CS270210B2 - Method of monocarboxylic acids continuous production,especially with 8 till 18 carbon's atoms,by means of n-alkanes' catalytic oxidation - Google Patents

Abstract

The present invention describes a continuous process for the preparation of fatty acids, in particular of C8-C18-fatty acids, by selective oxidation of n-alkanes using a gas containing the oxygen in the presence of catalysts in a gas-liquid system, the liquid n-alkanes being brought into contact with an added catalyst and optionally an initiating agent in countercurrent in an absorption column using a gas which contains oxygen in a 2-8-fold excess in relation to the liquid phase. The process is carried out at a temperature of over 160 DEG C under normal pressure or under a pressure increased up to 2 MPa and under a loading of the column with the gas of 800-6000 m<3>/m<2>h and with the liquid of 2.5-20 m<3>/m<2>h. The acids formed can be withdrawn from the upper part of the column together with the stream of waste gases if the loading of the column with the liquid is up to 2.5 m<3>/m<2>h and with the gas 6000-8000 m<3>/m<2>h. The time of initiation of the reaction can be cut by using an initiating system consisting of 0.1-0.5 % by weight of potassium permanganate and 0.05-0.1 % by weight of a phase transfer catalyst, in proportion to the amount of n-alkanes.

Description

The invention also relates to a process for the continuous production of monocarboxylic acids, in particular of 18 to 18 carbon atoms, by selective oxidation of n-alkanes and to the use of catalysts in a two-phase gas-capsule system. Synthetic monocarboxylic acids are widely used in the manufacture of laundry detergents instead of natural monocarboxylic acids, in the manufacture of lubricating fats, fatty alcohols as well as surfactants. In recent years, the use of synthetic monocarboxylic acids has been considerably expanded, due to the high degree of selectivity of the synthesis of these acids due to the possibility of producing narrower acid fractions. Such fractions allow the production of products with defined special properties. For example, the C8 -C20 acid fraction is used to make soaps and the C10 -C16 fraction is a raw material that replaces hard-to-reach coconut oil.

In particular, processes for batch production by oxidation of alkanes obtained from either oil or lignite, air or oxygen-enriched gas are known to produce monocarboxylic acids. . '

As a rule, the oxidation process is carried out at a temperature in the range of 120 to 160 ° C under normal pressure or at elevated pressure (88SR No. 351 826) in the presence of a catalyst system consisting mostly of salts of n-alkanoic acids with manganese and potassium. The duration of the reaction in this process requires 16 to 24 hours, the conversion reaches 40% and the selectivity is approximately 30 to 33%. \

US-A-613 * 713 also discloses a quasicontinuous method of oxidizing n-alkanes in column reactors, for example of the blow tube type. The process consists in the two-stage oxidation of the n-alkanes with an oxygen-containing gas, wherein in the first stage the n-alkanes are oxidized partially and periodically by the oxygen-containing gas at a temperature of 100 to 140 ° C. In the second stage, the oxidation is carried out continuously with respect to the gaseous stream which is fed in an amount of 0.3 to 2 liters per minute, based on 1 kg of feed. A small amount of reacted feedstock is continuously withdrawn from the lower part of the reactor, whereby 5 to 10% by weight of the oxidation product is returned to the first stage, and the waste gases are discharged through the condenser from the combustion of part of the reactor. The total residence time of the batch is up to 20 hours in this process, while the acid value reached is 30 to 80, which means that the conversion is small ·

An article by V. E. Agebekow et al. (Neftechimija 1982, 22/4), pp. 528-530) discloses a two-step process for the production of synthetic monocarboxylic acids on a laboratory scale by oxidation of alkene hydrocarbons with molecular oxygen in the liquid phase. In the first step ee, the process is carried out at a temperature of 120 ° C in the presence of nickel and chromium stearates as catalyst, and about 5% by weight of ketones are obtained. In the second step ae, these ketones then oxidize in the presence of manganese, cobalt or coru stearates. In this process, conversion is achieved under optimal conditions

71.7% at a selectivity of 70% and a maximum acid yield of ketones of 51.9%.

U.S. Pat. No. 727 * 620 discloses a process for the periodic oxidation of C--C n n alkanes with an oxygen-containing gas at a temperature of 100 to 160 ° C in the presence of a basic chromium-manganese catalyst used in an amount of 0 , 1 to 0.4% · The reaction takes about 8 hours.

Polish Patent Specification No. 114,126 discloses a method of oxidizing saturated hydrocarbons in the liquid phase with air oxygen to isolate the resulting acids from the reaction mixture by saponifying them with alkali, combining an aqueous emulsion of unreacted hydrocarbons and unsaponified compounds with fresh saturated hydrocarbons and returning the mixture continuously in the liquid phase to the oxidation zone countercurrent to the reaction vapors and gases · The soap melt obtained is diluted with water to a concentration of 35 to 46% by mass and acidified with sulfuric acid to give a crude product containing 70 to 85% by mass of acids · The resulting monocarboxylic acid mixture is separated by fractionated distillation into individual fractions. Batch tubes with blowing tubes are usually used to produce these acids.

The main disadvantages of these processes are the low selectivity, the impossibility to control the reaction as well as its course in different directions, leading to the formation of by-products and secondary synthesis products, namely esters, oxykyeeline and hydroxy acids. This is mainly due to the long-term reaction time of up to 10 and 24 hours, as well as the insufficient mixing of the feed in the reaction zone, which, due to the exothermic nature of the oxidation reaction, results in local overheating zones and thermal decomposition. Insufficient mixing of the batch also leads to the formation of secondary oxidation products. These processes are accompanied by the formation of explosive peroxides.

These methods are highly energy intensive and require the use of additional processes (for example, saponification of the resulting acids to separate them) and complicated production apparatuses, consuming additional reagents.

It has now surprisingly been found that selective synthesis of the carboxylic acids controlled by the process of the invention is possible to obtain a very pure product in high yield.

The object of the invention is therefore a process for the continuous production of monocarboxylic acids, in particular 8 to 18 carbon atoms, by catalytic oxidation of n-alkanes with oxygen-containing gases in a two-phase system in the presence of 0.1 to 0.5% by weight of manganese, potassium, nickel or cobalt. relative to the starting n-alkanes as catalyst and optionally in the presence of potassium permanganate in an amount of 0.1 to 0.5% by weight calculated as manganese as the initiator, the process comprising adding liquid n-alkanes 8 by addition thereto. of the dissolved catalyst and, optionally, the initiator, countercurrently contact the oxygen-containing gases in a two- to eight-fold excess relative to the stoichiometric amount of the n-alkanes contained in the liquid phase at a temperature of 120 to 230 ° C, preferably 140 to 205 ° C, at a pressure of 0.11 to 2 MPa in an absorption column with a pa 10 to 60% overflow and a liquid phase load of 2.5 to 20 and a gas phase load of 800 to 8000 m &^lt; -1 &gt; h &^lt; -1 &gt;.

When the process according to the invention is carried out in an absorption column in a tray having a light diameter of 10 to 30% at a temperature of 160 to 190 ° C under a liquid phase load in a volume of 2.5 to 20 m. m .h 7, 8 preferably 2.5 to 5.0 m. m .h, and under the loading of -2-2 column gas in the volume of 800 to 3000 m. m. m, the contact time of the reactants is from several tens up to thirty or forty minutes, and the reaction product containing 70 to 80 wt% monocarboxylic acids is removed from the bottom of the column and the off-gases from the combustion of the part of the column.

In carrying out the process according to the invention, it has been found that it is possible to remove the monocarboxylic acids resulting from the catalytic oxidation of n-alkanes together with the effluent stream from the combustion of part of the column when the batch has a temperature of 180 to 230 the liquid phase is 2.5 to 5 m .m .h, loading of the column the gas phase is from 4000 to 8000 m ^ .m ^"2 .h and ^el when used with the trays of the absorption column with a free diameter of 30 to 60%. The flow rate of the gaseous stream in the openings in the trays in the column then amounts to 8 to 14 m ^ .s' ^1. These amounts are close to and lower than the amount of column congestion, which allows the oxidation reaction products to be blown off by gases at temperatures substantially lower than the boiling points of the acids formed.

In the process according to the invention, conventional homogeneous oxidation catalysts, preferably a solution of manganese, cobalt, nickel or potassium ethers, are used, in a cell of a single ethers or a mixture thereof, in liquid n-alkenes. The amount of catalyst is 0.1 to 0.5% by weight, based on the amount of n-alkanes in the liquid phase. Preferably, potassium permanganate is also added as an initiating agent in an amount of 0.1 to 0.5, calculated as manganese and based on the amount of n-alkanes.

It has been found that the time required to initiate the reaction can be greatly reduced and the conversion of the n-alkanes in the acid can be increased when the oxidation, irrespective of the use of oxidation catalysts, is carried out in the presence of an initiation system consisting of potassium permanganate. 5 calculated as manganese, and a phase transfer catalyst in amounts of from 0.05 to 0.1% .vztaženo ₉ both on the weight of n-alkanes.

The phase transfer catalyst used is quaternary organic salts, in particular triethylbutylammonium chloride or tetraethylammonium bromide or tetraethylphosphonium chloride.

Phase transfer catalysts have hitherto been used in benzene and cyclohexane oxidation processes and have functioned to transfer manganese ions from the aqueous phase to the liquid organic phase. These processes are carried out at temperatures of 30 to 70 ° C. In the process according to the invention, for the continuous production of monocarboxylic acids, the process is carried out at temperatures above 160 ° C, i.e. where no other liquid (aqueous) phase is present, Phase transfer catalysts play the role of agents which contribute to better initiating the reaction and to reducing the reaction time.

The feedstock can be preheated to a temperature of 120 to 160 ° C prior to introducing the liquid feedstock with the 8 dissolved catalyst into the reactor. The air phase or oxygen-enriched air cell up to 80% by volume can be used as the gas phase. liquid phase.

Due to the use of the above oxidation conditions, undesired side reactions are substantially reduced or completely suppressed and the reaction proceeds in two basic stages of n-alkanes ----> diketones -----> monocarboxylic acids, whereby the chain of n-alkanes is cleaved. occurs selectively in the middle of a string. By using the narrow fractions of n-alkanes for the oxidation, the acids according to the invention can be selectively produced exclusively with acids of the desired chain length. Under these conditions, the reaction mixture does not contain any peroxide-type intermediates after the reaction, which guarantees a safe process according to the invention.

Compared to conventional industrial processes, it has also been shown that intensification of the mass exchange and temperature increase will increase the synthesis process and up to about 70% conversion within 20 to 30 minutes and about 98% conversion within 1 to 1.5 hours, with selectivity remains in the range of 50 to 70% · In addition to the monocarboxylic acids, the resulting product also contains 20 to 30% by weight of diketones.

In the process according to the invention, by using a multiple excess of the active phase of the gas phase over the liquid phase, which are opposed in countercurrent along the column height, an ideal mixing of the reactants and oxidation is achieved in the liquid phase according to kinetic laws of quasimonomolecular reaction. Excess oxygen increases several times during the synthesis under these conditions due to the reaction of the feedstock. The sizes of the gaseous and liquid streams depend on the residence time of the reaction mixture on one floor of the absorption column at defined tray parameters, while the conversion depends on the residence time of the reaction mixture in the absorption column.

The relatively short residence time of the reaction mixture in the absorption column allows the use of higher temperatures and ideal mixing in the one-tray region prevents the formation of degradation products.

The process according to the invention guarantees a high selectivity for the formation of the desired products, in particular unbranched aliphatic monocarboxylic acids having 8 to 18 carbon atoms or the corresponding diketones, which are the only intermediates found in the process according to the invention.

Example 1

The method of oxidation of n-alkanes is carried out in a column with 16 slatted trays without overflow. * Column diameter is 0.046 m, clear tray diameter 25%, rectangular openings on the floor have dimensions of 6 mm x 3 mm, distance between trays is 0.30 m.

For the burning of the column bed, a fraction of 140 DEG C. of preheated 18-36 carbon atoms of n-alkanes together with a catalyst dissolved therein consisting of a mixture of manganese, cobalt and potassium stearates in an amount of 0, 2%, based on the amount of n-alkanes supplied. Záti-

The liquid phase of the column is 3.14 m / m (4.63 kg / h). The ratio of the individual catalyst components is Mn: Co: K - 1: 1: 2.

At the bottom, oxygen-enriched air is fed to the column at a volume of 2300 m &lt; 2 &gt; h &^lt; -1 &gt; (3.818 m &lt; 2 &gt; h &^lt; ^-1 &gt;). is approximately 40% · The weight ratio L / G is 0.9, the flow rate of the gas stream is 0.64 ms ^-1 and in the apertures 2.53 ms ^-1 .

The liquid from above flows through the column and comes into contact with the upstream gas, creating on each floor conditions of ideal mixing and controlled reaction with oxygen in the liquid phase at 190 ° C. The liquid is enriched with monocarboxylic acids while running down the column. * The process is carried out under low pressure conditions (0.12 MPa) due to resistances at the bottom of the column.

The residence time of the reaction mixture in the column is 45 minutes. * The resulting product is removed continuously from the bottom of the column.

The amount of reacted n-alkanes is 4.3 kg.h- ¹ , the content of the desired C8-C18 carboxylic acids in the reaction product is 3.14 kg.h- ¹ , the ketone (mainly O-diketone) content is 1.23 kg .h “ ¹ , the amount of unreacted n-alkanes 0,231 kg.h“ ¹ and the loss of 0,1 kg.h “ ¹ ; based on the amount of starting n-alkanes, the conversion of n-alkanes is 95%, the selectivity of the process is 71.4, the amount of unreacted n-alkanes is 5, and the loss is 2.13%.

The resulting carboxylic acids are isolated from the reaction mixture by distillation. The distillation residue, consisting predominantly of diketones and unreacted n-alkanes, is returned to the manufacturing process after separation of the catalyst.

Analysis of the raw material and products is performed by chemical and physicochemical methods, gas and liquid chromatography and IR spectroscopy using standards. No by-products or decomposition products, i.e. no oxy- or hydro-acids, peroxides, formic and acetic anhydrides, no acids with less than 8 carbon atoms, aldehydes or alcohols, can be detected in the reaction mixture after the reaction.

Example 2

The process is carried out in an absorption column as described in Example 1, except that the clear diameter of the trays is 60%.

Light paraffinic fractions obtained from petroleum dewaxing, which contain n-alkanes of 18 to 36 carbon atoms in an amount of approximately 90% and mineral oils in an amount of approximately 10%, are used as raw materials.

Catalyst solution, i.e. a mixture of manganese, nickel, cobalt and potassium stearates in an amount of 0.2% by weight and in a molar ratio of 1: 1: 1: 2, is added to this feedstock. at the same time add potassium permanganate in an amount of 0.2 56, calculated as Mn, in the form of an aqueous saturated solution and tetraethylammonium bromide in an amount of 0.05% as a phase transfer catalyst, both based on the mass of n-alkanes .

Load on the column the liquid phase is 2.5 m ^ nT ^ .h ^"1 (3.28 kg · h" ^-1) · air enriched with oxygen content of 30 to 56, the ee preheated to 200 ° C and introduced into the column from below, whereby the vapor phase loading of the column is 6000 т ^ ' ² 2 “ ¹ (9.84. The gas phase throughput, based on the column cross-section, is 1.66 weight ratio

L / G - 0.28 and excess oxygen over n-alkanes 8.0.

The oxidant component of the gaseous countercurrent feed, which is in contact with the liquid phase at a temperature of about 230 ° C, induces a rapid reaction of the n-alkanes.

When eetrvání time of 20 minutes a conversion of the starting n-alkanes 3.02 kg.h ^-1 (92 · wt%), wherein the content of monocarboxylic acids in the reaction mixture was 2.11 kg-hr * ¹ (about 70 56 based on reacted product) · The amount of the ketones amounts to 0.845 kg.h ^-1 (28 56) and the loss of 0.064 ^Kghr-1 (2 56).

The content of un-diluted n-alkanes in the reaction mixture was 2.62 x 10 6 kg.h -1. The reaction product also contains 0.328 kg.h * ^ (about 10%) of mineral oils ·

After the isolation of the monocarboxylic acids as in Example 1 and the separation of the mineral oils, the undiluted n-alkanes and the intermediate (ketones, especially β-diketones) are removed with the fresh feedstock after removal of the catalyst and recycled as described * 1.

Example 3

For the burning of an absorption column of the same construction as in Example 1, with only 4 mm x 8 mm orifices and a clear diameter of 60 56, the dissolved catalyst feedstock of Example 2 is continuously fed, except that the ammonium salts used are triethylbutylammonium chloride in an amount by weight of 0.1 based on the starting amount of n-alkanes.

The liquid phase loading is the same as in Example 2, the gas phase loading being 7000 m @ ² · m @ ² · h @ (11.48 The gas phase throughput, based on the column diameter, is 1.94 m @ 8. ( ^C) 0.246, the excess oxygen, based on the amount of n-alkanes, is 5.8 and the oxygen content by volume in the gas phase is 20.56.

The procedure is as in Example 2, except that the monocarboxylic acids formed by the oxidation of n-alkariums are separated from the reaction mixture and fed together with the gaseous stream from the combustion of part of the column to a condenser (absorber) filled with cold water. they collect the water in solid form.

The residence time of the reaction mixture in the column is 60 minutes at 200 ° C.

The achieved conversion of n-alkanes is 2.73 kg.h * (83.3 56) at a monocarboxylic acid amount of 1.912 kg.h-1, which represents a selectivity of approximately 70 56 based on the starting amount of n-alkanes.

The amount of reaction product taken from the combustion of the column part is 2.75 kg.h-1 (84% based on the amount of n-alkanes supplied to the column), of which 2.31 kg.h-1 of monocarboxylic acids (8% by weight). 0.275 kg of diketones, 0.055 kg ^/ h of loss (2 wt%); the remainder being unreacted n-alkanes of up to 20 carbon atoms.

The reaction residue (distillation residue) is withdrawn from the bottom of the column. Its amount, based on the mass of pure raw material - n-alkanes, is 0.524 kg.h ¹ (16%), of which 0.367 kt.h ^-1 ketones, 0.157 kg.h ¹ unreacted 20-32 carbon atoms (30%) and 0.0007 kg.h -1 (0.15%) of the monocarboxylic acids.

Mineral oils are also contained in the distillation residue in an amount of 0.365 kg.h ¹ (10% of the total amount of raw material). During the oxidation of the n-alkanes, these oils undergo no reaction and are taken together with 8 unreacted n-alkanes and ketones from the bottom of the column, whereupon they are isolated. Unreacted n-alkanes and ketones are returned, as in Example 2, after recovery of the catalyst contained therein for reprocessing.

• Example 4

In order to carry out the process according to the invention, the same absorption column was used as in Example 1, but with 26 trays, the pale diameter being 60

The feedstock contains 99% by weight of n-alkanes of 16 to 36 carbon atoms. The initiator system includes a quaternary phosphonium salt, tetraethylphosphonium chloride, as a phase transfer catalyst.

The process is carried out at a temperature of 160 ° C and in the initial phase at a temperature of 120 ° C. Air preheated to 100 ° C is fed into the column bottom, wherein the loading of the column the gas phase is 6000 m ^ .m ^second! / ^'1 (9.84 m \ h "\), loading of the column the liquid phase is 5 (6 56 kg.h ¹ ), the ratio L / G = 0.56 and the excess oxygen in the ratio to n-alkanes is 2.2.

When the residence time of the reaction mixture in the column for 10 hours to a conversion of 5.56 kg.h ^first Amount of ketone (mainly β diketone) is 1.1 kg · h ^1, unreacted n-paraffins 0.8 kg.h ¹ and the amount of produced acids with 8 to 18 carbon atoms, 4.44 kg.h ^'1. The losses are 0.2 kg.h ¹ . The conversion of the reaction mixture achieved was 87.4% and the selectivity of the process was 80.0%, with a C12 to C16 monocarboxylic acid content of approximately 70 based on the product after the reaction. As in Example 1, the product is removed from the bottom of the column.

Example 5

An absorption column as in Example 4 was used to carry out the process, with 26 trays and a pore diameter of 25%.

The feedstock, i.e. n-alkanes of 16 to 36 carbon atoms, together with an 8% dissolved catalyst (0.2% w / w potassium stearate) preheats to 80 ° C and feeds the column tray to the combustion. consisting of potassium permanganate in an amount by weight of 0,5 calculated as manganese, and tetraethylphosphonium chloride in an amount of 0,1% by weight.

Load on the column the liquid phase is 2.5 m ^ nT ^ .h ^-1 (3.28 kg.h ¹⁾ and the gas phase т ^ .т 2000 ^second-1 (3.28 m ^ .h ^"1). The flow rate of the gaseous stream in the column cross-section is 1.66 ms ^-1 .

A double excess of oxygen is used; the temperature of the reaction mixture on the top of the column is initially 100 ° C and is raised to 160 ° C during the process. The residence time of the reaction mixture in the column is 2 hours.

The amount of reacted n-alkanes is 3.02 kg.h- ¹ , the conversion is 94% and the content of monocarboxylic acids having 8 to 16 carbon atoms is 2.41 kg.h- ¹ , i.e. the selectivity is

79.8% based on the final product. Content not dilute ago a substituted n-alkanes in the reaction mixture after completing the process is from ¹ 2,0.1ο kg.h ¹ and losses of around 2%.

Claims (7)

SUBJECT OF THE INVENTION Process for the continuous production of monocarboxylic acids, in particular β 8 to 18 carbon atoms, by catalytic oxidation of n-alkanes with oxygen-containing gases in a two-phase system in the presence of manganese, potassium, nickel or cobalt stearates as catalyst in an amount of 0.1 to 0.5 %, based on the amount of starting n-alkanes, and optionally in the presence of potassium permanganate initiator in an amount of 0.1 to 0.5% by weight, calculated as manganese, characterized in that the liquid n-alkanes are used. with the addition of a catalyst dissolved therein and optionally an 8 initiating agent, contact the oxygen-containing β gases countercurrently with a two- to eight-fold excess with respect to the stoichiometric amount of n-alkanes contained in the liquid phase at a temperature of 120 to 230 ° C. temperature 140 to 205 ° C, under pressure. 0.11 to 2.0 MPa in the absorption column of the β tray without overflow with a clear diameter of 10 to 60% and under the liquid phase loading from 2.5 to 20 and under the gas phase loading from 800 to 8000 _m 3 m ² H ' ¹ '' Ш о Ш · 2. A process according to claim 1, characterized in that it is carried out in an absorption column with trays having a clear diameter of 10 to 30% at a temperature of 160 to 190 [deg.] C. under a column load of 3-2-2 in an amount of 2.5 to 20 m .ha. under load of the gas phase in 7 - 21 amounts of 800 to 3000 m.m.h, and a product containing 70 to 80% monocarboxylic acids ее withdraws from the bottom of the column · 3. A process according to claim 1, characterized in that it is carried out in an absorption column with a parv of 30 to 60% clear diameter at a temperature of 180 to 230 [deg.] C. under load of the column. -2 -1 liquid phase in an amount of 2.5 to 5.0 m .m * ^J .ha for loading of the column the gas phase at 4000 8000 m EŽ ^J «m» HA product containing 80 to 84% of the monocarboxylic acid is removed from burning a portion of the column in an amount by weight of 65 to 85 based on the amount by weight of the n-alkanes fed to the column together with the effluent stream. 4. The process of claim 1 wherein the liquid n-alkanes with the catalyst dissolved therein are preheated to a temperature of 120-160 [deg.] C. prior to loading into the column. 5. A process according to claim 1, wherein air or oxygen-enriched air up to 80% by volume is used as the gas phase for the oxidation of the n-alkanes. The process according to claim 1, characterized in that it is carried out in the presence of an initiating system consisting of potassium permanganate in an amount of 0.1 to 0.5% by weight, calculated as manganese and based on the amount of n-alkanes, and of quaternary organic compounds. phosphonium or ammonium salts, in an amount of 0.05 to 0.1% by weight, based on the amount of n-alkanes. 7. The process of Claim 6 wherein the quaternary organic salt is triethylbutylammonium chloride or tetraethylammonium bromide or tetrabutylphosphonium chloride. . .