CA1140151A - Finishing step of c.sub.7-c.sub.9 saturated aliphatic monocarboxylic acids - Google Patents

Abstract

Docket 5906 ABSTRACT

A process is described to improve the quality of C7-C9 saturated aliphatic monocarboxylic acids, produced by the oxidation of C7-C9 aldehydes, by hydrogenating, as a finishing step, the recovered acid product in the presence of a palladium catalyst under mild temperature and pressure conditions.

Description

.. ~?

A LIPHATIC MONOCARBOXYLIC ACIDS
The present invention relates to a process for improving the quality of C7 -C9 saturated aliphatic monocarboxylic acid by hydrogenating, as a 5 finishing step, the acid product in the presence of a palladium catalyst under mild temperature and pressure conditions.

DESCRIPTION OF THE PRIOR ART
There are numerous references to techniques known for the hydro-genation of unsaturated hydrocarbons. Typical of these references are 10 U. S. Patents 1,023,753; 1, 174,245; 2,331, 915; 3,123,574; and 3,198, 816, which describe various processes for the hydrogenation of unsaturated fatty oils using various forms of palladium catalysts. However, there is no suggestion in any of these references of the use of hydrogenation as a step in the purification of saturated acids . U. S. Patent 3, 271,410 15 describes a process for improving the quality of a catalytically-hydrogenated fatty acid by rehydrogenating the fatty acid, in the presence of a palladium catalyst, at high temperatures (200 to 500F. ) and pressures of from 10 to 5000 p. s. i. g. At high temperatures, more impurities can be produced in the hydrogenation step than if the hydrogenation occurred under mild 20 temperatures and pressures. For this reason, the desired resulting product is distilled from the hydrogenated product rather than using the hydrogenation process as a finishing step. U. S. Patent 3,775,450 describes the hydrogenation of Cs-Clo saturated aliphatic acids produced by nitric acid oxidation at temperatures ranging from about room temperature 25 to about 300C. and high hydrogen pressures in the range from about 100 to 2000 p. s . i. g. Palladium catalysts are described as satisfactory hydrogenation catalysts. Utilizing high temperatures and hydrogen pressures, in general, causes the production of additional impurities and the desired products are obtained by distillation rather than using the 30 hydrogenation process step as the finishing step. Finally U. S. Patent .~

~ `~
114~1S~

2,884,451 describes a process for purifying a crude acid mixture produced by the oxidation of paraffinic hydrocarbons to form aliphatic acids having 1 to 4 carbon atoms. The desired acid is first distilled from the reaction mixture and then hydrogenated using a typical hydrogenation catalyst.
5 Palladium and platinum catalysts are both disclosed as being suitable at room temperature and atmospheric pressure to remove impurities, especially odorous impurities and those of a reducing nature, formed during the oxidation reaction. However, there is no teaching in thi~ patent of the purification of higher acids whether or not produced by oxidation of 10 the corresponding aldehydes, which acids are themselves highly odorous.
It would seem reasonable to assume that these higher acids also contain a different group of impurities from those in Cl-C4 acids produced by oxidation of paraffinic hydrocarbons. Furthermore, there is no indication in U. S. Patent No. Z, 88~,451 that palladium is a more effective catalyst 15 than platinum in the purification by hydrogenation of acids other than the C1-C4 acids dealt with in the patent and specifically in the hydrogenation of the C7-C9 acids purified by the process of the present invention.

SUMMARY OF THE INVENTION
A process has now been found for improving the quality of C7-Cg 20 saturated aliphatic monocarboxylic acids produced by the oxidation of the corresponding C7-C9 aldehydes. After recovery by distillation or other recovery procedures, the acid product is subjected to hydroge~lation in the p. esence of a palladium cata~yst using the combination of mild tempera-ture and pressure conditions such as temperature conditions in the range 25 from about 20C. to about 50C. and hydrogen pressures ranging from about 15 p.s.i.g. to about 75 p.s.i.g.

DETAILED DESCRIPTION OF THE INVENTION
In the production of saturated aliphatic monocarboxylic acids having 7 to 9 carbon atoms, a small amount of undesirable impurities can be 30 produced and carried with the desired product even though extensive ~ 114~151 ~

distillation or other recovery systems are used to purify the product.
- These impurities, whether they are unsaturated organic by-products or other reducible materials, can cause undesirable properties in the final product, For example, such impurities can lead to the formation of 5 undesirable color bodies in the acid product. They also react with materials with which the acid products are used or reacted, forming still other impurities which are thermally or chemically unstable.
The present invention comprises a process to improve the quality of C7-Cg saturated aliphatic monocarboxylic acids produced by the 10 oxidation of the corresponding C7-Cg aldehydes. Broadly stated, this process involves hydrogenating the saturated C7-C9 acids under excep-tionally mild temperature and hydrogen pressure conditions, using a palladium catalyst. The C7-C9 aldehydes which are used to produce the corresponding acids purified by the process of this invention, can be 15 prepared by the catalytic hydroformylation of the C6_CB alkenes, such as n-hexene, n-heptene or n-octene, in the presence of an appropriate catalyst, with carbon monoxide and hydrogen; see for example U. S.
Patent No. 3,239,566 to Slaugh et al; U. S. Patent No. 3,511,880 to Booth; U. S, Patent No. 4,158, 020 to Staut7enberger et al among others.
20 The present invention can advantageously be used as a f;nishing step (i. e. no further distillation or recovery system is required) to provide high quality C7-Cg saturated acids since no impurities are produced using these mild hydrogenation conditions. The finished hydrogenated C7-Cg saturated acid product has a significantly reduced iodine number 25 which measures unsaturation and can be an indication of how the acids will perform as regards to heat stability and color development, The acids purified by the process of this invention are produced by oxidation of n-heptanal, n-octanal and n-nonanal in the presence of a catalyst such as manganese, copper or combinations thereof, followed by 30 distillation to oi~tain the desired acid product containing small amounts of il40151 impurities. By the process of this invention the C7-Cg acids can be gently hydrogenated as a finishing step, utili~ing mild conditions to remove the detrimental effects of the impurities and not produce additional impurities as evidenced by typical gas chromatographic - 5 scans-The process of this invention involves the use of mild hydrogena-tion conditions which includes low temperatures and low hydrogenation pressures. The temperatures used for the hydrogenation step can range from about 20C. to about 50C., preferably from about 25~C.
10 to about 35C, The hydrogenation pressures can range from about 15 p. s . i. g. to about 75 p. s. i. g., preferably about 20 p. s . i. g. to about 60 p.s.i.g.
The hydrogenation catalyst used in practicing the present invention comprises palladium in such diverse forms as powder, pellets, rods and 15 the like. Unsupported palladium can be used or the palladium catalyst can be supported on silica, carbon, kieselguhr and the like. Particularly preferred as a catalyst is palla-dium supported on a carbon pellet. When supported palladium catalysts are used, the amount of palladium on the support can range from about Z 0. 01 to about 10 weight percent or higher based on the total catalyst, preferably in the range from about 0. 5 to about 5 weight percent on the same basis.
The amount of catalyst present must be sufficient to enable one to carry out hydrogenation until the lowest economically feasible iodine 25 value is obtained. The amount of palladium used can range from about 0. 001 to about 1 percent by weight (neglecting the weight of the support) based on the amount of saturated aliphatic monocarbo~ylic acid to be treated. Normally the amount of palladium used will be in the range of from about 0.001 to about 0.15 weight percent of the total acid to be 30 treated. A highly desirable catalyst is made of 0. 5 weight percent 114~:)151 palladium on carbon (4 x 8 mesh) to provide at least about 0. 01 weight percent palladium of the total acid treated.
The equipment used in the process of this invention can be any equipment normally used for hydrogenation in either batch or continuous operations. A Parr bomb or an equivalent piece of equipment can be used in a batch operation. Normally, a filtration of the catalyst from the hydrogenated product is required for this hydrogenation process.
Continuous hydrogenation procedures can be carried out either as a trickle bed (not mass transfer limited) or a flooded bed (mass transfer limited) operation and the same equipment can be used for both processes.
This equipment comprises a pressure unit containing a section which holds the catalyst through which the acid to be treated is flooded or trickled, as the case may be under a hydrogen atmosphere. The treated or hydrogenated product is then recovered. Catalyst fines generation which is possible in a flooded bed process, is minimized in a trickle bed process and thus the trickle bed technique is the preferred mode of ope ration .
The invention will be further illustrated by reference to the following examples:

Nonanoic acid, produced by the oxidation of n-nonanal in the presence of a combination of manganous acetate and cupric acetate catalysts, was distilled from the reaction mixture and then treated in a series of runs according to the procedure as follows:
A glass Parr bomb (approximately 300 milliliters volume) was charged with 100 milliliters of nonanoic acid (iodine number 0. 047 meq/g) and 10 milliliters of hydrogenation catalyst, then pressured with hydrogen. After agitation for a fixed time at room temperature (about Z0C. ) the hydrogen was vented and the contents of the reactor were filtered (millipore filte~ -0.45~1) and analyzed for iodine number.

~ 114~15 ~ ~

Table I indic~tes the differences obtained using palladium on carbon and platinurn on carbon as the hydrogenation catalysts.

15~1:

~o~, ~ ~ ~ W ~ ~ ~J W ~:
S ~D ~ ~ ~d ~ ~ ~ ~ ~ O
p ~D ~ ~ ~ ~ Ul ~p W ~ 1-g ~D~
r- ~Z

.

o o o o ~n o Ul o Ul o ~n P- ~ P ~P P P ~ P ~ ~ ~P ~ ~ ~
j:~ Q ~ ~ Q ~ Q Q o o j;~ S

~D ~ ;'p P~ p' pO ~ p p- CO ~
P- ~ P- ~ ~

--~ S
C~ ~ ~ ~ W
O O O O O O O O ~ ~D ,, r ~ r ~

GQ ,~ ~
o P tD~
@ a~' ~ w w o~ w ~ S ~ O
O O O O O O O O O

.~0 tD~ ~
~D Qo ~:
P, ~ ~3 o o o o o o o o o --Q. ~
. O O O O O O O O O
'-- o ~ ~ ~ o .-- o S ~ ~ o o~ Ul ~ o' ~r )l51.
The comparison of palladium on carbon and platinum on carbon for the hydrogenation of nonanoic acid indicates that at the mild conditions of room temperature tabout 20~C.) ancl low hydrogen pressure, palladium on carbon catalysts are more effective in regard to iodine number reduc-5 tion than the equivalent platinum on carbon catalysts.

WIJS METHOD FOR IOOINE NUMBER ASTM

_ A 500 milliliter iodine flask is charged with 15 grams of sample, 25 milliliters of carbon tetrachloride solvent and 20. 0 milliliters of 10 Wijs solution*. The flask is then stoppered and placed in a dark cabinet for 30 minutes. After removing the flask from storage 20 milliliters of potassium iodide solution** and 100 milliliters of distilled water are added. The contents of the flask are then titrated with 0.1 N thiosulfate to a starch end point.
A blank omitting only the sample should be conducted simultaneously with each group of samples.

Calculation: Iodine number = (B-S) x N x 12. 69 (meq/g) wt of sample where: B = titration of blank S = titration of sample N = normality of thiosulfate solution * Wijs Solution is 5 milliliters of reagent grade iodine monochloride in one liter of glacial acetic acid.
** 15 Weight percent of reagent grade potassium iodide in distilled water.

Heptanoic acid, produced by the oxication of n-heptanal in the presence of a combination of manganous acetate and c~pric acetate catalysts, was distilled from the reaction mixture and then treated in a series of runs according to the following procedure as follows:

l~L4015~L
A glass Parr bomb (approxinlately 300 milliliters volume) was charged with 100 milliliters of heptanoic acid (iodine number 0. 012 meq/g) and 10 milliliters of hydrogenation catalyst and then pressurized with hydrogen. After agitation for a fixed time at room temperature 5 (about 20C, ) the hydrogen was vented and the contents of the reactor was filtered (millipore filter - 0. 45 ~1) and analyzed for iodine number.
Table II indicates the differences obtained using palladium on carbon and platinum on carbon as the hydrogenation catalyst.

~ ~140151 k~

W W
X

~ ~1-- ~
n ~-~_ o o (D

o o ~n O ul O O O O O ~

b ~ ~ ~

o~ ~n ~ ~ ~
o o o o ~ ~ ~
..
o ~ ~ o Q

o o . , . ~- O
o o o ~,_ ~
~ o ` -` ~ 114{)151 In a trickle bed hydrogenation reactor containing a 2" x 12" catalyst bed 4 x 8 mesh 0, 5% palladium on carbon, nonanoic acid, as produced as described in Examples 1-8 is trickled over the catalyst bed at a controlled rate. The hydrogen pressure in the reactor is 20 p. s. i. g. and the hydro-genation temperature is 30C. Table III illustrates the results obtained in the hydrogenation of nonanoic acid under various conditions.
TABLE III

TRICKLE BED HYDRGENATION OF
] NONANOIC ACID
Mass Flux* Iodine Number (Kg/m2 sec) Meq/g Feed Produc t 0,53 0.05 0.015 0.30 0.05 0.020 0.23 0.05 0.015 0.15 0.05 0.015 0. 08 0. 05 0. 009 * Liquid feed rate per unit cross section-kilograms per square meter per second.
. Table III indicates that the quality of nonanoic acid can be improved in a continuous process using mild hydrogenation conditions.

Using the identical hydrogenation equipment and reaction conditions as in Example 13 and substituting heptanoic acid, produced as described in Examples 9-12 for nonanoic acid, the following result is obtained:
TAB LE IV

TRICKLE BED HYDROGENATION OF
HEPTANOIC A~ ID

Ma s s Flux Iod ine Numbe r (Kg/m2 sec) Meq/g Feed Product 0.15 o.oll 0.004 114~)151 a Table IV indicates that the quality of heptanoic acid can be improved in a continuous process using mild hyclrogenation conditions.

In theory, hydrogenation can be either a pre- or post-finishing 5 column treatrnent. In other words, hydrogenation of the oxidation product of n-heptanal or n-nonanal prior to distillation would be very desirable from the standpoint that distillation to obtain the desired acid product would act as a guard against entrainment of any catalyst fines in the finished product. A comparison of post-hydrogenation and pre-lo hydrogenation of nonanoic acid was conducted in the trickle bed equip-ment described in Example 14.
The nonanoic acid reaction product obtained from the oxidation of n-nonanal was separated into two portions. One portion of this reaction product was hydrogenated in the trickle bed reactor described in 15 Example 14 using identical hydrogenation conditions and catalyst. The product was then distilled to give a product which may be termed a pre-hydrogenated product. The other portion of the nonanoic acid reaction product was first distilled to isolate the nonanoic acid from the remaining reaction products. The distilled nonanoic acid was then hydrogenated in 20 the trickle bed hydrogenation equipment as described in Example 14 using identical hydrogenation conditions and catalyst to give a product which may be termed a post-hydrogenated product. The following results were obtained:

Non Hydrogenated Distilled Nonanoic Acid Post-Hydrogenated Pre-Hydrogenated Reaction Product Nonanoic Acid Nonanoic Acid Iod ine Numbe r Meq/g 0. 048 0. 010 0. 025 The above data demonstrates that pre-hydrogenation is less effective than post-hydrogenation in the reduction of the iodine number;

lZ_ however, both products are better than the noll hydrogenated distilled nonanoic acid reaction product. It was observed that the reaction product in the pre-hydrogenation step rapidly deactivated the hydro-genation catalyst while no deactivation was noted in the post-hydrogenation 5 finishing step of this invention. Therefore, the pre-hydrogenation process cannot be considered a viable process due to the deactivation of the hydrogenation catalyst.
In all of the above-described examples demonstrating the process of this invention, no additional products were observed in the hydrogenated 10 products of heptanoic and nonanoic acid as evidenced by typical gas chromatographic scans.

Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a method for producing C7-C9 saturated aliphatic acids by the oxidation of the corresponding C7-C9 aldehydes and recovery of the desired acid product, the improvement comprising hydrogenating said acid product as the finishing step aside from filtration to remove the hydrogenation catalyst if required, said hydrogenation conducted in the presence of a palladium catalyst under a hydrogen pressure ranging from about 15 to about 75 pounds per square inch gauge and temperatures ranging from about 20°C to about 50°C.

2. The process of claim 1 wherein the catalyst is palladium on carbon wherein the amount of palladium ranges from about 0.1 to 10 weight percent of the total catalyst.

3. The process of claim 1 wherein the temperature ranges from about 25°C to about 35°C.

4. The process of claim 1 wherein the hydrogen pressure ranges from about 20 to about 60 pounds per square inch gauge.

5. The process of claim 2 wherein the catalyst is palladium on carbon wherein the amount of palladium ranges from about 0.5 to about 5 weight percent, based on the total weight of catalyst.

6. The process of claim 5 wherein the saturated monocar-boxylic acid hydrogenated is heptanoic acid.

7. The process of claim 5 wherein the saturated monocar-boxylic acid hydrogenated is nonanoic acid.