GB2059419A - Production of organic saturated aliphatic monocarboxylic acids - Google Patents

Abstract

Saturated aliphatic monocarboxylic acids containing 6 to 9 carbon atoms are produced by oxidation of the corresponding aldehyde of the acid utilizing a combination of copper and manganese catalysts which are soluble in the acid produced.

Description

SPECIFICATION Production of organic saturated aliphatic monocarboxylic acids The present invention relates to an improved process for the production of organic saturated aliphatic monocarboxylic acids containing from 6 to 9 carbon atoms by the oxidation of the corresponding aldehydes to the acids utilizing a combination of copper and manganese catalysts which are soluble in the acids produced. The acids that are produced by the process of this invention are generally utilized in the production of esters for uses in dyes, artificial flavors, perfumes and the like.

Recently, a very specific interest has developed for the production of esters of heptanoic and nonanoic acids which are used as blend stocks in synthetic lubricating oils.

The acids produced in this invention which contain an even number of carbon atoms are frequently found in nature in substantiai quantities while the acids containing odd number carbon atoms are not generally found in nature in large quantities. To achieve production faciiities for recovery of the monocarboxylic acids having 6 to 9 carbon atoms from naturally occurring materials is generally not practical and extremely expensive. It is desirable to use petrochemical means providing good yields in the production of the acids from readily available hydrocarbon starting materials.

In producing the saturated aliphatic monocarboxylic acids of this invention, the starting materials can be olefins having 5 to 8 carbon atoms which, by hydroformylation, are converted to aldehydes containing 6 to 9 carbon atoms; these in turn are catalytically oxidized to their respective acids. The hydroformylation and oxidation processes to produce acids are well known in the art. What is sought after in these processes, are improved catalysts to provide a high carbon efficiency to desired product, at a high conversion thereby providing good overall yields.

In the oxidation of aldehydes to acids, various catalysts are known which include nitric acid oxidation catalysts and soluble metal catalysts such as manganous acetate, cobalt acetate and cupric acetate, among others. For example, manganous acetate is known to be used commercially in the production of acetic acid from acetaldehyde. Japanese Patent No. 52-33614, published March 14, 1977, describes the use of a combination of manganous acetate and cupric acetate catalysts in the oxidation of acetaldehyde to acetic acid. The patentees' stated reason for using a combination of manganese and copper catalysts is to reduce the amount of exceptionally small amounts of impurities produced, especially formic acid.Manganous acetate alone as a catalyst for producing acetic acid from acetaldehyde has been found to be as efficient in carbon selectivity to desired product conversion and yields as the combination of manganous acetate and cupric acetate. It also avoids certain disadvantages of such combinations, e.g., increased corrosion and rapid pump seal failures due to copper deposits.

In comparative tests, manganous acetate alone does not resuit in significantly greater loss of efficiency to formic acid in the oxidation of acetaldehyde to acetic acid when compared to the combination of manganous acetate and cupric acetate. Moreover, the use of manganous acetate as a catalyst yields results fairly similar to those obtained with the use of the combination of manganous acetate and cupric acetate as a catalyst in the oxidation of propionaldehyde to propionic acid and valderaldehyde to valeric acid.

However the production of acetic acid from acetaldehyde is different from the production of acids containing at least 6 carbon atoms from their corresponding aldehydes in that the atom oxidized in acetaldehyde oxidation is the oxygen-containing carbon atom which has a methyl group attached to it.

The presence of the methyl group provides more stable reaction intermediates when compared with aldehydes having 4 or more methylene groups between the oxygen-containing carbon and the methyl group. The products, among others, which can be produced in the acetaldehyde oxidation include acetic acid, methyl acetate, formaldehyde, methyl formate, formic acid, carbon dioxide, carbon monoxide, methane and water. On the other hand, products which can be produced in heptanal oxidation, for example, include most of the products produced in acetaldehyde oxidation plus heptanoic acid, hexane, hexene, hexanal, hexanol, hexanoic acid, valeric acid, butyric acid, propionic acid, and various esters, dehydrated adol dimers and lactones, among others.

Cupric acetate alone is an oxidation catalyst for acetic acid production from acetaldehyde but the carbon efficiencies to acetic acid with this catalyst are significantly lower compared to those of manganous acetate.

Contrary to what was found in acetaldehyde and propionaldehyde oxidation, the use of manganese acetate, alone, in the oxidation of higher aldehydes, such as heptanal, was found to require low conversions of aldehyde (7075%) to provide satisfactory carbon efficiencies to acids, which necessitates a recovery of unreacted aidehyde by distillation for recycle if this process is to be commercially feasible. Furthermore, significant losses of aldehyde occur via condensation to high boilers in the aldehyde recycle column.

An improved catalytic process has been discovered for producing organic aliphatic monocarboxylic acids containing from 6 to 9 carbon atoms by the oxidation of the corresponding aldehyde of the acid. This process utilizes as the catalyst, a combination of manganese and copper compounds which are soluble in the acids produced. The manganese and copper compounds can be used in amounts such that the molar ratio of manganese to copper ranges from about 5:1 to about 0.5:1. The organic aliphatic monocarboxylic acids containing from 6 to 9 carbon atoms which can be produced by the process of this invention can include hexanoic acid from hexanal, heptanoic acid from heptanaI, octanoic acid from octanal and nonanoic acid from nonanal.

The process of this invention provides commercially attractive high carbon efficiencies of aldehydes to acids at high aldehyde conversions (8090%). With high carbon efficiencies and high aldehyde conversions, a single stage liquid phase factor can be satisfactorily utilized. The process of this invention also permits the use of a two stage liquid phase single pass reactor system wherein the mixture containing the unreacted aldehyde from the first stage catalytic reaction can be passed to a second stage catalytic reaction providing overall conversions of aldehyde as high as 97% or higher with overall carbon efficiencies to acids as high as 90% or higher. With the two stage liquid phase single pass reactor system, a recycle operation of the unreacted aldehydes is generally not needed.

- In the single stage liquid phase and in each stage of a two stage liquid phase reactor system, the reactions can be operated under pressure in the range from about 20 to 150 pounds per square inch gauge, preferably from about 85 to about 90 pounds per square inch gauge, with air in the temperature range from about 500 C. to about 800 C.

Air is commonly employed as the source of molecular oxygen, although a pure oxygen gas may also be employed. The molecular oxygen may be provided in at least a stoichiometrically sufficient amount to convert the material to be oxidized to carboxylic acid and to compensate or allow for byproducts such as carbon dioxide. The ratio of total feed of oxygen to total feed of organic starting material is a highly variable number which depends upon the specific composition of the feed, the desired products, and other process design factors. Typically, the oxygen-containing gas is bubbled through the liquid reaction mixture in an amount sufficient to prevent oxygen starvation which may be indicated by a low concentration of oxygen or a high ratio of carbon monoxide to carbon dioxide, or both, in the vent gas.

The oxidation reaction can be conducted in the liquid phase i.e. the aldehyde to be oxidized is in liquid form. Typically the carboxylic acid reaction product serves as a solvent in which the reaction takes place. A problem of water phasing out in the oxidation reactors occurs when nonanal is oxidized but does not occur with heptanal oxidation. The water appears to extract and precipitate the catalyst reducing the efficiency by about 2%. Phasing does not occur when acetic acid is fed with the nonanai to maintain about 2 weight percent of acetic acid in the reactor liquid.

Reaction or reactor residence times may range from about 0.1 to about 5 hours, preferably from about 0.3 to 1 hour. The residence time is calculated as follows: volume of solution in reactor, ml Residence Time = feed rate of aldehyde, ml/hr The catalyst can be a combination of any copper and manganese compounds which are soluble in the acids they are producing. The preferred compounds are soluble manganous and cupric salts, and most preferred are manganous acetate and cupric acetate. Each of these compounds may be present in catalytic amounts during oxidation ranging from about 10 to 2,000 parts per million of manganese and copper, preferably 200 to 600 parts per million based on the weight of the liquid reaction medium. The mole ratio of manganese to copper can range from about 5:1 to about 0.5:1, preferably from about 3:1 to 1:1.

The carboxylic acid may be recovered from the oxygenated reaction product mixture by various means known in the art, and typically by distillation.

The major difficulty of the process of this invention is the presence of copper compounds in the product. On acid purification, copper can precipitage and can lead to mechanical problems such as erosion of reboilers and pump impellers, and rapid pump seal failures among other problems. The copper and manganese metals can be precipitated from the organic acid product as their oxalates by the addition thereto of oxalic acid. The resulting oxalates can then be filtered from the organic acid product prior to its purification and recovery. Also, copper and manganese can be separated from organic saturated aliphatic acid products having 6 to 9 carbon atoms by precipitating them, again as their oxalates, by adding aqueous oxalic acid. The manganese and copper oxalates are precipitated into the aqueous phase which can be readily separated from the organic acid product. The organic acid can be decanted from the aqueous phase and further purified by distillation. This process is described in copending Application No. 8025932 assigned to the same assignee and filed concurrently with this application.

The invention is additionally illustrated by the following examples: EXAMPLES 1-4 These liquid phase oxidations of acetaldehyde to acetic acid using cupric acetate as the sole oxidation catalyst were carried out in a tubular glass reactor 1.5 inch l.D. x 4 feet with external recirculation through a heat exchanger at 50 psig and 800 C. An oxygen-nitrogen mixture (mole ratio of 90:10) was used instead of air to facilitate vent measurements and decrease acetaldehyde loss due to flashing. These runs were conducted under conditions such that conversions (steady state acetaldehyd concentration) were controlled by the rate of oxygen fed to the reactor. After each reaction was completed, the products were batch distilled to obtain the desired products.The reaction conditions used and the conversion efficiencies obtained are listed in Table I: TABLE I ACETALDEHYDE OXIDATION TO ACETIC ACID WITH CUPRIC ACETATE CATALYST Example 1 2 3 4 -Catalyst conc, ppm (Cu++) 150 150 150 158 Time of run, hr 2.72 3.52 3.53 2.42 Feed rate, g/hr 849.8 826.6 768.8 832.8 Oxygen feed, moles/hr 14.0 14.6 14.6 14.2 Volume of solution in Reactor ml 530 500 500 490 Residence time, hr 0.50 0.48 0.52 0.47 Oxygen conversion, % 88.5 86.1 87.9 85.2 Acetaldehyde accountability, % 98.2 96.5 96.2 98.4 Acetaldehyde conversion, % 95.9 98.3 99.1 97.1 Efficiency to: % *Acetic acid 85.1 85.8 87.2 85.1 Methyl acetate 6.0 4.3 3.9 4.5 Formic acid 0.8 0.9 1.0 1.4 Carbon dioxide 6.1 6.8 6.2 7.4 *In addition to the designated products, small amounts of formaldehyde, methyl formate, carbon monoxide, methane and ethylidiene diacetate were produced.

In regard to Table I, some of the results were calculated using the following formulas: Volume of solution in reactor, ml Residence Time = feed rate of acetaldehyde ml/hr moles O2 fed - moles O2 in vent Oxygen conversion = ~ x 100 moles O2 fed moles of acetaldehyde and equiv. in product Acetaldehyde accountability = x 100 moles acetaldehyde fed moles acetaldehyde converted Acetaldehyde conversion % = moles acetaldehyde fed moles of product produced Efficiency to Product % = - x 1 100 moles acetaldehyde fed moles unreacted acetaldehyde EXAMPLES 5-8 These examples were carried out using conditions identical with those of Examples 1-4, except that a combination of manganous acetate and cupric acetate was used.The results obtained are given in Table II.

TABLE IT ACETALDEHYDE OXIDATION TO ACETIC ACID USING MIXED CATALYSTS OF MANGANOUS ACETATE AND CUPRIC ACETATE Example 5 6 7 8 Catalysts conc, ppm Cu 120 120 110 123 Mn 150 150 130 116 Time of run, hr 2.62 2.73 3.53 2.20 Feed rate, g/hr 842.2 844.7 844.2 900.0 Oxygen feed, moles/hr 14.3 13.0 . 11.5 11.7 Volume of solution in reaction, ml 500 520 550 550 Residence time, hr 0.47 0.49 0.52 0.49 Oxygen conversion, % 90.2 89.1- 91.1 -Aldehyde accountability, % 98.5 97.4 98A 96.2 Aldehyde conversion, % 98.8 98.4 97.0 92.3 *Efficiency td: % Acetic acid 88.4 90.6 94.2 96 0 Methyl acetate 1.5 1.5 1.6 0.8 Formic acid 0.3 0.2 0;2 0.2 Carbon dioxide 8.5 6.6 3.8 1.7 *In addition to the designated products, small amounts of formaldehyde, methyl formate, carbon monoxide, methane and ethylidiene diacetate were produced.

EXAMPLES 9-14 These examples were carried out using conditions identical with those of Examples 1 through 8 except that manganous acetate (114 parts per million Mn++ average) alone, was used as the catalyst.

The results obtained are given in Table Ill.

TABLE III ACETALDEHYDE OXIDATION TO ACETIC ACID USING MANGANOUS ACETATE CATALYST (114 PPM Mn++ AVERAGE) Example 9 10 11 12 13 14 Recycle Rate, I/hr 250 250 > 300 > 300 > 300 > 300 Time of Run, hr 3.45 3.53 3.0 3.50 3.50 4.0 Feed Rate, g/hr 755 853 841 774 765 786 Oxygen Feed, mol/hr 10.1 9.2 9.9 14.9 12.3 10.6 Vol. of Sol'n. in Reactor, ml 460 475 490 440 460 480 Residence Time, hr 0.48 0.44 0.46 0.45 0.48 0.49 Oxygen Conversion 86.2 91.6 84.6 76.6 85.0 91.4 Acetaldehyde Accountability 98.1 98.0 101.4 99.0 98.0 98.5 Acetaldehyde Conversion 97.1 93.0 91.4 99.3 98.3 97.8 *Efficiency to: % Acetic acid 92.8 95.4 94.7 85.6 87.9 91.9 Methyl acetate 1.0 0.8 0.9 1.0 1.1 1.2 Formic acid 0.3 0.2 0.3 0.7 0.5 0.4 Carbon dioxide 4.7 2.7 3.3 11.0 8.6 5.1 *In addition to the designated products, small amounts of formaldehyde, methyl formate, carbon monoxide, methane were produced.

EXAMPLES 15-20 These examples were carried out using conditions identical with those of Examples 1 through 8, using the same conditions and calculations, except that manganous acetate (600 parts per million Mn++ average) alone was used as the catalyst. The results obtained are given in Table IV.

TABLE IV ACETALDEHIDE OXIDATION TO ACETIC ACID USING MANGANOUS ACETATE CATALYST (600 PARTS PER MILLION Mn++ AVERAGE) Example 15 16 17 18 19 20 Recycle Rate, I/hr 300 300 300 300 300 300 Time of Run, hr 3.25 3.82 3.98 4.02 3.58 3.93 Feed Rate, g/hr 853 737 745 727 814 751 Oxygen Feed, mole/hr 10.4 11.4 10.1 9.1 8.9 11.4 Vol. of Sol'n. in Reactor, ml 480 460 465 500 430 420 Residence Time, hr 0.44 0.50 052 0.55 0.42 0.44 Oxygen Conversion 84.1 76.7 84.2 84.4 90.8 78.9 Aldehyde Accountability 96.9 97.8 99.9 101.2 96.7 Acetaldehyde Conversion, % 95.0 98.6 97.1 96.1 94.2 98.5 *Efficiency to: % Acetic acid 95.8 91.5 95.1 95.1 97.0 92.0 Methyl acetate 1.0 1.0 1.0 1.0 0.6 0.9 Formic acid 0.2 0.4 0.2 0.2 0.2 0.3 Carbon dioxide 2.5 6.3 3.1 3.1 2.0 5.9 *In addition to the designated products, small amounts of formaldehyde, methyl formate, carbon monoxide, methane and water were produced.

Examples 1 through 20 illustrate the comparison of liquid phase acetaldehyde oxidation reactions to acetic acid using the following catalysts: (1) cupric acetate alone (Exampies 1 4) (2) cupric acetate and manganese acetate (Examples 5-8) (3) manganous acetate alone (Examples 9-20) Comparing the use of cupric acetate alone with the combination of cupric acetate and manganous acetate under similar conditions, the efficiency of the acetaldehyde oxidation to acetic acid using the combination of salts is slightly better than the efficiency using cupric acetate alone. On the other hand, comparing the combination of cupric acetate and manganous acetate with manganous acetate alone under similar conditions, the efficiencies of the acetaldehyde oxidation to acetic acid are very similar.

This result was confirmed in a 3 day test using a combination of cupric acetate and manganous acetate as catalyst and manganous acetate alone at concentrations of 300 parts per million each of copper and manganese in the reactors compared with 300 parts per million of manganese alone. The difference which was observed is that the unit, using the combination of manganese and copper salts, when compared to the unit using the manganese salt alone, showed an increased corrosion rate and rapid pump seal failures on various pumps due to copper deposits.

EXAMPLES 21-28 The production of propionic acid by the oxidaiton of propionaldehyde was conducted in a onestage liquid phase reaction system. The reactor was a vertical 6-ft. section of 2-inch steel pipe with a flanged plate attached to the bottom with fittings for feed (air and aldehyde) lines. There were multiple product take-off points in the side of the pipe reactor so that the height of roused liquid above the air sparger could be controlled by selection of the take-off point. Reaction liquid was continually pumped via a centrifugal pump from the bottom of the reactor through a heat exchanger and discharged just above the surface of the liquid in the reactor. The pump around rate was approximately 1 25 liters per hour. The reaction temperature was controlled by controlling the cooling water flow to the heat exchanger on the pump around steam.

Product (both liquid and gas) was taken out through a line (1/4 inch) in the side of the reactor into a chilled water cooled (1 00C) gas liquid separator. The gases emerged through a chilled water condenser into a pressure regulating motor valve and were then passed through a dry test meter. The liquid products were collected, weighed and analyzed by gas chromatography. The vent gas was analyzed continuously for O2 with a polarographic detector and was analyzed periodically (at approximately 1 5 minute intervals) for CO, CO2, N2 and O2 by gas chromatography. The concentrations of propionaldehyde and propionic acid in the vent were calculated from the composition of the liquid phase assuming ideal behavior.

The liquid feed was a solution of 90 weight percent propionaldehyde and 10 weight percent propionic acid in which the desired amount of manganous acetate or manganese acetate in combination with cupric acetate had been dissolved. The actual weight of liquid feed fed to the reaction system was measured. The air was fed into the reactor through a Hasting's flow meter. Both the Hasting's flow meter and the dry test meter on the vent stream were recalibrated daily with a large soap bubble flow meter.

Tables V and VI illustrate the conversions and efficiencies obtained in runs in which propionaldehyde was oxidized to propionic acid in this one-stage reactor. The pressure was 95 p.s.i.g.

and the oxidant was air. The height above the sparger was about 60 centimeters. The conversions were controlled by the rate at which oxygen was fed to the reactor TABLE V OXIDATION OF PROPIONALDEHYDE TO PROPIONIC ACID WITH MANGANOUS' ACETATE ALONE AS CATALYST (300 PARTS PER MILLION) Example 21 22 23 24 Temperature, C. 60 60 60 60 2 in vent, mole % 2.06 1.99 1.96 1.98 Air feed rate, moles/hr 29.44 27.70 19.02 19.02 *Propionaldehyde Conversion 98.21 96.38 87.60 87.57 % Efficiencies Propionic acid 87.451 90.821 93.535 93.777 Acetic acid 6.667 4.599 2.460 CO2 4.790 3.326 1.920 1.889 Carbon Accountability % 100.87 98.59 97.64 97.15 Oxygen Conversion % 91.66 92.04 92.27 92;;19 Air feed rate, L/min 12.00 11.29 7.75 7.75' Gas Superficial Velocity Reactor Volume 1.386 1.216 1.083 1.083 *In addition to the designated products. small amounts of ethanol, ethyl propionate, ethyl acetate, acetaldehyde, dimethyl ether, 3-pentanone, methyl propionate and 3-pentanol were prdduced.

TABLE VI OXIDATION OF PROPIONALDEHYDE TO PROPIONIC ACID USING COMBINATION OF MANGANOUS ACETATE AND -CUPRIC ACETATE (EACH Mn AND Cu 300 PPM) Example 25 26 27 28 Temperature, C. 60 60 60 60 2 in vent, mole% 2.00 1.97 2.04 3.00 Air feed rate, moles/hr 21.74 21.74 25.81 32.71 *Propionaldehyde Conversion 87.19 87.18 96.38 97.77 %-Efficiencies Propionic acid 94.546 94.726 90.678 87.204 Acetic acid 2;;787 2.560 4.621 6.186 CO2 1.515 1.545 3.635 5.399 -Carbon Accountability 98.70 97.92 106.00 102.15 Oxygen Conversion 92.14 9226 91.81 87.72 Air feed rate, L/min 8.86 8.86 10.52 13.33 Gas Superficial Velocity Reactor Volume, L 1.170 1.170 1.256 1.386 *In addition to the designated products, small amounts of ethanol, ethyl propionate, ethyl acetate, acetaldehyde diethyl ether, 3-pentanone and methyl prnpionate were produced.

Comparing the catalyst combination of cupric acetate and manganous acetate with manganous acetate alone under similar oxidation conditions, the efficiencies of the propionaldehyde oxidation to propionic acid are very similar.

EXAMPLES 29-36 The production of valeric acid by the oxidation of n-valeraldehyde was conducted in the same one stage liquid phase reaction system described in Examples 21-28 under identical conditions.

Tables VII and VIII illustrate the conversion and efficiencies obtained. The pressure was 95 p.s.i.g., the oxidant was air and the liquid height above the sparger was about 50 centimeters.

TABLE VII OXIDATION OF N-VALERALDEHYDE TO VALERIC ACID WITH A CATALYST COMBINATION OF MANGANOUS ACETATE AND CUPRIC ACETATE (Mn++ 300 PPM AND Cu++ 300 PPM) Example 29 30 31 32 Temperature, C. 60 60 60 60 O2 -in vent gas, mole % 3.72 3.72 3.51 2.85 O2 conversion, /O 85.16 85.15 85.88 88.75 Air feed rate, mole/hr 24.56 21.37 28.49 19.95 Carbon Accountability 99.43 99.01 100.68 96.83 Valeraldehyde Conversion % 91.13 86.16 95.15 82.54 *Efficiencies % Valeric acid 94.872 94.726 92.415 95.424 2-MethylbutyPic acid 0.431 0.437 0.411 0.432 Butyric acid 2.949 2A89 3.589 2;;190 CO2 0.927 0.931 1.594 0.681 CO 0.027 082 0.065 Air feed rate, L/min 10.01 8.71 11.61 8.13 Liquid feed rate, ml/min 17.47 17.58 17.43 17.6 Superficial velocity Reactor volume, L 1.083 1.083 1.083 1.083 *In addition to-the designated products, small amounts of propionic acid, acetic acid, levulinic acid, a-valerolactone, methyl ethyl ketone, butanol, butyl valerate,5-penta none and butyraldehyde were produced. Efficiencies are based on the total C, aldehyde.

TABLE VIII OXIDATION OF N-VALERALDEHYDE TO VALERIC ACID WITH MANGANOUS ACETATE CATALYST (300 PPM Mn++) Example 33 34 35 36 Temperature, "C. 60 60 60 60 O2 in vent gas, mole% 2.79 2.82 2.80 3.05 O2 conversion, % 88.77 88.76 88.87 87.78 Air feed rate, mole/hr 17.18 15.12 19.88 16.78 Carbon accountability, % 97.36 98.69 97.35 97.20 Valeraldehyde Conversion % 94.49 87.14 82.24 90A0 *Efficiencies % Valeric acid 90.933 93.266 94.556 92.834 2-Methylbutyric acid 0.222 0.232 0.280 0.216 Butyric acid 4.029 2.754 1.975 2.914 CO2 1.838 1.093 0.961 1.258 CO 0.217 0.258 0.253 0.249 Air feed rate, L/min 7.00 6;;16 8.10 6.84 Liquid feed rate, ml/min 11.75 11.57 16.80 11.57 Superficial velocity Reaction rate HVal in Product Sparger depth, cm Reactor volume, L 1.083 1.061 1.061 1.061 *In addition to the designated products, small amounts of propionic acid, acetic acid, levulinic acid, a-valerolactone, methyl ethyl ketone, butanol, butyl valerate, 5-penta none and butyraldehyde were produced. Efficiencies are based on the total C, aldehyde.

Comparing the combination of cupric acetate and manganous acetate with manganous acetate alone under similar oxidation conditions, the efficiencies of each oxidation process of acetaldehyde to acetic acid, propionaldehyde to propionic acid and n-valeraldehyde to valeric acid are very similar. The major difference between the two catalysts is that in the use of the copper-manganese combination, the presence of copper deposits can provide corrosion problems as well as rapid seal failures on various pumps used. These problems are not present in the use of the manganese catalysts alone. In the presence of copper, extensive separation techniques are necessary to remove the copper from the reaction system after the reaction has been completed.

EXAMPLES 37-41 These examples illustrate the production of heptanoic acid from heptanal in a one-stage process wherein the oxidation reactor was a 36-inch long section of 2-inch glass pipe with a flanged plate attached to the bottom with fittings for feed and product lines and a condenser at the top. The reaction temperature was controlled by controlling the tap water to flow to the heat exchanger on a pump around stream. Reaction liquid was continually pumped via an Eastern centrifugal pump from the bottom of the reactor through the heat exchanger and discharged just above the surface of the liquid in the reactor. The pump around rate was approximately 125 liters per hour which was equivalent to about 1.6 reactor "turn overs" per minute.

Product (both liquid and gas) was taken out through a 22-1/2 inch tall 1/4 inch tubing "stand pipe" which set the reactor "roused" volume at about 1.3 liters. The liquid and gas products passed through a pressure regulating motor valve and into a chilled water cooled gas-liquid separator. The gases emerged through a chilled water condenser and passed through a wet test meter. The liquid products recovered were batch distilled to recover the reaction products.

Table IX indicates the reaction conditions and results obtained from these examples carried out as previously described using a manganese salt alone (330 parts per million of manganese average) as the catalyst at 90 p.s.i.g. and 50% oxygen in nitrogen as the oxidant. The hepantal feed material obtained by the so-called "oxo" reaction of 1-hexene and carbon monoxide contained 6 weight percent 2 methyihexanal. The catalyst solution added to the reactor contained 5 weight percent manganous acetate (or 1.12 weight percent manganese), the balance being acetic acid (81.6%) and water.

TABLE IX HEPTANAL OXIDATION TO HEPTANOIC ACID USING MANGANOUS ACETATE CATALYST (300 PARTS PER MILLION AVERAGE Mn++) Example 37 38 39 40 41 Temperatures, "C: Middle 80 80 80 80 80 Bottom 82 81 83 83 83 Feed Rates: C7 Aldehyde, cc/min 20.00 16.30 21.80 24.90 29.90 Catalyst sol., cc/min 0.50 0.42 0.54 0.62 0.75 Oxidant, moles/L/hr 10.44 0.58 11.46 12.34 13.62 Mn++ Fed as parts per million in liquid product 325 330 330 330 345 H2O Fed as wt% in liquid product .39 0.39 0.39 0.39 0.41 Acetic acid Fed as wt % in liquid product 257 2.40 2.40 2.40 2.51 Oxygen Feed, moles/L/Hr 5.22 4.79 5.73 6.17 6.81 Oxygen Conversion, % 89.7 90.7 92.8 90.2 86.8 Oxygen Consumed, moles/L/Hr 4.68 4.34 5.32 5.61 5.91 Est. Liquid Res.Time, Min 49 60 45 39 33 C7 Aldehyde Conversion %- 90.8 92.2 88.2 87.4 80.6 *Efficiency % Heptanoic Acid 76.36 75.96 74.04 74.37 76.81 2-methylhexanoic acid 3.34 3.47 3.93 4.03 4.13 Total C7 Acids 79.70 79.43 77.97 78A0 80.94 CQ - 0.60 0.55 0.68 0.69 0.70 CO2 2.75 2.69 2;53 2A8 2.37 Hexane 4.93 4.43 6.30 6.43 5.95 Hexanal 2.43 2.42 2.40 2.47 . 1.03 Hexanol 1.72 1.72 1.62 1.75 1.70 Hexanoic Acid 3.42 3.84 3.19 3.24 2.96 Esters 2.38 2.55 2.20 2.24 2.02 *In addition to the above-identified products, small amounts of high boilers, lactone, keto acid, succinic acid and propionic acid were also produced. Efficiencies are based on the total C7 aldehyde.

EXAMPLES 42--47 Table X illustrates the conversions and efficiencies obtained from another series of runs in which hexanal was oxidized to hepantoic acids in a one-stage reactor as previously described in Examples 37-41 using manganous acetate alone (300 parts per million manganese average) as the catalyst at 90 p.s.i.g. and 50% oxygen in nitrogen as the oxidant. The catalyst solution added to the reactor contained 5.39 weight percent manganese acetate (1.21 weight percent manganese) dissolved in heptanal.

TABLE X -HEPTANAL OXIDATION TO HEPTANOIC ACID USING A MANGANOUS ACETATE CATALYST Example 42 43 44 45 46 47 Temperatures, "C.

Middle 67 60 63 71 62 69 Bottom 62 61 65 70 66 73 Branched Aldehyde in Feed % 3.75 3.75 5.71 6.76 5.70 7.76 Feed Rates: C7 Aldehyde, cc/min 21.50 18.30 16.70 15.05 15.80 14.20 Catalyst sol,, cc/min 0.47 0.40 0.36 0.33 0.36 0.32 Oxidant, moles/L/hr 4.63 4.63 4.63 4.63 4.47 4A8 Mn++ Fed as parts per million in liquid product 280 270 265 270 290 280 Oxygen Feed, moles/L/hr 2.27 2.27 2.27 2.27 2.17 2.17 Oxygen Conversion, % 98.8 97A 96.6 95.7 97.3 96.9 Oxygen Consumed, moles L/hr 2.24 2.21 2.19 2.37 2.11 2.11 Est. Liquid Res.Time, min 46 54 59 65 62 69 C7 Aldehyde Conversion % 63.8 70.6 75.9 83.3 82.5 87.8 *Efficiency % Heptanoic Acid 87.61 88.00 86.84 80.89 82.33 77.37 2-methylhexanoic acid 2.80 2.80 3.66 5.1-1 3A4 5.92 Total -C7 Acids 90A0 90.80 90.50 85.99 85.77 83.29 CO 0.24 0.24 0.34 0.50 0.36 0.63 CO2 0.55 Q.63 0.78 1.01 0.97 1.15 Hexane 3.28 3.36 2.72 4.03 3.91 5.38 Hexanal 1.24 1.29 1.37 1.59 1.05 1.95 Hexanol 0.44 0.52 0.51 0.78 1.03 1.85 Hexanoic Acid 0.96 1.13 1.20 2.93 1.50 2A1 Esters 1.18 1.16 0.91 1.10 2.85 1.65 High Boilers 1.18 0.34 0.96 0.80 0.04 0.00 *In addition to the above-identified products, small amounts of high boilers, lactone, keto acid, succinic acid and propionic acid were also produced.Efficiencies are based on the total C7 aldehyde.

EXAMPLES 48 49 In a one-stage single reactor such as described in Examples 37-41, the oxidation reaction of heptanal to heptanoic acid was conducted using an average of about 600 parts per million of manganese alone (as manganous acetate) as the catalyst. In the 2-inch glass pipe reactor, a 24 inch roused liquid depth was maintained at a 1.24 liter roused liquid volume. The pressure was maintained at 90 p.s.i.g. and 50 weight percent oxygen in nitrogen was used as the oxidant distributed by a fritted 31 6 stainless steel sparger. The catalyst was fed to the reactor in the form of a solution of 10 weight percent manganous acetate (2.24 weight % Mn) dissolved in heptanoic acid. Table Xl indicates the conversions and efficiencies from this series of runs.

TABLE Xl OXIDATION OF HEPTANAL TO HEPTANOIC ACID USING MANGANOUS ACETATE ALONE (600 PARTS PER MILLION Mn++ AVERAGE) Example 48 49 Temperatures, OC.: 5'inches from bottom 65 65 16 inches from bottom 62 62 Catalyst solution fed, cc/min 0.31 0.25 Calc. Catalyst Conc., PPM 600 560 Oxidant Fed, moles/Liter/Hr 4.20 3.84 Oxygen'in the vent gas, mole % 4.4 4.5 Oxygen Conversion, % 94.1 94.0 Oxygen Consumed, moles/Liter/Hr 1.88 1.72 C7 Aldehyde Conversion, % 89.0 91.1 *Efficiency, % Heptanoic acid 82.78 81 A7 2-methylhexanoic acid 5.09 5.03 Total C7 acids 87.87 86.50 CO 0.33 0.30 CO2 1.00 1.15 Hexane plus Hexene 2.48 2.33 Hexanal 1.24 0.61 Hexanol 0.60 0.72 Hexanoic acid 2.21 2.99 Esters 2.69 2.66 *In addition to the above-identified products, small amounts of high boilers, lactone, keto acids, succinic acid, glutaric acids, dehydrated aldoldimer were also produced. Efficiencies based on total C7 aldehyde.

EXAMPLES 50-56 Utilizing the same single stage reactor equipment and the same conditions as used in Examples 37-41, a series of runs of the oxidation of heptanal to heptanoic acid were carried out using as the catalyst a combination of copper and manganese salts on a 1:1 molar ratio. The catalyst solution added to the reaction was 3.74 weight % cupric acetate (1.19 weight % Cu) and 5.31 weight % manganous acetate (1.1 9 weight % manganese) in heptanoic acid. The 2-inch glass pipe reactor was maintained at 90 p.s.i.g. and a 50% oxygen in nitrogen was used as the oxidant. Table XII indicates the conversions and efficiencies obtained from these runs.

TABLE XII SINGLE-REACTOR HEPTANAL OXIDATION TO HEPTANOIC ACID USING A CATALYST COMBINATION OF CUPRIC AND MANGANOUS ACETATE Example 50 51 52 53 54 55 56 Roused Liquid HT, inches 25 25 24 24 24 24 24 Roused Liquid Vol., Liters 1.30 1.30 1.24 1.24 1.24 1.24 1.24 Temperature, C.: 5 inches from bottom 63 66 62 62 67 75 76 16 inches from bottom 67 70 66 66 70 71 80 % 2-methylhexanal in aldehyde 7.8 7.8 5.7 6.3 6.3 6.3 6.3 Catalyst sol. fed. cc/min 0.35 0.33 0.30 0.22 0.17 0.17 0.17 Calculated cat. conc, parts per milion each of Mn and Cu 290 260 260 270 255 250 280 Oxidant fed, moles/liter/hr Calc.

from vent N2 4.43 4.72 4.13 3.61 3.62 4.22 4.49 Oxygen in the vent gas mole % 3.0 3.3 3.8 4.4 3.0 3.0 2.4 Oxygen conversion % based on vent N2 96.6 96.2 95.2 94.3 96.1 95.9 96.8 Oxygen Consumed, moles/liter/hr based on vent N2 2.12 2.25 1.87 1.62 1.66 1.93 2.07 Est. liquid Res. Time, hr 1.3 1.4 1.4 2.0 2.5 2.5 2.5 C7 Aldehyde Conversion, % 75.4 78.7 81.0 90.1 93.0 96.7 94.1 *Efficiency, % Heptanoic, acid 85.32 85.69 87.16 85.76 81.56 80.05 78.00 2-methylheptanoic acid 7.04 6.88 5.52 5.37 5.30 4.97 4.90 Total C7 acids 92.36 92.57 92.68 91.13 86.86 85.02 82.90 CO 0.30 0.37 0.26 0.25 0.26 0.26 0.39 CO2 0.46 0.56 0.49 0.75 1.41 1.92 2.23 Hexane plus Hexene 1.41 1.48 0.70 0.75 0.56 0.57 0.61 Hexanal 0.81 0.93 0.87 0.97 1.35 1.31 1.42 Hexanol 0.16 0.17 0.00 0.14 0.39 0.00 0.00 Hexanoic acid 1.00 1.23 1.38 2.19 3.28 2.98 3.81 *In addition to the above-iddentified products, small amounts of high boilers, esters, lactone, keto acid, succinic acid, dehydrated aldolimers were also produced. Efficiencies based on total C7 aldehyde.

In Examples 37-56, a direct comparison exists in the oxidation of heptanal to heptanoic acid using a manganese salt catalyst alone and a catalyst combination of manganese and copper salts. The use of manganese salts alone as oxidation catalysts for production of acetic acid from acetaldehyde, propionic acid from propionaldehyde and valeric acid from n-valeraldehyde provides high carbon efficiencies to acid at high aldehyde conversions. It has been found, however, that as the carbon content of the aldehyde increases, the carbon efficiency to acid decreases rapidly at high aldehyde conversions.

For example, the carbon efficiency of heptanal to C7 acids was 9091 % up to N7 5% aldehyde conversion and dropped rapidly to 86% at 82% aldehyde conversion. The low conversion of heptanal at high carbon efficiencies to acids per pass (7075%) with recovery of unreacted aldehyde (by distillation), requires a recycle procedure to obtain the best overall yields. The use of the combination of manganese and copper salts for heptanal oxidation to heptanoic acid provides carbon efficiencies to C7 acids in the range from 90 to 93% at 80 to 90% aldehyde conversions. The results of the combination of manganese and copper salts in the heptanal oxidation are significantly better than the results obtained from using a manganese salt alone.The use of the combination of manganese and copper salts permits the use of a second stage catalyst reactor to convert the small amount of unreacted aldehyde further into the desired heptanoic acid without using an aldehyde recovery and recycle system. This is demonstrated in the following examples: EXAMPLES 57-59 In these examples, it is demonstrated that heptanal can be oxidized to heptanoic acid at overall aldehyde conversions from about 94 to 98% with high carbon efficiencies to acids, using a catalyst a combination of manganese and copper salts in a two stage reactor.The two stage reactor process utilizes two 8 feet by 2-inch glass pipe reactors in sequence wherein the first stage converts heptanal in the range from about 80 to about 86% at a reactor height of 46 inches (2.37 liters), and the second stage at a reactor height of 30 inches (1.54 liters) receives the reaction product from the first stage, for further conversion of the unreacted aldehyde until approximately 95 to 98% overall aldehyde conversion has occurred. The reaction conditions of the two stages were 90 p.s.i.g. pressure; the oxidant was 50% oxygen in nitrogen distributed in the first stage through a 0.017-inch capillary sparger and in the second stage through an 0.007-inch capillary sparger.The catalyst solution contained 4.45 weight percent manganous acetate (1.0 weight percent manganese) and 3.14 weight percent cupric acetate (1.0 weight percent copper) dissolved in heptanoic acid (density 0.918 grams per milliliter) and was added to the first stage reactor only. The pump around rate was 1.98 liters per minute.

Using this process, high overall carbon efficiencies to heptanoic acid were achieved without utilizing a recycle operation as shown in Table XIII which describes the overall conversions and efficiences obtained from these examples. The first stage conversion results were estimated based on the C7 aldehydes content.

TABLE XIII 2-STAGE HEPTANAL OXIDATION TO HEPTANOIC ACID USING A CATALYST COMBINATION OF MANGANOUS ACETATE AND CUPRIC ACETATE Example 57 58 59 Temperatures, "C.

5 inches from bottom (1st stage) (2nd-stage) (53) (53) (53) (53) (53) (52) 16 inches from bottom (1st stage) (2nd-stage) (52) (53) (50) (53) (51) (52) C7 Aldehyde fed, cc/min 26.63 25.53 25.30 'Catalyst solution fed, cc/min 0.70 0.68 0.69 .Catalyst concentration, ppm each 260 260 265 Oxygen fed, moles/hr based on vent nitrogen 5.78 6.04 6;;43 Oxygen in the vent gas, mole % 2.4 3.0 3.1 Oxygen conversion, % based on vent nitrogen 90.4 88.1 87.8 C7 Aldehyde Conversion, % First Stage 81 86 86 Overall 95.2 96.1 96.8 *Efficiency, % Heptanoic acid 83.72 82.60 82.07 2-Methylheptanoic acid 4.34 4.41 5.05 Total C7 acids 88.06 87.01 87,12 CO 0.07 0.10 '0.07 -CO2 0.52 0.70 0.76 Hexane, Hexene 0.78 0.67 0.71 Hexanal 1.11 1.09 1.11 Hexanol 0.20 0.20 0.22 Hexanoic acid 2.16 2.54 2.81 OverallvC7 Acid Yield, % from heptanal 83.8 83.6 84.3 *ln addition to the above-identified products, small amounts of esters and light ends were also produced. Efficiencies based on total C7 aldehyde.

EXAMPLES 60-62 These examples were carried out using slightly different reaction conditions from Examples 57-59 and the same equipment, except that fritted stainless steel spargers were used in each stage. In the first stage reactor, the roused liquid height was 23 inches and its volume 1.18 liters. In the second stage the roused liquid height was 20.5 inches, and its volume 1.06 liters. Both stages were maintained at pressures of 90 p.s.i.g. and 50% oxygen in nitrogen was used. The catalyst solution (density 0.822 g/ml) contained 3.74 weight percent cupric acetate (1.19 weight percent copper) and 5.31 weight percent manganqus acetate (1.19 weight % Mn) dissolved in heptanoic acid. The catalyst solution was added to the first stage only and calculated as amounts in second stage.

Table XIV illustrates the conversions and efficiencies of the two stage heptanal oxidation under the specific conditions described.

TABLE XIV TWO-STAGE HEPTANAL OXIDATION TO HEPTANOIC ACID USING A CATALYST COMBINATION OF MANGANESE AND COPPER Example 60 61 62 First Second Overall First Second Overall First Second Overall Stage Stage Stage Stage Stage Stage Temperature, C.: 5 inches from bottom 66 65 - 66 65 - 66 66 16 inches from bottom 65 65 - 65 65 - 65 65 C7 Aldehydes fed, cc/min 11.80 - - 13.40 - - 13.50 - Catalyst solution fed, cc/min 0.29 - - 0.33 - - 0.34 - Calculated cat. conc. ppm each Mn and Cu - 290 - - 285 - - 295 Oxydant fed, moles/liter/hr Calc. from vent N2 3.44 - 4.61 3.87 - 4.75 3.82 - 4.81 Oxygen in the vent gas, mole % 7.6 13.1 - 7.4 3.9 - 6.8 5.0 Oxygen Conversion % based on vent N2 90.5 - 82.3 91.8 - 94.8 92.0 - 93.7 Oxygen Consumed, moles/liter/hr Based on vent N2 1.48 - 1.81 1.76 - 2.25 1.78 - 2.25 Est.Liquid Residence Time, hrs. 1.7 1.8 - 1.4 1.6 - 1.4 1.3 C7 Aldehyde Conversion, % 89.7 9.0 98.7 84.7 13.0 97.7 84.3 12.7 97.0 *Efficiency, % Heptanoic acid 84.59 - 83.29 85.94 - 82.58 86.22 - 85.68 2-methylhexanoic acid 5.52 - 5.15 5.87 - 5.57 5.72 - 5.39 Total C7 Acids 90.11 72.2 88.44 91.81 63.6 88.15 91.94 84.9 91.07 CO 0.33 - 0.32 0.32 - 0.29 0.39 - 0.37 CO2 0.55 - 0.97 0.36 - 0.77 0.38 - 0.70 Hexane plus Hexene 1.13 - 0.83 1.76 - 0.95 1.84 - 1.02 Hananal 1.03 - 1.00 0.91 - 0.91 1.00 - 1.00 Hexanol 0.24 - 0.22 0.24 - 0.22 0.00 0.09 Hexanoic acid 1.86 - 1.91 1.24 - 2.50 1.29 - 1.40 * In addition to the above-identified products, small amounts of high boilers, light ends, esters, pentanoic acid, butyric acid, propionic acid, acetic acid, lactone, keto acid, succinic acid, glutaric acid and dehydrated aldo dimers were also produced.Efficiencies are based on total C7 aldehyde.

EXAMPLES 63-68 In these examples, it is demonstrated that nonanal can be oxidized to nonanoic acid very effectively at overall aldehyde conversions from about 91-97 with high carbon efficiencies to acids, using as a catalyst a combination of manganese and copper salts in a two stage reactor. The two stage reactor used is identical to the equipment used in Examples 57-59 for oxidation of heptanal to heptanoic acid. This includes two 2-inch galss pipe reactors in sequence wherein the reaction medium in the first stage reactor was maintained at a height of 46 inches (2.37 liters) and the reaction medium in the second stage reactor was maintained at 30 inches (1.54 liters). The pump around rate was 1.98 liters per minute.The catalyst solution used was 2.81 weight percent manganous acetate (0.36 weight % Mn) and 1.98 weight percent cupric acetate (0.36 weight % Cu) in a mixture of 43 weight percent acetic and 52.2 weight percent nonanoic acid. The acetic acid was used to help solubilize the manganese and copper salts. Both stages were maintained at pressures of 90 p.s.i.g. and 50% oxygen in nitrogen was used as the oxidizing gas.

Results of these examples are shown in Table XV. The first stage conversion results were estimated based on the C9 aldehyde content.

TABLE XV TWO-STAGE NONANAL OXIDATION TO NONANOIC ACID USING A CATALYST COMBINATION OF MANGANESE AND COPPER Example 63 64 65 66 67 68 Temperature, C.: 5 inches from bottom (1st stage) (second stage) (62) (63) (63) (60) (53) (53) (53) (54) (52) (53) (52) (53) 16 inches from bottom (1st stage) (second stage) (60) (63) (61) (60) (51) (53) (51) (54) (51) (53) (51) (53) C7 Aldehyde fed, cc/min 23.0 25.3 28.6 25.6 24.6 25.6 Catalyst Solution fed, cc/min 1.27 1.36 1.51 1.32 1.30 1.36 Catalyst Concentration, PPM each of Mn++ and Cu++ 200 195 190 185 190 190 Acetic Acid Concentration, Wt. % 2.4 2.3 2.2 2.3 2.3 2.3 Oxygen Fed Moles/Hr: Based on Vent Nitrogen Oxygen in the Vent Gas, Mole % 4.4 4.4 3.3 4.4 4.0 4.3 Oxygen Conversion, %: Based on Vent Nitrogen 82.2 82.6 86.8 82.3 84.0 82.9 C9 Aldehyde Conversion, %: not not First Stage determined determined 75 85 87 84 Overall 97.2 96.0 90.8 95.3 96.1 96.6 *Efficiency, % Nonanoic acid 82.3 83.15 82.80 84.03 83.07 85.42 2-methyloctanoic acid 3.48 3.52 3.55 3.19 4.06 3.10 Total C9 acids 86.31 86.67 86.35 86.21 87.13 88.52 CO 0.08 0.07 0.00 0.00 0.00 0.00 CO2 0.76 0.67 0.57 0.75 0.70 0.63 Octane & Octene 1.31 1.49 1.90 1.46 1.50 0.65 Octanal 1.60 1.69 1.64 1.66 1.77 0.36 Octanol 0.53 0.62 0.70 0.59 0.50 0.20 Octanoic acid 2.53 2.49 2.21 2.37 2.52 2.01 *In addition to the above-identified products, small amounts of light ends, esters and dehydrated adol dimers were also produced. Efficiencies are based on total C9 aldehyde.

Claims (6)

1. A catalytic process for producing organic aliphatic monocarboxylic acids containing from 6 to 9 carbon atoms by the oxidation of the corresponding aldehyde of the acid, wherein the catalyst used is a combination of manganese and copper compounds soluble in said acid and wherein the molar ratio of manganese to copper ranges from 5:1 to 0.5:1.

2. A process according to claim 1 wherein the copper and manganese catalysts are cupric acetate and manganous acetate and the molar ratio of manganese to copper ranges from 3:1 to 1:1.

3. A process according to claim 1 or 2 wherein heptanoic acid is produced from heptanal.

4. A process according to claim 1 or 2 wherien nonanoic acid is produced from nonanal.

5. A process for producing monocarboxylic acids according to claim 1, substantially as hereinbefore described with reference to the Examples.

6. A monocarboxylic acid prepared by a process according to any of the preceding claims.