 1983, DuPont operated a butadiene chlorination process [91]. The intermediate 1,4-dichloro-2-butene was converted to 3hexenedinitrile with sodium cyanide and then
hydrogenated to adiponitrile. Current adiponitrile manufacture is based on either propylene
or direct hydrocyanation of butadiene.
In 1965 Monsanto introduced a process involving the electrolytic coupling of acrylonitrile
[92]. This process, or variations of it, is also used
in the United Kingdom and Japan. DuPont began the direct hydrocyanation of butadiene in
1972 [93]. Now all DuPont adiponitrile production, including a joint venture with RhonePoulenc (now Rhodia) in France, uses this technology. The process consists of a two step hydrocyanation, catalyzed by a nickel(0) phosphite complex and promoted by certain Lewis
acids [9496]. The mixture of isomeric pentenenitriles and methylbutenenitriles produced in
the rst step is isomerized to predominately 3and 4-pentenenitrile [9799]. Subsequent antiMarkovnikov addition of hydrogen cyanide to
the pentenenitriles produces adiponitrile.
Other routes that have been revealed include chemical dimerization of acrylonitrile to
3-hexenedinitrile [100102] and hydrocyanation of butadiene with a copper halide catalyst to yield 3-pentenenitrile [103], followed
by disproportionation to dicyanobutenes and

Adipic Acid
butenes. Finally, another dimerization route to
adiponitrile involves the addition of acrylonitrile to 2-methyleneglutaronitrile in the presence
of zinc or cobalt complexes and a Lewis base
[104]. The dimer is then hydrocyanated to 1,2,4butanetricarbonitrile followed by dehydrocyanation to 3-hexenedinitrile [105].

8.2. Other Derivatives

Salts. Adipic acid forms alkali metal and ammonium salts that are water-soluble and alkaline earth salts that are only moderately soluble.
Their solubilities in 100 g of water are: diammonium salt [3385-41-9] 40 g (14 C), disodium
salt [7486-38-6] 59 g of hemihydrate (14 C),
dipotassium salt [19147-16-1] 65 g (15 C), calcium salt [22322-28-7] 4 g of monohydrate
[18850-78-7] (13 C), 1 g of anhydrous salt
(100 C).
The most common salt is poly(1,6hexanediammonium hexanedioate), produced
by interaction of adipic acid with 1,6hexanediamine. This water-soluble salt, the precursor to nylon 66, is readily shipped or stored
prior to the nal polyamidation, which occurs
with the removal of water. The chemistry of this
step has been reviewed [106].
Esters and Polyesters. The esters and
polyesters of adipic acid constitute the largest
non-polyamide market for adipic acid. Esters
made from long-chain alcohols are used as
plasticizers and lubricants, while those from
short-chain alcohols are used primarily as solvents. Reuxing adipic acid with methanol in
the presence of an acid catalyst can produce
monomethyl adipate, along with the diester.
Electrolysis of the salt of the monoester (Kolbe
synthesis) produces dimethyl sebacate, another
polyamide precursor. The boiling points of some
esters are listed in Table 1. The esters dissolve
readily in most organic solvents. While dimethyl
adipate is the most commonly used solvent, di2-ethylhexyl adipate is the most widely used
plasticizer. Other simple adipate plasticizers include the n-octyl, n-decyl, isodecyl, and isooctyl
esters. More complex polymeric plasticizers,
prepared from glycols, account for a little less
than half the adipic acid based plasticizers. Low

molecular mass polyester polyols having hydroxyl end groups are used with polyisocyanates
to produce polyurethane resins.
Table 1. Boiling points of adipic acid esters
Ester
Monomethyl
Dimethyl
Monoethyl
Diethyl
Di-n-propyl
Di-n-butyl
Di-2-ethylhexyl
Di-n-nonyl
Di-n-decyl

[627-91-8]
[627-93-0]
[626-86-8]
[141-28-6]
[106-19-4]
[105-99-7]
[103-23-1]
[151-32-6]
[105-97-5]

p, kPa

bp, C

1.3
1.7
0.9
1.7
1.5
1.3
0.67
0.67
0.67

158
115
160
127
151
165
214
230
244

Anhydrides. The usual form of the anhydride produced by dehydrating adipic acid is the
linear, polymeric form [2035-75-8]. Distillation
of the polymeric anhydride is said to produce the
monomeric cyclic form, which is very unstable
and reverts readily to the linear, polymeric anhydride.
Amide. The
diamide,
C6 H12 N2 O2
[628-94-4], mp 228 C, is practically insoluble
in cold water. It has been traditionally prepared
from the dimethyl ester by treatment with concentrated ammonium hydroxide or by heating
the diammonium salt of adipic acid in a stream
of ammonia. Other substituted amides can be
prepared from amines by the usual synthetic
methods.

9. Uses
About 80 % of worldwide adipic acid consumption is used for the manufacture of nylon 66
bers and resins. This is down from about 87 %
in 1981. Table 2 summarizes consumption in
three major regions of the world. A small amount
of adipic acid is still used captively to produce
adiponitrile.
Large amounts are converted to esters for
use in plasticizers, lubricants and in a variety
of polyurethane resins. The monomeric esters
are important plasticizers for poly(vinyl chloride) and other resins, while polymeric esters
are used when unusually high plasticizer levels are required. Polyurethane resins employing
adipic acid are produced from polyisocyanates
and polyester polyols (adipates). These are used

Adipic Acid

in specialty foams, lacquers, adhesives, surface

coatings and spandex bers for stretch-wear.

Table 3. Worldwide adipic acid capacity as of January 1999 [113]

Region

Capacity, 103 t/a

Major producers
(capacity, 103 t/a)

North America

1058

Western Europe

841

DuPont (740), Solutia

(295), Allied (23)
Rhodia (280), BASF
(260), DuPont (220),
Bayer (55), Radici
(60), UCB
Asahi (120), DuPont
(115), China (139),
Korea (70)

Table 2. Adipic acid consumption, 10 t/a [107110]

United States
1991
Nylon 66
ber
Nylon 66
resin
Plasticizers
Polyurethane
resins
Miscellaneous

Western Europe

Japan

1995

1991

1995

1991

1995

611

629

267

225

35

34

115

193

86

110

23

26

30
38

38
39

21
28

24
45

13
18

14
13

17

23

66

88

19

17

Far East

Adipic acid is added to gelatins and jams as

an acidulant and to other foods as a buffering
or neutralizing agent. It is also used to modify the properties of unsaturated polyesters for
use in reinforced plastics and alkyd coatings.
Polyamide epichlorohydrin resins employing
adipic acid are used to increase the wet strength
of paper products. Other miscellaneous applications are in the adhesives, insecticide, tanning
and dying, and textile industries. Adipic acid and
mixed dibasic acids (DBAs) are being used as
buffers in ue gas desulfurization treatment in
power plants [111].

10. Economic Aspects

Capacities. Total worldwide annual capacity for adipic acid was 2.5 106 t/a in 1999 (Table 3). Although this reects only a 15 % growth
in capacity since 1980, it also reects the shutting down of several adiponitrile plants which
had used adipic acid as a starting material, thus
making it available for other uses. The North
American capacity was 1.06 106 t/a, or 42 %
of the total, whereas Western Europe accounted
for 35 %, produced mainly by the United Kingdom, France, Germany and Italy. Imports and
exports have become signicant. In 1995 U.S.
exports were 71 103 t [112] or 8.5 % of U.S.
consumption. This is up from 1.2 % in 1979
[113]. Since 1970, U.S. consumption of adipic
acid has increased by 80 %, or about 3 % per
year. Growth rates are expected to remain at
about 3 % per year through 2000. Regional capacities are shown in Table 3, along with annual
capacities for the major producing companies.

Others

70

115

Production. Adipic acid production is dominated by nylon 66 ber and resin manufacture;
as a result, the economic picture for the acid
is strongly dominated by the markets for these
materials. Less than 15 % of U.S. production
is sold on the merchant market, essentially for
non-nylon uses. This ratio is higher in Western
Europe and Japan. The synthesis of adiponitrile from adipic acid, once signicant, is no
longer used by any major manufacturers. However, it continues to a very limited degree in some
Eastern European countries. The non-nylon uses
for adipic acid have grown at about 6 % per
year since 1970. Production costs closely parallel raw material prices (cyclohexane and ammonia), which in the late 1990s have fallen with the
decline in crude oil prices. The largest growth
rate for adipic acid, as well as nylon 66, is in
China and the Far East. The projected growth
rate in the United States and Western Europe
is expected to be slow, so the supply/demand
picture should remain relatively constant for the
next few years.

11. Toxicology and Occupational

Health
Adipic acid is a minor irritant of low oral toxicity. The lowest published lethal dose (LDLo)
is 3600 mg/kg (rat, oral), LD50 275 mg/kg (rat
or mouse, i.p.), LD50 1900 mg/kg (mouse, oral)
[114]. Some delayed body weight increases and
changes in certain enzymes and in urea and chloride level in the blood were observed in chronic
feeding tests [115]. No teratogenic activity was
detected in studies with pregnant mice [116].
In metabolism studies with rats fed 14 C-labeled

Adipic Acid
adipic acid, both unchanged adipic acid and normal metabolic products were detected in the
urine [117], [118].
Exposure of the mucous membranes (eyes,
respiratory tract) produces irritation; prolonged
exposure to the skin can be drying or irritating. In
case of spills or leaks, personnel should be protected from inhalation or excessive skin contact.
Dusting should be controlled and static sparks
should be avoided. Water may be used to ush
the area.
Although no TLV or MAK has been established, the airborne exposure should be less than
that of an organic nuisance dust: ACGIH (1979)
8-h TWA 10 mg/m3 (total dust) and 8-h TWA
5 mg/ m3 (respirable dust) (OSHA TLV is 15
mg/ m3 for total dust). Toxicity data from representative types of adipic acid derivatives are
shown in Table 4.
Table 4. Toxicity data for adipic acid derivatives [119]
Derivative

Adiponitrile

Oral LD50 Inhalation

Other LD50 , mg/kg
(rat) mg/kg LC50 (rat,
3
4 h), mg/m
300

1710

Di-2-ethylhexyl 9110
adipate
Dimethyl

adipate
Adipamide
500
Magnesium

adipate

50 (guinea pig,
s.c.)
900 (rat, i.v.)
1809 (rat, i.p.)

180 (mouse, i.v.)

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36. Monsanto, US 3 186 952, 1965 (D. Brubaker,
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10

Adipic Acid

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38. Celanese, US 3 983 208, 1976 (J. Blay).
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96. DuPont, US 3 766 237, 1973 (W. Drinkard).

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97. DuPont, US 3 526 654, 1970 (G. Hildebrand).
98. DuPont, US 3 536 748, 1970 (W. Drinkard, R.
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99. DuPont, US 3 542 847, 1970 (W. Drinkard, R.
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Adiponitrile

Adipic Acid

11

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