MXPA00002639A - Methods of recycling catalyst in oxidations of hydrocarbons - Google Patents

Abstract

This invention relates to methods of recycling catalyst in oxidations of hydrocarbons, such as cyclohexane for example, to respective intermediate oxidation products, such as adipic acid for example, by a direct process. The catalyst remains in solution despite removal of water from the composition, since the water removal is controlled at such temperatures and such remaining water levels that prevent catalyst from precipitating. The water removal is preferably conducted before removal of the intermediate oxidation product. Also, preferably, some, and more preferably all steps of the process are conducted in a single liquid phase region.

Description

METHODS FOR RECYCLING A CATALYST IN HYDROCARBON OXIDATIONS TECHNICAL FIELD This invention relates to methods for recycling a catalyst in hydrocarbon oxidations, such as, for example, cyclohexane, to respective intermediate oxidation products, such as, for example, adipic acid, by a direct process.

BACKGROUND OF THE INVENTION There is a large number of references. { both patents and articles of literature) relating to the formation of acids, with adipic acid being one of the most important, through the oxidation of hydrocarbons. Adipic acid is used to produce fibers and resins of Nylon 68, polyesters, polyurethanes, and other miscellaneous components. There are different processes to make adipic acid. The conventional process involves a first stage of oxidizing cyclohexane with oxygen to a mixture of cyclohexanone and cyclobexanol (KA mixture) and then oxidizing the KA mixture with nitric acid to adipic acid. Other processes include, among others, the "Hydroperoxide Process" ", the" Boric Acid Process ", and the" Direct Synthesis Process ", which involve direct oxidation of cyclohexane to adipic acid with oxygen in the presence of solvents, catalysts and boosters. The Direct Synthesis Process has attracted attention for a long time. However, to date I have found little commercial success. One of the reasons is that although it seems very easy to first vistßj it is extremely complex actually. Due to this complexity, one can find results, comments and surprisingly conflicting points of view in different references. It is well known that after a reaction has occurred according to the Direct Synthesis, a mixture of two liquid phases occurs at room temperature, together with a solid phase consisting mainly of adipic acid. The two liquid phases have been called the "Polar Phase" and the "Non-Polar Phase". However, attention has not been given to the importance of the two phases, except to separate the adipic acid from the "Polar Phase". "and recycling these phases to the reactor partially or completely with or without additional treatment. It is also important to note that most studies on Direct Oxidation have been conducted in a discontinuous fashion, literally or for all practical purposes. There are a plethora of references that treat the oxidation of organic compounds to produce acids, such as, for example, adipic acid and / or intermediates, such as, for example, cyclobexanone, cyclohexanol, cyclohexylhydroperoxide, etc. The following references, among others, can be considered as representative of oxidation processes related to the preparation of diacids and other intermediate oxidation products. The U.S. Patent 5,463, 119 (Kollar), the U.S. Patent. 5,374,767 (Drinkard et al.), The U.S. Patent. 5,321,157 (Kollar), U.S. Patent 3,987,100 (Bamette et al.), E, U Patent. 3,957,876 (Rapoport et al.), The U.S. Patent. 3,932,513 (Russell), the U.S. Patent. 3,530, 185 (Pugi), the U.S. Patent. 3,515,751 (Oberster et al.), The U.S. Patent. 3,361, 806 (Udov et al.), The U.S. Patent. 3,234,271 (Barker et al.), The U.S. Patent. 3,231,608 (Kollar), the U.S. Patent. 3,161,603 (Leyshon et al.), The U.S. Patent. 2,565,087 (Porter et al.), U.S. Patent. 2,557,282 (Hamblet et al.), The U.S. Patent. 2,439,513 (Hamblet et al.), U.S. Patent 2,223,494 (Loder et al.), US Pat. 2,223,493 (Loder et al.), German Patent DE 44 26 132 A1 (Kysela et al.) And PCT International Publication WO 96/03365 (Constantini et al.). None of the above references, or any other reference known to the inventors, describe, suggest or imply, either simply or in combination, the control of oxidation reactions subject to the intricate and critical controls and requirements of the present invention as described and described. vindicates SUMMARY OF THE INVENTION As mentioned above, this invention relates to methods for recycling a catalyst in hydrocarbon oxidations, such as, for example, cyclohexane, to respective intermediate oxidation products, such as, for example, adipic acid, by a direct process It relates particularly to a method for maintaining a catalyst in solution after removal of water, outside a reaction zone, in a process comprising the oxidation of a hydrocarbon by a gaseous oxidant to a respective oxidation intermediate at a temperature of operation in the reaction zone containing a mixture comprising the hydrocarbon, the catalyst, the water, a solvent and an optional initiator, the method comprising the sequential steps of: (a) changing, outside the reaction zone. The temperature of operation of the mixture at a second temperature below a precipitation temperature, at which and over which temperature of precipitation, the catalyst in the first mixture would be precipitated, at least partially, if the level of water in the first mixture has been reduced to or below a rainfall water level (b) removing a quantity of water from the first mixture, but maintaining the niyei of water in the mixture above the water level of precipitation at the second temperature; (c) removing at least part of the oxidation intermediate; and (d) recirculating the remaining mixture to the reaction zone. It is preferable that all stages be conducted in a substantially single liquid phase region. Step (b) of the method may comprise a step of lowering the second temperature to a third temperature lower than the second temperature, and step (c) may comprise a step selected from a group consisting of centrifuging, filtering, and a combination of them. In addition, step (a) may comprise a step of atomizing the first mixture.

This invention further relates to a method for maintaining a catalyst in solution for recycling after removal of water, outside a reaction zone, in a process comprising the oxidation of a hydrocarbon by a gaseous oxidant to an oxidation intermediate. respective at an operating temperature in the reaction zone containing a mixture comprising the hydrocarbon, the catalyst, the water, a solder and an optional initiator, the method comprising the steps of; (e) at least partially precipitating the oxidation intermediate, while maintaining a single liquid phase; (f) removing at least part of the precipitated oxidation intermediate, (g) removing part of the water at a temperature below a precipitation temperature, at which and over which temperature of precipitation, the catalyst in the mixture would precipitate, at less evenly, if the water level in the mixture has been reduced to or J > garlic a precipitation water level; (h) maintain the water level above the precipitation water level; and (i) recycling at least part of a mixture created in step (b) back to the reaction zone. This invention is particularly applicable in case the oxidation intermediate comprises adipic acid, the hydrocarbon comprises cyclohexanone, the catalyst comprises a cobalt compound, the gaseous oxidant comprises oxygen, the solvent comprises acetic acid, and the optional initiator is selected from a group comprising cyclohexanone, cyclohexylhydroperoxide, acetaldehyde and a mixture thereof. In addition, the present invention relates to a method, wherein the oxidation intermediate comprises a compound selected from a group consisting of adipic acid, italic acid, isophthalic acid, and teraphthalic acid and the method further comprises a step of reacting said intermediate oxidation product with a third reactor agent selected from a group consisting of a polyamine or polyol, and a polyamide, so as to form a polymer of a polyester, or a polyamide, or a (polyimide and / or polyamideimide), respectively. The method may further comprise a step of spinning the polymer into fibers. It should be noted that the reaction products, by-products, and other compounds in the mixture influence the precipitation temperature of the catalyst and the precipitation water level. According to this invention, the precipitation temperature of the catalyst and the precipitation water level are considered in the presence of such residues in the mixture. By the term "permanent state" it is implied that the reaction has reached an equilibrium, equilibrium Which, however, can be adjusted periodically or continuously in order to achieve a desired result. If, for example, more water is needed in the reaction zone to avoid precipitation of the catalyst, the speed of water supply to the reaction zone can be increased appropriately, and the reaction can still be considered to be in a "permanent state". . Similarly, if less water is needed to avoid the formation of two phases, the rate of water feed to the reaction zone can be properly decreased, and the reaction can still be considered to be in a "permanent state". The terms "substantially single phase liquid" and "substantially unique liquid phase" are for all practical purposes synonyms for the purpose of this invention. Both claim to indicate that there is no second liquid phase present, while a solid phase may or may not be present. The terms "second phase formation" or "second phase formation" refer to a second liquid phase, and not to a solid phase, unless otherwise specified. The term "level" of an ingredient (reactor agent, reaction product, catalyst, water, inert material, or any other type of matter present) includes both "relative level" and "percentage level". According to the present invention, both methods and devices can work by using either one or the other type of "levels". Sometimes it may be easier to use one type instead of the other. The "relative level" of an ingredient denotes the amount of the ingredient present in units of weight or units of volume, in a reaction zone or in a cell for example, as compared to 100 units, in units of weight or units of volume, respectively, of the rest of the ingredients present, or the rest of the ingredients under consideration. The rest of the ingredients present or the rest of the ingredients under consideration, in this case, have a constant proportion to each other. On the other hand, the "percentage level" is the level expressed as a percentage based on the total amount of all or a desired number of specific ingredients. The percentages can also be expressed by weight or volume. A controller, preferably a computerized controller, can easily and accurately handle any type of "level". Programming a computerized controller to develop such functions is a routine process, well known in the art, According to this invention, a controlled based on the information received, from a reaction zone for example, controls the feed rates, temperatures , pressures, and other parameters in order to achieve the desired results. The controller can also be programmed, by techniques well known in the art, to include the flow diagram simulation, which can take responsibility for the effects of vapor / liquid balance and energy balance. Analytical techniques known in the art can be used for the determination of different levels of ingredients in the currents and miscellaneous chambers, and provide such information to the controller for further processing and action.

BRIEF DESCRIPTION OF THE DRAWINGS The reader's understanding of this invention will be improved by reference to the following detailed description taken in conjunction with the drawing figure, wherein: Figure 1 is a block diagram illustrating a preferred embodiment of the present invention, Figure 2 illustrates a block diagram of a preferred distillation column, which may be used in conjunction with the reaction chamber or the drainage chamber or any other appropriate chamber, or a combination thereof. This column is provided with a reheater, and is divided into a lower separating zone and an upper rectifying zone.

DETAILED DESCRIPTION OF THE INVENTION As mentioned above, this invention relates to methods for recycling a catalyst in hydrocarbon oxidations, such as, for example, cyclohexane, to respective intermediate oxidation products, such as, for example, adipic acid, through a direct process. The proper handling of the catalyst in the oxidation reactions has always been a considerable problem in the matter. According to the present invention, the process is controlled in a manner, that the water is removed from the system, while the catalyst remains in solution for direct recycling or recycling after any desired treatment. This has enormous advantages, because the catalyst can be recited easily and quickly for repeated use. As mentioned above, German Patent DE 44 26 132 A1 (Kysela ef al.) Describes a method of dehydrating acetic acid processed from the oxidation of liquid phase of cyclohexane with air, in the presence of cobalt salts as a catalyst after separation of the adipic acid after filtration, while simultaneously preventing the cobalt salt from being precipitated in the dehydration column, characterized in which the phase of acetic acid to return to the beginning of the process, is subjected to azeotropic distillation by the use of added cidohexane, under distillative removal of water below a residual content of 0.3 - 0.7%. The above description does not understand that depending on the catalyst or other ingredients in the composition, these water limits can change drastically, and that it is important to examine in each individual case the level of water to which the catalyst precipitates and thus remain above this water level. Furthermore, the description does not understand that the temperature, at which a mixture containing the catalyst is maintained, also drastically changes the level of water under which the catalyst is precipitated. According to the present invention, both the temperature of the mixture containing the catalyst and the level of water are controlled in coordination, by a predetermined level of catalyst, in such a way that the catalyst remains in solution, in the presence of other residues. , such as products, by-products, etc. In the case where it is desired to remove the maximum amount of water from the system, the critical water level, at which the catalyst is precipitated, is determined at the temperature of the mixture containing the catalyst, and the water level is maintained. above, but close to the critical level. It is preferable that the water level be maintained in a range of 10% to 100% of the critical value, above the critical value. It is more preferable that the water level be maintained in a range of 20% to 50% of the critical value, above the critical value. For example, if the critical value of the water level (precipitation water level) at the temperature of the The mixture containing the catalyst is 0.6% by weight (based on the total mixture containing the catalyst), it is preferable that the water level be maintained in the range of 0 66% to 1.2% by weight, and more preferably, in the range of 0.72% to 0.9% by weight, based on the total mixture contained in the catalyst. It is important to note that if a higher water withdrawal is desiredThe temperature of the mixture containing the catalyst can be lowered, and the water separation can be conducted at that lower temperature. The lower the temperature of the mixture containing the catalyst, the lower the critical water level (water level). of precipitation), to which the catalyst is precipitated. According to the description of the above-mentioned patent, water removal is conducted after cooling the mixture containing the catalyst, separating the mixture into a polar and non-polar phase, decanting the polar phase containing the majority of the catalyst and acid Adipic precipitate, recycling the non-polar phase back to the reaction chamber, removing the adipic acid from the polar phase, adding cyclohexane to the filtered polar phase, heating the mixture and removing the water as an azeotrope with the cyclohexane so that Water level moves to the range of 0 3% to 0 7%.

The process described includes many steps, which may be effected according to a highly preferred embodiment of the present invention. According to this highly preferred embodiment, the removal of water is conducted before the separation of the oxidation intermediate, such as, by example, adipic acid, after determining the appropriate temperature, at which the mixture containing the catalyst must be found and after determining the critical water level, to which the catalyst is precipitated at the temperature of the mixture containing the catalyst. The water level is then maintained at preferable levels, as described above. In a preferred mode of the same embodiment, the oxidation intermediate, such as, for example, adipic acid, is precipitated by rapid crystallization in one or multiple steps, as discussed below, thus avoiding the formation of two liquid phases, necessary for decanting, etc. For the best clarity of this invention, the examples given below assume that the hydrocarbon is cyclohexane, the oxidation intermediate is adipic acid, the solvent is acetic acid and the catalyst is a cobalt compound. However, it should be understood that the teachings of this invention are applicable to different hydrocarbons, intermediate oxidation products, solvents and catalysts different from those used in the examples. Only small modifications may be necessary to adapt each individual case. Referring back to Figure 1, a reactor system or system 10 is depicted, comprising a reaction chamber 12 containing a reaction zone 14. The reaction device or system 10 is only partially shown to demonstrate the components necessary to exemplify the present invention. Devices of miscellaneous treatment, separation of the product or by-product, recycling, etc., well known in the art, are not shown for purposes of clarity and brevity. Feeding means (for raw material, miscellaneous recycled material, gaseous oxidant, etc.) connected to the reaction chamber 12 are represented, and represented by a single feed pipe 16 for purposes of clarity and brevity. However, it should be understood that, in practice, a number of individual pipes may be used, including if appropriate, devices such as, for example, mixing vessels, heaters, chillers, etc. Preferably, a first distillation column may also be used. 18. The first distillation column 18 is connected at one end to the reaction chamber 12 through pipes 16i and 16ii, while the other end is connected to a first condenser 0 through the pipe 18i. The first condenser 20 is in turn connected to a first decanter 22 through the pipe 20i. The first decanter 22 has a first vent pipe 22i, a first cyclohexane removal pipe (or other hydrocarbon) and a first water removal pipe 22iii. The pipes 22i and 22i are connected to the valves 22 'and 22", respectively, the pipe 22ii is connected to the pipe 18ii to recycle the cyclohexane to the first distillation column 18. The reaction chamber 12 is also connected to the drain chamber 26 through pipe 16iii A second distillation column 28 is connected at one end to drain chamber 26 through pipes 26i and 26ii, while at the other end it is connected to a second condenser 30 through the pipe 28i The second condenser 30 in turn is connected to a second decanter 32 through the pipe 30i The second decanter 32 has a second vent pipe 3 i, a second cyclohexane removal pipe (u another hydrocarbon) 32i, and a second water withdrawal pipe 32iii Pipes 32i and 32ii are connected to valves 32 '(vent valve) and 32"(hydrocarbon sampling or withdrawal valve). The pipe 32u is also connected to the pipe 28¡¡ to recycle the cyclohexane to the second distillation column 28. The drain chamber 26 is also connected through the pipe 26iii to a cooler 36"which connects to its yaz. to a crystallizer 38 through the pipe 36i. The crystallizer 38 is preferably a fast crystallizer, which uses a pressure reducing pipe 38i, The pressure reduction (which can range from operating pressure to any lower pressure, including sub-atmospheric), in the crystallizer, results in a substantially instantaneous drop in temperature , which in turn causes the solids (such as, for example, adipic acid) to crystallize and precipitate. Rapid crystallization can be conducted in one or more stages. The crystallizer 38 is connected to a solids separator 40 through the pipe 38 i i. The crystallized solids are separated and removed from the solids separator 40 through line 40ii, while the remaining liquids are withdrawn through line 40L for direct recycling or recycling after further treatment. Instead of the drain chamber 28, a re-heater (not shown) can be used in the lower part of the column 28, in which case the pipe 16ii would be connected at a desired point in the column 28. The chamber 26 is useful to contain the catalyst accidentally precipitated and to avoid the filling of the column. In the operation of this embodiment, miscellaneous and recyclable raw materials, including in this example cyclohexane, acetic acid, cobalt compound, optional initiator (preferably cyclohexanone or acetaldehyde, or a mixture thereof), optionally water, and a gaseous oxidant, preferably comprising oxygen, they enter the reaction zone 14, inside the reaction chamber 12, through the feed means represented by the pipe 16. Preferably, the oxidation is brought to a permanent state, and preferably most or all the heat of the reaction is removed by evaporated condensable matter, which leaves the reaction chamber 12 as vapors through the pipe 16L and at least partially returns to the reaction chamber 12 as a condensate through the pipe 16 In this example, most of the yapores leaving the reaction chamber 12 are cyclohexane, acetic acid and water. Column 18 is designed, by techniques well known in the art, in a manner that, for all practical purposes, substantially all of the acetic acid in the vapors that exit through the pipe 16i, condenses in the first column 18 and returns to the reaction chamber 12 through the pipe 16Ü. For all practical purposes, most of the cyclohexane and substantially all the water in the vapors leaving the reaction chamber 12, which pass through the first column 18, condenses the condenser 20 and separates in the decanter 22 The cyclohexane The condensate is returned to the upper part of the column 18 through the pipe 18. As the condensed cyclohexane moves downwards, it causes condensation of the acetic acid, and both return to the reaction chamber 1 through the pipe 16. Preferably, a suitable amount of water is recycled, or fresh water is added, to the reaction chamber 12, such that the catalyst remains in solution under the operating conditions. At the same time, the amount of recycled or added water should preferably be sufficiently low, such that substantially a single liquid phase occurs in the reaction zone 14 of the reaction chamber 12. The formation or existence of a second liquid phase in the reaction zone 14 it considerably reduces the reactivity and reaction rate. The lower gases are removed from the pipe 22i through the valve 22 '. Most of the lower gases comprise mainly non-condensable gases, usually nitrogen, oxygen, carbon dioxide, carbon monoxide, etc., for example, with smaller amounts of condensable material, comprising for example such vapors as cyclohexane, acetic acid , water, etc. The recycling of gases (not shown) from the pipe 22i to the reaction chamber is often desirable in order to improve mixing and watering, to conserve oxygen, to reduce the treatment requirements of lower, final gases, etc., The valve 22"can be used in order to remove a sample, or part of the cyclohexane, if desired, the reaction mixture, which has reached a permanent state at a pressure, predetermined operating temperature and desired conversion in the reaction zone 14 of the reaction chamber 12, preferably it is continuously withdrawn from the pipe 16iü as a reaction mixture stream. towards the drainage means, such as, for example, the drainage chamber 26, In the case of the production of adipic acid, for example, if the operating temperature in the reaction zone 14 is 100 ° C for example, the temperature in the drainage chamber is brought to a temperature preferably in the range of 70 to 90 ° C the temperature in the drainage chamber 26 is maintained in the desired range by the supply of c For example, the heat may be provided to the drain chamber 26 by heating coils (not shown), inside or outside the drain chamber 26, or at least part of the contents of the chamber 26 circulates. through a heater (not shown), or by any other technique well known in the art. Adding heat to the contents of the drainage chamber 26 and maintaining the desired temperature is very important in order to - 13 continue to evaporate the cyclohexane, which azeotropically removes water from the contents of the drain chamber 26, as the azeotrope passes through the second distillation column 28 in the same manner as already described for the first distillation column 18. The cyclohexane / water azeotrope is condensed in the condenser 30 and the cyclohexane is separated from the water in the decanter 32. At least part of the cyclohexane is directed back to the top of the distillation column 28 and finally returns to the chamber. drain 26. Removal of cyclohexane, through line 32ii for example, helps in reaching a lower water level in the drainage chamber 26, at a given temperature, without precipitation of the catalyst. More than one drain chamber can be used with respective distillation columns and respective or common decanters and condensers, preferably in series for greater water removal. A stream containing an amount of water above the critical water level as explained above (and also as noted in the comments below), is routed through the pipe 26iii to an optional cooler 36. The stream can be cooled to down either by the cooler 36 or more preferably by rapid crystallization in the crystallizer 38, or both. Rapid crystallization is conducted by reducing pressure through line 38i in one or more stages. During the reduction of pressure, the cyclohexane and / or acetic acid evaporates from the mixture, causing a rapid temperature drop, so that the intermediate oxidation product, the adipic acid in this example, precipitates and forms a watery paste. , such slurry is transferred, preferably continuously, to the solids separator 40. The adipic acid is removed through line 40ii, while the filtrate is withdrawn through line 40i for recycling, cyclohexane it is withdrawn from the pipe 38, it can condense, and preferably it can also be recycled to the reaction chamber 12 through the feed pipe 16, with or without pre-treatment. The cooler 36 can be used by itself to cool the mixture or can be used in conjunction with the rapid crystallization process. EJ cooler 36 may also be part of crystallizer 38 for additional cooling of the crystallizer content. Liquid cyclohexane can be introduced into line 36i to cool in quick crystallizer 38. Due to the low water content in the mixture entering crystallizer 38 and removal of cyclohexane in the crystallizer, a second liquid phase is not formed under normal circumstances . It should be noted that part or the water also evaporates together with the cyclohexane due to the reduced pressure in the crystallizer. The amount of water leaving the system can very easily be found experimentally from the steam stream in the pipe 38i, or the condensate from the vapors at a later stage, for example. This amount of water, at the operating temperature of crystallizer 38, is to be taken into account when determining the amount of water to be removed by the second distillation column 28, so that no catalyst is precipitated in crystallizer 38, In a different embodiment of the present invention, the oxidation intermediate, such as, for example, an adipic acid, may be removed prior to removal of water. The operation of this modality is very similar to the one discussed above. Preferably, the precipitation of the oxidation intermediate is conducted in such a way that a single liquid phase is maintained by rapid crystallization. On many occasions, in the practice of this invention, it is preferable to use one or more distillation columns of the type shown in Figure 2, which can replace column 18 and / or 28, shown in Figure 1. The columns of distillation of this type are well known in the art. They have a separating zone S and a rectifying zone R, above the separating zone, as well as a reheating section 52, as shown in figure 5. They are characterized by a better separation of the constituents entering the column, although they use more energy due to the additional re-heater It should be understood that, in accordance with the present invention, any liquid or gas or lower gas may be recycled in whole or in part from any section into any other section, if so d &;be. Although the miscellaneous functions are preferably controlled by a computerized controller, it is possible, according to this invention, to use any other type of controller or even manual and / or manual controls to control one or more functions. Preferred computerized controllers are systems artificially intelligent (expert systems, neural networks and fuzzy logic systems, well known in the field). Of the three types of artificially intelligent systems, the neural network, which is a learning system, collects information from different places on the device (for example, pressure, temperature, chemical and other analyzes, etc.), stores this information together with the result (for example, rate of fall of pressure, reaction rate, reactivity and the like) and is scheduled to use this information in the future along with other data, if applicable, to make decisions regarding the action to be carried out in each case. Expert systems are programmed based on the experience of experienced human beings. Fuzzy logic systems are based on intuition rules in addition to expert rules. Oxidations according to this invention are non-destructive oxidations wherein the oxidation product is different from carbon monoxide, carbon dioxide and a mixture thereof, such as, for example, adipic acid. Of course, small amounts of these gases can be formed together with the oxidation product, which can be a product or a mixture of products. Examples include, but are of course not limited to, the preparation of CS-CJJ aliphatic dibasic acids from the corresponding saturated cycloaliphatic hydrocarbons, such as, for example, the preparation of adipic acid from cyclohexane. examples of aromatic carboxylic acids are benzoic acid, phthalic acid, isophthalic acid and terephthalic acid, among others. With respect to the adipic acid, the preparation of which is especially suitable for the methods and apparatus of this invention, general information can be found in a plethora of the Patents of E.i., Among other references. These include, but are not limited to: U.S. Patents, 2,223,493; 2,589,648; 2,285,914; 3,231,608; 3,234,271; 3,361,808; 3,390, 174; 3,530,185; 3,649,685; 3,657,334; 3,957,876; 3,987, 100; 4,032,569; 4, 105,856; 4,158,739 (glutaric acid); 4,263,453; 4,331,608; 4,806,863; 4,902,827; 5,221,800; and 5,321,157. The diacids (for example, adipic acid, italic acid, isophthalic acid, terephthalic acid and the like) or other suitable compounds can be reacted, according to techniques well known in the art) with a third reactor agent selected from a group consisting of in a polyol, a polyamine and a ppamide in a manner that forms a polymer of a polyester, or a polyamide or a polyimide and a polyamideimide, respectively. Preferably, the polyol, the polyamine and the polyamide are mainly a diol, a diamine and a diamide, respectively, in order to avoid excessive degradation. The polymer resulting from this reaction can be spun by fiber-forming techniques well known in the art. The examples demonstrating the operation of the present invention have been given only for purposes of illustration and should not be construed as limiting the scope of this invention, in any way. Furthermore, it should be emphasized that the preferred embodiments hitherto discussed in detail, as well as any other modality encompassed within the limits of the present invention, may be practiced individually or in any combination thereof, in accordance with common sense and / or the opinion of an expert.

The individual sections of the modalities may also be practiced individually in combination with other individual sections of the modalities or modalities in their entirety, in accordance with the present invention. These combinations are also within the scope of the present invention. In addition, any explanation proposed in the description is only speculative and does not attempt to narrow the limits of this invention.

Claims (12)

1. CLAIMS 1. A method to maintain a catalyst in solution after removal of water, outside a reaction zone, by coordinating the temperature with the water level, in a process that involves the oxidation of a hydrocarbon by a gaseous oxidant to a respective oxidation intermediate, at an operating temperature in the reaction zone containing a mixture comprising the hydrocarbon, the catalyst, the water, a solvent and an optional initiator, characterized in the method by: any of the steps sequentially (a) changing, outside the reaction zone, the operating temperature of the mixture to a second temperature below a precipitation temperature, at which and over which precipitation temperature, the catalyst is precipitated in the first mixture , at least partially, if the water level in the first mixture is reduced to or below a critical level of precipitation water; (b) removing a quantity of water from the first mixture, but maintaining the level of water in the mixture above the critical level of precipitation water at the second temperature; (c) removing at least part of the oxidation intermediate; and (d) recycling the remaining mixture to the reaction zone; or the steps of (e) at least partially precipitating the oxidation intermediate, while maintaining a single liquid phase; (f) removing at least part of the oxidation intermediate, precipitate; (g) removing part of the water at a temperature below a precipitation temperature, at which and over which precipitation temperature, the catalyst is precipitated in the mixture, at least partially, if the level of water in the mixture is reduced to or below a critical level of precipitation water; (h) maintaining the water level above the critical level of precipitation water; e (i) recycling at least part of a mixture created in step (h) back to the reaction zone; wherein all stages are conducted in a region of substantially a single phase. A method according to claim 1, characterized in that step (b) comprises a step of lowering the second temperature to a third temperature lower than the second temperature. 3, A method according to claim 1 or 2, characterized in that step (c) comprises a step selected from the group consisting of centrifugation, filtration and a combination thereof. 4. A method according to claim 1-3, characterized in that step (a) comprises a step of atomizing the first mixture. A method according to claim 1-4, characterized in that the oxidation intermediate comprises adipic acid, the hydrocarbon comprises cyclohexane, the catalyst comprises a cobalt compound, the gaseous oxidant comprises oxygen, the solvent comprises acetic acid and the optional initiator is selected from a group comprising cyclohexanone, cyclohexylhydroperoxide, acetaldehyde and a mixture thereof. 6. A method according to claim 5, characterized in that it further comprises a step of reacting said adipic acid with a reactor agent selected from a group consisting of a polyol, a polyamine and a polyamide, in a manner that forms a polymer of a polyester or a polyamide or a (polyimide and / or polyamideimide), respectively, 7. A method according to claim 6, characterized in that it further comprises a step of spinning the polymer into fibers, 8. A method according to claim 1-4, characterized because the oxidation intermediate comprises a compound selected from a group consisting of adipic acid, italic acid, isophthalic acid and terephthalic acid and the method further comprises a step of reacting said oxidation intermediate with a reactor agent selected from a group comprising a polyol, a polyamine and a polyamide, in a manner that forms a polymer of a polyester or a polyamide a or one (polyimide and / or polyamideimide), respectively. 9. A method according to claim 8, characterized in that it further comprises a step of spinning the polymer into fibers, 10. A method according to claim 1-9, characterized in that the water level is maintained in a range of 10% to 100% by weight of the critical value of precipitation, above the critical value of precipitation at the second temperature, 11. A method according to claim 10, characterized in that the water level is maintained in a range of 20% to 50% by weight of the value critical precipitation, above the critical value of precipitation at the second temperature. 12. A method according to claim 1-11, characterized in that the critical water level of precipitation is determined at the second temperature before conducting step (b) and / or (h).