BE706281A - - Google Patents

Description

  

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  Process for the preparation of acids & carboxylic acids from lower hydrocarbons
The present invention relates to the preparation of organic chemical compounds from lower aliphatic hydrocarbons.



   More particularly, the invention relates to an improved process for the preparation of carboxylic acids and other oxygenated aliphatic compounds from the products resulting from the liquid phase oxidation of aliphatic hydrocarbons with the aid of molecular oxygen. , in the presence of an oxidation catalyst.



   Particularly, the invention relates to a process consists in partially oxidizing a hydrocarbon @ so as to obtain a carboxylic acid as well as @

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 ancillary products comprising a free or esterified alcohol corresponding to said carboxylic acid as well as a ketone which is a precursor of said carboxylic acid and then carrying out a secondary oxidation of at least a portion of the ancillary products, in order to obtain additional carboxylic acid .



   The process according to the invention results in an increased yield of carboxylic acid from the hydrocarbon feedstock. Compared with previous processes for converting hydrocarbons to carboxylic acids, it also results in a substantial decrease in the degradation of the feed to industrially unusable by-products and the consumption of high pressure air required to produce a quantity. carboxylic acid data.



   According to a representative process for the preparation of a carboxylic acid by partial oxidation of a hydrocarbon, a hydrocarbon feed, in a liquid reaction medium containing an appropriate catalyst (such as a compound of cobalt, chromium or manganese soluble in carboxylic acid) ,. is converted into oxygenates comprising the carboxylic acid by mixing a gas comprising molecular oxygen with the resulting liquid reaction medium. Air is commonly used as a source of oxygen, although pure oxygen can be used if appropriate measures are taken to prevent the formation of explosive compositions in the reaction system.

   Various types of oxidation reactors are used, ranging from simple vessels with a high degree of internal back-mixing to long tubular reactors designed to minimize back-mixing. Reaction temperatures of 175-200 ° C are used; requires maintenance of

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 relatively high pressures in the oxidation reactor, i.e. about 40 to 70 atmospheres, in order to keep the reacting substances in the liquid phase. The reactors may or may not be agitated. The reaction temperature is controlled either by bringing the liquid contents of the reactor into contact with cooled heat exchange surfaces, or by condensing the vapors given off from the reactor and returning the condensate to the reactor.

   According to a representative mode of conversion of butane into acetic acid, the product of the oxidation reactor comprises acetic acid, ethanol, unoxidized butane, intermediate reaction products such as methyl. ethyl ketone, as well as by-products such as acetone. Also present are substantial amounts of acetic esters, eg, methyl and ethyl acetates, as well as lesser amounts of higher carboxylic acids such as propionic and butyric acids. These higher carboxylic acids are produced to a minor extent when the oxidation feedstock comprises butane, and to a greater extent when it includes higher hydrocarbons such as pentanes, hexanes and heotanes.



   Taking as an example again a method of obtaining acetic acid from butane, the acetic acid is recovered from the oxidation product by various means known in the art such as, for example, , distillation. The acetic acid contents of the acetic ester component of the product are also commonly collected by hydrolysis followed by extraction with solvents, and distillation.

   Intermediate oxidation products comprising contained in the reaction product, / in particular

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 methyl ethyl ketone were previously recycled to a large extent to the original oxidation reactor to undergo a more complete oxidation to acetic acid, although it has been possible to collect and purify, on a limited scale, a methyl fraction. ethyl ketone-ethyl acetate to be used as a solvent and, with the aid of additional treatments, to recover pure methyl ethyl ketone (abbreviated, below, as MEK).



   It has long been recognized that the existing technology, as described above, results in substantial degradation of the hydrocarbon to worthless substances, such as oxides of carbon and formic acid.



   It is also recognized that air or other oxygen-containing gas, used under high pressure, necessary for the oxidation reaction of the hydrocarbon constitutes a substantial cost of production, both from the point of production. from the point of view of operating expenses and from the point of view of necessary capital investment. It was not clear, however, how to remedy these shortcomings. Particularly, it was believed that it was necessary to operate the reactor at a temperature of J75 to
200 ° C. to maintain the reaction at an industrially satisfactory rate.

   It was also believed that it was necessary to recycle to the reactor the major portion of the ketone contained in the reaction product (which is, for example, methyl ethyl ketone when preparing acetic acid). , the reason for this being that the ketone acts as a reaction initiator in the oxidation of the hydrocarbon. Of course, the recycled ketone is largely converted to the carboxylic acid, although at the expense of some chemical degradation under relative conditions.

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 severely stringent existing in the reactor and also at the expense of additional high flow air, or other source of oxygen, necessary for its oxidation.

   Having to carry out the oxidation of the hydrocarbon under the stress imposed by these factors places a higher limit on the chemical efficiency obtainable in the conversion of the hydrocarbon into oxygenates, and a higher limit on the chemical efficiency that can be obtained in the conversion of the hydrocarbon to oxygenates. lower limit on the amount of air or other source of molecular oxygen which must be compressed and charged into the oxidation reactor to provide a given amount of carboxylic acid or carboxylates in the products collected from the reactor.



   The aims of the invention are: to provide an improved process for converting a lower hydrocarbon into a carboxylic acid with a chemical efficiency greater than the characteristic efficiencies of the current processes according to which the oxidation reactor of the gas is operated. hydrocarbon at a temperature of 175 C and above, and wherein the major portion of the ketone collected from the products of the oxidation oeration of the hydrocarbon is recycled to the oxidation reactor; - to provide a process for reducing the amount of high pressure air or oxygen required per unit weight of carboxylic acid produced in the preparation of carboxylic acid by processes comprising the liquid phase oxidation of a lower hydrocarbon;

     , - to provide a process for improving the overall transformation of the hydrocarbon into salable products, in a process comprising as an initial stage catalytic oxidation

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 in liquid phase of a lower hydrocarbon in order to obtain oxygenated derivatives thereof.



   Other objects, advantages and characteristics of the invention will become apparent from the detailed description and the examples which follow in which, for the sake of brevity, the abbreviation "MEK" will be used to denote methyl ethyl ketone.



   According to the present invention, and taking acetic acid as an example of representative carboxylic acid, the reactor in which the hydrocarbon is oxidized is operated at which is a lower temperature than that characteristic of the prior art. This results in a substantial increase in the proportion of MEK in the reaction product, this increase being of such magnitude that it is no longer to the reactor necessary to recycle / most of the MEK collected to initiate the reaction. .

   At least a portion of the MEK is removed for conversion to acetic acid, in a separate secondary oxidation system, in which high chemical efficiency is obtained and in which it is not necessary to use d. air or other gas containing oxygen at the high pressures characteristic of the primary reactor (oxidation of the hydrocarbon). Advantageously, is also included with the MEK charged into this secondary system a certain quantity of ethanol which is also present as a by-product of the original reaction and which constitutes an important source of additional acetic acid. silencing in secondary oxidation.



   It follows, from the use of the invention, at least two advantages, compared with the prior techniques .; res. First, there is a decrease in the amount of source

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 of high pressure oxygen required to produce a given amount of carboxylic acid. This is because in secondary oxidation all that is needed is a nominal reaction pressure of 3 to 25 atmospheres, and most commonly 5 to 7 atmospheres, while in primary oxidation , a pressure of 40 to 70 atmospheres is required. Second, the overall conversion of hydrocarbon to carboxylic acid and other products, such as alcohols, for example, is carried out more efficiently from the point of view of net material consumption. first per unit of weight of salable products obtained.

   The prior art did not provide these advantages primarily because it was not known that a relatively massive amount of ketone could be removed from the primary oxidation reaction system without delaying the reaction to the point of rendering it commercially unusable. Neither had it previously been thought to adjust the conditions in the hydrocarbon oxidation reactor so as to deliberately produce substantial quantities of substances (ketone and alcohol) which are not of the hydrocarbon. carboxylic acid, with the final aim of subsequently converting them to carboxylic acid in a separate process step and thereby increasing the final production of carboxylic acid from a given amount of a hydrocarbon feed.



   The detailed description below is based primarily on a system in which the hydrocarbon feed comprises normal butane and the carboxylic acid is acetic acid. Of course, the invention is also applicable to somewhat different oxidation systems and to a wider range of charges. nn can, like

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 The feedstock is to use hydrocarbons of higher molecular weight than butane, for example, pentanes, to obtain ketones corresponding to these hydrocarbons and carboxylic acids derived from the oxidative cleavage of ketones.

   Certain higher hydrocarbons can be used to prepare acetic acid; the most suitable, for obtaining acetic acid and the parallel production of ketone precursors of acetic acid, have a structure of 2-alkyl butane type. MEC is obtained largely from the butane chain of these higher hydrocarbons. In particular, these higher hydrocarbons, up to approximately 2-hexyl butane, give, by oxidation, substantial amounts of ECM and other ketonic precursors of acetic acid and can be used in the process according to the invention such as applied to the preparation of acetic acid. Saturated hydrocarbons are preferred, although olefins can be used at the expense of increased yield of byproducts.



   As used herein, the term "oxidation system for primary cation reaction" includes a liquid phase oxidation vessel, a device for injecting liquid feeds and molecular oxygen into said vessel, a device for removing the heat of reaction from said vessel and thereby controlling the temperature of the reaction, and a device for removing the reaction product and separating it into various primary fractions. Also included is a device for recycling various of these original fractions by returning them to the oxidation reactor.

   As used herein, the term "confined reaction zone" refers to the reactor itself, and "primary oxidation system"

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 designates the reactor and the auxiliary devices which have just been described.



   The existence of at least three liquids containing a ketone in the system is generally characteristic of any liquid phase oxidation system as described above. These three liquids are: (a) a first liquid containing a ketone which is the liquid contents of the reactor itself, (b) a second liquid containing a ketone which is a fraction derived from the liquid contents of the reactor and which constitutes the reaction product entering the product collection system, and (c) a third liquid containing a ketone, which is derived from the second, during the primary collection operations and which differs from the second in that it comprises substantially all of the ketone initially present in the second fraction while containing, in most cases, only minor amounts of the other reaction products,

   for example, carboxylic acid, acetone, etc. The relationships existing between these three liquids as well as their relationship with the invention as defined here will be specified below.



   According to a type of hydrocarbon oxidation process, which also relates to a particular embodiment of the invention, a hydrocarbon feed consisting mainly of normal butane, but also comprising, if desired. , in admixture, propane or higher hydrocarbons (such as pentane, for example), is transformed into acid. acetic, as follows: (a) A reactor is used which comprises a horizontal cylindrical vessel, the upper portion of which communicates with a condenser.

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   (b) A second vessel, adjacent to the reactor, is arranged to be used as a settling tank. This settling tank communicates with the condenser, so as to receive the condensate from the latter. The upper part of the settling tank, that is to say the part containing the upper phase of the two liquid phases which are contained in the settling tank, communicates with the oxidation reactor. The lower portion of the settling tank is provided with a discharge duct to remove the lower liquid phase. (c) During operation, a liquid reaction medium comprising acetic acid, in which a suitable oxidation catalyst soluble in acetic acid is dissolved, is maintained in the reactor.

   The catalysts normally used are cobalt and / or chromium compounds, which are normally charged to the reactor as salts / acetic acid. The hydrocarbon feed, along with the recycle streams, as will be explained below, is continuously charged into this reaction medium. Additional amounts of catalyst are also added as needed, to maintain at least a minimum effective concentration thereof, which is about 1 to 1000 parts per million. The oxidation of the hydrocarbon is accomplished by injecting air, or other gas containing molecular oxygen, below the surface of the liquid striker, through a suitable distri- bution.

   The liquid in the reactor is the first liquid containing a ketone according to which the invention is described herein. Of course, the ketone here is the MEC.



   (d) The reaction temperature can be controlled, in whole or in part, by applying exchange methods

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 thermal superficial to the liquid contained in the reactor.



   However, in the system described here, the temperature is controlled by allowing the vapors given off from the surface of the reaction medium to pass into the condenser. The uncondensed gases passing through the condenser are sent to a conventional installation to collect the hydrocarbons still contained therein, after which the fixed gases, for example nitrogen and carbon oxides, are vented to the atmosphere.



   (e) Condensate from the condenser is discharged to the decanter. In the decanter, the temperature of the liquid content is kept low enough for the condensate to separate into two liquid phases. The temperature required in the decanter will vary with the composition of the condensate being treated in a given case, but normally it should not exceed about 60 ° C. It is possible, if desired, to use even lower temperatures, which can even reach that at which a solid phase is formed. The normal operating range is approximately 10 ° C.

   Above about 120 ° C, two liquid phases usually do not form, although increasing the amount of water present may in some cases result in the formation of two phases of the temperatures. erasures as high as 180 C.



   (f) The upper liquid phase contained in the decanter is rich in hydrocarbon and also contains substantial amounts of MEK. It is advantageously returned directly to the oxidation reactor, in order to undergo there another oxidation. Its ECM content helps to maintain the oxidation reaction of the hydrocarbon. The lower phase is rich in acetic acid and other oxidation products, including water. We separate it and send it to the system

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 Primary Product Collection (g) The table below shows a representative example of the composition of the heavy phase. It is understood that it can vary considerably, depending on the nature of the hydrocarbon feed, the temperature of the oxidation reaction, the oxidation catalyst, etc.
 EMI12.1
 
<tb>



  Compounds <SEP> Concentration, <SEP> weight
<tb>
<tb>
<tb>
<tb>
<tb> Total <SEP> carboxylic <SEP> <SEP> acids,
<tb>
<tb> in <SEP> form <SEP> of acetic acid <SEP> <SEP> '<SEP> 45 <SEP> to <SEP> 50
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Propionic <SEP> <SEP> and <SEP> butyric <SEP> acids 3
<tb>
<tb>
<tb>
<tb>
<tb> Acetaldehyde <SEP> 1
<tb>
<tb>
<tb>
<tb>
<tb> Formates <SEP> of <SEP> methyl <SEP> and <SEP> of ethyl <SEP> 2
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Acetates <SEP> of <SEP> Me <SEP> thyle <SEP> and <SEP> of ethyl <SEP> 4
<tb>
<tb>
<tb>
<tb>
<tb> Methanol <SEP> and <SEP> ethanol <SEP> 2
<tb>
<tb>
<tb>
<tb>
<tb> Acetone <SEP> 1
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Methyl <SEP> ethyl <SEP> ketone <SEP> 8 <SEP> to <SEP> 12
<tb>
<tb>
<tb>
<tb>
<tb> Formic acid <SEP> <SEP> 3
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Water <SEP> 19 <SEP>

  to <SEP> 23
<tb>
 (h) The heavy phase described above is then treated by procedures not understood within the scope of the present invention but which are known in the art and include, for example, distillation, hydrolysis and purification. solvent extraction to collect at least a substantial portion of the free and esterified acetic acid contained therein, as well as various other by-products such as methanol and acetone. Regardless of how this collecting operation is carried out, a fraction results which comprises at least a substantial portion of the MEK contained in the heavy phase collected from the settler.

   This is the third of the three liquids containing a ketone based on which the invention

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 is described here. Its composition varies according to the composition of the second liquid containing ECM from which it is derived, and also according to the nature of the product separation techniques which have been used. It even wants to be obtained from the operation of collecting the primary oroduct, not in the form of a stream, but rather in the form of two or more streams. Regardless of how it is obtained, it is defined herein as a liquid containing, in a predominant proportion, methyl ethyl ketone which is collected during the separation of the oroduct from the oxidation reaction of the hydrocarbon in its major constituents, including acetic acid.

   This fraction mainly comprises MEK, of course, but also commonly contains an ethoxy fraction in the form of ethanol and ethyl acetate, since ethanol, ethyl acetate and other ethyl esters are. from the oxidation products of the hydrocarbon, and ethyl acetate, in particular, is difficult to separate from methyl ethyl ketone by simple distillation.



   When sufficiently purified, the third liquid containing MEK, described above, can be used as a ketone-ester solvent. It can also be separated into methyl ethyl ketone, ethanol and acid @ hydrolyzing its ester content. and separating the products thus obtained; this; eration is described in the patent application in the United States of America. No. 525,360 filed February 7, 1966,
However, in the prior art, half, or more, of this stream is recycled to the primary oxidation reactor in order to sustain the reaction and maintain yield.

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 The product is commercially satisfactory at the oxidation reaction temperatures normally used, for example between 175 and 200 ° C. approximately.



   If a substantial portion, i.e. about half, of this stream is withdrawn without being recycled to the primary reactor, the oxidation system continues to be usable if the temperature is maintained at the value just set. describe, but the overall yield of acetic acid, from the hydrocarbon, suffers, even when the MEK and other precursors of acetic acid, ethanol. for example, are converted to acetic acid by secondary oxidation.



   The following examples are given by way of illustration of the invention.



   In the following example I, the implementation of the above-mentioned hydrocarbon oxidation process is described, with most of the MEK contained in the lower phase of the settling tank (second liquid containing MEK, as defined here) being collected. from the oxidation products and being recycled to the oxidation reactor.



   In this example, as well as in the following Examples II and III, an oxidation reactor is used which is filled to about 75% of its total capacity with an aerated liquid, i.e. 'a liquid whose volume is somewhat expanded by the vapors which pass through it.



   EXAMPLE I
The following operation is carried out in a reaction system comprising a reactor consisting of a horizontal cylindrical striker container provided with a distributor for injecting air below the surface of the liquid. The reactor commu-

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 nique with a condenser from which the condensate is discharged to a settling tank fixed in such a way to the reactor that an upper liquid phase of the settling tank can be continuously returned to the reactor by pumping. There is a liquid discharge duct at the lower part of the settling tank, through which the heavy liquid ohase contained in the settling tank is continuously withdrawn and sent to a primary product collection system.

   In the primary collection system, a recycle fraction of ECM is collected for recycling to the oxidation reactor, while the other reaction products are processed to collect acetic acid and other oxygenated compounds produced in the reactor. All the acetic acid collected in the primary collection system was formed in the oxidation reactor, either as free acetic acid or as acetic esters. Secondary oxidation of MEK to acetic acid is not used.



   The reactor is maintained at a temperature of 175 to 180 ° C. and under a pressure of 48 atmospheres. Oxidation catalyst, in the form of chromium acetate and cobalt acetate, is added continuously to the reactor in an amount sufficient to maintain in the liquid reaction medium contained therein a concentration of about 4800. parts per million parts of dissolved chromium and J7 parts per million parts of dissolved cobalt. Maintaining these concentrations is not critical, but these are the concentrations actually used.



   For 2.83 m3 of reactor volume (representing approximately 2.12 m3 of aerated liquid content in the reactor), 312.5 kg per hour of fresh hydrocarbon feed is continuously added.

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 comprising 97% normal butane, 2.4% isobutane and one less than 0.5% each of propane and pentanes. The MEC recycling fraction comprising 74.8 kg per hour of MEK, 32.4 kg per hour of ethyl acetate, 21.2 kg per hour of acetic acid and stripper 11.29 is also charged to the reactor. kg per hour of water. Through the distri; is continuously injected below the surface of the reaction medium, 1883 m 3 per hour, of air, measured at 15.5 ° C. and 1 each atmosphere, for 2.83 m 3 of reactor volume.



   The vapors given off from the surface of the liquid in the reactor pass into the condenser operating so as to produce a mixture of condensate and residual vapor at approximately 55 C. This mixture passes into the part. upper decanter in which the condensate separates from the vaoeurs, the condensate being retained in the settling tank. The uncondensed vapor is removed from the reactor, washed with recycle hydrocarbon, and sent to a conventional hydrocarbon recovery system, oil absorbing, where the recovered hydrocarbon (approx. 1.3 kg per kg of free charge) is recycled to the settling tank. Lean gas is driven from the atmosphere; the hydrocarbon recovery is 99.6%.



   All of the condensate from the condenser is captured in the decanter described above, in which it is allowed to separate into two phases, at 55 C. The upper phase, which is returned in full, by pumping, to the reactor, continuously, as it is formed, comprises about 70%, by weight, of butane, 5%, by weight, of MEK, 10% of acetic acid, 0.5% to 1.5% of water, the remainder being constituted by various minor constituents comprising approximately 4 h 8% of

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 oxides of nitrogen and carbon. dissolved. decanter liquid
The lower / phase is removed in content as it forms, and is sent to the primary product collection system.

   It contains the following: Cbhstituents Weight Acetic acid, free and esterified 54.0 Formic acid, free and esterified 0.9 Methanol, free and esterified 1.8 Water 22.4 Butyric acid, free and esterified 0.8 Propionic acid, free and esterified 1.4 Acetone 1.5 Acetaldehyde 1.1 Ethanol, free and esterified 3.1 Butane 3.5 Butyrolactone 0.2 Tert-butyl alcohol 0.1
Methyl ethyl ketone 9.2
In the primary product collection system, a combination of / distillation, solvent extraction and hydrolysis is used to separate the primary product mixture described above into the ECM recycling fraction and products. primary, including acetic acid.

   The ECM recycling fraction which is recycled to the oxidation reactor represents 150.5 kg per hour, for 2.83 m3 of reactor volume, of a substance having the following composition:

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 EMI18.1
 
<tb> Constituents <SEP> Weight
<tb>
<tb> Methyl <SEP> ethyl <SEP> ketone <SEP> 49.7
<tb>
<tb> Water <SEP> 7.5
<tb>
<tb> Methanol <SEP> 1.0
<tb>
<tb> Acetaldehyde <SEP> 0.1
<tb>
<tb> <SEP> formic acid <SEP> 2.1
<tb>
<tb> Acetic <SEP> <SEP> 14.1
<tb>
<tb> Ethyl acetate <SEP> <SEP> 22.2
<tb>
<tb> Propionic <SEP> <SEP> 0.3
<tb>
<tb> Methyl <SEP> acetate <SEP> <SEP> 0.4
<tb>
<tb> Acetone <SEP> 2.6
<tb>
 
The acetic acid contained in the substance charged to the primary product collection system is collected by conventional distillation procedures,

   hydrolysis of at least a portion of the acetic ester contained to give free acetic acid, and recovery of the acid, from the hydrolysis product by solvent extraction and distillation.



   The above example has been given by way of illustration of the operation of a hydrocarbon oxidation system at the oxidation reaction temperature characteristic of existing techniques. It also serves as an illustration of a system in which the second liquid containing MEK is collected from the oxidation reactor as a stream of condensate collected from the vapors evolved from the reactor.



    Example II below is given by way of illustration of the application of the invention to substantially the same reaction system as that described in Example I, modified to the extent necessary for the implementation of the invention. .

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   Part of the invention resides in the discovery that lowering the temperature of the primary oxidation reaction results in increased production of ketone (MEK, in this case). The increase is such that substantial quantities of MEK can be removed from the reaction system without adversely affecting the operation of the reactor and with, in effect, an increase in the efficiency of the conversion of the hydrocarbons into available products. on the market.

   By integrating a primary oxidation system operating under these improved conditions with a secondary oxidation system to convert MEK and other acetic acid precursors to acetic acid, it becomes possible to produce acetic acid at Starting from hydrocarbon with improved yields over both hydrocarbon and oxygen-containing pressurized gas.



   The lower the temperature maintained in the hydrocarbon oxidation reactor (which may drop to the temperature at which the reaction cannot be safely sustained), the lower the conversion of hydrocarbon to MEK (or other ketones) is high compared to acetic acid (or other carboxylic acids). Without limiting the invention to any theory of operation, this effect is believed to be due - and illustrative - to the fact that a ketone (ECM, in this case) is a major reaction intermediate in oxidation of hydrocarbons to carboxylic acids (to acetic acid, in the present case).



  The reaction protocol, in simolified form, consists of (a) oxidizing the hydrocarbon to ketone (MEK), and (b) oxidizing the ketone (MEK) to carboxylic acid and carbon oxides.

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  Lowering the temperature of the reaction affects the speed of both reactions, but in any case the second reaction is delayed relative to the first. The result is an increased production of ketone, compared to that of other reaction products. The minimum reaction temperature which can be maintained while sustaining the reaction depends somewhat on such factors as the action. avoidance of the oxidation catalyst and its concentration, as well as the presence of initiators of the reaction; however, as established by experience gained in actual onerations, this temperature is about 140 ° C. Below this temperature, up to about 120 ° C., the reaction can still be sustained, but not so so sure that at higher temperatures.

   In practice, it is preferable to operate at a temperature of about 140 to 170 C, although even at 175 C the efficiency of the reaction and the production of ketone are noticeably better than at higher temperatures. for example at temperatures of up to about 200 ° C. which were common in the prior art.



   When operating the original oxidation reactor in the lower temperature range, it may become necessary or advantageous to remove the reaction products from the reactor in a manner different from that used in Example I. , that is to say consisting in collecting the product of the reaction entirely in the form of a condensate collected from the vapors given off from the reactor.



   This is because as the reaction temperature is lowered the vapor pressure of the products in the reactor also drops. The rectification action

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 produced by the gases leaving the reactor is not then sufficient enough to separate the entire reaction oroduct from the reactor by vaporization. This same condition also cannot occur even at higher temperature if, for example by using oxygen instead of air in the reaction, the flow rate of fixed gases in the reactor is reduced.



  The result is that the volume of liquid contained in the reactor tends to increase as the amount of substance contained accumulates. This cannot be allowed to happen continuously, because in such a continuous cyclic system the amount of substance in the reactor must be kept essentially constant. It cannot grow indefinitely. One possible solution to the problem posed here is to lower the reactor pressure and thus maintain the desired content of condensable vanors in the gases evolved from the reactor. This would allow the retort operation described in Example I to continue, in which all of the product from the reactor is removed as condensate.

   This has been found to be feasible, to some extent, but under conditions such, for example at a reactor pressure below 40 atmospheres, that the concentration of oxygen in the liquid phase tends to become rate limiting. reaction. As a result, the reaction is not as easy to maintain as at higher pressure, and the efficiency of using oxygenene is impaired. Another feasible solution to consider this problem is to recycle a portion of the inert gas discharged to the reactor as additional rectification medium.

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   Another way is to increase the concentration of the hydrocarbon in the reaction medium. This increases its volatility and the result is an increased valuation of the reaction product from the reactor due to the stripping effect of the additional hydrocarbon.



   It has been found, however, in accordance with a preferred embodiment of the invention that satisfactory reactor operation and satisfactory discharge of product can be maintained at a lowered reaction temperature by discharging a portion. of the liquid contained in the oxidation reactor itself. If desired, this can be accomplished by removing a portion of the contents of the reactor, directly from the reactor, the discharge stream then being separated by any of a choice of conventional procedures (by distillation, by example) in unreacted hydrocarbon and in a fraction comprising the products of the reaction, that is to say the second liquid containing the ketone which was discussed here.

   However, a preferred embodiment consists in combining this removal of liquid from the reactor with the operation of a condenser and a settling tank, as previously described. That is to say that a condenser and a decanter are used, as in Example I, to remove from the reactor the portion of the product which continues to separate from the reactor by vaporization, but now, in addition, an evacuation of the product. liquid is made directly from the oxidation reactor to the settling tank, the amount of this discharge being such that a more or less constant volume of liquid is maintained in the reactor.

   This allows the hydrocarbon to be separated from the discharged liquid stream (i.e., by settling in the decanter) without having% dis-

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 lay a separate facility to do this. At the same time, as it is continuously returned to the oxidation reactor, the upper phase of the settler serves both to recycle unreacted hydrocarbon to the reactor and, furthermore, by virtue of its dissolved ketone content, maintains an adequate level of ketone in the reactor to support the oxidation reaction of the hydrocarbon.



   A simultaneous advantage that there is at least some substance from the reactor in the form of liquid discharge, as compared to its entire recovery as condensate from the condenser, is that this discharge of liquid. liquid constitutes a means of continuously removing from the reactor certain non-volatile impurities which, although not identified, are known to accumulate in the reactor and indeed have a detrimental effect on the reaction, this deleterious effect progressively worsening. with time.



   The invention is not limited to a particular mode of operation for carrying out the evacuation of the product of the reaction and its subsequent separation into its constituent fractions. Many ways of doing this will be obvious to specialists; the essence of the invention is the operation of the oxidation reactor at reduced temperature, and the fact that at least a portion of the ketone produced in the reactor and collected therefrom is oxidized to the carboxylic acid. in a separate secondary oxidation system.



   EXAMPLE II
Basically the same reaction system as that described in Example I is used, with two modifications. All

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 first, the temperature of the primary oxidation reactor is lowered to 166 C. Then, an additional communication is provided between the primary oxidation reactor and the settling tank, allowing the flow of a regulated quantity of liquid from the reactor into the liquid content of the settling tank.



  The reactor is fitted with devices making it possible to maintain a constant liquid level therein, an oortion of the liquid contained in the reactor being sent continuously to the settling tank at a rate making it possible to maintain a constant liquid level in the oxidation reactor. original. Thus, the lower liquid phase discharged from the settling tank and sent to the primary product collection system comprises both condensate from the reactor condenser and a mixture comprising a portion of the liquid contained in the reactor. oxidation.



   The upper phase of the settling tank is returned continuously, by pumping, from the settling tank to the oxidation reactor, as in Example I. Its composition is roughly the same as in Example I. The MEK contained in this recycled light phase is the only ECM returned to the reaction medium contained in the oxidation reactor.



   For 2.8 m3 of volume in the oxidation reactor, the net feed rate of the hydrocarbon therein is 303.4 kg per hour. The air injection flow rate into the reactor is 1444 normal m3 per hour for 2.8 m3 of liquid contained.



   The reactor product, withdrawn from the lower phase in the settling tank, contains the following constituents:

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 EMI25.1
 
<tb> Constituents <SEP> Weight. <SEP>%
<tb>
<tb> Acetic <SEP>, free <SEP> <SEP> and esterified <SEP> <SEP> 52.1
<tb>
<tb>
<tb> Methyl <SEP> ethyl <SEP> ketone <SEP> 7.6
<tb>
<tb>
<tb> Formic acid <SEP>, free <SEP> <SEP> and <SEP> esterified <SEP> 4.8
<tb>
<tb>
<tb> Methanol, <SEP> free <SEP> and <SEP> esterified <SEP> 3,4
<tb>
<tb>
<tb> Water <SEP> 19.4
<tb>
<tb>
<tb> Butyric acid <SEP>, free <SEP> <SEP> and <SEP> esterified <SEP> 0.9
<tb>
<tb>
<tb> Propionic acid <SEP>, free <SEP> <SEP> and <SEP> esterified <SEP> 1,2
<tb>
<tb>
<tb> Acetone '<SEP> 0.6
<tb>
<tb>
<tb> Acetaldehyde <SEP> 1,2
<tb>
<tb>
<tb> Ethanol, <SEP> free <SEP> and <SEP> esterified <SEP> 4,

  6
<tb>
<tb>
<tb> Minor <SEP> constituents <SEP> 0.6
<tb>
<tb>
<tb> Butane <SEP> 3.5
<tb>
 
From the mixture of products described above, a crude fraction of MEK is collected (approximately 1.8% of free and esterified ethanol and 90% of MEK) having substantially the same composition as that described above in Example II. .



  Per kg of hydrocarbon charged to 2.8 m 3 of primary oxidation reactor, 0.176 kg of this crude MEK is collected. each For 2.8 m3 of volume of the original reactor, 55.16 kg per hour of this fraction at 90% MEK are obtained.



   The crude MEC fraction is charged to a secondary oxidation reactor comorienting a container maintained at a pressure of 5.4 atmospheres and a temperature of 130 ° C.



  The volume of this container is advantageously such that it contains 0.12 m3 of selected volume per 0.02% of the MEK stream charged therein. A reaction medium essentially comprising acetic acid in which cobalt acetate is dissolved in a concentration of 1000 ppm (parts per million), calculated as cobalt, is maintained in this reactor. We charge air to the party

 <Desc / Clms Page number 26>

 lower scorer of this reactor, through a distri; Advantageously, the air flow rate is 585 normal m 3 per m 3 of aerated liquid contained.



   The vapor emerging from the surface of the liquid is passed through a condenser in order to obtain a condensate which is returned to the reactor, as well as a lean gas which is washed and expelled from the atmosphere. Acetic acid is collected from the aqueous solution resulting from the washing operation, by conventional solvent extraction and distillation procedures. It is also collected from the reactor, by continuously removing part of the liquid contents therefrom and charging the withdrawn liquid into a distillation system of conventional design, in which it is collected.



   (a) acetic acid as the product, (b) unreacted MEK which is recycled to the reactor, and (c) a bottoms stream containing the oxidation catalyst which is recovered. it is recycled to the reactor. The discharge rate from the reactor is approximately 330 kg per hour per m3 of aerated liquid contained in the reactor. The bottoms stream represents about 20% of the reactor discharge rate.



   The acetic acid collected from the secondary oxidation is 0.217 kg per kg of hydrocarbon initially charged to the hydrocarbon oxidation reactor.



   The total yield of marketable products, including acetic acid, per kg of hydrocarbon is increased compared to Example I. The yield of acetic acid by volume, per unit of / d '. The high pressure air charged in the primary oxidation operation is 27% greater than that of Example I.



   The following example III, demonstrates another improvement

 <Desc / Clms Page number 27>

 from the conversion of hydrocarbon to acetic acid, based on incarrportation, in the raw ECM loaded at the secondary oxidation stage, from the increased amount of ethanol which is formed during the primary oxidation as a result of the lowering the reaction temperature in this operation.



  In the accompanying drawing, given only by way of example. Fig. unique is given by way of illustration of exemoles II and III.



   EXAMPLE III
The procedure is as in Example II, this difference ores that the operation of collecting the primary product is modified so as to include in the fraction of crude MEC (90%) charged in the secondary oxidation operation a substantial portion of the additional ethanol produced under the operating conditions for the oxidation of the hydrocarbon of Example II, by comparison with those of Example I.

   Including the fraction including the additional ethanol, the amount / of crude MEK charged to the secondary oxidation reactor is 82.1 kg per hour for 2.8 m3 of primary oxidation reactor, and its composition is as follows:
 EMI27.1
 
<tb> Constituents <SEP> Weight.%
<tb>
<tb> Methyl <SEP> ethyl <SEP> ketone <SEP> 58.1
<tb>
<tb> Methyl <SEP> <SEP> acetate <SEP> 0.1
<tb>
<tb> Methanol <SEP> 0.1
<tb>
<tb> Ethyl <SEP> acetate <SEP> 2.0
<tb>
<tb> Ethanol <SEP> (approximately <SEP> 95% <SEP> ethanol <SEP> free) <SEP> 35.0
<tb>
<tb> Water <SEP> 3.1
<tb>
<tb> Other <SEP> minor <SEP> constituents <SEP> 1.6
<tb>
 
After having oxidized the fraction in the secondary oxidation reactor, as in Example-II, it is collected from

 <Desc / Clms Page number 28>

 of the secondary oxidation system, 0,

  311 kg of acetic acid per kg of fresh hydrocarbon charged to the primary oxidation system.



   The total yield of acetic acid, per kg of hydrocarbon charged to the primary oxidation system, is about 0.1 kg higher than that obtained in Example II. The acetic acid yield per unit of high pressure air charged to the primary oxidation system is about 8% greater than that obtained in Example II.



   It is evident from the foregoing Examples II and III that removing ECM and other acetic acid precursors from the reaction system and converting them to acetic acid in a reaction system. Separate secondary oxidation results in both an improvement in the overall conversion of the hydrocarbon to acetic acid, and. a marked decrease in the amount of high-pressure air (i.e., compressed air at the pressure prevailing in the hydrocarbon oxidation reactor) required to produce a given amount of acetic acid.

   This latter advantage is in itself quite substantial, since the investment and operating costs required for the production of this high pressure air used in the reaction constitute a very substantial item in the cost tbtal. from the oxidation of hydrocarbons to their oxygenated derivatives.



   It is also evident that numerous variations can be made in the operating stages and apparatus described in the preceding examples, without departing from the scope of the invention. For example, instead of being a cylindrical vessel in which air is bubbled through, the hydrocarbon oxidation reactor may be a tube.

 <Desc / Clms Page number 29>

 elongate through which a liquid mixture of hydrocarbon and solvent is passed for the reaction, together with air or other source of molecular oxygen. In this case, of course, the evacuation of the vapors of the reaction medium containing the oxidation products is carried out in a separation apparatus attached to the reaction tube.



   The source of molecular oxygen, in both the primary and secondary oxidation stages, is normally air, but one can also, if desired, use the oxygen itself.



   Many variations are possible in the secondary oxidation stage in which the ketone is converted to the carboxylic acid. The catalyst which is used therein is advantageously a cobalt or manganese acetate.



  However, many other catalysts can be used if desired. For example, as described in the U.S. Patent No. 2,005,183 of Flemming and Speer, in addition to cobalt and manganese, one can use; vanadium, chromium, iron, nickel, copper, molybdenum, cerium, praseodymium, neodymium, lanthanum, samarium. earths of terbium, tungsten, platinum, iridium, osmium and gold. When a @ higher molecular weight than MEK to obtain a higher molecular weight carboxylic acid than;

   acetic acid, for example when oxidizing a propyl ketone to a product comprising pronionic acid, it is preferable to use an oxidation catalyst other than cobalt (eg, manganese). Cobalt tends to degrade higher carboxylic acids, for example propionic acid, when it is present in high amounts.

 <Desc / Clms Page number 30>

 substantial, giving lower acids, such as acetic acid, for example. Even in the oxidation of MEK, little propionic acid is normally produced, but, in the presence of cobalt catalyst, the oxidation product obtained from MEK is mostly acetic acid.



  Minor amounts of propionic acid can be recycled to the reactor. This constitutes a substantial advantage in the embodiment according to the invention in which the desired carboxylic acid product is acetic acid.



   When applying the process according to the invention to the preparation of higher carboxylic acids from higher hydrocarbons, substantially the same techniques as those described herein are used for the preparation of acetic acid from butane and 2-. alkyl-butanes, with the exception that, as indicated above, is avoided. to use cobalt at the secondary oxidation stage and that a different catalyst is used, for example manganese.



   Below is a list of representative higher hydrocarbons as well as the ketones obtained in major proportion from them during the primary oxidation, and the commercially valuable carboxylic acids obtained in the proportion of ketones from them. ketones, during secondary oxidation. A ketone will normally provide a mixture of acidic products that contain more than one acid. These mixtures are separated by simple distillation. When the higher ketones are oxidized, acetic acid can, if desired, be used as the solvent for the reaction, rather than the carboxylic acid which is being used. to prepare. This introduces some complications, because a

 <Desc / Clms Page number 31>

 some amount of acetic acid is usually present as a by-product anyway.
 EMI31.1
 
<tb>



  Hydrocarbon <SEP> Ketone <SEP> Acid <SEP> (1) <SEP>
<tb>
<tb>
<tb>
<tb>
<tb> Pentane <SEP> Diethyl <SEP> propionic, <SEP> acetic
<tb>
<tb>
<tb>
<tb> Methyl <SEP> propyl <SEP> propionic, <SEP> acetic? <SEP> butyri-
<tb>
<tb>
<tb> that
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Hexane <SEP>.

   <SEP> Methyl <SEP> propyl <SEP> Acetic, <SEP> butyric, <SEP> oronioni-
<tb>
<tb>
<tb> that, <SEP> valeric
<tb>
<tb>
<tb> Ethyl <SEP> propyl <SEP> Acetic, <SEP> butyric, <SEP> propioni-
<tb>
<tb>
<tb> clip
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Heptane <SEP> Methyl <SEP> amyl <SEP> Acetic, <SEP> valeric, <SEP> canroic
<tb>
<tb>
<tb> Ethyl <SEP> butyl <SEP> Acetic, <SEP> pronionic, <SEP> buty-
<tb>
<tb>
<tb> rique, <SEP> valeric
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Dipropyl <SEP> Propionic, <SEP> butyric
<tb>
 (1) Some formic acid is obtained in all cases and even in the case of diprooyl ketone some acetic acid will be formed in the degradation reactions.



   Of course, the invention is not limited to the embodiments and embodiments shown and described which have been given only as examples.

 <Desc / Clms Page number 32>

 



   LEGEND OF THE FIGURE.



  HF - fresh hydrocarbon HR = recycled hydrocarbon E - vent I - collection of the hydrocarbon CON - condenser PP primary products other than acid AP = primary acid A air PLE - light phase PL - heavy phase II collection and purification of the primary product RP primary reactor LR - reaction liquid D - settling tank
CAT - FCB catalyst = crude ketone fraction
R - residues
V - vapors
III - collection of the product in vapor form
COND - condensate
CR - recycled ketone
ACRV

    - acid collected from vapors
CAR - recycled catalyst
AS - secondary acid
RS - secondary reactor
IV - collection and purification of secondary acid
ER - reactor evacuation

 

Claims (1)

CLAIMS. 1 A process for the oxidation of an aliphatic hydrocarbon into a reaction product comprising a carboxylic acid as well as precursors of said carboxylic acid comprising a ketone as well as free and esterified alcohol corresponding to said carboxylic acid, according to which is introduced in Continuously said hydrocarbon in a confined primary reaction zone containing a liquid reaction medium in which is dissolved an oxidation catalyst, the hydrocarbon is continuously oxidized, bringing it into contact with molecular oxygen in the liquid reaction medium, at least one reaction product comprising the carboxylic acid, an ester of the carboxylic acid and the said ketonic precursor of the carboxylic acid is removed from the primary reaction zone, at least said carboxylic acid and a ketone fraction comprising said ketone are collected from the reaction product, and at least a portion of the ketone contained in said fraction is recycled to the primary reaction zone, characterized in that: (a) the temperature of the primary reaction zone is regulated between approximately 120 and 170 C, (b) the outlet of the reaction product from the primary reaction zone is regulated at a flow rate which makes it possible to maintain a quantity of liquid approximately constant in said reaction zone, and (c) oxidizing a portion of the ketone contained in said ketone fraction, with the aid of molecular oxygen, in a confined secondary reaction zone, in the linuide phase, in a secondary reaction medium containing a catalyst for the liquid phase oxidation of ketones, in order to convert said ketone into said carboxylic acid. <Desc / Clms Page number 34> 2 Process according to claim 1, characterized in that the hydrocarbon is a compound of structure EMI34.1 wherein R is hydrogen or an alkyl group containing up to 6 carbon atoms, the carboxylic acid is acetic acid, the keto precursor of the carboxylic acid is methyl ethyl ketone, the alcohol corresponding to the acid carboxylic is ethanol, and the primary and secondary reaction media include acetic acid. 3. Process according to Claim 2, characterized in that the catalyst for the liquid phase oxidation of ketones comprises a cobalt compound soluble in acetic acid. 4 A process for the oxidation of an aliphatic hydrocarbon to a reaction product, said reaction product comprising a carboxylic acid, an alkoxy moiety corresponding to said carboxylic acid and comprising free and esterified alcohol corresponding to said carboxylic acid, as well as a ketone which is a precursor of said carboxylic acid, a process according to water in which a starting material comprising said hydrocarbon is continuously introduced into a confined primary reaction zone which contains a first liquid containing a ketone which forms the liquid reaction medium comprising said. carboxylic acid in which at least said ketone, said alkoxy fraction and an oxidation catalyst are dissolved, the hydrocarbon is continuously oxidized, bringing it into contact with oxygen, afterwards, in said primary reaction zone , we remove: continuously from said reaction zone a vapor comprising fixed gases, <Desc / Clms Page number 35> a hydrocarbon fraction comprising a mixture of said hydrocarbon and reaction products soluble in the hydrocarbon as well as a second liquid containing a ketone comprising said reaction product is collected continuously from said first liquid containing a ketone, comprising said reaction product. continuously, from said second liquid containing a ketone, at least a third liquid containing a ketone comprising precursors of said carboxylic acid, as well as a fraction of an acid product comprising said carboxylic acid, said carboxylic acid is continuously collected. lic from said fraction of acid product, and at least one of said hydrocarbon fraction and said third ketone-containing liquid are continuously recycled to said primary reaction zone, additional carboxylic acid being produced and the overall yield of useful products from said. hydrocarbon being increased by (a) adjusting the temperature of the reaction zone to between 120 and 170 C, (b) continuously withdrawing a portion of said first liquid containing a ketone from said reaction zone as a stream d liquid discharge, (c) continuously collecting at least a portion of the carboxylic acid precursors contained in at least one of said liquid discharge stream and said second and third ketone-containing liquids, <Desc / Clms Page number 36> (d) introducing said portion of carboxylic acid precursors into a secondary reaction zone containing a liquid side reaction solvent comprising a carboxylic acid in which is dissolved a secondary oxidation catalyst comprising a carboxylate of a metal which is a catalyst for liquid phase oxidation of carboxylic compounds to their carboxylic acid derivatives, (e) introducing a gas comprising molecular oxygen into said secondary reaction solvent in said secondary reaction zone, (f) oxidizing said carboxy acid precursors - lic in said carboxylic acid in said secondary reaction zone, and (g) collecting said carboxylic acid from said liquid reaction solvent; Method according to Claim 4, characterized in cc Method collects the second liquid containing a ketone from the first liquid containing a ketone (a) by collecting a condensate comprising said hydrocarbon and said reaction product from the vapors withdrawn from said zone of. primary reaction, (b) cooling said condensate, in a settling xone, to a temperature at which it separates into two liquid phases, and (c) continuously removing a portion of the first liquid containing a ketone from of the primary reaction zone, and by introducing said portion into said settling zone whereby it mixes with non-content and is distributed between the two liquid phases, <Desc / Clms Page number 37> the lightest of said liquid phases of the settling zone comprising hydrocarbon as well as the oil-soluble reaction products comprising said ketone and the heaviest phase comprising said second liquid containing a ketone. 6 Process according to claim 5, characterized in that the pressure in the primary reaction zone is between approximately 40 and 70 atmospheres, and the pressure in the secondary reaction zone is between approximately 3 and 25 atmospheres. atmospheres. 7. A method according to claim 5, characterized in that the carboxylic acid is acetic acid, the keto is methyl ethyl ketone and the hydrocarbon is a compound of formula EMI37.1 wherein R is hydrogen or an alkyl group containing up to six carbon atoms. 8 Process according to claim 5, characterized in that at least a portion of said lightest phase is recycled to the primary reaction zone - 9 Process according to claim 8, characterized in that the temperature to which the liquids charged in the settling zone are cooled is less than approximately 170 C, and greater than the temperature at which the solid phase begins to appear when said cooling. li- Quides. 10 The method of claim 9, characterized in that the temperature at which the liquids are cooled in the settling zone is less than approximately 120 C. .